The Pb-Zn-Cu-Ag deposits of the Granadena Mine, San Francisco del Oro-Santa Barbara district, Chihuahua, Mexico

Mid-Tertiary polymetallic quartz sulfide vein deposits of the San Francisco del Oro-Santa Barbara district are among the largest Pb-Zn-Cu-Ag deposits in Mexico. The veins of this district are hosted by the Cretaceous Parral shale. Vein formation occurred in at least four distinct stages that define an unusual paragenetic sequence when compared to similar systems. Early massive sulfide veins are cut by veins rich in calc-silicates, quartz, and late sulfides. This group is cut by two stages of postore quartz-fluorite-calcite veins with minor sulfides. Early sulfides and late calc-silicates represent a paragenetic sequence which is the reverse of that normally observed in systems containing calcsilicates and sulfides. The variable temperature and salinity found in fluid inclusions, the distinct mineralogic differences observed between vein stages 1 and 2, and the variable age relations between veining and igneous activity suggest that the deposits of the San Francisco del Oro/Santa Barbara district were probably emplaced during several episodes and that these ores may represent the superposition of at least two distinct hydrothermal systems. -from Authors