Platinum-group elements in porphyry copper deposits: a reconnaissance study

Sulphide and flotation concentrates from 33 porphyry copper deposits have been investigated for platinum-group elements (PGE), Au, Cu and platinum-group minerals (PGM). The major sulphides in the samples studied are chalcopyrite and pyrite. Bornite is less frequent and molybdenite occurs in traces only. PGM (merenskyite, sperrylite and an unidentified Pd-Sb telluride) have been found as inclusions in chalcopyrite. Pd and Pt are present in concentrations above the analytical detection limit (>8 ppb) in 70% respectively 30% of the deposits studied. The contents of Os, Ir, Ru and Rh are below detection limits in all samples. The analytical results show that 7 deposits (six of island are and one of continental margin setting) reveal relatively high Pd contents (130-1900 ppb) which are associated with high Au contents (1-28 ppm). In five of them discrete PGM can be identified in accordance with elevated levels of Pd. Correlations of Au, Pd and Pt point towards a common origin. Even though the data base is relatively small, a trend is obvious, suggesting that Au-rich island are porphyry copper deposits might host more Pd and Pt than the continental margin type ones. Other aspects of intrusive rocks, such as geological age, chemical composition and magma type do not seem to influence PGE contents.