Genesis of the Florida Canyon Nonsulfide Zn Ores (Northern Peru): New Insights Into the Supergene Mineralizing Events of the Bongará District

Abstract

The Florida Canyon Zn deposit in the Bongará Province of northern Peru consists of sulfide and nonsulfide mineralizations within dolomitized strata of the Triassic Chambará Formation, a member of the Triassic-Jurassic Pucará Group. The nonsulfide mineralization, which represents one third of the total resource, formed by supergene alteration of Mississippi Valley-type sulfide bodies. The nonsulfide assemblages occur in stratabound or fault-related, discordant zones that mimic the shapes of the former sulfide zones. Two nonsulfide facies can be distinguished: facies 1 – red zinc ores, which are characterized by smithsonite, or hemimorphite-dominant bodies that formed by direct replacement of primary sulfide assemblages, and facies 2 – white zinc ores, which are characterized by masses of colloform smithsonite formed by replacement of wall rock. The facies are distinct in bulk chemical composition and stable isotope geochemistry. Facies 1 shows high concentrations of Zn, Pb, Fe, Ge, Mn, and As, whereas facies 2 shows only high Zn and Cd concentrations. Enrichments in Ge, which have been reported in other Zn deposits of the Bongará Province, are associated with hemimorphite, Fe hydroxides, and remnant sphalerite in facies 1. The δ13C and δ18O signatures of smithsonite in both facies suggest that meteoric waters infiltrating the precursor sulfide bodies were affected by kinetic fractionation and originated from multiple sources at different altitude.