STATEWIDE GEOCHEMICAL RECONNAISSANCE OF CALIFORNIA CRITICAL MINERAL DEPOSITS AND DISTRICTS: COLLECTING NEW DATA FOR A NEW CENTURY

Geologists at the Mineral Resources Program of the California Geological Survey (CGS) are conducting statewide geochemical reconnaissance sampling. Through focused sampling surveys, the CGS will enhance geologic understanding of priority critical-mineral research areas for both CGS-funded projects and U.S. Geological Survey (USGS)-funded Earth Mapping Resources Initiative projects. The mission of this project is to support current and future critical-mineral, precious-metal, base-metal, and industrial-mineral activities within California.

Reconnaissance sampling, beginning in 2023, focused on the laterites and ultramafic rocks of the Josephine Ophiolite in Del Norte County. This pilot project aimed to further our understanding of both mineralization and geochemical relationships between nickel, cobalt, and chromium deposits of northwestern California. These elements are essential to the transition from fossil fuels and the production of renewable energies. Analyses confirm expected enrichment of critical minerals in the laterites with values locally exceeding 7,000 ppm nickel, 500 ppm cobalt, and 10,000 ppm chromium. Results of this survey were recently published by the CGS in Data Release 2024-001.

Continuing in 2024, the statewide sampling project transitioned efforts to the Plumas County Copper Belt and associated mineral districts. Reconnaissance work was planned and coordinated with input from researchers at the California State University at Chico and mining companies active in the region. CGS geologists sampled a variety of deposits, including iron-oxide-copper-gold, porphyry copper-molybdenum, and volcanogenic-hosted massive sulfide, to investigate by-product critical-mineral potential and trace-element associations for these deposit types. Data from Plumas County is expected to be released in a new Data Release in 2025.

In 2025, the CGS is considering evaluating the historical East and West Shasta zinc-lead volcanogenic-hosted massive sulfide deposits for their critical-mineral potential, including gallium and germanium. This work would support cross-border geologic interpretations between the CGS, Oregon Department of Geology and Mineral Industries, and USGS by strengthening collaborative relationships and efforts on future critical-mineral initiatives.