THE CLAY MINERALOGY OF SEDIMENTARY LITHIUM DEPOSITS

Of the resources required for the global transition to sustainable energy and transportation infrastructure, lithium (Li) is projected to be among the most vulnerable to supply shortages as demand from automotive and electronics manufacturers threatens to outpace production over the next decade. Historically, Li was primarily sourced from spodumene pegmatites, although recent production has focused on exploiting salars containing Li-rich subsurface brines. Sedimentary Li deposits are generally intermediate between pegmatites and salars with respect to grade, tonnage, and operative costs—resulting in favorable economics as the price of Li continues to rise. Within sedimentary Li deposits, Li is typically hosted within Mg-rich smectite group minerals such as hectorite. Despite their rising prominence as potential sources of Li, the origins of these deposits are poorly constrained. This research aims to better understand the mineralogy and paragenesis of Li-rich clays in sedimentary Li deposits. Investigation will focus on the world-class Thacker Pass Li deposit in the McDermitt Caldera, northern Nevada, and will also include samples from other Li-rich clay localities to aid in generating a more coherent formation model for these occurrences. The intracaldera lake sediments at Thacker Pass include both smectitic and illitic clays—with higher Li grades (up to c. 9000 ppm) occurring in the illitic clays; such high Li grades have not yet been observed in any other clay-hosted Li deposit. Previous work has constrained the spatial distribution of clays and associated minerals at Thacker Pass—however, the specific mineralogical relationship (thermal diagenesis, replacement, etc.) between smectite and illite within the deposit is not well understood. In situ methods will be used to evaluate the textural relationship between smectite and illite, as well as to describe microtextures in the clays to determine their origin and paragenetic relationships. The results of this work will be used to refine formation models for sedimentary Li deposits and better elucidate the source and sink processes responsible for transporting and trapping Li in these systems. The results may assist in choosing exploration criteria for locating new sedimentary Li deposits around the world to help meet rising Li demand.