McDermitt Caldera

Region West, Southwest
Mineral systems
Deposit types
Critical minerals
Other minerals

Information leading to the delineation of this focus area

Basis for focus area McDermitt Caldera outline with 5 km buffer from USMIN.
Identified resources Identified lithium resources.
Production None.
Status Current development; Tacker Pass is a pre-feasibility project of Lithium Americas expected to go into production in 2022.
Estimated resources NI 43-101 compliant resources for Thacker Pass (2018): Measured 242,150,000 mt, average grade 2,948 ppm Li, 3,800,000 mt LCE; Indicated 143,110,000 mt, average grade 2,864 ppm Li, 2,182,000 mt LCE; Inferred 147,440,000 mt, average grade 2,932 ppm, 2,301,000 mt LCE (Ehsani and others, 2018).
Geologic maps Jenks and others (2007), scale 1:100,000; Henry and others (2016), scale 1:70,000.
Geophysical data Inadequate aeromagnetic and aeroradiometric coverage.
Favorable rocks and structures Hydrothermally altered volcaniclastic rocks of the Eocene-Miocene McDermitt caldera. Lithium occurs in tuffaceous rocks altered to zeolites and potassium feldspar (Rytuba and others, 2003).
Deposits Kings Valley (MRDS dep_id: 10222289: USMIN Site_ID NV00118), Thacker Pass.
Evidence from mineral occurrences MRDS; USMIN; Rytuba and others (2003); Ehsani and others (2018).
Geochemical evidence Lithium occurrences are located in tuffaceous rocks that are altered to zeolites and potassium feldspar. Sediments in the southern and western parts of the caldera basin have ≥1500 ppm Li (Rytuba and others, 2003). A laterally continuous lower sedimentary section has a zone with about 3000 ppm Li and also has high K, Rb, Mo, As, and Sb (and partly Mg and F). Lithium occurs as an illitic clay (tainiolite?) and smectite (hectorite) (Castor and Henry, 2020).
Geophysical evidence Unknown.
Evidence from other sources Active exploration by Lithium Americas.
Comments The McDermitt caldera region is a unique environment with aspects of at least 4 overlapping and interrelated mineral systems. Possible systems include: Magmatic REE system related to plume-related basalt-peralkaline rhyolite magmatism (Peralkaline syenite/ granite/rhyolite /alaskite/pegmatites deposit type). A related Climax-type mineral system, with steam-heated Lithocap alunite (K, Al, Ga) and Volcanogenic uranium deposit types (U); Meteoric convection system with Low sulfidation epithermal Hg, and, most importantly at this time, a Lacustrine evaporite system (Lithium clay and Residual brine deposit types) that created the large Li enrichments in caldera sediments.
Cover thickness and description Hosted in sedimentary rocks and an overlying lacustrine sequence consisting of tuffaceous sandstone and shale.
Authors Lisa L. Stillings.
New data needs Mapping focused on hydrothermal alteration and mineralization, geochemistry, geophysics.
Geologic mapping and modeling needs Updated geologic mapping.
Geophysical survey and modeling needs High-resolution, Rank 1 aeromagnetic and aeroradiometric surveys.
Digital elevation data needs Lidar inadequate.