GRAVITY CONCENTRATION METHODS TO RECOVER CRITICAL MINERALS FROM PLACER TAILINGS IN FLAT, ALASKA

Critical minerals are vital to the economy and national security of the United States due to their essential functionality and vulnerable supply chains. As such, there is an urgent need to develop multi-disciplinary, techno-economic workflows for critical mineral recovery from unconventional sources such as tailings. To work towards these goals, a case study of placer tailings in Flat, Alaska is conducted to determine the viability of reprocessing tailings and extracting critical elements. The town of Flat is a historic gold mine in the Kuskokwim Mountains consisting of fluvial placer deposits on creeks that drain multiple sources of mineralization. The tailings contain critical element contents of tungsten, chromium, nickel, and zirconium as well as other elements associated with or occurring within the structure of various mineral phases. The first stage of this project involves mineral processing and analytical techniques to define a workflow for processing tailings and determining their contents. Gravity concentration methods were utilized, due to the known effectiveness of these methods on placer deposits and because they are relatively cheap and simple methods of concentration. A shaking table was utilized for the <1680 µm material, while a jig was used for the >1680 µm fraction. Bulk geochemistry results suggest the effectiveness of our methods on <595 µm material, resulting in the concentration of target minerals into concentrate, middling, and tailings fractions. Critical mineral recovery from mine waste has the potential to contribute to the achievement of sustainable development goals and a circular economy, the reduction of mining waste, and the mitigation of environmental hazards associated with tailings.