High-temperature, carbonate-hosted Ag-Pb-Zn(Cu) deposits of northern Mexico

The high-temperature, carbonate-hosted Ag-Pb-Zn(Cu) deposits of northern Mexico occur in thick carbonate-dominant Jurassic-Cretaceous basinal sedimentary sequences floored by Paleozoic or older crust. Altered and/or mineralized volcanic and intrusive rocks of Tertiary age are found in all but three of the districts; mineralization apparently occurred during a restricted period 47 to 26 my ago. The deposits are characterized by irregular ore lenses that commonly reveal strong structural controls and are stratigraphically discordant. Orebodies are of three principal morphological types: mantos, chimneys, and pods and are composed of massive sulfides and/or calc-silicate skarn. Despite the variations between ore types, major similarities are seen in structural controls, host-rock characteristics, and sulfide mineralogy. Geochemical data for the deposits are sparse but indicate strongly contrasting conditions among some of the major districts. Fluid inclusion data indicate temperatures in the range 200° to 500°C and salinities ranging from 1 to 60 equiv wt percent NaCl. The hotter, more saline, solutions are typically from skarn zones. It appears that the spectrum of mineralization styles shown by these deposits represent differing responses to variations in intrusive associations, depth of emplacement, host-rock characteristics, and geochemical evolution of the individual systems. -from Authors