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Geologia e petrologia da Mina de Ouro schramm (Gaspar - SC)

2001; Sociedade Brasileira de Geologia; Volume: 31; Issue: 3 Linguagem: Inglês

10.5327/rbg.v31i3.942

2317-4889

João Carlos Biondi, Nilton D. Franke, Paulo R. S. de Carvalho, S. Villanova,

Geophysical and Geoelectrical Methods

The highlights of the Schramm gold mine are its position inside a high-angle shear zone and the association of gold with nickel, arsenic and cobalt sulfides in massive veins of siderite-ankerite (dolomite). The quartz-carbonate lodes are not sheared or deformed. They are hosted by gneisses and granulites with intense hypogenic alteration (carbonatization, cloritization, sericitization and silicification). Gold is found free or inside sulfides only in the carbonates lodes, with grades varying from 500 to 2,300 ppm. Together with the gold there is silver (150 to 300 ppm), arsenic (0.15 to 0.60%) and nickel (0.01 to 1.4 %). The ore also presents Zn (250 to 1,600 ppm), Pb (100 to 850 ppm) and Co (40 to 750 ppm). The amounts of Sb, Te, Se, W, Mo and Bi are very low. The quartz veins from the lodes show gold grades below 1 ppm and of As, Zn, Pb, Ni, Cu, Co, Mo, Te and Bi between 1 and 50 ppm. Outside the mineralized zones the gold grades are below 50 ppb and the other elements grades are greater than in mineralized zones, varying from 10 and 900 ppm. Rarely rocks with hypogenic alteration have gold and its presence in grades higher than 50 ppb does not increase the grades of the other elements, that vary from 1 and 200 ppm. The total amount of sulfide is about 0.5% of the rock volume. The sulfide paragenesis has galena (rare), chalcopyrite (little), arsenopyrite (very rare), sphalerite, nickel-cobaltiferous pyrite, pyrite, siegenite-violarite, millerite, gersdoffite, covelite and one unknown Ni-Fe-Co sulfo-arseniate with formulae (Co, Fe,Ni) 7 yx() As y (m S fi (KK| , optically similar to gersdorfite, but distinguished by its cream-gray color. The structural formulae calculation shows that gold contains 27.5% of silver and that siegenite is an iron-rich variety, transitional to violarite.