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

摘要

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)_4Si_3], polybasite [(Ag,Cu)_(16)Sb_2S_(11)]-pearceite [(Ag,Cu)_(16)As_2S_(11)] solid solution, pyrargyrite [Ag_3SbS_3]-proustite [Ag_3AsS_3] solid solution, acanthite-argentite [Ag_2S], 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)_2S solid solution + sphalerite encapsulated in quartz and sphalerite indicate a primaiy depositional temperature of approx 325 deg C for a depth between 725 and 960 m below the inferred palaeosurface, which is in accord with fluid-inclusion data for higher elevations in the mine.