Characteristics and Uenesis of Carrollite from Mylonite-type Oreshoot of the Hongtoushan Deposit

Cobalt is a critical strategic mineral resource and remain significant concerns in China due to the scarcity and heavy reliance on foreign countries. Volcanic-hosted massive sulfide (VMS) deposits are significant sources of cobalt resources. However, the occurrence state of cobalt and the genesis of cobalt minerals are still under debate. The Hongtoushan deposit, the oldest VMS deposit in northeast China, contains numerous Cu, Zn, and Au resources, as well as some cobalt resources. Based on systematic mineralogy observation by microscope and TESCAN Integrated Mineral Analyze (TIMA), the sulfide paragenesis and carrollite was identified in mylonite-type oreshoot of the Hongtoushan deposit. Additionally, TIMA and geochemistry analysis by electronic microprobe analysis (EMPA) show that carrollite grains in the mylonite-type oreshoot of Hongtoushan could be divided into early-stage anhedral granular, mid-stage euhedral granular, and late-stage subhedral-euhedral veined. These three types of carrollite grains have similar mineral characters and geochemical contents and thus might be products of different stages during one hydrothermal event. Through deformation under regional metamorphism and overprinting during later hydrothermal event, cobalt scattered in sulfide minerals was remobilized from VMS orebodies to hydrothermal with enrichment of Cu, Co, and Au. The Co-enriched hydrothermal solution transports through schistose and faults in mylonite VMS orebodies and wall rocks, formed carrollite grains and mylonite-type oreshoot eventually. This study provides a mineralogical basis for resource evaluation and comprehensive utilization of cobalt in the Hongtoushan deposit.