Geochemistry and mineralogy of Platinum-group elements in the Ransko gabbro–peridotite massif, Bohemian Massif (Czech Republic)

The Ransko gabbro–peridotite massif in Eastern Bohemia is a strongly differentiated intrusive complex of Lower Cambrian age. The complex hosts low grade Ni–Cu ores mainly developed close to the contact of olivine-rich rocks with gabbros, in troctolites and, to a much lesser extent, in both pyroxene and olivine gabbros and plagioclase-rich peridotites. The ore zone is characterized by strong serpentinization and uralitization. The total Ni + Cu locally reaches up to 4 wt%. Anomalous concentrations of platinum-group elements (PGE's) (maximum 532 ppb Pd, 182 ppb Pt, 53 ppb Rh, 15 ppb Ru, 41 ppb Ir) were detected in samples of Cu–Ni and Ni–Cu ores (maximum 2.63 wt% Ni and 2.31 wt% Cu) from the Jezírka orebody. The main ore paragenesis includes pyrrhotite, pentlandite, chalcopyrite, cubanite, pyrite, magnetite, mackinawite, valleriite, ilmenite and sphalerite. During this work, michenerite, froodite, sperrylite, gold, native bismuth, altaite, tsumoite, hessite, an unnamed Bi–Ni telluride, cobaltite–gersdorffite and galena were newly identified. The host rocks originated through partial melting of a slightly depleted mantle source with noble metals scavenged from this primitive magma prior to the development of these rocks.