Trace element concentrations in porphyry copper deposits from Metaliferi Mountains, Romania: A reconnaissance study

Abstract

There are fifteen Miocene intrusions with porphyry copper mineralization in the Metaliferi Mountains, Romania; most are associated with epithermal Au–Ag (±Te, Bi, Se, Ge) vein systems. The investigation of fifty samples from six deposits (Roşia Poieni, Bucium–Tarniţa, Colnic, Rovina, Valea Morii and Bolcana) indicated bulk rock mean values of 0.16–0.88ppm Au, <50ppm Mo, 0.02–0.35ppm Re, 0.06–0.6ppm In, 1.3–3.3ppm Ag, 0.23–1.17ppm Bi, 3.2–5.5ppm Se, 2.4–3.3ppm Ge, and 2.6–18ppm Te. Trace element analyses by electron microprobe suggest that part of the Au, Ag, As, Te and Se may occur as fine-particle inclusions hosted within common sulfide minerals (pyrite, chalcopyrite and bornite). Measured concentrations range from below the minimum limit of detection to as much as 1430ppm Au, 530ppm Ag, 1920ppm Te, 10,500ppm As and 2620ppm Se in pyrite, 970ppm Au, 1180ppm Ag, 1000ppm Te, 410ppm As and 420ppm Se in chalcopyrite, and 920ppm Au, 4830ppm Ag, 1470ppm Te, 4230ppm Se and 1540ppm Bi in bornite. Gold is concentrated preferentially in pyrite, while silver is consistently high (>1000ppm) in bornite. In the porphyry-type mineralization, galena forms microinclusions in pyrite, chalcopyrite and bornite, and contains up to 3750ppm Ag, 17,380ppm Se, 1570ppm Ge and 780ppm Te. Galena and pyrite from the epithermal mineralization in the Măgura–Bolcana–Troiţa system contain concentrations of Ag and Se ten times lower than in the same minerals from the porphyry copper mineralization. The present data show that Te is a significant trace element in the potassic zone of the investigated porphyry systems. The data also shows that this does not correlate with the presence or absence of ophiolitic basement, or with variation in the chemistry of the host intrusions. Tellurium enrichment in porphyry-type deposits of the Metaliferi Mountains supports their genetic relationship with the spatially associated epithermal systems.