Scientific African (Sep 2023)
Metallogenesis of the Cu-Ni sulfide type mineralization in the Bounhas vein deposit (Eastern Anti-Atlas, Morocco): Insights from ore mineral paragenesis and fluid phases
Abstract
The Moroccan Anti-Atlas hosts numerous precious metal (Au, Ag, Co, PGE...) and base metal (Cu, Pb, Zn...) mineralizations that are developed in various geological and geodynamic contexts. Some of these mineralizations, such as copper and nickel, are known in the form of deposits at the scale of the Anti-Atlas and are the subject of mining development and exploitation. This is the case of the Bounhas deposit, which is located in the southern part of the Eastern Anti-Atlas, 50 km SE of the city of Alnif. It is characterized by Cu, Ni, Pb and Zn mineralizations, which are essentially hosted in sedimentary terrains of a sandstone-pelitic nature of the upper formation of the second Bani group (Upper Ordovician). These terrains are affected by brittle deformations that have developed faults that host the lenticular vein mineralization in an E-W direction. The arrangement and textural relationships between the mineral phases of the Bounhas deposit have allowed to distinguish two distinct mineralizing events: (i) a primary hydrothermal event subdivided into 3 metalliferous episodes the first, with Fe, characterized essentially by pyrite mineralization in a carbonate gangue (ankerite and siderite); the second with Cu, Ni, As ± Zn ± Pb, precipitates most of the arsenopyrite, sphalerite I, galena I, gersdorffite and chalcopyrite mineralization in a quartz gangue; and the third, with Pb, Zn, and Ba, places galena II and sphalerite II in a barytic gangue. A late supergene alteration event, characterized by the appearance of minerals typical of cementation, sulfation, carbonation and oxidation zones (covellite, native copper, anglesite, malachite, azurite and iron oxides). Moreover, the study of the fluid inclusions associated with the Cu, Ni, As ± Pb ± Zn mineralization from the Bounhas deposit reveals the presence of two types of fluids: (i) a hypersaline fluid, characterized by a salinity varying between 25 and 30 wt% NaCl eq and a homogenization temperature: Th = 200 to 240 °C. This fluid would be responsible for the development of the copper-nickel-arsenic mineralization of this deposit and (ii) a late medium saline fluid (12 to 15 wt% NaCl eq) and a homogenization temperature Th = 80 °C to 120 °C, to which would be attributed the development of the Pb and Zn mineralization of this deposit.
