QE 75 7 DAY "?., Geology and Tungsten Mineralization of the Bishop District California ytls.. GE O LOGICAL SURVEY5BOFESSIONAL PAP ER 470 __ Prepared in cooperation with the State of California, Department of Conservation, Division of Mines and Geology {QTY OF CAZ m0? oct 26 1985 EARTH SCIENCES us LIBRARY \ Geology and "Tungsten Mineralization of the Bishop District California By PAUL C. BATEMAN With a section on Gravity Study of Owens Valley By L. C. PAKISER and M. F. KANE And a section on Seismic Profile Py L: C. PAKISER ErRoOoEOGICAL SURVEY PROFESSIONAL PAPEEK 470 Prepared in cooperation with the State of California, Department of Conservation, Division of Mines and Geology UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1965 EARTH SCIENCES UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 SCIENCES LIBRARY CONTENTS Cec eel iIntroduction-~. -.... lc een ee vic cel caked aenes Purpose, scope, and organization-_____________- ___ Previous geologic Methods of e sss Location and accessibility______.__________________ Surface features. . oren Settlements and culture. Chimate and Prebatholithic Upper Precambrian(?) and Lower Cambrian sedi- mentary rocks of the White Mountains-__-___--. Wyman formation-......-....-.-.....-......... Reed os sns Deep Spring formation.-............_...._._. Campitoformation....-..................... Andrews Mountain member-____________. Montenegro member....___..._______..._ c tel ie le ea ea. Poleta formation..............--..-...-......- Harkless formation.........--..-.............. Hornfel$. 5.2 csr ames ban ue oin Structures in the White Mountains-_--_---------. l cleo baa aer et reall nenas ss FANS 2. -se 22 eee er nee nan rein tanks e ~ m Faults south of Poleta Canyon--------__. Faults on the east limb and crest of the Cen- tral Faults associated with the West syncline. Faults in the Central syncline and West anticline between Silver Canyon and Gunter Cleavage. Metamorphic rocks of the Sierra Nevada_________ Metasedimentary rocks._..__..._.___._____ _.. Micaceous quartzite derived from argil- laceous sandstone and siltstone.____-._._. Pelitic hornfels derived from silty shale, argillaceous siltstone, and clay shale____. MebACHETDLL .. «eee ees Marble derived from Calc-hornfels derived from argillaceous and siliceous limestone and dolomite. ._. Tactite derived from marble and cale hornfels.c_....clll ___ ._... si Metavoleanic rocks__..._..._..____.__..__.___ Felsic metavolcanic rocks._______________. 434 Page «w co ~I Or Or Cr A wa Co bD ho + 20 20 21 28 23 23 24 24 25 25 26 26 27 27 Prebatholithic geology-Continued Metamorphic rocks of the Sierra Nevada-Continued rocks-Continued Mafic metavoleanic rocks_______________. Calc-hornfels derived from mafic igne- ous rock...... .2..40. c nan Kind and grade of Arrangement of metamorphic remnants in relation to the regional distribution of the prebatholithic rocks__........._..___sic..... Descriptions of metamorphic Pine Creek pendant.......-.....c..._... Pelitic hornfels, micaceous quartzite, and vitreous quartzite. Mathle. . cece Micaceous quartzite_______________._. Felsic metavoleanic rocks.__-_____._. Mafic metavolcanic Probable correlation with the Mount Morrison pendant....:-..........- Bishop Creek Pelitic hornfels with interbeds of marble. cage.. Marble. .... c deal =s Banded - calc-hornfels and - pelitic Metachert and andalusite-bearing pelit- io Siliceous calc-hornfels..__-_---_---_- Micaceous quartzite and pelitic horn- un oak Age of the strata in the Bishop Creek pendant... (Gneiss in the canyon of the South Fork of Bishop Marble and calc-hornfels in the northeast base of Mount Tom.:..:...1.......... Metamorphic rocks in the Tungsten Hills.. Round Valley Septum 2 miles east of the Round Valley be Metamorphic inclusions in the Deep Canyon ass Mafic metavolcanic rock in the south- western part of the Tungsten Hills Septa 3 miles west of Keough Hot Springs Remnants along the range front southwest of Big Pine Septa and inclusions in upper Big Pine Middle Palisade Split Mountain septum-__--_------------ Marble in the Poverty Hills________-----.- III Page 28 29 31 33 34 34 36 36 37 37 37 38 39 39 39 40 40 41 41 41 42 42 42 42 43 43 43 43 44 44 45 45 45 IV Geology of the Diorite, quartz diorite, and hornblende ___. Altered diorite of the White Mountains.______. Fiornblendé gabbro.. .. Layered gabbro in the Tungsten ___. Quartz diorite and related granodiorite._______. Granitic ea ins ss Mineralogy._L...:.:.._...ll.d Essential minprals._._._._..__._._.____ _. -_ ca bse ol. ans Potassium feldspar (K feldspar) Plagioclase. _L __ Varietal minerals __. Diotife carol curl dEn AIEEE! 2C ee ci cet cheer cree ak L us - Accessory minerals:: ._.: Aiteration LIL uR IEIL. . Analytical L. Rock Inconsolable granodiorite_____-_________. Tinemaha ___. Granodiorite of McMurry Meadows.____._. Wheeler Crest quartz monzonite_._______. Round Valley Peak Lamarck Granodiorite of Deep Tungsten Hills quartz Albite eranite Rocks similar to the Cathedral Peak eranite c l acl: lst IR L. Quartz monzonite facies...________._._ Maskite facies......-_L__L.......... Marginal dikes of aplite, pegmatite, and Intrusive relations --_-.-___._.._.__[___ Finer grained quartz Granodiorite of Coyote Flat..___._.___.._.__. Granodiorite of Cartridge Pass-__________. Mafic dikes -...... ree nen o ae Hele al ue a we Broad problems relating to the Bequence of _._. ACen bts o ana a ik a lE ar Bil a aie a Uinta a y a Broad chemical and mineralogical variations.... Systematic compositional variations within in- dividual masses.. { Correlation of normative compositions of the granitic rocks with experimental data_______. Comparison of compositional trends with trends of granitic suites from other areas..________._ Contacts between different granitic rocks. Contacts between granitic rocks and meta- morphic rocks or diorite. ...... Mafic Anclusions Emplacement of the batholith________________ Evidence of mechanical emplacement... Bends and dislocations in metamorphic remnants resulting from the intru- sion of granitic magma. CONTENTS Page 45 46 46 46 49 54 56 57 57 57 57 58 58 58 58 59 59 59 59 62 64 65 68 71 73 75 77 80 80 86 88 88 92 93 94 94 96 97 98 99 99 100 101 102 104 107 109 110 112 114 115 115 Geology of the batholith-Continued Broad problems relating to the batholith-Continued Emplacement of the batholith-Continued Deformation caused by intrusion of swarms of marginal dikes._________. Protoclastic borders, intrusive breccia, and related marginal effects________ Flattened mafic inclusions as indicators of forcible emplacement. Evidence for thermochemical emplacement _ Granitization of mafic rock.___________ Assimilation of mafic rock._.__________ Evaluation of processes of emplacement of the batholith. Contact-metasomatic tungsten mineralization. _ ___ Mining History ... amis endl (Grade of OTeS.__.....2.ocnno sc bere nuk Oull00K..- -_- anns tes Summary of geologic relations________________ Distribution of deposits._.___.-_-____sl_.l_c__. The contack L. . 02 lue cuse ctaene Characteristic minerals of tactite__________ Bleached and silicated marble-___________. Zones of silicified rock and quartz veins.... Chemical gains and losses in the formation Of nl.. Stability relations of garnet, pyroxene, and epidote... : -.- Layering and streaks in tactite____________ Distribution of scheelite_..._.____________._ Leached outcrops and secondary enrich- ments . L 52 2s cone cls hid 1+ U tew m whe arin al on' an a Factors that influence position, size, and shape of ore bodies:... _.... ice. ceseduens Irregularities in the intrusive contact_____. Steeply dipping salients of marble.... Benches or apophyses of granitic rock.. _ Small inclusions of metamorphic rock... Stratification and lithology of the meta- morphic 1 _-... Fractures along the intrusive contact and in the calcium-rich host Relation of the tungsten deposits to the granitic ros uneaten Summary of ene, Cenozole goolOgY -. LL.. esen cer ae ua nna an a Formations of Cenozolo Volcanic Basalt dikes, necks, and dissected flows.... Bishop Miff-.1.2..2.3 aun bias ae aet Basal pumice Principal tuff member__......__.__.. NGC. nee Rhyolite south of Big Pine_____. _...... Basalt flows and cinder ___ Sedimentary _ Glacial deposits of the Pleistocene epoch.. . . Sherwin and older tills_______________ Tahoe Tioga Hll-L._-_._...L- C gk Page 116 117 118 118 118 121 123 124 125 126 126 126 127 127 129 129 130 132 133 134 135 135 136 187 137 139 143 143 146 148 150 150 150 150 151 151 155 159 159 159 161 161 161 163 164 CONTENTS Cenozoic geology-Continued Pag® | Cenozoic geology-Continued Formations of Cenozoic age-Continued Cenozoic structure and evolution of the landscape-Con. Sedimentary deposits-Continued Cenozoic structural history of the Sierra Neva- Older dissected alluvial fan and lakebed da-Continued deposits lee el oll seer ade ul ale aes 165 The White Mountains escarpment. Dissected fanglomerate and lakebed Structures parallel with the range deposits along the base of the White front.. ~.. -l HEN Ee s wie aes ol 165 Transverse faults between Poleta and Dissected fanglomerate along the base Black of the Sierra Nevada-_____________ 166 Structures in the valley block-__________. Alluvial remnants in west part of Vol- Structures in the Volcanic Tableland. canic 'Tableland........_....__... 166 Structural relations of the terraces ._.. ABC: 2... ccie? rears ama alen to ale sale anes 166 Structures of Round es 167 Subsurface structure of the valley Terrace 167 plook:: _. it Undissected alluvial fan deposits____ -__- 167 Gravity study of Owens Valley, by - 168 L. C. Pakiser and M. F. Kane_____. Dune sands.: - lec len 168 Field methods and reduction of Talus and rock slaciers.._.._........_L._. 168 gravity readings........._...L Cenozoic structure and evolution of the landscape.. _ 170 Interpretation of the gravity data. Cenozoic structural history of the Sierra Nevada The gravity contours.:__..._.___.. and adjacent regiong 171 Analysis of gravity anomalies __. Cenozoic structural features of the Bishop area. _ 172 Conclusions and discussion-_._._. The Sierra Nevada escarpment.--_-____-_. 178 Seismic profile, by L. C. Pakiser_____. The Coyote )..}: cc 174 Interpretation of the deformation pattern... Crest and cast flank._......._._.. 174 Adjustment of streams to the structural move- Faults of large displacement west ments.. .s .._ n_ tai ee 20s io an ab ale of Big Ping: enne. 175 Adjustment in the Volcanic Tableland... North ule... 176 Adjustments in the Tungsten Hills_______. Wheeler Crest 177 Sculpturing of the mountains by water and ice. Tinemaha . 178 | Referencesicited-...._... ... al Conjugate joint system.__-____-____- 179 | Index... N HMI IANA UY cale «aa es naan as ILLUSTRATIONS [Plates are in separate volume] PLATE 1. Geologic map of part of the Mount Goddard 15-minute quadrangle. 2. Geologic map of the Mount Tom 15-minute quadrangle. 3. Geologic map of the Bishop 15-minute quadrangle. explanation ; it should be light tan as shown in the northwestern part of the map itself.] . Block diagram of the Pine Creek mine. 10. o o p a g pug Fraurs 1: . Geologic map of the Big Pine 15-minute quadrangle. . Geologic cross sections in the Mount Tom, Bishop, Big Pine, and part of the Mount Goddard 15-minute quadrangles. . Block diagram showing an interpretation of the structure of the White Mountains in the Bishop quadrangle. Structure map of the Mount Tom, Bishop, Big Pine, and part of the Mount Goddard 15-minute quadrangles. . Map of structures attributed to forcible emplacement of granitic rocks. Cross section from San Andreas rift eastward across San Joaquin Valley and Sierra Nevada to Panamint Valley. 11. Gravity profiles and interpreted structure sections. index map showing the area mapped for this report-... GE - am 2. Unfossiliferous upper Precambrian or Lower Cambrian strata along White Mountain front north of Black Canyons Ses er LLL Orc s dn -ur sale nee on onan aan o ok e be ae nad aas bund aan Sods sles bacs oo 5. Columnar sections of the Deep Spring .L _ oo 4. Cliff section on north side of Black Canyon showing irregular dolomitization of limestone in the top of the Deep Spring formation.... . .... : .L... n. Onl sen tL ans s ac m 5. Specimen of quartzitic facies of the Andrews Mountain member of the Campito formation showing cross- bedding. . ois. coc bul esa ole oa aa ae pae o aid ale o hae all ula false aie Mia in oo ia in n ana he te ra i Telos ho ie as ae e a alle 6. Slaty cleavage in Montenegro member of Campito formation showing divergent attitudes of bedding and cleavage... c dll. le .c bake nel aes oar ae aln ae allan ape ae ail aie a ela ane e a a mm i a aln Page 181 181 182 183 183 188 189 190 191 191 191 192 192 193 195 195 197 197 198 199 201 205 [The Bishop agglutinated tuff is erroneously shown as green in the Page 11 13 14 14 20 VI Frcur® 13. 14. 15. 16. C7: 18. 19. 20. 21. 22. 23. 24. 25. 26. 27-32. 38. 34. 35. 36. 37. 38-40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. CONTENTS . Geologic map of the Owens Valley region showing the distribution of the pre-Cenozoic rocks..___________._ ' Specimen of metachert showing light and dark . Products of metamorphic differentiation in hornfels and in sheared rock of the same bulk composition.... . Mafic dike rock partly altered to plagioclase-diopside . Suggested stratigraphic correlation of the Pine Creek pendant with the Bloody Mountain block of the Mount Morrison ies sens ass tenses ce . Banded calc-hornfels (light-colored) and pelitic hornfels in which calc-hornfels encroaches on and cuts across politic _ eile ccs s be ae ns us ae hss an s Bedrock map of the Bishop area showing the distribution of the plutonic Triangular diagram showing the classification system used in this Map of the main patch of layered gabbro in the Tungsten Hills Photographs of several exposures of layered lit Thin section cut across the layering and an "unconformity" in layered Thin section cut across the 'Isyoering in layered ss Partly granitized mafic rock cut by. a hornblende-rich Curve used to determine the anorthite content of plagioclase Typical granitic rocks from the Bishop »La» External contacts of the Inconsolable granodiorite in the drainage basin at the head of the South Fork of Big Pme L2 ILY avea th asa ag as an s saka rh sede teen t u ur Map showing the locations of modally analyzed specimens of the Round Valley Peak and Inconsolable grano- diorites, the granodiorite of Coyote Flat, the quartz monzonite of McMurry Meadows, the granodiorite of Cartridge Pass, and the granodiorite of Deep Plot of modes of Inconsolable granodiorite on quartz-K feldspar-plagioclase Brecciated Inconsolable granodiorite in the east side of Temple Map showing the locations of modally analyzed specimens of the Wheeler Crest quartz monzonite and of the Lamarck and Tinemaha -granodilorites. .. iL sw Plots of modes on quartz-K feldspar-plagioclase diagram- 27. Tinemaha c re eo rre seen s 28: Granodiorite «of McMurtry Meadows. .-. ses 20. Wheeler monsonite. . LCL 80. Round Valley Peak . _L sass S1. Lamarck LU... dnes askes ens alel ess tun l ul 92. Granodiorite of Deep Canyon... li anes ss sameness Map showing the locations of modally analyzed specimens of Tungsten Hills quartz monzonite___________. Plots of modes of Tungsten Hills quartz monzonite on quartz-K feldspar-plagioclase diagrams-___________. Map showing the locations of modally analyzed specimens of rocks similar to the Cathedral Peak granite and of finer grained quartz -monsonite.-. : ...n clo icin ans ans ans ik Plots of modes of rocks similar to the Cathedral Peak granite on quartz-K feldspar-plagioclase diagrams.... Aplite, pegmatite, and alaskite dikes along Pine and Morgan Plots of modes on quartz-K feldspar-plagioclase diagram- 38. Finer grained quarts Lr AEE cH «aaa a ana «ak nas an m 30; Granodiorite of Coyote Flat.... LLQ LAL OLLIE Accent a aln anale anl 40. Granodiorite of Cartridge Pass.. ...... 200000 ll ell avea ean inin sameness an ae Diagram showing the intrusive relations and probable age sequence of the granitic rocks-_________________ Variation diagram of common oxides in granitic rocks of the Bishop district plotted against SiO;-.._______. Plot of norms of granitic rocks on quartz-orthoclase-plagioclase diagram Plot of arithmetic modal averages of quartz, K feldspar, and plagioclase in different plutons-..______._____. Average percent of -modal quartz, K feldspar, biotite, and hornblende in different plutons plotted against average percent of modal Tetrahedron showing the liquidus relations in the system Qz(S10,;)-H:0 at 5,000 bars H;C) ._.. CLI Plots of norms for areas of granitic rocks in the western United States and Composite of median lines through fields of norms shown on figure Aerial view of Pine Creek pendant in north wall of Pine Creek Canyon-_________________________LL_____ Diagrammatic section through an intrusive and its marginal dikes to show the amount of plastic deformation in the wall rocks caused solely by the emplacement of the dikes. Typical sranitization effects in mafic rock: _._: lloc c L nen cama cns Selective replacement of mafic rock (dike or inclusion) over Lamarck granodiorite by aplitic material___-_-_. Selective reaction of aplite dike with mafic dike in Tinemaha Mafic inclusion cut by dikes nf slightly different ages, both of which are offshoots from the surrounding quartz monzonite similar -to the Cathedral Peak granite. 1. neue sean ain an Hypothetical sketch map showing common relations between marble, granitic rock, and tactite along a dis- cordant intrusive contact bernd as menecine steam ns Page 22 25 27 30 38 40 47 48 49 50 51 52 55 58 60 64 66 67 67 69 71 72 74 76 78 81 82 84 89 90 93 95 96 97 99 101 102 102 103 105 108 109 111 117 119 120 121 123 136 Ficur® 56. 57. 58. 59. 60. 61. 62. 63. 64. 65. 66. 67. . Geologic map of the rhyolite hill south of Big 69. 70. T3: 72. 73. 74. 75. 76. 77. 78. . Block diagram showing the relations between systems of en echelon faults and axes of warping on the Volcanic 80. 81. 82. 16. 17. 18. 19. 20. 21. CONTENTS Block diagram of the South ore body, Pine Cre@k Geologic sketch map of the Little Egypt prospect, see. 7, T. 8 S., R. 32 ss Sectional diagram of the North ore body, Pine Creek mine, showing the tungsten ore Sectional diagram of the Main ore body, Pine Creek mine, showing the tungsten and molybdenum ore shoots . Section through the Marble tungsten mine showing the relation of tactite ore bodies to the instrusive contact.. Geologic section through the Round Valley Geologic sketch map and section of the Munsinger prospect, see. 17, T. 8 S., R. 32 sean es Geologic map of the upper adit in the Hanging Valley Fence diagram showing the distribution of the Bishop tuff in the Bishop quadrangle....._..._.__......... Views of Bishop tuff in pit of Insulating Aggregates Co. in east side of Volcanic Tableland, see. 32, T. 5 S., R ela ieee aa antes ule a sed teta oun as me nen tanline o ann ans oon ana alnlk sit canis aa Two inversely graded layers of pumice resulting from dumping two batches of pumice into a beaker partly Sill Of WAbEL_ccll . nant abe ana ce re os sees sess ts Vertical sections through the Bishop tuff showing thickness, color, and specific gravity _ _____________-_--- Aerial view of the Sierra Nevada crest west of Rock glacier between Second and Third Lakes, North Fork of Big Pine Vertical view of rock-glacier apron southeast of Rock Creek View of probable landslide in the North Fork of Bishop Creek above North Lake which resembles an active rock glacier.. Profiles across mountain-down fault scarps in alluvium along the base of the east flank of the Coyote warp... Bench on northeast side of Mount Tom formed by mountain-down faulting parallel with the range front.. - . Werial view of HRierra crest southwest of occas ks ansi Joints crossing aplite dike in Tungsten Hills quartz Aerial view of the southeast part of the Volcanic Tableland showing systems of en echelon Tilted fault blocks along Fish Ieee ce decant on enne Pann ue ss alk ans a Ainls te ase on s aus en ts ues Map of the southwestern part of the Volcanic Tableland showing the location of three ancient stream channels and their relation to modern Seismic profile across Owens Valley south of Aerial view looking southwest into Pine Creek TABLES . Summary of weather data at Bishop and at South Lake, . Rapid chemical analyses of mafic dike rock and of hornfelsed rock derived from it_____________-_----------- . Summary of chemical and spectrographic analyses and norms of the granitic rocks-______________-_____---- . Modal analyses: 4; Intonsolable con -t- aa danken ake aan ant t ns be sn 6 oin nt be ak 5. Tinemaha sess 6. Granodiorite of MeMurry ts on 7; Wheeler Crest quarts 8. Round Valley Peak 0. Lamarck esos sss 10. : Granodiorite of Deep anns anes 11. Tungsten Hills quartz 12." Rocks similar to the Cathedral Peak granite 13. Finer grained quartz 14. Granodiorite of Coyote se also sance 15. Granodiorite of Cartridge ss sess Lead-alpha ages of granitic rocks from the Sierra Nevada near Averages of modal analyses for different Tungsten mines and prospects in the Bishop district showing the parent metamorphic and associated plutonic IL Lr eel in i ie Ge namie aie as bio b Hala ales o a aln in ol n ia a in race n in s m n hain o faa d Ilia an maen e mien ne ain a ea hae Chemical analyses of tactite and bleached and silicated marble from the Main ore body, Pine Creek mine, and gains and losses in the formation Of Chemical compositions of some common silicate minerals in Analyses of Bishop cents amb aln an oom st VII Page 138 139 140 141 142 144 145 146 152 153 155 157 160 162 169 169 170 175 178 180 181 184 185 186 187 196 200 Page 30 63 67 70 72 74 76 79 81 85 91 95 97 97 100 103 124 131 132 156 GEOLOGY AND TUNGSTEN MINERALIZATION OF THE BISHOP DISTRICT, CALIFORNIA By C. BarEemax ABSTRACT The Bishop district is in eastern California about midway be- tween Reno, Nev., and Los Angeles, Calif. The area mapped comprises a little more than 800 square miles and includes the Mount Tom, Bishop, and Big Pine and the northeastern part of the Mount Goddard 15-minute quadrangles. The crest and eastern escarpment of the Sierra Nevada occupy the western half of the area, and the western foothills of the White Moun- tains lie along the eastern margin. Between the Sierra Nevada and White Mountains is a structural trough that contains Owens and Round Valleys and the Volcanic Tableland. Altitudes range from approximately 4,000 feet on 'the floor of Owens Valley to more than 14,000 feet in the highest peaks of the Sierra Nevada. The White Mountains are underlain chiefly by strongly de- formed sedimentary strata, the Sierra Nevada by granitic in- trusive rocks in which remnants of metamorphic and mafic igne- ous rocks are scattered, the Volcanic Tableland by rhyolite tuff, and Owens and Round Valleys by alluvial deposits and a few masses of olivine basalt. A wide range of ages is represented, but much more of the record is missing than is present. The sedimentary strata of the White Mountains are of late Precam- brian (?) and Early Cambrian ages; the scattered metamorphic remnants in the Sierra Nevada are of Paleozoic and early Mesozoic ages; the granitic intrusive rocks are of Cretaceous age; and the rhyolite tuff of the Volcanic Tableland, the scat- tered masses of olivine basalt, and the alluvial deposits are of «Cenozoic age, chiefly Quaternary. The rocks and structures are divisible into three groups: those formed before the Sierra Nevada batholith was emplaced, those formed at the time of emplacement of the batholith, and those formed after the emplacement. The rocks of the oldest group include the Precambrian(?) and Cambrian strata of the White Mountains, and the remnants of Paleozoic and Mesozoic strata in the Sierra Nevada. In the White Mountains more than 10,000 feet of sedimentary rocks are present in which Olenellus has been found in the upper 3,500+ feet. In the Sierra Nevada, remnants of sedimentary rocks probably range in age from Cambrian or Ordovician to Pennsylvania and Permian(?) ; stratigraphically overlying (probably unconformably) meta- morphosed metavolcanic and intercalated metasedimentary rocks are probably of Triassic(?) and Jurassic age. In Late Jurassic or Early Cretaceous time these rocks were folded and faulted along north- to northwest-trending axes. The Sierra Nevada batholith is a mosaic of discrete intrusive masses of plutonic rock, which are in sharp contact with one another or are separated by thin septa of metamorphic or mafic igneous rock. The intrusive rocks range from diorite, quartz diorite and hornblende gabbro to alaskite. Most of the in- trusive rocks are grouped into formations on the basis of composition, texture, and intrusive relations, but a few are unassigned. In general the rocks were emplaced in order of increasing silica content, but with many exceptions. Some in- trusives are zoned, and their interiors are more siliceous than their margins. - The following features indicate that most of the plutonic rocks are magmatic: f 1. Contacts of individual plutons with each other and with older rocks are sharp, clean, and regular. 2. Finer grained rock is present in the marginal parts and apophyses of some plutons. 3. The geometry of the wall rocks suggests that some dis- locations were caused by forcible emplacement of magma. In one place a separation of 3 miles seems clearly attribut- able to forcible intrusion, and in another a separation of 8 miles seems probable. Intrusive breccias are present locally. 4. Internal foliation in the margins of plutons parallels external contacts. 5. The walls of aschistic dikes marginal to some plutons are dilated. 6. Granitization and assimilation effects are confined to amphib- olite and other wall rocks that consist chiefly of minerals earlier in Bowen's reaction series than those crystallized in the granitic rocks. The effects are in accord with theoretical expectations of reactions between granitic magma and wall rocks. 7. The metamorphic grade of the wall rocks and of inclusions is that of the amphibolite facies, which is in accord with the temperatures believed to exist in nonsuperheated granitic magmas. 8. Variations in the compositions of the intrusive rocks are in accord with variations predicted from experimental studies of melts. During cooling and solidification, the granitic intrusives expelled heated solutions that reacted with lime-rich rocks in metamorphic remnants and wall rocks to form contact-meta- somatic tungsten deposits. These deposits yielded 1.3 million units of WO; (tungsten trioxide) to the end of 1953 and were still at an early stage of exploitation. The Pine Creek mine of the Union Carbide Nuclear Co. contains the largest known deposit of tungsten ore in the district and has yielded more than a million units of WO; as well as substantial amounts of molybdenum and copper. The solutions given off by the cooling magma contained sili- con, aluminum, iron, manganese, titanium, tungsten, sulfur, and other metals. These solutions reacted with lime-rich rock to form tactite, a rock composed of dark silicate minerals such as garnet of the grossularite-andradite series, pyroxene of the diopside-hedenbergite series, epidote, idocrase, and amphibole. + 2 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA Scheelite, the most important tungsten-bearing mineral, is pres- ent locally in tactite. The largest tungsten deposits are in tac- tite composed mainly of garnet and pyroxene, which is believed to have formed at the highest temperatures, but smaller and richer deposits have formed in rock composed of quartz and epidote, locally accompanied by pyrite or pyrrhotite, which formed at somewhat lower temperatures. As the temperature fell quartz rather than silicate minerals was deposited in vein- lets; quartz also replaced fractured tactite and adjacent gra- nitic rock. Valuable sulfides were deposited locally with the quartz, but silicification of garnet-pyroxene tactite generally involved removal of scheelite. Most commercial ore bodies were formed in clean marble be- cause it can react completely with magmatic substances. De- posits formed in impure marble are generally of lower grade because silicate minerals that were formed isochemically by earlier thermal metamorphism could react only very slowly with introduced magmatic substances. Solutions expelled from the cooling intrusive mass collected along intrusive contacts and moved upward, especially along channelways that were kept open by fracturing caused by re- gional forces or by forces related to the emplacement and cool- ing of intrusives. Ore bodies were formed where these solu- tions were brought into intimate contact with lime-rich rock. Effective traps for solutions include irregularities in the in- trusive contact, especially those where granitic rock is wrapped around or protrudes over marble, in fractured lime-rich rocks, and in favorable beds. Small inclusions that contain lime-rich rocks were especially favorable traps; tactite was formed in the tops of many inclusions beneath an already solidified crust of intrusive rock. The contact-metasomatic tungsten deposits are preferentially related to the most silicic intrusives in the district. Of 53 known deposits, 38 are associated with either the Tungsten Hills quartz monzonite or with alaskite. Furthermore, all 21 de- posits that have yielded appreciable amounts of scheelite are closely associated with these two intrusive rocks. Evidently the distribution of these rocks determined the gross distribu- tion of deposits within the district, and the existence of the district in this particular place may be a result of their juxta- position with Paleozoic carbonate rocks. After a period of erosion that exposed the batholith and pro- duced a surface of low relief, the Sierra Nevada was tilted west- ward, probably as part of a broad upwarp that affected areas to the east and to the west. Stratigraphic studies in the San Joaquin Valley, which is on the downslope part of the Sierra Nevada block, show that tilting began in Late Cretaceous to Eocene time, recurred repeatedly during the Tertiary, and culminated in an orogeny in middle Pleistocene time. The struc- tural movements that resulted in the depression of Owens Val- ley began later than the tilting, probably in late Pliocene time. The subsidence was accomplished by means of countless small increments of movement, each probably of about the magnitude of those that occurred in connection with the Owens Valley earthquake of 1872, and with historical earthquakes elsewhere in the Great Basin. Evidence of repeated movement along many individual faults is clear, and abundant fresh fault scarps indicate that movements have continued to the present, and no doubt they will continue into the future, at a significant rate. As the trough subsided, alluvial debris eroded from the border- ing ranges poured into it. Basaltic cinder cones and associated flows broke out along bounding faults, and the rhyolitic Bishop tuff poured into Owens and Round Valleys from a source to the north. The White Mountains escarpment and segments of the Sierra Nevada escarpment north of Bishop Creek west of the Tungsten Hills and south of Tinemaha Creek are fault scarps. The in- tervening span of the Sierra Nevada, however, is warped rather than faulted. This warp is recorded in an old erosion surface, and geological and geophysical evidence show that it continues to slope eastward beneath the alluvial fill of Owens Valley to the fault that bounds the White Mountains, and northward under the Volcanic Tableland, where it bends upward along an east- trending synclinal axis. The maximum depth of alluvial fill, at the base of the White Mountains, is about a mile; the fill thins toward the Sierra Nevada. The east flank of the warped surface is broken by many anti- thetic normal faults, which indicate extension; the concept of Owens Valley as a keystone block that progressively subsided between the Sierra Nevada and White Mountains in the apex of an arch or in a zone of structural weakness along the east side of the batholith fits the known facts. En echelon fault sys- tems in the Volcanic Tableland, movements on the faults that formed in 1872, and consideration of the structural pattern sug- gest compressional forces, even though almost all of the faults are normal. Both the Sierra Nevada and the White Mountains escarp- ments have been deeply dissected by streams, and the higher ' parts of the Sierra Nevada have also been sculptured by glaciers. Since retreat of the last glaciers, erosion has been slight and many glacial phenomena are well preserved. INTRODUCTION PURPOSE, SCOPE, AND ORGANIZATION OF THE REPORT The purpose of this report is to present the scientific and economic-scientific results of a geologic study of the Bishop tungsten district in east-central California (fig. 1). The area is about midway between Los An- geles, Calif., and Reno, Nev., and includes part of the steep eastern face of the Sierra Nevada. An earlier re- port (Bateman, 1956) was prepared for persons inter- ested primarily in mining and prospecting; the present report is written especially for those interested in the many challenging geologic problems of the district, both economic and academic. Detailed descriptions of individual mines and prospects contained in the earlier report are not repeated here, but certain concepts re- garding the tungsten mineralization have been ampli- fied, and the emphasis has been shifted from a descrip- tive to a genetic standpoint. The geology of this report is discussed as "Prebatho- lithic geology," "Geology of the batholith," and "Ceno- zoic geology." "Prebatholithic geology" contains de- scriptions of the stratigraphy and structure in upper Precambrian(?) and lower Cambrian strata in the White Mountains, and in Paleozoic and Mesozoic strata in pendants, septa, and inclusions in the Sierra Nevada. "Geology of the batholith" includes descriptions of the intrusive rocks, their composition, structure, and mode INTRODUCTION 3 of emplacement. Contact-metasomatic tungsten de- posits for which the district is well known were formed during the cooling and consolidation of the granitic rocks, and the process of tungsten mineralization is con- sidered. "Cenozoic geology" contains descriptions of alluvial and volcanic deposits of Cenozoic age, and dis- cussions of the Cenozoic structures and the evolution of the landscape. Geophysical data are presented in two independently prepared sections. L. C. Pakiser and M. F. Kane pre- pared a section dealing with gravity studies, and Mr. Pakiser prepared a section on seismic studies. Some geologic interpretations made in these sections are not in agreement with interpretations made elsewhere in the report and reflect the views of the authors of these sections. : PREVIOUS GEOLOGIC WORK One of the early descriptions of the geology of the northern Owens Valley region is contained in a report of the Geological Survey of California, "Geology," by J. D. Whitney, published in 1865; no geologic map ac- companies the report. (Whitney's "Geologic Map of the State of California," listed in some bibliographies as having been published in 1873, was not actually ever published.) W. A. Goodyear, who traveled through Owens Valley in 1870 and again in 1888 examining the geology and ore deposits, gives an especially interesting early description of the geology of the area. His report is included in the 8th Annual Report of the State Mineralogist (1888, p. 224-309). A "Preliminary Min- eralogical and Geological map of the State of Califor- nia" published in 1891 by the California Mining Bureau as Map 1 is one of the earliest maps to show differences among the rocks of the region. On this map, the Sierra Nevada west of Bishop is shown to consist of Jurassic and Triassic rocks cut by northward-trending lenses of granite; the White Mountains are shown to consist of northwestward-trending Carboniferous and Permian strata along the range front and of Triassic and Juras- sic strata and granite farther east. Several extensive volcanic areas are shown along the Sierra Nevada front in the span between Bishop and Big Pine. A map by J. E. Spurr, published in 1903 as part of a report on a reconnaissance of Nevada south of the 40th parallel and adjacent parts of California, shows a threefold distinc- tion in the northern Owens Valley region of (a) granu- lar or coarse porphyritic igneous rock in the Sierra Nevada, (b) strata of Cambrian age in the White Moun- tains, and (c) strata of Pleistocene age in Owens Valley. A paper by W. T. Lee (1906) on the ground-water re- sources of Owens Valley includes descriptions of the surficial deposits and an interpretation of the structure of Owens Valley. In 1912 and 1913 Adolph Knopf (1918) made a geologic reconnaissance of the Inyo Range and eastern slope of the southern Sierra Nevada, which extended into the south half of the area described in the present report. About 20 years later, during the 1930's, a series of structural studies of the metamorphic and intrusive rocks of the crest and eastern slope of the Sierra Nevada was made by Evans B. Mayo. The re- port (1941) resulting from these studies, called "De- formation in the interval Mt. Lyell-Mt. Whitney, Cali- fornia," deals most fully with the Bishop district. Also during the 1930's, C. M. Gilbert studied the volcanic region north of Bishop, including Volcanic Tableland in the north-central part of the Bishop region (1938; 1941). Bateman and Merriam's geologic map of the Owens Valley region was published in 1954. The tungsten deposits within the Bishop region have been described in several papers, including my 1956 re- port on the economic geology of the region. The earli- est geologic report on the tungsten deposits was by Adolph Knopf (1917), who visited the deposits of the Tungsten Hills in 1916 when the deposits discovered in the preceding 3 years were being brought into produc- tion. Shortly afterward, in the summer of 1918, Esper S. Larsen, Jr., also examined the deposits in the Tung- sten Hills as well as the Pine Creek mine in Pine Creek Canyon. His report (Hess and Larsen, 1921) includes sketch maps of the Little Sister, Round Valley, and Pine Creek mines. The next geologic study of the tung- sten deposits was not made until 1934, when Randolph Chapman studied the contact metamorphism along the north side of the Round Valley septum, at the Round Valley mine (Chapman, 1937). After the outbreak of World War II in 1989, the Geological Survey intensified its investigations of the strategic minerals of the United States, and in 1941 published two preliminary papers by Dwight M. Lem- mon on tungsten-bearing districts within the area cov- ered by the present report. One of Lemmon's papers deals with the deposits in the Tungsten Hills (19412), and the other with deposits in higher parts of the Sierra Nevada near Bishop (1941b). Prior to publication of my report on the economic geology, two preliminary publications based on the pres- ent study were issued ; one of these is on the Pine Creek and Adamson mines (Bateman, 1945), and the other is on the tungsten deposits in the Tungsten Hills (Bate- man, Erickson, and Proctor, 1950). Brief descriptions of many deposits of both metals and nonmetals are included in reports of county or com- modity surveys by the California Division of Mines, in "Mineral Resources of the United States" published by the U.S. Geological Survey and the U.S. Bureau of 4 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA Mines, and in "Minerals Yearbook" published by the U.S. Bureau of Mines. Paul Kerr's memoir "Tungsten mineralization in the United States'" contains not only brief descriptions of most of the tungsten deposits in the Bishop district but also a theoretical discussion of the means by which tungsten is introduced into masses of metamorphic rocks such at the Pine Creek pendant (1946, p. 17-18, 142-147). METHODS OF INVESTIGATION Many of the tungsten deposits in the district were mapped between 1939 and 1944 in connection with strategic minerals studies of the Geological Survey; the data derived from this work served as a nucleus for the study of the district. Fieldwork for the district study was carried out chiefly during the summers of 1946 to 1950, inclusive, although a few weeks were spent in the field in 1951 and 1952. In all, about 30 months were spent in the field. During most of the fieldwork I was aided by one or two temporary assistants. Lab- oratory and office studies were chiefly by me, but I received some assistance in making modal analyses and in making routine determinations of the composition of plagioclase in granitic rocks. Chemical analyses, and certain mineralogical determinations, were made by members of the Geological Survey. Gravity studies were conducted by L. C. Pakiser and M. F. Kane of the Geological Survey, and seismic studies were made by L. C. Pakiser. 7 The data collected in regional mapping were plotted in the field on the aerial photographs from which the 15-minute topographic maps covering the area were prepared. These photographs are on scales ranging from about 1: 24,000 to 1 : 40,000-from 1 inch=2,000 feet to 1 inch=3,333 feet. Observations were plotted by use of a simple lens-type stereoscope having a X 2 magnification. The use of a stereoscope permitted more accurate plotting than would otherwise have been pos- sible and aided in planning traverses and in evaluating possible alternative interpretations of data. The data on the photographs were transferred to the topographic quadrangle base maps by multiplex. Later a few ob- servations were added to the maps and some modifica- tions made by simple inspection. In mapping, it obviously was not possible, because of the rugged terrane, to gain access to all parts of the area. Where the terrane is too rugged to be occupied, however, the exposures are generally excellent, and con- tacts can be drawn across inaccessible areas with con- siderable confidence-indeed, many contacts are visible on the aerial photographs, especially when viewed through a stereoscope. The coverage of ground was most thorough in the vicinity of ore deposits and in areas of metamorphic rock; granitic and alluviated areas generally were less thoroughly covered. Over 1,000 specimens were collected, about half of granitic rocks and about half of metamorphic rocks. More than 600 of the specimens were studied micro- scopically in thin section. In addition, larger samples were collected for chemical analyses and for age deter- minations by radiometric methods. The tungsten mines and prospects were mapped on scales of 1 inch=20 feet or 1 inch=40 feet. Plane table, alidade, and stadia rod were used in the preparation of surface maps, and plane table, open-sight alidade, and tape, or Brunton pocket compass and tape were used for underground maps. Base maps of mine workings were prepared only where none were available from the operator. Modal analyses of granitic rocks were made by using thin sections of finer grained rocks and stained slabs of coarser grained rocks. Plagioclase determinations and measurements of the optic angles of pyroxenes were made by using a 4-axis universal stage. All colors re- ferred to in the report are in accord with the Rock Color Chart issued by the Geological Society of America (Goddard and others, 1948 (1951)). This chart is based on the Munsell system of color identification. ACKNOWLEDGMENTS The study of the Bishop tungsten district is part of a cooperative program between the U.S. Geological Survey and the California State Division of Mines. Study of the mines was largely made possible through the cooperation extended to the writer both by mining companies and by individuals engaged in mining or prospecting. Among the company mine staffs that have extended assistance are those of the Union Carbide Nuclear Co., the Tungstar Corp., and Panaminas, Inc. I am especially indebted to Mr. Lawson Wright of the Union Carbide Nuclear Co., who supplied much of the data on the Pine Creek mine and participated in the integration of these data into a cohesive treatment of the geology of the mine. The following individuals aided materially by supplying information or assist- ance: D. R. Adamson, Morris Albertoli, "Cap" Aubrey, J. F. Brackett, George Brown, C. W. Churchill, A. L. Covington, C. W. Fletcher, Gale Green, Gerald B. Hart- ley, Jr., Charles M. Herron, Kenneth G. Irons, E. E. Ives, H. O. Johansen, Robert Kelso, Otis A. Kittle, Vic- tor E. Kral, Stanley Lambert, Fred R. Lee, Mike Mil- lovitch, J. E. Morhardt, F. L. Murphrey, Nick Pappas, A. H. "Salty" Petersen, Joseph Rossi, Bert Shiveley, Robert Simpson, Joseph Smith, Al Stephens, Howard , Stephens, Robert Symons, and B. W. Van Voorhis. The logs of water wells bored in Owens Valley were CEOGRAPHY 5 made available by the Los Angeles Department of Wa- ter and Power. Others too numerous to mention also contributed information that has been incorporated in this report. I was aided in the field by the following members, or former members, of the Geological Survey, most of whom assisted me for one summer field season: M. P. Erickson, 1943 ; P. D. Proctor, 1946; M. W. Ellis, 1947; J. W. Reid, 1947; R. M. Campbell, 1948; M. F. Car- man, 1948; E. D. Jackson, 1949; L. D. Clark, 1949; R. F. Johnson, 1950 ; R. L. Parker, 1950; H. S. Imholz, 1950; E. M. MacKevett, 1951; Dallas Peck, 1952. In the laboratory, many of the point counts of granitic rocks were made by S. H. Huddleson and A. C. Bettiga. During the preparation of this report the writer profited from discussions with colleagues of the Geo- logical Survey, and many of the ideas expressed are a result of these discussions. Edgar H. Bailey and Dwight M. Lemmon critically reviewed the manuscript, and vastly improved its accuracy and technical presen- tation. David B. Stewart served as consultant and critic on parts of the report dealing with the relations of the granitic rocks to experimental data. In the planning of the illustrations Esther McDermott provided coun- cil and assistance far beyond the mere mechanics of preparation. GEOGRAPHY LOCATION AND ACCESSIBILITY The study area is in east-central California about midway between Reno, Nev., and Los Angeles, Calif. (fig. 1). It lies between lat 37°00" and 37°30" N. and long and 118°45" W., and includes a little more than 800 square miles. The area is traversed by U.S. Highway 6 between Los Angeles and Tonopah, Nev., and by U.S. Highway 395 from Reno. Access to the Central Valley of California and to the San Francisco Bay area from the study area is difficult because the Sierra Nevada intervenes, and the nearest road cross- ing, 70 miles north of the area, State Highway 120 through Tioga Pass, is open for travel only during the summer months. U.S. Highways 50 and 40, through Echo and Donner Passes, respectively, 175 and 205 miles to the north, and State 178 and U.S. 466, through Walker and Tehachapi Passes, 130 and 170 miles to the south, generally are open all year. SURFACE FEATURES The area includes parts of two high mountain ranges, the Sierra Nevada in the west and the White Moun- tains in the east, separated by a deep trough that is oc- cupied by Owens Valley, Round Valley, and the Vol- canic Tableland. The area is one of considerable re- lief-altitudes range from less than 4,000 feet on the floor of Owens Valley to more than 14,000 feet in the Sierra Nevada. Nevertheless, great relief is confined to the two ranges; the relief within the trough generally is only about 1,000 feet, except in the Mount Tom quad- rangle where fans that flank Round Valley on the west and the Volcanic Tableland north of Paradise Camp ex- tend upward to altitudes of more than 6,000 feet. The crest and eastern face of the Sierra Nevada oc- cupy more than half of the mapped area. The Sierra Nevada divide culminates in North Palisade Peak at an altitude of 14,242 feet, and most of the named peaks along the crest attain altitudes of more than 13,000 feet. In most places the divide is a "knife-edged" ridge, passable on foot in only a few places. The upper slopes are largely steep-walled glacial cirques that are mantled with talus. Moraines commonly fringe the lower sides of cirque basins, and in the larger canyons extend down- ward to altitudes as low as 5,200 feet. Below the glaci- ated zone the slopes are less precipitous but, in most places, are still steep. The Sierra Nevada escarpment is precipitous only in the northern and southern parts of the area where the average slope of the escarpment exceeds 30°. The mid- dle span between the Tungsten Hills on the north and Fish Springs Hill on the south is a broad convex bulge having comparatively gentle slopes of about 10°. The summit surface of this bulge, a gently rolling, till-cov- ered upland that includes Coyote Flat, Coyote Ridge, and Table Mountain, occupies many square miles be- tween altitudes of 9,000 and 11,000 feet. Northward the surface slopes down to the Tungsten Hills, and east- ward and southeastward it slopes into the foothills southwest of Big Pine, and thus forms reentrants with the precipitous escarpments to the north and south. Deep canyons cross these slopes, but broad surfaces be- tween the canyons are composed of soil and weathered rock. Among the many steep canyons that drain the Sierra escarpment, those of Rock Creek, Pine Creek, Bishop Creek, Baker Creek, and Big Pine Creek are the largest and drain the most extensive areas. - The lower parts of all these canyons except that of Baker Creek are acces- sible by road; and in Rock Creek and Bishop Creek canyons, roads extend to altitudes of 9,500 feet or more. The average slope of the White Mountains escarp- ment within the mapped area is generally between 10° and 15°, a trifle steeper than the gently sloping middle span of the Sierra escarpment. Slopes generally are steeper in the south part than in the north part. Inas- much as the area extends only part way up the slope, altitudes do not exceed 9,600 feet, but summit altitudes GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA W >Rra RENO AND CENTRAL VALLEY K EXPLANATION via sonoma mass] \ . ~ \\ £ Valley bottoms 44,6 \\ M \\38°00 Central| Valley Adobe / Loke -" \\ ~- r/ ~ Sto & ro ~ ® TONOPA'y A ® ms: 9 \ San Francisco w /"\ ® \‘ 2 b3 395 f ~ ® #> \ % \ * 2 g \ | yammoth fr 0 \\ > q \ yen ¥ /,_/ 0 P l Mobean / AP VALLEYS ; ___ MT Tom [744g ' BISHOP" *~ QUADRANGLE [e# MT QUADRANGLE: \n l To / K TuNesTEN , , HILLS / A/[G® A P0 &a cl Florence HompnkEvé o f Lake ~ Huntington ke } A ; M ( W @ MT GODQARD“ ¥4 {1-0 ZA IG: PINE QUADRANGLE~ P* /// ADRANGLE \ i % V300 24 /\_;/h'o~ Galcier 1-73-1701"th z ef Teel Reservoir a 37° u < 0°! Amv ., ‘ r | , : f Z King s 3 \ ‘ o N . I ; ® ' 2 nt 19°00 118 ©00 {4-4 LLL ALAEA 1 1 FicUurE 1.-Index map showing the area mapped for this report. GEOGRAPHY 7 farther east exceed 11,000 feet, and White Mountain Peak to the north reaches 14,242 feet. In the north part, especially north of Silver Canyon, structurally controlled shallow valleys parallel with the trend of the range front are present in the interfluves. The range front is cut by several canyons, the three largest of which, Coldwater, Silver, and Black Canyons, contain perennial streams. The canyons are steep walled, and the streambeds are gravel covered and slope uniformly. South of Bishop, Owens Valley occupies the entire trough area between the Sierra Nevada and the White Mountains, but a few miles north of Bishop, Owens Valley proper terminates along a steep south-facing escarpment that bounds the Volcanic Tableland. How- ever, a narrow continuation of the valley extends north- ward beyond the quadrangle boundary between the east side of the Volcanic Tableland and the White Moun- tains. West of Bishop, Owens Valley is bounded by low river terraces that separate it from Round Valley. The floor of Owens Valley is a flat plain 3 to 5 miles wide, which is flanked on the east and southwest by extensive alluvial fans formed from debris carried out of the White Mountains and the Sierra Nevada. The valley floor slopes gently southward from about 4,100 feet at Bishop to 3,900 feet 16 miles to the south near Big Pine. South of Big Pine several hills rise above the alluvial apron from the Sierra Nevada. These in- clude Crater Mountain, Red Mountain, and a low hill 2 miles northwest of Red Mountain, all of volcanic origin, and Fish Spring Hill and the Poverty Hills, which are upfaulted blocks of the crystalline basement. Round Valley lies in a reentrant in the Sierra Nevada front which bounds it on the west and south; on the northeast it is bounded by the Volcanic Tableland. The valley is formed by the meeting of coalescent fans from the Sierra Nevada with the Volcanic Tableland. The lower, gentler sloping parts of the fans constitute the valley floor. The floor is a nearly flat area 6 miles long and as much as 2 miles wide, but the entire basin, in- cluding the upper parts of the fans, is at least twice as large. The Volcanic Tableland is a large plateau of rhyolite tuff, which extends into the northern part of the area. It slopes generally southeastward at about 125 feet per mile, except in the southwestern part, where it slopes southwestward into Round Valley. In the western part of the tableland, small rounded hills rise above the gen- eral level, and deep gorges have been cut by Rock Creek and the Owens River. In the eastern part the fairly even surface of the tableland is broken by many north- trending fault scarps and contains several undrained depressions. The longest and highest scarp, along the east side of Fish Slough, averages about 300 feet high, but most other scarps are less than a mile long and less than 100 feet high. On the south and east sides the Volcanic Tableland is bounded by escarpments. The average height of the escarpment on the south side is about 200 feet, but it is higher toward the west and lower toward the east. The maximum height of the escarpment on the east side is about 200 feet, but most of it is much lower. Elevated stream-cut terraces flank the Volcanic Tableland on the south and east sides. They are cut chiefly on the rhyolite tuff that composes the Volcanic Tableland, but the south-side terraces and locally the east-side terraces are gravel covered. The area is drained by the Owens River, which emp- ties naturally into Owens Lake at the south end of Owens Valley, but much of the water in the river has been diverted to an aqueduct which carries about 330,000 acre-feet annually to the city of Los Angeles. The principal tributaries from the Sierra Nevada to the Owens River within the map area are, from north to south, Rock Creek, Pine Creek, Bishop Creek, Baker Creek, Big Pine Creek, and Tinemaha Creek. In the northeast part of the Mount Tom quadrangle the Owens River flows toward the south in the deep gorge that it has cut into the Volcanic Tableland. On leaving the tableland it flows due east along the base of the cliffs that mark the south side of the tableland to the base of the fans along the White Mountains; from there it flows southward along the east side of Owens Valley. SETTLEMENTS AND CULTURE The population of Inyo County is about 11,500, at least half of whom live within the mapped area. Bishop, with a population of about 3 000, is the largest town. Smaller settlements are Big Pine, 16 miles south of Bishop; Laws, 3 miles northeast of Bishop; and in Pine Creek Canyon. Rovanna, at the mouth of Pine Creek Canyon, provides housing for employees of the Pine Creek tungsten mine of the Union Carbide Nuclear Co. The economy of Bishop and of most of the other settlements in Owens Valley is based primarily on tourist trade, but mining and cattle raising furnish additional income. Although the area is more than 200 miles from Los Angeles, the spectacular scenery in the Sierra Nevada and the many well-stocked lakes and streams attract many thousand tourists into the area every year. The area is also visited for deer, dove, sagehen, duck, and pheasant hunting, for winter sports, especially ski- ing, and for aerial gliding. Air plunging over the Sierra escarpment rises from the valley floor in a huge vertical updraft that reaches upward thousands of feet (Barnett, 1955, p. 74-75), and many of the world's glid- ing records have been made above Owens Valley. 8 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA Although since World War II the economy of Owens Valley has been based chiefly on tourist trade, it has not always been so. Early discoveries of gold caused some excitement, but the economy of the first settlers in the valley in the early 1860's was founded on sheep and cattle raising and to a lesser extent on agriculture. Irrigation districts were organized, and a network of canals for irrigation was constructed. At the turn of the century a ready market for produce existed in the booming mining camps of Nevada, especially at Tono- pah. The need for water in Los Angeles, 200 miles to the south, resulted in the building of an aqueduct to the lower end of the valley, and to acquisition by the city of Los Angeles of most of the arable land within the valley itself. In 1939 and 1940, as economic conditions improved throughout the nation, tourists appeared in the valley in large numbers, and the tremendous growth of popu- lation in southern and central California after World War II resulted in further increases. Many of the tungsten mines, idle or operated only intermittently since World War I, were reopened in the late 1930's because of increased price and demand for tungsten, and have been operated intermittently since then. In 1959, the price and demand were low and only the Pine Creek mine of the Union Carbide Nuclear Co. was in operation. CLIMATE AND VEGETATION Except for a few square miles west of the Sierra Nevada divide, the study area is in the western part of the Great Basin, a semiarid region in the rain shadow of the Sierra Nevada. Both temperature and precipi- tation vary widely in different parts of the area, corre- sponding to the wide differences in altitude. As in most arid regions, the diurnal range of temperature is large. On the floor of Owens Valley, daytime tempera- tures in the summer often exceed 100° F, but the nights are comfortably cool. . Winter days generally are pleasant with a temperature well above freezing; night temperatures, though below freezing, are rarely as low as zero. Most of the precipitation is during the winter, but summer thundershowers are common. At higher altitudes almost all of the winter precipitation is as snow, but at lower altitudes much of it is as rain. The amount of snow in the valley at any one time rarely exceeds a foot, although as much as several feet has collected. At higher altitudes the temperatures are progres- sively lower and the precipitation higher-snow col- lects to depths of many feet, and on north slopes banks of snow may persist through the summer. During July, thundershowers, accompanied by spectacular dis- plays of lightening, are common in the middle part of the day. Climatic data supplied by the U.S. Weather Bureau for Bishop and for South Lake are summarized in table 1. Data from the weather station at Bishop, altitude about 4,100 feet, are representative of lower altitudes, and those from the station at South Lake, about 9,600 feet, are representative of higher altitudes. At low altitudes the winters generally are mild enough to permit mining operations all year without undue difficulty, whereas at high altitudes the more severe winter climate requires careful, and generally costly, preparation for successful winter operation. Tastes 1.1-Summary of weather date at Bishop and at South Lake, Calif. [Pata from U.S. Weather Bureau, San Francisco office. Average-precipitation data at Bishop are for a 40-year period; all other data are averages of periods of at least 20 years. Temperature data in degrees Farhrenheit, other in inches] Bishop airport (alt South Lake (alt 4,108 ft) 9,620 ft) G A verage- January | July [Annual) January | July [Annual Maximum temperature... .. 52.8 | 93.8 72.8 38. 8 69. 1 51. 4 Minimum temperature... .. 21.1 | 54.3 36.2 12.5 45.2 27.2 Temperature............... 36.8 | 73.6 54.6 25.7 57.1 39.3 Precipitation......._.._.... 1.5 0.1 5.8 2.2 .6 17.4 5.5 .0 17.4 33.9 "r. 174.0 Native vegetation is sparse on the lower slopes of the mountains and also on the floor of Owens Valley, except along streams, where willow, alder, and other deciduous trees are found. Cottonwoods and Lombardy poplars planted by early settlers are common in settled parts of the valley, and in the towns a wide variety of shade trees has been introduced. Locally at altitudes of about 8,000 feet manzanita or sage is present, and much of the rolling upland east of Coyote Flat, which lies between 9,500 and 11,000 feet, is sage covered. Conifers are present locally in the mountain regions between altitudes of 6,500 and 10,500 feet in the Sierra Nevada and above 7,500 feet in the White Mountains, but even though some of the larger canyons are heavily wooded, continuously forested areas like those on the west slope of the Sierra Nevada are absent. Singleleaf pine and juniper grow at the lowest altitudes and are the only conifers growing in the part of the White Mountains discussed here. In the Sierra Nevada, juniper and singleleaf pine merge with groves of Jeffrey pine at about 7,500 feet, and at somewhat higher altitudes they are replaced by stands of lodge- pole pine. Limber pine and red and white fir are not common in this area. White bark pine is the timber- line tree and occurs in low windblown forms,. Aspen and willow are present along streams and in other well- watered areas. The trees are generally too small to sup- port a lumbering operation except for small stands of PREBATHOLITHIC GEOLOGY 9 Jeffrey pine, which are mostly in areas set aside for recreation. Lumber cut farther north in the Mammoth Lakes area or trucked in from Los Angeles can be pur- chased locally, and very little timber has been cut in the area in recent years. Brown (1954) and Schumacher (1962) give additional information about the flora of the area. PREBATHOLITHIC GEOLOGY Rocks older than the Sierra Nevada batholith are found in the Bishop district only as remnants. Strong- ly folded and faulted strata of late Precambrian ( ?) and Early Cambrian ages are exposed in the White Moun- tains, and similarly deformed metamorphosed strata of Paleozoic and early Mesozoic ages are present in the Sierra Nevada in scattered roof pendants, septa, and in- clusions (pl. 3). In spite of their scarcity and scat- tered distribution, these remnants yield information which, when used with data obtained from nearby areas, provides a generalized picture of the events that took place between late Precambrian(?) and Cretaceous time, when the Sierra Nevada batholith was intruded. During late Precambrian(?) and Paleozoic time many thousand feet of marine sedimentary deposits ac- cumulated in the Bishop district, and in Mesozoic time they were followed by thick dominantly volcanic de- posits. Unconformities have been observed in nearby areas and may be present in the Bishop district, within the Paleozoic and between the Paleozoic and Mesozoic. In the Candelaria Hills, 55 miles north-northeast of Bishop, Ferguson and Muller (1949, p. 7-8) report Per- mian strata resting with angular discordance on Ordo- vician rocks; they also report an unconformity between the Triassic and Permian. Kirk (in Knopf, 1918, p. 45-46) describes an unconformity between Triassic and Carboniferous rocks in the southern part of the Inyo Range. The structural movements that caused the folding and faulting of the prebatholithic strata probably began in Triassic time, probably contemporaneously with the onset of Mesozoic vulcanism, and ended in Late Jurassic or Early Cretaceous time. UPPER PRECAMBRIAN(?) AND LOWER CAMBRIAN SEDIMENTARY ROCKS OF THE WHITE MOUNTAINS More than 10,000 feet of strongly deformed sedi- mentary strata of late Precambrian(?) and Early Cambrian age crop out in a southward-tapering area of about 40 square miles mapped along the west slope of the White Mountains. The upper 3,500 feet of strata contain Lower Cambrian fossils, but no diagnostic fos- 'In the explanation of plate 3, the Bishop agglutinated tuff is errone- ously shown as green; it should be light tan as shown in the north- western part of the map itself. 735-925 O-65--2 sils have been found in the lower 6,000 feet of strata. The entire sequence appears conformable, but the area mapped is too small to rule out unconformities. A sum- mary of the exposed stratigraphic sequence with the approximate thickness of the mapped units follows: Formation Thickness Remarks (feet) Harkless __.. 1, 000+ Poleta formation_.._.._______ 1, 000+ Campito formation: Fossiliferous; Montenegro member. ___. 600 + Lower Cam- Andrews Mountain brian. 3, 000 + No diagnostic Deep Spring formation . __ _ ___ 1, 500 {1058123 £01311.le Reed dolomite 2, 000 + o S1 Wyman formation_.._........ 1,000 + Lower Cam- brian. 10, 100 + The stratigraphic nomenclature used in this report is in accord with that of Nelson (1962) who has studied generally better preserved sequences in the Blanco Mountain and Waucoba Mountain quadrangles, which adjoin the area on the east. No attempt has been made to measure and describe stratigraphic sections in de- tail, except for the Deep Spring formation ; indeed, the complexity of the structure precludes making detailed measurements of most units. Only formations that have yielded Olenellid trilo- bites are designated as unequivocal Lower Cambrian. The lowest Olenellid trilobites thus far reported were collected in the Blanco Mountain quadrangle by C. A. Nelson (written communication, 1959) from the An- drews Mountain member of the Campito formation about 900 feet below the top of the member. The Deep Spring and older formations are designated upper Precambrian or Lower Cambrian inasmuch as no basis exists for assigning them a more specific age. Kirk (in Knopf, 1918, p. 25) placed the base of the Cambrian in this region at the base of the Campito formation, although diagnostic fossils had not then been found in it. He felt that the Deep Spring forma- tion and rocks below it have little in common with the overlying Campito formation, and also believed a pro- nounced unconformity separated the two groups. Un- doubtedly, he was influenced by the prevailing belief that systems are separated by worldwide unconformi- ties, and further that the first sediments deposited would be sandstones. The basis for Kirk's unconformity beneath the Cam- pito formation was that the lithology of underlying but structurally conformable strata is different in the vicinity of Black Canyon from what it is along the west side of Deep Spring Valley 15 miles east in the 10 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA Blanco Mountain quadrangle. Kirk thought that at Black Canyon the Campito formation rested directly on the Reed dolomite; however, the upper part of what he identified as Reed dolomite is a facies of the Deep Spring formation. Although no unconformities were identified, the com- paratively small size of the area mapped and the highly deformed character of the strata make inadvis- able a categorical statement that no unconformities exist within the section. Previous workers have reported un- conformities in a similar stratigraphic section in the Blanco Mountain and Waucoba Mountain quadrangles, \vhich,.%djoin the area on the east. l WYMAN FORMATION The Wyman formation is exposed at two places about 3 miles apart. The smaller and more northerly ex- posure is in the north wall of a fault canyon in the NE! see. 19, T. 7 S., R. 34 E.; the larger and more southerly exposure is in sec. 5, T. 8 S., R. 34 E. (pl. 3). Both exposures are in the base of the range at the head of the alluvial apron. At the southern locality, where about 1,000 feet of strata are exposed in a prominent ridge south of the mouth of Black Canyon, the strata can be divided into four lithologically distinct units, each about 250 feet thick. The description of these units from the bottom up is as follows: 1. Platy thin-bedded dark-gray sandstone and silt- stone. 2. About 20 feet of well-bedded dolomite at the base of the unit is overlain by thin-bedded medium-gray limestone and dark-gray sand- stone. 3. Massive medium-gray, somewhat recrystallized dolomite and residual areas of thin-bedded medium light-gray limestone. Some of the limestone contains small oolitic nodules of con- centric structure. The nodules range in diam- eter from an eighth of an inch or less to half an inch and may be algal. 4. Thin-bedded dark-gray limestone and sandstone and a few shaly layers. The upper contact with the Reed dolomite is sharp. At the northern locality only about 280 feet of strata crop out. The lower 100 feet consists of thin-bedded medium-gray silty shale and limestone. Next overlying is 40 feet of thin-bedded limestone and some shale inter- beds, then a massive medium-gray limestone bed about 30 feet thick. The upper 110 feet consists of thinly interbedded medium-gray limestone beds 1 to 4 inches thick separated by an inch or two of sandy shale. In two places, however, shaly beds 3 to 4 feet thick occur. As at the southern locality, the upper contact is sharp. The 280 feet of strata at the northern locality is lithologically similar, though not identical, to unit 4 at the southern locality. If these strata are stratigraphi- cally equivalent, an unconformity at the base of the Reed dolomite is unlikely in this area. The name Wyman formation was applied by J. H. Maxson to 3,700 feet of strata lying unconformably beneath the Reed dolomite in the Blanco Mountain quadrangle to the east (Maxson, 1935, p. 314). He de- scribed these beds as spotted schist and phyllite and a few dolomite beds. Kirk had previously described the same strata as "oldest sandstones and dolomites." He wrote, "In general, the series as seen at several points seems to consist of thin beds of arenaceous slate, some beds of impure dolomite, and thin beds of sandstone" (Kirk, in Knopf, 1918, p. 23). These descriptions in- dicate that the strata beneath the Reed dolomite in the Blanco Mountain quadrangle are similar to the strata beneath the Reed dolomite in the Bishop district, al- though the presence of an unconformity beneath the Reed dolomite in the Blanco Mountain quadrangle casts some doubt on precise equivalence of the strata in the two areas. C. A. Nelson has restudied the Blanco Mountain quadrangle and also has inspected the strata on the south side of Black Canyon, and he regards the strata as belonging to the same general sequence (writ- ten communication, 1959). REED DOLOMITE The thick Reed dolomite is well exposed along the lower slopes of the White Mountains between Redding Canyon and a point 2 miles south of Black Canyon (pl. 3). The most notable characteristic of the forma- tion is its massiveness. Bedding, shown by thick mem- bers from a distance, on close examination is obscure and difficult to identify. Conspicuous joints a few inches to a few feet apart cut the dolomite almost every- where, and the rock breaks along joint planes into angular blocks that form rough talus slopes. In most places the dolomite is microcrystalline, but locally it is recrystallized to a medium-grained dolo- mitic marble. Fresh surfaces of typical fine-grained rock are white or pale gray, but weathered surfaces generally are grayish yellow and are etched by the curving lines and pock marks that constitute the "ele- phant-hide" surface typical of many dolomite rocks exposed in desert areas. South of Black Canyon the dolomite is medium gray and has been recrystallized. The only organic remains found are poorly preserved forms that Kirk says strongly suggest calcareous algae of the type of Géirvanella (in Knopf, 1918, p. 24). PREBATHOLITHIC GEOLOGY 11 The lower contact of the formation with the Wyman formation is sharp and is marked by a conspicuous lithologic break, but the upper contact with the Deep Spring formation is less well defined. The horizon chosen as the upper contact in mapping is the boundary between a thick yellowish-gray unit and a contrasting pale- or medium-gray dolomite below. In most places the outcrop of this horizon is recognizable on aerial photographs-a feature that proved to be an invaluable aid in mapping. The actual upper contact, based on color, is sharp; in a broad sense it follows a strati- graphic horizon, but it crosses beds locally and is stratigraphically a few feet higher in some places than in others. Although the formation is well exposed, a complete and unfaulted section was not found. Above the south- ern exposure of the Wyman formation south of Black Canyon, however, the formation appears to be cut by only one fault that causes the apparent thickness of the Reed dolomite to be greater than the true thickness. The apparent thickness at this locality is 2,200 feet, assuming no displacement on the fault. The throw on the fault is probably no more than 200 to 300 feet. In the construction of the structure sections (pl. 5) and block diagram (pl. 6), a thickness of 2,000 feet was assumed. Support for this assumption is derived from a measurement by Kirk (in Knopf, 1918, p. 24) of 2,000+ feet in the head of Wyman Canyon, a few miles to the northeast. Maxson (1935, p. 314), however, measured a thickness of 2,500+ feet in the same gen- eral area. A probable correlative of the Reed dolomite is the Noonday dolomite, which is widespread throughout the Death Valley region (Hazzard, 1937, p. 300-302). The two formations are of comparable thickness and lith- ology, occupy similar positions beneath fossiliferous strata of Early Cambrian age, and contain algae but no other fossils. Chemical analyses of specimens from the two formations reported by Hazzard (1937, p. 302) in- dicate that both are nearly pure dolomite and of al- most identical composition. DEEP SPRING FORMATION The strata assigned to the Deep Spring formation are well exposed along the White Mountain front southeast of Bishop, in the same area as the Reed dolomite on which it rests. Lithologically these strata are quite dif- ferent from the strata at the type locality of the forma- tion 15 miles to the east, but the two lithologies inter- finger in the intervening area and are clearly equivalent. According to C. A. Nelson (written communication, 1960), a few selected lithologies can be traced from the type locality to the exposures southeast of Bishop. The formation along the White Mountain front con- sists of 1,500+ feet of arenaceous dolomite containing limestone in the upper 150 feet and two conspicuous slaty quartzitic layers at 320 and 785 feet beneath the top. From the floor of Owens Valley between Bishop and Big Pine the formation can be seen to extend for 2 miles north from Black Canyon (fig. 2). In the late afternoon, the well-bedded, alternately brown and gray strata contrast with both the underlying massive gray- FicurE 2.-Unfossiliferous Upper Precambrian or Lower Cambrian strata along White Mountain front north of Black Canyon. rock on summits is Andrews Mountain member of the Campito formation. Underlying massive light-colored rock is Reed dolomite. member is Deep Spring formation. Dark Conspicuously banded rock beneath Andrews Mountain Middle foreground consists of older dissected alluvial fan and lakebed deposits of Cenozoic age, and foreground consists of undissected alluvial fan deposits. 12 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA ish-yellow Reed dolomite and with the overlying dusky- brown to grayish-black Andrews Mountain member of the Campito formation. This section, measured and de- scribed by Walcott (1895, p. 142-143), is reproduced in figure 3 together with two other sections, one on the south side of Black Canyon measured by me and one at the type locality on the north side of Deep Spring Val- ley measured by Kirk (in Knopf, 1918, p. 25). The section visible from Owens Valley and measured by Walcott lies just east of the boundary of the mapped area, but the one measured by me, though not visible from the floor of Owens Valley is equally satisfactory. This section was measured along a ridge on the south side of Black Canyon in the SWL sec. 4, T.8 S., R. 34 E. The upper 1,200 feet of the formation was meas- ured with telescopic alidade and stadia rod-a span that was thought, at the time it was measured, to in- clude all the strata that might be assigned to the Deep Spring formation-and the lower 300 feet of strata was calculated approximately from the trace of the unit on the quadrangle map. Unfortunately for comparative purposes, the aggregate thickness of the lithologic units tabulated by Walcott is 135 feet less than the 1,525 feet he gives for the total thickness of unit 2, which comprises the strata here assigned to the Deep Spring formation. Comparison with the section south of Black Canyon suggests that most and possibly all 135 feet should be added at the top of the column, but perhaps a part of it may represent omissions lower in the section. The upper contact with the Campito formation is sharp and offers no problem in mapping. The fact that beds in the basal part of the Campito formation and in the top of the Deep Spring formation are mainly conformable with each other and with the contact throughout the mapped area gives no support for the unconformity suggested by Kirk (in Knopf, 1918, p. 24-25). The lower contact with the Reed dolomite of- fers more difficulties, inasmuch as both formations are chiefly dolomite. The contact is placed at the base of a 500-foot-thick unit which contrasts in color with the underlying Reed dolomite. An interesting feature of the formation is locally con- spicuous crossbedding, which together with the arena- ceous character of the dolomite indicates that much, and possibly all, of the formation is of clastic origin. Some of the most conspicuous crossbeds are in avrenaceous layers, but in places crossbeds also are preserved in car- bonate layers. The height of the crossbeds ranges from a fraction of an inch to several feet, and heights of 2 to 6 inches are common. Generally the false beds meet true beds sharply at an angle of 25° to 30°. The common carbonate mineral is dolomite, but un- dolomitized residuals of blue or blue-white limestone are common in the upper 150 feet. In a single bed the limestone masses meet the dolomite with sharp trans- gressive contact. Figure 4 is a sketch of an outcrop that illustrates the most common relation between the limestone and dolomite within a single bed. According to Kirk (in Knopf, 1918, p. 24-25), the Deep Spring formation at the type section 15 miles to the east along the northwest side of Deep Spring Valley comprises 1,600 feet of quartzitic and calcareous sand- stone containing a few layers of arenaceous limestone. Maxson reports 3,100 feet (1935, p. 314). In the area between the type section and the west front of the White Mountains the dominantly arenaceous strata at the type locality interfingers laterally with the domi- nantly dolomitic strata along the west front of the White Mountains. In upper Black Canyon the Deep Spring formation consists of interbedded arenaceous dolomite and quartzitic sandstone in about equal amounts, and both the dolomite and sandstone are lo- cally crossbedded. Kirk (in Knopf, 1918, p. 24-25) included the strata in Black Canyon, assigned here to the Deep Spring formation in the upper part of the Reed dolomite, and concluded that at Marble Canyon (Black Canyon) the Campito formation rests directly on the Reed dolomite. From this and similar observa- tions in other areas he postulated an important uncon- formity at the base of the Campito formation. The only known formation that seems a possible correlative of the Deep Spring formation is the John- nie formation of southern Nevada and contiguous areas in the Death Valley region of California. The distance between the White Mountains and the closest outcrop of the Johnnie formation is too great to permit correl- ation at this time, but the two formations have many lithologic similarities and appear to occupy approxi- mately the same stratigraphic interval. CAMPITO FORMATION The Campito formation consists of two members, a lower sandstone member designated the Andrews Moun- tain, and an upper shale and slate member designated the Montenegro. The Andrews Mountain sandstone member was included by Kirk (in Knopf, 1918, p. 27- 28) in his Campito sandstone, but the Montenegro shale member may have been included, at least in part in his overlying Silver Peak group. The name Silver Peak was applied by Turner (1902, p. 264-265) to strata of Early Cambrian age near Silver Peak, about 45 miles northeast of Bishop. The term was extended by Walcott (1908, p. 185-188) to include the fossilifer- ous Lower Cambrian strata of western Nevada and east- ern California. In this report the term Silver Peak group will not be used because its lower boundary in the Section of Deep Spring formation at type locality in second canyon north of Antelope Spring on west side of Deep Spring Valley. (Kirk, in Knopf, 1918, p. 25) THICKNESS IN FEET Sandstone, massive, irregularly bedded, buff, calcareous 35 Sandstone, heavy, blue to gray, calcareous Sandstone and arenaceous slate; dark brown in fresh fracture; weathers black Sandstone, massive, bluish and gray, calcareous Limestone, buff, with well-marked iron-stained bands Sandstone, massive, blue, quartzitic Limestone, thin-bedded to massive, grayish white; weathers platy; iron stained in bands; near top distinctly banded bluish gray and white Shale, arenaceous, with interbedded quartzitic sandstone Sandstone, white, quartzitic, thinly bedded at base, more massive above Sandstone, shaly; merges upward into overlying blocky sandstone Sandstone, fairly massive, buff Sandstone, bluish, platy, quartzitic; weathers in blocky angular fragments; banded with browns, reds, and grays Sandstone, massive, fairly soft; grayish toward base, buff above Sandstone, quartzitic; buff toward base, grayish above; marked by a very characteristic, sharp, ribbonlike banding Sandstone, quartzitic to fairly soft, thin to heavy- bedded; ranges in color from buff to dark gray Sandstone, white, massive; weathers slightly buff Sandstone, quartzitic; irregular contact at base; basal part deeply iron stained; dark buff above Limestone, very coarse, crystalline Limestone, heavy-bedded, buff and white, sac- charoidal, arenaceous; weathers readily Limestone, dirty white Sandstone, massive, coarse-grained, banded, weathers buff Sandstone, thin-bedded, quartzitic; weathers greenish and buff Limestone, heavy-bedded; weathers buff Sandstone, thin-bedded, platy, grayish and buff; quartzitic in one or two fairly thick beds In part concealed; the greater part apparently grayish crystalline limestone. - Some heavy white quartzite banded with brown Quartzite, thin-banded, copper-stained (locally), brownish Walcott's unit 2 in ridge on north side of Black Canyon (Walcott, 1895, p. 142-143) THICKNESS IN FEET Discrepancy between total thickness of 1525 feet given for unit 2 and 1390 feet total for litho- logic components Limestone, bedded, gray, arenaceous; massive Quartzite, dark, banded Sandstone, brownish and buff-colored, calcareous, with inclosed brecciated thin-bedded brown sandstone Limestone, thick-bedded, bluish-gray Limestone, gray, arenaceous, with bands of buff- colored mostly thick-bedded limestone Limestone, bluish-gray, banded Limestone, buff-colored, shaly Limestone, massive, bedded, coarse, arenaceous, gray; passes into buff-colored and cherty beds above Limestone, shaly and thick-bedded, sandy; cross- bedded in places, with yellowish-buff layers, also with two bands of brown thick-bedded and shaly quartzite Limestone, gray, arenaceous; cherty at top Limestone, buff and gray, more arenaceous, with a band of cherty limestone 20 to 25 feet thick at 125 feet from its base Limestone, light-gray and white Ficur®E 3.-Columnar sections of the Deep Spring formation. Section of dolomite of Deep Spring formation measured on the south side of Black Canyon in secs. 4 and 5, T. 8 S., R. 34 E. - Measured by Paul C. Bateman THICKNESS IN FEET Limestone, massive, medium-grained, gray and white, thin-bedded; weathers brown Limestone and dolomite, medium-light-gray to 125 medium-dark-gray, thin-bedded. Beds are 1 to 25 nently crossbedded in places. Crossbeds commonly are 1 inch deep and 4 inches long Dolomite, medium-dark-gray, thin-bedded; weathers light olive gray Slate, dark-gray and light-yellow-brown, with inter- beds of yellowish-gray quartzite. - Poorly ex- posed Dolomite, medium thin-bedded; weathers yellowish gray Dolomite, medium-gray. . Massive at base, indistinct thin bedding near top Dolomite, light-gray to yellowish-gray. . Indistinct thin bedding in most outcrops. - Weathers yel- lowish gray Dolomite, medium- to dark-gray, thin-bedded. Indistinct cross-bedding Sandstone and quartzite, pale-brown, dolomitic; light yellowish-gray slate and arenaceous dolo- mite. - Poorly exposed Dolomite, mottled light-yellow-gray to grayish olive. Bedding indistinct. Silicified zone about 3 feet thick at top Dolomite, light-gray to pale-grayish-orange mot- tled, medium-grained, with abundant stringers and thin layers of quartz. - Thin bedded in part. Forms topographic highs Dolomite, yellowish-gray, thin-bedded. . Locally where fracturing and recrystallization have de- stroyed evidence of bedding, the rock is similar to the underlying rock Dolomite, white to pale yellowish gray, massive Dolomite, gray, medium-grained. - Generally ho- mogeneous partings taken to be bedding. Gradational into overlying unit 2 inches thick. Soft and friable at base. Promi- ADOTOWHD OIHLITOHILYVYHHd EI 14 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA T ; fl 7 z - De_eb Spll'mg. florm‘aTbn' z rp 1 ferrin I I- /m fz 2 Zz -Z-, I I C | 1 ~ Iy >- Dolomite ~-: I I L 3 3 Tn ln I |- :3 Limestone | | | | | I 1-1 I T_ T Is I~ " | ¢: ECF -T GT- -~ 7°, e z- Ef -t _L T OXre I -I- T- T-" |- 5 0 5 10 FEET CL ___ " ear ery: FrcurE 4.-Clif section on north side of Black Canyon showing irreg- ular dolomitization of limestone in the top of the Deep Spring formation. Silver Peak region is in doubt and because the term is not necessary to the discussion. ANDREWS MOUNTAIN MEMBER The dusky-brown to grayish-black Andrews Moun- tain member of the Campito formation is named from exposures at Andrews Mountain, approximately 15 miles southeast of the mapped area in the southern part of the Waucoba Mountain quadrangle. Within the mapped area it is widely exposed along the west side of the White Mountains. Between Silver and Poleta Can- yons and on the west flank of Black Mountain it crops out along the range front; between Poleta and Black Canyons and for 2 miles south of Black Canyon it crops out higher in the range and overlies the Deep Spring formation (fig. 2). North of Gunter Creek it is exposed in the cores of several anticlines. A readily accessible exposure of the member is in Silver Canyon where it has an outcrop width of about 3 miles. The top and bottom of the Andrews Mountain mem- ber are exposed in places, but a complete and unfaulted section was not found. The thickest and most com- plete section is in the south half of sees. 8 and 9, T. 8 S., R. 34 E., where about 2,700 feet of strata in good order rest on the Deep Spring formation and are trun- cated at the top by a fault. Seventeen hundred feet of strata of the Andrews Mountain member crop out south of Redding Canyon in see. 17, T. 7 S., R. 34 E., between exposures of the underlying Deep Spring for- mation and overlying Montenegro member, but the An- drews Mountain is cut by two reverse faults that have telescoped the section. Walcott (1895, p. 143) meas- ured a thickness of 2,000 feet in Silver Canyon, but the base of the member is not exposed there, and his description suggests that the top of his section is the fault contact on the east side of the Andrews Moun- tain member with the Poleta formation. Kirk (in Knopf, 1918, p. 27) gives a paced measurement of 3,200 feet for the thickness of his Campito sandstone on the west side of Deep Spring Valley, which he thought to be fairly accurate. Whether the Montenegro shale member was included is not known. Maxson however (1935, p. 814), reports a thickness of only 2,000+ feet, measured presumably in the same general area. In the construction of the block diagram (pl. 6) a thickness of 3,000 feet was assumed for the Andrews Mountain member. The member consists chiefly of dark, very fine grained sandstone, but locally contains shaly or slaty layers and quartzite layers. Dense grayish-black rock in which bedding planes are difficult to identify in hand speci- men is the most common type. In some layers intri- cate crossbeds having heights of less than an inch are marked by thin black streaks of magnetite (fig. 5). Locally, very light colored quartzitic rock contains crossbeds that are several feet long and have ampli- tudes of almost a foot. FicurE 5.-Specimen of quartzitic facies of the Andrews Mountain member of the Campito formation showing crossbedding. PREBATHOLITHIC GEOLOGY 15 Under the microscope, specimens of the common grayish-black rock are seen to consist of angular to sub- angular grains of quartz and a little plagioclase set in a matrix of sericite, greenish biotite (partly chlori- tized), and magnetite. Accessory minerals include tourmaline and zircon. Generally quartz and plagio- clase grains are well graded; equidimensional grains are about 0.1 mm across and inequidimensional grains are about 0.1 mm in the shorter dimension and as much as 0.5 mm in the longer. Overgrowths on the quartz can be seen in some sections but were not recognized in most. The angularity of the grains probably reflects overgrowth rather than original shape of the grains. Some quartzitic layers are cemented with carbonate, and some light-brown rocks contain abundant limonite in the matrix. The member is cut by numerous joints, and locally an imperfect cleavage is present. The rock breaks along these surfaces and along bedding planes into irregular- shaped slabs that ring when walked over. The cleavage ordinarily is wavy and imperfect, although it is almost as perfect in some slaty layers as in the Montenegro member. Locally, in the axial regions of folds, the rock has been brecciated; subrounded fragments of sand- stone are contained in a matrix of sand and smaller fragments. Following is a qualitative description of the unbro- ken 2,700-foot section in sees. 8 and 9, T. 8 S., R. 34 E.; no measurements were made in the field and the thick- ness and distances given are approximate : Base to 200 feet : Thin bedded and platy ; beds generally are less than 2 inches thick and many bedding sur- faces are marked with branching tubelike fucoid forms. Crops out poorly. 200 to about 1,000 feet: Sandy dark-gray beds 1 to 2 feet thick are interbedded with thin silty layers similar to those in lower 200 feet. A few layers 1 to 4 feet thick of grayish-yellow quartzitic sand- stone are also present. Both the dark-gray and grayish-yellow sandy layers commonly are con- spicuously crossbedded. The fact that the inter- faces between thicker sandy beds and thinner silty beds are exceedingly sharp causes the stratification to be conspicuous. This part of the section crops out boldly because of the sandy beds, and contrasts with the underlying and overlying strata which crop out poorly. 1,000 to about 1,500 feet: Silty and shaly strata that form poor outcrops. Interfaces between beds are not sharp and stratification is inconspicuous-in many outcrops, bedding is difficult to identify. 1,500 to about 2,500 feet : Much like the section between 200 and 1,000 feet, but contains more dark silty and shaly layers. 2,500 to about 2,700 feet (fault) : Chiefly dark silty shale and shaly siltstone. Cleavage common and generally more conspicuous than bedding, which is obscure. The progressively finer grain of the upper part of the section suggests transition to the overlying Monte- negro member, but the highest exposed beds are siltier than the shale. Lenses and beds that contain carbonates and that weather out cavernously are present through- out the formation and are increasingly common toward the top; they suggest transition toward the overlying shale member, which contains similar carbonate beds and lenses. In most exposures the contact between the Andrews Mountain member and the overlying Montenegro mem- ber is sheared or obscured by cleavage that extends from the shale into the sandstone. The least disturbed ex- posure of the contact is in the NW 14 see. 21, T. 7 S., R. 34 E., where the beds dip gently and the contact is gra- dational through about 50 feet. It is not at all unlikely that within areas mapped as Andrews Mountain mem- ber there may be infolded slate that properly belongs to the Montenegro member. No fossils were found other than the branching tube- like forms characterized as fucoids. Kirk (in Knopf, 1918, p. 28) reported finding only annelid trails and trilobite(?) tracks. The annelid trails possibly are the fucoids. The Andrews Mountain member may be correlative with the Stirling quartzite of the Death Valley region. MONTENEGRO MEMBER The Montenegro member of the Campito formation is named from Montenegro Spring in the Blanco Moun- tain quadrangle where it has been studied by C. A. Nelson (written communication, 1959). The least dis- turbed section, however, is in the SW1!4 sec. 16, T. T S., R. 34 E., 3 miles east of Bigelow Station, a siding on the Southern Pacific Railway. About 600 feet of flat-lying shale was measured along a line that extends northeastward and upslope from a point near the south- west corner of see. 16. Near the section corner the Montenegro member rests on the Andrews Mountain member, and at the northeast end of the line of measure- ment it is overlain by the Poleta formation. The lower contact with the Andrews Mountain member is grada- tional through about 50 feet of strata, and the upper contact with the Poleta formation is abrupt. In most places the Montenegro is pale olive to gray- ish olive, but locally, generally in the vicinity of faults. 16 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA it is grayish yellow, and in a few places it is medium to dark gray. Bedding commonly is shown by thin dark greenish-gray silty layers and by thicker brownish carbonate-cemented sandy layers. Slaty cleavage is conspicuous in most outcrops. Where both cleavage and bedding are distinguishable, the cleavage lies at all angles to the bedding; only locally are the cleavage and bedding parallel. Along the measured section the shale lacks cleavage, possibly because of less intense deforma- tion than elsewhere, but more likely because of slight thermal metamorphism caused by intrusion of a stock of granitic rock in upper Poleta Canyon. Under the microscope the common grayish-olive slate can be seen to consist of a fine felt of pale yel- lowish-brown mica and subordinate chlorite, tiny grains of quartz, and scattered sericite. Sandy beds consist chiefly of quartz grains in a carbonate matrix; a little plagioclase and mica are common in small amounts, and tourmaline is present locally. The Montenegro member is incompetent, and as a result its distribution is highly irregular (pl. 3). Not only does it pinch and swell in an erratic fashion, but in places it is missing entirely and the overlying Poleta formation lies against the Andrews Mountain member. Not uncommonly the bedding is at an angle to the bedding in contiguous formations, even where other evidence of deformation is not obvious. De- formation within the shale is especially evident north of Poleta Canyon. HORNFELS Adjacent to the diorite stock north of Coldwater Canyon and extending away from it for about half a mile, slate of the Montenegro member has been con- verted to hornfels. Most of it is unspotted or very faintly spotted, but locally it is conspicuously spotted. Most unspotted hornfels is dark gray on fresh surfaces and grayish brown on weathered surfaces. In hand specimen it resembles finer grained parts of the An- drews Mountain sandstone member. The hornfels is a little coarser grained than the slate from which it was formed and consists chiefly of pale yellowish-brown mica and quartz that contains microscopic streaks and spots of chlorite. Some specimens also contain a little magnetite. One specimen from the south side of the stock, composed chiefly of zoisite and tremolite in the ratio of about 3 to 1, doubtless was derived from a cal- careous shale or slate. The groundmass of the spotted hornfels is greenish gray to medium dark gray and is composed of the same minerals as unspotted hornfels. The spots are grayish black ovoids that generally are a millimeter or less in longest dimension. They consist chiefly of chlorite, quartz, and pale yellowish-brown mica. Many spots exhibit a concentric arrangement-cores of fine-grained chlorite, quartz, and mica are enclosed by an inner zone of large rounded quartz grains and by an outer zone of coarser chlorite. FOSSILS Fossils were collected from the Montenegro member at three localities marked on the geologic map (pl. 3) : F, in SEZ sec. 24, T. 5 S., R. 34 E., on north side of draw on northwest side of road to mines on bench between Piute and Coldwater Canyons. Written communication from G. A. Cooper, 1949 : "This collection consists of numerous specimens of an olenellid trilobite of Lower Cambrian age. Inasmuch as the specimens preserve the head and thorax only, I am unable to decide what the correct generic name for the trilobite is. Unfortunately the tail is needed for accurate generic identification but none is preserved. Furthermore I am unable to identify the specimens with any known species of olenellid in the National Museum collections. The Bishop quadrangle specimens are unusual in having the eyes originating almost at the anterior end of the glabella. No described species is like this and none like this occurs in the National Museum collections. I therefore con- clude that the specimens submitted are a new species. Some resemblance to Nevadella gracilis (Walcott) can be detected but the two are not the same. I cannot therefore state from what part of the Lower Cambrian strata the specimens were taken." F:, a few hundred feet northeast of the S% corner of see. 1, T. 6 S., R. 33 E., on the north side of the road along Gunter Creek just below the main fork. Identified by Edwin Kirk, 1947 : Archaeocyathus sp. Kutorgina sp. F, on the ridge on the south side of the south branch of Gunter Creek, half a mile north of peak 7824. Identified by Edwin Kirk, 1947 : Archaecocyathus sp. Kutorgina sp. POLETA FORMATION The Poleta formation includes all the carbonate se- quences in the northern two-thirds of the mapped seg- ment of the White Mountains, except those of the Deep Spring formation. The Poleta formation is chiefly limestone, but contains much shale in its upper half. It is named after Poleta Canyon where it is well exposed. The thickness there is at least 1,000 feet and may be sev- eral hundred feet more. In most places, the formation has been strongly deformed, as the outcrop pattern in- dicates (pl. 3). Commonly the direction of bedding is clearly recognizable, but some limestone outcrops are massive, and others exhibit conspicuous cleavage that can be confused with bedding. In mapping, only the trace of lithologically distinctive units was taken to in- dicate bedding. Both the lower contact of the Poleta formation with the underlying Montenegro shale member and the upper contact with the Harkless formation are sharp every- where that they were observed. In many places these PREBATHOLITHIC GEOLOGY 17 contacts are sheared, but they are equally abrupt where they are little disturbed. Although the Poleta formation is predominantly limestone, it includes interbeds of calcareous shale or slate similar in appearance to that in the underlying Montenegro member and in the overlying Harkless formation. Dolomite is present within limestone beds in the form of thin anastomosing layers that lie along bedding, cleavage, and fracture planes, and clearly has replaced limestone, chiefly after the deformation of the strata. Most of the limestone and dolomite is medium to dark gray on fresh surfaces, but some has been recrystallized to white marble. Weathered surfaces of the dolomite commonly are yellowish orange to light brown-a fea- ture which makes it easy to distinguish dolomite from calcitic limestone. In places archeocyathids and al- mond-shaped ovoids (G@irvamella?) consisting of calcite are embedded in a matrix of dolomite. Fossil collections from the Poleta formation were made at only two localities, which are marked on the geologic map (pl. 3). Fossils collected from the Poleta formation, Bishop quadrangle : F,, on north side of Silver Canyon, 1,000 feet east of contact between Andrews Mountain member of the Campito formation on west and the Poleta formation on east ; in green shale within limestone unit ; possibly the same as Kirk's locality 7 (in Knopf, 1918, p. 31). Identified by Edwin Kirk, 1947: Archaeocyathus sp. F;, on south side of second ridge north of Silver Canyon at an altitude of about 7,500 feet; one-quarter mile westerly from peak 7824; in green shales above buff limestone. Identified by Edwin Kirk, 1947: Archaeocyathus sp. Kutorgina sp. Olenellus sp. (fragments) HARKLESS FORMATION The Harkless formation, named after Harkless Flat in the Waucoba Mountain quadrangle, crops out discon- tinuously along the east side of the mapped area be- tween Poleta Canyon and Silver Canyon. In addition, an area of slate between Gunter Canyon and Coldwater Canyon that forms a dip slope is shown on the map as Harkless formation, although the identification of the slate is uncertain. Some of the slaty shale along the west edge of the White Mountains north of Silver Canyon may also belong to the Harkless formation rather -than to the Montenegro shale member of the Campito formation as shown on the map. Within the mapped area, the formation consists largely of greenish to grayish slaty shale much like the Montenegro member of the Campito formation, but farther east in the Blanco Mountain and Waucoba Mountain quadrangle it contains beds of siltstone and lenses of moderate reddish-brown to grayish-yellow massive to thick-bedded vitreous quartzite. According to C. A. Nelson (written communication, 1960), the Harkless formation is about 2,000 feet thick, but only the lower part-perhaps a thousand feet-is present in the area mapped here. HORNFELS Adjacent to the granitic stock in Poleta Canyon, slate of the Harkless formation has been converted to spotted hornfels. The hornfels is much like the spotted horn- fels formed from the Montenegro shale member of the Campito formation adjacent to the diorite stock north of Coldwater Canyon except that the spots are gen- erally larger, many being 2 to 3 mm. long. In some specimens the spots coalesce and make up half or more of the rock. A specimen collected within a few feet of the stock consists of approximately equal amounts of quartz, andalusite, and sericite, and a lesser amount of reddish- brown biotite, locally altered to chlorite. This hornfels represents a higher metamorphic grade than the spotted tornfels. STRUCTURES IN THE WHITE MOUNTAINS North-to northwest-trending folds and related faults in the sedimentary strata of the White Mountains and in remnants of metamorphosed sedimentary and vol- canic rock in the Sierra Nevada were formed during Mesozoic time. These structures are generally well pre- served in the White Mountains, and except in the vi- cinity of stocks have been modified only by Cenozoic faulting and warping. Tectonic movements probably began in Early Triassic time and culminated in Late Jurassic time. Movements no doubt took place earlier during the middle or late Paleozoic, but if structures were formed then in this area they were not recognized. The effects of deformation vary with different strati- graphic units because of differences in their structural competence. The results of deformation are most con- spicuous in the Montenegro member of the Campito formation and in the Harkless formation, are next most conspicuous in the Poleta formation, and are least con- spicuous in the Deep Spring formation, the Reed dolomite, and the Wyman formation. Cleavage is pres- ent in almost all outcrops of the Montenegro member and Harkless formation except adjacent to the por- phyritic quartz monzonite stock in Poleta Canyon and to the diorite stock north of Coldwater Canyon, and is present locally in the Andrews Mountain member and in the Poleta formation, but is lacking in the forma- tions beneath the Andrews Mountain member. The 18 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA discontinuous outcrop pattern, variable thickness, and discordant contacts of the Montenegro member indicate that during deformation it behaved almost as a paste. Probably every contact of the shale with other units is a plane of slippage, although on the maps and struc- ture sections only obviously discordant contacts have been shown as faults. The upper part of the Andrews Mountain member and the lower part of the Poleta formation commonly are almost as strongly deformed as the shale itself. This deformation in the strata ad- jacent to the Montenegro probably resulted from the relative incompetence of the shale. A fault transverse to the range front along Poleta Canyon marks the boundary between more complexly deformed younger strata on the north and less com- plexly deformed older strata on the south. This fault is the northernmost of three subparallel east-trending faults, all of which are downthrown to the north. The interpretation of the structure as shown in the block diagram (pl. 6), although consistent with the data, undoubtedly is simpler than the true structure, for many minor structures could not be shown on the scale of the diagram. In some complex areas the beds are isoclinally folded on both large and small scales. Most faults that lie wholly within single stratigraphic units are not shown, and features represented as drag folds could have been shown as fault slivers; both structures were observed in the field. e In interpreting the structure, such common geologic features as order of superposition, known thickness of units, bedding attitudes, and outcrop pattern were uti- lized; in addition, both cleavage and lineation formed by the intersection of beds and cleavage planes were used. In many places the cleavage can be demonstrated to parallel approximately the axial planes of folds as delineated by bedding attitudes; consequently, the cleavage can be used to determine the trace and atti- tude of an axial plane where the position of the axial plane is not otherwise apparent. The orientation of fold axes is shown by the intersection of bedding and cleavage. Where bedding and cleavage are not parallel, top directions can be determined as follows : Beds that dip in the same direction as the cleavage but more gently and beds that dip oppositely to the cleavage are right-side-up. Beds that dip in the same direction as the cleavage but more steeply are overturned. If the axial plane is more than 90° from vertical or the axis more than 90° from horizontal, the rules for tops of beds are reversed. The dips of axial planes shown on the cross sections (pl. 5) and block diagram (pl. 6) were derived by averaging the dips observed in ad- jacent cleavage. Likewise, the plunges of fold axes were determined by averaging the plunges of adjacent lineations formed by the intersection of bedding and cleavage (pl. 7). FOLDS South of Poleta Canyon the beds dip eastward at moderate angles, apparently in the west limb of a syn- cline, but the trough of the fold lies further to the east, outside the mapped area. North of Poleta Canyon, where the width of the mapped span is greater, the folding is complex, and is complicated by faulting. The Andrews Mountain member and exposed under- lying formations were folded and faulted in a compe- tent manner, whereas the overlying less competent Montenegro member and Poleta and Harkless forma- tions failed complexly, collapsing and sliding on the shale between growing folds in the Andrews Mountain. In the area north of Poleta Canyon the pattern of folds is broadly arcuate with the convex side to the east, except for an area extending northward from Poleta Canyon where the fold axes are convex to the west. The axial planes of the folds dip to the east and to the west, and both dips are equally common ; not un- commonly the dip of an axial plane changes along the strike. Most axial planes are steeper than 45°, but locally the axial planes of minor folds dip as low as 25°. The axes of most of the folds undulate and plunge locally from horizontal to vertical, although generally not more than 45°. The major folds are few although the details of their structure are complex. They consist of three anticlines marked chiefly by outcrops of the Andrews Mountain member of the Campito formation and three synclines marked chiefly by the Poleta formation (pl. 3). The anticlines are called the North, Central, and West anti- clines, and the synclines are called the East, Central, and West synclines. Several of these folds lose their identity just north of Poleta Canyon where the Poleta and Harkless formations bend westward across the trends of the fold axes. Intrusion of the granitic stock at the head of Poleta Canyon or movement along the fault that follows Poleta Canyon may have contributed to the complexities of this area. FAULTS Most of the prebatholithic faults strike northwest- ward and dip either to the east or west parallel with the axial planes of the folds and with the cleavage. Both normal and reverse faults are present, but never- theless most faults probably resulted from the same compressional movements that produced the folds. Faulting probably began after the folding was well advanced, and it increased in magnitude as the folds became tighter and as internal resistance to further folding built up. Although many and perhaps most PREBATHOLITHIC GEOLOGY 19 of the faults were deformed by contemporaneous fold- ing, no evidence was found of faults that are clearly older than the folds. Some normal faults seem to be best explained as the result of local tension in a domi- nantly compressional field, but these faults could have been formed during a later period of relaxation. In mapping it was difficult to distinguish some pre- batholithic faults from some Basin and Range faults inasmuch as the two types are roughly parallel in strike. The following three criteria proved helpful in making distinctions as to the affiliations of questionable faults: Basin and Range faults Prebatholithic faults 1. Commonly - normal 1. Mostly compressional faults with little or faults. no evidence of strong c o n t e m p oraneous compression. 2. No cleavage of contem- poraneous origin par- allel with the fault plane. 2. Parallel cleavage in the walls of some faults, which diminishes in in- tensity with distance from the faults. 3. Linear depressions along traces of faults, the resuit of erosion. 3. Scearps common as a di- rect result of fault movement. Many scarps wholly or partly in Cenozoic deposits. FAULTS SOUTH OF POLETA CANYON South of Poleta Canyon the only faults that can be ascribed with certainty to prebatholithic diastrophism . are two reverse faults that strike about N. 30° W. across the first prominent ridge south of Redding Canyon (pl. 6, see. 7). The faults are cut off to the south by an east-trending normal fault and are overlapped to the north by alluvial deposits. Both faults dip to the west, and the more westerly one steepens in depth. Be- cause the western fault dips generally more steeply than the eastern fault, the two faults are presumed to join in depth. The exposed segments of both faults are chiefly within the Andrews Mountain member, but along the eastern fault the Andrews Mountain locally has been carried eastward over the Montenegro mem- ber; along, the western fault, beds in the Deep Spring formation on the southwest side strike into inliers of the Andrews Mountain in the alluvium on the north- east side. The apparent stratigraphic thickness of the Andrews Mountain member has been reduced by about 1,000 feet on the two faults; if movement was approxi- mately equal, the stratigraphic displacement on each fault is about 500 feet. FAULTS ON THE EAST LIMB AND CREST OF THE CENTRAL ANTICLINE An interconnecting system of faults of highly var- iable strike and dip follows roughly the limb between Poleta and Silver Canyons. the Central anticline and the East syncline. Most of the faults are contacts between sandstone of the An- drews Mountain member and shale of the Montenegro member of the Campito formation and the Poleta for- mation, or between the shale and the limestone. The traces of the faults commonly are curved, partly be- cause of the effect of topography and partly because the fault planes curve both in dip and strike. In a general way the fault surfaces follow the folded struc- ture of the beds. The movement on most faults appears to have been small, although in places the total thick- ness of the Montenegro member plus an unknown thick- ness of the underlying or overlying formations have been cut out; a stratigraphic displacement in excess of 600 feet is thus indicated. The southernmost faults of this system are between Most of the faults here dip steeply to the east, but a few are almost flat, and one dips to the west. An especially interesting one fol- lows the contact between the Montenegro member and the Poleta formation near the head of the first drain- age north of Poleta Canyon. On the ridge between the two branches of this drainage the beds dip to the east, and no evidence of significant faulting of the con- tact was found. Northward the contact steepens and then overturns to the east concomitantly with increas- ing magnitude of shearing along the contact. Just south of a northwest-trending cross fault that offsets the contact, several hundred feet of strata from the bottom of the Poleta formation are cut out against the overriding Montenegro member. The steepening and overturning of the beds are pictured as early move- ments that culminated in the shearing. From the south wall of Silver Canyon north to Cold- water Canyon is a belt of faults that separate the Montenegro member, the Poleta formation, and the Andrews Mountain member. In the lower walls of Silver Canyon, the Poleta formation on the east is in contact with Andrews Mountain along a fault that strikes north and dips west (pl. 6, section 3). North- ward and topographically higher this fault steepens, then overturns to the west, and on the ridge on the south side of the south fork of Gunter Creek it dips gently west (pl. 6, section 2). Although the fault may be twisted along the strike, the spacial relations suggest that it is convex upward and toward the west and bends in dip through more than 100° (pl. 6, sections 2-4). Locally in this span, the Montenegro member is present along the contact, but in most places the Poleta forma- tion is in direct contact with the Andrews Mountain member. Farther north, in the canyons of the two branches of Gunter Creek, the Montenegro member lies between the 20 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA Andrews Mountain member and the Poleta formation, but in most places the bedding planes within the shale dip steeply and are discordant with the gently dipping upper and lower contacts-a feature that indicates structural ungluing of the shale from the overlying and | underlying formations. FAULTS ASSOCIATED WITH THE WEST SYNCLINE North of Poleta Canyon in sec. 6, and the NEY see. 7, T. 7 S., R. 34 E., the Andrews Mountain member along the front of the range is in fault contact on the east side with the Montenegro member and the Poleta formation. The fault trends N. 30° W.; in the north part the dip is vertical and in the south part is steeply east. At the north end, in the first canyon north of Poleta Canyon, the faulted contact grades into an ap- parently unfaulted contact between the Andrews Moun- tain and the Montenegro. The faulted segment of contact is clean and sharp, cuts across folds in the An- drews Mountain at a high angle, and truncates bedding in the Montenegro member and Poleta formation at a slightly smaller angle. Within the Andrews Mountain member on the west side of the fault is a thin sliver of shale and limestone bounded by faults. This sliver trends a few degrees east of north, approximately parallel with fold axes in the Andrews Mountain, and may mark the approximate position of the southward continuation of the West syncline. The faults that bound the sliver of shale and limestone are poorly defined, but appear to terminate against or bend into the fault that cuts off the Andrews Mountain member on the east. FAULTS IN THE CENTRAL SYNCLINE AND WEST ANTICLINE BETWEEN SILVER CANYON AND GUNTER CREEK The Andrews Mountain member exposed between Silver Canyon and Gunter Creek is cut by several east- dipping reverse faults. These faults are chiefly along northern projections of the Central syncline and the West anticline, which they have almost destroyed. A thin belt of slate probably marks the trough of the Cen- tral syncline. Most of the faults dip steeply, but some dip as low as 35°. No displacements were determined, but movement on most of the faults appears to have been small because the faults are either entirely within the Andrews Mountain member or between it and the Montenegro member and the Poleta formation. They are approximately parallel with axial planes of folds. Parallel faults are also exposed in the ridge of Andrews Mountain member on the north side of Silver Canyon near the range front, and the movements on these faults also appear to have been small inasmuch as only the Andrews Mountain is exposed in the walls of the faults. Along the range front at Coldwater Canyon and also about 1 mile farther to the south are two slivers of An- drews Mountain member that are surrounded by shale and limestone. Both slivers may mark anticlines, but the northern sliver is bounded on both sides by steep faults and at the south end is in contact with the Poleta formation. CLEAVAGE Slaty cleavage is prevalent in the shales of the Monte- negro member and the Harkless formation, and is also present in many outcrops of the Andrews Mountain member and the Poleta formation (fig. 6). Cleavage FIGURE 6.-Slaty cleavage in Montenegro member of Campito forma- tion showing divergent attitudes of bedding and cleavage. Above, steeply dipping cleavage in steeply dipping homoclinal section. Cleay- age strikes from left to right and bedding from upper left to lower right. Steep plunge of lineation formed by intersection of bedding and cleavage parallels locally steep axis of West syncline. Below, minor folds in slate shown by calcareous sandy bed. Cleavage is generally parallel to axial planes of folds. Late stages of folding caused competent sandy bed to bend cleavage. PREBATHOLITHIC GEOLOGY 21 is present throughout the shales, except adjacent to the stock of porphyritic quartz monzonite in Poleta Canyon and the diorite stock north of Coldwater Canyon, where thermal metamorphism destroyed the cleavage. The cleavage is pervasive and the shale splits readily along flat cleavage surfaces that generally are not parallel to the bedding. In the Andrews Mountain member the cleavage is approximately parallel with cleavage in ad- jacent shale, but the cleavage is not pervasive, and cleavage surfaces generally are wavy and branching | rather than flat. The character of the cleavage surfaces | appears to be chiefly a function of the grain size of the rock; the smoothest cleavage surfaces are in rocks com- posed of clay-size particles, wavy surfaces are indica- tive of silt-size particles, and rocks composed of sand- size particles generally exhibit no cleavage. In the Poleta formation, impure argillaceous limestone cleaves readily along flat surfaces, but in cleaner carbonate rocks tke cleavage is shown chiefly on weathered sur- faces by thin parallel ridges and troughlike depres- sions. This sculpturing along the trace of cleavage on weathered surfaces of limestone can be confused with the trace of bedding. Cleaved limestone tends to break along rough surfaces that are only subparallel to the cleavages. Most of the cleavage is approximately parallel to the axial planes of folds and, therefore, is related in origin to the folding. However, a second cleavage parallel with faults was also observed in a few places in the Montenegro member. This second cleavage is pervasive adjacent to faults and increasingly more widely spaced farther away. Cleavage in this orienta- tion was observed to transgress and in places obliterate cleavage parallel to axial planes and is clearly younger than the latter. Because this second cleavage is iden- tical in appearance to the first and was not recognized until the mapping was nearly completed, no attempt was made to discriminate between the two cleavages. With a few exceptions, the cleavage attitudes plotted on the structure map (pl. 7) fall into a systematic pattern that appears to parallel the axial planes of folds. The fact that many of the faults associated with the folding are approximately parallel with the axial planes permits the existence of two kinds of cleavage in such a pattern. Nevertheless, cleavage can be dem- onstrated to parallel the axial planes of folds in so many places that it seems likely that most of the re- corded cleavage is related to folding rather than to faulting. METAMORPHIC ROCKS OF THE SIERRA NEVADA Two large pendants (the Pine Creek and Bishop Creek pendants), several septa, and groups of small inclusions are distributed through the predominantly granitic terrane of the Sierra Nevada (fig. T). The rocks in these masses include metasedimentary, metavolcanic, and mafic intrusive and hybrid rocks that are older than the granitic rocks that make up the bulk of the batholith. Broadly, the metamorphic rocks can be separated into two series-an older one, probably of Paleozoic age, composed entirely of meta- | sedimentary rocks, and a younger one, probably of Mesozoic age in which metavoleanic rocks predominate over metasedimentary rocks. The rocks of sedimentary derivation include mica- ceous quartzite, pelitic hornfels, metachert, marble, cale- hornfels, conglomerate, gneiss, and mica schist. The metavoleanic rocks are chiefly mafic flows, tuffs, and shallow intrusives of andesitic to dacitic composition, and the Pine Greek pendant also contains felsic meta- volcanic dike rocks of quartz dacitic and tuff of rhyo- litic composition. Intercalated with the metavolcanic rocks are minor marble, calc-hornfels, pelitic hornfels, micaceous quartzite, and conglomerate. In the two pendants and in some of the larger septa, it has been possible to subdivide the metamorphic rocks into mappable units. However, the-relatively small ex- tent of the units, their strong deformation and high metamorphic grade, which makes detailed stratigraphic descriptions impractical, and the absence of fossils are strong deterrents to adding new formational names for these units to already overburdened lexicons. On the geologic map the units are designated in terms of the dominant lithologic assemblages. The rocks in smaller inclusions are classified simply, on the basis of the most abundant rock, into (1) marble, (2) calc-hornfels, (3) pelitic hornfels, and (4) mafic metavoleanic rocks. The units that were distinguished in mapping far ex- ceed in number the different kinds of rock that were recognized. All but a few of the mapped units consist of more than one kind of rock, and most kinds of rock are in more than one mapped unit. To avoid repeti- tious rock descriptions, the principal kinds of meta- morphic rock that were recognized are described in a section that precedes the systematic descriptions of the metamorphic remnants. Although no diagnostic fossils were found in the metamorphic rocks, a comparison with fossiliferous strata in the less highly metamorphosed Laural-Convict pendant in the Mount Morrison quadrangle adjoining the Bishop area on the northwest (Rinehart, Ross, and Huber, 1959) and in the Inyo Mountains (Knopf, 1918) indicates that the metasedimentary series is Paleozoic and that the dominantly metavolcanic series is Mesozoic. The only metamorphic remnants large enough to in- corporate more than a very simple structural pattern on 22 37°30° - 37°00! 119°00! GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA 830° EXPLANATION Cretaceous granitic rocks Including diorite and gabbro METAMORPHOSED ROCKS OF THE ROCKS OF ESTABLISHED AGES IN THE SIERRA NEVADA AND THE BENTON INYO MOUNTAINS, THE WHITE 5 RANGE MOUNTAINS AND THE MOUNT MORRISON PENDANT OF THE SIERRA NEVAD A 39NV3 NoLN3S Metavolcanic rocks Volcanic rocks of Middle Triassic age Include intercalated sedimentary rocks. - Chiefly of Include intercalated sedimentary rocks Triassic age, but may include Jurassic and Permian rocks m 37°30! Lower Triassic sedimentary rocks Tom NR SNS Permian and Carboniferous sedimentary rocks 3LIHM Devonian and Silurian sedimentary rocks \\\\ Metasedimentary rocks 'Oh May include rocks that range from upper Pre- lel i I xs . rocks that range from upper Ordovician sedimentary rocks Upper and Middle Cambrian sedimentary rocks sap Lower Cambrian sedimentary rocks Lower Cambrian or upper Precambrian (?) sedimentary rocks Unfoasiliferous strata conformably beneath fossilferous strata of Lower Cambrian age _ Bishop Creek pendant Contact hed where approzimately located Fault |- 37°00! 119900! 18°30" -o 1? 15 2ID MILES 18°00" FIGURE 7.-Geologic map of the Owens Valley region showing the distribution of the pre-Cenozoic rocks. Quaternary sedimentary and voleanic rocks } CENOzOIC MESOZOIC PALEOZOIC PRECAMBRIAN (7) OR CAMBRIAN PREBATHOLITHIC GEOLOGY 23 the map scale are the Pine Creek and Bishop Creek pendants. The rocks in these pendants have been sub- jected not only to the regional deformation that resulted in the north- to northwest-trending folds and compres- sional faults in the White Mountains, but also to later deformation caused by the forcible intrusion of the batholithic rocks. Although folds produced during earlier regional deformation cannot always be distin- guished from folds caused by later intrusion of a pluton, several criteria are generally applicable. The axes of the earlier regional folds are generally nearly horizontal and parallel with the north-to-northwest regional trend. These folds may extend for many miles and show no geometric relation to bordering intrusives. Folds caused by intrusion, on the other hand, generally are of more limited extent, their axes trend in directions that bear geometric relation to the configuration of the bor- dering intrusives, and the axes generally dip steeply rather than gently. The relation of intrusion to wall rock deformation is considered in a later section of this report dealing with evidence of mechanical emplace- ment of the intrusive rocks. The rocks in the Sierra Nevada pendants, though folded and faulted, are not mashed to the same degree as some of the rocks in the White Mountains, pre- sumably because of the greater structural competence of the strata. Cleavage was not recognized in the Bishop Creek pendant but is locally conspicuous in the Pine Creek pendant. If cleavage formerly was more conspicuous and widespread, it has been destroyed by subsequent thermal metamorphism. METASEDIMENTARY ROCKS The metasedimentary rocks were derived from mio- geosynclinal sedimentary rocks-shale or slate, lime- stone, sandstone, siltstone, chert, and sediments of inter- mediate composition. Shale or slate has been metamor- phosed to pelitic hornfels, marl and siliceous dolomite to calc-hornfels, limestone to marble, sandstone and silt- stone to quartzite, and chert to metachert, and so forth. MICACEOUS QUARTZITE DERIVED FROM ARGILLACEOUS SAND- STONE AND SILTSTONE The rock here designated micaceous quartzite is a dense fine-grained rock, commonly dark gray to gray- ish red, which was derived from dirty sandstone or siltstone. The largest mass is in the Pine Creek pend- ant, but it is a common rock type and is present in many of the metamorphic remnants. In the Bishop Creek pendant, together with finer grained pelitic hornfels, it constitutes a unit that is almost as extensive as the one in the Pine Creek pendant. Commonly the rock megascopically appears struc- tureless and breaks into angular fragments on weather- ing, but locally it has a more or less conspicuous cleav- age and breaks along cleavage planes into tabular slabs. Bedding generally is obscure, and to locate it requires careful searching for compositionally distinctive layers. Quartz is the most abundant mineral and generally makes up 50 to 60 percent of the rock. Most specimens also contain 20 to 30 percent of biotite and 10 to 15 percent of sericite. Many rocks also contain 5 to 10 percent of K feldspar and a few contain as much as 25 percent. Rocks that contain abundant K feldspar generally contain little or no sericite and are light yel- lowish gray. Minor accessory minerals, which com- monly are sporadically distributed through the rocks, include plagioclase, apatite, tourmaline, sphene, garnet, magnetite, and pyrite. In addition, small amounts of chlorite, epidote, hematite, and sericite are present. Fragments of fine-grained siliceous rock (chert?) also are common, though not abundant. Most of the quartz is in somewhat rounded grains, but the margins are rough in detail owing to overgrowths of new quartz. In some specimens, the quartz grains are all about the same size, but more commonly the quartz grains are not so well size sorted and consist of a wide variety of grain sizes. Pebbles, present locally in restricted strati- graphic zones, commonly consist of aggregates of quartz rather than of quartz in a single orientation. Generally, the quartz grains are seen under crossed- nicols to be unstrained and to extinguish uniformly. K feldspar is interstitial to the quartz grains. Most of the biotite is in tiny flakes that are evenly distributed through the rock, but some is in patches or streaks in which the individual biotite flakes are much larger than the dispersed flakes. All the biotite is pleochroic from reddish brown to colorless and causes the grayish-red color of fresh surfaces of many specimens. The biotite flakes show some degree of preferred orientation in al- most all the rocks, but the orientation is best in finer grained, more schistose ones. Sericite is present in tiny flakes in some rocks and in large poikiloblastic plates in others. Where the sericite is in tiny plates it is com- monly distributed with the biotite and oriented parallel with it, but with a lower degree of preferred orienta- tion than the biotite. Larger poikiloblastic plates, on the other hand, are oriented at random-a feature that suggests that they were formed late. METACONGLOMERATE Metaconglomerate was found only in the Deep Can-. yon area of the Tungsten Hills and in the northern seg- ment of the septum 3 miles west of Keough Hot Springs. In the Tungsten Hills subrounded pebbles that generally are less than an inch across are set in a calcium-rich matrix that consists chiefly of diopside. 24 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA Many of the pebbles consist of granoblastic quartz and interstitial diopside, and a few consist of zoisite or other cale-silicate minerals. In the septum 3 miles west of Keough Hot Springs, pebbles of felsic volcanic rock are contained in a matrix of quartz, K feldspar, and cale- silicate minerals, including epidote, tremolite, and diop- side. The pebbles consist chiefly of a very fine grano- blastic intergrowth of quartz and K feldspar in which broken crystals of quartz, K feldspar, and plagioclase are set. Pebbly beds are present locally within the micaceous quartzite unit of the Pine Creek pendant, but the peb- bles generally make up less than half the bulk of the rock. The pebbles consist of granoblastic quartz prob- ably derived from metachert and schist. The matrix is micaceous quartzite. PELITIC HORNFELS DERIVED FROM SILTY SHALE, CEOUS SILTSTONE, AND CLAY SHALE ARGILLA- The rock here classed as pelitic hornfels is one of the more ubiquitous of the metamorphic rocks. It com- monly occurs with micaceous quartzite, but is also inter- layered with other metasedimentary rocks. Megascopi- cally it is a dense fine-grained structureless rock that on fresh surfaces ranges from light yellowish or olive- gray to dark gray or even black; the reddish color and cleavage found in some micaceous quartzite is not pres- ent in pelitic hornfels, but otherwise the two rocks ap- pear megascopically similar. In terms of origin, pelitic hornfels is derived from finer grained, more argilla- ceous rock than micaceous quartzite. Parent sedimen- tary rocks probably include argillaceous siltstone, silty shale, and clay shale or slate, and consequently they are finer grained and contain less quartz and more feldspar and mica than the quartzite. The varieties having fin- est grain are carbonaceous and contain andalusite. The mineral content is quite variable and reflects the wide compositional range of the rocks included. Most specimens that were examined under a microscope con- tain quartz, mica, and feldspar, but the mica may be either biotite or sericite or both, and the feldspar may be K feldspar or plagioclase; a few specimens that con- tain abundant plagioclase lack quartz. Plagioclase and actinolite are present in rocks having a high content of CaO) and occur in assemblages that are transitional to calc-hornfels. The most common accessory minerals are apatite, magnetite, and sphene. Andalusite-bearing pelitic hornfels is not common, but with metachert it forms an extensive mappable unit in the Bishop Creek pendant. Typically it is dark gray to black, except for conspicuous white prisms of andalusite as much as half an inch long. The groundmass is fine grained, dense, and structure- less, and the andalusite prisms are randomly oriented. The content of andalusite generally falls between 25 and 35 percent, but in some specimens it constitutes as much as 50 percent of the rock. In all specimens that were examined under the microscope, the groundmass contains quartz, sericite, and carbonaceous material. In some the groundmass also contains biotite or albite. Apatite commonly is a minor accessory mineral. Most andalusite porphyroblasts are bordered by a dark rim of expelled carbonaceous material, and many exhibit the internal carbonaceous cross that is characteristic of the variety called chiastolite. Much of the andalusite has been replaced along the margins by sericite, and in some specimens it has been completely replaced by a sericite aggregate. METACHERT Metachert was identified only in the Bishop Creek pendant where it is interstratified with pelitic hornfels in an extensive mappable unit, but other rocks that resemble quartzite and consist chiefly of recrystallized quartz may also be derivatives of chert. The metachert in the Bishop Creek pendant occurs in two principal varieties, the more common of which is a light-gray vitreous rock megascopically indistin- guishable from quartzite. This rock grades locally into the less common second variety, a dark-gray fine- grained carbonaceous metachert." The dark carbonaceous chert consists of a very fine grained granoblastic mosaic of tiny quartz grains through which is disseminated finely divided carbo- naceous material. Some specimens contain a very small amount of interstitial K feldspar or sericite (esti- mated to be less than 2 percent), and others contain calcite or cale-silicate minerals such as garnet, epidote, or diopside. The calcite and cale-silicate minerals, though disseminated in the chert, are most abundant adjacent to thin veinlets that contain the same minerals. This association suggests that calcium was introduced into the rock prior to or during thermal metamorphism. In some specimens, nevertheless, microcline and diop- side occur together in thin beds that probably mark original marly layers. Although no fossils were identified in the metachert, small round masses of granoblastic quartz much coarser than the groundmass, and rimmed with carbonaceous material, probably are vestiges of radiolaria. - Similar- appearing structures in the cherts of the Franciscan formation in the California Coast Ranges, as well as in cherts elsewhere, are fossil radiolaria. Derivation of the more common coarser grained light- gray metachert from the dark-gray carbonaceous chert by recrystallization and expulsion of the carbonaceous material is readily demonstrable. Most specimens of dark carbonaceous metachert are cut by light-colored PREBATHOLITHIC GEOLOGY 25 veinlike streaks of quartz having a relatively coarse- grained granoblastic texture. These streaks are most abundant in transitional zones between dark-gray meta- chert and light-gray metachert. In the direction of the light-gray metachert the veinlike streaks are increas- ingly common, and the light-gray metachert is simply the end stage of this veination. The relations in the transition zones leave no doubt that the veins as well as the more extensive masses of light-gray metachert resulted from recrystallization of the dark-gray meta- chert (fig. 8). In the recrystallization the carbo- naceous material was expelled, and various stages of this process can be traced in thin sections. The carbo- naceous material was aggregated into irregular veinlets before complete elimination. The light-gray rock is commonly mottled in various shades of gray, and the different shades reflect the degree of recrystallization and elimination of carbonaceous material. Other con- FiGURE 8.-Specimen of metachert showing light and dark varieties. Light-colored rock was derived from dark rock by recrystallization and elimination of carbonaceous dust. 735-925 0-65 8 stituents, however, were not eliminated during recrys- tallization, and even the most coarsely recrystallized specimens contain a little K feldspar and sericite. MARBLE DERIVED FROM LIMESTONE Marble includes all the rocks that were derived from limestone and that consist predominantly of coarsely crystalline calcite. Marble ranges from very light gray (almost white) to dark gray, depending upon the con- tent of carbonaceous material, and in granularity from coarse to fine. In general the lighter colored varieties have been more intensively recrystallized than the darker varieties and are coarser grained. Carbo- naceous material was driven out of the rock during re- crystallization and almost completely eliminated in the coarsest grained rocks. The carbonate mineral in the marble is everywhere calcite; dolomite or dolomitic marble was not identified in the Sierra Nevada, presumably because it is not stable under the condition of thermal metamorphism that existed. The presence of diopside or tremolite in many silicated marbles indicates the rock formerly was impure dolomitic limestone or dolomite, and scarce bru- cite indicates that some varieties were clean dolomitic limestone or dolomite. Most marble in the Sierra Ne- vada contains argillaceous and siliceous impurities, which have combined with calcite and dolomite to form cale-silicate minerals. These cale-silicate minerals are disseminated through the marble, but are most abun- dant in thin well-defined layers that mark impure beds. Metamorphism was sufficiently intense to eliminate any carbonaceous material. Silicate minerals in addition to those already mentioned include grossularite, idocrase, plagioclase, and seapolite. Locally, quartz-rich layers represent layers of quartz sand or of chert. Most marble beds are at least tens of feet thick, and the more recrystallized ones are massive and structure- less. The bedding is best shown by compositional dif- ferences among beds. The thickest and most extensive marble lies along the west side of the Pine Creek pend- ant, and less extensive marble is present in most other metamorphic remnants. CALC-HORNFELS DERIVED FROM ARGILLACEOUS AND SILICEOUS LIMESTONE AND DOLOMITE Calc-hornfels is widespread, and in the Bishop Creek pendant constitutes an extensive stratigraphic unit. The rocks here designated as calc-hornfels are dense fine-grained, predominantly light-colored rocks that are composed of several different assemblages. Common minerals include plagioclase, diopside, tremolite, gros- sularite, wollastonite, K feldspar, quartz, and calcite. Fresh surfaces commonly range from light greenish gray to pale greenish yellow, or to light gray, but lay- 26 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA ers rich in diopsidic pyroxene are usually greenish gray to dark greenish gray, and layers rich in garnet gen- erally are light brown. In many places intercalated with calc-hornfels are a few thin medium- to dark- gray quartzose or feldspathic layers that contain a cloud of carbonaceous material. Weathered surfaces are lightly stained with limonite, but the stain does not affect the overall light tone of the rocks in outcrop. Bedding generally is shown by compositional layers that commonly are less than an inch thick. Secondary cleavage is lacking and the rock breaks on weathering into angular fragments, although some calc-hornfels splits along bedding planes into flat fragments. Cale- hornfels is one of the more resistant rocks to erosion, and commonly it crops out in ridges or forms cliffs. Common mineralogic assemblages include plagio- clase-diopside, quartz-diopside, quartz-diopside-tremo- lite, quartz-tremolite, quartz-diopside-K feldspar, di- opside-tremolite-K feldspar, quartz-diopside-K feld- spar. Assemblages that contain abundant tremolite and K feldspar are characterized as argillaceous calc-horn- fels, and those that contain abundant quartz are called siliceous calc-hornfels. - Plagioclase-diopside assem- blages were derived from argillaceous dolomite or mag- nesian limestone, and quartz-diopside assemblages from siliceous dolomite or from dolomitic sandstone. Trem- olite occurs in rocks that is relatively poor in calcium, where it takes the place of diopside. Quartz-tremolite rock was probably derived from dolomitic sandstone. K. feldspar is present only in rocks that originally con- tained significant amounts of argillaceous material. Calcite is present in calcium-rich, diopside-bearing assemblages, but does not occur with tremolite. Wol- lastonite is found most commonly near intrusive contacts, where it normally occurs with calcite and diop- side. - Locally, favorable beds and thin selvages be- tween marble and granitic intrusive rock consist almost entirely of wollastonite. Rock that contains large amounts of quartz might be more accurately characterized as sandy calc-hornfels or as silicated quartzite depending on whether quartz or silicate minerals predominate. - Similarly, calc-horn- fels grades to marble through calcitic calc-hornfels and silicated marble. As the content of argillaceous mate- rial increases calc-hornfels grades to argillaceous horn- fels, but no names have been designated for intermediate assemblages. TACTITE DERIVED FROM MARBLE AND CALC-HORNFELS Tactite is a rock of more or less complex mineralogy formed from calcareous or dolomitic rocks by contact metasomatism. It is the common host rock for schee- lite, the principal tungsten-bearing mineral in the Bishop district, and is more fully described in the part of this report that deals with tungsten mineralization. The term "tactite" is probably synonymous with the term "skarn." - No single mineral is essential by defini- tion to tactite, but most of the tactite in the Bishop dis- trict is composed chiefly of pale to moderate reddish- brown garnet of the andradite-grossularite series and grayish-green pyroxene of the diopside-hedenbergite series. Epidote, quartz, scheelite, and various sulfides are also common in tactite. GNEISS Gneiss was found at only two places within the mapped area. The largest mass is a lenticular septum about 3 miles long that is exposed in the canyon of the South Fork of Bishop Creek between Long Lake and Bishop Pass; and gneiss is present locally in several small metamorphic remnants that crop out in the lower part of the ridge between Red Mountain and Taboose Creek, in the vicinity of Stecker Flat. The gneiss in both places consists of thin lenticular alternating mafic and felsic layers that generally are an eighth of an inch or less thick. In the South Fork of Bishop Creek the mafic layers are generally thinner than the felsic layers, but in the vicinity of Stecker Flat the layers are about equal in thickness. In both places the felsic layers consist chiefly of a granoblastic intergrowth of quartz and feldspar. - In the mass in the South Fork of Bishop Creek the mafic layers contain biotite plates and horn- blende prisms oriented in the plane of foliation. The mafic layers in the gneiss in the vicinity of Stecker Flat contain biotite but no hornblende. Magnetite is a minor constituent in the mafic layers. $ The gneiss in the South Fork of Bishop Creek pro- vides little basis for speculation as to its origin ; its ap- pearance suggests highly sheared plutonic rock. The gneiss in the vicinity of Stecker Flat, however, grades to schist and to hornfels of the same mineral composi- tion, and all three rocks were produced from the same parent rock, presumably slightly feldspathic siltstone. All three structural varients are composed of quartz, plagioclase, and biotite, and accessory magnetite and apatite. Some specimens also contain as much as 15 percent of sericite associated with biotite and in aggre- gates interstitial to quartz and plagioclase. All the minerals in the hornfels are nearly equant and un- oriented, and the texture is granoblastic, whereas biotite in the schist and gneiss is in strongly oriented plates. In hornfels the quartz and plagioclase grains are of about the same size throughout the rock, whereas in schist and gneiss coarser grains of quartz and plagio- clase are bordered by finer quartz and plagioclase, and conspicuously fine-grained streaks are common. In gneiss the dark layers are both richer in biotite and finer grained than in the felsic layers. The finer grain size in streaks and marginal to larger grains was probably PREBATHOLITHIC GEOLOGY 27 produced by pervasive shearing at the time of meta- morphism. In figure 9, specimens of hornfels having recrystal- lized orbicular spots and gneiss containing relict horn- felsic areas are shown. The hornfels in the spotted rock is mineralogically and structurally identical with that in the gneiss. The orbicular spots were formed by recrystallization without obvious structural control ; nevertheless, the light and dark minerals were segre- gated during recrystallization. The gneissic structure probably formed in the same way, except that biotite recrystallized preferentially along shears. METAVOLCANIC ROCKS Metavoleanic rocks were mapped simply as either felsic metavolceanic rocks or mafic metavolceanic rocks. Mafic metavolceanic rocks are more abundant than the felsic metavolcanic rocks, which are limited to a small area in the Pine Creek pendant on the southwest side of Mount Tom. The felsic metavolcanic rocks include rhyolite and quartz latite, and the mafic ones include andesite and dacite. The rocks in the two groups are distinguishable megascopically by color index and spe- cific gravity. The specific gravities of hand specimens of felsic rock generally are between 2.60 and 2.65, and = the specific gravities of mafic rocks are between 2.75 and 2.85. FELSIC METAVOLCANIC ROCKS Metarhyolite tuff and quartz latite, mostly intrusive but some possibly in flows, are present in the south part of the Pine Creek pendant between micaceous quartzite on the north and mafic metavolceanic rocks on the south. Metarhyolite tuff is massive and struc- tureless except locally where it has a secondary folia- tion. Unweathered surfaces are light gray, but weathered ones commonly are stained pinkish gray. Small pheno- crysts of quartz 2 to 3 mm across and lens-shaped for- eign rock fragments, the largest less than a centimeter in greatest dimension, can be readily identified in hand specimen. Under the microscope the tuff can be seen to consist of about half mineral and foreign rock fragments and half a fine-grained granoblastic groundmass composed chiefly of quartz and feldspar. Angular fragments of quartz, microcline, and a little sodic plagioclase (oligo- clase) are abundant. Presumably the microcline was derived from original sanidine during thermal meta- morphism. The quartz, both in angular fragments and in crystals, has been converted to a granoblastic mo- FiGURE 9.-Products of metamorphic differentiation in hornfels and in sheared rock of the same bulk com- position. foliated rock. Left, recrystallization spots in quartz-biotite-plagioclase hornfels. Undifferentiated rock in the two specimens are mineralogically identical, and the min- Right, gneiss layers in erals in the dark and light parts of the spots are the same as in the dark and light layers in the gneiss. 28 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA saic. The boundaries of the mineral fragments and crystals are still quite sharp against the groundmass and have been only slightly modified. Most of the foreign fragments are composed of plagioclase grains of intermediate composition a millimeter or so across and clusters of hornblende prisms intergrown in and bordering the plagioclase, but some are composed of biotite, quartz, and plagioclase. Magnetite and apatite are present in both kinds of fragments. The grano- blastic groundmass of the tuff consists chiefly of quartz and microcline, but sodic plagioclase is also present, and some specimens examined contained as much as 10 percent of biotite. The angular shapes of the crystal fragments, the slight amount of corrosion of the original borders of mineral fragments by the groundmass, the presence of foreign rock fragments, and the absence of flow struc- ture are the chief lines of evidence that the rock is a tuff rather than a flow or dike rock. The absence of conspicuous metamorphic effects in the crystal frag- ments, except for the conversion of sanidine to micro- cline and the breakdown of quartz to mosaics, contrasts with the complete reconstitution of the groundmass. Finer grain size and the presence of glass may have made the groundmass more susceptible to recrystalliza- tion than the mineral fragments. Quartz latite, chiefly and perhaps everywhere, in dikes and sills is present south of the Tungstar mine and along the contact between micaceous quartzite and metavolceanic rocks. - Sills penetrate from the contact distances of. several hundred feet along bedding planes in the micaceous quartzite. Fresh quartz latite com- monly is medium light gray, slightly darker than the light-gray metarhyolite tuff. In most places the quartz latite is almost structureless, but in a few places it is strongly foliated. On weathering it breaks into polygonal blocks. The quartz latite is porphyritic and contains abun- dant phenocrysts of feldspar as much as 3 mm across and somewhat smaller aggregates of biotite. Under the microscope, most of the large feldspar grains can be seen to be zoned plagioclase, but some are microcline. The feldspars and biotite aggregates are set in a grano- blastic groundmass of quartz, microcline, and plagio- clase, which has corroded the margins of the feldspars. Biotite in small plates also is present in some rocks, gen- erally with a moderate to high degree of preferred orientation. - Present in minor amounts are hornblende (locally in amounts of as much as 5 percent), sphene, magnetite, ilmenite, and apatite. Locally, biotite is altered to chlorite and plagioclase to epidote. Following is a chemical analysis by the rapid method of Shapiro and Brannock (1956) of a typical specimen of dike rock from the west side of Mount Tom (lab. no. 138267; analysts, Harry F. Phillips, Paul L. D. El- more, and Katrine E. White; locality, NEL sec. 22, T. 7 S., R. 30 E., 2,000 ft south of the Tungstar mine). Comparison of the analysis with the average chemical compositions of Nockolds (1954) indicates that the dike rock is very similar to his dellenite. Weight percent Weight percent IOBA. sic ask 70.5 - Lec nds 4.3 M- Lee 15.6 TIO} seee akc .32 1.0 PX ccc A1 1.4 .06 MgO. lien .68 MD LL. L AT 2.2 .05 L Se ALEECL _._ 8.6 'Poldl-._--«l.««=« 100 MAFIC METAVOLCANIC ROCKS The most extensive remnants of mafic metavolcanic¢ rocks are in the southern one-third of the Pine Creek pendant; smaller masses are in a ring around Mount Humphreys, the western part of the Tungsten Hills, and 3 miles west of Keough Hot Springs. Most of the mafic metavolcanics are dark gray, slightly foliated nonporphyritic rocks of andesitic or dacitic composi- tion, which lack distinctive characteristics. Locally, however, units are porphyritic, amygdaloidal, or a breccia. The mafic metavolcanic rocks are closely associated with fine-grained rocks of panidiomorphic granular texture, which have been included with them on the map. These rocks are doubtless the hypabyssal equiva- lents of the mafic extrusives. The mafic metavolceanic rocks are also commonly associated with medium- grained quartz dorite, diorite, and hornblende gabbro of hypidiomorphic-granular texture. The medium- grained hypidiomorphic granular rocks are probably of diverse origins, and some may be genetically related to the mafic metavolcanic rocks. They have been mapped separately. Under the microscope, pilotaxitic, trachitic, and pani- diomorphic-granular textures can be seen among the metavoleanic rocks. A fine-grained granoblastic groundmass composed of plagioclase and hornblende generally is interstitial to plagioclase laths or plates, biotite plates, and hornblende prisms. Locally, the groundmass has encroached on the plagioclase crystals. Originally, the groundmass may have been glass or finely divided erystalline material, although no relicts of these materials were found. The total plagioclase content generally is between 45 and 65 percent, and the combined biotite and horn- blende content is between 30 and 40 percent. Com- monly biotite and hornblende vary inversely with each other in relative abundance. Rocks of dacitic compo- PREBATHOLITHIC GEOLOGY 20 sition generally contain 5 to 15 percent quartz, and a few specimens also contain 5 to 10 percent K feldspar. Accessory minerals are apatite, magnetite and ilmenite, and sphene. Locally, biotite is altered to chlorite and hornblende to epidote. Most of the euhedral or subhedral plagioclase crystals are strongly zoned and are undoubtedly relict primary igneous grains. In contrast, the plagioclase in grano- blastic intergrowths generally is untwinned and zoned only slightly. In most zoned crystals of plagioclase the zoning is progressive from calcic core to sodic rim, but oscillating zoning is present in places, and may be super- imposed on progressive zoning. Commonly, selected zones, usually the core, are strongly sericitized. Biotite is in thin pleochroic plates and generally exhibits mod- erate preferred orientation. Most of the hornblende is in small, elongate crystals, but locally larger and evi- dently later formed crystals poikiloblastically enclose small plagioclase crystals. Amygdules were found in the septum 3 miles west of Keough Hot Springs, in meta-andesite, and in the south part of the Pine Creek pendant, in dacite. These amygdules commonly are ovoid with the greatest dimension as much as 114 ecm. The core consists of a mosaic of quartz, which is bordered by a rim of horn- blende or diopside. On weathered surfaces the amyg- dules stand out and exhibit smoothly rounded external surfaces, which reflect the shapes of the vesicles. The presence of diopside marginal to some amygdules suggests that carbonate as well as quartz was pres- ent. In some amygdules a rim of antiperthitic plagio- clase lies outside the hornblende rim, and in a few places hornblende in the rock marginal to the amyg- dules is altered to epidote. Remnants of a layer of volcanic breccia are present in the south part of the Pine Creek pendant, in the floor of Horton Creek canyon ; the best exposure is in a knob that projects through the talus a few hundred feet northwest of the west end of Horton Lake. A second good exposure is a few hundred feet east of the small lake below Horton Lake. This rock is a ce- mented aggregate of flattened volcanic rock frag- ments. The largest fragments are several feet long, but most fragments are a few inches or less in length and less than an inch across. Fragments include both mafic and felsic metavolcanic rocks that are identical with rocks in the surrounding terrane. The matrix is andesitic or dacitic in composition and presumably is tuffaceous. The rocks containing amygdules are either flows or shallow intrusives, and the volcanic breccia layer is either of pyroclastic or sedimentary origin. Rocks having felty textures are presumed to be tuffs, flows, or shallow instrusives. Rocks of coarser panidiomor- phic-granular texture are presumed to be intrusive. If the granoblastic texture was formed most readily in glassy or very finely crystalline material, the bulk of the mafic volcanic rocks seems likely to have been tuf's or flows rather than small intrusives, but the local pres- ence of the granoblastic texture in rock having relict panidiomorphic-granular texture indicates that all rocks of granoblastic texture cannot be assumed to be tuffs or flows. The following rapid chemical analysis (Shapiro and Brannock, 1956) is of a typical rock of andesitic com- position from the southwest side of Mount Tom (lab. no. 138274; analysts, Harry F. Phillips, Paul L. D. El- more, and Katrine E. White; locality, SW 14 sec. 22, T. 7 S., R. 30 E., one-half mile southeast of the Hanging Valley mine). In this rock, crystals of biotite, horn- blende, and plagioclase are set in a granoblastic ground- mass of quartz and plagioclase. Weight percent Weight percent 55. 5 KsO_scl. LCi ILC] 1.8 AlsOs-_ scc _c LLL 18.5 Fezoa ____________ 8.2 P «Opell aul. . 87 5.3 . 16 3.9 . 85 2 7.0 (CO2... - Les . 05 3. 0 TOO—— Norm 9. 00 Hypersthene._.______ 15. T7 Orthoclase.._._____ 10. 58 Magnetite__________ 4. 64 25.18 Hmenite.........__ 1. 46 31. 69 Apatite... . 93 ... . 89 CALC-HORNFELS DERIVED FROM MAFIC IGNEOUS ROCK In several places, mafic metavoleanic rock and finer grained diorite have been converted to very light gray (almost white) plagioclase-diopside rock that is mega- scopically identical with plagioclase-diopside-hornfels derived from impure limestone. The altered rock dif- fers from true calc-hornfels in two ways: (1) Much of its original felty texture is retained, and the hornfelsic texture, though present locally, is not dominant, and (2) plagioclase commonly retains its primary zoning, although locally the zonal structure has been obliter- ated. The altered rock, nevertheless, is here called calc- hornfels because without microscopic study it cannot be distinguished from true calc-hornfels. Juxtaposition of mafic metavoleanic rock with felsic plagioclase-diopside rock indicates that the formation of hornblende in one and of diopside in the other can- not be explained in terms of different pressure-tempera- ture environments. Both plagioclase-hornblende and plagioclase-diopside are stable assemblages in the amphibolite facies, and the factor that determines whether diopside or an amphibole forms is composition, chiefly the content of CaO-diopside is the stable min- 30 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA eral in assemblages rich in CaO) (Barth, 1952, p. 328). CaO was introduced into the diopside-bearing rock either prior to or during the metamorphism, and the source is not likely to have been the granitic intrusive that caused the metamorphism. In some places CaO) was obviously derived from associated calcareous metasedimentary rocks, and in others it was supplied by carbonate-bearing veins and amygdules that were late stage accompaniments to the intrusion of dikes and sills or the extrusion of lavas. Some of the best examples of hornfelsed mafic ig- neous rocks are in the northeast part of the Bishop Creek pendant where dikes that cut marble are partly altered to calc-hornfels, and in the northern segment of the septa 3 miles west of Keough Hot Springs where amygdular lavas or shallow intrusives were partly hornfelsed. The mafic dikes in the Bishop Creek pend- ant are intricately penetrated by conspicuous light- colored calc-hornfels having geometrical relations that indicate the alteration involved no change in volume (fig. 10). Under the microscope the unaltered dike rock can be seen to consist chiefly of hornblende and plagio- FicurE 10.-Mafic dike rock partly altered to plagioclase-diopside hornfels. TABLE 2.-Rapid chemical analyses of mafic dike rock and of hornfelsed rock derived from it [Gains and losses in the alteration are given in milligrams per cubic centimeter. Analysts: Paul D. L. Elmore, Katrine E. White] Unaltered dike rock Hornfelsed rock (lab. No. 141352) (lab. No. 141351) Mg per cc gained or Weight | Mg per | Weight | Mg per lost in alteration percent | cc (sp gr | percent | cc (sp gr 2.91) 3.03) Oxides Elements 48. 6 1, 414 49. 4 1, 497 +83 || Si, +39. 16.1 469 15.0 455 -14 || Al, -7. 1.2 35 .6 18 -17 || Fe, -61. 7.4 215 5.0 152 -63 7.9 230 6.6 200 -30 || Mg, -18. 11.0 320 18.9 578 +253 || Ca, +187. 2.3 67 1.4 42 -25 || Na, -18. 1.4 41 . 63 19 -22 || K, -18. .76 22 . 66 20 -2 20 6 .18 5 -1 19 6 . 24 7 +1 2.3 67 1.1 33 -34 14 4 12 4 08 2 . 44 13 +11 100: ccs 100 - clase and the altered rock of diopside and plagioclase. In the altered rock, aggregates of tiny diopside grains have taken the place of the hornblende; in most speci- mens the plagioclase was not altered and retains its zonal structure. The boundaries between altered and unaltered rock generally are sharp, though in a few places they are gradational. The proportions of the altered and unaltered rock vary from place to place, from a few thin veinlets of calc-hornfels in unaltered dike rock to rock composed chiefly of calc-hornfels but containing a few residuals of unaltered rock. The CaO required to produce diopside probably was derived from the calcareous strata into which the dikes were intruded and was introduced into the dike rock along cracks either before or during the metamorphism. To determine what chemical differences exist in the al- tered and unaltered rocks, samples of rock sorted from a single specimen having a patchy alteration pattern were analyzed chemically. Table 2 gives the analytical results and the calculated gains and losses of oxides and of elements. The data show that Si, Ca, and CO; were gained in the altered rock, and that Fe, Mg, K, Na, Al, and H,O+ were lost. The percentage changes in the amounts of other constituents are too small to be sig- nificant. In the northern segment of the septa 3 miles west of Keough Hot Springs much of a mass of amygdular andesitic lava or dike rock is of mottled appearance because of splotchy alteration of the dark-gray rock to yellowish-gray calc-hornfels. The alteration is simi- lar to the one that affected the mafic dikes in the Bishop Creek pendant, but the lime that was added to the hornfelsed rock was derived from amygdules and vein- lets of quartz and carbonate. The dark parts of the mottled rock consist of a micro- crystalline felty mass of zoned plagioclase plates or PREBATHOLITHIC GEOLOGY 3l laths (compositional range about Anso-s,) and lesser amounts of hornblende and biotite, and minor K feld- spar, sphene, apatite, and magnetite. In some rocks plagioclase also occurs in phenocrysts. The yellowish-gray hornfelsic rock contains diopside rather than hornblende. The felty texture of the origi- nal flow rock is preserved in most parts of the altered rock, but locally the texture is granoblastic and the rock is true calc-hornfels. In rock that is granoblastic the plagioclase feldspar has lost its primary zoning. The light-colored pyroxene-bearing rock generally is adjacent to amygdules that have cores of grano- blastic quartz bordered by rims of diopside or green amphibole, or to veinlets composed of quartz and diop- side. The excess CaO required to produce diopside rather than hornblende in the amphibolite facies doubt- less was supplied by the amygdules and veinlets. Cal- cite is now a minor constituent in both, but diopside indicates an original higher content of carbonate. KIND AND GRADE OF METAMORPHISM The metamorphic rocks were subjected to weak regional metamorphism during the later stages of fold- ing prior to the emplacement of the batholith, and to higher grade thermal metamorphism later, at the time of the emplacement of the batholith. The most con- spicious products of the earlier regional metamor- phism are the slates of the White Mountains and relict slaty cleavage in metamorphic remnants in the Sierra Nevada. In the Pine Creék pendant cleavage is iden- tifiable in micaceous quartzite and in tectonically flat- tened fragments in metavolceanic breccia. The later thermal metamorphism resulted chiefly in the forma- tion of hornfelses, but also, locally, in the formation of mica schist and gneiss. The mineral assemblages in the metamorphic rem- nants are chiefly in the amphibolite facies of Eskola (1989; see also Turner, 1948, and Barth, 1952). In 1958, Turner (Fyfe, Turner, and Verhoogen, 1958, p. 199-239) separated facies of contact metamorphism from facies of regional metamorphism. In this scheme most of the hornfelses of the Bishop district fall into the hornblende hornfels facies, which formerly was called the cordierite-anthophyllite subfacies of the am- phibolite facies. Brucite and wollastonite in calcareous assemblages indicate transition to the pyroxene horn- fels facies, and garnet-bearing mica schist and assem- blages that include both epidote and intermediate to caleic plagioclase indicate transition to the amphibo- lite facies of regional metamorphism, renamed, how- ever, the almandine amphibolite facies. In the hornfelses of the Bishop district, amphiboles and plagioclase are common in all rocks of appropriate composition. Diopside is common in hornfels having a high calcium content, but the association of diopside and hypersthene, considered diagnostic of the pyroxene hornfels facies, was not found. One criterion suggested by Turner (Fyfe, Turner, and Verhoogen, 1958, p. 206) for distinguishing the hornblende hornfels facies from the pyroxene hornfels facies, incompatibility of potassium feldspar with andalusite or cordierite, does not apply in the Bishop area because K feldspar and andalusite are found together in a terrane in which amphibole also is present. Rose (1958, p. 1703), who also recognized this problem in the metamorphic rocks of the Sierra Nevada, concluded that if the upper limit of the amphibolite (or hornblende hornfels) facies is defined by the transition of hornblende and calcic plagioclase to clinopyroxene, hypersthene, and plagio- clase, the transition of the assemblage muscovite-bio- tite-quartz to andalusite-cordierite-microcline must occur well below the upper limit of the amphibolite facies. The presence of assemblages that include an- dalusite and potassium feldspar together indicates, however, that the associated rocks are in the upper rather than the lower part of the hornblende hornfels facies. No facies of lower grade in which the place of calcic plagioclase is taken by albite and epidote were found, although locally plagioclase has been saus- suritized. The mica schist and the gneiss pose a problem, since their formation requires both elevated temperatures and dynamic conditions. Their mineral grade is too high for them to have been formed during the earlier folding and regional metamorphism. It seems certain that they must have been formed approximately contemporane- ously with the hornfelses, but under kinematic rather than static conditions. The composition of the rock also is significant, and pelitic rocks become schistose more readily than rocks of any other composition. Durrell (1940, p. 100-115) explained similar relations in the western Sierra Nevada by postulating regional orogenic stress continuing into the period of magmatic intrusion. He concluded that the granitic magmas were emplaced passively and exerted no deforming force on the wall rocks because he found no relation between the wall- rock structure and intrusive contacts, because of an ab- sence of peripheral schistosity, and because of the pres- ence of antistress minerals in contact-metamorphosed rocks (Durrell, 1940, p. 30). He wrote further (Dur- rell, 1940, p. 108) : This high temperature in the wall rocks ahead of the mag- mas, combined with the stress existing there, would result in the _ formation, by recrystallization, of schists from such rocks as are capable of giving rise to minerals which can assume an orientation under such conditions. Close to contacts, in areas free of stress or where stress was very weak, where tempera- tures would be higher and recrystallization would be more in- tense, hornfelses would be expected to form. 32 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA Durrell's concept of regional stress contemporaneous with the intrusion of the granitic rocks cannot be tested within the Bishop district, but it does not afford a sat- isfactory explanation of the schist and gneiss there. Schist and gneiss are found in only two places, in septa along the South Fork of Bishop Creek and along Red Mountain Creek. The septum along Bishop Creek con- sists of hornblende-biotite-quartz-feldspar gneiss, and that along Red Mountain Creek of mica-quartz schist and associated garnetiferous gneiss. The fact that both the schistosity and gneissic foliation parallel the intru- sive contact suggests a relation to the intrusions. The rock in both septa is pervasively sheared, and the gneissic layering appears to have been produced by the migration of mafic minerals to shear planes. Accord- ing to Durrell's concept of regional stress, both septa should have been chiefly stress-free at the time of in- trusion, since they are bounded by granitic rocks. On the whole the schistosity appears to be the "peripheral schistosity" which was absent in the area studied by Durrell. A freely flowing magma would hardly pro- duce peripheral schistosity. Probably it could only be formed in rock of appropriate composition after the margins of the intrusive granite had achieved some strength through cooling and crystallization. Thus, pe- ripheral schistosity is akin to marginal protoclasis, ex- cept that it takes place in the wall rock rather than in the marginal parts of the intrusive. Forcible emplacement of certain other intrusives in the Bishop district is shown by wall-rock separations measurable in miles. Dislocations of wall rocks by in- trusions are discussed on pages 115-116. Bowen has distinguished thirteen steps in the pro- gressive thermal metamorphism of siliceous dolomite (1940, p. 225-274), and Turner (1948, p. 80) includes the mineral assemblages formed above steps 3 to 6, inclusive, in his cordierite-anthophyllite subfacies of the amphibolite facies (hornblende hornfels facies). The steps are marked by the upper limits of stability of various mineral assemblages as follows: Stable below step- Mineral assemblage Dolomite and quartz P t Dolomite and tremolite Seuuawacuel. Calcite, tremolite, and quartz Calcite and tremolite Dolomite | amt oni Calcite and quartz T Calcite, forsterite, and diopside Calcite and diopside 9... Des Calcite and forsterite 10.1... Calcite and wollastonite Hell Calcite and akermanite _ Spurrite and wollastonite Spurrite and akermanite Harker and Tuttle (1956, p. 239-256) have shown that for pressures of less than 40,000 pounds per square inch (equivalent to the weight of about 35,000 feet of rock) steps 5 and 6 should be in reversed order; wol- lastonite will form from quartz and calcite at a lower temperature than calcite and periclase will form from clean dolomite. Both diopside and tremolite are present in the meta- morphic remnants of the Sierra Nevada, but whereas diopside occurs in assemblages that include calcite, tremolite was found only in assemblages free of calcite. Therefore, Bowen's step 4 was attained and step 8 was not. Dolomite was not identified in any of the meta- morphic remnants, although its former existence is shown by diopside, tremolite, and in one place, brucite. The presence of brucite indicates clearly that step 5 (step 6 according to the data of Harker and Tuttle) was exceeded locally, but it cannot be assumed that it was attained everywhere because the paucity of brucite and the abundance of diopside and tremolite show that clean dolomite, necessary to record the step, was rare. Bowen's step 6 (step 5 according to Harker and Tuttle), reaction of calcite and quartz to form wollastonite, was attained in many smaller inclusions and in the marginal parts of larger ones, but calcite and quartz appear to- gether in apparent equilibrium in many specimens from larger metamorphic remnants. Forsterite, included in the critical assemblage that becomes unstable above step T, was not identified, and it could not be determined therefore whether step 7 was attained. In summary, it appears that step 4 was attained everywhere, that steps 5 and 6 were reached in most smaller inclusions and in the marginal parts of larger ones, and that step 8 was not attained anywhere. Among the pelitic rocks, andalusite is the common aluminosilicate, although sillimanite was tentatively identified in a few places. The occurrences of silliman- ite are too few to warrant speculation about the rela- tion of sillimanite to andalusite. The thermal metamorphism in most places appears to have been chiefly isochemical with introduction of ma- terial from the granitic magmas indicated only in con- nection with the formation of tactite, the host rock for the contact metasomatic tungsten deposits. The prev- alence of sharp boundaries between unlike mineral as- semblages, which coincide very closely with original boundaries between lithologically different sedimentary layers indicates that very little redistribution of ma- terial has taken place within the metamorphic remnants. The sharp boundaries between contiguous layers sug- gest further that the metamorphism was rather dry- that little water was present in the original sedimentary rocks and that little was introduced. PREBATHOLITHIC GEOLOGY 38 Nevertheless, locally some constituents were removed during metamorphism and others were redistributed. In the silication of limestone or marble to form silicated marble or calc-hornfels carbon dioxide was removed, and in the formation of tactite carbon dioxide was re- moved and calcium was removed in part. Carbona- ceous material was driven out of some marble, chert, and calcareous and argillaceous hornfels. In places, very dark gray to black rocks that contain carbonaceous ma- terial grade along their strikes into white or very light gray rocks from which carbonaceous material has been removed. Constituents that have been locally recirculated in- clude calcium, iron, and magnesium. Beds of ealc-horn- fels not uncommonly encroach unevenly on bordering layers of fine siliceous rocks and on amphibolite, and in places veinlike layers of calc-hornfels anastomose through these same rocks. The encroachment of cale- hornfels layers on adjoining layers probably took place during metamorphism by progressive enlargement and modification of the chemical systems within the cal- careous layers to incorporate the material in the trans- gressed layers. Dikelike stringers of calc-hornfels in siliceous hornfels or amphibolite may reflect premeta- morphic calcite or dolomite veins. The source of the calcium generally was calcium-rich layers, but in mafic metavolceanic or dike rock a common source was calcitic amygdules and veinlets. Iron and magnesium locally have been redistributed in mafic metavoleanic and plutonic rock to form vein- like layers and orbicular structures of hornblende and biotite. The septum at the Blue Star Tale mine is of interest because it is the site of a commercial tale deposit which is believed to have been formed by the redistribution of constituents contained in the adjacent rocks. The outcrop is somewhat elongate, having a maximum di- mension of about 1,000 feet and a minimum dimension of about 400 feet. Most of it consists of amphibolite, but its core is white and coarsely crystalline marble that contains brucite and small amounts of epidote. The mantle of amphibolite around the marble core suggests a large scale corona formed by the interaction of solutions from the enclosing granitic rocks with the marble. Petrographic study, however, indicates that at least part of the amphibolized rock was originally igneous. It is dense and very dark gray, and much of it consists chiefly of variable proportions of plagio- clase and hornblende, although part of it consists al- most entirely of amphibole with or without chlorite. Minor accessory minerals are biotite, sphene, magnetite (partly altered to hematite), and apatite. The amphi- bole commonly is pleochroic : X= pale brownish yellow, Y¥=brownish green, Z=olive green, but the pleochroism is variable, and some samples contain both a strongly colored amphibole and a very pale one. The habit of the amplibole also is variable. Some crystals are euhedral, and most are subhedral. Commonly the ends of larger prisms are frayed. In some specimens, the plagioclase also is of two compositions and of two hab- its. Zoned plates (Ano-s,) appear lathlike in thin see- tion and form a mat of unoriented crystals. In the in- terstices of these plates is oligoclase which has a lower index of refraction than that of the plates. The pres- ence of plagioclase of two compositions is the chief evidence for an igneous parent rock. In other rocks in this area all the plagioclase is in irregular plates hav- ing the composition of oligoclase. Such rocks as well as rocks composed entirely of amphibole have been thoroughly reconstituted. Tale is present locally in the amphibolite, adjacent to the marble. It is pseudomorphous after coarse radi- ating crystalline aggregates of amphibole as much as 4 inches across. Some of the adjacent amphibolite also contains small amounts of chlorite. The chemical change from amphibole to tale involves principally the addition of CO; and the loss of SiO;. If the alteration took place with constant volume, the reaction can be expressed by the following equations (Turner, 1948, p. 133): (1) CazMg5Si3022(0H)2 + 4002 —>2CaMg(COa) 2 + HQMggshOm + 48103 Tremolite Dolomite Tale (remov- (810 g; 270 cc) (368 g; 130 cc) (378 g; ed in 140 cc) _ solution) and (2) 4H4Mng128109 + 6H4Mg381309+ 1328102 => Pennine (2768 g; 1025 ce) 7.3H2Mg3si4012—1— 4.1 MgO + 4A1203 + 127H20 Tale (2759 g; 1022 cc) (removed in solution) The CO: required for the conversion of amphibole probably was derived from the adjacent marble, pos- sibly as a result of the formation of periclase (hydrated to brucite) and epidote. Near the tale are veins as much as 1-foot thick that are composed chiefly of magnetite and specular hema- tite. The distribution of these veins with respect to the tale suggest that they are byproducts of the formation of tale from amphibolite. The iron oxides from which they were formed could have been those expelled from the amphibolite during its conversion to tale. ARRANGEMENT OF METAMORPHIC REMNANTS IN RELATION TO THE REGIONAL DISTRIBUTION OF THE PREBATHOLITHIC ROCKS The regional distribution of the prebatholithic rocks provides a framework that makes possible an inter- 34 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA pretation of the stratigraphic and structural relations of the metamorphic rocks in pendants, septa, and inclu- sions in the Bishop district. The trends of the pre- batholithic rocks that crop out in the ranges east of Owens Valley can be projected into the Sierra Nevada. Even though the batholithic rocks in the Sierra Nevada have bent and dislocated the rocks which they intrude, and have engulfed or pushed upward large segments of the rocks, a highly deformed skeletal pattern of these rocks still can be deciphered in the metamorphosed remnants. The known distribution of pre-Cenozic rocks in the east-central Sierra Nevada and the adjacent White and Inyo Mountains is shown in figure 7. The general trend of the rocks is about N. 35°%-40° W., a trend that cuts across Owens Valley and locally strikes obliquely into the Sierra Nevada batholith. Although the rocks in the White and Inyo Mountains are strongly folded and faulted, the rocks exposed along the western fronts of these ranges are, on the whole, progressively younger toward the south, ranging in age from Early Cambrian or older at the latitude of Bishop to Middle Triassic in the New York Butte quadrangle east of Owens Lake. This distribution suggests that the strata are progres- sively younger toward the west and constitute the west limb of an anticlinorium or the east limb of a synclin- orium. Further evidence that the strata in this region are younger toward the west is found northwest of Bishop in the Mount Morrison and Ritter Range pend- ants, which contain a steeply dipping homoclinal sequence of Paleozic and Mesozoic strata of more than 60,000 feet (Rinehart, Ross, and Huber, 1959, p. 941- 945). These strata range in age from Ordovician in the east to Early Jurassic or younger in the west. In the western part of the Ritter Range pendant is a syncli- nal axis, west of which the section is reversed and the tops of beds are to the east. The Paleozoic and Mesozoic strata in the western foothills of the Sierra Nevada, on the west side of the batholith, strike N. 35°%-45° W. at the latitude of Bishop, parallel with the strata in the Owens Valley region. Studies by L. D. Clark (1960, p. 492-493) re- veal that the tops of beds in most exposures are to the east but that the sequence is cut by several eastward- dipping reverse faults of large displacement. Very likely these strata constitute the west limb of a syn- clinorium whose east limb is in the Owens Valley re- The batholith occupies the axial region of this synelinorium. The stratigraphic sequence in the White and Inyo Mountains can be divided into two lithologically dis- tinguishable series; an older one composed of limestone, dolomite, shale, and quartzite, and little or no volcanic gion. material, and a younger one that contains abundant volcanic material. The older series is chiefly Paleozoic and the younger series Mesozoic, but the nature and precise position of the contact between the two series are in some doubt. Near New York Butte (fig. 7) the volcanic series rests unconformably on Middle Triassic strata that contains little or no volcanic material (C. W. Merriam, oral communication, 1959). In the Mount Morrison and Ritter Range pendants, fossils of Permian(?) age have been found about 3,000 feet below the volcanic series, and fossils of Early Jurassic age have been found about 10,000 feet above the base of the volcanic series (Rinehart, Ross, and Huber, 1959) ; the contact therefore may be in about the same position as near New York Butte. In a span of more than 100 miles, between the New York Butte area and the Mount Morrison pendant, most of the remnants of the volcanic series lie west of the nonvolcanic series, as they should if the strata are in the east limb of a synclinorium. The trace of the contact between the two series is a remarkably straight line trending N. 30°%-35° W., although irregularities are present locally. The comparative straightness of the overall contact results from the prevailing steep or vertical dips of the beds. Inspection of figure 7 shows that the metamorphic remnants in the Bishop district lie between strata whose age is known or can be inferred within broad limits. Both the volcanic series and the nonvolcanic series are represented in the district and are in contact in the Pine Creek pendant. The highly generalized conclu- sion that the volcanic rocks in the metamorphic rem- nants are chiefly of Mesozoic age is warranted. Fur- thermore, sedimentary strata that stratigraphically underlie metavolcanic strata are likely to be of late Paleozoic age. DESCRIPTIONS OF METAMORPHIC REMNANTS PINE CREEK PENDANT The Pine Creek pendant (pl. 2; fig. 7) is a lens of metamorphic rocks almost 7 miles long and 1 mile wide. From the northeast face of Basin Mountain it extends N. 20° W. across Horton Creek, Mount Tom, and Pine Creek into the south end of Wheeler Crest. Outcrop altitudes range through more than 6,000 feet-from a low point of about 7,400 feet on the floor of Pine Creek to a high point of 13,652 feet on the summit of Mount Tom. Everywhere except at the north end where it is cut off by dark hornblende gabbro, the pendant is bounded by light-colored granitic rocks assigned to several different formations. Both north and south of the pendant, but separated from it by intrusive rocks, are thin septa and inclusions composed of metamorphic PREBATHOLITHIC GEOLOGY 30 rocks like those in the pendant. The northern continua- tion, the Wheeler Crest septa, extends beyond the north- ern boundary of the Mount Tom quadrangle and sepa- rates Round Valley Peak granodiorite on the west from Wheeler Crest quartz monzonite on the east. A south- ern extension from the pendant forms a ring of meta- morphic rock that circles Mount Humphreys and a septum that extends south from the ring to the North Fork of Bishop Creek, called the Mount Humphreys ring and septum on the map (fig. 7). The Pine Creek pendant and its extensions include three mappable metasedimentary rock units of Pale- ozoic ( ?) age and two predominantly metavolcanic units of Mesozoic(?) age. The metasedimentary rocks com- prise the northern two-thirds of the Pine Creek pend- ant, the Wheeler Crest septum, and the southern one- third of the ring around Mount Humphreys and the attendant septum that continues to the south ; the meta- volcanic rocks comprise the southern one-third of the pendant and the northern two-thirds of the ring around Mount Humphreys. The oldest metasedimentary unit is composed of pelitic hornfels, micaceous quartzite, and vitreous quartzite. - The next stratigraphic unit is marble, which is overlain, in turn, by micaceous quartzite. The meta- volcanic rocks are divided, simply, into a unit of felsic _ metavoleanic rocks and a unit of mafic metavolcanic rocks. Probably the felsic metavolcanic rocks are the older, but the age relations are uncertain. The main structure in the northern two-thirds of the Pine Creek pendant is a tight syncline whose axis lies within the micaceous quartzite. Except at the south end, the synclinal axis trends N. 20° W., and the axial plane is vertical. The beds in both limbs dip steeply and are generally parallel; gently dipping beds are found only within a few feet of the axial plane. Beds with gentle dips are visible on the south side of Pine Creek Canyon a few hundred feet west of the juncture of Pine and Gable Creeks, along the trail to the Tungstar mine. If the same general locality is viewed from the switch- backs on the road on the north side of Pine Creek lead- ing to the Pine Creek mill, beds can be traced visually through a half circle, from one nearly vertical limb to the other. The synclinal axis can also be identified in the north wall of Pine Creek Canyon and 1%4 miles to the south in the canyon cut across the pendant by Gable Creek. Because of the steepness of the terrane, the structure in the north end of the pendant was not worked out, but the syncline is presumed to continue into this area. Farther south on the northwest side of Mount Tom, the syncline is bent around to an easterly trend. At the bend it is cut by a wedge-shaped dike along which the pendant is offset laterally about half a mile. 4 The marble that flanks the micaceous quartzite on the west is absent from the east side of the pendant because it is cut out by quartz monzonite. However, a metamorphic remnant that consists chiefly of marble crops out in the ridge on the southeast side of the cirque at the head of Elderberry Creek. This remnant is separated from the pendant about half a mile by quartz monzonite. The presence of slivers of micaceous quartzite within the marble on the west side of the pendant suggests folding or faulting within the mar- ble unit, but the slivers may be the result of lenticular sedimentation. The metavolcanic and associated metasedimentary rocks in the south end of the pendant are in fault con- tact with the marble and micaceous quartzite in the central and north parts. An unconformity is unlikely because it would require an improbable series of events : folding of the micaceous quartzite and, rotation of the fold axes to near-vertical positions; then, after deposi- tion of the overlying volcanic rocks, rotation of the fold axes back to their present near-horizontal posi- tions. Nevertheless, in most places the angular dis- cordance between the micaceous quartzite and the meta- volcanic sequence is only a few degrees. Much of the contact is occupied by diorite and felsic dikes, some of which penetrate into the micaceous quartzite distances of a few hundred feet. Both the metavolcanic rocks and the south end of the micaceous quartzite have been bent into a broad S-fold which also affects, in part, the synclinal axis within the micaceous quartzite. The strata are bent from their N. 20° W. strike farther north to an easterly strike in the south side of Mount Tom for about 1% miles west from Horton Lake, and then are bent to the southeast in the northeast side of Basin Mountain. In this part of the pendant, horn- blende gabbro, quartz diorite, quartz monzonite, and thin granitic dikes have intricately penetrated, reacted with, and physically displaced the metamorphic rocks. The syncline in the northern two-thirds of the pend- ant parallels the regional fold axes and is probably the result of prebatholithic deformation. The S-fold in the south end of the pendant, however, can be most readily explained as the result of deformation caused by the forcible emplacement of the quartz monzonite. In the formation of the S-fold, the earlier structures were deformed, and the pattern is not one that suggests continuation of the same stresses that produced the pre- batholithic folds. On the contrary the S-fold is con- fined to a part of the pendant that is in contact with the quartz monzonite. Furthermore, the intricate pene- tration and shattering of the metamorphic rocks in the S-fold by dikes, sills, and irregular masses of granitic rocks that are satellitic to the quartz monzonite suggests 36 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA that the S-fold was caused by the forcible emplacement of the quartz monzonite. PELITIC HORNFELS, MICACEOUS QUARTZITE, AND VITREOUS QUARTZITE A lens of metamorphosed clastic sedimentary rock, including pelitic hornfels, micaceous quartzite, and vitreous quartzite, is preserved along the west side of the pendant in the vicinity of Pine Creek, and a smaller mass of similar rocks forms a dislocated mass along the east side. The beds in the west side of the pendant dip steeply and strike parallel with the long axis of the pendant. They have a maximum stratigraphic thick- ness of about 1,000 feet, but are cut off on the west by quartz monzonite. The strata are mostly iron-stained pelitic hornfels and micaceous quartzite, and are only locally unstained vitreous quartzite. The unit has been penetrated by numerous aplitic and pegmatitic dikes that are offshoots from a quartz monzonite pluton that lies to the southwest. A few hundred feet west of the clastic strata and separated from it by quartz monzonite is a mass of marble and tactite that has a stratigraphic thickness of about 100 feet. The tactite in this mass has been exploited in the Brownstone tungsten mine. Whether this remnant of marble and tactite represents a thin interbed in the clastic strata or part of a strati- graphically lower carbonate unit is not known. The small mass of pelitic hornfels, micaceous quartz- ite, and vitreous quartzite on the east side of the pendant is at the east end of a small mass of marble that contains the Lambert tungsten mine. This mass is in the oppo- site limb of the major syncline of the pendant, and the clastic strata lie on the east side of the marble. The presence of vitreous quartzite is considered good evi- dence of the stratigraphic equivalence of the strata here with those in the west side of the pendant, because it is such an uncommon rock in the region. MARBLE East of and stratigraphically overlying the lens of pelitic hornfels, micaceous quartzite, and vitreous quartzite in the west side of the Pine Creek pendant is an extensive belt of marble. This marble is more than 3 miles long, extending from the south wall of Pine Creek northward to the north end of the pendant, and about one-third of a mile wide at the widest place. The strata dip steeply or vertically, but the outcrop width probably does not represent the stratigraphic thickness because both isoclinal folds on a small scale and bedding plane shears are present. two lenses of micaceous quartzite, which may be either sedimentary lenses that were deposited with the marble or infolded segments of the stratigraphically overlying unit of micaceous quartzite. Enclosed in the marble are. The marble also crops out in the east side of the pendant in the dislocated mass that contains the Lam- bert tungsten mine. The apparent thickness of marble there, measured between the pelitic hornfels, micaceous quartzite, and vitreous quartize unit on the east and the overlying micaceous quartzite on the west, is about 800 feet. The marble in the west flank of the pendant is light gray to medium light gray away from granitic con- tacts. Near granitic contacts it has been recrystallized and bleached to very light gray (almost white). In most places this bleached and recrystallized zone in- cludes only a few feet adjacent to the granitic contact, but near the ore bodies of the Pine Creek mine it in- cludes most of the width of the marble. In hand specimen the marble appears to be fairly clean, but quartz and various cale-silicate minerals can be seen in thin section-grossularite, plagioclase, ido- crase, diopside, and wollastonite. Samples from the Pine Creek mine that were analyzed chemically con- tained only 70 to 80 percent CaCO;. Common impuri- ties are 15 to 20 percent of SiO», 3 to 4 percent of Al;0;, and about 3 percent of MgO. Because of its association with micaceous quartzite, the marble present in the Wheeler Crest septa is be- lieved to be correlative with the marble unit of the pendant. Marble in the south part of the ring around Mount Humphreys and in the septum that extends south from it also is associated with micaceous quartz- ite and may be correlative with the marble in the west flank of the Pine Creek pendant, but locally it contains abundant thin hornfels layers that are not found in the marble unit of the pendant. MICACEOUS QUARTZITE The micaceous quartzite unit makes up the larger part of the northern two-thirds of the Pine Creek pendant and most of the Wheeler Crest septa, and is probably represented in the septum that extends south from the Mount Humphreys ring. This unit is almost all micaceous quartzite, but locally it includes a few in- terbeds of calc-hornfels, and at the Ridge ore body of the Adamson mine it contains tactite formed from a bed of marble. All the micaceous quartzite is fine grained except for a few pebbly beds exposed in the glaciated floor of Pine Creek Canyon in the NW cor. see. 9, T. 7 S., R. 80 E. The bedding is steep and strikes parallel with the exter- nal boundaries of the unit except close to the axial plane of the syncline where the beds dip gently or are hori- zontal. Bedding is generally obscure and can be deter- mined only by careful searching for compositionally distinctive layers. In many outcrops the micaceous PREBATHOLITHIC GEOLOGY 37. quartzite is cleaved parallel with the axial plane of the major syncline. Generally the cleavage is at only a slight angle to the bedding, but near the axial plane of the syncline it is at a large angle. The whole unit is stained various shades of brown by iron oxides derived from pyrite, but on fresh surfaces most rocks are dark gray to grayish red. Feldspathic varieties generally are pale yellowish brown, and calc-hornfels layers are medium light gray. The rock weathers into polygonal blocks a few inches on a side. About 3,000 feet of steeply dipping strata are ex- posed in the north wall of Pine Creek Canyon between the axial plane of the syncline and the marble unit in the west side of the pendant. Inasmuch as the top of the micaceous quartzite unit is not present, the total thickness of the unit must be somewhat greater. Dupli- cation by folding is possible but unlikely, hence 3,000 feet is a reasonable figure for the minimum thickness. FELSIC METAVOLCANIC ROCKS Felsic metavolcanic rocks crop out on the south and southwest sides of Mount Tom in a belt about 9,000 feet long and 2,000 feet wide. They are in an area that is structurally complex and penetrated by numerous dikes of aplite, quartz monzonite, diorite, quartz diorite, and hornblende gabbro. On the north the felsic meta- volcanic rocks are in fault contact with micaceous quartzite, and on the south they are bordered by mafic metavoleanic rocks. They terminate on the west against metasedimentary rocks and diorite, and on the east against diorite, hornblende gabbro, and quartz mon- zonite. The principal felsic metavolcanic rocks are metar- hyolite tuff, and quartz latite sills, dikes, and probably flows. Metarhyolite tuff is well exposed in the western part of the area and quartz latite in the eastern part. Metarhyolite tuff is particularly well exposed along the ridge northwest of the Hanging Valley mine. The tuff is generally massive, but locally shows a foliation that probably is secondary. Euhedral quartz and microcline (originally sanidine) and small dark lithic fragments are visible in hand specimen. Quartz latite is well ex- posed south of the Tungstar mine. Many of these rocks are foliated. Rounded and corroded plagioclase pheno- crysts are conspicuous in hand specimens. Along the contact of the felsic volcanic rocks with micaceous quartzite, sills of quartz latite penetrate the micaceous quartzite along bedding planes. Associated with the felsic metavolcanic rocks are amygdular volcanic rocks of dacitic composition and such metasedimentary rocks as siliceous hornfels, mar- ble, and schistose rocks that probably are tuffaceous. Siliceous hornfels is the most abundant metasedimen- tary rock and is present in the Tungstar mine area. Marble is also present at the Tungstar mine, and a string of lenses extends east from the mine toward the summit of Mount Tom. The metasedimentary rocks east of the felsic metu- volcanic rocks, in the vicinity of Gable Lakes, are chieily feldspathic quartzite and pelitic hornfels, but include a thin belt of marble that can be traced northwest from the Lakeview mine for about half a mile. The Hang- ing Valley mine, about half a mile east of the Lake view mine, may be in the same marble bed. MAFIC METAVOLCANIC ROCKS Mafic metavolcanic rocks lie southwest of the felsic ones and extend from the south side of Mount Tom, across Horton Creek, into the northeast side of Basin Mountain. Similar rocks farther south in a ring around Mount Humphreys are separated from those in Basin Mountain by Tungsten Hills quartz monzonite. The most common mafic volcanic rock is dark-gray fine-grained andesite having a faint to conspicuous foli- ation that is probably secondary. The principal miner- als are intermediate plagioclase, quartz, hornblende, and biotite. Accessory minerals are magnetite, apatite, and, less commonly, sphene. Most specimens have a granoblastic groundmass, which locally encloses larger crystals of zoned plagioclase and hornblende. Oriented biotite gives some specimens a lepidoblastic texture. Some rocks are obviously bedded, and most of them are probably tuffs. Lenses of marble, calc-hornfels, and micaceous quartzite are present locally, and sev- eral lenses include tungsten prospects. The only marker bed recognized within the mafic metavolcanic rocks is a layer of volcanic breccia a few hundred feet thick, which extends from the northwest side of Horton Lake eastward along Horton Creek for more than a mile. This bed consists of angular flat- tened fragments of metavolcanic rock in a fine-grained tuffaceous matrix containing abundant quartz. The fragments range in length from less than an inch to more than 3 feet, and are fairly well sorted. Most of the volcanic rocks in the pendant are represented among the fragments. PROBABLE CORRELATION WITH THE MOUNT MORRISON PENDANT The metasedimentary strata in the Pine Creek pend- ant match closely those in the Bloody Mountain block of the Mount Morrison pendant 15 miles to the north- west (fig. 7), which contain fossils of Pennsylvanian and Permian(?) age (Rinchart, Ross, and Huber, 1959). The suggested correlation between the Pine Creek pendant and the Bloody Mountain block is shown in figure 11. Correlation of the strata in the 38 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA Mount Morrison pendant - Bloody Mountain block Pine Creek pendant o § i 8 «| Metavolcanic Fo rocks t = mnt a my € s z & a a $ « sooo n E j Bloody Mountain ren etfzgkiamc E a = formation > rd a. ;| Lake Dorothy sooo n |- ~.. Micaceous hornfels quartzite 3 Mildred Lake hornfels Mou‘ntEItfln‘marble 800 ft? Marble Pelitic hornfels Micaceous quartzite and vitreous quartzite / Bright Dot formation (chiefly metachert and siliceous hornfels) PENNSYLVANIAN Aree adits a 8 Contact with intrusive Fault or faulted granitic rock unconformity FIGURE 11.-Suggested stratigraphic correlation of the Pine Creek pen- dant with the Bloody Mountain block of the Mount Morrison pendant. two pendants is based on similarity of lithologic se- quence. In both pendants a thick marble unit strati- graphically overlies metachert or siliceous hornfels and is overlain by a thick section of fine-grained siliceous clastic rocks. The section of siliceous clastic rocks is overlain in turn by metavolcanic rocks, though in the Pine Creek pendant the contact is a fault contact. In the Mount Morrison pendant the strata above the mar- ble include a calc-hornfels unit about 750 feet thick, which was not identified in the Pine Creek pendant. Two explanations for the apparent absence of the cale- hornfels unit can be offered : (1) The calc-hornfels unit is present in the Pine Creek pendant but was not mapped separately-beds of calc-hornfels are present within the micaceous quartzite unit, and more detailed study might result in recognition of a calc-hornfels unit. (2) The calc-hornfels unit in the Mount Mor- rison pendant may grade to micaceous quartzite or pelitic hornfels in the interval between the Mount Mor- rison and Pine Creek pendants. Even within the Bloody Mountain block the calc-hornfels unit grades along the strike to more siliceous rock (Rinehart and Ross, 1964). BISHOP CREEK PENDANT The Bishop Creek pendant occupies an irregularly shaped area of about 20 square miles. The strata have been deformed, as in the Pine Creek pendant, by regional compression that resulted in tight north- to northwest-trending folds, and somewhat later by em- placement of the intrusive rocks, which caused complex and irregular deformation of the regional structures. Apophyses from the bordering granitic plutons and dikes, sills, and stocks of diorite and hornblende gabbro penetrate the pendant extensively. The heart and most cohesive part of the pendant lies along Coyote Ridge, on the east side of the South Fork of Bishop Creek. From this central core, lobes extend northwest across Table Mountain, northeast to Lookout Mountain and beyond, and south to the ridge southwest of Green Lake. From the northwest lobe a septum ex- tends northwest across the Middle Fork of Bishop Creek. Many small inclusions are peripheral to the pendant and separated from it by granitic rock. The pendant is composed of metasedimentary rocks, and in the central core six units were distinguished in mapping. These are, in order of decreasing age, (1) pelitic hornfels with interbeds of marble, (2) marble, (3) banded calc-hornfels and pelitic' hornfels, (4) metachert and andalusite-bearing pelitic hornfels, (5) siliceous calc-hornfels, and (6) micaceous quartzite and pelitic hornfels. Structural features that resulted from the earlier regional deformation are most readily identified in the central body of the pendant. The principal structures are a syncline on the east and an anticline on the west. Most of the beds are steep or vertical and trend north. The anticline is well exposed in the steep wall east of the South Fork of Bishop Creek about 1.6 miles north from Parchers Camp, but the syncline is only poorly exposed in Coyote Ridge, and its existence and position was established only by the duplication in inverse order of the stratigraphic sequence. Neither fold exhibits a geometric relation to any of the intrusive masses that indicates genetic relation, whereas the fold axes are approximately parallel with the regional fold axes. The anticline where exposed in the South Fork of Bis- hop Creek is generally symmetrical but pinched at the crest. As a result of this pinching the axis for about 1 mile southeast from the exposure of the anticlinal structure lies within a narrow band of calc-hornfels (pl. 1). _ The syncline shows little effect of the emplace- ment of the intrusives, except at the south end where strata have been pushed westward by a tongue of quartz monzonite of Cathedral Peak type. The west side of the anticline, on the other hand, has been deformed by a tongue of Tungsten Hills quartz monzonite along the South Fork of Bishop Creek, by a salient of Lamarck granodiorite that penetrates the cale-hornfels unit at the core of the anticline, and by the tongue of quartz monzonite that cuts off the syncline at the south end. Each intrusive pushed the strata in the syncline later- ally and produced irregularities in their strike. The pendant is cut off at the north end of the central body by Tungsten Hills quartz monzonite that pro- trudes southward and separates the two lobes of the pendant. The quartz monzonite pushed southward into the pendant and spread the strata in the lobes. PREBATHOLITHIC GEOLOGY 39 Distortion of the strata by the quartz monzonite is especially clear in the northeastern lobe where several stratigraphic units can be traced from the east flank of the syncline in the central body of the pendant through a broad curve concave to the northwest, which follows the margin of the quartz monzonite. In the south part of the lobe, the strata are bent smoothly and regularly, whereas in the north part, in the vicinity of Lookout Mountain, they are cut by faults and are penetrated by small apophyses from the quartz mon- zonite. These faults and intrusive apophyses have so dislocated the strata that it was not possible to match the strata of the blocks. In the very southeast corner of the Mount Tom quadrangle is a block that contains a synclinal axis, but the relationship of this structure to the syncline of the central body of the pendant was not determined. The fact that locally some faults have served as guides for apophyses of quartz monzonite suggests that the faults were formed during an earlier period of regional deformation. The northwest lobe of the pendant has been almost separated from the central body by a tongue of quartz monzonite exposed along the South Fork of Bishop Creek. Isoclinal folds along the east side of the lobe could have been caused by the emplacement of the tongue of quartz monzonite ; if they are regional folds they have been deformed by the quartz monzonite. Most of the beds in the north and northwest parts of the northwest lobe dip moderately toward the north- west. At the west edge of the lobe the beds were pushed upward by Tungsten Hills quartz monzonite, which may also have pressed the rocks in the septum against the earlier emplaced Lamarck granodiorite and caused the steep dips in the septum. PELITIC HORNFELS WITH INTERBEDS OF MARBLE The oldest strata that can be fitted into the strati- graphic sequence in the central part of the pendant are in a poorly exposed sequence that lies along the south- east side of the West Fork of Coyote Creek. The strata are chiefly dense medium-gray pelitic hornfels layers 100 feet or more thick separated by layers of marble 50 to 100 feet thick. The hornfels generally is com- posed of quartz and K feldspar in variable proportions. Coarser grained layers commonly contain more quartz than K feldspar, but finer grained layers generally con- tain more K feldspar. Diopside is a common constitu- ent and is most abundant in coarser layers. The horn- fels probably was derived from interlayered limy shale and very fine calcareous silt. The thickness of the unit is difficult to determine be- cause it has been irregularly intruded by granitic rocks. The beds dip steeply, and the maximum outcrop width is about 3,000 feet, which is the approximate thickness of the sequence if the strata are not duplicated. The sequence of pelitic hornfels and interbeds of marble is bounded on the southeast by granitic and mafic intrusive rock, but beyond the igneous rocks are several isolated masses of calc-hornfels. The relation of these masses of calc-hornfels to the pendant is un- certain, but it seems reasonable to assume that they are remnants of a once continuous formation that lay strati- graphically just below the pelitic hornfels and inter- beds of marble. The largest remnants, in sees. 29 and 31, T. 8 S., R. 32 E., and sees. 6 and 7, T. 9 S., R. 32 E., are shown on the geologic map (pl. 1) of the Mount Goddard quadrangle as calc-hornfels. The rock is dark greenish gray, dense, and structureless except for com- positional layering that reflects bedding. MARBLE Crystalline white marble lies stratigraphically above the sequence of pelitic hornfels and marble interbeds along the West Fork of Coyote Creek. It is also pres- ent in the escarpment on the east side of Coyote Ridge. The width of outcrop of the marble is about 500 feet, which probably approximates its thickness. Near the middle of the marble is a distinctive quartzite layer about 50 feet thick. This layer is present in several out- crops along the east side of Coyote Ridge, but appar- ently is absent to the northeast. BANDED CALC-HORNFELS AND PELITIC HORNFELS Contiguous with the marble on the northwest and west is a hornfels unit that is characterized by con- spicuously banded sequences of alternately light-gray calc-hornfels and dark-gray pelitic hornfels. The banded sequences are thin bedded-each bed is a quar- ter of an inch or less in thickness. The banded appear- ance is accentuated on weathered surfaces by staining of the light-gray beds to grayish orange. Although the banded sequences are the most distinctive assem- blages, grayish-black to brownish-gray or light olive- gray to yellowish-gray hornfels that are thin bedded but which are not conspicuously banded are also pres- ent. In the banded hornfels, the dark-gray pelitic beds are much finer grained than the lighter colored ones of calc-hornfels. The dark pelitic beds consist chiefly of very fine grained quartz, K feldspar, and carbonaceous material, accompanied in places by tremolite. The cale- hornfels beds contain abundant diopside, generally with quartz and K feldspar, although in some speci- mens diopside is the only mineral. Accessory minerals include apatite and pyrite. In beds where quartz is more abundant than diopside, the quartz is in grains 40 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA that commonly are size graded across the beds. The color difference between the pelitic hornfels and cale- hornfels beds is caused by the presence of much fine carbonaceous material in the pelitic hornfels. Light-colored calc-hornfels layers generally have wavy contacts with the contiguous darker pelitic layers ; streaks from the light-colored layers penetrate into the dark ones and indicate that the light-colored layers have grown at the expense of the dark layers. This encroach- ment involved movement of calcium from the light- colored layers into the margins of adjacent pelitic lay- ers and the removal of carbonaceous material. This re- placement could have taken place either before or dur- ing thermal metamorphism. In the Lookout Mountain area light-colored hornfels locally cuts across dark pel- itic layers, apparently along fractures (fig. 12). The hornfels that is not conspicuously banded con- sists chiefly of approximately equal amounts of tiny grains of quartz and unoriented biotite flakes, and a small percentage of sericite and carbonaceous material. Layers of predominantly quartz alternate with layers in which sericite predominates, and apparently reflect original alternate layers of silt and clay. METACHERT AND ANDALUSITE-BEARING PELITIC HORNFELS Metachert and andalusite-bearing pelitic hornfels are stratigraphically above the banded hornfels and com- prise the lowest unit that is exposed in both limbs of the syncline in the core of the pendant. In the eastern limb FicorE 12.-Banded calc-hornfels (light-colored) and pelitic hornfels in which calc-hornfels encroaches on and cuts across pelitic hornfels. Crosscutting calc-hornfels was formed by introduction of calcium into pelitic hornfels along fractures and elimination of carbonaceous ma- terial. Narrow white streaks within crosscutting cale-hornfels are composed of quartz. the unit lies along the east side of Coyote Ridge and the north side of the West Fork of Coyote Creek, and in the western limb it crops out along both sides of the South Fork of Bishop Creek. Disconnected masses having unknown structural relations are also present in the northeastern lobe of the pendant. The most abundant rock in the unit is light-gray vitreous metachert that closely resembles quartzite. Lo- cally this rock grades into dark-gray to black metachert from which it was derived by further recrystallization of quartz and expulsion of carbonaceous material. In- terbedded with metachert of both colors is dark-gray to grayish-black, carbonaceous andalusite-bearing pelitic hornfels. Although the metachert is the more abun- dant rock in most places, pelitic hornfels predominates over metachert in the northeast lobe of the pendant. Commonly metachert and hornfels are interlayered in beds ranging from 1 to 6 inches thick. Fine-grained micaceous or feldspathic quartzite or quartz-sericite hornfels is locally interlayered with the two rocks just described. The distribution of sericite in patches in some of these rocks suggests that the sericite was derived from andalusite. The rocks are readily dis- tinguishable from metachert by the abundance of K feldspar or sericite, and in some specimens also by either the microscopically visible size-grading of quartz grains or by the angular outline of the quartz grains. Many of these rocks contain abundant carbonaceous material. SILICEOUS CALC-HORNFELS Siliceous calc-hornfels stratigraphically overlies the metachert and andalusite-bearing pelitic hornfels unit in the flanks of Table Mountain and along both sides of Coyote Ridge. The calc-hornfels on the east side of Coyote Ridge crops out in a band that extends north- eastward toward Lookout Mountain where several dis- connected masses with unknown structural relations oc- cur. The unit consists predominantly of siliceous hornfels, but locally, especially along the lower strati- graphic boundary, it includes gray to white marble. Most beds of siliceous calc-hornfels are very light to yellowish gray, but some quartz-rich layers are dark- ened by carbonaceous material. Individual beds are usually an inch or less thick, but some are several inches thick. The mineral content varies from layer to layer, but quartz is a principal con- stituent of most layers and is generally accompanied by tremolite or diopside or both. Commonly quartz forms a fine-grained granoblastic groundmass in which larger crystals of diopside or tremolite are enclosed. Microcline is present in the groundmass of some layers and in a few it predominates over quartz. Tremolite is in prisms that in some specimens have a random PREBATHOLITHIC GEOLOGY 41 orientation and in others lie with their long axis in the plane of the bedding. Larger diopside crystals are poikiloblastic, and enclose many small grains of the groundmass minerals. Accessories include pyrite, mag- netite, sphene, and apatite. Some quartz-rich rocks are darkened by carbonaceous dust. These rocks were probably derived from dolomitic sandstone or siltstone, but beds derived from less silice- ous carbonate rocks also are present. They contain such minerals as calcite, diopside, wollastonite, garnet, ido- erase, scapolite, plagioclase, and zoisite. MICACEOUS QUARTZITE AND PELITIC HORNFELS A unit composed chiefly of micaceous quartzite and pelitic hornfels overlies siliceous hornfels in the north part of Table Mountain and in Coyote Ridge, and is the youngest unit in the pendant. Coarser grained rocks in which quartz is the most abundant mineral are in- cluded under micaceous quartzite, and finer grained rocks that contain abundant feldspar and biotite under pelitic hornfels, but the two kinds of rock are completely gradational. The only other rock in the unit is lenticu- lar calc-hornfels. Megascopically, the micaceous quartzite and the pelitic hornfels are similar. Fresh surfaces commonly are light to dark gray-less com- monly light olive gray, yellowish brown, or yellowish gray. Some surfaces are mottled gray, yellowish gray, and yellowish brown, and black lenticular streaks and equidimensional white spots are present locally. Weath- ered surfaces commonly are stained with iron oxides, though the staining is not as heavy or as widespread as in the micaceous quartzite unit of the Pine Creek pend- ant. Although the unit somewhat resembles the micace- ous quartzite of the Pine Creek pendant, the rocks are generally finer grained, pelitic hornfels layers are more common, and individual layers are better sorted. The grayish red color on fresh surfaces, so common in the micaceous quartzite of the Pine Creek pendant, is lacking. AGE OF THE STRATA IN THE BISHOP CREEK PENDANT The sequence of strata in the Bishop Creek pendant is unlike the sequence in the Pine Creek pendant, and probably includes a different stratigraphic interval. The absence of metavolcanic rocks indicates that the strata are older than those in the Pine Creek pend- ant. The only fossil remains are worm castings that were found at a single locality in the siliceous cale- hornfels. Charles W. Merriam, who examined them, states that castings of this sort are abundant in the Cambrian, although they are found in rocks of a wide age span (oral communication, 1959). The strati- graphic sequence does not appear to correlate with either the sequence of Ordovician strata in the Mount 725-925 0O-65--4 Morrison pendant (Rinehart, Ross, and Huber, 1959) or the Precambrian (?). and Lower Cambrian sequence mapped in the White Mountains in connection with this report, but it may fall between these sequences. C. A. Nelson (1962) has mapped 12,000 feet of Ole- nellus-bearing strata in the Inyo Mountains, only the lower 1,500 feet of which is represented in the Bishop district. Strata of Middle and Late Cambrian and Early Ordovician age also are present in the Inyo Mountains, and the strata in the Bishop Creek pendant may be wholly or partly equivalent to the Ordovician strata of the Mount Morrison pendant, but of a different facies. The Mount Morrison Ordovician strata belong to the western clastic facies of the Great Basin, where- as the Ordovician strata of the Inyo Mountains belong to the eastern carbonate facies (Kirk, in Knopf, 1918, p. 32-33). The Bishop Creek pendant is in a proper position for strata transitional between the two facies. GNEISS IN THE CANYON OF THE SOUTH FORK OF BISHOP CREEK A lenticular mass of gneiss 3 miles long and as much as three-quarters of a mile wide crops out in the canyon of the South Fork of Bishop Creek between Long Lake and Bishop Pass. The trail from South Lake to Kings Canyon passes through the gneiss for several miles. At the north end the gneiss is bordered on the east side by the metasedimentary rocks of Choco- late Peak, but farther south it forms a septum between the Lamarck granodiorite on the west and the Incon- solable granodiorite on the east. Foliation strikes generally N. 30° W., parallel with the long axis of the mass; the dip is vertical or nearly so. The appearance of the gneiss in the field and the mineral content and fabric suggest that it is a strongly sheared granitic rock. The gneiss is variable both in color and in composition. The most common rock is medium gray; less common rocks are medium light gray or light gray. The common dark-gray gneiss consists of 35 percent plagioclase (oligoclase), 30 per- cent microcline, 20 percent quartz, 7 percent biotite, 6 percent hornblende, and 2 percent accessory min- erals (magnetite, ilmenite, sphene, and apatite). A light-gray felsic type contains 45 percent microcline, 40 percent quartz, only 10 percent plagioclase (oligo- clase), 5 percent biotite, plus a little apatite, sphene, and pyrite. The foliation of the gneiss results chiefly from alter- nating felsic and mafic lenses an eighth of an inch or less in thickness. The lenses are subparallel and discontinuous; the trace of a single lens is seldom iden- tifiable for more than an inch. The mafic lenses con- sist chiefly of biotite, hornblende, and magnetite, and the felsic ones of quartz and the feldspars. 42 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA Biotite and hornblende are strongly oriented in the foliation plane, whereas the felsic minerals form a granoblastic intergrowth. Most of the felsic minerals are nearly equidimensional, but some quartz grains are flattened in the foliation plane. The average grain size of the felsic minerals differs materially in adjacent lenses or streaks, ranging from a tenth to half a milli- meter in finer lenses to half a millimeter to a millimeter in coarser lenses. The finer grained lenses are also the dark-colored lenses and contain most of the biotite and hornblende. A concordant lens of very light gray rock composed chiefly of quartz and microcline in granoblastic inter- growth and more than a mile long and 500 feet wide is enclosed in the southern part of the gneiss. Faint streaks of biotite and sericite are also present, and coin- cide with finer grained streaks within the rock as do the mafic minerals in the darker gneiss. MARBLE AND CALC-HORNFELS IN THE NORTHEAST BASE OF MOUNT TOM Two remnants of marble and calc-hornfels at the east base of Mount Tom are bounded by quartz mon- zonite and, on the northeast, by alluvial fan deposits. The eastern part of the larger and more northerly rem- nant contains noncalcareous hornfels and schist as well as marble and calc-hornfels, and all diminish in abun- dance toward the west. If the rocks are not isoclinally folded, the maximum stratigraphic thickness is about 600 feet. The smaller remnant, about half a mile south of the larger one, is largely calc-hornfels, locally altered to tale, and the south end has been prospected for tale. METAMORPHIC ROCKS IN THE TUNGSTEN HILLS In the Tungsten Hills, the largest masses of meta- morphic rocks are the Round Valley septum and a some- what smaller septum about 2 miles farther east. Both septa lie along a contact between alaskite of Cathedral Peak type and Tungsten Hills quartz monzonite. Smaller inclusions are present in the Deep Canyon area in the east-central part of the Tungsten Hills, and many small inclusions of meta-andesite are present in the southwest part of the Tungsten Hills. ROUND VALLEY SEPTUM The metamorphic rocks in the Round Valley septum are all metasedimentary ; they include micaceous quartz- ite, impure argillaceous marble, calc-hornfels, quartz- sericite hornfels, and tactite. The strata in the main part of the septum strike northward, across the long axis, and dip 55° to 70° to the west. The rocks in the east end of the septum are in fault contact with the main part of the septum ; they strike eastward and dip steeply south. The predominant rock in the eastern part of the septum is brown-weathering micaceous quartzite, but a thin layer of marble lies along the north side of the micaceous quartzite and extends westward along the contact between the two granitic rocks that bound the septum. Exposures in the Little Shot (Tungsten Hill) mine indicate that the width of the marble increases at depth. In fault contact with the micaceous quartzite and marble on the west is coarse-grained garnetiferous cale- hornfels which is the predominant rock in the central part of the septum. This rock is mottled pale red and grayish green. Skeletal garnet crystals as much as 1 cm across and idocrase crystals as much as 4 mm across give the rock its coarse granularity. Plagioclase and clinozoisite form finer grained aggregates. All these minerals enclose abundant tiny grains of diopside. In the vicinity of the Round Valley mine, the gar- netiferous calc-hornfels encloses impure argillaceous marble, which at the Round Valley mine grades through a zone of light-colored hornfels into tactite. The horn- fels is layered, and the different layers are composed of varying proportions of plagioclase, microcline, and diopsidic pyroxene, with or without garnet, clinozoisite, sphene, calcite, quartz, chlorite, altered magnetite, and muscovite or sericite. The field relations suggest that the argillaceous marble is the parent rock of both the calc-hornfels and the tactite. West of the garnet-diopside-idocrase-plagioclase- clinozoisite rock is a mass of quartz-sericite hornfels that contains two layers of garnetiferous tactite, which are the loci of the ore bodies in the Western Tungsten mine. The tactite is a layered rock that consists of al- ternate layers of garnet-epidote rock and diopside-rich rock. If the section west from the fault in the east end of the pendant is homoclinal, the thickness of the exposed section is about 2,500 feet, of which 1,500 feet is tactite and related argillaceous marble and calc-hornfels and 1,000 feet is quartz-sericite hornfels, including the in- tercalated tactite layers. Detailed mapping in the Western Tungsten mine area, however, suggests that the quartz-sericite hornfels may be isoclinally folded and that the true exposed thickness of strata in this unit may be no more than 500 to 700 feet. SEPTUM 2 MILES EAST OF THE ROUND VALLEY SEPTUM The septum 2 miles east of the Round Valley septum, at hill 5949, is composed chiefly of quartz-sericite horn- fels and micaceous quartzite, but the septum also con- tains lesser amounts of marble and calc-hornfels. Be- cause the rocks are poorly exposed and complexly de- formed, their distribution on the geologic map (pl. 2) is generalized. PREBATHOLITHIC GEOLOGY 43 METAMORPHIC INCLUSIONS IN THE DEEP CANYON AREA Small inclusions of metasedimentary rocks are abun- dant in the hornblende gabbro and quartz diorite of the Deep Canyon area and in the surrounding quartz monzonite. The most common rocks in these inclusions are vitreous quartzite, marble, calc-hornfels, and tac- tite. In the vicinity of the Aeroplane and Lucky Strike mines metaconglomerate accompanies the quartzite, and at the Aeroplane mine a unit composed of micaceous quartzite and biotite-plagioclase-microcline hornfels is found. The vitreous quartzite generally is clean, but con- tains minor interstitial feldspar and sericite. The con- glomerate which accompanies the quartzite is composed chiefly of pebbles of diopside-bearing quartzite and zoisite-clinozoisite rock in a matrix of tremolite, diop- side, quartz, and clinozoisite. The common cale- hornfels is a dense massive fine-grained rock composed chiefly of calcic plagioclase (Anso-,,) and lesser amounts of pyroxene and sphene. At the Aeroplane mine, coarse-grained cale-silicate rock is composed chiefly of equal amounts of grayish-pink garnet and light olive-gray idocrase, and contains minor amounts of pyroxene, clinozoisite, and plagioclase. This rock might be classified as a tactite, but would be an un- common variety. The micaceous quartzite and biotite-plagioclase- microline hornfels at the Aeroplane mine are medium dark-gray fine-grained rocks. A typical specimen of the micaceous quartzite is composed of 50 percent quartz in rounded grains, 25 percent muscovite, and 20 per- cent chlorite that appears to have been formed from biotite, and minor amounts of biotite, magnetite, and apatite. The biotite-plagioclase-microcline hornfels consists of approximately 40 percent microcline, 30 percent plagioclase, and 20 percent well-oriented biotite that gives the rock a faint cleavage, plus a little musco- vite, pyrite, apatite, and sphene. MAFIC METAVOLCANIC ROCK IN THE SOUTHWESTERN PART OF THE TUNGSTEN HILLS A small mass of meta-andesite in the southwestern part of the Tungsten Hills, in the SW1 see. 15, T. 7 S., R. 31 E., is visible from the unpaved road to the Butter- milk Country. It consists in part of volcanic breccia and in part of massive dark-gray rock containing abun- dant corroded relict phenocrysts of plagioclase as much as 2 mm across. Both rocks contain about 65 percent plagioclase in relict phenocrysts and in a granoblastic groundmass, variable proportions of biotite and horn- blende, plus minor quartz, magnetite, and apatite. SEPTA 3 MILES WEST OF KEOUGH HOT SPRINGS Three miles west of Keough Hot Springs are two dis- connected metamorphic remnants. The northern rem- nant, or septum, lies along a contact between alaskite similar to the Cathedral Peak granite and Tungsten Hills quartz monzonite, and the southern remnant ex- tends from the contact between the plutons into the alaskite. The northern remnant is more than 4,000 feet long and about 2,000 feet wide. It is composed chiefly of dark meta-andesite, but contains conglomerate, marble, and calc-hornfels in its northern part. The meta-andesite adjacent to the metasedimentary rocks is amygdaloidal and is mottled and veined with light yellowish-gray, diopside-plagioclase hornfels. The southern remnant is also about 4,000 feet long in a northwesterly direction, but is only about 800 feet wide. It is composed chiefly of metasedimentary strata in the northern part and of metavolceanic strata in the southern part. Beds strike northward, diagonally across the remnant, and dip westward. Dips are to the west, 55°-70° in the southern part and 15°-20° in the northern part. If the structure is homoclinal, as it appears to be, the stratigraphic thickness is in excess of 2,000 feet. The metasedimentary rocks in the northern part of the southern remnant are chiefly highly feldspathic quartzites. Light- and dark-colored beds an inch or two thick alternate. In thin sections the rock can be seen to consist chiefly of poorly sorted angular grains of microcline and quartz in a granoblastic groundmass of the same minerals. The light-colored layers contain a higher percentage of larger grains than the darker ones and also contain moderate amounts of epidote. The darker layers contain biotite, amphibole, and mag- netite. The volcanic rocks in the southern part of the rem- nant generally are felsic and may be tuffs. Plates and aggregates of biotite and hornblende and knots of epi- dote are set in a granoblastic matrix of microcline and quartz that locally includes biotite and magnetite. Scattered porphyroblasts of andalusite are generally present. Associated with these rocks are layers of micaceous hornfels, which may have been derived from pelitic sedimentary rocks. REMNANTS ALONG THE RANGE FRONT SOUTHWEST OF BISHOP Along the east-trending segment of range front southwest of Bishop and extending west into the range are several discontinuous remnants of metasedimentary rocks. The easternmost one is a small inclusion at the Rossi mine, and the westernmost is an inclusion at the Chipmunk mine. The metasedimentary rocks include marble, tactite, calc-hornfels, and carbonaceous felds- par-quartz hornfels. The masses are so discontinuous 44 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA that the stratigraphic sequence is unknown. Marble and calc-hornfels make up about half of the metamorphic rocks, and the remainder is dark car- bonaceous hornfels. Commonly the marble is coarsely crystalline and white, but at the Rossi mine the mar- ble is light bluish gray. Much of the marble is mod- erately clean, but in places it is thinly interlayered with calc-hornfels, and in places calc-hornfels predom- inates. The largest lens composed predominantly of calc-hornfels is half a mile west of the Bishop Anti- mony mine. A specimen of dark carbonaceous feldspar-quartz hornfels from the vicinity of the Bishop Antimony mine, which is typical of the dark carbonaceous rock in this area, consists of a fine granoblastic intergrowth of quartz and K feldspar, and contains abundant dis- seminated carbonaceous material and minor sphene, tremolite, and sericite. Thin light-colored layers in- tercalated with the dark carbonaceous hornfels have a a similar texture and mineral content, but contain large skeletal or poikiloblastic crystals of diopside and are almost devoid of carbonaceous material. A dark rock, slightly different from the inclusion at the Rossi ming, contains abundant grayish-red biotite and megascop- ically appears very similar to the micaceous quartzite in the Pine Creek pendant. f A rock unit at the Chipmunk mine consists of alter- nating very light gray wollastonite-rich layers and dark-gray quartz-rich layers. The wollastonite-rich layers contain small grains of diopside, which vary in amount from layer to layer. Tiny quartz grains are abundant in the margins of the wollastonite layers, and larger quartz masses locally are associated with pyrite in the central parts of the layers. The dark layers con- tain, in addition to quartz, plagioclase and K feldspar, plus minor diopside, sphene, calcite, and pyrite. BIG PINE SEPTUM Several inliers of metasedimentary rocks crop out through the moraines that lie between Big Pine and Baker Creeks. These outcrops are parts of a large buried septum, here designated the Big Pine septum, which extends west from the range front continuously for about 4 miles and appears to have a maximum width of about 1 mile. The septum lies between quartz monzonite on the north and granodiorite on the south. The rocks in the inliers-marble, tactite, calc-hornfels, micaceous quartzite, and micaceous hornfels-are prob- ably representative of the rocks in the pendant because the inliers are chiefly up-faulted blocks rather than erosional remnants. The most abundant rock in the Big Pine septum is coarsely crystalline, locally silicated, white to medium- gray marble. The marble commonly contains a few percent quartz, biotite, actinolite, and wollastonite. In a few places the marble next to intrusive granitic rocks has been converted to tactite. Calc-hornfels is present in only two outcrops. A small inclusion in the Tine- maha granodiorite on the south side of the septum con- sists of rock that is composed of approximately O per- cent of tale, 20 percent fibrous actinolite, and 10 percent magnetite. Dark-gray micaceous quartzite and quartz-mica horn- fels are only slightly less abundant than marble. The micaceous quartzite generally consists of silt-size de- trital quartz grains disseminated through a fine-grained matrix of sericite and a little quartz. Large poikilo- blastic plates of biotite, locally altered to chlorite, are common, and a few percent magnetite generally is pres- ent. Spotted quartz-mica hornfels is a common rock in the westernmost inlier. The groundmass of this rock consists of a fine intergrowth of approximately equal amounts of quartz, biotite, and sericite, and a little mag- netite. The spots are dark gray in hand specimen and consist of quartz-sericite intergrowths that are much finer than the groundmass of the rock. A thin mar- ginal rim of biotite causes the dark color of the spots in hand specimen. Another rock in the westernmost inlier is composed of about 50 percent plagioclase (oligoclase) and 25 percent each biotite and sericite. All these rocks appear to have been formed from miogeosynclinal sediments-limestone, argillaceous silt- stone, calcareous shale. However, the fact that a speci- men from the south side of Big Pine Creek consists of large corroded crystals of quartz and oligoclase in a fine sericitic matrix suggests derivation from an acid crystal tuff. SEPTA AND INCLUSIONS IN UPPER BIG PINE CANYON In the upper part of Big Pine canyon, west of the Blue Star tale mine, are many septa and inclusions that are composed chiefly of mafic metavolcanic or hypa- byssal rocks. The more easterly of these also contain marble and calc-hornfels. The most interesting septum is the one that contains the Blue Star tale mine (see p. 33). Most of the inclusions west of Glacier Lodge, in the North Fork of Big Pine Creek, are predominantly of fine-grained metavolcanic or hypabyssal rock ; in the South Fork of Big Pine Creek diorite predominates. The metavolceanic or hypabyssal rocks have been re- crystallized and corroded along their margins by the enclosing granitic rocks. Notable variation of the mineral content of metavoleanic rocks at contacts with granitic rocks suggests that they have also been altered metasomatically. The plagioclase content generally ranges between 40 and 60 percent, but some specimens contain no plagioclase and others contain as much as GEOLOGY OF THE BATHOLITH 45 TO percent. The hornblende content is exceedingly vari- able, but most rocks contain more than 45 percent. Specimens from inclusions of metadiorite in the North Fork of Big Pine Creek which have been corroded and embayed by granite, generally contain less than 15 per- cent hornblende, 10 to 25 percent biotite, 5 to 10 percent K feldspar, and 2 to 20 percent quartz. Locally, these highly altered rocks contain relict quartz xenocrysts with coronas of hornblende (Muir, 1953 b, p. 409- 428). The common minor accessory minerals are mag- netite, apatite, and sphene. Epidote or clinozoisite has - been formed from hornblende and plagioclase, chlorite from biotite, and hematite from magnetite. A large inclusion of mafic igneous rock at the east base of Mount Alice, at the junction of the North and South Forks of Big Pine Creek, consists of fine-grained mafic rock in association with coarser grained rock of variable texture, some of which is pegmatitic. The coarser grained rocks could conceivably have resulted from original crystallization as hypabyssal intrusives, but seem more likely to have resulted from the meta- morphism of fine-grained rocks. MIDDLE PALISADE SEPTUM The Middle Palisade septum is a thin belt of cal- careous rocks that extends south from the Middle Palisade Glacier for about 3 miles. The septum lies between the Tinemaha granodiorite on the east and the Inconsolable and Lamarck granodiorities on the west. About 2 miles farther south along the same trend, and half a mile southwest of the summit of Split Moun- tain, is an inclusion composed of similar calcareous rocks. The calcareous rocks include marble, calc-hornfels, and tactite; all the rocks were formed from limestone and from impure limy strata. Most of the marble is white and coarsely crystalline, and contains scattered blebs of silicate minerals. Much of the calc-hornfels contains plagioclase and pale-green pyroxene as prin- cipal constituents. The mineral content of the tactite is variable; some consists predominantly of grayish- green pyroxene and quartz and a little light-olive epidote, and some consists chiefly of reddish-brown garnet. A little scheelite occurs locally in the garnetif- erous varieties. SPLIT MOUNTAIN SEPTUM The Split Mountain septum is a thin lens of schist and calc-hornfels that extends from the range front westward along the north side of Red Mountain Creek to the east face of Split Mountain, then southward to the edge of the mapped area. The exposed length within the mapped area is about 51/4 miles, and the out- crop width is from a few feet to more than a thousand feet. The septum separates quartz monzonite similar to the Cathedral Peak granite from Tinemaha grano- diorite on the north and from Lamarck granodiorite on the west. The segment north of Red Mountain Creek dips steeply, whereas the south-trending seg- ment steepens westward from almost flat to vertical (pl. 5, section #-F"). Several small pods of schist and gneiss that crop out in Stecker Flat are along a gently dipping contact between quartz monzonite similar to the Cathedral Peak and Tinemaha granodiorite, and are probably also part of the septum (pl. 4). The dis- tribution and attitudes of the metamorphic rocks sug- gest that the septum is marginal to the quartz mon- zonite of Cathedral Peak type and that before erosion it discontinuously overlay the quartz monzonite along a gently east dipping upper contact (pl. 5, section F-F'). The most common rocks in the septum are schist and calc-hornfels, but pelitic hornfels and gneiss of the same mineral composition as the schist are present in the remnants in Stecker Flat. Locally, however, the septum contains calc-hornfels. In one place, fine-grained pyroxene-plagioclase horn- fels contains irregularly shaped coarse-grained zones as much as 2 inches across composed of large horn- blende and quartz crystals which have poikiloblastic margins. In hand specimen the coarse-grained rock superficially resembles diorite, but examination with the microscope reveals that plagioclase is present only in tiny grains that are enclosed in the sievelike margins of the large hornblende and quartz crystals. MARBLE IN THE POVERTY HILLS In the west side of the Poverty Hills, a mass of mar- ble having an outcrop area of about 1%4 square miles is embraced on the north and east sides by the Tinemaha granodiorite. On the west side the marble is bounded by alluvium and on the southwest side by basaltic lava. The marble is white and medium grained, and appears to be clean except in the south end where thin beds of calc-hornfels are interlayered with marble. No clastic beds were observed within the marble. GEOLOGY OF THE BATHOLITH The Sierra Nevada and the Sierra Nevada batholith are two different entities and are not to be confused. The Sierra Nevada is a physiographic feature-a mountain range-whereas the Sierra Nevada batholith is the plutonic terrane that makes up the central and eastern parts of the range. 'The metamorphic remnants between and enclosed in the plutonic rocks are not part of the batholith, although they are within it. The batholith is composite; it is a mosaic of discrete intru- 46 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA sives in sharp contact with one another or separated by thin septa of metamorphic rock or by late aplitic dikes that follow contacts. The individual intrusive masses are called plutons. The largest plutons are com- posed of felsic quartz-bearing granitic rocks ranging in composition from granodiorite to alaskite. Plutons of granitic rock comprise more than 90 percent of the batholith within the area mapped for this report (fig. 13). The rest of the batholith is composed of smaller scattered bodies of older and darker rocks ranging in composition from hornblende gabbro to granodiorite. For convenience and because the relation of the older and darker rocks to the granitic rocks is uncertain, the two groups of rocks are described separately. DIORITE, QUARTZ DIORITE, AND HORNBLENDE GABBRO The small bodies of diorite, quartz diorite, and horn- blende gabbro have been aptly referred to by Mayo (1941, p. 1010) as "basic forerunners," or simply as "forerunners." Their distribution is reminiscent of the metamorphic rocks; they occur as inclusions or small pendants within individual plutons of more silicic rock, or as septa between plutons. Commonly they are as- sociated with metamorphic rocks, and many are crowded with metamorphic inclusions. This relation is under- standable because diorite, quartz diorite, and horn- blende gabbro were the first of the plutonic rocks to be emplaced and they came into contact with metamorphic rocks on all sides. The original sizes and shapes of most masses were destroyed by later granitic intrusives, which tore apart the masses and recrystallized, granit- ized, and assimilated fragments. In this report the term "assimilation" is used to describe the incorporation of solid rock in magma and "granitization" to describe conversion, in essentially the solid state, of nongranitic rock to granitic rock. Partly as a result of original differences and partly as a result of subsequent modification, the rocks grouped under diorite, quartz diorite, and hornblende gabbro are heterogeneous in composition and texture; very likely they include rocks of diverse origin. Al- though they are discussed separately they are not de- lineated separately on the maps (pls. 1-4). Quartz diorite is used here for quartz-bearing plutonic rock in which quartz comprises more than 10 percent of the total felsic constituents and K feldspar less than 10 percent (fig. 14). It passes into granodiorite where K feldspar comprises more than 10 percent of the total felsic constituents and into diorite or gabbro where quartz comprises less than 10 percent. The plagioclase of diorite contains less than 50 percent anorthite, and the plagioclase of gabbro more than 50 percent. Horn- blende gabbro contains hornblende rather than augite, the usual principal mafic mineral of gabbro. ALTERED DIORITE OF THE WHITE MOUNTAINS The altered diorite of the White Mountains is equi- granular and has an average grain size of about 1 mm. The rock is of much the same appearance in the stock and in dikes. In thin section it can be seen to be highly altered; it consists chiefly of unzoned albite (Ani, approximately), chlorite, and epidote-clinozoisite. Quartz in small amounts is interstitial to most of the other minerals; sericite is disseminated through the albite; and sparse magnetite and hematite are present. The albite crystals have irregular boundaries in detail, but are generally euhedral in gross form-a feature that gives the rock a panidiomorphic-granular texture. Undoubtedly the original feldspar was more calcic than albite; sparce unaltered parts of grains indicate it was in the andesine range. The form of much of the chlo- rite and epidote suggests that these minerals were de- rived, at least in part, from original biotite and horn- blende, respectively, although some epidote-clinozoisite must have been formed from plagioclase as a by- product of its alteration to albite. The intrusive relations of the stock and dikes indi- cate that the diorite crystallized from a magma. No- where was the diorite found in contact with other plu- tonic rocks; its age relation to the intrusive rocks of the Sierra Nevada is therefore not known. No evidence was found to indicate that the diorite was involved in the deformation that affected the enclosing rocks. Very likely it is of about the same age as the masses of quartz diorite and hornblende gabbro of the Sierra Nevada, but it may be genetically related to and of the same age as swarms of mafic dikes that are younger than some of the granitic plutons. HORNBLENDE GABBRO The quartz diorite and hornblende gabbro of the Sier- ra Nevada are extremely variable in color index, grain size, texture, and proportions of constituent minerals. The darker appearing rocks (color index 40-60) gen- erally contain plagioclase having more than 50 percent anorthite and contain hornblende or uralitic amphibole rather than augite, and are therefore classed as horn- blende gabbro. Most of the hornblende gabbro ranges from 1 to 5 mm in average grain size and thus is medi- um grained, but these limits are so wide as to permit very great differences in the appearance of different rocks. In addition to hornblende and uralitic amphibole and calcic plagioclase, the hornblende gabbros generally contain magnetite, apatite, and sphene. Secondary GEOLOGY OF THE BATHOLITH 47 nets "30° 18157 320 11830 o 37°30 W BISHOP QUADRANGLE \\ aris BIG PINE QUADRANGLE Q aN dry ) «8 C < £\7\5\7\£\/I\£\7\£\7\fi\l\5\,\, yaya {AGA UTY AAA AEA (/A lsi¢ in hA u oris 4 Ade W AAAZ FH AS \l\;\’\ SAS t Granodiorite of Granodiorite of Cartridge Pass kt Coyote Flat Finer-grained quartz monzonite Rocks similar to Cathedral Peak granite Ke, quartz monzonite Kth Kea, alaskite Tungsten Hills quartz monzonite | p 2 0 Granodiorite of 3 Deep Canyon < "lago - Lamarck Round Valley Peak | 0 granodiorite granodiorite Granodiorite of Ktnx) McMurry Meadows Intrusive relationship Ktn Tinemaha Wheeler Crest Ostgnmtk granodiorite artz ite povigan qu monzoni Y, younger rocks Kin MBu Inconsolable granodiorite 2 h Diorite, quartz diorite, o and hornblende gabbro 0 g Sno No bwa 528 Met sedimentary A f and volcanic rocks, undivided f z 3700" am 37°00 18°45 nes 5 MILES ] Geology by Paul C. Bateman, 1954 FiGurRE 13.-Bedrock map of the Bishop area showing the distribution of the plutonic rocks. 48 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA Quartz C Quartz monzonite Granodiorite (adamellite ) Granite and alask ite Diorite and hornblende gabbro A B Plagioclase 19 s 62 Potassium feldspar FIGURE 14.-Triangular diagram showing the classification system used in this report. (Including perthite) Classification is modal. The plagioclase of quartz monzonite contains more than 10 percent anorthite, and the plagioclase of alaskite less than 10 percent. minerals include epidote, chlorite, sericite, and scant ser- pentine group minerals. Plagioclase generally is in al- most euhedral crystals that give the rock a panidio- morphic-granular texture. Commonly these crystals are strongly and progressively zoned from bytownite cores to calcic oligoclase or sodic andesine rims; discon- tinuities and reversals in zoning are common. Horn- blende generally is anhedral, but in many rocks is in euhedral prisms having a wide range of proportions of length to thickness. Uralitic amphibole is colorless or mottled colorless and pale green and is rimmed by pale- greenish amphibole that was probably formed at the time of uralitization by reaction with feldspar. Blades of pale-greenish amphibole are also usually present scat- tered through the adjacent rock. Uralitic amphibole locally contains residual cores of augite, and some horn- blende encloses augite or uralitic amphibole. Many of the rocks exhibit unusual and interesting textures. Locally coarse-grained, almost pegmatitic rock is found, which contains euhedral prisms of horn- blende 1 inch or more long and 14 to / an inch across. In several places, notably west of McMurry Meadows in the Big Pine quadrangle, hornblende gabbro contains almost equidimensional crystals of plagioclase. An in- teresting fabric is shown by elongate hornblende crys- tals that lie in a well-defined foliation plane, but which are randomly oriented within that plane. Rock of this fabric generally occurs in thin tabular masses that are bordered by younger silicic granitic rock-a spacial ar- rangement that suggests a metamorphic rather than an GEOLOGY OF THE BATHOLITH 409 igneous origin. However, the fact that many masses of hornblende gabbro intrude metamorphic rocks and ex- hibit panidiomorphic-granular texture, deep zoning of plagioclase, layered facies, and dikes that cut meta- morphic rocks indicates that they crystallized from magma and are truly igneous. LAYERED GABBRO IN THE TUNGSTEN HILLS A mass of gabbro in the Tungsten Hills locally con- tains layered facies that merit special attention. The gabbro crops out over an area of about a quarter of a square mile and is entirely surrounded by later quartz monzonite. Patches of layered rock are exposed in a low knoll about 500 feet north of the Tungsten Blue (Shamrock) mine. The largest patch has an area of only about a hundred square feet, and most of the others have outcrop areas of only a few square feet. The lay- ered patches exhibit "angular unconformities," "cross- bedding," and penecontemporaneous faults, which are strikingly similar to structures found in sedimentary rocks. Figure 15 is a large-scale map of the largest patch of layered gabbro, and figure 16 consists of photo- graphs of several interesting exposures. In figure 15, the largest mass shown is in place; the two outlying masses are slightly displaced from their original posi- tions. #2 Slope wash Structureless gabbro Spacing of lines and dots represents variation in the abundance of mafic minerals Banded gabbro Hornblendite \ss Strike and dip of banding sr Mafic basal layer above unconformity , showing dip #2777 Felsic basal layer © Numbers refer to apparent stratigraphic ages of unconformites. Whole number designates unconformity overlain by matic basal layer. Half number designates unconformity . overlain by felsic basal layer. Mapped by P.C. Bateman, 1947 FIGURE 15.-Map of the main patch of layered gabbro in the Tungsten Hills. In general, the more conspicuous "angular uncon- formities" are marked by dark basal layers. Other gen- erally less distinct "unconformities" are overlain by felsic basal layers. In figure 15, four "unconformities" having dark basal layers and one having a felsic basal layer interrupt the layering. All the "unconformities" are numbered in the order of their apparent ages ac- cording to sedimentary criteria. The layered sequence beneath some "unconformities," especially those overlain by mafic basal layers, are curved (see layers beneath "unconformities" 1 and 2 of figure 15). In one small mass, the ends of layers truncated by an "unconformity" bend sharply. In a few places, the layers beneath "unconformities" are not curved at all, as beneath "unconformity" 244, fig- ure 15. The southern part of the dark basal layer at "unconformity" 1 is broken into several segments, which are partly rotated and displaced as much as an inch from their original positions. The slip planes bounding these segments are not very evident, only the layers adjacent to the "unconformity" having been dis- placed. The layering is caused by the rhythmic alternation of light- and dark-colored layers. Most layers are parallel, but a few are wispy or "crossbedded." The layers dip 65° to 75° to the east and southeast, away from the nearest contact of the gabbro with quartz mon- zonite, which is about 300 feet distant. At the borders of the layered areas the layers become less distinct, and the layered rock merges imperceptibly with structure- less gabbro. In most places, individual layers can be traced for several feet with little change in thickness or in relative abundance of light- and dark-colored min- erals. Discontinuous wispy layering, however, is dis- - played in some places, for example in the isolated boulder shown in the lower part of figure 15. In fig- ure 16C, the mafic layers above the "unconformity" lens out where they overlap onto the "unconformity." The combined thickness of a dark layer and of the overlying light-colored layer averages about half an inch, but pairs of layers range from 14 to 1 inch in thickness. Immediately above the "unconformities" that are marked by mafic basal layers the layers are thin, but upward they gradually increase in width until they attain average thickness an inch or two above the basal layers. By contrast, the layers just above "un- conformities" with felsic basal layers are of average width. Faults offset the layers less than an inch, but they contain dark minerals that make them easily visible. The dark hornblendite shown in the central part of figure 15 dips to the southeast and cuts across the lay- ers to the southwest. From near the southwest end of 50 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA the hornblendite, a branch cuts "stratigraphically" downward and across "unconformity" 1 into the under- lying layers. The hornblendite follows along the lay- ering, and becomes less distinguishable and loses its identity a foot beneath the "unconformity." Microscopic study included the examination of sev- eral extra-large (2 by 3 inches) oriented thin sections. These sections were studied both under a petrographic microscope and between polaroid filters either without magnification or under a low-power binocular micro- scope. The polaroid filters made it possible to see in a single field the structures and textures over the full area of a thin section. The light- and dark-colored layers contain the same minerals, but in different proportions. The felsic layers consist mainly of calcic plagioclase (bytownite), where- as grains of uralitic amphibole, some having residual augite cores, are abundant in the dark-colored layers. Hornblende, magnetite, apatite, sphene, and locally bi- otite are common, especially in the dark-colored layers. Epidote and clinozoisite are uncommon derivatives of FIGURE 16.-Photographs of several exposures of layered gabbro. 4, Layering and "unconformities" 1 and 3 (fig. 15) from the south. B, Layering and "unconformities" 2 and 2% from the west. C, Boulder showing layering and an "unconformity" with a felsic basal layer. plagioclase, while chlorite sporadically replaces augite, the amphiboles, or biotite. Antigorite pseudomorphous after pyroxene is rare. The bytownite generally is in zoned euhedral to sub- hedral crystals. Compositions range from Ans, to but the compositions of many large areas of zoned crys- tals and of most unzoned crystals fall between An;; and Anss. Uralitic amphibole, in some places enclosing residual cores of augite, is ragged, but the gross out- lines of many crystals resemble augite. The uralitic amphibole is weakly pleochroic and contains numerous small grains of exsolved magnetite. Commonly the pale uralite is bordered by more deeply colored rims of amphibole, pleochroic in blue green. Small needles hav- ing approximately the same optical properties as the amphibole of these rims occur within and between the surrounding plagioclase crystals. Hornblende is in anhedral grains that are pleochroic in dark olive green, brownish green, and brown. Locally, brownish-green hornblende encloses augite or uralite. Plagioclase commonly is in euhedral to subhedral crystals tabular parallel to (010). Under the micro- GEOLOGY OF THE BATHOLITH 51 scope, consequently, the crystals showing albite twin- ning appear elongate, and the crystals not showing twinning appear equidimensional. Individual crystals are small, the average measurement on (010) being less' than 1 mm. The other minerals in the gabbro are of comparable size. Crystals are interlocking across contacts between felsic and mafic layers just as they are in the centers of layers. A few crystals are fractured, but evidence of widespread cataclasis or protoclasis is lacking. Locally, augite encloses plagioclase, but in general plagioclase, FieurE 17.-Thin section cut across the layering and an "unconform- ity" in layered gabbro. A, Ordinary light. B, Crossed nicols. C, Sketch of thin section with superimposed graph showing (in milli- meters) the average apparent length in thin section of plagioclase crystals in the layers above the mafic basal layer. augite, and magnetite seem to have mutual interference boundaries with one another. Hornblende and biotite appear to be late in the sequence of magmatic crystalli- zation. Uralitic amphibole probably formed from augite after crystallization of the gabbro, possibly at the time of intrusion of the adjacent quartz monzonite. The (010) planes of the feldspar crystals, especially of the larger ones, have a marked tendency to lie sub- parallel to the layering, although erystals in all orienta- tions are present (figs. 17, 18). Within the planes of layering the a and c crystallographic axes lie in any direction. Thin sections cut in the plane of the layering show the random orientation of crystals in this plane. T'wo kinds of systematic variation in the size of the feldspar crystals were observed. The first, present throughout the layered rock, is between adjacent dark- and light-colored layers, the feldspar crystals in the dark layers being larger than those in contiguous light- colored layers (figs. 17, 18). The second kind of varia- tion is limited to the thin layers immediately above "un- conformities" overlain by dark basal layers. In these layers the average size of the feldspar crystals in both light- and dark-colored layers increases systematically with distance from the "unconformity." Graphs drawn to show the size variations in these layers with mafic basal layers above "unconformities" are saw-toothed because of the effect of the difference in size of the plagioclase crystals in the light- and dark-colored GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA C FIGURB 18.-Thin section cut across the layering in layered gabbro. A, Ordinary light ; note fault offset and mafic minerals present along the fault. B, Crossed nicols. C, Sketch of part of thin section with superimposed graph showing (in millimeters) the average apparent length in thin section of plagioclase crystals in the layers above a mafic basal layer. layers, but the graphs also show the overall increase in crystal size with distance from the "unconformity" (figs. 17,18). Many hypotheses have been advanced to explain the origin of layering in mafic, ultramafic, and alkaline ig- neous rocks. Grout (1918, p. 452-454), Coats (1936, p. 407-412), and Wager and Deer (1939, p. 284-289) have summarized the hypotheses advanced up to the times of their respective publications. Faults and folds and unconformities have been described from the Stillwater complex (Hess, 1938, p. 264-268; 1960, p. 129-1831). Any acceptable hypothesis of origin for the various features in the layered gabbro should explain the layer- ing, the gradational relations between the layered patches and the unlayered gabbro, the faults, the cross- cutting mafic streaks, and the "unconformities," in- cluding those overlain by felsic basal layers as well as those overlain by mafic basal layers. The explanation GEOLOGY OF THE BATHOLITH 53 of the layering should consider the larger size of the plagioclase crystals in any particular mafic layer as compared with those in contiguous felsic layers, the pre- ferred orientation of the (010) faces of the plagioclase crystals in the plane of the layering, and the upward in- crease in the average size of the plagioclase crystals through the first few layers above dark-colored basal layers. The mechanism that seems best to explain the layer- ing is a process of gravity-controlled crystal settling in combination with magmatic flow. This is essential- ly the hypothesis advanced by Wager and Deer (1939, p. 271-275) to explain the layering in the Skaergaard intrusion. Hypotheses considered and rejected because they failed to explain one or more critical features of the gabbro are (1) other hypotheses based on sorting of continuously forming crystals in a magma chamber, (2) heterogeneous intrusion, (3) repeated sill-like in- trusion, (4) rhythmic erystallization, (5) deformation during consolidation, (6) replacement or migmatitiza- tion, and (7) metamorphic differentiation. The main feature that indicates gravity-controlled settling of crystals is the localization of the larger plagioclase crystals in the dark layers that contain heavier minerals. This size distribution of minerals is the kind found in clastic sedimentary rocks where the controlling factor is the relative settling velocities of particles from turbidity currents. The density relations between plagioclase crystals and magma of intermediate to calcic composition have been a subject of considerable controversy; descrip- tions in the literature suggest that plagioclase is a little heavier than some magmas and a little lighter than others. The gabbro of the Tungsten Hills is not an extremely mafic rock; consequently, the magma may have been less dense than that of many gabbros. The fact that augite (largely altered to uralite) is inter- | layered with plagioclase indicates that if augite was heavier than the magma, plagioclase was also heavier. The association of larger plagioclase crystals with the heavier mafic constituents lends further strong support to this view. Features most indicative of current action are (1) lateral variation in the content of mafic minerals with- in groups of layers, (2) the presence of wispy layer- ing or "crossbedding," (3) the association of large plagioclase crystals with the mafic constituents, which indicates good sorting, and (4) overlaps such as are shown in figure 160. Grout (1918, p. 453-454) has expressed the opinion that planar orientation of feld- spars cannot be accomplished by direct settling of crys- tals alone and must be accompanied by some move- ment of the magma, but the validity of this conclusion seems doubtful unless almost every crystal is oriented in the plane of the layering; tabular and linear min- erals in sediments are oriented preferentially parallel to bedding. If continuous crystallization of all minerals is as- sumed, the layering can be explained by crystal sorting through rhythmic changes in the velocity of currents in the magma. During periods of relatively greater current velocity, heavier mafic minerals and larger feldspars were deposited. With lesser velocity, the smaller feldspars and a few small mafic crystals held in suspension were deposited. The exceedingly small size of all the crystals in the dark basal layer present at most "unconformities" can be satisfactorily explained as an accumulation of newly formed crystals, the development of the "unconform- ity" having been accompanied by an influx of hotter magma that at first contained no suspended crystals. The first crystals to form and settle out were very small. Mafic minerals are more abundant in the basal layer because of their greater settling velocity. With time, larger percentages of the accumulating crystals came from greater distances and consequently had longer periods for growth. This hypothesis offers a reasonable explanation for the overall increase in crys- tal size through the first few layers above an "uncon- formity." The roughly uniform size of the crystals above these first few layers, except for the variation between light- and dark-colored layers, suggests that after the deposition of the first few layers their growth period approached constancy. The felsic basal layers may not reflect cessation of crystallization such as is postulated to precede the de- position of mafic basal layers, for the average size of the plagioclase crystals does not decrease toward the "unconformity." Probably they result from "strati- graphic" overlap. "Stratigraphically" lower layers would have lain to the right in figure 160, and it is con- ceivable that the very lowest is a fine-grained layer like those present above most "unconformities." The crosscutting dark streaks (including those along obvious faults) consist mainly of hornblende and a little biotite. Probably all the crosscutting dark streaks 54 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA (not including dark basal layers above "unconformi- ties") are localized along fractures. The hornblende in these streaks is similar to hornblende in layers and may be magmatic; nevertheless, some of the crosscut- ting hornblendite shown in figure 15 may in fact be metamorphic in origin, possibly a result of intrusion of the surrounding quartz monzonite. Probably most of the "unconformities" were pro- duced by corrosion by magmatic currents, which picked up or dissolved crystals previously deposited, but some sharp bends or even broad curves in the layers beneath "unconformities" could have been caused by slumping and sliding within the magma chamber during deposi- tion. One difficulty in evaluating such a process is that the original configuration of the layers is not known. Although the layers now dip steeply, their original in- clination very likely was more gentle. Slumping would require a sloping surface; the slope could have been initial or it could have resulted from tectonic move- ments. The possibility of deltaic deposition cannot be ruled out. QUARTZ DIORITE AND RELATED GRANODIORITE Quartz diorite includes rocks that are somewhat lighter colored than the hornblende gabbro, but darker than the large masses of granodiorite and quartz mon- zonite. In texture and in composition the quartz diorite is transitional between hornblende gabbro and rock in the larger plutons of granodiorite. The color index ranges from 20 to 40, plagioclase contains less than 50 percent anorthite (and commonly more than 40 per- cent), and the rock generally contains 10 percent or more quartz. Associated with the quartz diorite are slightly lighter colored rocks of granodioritic compo- sition. Many of these lighter colored rocks are hy- brids between more silicic granitic rock and quartz di- orite, hornblende gabbro, or mafic volcanic rock. The grains generally range from 1 to 5 mm, but more quartz diorite is in the lower part of this range than in the hornblende gabbro size range. Most quartz diorite is equigranular and hypidiomorphic-granular, but some is coarse inequigranular and in places con- tains poikilitic hornblende crystals an inch long. In quartz diorite of hypidiomorphic-granular texture, plagioclase commonly makes up 40 to 65 percent of the rock, hornblende about 15 percent, biotite 15 to 20 per- cent, and quartz 1 to 15 percent. Accessories include apatite, sphene, and magnetite; the usual secondary minerals are epidote, chlorite, and sericite. Plagioclase commonly is progressively zoned, but exhibits oscilla- tions and discontinuities or strong changes in composi- tion through narrow zones. Many crystals have a broad central zone and a compositional range of Ani, to An;,. This zone commonly contains small cores as calcic as An,, and is discontinuously rimmed with more sodic plagioclase that ranges in composition from An», to Ans,. Hornblende is similar to that in the hornblende gabbro except that the color in the Z direc- tion generally is grayish blue green. Most quartz diorite of hypidiomorphic-granular tex- ture appears to have crystallized directly from a magma. Rock of this kind is found in the Deep Can- yon area of the Tungsten Hills in the vicinity of the Little Sister mine, along the west side of the Pine Creek pendant, on the east side of Wheeler Crest north of the mouth of Pine Creek, and in many other places. The masses of quartz diorite north of Pine Creek may orig- inally have belonged to a single large east-trending mass that was broken up and partly assimilated and granitized by later more silicic intrusives. Much of the quartz diorite and associated grano- diorite of irregular fabric may well be hybrid rock pro- duced by metamorphic or metasomatic processes or by the contamination of silicic magma with femic wall rock (Bowen, 1928, p. 175-223 ; Nockolds, 1933, p. 561- 589). Some coarse inequigranular textures, such as are found in quartz diorite along Big Pine Creek in the vicinity of the junction of the two main forks of Big Pine Creek, could have been produced by recrystalliza- tion of hornblende gabbro, quartz diorite, or mafic vol- canic rock as a result of the intrusion of larger quartz monzonite or granodiorite masses. Small amounts of felsic material could have been added during recrystal- lization. In other places the indications of interchange of ma- terial between early more mafic rocks and larger more silicic intrusives, and consequent hybridization of one or both are much stronger. Along the North Fork of Big Pine Creek, progressive hybridization of mafic rocks by quartz monzonite similar to the Cathedral Peak granite is evident. This hybridization has been achieved in part by granitization of original mafic rocks and in part by contamination of the quartz mon- zonite magma. Weak panidiomorphic-granular tex- ture in the least altered rocks suggests that the orig- inal rock may have been an equigranular gabbro. The least altered rock contains about 50 percent plagioclase (strongly zoned approximately or less), 40 percent hornblende, 5 percent biotite, and about 1 per- cent each quartz, microcline, magnetite and ilmenite, and sphene. Locally, it contains rounded quartz grains 4 to 14 inch across, which are mantled with hornblende. These grains, which appear to be xeno- crysts, survived extreme changes in the rock and pro- vide a key to its original nature. GEOLOGY OF THE BATHOLITH 55 The least altered rock appears to have been granitized different amounts in different places. In general the granitization resulted in coarser grained rock that con- tains larger amounts of quartz, K feldspar, and biotite, and smaller amounts of plagioclase and hornblende. In slightly granitized rock that still retains weak pan- idiomorphic-granular texture, the approximate mineral content is 50 percent plagioclase (Anss-s>), 10 percent hornblende, 15 percent biotite, 10 percent quartz, 10 percent K feldspar, and about 1 percent each magnetite, ilmenite, and sphene. In more strongly granitized rock the texture is hypidiomorphic-granular, and the ap- proximate mineral content is 40 percent plagioclase (Anss-»,), 25 percent biotite, 20 percent quartz, 10 per- cent K feldspar, and about 1 percent each magnetite, apatite, sphene, and hornblende. Rocks of all stages of granitization have disintegrated marginally, and ragged fragments half an inch or less in the longest dimension are strewn through the adjacent quartz monzonite. As distance from the mafic rock increases, the fragments are progressively less distinguishable, and generally they are not identifiable at distances of more than a few tens of feet, although the resultant rock has a darker color than uncontaminated quartz monzonite, with which it is locally in sharp contact. During the granitization of the mafic rocks along the North Fork of Big Pine Creek, metamorphic differ- entiation was in operation along or near fractures. Figure 19 shows a partly granitized specimen of mafic rock that contains a veinlet of hornblende-rich rock, apparently localized along a fracture. The fact that the rock within an inch or so of the veinlet is deficient in mafic minerals suggests that the hornblende in the vein was derived from the walls. The thickness of the FIGURE 19.-Partly granitized mafic rock cut by a hornblende-rich vein. adjacent wall rock, which is deficient in mafic constituents. The hornblende in the vein appears to have been derived from the The thickness of the vein varies from place to place, generally in accord with variations in the thickness of wall rock deficient in mafic minerals. 56 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA vein changes from place to place, and the thickness of the zones in the walls deficient in mafic minerals varies accordingly. The vein consists of anhedral hornblende grains in a wide variety of shapes and sizes, accom- panied by a little magnetite and quartz. The horn- blende grains in the margins of the veinlet are highly poikiloblastic. The hornblende-poor wall rock consists of a ragged mosaic of plagioclase, quartz, and micro- cline. Large crystals of microcline are abundant close to the dikelet, whereas only small blebs enclosed in plagioclase occur farther away. __ In the south end of the Pine Creek pendant, mafic metavolcanic rock and diorite, quartz diorite, and horn- blende gabbro are all present. However, some of the rock mapped with quartz diorite may well be contami- nated quartz monzonite. In Shannon Canyon and in the east side of Wheeler Crest just north of the mouth of Pine Creek canyon, darker colored rock having good hypidiomorphic-granular texture grades marginally through lighter colored hybrid rocks to quartz mon- zonite. An example of the contamination of granodiorite magma where the contamination can be identified is found in the upper Pine Creek drainage, northwest of Pine Lake. There, hornblende gabbro has been in- truded on the north by granodiorite, which is increas- ingly darker toward the hornblende gabbro. The con- tact, though difficult to locate because the contaminated granodiorite so closely resembles the hornblende gab- bro, is sharp, and many details of the contact were mapped. The conclusion seems inescapable that here the granodiorite magma assimilated large amounts of hornblende gabbro. The contaminated gabbro was rec- ognizable here ,but how many isolated masses of dark- colored rock of similar origin have been mapped as quartz diorite ? Scattered along the southwest side of the area from Piute Pass southeast to Mather Pass is dark fine- grained granodiorite having odd textures that suggest hybridization. Typical of these rocks is the mass in which the glacial basin occupied by Lake Sabrina was carved. The odd texture is largely the result of the distribution of K feldspar, which is scattered through the rock in patches 14 to 14 inch across. These patches are crowded with all the other minerals in the rock. Conceivably the K feldspar could have been of late magmatic origin, but it seems equally likely that it was derived from the enclosing granodiorite. If so, the par- ent rock was a more mafic plutonic rock, or possibly even a mafic volcanic rock. One other possible origin for some masses of diorite as well as of hornblende gabbro is that they were de- rived from calcium-rich sedimentary rock. The meta- morphic grade of the innermost wall rocks is in the amphibolite facies; therefore, any rock of appropriate composition could be converted to a stable assemblage of hornblende and plagioclase. In many places where amphibolite is associated with calc-hornfels, the horn- fels has been formed from the amphibolite, but in a few places, especially in the margins of inclusions in granitic rock, calc-hornfels has been altered to amphi- bolite. Such alteration must have involved metaso- matic exchange of material between the calcareous rock and the granitic magma. The variety of calc-hornfels commonly associated with amphibolite consists chiefly of diopsidic pyroxene and plagioclase. Conversion of diopside to hornblende would require subtraction of calcium and addition of water and femic constituents. In places, amphibolite is also present along contacts between marble and granitic rock, but the formation of amphibolite from marble requires much greater ex- change of materials and is not common. Amphibolite margins in calcium-rich rocks adjacent to granitic rock can be seen at the Brown tungsten prospect, which is along the range front southwest of Bishop and a mile west of the Bishop Antimony mine, and at the Lake- view tungsten mine at the head of Gable Creek. GRANITIC ROCKS The formations of granitic rock in the Bishop dis- trict have been described in a preliminary paper (Bate- man, 1961b). They range in composition from grano- diorite to alaskite, but rocks in the compositional range of quartz monzonite are most abundant and are fol- lowed closely by granodiorite. The average granitic rock of the area is calcic quartz monzonite. The plutons of granitic rock are of variable orienta- tion and size. Most of the larger ones parallel the axis of the batholith, but some smaller ones are elongate in other directions or are not elongate at all. They generally range in outcrop area from 1 to 50 square miles. The largest continuous mass, of Lamarck granodiorite, underlies 54 square miles in the mapped area, and extends northwest, west, and southeast into bordering areas. Its total area may be several hundred square miles. Many of the plutons are grouped as formations on the basis of composition, texture, and intrusive rela- tions. Each mass assigned to & formation is given a name, and one has been selected as the type mass and contains the type locality. Thus the type mass of the Tungsten Hills quartz monzonite is the Tungsten Hills mass. Inclusion under one formational name of the rock in several discrete masses is not without hazard, but it is believed that most of the correlations that have been made are valid because the range in texture GEOLOGY OF THE BATHOLITH 57 and composition within most individual masses is small compared with the differences between intrusives as- signed to different formations. Nevertheless, most plu- tons are compositionally and texturally zoned, and in a few zoning is pronounced. The formally named granitic formations are the Inconsolable granodiorite, Tinemaha granodiorite, Wheeler Crest quartz monzo- nite, Round Valley Peak granodiorite, Lamarck grano- diorite, and Tungsten Hills quartz monzonite. Some plutons cannot, with confidence, be assigned to formations and are assigned to one of two informal rock groups, or are unassigned. The first informal rock group includes all plutons composed of rock similar in appearance and approximately correlative with the Cathedral Peak granite of Yosemite (Calkins, 1930, p. 126-127). These rocks are called "rocks similar to the Cathedral Peak granite," and include two lithologic facies, alaskite, and quartz monzonite. The second in- formal group includes all plutons composed of rela- tively fine-grained quartz monzonite and are designated "finer grained quartz monzonite." These intrusions are compositionally and texturally similar and seem to have been emplaced at about the same time. Some or perhaps all of them may be offshoots from the same parent magma and temporal equivalents, but the evi- dence is too weak to make any such assumptions. The rocks in four unassigned plutons are named informally in terms of locality and average composition. They are called "granodiorite of Coyote Flat," "granodiorite of Cartridge Pass," "granodiorite of Deep Canyon," and "quartz monozonite of McMurry Meadows." The granitic rocks are composed dominantly of quartz and feldspar, and can be conveniently repre- sented on a triangular diagram whose corners are the felsic constituents: quartz, K feldspar, and plagioclase. The classification used here differs only slightly from several other classifications that have been proposed. Quartz comprises at least 10 percent of the felsic con- stituents in all the granitic rocks. Boundaries between the fields of the different granitic rocks are in terms of the amount of K feldspar (including perthite) to total feldspar as follows: quartz diorite, 0 to 10 percent; granodiorite, 10 to 35 percent; quartz monzonite, 35 to 65 percent; granite, more than 65 percent (fig. 14). Few individual specimens and no average composi- tions of plutons fall in the granite field as defined. Rocks of such composition do not seem to be common. The abundance of granite reported in the literature results partly from other usages of the term "granite" : for all granitic rocks, for the most felsic rocks of a gra- nitic suite regardless of composition, and for granitic rocks in which the average composition of the plagio- clase is albite. The first two usages are loose and not 735-925 0O-65--5 acceptable for precise classification, but the third is part of several classifications and is incorporated in the classification used here with a modification-because the rocks in which the average composition of the modal plagioclase is albite contain only a few percent mafic minerals they are called alaskite rather than granite. Most of this alaskite plots in the quartz monzonite field on the diagram in figure 14. MINERALOGY The mineral content is similar in the granitic rocks and is discussed for the suite as a whole. Such differ- ences in mineral composition as do exist are dealt with in discussions of the distinguishing characteristics of each rock. The essential minerals are quartz, plagio- clase feldspar, and K feldspar. The varietal minerals include biotite, hornblende, and augite. Accessory min- erals are magnetite and ilmenite, sphene, apatite, zircon, allanite, thorite, and monazite. Secondary minerals include epidote, sericite, and hematite. ESSENTIAL MINERALS QUARTZ Quartz is in anhedral grains that have a wide range of size and shape. Commonly it contains numerous tiny liquid inclusions, but it contains few mineral inclu- sions. Most larger grains extinguish irregularly or consist of a mosaic of diversely oriented components, but in some rocks the larger grains extinguish regularly. The irregular extinction generally is either undulatory or by sharply defined polygonal areas that are visible near extinction, but in a few rocks linear twinning can be seen. Some of these conjugate twins are oriented symmetrically with respect to fractures that bisect the acute angle between the lineations. POTASSIUM FELDSPAR (K FELDSPAR) In hand specimen K feldspar is white or pinkish. Almost all of it is perthitic and most of it also exhibits the quadrille structure (grid twinning, gridiron struc- ture, or grating structure) of microcline, but in places quadrille structure is inconspicuous or absent. Most of the albite in perthite is in thin, generally parallel but somewhat irregular lamellae of the sort commonly thought to be products of exsolution, but some is in irregular streaks and blebs. Except for subhedral to euhedral phenocrysts, which are conspicuous in some rocks of intermediate composition, K feldspar is an- hedral and interstitial with respect to all the other minerals. - Euhedral phenocrysts twinned according to the Carlsbad law are characteristically tabular parallel to (010) in some rocks and elongate or nearly equi- dimensional in others. Some phenocrysts are several inches in greatest dimension. 58 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA Commonly the K feldspar contains inclusions of all the other minerals in the rock. Uncorroded prisms of plagioclase are the most common inclusions, and in phenocrysts generally are oriented parallel with the nearest crystal face. Inclusions of quartz are not abundant and are generally in rounded, possibly partly resorbed blebs. Phenocrysts of K feldspar commonly are accentuated by peripheral concentrations of mafic minerals, which are highly reminiscent of the dark carbonaceous material marginal to many andalusite porphyroblasts. The rough faces of the phenocrysts, caused by interference with the bordering grains dur- ing growth, can be seen in thin section and in pheno- crysts that have weathered out of the enclosing rock. PLAGIOCLASE Plagioclase is present in relatively small white to light-gray subhedral grains that constitute phenocrysts only in finer grained rocks from dikes or small apo- physes. The grains generally are smaller than most grains of quartz and K feldspar, and their size range is less. Many grains are twinned on the albite law, and some also are twinned on the pericline or Carlsbad laws. Lamellar albite twins generally are very closely spaced in albite and sodic oligoclase and more widely spaced in more calceic varieties. Inclusions are uncommon, but more calcic zones usually contain an abundance of sec- ondary sericite. The main part of almost all plagioclase grains is zoned continuously from a calcic core to a sodic rim, and many grains also exhibit thin oscillations that are superimposed on the broader zoning. Some grains also have unzoned, relatively albitic rims, or small ex- ceptionally calceic core areas. The average composi- tions of the plagioclase commonly range from albite to andesine; albite is present in alaskite, oligoclase pre- vails in quartz monzonite, and andesine is the common plagioclase in granodiorite. The composition of plagioclase was determined opti- cally for most of the modally analyzed samples. The method followed was to record the extinction angle X' A (010) in sections that were oriented by means of a universal stage perpendicular to the albite twin plane and (010) cleavage and to the basal cleavage (001). The extinction angle was converted to percentage of An (fig. 20) with the use of a curve determined by F. C. Calkins (unpublished data, 1940) and modified by H. H. Hess (unpublished data, 1941). This method is not generally considered to yield results as accurate as other more cumbersome methods, but it has two advantages that outweigh the lack of precision : (1) it is rapid and thus permits making determinations of the composition of the plagioclase in a large number of samples, and PERCENT ANORTHITE 50°O 10 20 30 40 50 60 70 so 90 100 40° s0° 20° 10° 00 F C. Calkins, 1940, amended by H. H. Hess, 1941 10° EXTINCTION ANGLE La, @aO10, IN DEGREES FicurE 20.-Curve used to determine the anorthite content of plagioclase. (2) it is ideally suited for determining the range of composition in zoned crystals Checks provided by calculating the normative compositions of analyzed specimens do indicate, however, that the optical deter- minations are in the proper compositional ranges. In tabulating the plagioclase compositions, three sets of figures are given. The first shows the composition of the rim where a discontinuity exists between the rim and the main body of the grain ; the second shows the composition of the main body of the crystal; and the third shows the composition of any small exceptionally calcic cores. In addition to these recorded zones, many intergranular contacts between plagioclase and perthitic K feldspar are occupied by albite that was derived from the perthite in accordance with observations of Tuttle (1952, p. 115 and pls. 3, 4). VARIETAL MINERALS BIOTITE Biotite is present in all the granitic rocks; in some it is characteristically in individual hexagonal plates and in others it is in clusters of smaller, irregularly shaped plates, associated with accessory minerals and with hornblende, where present. The pleochroic color in the X direction in almost all specimens is pale grayish yellow, but in the Z direction it ranges in different rocks through various shades of red, grayish red, brownish red, yellowish brown, olive brown, olive, grayish olive, and olive gray. HORNBLENDE Hornblende is present in all of the granodiorite and in calcic quartz monzonite but is absent in sodic quartz monzonite and in alaskite, except in hybrid rocks. It occurs both in well-formed prismatic crystals and in ragged anhedral grains, many of which poikilitically GEOLOGY OF THE BATHOLITH 59 enclose grains of plagioclase. The typical prismatic habit of hornblende in some rocks is one of the distin- guishing characteristics of those rocks. AUGITE Augite is present as cores in hornblende in the Tine- maha and Inconsolable granodiorites and in more mafic parts of the granodiorite of McMurry Meadows. ACCESSORY MINERALS The common accessory minerals include magnetite and ilmenite, sphene, apatite, zircon, and allanite. Thorite and monazite have also been identified; Lar- sen recovered sufficient thorite from the Lamarck gran- odiorite and sufficient monazite from the granodiorite of McMurry Meadows to make age determinations by the lead-alpha method (Larsen and others, 1958, p. 50). Magnetite and ilmenite are present in small grains in all the granitic rocks, but are most abundant in those having the highest color index. Much of the magnetite is altered to hematite. Sphene occurs in discrete double wedges and in irregular masses associated with ilmen- ite. Most of the sphene is brownish or yellowish and only faintly pleochroic, but some of it is pleochroic in brilliant shades of red, and superficially resembles pied- montite. Apatite is in euhedral prismatic crystals. Commonly the prisms are short and stubby, but in some rocks they are long and very thin. Tiny euhedra of zircon are present in all the rocks, but are most abun- dant in quartz monzonite and alaskite. Allanite is a rather uncommon accessory, but where present it is in elongate conspicuous grains. It is somewhat variable in color and in pleochroism ; colors range from reddish brown through grayish orange to yellowish orange. ALTERATION PRODUCTS Secondary minerals include sericite, epidote, and chlorite. Sericite is present chiefly in the cores and other calcic zones in plagioclase. Most chlorite is an alteration product of biotite, and most epidote is de- rived from hornblende or calcic plagioclase. TEXTURES Each of the granitic rocks represented on the map is characterized by a "typical appearance" which is largely determined by the color index, grain size, tex- ture, and fabric of the rock (fig. 21). These features as much as any others are the bases for correlating and discriminating among the granitic rocks, and are use- ful criteria for field use. Except for uncommon local variants, the granitic rocks are medium grained, and hypidiomorphic-granular, and have color indices that fall between 2 and 20. Most rocks are equigranular, but some are porphyritic, and a few are seriate. The term "color index" is the content of dark-colored min- erals-biotite, hornblende, and the opaque minerals expressed in volume percent. The average grain size of the common nonporphyritic rocks and the groundmasses of the common porphyritic ones ranges from 1 to 5 mm. Phenocrysts in porphyritic rocks range widely in size, and some phenocrysts of K. feldspar in the Wheeler Crest quartz monzonite are as much as several inches long. Although correlation be- tween kind of rock and common or "typical" grain size is apparent, the connection is probably largely indirect. Grain size appears to be primarily a function of the size and shape of the granitic mass; some rocks occur commonly in masses of larger size than others, and the average grain size of these rocks, therefore, is greater than that of rocks that commonly occur in smaller masses. The common grain size of the. fine-grained quartz monzonite, which occurs in relatively small masses having no more than a few square miles of out- crop, is 1 to 2 mm., but the common grain size in the main mass of the Lamarck granodiorite, which has an outcrop area of at least 50 square miles, is 4 to 5 mm. Shape, too, is a factor that determines grain size, for thin masses commonly are finer grained than thicker ones of the same area. The grain size within most intrusions is fairly uni- form, but in some rocks is finer grained toward the margins and in small apophyses. For example, the Morgan Creek mass of the Tungsten Hills quartz mon- zonite, which lies along the west side of the Pine Creek pendant, is increasingly finer grained toward the west- ern margin, where it is in contact with older granodio- rite and hornblende gabbro. Constricted projections of the Tungsten Hills quartz monzonite into the north- ern margin of the Bishop Creek pendant likewise are finer grained than is common for that rock. Equigranular rocks are more common than prophy- ritic rocks, but both are well represented. Generally one texture or the other prevails, but in some rocks one grades to the other. The Wheeler Crest quartz mon- zonite, for example, is porphyritic in most places, but locally grades to equigranular rock. In equigranular hypidiomorphic-granular rock, pla-. gioclase, hornblende, and biotite commonly are subhe- dral and quartz and K feldspar are anhedral. The Lamarck granodiorite is characterized by conspicuous euhedral or nearly euhedral crystals of hornblende and biotite, and most of the biotite in both the Tungsten Hills quartz monzonite and Wheeler Crest quartz mon- zonite is in streaky aggregates of subhedral grains. In some specimens, some or all of the hornblende is anhe- dral and poikilitically encloses smaller grains of pla- 60 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA FIGURE 21.-Typical granitic rocks from the Bishop district. A, tinemaha granodiorite. D, Round Valley Peak granodiorite. B, Inconsolable granodiorite. C, Lamarck diorite. GEOLOGY OF THE BATHOLITH 61 6 H Frour® 21-Continued-E, Wheeler Crest quartz monzonite. F, Tungsten Hills quartz monzonite. @, Quartz monzonite similar to the Cathedral Peak granite. H, Alaskite similar to the Cathedral Peak granite. 62 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA gioclase and the accessory minerals. Both quartz and K feldspar are interstitial to the other minerals, K feldspar being the more ramifying of the two. Much of the K feldspar is notably poikilitic and encloses grains of the accessory minerals, hornblende, biotite, plagioclase, and more rarely, rounded, apparently partly resorbed blebs of quartz. Most of the cores of K feldspar are clean, and included minerals are increas- ingly abundant toward the margins. The accessary minerals-apatite, magnetite, zircon, sphene, and al- lanite-commonly are closely associated with horn- blende and biotite. The porphyritic rocks can be conveniently placed into two groups, those with phenocrysts of K feldspar and those with phenocrysts of other minerals, usually plagioclase with or without hornblende, quartz, and K feldspar. The phenocrysts in plutons are gener- ally K feldspar whereas the phenocrysts in finer grained dikes, marginal rock, and small apophyses are generally earlier formed minerals such as hornblende or plagioclase. The phenocrysts in finer grained rocks are of about the same habit and size as the same min- erals are in coarser grained rocks of typical aspect, and not uncommonly are set in an allotriomorphic- granular groundmass. In some of these rocks plagio- clase is the only mineral that forms phenocrysts, and in others all the essential and varietal minerals occur both as phenocrysts and in the groundmass. These relations can be readily explained by the mechanism that is usually assumed for porphyritic rocks; for ex- ample, the phenocrysts are early crystallized minerals that were suspended in the magma when it was moved to an environment that resulted in the more rapid crystallization of the groundmass. The phenocrysts of K feldspar in more typical por- phyritic rock, however, cannot be explained in the same way because they formed during the later rather than the earlier stages of crystallization. Knopf infers from the abundance of included minerals that the large tabular phenocrysts of K feldspar in the porphyritic granite of Mount Whitney began to crystallize late and suggests that the rock owes its porphyritic tex- ture "to a superior velocity of crystallization and a superior power of attracting the crystallizing mole- cules to a few centers of erystallization" (Knopf, 1918, p. 60). In some rocks, notably the Wheeler Crest quartz mon- zonite and, locally, the quartz monzonite similar to the Cathedral Peak granite, the phenocrysts are euhedral; in others, such as the Tinemaha granodiorite and the Tungsten Hills quartz monzonite, they are anhedral to subhedral. Regardless of external form, the pheno- crysts enclose grains of the other minerals in the rock, including blebs of partly resorbed quartz, and are ac- centuated by thin peripheral concentrations of mafic minerals. The faces of even euhedral crystals are rough because of interference between the phenocrysts and the bordering grains. The inclusions and the marginal concentrations of mafic minerals support Knopf's hy- pothesis that the phenocrysts crystallized later than most of the other minerals. The peripheral zone of mafic minerals marginal to many crystals is highly rem- iniscent of the dark carbonaceous zones commonly asso- ciated with chiastolite, and suggests that the minerals in the dark zone were expelled or pushed aside by the growing phenocrysts at the time of their formation. It is true that in Becke's (1903) crystalloblastic series K feldspar occupies the lowest position, but the concept of simultaneous growth of all the constituents does not seem applicable here. If most of the growth of the phenocrysts was made after crystallization of most other minerals was well advanced, competition with other minerals for a euhedral form would be small. Phenocrysts of K feldspar are restricted almost en- tirely to rocks of intermediate composition (sodic granodiorite and calcic quartz monzonite). Experi- mental studies of artificial melts show that plagioclase is ordinarly the first of the essential felsic minerals in granite to form, and that quartz and K feldspar do not crystallize until the temperature has fallen to a point where sodic plagioclase or albite is being formed. In more calcic rocks a large part of the rock may already be crystallized before K feldspar begins to form, and consequently the K feldspar may be relegated to inter- stices. On the other hand, in very silicic rocks such as alaskite, the felsic constituents may all crystallize at about the same time and inhibit the growth of euhedral crystals of any one kind. Only in rocks of intermediate composition, where some minerals are formed in ad- vance of K feldspar but not so many that K feldspar cannot grow into euhedral crystals through its strength of crystallization, are conditions especially favorable for the formation of phenocrysts of K feldspar. ANALYTICAL DATA Two kinds of analytical data were obtained for the granitic rocks, (1) limited chemical data and (2) ex- tensive modal data. Fourteen samples were analyzed chemically, nine by standard methods and five by-the rapid method described by Shapiro and Brannock (1956). The nine specimens analyzed by standard chemical methods were also analyzed by spectrographic means for semiquantitative determination of the minor elements. The standard chemical analyses are all of granodiorite and quartz monzonite; four of the rapid analyses are of rocks similar to the Cathedral Peak GEOLOGY OF THE BATHOLITH granite (alaskite and quartz monzonite), and one is of quartz diorite. In addition to these analyses a partial analysis of a sample of alaskite similar to the Cathedral Peak granite published by Knopf (1918, p. 68) was utilized. The chemical and spectrographic analyses and norms are summarized in table 3. The modes of about 300 samples of granitic rocks were determined. First, modes for all samples were made by using thin sections of standard size (about a square inch of rock on the average) and a technique similar to that described by Chayes (1956). Plots of the modes made from thin sections on quartz-K feld- spar-plagioclase diagrams showed less scatter for the 63 finer grained rocks than for the coarser grained rocks. This and other comparisons of the modes of coarser and finer grained rocks showed that ordinary size thin see- tions are too small to be representative samples of coarser grained rocks. In early 1960, the coarser grained rocks were re- counted by using rock slabs in which K feldspar was stained yellow and plagioclase light red to reddish brown by a method described by Bailey and Stevens (1960). In this procedure K feldspar is stained with sodium cobaltinitrate and plagioclase is stained with rhodozonic acid, which acts on previously introduced barium. The actual counting was done by projecting 3.-Summary of chemical and spectrographic analyses and norms of the granitic rocks Tungsten Hills Rocks similar to Cathedral Peak granite Tine- Grano- | Wheeler | Round quartz monzonite, uartz | Inconsol-| maha diorite Crest Valley | Lamarck specimen- jorite [able gran-| grano- of Mc- quartz Peak grano- : Quartz monzonite, specimen- Alaskite, specimen- odiorite | diorite Murry mon- grano- diorite Meadows] zonite diorite 5 52 4 12 23 37 46 K Chemical analyses [1, Rapid rock lasnalysis analysts: H. F. Phillips, P. L. Elmore, and K. E. White. 2, Standard rock analysis; analyst: L. M. Kehl. 3, Rapid rock analysis; analysts: L. D. Elmore, S. D. Botts, and M. D. Mack 4, Partial analysis reported by Knopf (1918, p. 68) of alaskite from Rawson 'Creek canyon] Lab. No....| 138275(1) | 53-1303 -1209 | 53-1301 | 53-1205 | 53-1302 | 53-1300 | 53-1208 | 53-1207 |152445(3) | 152446(3) | 53-1206 |152443(3) | 152444(3) (4) SsCD(2) | SCD(2) | SCD(@) | SCD(@) SCD(2) sCD(2) | SCD(@) SCD(2) 61. 00 62. 82 64. 86 71. 42 63. 53 66. 92 71. 42 71.8 16. 06 15. 44 16 12 14.47 15. 61 15.19 14.03 14 89 15.3 1. 86 2. 50 1.90 1.03 2.35 1.45 . 89 1. 07 1.0 4.06 3.17 2. 52 1. 38 3. 25 2. 52 1. 63 1.99 . 65 3. 10 2.35 1. 55 -78 2. 54 1.74 .70 . 91 . 34 5. 46 5.04 3. 80 2. 86 4. 58 3.79 1. 91 2.70 1.8 3. 45 3.15 3. 44 3. 44 3. 31 3. 16 2. 86 3. 18 3.8 2. 95 3. 72 4. 03 3. 69 2. 98 3. 82 5.35 4. 45 4.1 . 05 . 03 . 06 . 06 . 04 . 06 . 08 . 08 } 48 . 58 .62 . 51 . 21 . 61 . 48 . 35 31 § . 88 . 64 . 57 . 25 . 63 47 .36 42 .22 . 00 . O1 . 00 . 03 . 08 .02 02 O1 . 08 . 25 . 30 .23 10 .23 18 . 09 12 . 05 .10 11 . 09 . 08 12 . 08 . 05 07 . 06 .................... ws beret len 99. 80 99, 99 99. 81 99. 80 99. 81 99. 88 99. 74 99. 80 100 [Looked for but not found: Ag, As, Au, Bi, Cd, Ge, In, Mo, Pt, Sb, Quantitative spectrographic analyses for minor element Sn, Ta, Th, Tl, U, W. A trace of Be (less than 0.00005) was found in all samples. Analyst: P. R. Barnett 0. 004 0. 001 0.0 0. 0 0.0 0.0 0. 0 6 .2 .2 2 .2 a Fo . 002 . 002 . 0009 . 0004 . O01 . O01 . 0005 . 004 . O01 . 001 . 0003 . 002 . O01 . 0006 . 002 . O01 . O01 . 0003 . 0009 . 0006 . 0004 . 002 . 002 . O01 . O01 . 002 . O01 . O01 . 006 . 01 . 009 . O1 . 009 . 009 . 008 . 002 . 002 . 002 . 002 . 002 . 002 . 002 . 003 . 0008 . 0004 . 0001 . 0007 . 0005 . 0003 . 002 . 002 . 002 . O01 . 002 . 002 . 002 . O01 . 001 . 0007 . O01 . O01 . O01 . 001 § . 09 . 06 . 05 . 09 . 07 . 03 . O1 . O1 . 007 . 005 . 009 . 006 . 004 . 003 . 005 . 005 . 003 . 003 . 004 . 004 . 0003 . 0004 . 0003 . 0002 . 0002 . 0002 . 0003 . O1 .0 .0 .0 . 01 0 .0 Di 02 . 02 Di OL 01 . 05 Norms 22. 62 22. 76 26. 72 15. 84 1. 83 6.18 2.09 . 90 .35 axles os a as __________ .10 31 1.33 1. 53 51 1.12 YT eel 99. 29 99. 32 99. 36 99. 04 99. 10 | 99. 55 99. 40 98. 88 {-..c......- 64 colored photographic transparencies of the slabs onto a grid of about 2,000 dots. Counting projections of transparencies permitted the use of larger and more representative samples than was possible with thin sections, and most plots of modes de- termined from stained slabs show less scatter than plots determined from thin sections cut from the same sam- ples. The average slab counted had an area about five times that of a standard thin section. The stained slabs have the disadvantage that they permit counting only four constituents: quartz, K feldspar, plagioclase, and mafic minerals ; biotite and hornblende cannot be count- ed separately. Modes of most samples of the Incon- solable granodiorite, Tinemaha granodiorite, Wheeler Crest quartz monzonite, Lamarck granodiorite, Round Valley Peak granodiorite, Tungsten Hills quartz mon- A Freur® 22.-External contacts of the Inconsolable granodiorite in the drainage basin at the head of the South Fork of Big Pine Creek. tact with Tinemaha granodiorite (left half of photograph) southeast of Elinore Lake about half a mile. GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA zonite, and rocks similar to the Cathedral Peak granite were counted on stained slabs, but a few modes of these rocks, which were of finer grain size or for which stained slabs could not be obtained, were counted in thin section. Modes of the other rocks were determined from thin sections. ROCK DESCRIPTIONS The plutonic rocks are described in order of their de- creasing age as interpreted from intrusive relations and from the map pattern. Slight divergence from this plan is made to permit bringing together the rocks within each of two sequences not in contact ; one of these, called informally the Tinemaha sequence, is confined to the area south of the septum along Big Pine Creek and the other, called informally the Bishop sequence, is con- A, Con- Mafic inclusions that are present in both rocks parallel to contact and to foliation suggest proximity to the original intrusive contact of both masses ; note greater abundance of inclusions in the Inconsolable. Relative ages are uncertain. about half a mile south of Contact Pass. B, Contact with quartz monzonite similar to the Cathedral Peak granite Note absence of flattened mafic inclusions in quartz monzonite, which is the younger rock. GEOLOGY OF THE BATHOLITH 65 fined to the area north of the septum. The Tinemaha sequence includes the Tinemaha granodiorite, the In- consolable granodiorite, and the quartz monzonite of McMurry Meadows; the Bishop sequence includes the Wheeler Crest quartz monzonite, the Round Valley Peak granodiorite, the Tungsten Hills quartz monzo- nite, and the granodiorite of Coyote Flat. The order of emplacement is usually also an order of decreasing silica content ; thus the first rocks described are rich in calcium, iron, and magnesium, and later rocks are in- creasingly richer in silicon and the alkalis. A notable exception is that the very last plutons emplaced are of granodioritic composition. INCONSOLABLE GRANODIORITE The Inconsolable granodiorite is represented by medi- um-grained, somber-hued rock that constitutes the Sier- ra-Nevada divide from Middle Palisade to Mount Agassiz, and extends northward in the Inconsolable Range to the latitude of Chocolate Peak. The spectacu- lar cirques at the heads of the main and the South Forks of Big Pine Creek, which are still occupied by glaciers, are carved in this rock. The main mass of rock is elon- gate in a northwesterly direction and has an outcrop area of a little more than 121% square miles. A second very small mass, having an outcrop area of only about a tenth of a square mile, is about half a mile south of the main mass. The type locality is in the Inconsolable Range; characteristic rock is also exposed in the Pali- sade Crest and the cirques at the head of Big Pine Creek. The Inconsolable granodiorite is megascopically equi- granular and medium grained, and the average grain size is about 2 mm (fig. 212). It is distinctly finer grained toward most margins. In overall aspect the rock is medium to medium-dark gray; this relatively dark hue results partly from a high average color index of about 18, and partly from the prevalent gray to gray- ish-red color of the feldspar. Many specimens, especial- ly those from marginal parts, contain scattered small but conspicuous grains of moderate-red to reddish- brown plagioclase. Primary foliation generally is recognizable and is especially conspicuous in the margins of the mass. The rock contains abundant mafic inclusions that are ori- ented parallel with the foliation and are increasingly flattened near external contacts (fig. 224). Mafic dikes, abundant in the adjacent Tinemaha granodiorite and present farther north in the Lamarck granodiorite, were observed only in the extreme north end of the Inconsolable granodiorite. Quartz and K feldspar are approximately equal in abundance, and plagioclase generally is more than twice as abundant as either. Biotite is the predominant mafic mineral, and hornblende and augite are also present. The accessories are the usual ones. The texture in thin section is seriate, and the largest grains are plagioclase. Plagioclase is in subhedral zoned crystals of a wide size range. The average composition is about An,, the most calcic plagioclase in any of the granodiorites. Commonly, it is zoned in the general range of Ans, to Ans); locally, small calcic cores are present, and many crystals are rimmed with calcic plagioclase (Ang,) (table 4). Quartz and K feldspar commonly are inter- stitial to the plagioclase. The quartz grains lack the irregular patterns of extinction prevalent in most other intrusives. In most specimens K feldspar does not exhibit the quadrille structure of microcline and is only weakly perthitic, although in places it contains a few laminae of albite. Biotite is in conspicuous plates having a pleo- chroism X=grayish yellow, Y=Z=grayish red to redddish brown. Especially at the margins of grains, the grayish red to reddish brown color grades to light olive, and in a few grains Y=Z=olive gray. Large plates of biotite not uncommonly enclose hornblende, which in turn may enclose augite. Both augite and hornblende also are found in discrete grains, although most. augite grains are irregularly bordered with horn- blende. Augite appears to be more abundant than hornblende, a feature that is unique to this rock. The locations of modally analyzed specimens are shown in figure 23. The plot of modes (fig. 24) which is elongate away from the plagioclase corner, indicates considerable range in the plagioclase content. Com- parison of the range of modes with the positions of the specimens within the intrusion fails to reveal any sys- tematic relation between composition and position. The Inconsolable granodiorite is probably the oldest granitic rock in the area south of Big Pine Creek, but its relations to the Tinemaha granodiorite are uncer- tain. The fact that about half a mile southwest of Mount Bolton Brown mafic dikes in the Tinemaha ter- minate at the contact with the Inconsolable granodiorite suggests they were cut off, but half a mile southeast of Lake Elinore a swarm of inclusions in the Inconsolable granodiorite terminates at the contact with the Tine- maha granodiorite in such a way as to suggest it was cut off. The age of the mafic dikes has not been defi- nitely determined, and they may be younger than either intrusive. Inasmuch as the Inconsolable granodiorite is more mafic than the Tinemaha granodiorite, it prob- ably crystallized at higher temperatures and a little earlier. The Inconsolable granodiorite is clearly intruded by the Lamarck granodiorite and by quartz monzonite sim- ilar to the Cathedral Peak granite. Both the Lamarck 66 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA 118°45" 118°30' 118°15¢ 37°30° 37°19" E Bishop /'\ 3 | \ EXPLANATION Round Valley Peak ganodiorite Inconsolable granodiorite Granodiorite of Coyote Flat Granodiorite of McMurry Meadows Quartz monzonite facies, stippled; granodiorite facies, lined 37°00" c- o ~ J ~ a C .7 ‘ lel imen y | cAM & q|l w -if YY *" 2.7 ll t\\\\\§ i 72W 2.7 C Granodiorite of Cartridge pass <=> Granodiorite of Deep Canyon S 2 ©2.74 Specimen with number and specific gravity 3 Big Pine 5 0 5 MILES I 1 1 1 1 1 old FisurE 23.-Map showing the locations of modally analyzed specimens of the Round Valley Peak and Inconsolable granodiorites, the granodiorite of Coyote Flat, the quartz monzonite of McMurray Meadows, the granodiorite of Cartridge Pass, and the granodiorite of Deep Canyon. GEOLOGY OF THE BATHOLITH 67 granodiorite and the quartz monzonite similar to the Cathedral Peak granite contain inclusions of the Incon- solable granodiorite and penetrate it with dikes. North of Contact Pass the contact between the Inconsolable granodiorite and the Mount Alice mass of quartz mon- Quartz Plagioclase Potassium feldspar 24.-Plot of modes of Inconsolable granodiorite on quartz-K feldspar-plagioclase diagram. zonite similar to the Cathedral Peak granite makes a westerly bend of about 40°, and the granodiorite in the east side of Temple Crag is embraced by the quartz monzonite. The granodiorite there is conspicuously brecciated and cemented by fine-grained felsic igneous rock and by quartz (fig. 25), which almost certainly Fisurs 25.-Brecciated Inconsolable granodiorite in the east side of Temple Crag. Fragments are cemented by fine-grained felsic igneous rock and by quartz. The cementing materials almost certainly were derived from adjacent quartz monzonite similar to the Cathedral Peak granite, which caused the brecciation. TaBtr 4.-Modal analyses of Inconsolable granodiorite, in volume percent [Where the content of biotite, hornblende, and accessory and secondary minerals is shown separately, the mode was determined from a thin section. Where only the total content of mafic minerals is shown, the mode was determined from a stained slab. Location of specimens is shown on figure 23] Acces Percent of anorthite Specific K Plagio- Horn- | sory and |_ Total in plagioclase Specimen gravity | Quartz | feldspar clase Biotite | blende secgildai'y mafics Remarks minerals Rim Body Core 10.5 13. 5 A99 | .s oo LO U. cein lee ao ne wield 20: T 36-43 55 Seirigte; grayish-red feldspar; high color ndex. 11.7 14.2 §0:2 [vede ceases 270 $2-808 Seriate; a few scattered reddish-brown feldspars; no augite. 13. 6 14. 6 8 A s 28.7 30 34-58 |..___..... Seriate; grayish-red plagioclase. 12.3 10.8 -| c cuse 248 ]-. 40, 36-53 72 | Seriate; scattered moderate red feld- spar. 12.8 20. 0 M4) 4 |... xe as dle eeu 22. 8 20 33-47 64 | Seriate. 16. 4 12.5 51.8 11.0 6.1 . 10.8 lcs C8 [cinco cles 0. 9.5 11.0 15.5 (cave | A ere nees 20 $1.0 36 51 | Seriate; scattered reddish-brown feld- spar. 9.7 10. 3 00-1 e -| emel eave [eve can seus 21.0 31 28-80 Seriate; somewhat foliated and coarser grained than usual. 10.8 20.0 44.3 11.0 10.1 24.9 20 36 45 | Seriate; scattered reddish-brown feld- spar. 6.9 17.0 Sl 5 |. . rece caine B- D L 40 51?) Seriate. 13. 6 20.1 46:5 enn i nene 21. 8 31 37 52 | Seriate; somewhat foliated; scattered moderate red feldspar. 10.7 9.7 60.0 :s ore ead ain ele nus be Buble 18.7 20 {cl su cave Seriate; some moderate red feldspar. 15.2 16.2 BC MN cele eo oreck cabe s os (nda 34, 32-86 |._...__... Seriate; some moderate red feldspar; specimen 6 inches from contact with Lamarck granodiorite. 2. 16. 0 24. 3 12.3 26 82-07 Seriate; somewhat foliated. 2.74 18. 0 24.3 18. 8 28 31-86 | 47-55, 50 Do. 16....<.... A 2. 75 20. 3 20. 4 20. 6 20 34 Seriate. Average... 2.75 13.1 15.6 22,0 |. ec eles conn l een oe nat 1 Standard chemical analysis, specimen 6 [Lab. No. 53-1303sed. Analyst: L. M. Kehl] 68 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA are differentiates of the quartz monzonite. - Many frag- ments of granodiorite have been recrystallized to finer textured rock (Joplin, 1935b), and locally the mafic minerals have collected into knots and layers much like those in pelitic hornfels at Stecker Flat (fig. 9). The presence of differentiates of the quartz monzonite sim- ilar to the Cathedral Peak granite as cementing mate- rial places the time of brecciation as not later than intrusion of the quartz monzonite, and localization of the breccia zone in the bend in the intrusive contact sug- gests strongly that the brecciation was caused by intru- sion of the quartz monzonite. Some facies of the granodiorite are similar in com- position and appearance to rock in the Deep Canyon area of the Tungsten Hills, which has been classified as quartz diorite. The granodiorite is also similar to some facies of the Sentinel granodiorite of the Yosem- ite region (Calkins, 1930, p. 125), but the Sentinel gran- odiorite also includes facies that show equal similarity to the Lamarck and Tinemaha granodiorites. TINEMAHA GRANODIORITE The Tinemaha granodiorite has an aggregate out- crop area in the south half of the Big Pine quadrangle of approximately 32 square miles (fig. 13). Most of the granodiorite is in a large oval mass containing in- clusions of diorite, nearly bisected by the granodiorite of McMurry Meadows. The western part crops out continuously in about 1814 square miles, whereas the eastern part crops out discontinuously in about 1314 square miles. The largest exposure in the eastern part, an outcrop area of about 12 square miles, is separated from several small outcrops, that project through the basalt of Crater Mountain. A small outcrop having an area of half a square mile lies south of Red Moun- tain Creek in the vicinity of Stecker Flat. The type locality is along Tinemaha Creek, and rock of typical appearance crops out in all the canyons be- tween Tinemaha Creek and the South Fork of Big Pine Creek. Granodiorite of typical appearance also occurs in road cuts on the south side of Big Pine Creek near the crossing at Bench Mark 5066, but the rock is more weathered than that exposed higher in the range. The appearance of the Tinemaha granodiorite is very nearly the same in all exposures throughout the mass; differences in texture and in color index do not materially affect the general appearance of the rock. Adjacent to the Inconsolable granodiorite, it is some- what finer textured than in most other places, but the difference in grain size is not great. Commonly the granodiorite is porphyritic and con- tains large subhedral to anhedral grains of perthitic microcline as much as 14 ecm across, although some specimens are equigranular or seriate (fig. 214). The texture of the groundmass is hypidiomorphic-granular, and the grain size generally ranges from 2 to 4 mm. The color index of the rock averages about 14, and ranges from 6 to 25. A characteristic of the Tinemaha granodiorite that is unique among the granitic rocks of the Bishop district is that hornblende generally is in excess of biotite, the average ratio being 4:3. Much of the hornblende is in euhedral or subhedral prisms, whereas biotite, unlike the biotite in the Lamarck granodiorite, is rarely euhedral. Plagioclase in the Tinemaha granodiorite is variable in amount, but gen- erally is more abundant than either K feldspar or quartz. Quartz is a little less abundant than K feldspar. Plagioclase commonly is zoned ; the main part of many grains is about An., near the center and about Anso near the margins, but some cores are as calcic as Ang,, and some rims are An», or less. Commonly the zoning is continuous except for minor but conspicuous oscilla- tions. Most of the K feldspar is perthitic microcline. Several thin sections of specimens (locations on fig. 26) from marginal parts of the western limb of the intrusion exhibit augite cores in the hornblende. The granodiorite contains numerous mafic inclusions, and in most places a foliation is defined by the in- clusions and by planar orientation of biotite and horn- blende. In the western part of the intrusion, steeply dipping foliation in the west side and gently dipping foliation in the east side adjacent to the granodiorite of McMurry Meadows define the western half of a foli- ation arch (pl. 5, see. E-"). Foliation was recorded in the eastern part at only a few places because it is obscured by poor exposure and deep weathering. The western part of the main mass of Tinemaha granodiorite ends to the south against the septum along Red Mountain Creek. However, rocks similar to those in the septum occur near Stecker Flat and form small septa along a gently dipping contact be- tween the small mass of Tinemaha granodiorite and underlying quartz monzonite similar to the Cathedral Peak granite. The quartz monzonite is underlain in turn by finer grained quartz monzonite. The relations suggest that originally the Tinemaha granodiorite ex- tended farther to the south but has been cut out by younger intrusions or eroded away (pl. 5, see. -F"). The Tinemaha granodiorite is cut by many mafic dikes (pl. 4), which generally dip steeply or are verti- cal and trend N. 70° W. These dikes do not continue in abundance into any of the bordering intrusives, and many terminate approximately at the contacts. The Tinemaha granodiorite is distinguished from the Wheeler Crest quartz monzonite and the Lamarck gran- odiorite, by the preponderance of hornblende over GEOLOGY OF THE BATHOLITH 69 {{848' 11830 ns'is' 37°30° ( ta 7 N E] Bishop kaenfoot Lake mass __, D Jé é az VD b‘ i =x f 37°15 Lamarck mass O Big Pine EXPLANATION Wheeler Crest quartz monzonite Lamarck granodiorite Tinemaha granodiorite 9 ® 2.67 2.7 Specimen with number Specific-gravity and specific gravity contour 37°00' , 5 o 5 miLes 1 ] FisurE 26.-Map showing the locations of modally analyzed specimens of the Wheeler Crest quartz monzonite and of the Lamarck and Tinemaha granodiorites. 70 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA biotite in the Tinemaha granodiorite, although the aver- age grain size and color index are about the same in all three rocks (fig. 21). Actually no problem arises in the field in distinguishing the Lamarck granodiorite from the Tinemaha granodiorite because the south end of the Lamarck granodiorite, where it is in contact with the Tinemaha granodiorite, is exceptionally light colored. The Tinemaha granodiorite also can be readily distin- guished from the Lamarck by the absence of euhedral biotite plates, which are characteristic of the Lamarck granodiorite, and by its generally porphyritic habit. The anhedral to subhedral habit of the phenocrysts distinguish it from porphyritic facies of the Wheeler Crest quartz monzonite. The modes and specific gravities of the 29 specimens whose locations are shown in figure 26 are tabulated in table 5 and plotted on a quartz-K feldspar-plagioclase triangular diagram in figure 27. The plot of modes forms a large elongate field that extends away from the plagioclase corner toward the quartz-orthoclase sideline. The elongate shape of the field reflects range in the plagioclase content of more than 35 percent. The Tinemaha granodiorite is not known to intrude any other plutonic rock except small masses of quartz Tasur 5.-Modal analyses of Tinemaha granodiorite, in volume percent [Where the content of biotite, hornblende, and accessory and secondary minerals is shown separately, the mode was determined from a thin section. Where only the total content of mafic minerals is shown, the mode was determined from a stained slab. Location of specimens is shown on fig. 26] Accessory Percent of anorthite in Specific | Quartz K Plagio- Horn- and Total plagioclase Specimen gravity feldspar clase Biotite | blende seclondai'y mafic Remarks minerals Rim Body Core 17.9 80-40 |..s-csclc. Weakly porphyritic; faint foliation. 12:0 §2-00 )| eves Weakly porphyritic; some hornblende grains enclose augite cores. 189 |......... 31-46 Porphyritic. T Weakly porphyritic. Porphyritic. Porphyritic; some intergranular grano- blastic mortar and myrmekite. __________ Weakly porphyritic. Porphyritic; some intergranular grano- blastic mortar and myrmekite. 40 | Equigranular to seriate; foliated; abun- dant granoblastic mortar and myr- mekite; hornblende encloses augite. 141 ] 38-44 48 | Porphyritic; abundant granoblastic mortar and myrmekite. 15.2 20- 32 38 | Porphyritic; some granoblastic mortar and myrmekite. 18 8 |ceccsccl«s 88-44 Equigranular. 18 $7-48, 88 |._.._..._. Porphyritic; some hornblende grains enclose augite. TTA en e Pornhyritic; some hornblende grains enclose augite. (Mode poor.) TWA 83-89, 36 |..._.__... Equigranular; some hornblende grains enclose augite. ATT es 40-44 21... acr Equigranular; very mafic; much grano- blastic mortar. 20. 4 12 $1-B2 |. Weakly porphyritic; some granoblastic mortar and myrmekite. 18.1 10, 27 $497 Seriate. 90 seen. 24-36 Porphyritic; some granoblastic mortar. 24 22-84 Seriate. 124 37-52 Porphyritic; both perthite and plagio- clase phenocrysts. 11.90 22-87 Seriate; much epidote. 17.2 21 20-43 Porphyritic; both perthite and plagio- clase phenocrysts. 20.1 34? Porphyritic (Plagioclase determination poor). 17.2 21-46 Seriate. 15.3 21 20-38 Porphyritic. 12. 4 22 30-43 Seriate. 17.8 | 34-40 Seriate; abundant quartz. 10.0 38-44 Porphyritic; plagioclase much seri- citized; some epidote; mafic mineral content too low. 10.9 28,990 Porphyritic; highly sericitized plagio- clase phenocrysts in hypidiomorphic groundmass. Average... 2.72 21.3 23.6 30. 0 16.1 2s a 1 Standard chemical analysis, specimen 10 Norm, specimen 10 [Lab. No. 53-1299sed. Analysts: L. M. Kehl] a Weia'llg Zégmm Weight 22.20 26.71 (Plagioclase composition Anss) 16.6% 5.16 6.18 3.74 1.22 69 GEOLOGY OF THE BATHOLITH TL Quartz Plagioclase Potassium feldspar FisurE 27.-Plot of modes of Tinemaha granodiorite on quartz-K feldspar-plagioclase diagram. diorite and hornblende gabbro, but it probably is in- trusive into the Inconsolable granodiorite. Inclusions of the Tinemaha granodiorite in the Lamarck grano- diorite and dikes of Lamarck granodiorite and of quartz monzonite similar to the Cathedral Peak granite in the Tinemaha granodiorite indicate that the Tine- maha granodiorite is older than these intrusives. The Tinemaha granodiorite is also intruded by the grano- diorite of McMurry Meadows. The position of the granodiorite of McMurry Meadows relative to the Tinemaha granodiorite and certain similarities of min- eral content and texture suggest that the granodiorite of McMurry Meadows crystallized from the core magma of the Tinemaha granodiorite following erys- tallization of the margins and movement of the still- liquid core. The Tinemaha granodiorite megascopically resem- bles the Wheeler Crest quartz monzonite, which like the Tinemaha granodiorite is apparently older than any of the plutonic intrusives with which it is in con- tact, except for masses of quartz diorite and horn- blende gabbro. Although correlation of these two rocks is an attractive possibility, differences in the quartz-K feldspar ratio, in the size and shape of the perthitic microcline phenocrysts, and the preponder- ance of hornblende over biotite in the Tinemaha grano- diorite suggest they are different rocks. Porphyritic granodiorite somewhat similar in appearance to the Tinemaha granodiorite also is found in the Benton Range, 30 miles north of Bishop, and at the Jumbo mine in the Inyo Range west of Independence. Ths granodiorite of the Benton Range contains more horn- blende than biotite and is porphyritic, but the K feld- spar phenocrysts are euhedral rather than subhedral as in the Tinemaha granodiorite. GRANODIORITE OF McMURRY MEADOWS The granodiorite of McMurry Meadows constitutes a single pluton that is intrusive into and enclosed by the Tinemaha granodiorite. It exhibits the greatest range in composition of any plutonic mass within the mapped area (fig. 28; table 6). The pluton is con- centrically zoned; it grades from quartz monzonite in the core to granodiorite in the margins. The southwest margin is more mafic than other parts and approaches quartz diorite in composition. Specific gravities of modally analyzed specimens range from 2.62 to 2.69 in the quartz monzonite core and from 2.69 to 2.82 in the granodiorite rim. (See fig. 23 for specimen locations and table 6 for specific gravities.) Modal analyses show that the plagioclase content ranges from 24 to 64 percent (fig. 28; table 6). The cause of the strong zonation has not been estab- lished. The presence of small masses of older mafic rocks around the margins suggests the possibility of contamination and hybridization by these rocks. Con- tamination of other intrusives, for example the south- ern part of the Chickenfoot Lake mass of the Lamarck granodiorite, by earlier mafic rock is demonstrable. However, this hypothesis seems incompatible with the presence of almost uncontaminated quartz monzonite in the southern part of the granodiorite of McMurry Meadows adjacent to large inclusions of hornblende gabbro. Many other plutons in the mapped area ex- hibit systematic compositional zoning, though none through as wide a range as the granodiorite of Mc- Murry Meadows, and several lack mafic rocks around their margins. The best explanation for zoning of in- trusive rocks where hybridization cannot be invoked is differentiation during cooling. Hand specimens of rock of quartz monzonite com- position from the pluton usually can be distinguished by their texture and mineral content from those of granodiorite composition. Commonly those of quartz monzonite composition are porphyritic, containing con- spicuous phenocrysts of microcline perthite and not more than 1.5 percent of hornblende. Specimens of granodiorite composition, on the other hand, are equi- granular and contain as much as 10 percent hornblende. Furthermore, much of the hornblende in the grano- diorite contains augite cores, whereas no augite was found in the hornblende of the quartz monzonite. An exception is specimen 9 (the chemically analyzed speci- men), which on the basis of the modal content of plagio- clase and K feldspar would be classed as calcic quartz monzonite, but which has an equigranular texture iden- T2 tical with that of the granodiorite specimens and con- tains hornblende having augite cores. Although the general appearance of the rocks sug- gests that the presence or absence of microcline perthite Quartz Potassium feldspar (including perthite) Plagioclase FicuRE 28.-Plot of modes of the granodiorite of McMurry Meadows on quartz-K feldspar-plagiocase diagram. GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA phenocrysts determines whether the rock is quartz mon- zonite or granodiorite, the plot of modes in figure 28 indicates quite clearly that difference in the amount of plagioclase is of greater significance. The plagioclase in both granodiorite and quartz monzonite is deeply zoned though about the same in compositional range. The central body generally is zoned within the limits of An», to An,, although the range in some specimens is as great as An», to An;,. Rims as sodic as Ans, and tiny cores as calcie as An,, to An;, are present locally. Two kinds of porphyritic texture are exhibited by the quartz monzonite, a common kind in which the phenocrysts are of perthitic microcline, and a less com- mon kind in which quartz, plagioclase, and K feldspar phenocrysts occur in a granoblastic groundmass of the same minerals plus biotite and accessory minerals. As with the other granitic rocks, the K feldspar pheno- crysts appear to have formed late, because they enclose plagioclase, hornblende, and magnetite and in a few places penetrate in thin veinlets into quartz. On the other hand, textural relations indicate that in rock that contains phenocrysts of plagioclase and quartz as well as K feldspar, the phenocrysts crystallized earlier than Tapur 6.-Modal analyses of the granodiorite of McMurray Meadows, in volume percent [Location of specimens is shown on fig. 23] Horn- Percent anorthite in plagioclase Specimen Specific | Quartz K Plagio- | Biotite | blende and Remarks gravity feldspar clase and _ |secondary Augite | minerals Rim Body Core 2.70 20. 3 28.0 50. 4 4.2 1.4 0.7 22, 28 82,86 Equigranular; augite cores in hornblende. 2. 74 16.3 17.3 47.8 10.1 6. 6 1.89 18, 25 30, 36 40, 44 0. 2. 66 12.0 49.6 20.3 6,6 2-0 -o hence 20, 24 27,80 [ els. Porphyritic; large and abundant microcline perthite phenocrysts. 2.74 16.0 17.7 45.2 13.0 6.2 1.8 23, 20 21, 30 45 | Equigranular; augite cores in hornblende. 2. 65 24.9 31.9 34.2 5.9 1.3 1.8 4, 2 80,80 J........_. Porphtyritic; large microcline perthite pheno- crysts. 2.12 11. 4 55.5 30. 8 1.6] hrd onl PLI eis ccie. Equigranular, but with abnormally high content of microcline perthite. 2.74 16.5 15.8 47.3 10.3 7.9 2.2 30, 33 clo Equigranular; Augite cores in hornblende. 2.64 38.1 30.0 28.5 4.9 1.5 1.8 15,19 9/07 Porphtyritic; large microcline perthite pheno- crysts. 2. 68 28.5 27.6 41.0 4.3 2.5 1.1 28, 27 32, 37 40 | Equigranular; augite cores in hornblende. 2. 69 21.3 19.9 42.0 11.9 2.9 1.9 21, 27 33, 37 42,45 | A few large perthite phenocrysts; hornblende contains augite cores. 2.72 15.1 13. 4 57.3 9. 4 4.7 0.1 17, 29 Equigranular; augite cores in hornblende. 2.71 20.1 21.7 44.6 7.8 3.9 2.0 17, 20 Do. 2.175 14.2 21.8 43.3 14.9 4.1 1.7 20, 28 Do. 2.71 23.9 31.8 32. 4 $10 [. 2.0 9, 21 Porphyritic; large microcline perthite pheno- crysts. 2. 60 31. 5 33.7 26.6 5. 4 0. 4 2. 4 18, 20 Porphyritic; plagioclase, perthite, and quartz in two generations; groundmass allotriomorphic. 2.82 6. 9 5.1 64. 4 9. 4 10.0 4.2 33 Equigranular; high color index; hornblende contains augite cores; high plagioclase content gives rock subpanidiomorphic texture. Iris.. 2.77 17.3 10.7 56. 3 8.0 - 5.9 1.8 30, 36 «0,50 Equigranular; high color index; hornblende contains augite cores. IBL - 2. 63 27.2 41.6 21.3 2.1 13, 25 S4 e Porphyritic, plagioclase quartz, and perthite in two generations; groundmass allotriomorphic. 2.62 32.3 33.9 24.9 7.2 0.5 1:1 20, 30 82,80 Do. Average. .. 2.10 20. 5 26. 4 40.1 8. 0 3.1 1.00] 221004 ee Hes (CSIL | se. NAL 1 Standard chemical analysis, specimen 9 Norm, specimen 9 Lab. No. 53-1301sed. Analyst: L. M. Kehl Weight percent | Weigh? ta I Fei Pleco seen 18. 90 BOH ..in f) ”5:fo n tlle ds (Plagioclase composition Ang:) BSOE. Nena GEOLOGY OF THE BATHOLITH 78 the accompanying allotriomorphic granular ground- mass. Even in such rocks, however, the marginal parts of K feldspar phenocrysts not uncommonly enclose rounded quartz grains, a relation which indicates that the phenocrysts continued to grow during the crystal- lization of the granoblastic groundmass. The granodiorite of McMurry Meadows is in contact with only two intrusives other than hornblende gabbro. It is intrusive into the Tinemaha granodiorite and is intruded by dikes of quartz monzonite similar to the Cathedral Peak granite. Its position relative to the Tinemaha granodiorite suggests that it crystallized from the core magma of the Tinemaha granodiorite fol- lowing magmatic movement that caused the intrusive contact between the two formations. WHEELER CREST QUARTZ MONZONITE The Wheeler Crest quartz monzonite is in a single mass that crops out principally in the steep eastern face of Wheeler Crest. It underlies a little more than 17 square miles within the mapped area and extends from the north edge of the Mount Tom quadrangle south across Pine Creek into the lower northeastern slope of Mount Tom. Typical quartz monzonite is exposed on both sides of the entrance to Pine Creek Canyon, and this area can be considered the type locality. Most of the quartz monzonite contains conspicuous phenocrysts of potassium feldspar, which are set in a medium-grained hypidiomorphic-granular groundmass (fig. 21E). The groundmass minerals commonly are 2 to 4 mm across, and the phenocrysts, many of which are euhedral tabular crystals, average about half an inch in thickness and range from 1 to several inches in maximum dimension. - Fresh surfaces are light gray, and the color index averages about 12, but ranges from a little less than 5 to 18 (table 7). Porphyritic facies are distinctive in appearance and superficially resemble only porphyritic facies of the quartz monzonite similar to the Cathedral Peak granite, which, however, is a much more felsic rock, and the Tinemaha granodiorite, which is more mafic. - By decrease in the abundance of phenocrysts, the porphyritic rock grades into equi- granular rock which has a texture identical with that in the groundmass of porphyritic rock. The dark min- erals, biotite and hornblende, are evenly scattered in small clusters through the rock, but in concentrations along the margins of phenocrysts of K feldspar. In- dividual grains are small, generally less than 1 mm across, and anhedral. Locally, the quartz monzonite contains irregular, fine- grained, dark-colored aggregates as much as an inch in the greatest dimension, which consist chiefly of biotite 135-925 0O-65--6 plates and lesser amounts of accessory minerals. These aggregates are thought to be small inclusions of schist or pelitic hornfels. In most places the quartz monzonite has a primary foliation that is marked by planar orientation of ovoid clots of mafic minerals and by lenticular mafic in- clusions. In a few places a secondary gneissic folia- tion is shown by layers of hornblende and biotite that lie along closely spaced shears. Modal analyses were made of 16 specimens, and one specimen was analyzed chemically. The plot of the modes on the triangular diagram (fig. 29) shows that the ratio of quartz to perthitic K feldspar is variable but averages about 1 to 1, and that the content of pla- gioclase is variable. Potassium feldspar is present as anhedral grains in the groundmass as well as in phenocrysts. Albite is regularly distributed in wavy streaks of about the same size and density in all the crystals of K feldspar; this distribution indicates that the albite was exsolved from the host crystal. Both Carlsbad twinning and the quad- rille structure characteristic of microcline are present in some crystals, but many exhibit neither. The plagio- clase in most specimens is zoned andesine having an average composition of about but the plagioclase in specimens from the northernmost part is more sodic. Many individual grains are zoned through determinable ranges of as much as 12 percent An. The plagioclase generally is more sodic toward the margin, but in some crystals minor oscillations are superimposed on the gen- eral trend. In most specimens the plagioclase is sub- hedral, but in specimen 12 (table 7), which is from a dike, much of the plagioclase is euhedral and the texture of the rock is panidiomorphic granular. Both hornblende and biotite are notably ragged as seen in thin section, and the hornblende commonly en- closes many tiny rounded plagioclase grains. Minor accessory minerals are magnetite and ilmenite, apatite, sphene, allanite, and zircon. Common alteration prod- ucts are chlorite and epidote. Most of the specimens of the quartz monzonite that were studied contain abundant evidence of cataclasis and recrystallization. This evidence includes fractured and dislocated grains, fine granoblastic mortar between many grains and across some, extensive myrmekite along boundaries between perthite and plagioclase, granoblastic texture in quartz masses that appear to pseudomorph primary quartz crystals, and undulatory extinction and strain shadows in quartz that has not ° been reduced to granoblastic aggregates. Many bound- aries between primary grains are occupied by a fine granoblastic mortar of quartz and feldspar together with small amounts of the mafic and accessory minerals. 74 Some zones of granoblastic mortar cut across individual crystals. The granoblastic mortar zones commonly coa- lesce in such a way as to show that the rock has been cut by through-going shears. In some sheared rocks the segregation of biotite and hornblende along the Quartz 4 6 ¢ a # 1-71? &.1; Aap a ag". 12+ (norm 10) *7 14, s Plagioclase Potassium feldspar FIGURE 29.-Plot of modes of Wheeler Crest quartz monzonite on quartz-K feldspar-plagioclase diagram. Modes were determined from stained rock slabs. GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA shears, presumably by a process of metamorphic differ- entiation, gives these rocks a secondary gneissic folation. Boundaries between grains of plagioclase and K feldspar are more commonly occupied by vermicular myrmekite than by granoblastic mortar, but the con- tinuity of myrmekite with zones of granoblastic mortar indicates that cataclasis along grain boundaries was a factor in its origin. The presence of "cats paws" of myrmekite that embay the contiguous perthite indicate that the myrmekite formed, in accordance with classi- cal theory, by replacing potassium feldspar (Tyrrell, 1929, p. 94). The areas of granoblastic quartz probably are prod- ucts of the recrystallization of fractured primary quartz crystals, but some masses of granoblastic quartz may have been precipitated from solutions. - Strain shadows in quartz are common. In most specimens the strain shadows are in a polygonal pattern, but in some speci- mens they are in the form of wavy lines that are not only parallel within individual grains but which are also parallel throughout a thin section. A few quartz grains exhibit two sets of shadowy lines that intersect at a wide angle and which superficially resemble micro- cline twinning. Locally the acute angle between the two sets is bisected by fractures that are sealed with Tast® 7.-Modal analyses of Wheeler Crest quartz monzonite, in volume percent [All modes were determined from stained slabs. Location of specimens is shown on fig. 26] Percent of anorthite in C Specific Total plagioclase Specimen gravity Quartz K feldspar | Plagioclase mafic Remarks Rim Body Core 2. 61 30.7 27.8 38. 9 BB I. icc A{ si 2.62 39. 4 26. 4 30. 2 4.0 4 14-20 [........ Porphyritic; phenocrysts smaller than in typical rock; rock unusually felsic. 2. 64 24.7 39.8 28. 4 12. 2. 60 30.7 | ~ 24.6 34.7 10. a : . 2.62 30.9 19.0 41.4 8. -| Equigranular; foliated; finer grained than usual and unusually felsic. | _ 2. 64 33.0 27.0 82.5 7+ Somewhat porphyritic. 2. 58 22.3 33. 4 31.6 12. Porphyritic; quartz is in ovolds about 14 inch across; notably cataclastic. 2. 64 36.6 30. 8 28. 4 9. Porphyritic; some cataclasis, not severe; aggregates of biotite, sphene, and magnetite. 2. 67 32.5 27.5 32. 2 POll‘phg'ritic, but phenocrysts anhedral; notably cata- clastic. 2. 68 25.2 27.8 39.0 Equigranular; moderate cataclasis; finer grained than typical rock. G A ,,,,,,,,,,,, 30.5 28. 4 36.3 Porphyritic; some granoblastic mortar, but not in abundance. p 2.74 18.8 14.8 45.5 20.9 Pariidiomorphic granular with finer grain than usual; a dike rock. 2. 68 27.8 20. 4 39.3 12.5 Porphyritic; extensive cataclasis. 2.67 30. 4 14.3 48.5 10.5 Do. 2. 64 26.9 25.2 36. 4 12.2 % Do. f 2.70 26. 2 21.2 37.2 15.4 Equigranular; extensive cataclasis. Average.... 2.65 20.3 25.3 35.3 10A TL. .<. BRCA ci laa selec n 1 Standard chemical analysis, specimen 11 Norm, specimen 11 [Lab. No. 53-1205scd. Analyst: L. M. Kehl] Weight Weight Weight percent percent percent 3:23 0: 2? (Plagioclase composition Ansi.s) 1.03 . 35 1. 38 . 03 .78 .10 2. 86 . 08 3. 44 BaO: lee Ase meals 3. 69 --- 99. 8 GEOLOGY OF THE BATHOLITH 70 secondary quartz of a different orientation than that in the enclosing grain. The Wheeler Crest quartz monzonite is intruded by all the plutonic rocks with which it is in contact, except quartz diorite and hornblende gabbro, and is the oldest major intrusive in the area north of Big Pine Creek. Finer grained quartz monzonite and the Round Valley Peak granodiorite send dikes into the Wheeler Crest. Marginal to the dike of alaskite similar to the Cathedral Peak granite, which extends along the east face of Wheeler Crest and clearly intrudes the Wheeler Crest quartz monzonite, are many thin fine-grained felsic dikes that dip gently toward the main dike. These satellitic dikes appear as thin white lines when seen from U.S. Highway 395 along Sherwin Grade in the forenoon, when the sun lights up the eastern face of Wheeler Crest. Evidence that the Tungsten Hills quartz monzonite intrudes the Wheeler Crest quartz monzonite was found on the northwest side of Mount Tom, on the west side of Elderberry Canyon. The contact there is sharp but featureless; it lacks dikes and other conspicuous diag- nostic features, although a few angular inclusions of Wheeler Crest quartz monzonite a few feet across were found close to the contact in Tungsten Hills quartz mon- zonite. Within 2 to 4 feet of the contact the Tungsten Hills quartz monzonite is finer grained than usual and has a mottled appearance caused by small rock frag- ments and phenocrysts of Wheeler Crest quartz mon- zonite. The Wheeler Crest quartz monzonite is cut by numerous shear zones that are generally about parallel with the contact, and along some of these the rock has been reduced to an augen gneiss. Shear zones were observed half a mile or more away from the contact, but they are increasingly abundant as the contact is ap- proached. These relations suggest that the shearing resulted from the emplacement of the Tungsten Hills quartz monzonite. The Wheeler Crest quartz monzonite resembles quartz monzonite similar to the Cathedral Peak granite where both rocks are porphyritic. However, the Wheeler Crest is darker colored and contains tabular phenocrysts of K feldspar, whereas phenocrysts in porphyritic quartz monzonite similar to the Cathedral Peak granite characteristically are more equant. The younger age of the quartz monzonite similar to the Cathedral Peak granite is clearly indicated by the fact that it intrudes the Round Valley Peak and Tungsten Hills quartz mon- zonites, both of which are younger than the Wheeler Crest quartz monzonite. The Wheeler Crest quartz monzonite also resembles the Tinemaha granodiorite, but is more silicic and its phenocrysts are more nearly euhedral. Nevertheless, | they may be temporal equivalents, for each rock is the oldest intrusive in its area except for quartz diorite and hornblende gabbro. ROUND VALLEY PEAK GRANODIORITE The Round Valley Peak granodiorite is represented within the mapped area by a single mass, which lies in the northwest corner of the Mount Tom quadrangle and extends into the adjoining three quadrangles. It underlies a little more than 18 square miles within the mapped area, and its total area is about 40 square miles. Good exposures can be examined along both sides of upper Rock Creek. The intrusive was mapped in the Casa Diablo quadrangle as granodiorite of Rock Creek by Rinehart and Ross (1957), and this usage was followed in the north half of the Mount Abbot quad- rangle by Sherlock and Hamilton (1958). Adoption of a formal name became necessary when a correlative mass was found farther to the northwest in the Mount Morrison quadrangle by Rinehart and Ross (1964, p. 44-47). Because Rock Creek has long been preempted in formal stratigraphic nomenclature, the name Round Valley Peak granodiorite was given the rock (Bateman, 1961); Round Valley Peak is a high point along Wheeler Crest, which is composed of granodiorite of typical appearance. The granodiorite is notably equigranular and me- dium grained (fig. 2170). Both biotite and hornblende are evenly distributed in discrete euhedral crystals that give the rock a distinctive "tidy" look. The average grain size is about 3 mm, but the grain size is about 2 mm in the eastern part, and 3 to 4 mm in the south- western part. The feldspars are white and quartz light gray, and the rock has an overall light-gray hue. The average color index of 13 modally analyzed specimens is 12.7, but the finer grained rock in the eastern part is darker than coarser grained rock in the southwest- ern part (table 8). The specific gravities of the 13 specimens range from 2.65 to 2.73; samples from the darker and finer grained eastern part are heavier, mostly above 2.7, whereas those from the southwestern part are less than 2.7. Foliation parallel to contacts with older rocks is pro- nounced near the eastern and southern contacts, and is progressively less conspicuous away from them. The foliation is shown best by mafic inclusions, which ap- pear in outcrop to be from a few inches to 2 feet across and from less than an inch to several inches thick at the middle. The inclusions decrease in abundance and are progressively less flattened with distance from con- tacts with older rocks. Near contacts with older rocks the foliation is also shown by orientation of the mafic minerals, but granodiorite more than a few hundred 76 feet from these contacts appears structurally isotropic. The modes group rather closely on a quartz-K feldspar-plagioclase diagram (fig. 30). The average mode is about 27 percent quartz, 19 percent K feldspar, 44 percent plagioclase, and 10 percent mafic minerals. The small content of K feldspar probably is partly the result of the relatively large amount of biotite (about 7 percent) in the rock, which contains about two-thirds as much K;0 as K feldspar. In thin section the texture of the granodiorite can be seen to be hypidiomorphic granular. No mortar structure or other evidence of cataclasis was observed. Biotite and hornblende are in euhedral to subhedral crystals; plagioclase is subhedral ; and K feldspar and quartz are anhedral. The body of most plagioclase crystals generally is unzoned or only slightly zoned in the compositional range of An», to Ans. However, specimens 12 and 13 (table 8) are of composition An; and An,. Small cores of about are present in some crystals, and most crystals are bordered by more sodic plagioclase that is zoned from Ans on the inside to An,, on the outside. Undulatory extinction in quartz is rare. Hornblende is of the ordinary kind. The Round Valley Peak granodiorite is clearly younger than the Wheeler Crest quartz monozonite and older than quartz monzonite similar to the Cathedral Peak granite. Dikes of Round Valley Peak granodio- rite intrude the Wheeler Crest quartz monzonite, and GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA dikes of quartz monzonite similar to the Cathedral Peak granite intrude the Round Valley Peak granodiorite. Intrusive relations with the Tungsten Hills quartz mon- zonite are less certain, although the Tungsten Hills quartz monzonite is believed to be the younger. At the contact, older hornblende gabbro, Round Valley Peak granodiorite, and Tungsten Hills quartz monzonite are all involved in a mixed zone. In a few places, dikes of probable Tungsten Hills quartz monzonite intrude the Round Valley Peak granodiorite. Quartz 9 § 2. 1. *% 3% 7 J" " 3% ’10 gxl (norm 5)! Plagioclase Potassium feldspar FIGURE 30.-Plot of modes of the Round Valley Peak granodiorite on a quartz-K feldspar-plagioclase diagram. TaBLE 8.-Modal analyses of Round Valley Peak granodiorite, in volume percent [All modes were determined from stained slabs. Location of specimens is shown on fig. 23] Specific Total Percent of anorthite in plagioclase Specimen gravity Quartz K feldspar | Plagioclase mafic Remarks Rim Body Core 2.78 25.1 11.2 49.0 14.7 21-30 80 |. Equtfranular hy'pldiomorphlc, typical of north east part of mass 2.71 21.2 19.1 48.6 11.1 21-28 Equigranular hypxdxomorphic, typical. 2.70 31.2 18. 4 42.0 8. 4 21-27 Do. 2. 67 28. 4 15.4 47. 4 8.8 22-30 Do. 2.71 28.3 16.1 39.9 15.7 22-30 Do. 2. 68 26.2 16.7 44.9 12.2 21-28 Do 2.70 26.8 13. 4 50.1 10.7 21-26 2. 65 30.3 290. 5 32.0 8.2 30 Equigranular hypidiomorphic; slightly coarser and more felsic than above. 2. 68 31. 2 11.2 47.0 10. 6 20 T Lenee dci Do. 2. 69 24.0 20. 9 48.5 6. 6 24-29 37 45 Do. 2. 68 28. 4 25.5 43.2 7.9 30 SS- X Do. 2. 66 24.9 28.8 41.8 9. 5 21-25 32 49 Do. 2. 66 27.1 21.7 42.9 7.7 21-25 09 Do. Average.... 2. 69 26.8 18.7 44. 4 10. 1 |: . 2.220 dE EER (eva vasa tn a ane 4 Standard chemical analysis, specimen 5 Norm, specimen 5 [Lab. No. 53-1302s¢d. - Analyst: L. M. Kehl] weight PMS Weight percent Weight percent 6 (Plagioclase composition Ans) 3 GEOLOGY OF THE BATHOLITH 7T. In composition and intrusive relations, the Round Valley Peak granodiorite is similar to the Lamarck granodiorite, and the two possibly should be considered the same formation. The Lamarck granodiorite is gen- erally somewhat coarser grained than the Round Valley Peak granodiorite and in some parts is subporphyritic to porphyritic. However, the Lamarck mass of the Lamarck granodiorite constitutes a much larger body than the Round Valley Peak granodiorite, and the difference in the sizes of the masses may explain the differences in grain size and texture. LAMARCK GRANODIORITE The Lamarck granodiorite is in two masses that lie along the west and southwest sides of the mapped area. The larger one, called the Lamarck mass, underlies about 54 square miles within the mapped area. The smaller one, called the Chickenfoot Lake mass following the usage of Sherlock and Hamilton (1958) in the ad- joining Mount Abbot quadrangle, underlies only 2.7 square miles of the area discussed in this report. Both masses extend west or southwest beyond the limits of the mapped area. The type locality is in the cirques east of Mount Lamarck, but typical rock crops out in all the cirques at the head of Bishop Creek. The mapped part of the granodiorite is chiefly within the Mount Goddard quadrangle, and extends into the southwest corner of the Big Pine quadrangle. The Lamarck mass is elongate and trends northwestward. Even though the contact on the southwest side was mapped only near the south end, it is obvious that the mass is widest near the north end and that it thins southward. In the Bishop Creek drainage it is at least 6 miles wide whereas in the Big Pine quadrangle, where the contacts on both sides are exposed, it averages little more than a mile wide. The Chickenfoot Lake mass is elliptical, the longer axis trending northwestward. The total outcrop area is about 7 square miles, most of which lies within the Mount Abbot quadrangle to the west of the mapped area. Although this mass is correlated with the Lamarck mass, the correlation is by no means certain, because the rock is generally finer grained and in the south part is darker colored than typical rock. The rock in the Lamarck mass appears in the field to be remarkably homogeneous in both composition and texture, except in the thin southeastern part, which is more felsic and appears somewhat porphyritic. The change in color index and texture between the northern and southern parts takes place gradually in the vicinity of Hurd Peak; the rock at Bishop Pass is identical in appearance with rock in the vicinity of the Palisade Lakes. Modal analyses (table 9) show that the north- ern part (fig. 26) is compositionally zoned and that a broad core area has a lower color index and specific gravity than the margins, though not as low as the southeast part. Rock typical of the main northern part of the mass can be collected along the roads into any of the forks of Bishop Creek, west of the Bishop Creek pendant. The rock is medium grained and generally seriate; less commonly, it is equigranular (fig. 210). ~The average grain size is 3 to 4 mm., but K feldspar is in grains as much as a centimeter across in the longest dimension. The seriate texture is especially conspicuous in the thin southeastern part, where in hand specimen the rock appears porphyritic. Biotite and hornblende generally are evenly distributed both in clusters and in discrete crystals. Both minerals commonly are subhedral, but plates of biotite and prisms of hornblende are present. The color index of the whole mass averages 11.5, but ranges from 4.4 to 18.4. The average color index of specimens 27 to 33, from the southeastern part of the mass (table 9), is 6.5 and the average of the northern part is 12.2. Specific gravity varies in accordance with the color index (table 9). The measured range in spe- cific gravity is from 2.63 to 2.73. In the margins of the main northern part of the mass the range is from 2.70 to 2.73; in the core it is from 2.65 to 2.69; and in the southeastern part it is from 2.63 to 2.65 except for specimen 28 which has a specific gravity of 2.68. Commonly the rock has a conspicuous planar folia- tion, which is best shown by numerous lenticular mafic inclusions, but which also is shown by planar orienta- tion of biotite and hornblende. The foliation is most conspicuous in the margins of the intrusive; the folia- tion becomes less conspicuous and the number of mafic inclusions diminishes toward the interior of the intru- sion. West of Chocolate Peak and adjacent to the north end of the Inconsolable granodiorite the Lamarck gran- odiorite contains clusters and individual plates of bio- tite half an inch or more across, and this rock is repre- sented separately on the geologic map (pl. 1). The large biotite plates are probably the product of hy- bridization of the magma with sediment, a hypothesis that is supported by the presence of small unassimilated inclusions of calcareous and siliceous metamorphic rock. The rock in the Chickenfoot Lake mass is finer grained and in the southern part is much darker than typical rock from the Lamarck mass. The finer grain size may be a function of the smaller size of the Chick- enfoot Lake mass; the increasing abundance of mafic minerals in the southern part is almost certainly the result of assimilation of hornblends gabbro which lies along the south edge. A sharp contact can be found in 78 most places between the Chickenfoot Lake mass and the hornblende gabbro but only after careful examina- tion of the rocks. The Chickenfoot Lake mass is in- creasingly contaminated toward the south, and at the contact the rock is almost indistinguishable in hand specimen from the hornblende gabbro. The average color index of four modally analyzed specimens is 16.5, and specimens 3 and 4 from the strongly contaminated part exceed 20. Thin sections show that the Lamarck granodiorite generally contains about equal amounts of quartz and K feldspar and variable amounts of plagioclase. Al- though the rock is designated granodiorite, the rock in the southeastern part and much of the core of the north- ern part of the Lamarck mass is quartz monzonite (table 9). Most thin sections show little evidence of cataclasis. Quartz GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA Quartz is in anhedral grains that have undulatory extinction, but only locally does it comprise a grano- blastic mosaic. Commonly the K feldspar is perthitic and shows the quadrille structure of microcline, but some grains show no quadrille structure, and a few are not perthitic. The K feldspar is in interstitial or an- hedral grains of small to medium size. Plagioclase commonly is in subhedral grains that exhibit a wide range of sizes. Most grains are zoned, but some are not. The bodies of plagioclase grains from the Lamarck mass (not including the felsic south- ern section) are generally zoned in the range of Ans, to Ans. Unzoned plagioclase from the same rock gen- erally has an An content of 38 to 40 percent, figures that agree well with the normative composition of the plagioclase in specimen 9 (table 9) of 37 percent. In the felsic southern part of the Lamarck mass the plagio- Quartz 33 15 £. ._ M48¢ 21 162] - 2% 22" 7 {noth 22) 12, - , 5 t cock 17" Plagioclase Potasium feldspar Chickenfoot Lake mass Quartz 233 .a #8 . - "29 30 32 Plagioclase Potassium feldspar Lamarack mass (main part) Quartz Plagioclase Potassium feldspar Lamarack mass (southern part) Plagioclase Potassium feldspar Composite FIGURE 31.-Plots of modes of Lamarck granodiorite on quartz-K feldspar-plagioclase diagrams. GEOLOGY OF THE BATHOLITH clase is progressively more sodic southward, and the average compositional range in the bodies of grains from the four most southerly specimens (specimens 80 to 33 of table 9) is Ani;.: to Ans;.,. The plagioclase in specimens from the Chickenfoot Lake mass is errati- cally zoned, the cores as well as the rims varying widely T9 in composition, but the average is close to that in the main part of the Lamarck mass. The plot of modes (fig. 31) produces an elliptical field elongate in the direction of the plagioclase corner. The field shows about the same amount of scatter as the plots for the Inconsolable granodiorite and the TABLE 9.-Modal analyses of Lamarck granodiorite, in volume percent [Where the content of biotite, hornblende, and accessory and secondary minerals is shown separately, the mode was determined from a thin section. 'Where only the total content of mafic minerals is shown, the mode was determined from a stained slab. Location of specimens is shown on fig. 26] Acces- Percent of anorthite in sory plagioclase Specific K feld-| Plagio- Horn- | and Total Specimen Gravity Quartz] spar | clase | Biotite | blende |second-| mafic Remarks ary min- Rim Body Core erals Tel 2. 67 28. 8 31. 9 $1.9 |e lea aus dav lens A 20-45, 38, 40 |.______. Porphyritic; a few potash feldspar phenocrysts; hornblende ragged and poikilitic. NAY 2.71 25. 5 20. 9 $7.9 {nile vely 16. 3 33 30-58, 30 |.__..._. Fine grained and equigranular; foliated owing to Bartlal parallel orientation of plagioclase and ornblende. HES 2.72 16. 4 34.7 BDB ssc cite [eee deer 13. 6 34 28-88, 38 |________ High mafic mineral content; foliated; seriate; largest crystals are plagioclase, AIC cee 2.72 15.8 20. 9 MAB [ee EAO. eas dull 19.0 34-49, 46 |_______. High mafic mineral content; porphyritic with plagioclase - phenocrysts in - allotriomorphic groundmass. 21.6 27.1 19.8 18.3 Seriate; large slightly strained quartz grains. 25.8 12.3 Equigranular; foliated. 22.9 22.2 Do. 28.0 18. 3 Seriate. 23.1 24.7 Porphyritic; phenocrysts are plagioclase and potash feldspar; granoblastic mortar is quartz. 24.1 19.1 Equigranular; foliated; some granoblastic mortar; quartz in granoblastic mosaic. 25.1 35.1 Equigranular; - nonfoliated; some - granoblastic mortar; quartz in granoblastic mosaic. 21.5 17.8 Seriate; large perthite, plagioclase, and quartz grains. 28. 0 29. 5 Seriate; large strained quartz grains; some grano- blastic mortar and myrmekite. 26. 5 18. 6 Seriate; large microcline perthite grains. 20. 4 21. 2 Do. 28. 5 17.4 Do. 15. 4 17.9 Seriate. 25.6 19.0 Do. 18. 5 20. 9 Do. 22.9 23. 9 Seriate, foliated. 24.9 22.6 Set-mm large quartz, microcline, and plagioclase grains. 28. 6 24.0 27-38, 40-46 Seriate. 28. 8 18. 6 25-39, 33 Seriate; quartz grains strained in layers. 14.7 26. 5 20-40 Porphyritic; finer grained than usual; plagioclase phenocrysts in allotriomorphic granular ground- mass. 23.3 20.6 Seriate; quartz grains strained in layers. 20. 3 16. 4 -| Porphyritic; finer grained than usual; plagioclase phenocrysts; microcline poikilitic. 25. 2 18. 8 Seriate. 28.1 21.0 28. 0 19.9 Seriate to porphyritic; large perthite crystals. 26. 6 34. 9 -| Porphyritic; large pink microcline perthite pheno- crysts. 27.0 24.0 Equigranular; abundant microcline perthite. 31. 2 30. 3 Equigranular. 27.6 30.3 Seriate. ’ 31.0 19. 6 Seriate; granoblastic mortar common between grains. Subaverage 2. 65 28. 6 26.5 38.2 |. 6.7 rele cules Average.... 2. 69 28.9 22.8 CLD |e 12.0 122. alee: uve 1 Standard chemical analysis, specimen 28 [Lab. No. 53-1300scd. Analyst: L. M. Kehl] Norm, specimen 28 Weight percent 22.62 22.16 26.72 (Plagioclase composition Ans?) 15.84 1.83 2.09 .90 .85 80 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA Wheeler Crest quartz monzonite. The rock there could as well be considered quartz monzonite as granodiorite, despite a color index that in some specimens is as high as 20. The Lamarck granodiorite is younger than the In- consolable and Tinemaha granodiorites, and older than the granodiorite of Cartridge Pass, the Palisade Creek mass of quartz monzonite similar to the Cathedral Peak granite (fig. 13), and the Basin Mountain mass of Tungsten Hills quartz monzonite. It contains inclu- sions of the Inconsolable and Tinemaha granodiorites and also sends dikes into both intrusives. The grano- diorite of Cartridge Pass contains inclusions of La- marck granodiorite; dikes from the Palisade Creek mass of quartz monzonite similar to the Cathedral Peak granite penetrate the Lamarck granodiorite southwest of the Palisade Lakes, and dikes of the Basin Mountain mass of Tungsten Hills quartz monzonite penetrate the Lamarck granodiorite along the North Fork of Bishop Creek in the vicinity of Loch Leven. The Lamarck granodiorite resembles the Round Valley Peak granodiorite, which occupies a similar position in the intrusive sequence, but which is some- what finer grained and is equigranular. The Lamarck granodiorite is much like the Half Dome quartz monzo- nite of the Yosemite region (Calkins, 1980, p. 120). The two rocks are of about the same grain size, though the Half Dome may be a trifle coarser textured in some places, have the same range in color index, and have euhedral crystals of biotite and hornblende distributed in the same ratio and in the same pattern. GRANODIORITE OF DEEP CANYON Two masses of dark-colored granodiorite having a combined area of about a square mile crop out in the eastern part of the Tungsten Hills, in the Deep Canyon area, and several small patches of similar rock lie along the north edge of the Tungsten Hills (pls. 2, 3; fig. 23). In hand specimen the granodiorite appears equi- granular, the average grain size being about 1 mm. The color index is variable and ranges from about 10 to more than 20. The darkest grandiorite is in the easternmost part of the larger and more easterly of the masses along Deep Canyon. Within this mass the rock is progressively a lighter shade and coarser grained toward the west. The rock in the smaller masses re- sembles average rock in the largest mass. In thin section the rock can be seen to be seriate or faintly porphyritic rather than equigranular ; embayed and corroded crystals of plagioclase, hornblende, -and biotite, 1 to 2 mm long, are set in a finer grained allo- triomorphic-granular groundmass of quartz and per- thitic microcline. In some thin sections, optically con- tinuous masses of quartz several millimeters across can be seen to enclose plagioclase, hornblende, and biotite. Modal analyses of three thin sections suggest that plagi- oclase constitutes a little less than half of the rock, that quartz is more abundant than K feldspar, and that biotite is two to three times as abundant as horn- blende (table 10 and fig. 32). The central bodies of most plagioclase crystals are of composition Anse... They contain small cores as calcic as An,; and are rimmed with oligoclase of composition Ani-so. Potassium feldspar is somewhat perthitic and exhibits the quadrille structure of microcline. Quartz contains abundant tiny liquid or gaseous inclusions, and most grains extinguish irregularly. Biotite and hornblende have the usual properties for these minerals. Common accessories are magnetite, sphene, and apatite. The granodiorite is older than alaskite similar to the Cathedral Peak granite, and it probably is also older than the Tungsten Hills quartz monzonite. Evidences of these relations are that the small patches of the grano- diorite along the north edge of the Tungsten Hills are inclusions in alaskite similar to the Cathedral Peak granite and that the smaller and more westerly of the two masses along Deep Canyon appears to be an in- clusion in Tungsten Hills quartz monzonite. How- ever, relations along the contact between the mass of granodiorite at the east end of Deep Canyon and the Tungsten Hills quartz monzonite suggest that the age difference between these intrusives may be small and that the granodiorite may be, in fact, an early marginal phase of the quartz monzonite. The granodiorite grades westward toward the quartz monzonite from dark fine- grained calcic granodiorite to lighter colored, coarser grained, more silicic granodiorite, very similar to the adjacent quartz monzonite, which at the contact is finer grained than usual. The actual contact between the granodiorite and quartz monzonite is exposed at only a few places; in some it is sharp and in others it appears gradational. TUNGSTEN HILLS QUARTZ MONZONITE The Tungsten Hills quartz monzonite crops out dis- continuously in a northwest-trending belt that passes through the central part of the mapped area (pls. 1-4; fig. 33). The hill just west of Longley Meadow in the southwestern part of the Tungsten Hills has been desig- nated the type locality because it is readily accessible and the exposed rock is representative of most of the formation. Fresher rock of similar appearance is ex- posed in Grouse Mountain and east of Bishop Creek below the junction of the South and Middle Forks. GEOLOGY OF THE BATHOLITH 81 TABLE 10.-Modal analyses of granodiorite of Deep Canyon, in volume percent [Location of specimens is shown on figure 23] Acces- Percent anorthite in Specific K Plagio } Horn- | sory and plagioclase Specimen gravity | Quartz | feldspar clase Biotite | blende secpndafy Remarks minerals Rim Body Core freer -n 2.75 20. 2 9.0 47.7 12.3 6.7 40 52 | Equigranular, hypidiomorphic. enne nebo evens 2. 66 26.3 19.2 41. 5 7.7 2.0 3.3 21-26 44 48 Do. B iene 2. 69 24.5 16.2 47.0 8.0 2.3 2.0 21-30 36 51 | Equigranular, hypidiomorphic, nearly panidio- morphic. Average. ._ 2.70 23.6 14.8 45. 4 9.3 3:7 AA lenee eved Quartz Potassium feldspar (including perthite) Plagioclase FiGurE 32.-Plot of modes of granodiorite of Deep Canyon on quartz-K feldspar-plagioclase diagram. The Tungsten Hills quartz monzonite underlies about 120 square miles within the mapped area, and con- tinues westward into the Mount Abbot and Blackeap Mountain quadrangles. It includes the following named masses: Morgan Creek, Tungsten Hills, Basin Mountain, Bishop Creek, and Shannon Canyon (fig. 33). The individual masses are irregular in shape, and exhibit no general parallelism either with one another or with the long axis of the belt. Originally there were probably only two plutons, one lying west and another east of the Pine Creek pendant and the metamorphic rocks around and south of Mount Humphreys. The western pluton was composed of the Morgan Creek and Basin Mountain masses, which are separated from each other only by younger quartz monzonite similar to the Cathedral Peak granite, and the eastern pluton was composed of the Pine Creek, Tungsten Hills, Bishop Creek, and Shannon Canyon masses. The Pine Creek, Tungsten Hills, and Bishop Creek masses are separated from one another only by alluvial deposits and doubt- less form a single continuous mass in bedrock. The Shannon Canyon masses are separated from the Bishop Creek mass and from one another by younger intru- sives-granodiorite of Coyote Flat, alaskite similar to the Cathedral Peak granite, and finer grained quartz monzonite. With a few notable exceptions, the quartz monzonite is homogenous both in composition and in appearance. The exceptions are rock of finer grain size than is usual in the Morgan Creek mass and locally in the west side of the Pine Creek mass, light-colored albitized rock adjacent to the north and east margins of the Bishop Creek pendant, and calcic rock of granodiorite composi- tion in the west half of the Basin Mountain mass. The typical quartz monzonite, away from the margins, is medium-grained and medium light-gray on fresh sur- faces. Commonly it is porphyritic or subporphyritic, containing subhedral phenocrysts of perthitic K feld- spar that are as much as 3 centimeters in the longest ex- posed direction, parallel with the composition plane of Carlsbad twins, and 1 em across (fig. 21/). The mafic minerals, chiefly biotite but including a little horn- blende, are in small irregularly shaped crystals and clusters of crystals that are distributed evenly through the rock. Peripheral concentrations of mafic minerals commonly provide frames for the K feldspar pheno- crysts. More rapid weathering of the groundmass fur- ther accentuates the prominence of the phenocrysts. Rock in the margins of masses generally is finer grained than rock that is considered to be typical, and the K. feldspar phenocrysts are absent, or smaller and less obvious. About a mile southwest of the Aeroplane mine, rock of typical appearance was observed in sharp contact with rock having a slightly greater abundance of pheno- crysts, but, though exposures are good, the contact could be followed along the strike for only a few hundred feet. This contact is thought to be a minor internal contact within the quartz monzonite, caused by the local move- ment of magma along an already erystallized part. In most places the rock appears structureless, and planar foliation was mapped in only a few places. Mafic inclusions are scarce, and most of those that were observed are ovoid rather than flattened or spindle 82 18°45" GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA 118°30" 18°15" 37°30° [ G /\ 30> R3 Tungsten Hills mass o T1] Bishop el x m e oak EXPLANATION Albite granite facies Quartz monzonite facies [NLD Granodiorite facies 25 ®2.64 Specimen with number and specific gravity Shannon Canyon masses 0 Big Pine 37°00° 5 L 1 1 1 1 -o 5 MILES I FiGuRE 33.-Map showing the locations of modally analyzed specimens of Tungsten Hills quartz monzonite. GEOLOGY OF THE BATHOLITH 83 shaped. Joints, on the other hand, are conspicuous. Commonly they are widely and regularly spaced. In the southern part of the Tungsten Hills and especially at the type locality, the hill west of Longley Meadow, weathering along two sets of nearly vertical joints that intersect at very close to 90°, has produced a rectalinear pattern of deep slots. Bold rounded forms produced by weathering along the joints are characteristic of the quartz monzonite. The finer grain of the rock in the northeastern end of the belt, in the Morgan Creek mass and in the south- western part of the Pine Creek mass, seems to be related to dikelike forms which could have cooled especially rapidly. In the Morgan Creek mass the grain size of the rock decreases gradually toward the west. This gradation is observable along the trail to Pine Lake. At the contact with the Pine Creek pendant the grain size is about 2 mm; it decreases westward and at Pine Lake is less than 1 mm, although scattered perthite phenocrysts and clots of biotite and hornblende are as much as 4 mm across. A similar gradation exists in the western part of the Pine Creek mass, from finer grain in the tongue that extends south along Gable Creek to coarser toward the north and east. Much of the rock in the eastern and southeastern part of the mass is nearly as coarse as typical rock from the Tungs- ten Hills. Readily recognizable planar foliation in the Morgan Creek mass is evident chiefly in flattened small clots of mafic minerals. Typical Tungsten Hills quartz monzonite consists of roughly equal amounts of quartz, plagioclase, and perth- ite (table 11). Biotite is always present, generally in the range 3 to 8 percent, although some rocks con- tain as little as 1.3 or as much as 11.0 percent. Horn- blende, on the other hand, is absent in most specimens and where present exceeds 2 percent of the rock only in rock of granodiorite composition in the western half of the Basin Mountain mass. Common accessory min- erals are magnetite and ilmenite, sphene, apatite, allan- ite, zircon, and zirconlike minerals (possibly monazite and thorite). Epidote is present locally; other com- mon alterations are fine sericite in cores and selected zones of plagioclase, chlorite after biotite, and hematite or limonite after magnetite. Plagioclase generally is in subhedral zoned crystals. Most of the crystals measured are zoned through some part of the range Ans, to An;;; in some, a central zone is rimmed by albite or sodic oligoclase. Changes in composition are both progressive, from calcic toward the interior of the crystal to sodic toward the exterior, and oscillatory. Albite twins are common, and Carls- bad and pericline twins are less common. Perthitic K feldspar is both in large twinned pheno- erysts and in smaller interstitial masses. Much of it exhibits the quadrille structure diagnostic of micro- cline, but some shows no such structure. Commonly it contains about 10 percent albite in perthitic inter- growths. In some crystals the albite is in somewhat irregular but generally parallel lamellae, and in others it is in irregular patches. Phenocrysts of K feldspar commonly enclose euhedral to subhedral crystals of zoned plagioclase, hornblende, and magnetite, whereas smaller masses of K feldspar are interstitial to these minerals. Quartz generally is in large grains that either ex- hibit conspicuous strain shadows or are composed of a granoblastic mosaic of differently oriented compo- nents. Grains that show strain shadows and extinguish irregularly may also show a polygonal internal pattern near extinction. All gradations can be found from grains having undulatory extinction and polygonal strain patterns to grains that consist of granoblastic mosaics. Biotite generally is in groups of small plates ciated with the minor accessory minerals and with horn- blende if it is present. Commonly the biotite is pleo- chroic-X=grayish yellow, Y¥=Z=olive gray or mod- erate olive brown. Hornblende is usually in euhedral or subhedral prisms that are pleochroio-X=grayish yellow or moderate yellow, Y¥=dark yellowish green, Z= blue green. The results of cataclasis are evident in thin sections of most specimens from the two northernmost masses (the Morgan Creek and Pine Creek masses) and from the north part of the Basin Mountain mass. Else- where, only a few scattered specimens yield evidence of cataclasis. The cataclasis is shown by fine granoblastic mortar between grains, by myrmekite that is most abun- dant in the areas where granoblastic mortar is conspic- uous, and by strained or granoblastic quartz grains. The modes of 73 thin sections (not including the al- bite granite facies) show that the bulk of the rock is of quartz monzonite composition, except locally in the Tungsten Hills and in the western part of the Basin Mountain mass where the rock is close to granodiorite in composition (fig. 34; table 11). Samples from the western part of the Basin Mountain mass, whose modes fall in the granodiorite field, contain appreciable amounts of hornblende. Hornblende is characteristic of granodiorite rather than quartz monzonite, and these rocks contain 1.5 to 3.7 percent as compared with a max- imum of 1.5 percent among all the other modes from the intrusive. Recognition of the near-granodiorite composition of the west part of the Basin Mountain mass in conjunction with a nonporphyritic texture sug- 84 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA Quartz 8 13 n #3 2 Be 25 4. g (norms) 29 ra » Quartz Plagioclase Potassium feldspar | Plagioclase Potassium feldspar Morgan Creek and Pine Creek masses Basin Mountain mass Quartz Quartz a3 98 57 67 go 71, }70 , ©68 62 gs. | "8 40°66. 50.72 Plagioclase Potassium feldspar . Plagioclase Potassium feldspar Tungsten Hills and Bishop Creek masses Shannon Canyon and associated masses Quartz Plagioclase Potassium feldspar Composite FiGurs 34.-Plots of modes of Tungsten Hills quartz monzonite on quartz-K feldspar-plagioclase diagrams. GEOLOGY OF THE BATHOLITH 85 TABLE 11.-Modal analyses of Tungsten Hills quartz mongonite, in volume percent [Where the content of biotite, hornblende and accessory and secondary minerals is shown separately, the mode was determined from a thin section; where only the total content of mafic minerals is shown, the mode was determined from a stained slab. - Location of specimens is shown on fig. 33] Acces- Percent of anorthite in sory plagioclase Specific K Plagio- Horn- | and Total Specimen grav- | Quartz] feld- | clase | Biotite] blende | second-| mafic Remarks ity spar ary min- Rim | Body | Core erals 2.62 26. 4 27.0 40.0 5.0 Bi 16-34 Less than average grain size; granoblastic mortar. 2. 62 30.0 27.8 33.0 5.7 1.2 2.3 ; poul Recon 21-B4 |...._... Fine grained; groundmass either allotriomorphic granular or granoblastic. 2. 59 33. 4 32.0 30.0 $:0 {. 1.0 MOre Fine graiined; porphyritic groundmass allotriomorphic granular. 2.66 $1.2 27.4 34.9 8.7 1.2 .6 10.8 |e se e| sel [oul none Less than average grain size; porphyritic with allotrio- morphic granular groundmass. 2. 61 30.1 32.8 30.6 1.3 6:5 22-84 |1.......l Fine grained; foliated; larger crystals in allotriomorphic granular or granoblastic groundmass. 2. 61 28. 0 31.6 38.7 1.1 6.7 0+ Fine grained; some granoblastic mortar and myrme kite 2. 59 32.7 28.7 29.1 7.4 . 1.4 95 Less than average grain size; some granoblastic mortar and myrmekite. 2. 61 40. 3 30.2 24. 5 1.8 3.7 5.0 22-83 |...... Average grain size; nonporphyritic. 2. 61 30.1 35.6 (e serre {renee all Bel (ehe ee dec co Filil'et grained; some granoblastic mortar and myrme- ite. B 2. 59 36.6 20.1 37. 4 RQ cuss Q eel | Fine grained (in narrow tongue); porphyritic with allotriomorphic granular groundmass. 2. 62 34.5 30. 3 B00 (+: aces l 4+ § 20-20 .si Average grain size; nonporphyritic; some granoblastic mortar, myrmekite, and quartz mosaics. 2. 61 28.3 38.0 B02 |- =u 95+. $56 28-84 Average grain size; nonporphyritic; granoblastic mortar and myrmekite. 2. 64 38.9 29.9 27.6 BS 0.8 BiG 23-62 |...:.... Average grain size; nonporphyritic; some grano- blastic mortar and myrmekite. 2. 65 34.0 24.9 MFL 94 | Average grain size; nonporphyritic; much granoblastic mortar, quartz mosaics, and myrmekite. 2.66 27.8 20. 4 MAL |e cece eae de ive see nal i o B 21-44 ( Average grain size; nonporphyritic; a little granoblastic mortar and myrmekite. Subaverage...| 2.62 31.9 29.1 Ieee ire 2. 64 26. 4 25.6 Typical porphyritic; local granoblastic texture, quartz mosaics, and myrmekite. Ifo 2. 62 28.8 38.7 Typical porphyritic; myrmekite bands of quart: mosaics common. Typical porphyritic; myrmekite, granoblastic mortar, and quartz mosaics abundant. Typical porphyritic; some granoblastic mortar and myrmekite. Nonporphyritic; granoblastic bands that suggest mortar,. Nonporphyritic. Typical porphyritic; some granoblastic mortar and quartz mosaics. 2. 62 34. 4 34.8 BD | ecw ns Typical porphyritic; granoblastic mortar between grains. 2. 66 27.8 28.3 9. 5 Nonporphyritic. 2. 63 27.7 31.3 5.6 Typical porphyritic. 2. 68 28.4 22.3 14.3 Nonporphyritic. 2. 63 29.9 30. 4 6.9 Typical porphyritic. 2. 67 25.3 20. 5 6.9 Nonporphyritic. 2. 68 32. 6 25.5 1.3 Nonporphyritic. (Mode questionable.) 2. 69 20.8 14.8 12.4 N onporphyritic. 2. 69 25.1 22.1 11.2 Nonporphyritic; some myrmekite. 2. 66 31.7 20. 5 9.3 Nonporphyritic; some myrmekite and granoblastic mortar; quartz mosaics. 2. 64 28. 0 28.3 8.2 Nonporphyritic; abundant granoblastic mortar. 2. 65 28. 4 25. 4 MYB ches eu 2. 64 26.9 29.3 6.0 22 27. |: Finer grained than typical and nonporphyritic. 2. 59 25. 6 28.3 8.41 12,18] 14,15 1. Fifnfn: grained than typical and nonporphyritic and elsic. 2. 68 32.0 36.6 5.8 8-22 20 {--l.l... Nonporphyritic. 2. 63 25.3 28. 5 DA serena alap ow Medium grained; moderately large plagioclase and larger perthite crystals. 2. 62 38. 6 29.1 A Ails cele seiner blende duce Typical porphyritic; granoblastic mortar and quartz mosaics. 2. 64 290. 8 31.9 5.8 Fine grained; perthite phenocrysts small. 2. 64 31.1 35.7 6.5 Typical porphyritic. 2. 62 27.7 26. 2 4.0 Do. 2. 66 26.9 20.7 9.2 Do. 2. 61 38. 8 42.3 6.0 Typical porphyritic; much fine granoblastic rock. 2. 67 21.2 24.6 3.9 Typical porphyritic. 2.62 35. 4 20. 4 SM |-? oc leann cans lee ven Do. 2. 65 27.6 20.3 10. 7 1220 oul uu onle unl ee reat Typical porphyritic; quartz in mosaics or in larger strained crystals. 2. 68 26. 4 21.3 5.7 Typical porphyritic; anomalous high color index. 2. 67 30.6 26. 0 8.5 Typical porphyritic. ______ 35.7 27.6 8.1 Do. 2. 60 28. 4 40.6 8. 4 Do. 2. 60 25.9 27.6 14.4 Do. ........ 30.7 36.6 3.2 Do. 2. 63 37.0 34.8 4.5 Typical porphyritic; a little myrmekite. 2. 60 33.8 40. 5 MDM en [ink ret Typical porphyritic. s 2. 63 22.3 20. 5 7.4 0-22] 80,31 |...___.. Finer grained than usual; nonporphyritic. ; 2. 64 26.9 40.5 4.9 20:1 19,19 ]:...._.. Finer grained than usual; larger crystals in granoblastic or allotriomorphic granular groundmass. Subaverage...| 2.63 29. 8 31.0 89.2 |. seee {epe cures 60 [doce dil a cach lari easy See footnote at end of table. 86 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA TABLE 11.-Modal analyses of Tungsten Hills quartz mongonite, in volume percent-Continued Acces- Percent of anorthite in sory plagioclase Specific K Plagio- Horn- | and Total Specimen grav- | Quartz] feld- | clase | Biotite] blende | second-| mafic Remarks ity spar ary min- Rim | Body | Core erals 2. 63 34.1 33.6 6.3 Typical porphyritic. 2. 64 34.7 23.7. 8.7 Typical porphyritic; a little granoblastic mortar. 2. 63 28.1 34.4 3.0 Finer grained than typical; nonporphyritic. 2. 65 24.6 32.3 6. 4 Typical porphyritic. 2. 65 26. 0 27.2 7.8 Do. 2. 61 20. 2 41.0 3.0 Do. 2. 59 28.1 28. 4 6.9 Do. 2. 60 38.1 42.6 1.7 Do. 2. 63 24. 8 38. 9 4.9 Felsic and shattered; much granoblastic mortar; some plagioclase with chessboard structure. 2.62 28.7 37.6 6. 4 Typical porphyritic. 2. 62 20. 2 38. 6 3.5 Do. 2. 63 27.3 31. 2 6.3 Do. 2. 63 28.0 20. 0 6.9 Do. 2.62 28.1 37.5 7.1 Do. 2. 61 20. 2 37.2 3.3 Typical porphyritic; quartz mosaics. 2. 60 28. 8 33.3 6.1 Typical porphyritic. 2. 61 28.9 26. 8 1.6 Do. 2.62 rrbd 38. 5 0.0 Average.... 2. 63 29. 2 20.7 6.6 ' Standard chemical analyses, Tungsten Hills quartz monzonite, in weight percent [Specimen 5: lab. No. 53-1298sed. Specimen 52: lab. No. 53-1207sed. Analyst: L. M. Kehl] Specg'men Specgmen 6 69. 60 14. 89 1. 07 1.99 . 91 2.70 8. 18 4.45 gests that the rock belongs to a different intrusive, but the fieldwork failed to reveal an intrusive contact; on the contrary the appearance of the rock changes from east to west across the mass from typical Tungsten Hills quartz monzonite to rock typical of the granodio- ritic facies. The Tungsten Hills quartz monzonite is younger than the Wheeler Crest quartz monzonite, the granodiorite of Deep Canyon, the Lamarck granodiorite, and the Round Valley Peak granodiorite, and older than quartz monzonite and alaskite similar to the Cathedral Peak granite and the granodiorite of Coyote Flat, and prob- ably older than finer grained quartz monzonite. The intrusive relations with the older rocks have been dis- cussed in connection with each of these rocks. Swarms of dikes satellitic to the Mono Recesses mass of quartz monzonite similar to the Cathedral Peak granite pene- trate the Tungsten Hills quartz monzonite along Pine Creek on the west side of the Pine Creek pendant. Dike- like masses of alaskite similar to the Cathedral Peak granite penetrate the largest of the Shannon Creek masses of Tungsten Hills quartz monzonite a mile north- west of Piper Peak. Intrusive relations with finer Norms, Tungsten Hills quartz monzonite, in weight percent Specimen Specimen 5 52 26. 52 26. 13 (Plagioclase com- position Ange.) (Plagioclase com- position Ans:.) grained quartz monzonite are not entirely certain, but the Sugarloaf mass of finer grained quartz monzonite appears to be a stock and to penetrate Tungsten Hills quartz monzonite. ALBITE GRANITE FACIES The albite granite adjacent to the north and east margins of the Bishop Creek pendant is a rusty-weath- ering light-colored rock that contains almost no mafic minerals but does contain pyrite. It may have been formed by the soda-metasomatism of slightly shattered quartz monzonite adjacent to the Bishop Creek pendant. Albite pseudomorphs the preexisting feldspars, and the resultant rock is not texturally very different from the adjacent quartz monzonite. The albite granite crops out in a discontinuous zone having an aggregate area of about 34 square miles, which ranges in width from a few inches to as much as 4,000 feet. The albitized rock grades imperceptibly into quartz monzonite through transitional zones that range in width from less than an inch to several feet, but broad zones of mixed rock as wide as several hundred feet are common. Although it has been possible to map the GEOLOGY OF THE BATHOLITH 87 albite granite separately from the unaltered quartz mon- zonite, the gradational contacts between the two rocks leave no room for doubt that the albitized rock is a facies of the quartz monzonite. Albitized rock can be readily examined along the road in the North Fork of Bishop Creek. The hill slope west of North Lake and a rock slide at the base of this slope, a quarter of a mile west of the lake, are composed almost exclusively of albitized rock. The albitized rock is hypidiomorphic-granular-and the average grain size about 2 mm. Although it is finer grained than typical Tungsten Hills quartz monzonite, it is of about the same grain size as the adjacent quartz monzonite. On fresh surfaces quartz is light gray and feldspar is mottled, commonly white to yellowish gray or grayish yellow. The composition ranges from rock composed of ap- proximately equal amounts of quartz, albite, and micro- cline, to rock composed of about 35 percent quartz, 65 percent albite, and almost no K feldspar. The rock commonly contains, in addition, a little biotite, traces of sphene and magnetite (or ilmenite), and rare grains of epidote. Very nearly pure albite is indicated by its low index and the extinction angles of 15° to 17° in the zone normal to (010) and (001). Albite with two kinds of structures can be distinguished, (1) albite with close- ly spaced, throughgoing lamellar twins, and (2) albite with chessboard structure. The chessboard structure results from intricate alternation of closely spaced poly- synthetic albite twins and polysynthetic pericline twins. The lamellar twinned albite with throughgoing twins may contain finely disseminated flakes of sericite and biotite, whereas the chessboard albite is clean except for a little fine dust. This difference in the two kinds of albite causes the mottled coloration of the feldspar of some specimens; the mica-bearing lamellar twinned albite corresponds with yellowish gray to grayish yel- low grains and the chessboard albite with light gray grains. Some of the chessboard albite is twinned ac- cording to the Carlsbad law. Chessboard albite and microcline are inversely pro- portional to each other in abundance. Where both are present, they commonly occur with one enclosed in or intergrown with the other. Commonly the chessboard structure of the albite is in parallel (or nearly parallel) orientation with the quadrille structure of the micro- cline. In places, the chessboard albite contains tiny blebs of quartz, which locally are sufficiently abundant to produce myrmekite. Some of the lamellar twinned albite is enclosed in microcline, as it is in the adjacent quartz monzonite; in specimens lacking microcline some lamellar twinned albite may be enclosed in chess- board albite. Quartz is in anhedral grains that have undulatory extinction and abundant tiny liquid inclusions, and ap- pears to be identical with the quartz in the adjacent quartz monzonite. Granoblastic mosaic structure with- in the quartz is present locally, though it is not con- spicuous, and most larger grains of quartz exhibit undulatory extinction. In albite-rich rock, sparse flakes of biotite generally are pale-X=colorless and Y =Z=moderate yellowish brown, whereas in rock with appreciable amounts of microcline the biotite is more strongly colored-X=grayish yellow and Y¥=Z=gray- ish olive. Some of the biotite is altered to green chlo- rite. Several considerations indicate that the albite granite probably is not a product of direct crystallization from a magma. - The most significant of these are the theore- tical improbabilities first, that a melt of the composition of the thoroughly albitized rock could exist and, see- ond, that albite more sodic than Ans is ever pyrogenic (Gilluly, 1933, p. 73-74). The manner of transition of the albite granite to quartz monzonite precludes the possibility that the granite is a separate intrusion, and it seems unlikely that ordinary quartz monzonite and albite-rich granite could crystallize from the same magma. A final argument against an origin by crystal- lization from a magma is the chessboard albite, which is generally held to be of a replacement origin (Gilluly, 1933, p. 73). The origin of the albite granite seems best explained by some postconsolidation process of metasomatism of the quartz monzonite by means of which Na was added and Ca, K, Fe, and Mg were removed. Unlike the albite granite at Sparta, Oreg. (Gilluly, 1933), the silica content in these rocks appears to have remained ap- proximately constant; indeed no evidence is apparent in the thin sections that quartz was in any way affected during the alteration. Only two sources for the albitiz- ing solutions seem possible: the metamorphic rocks in the Bishop Creek pendant, and some source deeper than the exposed level, possibly late magmatic solutions from the quartz monzonite or from younger intrusions. The fact that albitized rock is found only contiguous with the pendant strongly favors the pendant as a source for the required Na even though no sodium- rich metamorphic rocks have been found. Possibly the sodium came from a layer of salt, which was removed during metamorphism. Cataclasis of sufficient intensity to have produced permeability is indicated by weak cataclastic structures. Some relict granoblastic mortar borders larger crys- tals, the twins in lamellar twinned plagioclase are com- monly bent and offset on small fractures, and quartz is strained and locally reduced to a granoblastic mosaic. 88 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA The albitization probably took place chiefly by the pseudomorphic replacement of both the K feldspar and calcic plagioclase. Lamellar twinned albite, because it contains tiny mica flakes distributed similarly to the plagioclase in the quartz monzonite and because it is in grains of the same size and habit as the plagioclase of the quartz monzonite, is believed to have replaced plagioclase. However, in the thin sections that were studied none of the original plagioclase was observed. The chessboard albite, on the other hand, appears to have taken the place of microcline and to have acquired the chessboard structure thereby. Comparison of thin sections containing chessboard albite and very little microcline with thin sections containing abundant chessboard albite shows that texturally albite substi- tutes for microcline. The replacement of microcline by chessboard albite is strongly substantiated by the close association and parallel intergrowth of the two min- erals where they are present together. The fact that microcline is associated in some slides with lamellar twinned albite in which chessboard albite is lacking indicates that plagioclase was replaced be- fore microcline. The mafic minerals also were elimi- nated early. The replacement of microcline by chess- board albite was the last effect of the metasomatism. ROCKS SIMILAR TO THE CATHEDRAL PEAK GRANITE Alaskite and quartz monzonite similar in appearance to the Cathedral Peak granite of Yosemite (Calkins, 1930, p. 126-127) occur in several discrete bodies with- in the part of the Sierra Nevada mapped in connection with this report. The total area of rocks similar to the Cathedral Peak is about 68 square miles, divided al- most equally between quartz monzonite and alaskite (fig. 35). The largest mass that lies entirely within the mapped area is the Rawson mass of alaskite, but the North and South lobes of the Mono Recesses mass of quartz monzonite are both parts of a very large pluton, which extends entirely across the adjoining Mount Abbot quadrangle (Sherlock and Hamilton, 1958). Masses of alaskite and masses of quartz monzonite occur in geographically different areas. Alaskite is con- fined to the range front from Big Pine Creek north to Wheeler Crest; quartz monzonite lies west of the alas- kite in a belt that extends northwestward from near the southeast corner of the mapped area to near the northwest corner. At one stage of mapping, the alas- kite and quartz monzonite were considered to be differ- ent formational units, but overlapping mineral and textural characteristics and the absence of any evidence that rock of one composition intrudes the other favor the view that the rocks are genetically and temporally very closely related. Nevertheless, it is unlikely that the two facies are precise temporal equivalents, inas- much as their mineralogic differences probably reflect different temperatures of crystallization. QUARTZ MONZONITE FACIES Typical quartz monzonite similar to the Cathedral Peak granite is medium to coarse grained, has an aver- age color index of 3.5, and commonly is equigranular to weakly seriate, but locally is porphyritic (fig. 21G). The average grain size is 3 to 4 mm, but lecally the aver- age grain size may be 5 mm or more, and in some mar- ginal parts of masses it is less than 1 mm. Conspicu- ously porphyritic rock is present in the McGee Creek mass, in the stock between Poleta and Redding Canyons in the White Mountains, and locally in the South lobe of the Mono Recesses mass (fig. 35). Quartz is light gray, and both feldspars are white except in porphyritic rock where K feldspar phenocrysts may have a pink- ish caste. Inclusions are few except in the immediate vicinity of intrusive contacts with metamorphic or mafic igneous rocks. Foliation is rarely discernible, probably because of the paucity of mafic inclusions or minerals. Joints commonly are widely spaced and conspicious. Quartz, K feldspar, and plagioclase, which constitute more than 95 percent of the average rock, are present in variable amounts (table 12), but almost all of the modes fall within the quartz monzonite field (fig. 36). The average biotite content of the specimens analyzed modally is 3 percent; hornblende was found in only two specimens, where it probably reflects contamination. K feldspar commonly exhibits quadrille structure and is perthitic ; except for phenocrysts, which are generally euhedral, it is anhedral. Most larger grains contain smaller grains of the other minerals, and the outer sur- faces of phenocrysts are rough because of the abundance of inclusions in their outer parts. Quartz commonly is in large clear anhedral grains that extinguish cleanly. Plagioclase is generally in conspicuously zoned sub- hedral crystals having a compositional range of Ani, to An;, and an average composition of about The anorthite content varies considerably (table 12). The Mount Alice mass locally has been contaminated by inclusions of mafic igneous rock. The quartz mon- zonite adjacent to the mafic rock is darker than the ordi- nary quartz monzonite, and near rafic rock it contains numerous tiny inclusions of recrystallized and partly granitized mafic rock. Sharp contacts occur between uncontaminated and contaminated quartz monzonite, and in several places contaminated quartz monzonite forms inclusions in uncontaminated quartz monzonite. An especially interesting feature of the Mount Alice mass is the presence of compositionally layered rock. GEOLOGY OF THE BATHOLITH 118°30' 18°45" 89 18°15" -62 Sherwin Hill mass m MJ Rawson mass Approximate location Knoptf's Rawson Canyon sample $7818) EXPLANATION ROCKS SIMILAR TO THE CATHEDRAL PEAK GRANITE Alaskite Quartz monzonite L Finer grained quartz monzonite 25 ®2.67 Specimen with number and specific gravity 37°00' \ 5 C 1 1 1 1 FicurE 35.-Map showing the locations of modally analyzed specimens of rocks similar to quartz monzonite. 735-925 O-65--7 60), Shannon Canyon 60. mass _ °C chem fin arren Bench o mass 5 MILES 4 the Cathedral Peak granite and of finer grained 90 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA Quartz Quartz Plagioclase Potasium feldspar Plagioclase Potassium feldspar North and south lobes Mono Recesses mass, Mount Alice mass of quartz monzonite McGee Creek mass, Poleta stock of quartz monzonite Quartz Quartz Plagioclase . R Potassium feldspar Plagioclase Potassium feldspar Palisade Creek and Red Mountain Creek Composite of quartz monzonite masses of quartz monzonite Quartz (norm 46) 2 (norm (norm 37)" Plagioclase 3 ¢ Potasium feldspar Composite of alaskite FicurE 36.-Plots of modes of rocks similar to the Cathedral Peak granite on quartz-K feldspar-plagioclase diagrams. GEOLOGY OF THE BATHOLITH 91 Taste 12.-Modal analyses of rocks similar to the Cathedral Peak granite, in volume percent [Where the content of biotite, hornblende, and accessory and secondary minerals is shown separately, the mode was determined from a thin section; where only the total content of mafic minerals is shown, the mode was determined from a stained slab. Location of specimens is shown on fig. 35] Specimen Specific gravity) Quartz Percent of anorthite in plagioclase Rim | Body | Core Remarks 2. 64 28.3 3.8 Equigranular; somewhat finer grained than usual. 2.61 | 28.9 2. 4 Do. 262 | 32.0 3. 4 Do. 2.62 | 18.6 3.8 Do. 2. 60 26.1 40 |.c.olc.. 12-20 |........ Do. 2. 62 17. 4 3. 4 21-20 Somevtlhat porphyritic; contains K feldspar pheno- crysts. 2.61 | 30.8 3.6 15-25 Do. 2. 50 27.0 3.8 17-24 Do. 2. 61 24.6 2.5 17-28 Do. 2. 61 18. 6 $6 Seriate but with most grains in two size groups; finer grained than usual. 2. 62 23.8 3.0 16-22 Equigranular. 2. 62 28.7 2.4 |.....c.. 8-18 15 | Porphyritic; K feldspar phenocrysts. 2. 68 21.6 $8 [Epee ccie +20 | Porphyritic; pale-red microcline 11]:>heuocrysts in fine gfoundmass of biotite, quartz, hypersthene, plagio- clase. 25.1 20.6 Equigranular; fine grained. 37. 4 Seriate; fine grained. 30.5 Equigranular typical. 27.1 Equigranular; granoblastic mortar beetween many grains. 28. 2 Equigranular to porphyritic; a few large K feldspar grains. 30. 5 Equigranular; some granoblastic mortar between grains. 29. 4 Equigranular; conspicuous granoblastic mortar be- tween grains. 35.4 Equigranular; some granoblastic mortar between grains. 29.6 Do. 31.8 Do. 40. 2 Equigranular; typical granoblastic mortar between grains. 7:01. 06.8 | 29.7 (-l.. BRAE IAT Equigranular; two grain size groups; may be result of cactaclasis; strongly altered to muscovite. 28.7 9 j :...02.. Equigranular; some granoblastic mortar between grains. 29.9 | . 80.5 | © 82. 8 1-2. 220.0... ce uel A LID 2p ce 2a ec een cer Equigranular; typical granoblastic mortar between grains. ; 24.0 20 | 26-81 |...___.. Equigranular; some granoblastic mortar between grains; strongly altered to muscovite. $12.10: {; (27. (-a rss 22220 ee] - Beco eee cael erd es 26.8 Equigranular; typical granoblastic mortar between grains; strongly altered to muscovite. 30.6 Seriate; large poikilitic K feldspar grains. 25.9 Seriate; finer grained than usual; high biotite content. 31. 2 Seriate; slightly finer grained than usual. 35. 4 Equigranular; some granoblastic mortar between grains. 30.0 2.5 31.5 c 0.8 Equigranular to seriate. 35.1 £ 0.7 Equigranular; finer grained than usual. 22.6 54.6 1.9 Equigranular; average grain size. 33.1 33. 4 1.9 Equigranular; typical. 35.0 29. 8 2.6 Do. 30.8 49.8 2.7 Do. 38.9 45.0 6.0 Equigranular. 36.9 38.6 2.6 |. Do. 37.5 41.1 2.2 Do. 37.5 21.7 8.6 Mode poor; not plotted on fig. 34. 30.0 48. 2 0.2 Equigranular. 25.8 32.2 8. 0 Equigranular; fine grained; probably a hybrid. 34.9 40.5 2.7 Equigranular. 2. 58 32. 4 45.4 1.0 Do. 2. 61 20.5 33. 2 1.4 Equigranular; scattered conspicuous biotite. 2. 58 36.6 37.5 3.5 Equigranular. Subaverage....___.___. 2. 60 33.0 38.6 2.9 Average......:......... 2. 61 29. 9 37.1 3.0 See footnote on following page. 92 Layered rock crops out along the trail that follows the North Fork of Big Pine Creek between Second Lake and - Third Lake. The layered rock is in tabular masses of diverse orientation, which appear to be included in the quartz monzonite. Superficially the layered rock ap- pears to be part of the quartz monzonite, but careful examination reveals the presence of scattered grains of pink plagioclase, found only in the Inconsolable gran- odiorite. Most contacts between the quartz monzonite and the layered rock are concordant with the layering, but in a few places tongues of quartz monzonite pene- trate across the layers. Presumably the layering was caused by migration of the mafic material in the in- clusions to selected surfaces by a process of metamor- phic differentiation. - These surfaces probably are shear planes, which may have been formed as a result of fore- ible emplacement of the quartz monzonite. The gran- odiorite in nearby Temple Crag has been shattered and cemented with quartz and fine-grained felsic rock, very likely as a result of the emplacement of the quartz monzonite. Footnote for table 12: 1 Chemical analyses [a, Standard rock analysis. Analyst: L. M. Kehl. b, Rapid rock analysis. Ana- lysts: H. F. Phillips, P. L. D. Elmore, and K. E. White. c, Analysis reported by Knopf of sample of alaskite from Rawson Canyon (Knopf, 1918, p. 68)] Quartz monzonite Alaskite Specimen (lab. No.) 4(b) 12(b) |23(a) (53-| 37(b) 46(b) K(c) (152445) | (152446) | 1296-sed) | (152443) | (152444) 71.8 73.0 74. 11 71.0 75. 4 76. 28 15.3 15.2 13. 73 15.7 1.0 4 . 60 .9 .65 . 34 . 88 .81 . 34 16 .82 . 39 1.8 1.1 1.29 1.6 3.8 3.8 3. 44 3.8 4.1 5.0 4. £195 5.0 fe . 48 12} . "oo 22 . 09 .18 .22 08 10 . 01 .07 05 .05 . 06 .05 06 . 06 05 . 04 100 100 99. 89 100 100; 12; .css use. Norms Quartz monzonite Alaskite Specimen 4 12 28 37 46 K 29. 64 29. 22 31.92 25. 68 32. 58 20. 76 24.46 20. 47 28. 94 20. 47 26. 69 27. 24 31.96 31.96 28. 85 : 4 . 8.90 5.56 6. 40 .90 . 66 1.72 1.39 . 70 . 89 AMB .32 1.33 1. 53 . 51 99. 04 99. 10 99. 55 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA ALASKITE FACIES The alaskite was described by Knopf (1918, p. 67-69) as orthoclase-albite granite. Megascopically it closely resembles nonporphyritic facies of the quartz monzo- nite, although slight differences are generally recogniz- able (fig. 21H). The most obvious features of the alaskite that distinguish it from the quartz monzonite are a pinkish cast of the K feldspar, and a very low biotite content-about 1.6 percent on the average for uncontaminated rock, but many specimens contain less than 1.0 percent. However, the most distinctive fea- ture of the alaskite (plagioclase in the albite composi- tional range) can be ascertained only through micro- scopic study or by chemical analysis. The average grain size of the alaskite is 3 to 4 mm, but it ranges from less than 2 mm in the dike along Wheeler Crest to more than 5 mm locally in the Rawson mass. The rock is megascopically equigranular, but appears slightly seriate in thin section. The largest grains are of K feldspar. In the field, foliation is con- spicuous only in the dike along Wheeler Crest. In- clusions are scarce. Joints commonly are widely spaced and consequently conspicuous. Much of the rock that crops out in the Tungsten Hills and in the north part of the Rawson mass and in the mass just north of Baker Creek is deeply weathered to a loose iron-stained grils; consequently, few modes were made on rocks from these areas. The average mineral composition of 15 modally an- alyzed specimens is 33 percent quartz, 39 percent K feldspar, 26 percent plagioclase, and less than 3 percent biotite. Hornblende was found in only one specimen, which probably is contaminated. K feldspar generally is perthitic and exhibits con- spicuous quadrille structure. Quartz commonly is in large clear grains that extinguish with little undula- tion. Biotite is in subhedral plates, which generally are evenly distributed through the rock. Under the microscope, Z commonly is moderate brown, but in some specimens is moderate yellowish brown or mod- erate olive. Albite is in anhedral to subhedral grains that exhibit closely spaced lamellar twinning on the albite law. With the exception of contaminated rocks from the marginal zones, the plagioclase is in zoned crystals that generally have an average An content of less than 10 percent. - Knopf (1918, p. 67-69) originally determined the albite composition of the plagioclase. His optical determinations indicate a composition of Ani, ; a partial chemical analysis of a rock collected by him from Raw- son Canyon indicates a composition of An,. Knopf pointed out that An,, may be closer to the true com- position of the plagioclase than An, because the K feld- GEOLOGY OF THE BATHOLITH spar contains lamellae of almost pure albite. The sodic nature of the plagioclase is supported by optical deter- minations of the composition of the plagioclase tabu- lated in table 12, and the calculations of two additional norms. - It is evident, however, that the composition is variable and that the plagioclase of some specimens is more calcic than that in some specimens from the quartz monzonite facies. The maximum range of zoning in all the uncontaminated specimens is from An; to Anis, but most grains are zoned through only a small part of the total range. MARGINAL DIKES OF APLITE, PEGMATITE, AND ALASKITE A notable feature of both the quartz monzonite and alaskite facies is that some masses are parent to mar- ginal swarms of felsic dikes that dip gently into and A FiGURE 37.-Aplite, pegmatite, and alaskite dikes along Pine and Morgan Creeks. similar to the Cathedral Peak granite, commonly at 20° to 45°. Hills quartz monzonite (Kth) and quartz diorite (Kdg) and finger out in marble (m). 983 merge with the parent body. Dips of dikes generally are less than 40° and mostly between 20° and 830°. Dikes marginal to the south lobe of the Mono Recesses mass of quartz monzonite are well exposed and can be readily examined on the north side of Pine Creek be- tween Pine Lake and the Pine Creek pendant (fig. 37). Marginal dikes are also abundant on the north side of the Palisade Creek mass, and marginal to the alaskite dike along Wheeler Crest. The dikes consist chiefly of quartz and feldspar, but locally contain garnet, sphene, biotite, magnetite, and other minerals. Most of the plagioclase in the dikes along Pine Creek is conspicuously zoned in the oligo- clase range, as is the plagioclase in the parent mass. The dikes range from aplitic to pegmatitic, and not un- commonly both textures are present in the same dike. The dikes dip toward the parent mass of quartz monzonite A, Along the west side of the Pine Creek pendant dikes cut Tungsten B, At the Brownstone tungsten mine dikes cut Tungsten Hills quartz monzonite (right), tactite (center), and marble (left). 94 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA Dikes having a predominant pegmatitic texture almost invariably cut dikes having a predominant aplitic tex- ture, although no great age difference seems likely. Matching irregularities in the opposing walls of many dikes indicate that the dikes were emplaced by dilation of their walls, although a component movement parallel to the dike walls is required by the geometry of some matching walls. In a few places, thin marginal zones of fine-grained aplite appear to have accreted to the dikes without dilation, and presumably by replacement. Dikes extend in abundance from the north side of the south lobe of the Mono Recesses mass for more than a mile, and a few dikes are found at distances of more than 2 miles. Along the south side of Pine Creek in the vicinity of the Brownstone mine, close to the parent mass, dikes comprise at least half of the rock exposed in cliff faces, whereas half a mile away, in cliffs on the north side of Pine Creek, dikes comprise only about 10 percent of the exposed rock. Few of these dikes con- tinue into the Pine Creek pendant even where it is very close to the intrusive mass parent to the dikes; most dikes finger out in the marble along the west side of the pendant (fig. 374). Similar dike swarms have been described by Hans Cloos and his associates (in Balk, 1948, p. 101-106). They interpret the fractures occupied by the dikes as the result of tension caused by the upward movement of magma along a steep or vertical face. According to Balk (1948, p. 104), "The zones of marginal fissures are of utmost importance for the evaluation of the forces acting during the consolidation of many igneous masses. Even where the rock may be structureless, marginal dikes and upthrusts must be regarded as evidence of a strong upward motion of the plutonic mass." This con- cept of origin fits the known facts in the Bishop district. Matching dike walls indicate dilation, locally accom- panied by slight movements parallel with the walls. The fact that the dikes die out away from the parent mass indicates progressively greater dilation toward the parent pluton, which, in turn, must signify upward drag of the wall rocks adjacent to the parent mass. The fact that the dikes maintain a constant range of dips indi- cates that the fractures they occupy must have formed contemporaneously with the bending, else they would not have been formed or would have been bent upward near the parent pluton from their original con- figuration. These considerations indicate the fractures must have been formed and the dikes emplaced gen- erally in order from bottom to top as the parent pluton rose. INTRUSIVE RELATIONS Rocks similar to the Cathedral Peak granite are among the youngest of the plutonic rocks, and only the granodiorites of Coyote Flat and Cartridge Pass and masses of finer grained quartz monzonite could have been emplaced later. Intrusive relations with older rocks were discussed in connection with each of these rocks. The granodiorite of Coyote Flat was observed to intrude rock similar to Cathedral Peak granite, but evidence of the younger age of the other rocks rests primarily on the gross geometric relations of the rocks, as shown by the map pattern. The granodiorites of Coyote Flat and of Cartridge Pass occur as rather symmetrical bodies that appear to cut across the quartz monzonite similar to the Cathedral Peak granite. Likewise the Wheeler Crest mass of finer grained quartz monzonite appears on the map to cut off the north end of the alaskite dike along Wheeler Crest. Additional suggestive evidence is that thin flat-lying aplite dikes marginal to the alaskite dike, present in the older Wheeler Crest quartz monzonite, were not found within the finer grained quartz monzonite. The Red Mountain Creek mass of quartz monzonite, unlike any other mass assigned tentatively to the Cathedral Peak, is cut by mafic dikes; this relation suggests the possibility that the Red Mountain Creek mass is older than other masses of rock similar to the Cathedral Peak granite and improperly assigned. Evaluation of this possibility can be made only after the time of emplacement of the mafic dikes, now in doubt, has been established. The Red Mountain Creek mass has a concentric pattern on the map and in section, which suggests that it is younger than the overlying Tinemaha granodiorite and older than the underlying Taboose mass of finer grained quartz monzonite (pl. 4; pl. 5, section #-A" ). FINER GRAINED QUARTZ MONZONITE The finer grained quartz monzonite includes five small masses having an aggregate outcrop area of only a little more than 6 square miles (pls. 34; fig. 35). Although most or perhaps all of the masses may have been emplaced at about the same time, evidence bear- ing on their relative ages is too meager for them to be considered a formational unit. The two largest masses, the Sherwin Hill and Taboose Creek masses (fig. 35) continue beyond the boundaries of the mapped area. The three smaller masses are closely grouped in upper Freeman and Shannon Canyons and in Sugarloaf. The rock in all the masses is generally similar in tex- ture and mineral content, although minor differences are recognizable. Typical rock is medium grained, though finer grained than any other intrusive, and lo- cally porphyritic. The average grain size is 1 to 2 mm. Phenocrysts of K feldspar 14 to 11/4 ecm across are pres- ent in some parts of the Sherwin Hill and Freeman GEOLOGY OF THE BATHOLITH Canyon masses. Although the average grain size varies slightly from mass to mass, generally the grain size throughout a single mass is nearly constant. The rock ranges from very light gray to yellowish gray. Biotite, ordinarily the only dark mineral, is present in amounts ranging from 1.0 to 6.5 percent; most rocks contain between 2.0 and 5.0 percent. Much of the rock appears structureless, but locally feldspar grains and biotite flakes are oriented, and aggregates of biotite flakes form thin layers that give the rock a planar foliation. Mafic inclusions are rare. Some of this foliation may be the result of cataclasis after the original consolidation of the rock. Much of the mass along Taboose Creek is composed of two very similar appearing rocks of about equal abundance, one of which intrudes the other in narrow irregularly branching dikes. The rock in the dikes is lighter colored than the intruded rock, because the feldspars are white rather than light gray or yellow- ish gray. Under the microscope the two rocks are in- distinguishable, and for this reason are thought to be very closely related to each other. Average rock consists of about equal amounts of quartz, K feldspar, and plagioclase (table 13). Biotite, with Z=dark yellowish brown, is the only varietal mineral. Accessories are apatite, zircon, allanite, mag- netite, and pyrite. The plot of modes (fig. 38) shows considerable scatter, which, in view of the relatively fine grain-size probably reflects real differences in com- position. Perthitic K feldspar is commonly in large anhedral grains that enclose smaller subhedral to eu- hedral plagioclase grains. Most K feldspar exhibits conspicuous quadrille structure. Plagioclase common- ly is finely twinned according to the albite law ; it gen- 95 erally ranges from An;-,, in the cores of crystals to An;, in the rims, but cores more calcic than Ans, and rims more sodic than An», are not uncommon. Quartz is in anhedral crystals of moderate size, many of which consist of granoblastic aggregates which may have been produced from original homogeneous grains by strain. The texture in nonporphyritic rocks is hypidiomor- phic-granular. Granoblastic mortar is present along the boundaries of some grains, and is associated with myrmekite along boundaries between perthitic K feld- spar and plagioclase. Myrmekite also is present locally in thin veins that lie along contacts between two K feldspar crystals or more rarely cut across perthite crystals. Quartz Potassium feldspar Plagioclase (including perthite) FiGURE 38.-Plot of modes of finer grained quartz monzonite on quartz-K feldspar-plagioclase diagram. TABLE 13.-Modal analyses of finer grained quartz monzonite, in volume percent [Location of specimens is shown on fig. 35] Percent anorthite in $ Accessory plagioclase Specimen Specific | Quartz K Plagio- | Biotite Horn- and Color Remarks gravity feldspar clase blende |alteration index Rim | Body | Core 2. 69 26. 8 22.7 43.0 4.5 1.4 2l 27-36 40 6.7 2.62 37.9 36.6 21.9 2. 4 1.1 2-12 | 28-24 |._______ 3.5 2.62 41.8 27.2 27.8 2.3 .9 8-17 | 22-25 |._______ 2.3 2. 60 30. 3 42.7 22.2 2.8 1.9 417 | 2-27 |...._.... 4.7 2. 61 29. 8 37.1 31. 8 1.1 .2 12-18 :...... 1.3 2. 62 51.8 19. 5 21.6 6. 4 v4 4-5 | 16-17 |._.___... 7.8 2. 67 30. 3 20. 2 44.9 3.9 4 5 | 24-38 | 38-42 4.6 2. 66 24.7 29. 6 39.7 4.9 ned f I. 6. 0 2. 63 29.1 28. 4 37.8 3.6 28-91 |...___.. 4.7 2. 64 7.3 19.8 66. 3 5.7 .8 8 | 21-33 |._..____. 6.5 | A few large perthite crystals; plagioclase is in small subhedral zoned crystals. 2.60 30. 2 39. 2 25. 5 L0 .6 5,16 | 26-82 |___... 5.2 2. 63 34.3 35.6 25.9 B0 -se .6 | 21,28 | 28-86 |__..._._ 4.2 2. 58 34.3 40. 0 20 4.0 2-11 2.1 2.62 36.1 25.0 35.3 2.9 .6 8 17-88 j........ 3.5 2.62 34.6 25.9 34.5 4.3 eB rece 21-39 40 4.9 .......... 38.7 28. 2 30.1 2.8. .2 23 2. 63 290. 2 82.7 31. 8 3.9 2.4 2. 60 40.1 30. 2 25.5 3.9 .4 5,8 __________ 32.5 31.5 31. 2 $ 4.......... 14 96 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA Few intrusive relations of masses of finer grained quartz monzonite to the rocks with which they are in contact were established by field observation. In part this lack results from the fact that the finer grained quartz monzonite is closely jointed and breaks down to rubble that obscures the intrusive contacts. Among the older intrusives, only the Wheeler Crest quartz monzonite is in contact with finer grained quartz monzonite. Small dikes from the Sherwin Hill mass of finer grained quartz monzonite penetrate the W heeler Crest quartz monzonite and clearly indicate the younger age of the finer grained quartz monzonite. The three small masses at the heads of Freeman Creek and Shan- non Canyon are in contact with the Tungsten Hills quartz monzonite, alaskite similar to the Cathedral Peak granite, and the granodiorite of McMurry Mead- ows, and the Taboose mass is in contact with quartz monzonite similar to the Cathedral Peak granite. The Sugarloaf mass has the general appearance of a stock intrusive into the Tungsten Hills quartz monzonite, but all contacts are covered with rubble. The nearly cir- cular shape on the map of the granodiorite of Coyote Flat gives the impression that it is younger than the Freeman Creek mass of finer grained quartz monzonite, but such a relation was not established. The Taboose mass of finer grained quartz monzonite underlies the alaskite of Red Mountain Creek and Tinemaha grano- diorite in a concentric arrangement in plan and section and is probably younger (pl. 4; pl. 5, section F-F"). Some or all of the masses of finer grained quartz monzonite may be correlative with the Johnson granite porphyry of the Yosemite region (Calkins, 1930, p. 127-128). The Johnson granite porphyry is similar in appearance to the finer grained quartz monzonite, and its intrusive position as the youngest formation of the Tuolumne intrusive series is compatible with the in- ferred position of the finer grained quartz monzonite in the intrusive sequence. GRANODIORITE OF COYOTE FLAT Granodiorite underlies about 13 square miles in the northeastern part of Coyote Flat and adjoining areas to the north and east. It constitutes a nearly equidimen- sional pluton in map pattern except for a tongue that extends northeastward along upper Rawson Creek. Most of the pluton is well exposed, but the west-central part is covered by alluvial fill in Coyote Flat. Most of the rock is light gray and medium grained ; the average grain size is 1 to 2 mm. A marginal zone a few hundred feet thick is generally present, which is darker and finer grained than the more abundant rock from the interior of the pluton. The marginal rock is conspicuously foliated parallel with the external contacts; it contains few mafic inclusions, and the folia- tion is shown by orientation of the constituent minerals. In composition the rock is granodiorite. The average mineral content of nine modally analyzed specimens is 22 percent quartz, 13 percent K feldspar, 48 percent plagioclase, 9 percent biotite, 5 percent hornblende, and 4 percent accessories (table 14). Except for specimens 1, 6, and 8, from the margins of the pluton, the plot of modes shows little scatter (fig. 39). Samples 1, 6, and 8 are considerably richer in plagioclase than most other specimens. The average color index of all the speci- mens is 17, but ranges from 12 to 25. In thin section the most striking feature of the gran- odiorite is that it is conspicuously poikilitic; large an- hedral grains of quartz and K feldspar having quad- rille structure comprise a groundmass, which encloses euhedral to subhedral grains of the other minerals in the rock. The range of zoning of the small euhedral plagioclase grains is exceptionally great. Large un- zoned or slightly zoned central body areas generally fall in the compositional range of Anse to Anu. The body areas contain small cores as calcic as An;, and are enclosed by rims of sodic plagioclase that may be as calcic as Ans, at the inner edge and as sodic as Anz, at the outer edge. Biotite is somewhat unusual in that it is grayish red in the Z direction. The granodiorite of Coyote Flat sends dikes into and contains inclusions of the Tungsten Hills quartz mon- zonite and alaskite similar to the Cathedral Peak gran- ite, and is clearly younger. Intrusive relations with finer grained quartz monzonite were not established by field observations, but the roundish shape in plan of the granodiorite suggests that it intrudes all the rocks Quartz Potassium feldspar Plagioclase (including perthite) FIGURE 39.-Plot of modes of granodiorite of Coyote Flat on quartz-K feldspar-plagioclase diagram. GEOLOGY OF THE BATHOLITH 97 TaBtr 14.-Modal analyses of granodiorite of Coyote Flat, in volume percent [Location of specimens is shown on fig. 23] Accessory Specimen Specific Quartz | K feldspar | Plagioclase| Biotite |Hornblende and Remarks gravity secondary minerals 2.73 18. 5 7.6 56. 2 10.5 4.0 3.2 Megafimpically equigranular but notably poikilitic in thin section. 2.65 22. 4 13.5 51. 6 8.2 3.4 .8 Do. 2.70 27.2 12.6 43. 6 8.6 4.6 3. 4 Do. 2. 69 25.7 19.2 38.8 7.3 3.6 5. 4 Do. 2. 69 28.5 12. 4 44.7 5.7 8.7 5.0 Do. 2.82 8.5 8.1 58. 4 11.5 8.5 5.0 | Megascopically equigranular but notably poikilitic in thin section; finer grained and darker than typical. 2.70 22.3 17. 4 41.3 9.0 5.7 4.3 Megfimpically equigranular but notably poikilitic in thin section. 2.176 16.5 8.7 54.3 9.3 6.0 5.2 | Megascopically equigranular but notably poikilitic in thin section; finer grained and darker than typical. 2.71 20.3 15. 4 42.0 7.8 2.5 3.0 Megfiwpically equigranular but notably poikilitic in thin section. 2.71 22.1 12.8 47.9 8.7 4.7 3.9 with which it is in contact, including finer grained quartz monzonite. It may be correlative with the gran- odiorite of Cartridge Pass. GRANODIORITE OF CARTRIDGE PASS Light-gray equigranular granodiorite having an av- erage grain size of 1 to 2 mm occupies a little less than 3%, square miles in the southwestern corner of the mapped area, and extends into adjoining areas to the south and west (pl. 4; fig. 23). James G. Moore has made intensive studies of the pluton in the Mount Pin- chot quadrangle in the vicinity of Cartridge Pass and has found that it is concentrically zoned and that the average composition is granodiorite close to quartz mon- zonite (Moore, 1963, p. 60). Only two thin sections were studied; one of granodiorite, and the other of quartz diorite (table 15; fig. 40). Both specimens are from outer, more calcic and ferromagnesian zones. The texture of both specimens is hypidiomorphic-granular, but the plagioclase, especially in the specimen of quartz diorite, approaches euhedral, and the rock texture is close to panidiomorphic-granular. In both specimens the central parts of plagioclase crystals are of andesine composition (An;;-;;), and they are rimmed with calcic oligoclase. The pluton contains inclusions of Lamarck granodi- orite, and is therefore younger. Along the north side it is in contact with quartz diorite and with quartz monzonite similar to the Cathedral Peak granite. It clearly intrudes the quartz diorite, but its intrusive re- lations with the quartz monzonite were not established. Whether the granodiorite of Cartridge Pass is cor- relative with either the quartz monzonite of McMurry Meadows or the granodiorite of Coyote Flat depends on whether it is younger or older than rocks similar to the Cathedral Peak granite. Quartz Potassium feldspar (including perthite) Plagioclase 40.-Plot of modes of granodiorite of Cartridge Pass on quartz-K feldspar-plagioclase diagram. TaBt® 15.-Modal analyses of granodiorite of Cartridge Pass, in volume percent [Location of specimens is shown on fig. 23] A y Percent anorthite K Plagio- Horn- and in plagioclase Specimen Quartz | feldspar clase Biotite | blende |secondary Remarks minerals Rim Body Core 15.9 3.8 54.6 15.7 6.8 3.2 28 38 55 | Dark, fine-grained and equigranular. 22.8 12.3 46.1 12.1 1.7. 5.0 21.27 S7 ecuesiuess Lighter colored, and coarser than specimen 1; equigranular. 98 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA MAFIC DIKES Swarms of dark-colored dikes of dioritic composi- tion are present locally in the Bishop district. The rock in these dikes has been termed "malchite" by Gilbert (1941, p. 784). The most extensive swarm is in the south half of the Big Pine quadrangle and extends southward many miles into the Mount Pinchot quad- rangle (Moore and Hopson, 1961). Most of the dikes dip steeply, and within the Big Pine quadrangle strike about N. 70° W., but to the south in the Mount Pinchot quadrangle the average strike is about N. 30° W. A second dike swarm extends westward through the cen- tral part of the Tungsten Hills and across the north side of Mount Tom to the Pine Creek pendant. Dikes of this swarm are well exposed in the walls of Pine Creek canyon above the village of Scheelite. These dikes dip steeply and strike westward, parallel with the long axis of the swarm, except just east of the Pine Creek pendant where the dikes swing to the southwest. A third swarm is in the northwest corner of the Mount Goddard quadrangle, along the Glacier Divide. Mafic dikes are also in the cirques at the head of the South Fork of Bishop Creek; dikes in the east face of Hurd Peak can be seen from the trail to Bishop Pass. The dikes are generally a few inches to a few feet thick; the thickest observed, in the northwest side of Mount Tom and in the north-central part of the Tungsten Hills, are 15 to 20 feet thick. All the rock is fine grained, but differences in grain size and texture are evident. Most dikes are equigranular but some ap- pear porphyritic. Many dikes have been strongly sheared parallel to their walls and appear schistose. Commonly the dark minerals in sheared dikes are in lenticular streaks. Only a few specimens from the mafic dikes were ex- amined in thin section, and in all these the primary con- stituents are plagioclase, hornblende, and biotite, ac- companied by accessory magnetite, apatite, and sphene. A comparatively coarse grained and little-altered dike from the Tungsten Hills consists of about 'O percent plagioclase and 15 percent each of hornblende and biotite, plus the accessories. The plagioclase is in unoriented thick tabular euhedral to subhedral crystals that average about 2 mm across and 14 mm thick. Most crystals are discontinuously zoned from cores of about Ans; to rims of about Anss. Interstitial to the plagioclase are jumbled aggregates of the mafic min- erals and accessories. The hornblende and biotite in these aggregates are in small anhedral grains. A sample of dike rock from Fish Springs Hill in the Big Pine quadrangle is highly altered to chlorite and epidote, but scattered relicts of original plagioclase crystals indicate an original weak panidiomorphic- granular texture. Other specimens are all very fine grained and schistose. In these rocks some of the plagioclase is in larger (5 mm) rounded unzoned grains. Hornblende in subhedral to anhedral grains of about the same size range as the plagioclase generally is about as abundant as plagioclase, whereas biotite is much less abundant than either. - Streaks of aggregates of the mafic minerals impart a foliation to the rock. The texture of these rocks may be metamorphic rather than igneous-granoblastic rather than allotriomorphic granular. Apparently swarms of mafic dikes have been in- truded at several times during the period of emplace- ment of the granitic rocks. The oldest swarm, in the Tinemaha granodiorite, does not extend into the adja- cent Lamarck granodiorite or Mount Alice mass of quartz monzonite similar to the Cathedral Peak granite, although a few dikes extend into the Red Mountain Creek mass of quartz monzonite similar to the Cathedral Peak granite. Nevertheless, mafic dikes are present in the Lamarck granodiorite in and near Hurd Peak and along the Glacier Divide where they are clearly truncated by the Tungsten Hills quartz monzonite. The dikes that are probably youngest are in the Tung- sten Hills quartz monzonite along Pine Creek and in the Tungsten Hills. These relations suggest three pe- riods of dike formation if the Red Mountain Creek mass is assumed to be older than other masses of quartz monzonite similar to the Cathedral Peak granite. The possibility also exists that the Tungsten Hills quartz monzonite along the Glacier Divide is younger than the Tungsten Hills along Pine Creek and in the Tungsten Hills; if so, only two periods of dike emplacement are required. The source of the dike magma is an unsolved prob- lem. It is difficult to understand how usual processes of magmatic differentiation could produce magma of dioritic composition from a parent magma, which be- fore, and afterward, yielded magma of granodioritic or quartz monzonitic composition. In view of this diffi- culty two other sources for the mafic dike magma merit consideration : (1) the magma for the dikes was derived from a deep earth layer, and (2) the dike magma was remobilized from masses of older diorite, gabbro, and mafic volcanic rock. The chief argument in favor of the first suggestion is that the dikes are in swarms that extend many miles along the strike. - The arguments for the second suggestion are that many dikes are indis- tinguishable on the basis of their texture and mineral content from mafic inclusions and that in many places, as along the north side of the Glacier Divide and along the South Fork of Big Pine Creek, the dikes are closely associated with abundant inclusions of dark-colored GEOLOGY OF THE BATHOLITH 99 plutonic or volcanic rocks. Further support for the second suggestion is that in gross distribution the dikes are associated with the string of Mesozoic metavolanic roof pendants that extend southward to the Alabama Hills (fig. 7). BROAD PROBLEMS RELATING TO THE BATHOLITH SEQUENCE OF EMPLACEMENT The age relations of the granitic rocks were estab- lished wherever possible by observing the contacts between pairs of rocks in the field. The principal fea- tures that were used to determine the relative ages were aschistic dikes and apophyses, inclusions, trun- cated structures, and the presence of characteristic marginal features. Not all of the granitic rocks are in contact with one another, and the relative ages of some that are could not be determined. Contacts that pro- vided no critical data include those where two intru- sions meet along a featureless surface, those occupied by dikes or by septa of metamorphic rock, and those obscured by weathering and cover. The intrusive relations of the granitic rocks, based on the available data and an interpretation of the sequence of intrusion, are given in fig. 41. The granitic rocks can be conveniently divided on the basis of geographic distribution into three se- quences, two of which are not in contact with each other. These are the Tinemaha sequence, which lies entirely south of Big Pine Creek; the Bishop sequence, which lies entirely north of Big Pine Creek ; and a third group, which is present both north and south of Big Pine Creek. In the Bishop sequence the oldest rock is the Wheeler Crest quartz monzonite, followed successively by the Round Valley Peak granodiorite, the Tungsten Hills quartz monzonite, and the granodiorite of Coyote Flat. In the Tinemaha sequence the oldest rock is probably the Inconsolable granodiorite, followed by the Tine- maha granodiorite, and finally by the quartz monzonite of McMurry Meadows. However, the intrusive rela- tions between the Inconsolable and Tinemaha grano- diorites are uncertain; in one place the Tinemaha granodiorite appears to intrude the Inconsolable granodiorite, and in another place the reverse is sug- gested. The quartz monzonite of McMurry Meadows intrudes the Tinemaha granodiorite and is not in con- tact with the Inconsolable granodiorite. The relative ages of the rocks in these two sequences is fixed within broad limits by their intrusive relations with rocks of the third group, but their positions as shown in figure 41 also reflect textural and composi- tonal similarities and differences in the rocks of the two sequences. Thus, the Tinemaha granodiorite is Granodiorite Granodiorite of Cartridge of Coyote Pass Flat (~ ’J’ ~ a \\ a= \ Finer-grained x quartz s monzonite x I \ ~ i C Rocks similar to Xx the Cathedral XJ Peak granite "< ~ N ~ Tungsten Hills quartz monzonite I \ 1 I Granodiorite | j | of Deep | | Canyon I | 1 x L1 6 11 [4 / I é Lamarck “Hits/EH“ i granodiorite granodiorite ‘| I Granodiorite i of McMurry Meadows /| / Tinemaha Wheeler Crest MOP quartz granodiorite monzonite I 1 Inconsolable granodiorite Diorite, quartz diorite, and hornblende gabbro FiGurE 41.-Diagram showing the intrusive relations and probable age sequence of the granitic rocks. Solid lines indicate observed rela- tions; dashed lines indicate probable relations inferred from the map patterns, or from inconclusive field observations. somewhat similar in appearance and composition to the Wheeler Crest quartz monzonite; in lieu of any other age criteria these rocks are shown to be temporal equivalents. The rocks of the third group, which occur both north and south of Big Pine Creek, include the oldest and some of the youngest rocks. Masses of mafic rock- diorite, quartz diorite, and hornblende gabbro-are in- truded by all the other rocks. The Lamarck grano- diorite intrudes both the Inconsolable and Tinemaha granodiorites of the Tinemaha sequence, and is intruded by the Tungsten Hills quartz monzonite of the Bishop sequence. It also is intruded by quartz monzonite sim- ilar to the Cathedral Peak granite. With the excep- tion of the granodiorite of Coyote Flat and the possible exception of the granodiorite of Cartridge Pass and finer grained quartz monzonite, alaskite and quartz monzonite similar to the Cathedral Peak granite in- trude all the other rocks. The rocks mapped as finer grained quartz monzonite are closely jointed and are weathered to rubble that drifts across and obscures most - contacts, but the map pattern suggests that at least 100 some masses intrude quartz monzonite similar to the Cathedral Peak granite. The map pattern also indi- cates that the granodiorites of Coyote Flat and Car- tridge Pass may be intrusive into all the rocks with which they are in contact. On the whole the rocks appear to have been emplaced generally in order of their increasing silica content. Notable exceptions are the granodiorites of Coyote Flat and Cartridge Pass, which may be early members of a younger sequence that is not otherwise represented. AGE The Sierra Nevada batholith has been variously referred to as of Jurassic or Cretaceous age; the geo- logic relations provide no basis for discriminaton. In the western foothills, granitic rocks intrude Upper Jurassic strata (Mariposa formation), and the meta- morphic terrane which the granitic rocks intrude is unconformably overlain by Upper Cretaceous strata (Chico formation). In the Devils Postpile quadrangle, northwest of the Bishop area, granitic rocks intrude fossiliferous strata of Early Jurassic age (Rinehart, Ross, and Huber, 1959), and in the Inyo Mountains they intrude Middle Triassic strata. Hinds (1934) demonstrated that the Shasta Bally batholith, a granitic mass near Redding, Calif., on the trend of the Sierra Nevada but separated from it many miles, is almost certainly of Late Jurassic age, and sug- gested that the Sierra Nevada batholith is of the same age. Although this suggestion was accepted by many, the reported presence in Lower California of fossili- ferous Lower Cretaceous and lower Upper Cretaceous strata in a terrane intruded by granitic stocks and batholiths raised doubt in the minds of some (Wood- ford and Harriss, 1938, p. 1330 ; Bose and Wittich, 1913, p. 894). The first radiometric determinations of Sierran rocks were of eight samples collected from the Bishop area. GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA The determinations were made by E. S. Larsen, Jr., and associates by using the lead-alpha method (Larsen and others, 1958, table 9, p. 52-53). The results are summarized in table 16. The calculated ages range from 88 to 116 million years, and the average is 105 million years. The lead-alpha ages show little relation to observed intrusive relations. Larsen and others (1952) believe that the error inherent in the lead-alpha method is about 10 percent; this error probably is too large to permit comparing the age of one intrusive with another. Later the ages of a suite of granitic rocks from Yosemite National Park were determined by the potas- sium-argon method (Evernden, Curtis, and Lipson, 1957, p. 2120-2125 ; Curtis, Evernden, and Lipson, 1958, p. 7-9). The calculated ages of these rocks range from 76.9 to 95.3 million years and show remarkable agree- ment with the order of intrusion as established in the field by Calkins (1930, p. 120-129). The error in the method is thought to be only about 1 to 2 percent. The Cathedral Peak granite was determined to have an age of 83.7 million years; if masses in the Bishop district are correctly assigned to the Cathedral Peak this figure provides an index to the ages of the Bishop district rocks by the potassium-argon method. The Cretaceous period lasted from 135 to 70 million years ago according to Holmes' revision of his time scale (1960), and from 133 to 58 million years ago ac- cording to a calculation by Curtis, Evernden, and Lip- son (1958, p. 11). On these scales both the lead-alpha determinations of Bishop district rocks and potassium- argon determinations of the Yosemite rocks fall close to the middle of the Cretaceous. Many difficulties are still to be worked out in integrating radiometric age with paleontologic age, but it seems reasonable to assume that the main part of the Sierra Nevada batholith is of Cretaceous age, although some plutons intrusive into the metamorphic terrane on the west side of the main TABLE 16.-Lead-alpha ages of granitic rocks from the Sierra Nevada near Bishop [Data from Larsen and others (1958)] Probable Activity Calculated Intrusive Mass Location order of Mineral (a per mg| Lead (parts per age (10 emplace- per hr) million) years) ment Quartz monzonite similar to | Mount Alice.___.. Big Pine quadrangle S W34 sec. 26, T. 9 S., R. 32 6 | 18 1 105 Cathedral Peak granite. E. At end of Big Pine Creek road. Tungsten Hills quarts mon- | Morgan Creek____| Mt. Tom quadrangle West of surface workings b:... do:.-... 106 | 116 zonite. Pine Creek mine. Tungsten Hills quarts mon- | Bishop Creek.... Mt. Goddard quadrangle NEJ see. 20, T. 8 S., B (10... 2 T92 1 862.1. 2rd. 110 zonite. R. 31 E. Along Bishop Creek road. Zireon 400 | 15 93 Lamarck Mt. Goddard quadrangle N W34 sec. 14, T. 9 S., 4 {Thotité """ 4 670 | Abc 88} 91 R. 31 E. NF side of South Lake. ' lii |) c sol { MWe [Sear af e MIII Round Valley Peak grano- | Round Valley Mt. Tom quadrangle 14 mile NE of Rock Creek 4) Zircon...._.. 396 | 12, 13, 14, 16 (13.8). 88 diorite. Peak. Lake. Grfinogiorite Of | MeMutry nga I)?“ quadrangle NEX see. 9, T. 10 S., R. 3 | Monazite... 4,897 | 234, 238 (236)....-- 100 eadows. 4 Tinemaha granodiorite. Bi3g3 Iéme quadrangle NW1I4 see. 14, T. 10 S., R. 9 | Zircon... 331 | 15, 16 (15.5)......._ 116 Inconsolable granodiorite.......}.................... Big Pine quadrangle SE cor. sec. 33, T. 9 S., R. do...... LL A0. c. cence uue. 112 33 E. 14 mile S. of Third Lake. GEOLOGY OF THE BATHOLITH batholith are older (Curtis, Evernden, and Lipson, 1958, p. 6). BROAD CHEMICAL AND MINERALOGICAL VARIATIONS A broad trend from calcic and ferromagnesian to silicic and alkalic is shown by the sequence of intrusion. The chemical and modal analyses provide a basis for examining variations in compositions and mineral con- tent in a quantitative as well as a qualitative way. The curves in figure 42 are based on 15 chemically analyzed specimens; 14 of the specimens were collected during this study, and the 15th is a specimen of alaskite similar to the Cathedral Peak granite that was collected by Knopf (1918, p. 68). The chemical analyses are given © a s a o - £2 3 fo 5C $ § = g o ao V 'C N N i with - 6 55 o£ N 9 o 5 2 5 E E o 2 2 > F4 N Nn £ € cof £9 C 2 6 6 2 2D < o N 3 8 a w L 0 5 = € 03 E ° 8 5 [3 9 e C UG 3 M 2 a+ roll:) s ee T hel T - s¢ a 9 ch 's 0 w I & s 0 ho © ~ C = 0 E% € o bo ® 6 = & -G = 4 m* a- £ T © x a & 2 § s® 5 wo -: 48 kel $ 4 s £ ' « $ {o a o o G 3 o a 2 ® o£ bl @ £0 o = w 55 fell) s "Ns e5 $ - f 8 cs,. £9 § vs E8 3° & B 0 5 Fe 0 S e 25 |- ~ in ib x) - 50 \ 3.8 * A An in plagioclase 20 |- 10 |- PERCENT OF COMMON OXIDES PERCENT OF An IN NORMATIVE PLAGIOCLASE o e Nn w A o T o- n w a o Eel ford 60 65 70 75 80 PERCENT OF SiO, Ficurs 42.-Variation diagram of common oxides in granitic rocks of the Bishop district plotted against SiO,. 101 in table 3. In figure 42 the principal oxides are plotted against SiO;; the anorthite content of normative pla- gioclase also is shown. The SiO; in the 15 specimens ranges from 59.0 per- cent in quartz diorite to 76.3 percent in Knopf's speci- men of alaskite. Except for minor variations, the curves of the oxides appear regular. As SiO; increases, A1;0;, CaO, MgO, FeO, and Fe;0; all decrease. Na,0 is nearly constant below 70 percent SiO;, but increases slightly above 70 percent, and a single analysis suggests it rises sharply above 75 percent. K;,0 increases regu- larly with SiO; to 70 percent SiO», and is nearly con- stant above 70 percent SiO,. The curve for plagioclase composition shows that the normative content of anor- thite diminishes with increasing SiO, and that the amount of decrease is greater in the lower and higher ranges of SiO, and smaller in the intermediate range (62-70 percent SiO,). The normative compositions of the 15 chemically analyzed specimens were calculated according to the CIPW method, and are reported in tables 4-9, 11, and 12. Quartz, orthoclase, and plagioclase (albite plus anorthite) were calculated to 100 percent and plotted on a triangular quartz-orthoclase-plagioclase diagram (fig. 43). On this diagram the norms fall in a narrow band that extends from the center of the diagram to- ward the plagioclase corner. This pattern shows that the ratio between normative quartz and orthoclase is virtually constant, very close to 1:1, and that quartz plus orthoclase is inversely proportional to plagioclase. The arithmetic average of the modal analyses from different masses and plutons are given in table 17, and the figure 44 the modal averages of quartz, K feldspar, and plagioclase for different plutons and masses have been calculated to 100 percent and plotted on a trian- gular diagram. In a general way the plot of modes re- sembles the plot of norms (fig. 43). The chief differ- ences are that the field of modes extends farther away from the plagioclase corner, past the center of the tri- angle, and that the long axis of the field of modes is slightly inclined to that of the field of norms. Inas- much as modes are determined from real minerals and norms are theoretically pure molecules computed from chemical analyses, it is hardly expectable that they would plot in the same positions on a triangular diagram. The differences in the fields of norms and modes probably result chiefly from two factors: (1) crystal- lization of increasingly larger amounts of biotite in the rocks toward the plagioclase corner, and (2) increas- ingly larger amounts of albite in K feldspar in rocks away from the plagioclase corner. Crystallization of biotite deletes K,0 from the magma, and results in 102 Quartz Plagioclase Orthoclase 43.-Plot of norms of granitic rocks on quartz-orthoclase- plagioclase diagram; od, quartz diorite; T, Tinemaha granodiorite; I, Inconsolable granodiorite; M, granodiorite of McMurry Meadows; W, Wheeler Crest quartz monzonite; R, Round Valley Peak grano- diorite; L, Lamarck granodiorite; T, Tungsten Hills quartz mon- zonite; C, Rock similar to Cathedral Peak granite. less modal K feldspar than normative orthoclase; be- cause biotite increases in abundance with plagioclase, toward the plagioclase corner the modal field is shifted progressively away from orthoclase as compared with the normative field. Solid solution of albite in K feldspar increases the amount of modal K feldspar over normative orthoclase. The amount of albite in K feldspar is greatest in rocks having the least plagio- clase because these rocks contains the most K feldspar and because the K feldspar is conspicuously perthitic. The result is that the field of modes is expanded at the end most distant from plagioclase away from plagio- clase and toward K feldspar. In figure 45 the average percent of modal quartz, K feldspar, biotite, and hornblende, given in table 17, are plotted against average percent of modal plagio- clase. The diagram shows that quartz and K feldspar are about equally abundant in all rocks and that they decrease systematically as plagioclase increases. Bio- tite and hornblende increase with plagioclase, and bio- tite is, on the average, about 4 percent more abundant than hornblende. A notable exception is the Tinemaha granodiorite, which contains more hornblende than bio- tite. Hornblende generally is present only in trace amounts in rocks that contain less than 37 percent of plagioclase, although a few masses of rock having less than this amount of plagioclase, such as the Morgan Creek and Pine Creek masses of Tungsten Hills quartz monzonite, contain several percent of hornblende. Thirty-seven percent of the modal plagioclase falls in GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA Quartz Potassium feldspar Plagioclase (including perthite) R, Round Valley Peak granodiorite L, Lamarck granodiorite M, Granodiorite of McMurry Meadows W, Wheeler Crest quartz monzonite T, Tinemaha granodiorite 1, Inconsolable granodiorite Cy, Granodiorite of Coyote Flat D, Granodiorite of Deep Canyon Finer grained quartz monzonite : Fw, Sherwin Hill mass Fr, Freeman Creek, Shannon Canyon, and Sugarloaf masses Fi, Taboose mass Rocks similar to the Cathedral Peak granite : Cm, Lobes of Mono Recesses mass Ca, Mount Alice mass Cp, Palisade Creek mass Cak, Alaskite masses Tungsten Hills quartz monzonite : Tm, Morgan Creek and Pine Creek masses T», Basin Mountain mass T+, Tungsten Hills and Bishop Creek masses Ts, Shannon Canyon mass FicurB 44.-Plot of arithmetic modal averages of quartz, K feldspar, and plagioclase in different plutons. the lower part of the quartz monzonite field near the boundary between the quartz monzonite and grano- diorite fields, and the presence or absence of appreciable hornblende is a useful and generally reliable criteria for distinguishing between granodiorite and quartz monzonite among eastern Sierra granitic rocks. Calcic quartz monzonite generally contains a few percent horn- blende, however. SYSTEMATIC COMPOSITIONAL VARIATIONS WITHIN INDIVIDUAL MASSES Some masses of granitic rock are obviously composi- tionally zoned, and many others that are superficially of uniform appearance and mineral composition are found on careful study to vary systematically in com- position from place to place. Compositional varia- tions are either concentric or lateral. The granodiorite of McMurry Meadows is an ex- cellent example of a concentrically zoned intrusion; GEOLOGY OF THE BATHOLITH 103 TABLE 17.-Arithmetic averages of modal analyses for different plutons, in volume percent [Percentages of biotite, hornblende, and accessory and secondary minerals were determined from thin section, and their sums do not necessarily equal the percentages of total mafic, which were determined chiefly from stained slabs] Accessory Formation and mass Specific Quartz K feldspar Plagioclase Biotite Hornblende | and second- | Total mafic gravity ary minerals Granodiorite of Coyote Flat......_._.___._.___..._...__ 2.71 22.1 12.8 47.9 8.7 4.7 3.9 17.3 Finer grained quartz monzonite: SREEWIA Hill cr crece cece nece ces eens eens. 2. 63 36.3 31.0 28.1 3.3 4 1.0 4.7 Freeman Creek, Middle Fork, and Sugarloaf masses......... 2. 64 26.0 28. 8 40.0 4. 4 0 .8 5.2 'Taboose mass. ___ 2.62 35.7. 28. 4 31. 4 3.6 0 18 4.4 Rocks similar to the C: Lobes of Mono-Recesses mass... 2. 62 25.1 32.7 38. 3 2.9 0 2.2 3.8 Mount MASES LL cL, LLL o CL 2. 61 31.2 38. 8 27. 4 2.1 0 2.8 2.6 Palisade Creek and Red Mountain Creek masses... 2. 60 30.0 38. 3 290. 2 2.1 .2 1.7 2.5 :cool: ee ne one ln coe een even er 2. 60 33.0 38.6 25.8 1.8 12 2.2 2.9 Tungsten Hills quartz monzonite: Morgan Creek and Pine Creek masses.._._.._....~ 2.62 31.9 20.1 32. 5 4.8 3.9 1.4 6.5 Basin Mountain mass.. ._._..__.__.--___-- 2. 65 28. 4 25. 4 38. 4 5.9 1.4 2.7 8.2 Tungsten Hills and Bishop Creek masses.. 2. 63 20.8 31.0 38. 2 5.5 2 2.1 6.0 Shannon Canyon masses.........._..._...... 2. 62 27.1 33.5 32.9 4.0 * 2.9 5.9 Granodiorite of Deep Canyon.... 2.70 28.6 14.8 45. 4 9.3 3.7 3.1 16.1 Lamarck granodiorite: Chickenfoot Lake mass.... 2.71. 21.6 27.1 36. 2 6 1 8.1 3.2 15.1 Lamarck mass (main part) . 2. 70 23.1 21.0 43. 2 6.8 8.3 1.5 12.9 Lamarck mass (south part) . 2. 65 28. 6 26. 5 38. 2 5.3 .6 1.0 6.7 Round Valley Peak granodiorite... 2. 69 26. 8 18.7 44. 4 7.2 3.6 1.9 10 1 Wheeler Crest quartz monzonite..... 2. 65 290. 3 25.3 35.3 5.8 1.6 1.6 10. 1 Granodiorite of McMurry Meadows.. 2.70 20. 5 26. 4 40.1 8.0 3.1 1.6 12.7 Tinemaha granodiorite............---- es 2.172 21.3 23.6 39. 0 4.6 6.0 3. 4 16.1 Inconsolable eranodiorite.........._..._.._..___..___.. 2.175 13.1 15.6 49. 3 10. 4 5.7 2.9 22.0 $99: the core. Concentric zoning is also shown by the grano- _=a diorite of Cartridge Pass, the Round Valley Peak granodiorite, and to a lesser degree, by the granodiorite of Coyote Flat. Even the Tinemaha granodiorite and the main northern part of the Lamarck granodiorite a ag have core areas in which the specific gravity is less than ® le - & : in marginal areas. § Lateral variations are obvious chiefly in the largest a EXPLANATION 11.1tru51ve masses, espec1-ally in the Lamarck granodlo- - rite and the Tungsten Hills quartz monzonite. The & 4 o Quartz narrow southern extension of the Lamarck granodio- [n] a 20 |- 4 rite south of Hurd Peak and Bishop Pass is notably R Potassium feldspar lighter in color, lower in specific gravity, and less H a e calcic than the thicker northern part. The granodiorite 5 Biotite ye. part of the Basin Mountain mass of Tungsten Hills 5 l e uartz monzonite that lies west of Desolation Lake is £ m Hornblende - P + 0 darker and heavier, and contains more plagioclase than €. 19 / most of the rest of the mass. The Tungsten Hills quartz monzonite also may grade in the Tungsten Hills & into the largest mass of granodiorite of Deep Canyon, N U U * //// Q@\\\°‘\ but this relation was not established. « s ; 4 3 W \§}\ ® In most intrusive masses, systematic changes in com- \ *, * - ® - - ® $ o m § position probably reflect dlfi'grenplatlon during cooling, 20 30 40 50 but in some masses contamination by wall rocks has PERCENT OF PLAGIOCLASE FIGURE 45.-Average percent of modal quartz, K feldspar, biotite, and hornblende in different plutons plotted against average percent of modal plagioclase. the rim is granodiorite rich in plagioclase and ferro- magnesian minerals, and the core is light-colored quartz monzonite. The specific gravities of specimens from the margin are greater than of specimens from been the cause of compositional differences. The usual basis for distinguishing between the effects of con- tamination and of differentiation is the presence or absence of rock of the proper composition and in the proper position to indicate the cause of compositional variations in an intrusive. In places where contamina- tion has been effective in modifying the composition of a granitic intrusive, the contaminating rock generally is either early mafic intrusive rock or mafic volcanic 104 rock. A good example of contamination of an intrusive by mafic igneous rock is in the Chickenfoot Lake mass of Lamarck granodiorite, which is progressively dark- er and more calcic toward its southern margin where it is in contact with hornblende gabbro. Calcium-rich wall rocks also seem likely to influence the composition of a magma. Where no evidence is found of contamination by wall rocks, crystal fractionation is usually invoked to ex- plain systematic variations in composition. In a granitic intrusive, early formed crystals of plagioclase, hornblende, and the accessory minerals are presumed to settle or to accrete to the walls. Convection could be effective in the marginal accretion of erystals by bringing erystals into contact with the walls. A possible contributing process may be that of thermodiffusion. At one time the Soret effect was thought to be a principal cause of differentiation in magmas, but this explanation has been in disfavor for many years because of the presumed slow velocity of diffusion in viscous silicate melts. Wahl (1946) is one of the few advocates in recent years of diffusion in mag- matic differentiation. My concept of the kind of dif- fusion that might operate is that of a gradual shift of calcium and the femic constituents outward from the core of the magma body in response to impoverishment of these constituents in the liquid phase near the mar- gins as a result of crystallization. Even though the rate of diffusion may be very slow-perhaps only a few centimeters a year-over the period of erystallization of a pluton, which may extend over hundreds of thou- sands of years, diffusion could play a significant role in differentiation. Both crystal fractionation and thermodiffusion per- mit formation of rock in the margins of an intrusion that is more salic than the magma, and can be respon- sible for a concentrically zoned intrusive. The mar- ginal part of a zoned intrusion does not necessarily represent the original composition of the magma, even if it is fine grained as compared with the interior of the intrusion (unless it is glass). On the contrary, if it can be assumed that either or both convection and high viscosity inhibited the sinking of significant amounts of crystals, the initial composition of the magma will be represented more accurately by the average com- position of the exposed rocks. Lateral changes in composition from one side or one end of an intrusive to the other can be most easily explained if it is assumed that after partial differentia- tion and solidification of the margins, renewed move- ments of the still liquid magma in the central part took place. Abrupt contacts could result from movements of the magma after consolidation of the margins. A GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA local internal contact in the Tungsten Hills between two different facies of the Tungsten Hills quartz mon- zonite could be a result of such movement. However, abrupt contacts would result only if parts of the intru- sive were rather completely crystallized; otherwise gradational contacts should result. The Lamarck granodiorite may have been intruded initially as an el- liptical body whose southern limit was near Bishop Pass. After partial crystallization in the margins and differentation of the core magma to quartz monzonite composition, the magma may have broken out of its chamber southeastward, probably along a fracture, to form the felsic southern extension. Inasmuch no sharp contacts have been found, it is not likely that the mar- gins of the original elliptical body were entirely solidi- fied. An excellent example of a concentrically zoned intrusive in which the residual core magma moved re- peatedly is the White Creek batholith in British Columbia (Reesor, 1958). CORRELATION OF NORMATIVE COMPOSITIONS OF THE GRANITIC ROCKS WITH EXPERIMENTAL DATA Since granitic rocks consist chiefly of quartz and feld- spar, they can be approximately experimentally by mix- tures of SiO,, KAISi;O;, NaAISi;0, and CaA¥Al,851;0;, hereafter referred to as Qz, Or, Ab, and An. In the east-central Sierra Nevada the content of normative feldspar and quartz ranges from 79.4 in a specimen of quartz diorite to 99.3 in a specimen of alaskite. A con- siderable amount of experimental work has been car- ried on which such artificial mixtures, particularly by N. L. Bowen, J. F. Schairer, and O. F. Tuttle at the Geophysical Laboratory of the Carnegie Institution of Washington, D.C. These three workers, together with R. R. Franco, have experimentally studied the liquidus relations at atmospheric pressure in all the binary and ternary combinations of this four-component system. The ternary system Qz-Or-Ab was studied by Bowen (1937), the system Qz-Or-An by Schairer and Bowen (1947), the system Or-Ab-An by Franco and Schairer (1951), and the system Qz-Ab-An by Schairer (written communication, 1957). Bowen and Tuttle have also de- termined certain liquidus relations in systems that in- clude H0 under pressure (Bowen, 1954; Tuttle and Bowen, 1958). Yoder, Stewart, and Smith (1957) have studied the system Or-Ab-An-H.0 at 5,000 bars, and Stewart (1958) has studied the system Qz-An-H.,0 at various pressures. The liquidus relations in the system Or-Ab-An-Qz- H,0 at 5,000 bars H,O pressure are shown in figure 46. In figure 464 projections of norms of the granitic rocks from the east-central Sierra Nevada are shown on the faces of the tetrahedron. The positions of the norms can be misleading if due allowance is not made 748° Ab An Qz An (CaAl;Si;0§) (SiO) (CaAfiSIDZOg) 1235° a15° 1065° 1065° a15° 1235 6/ / ’/ ’/ i e a 35 "3 s £9 Plagiolclase f [l Beta quartz C, \ \ P|ag|o€lase 3 \ \ I \ d / \ \ yi 094 \ * \ \\ j \‘ ~~-10004-~ l‘ \ \ \ | I I \ ute: L Beta quartz t>. 3 5 ¥ ~ "f b h *x~--9004~ I \ \ Position of quartz-feldspar \‘ \ \ boundary and temperature € \ minimum atffiargaus pets o s pressures 0 e ca L 0L__2;°0 gars & An TA t An 1235" Z Or-Ab feldspar 1235° P e 0/ Ab 748° "*S" or ; 748° a76° ; 748° 700° are» /-_1200%- Or-Ab feldspar 800 849" Plagioclase f Plagioclase ; Qz Plagioclase Qz 1065° 1065° 1 100% Beta quartz 695 Erou' a Amar 650 Ab .Pected trace of p 748° roj r feldspar - f Alpha quartz Alpha'quartz boundary curve between quartz, plagioclase, and Or-Ab feldspar ields 698° - B 876° 1235° C 876° Or An Or A FiGurE 46.-Tetrahedron showing the liquidus relations in the system Or (KA1S1,0,)-Ab(NaA1S1,0,)-An(CaA1,8i;0,)-Qz(S10,)-H,0 at 5,000 bars H,O pressure. -All components are in weight percent. A, Faces of tetrahedron showing field boundaries (heavy lines), isotherms (light lines and dashes), and projections of norms of granitic rocks from the east- central Sierra Nevada (points). Or-Ab-An face is after Yoder, Stewart, and Smith (1957). An-Qz join is after Stewart (1958). Inversion temperature of quartz is after Yoder (1950). Temperature and position of Or-Ab-Qz minimum and positions and temperatures of other field boundaries were projected by D. B. Stewart (written communi- cation, 1958) from data of Tuttle and Bowen (1958) and H. R. Shaw (Stewart, written communication, 1960). Quartz-feldspar boundary and temperature minimum at various H,O pressures after Tuttle and Bowen (1958). Isotherms, except on Or-Ab-An face and along An-Qz join were constructed with reference to the above data and are approxi- mate. B, Three-dimensional drawing of tetrahedron showing field boundaries. The minimum lies at 650°. C, Bisecting section through tetrahedron passing through Ab and An corners and intersecting the Or-Qz join at midpoint. On the section are plotted isotherms; field boundaries between alpha quartz, beta quartz, and plagioclase ; projections of norms of rocks from the east-central Sierra Nevada; and projected trace of boundary curve between quartz, plagioclase, and Or-Ab feldspar fields. HLITIOHILYVY HHL AXO ADOTOMD SOT 106 for the fact that they are projections. Their positions were determined by calculating to 100 percent the three constituents represented in each face. From a visual standpoint, the points are plotted as they would appear within the tetrahedron if they were viewed by looking at each face with the eye at the opposite corner. As a consequence of the construction, the spread of norms on the tetrahedron faces is greater than the true field within the tetrahedron. The tetrahedron is shown in three-dimensional form in figure 46B. The plagio- clase field occupies most of the tetrahedron, a quartz field occupies a part of the tetrahedron near the Qz corner, and a flattish Qz-Ab feldspar field extends out- ward from the Or corner toward Ab and Qz. Because most of the granitic rocks contain almost equal amounts of normative quartz and orthoclase, the plane within the tetrahedron that approximates most closely the true field of the norms is one which bisects the tetrahedron as shown in figure 46C. The norms are projected only short distances to this plane and appear in very nearly their true positions. The plane intersects the boundary between the plagioclase and quartz fields at a small angle, and does not intersect the Or-Ab feldspar field at all. However, the boundary line between quartz, Or-Ab feldspar, and plagioclase converges on the sec- tion at a small angle and very nearly intersects it at the minimum. Because this boundary line is so close, it is projected onto the section. It is apparent from the section that the norms fall either within the plagioclase field or very close to the field boundary between quartz and plagioclase. In general, but not in detail, the oldest rocks are those whose norms plot highest in the diagram and nearest An, and the youngest plot closest to the temperature minimum. - The pattern of norms is very close to that of a theoretical path for the composition of a differ- entiating liquid, and strongly supports the view that the granitic rocks in the east-central Sierra Nevada are fundamentally of magmatic origin (Barth, 1952, fig. 20, p. 101). Magma of the composition of the norm having the most An (quartz diorite) would first crystal- lize calcic plagioclase at the HO saturated liquidus (slightly below 1000°C). Crystallization of the calcic plagioclase would cause the composition of the remain- ing liquid to be displaced away from An and, to a les- ser degree, Ab. With falling temperatures the amount of Ab in the crystallizing plagioclase would increase, which would cause the composition of the remaining liquid to change along a curved path, convex toward Ab. On reaching the quartz or Or-Ab feldspar field boundary, a second mineral would begin to crystallize. If the quartz boundary surface were intersected first, as appears to have happened, quartz would begin to crys- GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA tallize in addition to plagioclase, and the composition of the melt would move away from the SiO; corner of the tetrahedron as well as from the An and Ab corners in a path that would be determined by the relative amounts of quartz and plagioclase crystallizing and by the composition of the plagioclase. This path would ultimately so change the composition of the remaining liquid that Or-Ab feldspar also would begin to crystal- lize. The liquid would then lie on the common bound- ary line of the quartz, plagioclase, and Or-Ab feldspar fields. Inasmuch as the path along this boundary curve is toward Ab, and because at the low temperature (about 700°C) the plagioclase crystallized would be Ab rich, much more quartz and Or-Ab feldspar would erys- tallize than plagioclase. At the temperature minimum the relative amount of albitic plagioclase erystallizing probably would increase ; the theoretical composition of the liquid and of the crystallizing constituents would be Ab 44.5 percent, Or 28.5 percent, and Qz 27.0 percent. However, extreme fractionation would have to occur for the minimum to be reached, and separation of a gas phase may affect the ratio of constituents in the liquid. If no crystals were subtracted from the melt during cooling and crystallization, the final rock would have the same composition as the initial melt. However, if during crystallization some crystals were removed, the bulk composition of melt plus the remaining crystals would keep changing. If parts of this residual magma were intruded at different times, the rocks formed from them would have different compositions. The norms as plotted on the section (fig. 46C) seem to be in a plane parallel to, and nearly coinciding with, the position of the field boundary between quartz and Or-Ab feldspar at 5,000 bars of water-vapor pressure; however, it must be remembered that the norms are pro- jected, even though for only short distances, and the field boundary is cut at an unfavorable angle for ac- curately depicting the position of the norms with respect to this field boundary. It is therefore possible that the position of the quartz Or-Ab feldspar field boundary at some other vapor pressure would fit the distribution of norms better. The position of the boundary shifts toward the SiO; corner at lower pressures of H;0, as is shown in figure 464 (Bowen, 1954). Goranson (1931) determined the solubility of water in glass made from granite from Stone Mountain, Ga., to be-at 800° C-about 8.9 percent at 3,000 bars and 9.3 percent at 4,000 bars. These figures are in close agreement with figures obtained by Tuttle and Bowen (1958, fig. 28, p. 58) for melts of minimum melting com- position in the system Or-Ab-Qz-H.0. The amount of HO present in an undifferentiated magma is probably less than the maximum amount that is soluble in the GEOLOGY OF THE BATHOLITH magma. In all probability an amount of H0 equal to the amount soluble is attained only in the late stages of crystallization, after the crystallization of substantial amounts of anhydrous or nearly anhydrous minerals. The diagrams indicate that plagioclase began to crystallize in the most calcic magma represented by a point on the diagrams at about 970° C and that quartz and alkali feldspars completed crystallization in the most silicic magma represented at about 650° C. How- ever, these temperatures would be correct only if the magmas represented were saturated with H,O through- out crystallization and only if the additional compo- nents in the magma not represented on the diagrams did not affect the crystallization temperatures. Experi- mental evidence suggests that additional components may lower the crystallization temperatures markedly (D. B. Stewart, written communication, 1960). If saturation of the melts with HO was achieved only in the later stages of crystallization, the first plagioclase may have crystallized at temperatures higher than 970° C. Another possibility is that the most calcic rocks repre- sent collections of early crystallized crystals in magma less calcic than the rock. This possibility is partly negated by the fact that the norms of these rocks plot along the theoretical path followed by a silicate melt during cooling. If the pressure of HO in the closing stages of dif- ferentiation was about 5,000 bars, as the data suggest, and if the pressure of H;0 at that time was roughly equal to the rock pressure resulting from load, the depth of differentiation was at least 11 miles. The depth of final crystallization could have been less, for masses of magma from a parent body differentiating at depth could have moved higher into the crust with only local additional differentiation. Nevertheless, the zonation of many plutons suggests that significant differentiaton took place at the present level of exposure. I infer from these considerations that the present level of exposure was about 11 miles beneath the surface of exposure at the time of emplacement of the granitic rocks. COMPARISON OF COMPOSITIONAL TRENDS WITH TRENDS OF GRANITIC SUITES FROM OTHER AREAS For comparison with suites of granitic rocks from other areas, plots of norms on triangular Qz-Or-PIl (Ant+Ab) diagrams (fig. 47) are used because signifi- cant similarities and differences can be represented readily without resorting to oxide variation diagrams or four-component Qz-Or-Ab-An diagrams. Plots of modes would be useful for making comparisons of suites of rocks, but unfortunately few suites have been ana- lyzed with sufficient accuracy and in sufficient detail. 107 Plots of norms of granitic rocks from various areas in the western United States and Canada are shown in figure 47. All the plots are elongate and extend away from the PI corner to an area of convergence near the center of the diagram. Some plots extend nearly to the PI corner, whereas others, including that of the eastern Sierra Nevada, terminate at considerable distances from the Pl corner. In part the failure to extend closer to the PI corner results from a lack of chemical analyses rather than from a lack of rocks that would plot near the PI corner. Nevertheless, the absence of analyses of plagioclase-rich rocks generally reflects a paucity of such rocks in the terrane. In the eastern Sierra Nevada, plagioclase-rich rocks are generally in small bodies of variable texture and percentage mineral content ; conse- quently, analyses of these rocks are not of much signifi- cance for general purposes, and few have been made. On the other hand, in granitic areas such as the batho- lith of southern California, where plagioclase-rich rocks are in large bodies and constitute a significant part of the terrane, abundant analyses have been made. All the plots except those of the Idaho and Boulder batholiths, which are irregular, converge at the center of the diagram, and the most elongate ones also con- verge at the Pl corner. Between these two areas of convergence the plots follow different trends. On the basis of these trends the plots can be categorized into three groups, although it is recognized that the groups are completely gradational. The plots of the batholith of southern California, the Bald Mountain batholith, and the Mount Garibaldi area lie along trends that extend away from PI in a direction toward Qz; at about 30 to 40 percent of quartz they bend toward the center of the diagram. In contrast, the plots of the Laramide stocks of Colorado and New Mexico and of rocks from the Kuskokwim region, Alaska, lie along trends that extend from the PI-Or sideline between 20 and 50 per- cent of Or toward the center of the diagram. The third group, which includes the eastern Sierra Nevada and the Cowichan Lake area of Vancouver Island, British Columbia, is intermediate to the other two; these plots of norms extend away from PI almost directly toward the center of the diagram. The patterns of the trends show close correlation with experimental data. In figure 48, the interpreted median lines of the various fields of norms are plotted on a triangular quartz-orthoclase-plagioclase diagram on which the experimentally determined boundary curve between quartz and feldspar is shown for Pz, 1,000 and 5,000 bars, since this boundary shifts with dif- ferences in water vapor pressure. The plagioclase of the rocks is, of course, not albite, but the field boun- daries shown, nevertheless, are as good approximations 108 Qz GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA Qz PI - Mount Garibaldi area, southwestern - Or PI British Columbia (Mathews, 1958) Bald Mountain batholith, northeastern Or PI Oregon (Taubeneck, 1957) Batholith of southern California Or (Larsen, 1948) Qz Qz pL ~ ~- Idaho batholith Or PI Cowichan Lake area, Vancouver Island, Or PI Eastern Sierra Nevada Or (Larsen and Schmidt, 1958) British Columbia (Fyles, 1955) Qz Qz Qz pris ain arin ann ¢ 2.9 - PI Boulder batholith, Montana (M. R. Klepper, Or PI _ Laramide stocks of Colorado and New Or PI Kuskokwim region, southwestern Alaska Or written communication, 1956) Mexico (various published sources) (Cady and others, 1955) FIGURE 47.-Plots of norms for areas of granitic rocks in the western United States and Canada. as can be made. By comparing figure 47 with figure 46, it can be seen that the norms of most suites of rocks lie either within or very close to the plagioclase (albite) field. The field boundaries of the field of norms ap- proximate the positions of the field boundaries between quartz and feldspar and between plagioclase and Or-Ab feldspar. It is known that in a general way the norms that plot closest to the Pl corner in each suite were the earliest rocks emplaced, and that those that plot near the center of the diagram were the latest, although exceptions to this generalization no doubt exist. The distributions of the norms and the sequence of em- placement of the rocks which they represent are strong arguments for considering all the different suites to be chiefly products of differentiation under conditions of general crystal-liquid equilibrium. The different paths followed by the various plots can be explained as a result of differences in the pro- portion of normative quartz to orthoclase in the melt. These differences may have been original, resulting from differences in the bulk composition of the rock that was liquified, or they may have resulted from early crystallization of some such mineral as horn- GEOLOGY OF THE BATHOLITH 109 Quartz Experimentally determined field boundaries between quartz and feldspar in the system Q-Or-Ab-H;, 0 at: 1000 bars and P,,, p 5000 bars Plagioclase 48.-Composite of median lines through fields of norms shown on figure 47. lumbia. 2, Bald Mountain batholith, northeastern Oregon. Lake area, Vancouver Island, British Columbia. Colorado and New Mexico. 9, Kuskokwim region, Alaska. blende, which could have altered the proportion of normative quartz to orthoclase in the liquid. A very slight change could have a significant effect on the path of differentiation. Moore (1959) has suggested that the different trends of crystallization in the gra- nitic rocks of different parts of the western United States are related to the composition of the initial melt and that this initial composition is a product of the position of the magma chamber relative to the edge of the continent. The median lines (fig. 48) of the batholith of south- ern California, the Bald Mountain batholith, the Mount Garibaldi area, and the Cowichan Lake area at the ends near the center of the diagram lie closer Orthoclase 1, Mount Garibaldi area, southwestern British Co- Batholith of southern California. 4, Idaho batholith. 5, Cowichan 6, Sierra Nevada batholith. 7, Boulder batholith, Montana. 8, Laramide stocks of to the quartz-feldspar field boundary at 1,000 bars than at 5,000 bars. Smaller water-vapor pressure could reflect either smaller load pressure than pertained during differentiation of the eastern Sierra Nevada granitic rocks, or a deficiency of water at the same load pressure, or both. CONTACTS BETWEEN DIFFERENT GRANITIC ROCKS Most observed contacts between the different granitic rocks are sharp and nearly vertical; plutonic breccias occur locally along only a few contacts. Generally the traces of contacts between granitic rocks are flow- ing curves, but in places straight-line segments meet at sharply angled corners. Dikes of the later rock in the 110 earlier one are present near contacts, but are rarely abundant. At many contacts adjacent granitic rocks are separated by thin discontinuous septa of metamor- phic rock or by later aplitic dikes. A notable feature along all contacts between granitic rocks is the absence of any evidence of chemical reaction between the rocks in contact. Typical sharp contacts are shown in figure 22. Both contacts shown were followed in the field for many miles. The contact between the Mount Alice mass of quartz monzonite similar to the Cathedral Peak gran- ite and the Inconsolable granodiorite is the same everywhere that it was examined ; the contact between the Inconsolable and Tinemaha granodiorites, on the other hand, is occupied intermittently by thin discon- tinuous metamorphic septa, only the largest of which are shown on the map (pl. 4). A typical septum that crosses Bishop Creek just below Camp Sabrina sep- arates Tungsten Hills quartz monzonite from Lamarck granodiorite (pl. 1). Steep joints appear to be en- tirely later than the granitic rocks, and therefore do not influence the intrusive contacts; however, some gently dipping joints are early and in cliff sections offset contacts in places. The most extensive zone of plutonic breccia, and the only one of sufficient size to be represented on the quadrangle maps, is between the Tungsten Hills quartz monzonite and the Lamarck granodiorite in the vicinity of Piute Pass. A good deal of metamorphic and di- oritic or mafic hybrid rock is present along the contact, and the metamorphic and mafic rock and the Lamarck granodiorite are intricately penetrated in the breccia zone by anastomosing dikes and apophyses of Tungsten Hills quartz monzonite. Mixed rock also is present along Big Pine Creek on the hillside south of Big Pine Lodge, where scattered angular fragments of the Tinemaha granodiorite are present in the Mount Alice mass of quartz monzonite similar to the Cathedral Peak granite. Farther west, south of Second Lake along the North Fork of Big Pine Creek, the Incon- solable granodiorite adjacent to the Mount Alice mass of quartz monzonite similar to the Cathedral Peak granite is shattered, and the interstices between frag- ments are filled with felsic rock and with milky quartz (fig. 25). Local small-scale segregations of the light and dark minerals in the Inconsolable granodiorite have formed ; some of the segregations are linear and follow lines of fracture and some are ovoid. The shattered zone coincides with a bend in the contact in which the quartz monzonite lies on the convex side. Aschistic dikes, though not abundant, generally are common enough to provide a means of determining the relative ages of the granitic rocks. In general, masses GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA of rock similar to the Cathedral Peak granite are ac- companied by more dikes than the other intrusives, and marginal dike swarms are present along the north- ern margins of the Palisade Creek mass and the south lobe of the Mono Recesses mass. CONTACTS BETWEEN GRANITIC ROCKS AND METAMOR- PHIC ROCKS OR DIORITE Most contacts between granitic rocks and metamor- phic rock or diorite are sharp and clean, but in places irregular contacts and broad zones of mixed rock are present. - The sharpest, cleanest, and most regular con- tacts are between granitic rocks and metasedimentary or felsic metavolcanic rocks. Mixed zones involving these rocks are intrusive breccias that consist of angu- lar fragments of metamorphic rock enclosed in granitic rock. The angular outlines of the fragments and the straightness of their sides indicate that little or no chemical reaction has taken place between the frag- ments and the invading granitic rock. Contacts that are concordant with the layering or bedding of the metamorphic rocks generally are more regular than con- tacts that are discordant. The generally concordant contacts along the sides of the northern two-thirds of the Pine Creek pendant are especially regular (fig. 49). Intrusive breccias generally coincide with zones in the metamorphic rocks where prebatholithic struc- tures in the metamorphic rocks have been strongly dis- turbed and the rocks fragmented, generally by the in- vading granitic magma. - For example, at the south end of the Pine Creek pendant the major fold axes have been bent sharply and the rocks fractured and intri- cately penetrated by dikes and apophyses of the Tung- sten Hills quartz monzonite. Locally, in places where quartz-rich metasedimentary rocks predominate, the pendant rocks have been expanded into clusters of slightly displaced angular blocks that are separated from one another by thin branching dikes of quartz monzonite. Most contacts between granitic rock and older mafic metavolcanic rock, diorite, or hornblende gabbro also are sharp, but many are highly migmatitic because of chemical reaction between the granitic rocks and the in- vaded rocks. Sharp contacts, nevertheless, are com- monly cuspate because of reaction between granitic magma and mafic rock. The products of reaction are irregular, both in composition and in texture. They are hybrid rocks of convergent compositions, which are in part the products of contamination of the granitic rock with more or less assimilated mafic material, and in part the products of additions of quartz and feldspar to metavolcanic rock. In the part of the south end of the Pine Creek pendant where meta-andesite predominates, rocks of all compo- FIGURE 49.-Aerial view of Pine Creek pendant in north wall of Pine Creek Canyon. Contacts between the pendant rocks and the bordering Tungsten Hills quartz monzonite are generally clean and sharp. Mono Recesses mass of quartz monzonite similar to the Cathedral Peak granite is light-colored rock along skyline. This mass is parent to aplitic, pegmatitic, and alaskitic dikes, which penetrate the granitic rocks on the far side of the pendant. Few dikes penetrate the pendant itself. The dikes generally dip 20° to 45° into the parent mass. Photo by Symons Flying Service. HLITIOHILVEY HHL JO ADOTOWD III 112 sitions between quartz monzonite and diorite and ande- site are complexly scrambled. Most contacts between rocks of different composition or texture are obscure, but enough relations can be established to demonstrate that the rocks are hybrids and that the parent of some is quartz monzonite and of others meta-andesite. In general, later dikes of quartz monzonite have sharper contacts with the meta-andesite than earlier ones. Northwest of Pine Lake a mass of hornblende gabbro appears to grade over a distance of about half a mile to granodiorite. Nevertheless, the gradational zone con- tains a sharp though highly irregular contact between gabbro and heavily contaminated granodiorite of only slightly different appearance. The compositional gra- dation here appears to have taken place largely within the granodiorite by means of progressively greater con- tamination in the direction of the hornblende gabbro. Reciprocal hybridization of the hornblende gabbro was not established. Most contacts between granitic rocks and metamor- phic rocks are steep. The nearly vertical sides of the Pine Creek pendant are exposed through a relief of more than 5,000 feet. Flat or gently dipping contacts, nevertheless, occur locally. In Table Mountain, quartz monzonite underlies the northwest end of the Bishop Creek pendant with an almost flat contact. In the Tungsten Hills, alaskite dips under the north side of the Round Valley septum at 60° or less in the Round Valley mine and at somewhat flatter angles in the Western mine. MAFIC INCLUSIONS Inclusions of fine-grained mafic material, here re- ferred to as mafic inclusions, constitute the most abun- dant xenolithic material in the granitic rocks. These or similar inclusions have been called "basic segregations" (Knopf and Thelen, 1905, p. 239), "autoliths" (Hol- land, 1900; Pabst, 1928), "basic concretions" (Gruben- mann, 1896), and "inclusions" (Hurlbut, 1933, p. 614). The mafic inclusions have regular shapes and mega- scopically sharp boundaries with the enclosing granitic rock; they cannot properly be described as schlieren, which generally are conceived as streaky masses of irregular form. The inclusions are variable in size, shape, texture, and mineral content, but the range of variation is rather narrow. They range from less than an inch to several feet across, and from ovoid to lenticular, spindle shapes reported elsewhere in the Sierra Nevada (Balk, 1948, p. 12, pl. 2 (fig. 2), pl. 3 (fig. 1) ; Pabst, 1928, p. 334) were not recognized in the Bishop region. Some lenticular inclusions less than an inch in thickness are many feet in outcrop length. GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA The minerals in the mafic inclusions are the same as in the enclosing granite, but they are present in very different proportions. Plagioclase generally makes up 40 to 60 percent of the inclusion, biotite 5 to 20 percent, hornblende 20 to 50 percent, and quartz 5 to 15 percent. K feldspar is scarce, and apatite and mag- netite are relatively abundant. The composition of the plagioclase appears to be about the same as in the en- closing granitic rock, but in some inclusions it may be a trifle more calcic. The common texture is granoblastic or allotrimor- phic-granular. Most inclusions are structureless, but some lenticular ones have a planar foliation that is caused by the planar orientation of platy and elongate minerals. Porphyroblasts of plagioclase, hornblende, and biotite are present in most inclusions, although in larger ones they are confined to the marginal parts. These porphyroblasts are of the same size and habit as in the surrounding granitic rock. Locally, especially near the margins of inclusions, aggregates of porphyro- blasts exhibit a texture indistinguishable from that of the surrounding granitic rock, and make identification of the contact difficult or impossible. Although amphibolite inclusions are in almost all of the granite rocks, they are common only in the gran- odiorites. The finer grained quartz monzonite, rocks similar to the Cathedral Peak granite, and Tungsten Hills quartz monzonite contain only a few inclusions, except in the immediate vicinity of mafic igneous or amphibolitic wall rock. The inclusions that have been observed in these rocks are ovoid or irregular in shape and not lenticular. In the granodiorites, mafic inclusions are generally more abundant near the margins than in the cores of intrusive masses. They are most abundant within a mile of the contact, common between 1 and 2 miles, and uncommon beyond 2 miles. In the Inconsolable gran- odiorite, however, amphibolite inclusions are common throughout the mass, though more abundant near the margins. The inclusions are also more flattened toward the margins of the granodiorite masses. At the contact, inclusions an inch or less thick and several feet in out- crop length are common (fig. 22). With distance from the contact the inclusions appear thicker and shorter in outcrop, and beyond a mile or two from the contact generally are ovoid or irregularly rounded. Lenticular inclusions generally parallel the nearest contact of the enclosing intrusive rock, and because most of the intrusive contacts are steep, most lenticular inclusions also are steep. Recognition of elongation within the plane of flattening is difficult unless the elon- gation is extreme. Most extensive faces of granitic GEOLOGY OF THE BATHOLITH rock are along joint planes, and the trace of the in- clusion on these faces is a function of the angle of in- tersection of joint and inclusion. In an effort to determine whether tabular inclusions are elongate in the plane of flattening, careful watch was kept during mapping for places where the inclusions are perfectly parallel to a joint set. Strict parallelism is rare, and the effort was not successful. It is unlikely, however, that the inclusion are very greatly elongate in one direction. The origin of mafic inclusions has never been com- pletely explained, but three alternative hypotheses merit consideration: (1) the inclusions are clots of early formed minerals; (2) the inclusions are refractory material that was not melted when the magma was formed; (3) the inclusions are fragments of wall rocks of appropriate composition. The first and second al- ternatives are difficult to evaluate. How early crystal- lized minerals would collect into clots of roughly the same size is not obvious. The second alternative is attractive because it explains what happens to material that is left over after selective fusion of part of the earth's crust, and because it provides an explanation for the dissemination of mafic inclusions of the same size range throughout an intrusive mass, especially where wall rock of appropriate composition to form the inclu- sions is not exposed. Unfortunately, it is an alterna- tive that cannot be tested in the Bishop area. Deeper level migmatic terranes where magmas are presumed to have formed are suitable for testing this hypothesis. The third alternative, that the mafic inclusions are truly inclusions of wall and roof rock, has been investi- gated, and it can be shown that at least some mafic inclu- sions are of this origin. Any rock of appropriate chem- icafl composition can be converted into amphibolite like that in the mafic inclusions by recrystallization. The formation of mineral assemblages such as are in mafic inclusions is assured because the metamorphic grade is in the hornblende hornfels facies (Fyfe, Turner, and Verhoogen, 1958). Mafic volcanic rocks can be made over by recrystallization, and coarser grained mafic plutonic rocks can be converted by reduction of grain size, possibly followed or accompanied by recrystalliza- tion (Joplin, 1935b). Probably some exchange of mate- rial is always involved. Hurlbut (1933) has presented a strong case for the making over of gabbro fragments into the mafic inclusions in the batholith of southern California. The conversion involved both recrystalliza- tion and minor exchange of material with the enclosing magma. The most common parent rock for the forma- tion of inclusions of known origin in the Bishop area was mafic volcanic rock of basaltic and andesitic com- 113 position, and in a few places hornblende gabbro also appears to have served as a parent. Other rocks such as marble and calc-hornfels require metasomatic interchange of larger amounts of material between wall rock or fragments of wall rock and magma for the formation of amphibolite inclusions. The con- version of plagioclase-diopside hornfels to amphibolite requires the addition of small amounts of H;0, Fe, Mg, and possibly Al, and the subtraction of Ca. Cale- hornfels that has been partly converted to amphibolite was observed at several places, for example, at the Lake- view mine at the head of Gable Creek, but it was not observed in any great volume. On the other hand, no examples were found on a hand-specimen scale of resid- ual cores of plagioclase-diopside in amphibolite; such cores as were found are composed of quartz and diopside and have rims of quartz and hornblende. Apparently diopsidic pyroxene is more easily converted to horn- blende if plagioclase is present than if quartz is pres- ent, presumably because the plagioclase supplies con- stituents necessary for the formation of hornblende. Clean marble also was observed to have been con- verted to amphibolite by the metasomatic exchange of much larger amounts of material than is required to convert plagioclase-diopside hornfels to amphibolite. At the Brown tungsten prospect, southwest of Bishop and at the Scheelore mine in the Mount Morrison quad- rangle to the north, an amphibolite selvage has been formed along contacts between marble and granitic rock. At the Scheelore mine the amphibolite in the selvage is identical with abundant inclusions in the adjacent granodiorite. Several stages in the breaking up of amphibolite wall rock into inclusions can be seen. The amphibolite is intricately penetrated with anastomosing dikes of granitic rock, which separate or nearly separate in- dividual masses of amphibolite. These dikes appear to be chiefly granitization effects and to have formed by reaction of magmatic substances with the amphibolite in accordance with principles laid down by Bowen (1928, p. 197-198). Fractures presumably served as avenues for the movement of the magmatic substances. In a few places along the margins of the amphibolite, individual rounded remnants of amphibolite appear to have been caught in the act of drifting away from the main mass. This relation suggests that the granitic rock formed by reaction with the amphibolite was not completely rigid, possibly because it was close to its melting point. The presence of inclusions in granodiorite and their scarcity in quartz monzonite and granite can be ex- plained in two ways. The first is that the mafic inclu- sions were all picked up during intrusion, and that 114 granodiorite, having been generally emplaced earlier than quartz monzonite and granite, had greater oppor- tunity to come in contact with wall rocks of suitable composition to form amphibolite. The alternative ex- planation, which seems to fit the observed relations better, is that mafic inclusions were semistable in magma of granodioritic composition, but were unstable in more salic magmas. Granitic or quartz monzonitic magma could be expected to react with mafic inclusions in ac- cordance with Bowen's reaction principle more readily than granodioritic magma, which is closer to amphibo- lite in composition. It may be significant that mafic inclusions are present in the hornblende-bearing rocks and absent in the hornblende-free rocks. The Wheeler Crest quartz monzonite is the only mass of quartz mon- zonite that contains abundant mafic inclusions and also the only one that contains appreciable hornblende. With respect to the batholith of southern California, Larsen (1948, p. 162) states that the inclusions were in almost perfect equilibrium with the granitic magma and probably would persist in stagnant magma for a long time without mixing to give a homogeneous rock. The magma to which he chiefly refers is tonalitic. Progressive decrease in the abundance of mafic in- clusions away from the margins of many intrusives can be explained by a change of composition of the re- sidual magma and a progressively longer period during which inclusions can be digested. Generally there is some evidence of compositional zoning in intrusives in which mafic inclusions become less abundant away from the margins. A likely explanation for the residual magma's becoming more felsic when it is digesting mafic inclusions is that the effect of differentiation out- weighs that of contamination. Reesor (1958, p. 47-48) has postulated that the in- clusion-bearing marginal granodioritic shell of the strongly zoned White Creek batholith in British Co- lumbia is simply contaminated quartz monzonite. Two objections can be made to Reesor's hypothesis as applied to Sierra Nevada plutons. First, demonstrable con- tamination of the Sierran granitic rocks is spacially related to specific rock types, notably mafic ones, and the contamination of a pluton is not concentric, most particularly where several different kinds of rocks are intruded by the pluton. Second, the hypothesis im- plies that granodiorite that contains mafic inclusions whether in zoned plutons or not is contaminated rock that originally was more felsic. The compositional range of plagioclase in granodiorite, however, is sys- tematically more calcic than in quartz monzonite, and except in obviously contaminated zones contains no relict picked-up crystals of calcic plagioclase. These relations suggest strongly that granodiorite crystal- GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA ized at higher temperatures than quartz monzonite and was not derived from it by contamination. The progressively flatter shapes of inclusions toward the margins of many intrusives doubtless represents physical flattening of the inclusions, and must have been accomplished by plastic flow. During flattening the inclusions probably were not much stiffer than the enclosing granitic magma. The inclusions doubtless were softened by incipient or actual melting of the lowest melting constituents, and the magma was stiff- ened by crystallization and increased viscosity of the melt as a result of lowering temperature. The nearly circular shapes of inclusions in their planes of flattening can be explained if it is assumed that during emplacement the plutons grew by expan- sion, much as a balloon grows as it is blown up. Note that not all balloons are spherical. Mackin (1947, p. 26-32) has made the very significant point that the di- rection of flow in a radially spreading horizontal tab- ular intrusive body is toward the contact and that the direction of elongation of an equidimensional clot would be normal to that direction. Thus the foliation in granitic rocks defined by lenticular mafic inclusions does not show the flow plane. On the contrary, it is normal to the direction of flow and shows a plane of stretching. If the surface of an intrusion were hemi- spherical, the inclusions would be stretched equally in all directions perpendicular to the direction of flow. However, any departure from the hemispherical form should be reflected in elongation of the inclusions in the plane of flattening. If magma is pictured as flow- ing toward the margins of a hemisphere as it expands, the area of the external surface and parallel phantom surfaces within the magma will be expanded propor- tionally to the squares of the radii of the hemispheres. The inclusions nearest the margins will be flattened most, and those farther away will be flattened progres- sively less. In a cylindrical pluton the circular cross section of the surface also will stretch proportionally to the square of the radius. In the axial direction, however, stretch- ing will be equal to the elongation. Thus whether an inclusion in the margins of a cylindrical pluton will be stretched more in one direction than the other depends on whether the extension in the axial direction is greater or less than the increase in the square of the radius. EMPLACEMENT OF THE BATHOLITH In much of the foregoing discussions, crystallization of the granitic rocks from magma that was intruded from greater depths has been tacitly assumed. The fol- lowing lines of evidence taken together indicate that the major part of the granitic rocks crystallized from a melt. GEOLOGY OF THE BATHOLITH 1. Contacts of individual plutons with one another and with older rocks commonly are sharp, clean, and regular. . Finer grained rock is present in the marginal parts and apophyses of some plutons. 3. In areas of diverse wall rocks, most plutons are either homogeneous or are compositionally zoned in patterns that bear little or no relation to the wall rocks. 4. The geometry of some dislocations of the wall rocks suggests strongly that the dislocations were caused by the forcible emplacement of magma. 5. The internal foliation in the margins of plutons parallels external contacts and results from flow. 6. Mafic inclusions are oriented parallel to intrusive contacts rather than to features in the wall rocks, and in many plutons are progressively less flat- tened and less abundant inward-all facts that are compatible with a magmatic origin, but not with origin by granitization. 7. The walls of aschistic dikes marginal to some plutons are dilated. 8. Granitization and assimilation effects are confined to amphibolite and other mafic wall rocks that con- sist chiefly of minerals earlier in Bowen's reaction series than those crystallized in the granitic rocks. The effects are in accord with theoretical expecta- tions of reactions between granitic magma and wall rocks. 9. The metamorphic grade of the wall rocks and of in- clusions is that of Turner's hornblende hornfels facies and almandine amphibolite facies (in Fyfe, Turner, and Verhoogen, 1958, p. 199-239), which form at temperatures believed to exist in the wall rocks of nonsuperheated granitic magmas. 10. Variations in the compositions of the granitic rocks are in accord with variations predicted from ex- perimental studies in melts. Nevertheless, even though the evidence indicates over- whelmingly that the larger part of the granitic rocks were molten, the further problem of the relative impor- tance of different processes of emplacement remains to be considered. Before this can be done, evidences of different processes that were involved in emplacement must be summarized. In a broad way, these evidences can be divided into mechanical processes and thermo- chemical processes. bo EVIDENCE OF MECHANICAL EMPLACEMENT The best evidence of mechanical emplacement of the granitic rocks is deformation in wall and roof rocks that can be attributed to intrusion of magma. Several other lines of evidence are also cited, but this line is the most convincing one and the only one that permits 115 quantitative measurement of deformation. The follow- ing topics relating to mechanical emplacement will be discussed: (1) bends and dislocations in the metamor- phic remnants resulting from the intrusion of granitic magma, (2) deformation caused by intrusion of swarms of marginal dikes, (3) protoclastic borders, intrusive breccia, and related marginal features, and (4) the sig- nificance of flattened mafic inclusions. BENDS AND DISLOCATIONS IN METAMORPHIC REMNANTS RESULTING FROM THE INTRUSION OF GRANITIC MAGMA In the study of deformation in the metamorphic remnants, the deformation caused by intrusion must be distinguished from the earlier regional deformation. The regional deformation resulted for the most part in folding and faulting along north- to northwest-trend- ing lines. Although the axes of regional folds un- dulate they average about horizontal. Deformation caused by intrusion, on the other hand, only coinciden- tally follows north- to northwest-trending lines, and most folds caused by intrusion have steep axes. The pattern of deformation is directly related to the shape of the intrusion. Plate 8 is a map showing the distribution of meta- morphic remnants in the area mapped in connection with this report. The adjacent intrusive masses also are shown. On this map the metamorphic rocks are subdivided into a metasedimentary series, chiefly of Paleozoic age, and a metavolcanic series, chiefly of Mesozoic age. Principal fold axes and the traces of bedding planes are shown in the larger remnants. Deformation caused by the intrusion of granitic masses is most clearly demonstrable in the Pine Creek and Bishop Creek pendants, and the resultant struc- tures in these pendants are Uescribed in detail in an earlier section of this report. The south end of the Pine Creek pendant, including its major synclinal axis, was bent eastward into an S-shaped structure by the intrusion of Tungsten Hills quartz monzonite. In the Bishop Creek pendant the two lobes at the north end were spread apart by the intrusion of the Tungsten Hills quartz monzonite. Faults in the northeast lobe may also have been caused by the intrusion. The strata in the west side of the northwest lobe, along the west side of Table Mountain, probably have been bowed up- ward by Tungsten Hills quartz monzonite. In the south part of the pendant the beds have been bent westward around a protrusion of quartz monzonite similar to the Cathedral Peak granite, which appears to have pene- trated from the east. The magnitude of separations represented in these structures is variable; the largest separations-the S-fold in the south end of the Pine Creek pendant and the spreading of the north end of the Bishop Creek pendant-are about 3 miles. 116 Less clearly demonstrable dislocations caused by fore- ible intrusion of the granitic masses can be inferred from the relations between two or more separated metamorphic masses. The magnitude of displacement inferred from these relations is somewhat greater than is shown by structures within single masses. One such structure is continuation of the S-fold in the south end of the Pine Creek pendant. The contact in the Mount Humphreys ring between metavoleanic rocks and metasedimentary rocks suggests that these rocks represent the opposite limb of the fold at the south end of the Pine Creek pendant. In this interpretation, the rocks in the span between Mount Tom and Mount Humphreys would have been pushed eastward and per- haps broken through by a lobe of Tungsten Hills quartz monzonite. The largest dislocation inferred from the arrange- ment of metamorphic rocks is just north of the mapped area between the south end of the Mount Morrison pendant and the north end of the Wheeler Crest septum. Strata in the Pine Creek pendant strike roughly, though not precisely, in the direction of the Pennsylvanian and Permian(?) formations in the Mount Morrison pendant with which they are correlated. The strata in the Pine Creek pendant continue to the north in the discontinuous Wheeler Crest septum, and at the north end of the septum are offset 8 miles to the east of the probable correlative strata in the Mount Morrison pend- ant. Round Valley Peak granodiorite occupies the region between the north end of the septum and the south end of the Mount Morrison pendant (pl. 8). The overall pattern suggests that the correlated strata in the Pine Creek and Mount Morrison pendants were once connected, and that the strata in the Wheeler Crest septum have been bent eatward and broken off from the south end of the Mount Morrison pendant. The present distribution of strata is difficult to explain on the basis of regional deformation but could have been caused by the forcible emplacement of either the Round Valley Peak granodiorite or of the Mono Recesses mass of quartz monzonite similar to the Cathedral Peak granite. Inasmuch as the Wheeler Crest quartz monzonite was emplaced along the east side of the septum before in- trusion of the Round Valley Peak granodiorite, it must also have been involved in the deformation. This may explain an abundance of cataclastic structures in the Wheeler Crest quartz monzonite. Most of the cited examples of mechanical dislocation involve lateral separation, although the one on the west side of the northwest lobe of the Bishop Creek pendant involved upward bulging. Nevertheless, if all the metamorphic remnants were pushed together, large amounts of rock would still be missing; in other words, GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA only part of the space for the granitic rock was made by pushing aside the wall rocks. Undoubtedly some of the missing rock was pushed upward, but some was also incorporated in the magma. DEFORMATION CAUSED BY INTRUSION OF SWARMS OF MARGINAL DIKES Several intrusives are bordered locally by swarms of aschistic felsic dikes. The most notable swarm is ex- posed in the walls of Pine Creek Canyon and is satel- litic to quartz monzonite similar to the Cathedral Peak granite. These dikes dip into their parent masses at angles that commonly range from 20° to 45°. A nearly perfect match of the opposite dike walls indicates that they are simply spread apart. Inasmuch as the dikes thicken and are more abundant in the direction of the parent mass, their emplacement must have caused con- siderable deformation of the wall rocks. In a highly diagrammatic section through a marginal dike swarm (fig. 50), all the dikes dip 25° into the parent mass, and the external contact of the parent mass is vertical. Figure 50 shows the traces of hypothetical planes which, before emplacement of the underlying dikes, were parallel to medial planes through the dikes. These traces show the amount of deformation of the wall rocks that must have been caused solely by em- placement of the underlying dikes; that is, the amount of upward displacement of these traces at any place equals the aggregate thickness of the dikes below the planes of reference measured perpendicular to the medial planes of the dikes. The lifting is accumula- tive through only limited distances, and the amount of lifting at any place equals the thickness of under- lying dike rock measured perpendicular to the dip of the dikes; it does not equal the aggregate thickness of all the underlying dikes. The dikes as represented in the diagram (fig. 50) are parallel and unfolded and are emplaced in order from bottom to top. In nature the dikes are generally paral- lel, though intersecting ones are common, and along Pine Creek the dikes most distant from the parent in- trusive dip more steeply than dikes closer to the parent intrusive. These relations suggest that the dikes may be convex upward and that the flatter dips closer to the parent intrusive may have been caused by upward drag by the parent intrusive or by the later emplace- ment of dikes below. A correct statement might be that the dikes are emplaced in the general order of bot- tom to top, but with many exceptions. The fractures which the dikes occupy appear to be feather joints caused by upward movement of the magma mass parent to the dikes. Cloos (1932) has ex- perimentally determined that the angle between the direction of movement and tension joints in soft clay GEOLOGY Wallrocks FicurE 50.-Diagrammatic section through an intrusive and its mar- ginal dikes to show the amount of plastic deformation in the wall rocks caused solely by the emplacement of the dikes. Dotted lines show traces of planes of reference originally parallel to the medial planes through dikes before the underlying dikes were emplaced. Inasmuch as dikes are parallel and dip into the parent intrusive, it is assumed they were emplaced in order from bottom to top and that space for the dikes was made by lifting the overlying rock in a direction normal to the dike. is about 45°; he made field observations of about 30°. The angle between the dikes and principal contact of 45° to 70° is somewhat anomalous in the light of these data, but the higher angles could have been caused by drag from the parent intrusive or by late emplacement of dikes at depth. PROTOCLASTIC BORDERS, INTRUSIVE BRECCIA, AND RELATED MARGINAL EFFECTS No protoclastic borders have been recognized within the Bishop area, but Sherlock and Hamilton (1958, p. 1261) and Rinehart and Ross (1964, p. 48-49) report a protoclastic zone farther west in the north margin of the Mono Recesses mass of quartz monzonite similar to the Cathedral Peak granite. According to Sherlock and Hamilton (1958, p. 1261), the deformation occurred after the emplacement of marginal dikes and involved the marginal parts of both the pendant and the quartz monzonite. Within the Bishop area two intrusives, the Wheeler Crest quartz monzonite and the Red Mountain Creek mass of quartz monzonite similar to the Cathedral Peak granite, exhibit shearing, granulation, and recrystalli- zation which may have been caused by the forcible emplacement of neighboring plutons, However, the OF THE BATHOLITH 117 Wheeler Crest quartz monzonite is the oldest granitic rock in the northern part of the Bishop area and the Red Mountain Creek mass of quartz monzonite may be one of the oldest in the southern part; the structures in the two bodies of quartz monzonite could have resulted from regional deformation. Shearing and granulation in the south end of the Wheeler Crest quartz monzonite increase in intensity westward toward a con- tact with Tungsten Hills quartz monzonite-a feature that suggests that the deformation resulted from intru- sion of the Tungsten Hills quartz monzonite. Shearing and granulation elsewhere in the Wheeler Crest quartz monzonite may have been caused by intrusion of the Round Valley Peak granodiorite and quartz monzonite similar to the Cathedral Peak granite west of the grano- diorite. Likewise, cataclasis within the Red Mountain Creek mass of quartz monzonite similar to the Cathe- dral Peak granite may have been caused by the intru- sion of a pluton of finer grained quartz monzonite that borders it on the south and east. Schist peripheral to the quartz monzonite on the north and east sides was formed from pelitic rocks during the emplacement of the intrusive rocks by shearing, granulation, and recrys- tallization. Although the schistosity could have been caused entirely by the emplacement of the quartz mon- zonite similar to the Cathedral Peak granite, it may have been caused in part by emplacement of the finer grained quartz monzonite ; this emplacement could also have caused the shearing within the quartz monzonite similar to the Cathedral Peak granite. The origin of the schist was discussed on page 31. Contact breccias were described briefly in descrip- tions of the granitic rocks. Most breccia zones are in places where the wall rocks also have been bent by the intrusive magma, and the shattering of the wall rock was caused by the same forces that caused the bending. Some wall rocks may have been shattered during pre- intrusive deformation, but generally the pattern of breaking indicates that the force causing the shattering and bending was supplied by adjacent intrusives. An excellent example of intrusive breccia occurs at the south end of the Pine Creek pendant, along Horton Creek. Shattering of the marginal part of the Incon- solable granodiorite by intrusion of quartz monzonite similar to the Cathedral Park granite is described on p. 6. Most of the larger remnants of metamorphic rock surrounded by granitic rock have been so modified in outline that adjacent blocks of similar lithology cannot now be related to one another by the shapes of their walls. Nevertheless, lithology and shape of a few mod- erately large blocks indicate they were split off from adjacent masses. One such block is at the north end of 118 the Pine Creek pendant, on the west side, and contains the principal workings of the Adamson tungsten mine. Another block is on the southeast side of the Pine Creek pendant and contains the Lambert tungsten mine. Two masses of diorite and hornblende gabbro in the Deep Canyon area of the Tungsten Hills are separated by a tongue of quartz monzonite that apparently split them apart. FLATTENED MAFIC INCLUSIONS AS INDICATORS OF FORCIBLE EMPLACEMENT The conclusion was reached on page 114 that mafic inclusions of random shape are flattened as a result of stretching of the outer, more viscous shell of a cooling pluton through increase in size. Growth of a pluton requires space, and unless large amounts of wall and roof rock were incorporated in the magma the walls must have been crowded upward and outward. The mafic inclusions themselves may represent wall-rock material, and some additional material probably has been digested by magma. Nevertheless, most intrusions appear to have incorporated far too little of the exposed wall rock to provide the needed space. The conclu- sion seems inescapable that during emplacement most plutons grew primarily by pushing their walls upward and outward. Deformation of the wall rocks is evident in many places, but not in others, especially where the walls are granitic. One possible explanation for the apparent near absence of deformation in granitic rocks intruded by later plutons is that the earlier rocks were still not entirely crystallized and so show no evidence of deformation; another is that the evidence of de- formation has simply been overlooked and that the problem needs further investigation. EVIDENCE OF THERMOCHEMICAL EMPLACEMENT Thermochemical effects include all the effects that in- dicate chemical reaction between granitic rock or its magma and wall or roof rocks. These are the effects that have been variously attributed to granitization or to assimilation. Tendencies to broaden the term "gran- itization" to include all reactions between magma and solid rock give the term a double or uncertain meaning and lessen its value for precise description. In this re- port "assimilation" is used to describe the incorpora- tion of solid rock in magma by partial reaction, solution, or melting, and "granitization" is reserved for the con- version in the solid state or nongranitic country rock to granitic rock. Undoubtedly these processes have an area of overlap, and discrimination between them com- monly is difficult or impossible ; nevertheless, some merit is attached to at least theoretical distinction. Thermochemical effects in the Bishop district include two general kinds of features-mixed zones of granitic GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA rock and wall rock in which sharp contacts predominate but in which wall rock dilation has been negligible, and hybridized granitic rocks that have been contaminated by wall or roof rock. Almost all of the conspicuous thermochemical effects involve mafic, generally fine- grained igneous rock; locally calcareous metasedimen- tary rocks have been converted to amphibolite which is chemically and mineralogically similar to the mafic igneous rocks and exhibits similar thermochemical effects. Extensive areas of sedimentary or volcanic country rock characterized by porphyroblasts or the local formation of igneous texture, such as are present in many Precambrian terranes, are absent here. GRANITIZATION OF MAFIC ROCK Examples of mixed zones that result from the gran- itization of mafic igneous rocks are shown in figures 51, 52, and 53. The geometric relations of many irregu- larly shaped masses of granitic rock that penetrate mafic igneous rock indicate that the granitic rock has taken the place of mafic igneous rock and has not been emplaced by simple dilation of the walls. Small inclu- sions of mafic igneous rock in granitic rock could be in- terpreted equally well as either undisplaced residuals of chemical attack by granitic rock or its magma, or as dis- located inclusions whose boundaries have been irregu- larly corroded chemically. The geometry of the walls of the early aplite shown in figure 514 is such that emplacement of the aplite forcibly by spreading of the walls would have been very difficult unless the mafic rock was quite soft and plastic. Darker colored, somewhat rounded areas of mafic rock adjacent to or enveloped in aplitic material are areas in which the grain size has been reduced and in which new minerals have been formed. This process is ac- complished by recrystallization in conjunction with ex- change of substance. Common changes are the disap- pearance of hornblende and plagioclase, which are the most abundant minerals in most mafic rocks, and the appearance of a fine-grained granoblastic or schistose intergrowth of biotite, quartz, K feldspar, and, near the granite, epidote. - These new minerals require addition of Si and K and subtraction of Ca, Mg, and Fe. Re- duction of grain size is a common feature along con- tacts between earlier mafic rock and later granitic rock. In figure 512, contacts between mafic rock and granitic rock are embayed and cuspate, typical features of reaction contacts. - The shapes of the dikelike masses of granitic rocks indicate they replaced the mafic rocks. Careful examination of many outcrops like that shown in figure 512 indicates no movement in the third dimen- sion. Mafic dikes younger than the enclosing granitic rock and mafic inclusions in the granitic rock have been at- GEOLOGY OF THE BATHOLITH B 51.-Typical granitization effects in mafic rock. A, Replace- ment of mafic rock by aplitic material; later aplite dike, emplaced by dilation, cuts earlier replacement aplite; note areas of darker, finer grained mafic rock (L) present locally adjacent to replacement aplite. B, Replacement of mafic rock by medium-grained felsic granite rock. Note irregularly embayed contact. 119 tacked and selectively replaced by aplitic material. Commonly the first signs of such replacement of a mafic body are thin stringers of aplitic material in the mar- gins. The contact of the aplitic stringers with the en- closing granitic rock is straight and sharp, and coin- cides with the original contact of the mafic rock, as is shown in figure 52. The contact of the aplitic material with the mafic rock, in contrast, is irregularly pene- trating or conspicuously cuspate. Stringers may ex- tend entirely across a dike or inclusion, and in places the mafic material is cut by many such stringers which may irregularly pinch and swell. Mafic dikes were ob- served that could be traced through segments contain- ing progressively thicker marginal stringers of aplite into a dike entirely of aplite. Reaction between an aplite dike and an older mafic dike is illustrated in figure 53. In the lower right-hand corner of the photograph, where the aplite dike cuts Tinemaha granodiorite, the positions and shapes of the dike walls indicate that they were spread to ac- commodate the dike. At the upper end where the thin dike intersects an older mafic dike, reaction has taken place within the mafic dike to produce the mixed and aplitic rock. The granodiorite was not involved in this reaction, and the conspicuous contact across the lower part of the photograph between granodiorite and aplitic rock marks the original wall of the mafic dike. Progressive hybridization of mafic rocks by quartz monzonite similar to the Cathedral Peak granite along Big Pine Creek was discussed in connection with the description of quartz diorite and related granodiorite. The early stages of hybridization involved progressive granitization of the mafic rock through recrystalliza- tion, accompanied by interchange of substances. The later stages involved disintegration of the granitized rock at the margins and incorporation of the fragments in the granitic magma. At some distance from the mafic rock the granitic rock is even textured, but has a higher content of dark minerals than uncontaminated quartz monzonite with which it is locally in sharp contact. The mechanism by which ganitic rock replaces mafic igneous rock can be explained most satisfactorily in terms of Bowen's reaction series. The fine-grained mafic rocks are composed of minerals that would crys- tallize from a silicate melt at higher temperatures than. the minerals of the quartz-bearing granitic rocks. When a mafic rock is brought into contact with granitic magma, the mafic rock is so modified as to bring its mineral assemblage into equilibrium with the magma. The granitic magma does not dissolve the mafic rock because it does not contain sufficient heat; it works it over by reaction. Bowen states (1928, p. 198), "These 120 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA Mafic rock (dike or inclusion Replacement aplite 0 1 FOOT FiGuRE 52.-Selective replacement of mafic rock (dike or inclusion) over Lamarck granodiorite by aplitic material. Late intrusive aplite dike is present in upper right-hand side of photograph. remarks are tantamount to the statement that saturated granitic magma cannot dissolve inclusions of more basic rocks. The magma will, however, react with the inclusions and effect changes in them which give them a mineral constitution similar to that of the granite. These changes will often be accompanied by disintegra- tion of the inclusions and the strew ing about of the prod- ucts which may be indistinguishable from the ordi- nary constituents of the granite." Several problems can be envisaged in connection with the actual operation of the process. One is the mech- anism by which material (chiefly Si, Na, and K) is in- troduced into the mafic rock and excess material (Ca, Mg, Fe, and Al) is removed. Another problem is the nature of the contact between granitic rock that erystal- lized from a magma and similar rock that formed by the replacement of mafic rock. The irregular penetra- tion of granitic rock into mafic rock and the dikelike GEOLOGY OF THE BATHOLITH FicuRR 53.-Selective reaction of aplite dike with mafic dike in Tine- maha granodiorite. Aplite was intruded into Tinemaha granodiorite, with which it shows no evidence of reaction. Clean straight walls and geometry of walls where aplite enters mafic dike indicate em- placement by dilation. Reaction with mafic dike is apparent. Prob- ably both granitization and assimilation effects are represented. Note darker appearing, finer grained rounded masses of mafic rock adjacent to aplitic material. form of some thin granitic layers suggest that the gran- itization was guided by fractures. That true magma entered along these fractures seems dubious. Nockolds (1933) has emphasized the role of volatiles which he suggests furnish a medium of low viscosity through which material can travel by diffusion from a magma both into and from a xenolith. This medium could be a hydrous melt of ternary minimum composition, for although a silicic magma cannot totally melt a ferric one, it can supply sufficient heat to melt the least refrac- tory fraction. Garrels, Dreyer, and Howland (1949) have shown experimentally that solute diffusion through intergranular spaces in rocks can be an effec- tive geologic process. Conceivably the contact between granitic rock that erystallized from a magma and simi- lar rock that formed from granitization could remain in its initial position, but both Nockolds (1933) and Turner and Verhoogen (1951, p. 121-122) suggest that marginally the granitized rocks would tend to dis- integrate, chiefly by mechanical means, and the minerals and rock fragments would be scattered through ad- jacent magma. If the granitized rock disintegrates marginally, the magma will encroach on the wall rock and thus reduce the distance through which diffusion must operate. 735-925 O-65--9 121 ASSIMILATION OF MAFIC ROCK Complementary to granitization of mafic igneous and metamorphic rock is assimilation of the same rock by granitic magma. The product of assimilation is a dark- colored hybrid rock having a splotchy appearance that is caused by uneven distribution of the mafic minerals and by variations in texture. Most of the hybrid rock is granodiorite in composition, but some is quartz diorite. Generally the hybrid rock is darker than the rock in large intrusive masses of granodiorite composi- tion. On a small scale, some dikes intrusive into mafic host rock are progressively more contaminated with greater distance into the host rock. Contaminated granitic rock is extensive in the south end of the Pine Creek pendant, on the north side of Pine Creek northwest of Pine Lake, and in the ridge between the Middle and South Forks of Shannon Can- yon. An illustrative area (described on p. 56) is north- west of Pine Lake where hornblende gabbro and diorite grade laterally into granodiorite through a distance of about half a mile. Nevertheless, the intrusive contact between the two rocks is sharp but highly irregular, although the rocks are very similar in appearance at the contact. The earlier hornblende gabbro does not appear to have been much affected by the granodiorite, but the gabbro obviously contaminated the intrusive granodiorite magma. Assimilation of the mafic material and consequent contamination of the granitic magma are probably ac- complished by diffusion through volatiles or a pervasive hydrous melt of ternary minimum composition in con- junction with the physical incorporation in the magma of fragments of the wall rock. Accompanying the in- troduction of material into wall rock in granitization is the reciprocal process of removal of material (prin- cipally Ca, Mg, Fe, and probably some Al). No evi- dence was found to indicate that the removed material was driven ahead of the granitization; presumably it moved in the reverse direction, back into the magma. A difficult problem in this connection is the absence in so many places of any evidence of contamination of the granitic rock adjacent to granitized mafic rocks. Whether the material that was expelled from the wall rock traveled only far enough after reaching the magma to produce a zone of hybrid rock or whether it was dispersed so widely as to leave no recognizable trace probably was determined by the rate of dispersal after reaching the magma. - Very little is known about the rate of diffusion in siliceous magma except that the rate decreases as the magma cools, becomes more vis- cous, and crystallizes. Certainly, movements within the magma, which would aid in the dissemination of 122 material and homogenization of the magma, would de- crease with cooling. Marginal disintegration of the granitized or partially granitized mafic wall rock and strewing of rock or crystals through the adjacent magma may also con- tribute to the formation of the hybrid rock. The tex- ture of some areas in the hybrid rock is sufficiently similar to that of the wall rock to suggest a xenolith. Partially granitized xenoliths would, of course, be fur- ther granitized, and the displaced elements diffused into the surrounding magma. The splotchy texture of the hybrid rock may be due to the partly granitized frag- ments of wall rock distributed through contaminated granitic rock. EVALUATION OF PROCESSES OF EMPLACEMENT OF THE BATHOLITH The Sierra Nevada batholith at the latitude of Bishop is about 60 miles wide. It has been established that the batholith consists of a mosaic of separate intru- sive masses and that magma was involved in the forma- tion of these masses, although a minor amount of rock was formed by granitization. The chief problems to be considered here are the means by which space for the intrusives was provided and the relative effectiveness of forcible displacement of the country rock by magma, stoping, granitization, and assimilation in their em- placement. These two problems are interdependent and can conveniently be considered together. One of the difficulties of evaluating the different proc- esses related to the emplacement of the intrusives is that they are characteristically on different scales. Nei- ther the eye nor the camera is equally receptive to features of all sizes. Outcrops a few inches or a few feet across can be observed in considerable detail ; out- crops a few hundred feet across if viewed in their entirety can be seen in much less detail, and larger features can be viewed only in a broad way and only if conditions that affect visibility are exceptionally good. Effects associated with emplacement of the intru- sive masses of about the right size for field inspection include replacement dikes and other granitization effects, zones of intrusive breccia, and dike swarms. Somewhat larger features that can be seen in the field in some places are hybridized zones in granitic rock and large foundered blocks of wall rock that are separated from an originally conjoined mass by granitic rock, but the understanding of the significance of these features commonly is aided by maps or diagrams. Large fea- tures that ordinarily escape the eye and which can be satisfactorily understood only after they have been represented on a map include large-scale bends or dis- locations of the country rock that were caused by the forcible emplacement of intrusive magma. Thus the GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA small-scale effects of granitization and brecciation can be readily observed and photographed in many places in the Sierra Nevada, whereas larger scale physical dis- locations of the wall rocks by forcibly emplaced magma commonly can be recognized only after a map has been prepared. Physical separations of as much as 3 miles, caused by the forcible emplacement of intrusives, have been demonstrated for structures within individual pendants, and a separation of about 8 miles has been inferred between the Wheeler Crest septum and the Mount Mor- rison pendant. Separations of these magnitudes are by far the most impressive effects associated with the emplacement of the intrusives. In some places the entire space for the granitic rocks apparently was made by pushing aside the wall rocks. All evidence indicates that dislocation by intrusion must certainly be assigned an important role in making space for intrusive masses. The role of stoping is difficult to assess because the boundaries of most blocks of pregranite rock have been so modified that blocks of similar lithology cannot be related to one another by the shape of their walls. At only a few places can large blocks (blocks at least a quarter mile long) be shown to have been split off from adjacent blocks of similar lithology. Fragmentation and piecemeal stoping are locally demonstrable in zones of intrusive breccia, but appear to be secondary to either large-scale bending or to granitization and assimilation. Nevertheless, it seems reasonable to sup- pose that magma intruded with such force as to cause more than 3 miles of lateral separation of the wall rocks would have entered along lines of weakness and would have split off blocks. Once these blocks were sepa- rated they would be moved in accordance with their specific gravity and the currents and viscosity of the magma. Some of the exposed masses of pregranitic rock probably came from higher or lower levels than the present erosion level. Visible traces of granitization and assimilation are quantitatively insignificant, though conspicuous because of their optimum size for observation. Nevertheless, the end stage of granitization and assimilation is gra- nitic rock that is virtually indistinguishable from rock that crystallized directly from magma; hence these processes are self-effacing. Granitic magma does not appear to have reacted appreciably with most meta- sedimentary rocks-nor with earlier granitic rocks. Reaction is largely confined to the mafic igneous rocks and to amphibolite, and it is in these mafic rocks that granitization and assimilation are conspicuous. Time as well as composition is important to reaction. Dila- tion dikes having sharp walls invariably are later than granitization effects in the same area (figs. 514, 52), GEOLOGY OF THE BATHOLITH and earlier dikes generally are more strongly hy- bridized and have less sharply defined walls than later dikes (fig. 54). These relations indicate that the chemi- cal activity of granitic magma decreases with lowering temperature and that reaction is only important during the earlier stages when the magma is hottest. Compton (1955) has studied an area in the western Sierra Nevada where plutons west of the main Sierra Nevada batholith intrude a terrane that is composed predominantly of mafic metavolcanic rock. For the Bald Rock batholith he estimates from approximate projections of the country rock units through the batho- lith that most of the space for the batholith was pro- vided by forceful intrusion and outward forcing of the country rock, but that about a quarter of the required space was provided by stoping, assimilation, or granitization of the country rock. For the adjacent Swedes Flat pluton, which has a broad gradational con- _ tact zone with the metavolcanic country rocks, he ex- presses the opinion that most of the granitic rock is of replacement origin, but that the granitization was pro- duced by fluids that emanated from a core of magma. His estimates, which appear to be well founded, suggest that in terranes composed of mafic igneous rock a very significant part of the space required for the emplace- ment of an intrusive can be provided by granitization, FiGurE 54.-Mafic inclusion cut by dikes of slightly different ages, both of which are offshoots from the surrounding quartz monzonite similar to the Cathedral Peak granite. The earlier dikes extend from upper left to lower right. 'They are darker than the parent rock, apparently because of contamination. Although it seems clear that the dike walls are dilated, they are ragged and do not match perfectly across the dikes, presumably because of reaction. In con- trast, later dikes, which extend from top to bottom, are uncontami- nated, and the walls are smooth and match perfectly. 123 probably in conjunction with the complementary process of assimilation. Physical dislocations caused by forcible intrusion of granitic magma are most conspicuous in metasedimen- tary terranes, where the rocks are of such a composition as to react very slowly with the magma, or in terranes composed of igneous rocks compositionally similar to the intrusive magma. Nevertheless, there is little reason to believe that intrusions were less forcible in terranes composed of mafic igneous rocks and other rocks re- active toward granitic magma; however, granitization and assimilation obscure the effects of forcible intru- sion. In summary, the most important role in the emplace- ment of the granitic rocks in the Bishop area must be assigned to forcible intrusion which thrust aside, and ultimately upward, the older rocks. These dislocations were accompanied locally by piecemeal stoping, and in places stoping may have provided substantial amounts of space now occupied by intrusive rocks. Thermochemical processes were most effective where the wall rocks were mafic igneous rocks or amphib- olite, but even there were probably of less importance than mechanical processes. Where volcanic rocks pre- dominate, as in certain parts of the western Sierra Nevada, thermochemical effects may be of greater im- portance in the emplacement of granitic rocks. CONTACT-METASOMATIC TUNGSTEN MINERALIZATION The contact-metasomatic, scheelite-bearing tungsten deposits contain the principal ores of the Bishop dis- trict. To the end of 1953 they had yielded about 1.3 millions short-ton units * of WO; (tungsten trioxide) - about 12 percent of the total domestic production of the United States. More than 50 tungsten deposits have been discovered in the district, including 21 that have yielded more than 100 units of WO; (table 18). The Pine Creek mine of the Union Carbide Nuclear Co. has supplied more than three-fourths of the district's past production of tungsten, and substantial amounts of copper and molybdenum as byproducts. To the end of 1953, it yielded 1,057,498 units of WO;, 1,967.97 tons of copper, and 6,130,559 pounds of molybdenum. In an earlier report (Bateman, 1956), individual tungsten deposits as well as deposits of other mineral commodities mined in the Bishop district-gold, silver, antimony, cobalt, barite, expansible rhyolite (perlite), marble, tale, clay and feldspar, and sand and gravel- * The tungsten content of ore and of concentrate is commonly given in terms of units of WOs, regardless of the actual form of the tungsten. A unit is one percent of a ton. Thus, a short-ton unit (the unit of this report and the one commonly used in the United States) is equivalent to 20 pounds of WOs. 124 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA TABLE 18.-Tungsten mines and prospects in the Bishop district showing the parent metamorphic and plutonic rocks [Closest silicic rock is shown by dashed arrow for deposits in inclusions in quartz diorite or hornblende gabbro. Question mark indicates probable parent rock] Parent metamorphic rock Mines (production greater than 100 units WOs) and prospects Marble Calc-hornfels Associated plutonic rock Tungsten Hills, Quartz diorite Alaskite quartz monzonite | and hoggblende Other gabbro Pine Creek pendant: Ting CIOCKL..... .. . cols ele ser Adamson . ._. Brownstone... Tungstar......- Hanging Valley Lakeview.... Lambert..._.-:.- Round Valley. 2 miles N. 25° W. from Scheelite._............ Blue 222 ore center Moore (Sunnyboy). Mountain Bishop Creek pendant: BCHODEE I. ners. Ciel cen cess Merrill....... Lindner...... Snow Queen. Black Monster Munsinger. Hilltop... Little Egyp Coyote Creek.. Lookout - Waterfall._......-_. Stevens:......... North Lake...... Green Lake de Chocolate Peak (Bishop silver-cobalt prospect) . Tungsten Hills: Round 0 lent Tungsten Hill (Little Shot) - Little Sister_.............. Jackrabbit. .......- Lucky Strike. Tungsten Blue (Shamrock). Acroplane........._...... White Caps..___... Tungsten Peak.. Lookout. Hilitop..:.-......-- Van Loon (Raindrop) Range Front south of Bis .o liters uue. Early-Morhardt. . ._......- West of Keough Hot Springs. 000 .- clit. Middle Fork Shannon Creek. Rattlesnake......___._.._.... Tabbo§e .... pe 00-4004 Wheeler Crest quartz monzonite. Wheeler Crest quartz monzonite. Lamarck granodiorite. Granodiorite of Coyote Flat. Lamarck or Inconsol- able granodiorite. Granodiorite of Deep Canyon. Finer grained quartz monzonite. IL eel s ran ens fel Lath bo (Re stupa ee paua ans Adjusted totals (deposits enclosed in quartz diorite or hornblende gabbro reassigned to closest sili¢it intrusive) ..|....._.__._.._______]____._____._._____.. were described in detail. The focus of this report is primarily on the process of tungsten mineralization as interpreted in the light of information acquired in the study of the Bishop district. To be considered are the mineral content and internal constitution of the de- posits; factors that influenced the localization, size, and grade of the ore bodies and ore shoots; and regional relations that may explain the existence of the district. Among other mineral commodities, only byproducts of tungsten mining, which were deposited as part of the tungsten mineralization, will be dealt with. MINING HISTORY Tungsten was not discovered in the Bishop district until 1913 and not mined until 1916, but prospecting, chiefly for gold, was carried on by the earliest settlers. The Golden Wedge mine, later part of the Silver Belle mine, 4 miles north of Laws at the base of the White Mountains, was worked in the early 1860's. The Po- leta mine, east of Bishop in the White Mountains, and 'the mines in Fish Spring Hill were worked in the 1880's and may have been worked earlier. The Car- dinal mine, on Bishop Creek, by far the largest pro- GEOLOGY OF THE BATHOLITH ducer of gold in the Bishop district, was operated from 1911 to 1922 and from 1934 to 1940. During the de- "pression years of the 1930's many deposits of gold were worked. Gold mining ceased at the beginning of World War II, and no gold mine in the Bishop district had been reopened by 1958. Sand, gravel, granite, marble, and rhyolite tuff have been also mined intermittently since the time of the earliest white settlers. The Bishop tuff was used for building block in Owensville in 1863, and was locally a popular building material until the 1930's, when cement blocks with pumice aggregate proved to be cheaper and easier to use. Pumice for aggregate and for use in plaster has been mined more or less constantly since then. Barite was mined from the Gunter Can- yon barite mine in 1928 and 1929, but the deposit was idle from 1930 to 1958. Tale was most recently mined at the Blue Star tale mine in 1945. The newest non- metallic mineral commodity is expansible ryholite (perlite), which has been mined from a rhyolite hill south of Big Pine only since 1949. Tungsten mining has been very sporadic because of tremendous fluctuations in the price of concentrate. During World War I and again in World War II the price rose to high levels, then at the end of the wars dropped abruptly to low levels. Tungsten ore was first discovered in August 1913 at the site of the Jackrabbit mine in the Tungsten Hills. Early in 1916, when the price of tungsten rose to unprecedented heights, mining was begun in the Deep Canyon area. The first mining was on the Aeroplane claims by the Standard Tungsten Co., and shortly thereafter the Little Sister, Jackrabbit, and Lucky Strike mines were brought into operation by the Tungsten Mines Co. The town site of "Tung- sten City" was laid out in Deep Canyon, below the mines. In the following year, mining was begun at Nobles Camp (Round Valley mine), and exploratory work was carried out at the Chipmunk mine, the Min- eral Dome Prospect (Rossi mine), the McVan claims, and the Buckshot prospect. High-grade molybdenum ore was handpicked from the outcrop at the Pine Creek mine in 1916, but the first mining for tungsten there was not until 1918, by the Pine Creek Tungsten Co. The tungsten market collapsed at the end of World War I, and between 1920 and 1923 no production of tungsten was reported in the United States. In the following decade, however, most of the known mines in the district were in operation for brief periods at one time or another. In 1924, the Tungsten Products Co. reopened the Pine Creek mine, and it was in operation through 1925 and part of 1926, but was shut down be- tween 1926 and 1936. 125 In the middle 1930's increased demand and higher prices for tungsten resulted in the reopening of many mines. A wave of prospecting followed the introduc- tion of the ultraviolet light, and by 1941 all the known deposits in the Bishop district, except the Yaney mine, had been discovered. New discoveries were made dur- ing the period between 1936 and 1941 at the Tungstar, Brownstone, Hanging Valley, Lakeview, Schober, Lam- bert, Tungsten Blue, and Marble tungsten mines. The main period of exploitation of the Pine Creek mine began in 1936 when it was purchased by the U.S. Vanadium Co. (Union Carbide Nuclear Co.). Between 1937 and 1939 the upper part of the mine, above level A, was developed for mining (pl. 9). All the ore mined prior to 1948 was from above level A ; in 1948 the Zero adit, having its portal 7,000 feet south of the outcrops of the ore bodies and 1,500 feet lower than level A, was completed. By 1948 the ore reserves in the upper part of the mine were depléted, and most of the ore mined between 1949 and 1958 was from between the Zero adit and level A. In 1937, ore was discovered at the Tungstar mine, second in total production to the Pine Creek mine, on the west side of Mount Tom at an altitude of 12,000 feet. Mining was begun in 1939 and carried on until October 1946, when the mine installations and upper tram terminal burned. Peak production for the district was reached during World War II, when the price and sale of tungsten con- centrates were fixed by Federal law ; but at the end of the war, discontinuation of Government purchases of tungsten concentrates caused a price decline that once again forced curtailment or abandonment of most operations. In 1951, following the outbreak of war in Korea, the Federal Government increased its purchases of tung- sten concentrate and stimulated domestic production by offering to purchase 3 million units of WO; at $63.00 per unit. Tungsten mining flourished in the United States until mid-1956 when the Government stockpile was filled and purchasing was terminated. In early 1958 the price on the open market was only about $20.00 per unit, too low for profitable exploitation of any of the mines in the Bishop district. In 1958, only the Pine Creek mine was in operation and that on a limited scale. GRADE OF ORES The average grade of ore mined in the district is about 0.5 percent of WO;, but a substantial amount of ore having several percent of WO; was mined from the Tungstar, Schober, and Yaney mines. The lowest grade ore that has been profitably exploited exclusively for tungsten, from the Shamrock and other deposits in the 126 Tungsten Hills, contained about 0.4 percent of WO;. From time to time, ore containing even less tungsten but with recoverable copper and molybdenum has been prof- itably produced at the Pine Creek mine. Factors favor- able to the profitable exploitation of lower grade ores are low altitude of the deposit, large volume of ore mined daily, reliable and inexpensive transportation, and an ore body of sufficient size and of such configura- tion as to favor cheap methods of mining. In most deposits the ore shoots have fairly sharp walls and do not grade through a zone of submarginal ore into barren or nearly barren tactite. Common prac- tice in most mines is to examine each face under ultra- violet light before blasting. In this way the ore mined is kept at a profitable grade, and low-grade or barren tactite is left in pillars or discarded as waste. In the Pine Creek mine, where mining is by means of blast hole stopes, the distribution of ore is determined by examination of cores taken from holes to be used for blasting. The grade of the ore within most ore shoots is con- stant, but not in all ore shoots. In deposits containing both high-grade and low-grade ore, the ore is commonly mixed to maintain an average grade. Hand sorting under ultraviolet light has not been employed widely in the district. OUTLOOK Ore reserves are large, even though some formerly productive deposits are exhausted and others contain only submarginal ore. Recently discovered extensions of known ore bodies provide a basis for considerable optimism regarding the life of the district. New de- posits undoubtedly will be discovered, but their dis- covery will require increased use of geologic and engi- neering skill. As in the past, most new discoveries will probably be relatively small. SUMMARY OF GEOLOGIC RELATIONS The tungsten deposits in the Bishop district, with one or two exceptions, are contact-metasomatic tactite de- posits. Such deposits are generally conceived to have formed at high temperatures by the interaction of cal- cium-rich sedimentary or metamorphic rock with hot solutions that emanated from intrusive magma. The term "contact metasomatic'" is used here in preference to the more commonly used term "contact metamor- phic" in order to distinguish between two different though related processes: recrystallization under high temperatures without addition of substances, and re- crystallization under high temperatures with addition of substances. As used here "contact (or thermal) metamorphism" is restricted to the high-temperature re- crystallization of rocks without significant addition of GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA substances from an intrusive magma. Barrell (1907) made this same distinction and pointed out that non- additive contact metamorphism generally precedes metasomatism and takes place with rising temperatures, whereas contact metasomatism takes place later with falling temperatures, after partial recrystallization of the intrusive rock. He pointed out further that the effects of nonadditive contact metamorphism are most striking in impure limestone, whereas metasomatism takes place most readily in purer limestone. The principal product of contact metasomatism is tactite, which locally contains scheelite (CaWO.). Tactile generally is marginal to masses of calcium-rich rock adjacent to intrusive granitic rock. Some masses of tactite are bordered by a peripheral zone of bleached and silicated marble that may have been formed either contemporaneously with the tactite or earlier, at the peak of thermal metamorphism. In addition, in many deposits thin quartz veins and thicker silicified zones locally penetrate the tactite and the adjacent granitic rock. These quartz veins and silicified zones formed somewhat later than the tactite and at lower tempera- tures, but nevertheless as part of the same process. The quartz veins and silicified zones are accompanied in places by valuable sulfides Generally they contain little or no scheelite, but where present it is abundant and may form rich, though small, ore bodies. Although the contact metasomatic tungsten deposits commonly are called tactite deposits, all tactite does not contain commercial amounts of scheelite. On the contrary, many tactite masses contain no scheelite; where scheelite is present it usually is restricted to cer- tain zones within the tactite. Tactite masses that con- tain scheelite-bearing zones of a grade that is commer- cially exploitable are called ore bodies; the exploitable scheelite-bearing zones themselves are called ore shoots. DISTRIBUTION OF DEPOSITS The tungsten deposits are confined to masses of cal- cium-rich metamorphic rock adjacent to intrusive gra- nitic rock. Most of the deposits are in groups, but a few are isolated. The largest groups are in the mar- ginal parts of the Pine Creek and Bishop Creek pend- ants and Round Valley septum, in a belt of metamor- phic rocks along the Sierra Nevada front southwest of Bishop, and in groups of inclusions of metamorphic rock along Deep Canyon in the Tungsten Hills and in Shannon Canyon. Of 21 commercial deposits, 7 are in the Pine Creek pendant, 1 is in the Bishop Creek pendant, 9 are in the Tungsten Hills, 3 are along the Sierra Nevada front southwest of Bishop, and 1 is in Shannon Canyon. The mines in the Pine Creek pend- ant have produced by far the greatest amount of tung- GEOLOGY OF THE BATHOLITH sten and they include the two deposits with the greatest individual yields; the mines in the Tungsten Hills are next. THE CONTACT ZONE The term "tactite" was introduced by F. L. Hess (1919) and defined by him as "a rock of more or less complex mineralogy formed by the contact metamor- phism of limestone, dolomite, or other soluble rocks into which foreign matter from the intruding magma has been introduced by hot solutions or gases. It does not include the enclosing zone of tremolite, wollastonite, and calcite." The term "tactite" is now deeply en- trenched in the United States, both in the literature and in local usage, in connection with tungsten deposits. An older synonymous term is "skarn," which was origi- nally used to described similar assemblages of silicate minerals associated with Swedish iron ores. Garnetite is a variety of tactite in which garnet predominates. Although no single mineral by definition is essential to tactite, most of the tactite in the Bishop district con- sists chiefly of various proportions of pale to moderate reddish-brown garnet of the andradite-grossularite series and grayish-green pyroxene of the diopside- hedenbergite series. Light-olive to grayish-green epi- dote is present in many tactite masses and in a few is a principal constituent, but it is not ubiquitous. Some of the richest tungsten ore consists chiefly of quartz and epidote, accompanied in places by pyrite or pyrrhotite and scheelite. Green to black amphibole is present locally in some tactite, but is not common or abundant. Quartz usually is present in only minor amounts in garnet-pyroxene tactite, except where the tactite has been partly silicified. Scheelite is sporadically dis- tributed. In addition to these more typical minerals, many tac- tite masses contain subordinate amounts of calcite, fluorite, idocrase, sphene, and such light-colored silicate minerals as wollastonite, diopside, grossularite, zoisite, and feldspars. However, if these minerals predominate, the rock is not, properly speaking, tactite, but rather a cale-silicate rock or hornfels. Metallic sulfides and oxides locally are disseminated in tactite, but generally were deposited with quartz after the silicate minerals were formed. In the Pine Creek and adjacent mines, molybdenite, chalcopyrite, and bornite are the most com- mon sulfides; sphalerite, galena, and magnetite are found locally in other parts of the district. The grain size ranges from less than a millimeter to more than a centimeter, but the average is probably closer to a millimeter than to a centimeter. Larger and more nearly euhedral grains of garnet, epidote, schee- lite, or sulfides are locally associated with masses of quartz, which are present in many tactite bodies. The 127 fabric of tactite ranges from isotropic to layered or veined. Veins are especially common in dark garnet- pyroxene tactite, and layering is more abundant in lighter colored varieties, especially those that contain light-colored silicate minerals. Tactite bodies vary widely in size and shape-from thin layers a few inches thick to masses several hundred feet long and more than a hundred feet thick. The con- tact with granitic rock generally is sharp, but in places is obscured by silicification. Diorite or hornblende gabbro commonly is altered to epidote adjacent to tactite, and where the tactite also contains appreciable epidote the contact may be difficult to place within a few inches or even a few feet. The contact with marble generally is sharp or is gradational through a few feet, and may be irregular, especially where the granite cuts across bedding and tactite extends outward from the contact different distances along different beds. Along some contacts, discrete crystals of garnet or idocrase may trail off from the tactite into the adjacent marble through distances of several feet. In detail, these crys- tals may lie along beds or fractures. CHARACTERISTIC MINERALS OF TACTITE Following are brief descriptions of the more charac- teristic minerals of tactite. Calcite, quartz, and the light-colored silicates locally present in but not typical of tactite are not included. Garnet.-Garnet generally is pale to moderate red- dish brown, but may be pale pink in the marginal parts of tactite masses adjacent to or interfingered with marble. In contact with other crystals of garnet or of pyroxene, external crystal faces are rarely formed, al- though inner zones may be euhedral. Against quartz and calcite, garnet crystals generally are euhedral, com- monly with dodecahedral habit. Most garnet is iso- tropic to weakly birefringent ; birefringent crystals are twinned parallel to crystal faces and are in pyramidal sectors whose bases are crystal faces. Some garnet crys- tals are zoned in a narrow range of composition and color. Most determinations of index of refraction fall between 1.78 and 1.80; the highest determined index is 1.85 for moderate to dark reddish-brown garnet from the Lakeview mine. This garnet is color mottled with lighter colored garnet (»=1.81) that is increasingly abundant toward the crystal margins. The lowest determined index is 1.76, for pale pink garnet associ- ated in many places with calcite, idocrase, and light- colored silicates in the marginal parts of tactite masses. The occurrence and properties show that the garnet belongs to the grossularite-andradite series. If small amounts of spessartite and possibly almandite are 128 ignored, the indices indicate the following compositions according to Winchell and Winchell (1951, p. 492) : M Andradite (percent) TTB c sL LL L ae leu 27-41 (most common range) TBD -z ECII EEC coma anat 72 (highest andradite) 10. 2 eA nin ane a amie arenes 10 (lowest andradite) R. G. Coleman (written communication, 1958) found isotropic garnet from the Pine Creek mine to have the following properties : @4o=11.92 A n=1.787 +.005 Dxce=3.72+.02 (measured) D=3.694 (calculated from ao) According to charts given by Winchell and Winchell (1951, p. 485), the andradite-grossularite ratio is about 3:7, and the garnet also contains notable amounts of spessartite or almandite. An analysis of tactite from the Pine Creek mine indicates 2.9 percent MnO (table 19), which suggests 10 percent or more spessartite in the garnet. Pyrozene.-The pyroxene generally is grayish green ; it may be somewhat lighter colored in the marginal parts of tactite bodies adjacent to marble. Locally black pyroxene is present in the Pine Creek mine. In thin section both green and black pyroxene is pale green. Commonly it occurs in small stubby prisms, but in places is in elongate prisms and larger anhedral grains that enclose grains of calcite and. silicate minerals. The optical properties vary, but common ones are as follows : «=1.70-1.71 Ny=1.12 N,=1.7385-1.74 2Vv=60°-62° 7 \c=46°-47° These properties indicate a pyroxene of the diopside- hedenbergite series that contains 60 to 70 percent of the hedenbergite molecule (Winchell and Winchell, 1951, fig. 302, p. 413). Another sample of grayish-green py- roxene from the Pine Creek mine having approxi- mately these optical properties was studied by R. G. Coleman by X-ray methods; it has the following physi- cal properties (written communication, 1958) : hkl aA B90, - erea 3.27 D91 cl algae $10 clt ad.. $:008 181 Hl ac 2.91 BoT L. aclu 2.555 According to Zwaan (1954), these physical properties indicate 93 to 95 percent of the hedenbergite molecule. A black pyroxene from the Pine Creek mine has the following optical properties: GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA Ny=1.71 BY =65° 7 A~c=43°%-44° The values of N, and Z Ac suggest a pyroxene of the diopside-hedenbergite series having about 55 percent of the hedenbergite molecule. Possibly a small amount of MnO present as the Johannsenite molecule could cause the black color and large optic angle. Epidote.-Epidote is not common in tactite, but is present locally, and in a few places is abundant. The variety present is iron rich and is megascopically light olive to grayish olive green. The pleochroism in thin section is colorless to greenish yellow. Epidote occurs in irregular-shaped masses and with quartz in elongate crystals that are conspicuously striated parallel with the long dimension of the crystals. Crystals an inch long are common, and some several inches long are found in places. The epidote of tactite always has a large (-) optic angle, and the fact that the value of N, generally is about 1.75 indicates about 25 percent HCa,.Fe;,S8i;,0;1; and 75 percent Idocrase.-Idocrase is not a common mineral in tac- tite. It is apparently confined to iron-poor varieties and has not been observed in iron-rich or scheelite-bear- ing varieties. In the Round Valley mine it is re- stricted to certain bedded zones, in the Aeroplane mine it occurs with grossularite in a widespread mass, and in the Pine Creek mine it is in the marginal parts of the tactite in a narrow zone transitional to silicated marble. The idocrase at the Aeroplane mine is in elongate olive-gray prisms that commonly are arranged in con- spicuous radial structures as much as 2 inches across. It is intergrown with grossularite and accompanied by clinozoisite, which appears to have partially re- placed the idocrase. In thin section {110} cleavage is conspicuous, and under crossed nicols the mineral is birefringent and shows zonal structures. The optic angle is small and the optic sign negative. Both N, and N. fall between 1.70 and 1.71. The idocrase in the marginal parts of the tactite at the Pine Creek mine is in dark yellowish-brown to moderate olive-brown, irregularly shaped masses as much as 6 inches across. Individual crystals are sur- rounded by numerous tiny crystals of diopside and wol- lastonite, some of which are also enclosed in the idocrase. The idocrase is cut by narrow veinlets of calcite, which follow fractures. These relations indicate that the idocrase was formed somewhat later than diopside or wollastonite and grew, partly at least, at their expense. Under crossed nicols, mottled and irregularly concen- tric zonal structure can be seen. GEOLOGY OF THE BATHOLITH Sphene.-Sphene is a sporadically distributed minor constituent of many tactite masses, but locally it con- stitutes as much as several percent of the tactite. Com- monly it is in tiny wedges that can be identified only in thin section, but in the Stevens ore body at the Tung- star mine it is in yellowish veinlike chains of erystals that are easily seen. In the Pine Creek mine, sphene is locally abundant in quartz-pyroxene tactite in small wedges having a bright violet color in the Z direction. Scheelite.-Generally scheelite is very light gray, but some is pale olive or clear. The size and shape of grains is variable. In tactite that consists chiefly of garnet and pyroxene, scheelite commonly is scattered through the tactite somewhat sporadically in tiny equidimen- sional grains the size of a pinhead or smaller; in tactite that consists chiefly of quartz and epidote, crystals a quarter to half an inch across are common. Scheelite also occurs in irregular streaks and masses, and in thin sheets along fractures. Crystal faces generally are not present against garnet or pyroxene, but commonly are numerous against quartz and in places against epidote. Under ultraviolet light scheelite composed of pure CaWO, fluoresces bluish white; with increase of powel- lite molecule (CaMoO,) the fluorescence is increasingly yellowish. Most scheelite in the Bishop district fluor- esces yellowish, and the intensity of yellow is extremely variable within short distances. Some single crystals exhibit several shades of yellow and bluish-white flu- orescence. Most bluish-white fluorescent grains are associated with quartz. BLEACHED AND SILICATED MARBLE In many places the calcium-rich rock peripheral to tactite is bleached and silicated. In dominantly sedi- mentary terranes, where tactite bodies are formed ad- jacent to stocks or other smaller intrusive masses this zone can usually be identified. In dominantly granitic terranes such as the Bishop district, however, the masses of calcium-rich rocks are generally so small that they are bleached and silicated throughout. The only place in the Bishop district where the calcium-rich rock is extensive enough to show the spacial relations between tactite, bleached and silicated marble, and unbleached marble is in the Pine Creek mine. There, marble pe- ripheral to the tactite is bleached and silicated across an outcrop width of several hundred feet. The inner contact between the bleached and silicated rock and tactite is sharp or gradational through a few feet or less. In places, euhedral crystals of reddish- brown garnet or brownish or greenish idocrase are ir- regularly distributed in discrete crystals through the marble that lies within a few feet of the tactite. The 129 outer contact of the bleached and silicated zone is highly irregular and is gradational in places. The most common minerals in the bleached rock other than calcite are highly variable amounts of diop- side, wollastonite, potassium feldspar, grossularite, and quartz. In places, zoisite accompanies diopside. All these minerals are in layers that appear to be parallel to bedding and are believed therefore to mark originally impure beds. This interpretation implies that little ma- terial has been added to the rock and that the chief process involved was recrystallization and loss of car- bon dioxide. In most thin sections studied, wollastonite appears to be stable, and quartz and calcite are not in direct contact with each other where both are present. However, in one thin section wollastonite is present in one layer and blades of calcite are present in a con- tiguous quartzite layer. A similar anomalous situation has been explained by Watters (1958, p. 715-716) to result from the growth of a compact layer of wol- lastonite which hindered the escape of carbon dioxide and inhibited reaction between quartz and calcite. An equally acceptable though less likely explanation is that the pressure-temperature conditions were at the posi- tion where calcite and quartz as well as wollastonite are stable. The geometrical pattern of the bleached and silicated zone with relation to the tactite seems to indicate that the bleaching and recrystallization of the carbonate took place in conjunction with the formation of tactite. Pos- sibly carbon dioxide expelled during the formation of tactite contributed in some way to the bleaching and recrystallization. Most of the silicate minerals, how- ever, seem likely to have been formed earlier during the period of thermal metamorphism when peak tem- peratures reached the range in which wollastonite is formed. ZONES OF SILICIFIED ROCK AND QUARTZ VEINS In many contact-metasomatic tungsten deposits, late quartz in veins and in silicified zones has been in- troduced into both tactite and the adjacent granitic rock. The zones of silicified rock and quartz veins are economically important because in places valuable sul- fides accompany the quartz and because scheelite is usually removed from tactite during silicification. The main loci for quartz are the intrusive contacts, but quartz is not confined to these contacts; silicified rock and quartz veins occur in both the granitic rock and in tactite, in places at considerable distance from the in- trusive contact. Some quartz-rich tactite may have been silicified. Obviously much, and perhaps all, of the quartz was introduced after the formation of tactite, doubtless as a continuation of the process that resulted in the formation of tactite. 130 The introduction of quartz has been guided by frac- tures. Zones of silicified rock can be traced into brec- ciated tactite or granitic rock, and thin sections of rock adjacent to silicified rock commonly reveal mortar be- tween grains. In partly silicified rock, fractures are evident in the structure of the rock. Small veinlets occupy fractures in which the offset walls either match or very nearly match each other. Mineral and structural relations suggest that quartz has been introduced over a long period and with falling temperatures. The earliest quartz introduced at any one place is in zones of silicified rock that were formed at least in part by replacement, and the latest is as fracture fillings in veins; however, transitions between these two kinds of- occurrences can be found, and in ideal form they appear to represent end members of a continuous sequence. Zones of silicified rock were formed earlier than veins, and presumably at higher temperatures. Evi- dence that they were formed, partly at least, by replace- ment is found in incompletely silicified rock present in many silicified zones, especially near the margins, which still retains the texture of the tactite or granitic rock. In many places, silicified rock contains unreplaced resid- ual masses of the granitic rock or tactite whose orienta- tion was not noticeably disturbed during silicification. In places where no relicts remain it could not be deter- mined whether the quartz has replaced preexisting rock or simply filled open fractures. Probably the earliest rock to form in the Pine Creek mine during silicification is composed of quartz and green pyroxene. Its presence along the margins of silicified zones in garnet-pyroxene tactite indicates that it was formed through the silicification of the tactite. In this process, scheelite was removed and garnet re- moved or converted to pyroxene. This rock probably formed at relatively high temperatures, possibly only slightly below those that prevailed at the time of forma- tion of tactite. In other places in the Pine Creek mine where the garnet in the tactite has not been selectively removed, silicification probably took place at somewhat lower temperatures. Narrow zones of silicified rock are transitional to veins in which the walls have been so extensively replaced that no larger irregularities in the opposing walls can be matched. In the youngest veins no evidence of replacement of the walls can be found, and every irregularity in the vein walls matches-a feature that indicates that dilation was the sole means by which space was made available for the emplacement of the quartz. In the Pine Creek mine, rich ore shoots of molyb- denite and of chalcopyrite and bornite have yielded notable amounts of molybdenum and copper. Else- GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA / where in the district, sulfides other than pyrite or pyr- rhotite have been found in tungsten deposits only in small amounts and have not been recovered. Quartz is accompanied in the Aeroplane mine by sphalerite, in the Round Valley mine by galena and ramdohrite (Ph;Ag;.Sb;85,; ?), in the Tungstar mine by pyrite, in the Schober mine by pyrrhotite and scheelite, and in the Coyote Creek prospect by galena that contains inclu- sions of bismuth and schapbachite? (AgBiS,). These sulfides and sulfo-salts are not likely to have been deposited at the same temperature. Molybdenite, chal- copyrite, bornite, and sphalerite probably were de- posited in the highest temperature range, galena in a medium range, and the sulpho-salts in the lowest range. No direct correlation was recognized between the sul- fides and the habit of the associated quartz. In the Pine Creek mine, molybdenite, for example, occurs in quartz- rich (presumably silicified) tactite, in silicified granite, and in quartz veins having sharp walls. Molybdenite was locally very abundant in quartz-rich rocks in both the North and South ore bodies above level A, but exten- sive masses of similar appearing rocks in the Main ore body below level A contain only small amounts of molybdenite. CHEMICAL GAINS AND LOSSES IN THE FORMATION OF TACTITE Inasmuch as the constituents of tactite are very dif- ferent from those of the host carbonate rock and its specific gravity is 25 to 30 percent greater, a large amount of material must have been introduced and a somewhat smaller amount removed in the formation of tactite. In order to calculate gains and losses of sub- stances, the chemical compositions and specific gravities of the host carbonate rock and of tactite must be known, and an assumption must be made regarding the volume relation. Since Lindgren's study of the Clifton-Morenci dis- trict (Lindgren, 1905), it has been customary to assume that the volume has remained almost unchanged during contact metasomatism. Nevertheless, uncertainties ex- ist. It is well known that sediments of mixed calcar- eous nature can lose considerable volume if thermally metamorphosed without addition of material (Barrell, 1902 and 1907; Cooper, 1957). Barrell (1907, p. 148) states that no general basis exists for calculating vol- ume changes where metasomatism accompanies meta- morphism, for not only are some substances brought in but others are taken out. The problem is extremely difficult to deal with in the Bishop district because layers altered to tactite cannot be followed into un- altered rock and the thicknesses of altered and unaltered strata therefore cannot be compared. Most marble con- tains silicate minerals such as diopside, wollastonite, GEOLOGY OF THE BATHOLITH garnet, and feldspar, which are distributed along bed- ding planes with no apparent relation to fractures or to intrusive contacts, and apparently formed from im- purities in the original limestone without addition of material. These minerals were formed as a result of thermal metamorphism, which is believed to have reached a maximum before contact metasomatism. It seems certain that CO; was lost as a result of the forma- tion of the new minerals, and this loss, together with the greater density of the new minerals, implies some shrinkage of the rock. The amount of shrinkage would depend on the kinds and amounts of new minerals formed; impure silicated marble such as is present in the Round Valley septum in the vicinity of the Round Valley mine undoubtedly has shrunk more than lightly silicated marble such as is present in the west side of the Pine Creek pendant. Fortunately, shrinkage caused by nonadditive thermal metamorphism should not affect calculations of gains and losses during con- tact metasomatism because it can be assumed that both the tactite and the adjacent host rock, with which the tactite is compared, underwent the same changes. The only evidence bearing on volume relations during contact metasomatism itself is in small irregularities in the contact between tactite and the host rock. These contacts do not indicate any change of volume, although the evidence is not conclusive; therefore, it is assumed in calculating gains and losses that any volume change was negligible. To gain a quantitative concept of the gains and losses involved in the formation of tactite, five samples from the vicinity of the Main ore body of the Pine Creek 131 mine were analyzed (table 19). Samples 1 and 2 are of partially bleached and silicated strata east of the Main ore body and were not used in the calculation. Samples 3 and 4, which were used, are from strata that, closer to the granitic rock, have been converted to tac- tite. Sample 5 is of typical tactite from the Main ore body. The chemical analyses show that the marble is im- pure and contains significant amounts of SiO;, Al;0O;, Fe, MgO, and K,0. In thin sections, the minerals con- taining these constituents are recognized to be diopside, orthoclase, grossularite, and pyrite. The calc-hornfels (sample 2) from strata east of the ore zone also contains quartz, grossularite, and wollastonite. The fact that silicate minerals and quartz are distributed along bed- ding planes suggests that they were formed by simple recrystallization of sedimentary layers without addi- tion of material. If this assumption is true, then it can be assumed further that these impurities were also present in the limestone that has been converted to tactite, and that gains and losses can be calculated directly. Gains and losses were calculated as follows : The mil- ligrams per cubic centimeter of each oxide present in samples 3, 4, and 5 were calculated. The values ob- tained for samples 3 and 4, of gray marble continuous with the ore zone, were then averaged, and differences between these average values and the values for tactite were determined. These differences represent the gains and losses in terms of oxides. Gains and losses were also calculated in terms of the metallic elements. How- ever, if, as seems highly probable, the principal loss was TaBu® 19.-Chemical analyses of tactite and bleached and silicated marble from the main ore body, Pine Creek mine, and gains and losses in the formation of tactite [Rapid rock analyses (Shapiro and Brannock, 1956). Analysts: P. L. D. Elmore and K. E. White] Marble and calc-horn- Gains and losses in fels east of tactite zone Marble continuous with tactite zone Typical tactite transformation of mar- (weight percent) ble to tac)tite (mg per ce 1 2 3 4 3 and 4 5 Oxides Elements Lab. NO :-: er lc 138271 138272 138270 1982784 ( | > 198277! _ Ai «oe Weight Weight Average mg Weight percent | My per cc percent My per cc per cc percent My per cc 19.7 61.0 17.1 465.12 16. 444. 80 455.0 40. 4 1, 426.1 4+-971.1 | Si +456.4 3.6 8.3 3.8 103. 36 3.3 91. 74 97.6 11.1 ggig igggg Al +155. 9 7.4 . s 1.4 2.4 1.2 32. 64 1.2 33.36 33.0 { 42 148.3 4148.3 } Fe 4275.4 2.9 1.8 3. 84. 32 3.0 83. 40 83. 3.9 137.7 453.8 | Mg+ 32.3 44.7 19.0 43.6 1, 185.92 45.1 1, 253. 78 1, 219.9 29.1 1,027. 2 -192.7 | Ca -142.6 . 24 . 86 £ 5. 44 s 5.56 5.5 15 t + . 60 2.6 .76 20. 67 76 21.13 20.9 . 06 .16 41 .16 4.35 14 3.89 4.1 . 29 . 07 .10 . 05 1.36 . 06 1.67 1.5 .06 . 06 14 . 09 2. 45 A2 3. 34 2.9 2.9 12 . 46 . 84 22. 85 . 46 12.79 22.8 .20 26.7 2.0 29.0 788. 80 30.1 836.78 812.8 .35 1. Gray marble (1100 level; coordinates 36,750N; 35,560E). 2. Calc-hornfels (1100 level; coordinates 36,450N; 35,730E). 3. Gray marble(1500 level; coordinates 36,265N; 35,680E); sp gr 2.72. 4. Gray marble(1300 level; coordinates 36,200N; 35,660E); sp gr 2.78. 5. Tactite(1500 level; DDH 408); sp gr 3.53. 132 of CO;, approximately as much O must have been added as is represented by O in the gained oxides. The chief calculated losses were of CO; and CaO; much smaller losses were of K,O and H0. Total cal- culated losses in terms of oxides =1027.8 mg per ce, or more than 37 percent by weight of the marble. The amounts of K0 and H0 lost, though small, are sig- nificant because the losses represent very large parts of these constituents. The principal calculated gains are of SiO;, FeO, Fe;O;, Al;0;, MnO, and MgO, and a smaller gain of TiO,. The calculated gains total 1801.7 mg per cc, or 51 percent by weight of the tactite. Not reported in the chemical analyses are small amounts of tungsten and fluorine known to be present in scheelite and fluorite. Although the apparent gain of MgO is substantial it is not large, and the MgO content of the gray marble could have been sufficiently variable to cause the appar- ent gain. On the other hand, an abundance of sphene in some thin sections of tactite indicates that TiO; was added. A very small gain of P;0; is indicated, but the amount is so small that its reality is dubious. appears to be the only oxide that is clearly unaffected. During conversion of the impure limestone to sili- cated marble prior to the formation of tactite, the vol- ume of the rock was reduced about 10 percent, if we assume no addition of substance and loss only of car- bon dioxide. This shrinkage is calculated as follows: The analyses of samples 3 and 4 (table 19) show that the gray marble stratigraphically continuous with the tactite contains as impurities about 16.5 percent SiO)», 3.5 percent Al;0O;, 3.0 percent MgO, and 0.76 percent K0, plus 1.2 percent Fe expressed as Fe,0;,. The Fe is contained in pyrite and can be neglected. The other oxides are distributed among the following minerals, known to be present in the gray marble: 16.2 percent diopside, 4.5 percent orthoclase, and 11.9 percent gros- sularite. The diopside contains 3.0 percent of the rock as MgO and 4.2 percent as CaO, and grossularite con- tains 4.4 percent of the rock as CaO. These quantities of CaO and MgO were derived from dolomitic lime- GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA stone by expulsion of CO; equivalent in weight to 10.1 percent of the rock. This loss figure could be further refined, but in view of the crudity of the basic data and possibility of erroneous assumptions, it suffices to con- clude that the volume loss has been about 10 percent. STABILITY RELATIONS OF GARNET, PYROXENE, AND EPIDOTE Comparison of chemical compositions (table 20) shows that garnet contains substantially more CaO than pyroxene or epidote, that pyroxene contains more S10; than epidote or garnet, and that epidote is rich in Al;0; and contains H.O0. MgO and FeO are confined to pyroxene, which contains no Fe:Os or Al;O;. Thus, a high CaO content probably favors formation of garnet, a high silica content and the presence of MgO and FeO pyroxene, and a high Al;0; content and the presence of H,O epidote. Pyroxene is absent or present in small quantities in tactite adjacent to marble or carbonate veins, whereas garnet is common. Conversely the silic- ified wall rock of many quartz veins in tactite consists of quartz and pyroxene and lacks garnet. The state of oxidation of Fe may also be significant in determining whether garnet or pyroxene will form. Butler (1923, p. 398-404) suggested that the larger ratio of ferric to ferrous oxide in limestone contact zones than the ratio in the intrusive rock may result from the high concen- tration of CO: in the contact zone. The equation pro- posed by Butler is: FeO, +CO=8 FeOQO+CO,. Ac- cording to Butler the temperature most favorable for the reaction to move to the left is 490° C. Field and petrographic relations of ordinary tactite unveined by quartz or calcite indicate that garnet and pyroxene formed approximately contemporaneously, and it seems reasonable to suppose that the concentrations of avail- able constituents determined which of these two miner- als formed. The relation of epidote to the other two minerals, however, is uncertain. In some tactite, garnet and epidote appear to be in stable equilibrium with each other, but the textural relations in other masses of tactite and the common association of epidote with TaBLE 20.-Chemical compositions of some common silicate minerals in tactite [Common pyroxene: approximately 25 percent diopside and 75 percent beggerigergitil (Fl‘omgman garnet: approximately 10 percent spessartite; andradite: grossularite=3:7 pidote: Al: Fe=3:1 Pyroxenes Garnets Diopside |Hedenbergite Epidote Common garnet Common Grossularite | Andradite Spessartite pyroxene GEOLOGY OF THE BATHOLITH quartz suggest that it formed a little later than pyroxene and garnet. Goldschmidt (1911) identified the assem- blage diopside-grossularite among the quartz-bearing hornfels of the Oslo region, which Turner (1948) in- cludes in his pyroxene hornfels facies. Both Barth (1952) and Turner (1948) also represent the diopside- grossularite assemblage as being stable in the amphib- olite facies, and Turner (in Fyfe, Turner, and Ver- hoogen, 1958, p. 205-211) has also included it in his hornblende hornfels facies. Epidote is considered by both Turner (Fyfe, Turner, and Verhoogen, 1958, p. 229-230) and Barth (1952, p. 341) to be stable in the lower temperature range of the amphibolite facies. In- asmuch as there is no evidence in the hornfelsed sedi- mentary rocks that temperatures attained were as high as those required for the pyroxene hornfels facies, it seems likely that the assemblage pyroxene-garnet formed under conditions of Turner's hornblende horn- fels facies. Epidote may have formed in part contem- poraneously with pyroxene and garnet in this facies, but in part probably formed somewhat later at lower temperatures and at probably higher HO pressures. LAYERING AND STREAKS IN TACTITE Much of the tactite is structurally isotropic, and the minerals are evenly distributed, but layered structures and streaks composed of any of the constituent minerals are common. The layers and streaks are of two general types-those that coincide with and appear to be in- herited from original bedding, and those that are un- related or only accidentally related to bedding. Layering inherited from original bedding generally is regular and exhibits considerable continuity. It is shown by alternating layers of different color and min- eral content, and appears to reflect alternating pure and impure layers in the parent limestone. During thermal metamorphism impurities react with one an- other and with carbonate to form light-colored silicate minerals. Metasomatic solutions, introduced later from the granite, react readily with the remaining carbonate to form the usual iron-rich silicates of typical tactite, and more slowly with the relatively insoluble and inert light-colored silicate minerals already formed. The resultant rock has an overall lighter color than tactite formed from clean marble and consists of alternating darker tactite layers and lighter colored cale-silicate layers. In some tactite, layering is inconspicuous near the granitic rock but becomes progressively more pro- nounced in the rocks farther from the intrusive. An excellent example of layered tactite formed from impure limestone is in the Western tungsten mine area where granitic rock transects bedding in what must have originally been thin-bedded shaly and sandy dolo- 133 mite or magnesian limestone. Alternate layers are rich in garnet (containing some epidote) and in pyroxene. At the contact with granitic rock the tactite is quite dark and obviously layered, though not as conspicuously as it is farther away from the granitic rock where the tactite is lighter colored and where less substance has been introduced. During thermal metamorphism the original sediment must have been largely converted to silicate minerals-argillaceous layers to grossularite and epidote, and siliceous magnesian layers to diopside. Other light-colored minerals also were formed, and cal- cite probably was present in some layers. Substances introduced from the granitic magma worked away from the contact along bedding planes and reacted readily with the remaining calcite and more slowly with the already formed silicates. Some parallel layers are of a more subtle nature, and their inheritance from bedding is difficult to prove. In parts of the Pine Creek mine the rock is layered in dis- continuous parallel streaks of garnet and pyroxene. The most conspicuous layering is in tactite that is nota- bly lighter colored than usual, but obscure layering is also present in tactite of typical darker color. Some of the layered tactite of lighter color is in marginal parts of the tactite, and the layering is parallel to bedding in adjacent marble. Lighter colored tactite generally con- tains less scheelite than darker tactite from the same mass, and where the tactite is layered, scheelite is in streaks parallel with the layers. The lighter colored layers having a lower scheelite content originally con- tained more impurities than the darker layers and re- ceived smaller amounts of substance from the magma. The observed parallelism of layering with bedding sug- gests that some and perhaps all of the layering in ab- normally light-colored tactite is inherited. Streaks of silicates independent of bedding control are believed to follow fractures that formed in tactite while it was still quite hot, and while solutions from the granitic magma were still circulating. Streaks and irregular masses of garnet and of pyroxene and quartz are common, and streaks and masses of epidote are present locally. Formation of garnet is probably condi- tioned by circulating calcium-bearing solutions, which reacted with pyroxene to form garnet, inasmuch as the common garnet of tactite contains considerably more calcium than diopside. Magnesia must have been sub- tracted and some alumina probably was added in the transformation. Small amounts of quartz present locally in garnet streaks and masses may actually have been released as a consequence of the conversion of py- roxene to garnet. Quartz-pyroxene streaks that may or may not contain sulfides appear, on the other hand, to result from the introduction of silica. Many early 134 formed quartz veins in tactite are bordered by zones of quartz and pyroxene unaccompanied by garnet. The common pyroxene of tactite contains more silica than the common garnet (table 20). Alumina must have been removed and magnesia probably was introduced. Most quartz-pyroxene streaks contain no scheelite, al- though sulfides are common. Locally, however, schee- lite is abundant in large euhedral to subhedral crystals. These crystals generally lie in the marginal parts of the quartz-pyroxene streaks adjacent to common tactite. In a few places scheelite lies in thin sheets along frac- tures in tactite, quartz, and even granite. DISTRIBUTION OF SCHEELITE The distribution of scheelite in tactite is often spoken of as "spotty," and this characterization is apt. Never- theless, the spotty distribution cannot be dismissed as the result of capriciousness-it must result from defi- nite processes and relations. A complete explanation of the distribution of scheelite in tactite will require extensive investigations, and at this time only a few simple relations can be described on the basis of data available. In the Bishop area, scheelite-bearing ore shoots in tactite can be considered to be of two general kinds, those in ordinary garnet-pyroxene tactic composed of iron-rich silicates and poor in quartz, and those in rocks abnormally rich in quartz. Ore shoots in ordinary tac- tite are more abundant and generally more extensive than those in quartz-rich tactite, but those in quartz- rich tactite include the highest grade ore shoots. Most quartz-rich tactite contains very little sheelite, and the local presence of rich ore bodies in such rocks is de- cidedly anomalous. In garnet-pyroxene tactite, scheelite usually is dis- seminated through the tactite in rounded grains that range from pin-point size to half an inch across. Gen- erally the distribution of scheelite is not uniform, and the quantity present from place to place may range widely. If the tactite is structurally isotropic, the pat- tern of scheelite distribution also is structureless, where- as if the tactite is layered, the scheelite generally is dis- tributed in streaks parallel to the layers. In garnet-pyroxene tactite, dark-colored tactite is a commoner host for scheelite than lighter colored tactite. A reasonable explanation for this association is that such tactite usually is formed from relatively pure marble, and consequently its formation involved in- troduction of the maximum amounts of silica, alumina, iron, and other substances, including tungsten, from the granitic magma. Tungsten is, of course, simply one of the constituents introduced during metasomatism. Variations in the amount of scheelite within apparently GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA homogeneous tactite are difficult to explain. However, even in the most homogeneous tactite some variation in the proportions of minerals is present, probably as a result of variations in the amount of available silica, lime, alumina, magnesia, iron, manganese, and other constituents at the time of formation. Fluorite is pres- ent in some of the richest tungsten ore in the Pine Creek, Adamson, and Brownstone mines, but was not . identified in ore from any other mines in the district. Scheelite is generally appreciably less abundant in light-colored tactite whose formation involved the in- troduction of a smaller total amount of substance. Light-colored tactite can be formed under at least two cireumstances. Most commonly it is formed from im- pure limestone that was already partly altered to silicate minerals at the time of metasomatism. Such tactite commonly is layered, and scheelite is largely con- fined to darker layers to which the greatest amount of magmatic substance was introduced. Light-colored tactite may also constitute transitional zones between dark tactite and marble. Tactite in this setting gener- ally is composed of grossularite, idocrase, and other iron-poor silicate minerals, and possibly calcite. Its formation from clean carbonate rock involves the ad- dition of as much silica as does the formation of iron- rich tactite, but obviously smaller amounts of iron and tungsten were introduced. Watters (1958, p. 03-724) has shown that silica has traveled farther from the granite contact than alumina, iron, and titanium in skarn in the eastern Pyrenees. Possibly some light- colored tactite formed from clean marble results from a paucity of iron, titanium, manganese, and tungsten, and a preponderance of silica and alumina among the introduced substances. Tactite containing more than a few percent quartz ordinarily is poor in scheelite, probably because schee- lite was soluble in the solutions from which quartz was deposited. Quartz commonly is a late mineral in tac- tite, and its appearance may mark the beginning of the period of silicification that followed immediately after the period of tactite formation. Locally, scheelite is present in late quartz masses, generally in clusters or masses of large euhedral to subhedral crystals that pro- vide an impressive display under fluorescent light. The presence of these sporadically distributed masses of scheelite in quartz is consistent with the hypothesis that tungsten was contained in the solutions that deposited the quartz but that special conditions were required to bring about the precipitation of scheelite. Possibly the essential condition for scheelite precipitation was the availability of calcium, for quartz has been de- posited not in limestone or marble, but in tactite and GEOLOGY OF THE granite where calcium was usually bound in silicate minerals and was not available to form scheelite. Whatever the special conditions required may be, they have been met in the district at several deposits where the richest ores, containing several percent WO;, have been mined. These deposits include the Schober mine, where the ore consisted chiefly of quartz and pyrrhotite, and lesser amounts of garnet, epidote, and calcite; and the Lakeview mine, where the ore consists of epidote and quartz, and some calcite. Equally rich ore from the Tungstar mine was composed of pyrite, oligoclase, and quartz, accompanied locally by garnet and epidote. Although quartz is not abundant, the presence of pyrite, which like the other sulfides com- monly is associated with quartz, suggests that silica was present in the depositing solutions. These quartz-rich deposits appear to have been de- posited a little later, and presumably at lower tempera- tures, than deposits in quartz-poor but iron-rich tactite, and may constitute a transition to hydrothermal vein deposits. In a few places scheelite has been observed in fractures, where it obviously was formed later than the enclosing rock. In the Western tungsten mine, where the tactite is conspicuously layered because it was formed from thinly interlayered marble and cale- hornfels, much of the scheelite is along fracture planes in paper-thin crystals as much as an inch across. The tactite breaks preferentially along these fractures, yield- ing surfaces that fluoresce brilliantly under ultraviolet light and give an erroneous impression of high-grade ore. In the Pine Creek mine, thin veinlets of scheelite cut across quartz veins, and on the east side of Mount Tom, in the vicinity of the Lambert mine, scheelite is present in places along fractures or joints in the granitic rock adjacent to marble. LEACHED OUTCROPS AND SECONDARY ENRICHMENT Leaching of tungsten from the outcrops of ore bodies and its secondary enrichment at depth are controversial subjects among geologists and engineers who have worked with tungsten deposits. Gannett (1919) showed that preferential leaching of tungsten from outcrops by sulfate-bearing waters is theoretically possible, but almost no reliable field observations in support of either leaching or secondary enrichment of tungsten have been published, and the differences of opinion are not likely to be resolved until more observational data are avail- able. In the Bishop district, geologically recent, deep dissection of most parts of the region precludes the kind of ground-water circulation that favors surface leach- ing or secondary enrichment at depth, and the tactite in most outcrops is little altered. Nevertheless, abundant pyrite in the Tungstar mine and abundant pyrrhotite in the Schober mine were BATHOLITH 135 oxidized near the surface. Both deposits were notably high-grade at the surface, and the grade of the ore fell at depth. These deposits are in small inclusions, how- ever, and a characteristic of such deposit is decreasing grade at depth as a result of the primary mineraliza- tion. The ore in the oxidized zone doubtless was en- riched as a result of the removal of the sulfides. The scheelite in the surface outcrop of the Tungstar mine exhibited no evidence of leaching or enrichment. No record of the mineral content of the near-surface oxidized ore is available for the Schober mine, and it is not known whether the scheelite was altered. At the Yaney mine the disposition of minerals pro- vides a basis for postulating secondary enrichment (chiefly residual), but the mine is unique in the district. The chief tungsten-bearing mineral is ferberite, which occurs in pyramidal crystals that are pseudomorphs after euhedral scheelite. These crystals are embedded in a matrix of jarosite, opal, and quartz, and the matrix also contains dispersed tungsten in an unknown form. A small amount of scheelite also is present, and tungstite has been identified. The setting of the deposit, which is in the marginal part of a small calcareous inclusion adjacent to alaskite, and the presence of partly altered remnants of tactite and cale-hornfels layers suggest that the deposit is an altered tactite deposit. The position of the deposit, adjacent to a range-front fault, sug- gests that hot spring waters were the agents of altera- tion. The average grade of the ore is about 2.0 per- cent, which is high for an average tactite body, but not abnormally high if the change in density through loss of calcium, iron, and other substances is considered. The fact that some of the tungsten is dispersed indi- cates some movement of tungsten, though perhaps through only limited distances. The euhedral form of the pseudomorphs probably results from growth of the original scheelite crystal to obtain the euhedral form, for the scheelite in tactite is not generally in euhedral crystals. FACTORS THAT INFLUENCE POSITION, SIZE, AND SHAPE OF ORE BODIES Tactite bodies exhibit great diversity in their size, shape, internal structure, and scheelite content. Tactite does not occur along all contacts between marble and intrusive rock, and it is notably irregular in thickness and scheelite content where it does occur. Along some contacts between intrusive granitic rock and marble only a thin selvage of tactite a few inches thick is pres- ent, whereas along others great masses 100 feet or more thick occur. At the Marble tungsten mine a few inches of wollastonite is present along most contacts between quartz monzonite and marble, but two tactite masses having average thicknesses of about 10 feet are also 136 present, and one of these has been followed under- ground more than 200 feet. Along the west side of the Pine Creek pendant, granitic rock is in contact with marble for more than 3 miles, yet all the thick masses of tactite that constitute known ore bodies are localized along a 3,000-foot segment at the north end. Within this span only about 1,000 feet is occupied by tactite ore bodies. Here, tactite is present everywhere along the intrusive contact, but is a few inches, or at most a few feet, thick between ore bodies; the ore bodies, in contrast, range from 50 to 200 feet thick. Much of the tactite between ore bodies is partially silicified and contains little or no scheelite. Some tactite masses are tabular, some are tubelike or chimneylike, and many exhibit complex shapes that defy simple descriptive terms. The longer dimensions of some tactite masses lie along intrusive contacts, whereas the longer dimensions of others extend outward from the contact along beds or fractures in the meta- morphic rocks. Tactite masses having regular shapes dip and plunge in various directions. The distribution of scheelite in commercial amounts within tactite is almost as varied as the distribution of tactite itself, but in many places the shapes of ore shoots reflect in a modified way the configuration of the enclos- ing tactite masses. In some places it is possible to relate the size, shape, or tungsten content of tactite to recognizable features of the geologic setting, and every irregularity of the tactite bodies no doubt has its explanation, even though no relation has been established. Three features seem to have been of special significance in determining the size and shape of tactite masses: (1) irregularities in the intrusive contact, (2) the stratigraphy and lithol- ogy of the metamorphic rock, and (3) fractures along the intrusive contact and in the calcium-rich host rock. IRREGULARITIES IN THE INTRUSIVE CONTACT Many tactite bodies that constitute ore bodies are localized in embayments, troughs, and other irregulari- ties in intrusive contacts. Irregularities are most com- mon where the beds in the metamorphic rocks meet the intrusive contact at an angle in dip, in strike, or in both. Along such contacts the granitic rock commonly alter- nately follows and cuts across the bedding-a feature that produces steps in the contact. At crosscutting seg- ments of contact, sills and apophyses of granitic rock may penetrate along bedding planes in the metamorphic rock. In the Bishop district, irregularities in which gra- nitic rock wraps around and embraces a salient of mar- ble are especially effective as traps for tactite. The largest number of ore bodies are associated with irregu- GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA larities in which granitic rock overlies marble; fewer ore bodies are associated with irregularities having steeply dipping axes in which granitic rock wraps around tactite in plan. Irregularities formed by a salient of granite in marble are apparently much less effective traps. Only one small ore body, that at the Lambert mine, was associated with a bench in the intru- sive contact where marble overlies granitic rock, and no tactite bodies of commercial size or grade have been found associated with steeply dipping salients of gra- nitic rock in marble. Large tactite bodies at irregularities in igneous con- tacts may .be the result of extra heat supply and of movement of mineralizing solutions. Metamorphic rocks that projected into granitic magma received the maximum available heat because a large area per unit of volume was exposed to the magma. The metamor- phic projections into the magma chamber were also exposed to magma for a longer period because the gra- nitic intrusives cooled inward from their margins (see fig. 55A). Control over the movement of mineralizing solutions is suggested by the shape of many ore bodies and ore shoots. Vertical elongation of many ore bodies and preferential localization of others beneath granitic dikes and apophyses in marble suggest that these solutions moved generally upward along the intrusive contact. Irregularities having steeply dipping axes very likely acted as channelways, whereas irregularities having horizontal or gently dipping axes probably forced the solutions to spread laterally and thus acted as traps. Control of the movement of mineralizing solutions was probably aided by fracturing, which provided greater permeability. Fracturing could have been caused by stresses related to the emplacement and cooling of an intrusive or from regional forces. Whatever the cause, fracturing was probably more intense where irregu- larities were present than where the intrusive contact was smooth and regular. In addition to providing in- creased permeability conducive to the movement of mineralizing solutions, fracturing would also provide 50 FEET FicurE 55.-Hypothetical sketch map showing common relations be- tween marble (m), granitic rock (g), and tacite (t) along a dis- cordant intrusive contact. Dashed lines in granite represent succes sive boundaries between magma and crystallized rock as the magma crystallized away from the contact. GEOLOGY OF THE BATHOLITH greater surface area for the solutions to come into con- tact with large volumes of rock, including marble. STEEPLY DIPPING SALIENTS OF MARBLE The South ore body in the Pine Creek mine is the best example of a tactite body localized in a steeply plung- ing irregularity in an intrusive contact where granitic rock wraps around metamorphic rock in plan. Except for the Main ore body in the Pine Creek mine, the South ore body has yielded more tungsten, molybdenum, and copper than any other in the district. The ore body is at the nose and on the west side of a wedge-shaped marble salient in quartz monzonite along the west side of the Pine Creek pendant (fig. 56). At the surface, quartz monzonite envelopes the north end of the marble salient, and a tongue of quartz monzonite penetrates south into the east side of the marble for about 100 feet. The marble salient dips vertically, and the nose plunges southward at about 60°. The tactite ore body dips vertically, rakes about 60° to the south, and has been followed downward from the surface for more than a thousand feet. The greatest thickness is near the surface. The ore body was more than 150 feet wide and 300 feet long in an open pit, but less than 100 feet wide on level C, about 90 feet deeper, and not more than 50 feet wide on level A, about 275 feet beneath the open pit ; 600 feet beneath level A it is only about 15 feet thick. The ore body contained a single ore shoot, which became narrower and shorter at depth with diminishing size of the enclosing tactite. At levels A and C the tactite in the tip of the salient is barren, probably as a result of late silicification. Molybdenum in commercial amounts was restricted to the upper part of the ore body, where it was associ- ated with silicified tactite and quartz veinlets. Only insignificant amounts were present on levels A and C. Exploration of the deeper part of the South ore body shows that its bottom coincides with the lower limit of the reentrant in the intrusive contact ; the reen- trant was obviously the dominant control in the locali- zation of the ore body. Nevertheless, other types of controls are suggested by the shape of the ore body. The thin tail at the south and at depth may have resulted from a favorable bed that lay along the contact, or from premineral fracturing along the contact. The abrupt upward thickening of the ore body and the pres- ence upward of rich molybdenum ore suggest a former bench or protrusion of granite above the ore body analogous to the one at the Main ore body. Several smaller masses of tactite elsewhere in the district are also embraced in granitic rock in reentrants in the intrusive contact. Among these are the Little Egypt (fig. 5%) and Coyote Creek prospects in the 135-925 O-65--10 137 Bishop Creek pendant and the Tungsten Peak prospect in the Tungsten Hills Each of these tactite masses occupies a small segment of an otherwise regular intru- sive contact along which a thin selvage of tactite is present. They have not been explored underground because the scheelite content is low. BENCHES OR APOPHYSES OF GRANITIC ROCK Examples of ore bodies beneath benches or apophyses of granitic rock are numerous and include the North- west ore body of the Adamson mine, the North ore bodies of the Pine Creek mine, the upper part of the Main ore body of the Pine Creek mine, and smaller bodies in the Marble tungsten mine. At all the deposits the marble just beneath intrusive rock has been con- verted to tactite. Downward the tactite passes into marble, which is usually silicated, except along intru- sive contacts where tactite may persist downward with diminishing thickness. In some deposits the lower con- tact of tactite is with silicated marble at a sharp, though in places highly irregular, contact. In others, tactite passes downward through progressively lighter colored tactite to silicated marble. The mineralizing solutions probably worked upward along the intrusive contacts and reacted with the adjacent marble to form tactite; they were slowed down or stopped upward beneath benches of granitic rock and permeated into the adja- cent marble. The Northwest ore body of the Adamson mine was at the end of a nearly vertical slab of metamorphic rock, principally marble, which was split off from the west side of the Pine Creek pendant at the time of the intrusion of the quartz monzonite. The northwest end of the slab is enveloped by quartz monzonite. Tac- tite was present everywhere along the intrusive contact, but was much thicker in the upper part of the marble beneath quartz monzonite than in the sides or bottom of the marble. The North ore body of the Pine Creek mine lay along a segment of intrusive contact where the contact and beds are discordant in dip. The general attitude of the contact is vertical, and the adjacent beds dip 75° east. Sills penetrate from the main contact downward along bedding planes. The ore body consisted in reality of several small ore bodies; an upper one cropped out at the surface, and lower ones lay beneath apices formed by the intersections of sills with the main body of quartz monzonite (fig. 58). The lower ore bodies widened downward for a distance, then split into two limbs sepa- rated by marble. The upper ore body widened upward to the surface where it was split longitudinally by a sill- like mass of quartz monzonite. The upper body, like the lower body, was probably localized beneath a cap of quartz monzonite, which has been eroded away. 138 36,000 SCALE GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, IN FEET W s '\\\\\\ X 1 ou! F3 7 u- fats / 7 han S- Ct * $ 2 2 gas s \\\\\\\\\\\\\\\\\\\\\\\\\\\\\ (ws os mise ~4 ori- of ars 22 pus" gpm ,_ SS oS 24 as Kak 7 en fm to eas A: CALIFORNIA EXPLANATION & Detritus-filled solution channel & © Molybdenum ore shoots Cutoff 0.4, percent MoSq © Tungsten ore shoots Cutoff 0.4, percent WO & Marble with some silicate layers & Quartz monzonite Note: No assay data from pit is available. _ Outline of tungsten ore shoot is in- ferred . Much of the tactite also contained rich molybdenum ore, but the data are not adequate to show the distribution of molybdenum ore in the pit Geology by Paul C. Bateman and Lawson A. Wright, 1954 FieurE 56.-Block diagram of the South ore body, Pine Creek mine. GEOLOGY OF THE BATHOLITH «calf-1“ ¥ whornfels oy + \\\>7 7 € \\\ K vk % N Quartz Y IX monzonite N L n 3 aA * x t N SX A4 AJ p C; § C fs * O 50 FEET [L.. 01 cor" Geology by Paul C. Bateman, 1951 Freur® 57.-Geologic sketcl’i‘ map of 2131203 IElittle Egypt prospect, sec. 7, *» Although the principal control over localization of the Main ore body of the Pine Creek mine was not an irregularity in the intrusive contact, the ore body is locally thicker and contains rich molybdenum ore be- neath two benches of granite. The upper bench is about 150 feet and the lower bench about 500 feet beneath the outcrop (fig. 59). At the lower bench a wedge- shaped mass of silicified granitic rock extends more than a hundred feet downward along the bedding in the marble. The thickness of the ore body averages about 60 feet above the upper bench, about a hundred feet between the benches, and more than 130 feet below the lower bench for about 150 feet. Between the benches the molybdenum ore lies along the intrusive contact, and below the lower bench it follows the wedge of silicified granitic rock. 'The tactite body probably was more fractured near the benches in the contact be- cause of the irregularity in the contact. Such frac- turing would have permitted late introduction of quartz and sulfides. At the Marble tungsten mine in Shannon Canyon, tactite was formed locally along the main intrusive contact and also within the marble beneath a thin dike of quartz monzonite (fig. 60). This dike enters the marble flatly, but sends offshoots downward along the 139 beds. Tactite bodies underlay the dike and extended downward along the main quartz monzonite contact and along contacts with the sill-like offshoots from the dike. SMALL INCLUSIONS OF METAMORPHIC ROCK Deposits in small inclusions of metamorphic rock are closely allied with deposits localized beneath benches or apophyses of granitic rock in terms of the factors that controlled the mineralization. Deposits in small in- clusions have yielded disproportionately large amounts of tungsten ore, and it would be erroneous to equate small inclusions with small tungsten deposits. Most inclusions, though small in terms of the features that can be represented on the maps (pls. 1-4), are suffi- ciently large to contain extensive tungsten ore bodies. The yield from the Tungstar mine, which is in a small inclusion, is exceeded only by that from the Main and South ore bodies of the Pine Creek mine. Large yields have also come from the Schober, Rossi, Little Sister, Tungsten Blue, and Aeroplane mines, and lesser yields have come from the White Caps, Chipmunk, and Jack- rabbit mines, all of which are in small inclusions. The term "inclusion" implies that the body is en- closed in intrusive rock in outcrop, and is underlain and before erosion was overlain by intrusive rock. The bot- toms of inclusions at the Jackrabbit and Tungsten Blue mines were determined in mining, and the inclusion at the White Caps mine is capped by quartz monzonite. Furthermore, at the Tungsten Blue, Schober, and Tungstar mines, the fact that the inclusions broadened downward from very small outcrops suggests that the inclusions were capped by igneous rock at a level not much higher than the present erosion surface. Although an ore body can occupy an entire inclusion, and apparently does at the Tungsten Blue mine, most inclusions contain nonscheelite-bearing rocks. All the stratigraphic, lithologic, and structural controls that are effective in localizing ore bodies in the margins of larger pendants or septa are also effective in small inclusions; nevertheless, the capping of intrusive rock over inclu- sions overshadows all other controls. Where tactite is present it generally is in the tops of inclusions, and it passes downward into marble in a fashion similar to that of tactite beneath benches and apophyses along more extensive intrusive contacts. The amount of scheelite commonly also decreases with depth as the tactite becomes lighter colored or passes into other cal- careous rocks in which the effects of additive meta- somatism are less apparent. The distribution of the rocks suggests that mineralizing solutions worked up- ward along the sides of the inclusions to their tops where the solutions accumulated and reacted with the marble to form tactite. 140 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, EXPLANATION Tungsten ore shoots Cutoff 0.4 percent WO 3 Tactite with little or no scheelite Quartzose rock Silicified quartz monzonite and siliceous tactite Quartz monzonite Quartz diorite ® Level C Marble Silicated in part SCALE IN FEET CALIFORNIA Level C Geology by Paul C. Bateman and Lawson A. Wright, 1954 FicurE 58.-Sectional diagram of the North ore body, Pine Creek mine, showing the tungsten ore shoots. GEOLOGY OF THE BATHOLITH | f Cxx -y -~ -A G a a y C rse Sublevel C-7 i"? Level C t+ ‘tv => \\’v/’/ \\,W¢’ //, CS4 o @ est 250 level 500 level 700 level 900 level 1100 level 1300 level 1500 level 141 EXPLANATION Talus on surface and detritus in solution cavities ¥2 Molybdenum ore Cutoff grade 0.4 percent MoSy Tungsten ore Cutoff grade 0.4 percent WOs Tactite with little or no scheelite V Quartzose rocks Includes quartzose tactite, silicified quartz monzonite, rock composed largely of quartz veinlets, and dikes and sills of quarte-feldspar rock Marble Silicated in part Quartz monzonite Includes small masses of quartz diorite SCALE IN FEET Geology by Paul C. Bateman and Lawson A. Wright, 1954 Z2 -<---_- FrcurE 59.-Sectional diagram of the Main ore body, Pine Creek mine, showing the tungsten and molybdenum ore shoots. 142 Northwest 5600 - Southeast 12 (f] EXPLANATION ~. e J/\7/‘ s A200 § 5550 - TNIC i "(x Tactite CAS ~. LLIA NKK /V>/\/L\‘/>(‘/> | Bx LDA } Cast e 71 £+ J%\//\7\/)\ , Marble < ~ NZS 5500- lts. . ~/jyE AJ " l/,\//./: 4 ag ~A F/\\/|\ £ PAL/Q As. 50 0 L i i i i L DATUM IS MEAN SEA LEVEL 50 FEET ] FicurE 60.-Section through the Marble tungsten mine showing the relation of tactite ore bodies to the intrusive contact. Where many small inclusions are present in a small area, as in the Deep Canyon (Tungsten City) area of the Tungsten Hills, inclusions containing tactite ore bodies are generally accompanied by more numerous in- clusions composed of marble, light-colored silicated rock, or noncalcareous rock. Some of the calcareous inclusions exposed at the surface may be the roots of inclusions that contained tactite ore bodies in their eroded upper parts. Concealed inclusions must also be present in these areas and, if a practical method for lo- cating them were found, they might provide a signif- icant source for tungsten ore. An attempt to locate them with a magnetometer proved unsuccessful (Bate- man, 1956, p. 21-22 and fig. 2, p. 50). Following are brief descriptions of the geological re- lations in some of the deposits in small inclusions: The Tungstar mine, on the west side of Mount Tom at an altitude of 12,000 feet, consists of two ore bodies in separate inclusions in quartz-diorite. Almost all of the production came from the Greene ore body, a steep- ly dipping tabular inclusion having a vertical extent of more than 400 feet, an average width of about 100 feet, and an average thickness of about 25 feet. Most GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA of the inclusion was tactite, but the upper part con- tained some pelitic hornfels and the lower part had relicts of coarse white marble. The mineral content of the tactite is somewhat unusual : it consists chiefly of garnet, epidote, and pyrite (oxidized in the upper part of the ore body), but locally includes quartz, oligo- clase, apatite, and sphene. The scheelite generally oc- curs in large crystals, a quarter to half an inch across. Decrease in the WO; content of the mill heads during the life of the mine indicates that the scheelite content of the ore decreased with depth. The grade diminished from 2.6 percent of WO; for the first 17,000 tons of ore mined in 1989 (Lenhart, 1941, p. 67-71) to about 2.0 percent in 1943, then to a little more than 1.0 percent in 1946 (Bateman, 1956, p. 37). Analyses of cores taken below the 280-foot level indicate further decrease in grade to 0.73 percent WO.. The Schober mine, in the Bishop Creek pendant, is in an inclusion composed of tactite and hornfels in the marginal part of a mass of hornblende gabbro. In a shallow glory hole the inclusion is elliptical in plan- about 100 feet across in the longer direction and about 60 feet across in the shorter. Tungsten ore of com- mercial grade was found only in the upper part of the inclusion; the floor of the glory hole is approxi- mately the lower limit of ore. The ore was coarsely crystalline rock composed chiefly of pyrrhotite (oxi- dized to about 20 feet beneath the surface), quartz, and scheelite, and a little garnet, epidote, and calcite. The typical garnet-bearing tactite here contained very little scheelite. The contact between the inclusion and the enclosing hornblende gabbro is steep except on the west side where the inclusion clearly dips under the hornblende gabbro. Before erosion the inclusfon was probably covered by hornblende gabbro only a short distance above the outcrop. The grade of the ore in all the ore bodies in the Deep Canyon (Tungsten City) area of the Tungsten Hills decreased with depth, and the tactite passed downward into light-colored silicate rock and marble. Only at the Tungsten Blue and Jackrabbit mines. however, can a capping of intrusive rock be observed. At the Tung- sten Blue mine the deposit was partly covered at the surface by epidotized gabbro. The only outcrop of tactite at the White Caps mine is a nearly barren showing which is entirely surrounded by quartz monzonite. This unpromising outcrop is one end of an elongate, steeply dipping mass of tactite that extends laterally beneath quartz monzonite for more than 100 feet. The upper contact of the tactite with quartz monzonite is very nearly horizontal. An ore shoot within the tactite was stoped downward to the water table, which is only about 25 feet beneath the top GEOLOGY OF THE BATHOLITH of the ore body. The ore body has not been explored below the water table, but the presence of marble in the bottom of the stope and analogy with other deposits in inclusions suggest that the grade of ore will diminish with depth and that commercial ore may not continue to the bottom of the inclusion. STRATIFICATION AND LITHOLOGY OF THE METAMORPHIC ROCKS The limitation of tactite to calcium-rich rocks and especially to cleaner marble is an obvious example of lithologic control. Because the lithology can change ab- ruptly from bed to bed, though it changes more gradual- ly along beds, the lithologic control generally is also stratigraphic. This kind of control is common where beds of clean marble are interlayered with heavily silicated marble, with calc-hornfels, or with noncalcare- ous strata. Excellent examples are present at the West- ern and Round Valley mines in the Round Valley septum. At the Western tungsten mine thinly bedded calc-hornfels and silicated marble is interstratified in pelitic schist and hornfels. The calcareous rocks have been converted to tactite and light-colored silicate rock in alternating layers. At the Round Valley mine the prevailing rock is some- what argillaceous marble, which is bounded on the west by pelitic schist and hornfels and on the east by partly garnetized cale-silicate rock. The ore body apparently was formed in argillaceous marble in preference to other strata that contained little or no free calcite after ther- mal metamorphism. Within the ore body, the schee- lite-bearing ore shoots are closely restricted to the cleaner beds (fig. 61). Stratigraphic control is indicated in some places where no compositional or lithologic differences between the mineralized and unmineralized beds are recogniza- ble. For example, at the Munsinger prospect in the Bishop Creek pendant, quartz monzonite cuts across the bedding in calc-hornfels at a large angle, and a few beds are mineralized outward from the intrusive contact (fig. 62). Beyond the mineralized zone all the beds in the cale-hornfels appear to be of about the same lithology. Almost identical relations exist in the nearby Lindner, Waterfall, and Stevens prospects. Conceivably some subtle differences of lithology exist between the miner- alized and unmineralized beds, but it seems equally likely that the mineralization followed premineral bed- ding-plane fractures. Another example of stratigraphic control where no obvious differences in the lithology of the mineralized and unmineralized beds were recognized is the Main ore body of the Pine Creek mine (fig. 59). The east boundary of this ore body coincides in most places with a stratigraphic horizon. The marble in extensions of 143 the mineralized beds appears to be very similar to mar- ble in beds just outside the ore zone. Here also, slight differences in lithology could have escaped notice, but a premineral bedding-plane fracture that has been ob- scured by the formation of tactite or by recrystalliza- tion in the marble is equally likely to have controlled the boundary of the ore body. FRACTURES ALONG THE INTRUSIVE CONTACT AND IN THE CALCIUM-RICK HOST ROCK Fractures open at the time of tactite formation along the intrusive contact and in the adjacent calcium-rich host rock probably contributed to the localization of virtually every tactite ore body in the district, includ- ing those localized in "favorable beds" and those asso- ciated with irregularities in the intrusive contact. Per- meability was required for the movement and accumu- lation of mineralizing solutions along intrusive con- tacts; fractures seem to provide the most likely avenues for such movement. The lithology of the beds can gov- ern the intensity of additive metasomatism once the solutions come in contact with the calcium-rich rocks, but the permeability of the beds must have been too small for the movement of ore solutions, else ore bodies would not be as closely limited to the intrusive contact as they are. Nor could irregularities in the contact have provided permeability in themselves. Contact irregu- larities are probably effective principally in that they are apt to be loci for fracturing. Many detailed descriptions appear in British litera- ture of reciprocal exchange of substance along contacts between granitic rock and marble (Joplin, 1935a ; Muir, 1953a; Gindy, 1953; Watters, 1958.) In all these de- scriptions it is shown that silica, alumina, and iron, and in some places magnesia and alkalis have been intro- duced into the marble, and that calcium has been intro- duced into granitic rock. In all places where reciprocal exchange of substance has been demonstrated the con- tact zone is narrow, generally measurable in inches rather than in feet. The relations along such contacts seem entirely compatible with the concept of a frozen contact along which limited amounts of material moved from the cooling granitic magma into the adjacent mar- ble and from the marble into the adjacent granitic rock or magma. The accumulation of masses of tactite a hundred feet or more thick, however, such as form many tactite ore bodies, seems unlikely to have resulted from the direct flow of material across the contact from the contiguous granitic rock. The mere irregularity in distribution and thickness of tactite requires the accumulation of material bled to the contact from a large volume of igneous rock and also demands circulation along the contact. The tactite beneath granitic apophyses in the EXPLANATION EAST T e sail. d. ___ ArAJ< Gq - aye. Contact 7 “7623/P/é) P j ? AIN Dashed where approximately located Mine workings Vfl/EIM ‘(lfufhe i i h h roject Soil cover and slope wash Tactite and calc-hornfels Dashed wherelpislecied fivlcé‘gli‘IPLfixl/‘x Contains little or no scheelite (1213.1sz ‘V‘Lr/ - 5150 SSCA Fault so l’)\//\\/|//\\l(:y“l\ -\£\:/\/ P MAME was + re Bo Dashed where inferred r Ses 9,6 Fib Mine muck Fin 1" Granite mA - 5100' ,/\,\7A>—\{< <=" 7\_I\/:’\I 75 SIN aas ee i aan ae s 6 75 5050 -= 51?“ Fars if/3 Sect SM iS AC/ rd YZ oona Lai mime . ~ > L DK eee ane am sO may risyel iof l)‘\7\\,9,\—(ly\“l\l 73:31‘ 98 (fig/3,7? 50 0 50 100 150 FEET ead I | ] FicurE 61.-Geologic section through the Round Valley mine, PPI 'LOIMLSIG dOHSIY 'NOLLVZITIVHMNIN NMLSPNAL GEOLOGY OF THE BATHOLITH Opencut X x ngrtzvm7onzon|te L * VA b e1.42 White pumice 20 feet Granite sand 63 feet 1 2 (specific gravity) Bishop tuff in cliff along south margin of Volcanic Tableland in $% sec. 20, T. 6 S., R. 32 E. FiGuRB 67.-Vertical sections through the Bishop tuff showing thickness, color, and specific gravity. Bab 158 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA dant small devitrified pumice fragments that weather out readily. The variation in specific gravity suggests that the four lower layers were extruded closely enough to have been somewhat fluid during cooling and to have cooled together as a single cooling unit. The top layer, however, must have been extruded somewhat later, its high density as compared with the immedi- ately underlying tuff may be the result of loss of vol- atiles without replacement from cooling tuff at depth. Furthermore, the devitrification of the pumice frag- ments in the white layer and in the upper part of the pale red-purple layer was almost certainly caused by escaping gases. The fresh pumice fragments in the top layer indicate that this layer was extruded after gas activity had greatly diminished. The white layer can be followed in the walls of the Owens River Gorge downstream to about a mile above Birchim Canyon. The fact that in this distance the white layer is just below the rim indicates that the sur- face is a dip slope. For a mile above Birchim Canyon exposures are poor because of loose rubble on the walls of the gorge, and in Birchim Canyon the rocks are sig- nificantly different. Pale-red tuff in the canyon rim, identical in appearance and specific gravity to the pale- red tuff exposed halfway down the walls of the Owens River Gorge upstream, is underlain by less dense pale orange-brown tuff resembling the grayish orange-pink layer that forms the rim rock in the Owens River Gorge upstream (fig. 67). If the pale-red layer in Birchim Canyon is the same as the one upstream, and the under- lying pale orange-brown layer is either the lateral equivalent of the pale grayish-purple layer upstream or, more likely, is a unit not exposed upstream. Very likely the pale orange-brown layer is a new layer not exposed in the section upstream, for even though layers do change laterally, a layer could hardly have been emplaced at one locality so close in time with an over- lying layer as to have cooled with it, and in another to have preceded the same layer so far as to have solidified alone. Downstream from Birchim Canyon the pale orange- brown tuff gradually rises along the walls of the gorge to the surface and forms the rim along the south mar- gin of the Volcanic Tableland. In the south half of sec. 20, T. 6 S., R. 32 E., less than 50 feet of pale orange- brown tuff is present overlying more than 200 feet of pale-pink unconsolidated tuff, which rests on 20 feet of pumice of the basal member (fig. 67). - Eastward the pale orange-brown tuff thins; it is missing over part of the Volcanic Tableland east of Fish Slough. The unconsolidated pale-pink tuff is composed of the same constituents as agglutinated tuff, but is very dif- ferent in appearance because of the absence of any ag- glutination. Typically, pumice fragments as much as several inches across are embedded in an ashy matrix. The pumice fragments are rounded and are physically much weaker than in the underlying basal pumice layer, probably because they contain larger, less sym- metrical vesicles having thinner walls. The formation is generally unsorted, but mounds 5 feet high of pumice fragments as much as 8 inches in maximum dimension are present locally in the base of the tuff (fig. 654). The color of the tuff changes slightly from place to place, and in the eastern margin of the Volcanic Table- land is locally light red adjacent to a tongue of agglutinated tuff. Unconsolidated tuff is exposed in the south and east margins of the Volcanic Tableland where it rests on the basal pumice member along a very sharp and regular contact (fig. 654). At the top it grades through about 15 feet into the overlying agglutinated tuff. However, along Fish Slough it is increasingly coherent north- ward and intertongues with and grades into aggluti- nated tuff. Much of the tuff in the northern part of Fish Slough shown on the geologic map (pl. 3) as ag- glutinated tuff is physically intermediate between typi- cal agglutinated and unconsolidated tuff. Unconsolidated tuff is much more widespread than its outcrop area. Driller's logs of borings show that the principal member of the Bishop tuff continues into the alluvial fill of Owens Valley and thins progres- sively southward. Although the driller's logs make no distinction between agglutinated and unconsolidated tuff, the tuff underlying the valley is almost certainly unconsolidated. Unconsolidated tuff is exposed in a few places in the terraces south and east of the Volcanic Tableland and also in a quarry in the SE14 sec. 14, T. 6 S., R. 33 E., at the base of the White Mountains. Also the tuff beneath the valley rests directly on the basal pumice layer, and only unconsolidated tuff has been observed in this stratigraphic position. Unconsolidated tuff also was intersected at the base of the formation in at least one tunnel driven for the Los Angeles Department of Water and Power in the west wall of the Owens River Gorge north of the mapped area. Here, and in a road cut along U.S. Highway 395 just east of Rock Creek, unconsolidated tuff rests on glacial till of Blackwelder's Sherwin stage. Elsewhere along Rock Creek unconsolidated tuff rests on granitoid and metamorphic rocks. Rounding of the pumice fragments indicates abra- sion, but lack of sorting, the presence of only sparse exotic materials, widespread areal distribution, and lateral gradation to agglutinated tuff indicate the trans- porting agent was something other than normal winds or water. The distribution of the unconsolidated tuff CENOZOIC GEOLOGY %. indicates that it is a marginal facies of the agglutinated tuff, and must therefore have been deposited as mar- ginal, distal, and basal parts of nuées ardentes, which lacked sufficient heat to weld themselves. According to Gilbert (1988, p. 1853), the "ignimbrite" of the North Island of New Zealand, which is petrographically simi- lar to the Bishop tuff, grades downward to unwelded tuff at its base. Water or ice at the base of tuff would, of course, have increased the cooling rate and favored the formation of unconsolidated rather than agglutinated tuff. AGE At several places north of the Bishop quadrangle the Bishop tuff is locally interstratified with tills, and there- fore is of Pleistocene age. The tills have been inten- sively studied by Putnam (1938, 1949, 1950, 1952) who has concluded that the Bishop tuff rests on Sherwin till along Rock Creek and is overlain by Tahoe till west of the Mono Craters. A. potassium-argon age determination of 870,000 years for the Bishop tuff was published by Evernden, Curtis, and Kistler (1957) ; subsequent work by D.G. Dalrymple (oral commun. 1964) indicates that 0.7 mil- lion years is a better figure. RHYOLITE SOUTH OF BIG PINE Pumiceous rhyolite in the central part of a low rounded rhyolite hill which rises above the alluvial fan 2 miles west of the Poverty Hills was being exploited in 1958 for expansible rhyolite (perlite). The hill is a mile long in an easterly direction, has a maximum width near the middle of half a mile, and rises about 200 feet above alluvial fans from the Sierra Nevada. The geol- ogy of the hill was studied some years ago by Mayo (1944), and his report includes detailed descriptions of the rocks and structures. The hill is probably an extrusive dome having short flows. The distribution of rocks and the attitudes of flow banding suggest that the dome is shaped like an asymmetric mushroom and that the vent is approxi- mately beneath the high point in the east end of the hill. From the vent viscous rhyolite flowed in all directions, but more flowed down the alluvial slope than in other directions. In the central and north parts of the hill the flow layers generally are steep, whereas along the south and east sides they are flat or gently dipping. Buckles are present in the layers along the north side of the hill. Three kinds of rocks were distinguished : (1) dense, gray vitrophyre, (2) thinly interlayered black glassy obsidian and gray vitrophyre, and (3) light-gray pumi- ceous rhyolite (fig. 68). In most places the rocks are in sharp contact and readily distinguishable from one another. Pumiceous rhyolite occupies the central part 159 of the hill and, except at the west end where alluvial fan deposits overlap the pumiceous rhyolite, is flanked concentrically first by a discontinuous obsidian-bearing layer, then by gray vitrophyre. Locally on the north- east side of the hill, a second obsidian-bearing layer is intercalated in the gray vitrophyre. In the western - part of the hill an obsidian-bearing layer is missing between the pumiceous rhyolite and gray vitrophyre. In the east and southeast sides of the hill, where the flow layers generally are flat, gray vitrophyre appears as the lowest layer and is overlain approximately con- formably by an obsidian-bearing layer; the pumiceous rhyolite occurs at the top. It seems certain that here the gray vitrophyre was extruded first and the pumi- ceous rhyolite last. Dikes of pumiceous rhyolite that cut both the gray vitrophyre and the obsidian-bearing layers clearly indicate that it was the last extruded rock. Probably the time that elapsed between extru- sious was slight and they were all part of a single period of volcanism. At the surface the pumiceous rhyolite is highly brec- ciated, but in quarries at the two ends of the hill it is increasingly coherent at depth. The obsidian-bearing units crop out only locally, but their presence is clearly marked by dark-gray soil that contains abundant obsid- ian pellets. In most exposures, the obsidian bands have been stretched into thin discontinuous lenses, and, locally, where the rock is most strongly contorted, the obsidian is in rounded pellets that are enclosed in gray vitrophyre. At least part of the contortion in the rock may have been caused by partial remelting at the time of extrusion of the pumiceous rhyolite. The rhyolite probably is of Pleistocene age, possibly of the same general age as the Bishop tuff. The gross shape of the dome may not be very different from the original shape, but it is considerably modified in detail. Certainly it is older than adjacent basaltic cones and flows of late Pleistocene age. BASALT FLOWS AND CINDER CONES Well-preserved cinder cones and associated basalt flows are present in the fan slopes south of Big Pine in the southeast corner of the Big Pine quadrangle. They compose the northern half of a volcanic field that extends to the east and south into the Waucoba Moun- tain and Mount Pinchot quadrangles. The cones con- sist chiefly of grayish-red cinders, but contain abundant bombs and large angular blocks of basalt. The mineral content of the basalt is similar to that of the older basalt west and southwest of Bishop. Conspicuous phenocrysts of olivine together with smaller crystals of augite are contained in a groundmass of augite, plagio- clase, and magnetite, in places accompanied by glass. 160 R.33€. GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA R. 34 E. T. 10 S. EXPLANATION (2 Alluvial-fan deposits T $. 905.8 §! Light-gray pumiceous rhyolite (perlite) Gray vitophyre and black obsidian thinly interlayered Gray vitrophyre Contact Dashed where approximately located 35 Hva ¢ DM ish Spn‘flmgs Strike and dip of lest Stes flow banding + Vertical flow banding -+- Horizontal flow banding N 1000 0 1000 adele doe S60 toa | DATUM IS MEAN SEA LEVEL CONTOUR INTERVAL 40 FEET Geology by Paul C. Bateman, 1951 2000 FEET sad FiGurE 68.-Geologic map of the rhyolite hill south of Big Pine. Although the cones and flows are exceedingly fresh, they are, nevertheless, probably of late Pleistocene age. A flow in a similar state of preservation a few miles to the south in Sawmill Canyon is, according to Knopf (1918, p. 77-78), overlain by a lateral moraine of his later glacial epoch, which is equivalent to Blackwelder's (1931) Tioga stage. Red Mountain and Crater Mountain are the two main volcanic centers within the mapped area. Red Moun- tain is a very nearly symmetrical cinder cone that rises 700 feet above the alluvial slope on which it rests. A flow of dark lava has broken out from its eastern base and extends to beyond the eastern boundary of the mapped area. This flow is extremely rough and scoriaceous, and at the lower end exhibits row on row of arcuate pressure ridges. Crater Mountain, on the other hand, consists chiefly of lava; cinders are present only adjacent to two vents in the crest of the mountain. Crater Mountain rises at least 1,500 feet above the alluvial slope, and more than 2,000 feet above the floor of Owens Valley. Because it stands well out into the valley, it is readily visible for many miles to the north and south. It is, however, built on an upfaulted horst of granite that crops out at the south end of the mountain in Fish Springs Hill and on the north side in several smaller areas. Fish Springs Hill rises 1,400 feet and the higher patch to the north 1,200 feet above the alluvial slope. The logs of water wells along U.S. Highway 395 show that along the east edge the basalt interfingers with alluvial fill to a depth of at least 200 feet beneath the valley floor. All the volcanic feeders are localized along faults. Crater Mountain, Red Mountain, and an intervening mass of basalt lie along the same north-trending fault. A west-facing scarp in the alluvium between Red and Crater Mountains and extending into the Crater Mountain flows was formed at the time of the Owens Valley earthquake of 1872, according to Knopf (1918, p. 77). Earlier movements along the fault are indi- cated by the presence of the granite mass of Fish CENOZOIC GEOLOGY Springs Hill, which required large vertical movement for its exposure. A small cinder cone west of Fish Springs lies along a parallel fault marked by a scarp that breaks the al- luvial fan as well as the cinder cone itself. The fresh- ness of the scarp suggests that it too may have been formed at the time of the earthquake of 1872. Basaltic lava at Fish Springs on the upthrown side of a fault may be part of a flow, elsewhere buried, that broke out of the base of the cinder cone. SEDIMENTARY DEPOSITS GLACIAL DEPOSITS OF THE PLEISTOCENE EPOCKH Huge piles of unstratified glacial drift of Pleistocene age lie at the mouths of all the larger canyons in the eastern Sierra Nevada from Big Pine Creek north, and extend high into the range along some. Glaciation in the Sierra Nevada has been studied most thoroughly by Knopf (1918), Matthes (1930), Blackwelder (1931), Putnam (1949, 1950), and Birman (19542, b). Black- welder's paper is still, after more than 30 years, the standard reference to glaciation in the eastern Sierra Nevada. I did not study the glacial deposits of the Bishop district in detail. The distinctions made on the geo- logic maps (pls. 1-4) ) are those that can be made in a general geologic study without recourse to the time- consuming techniques of a glaciologist. The informa- tion gained, however, should provide a basis for further detailed studies. Wherever possible, the deposits are separated into different age groups chiefly on a physio- graphic basis with the aid of aerial photographs, which were intensively studied under a stereoscope. The prin- cipal criteria used are the spatial relations of deposits to one another and to other Cenozoic features, the de- gree of dissection, the relative abundance of faults, the differences in displacement along individual faults, the general abundance of boulders at the surface, and the general condition of weathering of boulders. The tills, subdivided in accordance with the glacial stages of Blackwelder (1931) , are from youngest to old- est, Tioga, Tahoe, Sherwin, and McGee. According to Blackwelder, the Tioga glaciation is represented by rela- tively small fresh undissected moraines, the Tahoe glaciation by much larger more dissected moraines, the Sherwin by generally formless piles of till, and the Mc- Gee by ancient accumulations of boulders, especially at high altitudes. In this report the Tioga and Tahoe tills are mapped separately, and all older tills are included under Sherwin and older tills In addition to these main divisions, two subdivisions were recognized locally-a late subdivision of the Tioga, and an early subdivision of the Tahoe. The late Tioga till appears to represent a brief readvance of a retreating Tioga 161 glacier. The early Tahoe till, on the other hand, in- cludes morainal ridges more dissected and apparently older than the later Tahoe moraines, and may in fact represent an unnamed period of glaciation suggested by Blackwelder between his Tahoe and Sherwin glacia- tions. If detailed work indicates the existence of glacial till in this position, such till will include parts of the glacial deposits mapped here with both the Tahoe and the Sherwin and older tills. The most complete representation of glacial deposits in the mapped area is along Bishop Creek, and in the descriptions of the different tills special attention is given these deposits. This place is the most favorable within the area for making more detailed glacial studies (pls. 1, 2; fig. 69). Differences in the degree of dissec- tion and in the throws along two faults that cut across the different tills on the northwest side of Bishop Creek indicate that the glacial deposits are successively younger to the southeast. Each successive glacier was southeast of its predecessor, and all the morainal ridges on the northwest side of Bishop Creek are lateral mo- raines that were deposited along the northwest sides of these glaciers. The glacial deposits along Big Pine Creek (pl. 4) are as extensive as those along Bishop Creek, and the deposits there also are successively younger toward the south. However, relations along Big Pine Creek are less clear than those along Bishop Creek because the older tills there have been cut by many normal faults, and the uplifted segments are deeply eroded. SHERWIN AND OLDER TILLS Sherwin and older tills include all the deeply eroded glacial deposits of pre-Tahoe age. Several glaciations may be represented. Surfaces of such tills generally are hummocky, and only the largest of original glacial features can be dubiously identified. Boulders are gen- erally less abundant at the surface than on younger moraines, and many are deeply weathered and cavern- ous. In road cuts and other exposures of lower levels of the tills in place, the granitic boulders commonly are so deeply weathered that they can be sliced through easily with a shovel. Much of the extensive till on Coyote Flat and adja- cent areas shown on the maps (pls. 1-4) as undiffer- entiated is probably Sherwin. U-shaped valley forms indicate that ancient glaciers existed in the upper reaches of Coyote and Rawson Creeks and along upper Onion Creek. Early glaciers probably also mantled the east side of Coyote Ridge, where Tioga and prob- ably Tahoe glaciers existed later, and may have ex- tended into Coyote Flat. Small patches of older till or drift are present on the southeast side of Bishop FicurE 69.-Aerial view of the Sierra Nevada crest west of Bishop. Lateral moraines along Bishop Creek are in center and right foreground. The light-colored rock in the escarpment in the right central part of the photograph is porphyritic quartz monzonite similar to the Cathedral Peake granite. To the left and lower than the picture center is a probable landslide that resembles a stabilized rock glacier. Lake Sabrina is near the left edge of the photograph; in the right middle distance is Desolation Lake. Photo by Symons Flying Service. C91 VINYOAITYD 'LOIXLSIG NMLSDPNAL (2907049 CENOZOIC GEOLOGY Creek at higher altitudes than the crests of nearby Tioga and Tahoe lateral moraines. Two patches near Andrews (Shreves) Camp, one about a mile north and the other about a mile and a half east, are probably erosional remnants of a lateral moraine deposited by an early glacier along Bishop Creek. Three patches along Coyote Creek at altitudes of 6,600 to 8,000 feet, however, had their source in a glacier that headed in the Coyote Flat area. These patches rest on remnants of basalt flows. The antiquity of the till is indicated by the depth of Coyote Creek canyon, locally as much as 800 feet below the base of the till. This cutting must have taken place largely before the deposition of the Tahoe and Tioga moraines along Bishop Creek, else extensive destruction of the lower parts of the moraines below the junction of Coyote Creek with Bishop Creek would have occurred. On the northwest side of the Bishop Creek mo- raine, several small disconnected mounds of bouldery gravel are assigned to the Sherwin and older glaciations. Some doubt exists as to whether these mounds are till from Bishop Creek or uplifted and dis- sected outwash, possibly from the part of the Sierra Nevada escarpment west of the Buttermilk Country. In gross appearance the material in them resembles the till on Coyote Flat. The largest mound is cut longitu- dinally by a stream channel tributary to Birch Creek. Flat-topped ridges on both sides of the channel parallel Tahoe and Tioga lateral moraines, and possibly are themselves terraced morainal ridges. West of Dutch Johns Meadow these ridges are cut by a northwest- ward-trending normal fault that is downthrown to the southwest. The escarpment along the fault is more than 200 feet high in the northwest ridge, but only 80 feet high in the southeast ridge. - This difference results from unequal planation of the downthrown side of the fault by ancestral Birch Creek, and does not reflect dif- ferent amounts of throw in the two ridges. - However, progressively diminishing heights of escarpment to- ward the southeast in progressively younger lateral moraines is attributed to lesser total throw during the smaller time intervals presumed to be represented. The Sherwin or older till in the north side of the Big Pine moraine and in the north side of the moraine along the Birch Creek in the Big Pine quadrangle is weath- ered and dissected as much as the old till on Coyote Flat and in the north side of the Bishop Creek moraine. However, the till along Big Pine Creek is cut by a group of parallel north-trending faults, which may have accelerated erosion and produced a high degree of dis- section in a brief period. A lateral moraine in Bishop Creek assigned to an older subdivision of the Tahoe was not recognized along Big Pine Creek and may be 163 included with the dissected till. Tills along McGee Creek, in the Mount Tom quadrangle, and along Tine- maha Creek, in the Big Pine quadrangle, mapped as Sherwin and older tills may also be correlative with the older subdivision of the Tahoe. This possibility is sug- gested by probable morainal ridges in these tills, by the abnormally small mass of debris assigned to the Tahoe, and by the apparent absence of the older Tahoe deposits. Undoubtedly the Sherwin and older till formerly was much more widespread and has either been re- moved by erosion or concealed by younger deposits. Too, some older till may be included with Tahoe de- posits on the geologic maps (pls. 1-4). TAHOE TILL According to Blackwelder (1931, p. 884), "The most conspicuous moraines in the Sierra Nevada are those of Tahoe age. They are well developed and easily studied in the Big Pine, Bishop, and Pine Creek dis- tricts of Owens Valley, and in nearly every important canyon northward to Truckee and beyond. In general, moraines of this age have been recognized in all the valleys that also contained glaciers of the Tioga age and also in some that did not." In the Bishop district, in addition to the moraines mentioned by Blackwelder along Pine, Bishop, and Big Pine Creeks, Tahoe mo- raines were mapped in the morainal piles of most other canyons along the Sierra Nevada front. The original glacial form of Tahoe moraines gener- ally is easily recognized, but the crests of glacial ridges have been rounded by erosion and finer textured de- tails are obscured. Boulders in the till are fresher and more abundant at the surface than in older tills, but not as fresh and abundant as in Tioga till. Tahoe till is especially well represented along the northwest side of Bishop Creek where it lies between Sherwin and older till on the northwest and Tioga till on the southeast. _ f T'wo parallel morainal ridges of. considerably dif- ferent aspect are included within thegahoe till mapped along Bishop Creek; a younger, higher, sharp-crested one to the southeast, and an older, lower, round-crested one to the northwest. Both ridges are believed to be lateral moraines. In the vicinity of Dutch Johns Meadow, the crest of the younger moraine stands 150 to 200 feet above both the Tioga moraine to the south- east and the older Tahoe moraine to the northwest. This younger moraine nearly parallels the Tioga lateral on the northwest side of Bishop Creek in most places, assigned to an older subdivision of the Tahog, although but is cut into by the Tioga moraine in sees. 34 and 35,, . T. 7 S., R. 31 E. The older lateral moraine is here _ 164 it might represent an independent glaciation. A sub- stantial difference in the ages of the two lateral moraines is suggested by degree of erosion and by greater heights of fault escarpments in the older lateral moraine in the vicinity of Dutch Johns Meadow. A fault southwest of Dutch Johns Meadow has a 60-foot escarpment in the older lateral moraine and displaces minor ridges on the northwest side of the younger one, but does not cut the crest. Presumably the crest is younger than the last displacement along the fault. Northeast of Dutch Johns Meadows, a fault displaces both morainal ridges, but the scarp in the older ridge is greater and suggests that more increments of movement are repre- sented in the older ridge than in the younger. Neither fault displaces the Tioga moraine. The Tahoe terminal moraine is exceptionally well pre- served in Bishop Creek canyon over an area of more than 2 square miles. Southeast of Sand Canyon, glacial ridges and depressions that probably were caused by lobes of ice are present. The excellent preservation of these features suggests that they are of the same age as the younger Tahoe lateral moraine, but some of the debris in the terminal moraine may be correlative with the older lateral moraine. Along Big Pine Creek, Tahoe lateral moraines are present on both sides of the canyon below the Tioga terminal moraine at Sage Flat. Above this point, the Tahoe moraine is present only on the north side of the canyon westward to the fault in the east half of sec. 30, T. 9 S., R. 33 E. West of the fault the moraines are deeply dissected and were not mapped separately. The main Tahoe moraine is probably equivalent to the younger Tahoe moraine along Bishop Creek because of similar dissection. Northwest of Sage Flat two morainal ridges, south of the main Tahoe moraine and between it and the Tioga moraine, are younger than the main moraine and may represent a late subdivision of the Tahoe that was not recognized along Bishop Creek. The older Tahoe till of Bishop Creek was not recognized along Big Pine Creek and may have been mapped with the Sherwin and older tills. The older subdivision of Tahoe till was recognized elsewhere only along Pine Creek and Taboose Creek where short well-preserved lateral spurs are truncated and overlapped by more extensive younger Tahoe lateral moraines. Undoubtedly, this till is also present in other piles of glacial debris where it may be included in un- differentiated Tahoe till or in Sherwin and older till. Moraines assigned to the Tahoe glaciation are pres- ent along both sides of Rock Creek canyon. The high- est and most distinct lateral moraine on the east side, which is considered correlative with the younger lateral moraine of Bishop Creek, extends from the northern GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA margin of the Mount Tom quadrangle south about 3 miles, then southeast toward Round Valley Peak to the base of Wheeler Crest. On the west side of Rock Creek canyon all the glacial debris on the broad flat in the northeast corner of the Mount Tom quadrangle is shown on the map (pl. 2) as Tahoe till. This flat is flanked on both east and west by morainal ridges that are probably correlative with the younger Tahoe laterals of Bishop Creek. The central part of the flat is covered with angular fragments belonging to a deposit of unknown age. TIOGA TILL Moraines assigned to the Tioga glaciation are much fewer and smaller than the moraines of the Tahoe gla- ciation, but are better preserved. Most Tioga moraines are "nested" in Tahoe moraines, but Tioga glaciers did not occupy all canyons that held Tahoe glaciers; some smaller canyons that underwent glaciation in Tahoe time escaped glaciation during Tioga time. Tioga lat- eral moraines are sharp crested, and the details of ter- minal and recessional ridges are clearly visible. Knob and-kettle topography, common at altitudes of 10,000 feet or more between lateral moraines, appears as fresh as if formed very recently. In most canyons only one period of Tioga glaciation was recognized, but along Bishop Creek a late subdivi- sion is represented. The Tioga end moraine of the Bishop Creek glacier is largely in sec. 25, T. 7 S., R. 31 E. It consists of two lobes, one north of Bishop Creek in the old Tahoe valley, and the other along the stream-cut canyon of Bishop Creek. An outcrop of quartz monzonite at the juncture of the lobes may have contributed to the split of the glacier. Upcanyon, nu- merous recessional moraines cross the canyon floor, and are cut through only by a narrow slot about 20 feet deep that contains Bishop Creek. A single lateral mo- raine flanks the canyon on the southeast side as far up- canyon as Egypt Creek, and its mate flanks the canyon on the northwest side to the south boundary of the Mount Tom quadrangle. The late subdivision along Bishop Creek is repre- sented only in the Middle Fork of Bishop Creek above the junction of the Middle and South Forks. One lat- eral moraine of the subdivision extends along the north- west side of the Middle Fork from the junction of the forks to a ridge of bedrock northeast of North Lake. The other on the opposite side of the canyon lies across the mouth of the canyon of the South Fork. These lat- eral moraines descend rapidly and are at the level of the canyon bottom at their lower ends. The features of the younger subdivision are not discernibly sharper than those of the older Tioga glaciation. Nevertheless, the configuration of the moraines indicates that the CENOZOIC GEOLOGY Tioga glacier withdrew and then readvanced, and that the moraines are not simply parts of a recessional mo- raine. Till between the North and Middle Forks of Bishop Creek, in the vicinity of George Lake and below Green Lake, probably also belongs to the younger sub- division. In Big Pine Creek the Tioga moraines terminate in and below Sage Flat. Two steeply descending laterals on the north side of the canyon curve at their lower ends across the canyon and may be recessional moraines, or one or the other may be correlative with the younger Tioga subdivision along Bishop Creek. Extensive Tioga moraines are present along upper Baker Creek and along the east side of Coyote Ridge. The glacial deposits along Coyote Ridge are unusual in that they extend in a broad loop into Coyote Flat. Much of the loop consists of knob-and-kettle topogra- phy. In Pine Creek the precise boundary between the Tahoe and the Tioga tills is not clear. On the geologic map (pl. 2) the boundary is shown to be well toward the lower end of the morainal pile, but the proper divi- sion may be at a morainal loop present where the can- yon leaves bedrock. Extensive Tioga glacial deposits are present in Rock Creek, but the relations there are obscure. The princi- pal lateral moraine on the east side of the canyon is plastered on the side of the Tahoe lateral moraine. Its crest generally lies a hundred feet or so below the crest of the Tahoe moraine, but extensive slumping causes it to be very irregular. On the north side, several lat- eral moraines are present, most of which probably bend into recessional moraines. Smaller Tioga moraines are present in the morainal piles of Horton, Birch (Mount Tom quadrangle), McGee, Birch (Big Pine quadrangle), and Tinemaha Creeks. All these piles consist of a series of looped end moraines that lie within older till just outside the mouths of bedrock canyons. OLDER DISSECTED ALLUVIAL FAN AND LAKEBED DEPOSITS The White Mountains in the mapped area and the Sierra Nevada locally between Bishop Creek and the Birch Creek in the Big Pine quadrangle are flanked by alluvial deposits, some of which have dissected surfaces whereas others have depositional upper surfaces (Knopf, 1918, p. 54-57). Remnants of alluvial fans also are present in the eastern part of the Volcanic Tableland. Some of the dissected deposits have rem- nants of their original upper surfaces, which slope parallel with adjacent, more recent alluvial fans but which stand at higher altitudes. Such untilted de- posits are present along the westward trending segment 165 of the Sierra Nevada escarpment southwest of Bishop and along the White Mountains south of Poleta Can- yon, where they extend upward to altitudes of more than 6,000 feet within the mapped area and to higher altitudes farther to the east (fig. 2). Other dissected deposits in fault blocks that have been rotated toward Owens Valley are exposed along the Sierra Nevada front south of Rawson Canyon, along the White Moun- tains north of Poleta Canyon, and, locally, in a narrow belt adjacent to the alluvial fill of Owens Valley, south of Poleta Canyon. The basis of distinction between the dissected series and undissected fan deposits-whether the surface in the aggregate is erosional or depositional-precludes many of the common stratigraphic relations between formations. The dissected series cannot be defined in terms of top and bottom, or assigned an age span that is distinct from that of the undissected fan deposits. The upper beds of some dissected blocks conceivably may be as young as the upper beds of undissected fans. The dissection of the deposits is the result of struc- tural movements related to progressive depression of Owens Valley relative to the bordering ranges. Two periods of faulting can be clearly identified in the White Mountains, and the probable structural history requires a great many periods, the evidence of which has been concealed or obliterated. Because the dissec- tion results from movements of different magnitudes which occurred at different times, distinction between the dissected and undissected fan deposits is difficult in some places, although clear enough in most. A typi- cal difficult place is along the Birch Creek drainage in the Big Pine quadrangle, south and southwest of Crater Mountain, where fans have been faulted so recently that erosion is confined to the scarps. DISSECTED FANGLOMERATE AND LAKEBED DEPOSITS ALONG THE BASE OF THE WHITE MOUNTAINS In the White Mountains the thickest unbroken ex- posed sections of dissected material are in Black and in Redding Canyons, where about 600 feet of coarse, crudely bedded fanglomerate is exposed. Virtually all of the material in the fanglomerate in these canyons was derived from older rocks that crop out higher in the same drainage basins. Much of the fanglomerate, except in the upper part, is cemented with carbonate, which produces a tough cohesive rock that stands in ver- tical or near vertical cliffs where it has been cut by streams. White pumice that is considered to belong to the lower basal unit of the Bishop tuff locally is in- tercalated in the fanglomerate. One of the more ex- tensive and better exposed outcrops of pumice, in the south wall of Black Canyon, is at an altitude of 5,200 166 feet, about 150 beneath remnants of the original upper surface of the fan. The material exposed in these larger canyons, how- ever, is not typical of the entire formation. Much of the material that crops out lower in the alluvial slope, and between the larger canyons, contains finer grained deposits, including granitic sand and pebble beds whose source could not be found in adjacent parts of the White Mountains. Locally, thin layers of fresh-water lime- stone and calcareous shale that contain abundant rem- nants of the thin-shelled gastropod HZydrobic sp. are present. According to Dwight W. Taylor (written communication, 1956), this gastropod lives in quiet water-in lakes, ponds, or in a backwater along a stream. Such finer grained material is well exposed between Redding and Black Canyons and in dissected slopes north and south of the mouth of Silver Canyon. In the north wall of Poleta Canyon, in the northwest cor- ner of see. 18, T. 7 S., R. 34 E., limestone and gastropod- bearing marly shale and finer grained pumiceous sandy layers, are interstratified with coarse-grained layers identical with the fanglomerate of Black and Redding Canyons. The detailed stratigraphy of the dissected alluvial deposits along the base of the White Mountains was not determined; in particular, neither the lateral nor the vertical extent of finer grained sediments that appear to be at least in part lacustrine nor their rela- tion to coarse fanglomerate was established by direct observation. The overall distribution of materials sug- gests that the finer grained sediments grade laterally into the coarser-at the mouths of powerful streams that flowed in the main canyons, fanglomerate was deposited simultaneously with finer grained materials in interfluves and peripheral to the fans. One interpretation of these relations is that the finer grained sediments were deposited in a single very exten- sive lake in Owens Valley. Fans would have flanked this lake, and their lower ends would have extended into the lake, where deposition would, in fact, have been deltaic. Intertonguing of very coarse material with lacustrine sediments could result from periodic torrential storms which caused coarse fanglomerate to be carried by rain-swollen streams into the lake, or from fluctuations in the lake level. If such a lake existed, it probably extended at least as far north as Benton, 30 miles north of Bishop where the northern- most exposures of the basal pumice layer of the Bishop tuff are found, and as far south as Zurich where exten- sive lakebeds lie in an embayment in the White Moun- tain front (Walcott, 1897). According to L. C. Pakiser and M. F. Kane (oral communication, 1958), gravity studies indicate very shallow bedrock in the floor of GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA Owens Valley just south of the Poverty Hills, which could mark the southern limit of the lake. A second possible interpretation of the relations is that no single large lake existed. All the demonstra- ble lacustrine deposits could have been deposited in small ephemeral ponds such as are present in low-lying places on the floor of Owens Valley today. Ponds may even have been formed high on the fans behind fault scarps that faced upslope. Such searps are abundant today, and although none dams a pond or lake, many bound marshy areas. DISSECTED FANGLOMERATE ALONG THE BASE OF THE SIERRA NEVADA The dissected deposits along the Sierra Nevada front are less deeply incised, and consequently are less well exposed, than those along the base of the White Moun- tains. The material exposed is coarse fanglomerate, similar to material in undissected fans, and consists of well-rounded granitic pebbles, cobbles, and boulders set in a sandy and clayey matrix. The material prob- ably represents outwash from glaciers that existed higher in the range during the Pleistocene epoch. ALLUVIAL REMNANTS IN WEST PART OF VOLCANIC TABLELAND Scattered remnants of fanglomerate are present along the west side of the Volcanic Tableland in the north- central part of the Mount Tom quadrangle. The remnants are thin and probably are nowhere more than 50 feet thick. Formerly, fans extended from the north into this area, but structural depression of Round Val- ley has caused dissection of these older fans and the building of new ones west of the Volcanic Tableland. AGE The strata in the dissected series are almost certainly of Pleistocene age. The preservation of original fea- tures in the youngest Pleistocene glacial deposits, includ- ing easily eroded recessional ridges in canyon bottoms, indicates that little erosion of the ranges, and con- sequently little deposition, has taken place since the end of the Pleistocene epoch. It seems probable that not only are the dissected alluvial deposits older than Re- cent, but that a large part of the undissected alluvial fans must also be older than Recent. The presence of the basal pumice member of the Pleistocene Bishop tuff among the strata of the dissected series along the base of the White Mountains indicates a middle Pleistocene age for the adjacent beds. The stratigraphically high position of this pumice layer in the section exposed in Black Canyon, only 150 feet beneath the original sur- face in an exposed section of 600 feet, suggests that the lower beds may be early Pleistocene or even late Ter- tiary in age. 3 - CENOZOIC GEOLOGY LANDSLIDE Landslide material on the south side of Bishop Creek at the lower end of the younger substage of the Tioga moraine includes both quartz monzonite and glacial till. The landslide probably resulted from oversteepening caused by glaciation and may have occurred during the Pleistocene. TERRACE GRAVELS Thin veneers of river gravels cap elevated terraces along the south and east sides of the Volcanic Tableland. The gravels consist of well-rounded particles that range - from sand to cobbles 6 inches or more in diameter. The gravels are in crudely stratified, poorly sorted layers. The material in the south-side terraces is chiefly granitic and obviously had its source in the Sierra Nevada. The material in the east-side terraces, on the other hand, is largely metamorphic, similar to rock exposed in the north end of the White Mountains. Three terrace levels are distinguishable in the south-side terraces, but only two in the east-side terraces. The highest and oldest terraces are most distant from the modern stream chan- nels, and the terraces closer to these channels are pro- gressively lower and younger. The terraces on the south side of the Volcanic Table- land were cut by the Owens River and a tributary from the west that joined the Owens River where it leaves the Volcanic Tableland. Gravels cover the terrace levels almost continuously to depths of several feet, and have slumped over the edges of the terraces. Outcrops of the underlying rock are mostly in the terrace edges or in road cuts, although a mound of olivine basalt projects through the middle terrace in the N%% sec. 32, T. 6 S., R. 32 E. Most of the outcrops are of Bishop tuff. The terrace gravels on the east side of the Volcanic Tableland are much less continuous than those on the south side, and are in long north-trending strips that are separated from one another by gullies in which Bishop tuff is exposed. The east-side terraces were cut by an ancient tributary to the Owens River from the north, which at one time carried a large volume of water, but which at present is dry except immediately after storms. The metamorphic material in the gravels indicates that some tributaries to this stream headed in the western flank of the White Mountains. Some water also may have come from Mono Lake during periods of overflow in the Pleistocene epoch. The middle terrace on the south side of the Volcanic Tableland and the upper terrace on the east side are con- sidered correlative because they are more extensive than any other terraces and because the 4,400-foot contour crosses both terraces at about equal distances from the probable point of confluence of the streams that cut the terraces.. Such correlation, nevertheless, is hazardous "487 because the south-side terraces have been slightly de- formed by faults and warps; the east-side terraces may also have been deformed. The fact that gravels in the terraces are much coarser than the gravels in the bed of the Owens River indicates that the terrace gravels were deposited by faster flow- ing and presumably larger rivers capable of carrying larger particles. More water was, of course, available during certain parts of the Pleistocene epoch, and quite likely the terraces were cut and the gravels deposited in late Pleistocene time. Nevertheless, the lowest terrace at least may have been cut more recently, during a pluvial period in which many ancient lakes in the Great Basin were filled. UNDISSECTED ALLUVIAL FAN DEPOSITS Alluvial fans having constructional forms and no greater dissection of their surfaces than is usual in the ordinary processes of fan formation border Owens and Round Valleys and extend into canyons of the White Mountains and the Sierra Nevada. Much smaller fans have been deposited in broad glaciated canyons in the Sierra Nevada by streams flowing in from the sides. The material in the fans along Owens Valley has been derived both from bedrock formations and from older raised and dissected alluvial deposits. The proportion of material derived from each source varies from fan to fan ; presumably larger proportions of White Moun- tain fans than Sierran fans have been derived from older alluvial deposits. Individual fans have distinct forms even though they merge to form piedmont al- luvial slopes, and each fan has its own distinct dis- tributary stream pattern. . The crests of the larger fans slope toward the valleys at an average rate of about 300 feet per mile, but the upper part slopes more steeply and the lower more gently. The upper boundaries of the fans with bedrock or with older sedimentary or volcanic deposits commonly are easily distinguished, but because all the fans are progressively finer grained and better sorted downslope and many grade imperceptibly into fine-grained alluvial fill that constitutes the valley bottoms, some difficulties arise in mapping the lower boundaries. Among the fans having gradational lower boundaries are those of Bishop Creek, Big Pine Creek, and all the fans that flank Round Valley. A distinct train of material from Bishop Creek can be traced on aerial photographs into Owens Valley as far south as Big Pine. Both Bishop and Big Pine Creeks appear to have contributed larger volumes of material to Owens Valley recently than the Owens River, although the Owens River may have supplied a larger proportion of material earlier. On the map the boundary between these fans and valley fill 168 is a line that approximately separates fine well-sorted sandy, silty, and clayey alluvial fill in the valleys from pebbly and conglomeratic material in the fans. In Round Valley this line approximates the boundary be- tween cultivated and barren cobble-covered fan slopes. The fans along the White Mountain front and along the Sierra Nevada front between Bishop and Big Pine Creeks have been overlapped by alluvial fill carried into the valley by the larger, more powerful streams, and this overlapping provides a basis for the separation of the fans from alluvial fill. The general slope of the valley floor is southward, whereas the fans slope radi- ally from the points where the parent streams emerge from their canyons. Thus the contours bend sharply where the fans meet the valley floor, and the boundary contact can be drawn through these bends. The bulk of the material in fans must have been de- posited during Pleistocene time when the rates of erosion and deposition were accelerated because of heavier precipitation, although some smaller fans in glacial canyons are Recent. The fans of Pine, Bishop and Big Pine Creeks almost certainly were formed by out wash from glaciers higher up, and other fans along the Sierra front may have been built partly from gla- cial debris washed down from higher altitudes. Locally the upper surfaces of fans have been veneered by material deposited by floods in Recent time. Blackwelder (1928, p. 471) reports bouldery mudflows in the alluvial fans along the east side of the Sierra Nevada south of the Bishop district. In 1946, a cloud- burst in the Gable Creek drainage caused a fan to be built in Pine Creek canyon at the mouth of Gable Creek within a few hours time. Buildings near the head of the fan belonging to the Tungstar Corporation were destroyed, and houses lower down on the fan occupied by employees of the Union Carbide Nuclear Co. were partly buried. ALLUVIAL FILL Alluvial fill includes the detrital material in the lower central parts of Owens and Round Valleys and in Fish Slough. In general, alluvial fill is finer grained and better sorted than fan material or terrace gravel, but nevertheless exhibits considerable range in the de- grees of sorting and in the average size of particles. The fill was deposited chiefly on flood plains by streams and in shallow ephemeral ponds and lakes such as War- ren and Klondike lakes north of Big Pine and the small ponds along Fish Slough. At the surface the alluvial fill probably is chiefly Recent in age, although detritus of Pleistocene age must be present at shallow depths, and may be exposed locally at the surface. The Bishop tuff has been in- tersected in borings into Owens Valley as far south as GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA Bigelow station, and the adjacent beds are certainly of Pleistocene age. DUNE SAND Sand dunes that have been stabilized and are over- grown with vegetation are present 414 miles west of Bishop where U.S. Highway 395 crosses the highest terrace. Accumulations of sand also are present in the WL sec. 21, T. 7 S., R. 32 E., where the sand is in pockets on the northeast side of a rounded spur of the Sierra Nevada. Most of the dunes are formless, but several are crescentic. The fact that the convex sides of the crescentic dunes face northeastward indicates that the prevailing wind was from that direction at the time of deposition. The dunes probably are of the same age as the highest terrace. TALUS AND ROCK GLACIERS Talus is present in both the Sierra Nevada and White Mountains, but is especially abundant along the lower slopes of the Sierra Nevada escarpment and in glacial cirques at higher altitudes in the Sierra Nevada where frost action is effective in fragmenting the well-jointed granitic rocks. In the White Mountains, talus gener- ally occurs in areas too small to be mapped, whereas in higher glaciated parts of the Sierra Nevada individual areas of talus exceed a square mile, and extensive tracts are more than 25 percent covered with talus. The size and shape of the fragments in the talus depends largely on the nature of the source rock. Talus from the Andrews Mountain standstone member of the Campito formation generally is in relatively large angu- lar fragments, whereas talus from Montenegro shale is slabby and breaks down rapidly to clay. In granitic rocks, the size of the fragments is largely a function of the spacing of joints, which in a measure is correla- tive with grain size-finer grained granitic rocks gen- erally yield smaller fragments than coarser grained ones. Granitic fragments several feet on a side are com- mon near the bottoms of some talus slopes. Older talus in the White Mountains commonly is cemented by carbonate derived from limestone and dolomite in the bedrock, but no cemented talus was observed in the Sierra Nevada. Most talus cones differ from small alluvial fans by their steeper slopes and by the fact that material is coarser downslope rather than upslope as in a fan. In a few places, however, distinction on this basis is diffi- cult or impossible because partial reworking by seasonal flow of water down talus-filled channels results in a hybrid deposit. At higher altitudes in the Sierra Nevada, talus in glacial cirques in many places grades downslope into rock glaciers and allied forms transitional from talus CENOZOIC GEOLOGY to rock glaciers. The rock glaciers appear to be formed from and fed by the talus. At several places along the Sierra Nevada crest and along the Glacier Divide, rock glaciers lie below active ice glaciers rather than below talus slopes. Possibly the debris required for the rock glacier is derived from the glacier, but it is also possible that the rock glaciers formed earlier than the glaciers and are now being pushed ahead of them. Most rock glaciers are at the base of north and north- east slopes, above altitudes of 10,400 feet, but a few are lower. Fully formed rock glaciers are tongue-shaped or spatulate and have steep fronts and sides on which the talus fragments lie at the maximum angle of repose (fig. 40). The upper surfaces slope gently toward the rock glacier fronts and, especially near their fronts, are marked by arcuate ridges that are convex down- slope. Longitudinal ridges and furrows may extend almost the full length of the rock glaciers. The longi- tudinal profiles of active rock glaciers are convex upward, whereas the the profiles of inactive ones are concave upward. Melting of interstitial ice is accom- panied ky partial collapse and change of the surface configuration (Wahrhaftig and Cox, 1959, p. 427). On the geologic maps (pls. 1, 2, and 4) rock glaciers and related forms are shown by semidiagrammatic rep- resentation of the principal arcuate and longitudinal FiGuURE 70.-Rock glacier between Second and Third Lakes, North Fork of Big Pine Creek. 135-925 0-65--12 169 ridge crests. The largest rock glaciers are a mile or more long and more than a quarter of a mile wide, but most are considerably smaller. Related forms range from isolated, generally arcuate ridges that cross talus slopes approximately horizontally to complexes of ridges and furrows called by Wahrhaftig and Cox (1959) rock-glacier aprons (fig. 71). In some cirques several rock glaciers and allied forms are present, fed by different talus slopes, and in the cirque at the head of the south fork of Red Mountain Creek rock glaciers from high in the cirque override some that originate lower in the cirque. Convex-upward longitudinal profiles, absence of veg- etation on fronts, and delicate balance of many large fragments on ridge crests indicate that many of the rock glaciers above about 11,000 feet are moving. Inactive rock glaciers are shown by growth of vegetation on their Ficur® 71.-Vertical view of rock-glacier apron southeast of Rock Creek Lake. 170 GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA fronts and by the presence of broad, concave depressions in their upper surfaces. These inactive rock glaciers must date from older, colder periods. Just above North Lake the road into the North Fork of Bishop Creek passes along the base of the front of a physiographic form that has all of the characteristic features of inactive rock glaciers but which is probably a landslide (fig. 72). The altitude of only 9,400 feet and the fact that the form is at the base of a south slope are the principal lines of evidence that it is not an inactive rock glacier. Wahrhaftig and Cox (1959) conclude that the rock glaciers of the Alaskan Range are mixtures of debris and ice to within a few feet of the surface, and that they move as a result of the flow of the interstitial ice. Steep cliffs, a near-glacial climate cold enough for the ground to be perennially frozen, and bedrock that breaks by frost action into coarse block debris having large inter- connected voids are listed by Wahrhaftig and Cox as favorable to the formation of rock glaciers. These con- cepts of the composition and movement of rock glaciers and of the factors necessary for their formation are compatible with the limited observations made of Sier- ran rock glaciers. The Sierran rock glaciers are con- fined to steep-walled cirques where a near-glacial cli- mate and frozen ground prevail. The granitic rocks are readily broken along joint planes by frost action and supply abundant talus. Some straight ridges in the lower parts of talus slopes conceivably may have been formed as protalus ramparts by the sliding of talus over snow banks, but the arcuate form of most ridges is more easily explained as the result of flow in interstitial ice. CENOZOIC STRUCTURE AND EVOLUTION OF THE LANDSCAPE Landscapes represent the resolution of two opposing groups of processes. On the one hand are the leveling processes of erosion and deposition, which work toward the reduction of the land to a featureless plain; on the other hand are the processes that interrupt the leveling processes and increase the relief. In the Bishop area, situated in an active orogenic region, most of the larger features of the landscape, and many of the smaller ones, owe their existence to struc- tural movements or to vulcanism. Of these two, struc- tural movements have been far the more important. The Sierra Nevada, the White Mountains, and the broadest features of Owens and Round Valleys are the products of faulting and warping; the Volcanic Table- land, Crater Mountain, and Red Mountain are the prod- FicurE 72.-View of probable landslide in the North Fork of Bishop Creek above North Lake which resembles an inactive rock glacier. / t CENOZOIC GEOLOGY ucts of vulcanism. None of these features exists be- cause it is made of rock that is especially resistant to erosion. Nevertheless, erosion has been effective in modifying almost all slopes, steepening some and flattening others, and in carving out canyons, cirques, and peaks, all nota- ble features of the landscape. Sedimentation, likewise, has been effective, and has formed the floors of Owens and Round Valleys, the huge alluvial fans that flank these valleys, and moraines and talus cones. CENOZOIC STRUCTURAL HISTORY OF THE SIERRA NEVADA AND ADJACENT REGIONS During and after the emplacement of the Sierra Nevada batholith, thick sections of rocks were stripped away, and by the beginning of Cenozoic time the bath- olith was exposed and a broad region that extended many miles to the east and to the west was degraded. Probably beginning in Late Cretaceous or Eocene time .and continuing into middle Tertiary time, the area of the present Sierra Nevada began to tilt westward. By middle Pliocene time these structural movements and concomitant erosion had produced a broad low topo- graphic arch whose crest lay somewhat east of the pres- ent Sierra Nevada divide in about the position of Owens Valley. In late Pliocene time, stronger deformation began, which caused further arching accompanied by block faulting. During this time, east-central Cali- fornia and adjacent parts of Nevada were broken up into a series of warped and tilted, fault-bounded blocks, the largest of which is the Sierra Nevada. Structural movements have continued to the present, but were greatly accelerated in middle Pleistocene time, when movements of exceptional magnitude took place. The most complete record of the progressive west- ward tilting of the Sierra Nevada block during Cenozoic time probably is that found in the geosynelinal sequence of the Central Valley of California. The record there has been interpreted by Hoots, Bear, and Kleinpell (1954). They state (p. 116): "The comparatively gentle eastern flank is in reality the down-dip western part of the Sierra Nevada block; its broad structural character has resulted principally from westerly tilt of this fault block throughout much of Cenozoic time." Sections drawn by them (Hoots, Bear, and Kleinpell, 1954, pl. 6) show considerable westward thickening of the strata above the base of the Miocene but only slight thickening of the strata between the base of the Eocene and the base of the Miocene. These relations suggest that tilting was slow during the Eocene and Oligocene, and greatly accelerated after the beginning of the Miocene. - Unconformities in the stratigraphic section mark the following events: middle Eocene up- 171 lift, post-"Oligocene" uplift, middle early Miocene uplift, post-early Miocene uplift, orogeny near the end of Miocene time, and middle Pleistocene orogeny (p. 127-128). Regarding the middle Pleistocene orogeny, they state (p. 128) : "At the close of Tulare deposition, in mid-Pleistocene time, there occurred a pronounced orogeny, the magnitude and intensity of which exceeded that of any disturbance since the Nevadan revolution of the Late Jurassic. It was this orogeny that ex- pelled remaining small seas from several parts of Cali- fornia and produced through folding, faulting, and sub- sequent erosion, most of the present structure and topography." Matthes (1980, 1947), Hudson (1955), and Axelrod (1957) have all outlined the Cenozoic history of the Sierra Nevada from different kinds of data found with- in the Sierra Nevada itself. Their interpretations of the structural history agree quite well on the whole; principal disagreements concern the magnitudes rather than the times of structural movements. Matthes (1930, p. 27-30 ; 1947, p. 179-180) concluded from the physiographic record in the Yosemite region and along the eastern escarpment that up warping of the Sierra Nevada and adjacent areas to the east began in the Eocene, and that strong movements in the Miocene raised the Sierra Nevada crest near Tioga Pass to about 7,000 feet. He thought that in late Pliocene or early Pleistocene time further arching raised the range to about its present height. After the McGee glaciation, the area east of the Sierra Nevada, including Owens Valley, was faulted down. Matthes considered faulting later in the Pleistocene and Recent along the east side of the Sierra to represent minor adjustments, and con- cluded that the Sierra Nevada and its neighboring blocks are in fairly stable adjustment. Hudson (1955) concluded from studies of the Yuba River drainage that the altitude of Donner Pass in Miocene time was about 5,500 feet and that the Pliocene - and Pleistocene uplift was only about 2,000 feet. He thought that the northern Sierra Nevada was not tilted as a rigid block, as has been rather generally assumed, but that at least five zones of deformation were internal to the Sierra Nevada. He also concluded that the ag- gregate throw of the faults on the east side of the Sierra amounted to more than the absolute uplift of the range since middle Eocene, and that the valleys east of the Sierra Nevada in the vicinity of Reno, Nev., were down- faulted in an absolute sense. Axelrod (1957) concluded from studies of the Ter- tiary floras that the Sierra Nevada was quite low just before the inception of vulcanism in Miocene and Plio- cene time. At that time the Sierra Nevada was a broad ridge having its summit near an altitude of 3,000 feet 172 in the vicinity of Donner and Carson passes, and low- lands in central Nevada had an average altitude of 2,000 to 2,500 feet. Axelrod inferred that the major vertical displacement of the range took place during late Pliocene and early Pleistocene time, and that the uplift was partly the result of faulting and partly the result of general regional uplift. His figure 6 (p. 39) is illustrative of this concept. Axelrod's interpre- tation of the magnitude of the Pliocene and Pleistocene movement seems more compatible with the sedimentary record in the San Joaquin Valley than does Hudson's interpretation of smaller Pliocene and Pleistocene movement. Matthes' belief that the valleys adjacent to the Sierra Nevada on the east were downfaulted only after they had been uplifted with the Sierra Nevada to nearly its present height and after the McGee glaciation is not supported by the evidence of late Tertiary block fault- ing close to the Sierra Nevada escarpment elsewhere (Thompson, 1956, p. 64-65). The evidence that per- suaded Matthes of the middle Pleistocene downfaulting of Owens Valley is the presence of McGee till on flat- topped McGee Mountain several miles to the north of Owens Valley, bounded on the north by the Sierra Ne- vada escarpment and on the east and west by deep can- yons. Matthes inferred that the crest of the range must have been at approximately its present height for the McGee glaciation to have taken place and that the range front escarpment could not have existed in McGee time. The McGee till has not been identified east of the escarpment, any eastward extension is presumably buried beneath fill in Long Valley, which lies at the east base of McGee Mountain. However, Long Valley has been shown by geophysical studies (Pakiser and Kane, 1956; Pakiser, Press, and Kane, 1960) to be filled with sediments and volcanics to a depth of 12,000 or more feet. Unless all this fill has accumulated since McGee time, which seems unlikely, a fault, though possibly not much of an escarpment, must have existed in McGee time. Even if Matthes' interpretation of the signifi- cance of the McGee till is correct, extrapolation of the age of faulting there to Owens Valley is hardly war- ranted. Probably the most reasonable picture for Owens Valley is that significant faulting began in late Pliocene or early Pleistocene time, that faulting move- ments were greatly accelerated in middle Pleistocene time after the McGee and before the Sherwin glacia- tions, and that movements at a reduced rate continue to the present. A cross section (pl. 10) shows the structural relations of the Sierra Nevada to the San Joaquin Valley on the west and to the desert ranges on the east. The east part of the section is through the Darwin and Panamint GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA Butte quadrangles mapped in detail by Wayne E. Hall, and the section was drawn with his help. The cross section is very similar to one drawn by Hopper (1947), with which it is in good agreement. The major structure shown is a great faulted arch having the Sierra Nevada as its west limb and the desert ranges as its east limb. The southern extension of Owens Valley, and presumably Owens Valley itself, is a graben in the axis of the arch. The sedimentary his- tory in the desert basins and ranges shows that the nor- mal faults that bound the ranges formed after late Pliocene time simultaneously with arching. There is no evidence to suggest that the arch was completely formed before it was faulted, although the faulting may have been confined to the later stages of arching. In the Argus and Panamint Ranges, lower Pleistocene deposits dip generally about 10° to 15° E. parallel with an underlying erosion surface of low relief and sub- parallel with the Paleozoic strata except where the Paleozoic has been deformed by thrust faults or by intrusive rocks. Middle and upper Pleistocene deposits rest unconformably on the early deposits, and dip east less steeply. Faults that cut across Cenozoic deposits of different ages exhibit successively greater displace- ments in the older deposits, and show that faulting has been progressive (W. E. Hall, oral communication, 1959). The middle Pleistocene unconformity marks a period of intensified deformation and may coincide with the period of faulting along the Sierra Nevada escarp- ment that followed the McGee glaciation. A late Pliocene or early Pleistocene erosion surface of low relief is preserved in many places in the desert ranges beneath sedimentary deposits of early Pleisto- cene age, and it is assumed that this surface was origi- nally widespread. In the Sierra Nevada the Pliocene and Pleistocene surface has been modified and in many places entirely destroyed by erosion, but was probably only slightly above the present general upland surface. CENOZOIC STRUCTURAL FEATURES OF THE BISHOP AREA The structural features formed in late Cenozoic time, which include most of the larger and many of the smaller features of the landscape, are chiefly normal faults and broad warps and open folds related to the uplift of the Sierra Nevada and White Mountains and the correlative subsidence of Owens Valley. The Owens Valley is generally termed a graben, and this designa- tion is correct if boundary slopes that result from warp- ing as well as from faulting are included. Along both the Sierra Nevada and White Mountains escarpments various combinations of warping and faulting occur. The structural relief of the central part of the Sierra Nevada escarpment within the mapped area is princi- CENOZOIC GEOLOGY pally the product of warping, but elsewhere along Owens Valley faulting predominates Owens and Round Valleys have subsided as virtually coherent blocks, but nevertheless have suffered internal deforma- tion. This deformation consists chiefly of broad warps and related faults. Most of these late structural features were recognized by their effect on the topography, and only rarely were internal layers of use in identification. The escarp- ments along faults are, almost without exception, true fault scarps, though most of them have been modi- fied to varying degrees by erosion. The traces of faults across irregular topography and scarce exposures of fault planes indicate that almost all the faults are nor- mal, although on the Volcanic Tableland a few high- angle reverse faults and a low-angle thrust fault were identified. Warps are reflected in surfaces that have been bent or warped to very different forms from the original. To the casual observer the faults are far more obvious than warps or open folds where both are reflected in the topography, because abrupt fault scarps are more conspicuous than surfaces that have been bent a few degrees. Nevertheless, some of the largest fea- tures are warps, and some conspicuous faults are merely secondary features on warps or folds. In the evolution of the Sierra Nevada and White Mountains escarpments, the two most significant struc- tures are warps and faults in which the block on the side nearest Owens Valley has been relatively dropped. In contrast with the faults that are downfaulted on the valley side, here called valley-down faults, are faults having the mountain side downfaulted, or mountain- down faults. Mountain-down faults generally are sub- sidiary features that are closely related to warps. The association of mountain-down faults with warps is so general that in places where mountain-down faults are abundant warping might be inferred even in the absence of other evidence. Mountain-down faults in a similar gross setting have been explained by Hans Cloos (1939, p. 416), on the basis of experimental models and observations in a tun- nel that cuts the eastern border fault of the Rhine graben, as minor complementary faults that dip into a master fault on the downthrown side. This explana- tion does not fit the mountain-down faults of the Owen Valley because a master fault is absent in those areas where mountain-down faults are most abundant. A closer analogy is found in faults on the flanks of anti- clinal folds, which strike parallel with the fold axes and are downthrown toward the anticlinal core. If the warps were formed in less brittle rock or under high confining pressures such as pertain at great depths, the rocks would be expected to bend. Inasmuch as they 173 were formed at the surface, the warping must have been accompanied by breaking along planes perpendicular to the stretching caused by warping. Thus, the warps are composed of a series of discrete blocks, each tilted toward the valley. The planes of separation between blocks in the arrangement are marked by escarpments that face toward the mountains. The fact that the faults are normal implies extension and indicates ten- sion at the surface. The observed throw on most mountain-down faults is relatively small, rarely exceeding 100 feet. Many of these faults, however, have moved repeatedly, and the throw observed in the dislocation of a surface may rep- resent only a small component of the total throw. Nevertheless, neither the total displacement on a given fault nor the aggregate throw on a series of faults is of any great structural consequence as compared with the difference in structural elevation achieved by warping and accompanying tilting of groups of fault blocks in the same direction. Narrow grabens a few hundred feet or less in width and a mile or more in length are present at several places along the range fronts, both in alluvial fans and in older rocks. Along some grabens the fault having the larger throw is a valley-down fault, and along others it is a mountain-down fault. In either setting the secondary fault is interpreted to be the result of local tension in the hanging wall of the primary fault. The downthrown side of most faults is clearly evident in displaced surfaces, but the scarps of valley-down faults appear to erode more rapidly than those of moun- tain-down faults. Ordinarily, the height of the scarp of a mountain-down fault is diminished by alluviation behind the scarp as well as by erosion of the scarp, but in places where subsequent drainages follow mountain- down faults, the height of the escarpment may be tem- porarily increased. Among a group of faults of the same age, the fact that more mountain-down faults are likely to be identifiable by their scarps gives an errone- ous impression of their relative abundance. THE SIERRA NEVADA ESCARPMENT Along the Sierra Nevada escarpment within the mapped area, the broad, gently sloping central span that extends from the Tungsten Hills on the north to the lati- tude of Crater Mountain on the south, a distance of more than 20 miles, is chiefly the product of warping, whereas the steep scarps to the north and south are chiefly the products of faulting. The central warped span is called the Coyote warp, the northern faulted span is called the Wheeler Crest scarp, and the southern faulted span is called the Tinemaha scarp. Because of the gentle slope of the warp, the range front in the 174 E } GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA warped span projects farther into the valleys than it does along the more precipitous faulted spans, and nar- rows the valley by several miles (pls. 1-4, 7). The faulted spans extend from the northern and southern boundaries of the mapped area into the warped span with progressively diminishing throw. The faulted spans are offset from each other and do not join. THE COYOTE WARP The Coyote warp has little in common either phys- iographically or structurally with the precipitous fault scarp that is ordinarily envisaged when thinking of the Sierra Nevada escarpment. Within the area of the warp, broad interfluvial areas between steep-walled canyons slope gently north, northeast, and east into Owens and Round Valleys. These interfluvial areas are parts of an old erosional surface-presumably the mid- to late-Pliocene surface-whose present configuration is the result of structural warping. The old surface is preserved in Coyote Flat, Coyote Ridge, and Table Mountain, and in the sloping interfluvial areas south of Shannon Canyon to Big Pine Creek, and north and west from Freeman Creek, across Bishop Creek and into the Tungsten Hills. The surface is missing over a broad area between Rawson Creek and Shannon Can- yon because of deep dissection caused by headward ero- sion of Rawson, Freeman, and Shannon Creeks. How- ever, the sloping surfaces south of Shannon Canyon and north of Freeman Cayon can be projected across this span without serious adjustments. The ancient surface that records the warp is deeply weathered and in places has a cover of residual soil. Locally, as in Coyote Flat, it is covered with glacial moraine and outwash. Where the surface is best pre- served, it is gently rolling and has a relief of a few hun- dred feet at right angles to the average slope. Part of this relief is assignable to recent dissection and to dis- locations along faults. The local relief increases with dissection, to a point where the old surface is no longer identifiable. Local deep dissection of the old surface by such streams as Bishop Creek, Rawson Creek, Free- man Creek, Baker Creek, Big Pine Creek, and especially Shannon Creek indicates that the surface is not in equilibrium. with its present environment and could not have been formed in its present configuration. Almost certainly it was formed with a gentler slope than it now exhibits, and there is no reason to presume any relation between the original configuration of the old erosional surface and its present configuration. The warp is two sided-one flank slopes northward, and the other flank slopes eastward (pl. 7). The two flanks meet along an anticlinal axis that plunges north- eastward and passes through the northeast-facing salient in the range front south of Bishop. The form of the surface is shown by the traces of topographic con- tours, modified where they cross slightly eroded areas and extrapolated where they cross deeply eroded areas (pl. 7). The 6,000- and 7,000-foot contours are especially illustrative. South of Shannon Canyon the old surface slopes eastward about 6,000 feet in 6 miles, or less than 11°-hardly a precipitous slope (pl. 5, see- tion D-D'). On the north flank of the warp the upper slopes from Coyote Flat are at about this same angle, and the lower ones across Grouse Mountain and the Tungsten Hills are even gentler (pl. 5, section G@-G@'). The downwarped nature of the north flank was first recognized by Taylor (1934), who believed that it was bounded on the east by a fault that died out northward. A significant and interesting feature of the Coyote warp is the abundance of mountain-down normal faults, although valley-down faults are also present. Almost all of these faults are north-trending, and they are mostly confined to the summit and east flank of the warp. The north flank is broken by relatively few faults. Crest and east flank A shallow graben bounded by north-trending normal faults of relatively small displacement occupies the topographically low eastern part of Coyote Flat. West of the graben are several nearly parallel faults along which the western part of Coyote Flat has been stepped up. Coyote Flat is believed to be separated from Coyote Ridge by two en echelon faults that are about a mile apart. If Coyote Flat and Coyote Ridge are faulted segments of the same surface, the throw along the north- ern fault is about 800 feet at the south end and dimin- ishes northward to nothing. - These faults are the north end of the fault system that lies along the base of the Tinemaha scarp and bounds the Coyote warp on the west. East of the graben, subparallel north-trending faults are present eastward down the east flank of the warp to the base of the range and beyond into the alluvial fans. Almost all of these faults are downthrown to the west, but a few are accompanied by faults of opposite throw and define long narrow grabens. Topographically the mountain-down faults are expressed in bedrock by long narrow alluviated trenches parallel with the range front. . These are most conspicuous in the broad sloping surface south of Shannon Canyon. Section D-D' of plate 5 illustrates the relation of the faults to the de- formed surface in the summit and east flank of the warp. The mountain-down faults between Baker Creek and Shannon Canyon continue southward across Big Pine Creek and into the area west of Crater Mountain. Bed- CENOZOIC rock is exposed through the moraines of Big Pine and Baker Creeks as a result of faulting. South of Big Pine Creek are several scarps a hundred feet or more in height. The largest of these bounds McMurry Mead- ows on the east and has acted as a trap for the alluvial detritus there. The height of the scarp indicates a throw of several hundred feet. A prominent bench at half height in the range front south of Rawson Creek was formed by alluviation behind the composite scarp of a closely connected chain of mountain-down faults. Where the scarp has not been cut through by gullies, a narrow alluviated valley paral- lel with the range front is preserved. From the floor of Owens Valley the bench gives the erroneous impres- sion of a stepped block bounded by valley-down faults, but careful search of the walls of the canyon of Raw- son Creek, where the plane of such a fault would be exposed, proved fruitless even though exposures are excellent. Smaller parallel benches formed by moun- tain-down faulting are present about a mile to the west in sec. 13, T. 8 S., R. 32 E., and also about a mile to the east near the range front, where they extend about N. 20° W. for nearly a mile from the triangulation sta- tion at 5,398 feet just west of Keough Hot Springs. Mountain-down faults displace alluvial fans along the base of the east flank of the Coyote warp at several places. Profiles across two faults, one cutting the Shan- non Creek fan and the other cutting the Rawson Creek fan, are shown in figure 73. Fault scarps that cross the Shannon Creek fan are continuous with fault- controlled trenches in the old surface to the south. The fault represented by A and B in figure 73 extends south from sec. 20 into the east half of sec. 29, T. 8 S., R. 33 E. The fault was dug into where it crosses the north bank of Shannon Creek, and the dip of the fault plane was found to be 60° W. The block east of the fault A 200 0 200 FEET an fe te.. FicurE 73.-Profiles across mountain-down fault scarps in alluvium along the base of the east flank of the Coyote warp. A and B are across a scarp in the fan at the mouth of the Shannon Canyon. A is in the SE% sec. 20, T. 8 S., R. 33 E., and B is one-half mile to the south in see. 29. C is across a scarp in the fan of Rawson Creek which extends from the NW % sec. 5, T. 8 S., R. 33 E., northward into secs. 31 and 30. 175° has been tilted strongly to the east, and its lower end has obviously been lowered substantial amounts by the tilting. Alluviation has taken place upslope from the scarp, which is about 25 feet high. The faulting and tilting have caused the entrenchment of Shannon Creek into the fan. The more easterly of two faults that cross the Rawson Creek fan also bounds a block of bouldery fanglom- erate, which is tilted strongly toward the valley. This fault has diverted Rawson Creek, which flows along the face of the scarp and around the end of the tilted block. Several wind gaps in the scarp together with fine alluvial material that has collected west of the scarp as a result of the faulting indicate that the course of the stream has changed several times, presumably as a re- sult of a succession of small movements along the fault. South of the scarp and on line with it, the alluvial slope steepens downslope, undoubtedly as a result of warp- ing, inasmuch as the depositional surface of a fan nor- mally flattens downslope. Just north of Keough Hot Springs a prominent gra- ben lies along the base of the range. On the west the graben is bounded only by granitic rock, but on the east side it is bounded by a small area of granitic rock that is covered on the north, east, and south sides by dissected alluvial deposits that are tilted several degrees toward the east. A steep contact between these deposits and the underlying granitic rock suggests the prob- ability that, as a result of earlier movements, the granitic rock has been tilted still more than the allu- vium. The dissected alluvial deposits at the south end slope about 7° E., whereas adjacent unfaulted alluvial fans slope only 3°. Alluvial fill and water were trapped behind the mountain-down fault and support a flourish- ing orchard in the north end of the graben. Similar situations exist in many places along both sides of Owens Valley in connection with mountain-down faults that cut alluvial fans. The graben may well con- tinue northward in bedrock along the range front and west of the Rossi tungsten mine as suggested by the topography, but the valley-down fault on the west side of the graben was not identified along this span. Faults of large displacement west of Big Pine Although the north and east flanks of the Coyote warp north of Shannon Canyon are known to continue into the valley block beneath alluvial fill (pl. 5, sections C-C', G-G'), south of Shannon Canyon the downdip part of the warp is cut by several faults of large dis- placement, including at least two valley-down faults. At Keough Hot Springs a valley-down fault displaces all but the very youngest fan deposits along the range front, and also provides a conduit for the water of the hot springs which break out at the lowest exposure of GEOLOGY 176 the fault. This fault ends just north of Keough Hot Springs about a quarter of a mile east of the valley- down fault of the graben. The fault can be traced in alluvium only about half a mile south of Keough Hot Springs, but it probably continues southward in bedrock, and very likely is the valley-down fault east of Warren Bench ; a valley-down fault along the intervening span is suggested by the steep escarpment. The fault at Warren Bench is marked by an eroded escarpment in granitic rock. The fault probably passes along the east side of the outcrops of metamorphic rock between Big Pine and Baker Creeks to an escarpment in granitic rock along the west side of the Crater Mountain basalt field. The rhyolite dome 3 miles south of Crater Mountain may mark this fault. The height of the scarp opposite Crater Moun- tain indicates a throw of about 800 feet. No scarps in alluvium are present along this fault south of Freeman Creek, but the moraines along Big Pine and Baker Creeks terminate along the line of the fault and have no doubt been downdropped along it. East of this fault is a mountain-down fault along which the feeders for Red Mountain and Crater Moun- tain are localized. In bedrock this fault bounds the west side of a horst that projects through the basalt flows of Crater Mountain in Fish Springs Hill and in small inliers of Tinemaha granodiorite in the northern flank of Crater Mountain. A recent scarp is present in the alluvial fans between Red Mountain and the south flank of Crater Mountain, and an alined scarp in the alluvial fan of Big Pine Creek probably is along the same fault. Orchards are present in alluvium collected against these scarps along Big Pine Creek and north of Tinemaha Creek. West of Big Pine the alluvial fan is displaced along a valley-down fault having a very large aggregate dis- placement (pl. 5, sections D-D', F-F"). - Gravity measurements and strong movements at the time of the earthquake of 1872 indicate that this fault extends southward for at least 100 miles and separates shallow bedrock in the west side of Owens Valley from deep bedrock in the east side. Undoubtedly this is one of the major Cenozoic faults of the region, and is a major step fault in the downdropping of Owens Valley. The fault can be followed south of Big Pine along a scarp that crosses the east side of the basalt field of Crater Mountain. At two places the throw along this scarp is reversed, but in each place companion faults to the west are downthrown to the east and the net throw on the pairs of faults is the same as elsewhere along the scarp. This anomalous situation probably reflects local near-surface deflection of the principal fault plane to the positions of the companion faults; the segments GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA having reverse throw along the line of the main scarp are merely secondary fractures. In the south margin of Crater Mountain the fault splits, one branch bends eastward toward the east side of the Poverty Hills, and the other branch bends west- ward to the west side of the Poverty Hills, where with a companion mountain-down fault it forms a narrow graben. A small cinder cone along the west branch between Crater Mountain and the Poverty Hills has been displaced by the most recent faulting, which here has downdropped the fan on the east side of the fault about 15 feet. Movements in this area at the time of the earthquake of 1872 were described by Whitney (in Goodyear, 1888, p. 295). * * * nowhere are the effects of the earthquake in fissuring and depressing the surface so manifest as in the vicinity of Big Pine. A large body of water issues from the gorges of the Sierra west of this place, and this water spreads out after leav- ing the sagebrush slope, and runs in numerous channels through a low and swampy meadow, several hundred acres in extent. Here there is a series of extensive fissures, which may be traced uninterruptedly for several miles. In one place an area of ground, two or three hundred feet wide, has sunk to the depth of twenty or thirty feet in places, leaving vertical walls on each side, and these depressions have become partly filled with water, so that ponds have been formed of no inconsiderable size. One noticed was fully one-third of a mile in length, and would have been much larger had not the depression been so situated as to afford: partial drainage of the area at one end, so that the basin could not be entirely filled. North flank The north flank of the Coyote warp, unlike the east flank, is broken by relatively few faults. Those that are present fall into the following three groups: (1) east-trending faults along the range front south and southwest of Bishop, (2) northeast, and northwest- trending faults in the vicinity of Lookout Mountain, and (3) northeast- and northwest-trending faults in Grouse Mountain and along the west side of the Tung- sten Hills Although additional unrecognized faults may be present, faults having significant recent throw could hardly have been overlooked. East-trending faults were observed southwest of Bishop, and one of these faults contains the vein that has been worked in the Bishop Antimony mine. Faults downthrown either to the east or to the west are pres- ent, but the dips of most fault planes were not ascer- tained. The fault exposed in the Bishop Antimony mine is downthrown to the north and is nearly ver- tical. Minor slips within the fault zone dip north or south. The mapped faults are all short and fall within an area of only about a square mile, but the physi- ography of the range front between Bishop Creek and the Rossi mine suggests that the Coyote warp may be splintered by two or three east-trending northwesterly CENOZOIC en echelon faults that die out toward the west. One fault probably lies along the edge of bedrock from the Bishop Antimony mine westward about 2 miles into the lower part of the canyon in which the Chipmunk mine is located. A second fault almost certainly lies along the north edge of the spur that contains the Yaney mine, particularly since the ore in the mine has been altered by hot spring action. And a third fault may lie along the northern edge of the next spur to the northwest. In the vicinity of Lookout Mountain only two faults have physiographic expression, and some or all of the others may be relatively old features; some of those in metamorphic rock may possibly be of prebatholith age. The two faults having physiographic expression are northeast of Lookout Mountain. These faults trend northeast and each are downthrown to the southeast several feet. The faults in Grouse Mountain and along the west side of the Tungsten Hills separate the Coyote warp from the southerly extension of Round Valley. The northwest-trending faults lie in and adjacent to Grouse Mountain. The most easterly of these faults appears to be downthrown to the northeast, and two other faults are downthrown to the southwest. Dis- placement on the easterly fault probably is minor. Repeated movements along the faults downthrown to the southwest are indicated by progressively greater displacement in older moraines and outwash, and obvi- ously greater throw in bedrock than in the moraines. The Tioga moraines, however, are not cut by these faults. The northeast-trending faults comprise two en eche- lon segments along the west side of the Tungsten Hills. The more northerly fault continues northeast of the Tungsten Hills, and recent movements along it have displaced the surface of the Volcanic Tableland and faulted off the terraces on the north side of the Tung- sten Hills. A succession of movements is shown by the difference between the throw required to cause the escarpment along the west side of the Tungsten Hills and the throw in the Volcanic Tableland. Recurrent movements along the southern fault segment have caused both McGee Creek and Horton Creek to change their courses at least twice. Both streams have been forced from original courses directly across the Tung- sten Hills-McGee Creek into a course farther to the north, and Horton Creek into a northward course into Round Valley. WHEELER CREST SCARP The Wheeler Crest scarp is one of the highest and most precipitous escarpments along the east face of the Sierra Nevada. The base of the scarp in the span north 177 of Pine Creek is at altitudes of 5,200 to 6,200 feet at the head of the alluvial slope, and summit altitudes about 2 miles to the west range from a little less than 11,000 feet to a little less than 13,000 feet. The average slope angle thus is about 30°, although in places it is as much as 35°. Profiles across the slope, following ridge crests, are approximately straight lines; neither the upper part nor the lower part of the escarpment is systematically steeper than the other. South of Pine Creek, the escarp- ment is less precipitous, and because the base rises to the south in the Coyote warp, the height progressively diminishes southward. The progressively lesser height of the scarp reflects, of course, progressively smaller throw on the faults. Along most parts of the escarpment, valley-down faults can be identified along the base. North of Pine Creek an almost continuous line of faults was mapped, but south of Pine Creek some segments lack mapped faults; thus the south part of the scarp may not have been as completely involved in recent faulting as the north part. High on the east side of Wheeler crest and in the lower eastern slopes of Mount Tom, moun- tain-down faults occur, but elsewhere the escarpment itself appears unbroken. The fault zone along the base of the escarpment is made up of interconnecting straight or gently curved segments. The fact that fault segments follow every reentrant in the base of the scarp indicates that, even though the scarp is deeply eroded, the base has not re- treated.. Although actual fault planes were observed in only a few places, the positions of the fault segments can be established by other means. The most useful criterion was low scarps that offset alluvial fans, talus cones, or moraines. Almost as useful are lines of springs. Not uncommonly the bedrock adjacent to fault segments is sheeted parallel to the fault plane, and sheeted zones were taken to indicate faulting in a few places where other clear evidence of faulting was lacking. The full width of a fault zone was observed at only one place, in the wall of an entrenched gulley a few hundred feet west of the west quarter corner, see. 13, T. 6 S., R. 30 E. At this locality the fault lies within Wheeler Crest quartz monzonite and is a brecciated and mylonitized zone about 20 feet wide; sheeting in the quartz monzonite west of the fault dips 70° E. In other places along the base of Wheeler Crest, sheeting dips from 60° to 65° E. A branch of the fault system along the base of the range north of Pine Creek probably follows into the range along Pine Creek, and joins a fault along the west side of the thick dike of quartz monzonite that penetrates southward from Pine Creek into the Pine GEOLOGY 178 Creek pendant. This fault can be traced south from Pine Creek into Horton Lake by means of a low scarp so recent that it offsets talus cones. An exposure of the fault plane at the summit of the escarpment on the north side of Horton Creek dips 65° E. At Wells Meadow a small alluvial-filled graben is present at the base of the scarp. On the east the graben is bounded by a horst of granitic rock. Apparently the graben and horst lie between overlapping segments of the principal valley-down fault. Mountain-down faults, so abundant in the Coyote warp, were identified by their effect on the topography at only two places along the Wheeler Crest scarp-on the lower eastern slope of Mount Tom, and along the east side of the summit surface of Wheeler Crest. The mountain-down faults in the lower east slope of Mount Tom are most conspicuous in the broad ridge south of Elderberry Canyon, but they extend northwest onto the ridge just south of Pine Creek.. South of Elderberry Canyon these faults are subparallel with the contours and cut metamorphic and granitic rocks, and some also cut fan surfaces. Each of the faults is marked by a small valley or bench that runs along the slope (fig. 4). These valleys and benches are caused by alluviation behind the scarps. The traces of the fault planes across the topography indicate that most of them dip west at angles close to 45°. These faults are in a salient in the range front that is bounded along the base by valley- down faults, and may result from the downward drag of the salient. GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA - The mountain-down fault on the east side of Wheeler Crest furnishes a smooth bench which makes for rela- tively easy access for about 4 miles along the very crest of the Wheeler Crest scarp. The fault has resulted also in alluviation behind the fault scarp at the heads of several steep canyons. One alluviated canyon head is north of the Adamson Round Valley Peak tungsten deposit, a second is about 2 miles farther north just south of peak 11,498, and a third is about three quarters of a mile south of the north boundary of the Mount Tom quadrangle. The northernmost alluviated canyon head contains a pond or small lake, and the others probably also contained lakes in the recent past. The position of the valley-down faults immediately at the base of the escarpment indicates that dislocation has continued to the present. Had it not, the base of the escarpment would have retreated from the position of the bounding faults, especially along larger streams. The dislocations of slope surfaces by recent movement on the faults also indicate that dislocation has con- tinued, except that they might be dismissed as minor movements that followed the main movements after a long period of stability. TINEMAHA SCARP The span of the Sierra Nevada escarpment that is here designated the Tinemaha scarp is the north end of a scarp that continues to the south many miles, although in several places it is offset. In the mapped area, the scarp can be traced for about 8 miles, from Taboose FIGURE 74.-Bench on northeast side of Mount Tom formed by mountain-down faulting parallel with the range front. ~CENOZOIC Creek at the south edge of the Big Pine quadrangle northwestward into the south side of Kid Mountain. The northwest half of this span, from Tinemaha Creek northwestward, lies west of the Coyote warp and pro- gressively diminishes in height into the warp. The escarpment is about as steep as the Wheeler Crest scarp south of Pine Creek, which has a similar structural set- ting. Farther north, across Big Pine Creek, the more southerly and easterly of two east-facing escarpments that bound Coyote Flat on the west is alined with the Tinemaha scarp, and no doubt reflects northward con- tinuation of the faulting that produced the Tinemaha scarp. The fault pattern is similar to the pattern along the base of the Wheeler Crest scarp and consists of an inter- connecting system of curved and straight-line segments. The height of the scarp is certainly chiefly the product of displacement along valley-down faults at the base of the scarp. However, south of Red Mountain Creek both valley-down and mountain-down faults were mapped along the face of the escarpment to altitudes as high as 10,000 feet. Some of these faults may continue farther to the northwest, but were not recognized because of the greater recent dissection of the scarp to the northwest. The principal valley-down fault dips 70° E. where it is exposed along the east face of Birch Mountain, and 45° E. in the lower east slope of Mount Tinemaha as in- dicated by the trace across talus. Recent movement on most of the faults is shown by physiographic dis- placements. At Tinemaha and Birch Creeks, faults displace moraines of both Tahoe and Tioga age, and in Birch Creek all but the most recent stream deposits are displaced. The faults in the escarpment south of Red Mountain Creek are shown by physiographic dislocations in the slope. The faults here fall into two groups; those be- tween the base of the escarpment and the east side of Stecker Flat are all mountain-down faults, whereas those farther west and higher are valley-down faults. Inasmuch as the traces of the faults across irregular topography indicate that the mountain-down faults dip gently to the west and the valley-down faults dip mod- erately to the east, all the faults are normal. The dis- placement on most of them is believed small, but the highest and most western fault at the upper edge of Stecker Flat may have a throw of several thousand feet. The fault pattern here is similar to the pattern along much of the White Mountain escarpment within the mapped area in that a broad zone that includes both valley-down and mountain-down faults is present in the mountain block behind a principal valley-down fault. The presence of mountain-down faults suggests that warping as well as faulting was involved in the GEOLOGY 179 production of the escarpment. The warping may be caused by drag along the principal valley-down fault. The probable structure of this part of the range front is shown in section F#-F", plate 5. CONJUGATE JOINT SYSTEM A regional system of steeply dipping conjugate joints is present almost everywhere in the granitic rocks of the Sierra Nevada. The joints are most conspicuous in areas of low topographic relief where the rock adjacent to joints is subject to rapid weathering, chiefly by chem- ical action and hydration. Erosion of the weathered rock has resulted in linear depressions along the joints. At low altitudes, erosion has been chiefly by wind and water, and at high altitudes glaciation has also been effective (fig. T5). Joints locally exert considerable control over the drainage pattern, and even in deeply dissected regions straight segments of streams coincide with joints. The steeply dipping joints occur in all the granitic rocks and cross boundaries between different intrusive masses without obvious deflection (pl. 7). Generally two principal joint sets almost at right angles can be identified. One of these strikes northwestward and the other northeastward ; the precise direction of strike changes from place to place although the two sets main- tain their right-angle relation to one another. Individual steep joints can be traced for several miles. Most are straight or gently curved. The joints in a given set generally are subparallel, and not un- commonly one joint cuts across other joints only slightly different in strike. Where significant change takes place in the strike of the sets, joints of one strike gen- erally interfinger with joints of slightly different strike, and rarely does a single joint curve from one direction to another (pl. 7). The spacing of the steep joints ranges from an inch or less to many feet. Regional differences in the spac- ing undoubtedly reflect differences in the intensity of the regional stresses causing the joints. The paucity of joints in the Yosemite region, which makes possible the formation of magnificent topographic domes, prob- ably reflects less intense stress than existed in the Bishop area. The spacing within a given broad area, however, appears to be primarily a function of the grain size of the rock in which the joints occur: The widest spacing is in the coarsest grained rock, as is illustrated in figure T6, which shows joints that cross an aplite dike within the Tungsten Hills quartz monzonite. The joints in the aplite are much more closely spaced than those in the quartz monzonite. The most conspicuous joints are the widest spaced; where the joints are closely spaced, the rock breaks into rubble and does not permit the & DOTOMD H a 2 © _ H3 isl a E is] 20 p> E i N p> H is O A & F t H O "d = 2) hel Ed 3 a > E - feel O Ed 2 +- p> FIGURE -Aerial view of Sierra crest southwest of Bishop; Blue Lake in center foreground. Grid pattern in right foreground results from the influence on erosion by a conjugate system of steeply dipping joints. Photo by Symons Flying Service. CENOZOIC GEOLOGY 181 Ficurs 76.-Joints crossing aplite dike in Tungsten Hills quartz monzonite. Closer spacing of joints in aplite is a function of its finer grain size. formation of deep and continuous linear depressions or trenches along individual joints. 'Most steep joints exhibit no evidence of movement, but a few offset dikes as much as several inches. The movement along these joints was parallel to the joint. The fact that the joints continue without interruption across boundaries between intrusive masses and that the pattern is regional indicates that the joints are younger than the batholith. It seems likely that the joints are the product of regional forces. The principal stress was very likely horizontal, and the joints can therefore be regarded as incipient shears. Because displacements along the joints were not systematically recorded, the stress pattern cannot be analyzed. Gently dipping joints are conspicuous at higher alti- tudes where frost action has opened them. In most places they strike parallel to the prevailing direction of the topographic contours and dip a trifle less steeply than the ground surface but in the same direction. This relation between the orientation of the gently dipping joints and the average local slope of the surface suggests genetic connection. The most likely explanation is that the joints were formed as a result of unloading through erosion. Any movement along the gently dipping joints would have been normal to the joint surfaces and not parallel with it as is inferred for the steep joints. THE WHITE MOUNTAINS ESCARPMENT The western side of the White Mountains within the mapped area slopes gently toward Owens Valley, although farther north at the latitude of White Moun- tain Peak the range front is very precipitous. Nu- merous faults having both valley-down and mountain- down displacements are present in the lower slopes of the range in a belt that averages about a mile wide. In this belt, mountain-down faults are at least twice as abundant as valley-down faults but have much smaller throws and are structurally significant because they indicate warping and mark the boundaries of tilted blocks. Older than the range-front faults and lacking recent scarps are three faults between Poleta and Black Canyons, which are transverse to the range front. The middle and southern faults are cut off by range-front faults, but the northern fault may bend near the range and join a range-front fault beneath alluvium. STRUCTURES PARALLEL WITH THE RANGE FRONT Near the south boundary of the Bishop quadrangle, in the vicinity of Black Canyon, almost all of the faults parallel with the range front are downthrown on the valley side, and most of the displacement appears to have been on a single fault. Elsewhere, valley-down 182 faults and tilted blocks combine to give the visible struc- tural relief along the range front. Several valley-down faults that bound stepped blocks 3 to 6 miles long can be identified. One such fault ex- tends in fan deposits just west of the base of the crys- talline rocks, from Coldwater Canyon southward to about a mile north of Silver Canyon ; a second extends from Silver Canyon south to Poleta Canyon, and a third lies along the west side of the older dissected fan de- posits from Poleta Canyon to Black Canyon. Moun- tain-down faults generally are much shorter and most can be traced less than a mile. One of the most promi- nent mountain-down faults crosses the alluvial deposits at the mouth of Poleta Canyon in the north-central part of sec. 13, T. 7 S., R. 33 E. This fault lies on the east side of a tilted block and is marked by an east-facing scarp almost 100 feet high. The beds in the tilted block west of the fault dip about 15° W., whereas those east of the fault dip only about 6° W. The 15° dip is not exceptionally steep-beds exposed in a pumice pit in the SE! see. 14, T. 6 S., R. 33 E., dip 45° to 55° toward the valley. The 15° angle of the dip in the tilted block carries the beds downward at a rate sufficiently great to offset the mountain-down displacement on the bounding fault within a distance of about 600 feet. Beyond that distance the beds are structurally depressed relative to their position before they were tilted. Another illustrative fault, a hinge fault, extends southward from the mouth of Coldwater Canyon. The scarp at the north end of this fault faces the mountains and that at the south end faces the valley. The height of the scarps diminish toward the hinge, and they meet in a small area of no displacement. The area west of the fault was dropped at the south end on the valley- down segment of the fault and at the north end by the tilted block west of the mountain-down scarp. Recurring movement is shown in the part of the scarp that faces the mountains. Two periods of dislocation can be identified in the scarp both to the north and to the south of the stream that flows from Coldwater Can- yon. Near the stream the fan deposits are broken by a low, very slightly eroded scarp; farther away from 'the stream they are broken by a higher and strongly eroded scarp. The most recent fan deposits immedi- ately adjacent to the stream are unfaulted. In other places, comparison of the dissection in different tilted blocks and different parts of the same blocks suggests two or more periods of movement. The mapped structures taken alone lead to the sup- position that the belt of faults and tilted blocks along the range front are but part of a system of faults of distributive deformation, which continues beneath the valley floor. The aggregate deformation of the bedrock GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA surface can be presumed to be far greater than the de- formation in the exposed rocks, many of which are fan or lake deposits and record only very recent movements. No single fault was recognized through geologic map- ping which alone would explain a major part of the structural relief. However, gravity studies by L. C. Pakiser and M. F. Kane of the U.S. Geological Survey indicate the pres- ence of a steep buried escarpment about 5,000 feet high along the west side of the exposed belt of deforma- tion. The westernmost mapped valley-down fault between Silver and Black Canyons probably marks the projection of this escarpment to the surface. The most reasonable interpretation of the combined gravity and geologic data is that the concealed escarpment is a steep master fault and that the exposed faults and tilted blocks are subsidiary structures. According to this interpretation, all or almost all of the structural relief of the concealed part of the range front and probably also part of that in the exposed escarpment is a result of movement on the master fault. Nevertheless, the mapped structures must explain a substantial part of the structural relief within the exposed part of the range front. The situation here is somewhat similar to that along the southern part of the Tinemaha scarp within the mapped area and also to that along the southern part of the east flank of the Coyote warp oppo- site Big Pine and southward. Sections 4-4" and C-C" (pl. 5) illustrate the structure of the range front. TRANSVERSE FAULTS BETWEEN POLETA AND BLACK CANYONS The northernmost transverse fault follows Poleta Canyon and passes just north of the Poleta stock; the next fault to the south lies in the northern margin of secs. 19, 20, and 21, T. 7 S., R. 34 E., and the most southerly fault follows closely the south boundary of see. 21. All three faults continue to the east beyond the limits of the quadrangle, and to the west are over- lapped by alluvium. The two southern faults strike almost due east, but the fault along Poleta Canyon . strikes northeastward. All the faults are normal faults and are downthrown to the north. Two other smaller faults that may belong to this group are north of Poleta Canyon in see. 4, T. 7 S., R. 34 E. These faults strike about N. 35° E., and are downthrown on the northwest. The transverse faults explain the exposure south of Poleta Canyon of the formations beneath the Campito formation. Along the southern two faults, Reed dolo- mite on the south has been brought into contact with the Andrews Mountain sandstone member of the Cam- pito formation on the north ; indicating a stratigraphic displacement on each fault in excess of the thickness of the Deep Spring formation (1,500 feet). Along the CENOZOIC GEOLOGY Poleta fault the Andrews Mountain member on the - south is in contact with the Montenegro member and the Poleta formation on the north-relations that pro- vide little basis for calculating the stratigraphic dis- placement. - Nevertheless, the gross distribution of for- mations in the vicinity of Poleta Canyon suggests that the movement along the Poleta fault has been at least as great as along the other two faults and that it may have been much greater. Lateral movement of about 1 mile is suggested on the Poleta fault by the fact that slate having excellent cleavage occurs north of the fault adjacent to the Poleta stock, whereas spotted hornfels derived from similar slate by thermal metamorphism is exposed on the north side of the fault about 1 mile west of the stock. These relations also indicate that the principal movement on the fault was after the emplacement of the stock in Poleta Canyon. Lateral movement along the southern two faults is a distinct possibility, but no criteria were found to identify such movement except for a faint suggestion of drag in the Deep Spring formation on the south side of the middle fault. STRUCTURES IN THE VALLEY BLOCK The block referred to here as the valley block lies between the Sierra Nevada and the White Mountains, and includes Owens Valley, Round Valley, the Volcanic Tableland, and the river terraces south and east of the Volcanic Tableland. Each of these physiographic units contains structures of interest in themselves, and in the aggregate they provide a basis for interpreting the overall structure of the relatively depressed inter- montane block. To augment the geologic data a geo- physical study of the variation in gravity in the inter- montane area was made by L. C. Pakiser and M. F. Kane of the U.S. Geological Survey, and is reported herein. A seismic profile across Owens Valley is also described by Mr. Pakiser. STRUCTURES IN THE VOLCANIC TABLELAND Within the mapped area the surface of the Volcanic Tableland almost everywhere parallels internal layer- ing in the Bishop tuff. The central and eastern parts have undergone relatively little erosion, and the surface provides a reference plane that is sensitive to deforma- tion and resistant to erosion; fault searps and broad warps are remarkably preserved. The western part has been more deeply eroded, and all but the largest features of the original surface were destroyed by streams that headed in the Sierra Nevada. The most conspicuous features of the landscape are mounds and ridges of resistant tuff that has been indurated by gas action. The following discussion deals mainly with the struc- 188 tures preserved in the central and eastern parts of the Voleanic Tableland. The largest structure on the Tableland is a broad asymmetric arch that plunges S. 30° E.; the crest lies 1 to 2 miles east of the Owens River Gorge. The east flank of this arch slopes southeastward toward Owens Valley and the southwest flank slopes southwestward toward Round Valley. Superimposed on this broad arch are many minor warps and faults. In the central and eastern part of the Tableland the most conspicuous structures are steep, fresh-appearing, north-trending scarps (fig. T7). largest scarp, along the east side of Fish Slough, is more than 5 miles long and consists of two en echelon segments. A few other faults are as much as 3 miles long, but most are less than a mile long. The scarp on the east side of Fish Slough is more than 300 feet high locally, and a few others are 100 to 200 feet high, but most searps are less than 50 feet high at the center and progressively lower toward the ends. Alluviation has taken place locally in basinlike depressions at the bases of some of the scarps, but except in Fish Slough the amount of alluvium deposited is generally negligi- ble. Thus, the height of most scarps is a measure of the throw on the fault since the extrusion of the Bishop tuff. Searps downdropped to the east and to the west are equally abundant, and are of the same average height and length. Most fault planes exposed in cliff faces, road cuts, and pumice quarries along the south and east margins of the Volcanic Tableland are vertical or dip steeply toward the downthrown side, but a few dip toward the upthrown side. Most of the faults having larger throws appear to be vertical or nearly vertical, whereas some minor faults dip at angles as low as 55°. Many of the faults can be observed to pass downward through the Bishop tuff and into the underlying allu- vial deposits without recognizable change in throw. The two en echelon segments of the fault along Fish Slough are offset about half a mile. As the southern segment dies out at the north end, the displacement in-. creases on the northern segment, which is offset to the west.. Although the scarp attains a maximum height of about 300 feet, the downthrown side is covered with alluvial fill, and the throw on the fault may be 400 feet or more. A gravity high in the part of the Volcanic Tableland east of Fish Slough was noted by Pakiser and Kane. If caused by upfaulting of the basement, throw of several thousand feet on both sides of a horst is indicated, and basement rock must lie very close to the surface. In the lower end of Fish Slough, in the W1/ see. 7 and NW! see. 18, T. 6 S., R. 83 E., three tilted blocks lie a sal O & O & x4 H o '2 a _ H3 is! 2 = fas A isl 20 [> & hs N > H Hd O A & faut _ jas) O "d =] E4 & H fas 3 a > E* last i O Ed 2, i- > FIGURE 77.-Aerial view of the southeast part of the Volcanic Tableland showing systems of en echelon faults. Fish Slough extends across the lower right corner of photograph. Photo by Roland von Huene. \ CENOZOIC GEOLOGY along the fault (fig. 78). All these blocks have been so - tilted that the south end of each block is lowest and the _north end highest. The north ends of the two northern- most blocks are not quite so high as the upthrown side of the scarp, but the north end of the south block is even higher. Because the lower ends of all the blocks are covered by alluvial fill, the relation of the lower ends to the downthrown side was not established. The posi- tions of these blocks can be most readily explained if oblique slip movement on the fault is assumed, with the east side moving relatively upward and to the south. The amount of lateral movement, at least since the deposition of the tuff, probably is commensurate with the amount that is represented in the warp that exists at the offset of the two segments of the main fault along Fish Slough. Just east of the Fish Slough scarp the upper surface of the Tableland is broken by a closely spaced group of faults, some of which are downthrown to the east and some to the west. Farther east the surface has been beveled by stream action, which has effectively destroyed any scarps that may have existed. Neverthe- less, the surfaces of many faults are exposed in pumice pits along the eastern escarpment of the Tableland. Most of the faults are vertical or high-angle normal faults, but a few are high-angle reverse faults, and one is a low-angle thrust fault. Slickensides identified on about 25 percent of the faults suggest that the normal faults and most of the vertical ones were formed by dip-slip displacement but that the reverse faults and some vertical faults were formed by oblique-slip move- ment. Both the normal and reverse faults range in 185 strike from a few degrees east of north to a few degrees west of north, but there are no obvious differences in the average strike of the two kinds. The single thrust fault strikes N. 75° W., almost at right angles to the other faults, and dips 80° N. About half a mile to the northwest of the thrust fault, pumice identical in appearance with the pumice in the base of the Bishop tuff rests on unconsolidated tuff. The pum- ice outcrop is too small and exposures are too poor to arrive at any definite conclusion about this anomalous outcrop, but it is probably part of the basal pumice layer carried to its present position along a thrust. The stratigraphic throw required would be only about 50 feet, and the dip-slip displacement, assuming a 30° dip, would be about 100 feet. $ Most of the faults west of Fish Slough are arranged in northwest-trending en echelon systems. All the faults in a system are downthrown in the same direc- tion, and systems in which the faults are downthrown to the west alternate with systems in which the faults are downthrown to the east. Several of these systems can be readily identified on the maps (pls. 1-4, 7), but even where these systems are not readily apparent, as in the south-central part of the Tableland where the faults are very closely spaced, en echelon systems can be shown to exist by plotting the east-facing and west- facing scarps separately. Although the average trend of the faults is about due north, the faults range in strike from northwest to northeast. In places, faults having opposing directions of throw make grabens or horsts, but most blocks are tilted and upfaulted on only one side. In a few places the throw on a fault dimi- FicuRB 78.-Tilted fault blocks along Fish Slough. foreground, was once continuous and unbroken. 735-925 O-65--13 Surface on ridge in middle distance, on tilted blocks in front of ridge, and in 186 nishes along the strike to no displacement, then in- creases with the throw in the opposite direction. In such faults the segments with opposing throw belong to adjacent systems. Here it is evident that two systems of en echelon faults whose scarps face inward define a structural low, and that two systems that face outward define a struc- tural high. Along the lines of the structural lows, sev- eral undrained basins have been formed in the surface, whereas the topographically highest areas are in the structural highs. The structural highs can be con- sidered to mark the axes of anticlinal warps and the structural lows to mark the axes of synclinal warps (pl. 7). The broad inconspicuous anticlinal and syn- clinal warps are really the primary structures here and the fault systems are merely secondary features of contemporaneous origin that help define the warps. To understand the deformation pattern better, the faults in part of the area were traced onto a sheet of paper and the lines showing the faults were slit. When GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA the paper was pushed in a direction normal to the fold axes, folds formed but the slits remained closed. How- ever, when the east side of the sheet was moved south relative to the west side, both folds and faults formed in a pattern that is in agreement with the field observa- tions; the fact that a rotational couple was involved is thus indicated (fig 9). The movement on the faults was dip-slip even though it is the product of a couple. This experiment is concerned only with the duplication in a reference sheet of the geometry of the surface of the Bishop tuff; it is not a scale model, which would entail use of material of appropriate strength and re- production of the structural features without the ini- tial aid of slits for the faults. The geometrical ap- proach is believed to be valid because the structures were formed at the surface in brittle rock without the confining pressures that would be required for plastic flow in the tuff. En echelon faults are commonly ascribed to a rota- tional couple, but so far as I have been able to deter- FicurE 79.-Block diagram showing the relations between systems of en echelon faults and axes of warping on the Volcanic Tableland. A clockwise rotational couple, shown by the arrows, provides a satisfactory explanation of the structure. CENOZOIC GEOLOGY mine from a cursory search of the literature the pre- cise situation here has not previously been described. In the extended controversy during the 1920's over the cause of the en echelon faults in east-central Oklahoma several explanations were advanced, but only Sherrill's (1929) suggestion of regional torsion augmented by slight uplift is very much like the mechanism suggested for the en echelon fault systems in the Bishop tuff. Fath (1920) and Foley (1926) postulated horizontal shifts in the basement beneath each en echelon system. Link (1929) suggested tension in the crest of folds that were produced by compaction over buried ridges in the basement. The Oklahoma faults extend over a much larger area than is represented by the Volcanic Table- land, and the fault systems are longer, but the indi- vidual faults are of about the same average length and the range in throw is about the same. The Oklahoma faults are downthrown both to the east and to the west, but no statement was found in the literature to indi- cate that all the faults in an en echelon system are down- thrown in the same direction, or that adjacent systems are composed of faults of opposing throw. The few eroded fault scarps in the western part of the Volcanic Tableland trend either northeast or north- west. These directions parallel the two principal joint sets in adjacent parts of the Sierra Nevada, and joints in the basement may have controlled the pattern of faulting. The only fresh scarp among this group of 118° 30° 187 faults is one along the northeast-trending fault that is alined with the west side of the Tungsten Hills. Before summarizing the data on the deformation of the Volcanic Tableland, it is necessary to inquire into the relation of the present configuration of the Vol- canic Tableland to its initial configuration. The best clue to the initial configuration of the surface is found in three ancient stream channels that run parallel and in a southeasterly direction (fig. 80). One includes the anomalous drainage of Rock Creek through Birchim Canyon and the Owens River below Birchim Canyon to the south edge of the Volcanic Tableland. The see- ond is represented only by a short drainage in the south margin of the Tableland in sees. 19 and 20, T. 6 S., R. 32 E. The third is represented by a once continuous channel that extends from sec. 22, T. 6 S., R. 32 E., where the channel intersects the south margin of the Tableland, northwestward for about 5 miles to the SE14. see. 12, T. 6 S., R. 31 E. This channel, which probably was formerly occupied by the Owens River, has been broken into segments by faults, and some segments are lifted high above others (fig. 77). All three channels were probably formed by consequent streams that flowed down a southeastward sloping initial surface. This conclusion is in agreement with other considerations, such as the probable source of the Bishop tuff and its probable direction of flow. If the original slope of the Tableland was to the southeast, the southwesterly F ___L.__& ___ _ 2222 Hn nine as meres ne ane as oo T mono County INYO County 37° Vou aa Pa 1.- s e f 5' 25 %. 5 80.-Map of the southwestern part of the Volcanic Tableland showing the location of three ancient stream channels and their relation to modern topography. River. One channel, Birchim Canyon and the lower part of the Owens River Gorge, is occupied by the Owens The other two have been disrupted by faulting and warping and are dry. 188 slope in the vicinity of Round Valley must then be the result of later warping. Both the northwest-trending folds and associated systems of en echelon faults and the tilted blocks along Fish Slough fit well into a rotational couple in which the east side has moved to the south with respect to the west side (right-lateral movement), and a rota- tional couple seems the best explanation for all the structures in the Tableland. In this mechanism, dip- slip normal or vertical movement on the faults in the en echelon systems is the rule. However, it is possible in the same movement pattern for both lateral and thrusting movements to have existed. Lateral move- ments could take place on faults that ordinarily would have dip-slip movement, if the faults bent at the ends into thrusts or ended in warps. The Fish Slough fault provides an example of a fault along which lateral movement was made possible by a warp (the warp at the offset in the scarp). Two northeast-trending faults, one in the NW14 sec. 9 and the one alined with the west side of the Tungsten Hills, bend eastward at their north ends toward the upthrown block, presum- ably as south-dipping thrusts which are perhaps simi- lar to the thrust exposed in the pumice pit along the east edge of the Volcanic Tableland. The north-trend- ing segments of faults bend into thrusts or terminate at warps, and must have lateral components of move- ment in the part adjacent to the thrust or warp com- mensurate with the amount of thrusting or warping; the lateral component must decrease away from the thrust or warp. The destruction of the scarps of faults in the west side of the Volcanic Tableland by erosion must have taken place largely before the Owens River and Rock Creek entrenched themselves in their gorges. Hence, the principal post-Bishop tuff movement along the faults must have taken place not long after the extru- sion of the Bishop tuff. It might be inferred that the displacements on the faults would diminish in depth because of increasing confining pressures downward, but the regional pattern of faulting and a few specific observations indicate that the reverse is true. Succes- sive movements can be demonstrated for many faults along range fronts and, inasmuch as all the faults prob- ably are part of the same system, recurrent movements seem likely for the faults in the Volcanic Tableland. If the faults have moved repeatedly, only the later movements are recorded in the Bishop tuff. Within the mapped part of the Volcanic Tableland, the fault that continues into the Volcanic Tableland from the west side of the Tungsten Hills has clearly had earlier movements along it. If the gravity high east of Fish Slough (pl. 7) signifies a horst, pre-Bishop tuff move- GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA ments of large magnitude must have taken place there also. In the Casa Diablo Mountain quadrangle to the north, Rinehart and Ross (1957) have demonstrated that the displacement in the basement is greater than in the Bishop tuff along a fault on the west side of Casa Diablo Mountain and along a fault exposed in the Owens River Gorge. STRUCTURAL RELATIONS OF THE TERRACES The river terraces on the south side of the Volcanic Tableland between Round Valley on the west and Owens Valley on the east and southeast are considered to be correlative with the terraces that are cut across the east side of the Volcanic Tableland. They prob- ably were formed at the same general time as the dis- sected fans south of Bishop along the Sierra Nevada front and also at the time of the faulting along the west- ern base of the White Mountains that resulted in the dislocation of older fan deposits. This faulting is be- lieved to have been at the time of the Tahoe glacia- tion because it was then that Mono Lake overflowed into Adobe Valley, and from there flowed southward into Owens Valley (Putnam, 1949, p. 1296). Three terrace levels are present on the south side of the Table- land whereas only two are present on the east side. In general, the terraces are above the depositional surfaces of Owens and Round Valleys, although the east-side ter- races plunge under valley fill at the south end and the south-side terraces plunge under valley fill at the east end. The terraces on the south side of the Tableland are structurally the more interesting, and most of the dis- cussion concerns them. The terraces on the south side of the Volcanic Table- land are the products of the Owens River and an an- cestral tributary that flowed along the north side of the Tungsten Hills The maps (pls: 2, 3) show that the southern margin of each succeeding lower and younger terrace lies north of the southern margin of its next higher predecessor. Although the original northern limits of the terraces cannot be determined precisely because each succeeding lower terrace was cut into the northern margin of its predecessor, local benches and accumulations of gravel hang on the cliff on the south side of the Volcanic Tableland and indicate that some of the terraces, at least, extended north to the cliff. Each period of terrace formation started with east- ward tilting, which caused the Owens River to flow east- ward along the base of the Volcanic Tableland. The river would gradually broaden its valley by cutting laterally toward the southeast. Lateral cutting would continue until tilting restored the river to an easterly course and initiated a new period of terrace formation. CENOZOIC GEOLOGY A test for this hypothesis is found in the slope angle and amount of deformation of the terraces. If the hy- pothesis is correct, the youngest and lowest terrace should slope more gently eastward than the older;, higher terraces, and apparently it does. In sees. 21, 22, and 23, the present flood plain slopes east at an aver- age rate of less than 30 feet per mile, whereas the low- est terrace slopes at 40 feet per mile, and the middle ter- race slopes at TO feet per mile-the area of the highest terrace is too small to determine the slope angle. As a consequence of their different slope angles, the ter- races converge toward the east and plunge under val- ley alluvium at about the same place. South of Bishop, in the vicinity of the Rossi mine, the salient in the base of the Sierra Nevada is flanked by dissected fans that probably are of the same general age as the terraces. These dissected fans, like the ter- races, plunge eastward beneath recent alluvium. Be- tween the terraces and the dissected fans lies the recent fan of Bishop Creek, which lies somewhat lower than either the terraces or the dissected fans. The fan oc- cupies a trough that was cut by Bishop Creek as a con- sequence of eastward tilting that affected both the ter- races and the dissected fans. The absence of conspicuous scarps on most parts of the terraces indicates not only that the terraces were cut after the deposition of the Bishop tuff, but also that they were cut since most of the fault scarps on the V ol- canic Tableland were formed. This relation also is indicated in a few places by faults that cut the strata exposed in the margins of both the south-side and east- side terraces, most of which are overlain by a thin un- faulted layer of gravel. Nevertheless, the south-side terraces have been faulted off on the west and tilted to- ward the east. The east end of the middle terrace is broken by several faults having scarps of as much as 20 feet that face either east or west. These faults may have formed in connection with the tilting or warping. The most easterly scarp faces west and bounds a block that plunges eastward beneath the alluvium. Further- more, although the terraces contain few conspicuous scarps, north-trending lineaments that make a pattern similar to the fault pattern in the Volcanic Tableland are visible on aerial photographs of the south-side ter- races. These lineaments are low scarps generally 2 to 3 feet in height. Because the gravels capping the ter- races are not as resistant to erosion as the Bishop tuff, the scarps are rounded. Presumably these scarps re- flect a late increment of movement on the same system of faults that cuts the Volcanic Tableland. The terraces along the east side of the Volcanic Table- land were cut by a strong river ancestral to the Owens River, which during the Tahoe glaciation probably car- 189 ried the overflow from ancestral Mono Lake. The escarpment on the east side is in a single step in some places and in two steps in others. The tread of each step is a terrace and the escarpment is erosional. The escarpment coincides closely with the axis of warp along which the Bishop tuff is bent down to the east. This warp may overlie a fault in the basement rocks- it coincides with a strong gravity anomaly. Probably the escarpment was produced by the lateral cutting of a stream that was first entrenched in more easily eroded alluvial material that lay to the east of the warp. Such lateral cutting could have been induced by fans from the White Mountains which pushed the stream west- ward. The southward plunge of the terraces beneath the fill of Owens Valley strongly suggests a southward component of tilting since the terraces were cut. STRUCTURES OF ROUND VALLEY Round Valley is a structurally depressed block that is bounded by faults on the west and southeast, and by a warp accompanied by relatively minor faults on the northeast. The fault on the west side follows the base of Wheeler Crest and the range front south of Pine Creek, and the fault on the southeast side follows the west side of the Tungsten Hills. The part of the Vol- canic Tableland adjacent to the northeast side of Round Valley slopes southeastward toward the valley as a re- sult of warping, and the downward projection of this surface carries the Bishop tuff beneath the alluvium in Round Valley. Nevertheless, this warp is modified by one and possibly two faults that are downthrown to- ward Round Valley and which locally control the con- tact between the Bishop tuff and alluvium. One fault that trends N. 30° W. and is marked by an eroded scarp that faces toward Round Valley inter- sects the contact between the Bishop tuff and alluvium about half a mile north of Birchim Canyon at a point where the contact turns southward parallel with the direction of the scarp. The scarp is about 50 feet in average height and is somewhat rounded by erosion. The fault does not displace the alluvium, but straight- ness of the contact between the Bishop tuff and allu- vium south of the point of intersection and alinement of this contact with the projected trace of the fault sug- gest that the alluvium may have been deposited against the eroded scarp of the fault. A fault along the west side of the Volcanic Table- land was drawn at the base of a prominent escarpment. Although faulting seems the most likely explanation for the escarpment, it could have been caused by lateral erosion of streams flowing from the Wheeler Crest escarpment. 190 Gravity data indicate that the alluvial fill in Round Valley is relatively shallow. No bedrock outcrops are present in Round Valley proper, but bedrock is exposed at one place in the bottom of a stream channel that crosses the Buttermilk Country. SUBSURFACE STRUCTURE OF THE VALLEY BLOCK The ancient surface preserved in the Coyote warp is believed to continue beneath the Volcanic Tableland, Round Valley, and Owens Valley north of Big Pine, and to dominate the bedrock configuration. South of Big Pine, however, the warp is faulted off along the fault that displaces the basalt in the east side of Crater Mountain and along which strong movements took place at the time of the earthquake of 1872. If the eastern flank of the warp north of Big Pine is pro- jected eastward at its 10° average slope, the bedrock surface will lie about 5,000 feet beneath the valley floor at the western base of the White Mountains (pl. 5, see- tion C-C"'). The north flank also can be projected northward beneath valley fill and the Volcanic Table land, but it must turn upward along an easterly trend- ing synelinal axis because granitic and metamorphic rock crop out not far north of the quadrangle bound- ary and because evidence for large easterly trending faults in the critical area is lacking. * The postulated configuration of the bedrock has been substantiated by the gravity studies of Pakiser and Kane and more recently by seismic data of Pakiser. Although this information is of the utmost significance, several lines of geologic evidence, including data from well logs, also bear on the bedrock configuration. The slopes of the ancient erosional surface in the Coyote warp, together with the absence of marginal valley-down faults of large throw north of Big Pine, constitute a first point of evidence. A second is pro- vided by the eastward course of the Owens River along the south edge of the Volcanic Tableland to the foot of the fans from the White Mountains and its course southward along the east side of Owens Valley, in con- junction with the greater slope toward the east of older river terraces along the southern margin of the Vol- canic Tableland. The course of the river merely sug- gests that the most recent depression of the valley has been along the east side, but the progressively greater easterly slopes of the older and higher terraces indi- cate that the east side of the valley has been subsiding for an extended period and that tilting was involved in the subsidence. The possibility that the tilting of ter- races and the cutting of new ones coincided in time with periods of deformation along the base of the White Mountains is a third point. GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA A fourth clue is provided by a study of well logs sup- plied by the Department of Water and Power of the City of Los Angeles. A great many borings for water have been made into Owens Valley, but only about 40 were of use in interpreting the subsurface structure in the northern part of the Valley. All the logs used recorded penetrations of the Bishop tuff and the layer of white pumice at its base. This layer provides an ex- cellent reference marker because it is relatively easy to identify in the well logs which were kept by drillers, because it is a continuous sheet except near the range fronts, and because it was deposited in a brief interval of time. The pumice is conspicuously white and a good aquifer-properties that usually were noted by the drillers. All the wells that supplied useful data are at the north end of Owens Valley, in the Bishop quad- rangle. The geologic structure is shown in a fence dia- gram (fig. 64) in which the sections were drawn in such directions as to make maximum use of the well data as well as of outcrops of the Bishop tuff and of the pumice layer. Structure contours drawn on the base of the pumice are shown on the structure map (pl. T)« In a general way the pumice layer intersected in wells slopes southeastward at a rate of about 100 feet per mile beneath valley fill, from 4,300 feet in the south margin of the Volcanic Tableland in the western part of the Bishop quadrangle to 3,300 feet at the base of the White Mountains near Redding Canyon. This slope, however, is not smooth; it is interrupted by faults in the Volcanic Tableland and in particular the fault along Fish Slough, and by a northwest depression whose deepest part is just north of Bishop. The depression lies between the northeastward-plung- ing anticlinal axis of the Coyote warp and the south- ward-trending structural high east of Fish Slough, and very likely marks a structural trough between these features. This interpretation is supported by the line of gravity lows (pl. 7), which extends northward along Owens Valley and splits near the depression in the Bishop tuff ; one branch continues northward along the base of the White Mountains, and the other extends along the depression northwestward into the south mar- gin of the Volcanic Tableland, where it bends westward to Round Valley. The differences between the present configuration of the pumice layer and a horizontal surface cannot be taken to be entirely the result of deformation, for un- doubtedly the pumice layer had an initial dip. As in- terpreted from old stream channels the south part of the Volcanic Tableland originally sloped in a S. 60° E. direction and swung more southward along the south edge. Almost certainly the swing in slope direction continued southward into Owens Valley where the slope CENOZOIC GEOLOGY direction was probably about the same as the present surface. It also seems reasonable to assume that the magnitude of the slope of the valley floor was about the same then as now. A reasonable interpretation is that the present slope of the pumice layer is the result of southeasterly initial dip and easterly tilting. GRAVITY STUDY OF OWENS VALLEY By L. C. Pakiser and M. F. Kane A gravity study of Owens Valley north of Poverty Hills was completed by a U.S. Geological Survey party headed by M. F. Kane during three weeks of fieldwork in February 1954. This survey is part of a large, re- gional geophysical study of the structural geology of the area included within the modern drainage basin of Owens River. Earlier, in the summers of 1952 and 1953, Howard Oliver (written communication) made some gravity measurements in the Bishop area in con- junction with a regional gravity survey of the Sierra Nevada, and these measurements revealed that the val- ley block is expressed by a pronounced gravity low. The existence of this gravity low was confirmed by the later work, which permits it to be described and inter- preted in considerable detail. About 300 gravity sta- tions were established in an area of about 300 square miles in 1954, and 40 gravity stations that had been previously established by Oliver have been incorpo- rated into the present study. Field methods and reduction of gravity readings All gravity stations were run from two base stations, at Bishop and at Big Pine, for which the relative ob- served gravity values had been accurately determined by several readings taken between them. These bases in turn were tied to Howard Oliver's earlier survey and more recent work in the area to the east by D. R. Mabey (written communication). Two instruments were used to make the survey: a Worden gravity meter with a sensitivity of 0.5046 milligal per scale division, and a Frost gravity meter with a sensitivity of 0.0729 milli- gal per scale division . The more sensitive instrument was used mainly in the valley floor where greater ac- curacy was desired; the less sensitive one was used mainly in the adjacent mountain slopes where its larger reading range and portability were useful. Gravity stations were run in single loops from an initial reading at a base station. Base readings were repeated at intervals of four hours or less to determine the instrument drift and tidal variations. In each loop a station from a previous loop was read to check on the accuracy of the gravity data. A maximum of 0.3 milli- gal difference between the two readings was permitted. The elevation and position control for about 40 per- 191 cent of the stations was obtained from U.S. Geological Survey topographic maps and bench marks. Bench marks, section corners, and road intersections were used as stations where their elevations were known and where they could be identified in the field. The con- trol for the remainder of the stations was surveyed by plane table and alidade. A maximum vertical error of closure of 3 feet was permitted in the valley; 10 feet was allowed on the mountain slopes. The horizontal error of closure did not exceed 500 feet. Thus the per- missible errors of closure for the gravity readings and the equivalent gravity errors of closure for the survey control were about the same. All gravity measurements were referred to the base at Bishop which was tied, through the surveys of Oliver and Mabey, to absolute gravity bases of the U.S. Coast and Geodetic Survey and the University of Wisconsin. Elevation and latitude corrections were computed by using standard methods (Nettleton, 1940, p. 51-56). An elevation correction factor of 0.060 milligal per foot was used, corresponding to a density of 2.67 g per cm', the average density of the crystalline rocks in which the greatest variations of elevation are found. Latitude corrections were determined from the tables of theoretical gravity on the International Ellipsoid computed from the International Gravity Formula (Nettleton, 1940, p. 137-143). Terrain corrections through zone "O" were determined by using the Bul- lard modification of the Hayford-Bowie method (Swick, 1942, p. 67-68). (The outer radius of zone "O" is 546,914 feet.) Finally, the gravity field was contoured at a scale of 1: 62,500 and a contour interval of 1 milligal. On plate 7 this gravity contour map is reproduced with a contour interval of 2 milligals. The gravity contours are complete Bouguer gravity plus 1,000 milligals to make all values positive. Interpretation of the gravity data The predominantly clastic deposits of Cenozoic age that fill the valley block have a much lower density than the pre-Cenozoic rocks that confine them and that form the surrounding mountain masses. Therefore the gravity field (corrected for elevation, latitude, and ter- rain) in the valley area should be lower than that in the surrounding mountain slopes. By a careful study of the corrected gravity field, at least qualitative con- clusions can be reached on the subsurface configuration of the buried bedrock floor. If the density contrast between the Cenozoic and the older rocks is known, or if some depth control is available from drill hole or seismic information, the depth and attitude of the buried bedrock floor can be determined within narrow limits along selected profiles. From the subsurface 192 information thus determined, it is possible to draw some conclusions on the results of the tectonic movements. In the valley block the average density contrast be- tween the valley fill and the buried pre-Cenozoic rocks is not known accurately. It is assumed to be between 0.3 and 0.7 g per em, and 0.5 is taken as the most prob- able density contrast. All theoretical interpretations in this study are based on these limiting and most prob- able assumed density contrasts. (Seismic refraction data given on p. 195 of this report support a density contrast near 0.5 g per cm*.) In this study, the interpretation of the gravity data has been approached in the following order : 1. A qualitative study was made of the gravity contours (pl. 7) to reach broad, general conclusions on the con- figuration of the buried surface of the pre-Cenozoic rocks. 2. Selected profiles were analyzed by using a two-di- mensional gravity graticule designed by D. C. Skeels (in Dobrin, 1952, p. 98-99) and an assumed density contrast of 0.5 g per em*. Then upper and lower lim- its of the greatest depth were computed for the as- sumed limiting density contrasts of 0.3 and 0.7 g per cm. Certain local gravity anomalies were analyzed in detail. 3. The subsurface structure of the valley block was re- described on the basis of the quantitative information obtained from the detailed analyses above. 4. Some conclusions were reached on the nature of the tectonic movements that led to the erosion of the mountain masses and deposition of the thick valley fill. The gravity field shown by the gravity contours is assumed to be a true representation of the gravity field on the surface of the ground, corrected for elevation, latitude, and terrain effects. This assumption is be- lieved to be valid over most of the area, except on the Volcanic Tableland, which has considerable topograph- ic expression in materials of lower density (the Bishop tuff) than the 2.67 g per cm* assumed for the elevation corrections. The gravity field on the Volcanic Table- land may, therefore, actually be a few milligals higher than that shown on the map, but the general shape and amplitude of the anomalies is reliable and the theoreti- cal interpretation of the subsurface structure in this area is valid. The assumption that the subsurface masses analyzed by using a graticule are two-dimensional (that is with infinite extent along their axes) is not literally true, but the errors that result from this assumption are not great. Because of the uncertainties concerning densi- GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA ties, no further refinements are considered to be worth- while, but the error, if any, in this assumption of two- dimensional masses results in depths somewhat less than the true depths. The gravity contours Owens Valley is an area of great gravity relief; the maximum range is about 45 milligals from the low southeast of Bishop in the valley block to the high northeast of Big Pine in Waucoba Canyon (pl. 7). There is a broad regional gravity gradient, and the gravity field generally decreases in a westerly direction. This regional gradient has been removed from each of the profiles analyzed in detail. f The most striking feature shown by the gravity con- tours is the elongated gravity low in the valley block. This low has extremely steep gradients along the White and Inyo Mountains and relatively gentle gradients along the Sierra Nevada, except near Big Pine where the gradients are steep. The axis of this low lies near the base of the White and Inyo Mountains and very nearly coincides with the present course of Owens River. The greatest gravity relief of this low, along profile X-X', plate 11, is 27 milligals (corrected for the regional gradient). The steep gradient along the White-Inyo mountain chain indicates that the inter- face between the pre-Cenozoic and Cenozoic rocks there dips very steeply to the west. This zone of steep gradi- ents extends to the northern limit of the area covered. Along the Sierra Nevada front just north of Big Pine the steep gravity gradient suggests that there the bed- rock floor dips steeply to the east. Elsewhere along the Sierra Nevada front the bedrock surface probably slopes rather gently to the east, The deepest part of the Owens Valley structure lies very close to the base of the White and Inyo Mountains. The conspicuous gravity high north of Bishop and just east of Fish Slough is the expression of a mass of dense rocks of unknown origin that stands in great vertical relief above the bedrock floor. The conspicuous gravity low swings sharply to the west north of Bishop and into Round Valley. In this area the gravity gradients are gentle in all directions a feature that indicates that the surface of the buried bedrock slopes gently toward the center of the gravity low from the Sierra Nevada front to the south and west and from a large mountain block to the north. A gravity high trends northeastward through Bishop and divides the gravity low into two parts. Analysis of gravity anomalies Three gravity profiles (W-W', X-X', and Y-¥" of pl. 7) were analyzed in detail by using a two-dimen- sional graticule (pl. 11). CENOZOIC GEOLOGY The total gravity relief along profile W-W*', after removal of the regional gradient, is about 19 milligals. The gravity gradients are rather gentle on both sides of this profile. The interpretation shown, which is reasonably consistent with the gravity data, indicates that the bedrock floor slopes off gently into a syncline from the Sierra Nevada front to the south and from a large mountain block to the north. The probable depth of the valley fill is about 4,000 feet, and the depths range from 3,000 to 7,000 feet. The field and calculated gravity profiles could have been fitted much more closely, but the uncertainty about the elevation correc- tion over the Volcanic Tableland would make this re- finement meaningless. There is no geophysical evi- dence of faulting along this profile. Profile X-X' (pl. 11) was drawn across the largest local gravity relief in the part of Owens Valley in- cluded in this report. A total gravity relief of 27 milli- gals remains after removal of the regional gradient. The gravity gradients along the front of the White Mountains are much steeper than those along the Sierra Nevada front. The assumed geologic cross section meets the requirements of the observed gravity data almost exactly, although variations of this interpretation are possible. The valley fill is assumed to be in fault con- tact with the older rocks along the steeply dipping (about 60°) wall of the east side of the valley. On the west side, the bedrock floor slopes off gently from the Sierra Nevada front to the deepest part of the valley near the base of the White Mountains. Along the west side of the valley, the gravity profile is convex upward. In order to explain this condition, part of the buried bedrock surface is assumed to be convex upward also. The prominent steepening of the bedrock floor about 3 miles east of the Sierra Nevada front may reflect a buried fault scarp, possibly a continuation of one farther south of the west side of Owens Valley shown on profile Y-¥'. Density changes within the valley fill, which may result from a gradational change eastward from dense coarse, poorly sorted alluvial fan materials to less dense finer well-sorted clastic rocks, may possibly cause the convex upward gravity feature. The deepest part of the valley along profile X-X' is filled with 4,000 to 10,000 feet of Cenozoic rocks. The most prob- able depth is about 6,000 feet. Along profile ¥-¥"' through Big Pine the total gravy- ity relief, after the regional gradient has been removed, is 24 milligals. The gravity gradients are similar on the two sides of the valley, and the gravity low lies very near the center of the valley. The computed theo- retical gravity profile for the assumed subsurface con- figuration nearly coincides with the field gravity profile, and the assumed structure therefore meets the require- ments of the gravity data, although other similar geo- 193 logic cross sections would do so as well. The greatest depth of the valley fill, if a density contrast of 0.5 g per cm: is used, is about 6,000 feet. The maximum and mini- mum depths of the deepest part of the valley based on assumed limiting density contrasts of 0.3 and 0.7 g per cm>® are, respectively, about 10,000 and 4,000 feet. The steep gradients indicate that the valley walls dip steep- ly (roughly 60°) toward the center of the valley from both sides; the pre-Cenozoic and Cenozoic rocks are as- sumed to be in fault contact. A detailed study was made of the conspicuous posi- tive anomaly north of Bishop and east of Fish Slough. This anomaly has a total relief of about 21 milligals after subtracting the assumed anomaly of the valley structure. If a density contrast of 0.5 g per cm* be- tween the causative mass and the surrounding Cenozoic sediments is assumed, the gravity anomaly can be ex- plained by a truncated rectangular pyramid rising above the bedrock floor of the valley (about 6,000 feet deep) to the height of about 5,000 feet. The base of the mass is a rectangle about 314 miles wide and 7 miles long, and strikes in a northerly direction. The top of the mass is a rectangle about 1 mile wide and perhaps 4 miles long, rising to within about 1,000 feet of the surface. The gravity gradient on the east side of the anomaly is probably somewhat greater than that to the west, therefore the east slope of the pyramid may be significantly steeper than the west slope. Other hypo- thetical masses could be used to explain the gravity data, but that described above is a reasonably accurate representation of the actual subsurface body. The ac- tual subsurface body, however, is probably much more irregular in shape. If the density contrast were greater than 0.5 g per cm* the vertical relief of the causative mass would be less. The origin of the mass is unknown. The mass could be an igneous intrusive, a series of lava flows that were deposited concurrently with the sediments, or a fault block. The gravity high trending northeastward through Bishop may be caused by a large dense mass within the pre-Cenozoic rocks. It may be caused by a bedrock high, although several thousand feet of relief in the bedrock floor would be required to explain the gravity anomaly. It is equally possible that a thick section of lava may be buried under the gravity high. The cause of the anomaly remains indeterminate. Conclusions and discussion Owens Valley is a deep structural trough filled with about 6,000 feet of predominantly clastic rocks of Cenozoic age. A narrow, nearly linear fault zone dipping from 50° to 70° to the west (pl. 7) extends along the front of the White-Inyo mountain chain, and 194 along this fault zone the valley fill is in fault contact with the pre-Cenozoic rocks. Along most of the Sierra Nevada front, the buried surface of the pre-Cenozoic rocks slopes rather gently to the east and north into Owens Valley and Round Valley. There is a fault zone near Big Pine, however, where the interface be- tween the older rocks and the valley fill dips steeply from the Sierra Nevada front into Owens Valley (pl. T). Here the Cenozoic and pre-Cenozoic rocks are probably in fault contact. There is a suggestion of a possible buried fault scarp about 3 miles east of the Sierra Nevada front along profile X-X' (pl. 11). Un- der the Volcanic Tableland, the buried surface of the pre-Cenozoic rocks slopes gently to the south from a large mountain block to the north. North of Bishop, and east of Fish Slough, a large buried mass of dense rocks of unknown origin rises to within about 1,000 feet of the surface. There is also a dense buried mass trend- ing northeastward through Bishop, but it is not known whether this mass lies within the pre-Cenozoic rocks or projects above the general level of the bedrock floor. Northeast of Big Pine, near the juncture of the White Mountains and the Inyo Mountains, the gravity contours and the postulated fault zone sharply change trend to nearly due north. This offset in the otherwise nearly linear fault zone may be caused by a northeast- ward-trending system of faults that continues into the White-Inyo mountain chain toward Deep Spring Val- ley. The volcanic field at Crater Mountain lies to the southwest in this zone. The most satisfactory explanation of the steeply dip- ping interface between the clastic rocks of the valley block and the older rocks of the White-Inyo mountain block is that these rocks are in fault contact along a narrow fault zone. The interface cannot be buried topography, because such steep slopes would be quickly reduced by erosion to slopes comparable to those of the present Sierra Nevada and White Mountain es- carpments (30° or less). Although warping is prev- alent in this area, the warped surfaces all dip rather gently (as much as 20°). A system of faults in which displacement has been distributed through a wider zone, but in which the greatest amount of movement took place within the narrow zone described may exist. The fact that the Cenozoic and pre-Cenozoic rocks along this narrow zone are in fault contact indicate that the younger rocks must have been displaced by faulting against the older rocks. It seems unlikely that as much - as 6,000 feet of clastic rocks could have accumulated prior to this faulting, for it is presumably the fault- ing that created the steep escarpment on which vigor- ous stream action eroded the older rocks and trans- ported them as clastic sediments into Owens Valley. GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA Therefore, it is concluded that the subsidence of the valley block was continuous or repeated at frequent in- tervals and concurrent with the accumulation of the clastic rocks. Repeated movement of the fault zones along the White-Inyo mountain chain is supported by the geologic evidence. Subsidence of the valley block must have been prolonged and may have begun in Ter- tiary time and continued to the present. The bedrock floor was tilted downward to the east of the Coyote salient as the valley block subsided, but in the Big Pine area the floor of Owens Valley subsided as a graben along faults on both sides of the valley. The gently sloping bedrock surface in the synclinal area northwest of Bishop was formed primarily by downwarping but perhaps in part by distributive fault- ing. It is also possible that the gravity high trending northeastward through Bishop coincides with a bed- rock high. The coincidence of the gravity low axis along the base of the White-Inyo mountain chain with the course of Owens River suggests that the Owens River course was in about the same position throughout much of the period of subsidence of the valley block. Periodic shifting of the river channel to the east as the Owens Valley floor was tilting to the east is substantiated by the geologic evidence. Clastic sediments pouring into Owens Valley from the White Mountains held the river away from the base of the range. The mass of dense rock north of Bishop and east of Fish Slough can be interpreted either as a series of lava flows that were deposited concurrently with the clastic sediments derived from the White Mountains to the east, a volcanic plug, a combination of these, or a fault block. The close relation of this feature to well-defined fault trends tends to support the fault- block interpretation, but it is difficult to understand how such a small mass could have been elevated as much as a mile relative to the bedrock floor around it. The local stress distribution required for such fault deformation is particularly puzzling in view of the fact that the mass is completely separated from the White Mountain block. On the other hand, there is no geologic evidence to support the interpretation of this feature as a mass of volcanic rocks, although vol- canism is more readily understood than block faulting in terms of locally concentrated forces. (Aeromag- netic data obtained in 1956 and 1957 show that the material composing the mass is more magnetic than the material that surrounds it, but either plutonic rock of, say, dioritic composition or volcanic rock corre- sponding roughly to basalt could explain adequately the magnetic anomaly.) CENOZOIC The total throw on the fault zone bounding the west side of the White-Inyo mountain chain may have been as much as 13,000 feet. While the bedrock floor of Owens Valley was subsiding to its present altitude of about 2,000 feet below sea level, the White Mountains to the east were rising to an elevation of over 11,000 feet. However, warping may have caused part of the deformation. SEISMIC PROFILE By L. C. Pakiser Five seismic-refraction profiles were shot in Owens Valley by a party under the supervision of W. H. Jack- son during the summer of 1958. One of these (fig. 81) is in the area discussed in this report. Measurements were made by using conventional seismic-refraction in- struments and methods, and the interpretation was done by conventional intercept-time and delay-time compu- tations (Nettleton, 1940, p. 250-251). The profile shown in figure 81 was run along an east-trending road 2%%4 miles south of Bishop (pl. 7, section Z-Z'). The maximum shot-point offset of the 12-geophone, 5,400-foot spread was 13,000 feet. A weathered layer having a velocity of 1,000 fps (feet per second) and a maximum thickness of 10 feet was assumed in making the calculations. The 5,820-fps segments recorded from shot points 1 and 3, together with the 6,050-fps segments from shot points 2 and 8, yield a true velocity of 5,900 fps, which is assumed to be that of the younger Cenozoic deposits. The inter- face between younger and older Cenozoic deposits dips to the east beneath the spread. The 6,720-fps segments are taken as the apparent downdip velocity, and the 7,120-fps segments as the apparent updip velocity to give a true velocity for the older Cenozoic deposits of 6,900 fps. Velocity layering for the part of the profile between shot points 1 and 8 was determined by using formulas for dipping beds; at shot points 3, 4, 5, 6, and 7, one-way delay times were used. A. precise calculation of the pre-Tertiary velocity was not possible for this profile because of small irregular- ities in arrival times; however, a reasonable interpreta- tion of the data is made by taking 21,600 fps as the ap- parent updip velocity of the shots to the east and 12,300 fps as the apparent downdip velocity of the shots to the west. This correlation yields a true velocity of approxi- mately 15,700 fps. No quantitative interpretation was made of the travel-time curve recorded from a shot point midway between shot points 3 and 4 because of an error in the shot-point location; however, the data are included to supply additional evidence of the 12,300 fps apparent downdip velocity of pre-Tertiary rocks. GEoLoGyY 195 The greatest depth computed to the pre-Tertiary rocks along this profile is approximately 4,800 feet (shot point 5). This depth and those calculated at shot points 6, 7, and 8 are assumed to be minimum depths, and the true depths may be 500 to 600 feet greater. This con- clusion is based on the probability that the velocity of the older Cenozoic deposits east of the spread will in- crease with depth. The configuration of the pre- Tertiary bedrock as found from seismic measurements corresponds closely with that deduced from gravity nearby (pl. 11). INTERPRETATION OF THE DEFORMATION PATTERN The type of deformation active in the region today, represented by block faulting and warping, has char- acterized the structural history since the late Pliocene or early Pleistocene, and warping movements, pre- cursors to the modern deformation, probably began as early as Eocene. The sedimentary record in the San Joquin Valley in- dicates that although the Sierra Nevada region prob- ably began to tilt westward at least as early as the Eocene, the rate was very slow before the beginning of the Miocene (Hoots, Bear, and Kleinpell, 1954). By late Miocene and Pliocene time a broad low topographic arch had been formed across the batholith and the ad- jacent area to the east (Axelrod, 1957). Approxi- mate coincidence of the axis of this arch with the eastern edge of the batholith and with the axis of subsequent arching in late Pliocene and Pleistocene time suggests that the Miocene and Pliocene arch was an early product of the modern deformation pattern. Evidence of progressive movements in the same sense along many individual faults and warps indicates that the subsidence of the valley block relative to the border- ing ranges was accomplished by countless small incre- ments of movement, each probably of about the magni- tude of those that occurred in connection with the Owens Valley earthquake of 1872 (Whitney, 1872; Gil- bert, 1884; Hobbs, 1910) and with other earthquakes in the Great Basin. Abundant fresh scarps indicate that movements have continued to the present at a sig- nificant rate and no doubt will continue into the future. The apparent continuity in the long and complicated sequence of structural events strongly suggests that con- tinuous movement and stress patterns dominated events throughout the period of block faulting and warping. Owens Valley is doubtless a keystone block in the crest of a broad north-trending regional arch of which the Sierra Nevada forms the west side and the desert ranges at least as far east as the Panamint Range form the east side (pl. 10). North-trending normal faults along Owens Valley and bounding the desert ranges in- x. EXPLANATION 0 Arrival time, shot point west of spread 4 2d arrivals A Arrival time, shot point east of spread 2.0 & TIME, IN SECONDS u : d A T Intercept time A SP 2¢ arrivals, 20 arrivals Shot point 21,50 A 0 7; 2 s 1.6 4 5:00 io, Y E 1.2 0.8 0.4 0.0 |P G SP 4 SP 3 5400 ft SP 5 o Z Vi 1000fps Surface FA _______ V; 5900fps 1000 - Tmt te done ane noid Hone anne, Hone none a aes cuse oen men [aot rey mae ans Les __ seige men A ml U / 4 Ls 2000' |-*~,'~ "i SF- V, 6900fps ix ay 2% /\ Xz se eZ rr» 3000' |- PX AZX A _ SZ -T» / \N A 4000" |- N ANNs =c & V 3 15,700fps = (Pre-Tertiary Rocks) No zk (-t- 5000' |- f 4a v Aer s i- 41 de L. C. Pakiser, 1958 1 0 1 MILE L mau 1 1 | FIGURE 81.-Seismic profile across Owens Valley south of Bishop. 961 VINYOAITVD 'LOIMILSIG dOHSId 'NOLLVZIIYVUZANIN NTLSPNAL CENOZOIC dicate east-west extension. The faults probably are merely near-surface secondary features that formed as a consequence of arching. Similar relations between faults and warps or broad folds very likely exist elsewhere in the Great Basin, and mapping of the warps should lead to a better under- standing of the nature of Basin and Range structure than we now have. The faults, marked as they are by conspicuous scarps, are usually given considerable at- tention. Warps, on the other hand, are seldom identi- fied because they generally involve slopes of only a few degrees and must be delineated by mapping out refer- ence surfaces. Thompson (1960) has suggested that both the verti- cal uplift and lateral extension of the arch of which the Sierra Nevada forms the west limb were caused by in- ternal expansion of the upper mantle, possibly as a re- sult of abnormally high heat flow. Hafner (1951) has computed the probable deformation pattern in a block subjected to variable vertical and shearing stresses along its bottom. The similarity of Hafner's model (Hafner, 1951, pl. 1D) to the arch across the Sierra Nevada to the Panamint Range (pl. 10) is striking. Within the Bishop district are structural features that indicate north-south shortening or a north-south clockwise couple. The absence of normal faults across north flank of the Coyote warp is in sharp contrast with the abundance of faults across the east flank and sug- gests north-south shortening. The small horsts, gra- bens, and tilted blocks on the Volcanic Tableland have been shown to be subsidiary features related to north- west-trending anticlinal and synclinal warps, and the deformation has been explained in terms of a north- south clockwise couple. This couple could have resulted from the buttressing effect of the Coyote warp in con- nection with southward-directed stresses. A general north-south clockwise couple all along the edge of the batholith is suggested by the northwest- trending system of en echelon faults along the east side of the Sierra Nevada between Bishop and Lake Tahoe. Nevertheless, before lateral movement can be considered to have been systematic along the east side of the Sierra Nevada much more detailed geologic mapping is needed. Whitney (in Goodyear, 1888, p. 296) reported left-lateral movement east of Independence along a fault that moved in 1872, and Gianella (1959) has con- cluded on the basis of a review of the literature and undescribed field observations that the dominant hori- zontal movement in 1872 was left lateral. In the over- all Cenozoic pattern, strike-slip movement undoubtedly was subordinate to dip-slip movement. Such strike- slip movements as occurred may have been caused by local inhomogeneities, and may have varied in sense 197 from place to place and perhaps also from time to time. The conjugate joints in the Sierra Nevada are inter- preted to represent incipient shear planes but, lacking information as to the sense of movement on joints along which displacement took place, no conclusions can be made as to the orientation of the axis of greatest stress except that it probably was horizontal. If nonrota- tional stress is assumed, the axis of greatest compres- sional stress would have been north-south or east-west and would have bisected the average strikes of the joint sets. GEOLOGY ADJUSTMENT OF STREAMS TO THE STRUCTURAL MOVEMENTS Because the structural movements have been progres- sive and in the same general sense, the chief adjust- ment of the streams within the mountain ranges has been simply to cut deeper. In certain areas, however, the stream drainages have been affected by structural movements strong enough to have changed the direc- tion as well as the amount of slope. The adjustment of drainages to structural movements in two areas of ex- ceptional interest will be described : that in the Volcanic Tableland and that in the Tungsten Hills. The diver- sion of Rawson Creek by a mountain-down fault in its fan has been described (p. 175) in connection with the discussion of the east flank of the Coyote warp. ADJUSTMENT IN THE VOLCANIC TABLELAND Three ancient consequent drainages that flowed southeastward across the Volcanic Tableland transverse to the present slopes can be identified (fig. 80). Of these, only one coinciding with Birchim Canyon and the Owens River Gorge below Birchim Canyon has maintained itself against the structural deformation that affected the Volcanic Tableland. A short drain- age in sees. 19 and 20, T. 6 S., R. 32 E., seems never to have had any great length, and perhaps would never have maintained itself even without structural defor- mation. However, drainage farther northeast, now broken by faults into segments that stand at different altitudes, before deformation was a continuous drainage at least several miles long. Faulted segments of the old channel are identifiable from the south edge of the Volcanic Tableland in see. 22, T. 6 S., R. 32 E., north- westward to the SEL sec. 12, T. 6 S., R. 31 E. No evidence of the channel was found farther to the north- west, probably because of increasingly intensive ero- sion in that direction. ; If this stream were projected a little more than a mile and a half farther to the northeast along its course, it would intersect the Owens River Gorge in see. 2, T. 6 S., R. 31 E., at an elbow. Below this elbow to Birchim Canyon, the gorge cuts directly across contours, whereas 198 upstream it crosses contours obliquely. These relations probably indicate that the course of the stream above the elbow was established before the major deformation of the Volcanic Tableland and that the course below the elbow was established afterwards. The most prob- able explanation for this situation is that the Owens River below the elbow originally flowed downstream in the ancient fault-segmented drainage. This course makes a smooth sweeping curve from the north edge of the mapped area southeastward into Owens Valley, which would be a reasonable path for a consequent stream flowing across the original surface of the Vol- canic Tableland. The major structure formed in the Volcanic Table- land is a broad asymmetric arch, the crest of which plunges in a S8. 30° E. direction. Warping of the south- west side of this arch toward Round Valley has changed the direction and amount of slope in the critical region from southeast to southwest. The stream in Birchim Canyon and the one that flowed through Birchim Can- yon and the Owens River Gorge below Birchim Canyon was able to maintain itself across the new slope by downcutting. However, it seems evident that the Owens River was not able to maintain its course against the warping and faulting movements and that it spilled out of its channel at the elbow in see. 2, T. 6 S., R. 31 E., and flowed down the new slope to the stream flowing through Birchim Canyon. At that time the Owens River was not yet deeply entrenched and spillover could easily have taken place. The principal cause for doubt of this explana- tion is that the Owens River successfully maintained its course across a 100-foot-high scarp 2 miles upstream from the elbow while being defeated at the elbow where no evidence of a fault has been found. Very likely the relative rates of faulting and of warping in the two places were critical. An unlikely alternative explanation of the changed course of the Owens River is that a capture was made at the elbow by a tributary from the stream that flowed through Birchim Canyon. The difficulty with this hypothesis is that the capture would have had to have been made at or before the time of principal warping, and faulting; yet the adjustment of the segment of the Owens River between the elbow and Birchim Canyon to the present slope requires that the tributary worked its way headward after the present slope was estab- lished. ADJUSTMENTS IN THE TUNGSTEN HILLS Progressive movements along the west side of the Tungsten Hills have caused both McGee Creek and Horton Creek to change their courses at least twice. McGee Creek originally flowed across the Buttermilk GEOLOGY, TUNGSTEN MINERALIZATION, BISHOP DISTRICT, CALIFORNIA Country in its present channel, through a wind gap on the south side of Grouse Mountain, and joined Birch Creek in the center of sec. 33, T. 7 S., R. 31 E. Differ- ential movements between the Tungsten Hills and the graben between the Tungsten Hills and the main escarp- ment of the Sierra Nevada defeated the stream at Grouse Mountain and forced it to flow across a westerly spur of Grouse Mountain, in which it is now deeply entrenched as a result of later movements. For a time McGee Creek flowed eastward through a wind gap on the east side of Wells Upper Meadow, but further movements forced it into its present course. Horton Creek at one time flowed across the Tungsten Hills through Deep Canyon ; the stream that now occu- pies Deep Canyon is underfit. Horton Creek was de- feated by structural movements and for a time flowed through a wind gap in the southwest corner of sec. 9, T. 7 S., R. 31 E., which it cut deeply, until further movements forced it into its present course. In the defeat of Horton Creek, warping rather than faulting may have been the effective structural agent inasmuch as the locale of the defeat is at the offset of the two fault segments that bound the west side of the Tungsten Hills. An oddity in the drainage pattern is present in the east side of the Tungsten Hills, where McGee Creek and the stream that now occupies Deep Canyon leave the Tungsten Hills. There, McGee Creek flows through a notch that appears to have been originally occupied by the stream that carved Deep Canyon, and the stream in Deep Canyon spills over upstream from this notch through a deep slot in bedrock on the north side of its former course. A possible clue to solution of the drain- age changes here is a terrace along the south side of the abandoned segment of Deep Canyon, opposite the notch through which the stream in Deep Canyon now flows. The terrace is level and lies close to the 4,880- foot contour. It may mark the shoreline of a small lake or pond that existed for a brief period. The pond very likely was caused by damming behind a fan built by outwash from the Bishop Creek glacier across the lower end of the valley. The height of the pond was regulated by a low point in the bedrock in its north side, through which the pond overflowed. Downcutting at this spillway eventually drained the pond and estab- lished the ancestral stream in Deep Canyon in its pres- ent course. It was probably subsequent to these events that McGee Creek was forced into its present course by the structural movements along the east side of the Tungsten Hills. Since then it has entrenched itself in the outwash from the Bishop Creek glacier, across sev- eral spurs of the Tungsten Hills, and through the notch formerly occupied by the stream that cut Deep Canyon. CENOZOIC SCULPTURING OF THE MOUNTAINS BY WATER AND ICE While the valley block was being downdropped rela- tive to the bordering ranges, valleys and canyons were carved in the ranges by stream and by ice, and the re- sulting sediment was deposited in the valleys. Many of the consequent streams along the range fronts are not related in any significant measure to the structures within the rocks, but flow directly down mountain fronts; however, Rock Creek, Pine Creek, Bishop Creek, the creek in Shannon Canyon, and many shorter drain- ages are adjusted along northeast-trending joints and faults. Bishop Creek and the creek in Shannon Can- yon follow decidedly anomalous courses in the light of the present gross topography. Headward erosion and entrenchment of streams was most rapid along the steep Wheeler Crest and Tine- maha scarps, and less rapid in the Coyote warp. Even now, Coyote Flat has not been reached, although head- ward eroding streams threaten it on all sides. Except for fault scarps, the local relief on Coyote Flat very likely has continued to be reduced during the defor- mation, and will continue to be reduced until dissected by headward eroding streams. ~- The streams in the White Mountains are smaller and less powerful than those in the Sierra Nevada because the White Mountains are in the rain shadow of the Sierra Nevada. Very likely the smaller amount of precipitation is the reason for the preservation of a gently rolling upland in the White Mountains. Broad rounded interfluvial areas between major stream can- yons also reflect the slower rate of dissection by streams. Direct comparison of stream erosion in the Sierra Nevada and White Mountains is difficult because of the different kinds of rock of which these ranges are composed. Very likely the shale and slate, and possibly some sandstone, would erode more rapidly than granitic rocks under similar conditions, and carbonates would probably erode more slowly. The contrasting landscapes of the two ranges are only partly the result of differences in the abundance and power of streams; during the Pleistocene the White Mountains were less severely glaciated than the Sierra Nevada and had only a few rather small glaciers (Blackwelder, 1934, p. 221). Inasmuch as both ranges have been uplifted to comparable heights, the less se- vere glaciation in the White Mountains cannot be at- tributed to a higher average temperature. The cause lies in the smaller precipitation in the White Moun- tains; annual snowfall was insufficient to form a cumu- lative snow pack. This explanation of the scarcity of glaciers in the White Mountains during the Pleistocene carries with it two implications. The first is that in this area, in- GEOLOGY 199 creased precipitation could have been a more signifi- cant cause of glaciation than decreased temperature. After winters of exceptionally heavy snowfall in the Sierra Nevada, snow banks often survive the following summer. Present temperatures are low enough for glaciers to form if the winter precipitation were syste- matically increased over an extended period. Lower summer temperatures or summer cloudiness would, of course, favor the accretion of snow and the eventual formation of glaciers. The second implication is that the glacial periods probably ended because the glaciers wasted away owing to decreased snowfall, rather than melted away owing to increased temperatures. Accordingly, the runoff was probably greatest and associated lakes at their highest levels at the peak of glaciation rather than during gla- cial retreat. At the height of the Tahoe and Tioga glaciations the crest of the Sierra Nevada was a vast icefield through which the main divide and the principal ridges lead- ing to the divide projected, and glaciers moved down the larger canyons to relatively low levels. These gla- ciers widened and deepened their canyons and deposited huge amounts of debris at lower altitudes in moraines and in outwash fans. When they retreated, the gla- ciers left behind them a legacy of glacial features, which add vastly to the beauty and interest of the land- scape. Although the positions of the drainages were determined largely by streams, the modifying effects of glaciation were of very large magnitude, as has been emphasized by Matthes (1930, p. 84-103). Chiefly because of the glacial features it illustrates the Mount Tom quadrangle map has been included in two sets of topographic maps, one of 100 maps and another more select group of 25 maps, that have been chosen to illustrate specified topographic features (Up- ton, 1955). In the southwest part of the Mount Tom quadrangle, along the Sierran divide and in the Humph- reys Basin and French Canyon areas (fig. 69), features cited include Alpine topography, aréte, basin, cirque, cirque headwall, cirque lake, col, cyclopean stair, glacier, Pater Noster lakes, and tarns. Pine Creek and Rock Creek canyons are given as examples of glacial troughs, and Pine Creek canyon is also cited for its U-shaped valley in cross section and for the lateral moraines at its mouth (fig. 82). Since the last glaciation the rates of erosion and dep- osition have probably slowed down, especially at lower altitudes, because of the arid climate that prevails and because the modern landscape is almost completely fos- sil. Such easily destroyed constructional features as recessional moraines can be readily identified along most of the larger stream canyons, and they show that fep) sol O % O Q x4 H- a 2 [epl O H is] 'A s l A [ss 4 & y N pe H - O 4 Ud [ed o H O rd O n H- Ed 3 € E Fo leo O g A >> ~ FIGURE $2.-Aerial view looking southwest into Pine Creek Canyon. Note typical |-shape of glacial canyon, lateral moraines extending outward from canyon mouth, and loops of Tioga stage end moraine. Dark rock that crosses canyon at head is micaceous quartzite of the Pine Creek pendant. Photo by Symons Flying Service. REFERENCES CITED only minor erosion can have taken place since their deposition. Flash floods have locally added to the fill in canyon bottoms and along the range fronts, and talus continues to accumulate at higher altitudes and to form rock glaciers at the base of north slopes at altitudes above 11,000 feet. Otherwise, only rare periodic structural movements modify the landscape signifi- cantly. 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C., 1954, On the determination of pyroxenes by X-ray powder diagrams: Leidse Geol, Mededelingen, pt. 19, p. 167-276. mes s p os A Page Accessibility of 5 4 Actinolite. ...... due o (C4 Adamson - 134, 137 Aeroplane claims. [20 125 Aeroplane mine. ...____.______._____ 43, 81, 130, 139 Age, basalt flows.. 160 Bishop Creek pendant.....___..__..______ 41 Bishop tuff.__.______._.. 159 dissected deposits. 166 granodiorite of Deep Canyon._.___________ 80 Lamarck granodiorite............_.______ 80 Round Valley Peak granodiorite. a 76 Sierra Nevada batholith......__......___. 100 Tinemaha granodiorite...._.____________ 71 Tungsten Hills quartz monzonite....__._. 86 Age relations, granitic rocks...__.._.____.___. 99 Agglutinated, defined....____._______________ 155 Alaskan Range, rock glaciers....__._____.____ 170 ATASMINELL L L. cl beeen noon ado n 56, 88, 135 Alikes 2-022... . _._... . ou ILI 93 Alaskite facies.... . ~. eo odue ure 92 Albite 46, 87, 92 Albite granite facies, Tungsten Hills quartz 86 'Alanite: 59, 62, 73, 83, 95 Alluvial fan deposits, dissected._.______.____.. 165 tindissected.. ... 2.00. 2000200 0 167 - 168 Alteration products, granitic rocks...___.__... 59 z.... :. . 2C 20 oilers beeen 5 Amphibole 48, 50 granitic rocks.._..._... Inconsolable granodiorite_..._.......__._. 67 mafic dike rook. --. 05000-00000, 30 142 2121.0. 0.00000 r. Longs 58 silicate minerals in tactite......_..._..... 132 tactite 131 Tinemaha granodiorite........._..._..... 69 Analytical data, granitic rocks... ax 62 Andalusite...-......_..... __ 24, 31, 32 Andalusite-bearing pelitic hornfels, Bishop Creek pendant......______.____._.__ 40 EI Pence neon dein eae ns 37 Andrews Mountain member, Campito forma- fion, description........._.. ILI. 14 20 sis L220 000. SCL OOT Ce 50 Apatite...._....... 24, 28, 20, 31, 33, 37, 39, 41, 43, 45, 46, 50, 59, 62, 73, 80, 83, 95, 98, 112, 142 Aplite dikes, description...._......_..___._... 93, 148 reaction with mafic dike.........____..... 119 'Archaeveyathtis 8D :. : :.. .. 20. sss oul cece 16,17 Assimilation, defined. INDEX as [Italic page numbers indicate major references] B Page Baker - 2. oon ener ihc ce enas 7 Bald Mountain batholith, norms............. 107 Balk, Robert, quoted...-.-.--- 94 Bafite. --. -c Otc canes neues cele 125 Barth; T. F. W., quobed 148 Basalt, general ._.... 150 Basalt er oc- .-150 Basin and Range faults, criteria for distin- pn cl.. 19 Basin concretions...-....___.___.__.. 49 Basin Mountain mass of Tungsten Hills quartz monzonite.......__....___. 81, 83 Basin segregations._...._.~~ Cerec 112 Batholith. See Sierra Nevada batholith. Big Pine, faults west of........_._.____.__._... 175 gravity profile. .-- 2. i. LO cles 193 Big Pine Canyon, septa and inclusions.._---. 44 Big Pinc 5,7 Big Pine Creek sequence. _..._.__.___.._____. 99 Big Ping .... 163 'Big Fing RepRINL: Lor ccs ock enc 44 Biofite ®} ...on i ive ool Pegues ae death 23, 26, 28, 29, 31, 33, 37, 41, 42, 50, 55, 58, 62, 65, 78, T7, 80, 83, 87, 88, 92, 93, 95, 96, 98, 101, 112, 118, 151. Bishop, population.... lL 7 remnants southwest._-...__.____._..____._ 43 Bishop Antimony 44, 56, 176 Bishop area, Cenozoic structural features..... 172 Bighop 0000. ec 5,7 Bishop Creek MASK... 81 Bishop Creek 163 Bishop Creek pendant, calc-hornfels._.__..... 25 deformation by intrusives.._..__.______._. 115 description.._........- 38 metachert......._.. % 24. Bishop sequence. lcd.. 99 Black Canyon, transverse faults.......__._._. 182 Blackwelder, Eliot, quoted. - 163 Bleaching, ..; 129 Bloody Mountain block, correlation with Pine Creek pendant-..........._. 37 Blue Star Tale ming.._............-. -- 33,125 009 an ols. 127, 130, 150 Botts, Samuel D., analyst. sos 150 Boulder batholith, norms.. 2407. Bowen, N. L., quoted----- aA MP thermal metamorphism . y 32 Brown tungsten prospect.. -_ 56,113 Brownstone mine. . ..- - 125,134,148 S- dh Buckshot prospect =s col 125 : 2. - "L. cocco cepa ain canes 50 C Calc-hornfels, analyses... __..___._____________ 131 Bishop Creek pendant. ._..-..... 39 derived from argillaceous and siliceous limestone and dolomite...-.-.~.~. 25 derived from mafic igneous rock . a 20 Mount * 42 near Bishop..-..---- h 44 Round Valley septum. x 42 Split Mountain septum ..._._._____.__.___ __ 45 Page 24, 25, 41, 42, 44, 127, 135 Calofuth ... cso LAC Acorn A rel acoso even 33 Campito formation, description.. 12 unconformity beneath....__..._._______.. mg Cardinal ming. .... .... __.... . . 124 Carlsbad twinning.._..------- 73 Cathedral Peak granite, rocks similar to.. ..-. 88 Cenozole geology «.-... -_ 0.000 .cc 150 Cenozoic structural features, Bishop area.... 172 Cenozoic structural history, Sierra Nevada_.. . 171 Centralanficling. ... 02, 30004 -.. 18,19 Central syncline....-----.. --- 18, 20 Central Valley of California, geosynclinal gequienice.. Tec Lc. 171 Chalcopyrite....------ 127,130 Channon Canyon mass.... Jis 94 Chemical data, granitic rocks.._-_----. 62 Chemical variations, granitic 101 Chickenfoot Lake mass of Lamarck granodio- rite, contamination by mafic I@NO0UR TOCK. circle lee 104 description.. ..- T7 Chipmunk mine -- 44,125,139, 177 ---.. 16, 23, 29, 42, 45, 46, 50, 59, 73, 83, 98 Cinder cones. ...-- -- ~ Classification, granitic rocks. Cleavage. :... .cone. Clinozoisite...._--- bees Compositional variations, individual granitic MBS§OS: LCC:. 0) oud ouch anns 102 Coldwater Canyon, faults....-.....----. 19 Conjugate joint system, Sierra Nevada.... 179 Contact metamorphism, defined....._~~. s A26 Contact metasomatic, defined...._......_.... 126 Contact-metasomatic tungsten mineralization.. . 123 Contact relations, granodiorite of McMurry Meadows..-.cl 202.00. 0000 73 Contacts, different granitic rocks___......_... 109 fractures AIOHG. . 2.2 2002. sue neuen te naum s 143 granitic rocks and metamorphic rocks or dforite 2s Tro. uce e L NC 110 mafic rock and granitic 118 Cooper, G: A., 16 Copper, Pine Creek ming...._..-...._-....--- 126 prodHction: -.... 2. here ode cea neu eal ont 123 Cordierite.. -< .. . 2. on u 222. 22 oe SNAC Ns io ae the 31 Cowichan Lake area of Vancouver Island, British Columbia, norms_....-~~. 107 Coyote Ureck - .. . Ju oui tant Cube a 130 Coyote Creek 137 Coyote Warp. L2. R Luss 174 Crater Mountain, volcanic center...._._.._.-- 160 Crystal fractionation..............__...__.._.. 104 Culfuire. : _ Coote xue. ull one soin ar 7 D Deformation pattern, interpretation. ...--... 195 Deep Canyon, metaconglomerate.._....-.-~-- 23 Deep Canyon area, grade of ore.... 142 metamorphic inclusions. .---------------- 43 Deep Spring formation, description.......~--- 11 Dellenite LO Co- eceaud / use 28 Dike magma, souif¢e- -.. __. 98 205 206 Page Dikes, basalti¢ = as -.- 52. 20000 .eu ELT ngan we 150 deformation caused by intrusion......~~~. 116 223. -. 37, 38, 65, 71, 96, 113. 118% mafic. ..: -c ceeds ol nl dee a een eso 30, 98 Margingl EWarMI®:. _. 93 putlicecus 159 quarts .C. .s lede dual doce 28 Diopside. ss l else nl Luck 23, 24, 30, 31, 32, 36, 39, 40, 41, 44, 127, 129, 131, 132, 133 Mopsidi¢ .. 0L02 42 Diorite, contacts with granitic rocks.......... 110 @CNeral2-7 2002. 0e wok d 38, 44, 46 origin...... LNT AL sacks ree 56 Donner Pass, alfifiide..-.2.._......,_....in.. 171 Drainage o. coxa loc JL 0C. 004 GCAO L. «ancl e oa 5 L1 e- croc Srna niks 168 Durrell; Cordell, 31 E Fast syncline: co. 222.0 us falc cE DHL 18, 19 Economy, Owens Valley .«_\__:_._______._.__.__ 7 Elmore, Paul L. D., analyst.... 28, 29, 30, 92, 131, 156 Epidote, distribution. 23, 24, 26, 29, 33, 45, 50, 59, 73, 83, 98, 118, 128, 132, 133, 135, 142, 147 stability relations.. 132 Epidote-clinozoisite....__._______.__..._._-... 46 p Faults, Bishop 178 Bishop Creek pendant......._......-.-.-- 39 general. ...- Ceed reborn reds Le dey oa 17, 49 large displacement west of Big Pine.... 175 Mls Su. over - eRe ede oh sen dem a - _ 164 White 18 Feldspar. col nal 20 24, 27, 43 Felsic metavolcanic rocks, description.. 27 Pine Creek pendant.. 37 Foerberite >. 22.2 c2u9. 000008. cou ares 2h hoe 135 Field methods and reduction, gravity read- (HGS AT- Ge uel a. eel ool dies 191 Fish Slough ...-. Fish Spring Hill.. PIGONifG:. s- sen in. Folds, Bishop Creek pendant.... 38 @enerale 12.2000 el ave close ol oped Ag vias 17 Pine Creek pendant. 35 White Mountains. 18 G0 onn del mens s nacht 32 Fossils, Montenegro member, Campito forma- BON. . aL arenas ies hew 15, 16 Poleta formation.. . § 17 Pime.Creek pendant..._.-:.-:._____..... 37, 41 Freeman Canyon 94 G Gabbro, hypothesis of origin..............._.. 52 Pumgsten _.. 49 -. 127, 130, 150 Gatnet; distribution--..-.._.:........ 26, 31, 41, 42, 127, 130, 182, 133, 185, 142, 148, 150 Stability relations..-....l;..._.......}1.l. 132 Garnet-pyroxene tactite, scheelite in._..---.-- 134 Genesis, tactite deposits.........~--- 148 6 10 Glacial deposits, Pleistocene epoch.....------ _ 161 Cnelss, 26 South Fork of Bishop Creek ... 41 Gold, mining... ix 125 Golden Wedge mine..............----- 124 Granitic rocks, benches or apophyses.- -- 137 correlation of normative compositions with experimental data..---..-.- 104 CestripHon. 221. 000... 56 relation to tungsten deposits..........-_.. 146 replacement of mafic igneous rock..._.... . 119 sequence of 99 INDEX Page Granitization, defined__..._.___....._.._._.... 118 mafic rock.. -_. 54, 118, 122 Granodiorite: ** -Set CdS CL l Agee tes 54, 56 Granodiorite of Carthridge Pass, description .- 97 Granodiorite of Coyote Flat, description..._~. 96 Granodiorite of Deep Canyon, description.... 80 Granodiorite of McMurry Meadows, descrip- HOH . - .o. Oe cti - L denise - wen 71 Gravels, terrace_.....__..... 167 Gravity anomaly, north of Bishop..---.-.---- 193 Gravity-controlled crystal settling, gabbro..-- 58 Gravity study, Owens Valley. 191 Greenpore body2. > JA... .c. . ol ce 142 Grosgularite_.:/.:.___..._ 25, 36, 127, 129, 131, 132, 133 Gunter Crook, faults.. __. 2_._2ll 19 H Hanging Valley mine.._.________...._._. 37, 125, 145 Harkless formation, 20 description, }. .E 0A 17 FHedenbergite /.. LOA. ce sels de 128 HemAbite®. . .% : 24 26 oh seu ae. 23, 45, 46, 83 Hoots and others, quoted. 171 :..? .s. ... col slc ule tno un 29, 30, 31, 37, 41, 43, 45, 48, 50, 55, 58, 62, 65, 71, 72, 73, T7, 80, 83, 88, 92, 96, 98, 102, 112, 118. Hornblendé gabbro......_______.______.___. 38, 46, 56 Hornfels, Aeroplane mine.........___._..____- 43 handed .s .. 22s - se dete re och 39 conversion to amphibolite. 113 Harkless 201. 17 Montenegro member, Campito formation . 16 Horton Creek, adjustment to structure..._... 198 Hybridization, granodiorite of McMurry cos eau 71 mafic ucc 10% 54.119 Hydrob Sp... luz e ltl 20 lanl 2200002. ESCA Lw. 166 Ty persthiene ".. so. 0 1. ALT 31 I Ice, effects on topography. _.._______________. 199 J. E0 .M. AEL L 25, 36, 41, 127, 128 Idaho batholith, 107 imenite:!.._..}.... _ 28, 20, 41, 55, 59, 73, 83 Inclusion, defined. 12.210. £1 204.000 000 139 q AIC secede runes enc reais 112, 118 Inconsolable granodiotite, description...... .... 65 Index of refraction, minerals of tactite. . go (A27 Intrigive sou cc OIC 117 Intrusive contact, irregularities in...__.._._-. 136 Intrusive relations, rocks similar to the Ca- thedral Peak granite....___...__.. 94 Intrusives, fractures caused by emplacements. . 145 Inyo County, population..........___...._...- 7 TYOn cis 20. seu OINT HA EL L sda ales 33 3 Jackrabbit mine-ccuc sc. 12.00. 020.00. 125, 139, 142 JatoRibe 2.000 ss COIL Lap ul ou uel cece uu t den 135 Jobanfiseftife s s. 23 DOO centa Cot ASC 128 Johnnie formation, correlative of Deep Spring formation. a 12 Johnson granite. .... 96 Junibo nine 1.000. LC Aout au 71 K IC feldspar ... :s OL L 0s bec pt en 28, 31, 39, 44, 55, 57, 62, 68, 73, 74, 78, 80, 83, 87, 88, 92, 96, 112, 118. Kehl, L, M., analyst..._......... 67, 69, 74, 76, 79, 92 Keough Hot Springs, septa 3 miles west...... 43 Kirk, Edwin, quoted.. 10 de meres nade 16, 17 L Lakebed 10. .L IY 165 Lakeview mine...... 37, 56, 113, 125, 127, 135, 149, 150 Page Lamarck granodiorite, description._..._._._... 38, 77 lateral variations s- (108 Lambert mine...... 125, 135, 136 Landscape, 2.2000 170 Landslide material...... 2.1 2. 167 Laramide stocks, norms.... cao A07 Laural-Conviet pendant.._..... s 21 Leaching, tungsten....________.__.______.__ {aslo 186 Lead-alpha age determinations, granite rocks. 59 Sierra Nevada batholith............_....« 100 Limonite L b .. 83 Lindner prospéct..._.__.._..._.._. _. _ 148 Lithology, Campite formation.... 12 Deep Spring formation..........__.___._.. 11 Harkless foPmobiON -. .L c. D. ce- 17 metamorphic rocks. .... 143 Poleta formations c- 1000... 16 Reed dolomite.... ... 10 Wyman formation....._...______._.___..__ 10 Little Egypt prospect.....__.________________ 137 Lithe Sister mine... .. 20. 125, 139 Lower Cambrian sedimentary rocks, White . . .co nu cheese nets 9 Location of area._._....__...._ aie 5 Lucky Strike mines I4 43, 125 M McGee Creek, adjustment to structure. ...... 198 Mack, Marvin D., analyst. .__...__...__.__._.__ 156 . 21 1200 00s. eres ee 125 Mafic dikes. 1-4 51200030 LCV 11 68, 118 Mafic -\ . "k- 56 once 112,118 Mafic metavolcanic rocks, distribution. 28 Fine Creek 2s . 37 Tungsten Hill$) . _s. 10002000000 IECI -e 48 Mafic rock, assimilation......._...______..__... 121 c -o 200 Peca 118 Magnesium... 2... LAPRELE 33 . ..o. cous Boone beaten anke 24, 28, 20, 31, 33, 37, 41, 41, 43, 45, 46, 50, 55, 59, 62, 72, 73, 80, 83, 93, 95, 98, 112, 127, 150, 159. Main ore body, Pine Creek mine...... 131, 137, 143 Mapping. . c..... LL 0003.22.00. 0, MLE LY 4 Marble, alteration - . II. 149 SCR . 02 2.0. 9200000 P22. 20 PAn eS ub 131 Big Pine septum ._.. clic uenst 44 Bishop Creek pendant......__.__________. 39 bleached and silicated.. _......_..__.___.. 129 conversion to amphibolite. ............._. 113 derived from limestone. ....._..__.________ 25 MOUAE TOM. 32-001 42 near Bishop........ Pine Creek pendant.. Poverty Hills........... 45 Round Valley septum.-._._.__._.____.__._ 42 steeply dipping salients. ..____.._.___.__._.. 137 Marble tungsten mine..... .. - 125, 145 Mesozoic strata, distribution...-...-_-...---- 34 Meta-andesite, Tungsten Hills...._.---.------ 43 Metachert, Bishop Creek pendant. -. 24, 40 28 Metamorphic inclusions, Deep Canyon area.. 43 Metamorphic remnants, deformation by in- C.... C220 ce- rence 15 description. . ._. Loral ec cL paese 34, relation to prebatholithic rocks. .. tee 33 Metamorphic rocks, contacts with granitic TOOK. 2.00 .. Ln coe se de o tana 110 deposits in small inclusions-.~-.-----.---- 139 Sierra Nevada._....._---- a 21 £0.12 09.00.0000 uu cous 143 Tungsten .... (re 42 Metamorphism, kind and grade..-.-.-.~----- 31 s 000.0. Puc A180 Metarhyolite tuff__._.----- etl, 07 Metasedimentary remnants. ... 43 Page Metasedimentary .. 23, 43 Metasedimentary series, age._..._--- 21 Metasomatism, volume changes with meta- 130 0. 27 Metavolcanic series, ago__.___________________ Pal Methods of investigation.. _...____.__..__.___. 4 . 2282. ei ALH a. Ace aicas , 16, 24, 87 Micaceous quartzite, Aeroplane mine. 43 (Big Pine 44 Bishop Creek pendant...._...._.___.____. 41 derived from argillaceous sandstone and siltstone... .~. 23 Pine Creek pendant.-..- 36 Round Valley septum_.___._____________ 42 .. 24, 27, 28, 40, 41, 42, 68, 87 Microcline perthite.........-_- 71 Middle Palisade Glacier._..--.~. 2 45 Middle Palisade septum, description.. a 45 Mineral assemblages, calc-hornfels.....-..... 26 thermal metamorphism...._.............. 32 Mineral Dome Prospect............. 125 Mineralogical variations, granitic rocks. 101 Mineralogy, basalt.. ___ 150 0000000000. 020000284 87 Mining, Aistory 2: 22.) 1. . 0s cL L a cans 124 Modes, 63 finer grained quartz monzonite. ..-.--.... 95 granodiorite of Cartridge Pass. 97 granodiorite of Coyote Flat.........__.... 96 granodiorite of Deep Canyon.-....._. bets 80 granodiorite of McMurry Meadows... ... 71 Inconsolable granodiorite............_.__. 65, 67 Lamarck granodiorite. .. _____._. 77 Round Valley Peak granodiorite 75 Tinemaha granodiorite...__.__._ 68 Tungsten Hills quartz monzonite...__.__. 83 Wheeler Crest quartz ___. 73 127, 130, 148, 150 Molybdenum...._.__.. - 123, 126, 137 222. AN AALA oe cas- Ens cl ig chs aru 59 Mono Recesses mass similar to the Cathedral FPéeakigranite. 88 Montenegro member, Campito formation, de- scription. 15 Morgan Creek mass of Tungsten Hills quartz 81, 83 163 156 Mount Alice mass of quartz monzonite Similar to the Cathedral Peak granite.... 88 Mount Garibaldi area, norms ..._________.____ 107 Mount Humphreys septum. 35, 36 Mount Morrison pendant, correlation with Pine Creek pendant a 37 dislocation by intrusives........... 204 MG Mufisinger 143 Muscovites: 25228, 22205. DE LUT AOL acs 42 2-80.22 0000. uA ELC 74 N Necks, basaltiG cc: -II. 150 Noonday dolomite, correlative of Reed dolo- :H | Ler aer nve nici aie Gel 11 Norms, correlation with experimental data... 104 granitic 0.00. 63, 101 Inconsolable granodiorite...___...__..____ 67 Nort afitipling. cso, oy U IU. 18 North ore body, Pine Creek mine_.___.___. 137, 145 0 2s 22002000. 2.0.00. eil del ece eus 17 ONEOCIASELL 22 I2 e HEAT ALL. ce a alue 142 Olivine. - 150, 159 ODA se E ee code enna anna be ue ole cereal 135 Optical properties, minerals of tactite ao #s 428 Or-Ab-An-Qz-H20 system......._____________ 104 Ore bodies, position, size, and shape....._____ 135 Ores, @rader onl lush Lo ie ull. alll 125, 142 INDEX Page ~.. .. 222000000000. 00000000. 101, 131, 132 Owens River, adjustment to structure........ 198 CGSCTIpHON. ~~. ... ... en IATL Aue 7. Owens Valley, description.... 2 7 earthquake............. ' gravity profile..._..._.. -. 193 gravity study -. . . .. .on uus lens 220 191 P Paleozoic strata, distribution........._._..__. 34 Fegmatite dilees. .. . 22. 09200000 CL.. LY 93, 148 Pelitic hornfels, Bishop Creek pendant....... 39, 41 derived from silty shale, argillaceous silt- stone, and clay shale.............. 24 PinQCrock .. 36 Split Mountain septum.... 45 Porthite._.._... 83 Petrography, amphibolite. ..... 33 Phillips, Harry F., analyst. ._____.____.__. 28, 20, 92 FRIogODING: ... : .- cine oso o cos band 148 PIMC OIeGK .. v. 22... SATAII EL Suc ch 5,7 Pine Creek mass of Tungsten Hills quartz 0000000200. - 83 Ping: Cregl fing. . 00600 125,128, 129, 130, 131, 133, 134, 135, 139, 149 Pine Creek pendant, contact relations......-. 110 deformation by intrusives.. ._.... 2115 \ 34 intrusive 117 quartzite,. .cc...2.20....000l.. 28 structure. __.._.__... * 35 Plagioclase, distribution. een +4, 25, 27, 28, 29, 30, 31, 36, 37, 41, 42, 43, 44, 48, 50, 54, 55, 57, 58, 65, 68, 72, 73, 74, 78, 80, 83, 88, 92, 95, 96, 98, 101, 112, 118, 150, 159. density relation to magma._.............. 53 Plagioclase zoning, quartz monzonite facies... 88 PlutoftIC rOUk® .=. . : oo.. 0.2 .oo uce . Oe ous allele ane 56, 64 Poleta Canyon, faults. 19,182 108! 1 n.. 2000 Ne Usk a en 18 Poleta formation, cleavage..........~... 20 . (2 - 20, oor Cont cua 16 Poleta Mite 5 .-- 2 are ao owe 124 7 Porphyry, correlation with finer grained quartz monzonite................. 96 Porphyritic rocks, classification............. .~ 62 Potassium-argon age determination, Bishop PU.. 11 ALTEC TL n ce acne 159 PotAssinm feldspar.. 57,129 Foverty Hille, marble: 10 45 Prebatholithic rocks, regional distribution.... 33 Prebatholitic geology... ......_.._.___._.__._._. 9 Pre-Cenozoic rocks.. _. MOP 34 Precipitation, annual.~.----- sees 8 Pressure, tactite formation.. sass 'Add Previous geologic work. ._.._.___.._._._________ 3 Production, copper molybdenum..........___. 123 tungsten trioxide. ._.....~- 123 Profiles, gravity..--..- 192 Protoclastic borders. . __--- 117 Prthice, apgregato.s l coool rene ece 125 Pumice layer, Bishop tuff. ..__._._._..___.__.. 151 Purpose, scope, and organization.. . 2 PyHLE.. . 1.0. .so cbs doce. 39, 44, 95, 130, 131, 135, 142 Pyroxene........... 26, 31, 43, 50, 128, 130, 133, 148, 150 stablilfy relations.. 2002220 L000. CSL se 132 Ryithotibes. s . ooc ted sop ca Pil iaa cans 130, 135, 142 Q ! :L O22 O0 . cell o un wales cle ake aie ae wald aid 16, 23, 24, 26, 27, 28, 37, 39, 40, 41, 42, 43, 44, 55, 57, 65, 68, 72, 78, 80, 83, 87, 88, 92, 93, 95, 96, 101, 112, 118, 129, 131, 135, 142, 150, 154. Quarta diorihe ; *... J Ju comes i NAL Ee ae 46, 54 Quarts laties 20%. . anol Lint mln eC ela Pees 27, 37 207 Page Quartz monzonite, finer grained ._...._____._. 94 Quartz monzonite facies........... 88 Quartz-sericite hornfels, Round Valley septum. 42 Quartz velfis, sores.. _:..0. 1200 129 R Radiolaria vestiges in metachert 24 . TL. - Eef 130 Rawson mass of alaskite similar to the Cathe- dral Peak ___I. 88 Red Mountain, volcanic center....._.__...... 160 Red Mountain Creek mass, age.. Cech 94 deformation by intrusives. .. 117 Reed dolomite, description...... 10 Rellefiof arom.... 46-0. ln uds cedh aud 6 . bc fT LUT leon eedect s recused 126 Rhine graben 173 Rhyolite, south of Big Pine..... 159 Creek 2.9.00 nl.. IA.. er s Bet Rock glaciers.. . 0003 .. EL edd 168 Rossi C05 44, 125, 139, 176, 175, 189 Round Valley, description......______.___._.. 7 structure.... 189 Round Valley mine............ 112, 125, 128, 130, 143 Round Valley Peak granodiorite, description... 75 Round Valley septum, description..._._.____. 42 S San Joaquin Valley, structural relations to Sierra Nevada.....2......0..000.. 172 Sanidine .. 11.0. 1.0000, (Oo Lds s :y 484 Scapolite..... .. 120 ea ons laces 130 Scheelite, description............ 26, 129, 130, 142, 150 1 . 202 20.0000 ANTI 134 ming. 11 .. w. +118 Schober mine...... . 125, 130, 135, 139, 142, 149, 150 Secondary enrichment... ..____._._..___..___.._.._. 135 Sedimentary deposits. .........____.._.___._._._.. 161 Seismic profile...... wisi +108 Sericite......... 16, 23, 26, 42, 43, 46, 59 Sethloments .. _.. 20 Muu. uden 7 Shamrock ming. 2. . c. 2400. Us st 49 Shannon Canyon mass........._._..____._.__. 81 Shasta Bally batholith . 100 Sherwin and older tills. 161 Shorwin Hill mase..s. :.. 000. 12 Ai COIN 94 Sierra Nevada, Cenozoic structure, history... _ 171 conjugate joint system....._.._.__.____._._... 179 description......... 5 fanglomerate..... 166 metamorphic rocks...._._._..._._..... 21 Sierra Nevada batholith, emplacement... ... 99 14 evaluation of processes of emplacement... . 122 evidence of mechanical emplacement... . 115 evidence of thermochemical emplacement. - 118 gEOIOBY . .1 ou. 20 not cll LT ei seb vevey 45 Sierra Nevada escarpment....___.__.._____._.. 173 Siliceous calc-hornfels, Bishop Creek pendant . 40 SiHtcification, marble. ...... .. .22. 2420.5. 120 Silicified rock, zones....-~ . 129 # 32 Si118 2. 22, of ret eee Loup bane souk A. 37, 38 qUdIER ...... Levu sone AL war's 28 Silver Belle mine... ~-. ___ 00.01.0000 124 Sliver Canyon, fault#. s. . Ls 19 Silver Peak group...... 022. SATC: 12 Skarn, defined:. uu e ue, bee 28, 127 .. cance v. 104 South Fork of Bishop Creek, gneiss........--- 26 South ore body, Pine Creek mine...........-- 137 Specific gravity, granodiorite of McMurry . - 71,103 Lamarck granodiorite.....----.-- 77 Round Valley Peak granodiorite.......--- 75 fachite} :2.. coos cr l Al 14 4+ oo 130 Tinemaha granodiorite. ._.--...-----.----- 69 208 Page Specific gravities, metavolcanic rocks.._...... 27 Sphalerite. . nosen eac encase 127,130,150 2000. ase ae sh an cone 24, 28, 20, 31, 33, 37, 41, 42, 48, 44, 45, 46, 50, 55, 59, 62, 73, 80, 83, 93, 98, 127, 129, 142. Split Mountain septum, description-.....-.-- 45 Stocker Flat, .l. .ie colection den + 26 Stevens ore body.--- 129 Stevens prospect. . . 148 Stirling quartzite. 15 StoBing. s LLL ALL ca nere as 122 Stratigraphic nomenclature...............---- 9 Stratigraphic section, Andrews Mountain member, Campito formation .. . .. 15 Stratigraphic sequence, White and Inyo Mounitains: cols: ce- i 0 ave. 34 Streams, adjustment to structural movements. _ 197 erosion by.... .-. 23.0. Gak 199 Structural features, Bishop area- s xATe 2.02 .. Prue ges noe es «2 Ags Structure, Bishop Creek pendant..---.--.--- 38 .. ACs A. cocoa soup oa Cous und aude 170 internal, pumice....-..----- i AB valley block.............. -. 183 White Mountains. .-- C 17 Sugarloaf mass... . 94 Surface 0300. 5 Swedes Flat pluton, origin of granitic rock---- . 123 T. Table Mountain, contact relations-...-.--.~.. 112 Taboose Creek mass ._.. 94 Tactite, characteristic minerals..-.-....----.- 127 chemical gains and losses in formation.... _ 130 derived from marble and calc-hornfels. ... 26 description sls d coa ee. 126 distribritionw. ._.. .2 2.20 nue 0 a 142,143 layering and 133 Round Valley septum. 42 silicification . . Tahoe moraine. Tabos HIL UTY Eire se canons Temperature, annual. 8 crystallization.... 106 factite 149 ETaVO®-2 2.0. -2.000 00, n Wea ieee anl 167 Terraces, structural relations. ._....___....... 188 INDEX Page Texture, granitic rocks. ..___________________._ 59 Thermal metamorphism. ....._... -__ 130 Thermal metamorphism, defined.. a- #100 Thermodiffuasion.. ..- ._ 104 TPROFIbG 2 0202s tt Shs ce cone db ede apon 59 C00 0000.0L LoL nee 161 Tinemaha Crook & 7 Tinemaha granodiorite, description.. at 68 Tinemaha Starp...___..__._____.L__ v 478 Tinemaha sequence. . .. ._ _.. 99 Tiogd MIOFAING.. 02-1... .-. sto 163 Tioga till.... 164 Trachy basalt. 151 Tremolite. . .. 24, 26, 82, 40 Trilobites. ... 9 Tuff member, Bishop tuff....._._.__._.___._- 155 Tungstar mine, description.........- 35, 37, 125, 130, 135, 139, 142, 149, 150 quarts 28 Aor eela /l ie lori cbs 134, 150 Tungsten Blue ming. ..........__--- 49, 125, 139, 142 Tungsten deposits, geologic relations and distribution. .... 30126 relation to granitic rocks.... 3% 146 Tungsten Hills, contact relations.........._.~ 112 levered gabbro . 2.002 0000000 us oden e 49 mafic metavolcanic rock...... 43 metamorphic rocks.............- 42 stream adjustment to structure.. 198 Tungsten Hills mass...-....._...._.... mane 81 Tungsten Hills quartz monzonite, description. 80 intrusive effects-..........._______. 115, 117 Asteral variations 00.0 103 Tungsten mineralization, contact metaso- AbIC S-. real noe sin ones 123 Tungsten Peak prospect...__._.__._..__...... 137 Tungsten trioxide, production... 123 Tuolumne intrusive series...... 96 'Porner, F. J., quoted. 149 U 20000 C02 » wen 49 ens ode 9 Upper Precambrian(?) sedimentary rocks, White Mountains. ......._.......~ 9 v Valley block, elongated gravity............... 192 subsurface structure......_____...___.___. 190 L Cecon sc reins ine denes 183 C& cs 220020000002. 200.000 ce 49 Y Vitreous quartzite, Deep Canyon area.. Pine Creek pendant-....._....____..____. 36 TOCS asl Lc 43, 150 Volcanic Tableland, alluvial remnants. 166 description. 02000 7 stream adjustment to structure.. 197 : _ 02200200. 12 daar d unten ake 183 w Water, solubility in glass. _.....-- 106 Water-vapor pressure, magma.... 106 Welded, defined soll 0A ll 155 West anticline... -.. 18, 20 West syncline. Pacco 118, 20 Western 112, 133, 135, 143, 145 Wheeler Crest quartz monzonite, deformation by 2200000200 117 description. - 2.202, .0000 ._ oo Ae ae 2 73 'W Beeler Creat scarp. . 177 Wheeler Crest 35, 36, 116 White, Katrine E., analyst.-- 28, 29, 30, 02, 131 White Cape mine.... c. lez. cll le- 139, 142 White Creek batholith, 114 White Mountains, altered diorite.......-..... 46 description . «dau Cp 5 fanglomerate and lakebed deposits. s) - 105 sedimentary rocks-.......--- abe 9 StructHre; . lM ave tna seee ne 17 White Mountains 181 W bitney, J. D., quoted .:.. 176 Wollastonite.....-.-..- 31, 32, 36, 41, 44, 127, 131, 145 Wyman formation.... /. c. -. 22 x edes 10 ¥. Yanéy Mino: .... o.. 125,135 Yosemite National Park, ages of granitic rocks. 100 Z Zircon i...l.0. 2. 20 JL. 160 02/13, 88, 05 Zoning, granodiorite of McMurry Meadows.. 71 granitic -.... 102,114 Lamarck granodiorite. . a 78 PIRION. -.- 24s 97 Round Valley Peak granodiorite. _...... -- 76 Tungsten Hille. 00000 83 .. }. revised suss ol ___ 24, 41, 127,120 Zones, silicified rock and quartz veins.... 120 , )\ y. UNITED STATES DEPAREMENT OF THE INTERIOR x0? 3 GEOLOGICAL SURVEY & 118°45 40" (mt. Tom) # R. 31 F R s2 r, 118°30 37°15" pae a f m ame ; § Za (he a ; ras f ¢ % ovens m; 37°15 EXPLANATION ® Qal ot :: Qyt C . $ Alluvial fill Talus Younger alluvial fan ( Includes rock glaciers and deposits T Recent moraines; ridge May be, in part, of Pleisto- cults crests shown semidia- cene age grammatically GLACIAL DEPOSITS i> Tioga till Qtiy, deposits of younger advance delineated only along Bishop Creek. Crests of moraines and other glacial s ridges shown by dotted lines » Qt“ § a Undifferentiated till Ota : © Tahoe till Crests of moraines and other glacial VOLCANIC DEPOSITS ridges shown by dotted lines RSs Brit necks Sherwin and older tills C May be of late Tertiary age | UNCconFoRmiTty g Hunchback < \ GRANITIC ROCKS #: 89 Granodiorite of Coyote Flat | Felsic dikes and masses k 10% 10 Chiefly aplite, pegmatite, and alaskite f rte i" ee Rocks similar to the Cathedral To's mies Peak granite Mafic dikes Quartz monzonite ®, ® \ (C C \% x/ aA -an 6 a Spl Pre-Cathedral Peak; precise Kt #27 \ ie tes? sax] \x f yy (tD. z S ‘ 3 > f= m age uncertain *= : /A GX > SSS NCC G A. \\ "** } s= <- < 0 an y =I: C } Tungsten Hills quartz monzonite /% ga. £" Q JM, 4 8 { & 3 i( | + MceGee ~ Q| | & \ & d CZ 2 , © C y Kta, albitized rock < Lamarck granodiorite --A Dark hybrid facies shown by F stippled pattern f & f73xl\3 /Hv s . l ilbert\ \ C \)>///, A Kin F3W iaa s & Inconsolable granodiorite at < 0 ad Diorite, quartz diorite, and a) hornblende gabbro A WW \p RNZN ; Includes some hybrid rocks of gramodiorite ~s \ 1), 0\ ¢ ,D composition Z --Muir-Pass Toss ;*/ <<. \- METAMORPHIC ROCKS a 7 o ¢ ( METAMORPHIC ROCKS IN SMALLER MASSES Ifo ) 5 UV § AWA) wass o) aris! a - ) rR f y) | Wl - / Z \oS 1 Be ti mh area S007 ~- ‘ Little Pete as- C / d : V C y/ft Gffidilk'flrfé—H \ i (¥ s UGA \ | Bi Barat! (Ne- 3°C, | x‘MeiquZr/ s t> f § lc § JRE g S t f G / 4 > (franggt. S & \ Gneiss in the South Fork of Bishop Creek % P ? felsic lens. - May be sheared il &oim C MGR || \ S S granitic rock aA nate ~) a NI C/ x likc ( 2 anf +o) i( &n r bukn C*_( charyBuis C CC < T l |/ eel |R \\Peak: aa | = ce l Marble Cale-hornfels Pelitic hornfels, 09 ste {O fs e C mica ceo us BU) /mgh <% \ quartzite, and t & {LLL iLL; easd (~ schist 2’ az Micaceous quartzite and pelitic HG a hornfels Siliceous calc-hornfels ' ¢th | Metachert and andalusite-bearing pelitic hornfels § [ £4 o %) 4 ) a p ( f | ( ) (ee \A wh - aS < H \ (G N C Banded calc-hornfels and pelitic " o ) ( (((4 * flea Sta S R \ Moses o ltr) SAlites (|f CG - sy G2 ilt t ooS®E ! 2. 4s é hornfels yee , ( 16323 @//) +J Ta- _| |< - N &A. \ N \ \ ) as 7 x: ) S YC 5 PE Ul \ E., SS f | C 1) y) hG | \Doe Lake & J°o a kph/(Mb!) ,\// 4 K > t 1 A\ & I dads ( \ \t s & J V | AU C S )) IA wz \\ AC ) : \ Tn t s B) juke/ ‘ // ‘r eca C & \) PRE: \ esl \to IVAR f Ce- 2, \ ~d) I \ - ) J NAGA Y } AAP (Al 3/7 3 Z y || M R \ 3) Rt siv, T C2 Rar STES t A\ A3 F) hae -A] stp / FAT sols APPROXIMATE MEAN ' M/ ( PINXZ (g {t)) \I & mu N ~ Abeviie@s>~ ~ toy C mle eZ mus a)) PEOHINMHON 1994 Marble (Ca #1 Hf rnhs & PB MGs fers e a\ // a ots , ‘ An / SG lL AUL Ge a,,) | sa) isa a er PR LO o/ f os / U \‘ \ \ ( A ill ( { / \ »\1 jus C 2 NSP D r) PH l, \ \ S ha f L‘ U §] } C phm hen 12502 >WTE de|Cany6 U, \ ult s ) oo nt )| Amphitheator] ¥ hell -> ~ A sg) y [CC 5 Sme ) fi C U.ake Pelitic hornfels with interbeds "in deas A i \ N minty) 1h ) 5 ) \ (C \ «G ecco f iT s sual AF, of marble ¢ V’MtNXO 7 \ \ yo -G p J) ( j -,) Observation C \,,,A\\ Z A 7 7 = : ( \ ) {2362 ) [l/flf/lsfif ( \ MMIS wn S ) ‘O NM 'A} z j NW I ) , Z peak a C He -g r. s, Strike of folded beds Contact Anticline Dashed where approximately located _ Showing trace of axial plane. Dash- ro & \ P een econ enate ravers ed where approximately located Strike and dip of primary foliation in s))) Nxt >>>) Ca | AN p" § s Fault ___*__-____ granitic rocks (§ , ife aA )t akes 4 . Wind? CE s Ayo ven I[ - C Dashed where approximately located; % R sss oss) 7 K JN | PUG dotted where concealed Syneline a 4 a yo : / f NC zo) & AT, = i I1] S § ( AZ ) é Showing trace of axial plane. Strike of vertical primary foliation in % OLD/184g - § e f V (MAR/ON, PEA‘K‘)‘ ¥ T % as . 5 : INTEFUOR7‘GEOLOHG‘ICAL’ SUR‘VEY’. WASHN‘NGTON D. C.-1964-G6é2269 1189155000, I ate Dashed where approximately located granltlc rocks Vb?) Basse glap by Topsographic Division Geology by Paul C. Bateman, assisted by __ High-angle fault with searp so so o .S. Geological Survey, 1950; M. F. Carman and R. M. Campbell +. Dashed where approximately lo- ik d a R A essam R % of beds Strike and dip of foliation in gneiss «$0 modified 1963 cated; dotted where concealed. and cip of be P st € Includes a few low-angle normal {- 'a C ¥ 0A L - faults. Bar and ball on down- 0 aA GEOLOGIC MAP OF PART OF THE MOUNT GODDARD 15-MINUTE QUADRANGLE, CALIFORNIA o ay" SCALE: 1:62 500 2 1 £ 0 1 2 3 4 5 KILOMETERS AGP B f--- CONTOUR INTERVAL 80 FEET DATUM IS MEAN SEA LEVEL Strike of vertical beds PROFESSIONAL PAPER 470 PEATE 1 Strike of vertical foliatio n in gneiss Y LOWER PALEOZOIC(?) V QUATERNARY soy" CRETACEOUS TRIASSIC(?) AND JURASSIC O47» UNITED STATES DEPARTMENT OF. THE: INTERIOR (gaff) * « - GEOLOGICAL SURVEY © f u % R. 32 E. (WHITE MOUNTAIN, 1:125 000) MSi§ __ s e C : \§ 37°30 EXPLANATION O\ : Np a & $ Alluvial fill Dune sand Talus 5 S. s May be, in part, of Pleistocene age ; Qtu Undifferentiated till Qg oss " ~ Qof . Terrace gravels Older dissected alluvial fan and Qg;, youngest and lowest, may be of lakebed deposits Recent age Some beds may be of late Tertiary age $ 4 § VOLCANIC DEPOSITS £: g - Bishop tuff Qba, hard agglutinated tuff Qbp, basal layer of white angular pumice Qob . Basalt dikes, necks, and: dissected flows C May be of late Tertiary age RIVER it +080 -~ m_ 4 BM 4072 \ (BLANCO MTN.) Sewage f Disposal JRkm Mafic metavolceanic rocks _ Te Marble Calc-hornfels 1 I I t i i 20° Ate-{$53 p rest}, T. 7 5-p Lower Cambrian A Upper Precambrian or Lower Cambrian A t ~ \ yq's‘h‘gev pect 37°15 bos C: oT 4 @ ’ At py- Its - 3 2 Qt o WB ,-- (BIG PINE) 37°15 a Asics. INTERIOR-GEOLOGICAL SURVEY, WASHINGTON. D. C.-1964-Gez2269 R.34E. 118°30' [do 118°15 <9 Base map by Topographic Division Geology by Paul C. Bateman, assisted by _ ,. Contact, showing dip ~ US.‘ Geological Survey, 1950; : J. W. Reid and M. W. Ellis 4:70 Dashed where approximately located (900 modified 1963 v 006» onine, aes “(V *%, Fault, showing dip § ap Dashed where approximately located; wt dotted where concealed GEOLOGIC MAP OF THE BISHOP 15-MINUTE QUADRANGLE, CALIFORNIA : Ca cs. é High-angle fault with searp t Dashed where approximately lo- SCALE 1:62 500 Pr cated; dotted where concealed. 1% g Includes a few low-angle normal L re _ - 0 1 2 3 4 5 MILES fqults.Bar and ball on downthrown fi noo o APPROXIMATE MEAN side DECLINATION, 1964 I 1 6 0 1 2 3 4 5 KILOMETERS 40:22 SCH-H-H- Ht I al v - \ Fault breccia CONTOUR INTERVAL 80 FEET DOTTED LINES REPRESENT 20-FOOT CONTOURS DATUM IS MEAN SEA LEVEL Pelitic hornfels, Qbu, soft tuff with rounded pumice fragments UNCONFORMITY GRANITIC ROCKS Rocks similar to the Cathedral Peak granite Ke, quartz monzonite Kea, alaskite PROFESSIONAL PAPER 470 PLATE 3 Qyf Younger alluvial fan deposits May be, in part, of Pleisto- . cene age GLACIAL DEPOSITS ‘_‘Qtafi I Tahoe till ~- > Sof Sherwin and older tills Granodiorite of Coyote Flat Kt Tungstén Hills quartz monzonite Granodiorite of Deep Canyon May be an early marginal facies of the Tungsten Hills guartz monzonite Diorité, quartz diorite, and hornblende gabbro Includes some hybrid rocks of gramodiorite composition METAMORPHIC ROCKS IN SMALLER MASSES mic ace ous quartzite, and schist j PALEOZOIC -__ AND MESOZOIC MISSING INTERVAL ch iss Harkless formation Stippled where hornfelsed go Poleta formation €em: €ca Campito formation €cm, Montenegro member, stippled where hornfelsed €ca, Andrews Mountain member €CpEd Deep Spring formation {Ia—Cr Reed dolomite Wyman formation ~a» 1 Quartz veins and masses $ ° °. Anticline Showing trace of axial plane. Dash- ed where approximately located [f Syneline Showing trace of axial plane. Dashed where approximately located Sp.. ~.~ Overturned anticline Showing trace of axial plane and bearing and plunge of axis. Dashed where approximately lo- cated METAMORPHIC ROCKS OF THE SIERRA NEVADA MISSING INTERVAL 'BISHOP CREEK PENDANT Siliceous calc-hornfels SEDIMENTARY. ROCKS OF THE WHITE MOUNTAINS n a aa Overturned syncline Showing trace of axial plane and bearing and plunge of axis. Dashed where approximately located 50 Strike and dip of beds F385 Strike and dip of overturned beds + Strike of vertical beds © Horizontal beds p O4 Fossil locality NOTE: True color for Marble shown at Latitude 37°18" Longitude 118°28' V QUATERNARY LOWER PALEOZOIC(?) CAMBRIAN PRECAMBRIAN OR CRETACEOUS TRIASSIC (?) CAMBRIAN AND JURASSIC UNLTED SFATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY S Blacked, g é. y g ~ i wecond _(MmT. GopbaRo) les > a & Ress ihe - < S- Base map by Topographic Division U.S. Geological Survey, 1950; modified 1963 3s Round Mtn Z & (%. (x5 y Kt TaC UJ TCI * \ Z:Qob), /] Qtu ® \ | $2) s Naf * J cl T\ I Y ) O\)\' Buckshot )| | Prospect ( Lungsten Prospects Los 36} p dunt of Warren | t Lake | - saad < (-A INDIAN NATIONAL 7 > Bp X C % %F\ .-\ w F yA /I Ke " -E _ ~ - PA*. . \ A J Jl/A/ -- ‘_ m" ___. 4 (epe o. snl | I Qyb is LAV A u ‘ | 4 mms on red memes 370001 (MT. PINCHOT) \%¢’iteb.%se Creek | Rrospe OI shims INTERIOR-GEOLOGICAL SURVEY, WASHINGTON, D.C.-1964-G62269 R.34 E. SAIS Geology by Paul C. Bateman, assisted by M.-F..Carman, L. C. Clark, E. D, Jackson and R. L. Parker GEOLOGIC MAP OF THE BIG PINE 15-MINUTE QUADRANGLE, CALIFORNIA SCALE : 1:62 500 5 MILES 4 5 KILOMETERS pu- CONTOUR INTERVAL 80 FEET DOTTED LINES REPRESENT 20-FOOT CONTOURS DATUM IS MEAN SEA LEVEL TRUE NORTH APPROXIMATE MEAN DECLINATION, 1964 PROFESSIONAL PAPER 470 PLATE 4 EXPLANATION Qal 7 Qyf Alluvial fill Talus Younger alluvial fan May be, in part, of Pleistocene age Includes rock glaciers and Recent deposits moraines; ridge crests shown May be, in part, of Pleisto- semidiagrammatically cene age GLACIAL DEPOSITS VOLCANIC DEPOSITS Otu Qyb -- Undifferentiated till Tioga till : Crests of moraines and other glacial C79?“ of moraines and other glacial Basalt flows and cinder cones ridges shown by dotted lines ridges shown by dotted lines Cinders shown by strippled pattern. Probably of late Pleistocene age Qof Obra Older dissected alluvial fan and Tahoe till lakebed deposits Qtao, deposits of older advance, Or Some beds may be of late Tertiary age delineated locally. Crests of mor- aines and other glacial ridges shown by dotted lines Pleistocene Rhyolite south of Big Pine Stratigraphic position uncertain; may be of same age as Bishop tuff . Qob to a F Sherwin and older tills Basalt dikes, necks, and dissected flows s ; # Crests of probable morainal ridges May be of late Tertiary age shown by dotted lines UNconFoRrmiTty GRANITIC ROCKS y xo Granodiorite of Cartridge Pass Granodiorite of Coyote Flat Concentrically zoned from quartz diorite in the margins to gramo- diorite in the interior ( c ‘ Kf ’©\ap Felsic dikes and masses Chiefly aplite, pegmatite, and alaskite Finer grained quartz monzonites l Ke |Kea Rocks similar to the Cathedral Peak granite Kt Mafic dikes Kc, quartz monzonite Kea, alaskite Tungsten Hills quartz monzonite Pre-Cathedral Peak; precise age uncertain [___. Lamarck granodiorite E Granodiorite of MecMurry Meadows Concentrically zoned from quartz diorite in the margins to quartz monzonite in the interior Ktn Tinemaha granodiorite Kin Inconsolable granodiorite Diorite, quartz diorite, and hornblende gabbro Includes some hybrid rocks of granodiorite composition METAMORPHIC ROCKS METAMORPHIC ROCKS IN SMALLER MASSES Marble Cale-hornfels Pelitic hornfels, mica ceo us quartzite, and schist BISHOP CREEK PENDANT Siliceous calc-hornfels MESOZOIC "cth PALEOZOIC AND Metachert and andalusite-bearing pelitic hornfels phim" Pelitic hornfels with interbeds of marble MISSING INTERVAL SEDIMENTARY ROCKS OF THE WHITE MOUNTAINS €p Poleta formation €ca . Lower Cambrian Campito formation Andrews Mountain member \s5 Quartz veins Showing dip 55 Contact Strike and dip of beds Strike of vertical primary foliation in Dashed where approximately located Or granitic rocks y 12. a#)~ High-angle fault with searp, showing dip Strike of vertical beds + Dashed where approximately lo- cated; dotted where concealed. Includes a few low-angle normal 4 s s oo 4 faults. Bar and ball on down- Strike and dip of primary foliation thrown side in granitic rocks Horizontal primary foliation in %, _ granitic rocks 70 QUATERNARY CRETACEOUS LOWER PALEOZOIC(?) CAMBRIAN UNITED STATES DEPARTMENT OF THE INTERIOR | f PROFESSIONAL PAPER 470 - _ _ GEOLOGICAL SURVEY } PLATE 5 §. EXPLANATION AL 4 3 § i BISHOP CREEK PENDANT s Be A' As 12,000" 5 S 0 3 PRR 12,000" 8 § $ . f % sa % 3 op 3 . 33 Undifferentiated alluvial deposits al} $ 3 WHITE MOUNTAINS & ; - 3 10,000" fg (5 10,000" Micaceous quartzite and pelitic i VOLCANIC DEPOSITS hornfels # z 3 $ L. se o - & n a* fas I be "*/ e 'o R i F 8. & % 3 & _ Basalt flows and pmder cones < Sificeous calc-hornfels a . R a § ,Qbu Qba O Qbp s Cinders shown by stippled pattern Z > 5000' rex mas 3 5000" F5 U f & Qba ~ o Il A\ Fat $ - L 8 £: I 5 a #. § 3 t-. Oppi 8 Metachert and andalusite-bearing 8 t © < (P = £2 Bishop tuff pelitic hornfels 3 is 8 0 R, Qba, hard agglutinated tuff as at. T9. w Qbu, soft tuff with rounded pumice fragments cph - a SEA LEVEL SEA LEVEL Qbp, basal layer of white angular pumice E] s Banded calc-hornfels and pelitic 3 7 § 9% hornfels _. 0 5 "& C 3 5 6 az ® » * 12,000 - tks, al S § \\ __ Basalt dikes, necks, and dissected flows J _ Q‘ “8 o * C ® 6 s 4 o F 10,000 - "g UNCONFORMITY Marble 10,000" "$ W 3 $ 10,000" * ® C 4 C Kt T.t.t,.3 T gud. _- Key § . Kt GRANITIC ROCKS J x 7 x r § +++ +++++++ no _ _phm J tg" < + +++++ 4 ¥ tit, +\\¢ +/+ /+ f & it} cls wih } tf Coded .".'.l", ROUND VALLEY -| # +/ + a¢¥+ i', S$ E Pelitic hornfels with interbeds $ +0 + + A +/+ +f -$ hast. A Fa 1.4.3 £, ++?‘+ fs" Et + 4 ¥ 1 + xt VALLEY | Granodiorite of Cartridge Pass Granodiorite of Coyote Flat of marble J te (+ * " + + + + +«tl+ +i to ¢ 4 + ++ t % +) + + 1 + + i m t 4 § n ~ 0 G INTERVAL 5000' ++++++ 4++++++ +++++ f+++++++++¥4+ € g wake 7 F le . : +044) {# +54 . f cal Pals Finer-grained quartz monzonites © or t s + m 4 vic as SEDIMENTARY ROCK HE 4 ~ u | z Felsic dikes and masses WHITE MOUNTAINS Te h \ O| 0 : a I o w |e 9 | 9 ( ~ a A &i Cay , the ooc s = 23: i 8 ce" Rocks similar to the Cathedral Kt acs n" Ac" a. an Peak granite Kta & : Sher SEA LEVEL ® ;: SEA. LEVEL z SEA LEVEL Mafic dikes ke. daart; L f < Poleta formation Z tal a & . $ r * Tungsten Hills quartz monzonite -S T .$ n c o & Kca, alaskite K § ~ 23% s < o ®: l O Kta, albitized rock e [1d ~* S f fa S s U 8 U S 4 m f } e u 5 s & S 'o 8 & 3 Humphreys §% BASIN f 3 5 a S 7 3 #8 - $ . 7 : gs ' D C € 3 s 8 D o D t S . f U $ 3 ee S a € y , ssg CO 3 Campito formation 3 > - $ g ig] ¥ 8 G covoTE FLAT s [- o Lamarck granodiorite Round Valley Peak granodiorite < Cem. Montenegro member f ; =p 0 (ii % 3 : > 6 Oud, ; 2 M s = ( f: Km _- LI—LI €ca, Andrews Mountain member sos esas re ris y uly ..'s anal $ 5. + sy aie" 1" § «ta _ \_ mah 5 a \t=-- Qud lims re A 3 + + + ¢ c 5 aree & lls 10 gp o of t + + _+ 4 #, £ + 5+. +/ + + ++ + + I6. 4 . i mt“ V Granodiorite of McMurry O > i= ~ | op | e Uff y+ to + t -p 3 C t + ¢ + { % {if +{ + es K St" m oud MW - + t + €: + + K" + to4 + +. $4 +2 # + +b C A\ - Meadows» & -s z z * +o4+0+o+ * "E Hp ts Ts = \\ \ \\\ \ "3 A ig" #2 E g Deep Spring formation T 4T 3 \ \of \ 8 1: & & < # aa I i 8 m m & ® & y C € as owEns & VALLEY (> Tinemaha granodiorite $ o 5 5 a Q3 & 8 Wheeler Crest quartz monzonite L S f T 4 5000' _- o Qvb 8 -$ \- ae | Reed dolomite UQ 0 a C a caa § - Qud S LLJ x4 0 er. = 2 r C : n s LoL Inconsolable granodiorite x s t / - C Wyman formation C- z SEA LEVEL % Diorite, quartz diorite, and a ciare. f 3€ { $ hornblende gabbro 2 ~~ ca "z 5 [d - g : 5 g g pre METAMORPHIC ROCKS Dashed where approximately located 6 + © > $ #6 § i525 METAMORPHIC ROCKS IN SMALLER MASSES Tag ~* a - > A f a 9 - E/ Md 49 F' % £ y oa A phq G r J_ U Dashed where approximately located 13,000 F 13,000 € A & 13,0080 - . on z phg 5 & PINE CREEK PENDANT AND . ® C 9 ge gog ASSOCIATED SEPTA AND INCLUSIONS _ , & € un £ Marble Cale-hornfels Pellitic hornfels, 220 f $ | n S [= 35 F4 micaceous |W

( E LL. ; © : \ e | [;); A. - (0 Qud Rin 0 s , 3 B * | m z rage \ . ts. t Marble zn J ¢ Sartor. Qud ' 9 Cette - be 5000' 74 Z < 5000 > 5000" \ MISSING INTERVAL LW < U U se Ul a \ anu s S . n LL. 0 L z 3 SEA LEVEL SEA LEVEL SEA LEVEL s ® O $ U p i é) se s A 0 f 6 x S S O mj g & $3 3G, A Gil 13,000" g € g & § ~ 13.000" § 8 € $ CcoYOoTE FLat o ( m A E: Qud Qud Ase id S | > 2 kd sn & 10,000" s y |- 10,000" S, [= 5 nS ee F [ f £ O+ + ~- Gud 5 o + + t + + c ~ 1 z £ + + + + S m 3 + + % + + -S [- Z 'l +++ tty." g 5000' , o U £" r" ¢ + + I- 5000' £ u l 0 w J f x lu L. C A 5 @ - 0 < C- a 4 § C 3 (g = n SEA LEVEL 2 SEA LEVEL INTERIOR-GEOLOGICAL SURVEY, WASHINGTON, D. C.-1964-G62269 Geology by Paul C. Bateman GEOLOGIC SECTIONS IN THE MOUNT TOM, BISHOP, BIG PINE, AND PART OF THE MOUNT GODDARD 15-MINUTE QUADRANGLES, CALIFORNIA SCALE 1:62 500 2 5 KILOMETERS mmmmuuy PROFESSIONAL PAPER 470 UNITED STATES DEPARTMENT OF THE INTERIOR PLATE 6 GEOLOGICAL SURVEY EXPLANATION NARY Alluvial deposits L Granitoid rocks \ QQMQNKX ER Qh“\( Q“ Include granite stock in Poleta Canyon, diorite stock north of Coldwater Canyon, and smaller bodies of diorite between Coldwater and Silver Canyons J CRETACEOUS QUATER- ~ S Harkless formation @umitR® CGREEL Poleta formation Lower Cambrian CAMBRIAN } SONIA FORC ““XER CREXCX Campito formation Montenegro member above, Andrews Mountain member below. Hornfelsed shale adjacent to gramitoid rocks is shown by stippling Deep Spring formation Reed dolomite Wyman formation Upper Precambrian or Lower Cambrian PRECAMBRIAN OR CAMBRIAN GhNnNGH Contact Fault Dashed where inferred. Normal faults of small displacement are not shown SCS NOL 5 roLEn~h B &°00 comone ) I~) scale In FEET "CONTOUR INTERVAL 400 FEET --> DATUM Is MEAN $EA LeveL - S .o ale 3 b sesuion 19 NS x Y¥E8 fe INTERIOR-GEOLOGICAL SURVEY, WASHINGTON, D.C.-1964-G62269 DIAGRAM SHOWING AN-INTERPRETATION OF THE STRUCTURE OF THE WHITE MOUNTAINS IN THE BISHOP QUADRANGLE, CALIFORNIA PROFESSIONAL PAPER 470 PLATE 7 UNITED STATES DEPARTMENT O- THE INTERIOR GEOLOGICAL SURVEY 11845" ©7180: os R. 31.6 118°30" R. 32 C. R.:34 E: 118'15' 37°30 G INYO COUNTY MONO Co T.B S. 37°15" 118*45' EXPLANATION Alluvial deposits Olivine basalt c_ Bishop tuff and rhyolite south of Big Pine Granitic rocks Showing contacts between plutons. Dashed where approximately located Diotite and quartz diorite __I._ Kal Anticline Felsic dikes : 5 s Showing trace of axial plane Part of swarm along Pine Creek shown 60 diagrammatically by dashed lines , y % d as ¥ Strike and dip of primary foliation I so in granitic rocks fAtas A Overturned anticline #2 Showing trace of axial plane and bearing e a ed on} 25% Mafic dikes . and plunge of axis Strike of vertical foliation in granitic rocks + —‘_—‘+—’_ -- Horizontal foliation in granitic rocks Anticlinal warp axis in Bishop tuff 28" "% + I \ Metamorphic rocks and Cambrian T- -- __ sedimentary rocks , ——*——— Interpreted trends of foliation Syncline in granitic rocks Showing trace of axial plane sa '* Strike and dip of foliation in gneiss . | -- ~~. . . _;. .; _ $000:': *** ARA sf s. Contours on Coyote warp Contact a Dashed where approximately located Overturned syncline . Extrapolated across deeply eroded areas. Showing trace of axial plane. and bearing and Simte af vorbieal follatior in ghoiss Contour interval Toop feet --- nets mire ath plunge of axis o rake [i 760 a Fault, showing dip and horizontal component a ae +___ 2p tance oot a. f y ike and dips of 46) my of movement Synclinal warp axis in Bishop tuff girike and dips of g0!8!s values plus 1000 milligals Dashed where approximately located; dotted ¥ e L. Contour interval 2 milligals where concealed 70 22 Strikes of vertical joints e High angle faults with scarps Strike and dip of cleavage Gravity station Diagonal lines are on downthrown side Showing direction and plunge of lineation M resulting from intersection of beds and ae e e e ts ure t s oe 0 o 00 Bsa. GT rf 4 ALC caf, R foam pleavage Lineaments in granitic rock m Lines visible on aerial photographs; joints a ure h AK \\( , 73% was fa t ALT! Approximate position of major fault s aet Lineaments in alluvial deposits Strike of vertical cleavage 4000 defined by gravity x, a Lines visible on aerial photographs; faults Contours on base of Bishop tuff igs - A 7 of small displacement * Contour interval 100 feet Positions of geologlcgl sections A-A through Vertical ncation - sections of fence diagram s i.. Jx showing distribution of the Bishop tuff yaro (fig. 64), and geophysical sections W-W ' Borings for water, which intersected the base through Z-Z' (pl.1l1 and fig. 81) are § R has Fault breccia Horizontal lineation of the Bishop tuff shown 37°00 fms : 23. . $ 37°00 1180 30! INTERIOR-GEOLOGICAL SURVEY. WASHINGTON, D C.-1964-G62269 R 34 E 1180 15! STRUCTURE MAP OF THE MOUNT TOM, BISHOP, BIG PINE, AND PART OF THE MOUNT GODDARD 15-MINUTE QUADRANGLES, CALIFORNIA 10s? SCALE 1:62 500 m 1 ¥2 o 1 3 3 4 5 MILES G < L I E 1 5 0 1 2 3 4 5 KILOMETERS APPROXIMATE MEAN DECLINATION, 1964 GEOLOGICAL SURVEY MT MORRISON PENDANT EXPLANATION QTu‘ Quaternary and Tertiary deposits, undivided ) Granodiorite of Coyote Flat Fine-grained quartz monzonite and rocks similar to the Cathedral Peak granite Kt Tungsten Hills quartz monzonite TERTIARY Round Valley Peak granodiorite Lamarck granodiorite CRETACEOUS Tinemaha granodiorite Wheeler Crest quartz monzonite Inconsolable granodiorite Diorite, hornblende gabbro, and mafic hybrid rocks Gneiss in South Fork of Bishop Creek Metavoleanic rocks J Metasedimentary rocks. Correlative formations shown by patterns y PALEOZOIC TRIASSIC(?) Contact Fault Axis of anticline ce Axis of syncline Trace of planar foliation in granitic rock fee ¥. /—\\ //// Trace of beddmg or flow structure in ; metamorphic rocks § IDENTIFICATION OF STRUCTURES 1. S-Fold in south end of Pine Creek pendant 2. Lobes in north part of Bishop Creek pendant , 3. Faults in northeast lobe of Bishop Creek pendant ito 4, Upward-bowed strata along west side of northwest } lobe of Blshop Creek pendant - y ~~5. Bent strata in south part of Blshop Creek pendant ~> 6. Possible bight in contact between metasedlmentary and metavoleanic rocks f 7. Off-set of lithologically and probably stratigraphically correlative strata - TRUE NORTH APPROXIMATE MEAN «DECLINATION, 1964 " g7® oo' j 118 45' AND QUATERNARY AND JURASSIC 37°15" 118 °45' UNITED STATES DEPARTMENT - OF THE INFERIOR 118°30' PROFESSIONAL PAPER 470 PLATE 8 118°15' 27°30 PENDANT Kt BISHOP CREEK PENDANT 38. % " 118°30' INTERIOR-GEOLOGICAL SURVEY, WASHINGTON, D.C.-1964-G 62269 Geology by Paul C. Bateman MAP OF STRUCTURES ATTRIBUTED TO FORCIBLE EMPLACEMENT OF GRANITIC ROCKS BISHOP DISTRICT, CALIFORNIA 5 KILOMETERS 1 37°15" 37°00: 118"15' PROFESSIONAL PAPER 470 UNITED STATES DEPARTMENT OF THE INTERIOR PLATE 9 7 // Lr212P GEOLOGICAL SURVEY EXPLANATION ' Quartzose rock Includes quartzose tactite, silicified quartz monzonite, rock composed largely of quartz veinlets, and dikes and sills of quartz-feldspar rock Quartz monzonite Includes small masses of quartz diorite Scheelite bearing in part y Sp Marble Locally contains silicate minerals Biotite- quartz hornfels /7 12107 14112147 7 22/1" 721127 121414 RQ T " I | 7 T T SCALE IN FEET CONTOUR INTERVAL 50 FEET DATUM APPROXIMATE MEAN SEA LEVEL GEOLOGICALSURVEY, WASHINGTON, D. C:-1964-G62269 INTERIOR Geology by Paul C. Bateman and Lawson A. Wright BLOCK DIAGRAM OF PINE CREEK MINE, CALIFORNIA GEOLOGICAL SURVEY a PLATE 10 to 5 § $ 4 0 2 a -_ "A Near av -A > i- E he Southern extension $ 9 d £ 3 of Owens Valley § n 5 os z € #5 $ E 8, 0,000' - & > 4 B x 5 5 H €: $1 i $ g e o 20, & a 3 S A N J O.AQ U 1 -N ViAl Y 5 & # 3 S S¢-€5. 5 i 2 8 g B © 3 e € p 3 5 & 6 & 50 €s E v o r s) c. € € § a to 0 § c 0 € 0 55 £ 9 2 2 u Centenial! = .* § L z 9 & ® i o S Is 4 6 fal mg in 3 $ § p per Gentenia & f & 3 r 3 o % nm G m 5 £ o Flat $o & 2 |- < £ e w a R ® x L = 0 a 0 < C < e s 3 u siri maas X G a 1 Rep Ao dopest brs n' t R f 3 s- Aes cor: ele la bsa isin 8 r snp ost Y yA AA SE Gai sir aid / NA ' *s Panamint Valle a T= hin Co im" SEA LEVEL -'"ZT‘obtofLéfier'Pliéc‘ene'f."3" mas tela 2. l ( f ine f or' . /;<'\;-,,. mesin A7 * Bear, und_KIei_npeIl,| M moo, f : Fe Hs Geology east of Sierra Nevada after Jennings,(1958} with faults added according to Wayne E. Hall (oral communication) L 20,000 F L - 40,000" n SECTION FROM SAN ANDREAS RIFT EASTWARD ACROSS SAN JOAQUIN VALLEY AND SIERRA NEVADA TO PANAMINT VALLEY, CALIFORNIA 4 4 0 4 8 I12 MILES 735-925 O - 65 (In seperate volume) No. 10 UNITED STATES DEPARTMENT. OF THE INTERIOR P f PROFESSIONAL PAPER 470 20,000' SEA LEVEL |- 20,000 40,000' UNITED STATES DEPARTMENT OF THE INTERIOR ix; GEOLOGICAL SURVEY PROFESSIONAL PAPER 470 PLATE 11 m $ ws {o u_ t Weooo 6000 6 g- SURFACE ax a a 5000 a. ~ a > < "4 e - 4000 pj w « // = 5 a wi. |- 3000 FILL aw E u 2000 =~ > Z o < 0 / /C a 2 st). ow roinT 4 / W” LOW POINT ul < S f SEA LEVEL > g SEA LEVEL /////// / ////////////// # //// / // E & A 2 WIM 7 Section-along profile W=W ' from graticule analysis. Assumed ~ density contrast, 0.5 / W (We 0 & & -l < < s el fast ai AT Z < 3 LOW POINT z Low Point 0 Actual gravity along profile W- W ' --- Calculated gravity along profile W- W ' INTERPRETATION ALONG PROFILE W-W!' X 7 a (4 6000 7 |_ LJ Ho SURFACE /// 3 T4, —4000/ 490°“ P4 2 l; - 3000 */ AOOO - 2 E <2: "3 (+ 2 i 2. [|- 2000 * FILL BEDROCK 2000 - 5 25 = 9 ES |- 1000 //// i iste 1 2 9 J i- uu s é |- SEA LEVEL C SEA LEVEL {| z 3 £ *~. to # * _- 1000 / 1000 4 - ui < 2 > E P2 Low point Low roint "°- E < -4 < - 3000 / / 3000 4. < Section along profile X-X' from / // graticule analysis. Assumed i / // density contrast, 0.5 X X/ MILIGALS LOW POINT 30 Actual gravity along profile X-X ' 0---0 Calculated gravity along profile X-X ' MILIGALS LOW POINT 30 INTERPRETATION ALONG PROFILE X-X/' SURFACE FILL DROCK w -- LOW POINT iis Section along profile Y-Y ' from graticule analysis. Assumed density contrast, 0.5 ALTITUDE, IN THOUSANDS OF FEET ABOVE SEA LEVEL ALTITUDE, IN THOUSANDS OF FEET ABOVE SEA LEVEL MILIGALS Actual gravity along profile Y- Y ' O---0 Calculated gravity along profile Y- Y ' MILIGALS INTERPRETATION ALONG PROFILE Lines of profiles shown on plate 7 GRAVITY PROFILES AND INTERPRETED STRUCTURE SECTIONS 1 0 1 2 MILES 1. 1 1 1 | | | 735-925 O - 65 (In seperate volume) No. 11