Index Minerals of the Hydrothermal Arsenide Process of the Formation of Cobalt Deposits of the Bou Offro–El Graara Ore Belt in the Anti-Atlas Province, Morocco

Abstract

The distribution of index minerals of the hydrothermal arsenide process of the formation of Ni‒Co–As (±U–Ag), Co–S–As (±Au–W), and Cu–Co–As (±Sb–Ag) quartz–carbonate veins of deposits of the Bou Offro–El Graara ore belt (Morocco) are discussed. The Co arsenide objects of the Bou Azzer ore cluster with typical low-temperature Ni–Co–As (U–Ag) deposits of the five-element hydrothermal type are of special interest: El Jir, Mechoui, Tarouni, Central and East Bou Azzer, Aghbar, Tamdrost, etc. The ores of most of the studied deposits are strongly enriched in Co relative to Ni (Co/Ni ratio = 10/1), have high grades of Au (up to 100 g/t) and Mo (up to 0.1%) with relatively low Ag, Ni, and U contents. Based on the analysis of the interrelations of ore and gangue minerals, the sequence of the formation of mineral assemblages is identified and their mineralogical–geochemical zonation is studied. The range of the most favorable physicochemical parameters of ore deposition is determined from the fluid inclusions in the gangue minerals. The indicative role of mineralogical–geochemical features of ore assemblages is shown for the forecast and survey of blind ore bodies.