Critical minerals: Germanium and cobalt in the Bornite deposit, southwestern Brooks Range, Alaska

Increasing demand for Ge and Co has led to a renewed interest and focus on advancing our understanding of the occurrence, distribution, and sequestration of these critical elements in known ore deposits. A workflow using a variety of analytical techniques and co-registered datasets has been developed and was applied to the carbonate hosted Bornite Cu-Co (Zn,-Ge) deposit in Alaska, where a new orebody (“the South Reef”) was discovered in 2011. The South Reef is host to substantial amounts of high-grade Cu, Co, and appreciable Zn, but also contains localised elevated concentrations of Ge. We describe the mineralogy and paragenesis of the South Reef based on detailed optical petrography, scanning electron microscopy, scanning electron microscopy-based automated mineralogy, and mapping μ-X-ray fluorescence analysis. Germanium was found to exist in renierite, white mica, illite, galena and feldspars within the South Reef. Cobalt was found to occur in cobaltiferous pyrite, carrollite, and cobaltite.