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I I i iI ,F il I '-iI i| ,!..I J *I *I i' i | !I I ~| ASARCO I LIBRApv I I I' I MOJAVE PROJECT I A Regional Tectonic-Metallogenic Study of Parts of Bakersfield, Los Angeles, Trona, San Bernardino, I Santa Ana, Kingman, Needles, Salton Sea, and El Centro l ° x 2° sheets, southern California I I Prepared by I Robert T. Wilson, William A. Rehrig and C. Jean Cone I Applied Geologic Studies Inc. I August, 1983 I {..I I I ASARCO I LIBRARY I TABLE OF CONTENTS il i VOLUME I PAG__..EE SUMMARY AND CONCLUSIONS ....................... ] II RECOMMENDAT IONS ........................... 6 i TECTONIC OVERVIEW .......................... I0 L ITHOTECTON IC UNITS ......................... 21 METALL I ZAT I ON ........................... 75 i Overview and Regional Distribution ................ 76 District Focus .......................... 83 MetaI]ization Sumary ............. 152 i Permissive Terrains'&'Geo;o;ic t~o~le;s ............ 153 i REGIONAL GEOCHEMISTRY ........................ 171 EXPLORATION - TARGET DELINEATION .................. 181 i REFERENCES CITED .......................... 199 ! VOLUME II References used in compi]ing CDCA computerized data base ! used for Mojave Desert Project .................... Appendix 1. GEOREF Listings for Mojave Desert Project .............. Appendix 2. I I I I I LIST OF FIGURES, PLATES AND OVERLAYS PAGE Figure I. Detachment faulting in southeastern California ......... 22 2. Upper Precambrign and lower Cambrian strata .......... 30 . Correlation of strata in San Bernardino Mountains with strata in the Nopah Range and Providence Mountains ......................... 34 . Correlation of miogeoclinal strata in San Bernardino Mountains to sections in the eastern Mojave Desert . ....... ..... 35 . Stratigraphic columns of upper Precambrian-Cambrian rocks in the San Bernardino Mountains, California ..... 39 . Present distribution of middle Early Permian deposi- tional provinces in the western U.S. .......... 42 • California and Nevada in the Permo-Triassic • • o • • • • • • • 44 8. Pale•geographic map illustrating relationships of eolian, fluviatile and, eolian-volcanic facies during Rhaetian to Sinemurian time ............. 53 • Stratigraphic columns of Cowhole and Mescal Range ....... 54 lO. Correlation of Mesozoic Sedimentary rocks across the Moj ave Desert ....................... 63 II. Colosseum Breccia Pipe Complex, Clark Mountain 89 12. Generalized geologic map of the Lava Mountains and vicinity .......................... 143 13. Ord Mountain district showing areas of priority ........ 150 14. Distribution of the Pelona-Orocopia schist and Vincent-Chocolate Mountains thrust system ......... 154 15. Generalized cross-section of the Vincent-Chocolate Mountains thrust zone ................... 155 16. Model for mineralization in the Upperplate rocks of Vincent-Chocolate Mountains thrust .... ; ...... n~ 1 59 17. Settings of Mineralization in the metamorphic I core co.mplexes ....................... 168 I I LIST OF FIGURES, PLATES AND OVERLAYS ! Continued P 1ate 1 L i t hotecton i c Map-Mojave Desert Proj ect 2 Mountain Ranges-Mojave Desert Project i 3 Sources for the Geologic Map Overlay Geographic Features I Major Tectonic Features Major Tertiary Tectonic, Intrusive and Sedimentary Feat u re s ! 4 Precious Meta|s 5 Other Metals 6 NURE Geochemical Anoma]ies 7 Mining Districts, Exploration Targets .and Withdrawn i Areas Tertiary Intrusive Rocks ,i ! I ! il I ! I I I I ! I I SUMMARY AND CONCLUSIONS The Mojave study area is a known gold province• Within the study area, two districts have had historical production in the 750,000 to l million ounces of gold; five others have produced greater than 150,000 ounces of gold; and several more have had production in the 50,000 to lO0,O00 ounce range• Since the deregulation of gold prices in 1971, the rapid rise in the world gold price has resulted in renewed activity and several significant recent discoveries in old producing districts. These include: Deposit Size Grade l • Mesquite (Goldfields) 50-70 million tons 0.05-0.07 opt Au 2. Colosseum (Draco & 8 million tons (proven) 0•05 opt Au Amselco) 8-I0 million tons (prob- 0•03-0.05 opt Au able) 3. Picacho (Chemgold) 6-7 million tons 0.05 opt Au 4. American Girl Unknown 300,000 oz. contained (Newmont) Au. Expioration continuing. 5. Black Hawk Reports circulate that a deposit containing about lO0 million tons grading 0.03 opt Au has been delineated in this district. 6. Hart (Freeport & Deposit is not yet explored but has ear- Noranda) markings of a major disseminated deposit. From such "statistics," we can with confidence state that the gold potential for the Mojave study area ~s justly established. The gathering and incorpora- ! tion of fairly oetailed structural and lithostratigraphic information from ' -t all scales of geologic reference material onto a 1:250,000 base map has i! provided a better understanding of the metallogenesis and mineral potential L'- of the region• This understanding is manifest in two general ways: a. Correlation of lithostratigraphic units across quadrangle boundaries permitting a coherent understanding of the tectonic evolution of the entire region. b. Establishment of regional structural and lithologic controls of gold metallization in the region in a way unachievable through the use of smaller scale maps. Computerized metals data bases (i.e. Terradata, CRIB) were used to integrate large quantities of metal occurrence data and NURE HSSR geochemistry into composite overlay maps of the same scale as the lithotectonic map. Integration of these da~a with the lithotectonic map, coupled with def,'led analysis of same has provided important insights into the understanding of regional metallogenesis in the Mojave study area. More importantly this process has facilitated the development of exploration models that we feel offer the best chances for finding undiscovered deposits in the region of the size to interest most clients. Important findings resulting from the data integration for the Mojave reqion include: a. 'Recognition of the previously unknown importance of the Vincent- Chocolate Mountains thrust-system to the localization of certain large bulk tonnage gold deposits and several mining districts. Examples are thought to include the newly discovered Mesquite deposit, the Picacho deposit and the Yellow Aster Deposit. These deposits as well as abundant occurrences strung out along this structural zone are believed to warrant intense exploration for similar, yet to be discovered~ deposits. :| b. Establishment of the importance of Miocene rhyolitic intrusive and volcanic rocks to the regional proliferation of metals occurrences, i| I I in the northern half of the study area. Recognition that certain permissive terrains into which the rhyolites were intruded offer settings similar to ones which host hotspring related disseminated gold deposits in nearby regions. c. Determination that the impressive northwest-striking wrench fault system (i.e. Helendale fault, Linwood fault, etc.) that traverses the western ;I and central portions of the Mojave and gives much of this region its present- day physiography has had little or no effect on metals distribution (except I for possible offsets). Formation of the stress field that produced this ! system may have had some influence on the localization of some of the Miocene rhyolites (i.e. dike direction), but the faulting occurred largely after I regional metallization. d. Recognition that thrust faulting other than the Vincent thrust has I been important in localizing some gold deposits. Several different ages of I thrust faultingare recognized in the region ranging in age from possibly as old as the Antler orogeny (Devonian) to as young as Miocene in the San Bernadino Mountains. e. Identification of an early Mesozoic