EMPLACEMENT AND MINERALIZATION OF THE SAN CRISTOBAL AG-ZN-PB DEPOSIT, SOUTHERN BOLIVIA

摘要

The Late Miocene San Cristobal Ag-Zn-Pb depositrnrepresents syngenetic and epigenetic mineralizationrnwith low- and high-sulfidation characteristics.rnGeology is characterized by barren dacitic ringrnfracture domes, mineralized resurgent rhyodaciterndomes, strongly altered and mineralized tuffaceousrnlacustrine sedimentary rocks, and an extensiverncrystal-lithic tuff debris apron. The ore body isrnhosted by intra-cauldron sedimentary rocks andrnbreccias. Fluid inclusions suggest that silver, lead,rnand zinc were transported as chloride complexesrnand precipitated by cooling in veins from <5 wt. %rnNaCl eq. Fluids at 170°-215° C. Silver associatedrnwith resurgent rhyodacite was transported as arnchloride complex and precipitated by increased H_2 Srnactivity or increased fluid pH.