Geologic setting of Miocene volcanogenic gold mineralization near the western margin of the Colorado River extensional corridor--Eastern Mojave Desert, California and Nevada

The importance of the volcanotectonic environment to the origin of synvolcanic gold mineralization in areas of crustal extension is of fundamental importance in economic geology. The Castle Mountains--Lanfair Buttes--Hackberry Mountain area in the Eastern Mojave Desert is ideally suited for developing models linking gold mineralization to volcanic and structural processes. The Hackberry Mountain volcanic sequence (HMV) is about 25 km southwest of the Castle Mountains volcanic sequence (CMV) and the Lanfair Buttes volcanic sequence (LBV) occurs between as isolated outcrops in Lanfair Valley. The area contains significant gold mineralization associated with adularia-sericite alteration ofvolcanic rocks, including Viceroy Precious Metals' Castle Mountains Mine, in the southern Castle Mountains; a world class gold mine composed or six deposits containing over 2 million ounces (62,000,000 g) of pre-mine reserves in the ground.; CMV isotopic analyses are consistent with lithospheric mantle origins for three separate stages of mafic parental melts each modified by commingling with crust ({dollar}varepsilon{dollar}Nd = {dollar}-{dollar}4.5 to {dollar}-{dollar}9.9; {dollar}sp{lcub}87{rcub}{dollar}Sr/{dollar}sp{lcub}86{rcub}{dollar}Sr = 0.706 to 0.709; {dollar}sp{lcub}206{rcub}{dollar}Pb/{dollar}sp{lcub}204{rcub}{dollar}Pb = 18 to 18.9). The largely andesitic postmineralization Piute Range volcanic rocks, which border the CMV on the east, are the third stage and uppermost mafic melts, and have the most lead-enriched source ({dollar}sp{lcub}206{rcub}{dollar}Pb/{dollar}sp{lcub}204{rcub}{dollar}Pb = 18.9). CMV Hart Peak (HP) and Linder Peak rhyolites retain some lithospheric mantle signature but are interpreted as largely crustal melts ({dollar}varepsilon{dollar}Nd = {dollar}-{dollar}7 to {dollar}-{dollar}8.1; {dollar}sp{lcub}87{rcub}{dollar}Sr/{dollar}sp{lcub}86{rcub}{dollar}Sr = 0.708 to 0.710; {dollar}sp{lcub}206{rcub}{dollar}Pb/{dollar}sp{lcub}204{rcub}{dollar}Pb = 18 and 18.3). Faulting and structural basin formation accompanied each of the three major eruptive series and these structures provided controls for mineralization as well as magmatism.; HMV gold mineralization (GM, about 17 Ma) is possibly older than CMV gold mineralization (GM, about 15 Ma). HMV-GM was late in a phase ofrenewed volcanism(LP) and CMV-GM was early in a similar phase ofvolcanism (HP). The HMV rocks of Lucky Penny pheno-latite-dacite (trachydacite-trachyandesite) and the CMV rocks of Hart Peak pheno-latite-dacite(trachydacite-trachyandesite) are closely associated both spatially and in age with gold mineralization.