Trace element contents in bornite, chalcopyrite and pyrite (LAICP- MS) from Miocene porphyry copper-gold deposits from Metaliferi Mountains, Romania: Trace elements in sulfides from porphyry Cu-Au deposit

Abstract

In porphyry systems, valuable elements such as Au, Ag, Te, Se and Bi are found in trace contents associated with Cu and Fe sulfides. The relations between sulfide and the trace element contents, as well as the role of physicochemical factors in the uptake of different trace elements are still being assessed. This study focused on understanding how these elements are concentrated in selected sulfides (pyrite, chalcopyrite and bornite) and on the relation between the measured trace element composition of these sulfides and the hydrothermal alteration types in six porphyry deposits from Romania: Roșia Poieni, Bucium-Tarnița, Colnic, Rovina, Valea Morii and Bolcana. Based on LAICP-MS micro-analytical data, bornite is revealed as the main host for Bi (1077ppm), Se (810ppm), Ag (312ppm) and Te (43.73ppm). Chalcopyrite is also relatively rich in Se (199-403ppm), Ag (1.88-49.97ppm) and Te (1.95-36.06ppm). Pyrite is enriched in Co (98.81-704ppm), Ni (3.81-20.68ppm), As (2.13-166ppm), Se (24.65-729ppm) and Te (0.99-11.75ppm). These elements occur in the host sulfides as solid solution and as mineral microinclusions. Gold content is <0.2ppm in both Cu-Fe sulfides and pyrite. There is no significant variation in trace element ratio in chalcopyrite (Se/In) and in pyrite (Co/Ni, Co/Cu, Ag/Co) when comparing results from potassic-altered with chloritic-sericitic altered samples. Based on trace element results and micro-textural features of studied minerals, we suggest that these elements were initially incorporated in the crystal lattice during the potassic alteration and the overprinting of chloritic-sericitic alteration caused the exsolution and redistribution of trace elements within their host minerals