GEOLOGY OF U.S. CRITICAL MINERAL DEPOSITS AND RESOURCES FOR THE GREEN ECONOMY

Critical minerals for the green economy include aluminum (Al), graphite, lithium (Li), manganese (Mn), and rare earth elements (REEs), which are produced as primary products; and antimony (Sb), arsenic (As), cobalt (Co), gallium (Ga), germanium (Ge), indium (In), and tellurium (Te), which are byproducts. The USGS Mineral Deposit Database (USMIN) contains data that allow us to evaluate the geological controls on important U.S. critical mineral deposits and resources for the green economy. Some commodities, such as Mn, lack significant deposits in the U.S. because the processes that form large deposits were optimized elsewhere. Others, such as graphite, occur in a restricted range of deposit types that reflect the conditions necessary for their formation. Some commodities are currently recovered from only one type of mineral deposit because metallurgical processes dictate what is recoverable and the efficiency of recovery. For example, Te is almost exclusively recovered from anode slimes from electrolytic copper refining of porphyry copper deposits, but only 5% of the available Te is recovered. Some byproduct commodities occur in a diverse array of deposit types in the U.S., such as Co, which occurs in volcanic-hosted and sediment-hosted massive sulfide deposits, conduit and stratiform Ni-Cu-PGE deposits, Mississippi Valley-type deposits, Kipushi-type deposits, and iron oxide-apatite deposits. Some commodities, such as Li, have historical U.S. production from deposit types—brines and pegmatites—that mirror global production, but have large resources in unconventional deposits—including oilfield brines, geothermal brines, saline lakes, and clay minerals—that may contribute significantly to future production. Similarly, global production of REEs comes from carbonatites, alkaline intrusive rocks, and clay deposits, but some phosphate rock that is mined for the global fertilizer industry is significantly enriched in heavy REEs; recovery from these deposits could transform global REE supply. Lack of data on the production and resources of many byproduct critical minerals hampers our ability to evaluate their potential availability in the U.S. For some commodities, metallurgical advances or development of unconventional deposits could transform supply of critical minerals for the green economy.