Ore genesis at La Colorada Ag-Zn-Pb deposit in Zacatecas, Mexico

La Colorada, in Zacatecas State, Mexico is an epithermal Ag-Zn-Pb system hosted in Mesozoic calcareous sedimentary rocks overlain by Tertiary volcanic rocks. The dominant vein is associated with a fault system that accommodates Tertiary normal and strike-slip faulting. The ore consists of fahlore [(Cu,Ag)(10)(Zn,Fe)(2)(Sb,As)(4)S-13], polybasite [(Ag,Cu)(16)Sb2S11]-pearceite [(Ag,Cu)(16)As2S11] solid solution, pyrargyrite [Ag3SbS3]-proustite [Ag3AsS3] solid solution, acanthite-argoentite [Ag2S], and native silver; associated sulphides include galena, sphalerite, chalcopyrite and pyrite. The Ag:Sb of the bulk concentrate from the mine is 1.076 and the Ag:Pb is 0.088. Compositions of the assemblages fahlore pyrargyrite-proustite + sphalerite, and fahlore + polybasite-pearceite solid solution + (Ag, Cu)(2)S solid solution + sphalerite encapsulated in quartz and sphalerite indicate a primary depositional temperature of similar to325degreesC for a depth between 725 and 960 in below the inferred palaeosurface, which is in accord with fluid-inclusion data for higher elevations in the mine.