Trace element composition of base metal sulfides from the sediment-hosted Dolostone Ore Formation (DOF) Cu-Co deposit in northwestern Namibia: Implications for ore genesis

The Dolostone Ore Formation (DOF) copper-cobalt mineralization is a recently discovered sediment-hosted deposit in Neoproterozoic low-grade metamorphosed carbonates and fine-grained siliciclastics in the PanAfrican Kaoko Belt in Namibia. Six mineralization styles have been identified in the DOF. They comprise both brittle and ductile (micro)textures and include sulfides occurring in disseminations, clusters, nodules, pressure shadows, veins and the locally termed "DOF event". Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) in situ trace element analyses of base metal sulfides (sphalerite, chalcopyrite, pyrite and pyrrhotite) show distinct groupings of the mineralization styles. Sphalerite and chalcopyrite from the dissemination, cluster and nodule mineralization styles show similar trace element composition trends (e.g., Fe, Co, Ni, Se, Cd for sphalerite and Co, Ni, Se and Bi for chalcopyrite) that differ from vein and pressure shadow sphalerite and chalcopyrite which group together. Pyrite compositions in cluster and nodule types show a similar trace element grouping in elements such as Co, Ni, As, Se, Sb, Tl and Pb. In contrast, pyrites from pressure shadows and veins show a decoupling in elements such as Se, Sb, Tl and Pb, that grouped together in the aforementioned pyrite mineralization styles. Ge-Ga-In-Mn-Fe in sphalerite (GGIMFis) geothermometry indicates that the sphalerite (and associated sulfides) from all mineralization styles crystallized at temperatures at or above 310 +/- 50 degrees C. This temperature range corresponds with the regional metamorphism induced by the Damaran omgeny. Thus, the DOF copper-cobalt mineralization is related to, or at least strongly overprinted by, Damaran metamorphism and deformation. Trace element differences in the sphalerite-chalcopyrite groupings reveal that the vein and pressure shadows mineralization styles were formed at lower temperatures than the other ones but still above the GGIMFis closing temperature of 310 +/- 50 degrees C. Evidence is vacant for a typical low-temperature, early sediment-hosted copper mineralization. This work demonstrates the strength of using trace elements for deducing the ore-forming system of polyphase sulfide deposits.