The occurrence state and enrichment regulation of cobalt in the Dahongshan Fe-Cu deposit in the Kangdian area, SW China

<p indent="0mm"> As a typical Fe-Cu deposit in the Kangdian region,the occurrence state and enrichment regulation of the associated critical metal cobalt in the Dahongshan deposit has been limitedly researched. In this study, we have conducted analyses of major and trace elements of pyrites of two stages and host rocks, as well as sulfur isotopes of those pyritest in the deposit, and made a preliminary summary on the cobalt enrichment regulation in the deposit. The results indicate that the average cobalt contents of various rocks are 69.8×10^–6 for the ore-bearing metasodium tuff, 28.5×10^–6 for marble, and 84.5×10^–6 for the garnet mica schist, respectively. Stage I pyrites (Py I) are characterized with high cobalt contents (from 2513×10^–6 to 50763×10^–6), low nickel concentrations (from 11.7×10^–6 to 3704×10^–6), and low δ³⁴S values (from –1.55‰ to –0.71‰), suggesting that the cobalt-rich pyrite could be associated with the mantle-sourced magma. In contrast, Stage II pyrites (Py II) are characterized with relatively low cobalt contents (from 38.8×10^–6 to 3301×10^–6), high nickel concentrations (from 889×10^–6 to 8784×10^–6), and high δ³⁴S values (from 7.28‰ to 9.08‰), indicating that the ore-forming fluid could be of metamorphic origin. Our study shows that the cobalt in the Dahongshan deposit occurred mainly within pyrite in the form of isomorphic substitution, and occasionally occurred as independent cobalt mineral of siegenite. It is believed that cobalt was predominantly originated from the mantle-sourced magmatic fluids and its enrichment occurred mainly during the sedimentary diagenesis and mineralization period. The cobalt-bearing ore is closely associated with the high-grade iron and copper ores.