VOLCANIC GLASS DIAGENESIS AS A POTENTIAL CONCENTRATION MECHANISM FOR LITHIUM WITHIN INTRACALDERA SEDIMENTS IN THE MCDERMITT CALDERA, SE OREGON

Driven by the advent of electric cars, there is significant interest in identifying new sources of Li. A large deposit of Li clay is found in the McDermitt caldera, a Miocene-age volcanic collapse feature on the northwestern Nevada border with Oregon. Highly alkaline and saline intracaldera lake waters deposited lacustrine sediments consisting of clays, mudstones, and sandstones.

The McDermitt caldera is one of the world’s largest clay-hosted Li resources. Exploration of the northern portion of the caldera by Jindalee Resources, Ltd., the industry sponsor of this research, revealed an inferred mineral resource estimate of 150 Mt at 2,000 ppm Li at a cutoff of 1,750 ppm Li. In the southern portion of the caldera, higher Li concentrations have been recognized within the illite clay.

While the formation of illite clay is typically associated with elevated temperatures, it has also been observed as a diagenetic phase formed in highly alkaline and saline lakes at ambient temperatures comparable to conditions thought to have existed in McDermitt caldera lake waters.

To test whether elevated Li concentrations and illite clay may be the consequence of diagenetic alteration of sediments, chemical and XRD analyses were performed on bulk samples and clay separates from drill holes in the northern caldera study area. Textural relationships and phase identification of authigenic minerals were achieved via thin section microscopy and SEM/EDS analyses.

Preliminary observations reveal the presence of authigenic zeolites analcime and chabazite. Pitting and dissolution textures in analcime and replacement by chabazite offer evidence of evolving pore water chemistries. Diagenetic pyrite is present as anhedral masses and casts of organic fragments. Fragmented clinopyroxene and plagioclase are common within imbricated tuffaceous sediments along with secondary calcite and dolomite. Discrete veins of euhedral pyrite and the occurrence of titanite as interstitial sprays between pore spaces raise interesting questions about the potential interactions between pore waters and hydrothermal solutions.

Results from this study will provide insight into the occurrence of Li mineralization in the world-class McDermitt caldera resource and contribute to the refinement of genetic models for clay-hosted Li deposits.