Cerro León Polymetallic (Sn-Cd-In-Zn-Ag-Au) Epithermal Vein Deposit,

JOVIC, SEBASTIÁN; GUIDO, DIEGO; SCHALAMUK, ISIDORO

Keystone, Colorado, USA

Conferencia; SEG 2006 Biennal Conference; 2006

Society of Economic Geologists

Cerro León deposit is located in the central part of the Deseado Massif, 40-km northwest from Cerro Vanguardia. This deposit is composed of more than twelve NW WNW strike structural controlled quartz veins that are hosted in an atypical lithology for the DM, Triassic continental sedimentary rocks and lower Jurassic epi-volcaniclastic rocks, that are intruded by lower Jurassic subvolcanic intermediate to basic rocks that presents as sills and andesitic porphyries.The veins are poorly exposed in surface and are characterized by the presence of grey to white quartz with cavities fill with limonite and minor sulfides, quartz-limonite veinlets, ferruginous silica breccias and Fe-Mn oxide breccias. Some parts of the veins are represented by a high concentration of limonite, an important pyritization, red clays and oxidation and alteration zones, similar to Fe-rich gossan. Quartz textures are massive, crustiform banding, with important comb and cockade textures and minor colloform and lattice bladed textures. At depth, these veins are characterized by three mineralization pulses. The first one comprise veinlets and breccia with fine white to grey quartz and with massive texture, the second pulse has a variable degree of sulfide content (5 to 90% in volume), banding and cockade and the third is characterized by thick crystalline quartz with comb texture and breccia with Fe-rich silica and Fe-Mn oxides. The hydrothermal alteration is confined to the proximity of the veins and it is represented by silicification, argillization (illite and kaolinite), sericitization and pyritization. In some veins, the second pulse is formed by a concentration of sulfides (up to 90% in volume) and present a complex sulfur-rich mineralogy (Fig. 1-C). This mineralogy association is represented by pyrite, arsenopyrite, chalcopyrite, sphalerite, kesterite, cassiterite, stannite, wolframite (hübnerite-ferberite), Ag-Pb-Bi sulphosalts (possibly new minerals), freibergite, acanthite, In-rich sphalerite, tetrahedrite, enargite, galena, bournonite, greenockite and wurtzite (Fig. 1-D and E).The geochemical signature is characterized by the anomalous presence of Sn, Cd and In, together with anomalies of Zn and Ag, and also high contents of Cu, Mn, Pb, W, Bi and Au. The Ag:Au ratio is 213:1. In table 1 the geochemical values are summarized and compared with mineralized veins that represent different types of LS mineralization of the DM. The complex mineralogy and the geochemical signature present in the mineralization, represent a new mineralogical assemblage and a new metallogenic association for the DM mineralization.Deeper quartz textures, differential and unique host rocks, a possibly basic to intermediate magmatic source characterize Cerro León mineralization. The high content of sulfides, the complex sulfide mineralogy and the geochemical signature clearly differ from LS DM mineralization. The abundance of a thick comb quartz texture, the presence of higher temperature metals and the higher Ag:Au ratio could be related to a higher temperaturemineralization, which is in agreement with the lower relative contents of shallow epithermal elements such as Au, Sb and Hg The modeling of the deposit is one of the main objectives of the PhD, but the deposit could be preliminary defined as polymetallic high-temperature epithermaldeposits. This type of veins have some attributes of “carbonate-base metals-Au” or polymetallic Au-Ag veins” of Corbett (2002) or the “Sn-Ag-base metals-rich LS deposits” of White & Poizat (1995) or the variation into high sulphidation deposits recently proposed by Hedenquist et al. (2004). Independently of its genesis, it is clear that these sulfide-rich veins have potential to have precious metals ore-shoots and also to add the polymetallic ore (including the anomalous elements In and Cd) into the economical minerals. This new style of deposit increases the mining potential of this metallogenic province and must be considered during future exploration duties in the region.