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Raw petrographic microscopy photos and XRD data used in assessing the mineralogy of the Li-b enriched stratiform ore zone in the Cave Spring Formation, Rhyolite Ridge, NV, USA

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Jan 16, 2024 version files 40.47 GB

Abstract

The Rhyolite Ridge Project in the Silver Peak Range contains lithium and boron mineralization hosted by late Miocene-early Pliocene strata-bound sediments in an intermontane valley. The ioneer USA Corporation is developing this project and is the industry-sponsor for this research along with the USGS and CREG. A lacustrine section called Cave Spring Formation, measuring up to 1,500 feet thick, hosts the sediments of interest. The unit with economic potential is the middle unit, a 60-foot interval called the Searlesite layer that is mineralized with both lithium clays and boron and is the targeted ore zone and the focus of this research. The younger, marl-rich member of this unit, the Li-Marl layer, shows no searlesite but has higher concentrations of lithium, hosted in smectite-rich interbeds.

This research characterizes the lithium and boron mineralization and examines whether diagenesis of tuffaceous sediments (including precipitation of zeolites and searlesite) enhances Li concentration in Li-bearing clays. Detailed mineralogical and geochemical analysis of the Li-Marl and Searlesite layers distinguishes the two layers and provides insight into the depositional environment of the ore zone and the evolution of the pore water during deposition of the younger material. The abrupt change in geochemistry between these layers is striking, and the genetic relationship between the mineralogy and the economic value of the sediments is directly related to the paleo lake conditions. 17 samples from one core hole – SBH-086 – characterize the lacustrine sediments of the Li-Marl and Searlesite layers of the Cave Spring Formation. The minerals identified include carbonates such as calcite, dolomite and strontianite; searlesite; zeolites such as analcime, heulandite and phillipsite; celadonite; and Li-bearing clays that form as disordered I/S mixed-layer clays composed of primarily montmorillonite and illite. The highly mineralized zone represents the most diagenetically altered material, and the mineral suite in the searlesite layer is the result of this diagenesis in the presence of boron. X-ray diffraction techniques are employed to distinguish the fine-grained sediments, and geochemistry assists with understanding the clay structural formulas of the I/S mixed-layer clays. These data enhance understanding of ioneer’s resource and the conceptual deposit model, which could prove useful for additional discovery of analogous deposits in other locations. Additionally, recovery and processing of the ore may be enhanced by quantifying variation in grade as a function of clay and borate mineralogy. The entire sample suite is represented here, and a model of clay structural formulas is informed by geochemical analysis and XRD interpretation of bulk material and clay separates.