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

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.