LITHIUM SOURCE AND STRUCTURAL DEVELOPMENT OF SEDIMENT-HOSTED LITHIUM DEPOSITS AT RHYOLITE RIDGE, SILVER PEAK RANGE, WESTERN NEVADA: NEW INSIGHTS FROM DETAILED GEOLOGIC MAPPING

Demand for lithium (Li) has increased dramatically throughout the United States and the world due to a societal transition toward renewable energy and use of electric vehicles. The Rhyolite Ridge area lies within one of the richest lithium districts in the nation and adjacent to North America’s only active Li production in Clayton Valley (Albemarle). Sediment-hosted Li deposits at Rhyolite Ridge are nearing development (Ioneer), yet little is known about the primary source of Li, the relative influences of structural, stratigraphic, and magmatic controls on Li enrichment in the basin, and its spatiotemporal relation to the purported Silver Peak caldera. The Li-bearing Cave Spring Formation is mostly contained within a single basin in the study area and was deposited in an alluvial-lacustrine environment on a substrate of 6.0-5.8-Ma rhyolitic tuffs and lavas including the Rhyolite Ridge tuff (RRT). Completed 1:24,000-scale mapping provides additional context for the structural development of the lithium-bearing Cave Spring Basin. Detailed geologic mapping reveals a system of basin-bounding conjugate normal faults that controlled deposition of the Cave Spring Formation in a hydrologically closed basin that has undergone WNW-directed extension since late Miocene time. Geochemical data from pre-basin volcanic rocks reveal exceptionally high lithium concentrations up to 211 ppm, though with notable heterogeneity that inversely correlates with degree of alteration. Field relations, subsurface data, and new U-Pb geochronology reveal the RRT to be ~300-400 m thick not only at Rhyolite Ridge, but also along an 80 km-long NW-SE transect from the northern White Mountains to the southern Montezuma Range, which challenges the existence of the Silver Peak caldera, for which we find no direct field evidence. These findings support the RRT as the primary source of Li in Clayton Valley, and that the Cave Spring Fm. was deposited in a closed, syntectonic basin rather than the more typical intracaldera setting of other large sediment-hosted Li deposits (e.g., McDermitt caldera). A tectonic, non-caldera origin for sediment-hosted Li deposits at Rhyolite Ridge may stimulate enhanced exploration efforts in these common structural settings across the Great Basin.