STRUCTURAL EVOLUTION OF SEDIMENT-HOSTED Li-B DEPOSITS AT RHYOLITE RIDGE AND REGIONAL CORRELATION OF Li-ENRICHED ASH-FLOW TUFF ACROSS CLAYTON VALLEY, SOUTHWESTERN NEVADA

Global interest in decarbonizing the energy industry has driven a surge in demand for Li that makes sediment-hosted Li deposits associated with volcano-sedimentary systems an emerging resource target. Sediment-hosted Li (and B) deposits at Rhyolite Ridge (Nevada) are poised for development, yet critical aspects about the Li system – from the original Li source to the structural setting and its relation to a hypothetical ‘Silver Peak caldera’ – are not well understood. We use geologic mapping, structural analysis, petrography, geochemistry, U-Pb geochronology, and airborne electromagnetic (AEM) data to elucidate the structural evolution and probable source of Li enrichment in lacustrine strata of the Cave Spring fm at Rhyolite Ridge.

Three major events set the stage for regional Li-enrichment and basin development: (1) extension via low-angle detachment faults and sedimentation in a broad Esmeralda basin from ~15 to 8 Ma; (2) regional emplacement of the ~6.05 Ma Rhyolite Ridge tuff (RRT); and (3) a switch to high-angle transtensional faulting and dismemberment of the Esmeralda basin into smaller, hydrologically closed, half-graben basins since ~6 Ma (e.g., Cave Spring, Clayton Valley, N. Fish Lake Valley). Our results indicate that the Cave Spring fm was deposited in a syn-extensional, modified half-graben from ~5.8 to 4.7 Ma, that Li-B enrichment was likely syndepositional, and that WNW-directed extension and subsidence progressively migrated westward since then.

The Cave Spring fm overlies local metaluminous silicic tuffs and lavas of the Argentite Canyon fm and the RRT that contain unusually high Li up to 358 ppm (mean = 70 ppm). AEM data reveal moderately conductive structure at depths of ~300–500 m below the central Silver Peak Range that is incompatible with a thick, resistive intra-caldera RRT inferred at depth, refuting the existence of a concealed ‘Silver Peak caldera’ source for the RRT. We identify and geochemically correlate outcrops of RRT with similarly high Li from northern Fish Lake Valley to the Montezuma Range that suggest confined deposition in a ~80 km-long, NW-SE-oriented paleovalley. Our results suggest the RRT as the primary source of Li in both brine and sedimentary deposits throughout greater Clayton Valley, which may support regional exploration and promote enhanced efforts in these common structural settings across the Basin and Range Province.