DOI: 10.5061/dryad.rxwdbrvft
title: 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

description: 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.
description: Section 5.7 - Petrographic Microscopy
 One hundred seventeen polished thin
 sections have been prepared using the Wagner Petrographic thin section
 service in Lindon, UT. Twenty-five of these thin sections were prepared
 from the 17 Crux Samples and are the focus of microscopy analysis. Fifteen
 of the non-Crux Sample thin sections were used to select samples for Ar-Ar
 geochronology, as described in section 5.9. Petrographic microscopy
 allowed for textural analysis of bedding, depositional features, position
 of zeolites relative to clays and glass, correlations between phases and
 sanidine freshness evaluation. It also refined target areas for Scanning
 Electron Microscopy (SEM) work. The ore zone is extremely fine-grained and
 optical microscopy is not powerful enough to characterize the
 relationships between minerals. Refining target areas by use of optical
 microscopy focused and expedited observations in preparation for SEM
 analysis. Section 5.5 -
 X-Ray Diffraction (XRD) X-ray diffraction (XRD) was used to
 identify mineralogical components of samples that are too small to be
 identified using standard techniques of optical microscopy. Using
 additional material saved during centrifugation (Section 5.3) of samples
 that were not submitted for geochemistry, clay-sized fractions of
 &lt;0.5 μm and coarse size fractions of 2-595 μm were analyzed using
 the Bruker D-2 Phaser X-ray Diffraction instrument at the University of
 Nevada Reno. Typically, clay-sized material is &lt;2 μm, however the
 fine-grained nature of the lacustrine sediments in Unit 2 resulted in clay
 separates with a significant percentage of impurities. Isolating the
 &lt;0.5 μm size fraction is intended to concentrate the clay mineral
 phases and minimize non-clay phases. Mineralogy was determined by XRD, using
 randomly oriented powder and oriented clay sample mounts. The random
 powder mounts – scanned from 4 to 70 degrees two-theta using Cu K-alpha
 radiation, with a step size of 0.02 degrees two theta, and a count time of
 one second per step – allow the crystals in the sample to be unoriented;
 this produces a pattern that is compared to the AMCSD 2019 database for
 mineral phase identification (Downs & Hall-Wallace, 2003) through
 the MDI Jade program (MDI, 2017). Oriented mounts – scanned from 4 to 45
 degrees two-theta using Cu K-alpha radiation, and a count time of one
 second per step – are prepared by air-drying a wet sample onto a glass
 slide overnight while covered. With a properly prepared oriented slide,
 the clay crystals are oriented with the c-axis pointed up so the x-rays
 can interact with the 001 face and identify the d-spacing easily (Moore
 & Reynolds, 1997). Oriented mounts are run 4 times – first air
 dried, then glycolated, then heated to 400°C, and finally heated to 550°C
 – and peaks in the resultant pattern behave distinctly depending on the
 clay phases present. An air-dried swelling clay will have a d-spacing of
 between 12-14Å. Treatment with ethylene glycol will swell the d-spacing to
 approximately 17Å. Heating of the clay will then collapse the swollen
 clays to a d-spacing of approximately 10Å (Figure 30). A flow chart and
 the methods defined in Poppe, et al. (2001) are used to determine specific
 clay phases.
description: # 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
 ## Description of Appendix
 III Raw Data See Appendix III for interpreted images. This is the
 repository for high-resolution original photos that remain uninterpreted.
 ### Description of the data and file structure Each folder, labeled by
 sample number, contains all images from a given sample. Each image is
 labeled with: Figure number (correlated to its image in the text), Sample
 number, Location letter, power of magnification, PPL (plane-polarized
 light) or XPL (cross-polarized light), and, if applicable,
 "rotated" (representing 45 degree rotation to show variability
 of extinction phases). Example file name: Figure III-2.3 DCC-062, locA,
 20x, XPL, rotated ## Description of Appendix VI - XRD Raw Data Grain
 mounts were constructed for topographic imaging using XRD. ### Description
 of the data and file structure Six (6) Excel spreadsheets comprise the
 contained .zip file labeled XRD_Raw_Data. Every column labeled
 "Degrees_two_theta" is the x-axis for all samples to the right
 of it, where counts are in whole numbers. Subsequent columns labeled
 "Degrees_two_theta" are a new x-axis for subsequent samples and
 their associated count to the right. 1. Data Dictionary - defines all
 headings and indicates units as well as min and max counts for each sample
 and associated date that analysis was run. 2. RR XRD BulkSediment
 RandomPacked Samples - Raw data of bulk sediments in a random packed mount
 from the Crux Samples, with associated dates in the sample name, listed in
 counts vs degrees_2theta. 3. RR XRD 0.5micronClay RandomPacked Samples -
 Raw data of clay separates in a random packed mount from the Crux Samples,
 with associated dates in the sample name, listed in counts vs
 degrees_2theta. 4. RR XRD 0.5micronClay Oriented Samples - Raw data of
 clay separates in an oriented mount from the Crux Samples, with associated
 dates in the sample name, listed in counts vs degrees_2theta. Each sample
 has four columns of data: air-dried, glycolated, heated to 400 degrees C,
 and heated to 550 degrees C. Some samples have a 5th column in the form of
 a re-run test on the glycolated pattern to see if the glycolated sample
 was run quickly enough to test the expanded clays before the ethylene
 glycol evaporated off. 5. RR XRD QC Standards Measured Peak Positions -
 Raw data collected of ZnO powder and NIST 1976c corundum standards, with
 associated dates in the sample name, listed in counts vs degrees_2theta.
 6. RR XRD QC Standards Expected Peak Positions - Worksheet with expected
 peaks at 6 different values of degrees_2theta for the NIST_1976c standard
 and expected peaks at 3 different values of degrees_2theta for the ZnO
 powder standard.