Cenozoic collisional tectonics and origin of Pb-Zn-F mineralization in the Bitlis Massif, SE Turkey

Abstract

Hasbey Pb-Zn-F mineralization in the Bitlis Massif, south of Lake Van, lies within the Neotethyan suture of the Alpine orogenic belt. Mineralization occurs in two different lithologies and locations: Type-I is present in dolostone fractures and faults as veins and veinlets, whereas Type-II occupies a fault zone between black marbles and calc-schists. Sphalerite and argentiferous galena are the main ore minerals in both types. The dominant gangue minerals are quartz and dolomite in Type-I ore and calcite, quartz, and green-white fluorite in Type-II. Analysed fluid inclusion data from sphalerite, fluorite, and quartz indicate that high-temperature (>500°C) mineralization was initiated from low-salinity fluids (4.3 wt.% NaCl equiv.). As temperatures dropped from 400°C to 160°C, the salinity of solutions increased and appreciable CO2 was contributed to the fluid system. In the absence of immiscibility, assemblages of fluid inclusions containing CO2 indicate that the solutions were homogeneous during entrapment and that mineralization took place under pressure conditions between 5 and 2 kb. Analysed δ34S CDT (‰) values (−1.5 and −3.8, n = 15) of sphalerite and galena indicate that the source of the sulphur is consistent with a magmatic origin for Hasbey Pb-Zn-F mineralization. The stable isotopic compositions and fluid inclusions in fluorite are also suggestive of an origin related to high-temperature, high-salinity magmatic fluids. In the region, volcanic rocks are abundant, and they document the magmatic events associated with the closure of the neo-Tethys. The timing of mineralization is restricted to post-early Oligocene, inasmuch as mineralization occurs in faults that cut post-Eocene–Oligocene thrust faults and because of the relationship between mineralization and wall-rock deformation.