Low temperature, late Zn-Pb-(Bi-Ag-Cu) mineralization and related acid alteration replacing carbonate rocks at Cerro de Pasco, Central Peru

摘要

Carbonate-hosted Zn-Pb-(Bi-Ag) ores presently being mined from areas at the eastern part of the open pit at Cerro de Pasco, Peru, contain Fe-poor sphalerite, galena, and pyrite, and display argillic to advanced argillic alteration (including kaolinite, dickite, and the alunite supergroup minerals hinsdalite and svanbergite). This Zn-Pb-(Bi-Ag) mineralization is structurally controlled and shows zoning. Cores rich in Cu grade outwards successively to pyritic zones rich in Bi-Ag-Sb (with matildite), sphalerite-galena ores, and to hematite, magnetite, siderite-rich and Mn-Fe-Zn carbonates. Crosscutting relationships indicate that the Fe-poor sphalerite stage postdates the higher temperature, Fe-rich sphalerite-galena ores spatially associated with pyrrhotite pipes long mined at Cerro de Pasco underground and in the central part of the open pit. It is proposed that the same hydro-thermal stage characterized by high sulfur and oxygen fugacities and low temperatures related to E-W trending enargite veins in the western part of the open pit is responsible for the Fe-poor sphalerite-bearing Zn-Pb-(Bi-Ag) mineralization in the eastern part of the deposit.