Pingüino In-bearing polymetallic vein deposit, Deseado Massif, Patagonia, Argentina: characteristics of mineralization and ore-forming fluids

Abstract

The Pingüino deposit, located in the low sulfidation epithermal metallogenetical province of the Deseado Massif, Patagonia, Argentina, represents a distinct deposit type in the region. It evolved through two different mineralization events: an early In-bearing polymetallic event that introduced In, Zn, Pb, Ag, Cd, Au, As, Cu, Sn, W and Bi represented by complex sulfide mineralogy, and a late Ag-Au quartz-rich vein type that cross-cut and overprints the early polymetallic mineralization. The Indium-bearing polymetallic mineralization developed in three stages: an early Cu-Au-In-As-Sn-W-Bi stage (Ps1), a Zn-Pb-Ag-In-Cd-Sb stage (Ps2) and a late Zn-In-Cd (Ps3). Indium concentrations in the polymetallic veins show a wide range (3.4 to 1184 ppm In). The highest indium values (up to 1184 ppm) relate to the Ps2 mineralization stage, and are associated with Fe-rich sphalerites, although significant In enrichment (up to 159 ppm) is also present in the Ps1 paragenesis associated with Sn-minerals (ferrokesterite and cassiterite). The hydrothermal alteration associated with the polymetallic mineralization is characterized by advanced argillic alteration within the immediate vein zone, and sericitic alteration enveloping the vein zone. Fluid inclusion studies indicate homogenisation temperatures of 308.2 - 327ºC for Ps1 and 255 - 312.4ºC for Ps2, and low to moderate salinities (2 to 5 eq. wt% NaCl and 4 to 9 eq. wt% NaCl, respectively). δ34S values of sulfide minerals (+0.76 to +3.61 per mil) indicate a possible magmatic source for the sulfur in the polymetallic mineralization while Pb isotope ratios for the sulfides and magmatic rocks (206Pb/204Pb, 207Pb/ 204Pb and 208Pb/ 204Pb ratios of 17.379 to 18.502; 15.588 to 15.730 and 38.234 to 38.756 respectively) are consistent with the possibility that the Pb reservoirs for both had the same crustal source. Spatial relationships, hydrothermal alteration styles, S and Pb isotopic data suggest a probable genetic relation between the polymetallic mineralization and dioritic intrusions that could have been the source of metals and hydrothermal fluids. Mineralization paragenesis, alteration mineralogy, geochemical signatures, fluid inclusion data and isotopic data, confirm that the In-bearing polymetallic mineralization from Pingüino deposit is a distinct type, in comparison with the well-known epithermal low sulfidation mineralization from the Deseado Massif.