An initial characterization for revalorization of the Joma mine tailings, Norway

• Joma mine tailings are dominantly pyritic with elevated Cu, Zn, Co, and Ag. • Underwater disposal has preserved tailings from oxidation. • Co, Ag and Au are lattice-bound elements in sulfides. • Joma tailings represent a potential secondary source for critical raw materials. The reprocessing of historical mine tailings is gaining increasing attention as a more responsible approach to resource management and environmental remediation. However, comprehensive mineralogical and geochemical characterizations of submerged tailings remain scarce. This study provides the first detailed investigation of sulfide-rich tailings stored underwater in Hudningsvatnet Lake from the former Joma mine, which exploited one of Norway’s largest volcanogenic massive sulfide (VMS) deposits. The study assesses both the environmental stability of these tailings and their potential for revalorization, contributing to the broader understanding of submerged mine waste and secondary resource recovery. To achieve this, a multi-method characterization using scanning electron microscope-based automated mineralogy (SEM-AM), electron probe microanalysis (EPMA), and geochemical analysis is conducted to determine mineralogy, metal deportment, and assess reprocessability of the Joma mine tailings. The results show that the tailings contain significant concentrations of copper (7080 ppm), zinc (5140 ppm), cobalt (255 ppm), and silver (11 ppm), with critical raw materials such as cobalt (Co) and silver (Ag) hosted within pyrite and pyrrhotite, rather than discrete mineral phases as previously assumed. Furthermore, subaqueous storage has effectively prevented sulfide oxidation, with pyrite (54.7 wt%) and pyrrhotite (13.5 wt%) remaining largely unweathered. Chalcopyrite (2.1 wt%) and sphalerite (0.9 wt%) are the main ore minerals with a considerable fraction occurring in potentially recoverable liberation state. Their distribution varies with particle size, with sphalerite enriched in the −38 μm size fraction, while chalcopyrite is more evenly distributed as a consequence of the employed flotation circuit and the original ore textures. Electron Microprobe analyses on sulfide phases indicate Co, Ag and Au distribution within pyrite, pyrrhotite and chalcopyrite with up to 0.3 wt% Co, 362 ppm Ag and 494 ppm Au, which has important implications for their revalorization. The results of this study show that the historical Joma mine tailings contain potentially recoverable amounts of copper, zinc, cobalt and silver making them a viable secondary resource. Additionally, their high content of unweathered sulfides indicates a substantial potential for environmental impact, reinforcing the need for further assessment and management. The results can be used to design a more comprehensive sampling campaign of the Joma tailings and evaluate reprocessing strategies.