Mineralogy and geochemistry of sulfosalts from Baia Sprie ore deposit (Romania) — New bismuth minerals occurrence

The Baia Sprie epithermal ore deposit is one of the best-known deposits in Romania and Europe. It consists mainly of a vein system with two major veins: (1) Principal Vein and (2) Southern Vein, along fractures that delimitate an andesitic block and a subvolcanic intrusion. The Principal Vein is one of the longest hydrothermal veins in Europe, with more than 5 km in length, a thickness that varies between 0.5 and 22 m and it extends vertically on more than 800 m. Samples belonging to different levels of Principal Vein have been analyzed using electron microprobe. A new occurrence of bismuth minerals was identified within the deeper part of the deposit: bismuthinite, lillianite–gustavite, disordered intergrowths of lillianite homologues, heyrovskyite and cosalite. The presence of Bi-sulfosalts suggests temperature of ~ 350 °C, while the As content in arsenopyrite indicates formation temperatures between 320 and 360 °C. The oscillatory zoning bands of pyrite and tetrahedrite–tennantite members indicate an increased Sb and As concentration in hydrothermal solutions. The zoning textures suggest a high S and low As concentration in the early fluids followed by multiple pulses of As-rich solutions in the late fluids. The high content of As in pyrite and the presence of bismuth minerals at Baia Sprie deposit can represent indicators for significant Au concentrations within the lower level of the mineralization. From the type locality Baia Sprie new analytical data for semseyite were presented and for the first time a new occurrence of geocronite–jordanite series was identified in the intermediate and upper part of the deposit.