Multi-stage cobalt mineralization in the Meta-sedimentary rock-hosted stratabound Dahenglu Cu–Co Deposit, northeast China

Abstract

Co is an essential metal for various emerging industries. (Meta-) sediment-hosted stratabound Cu–Co deposits (SSCC) account for over 60 % of global Co production. The role of sedimentation in Co mineralization in SSCC has been reported; however, the effects of metamorphism and associated hydrothermal fluids remain unclear. Herein, we developed an orogenic-type metallogenic model for the graphitic micaschist-hosted stratabound Dahenglu Cu–Co deposit (DCCD) in the northeast Jiao–Liao–Ji orogenic belt, China. The drill holes and stratum samples revealed that the DCCD underwent diagenesis, Paleoproterozoic metamorphism, and hydrothermal overprinting. No sediment-derived sulfides were observed in the DCCD. The graphitic micaschists geochemically resemble shale, with highly negative δ¹³C values (−25.9 ‰ to −22.2 ‰), consistent with organic matter transformed into graphite in a semi-enclosed restricted lagoon. The Co in the Dalizi Formation (DF) originated from the weathering of 2.18–2.15 Ga Fe–Co sulfide deposits in the Lieryu Formation. Co was captured by clastic minerals and organic matter during sedimentation. The metamorphic transformation involved Co-poor pyrite decomposition and pyrrhotite, sphalerite, chalcopyrite, linnaeite, and cobaltite formation. CO₂- and Cl-rich fluids mobilized metals during foliation under greenschist–amphibolite facies metamorphism. Hydrothermal overprinting formed sulfide-rich stockwork and veins. They were mainly represented by Co-rich pyrite, pyrrhotite, chalcopyrite, siegenite, and cobalt pentlandite. Analysis of the compositions and proportions of silicates, sulfides, and sulfoarsenides from 189 drill holes revealed that metamorphism-derived linnaeite and cobaltite account for over half of the Co content in the DCCD, followed by hydrothermally derived Co-rich pyrite. In summary, the sedimentary precursors of DF provided critical metallogenetic materials for Co pre-enrichment. The Paleoproterozoic metamorphism and hydrothermal fluids induced Co mineralization and re-enrichment in DCCD. These results show that DCCD is an orogenic Cu–Co deposit broadly similar to the Central African Copperbelt.