Cobalt occurrence and enrichment of the Kendekeke cobalt-rich Fe skarn deposit in the East Kunlun orogenic belt, western China

Abstract

The East Kunlun orogenic belt (EKOB), one of the most significant Co-Ni metallogenic belts in China, hosts numerous Co-Ni deposits of both magmatic and hydrothermal types. The Kendekeke cobalt-rich Fe deposit, a notable skarn deposit, is located in the North Qimantagh belt of the EKOB. Co mineralization is concentrated mainly in the northern mining zone, with four distinct mineralization stages identified. Co mineralization primarily occurred in the early sulfide stage. Two independent Co-Ni minerals, namely, cobaltite (Co) and ullmannite (Ni), have been identified as closely coexisting with chalcopyrite and pyrrhotite in the Kendekeke deposit. U–Pb dating of apatite in both the northern and southern mining zones yields consistent results, with ages concentrated at approximately 225 Ma, closely related to the monzogranite in the Kendekeke ore district. Cobalt occurs in two forms: as an independent mineral, cobaltite, and as an isomorphic substitute in sulfides or sulfarsenides, including pentlandite and pyrite. Pentlandite, with an average chemical formula of (Ni₅.₀₄Fe₃.₅₆Co₀.₃₅)S₈. ₀₀ on the base of EPMA results, has an average Co content of 2.67 wt%. Compared with the theoretical S/Fe atomic molar ratio and the binary diagram between Fe and Co, Co is more likely to substitute for Fe in pentlandite. By combining fluid inclusion and mineral paragenesis data, it has been determined that the controlling factors of Co mineralization are temperature and oxygen fugacity. Finally, a Co mineralization model was established for the Kendekeke cobalt-rich Fe deposit.