Fluid inclusion and stable isotope studies of the Mesloula Pb-Zn-Ba ore deposit, NE Algeria: Characteristics and origin of the mineralizing fluids

In the Saharan Atlas (NE Algeria), the Triassic evaporitic formation was brought to the surface through the thick Cretaceous and Tertiary sedimentary cover as diapirs due to the effect of Atlasic tectonic events. The diapir piercing began in the Jurassic and has continued through present day. Many outcrops of several square kilometres are distributed in a large area (approximately 80 km wide) that extends northeasterly over 300 km towards Tunisia. The diapiric evaporitic formation is often accompanied by the emplacement of Pb-Zn-Ba-F mineralization. The Mesloula massif is an example of these deposits. Fluid inclusion and sulphur, carbon and oxygen isotope studies were carried out on Pb-Zn-Ba mineralization and associated gangue carbonates. Gypsum of the Triassic formation was also analysed for its sulphur isotope composition to show the role of evaporates in the generation of this typical peridiapiric deposit. Gypsum from the Triassic formation showed a narrow range of delta S-34(VCDT) values, ranging from +14.6 to +15.5 parts per thousand (n = 8). This range is comparable to that of Triassic seawater sulphates. Sulphide minerals yielded delta S-34(VCDT) values between 0 and + 11.7%0 (n = 15), indicating that sulphide sulphur was likely derived from Triassic sulphates through thermochemical sulphate reduction (TSR) because fluid inclusion microthermometric measurements yielded a mean temperature of 150 degrees C. Residual sulphate in such a system would have been enriched in S-34; this is reflected in the barite delta S-34(VCDT) values, which range from +21.1 to +33.5 parts per thousand (n = 5). The delta C-13(VPDB) values of calcite minerals, ranging from +2.1 to +6.3 parts per thousand (n = 4), indicate an inorganic carbon origin, likely from the host carbonate rocks. delta O-18(VSMOW) values were between +21.9 and + 24.9 parts per thousand, indicating that the most likely source of mineralizing fluids was formation water. (C) 2016 Elsevier Ltd. All rights reserved.