GEOLOGIC MAPPING AND GEOCHEMICAL CHARACTERIZATION OF CALIFORNIA’S POTENTIAL LITHIUM RESOURCES

The California Geological Survey (CGS) is conducting geologic mapping and geochemical characterization under two USGS Earth MRI agreements to investigate lithium (Li) resource potential in southeastern California:

• Geologic mapping and geochemical characterization of geologic units related to Salton Sea Geothermal System (SSGS) reservoir rocks in the Salton Trough;
• Geologic mapping and geochemical characterization of the lacustrine Miocene Barstow Formation and age equivalent units in the Mojave Desert.

Preliminary evidence suggests Li in both project areas was initially concentrated through closed basin processes. Closed basin Li deposit models propose that felsic volcanic rocks within a basin watershed may represent sources of Li for conventional brines and sedimentary-hosted Li deposits. CGS conducted new mapping in the southeastern Salton Trough, aimed at investigating whether a thick package of felsic Tertiary volcanic and volcaniclastic rocks could represent potential sources of Li within the SSGS. Preliminary geochemical data shows elevated Li concentrations in tuff samples adjacent to Tertiary gold mineralization. These findings are notable considering that hydrothermal alteration may also play a role in closed basin Li enrichment, through further concentration of Li and other elements necessary for the formation of Li-bearing minerals. Further sampling is needed to characterize the extent of Li enrichment and understand how these field relationships relate to Li in modern hydrothermal Li brine resources.

In the Mojave Desert, preliminary geochemical data collected by CGS show elevated Li concentrations in lacustrine mudstone intervals within the Barstow Formation. This data is consistent with geochemical samples collected by previous USGS researchers and shows Li concentrations up to 2,000 ppm within these rocks. Miocene sedimentary rocks within the vicinity also host epithermal silver mineralization. This project is investigating the potential for other Li rich intervals within the sedimentary sequences, as well as the relationship between epithermal mineralization and Li concentrations.