Trace Element Concentrations in Porphyry Copper Deposits from Metaliferi Mountains, Romania: A Reconnaissance Study - 2014

Mining & Minerals - Evaluations / Mineral Exploration Activities - General

Cioacă, and three co-authprs, reported in 2014 that 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 (RoÅŸia Poieni, Bucium–TarniÅ£a, Colnic, Rovina, Valea Morii and Bolcana) indicated bulk rock mean values of 0.16–0.88 ppm Au, < 50 ppm Mo, 0.02–0.35 ppm Re, 0.06–0.6 ppm In, 1.3–3.3 ppm Ag, 0.23– 1.17 ppm Bi, 3.2–5.5 ppm Se, 2.4–3.3 ppm Ge, and 2.6–18 ppm 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 1,430 ppm Au, 530 ppm Ag, 1,920 ppm Te, 10,500 ppm As and 2,620 ppm Se in pyrite, 970 ppm Au, 1,180 ppm Ag, 1,000 ppm Te, 410 ppm As and 420 ppm Se in chalcopyrite, and 920 ppm Au, 4,830 ppm Ag, 1,470 ppm Te, 4,230 ppm Se and 1,540 ppm Bi in bornite.

Gold is concentrated preferentially in pyrite, while silver is consistently high (>1000 ppm) in bornite. In the porphyry-type mineralization, galena forms microinclusions in pyrite, chalcopyrite and bornite, and contains up to 3,750 ppm Ag, 17,380 ppm Se, 1,570 ppm Ge and 780 ppm Te. Galena and pyrite from the epithermal mineralization in the Măgura–Bolcana–TroiÅ£a 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.