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The Impact of Geological Environment on the Lithium Concentration and Structural Composition of Hectorite Clays
AuthorMorissette, Claude L.
AdvisorStillings, Lisa L.
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Hectorite is a Li-rich trioctahedral smectite where Li can occur both in the octahedral and the interlayer sites of the mineral structure. It forms either authigenically or as an alteration product under low temperature and hydrothermal conditions. This research characterizes the Li concentration and structural composition of hectorites from 4 sites in the western USA believed to have formed under different geological environments. Results will have implications for evaluating clays as a source of Li, and will also contribute to understanding the global geochemical cycle of Li. A suite of 18 samples was collected: 6 from Clayton Valley NV, believed to have formed under low temperature conditions (<100°C); 1 from Fish Lake Valley NV, 1 from Hector CA and 9 from McDermitt NV, believed to have formed under elevated temperature conditions (>100°C); and 1 sample of synthetic hectorite. Clay chemistry was analyzed using XRF, ICP-MS, cation exchange capacity and layer charge analyses, while structure was analyzed using XRD. Hectorite was identified in all locations except Clayton Valley, where a dioctahedral illite was identified instead. A mineral consistent with tainiolite, a trioctahedral, Li-rich mica, was also identified in McDermitt. Results indicate the clays formed in a high-temperature environment have a trioctahedral structure and are enriched in Li and F, with Li located in the octahedral site, and compositions averaging 0.54% Li for hectorite and 1.20% Li for tainiolite. Clays formed in a low-temperature environment have a dioctahedral structure with Li located in the interlayer site and compositions averaging 0.34% Li.