Alteration of lithium clay resources and its effect on lithium concentration

Abstract:

Several western U.S. basins and a caldera with Neogene lacustrine sediments contain lithium-clays. Research has shown that lithium can be sorbed to the clay structure at either surface or exchangeable sites and it can also be bound within the octahedrally-coordinated structural sites. Lithium-clay minerals from these locations have been identified as smectite, mixed layer smectite-illite, and illite, and it is the illite structure that appears to contain the highest concentration of lithium (up to 12,400 ppm Li observed in illite, up to 4190 ppm Li observed in smectite, both from the McDermitt Caldera in Nevada). The source of lithium to these sediments remains a point of debate as do the processes responsible for crystallization of lithium-illite. Illite may form through alteration of smectite during low temperature sediment diagenesis, and it may also form during alteration of smectite and other phases by hydrothermal fluids. Models have been proposed to explain the mechanism by which the smectite->illite reaction occurs, including solid-state transformation and dissolution-crystallization. Some argue that the mechanism of illitization is determined by the geologic environment with solid-state transformation occurring during diagenesis and dissolution-crystallization occurring during hydrothermal alteration. Analysis of the mineral assemblages associated with lithium clays may assist in discriminating between low- vs. high-temperature alteration mechanisms. Identification of the lithium-clay phases in lacustrine sequences in Nevada, California, and Oregon will be combined with information on the accompanying mineral assemblages to interpret the alteration mechanism responsible for an enrichment of lithium in illite clays.