Indium in a Canadian critical minerals context: geology, mineralogy, and potential resources for Canada’s future

Indium (In) is a critical mineral used in communications technology, optical displays, and alternative energy delivery, and is a byproduct of Zn and/or Sn mining. It is often found in low concentrations (10 s to 100 s of ppm) in Canadian clastic-dominated sediment-hosted Zn–Pb, polymetallic volcanogenic massive sulfide (VMS), magmatic–hydrothermal, and orogenic vein deposits. Indium in Zn-rich mineralization is associated with sphalerite that is spatially associated with chalcopyrite and was influenced by Cu-rich fluids; it is commonly hosted in roquesite (CuInS 2 ) or as Cu–In nanoparticles within sphalerite. In Sn-rich mineralization, In is associated with roquesite, and to a lesser extent sphalerite, chalcopyrite, wolframite, and Sn-phases (e.g., cassiterite and stannite). Indium occurs in deposits that had evidence for magmatic–hydrothermal fluid input and/or with deposits that have strong associations with black shales/organic-rich mudstones. Future resources will likely come from similar deposits outlined above, but additional resources may be found in carbonate-hosted Zn–Pb deposits and porphyry Cu–Mo deposits, in addition to historic mine tailings. Understanding baseline geochemical and mineralogical distributions of In in rocks and minerals in historic and existing deposits is essential if we are to secure future supplies of In from Canadian mineral deposits.