MINERAL CHEMISTRY OF THE BI-AG-PB-FE-CU-SB-ZN SULFOSALTS FROM VETIFORM STRUCTURE MINERALIZATION, IBAGUE, COLOMBIA: A POSSIBLE MID-TEMPERATURE LOW TO INTERMEDIATE SULFIDATION SYSTEM

This study is an approach to the La Veta mineral occurrences that lie on the eastern flank of the Colombian Central Cordillera, NE of Ibague city. Quartz ± carbonate veins with Zn-Fe-Pb-Cu-Sn sulfides and Pb-Bi-Ag-Cu-Sb sulfosalts represent these occurrences. These structures are hosted by the Tierradentro Gneisses and Amphibolites (Permian-Triassic) and the Ibague Batholith (Late Jurassic) and develop local alteration halos of short extension. The current study means the first research focused on this type of mineralization within the area. Several veins were analyzed through petrography, mineral chemistry (EPMA), reflectance spectroscopy (SWIR), and geothermometry (stannite-sphalerite and fahlore). It was possible to characterize many Ag-Bi-Pb sulfosalts (matildite, ourayite, vikingite, eskimoitite, treasurite, arcubisite, gustavite, and benjaminite), some minerals from the tetrahedrite-freibergite series, base metals sulfides, stannite, and native metals (gold and bismuth); also, multiple physicochemical features of the fluids were constrained. The alteration assemblages include muscovite, kaolinite, illite, sericite, dickite, chlorite, and epidote, indicating a neutral to slightly acid pH. Three main events were recognized in the system: (1) an early event with high Ag-Bi-Pb-Sn-Au, mid-temperatures (ca. 290°C), and conformed mainly by quartz, carbonate, pyrite, chalcopyrite, sphalerite, pyrrhotite, stannite, galena, Ag-Bi-Pb sulfosalts, bismuthides, tellurides, electrum, and native bismuth; (2) a mid-event dominated by pyrite, sphalerite, galena, and chalcopyrite related to sericite, muscovite, titanite, and clay minerals; (3) a late event rich in Cu-Ag-Sb, with temperatures lower than 225 °C, and characterized by the introduction of small quantities of quartz, carbonates, fahlores, and chalcopyrite within the structures. According to the results, the veins display typical characteristics of a mid-temperature low to intermediate sulfidation epithermal system, which evolves to intermediate sulfidation and low temperature. The La Veta mineralization is consistent with magmatic-hydrothermal deposits related to Jurassic intrusions elsewhere in the Colombian Andes.