Exploration potential for sulphide-rich vein deposits in the Argentinean Patagonia

JOVIC, S.; GUIDO, D.; SCHALAMUK, I.

Colorado, USA.

Conferencia; SEG 2006 Biennial Conference “Wealth Creation in the Mineral Industry”; 2006

Society of Economic Geologist (SEG).

The Deseado Massif geological province is located in southern Argentinean Patagonia. The region is an important Au-Ag producer, with two active mines (Cerro Vanguardia and Martha), and there is also intense exploration activity in the area. This region is characterized by the presence of low sulfidation (LS) epithermal deposits that are spatially, temporally and genetically related to a complex, middle to late Jurassic bimodal volcanic event that was associated with tectonic extension. Cerro León deposit is located in the center of the Deseado massif, 40km northwest of Cerro Vanguardia, and is characterized by sulfide-rich vein mineralization. The veins are poorly exposed at surface and are characterized by the presence of grey quartz with cavities filled by limonite and minor sulfides, quartz-limonite veinlets, ferruginous siliceous breccias, and Fe-Mn oxide breccias. Some parts of the veins are represented by a high concentration of limonite, strong pyritization, red clays, supergene oxidation and alteration zones, forming a Fe-rich gossan. This weathering oxidation represents sulfide-rich mineralization at depth, where drill cores show a high concentration of sulfides, with values greater than 20 percent by volume and up to 90 percent in some veins. This sulfide-rich mineralization has an atypical geochemical signature composed of Sn, Cd and In, together with anomalies of Zn, Ag and Au, and also high contents of Cu, Mn, Pb, W and Bi. The Ag:Au ratio is 213:1. The veins, in addition to quartz, have a complex metallic mineralogy composed of acanthite, ferrokesterite, pyrite, arsenopyrite, sphalerite, In-rich sphalerite, galena, chalcopyrite, cassiterite, tetrahedrite, bournonite, freibergite, greenockite, hübnerite, ferberite, Ag-sulfosalts, Pb-Bi-Ag-sulfosalts, enargite, and Mn oxides. The geochemical signature, the complex sulfide-rich veins and the assemblages are new for mineralization in the Deseado massif and represent a variation from typical LS deposits in the region. The deposit could be preliminary defined as a polymetallic high-temperature epithermal deposits. This type of veins has attributes of intermediate sulfidation epithermal deposits, as well as Sn-Ag-base metals-rich LS deposits. Independent of their genesis, it is clear that these sulfide-rich veins have potential to have precious metals ore shoots and also to contain polymetallic ore (including the anomalous elements In and Cd). To find this type of sulfide-rich veins, it is recommended to make image satellite processing, then a detailed mapping of this oxidation zones, soil geochemistry, geophysics (geoelectric surveys), in order to identify Fe-Pb gossans with associated sulfide-rich ore shoots to define drill targets. This new style of deposit increases the mining potential of this metallogenic province and must be considered during future exploration of the region.