Critical metal deportment in polymetallic ores: Advancing the understanding of cobalt in the Zinkgruvan deposit, Bergslagen district, Sweden

Cobalt (Co) is a critical metal, and its importance in the green transition has triggered an interest in understanding its deportment in polymetallic deposits. In these deposits Co may occur as a trace element in sulfides (e.g., sphalerite, pyrrhotite, chalcopyrite), influencing flotation and reagent regime during the Zn–Pb flotation process (Babedi et al., 2021), and decreasing the value of Zn concentrate. At the same time, Safflorite (CoAs₂) offers potential to recover Co as a by-product while reducing arsenic in tailings, lowering environmental impact. A multi-method approach to characterize Co-bearing minerals in polymetallic ores is necessary to predict processing performance. This study builds on the initial assessment of Co occurrence in the Zinkgruvan deposit and aims to expand mineralogical and geometallurgical understanding across spatial and lithological domains. The Zn–Pb–Cu–Ag Zinkgruvan deposit in southern Sweden comprises diverse ore bodies with variable mineralogical associations and characteristics. Two main mineralization styles have been defined: stratiform Zn–Pb–Ag ore hosted in quartz- and calc-silicate-rich metatuffite, and dolomite marble- and skarn-hosted Cu–Zn ore (Jansson et al., 2017). The complexity and polymetallic nature of the ores increases towards the western part of the deposit, where available geochemical and mineral chemical data outline a trend of increasing Co, Ni, As, and Sb. Hjorth (2022) showed that Co in Zinkgruvan occurs as free minerals (cobaltite, safflorite, cobalt pentlandite) and within the lattice of pyrrhotite and sphalerite, based on samples from the Dalby–Mellanby ore body in the westernmost part of the deposit. Detailed core logging of this area shows small amounts of Co minerals. Cobalt-rich core intervals, according to chemical assays, coincide with sphalerite and pyrrhotite occurrence, yet no Co minerals are observed. Based on this initial assessment of Co presence in Zinkgruvan, further steps will include mineralogical characterization of Co-bearing minerals across spatial and lithological domains, as well as evaluating Co deportment variability among ore types. This research is funded by Zinkgruvan Mining AB, the Centre of Advanced Mining and Metallurgy (CAMM) and CAMM-CRM, a Swedish government-supported initiative on critical raw materials at Luleå University of Technology. References: Babedi, K. E., Oyekola, O. O., & Ntuli, F. (2021). Effect of cationic substitutions on the flotation and electronic properties of sphalerite: First-principles and experimental investigations. Minerals Engineering, 172, 107153. Hjorth, I. (2022). Characterization of the cobalt content in zinc ore from Zinkgruvan, Sweden. Master’s thesis, Luleå University of Technology. Jansson, N. F., Zetterqvist, A., Allen, R. L., Billström, K., & Malmström, L. (2017). Genesis of the Zinkgruvan stratiform Zn-Pb-Ag deposit and associated dolomite-hosted Cu ore, Bergslagen, Sweden. Ore Geology Reviews, 82, 285–308.