Rhyolite Ridge is a geologically unique lithium-boron deposit that occurs within lacustrine sedimentary rocks of the South Basin, peripheral to the Silver Peak Caldera. The South Basin within the project boundaries measures 6 kilometers by 2 kilometers and covers an area of 800 hectares.

Rhyolite Ridge is one of only two major lithium-boron deposits globally and the only known deposit associated with the boron mineral searlesite. This mineralization style is different to the brine and pegmatite deposits that are the source of nearly all the lithium produced today. The lacustrine (lake) beds that host the mineralization lie within the Cave Spring Formation and overlie the 6-million-year-old Rhyolite Ridge Tuff and Argentite Canyon volcanic rocks. The lacustrine section that measures up to 457 meters thick is composed of three members, divided by marker beds of “gritstone” comprised of airfall debris with abundant pumice lapilli. The middle member, which is bounded top and bottom by distinctive gritstones, is dominantly marl, composing nearly 60 meters of section, and bears anomalous lithium in its upper half. About 18 meters of this section contains high concentrations of boron –contained in the sodium borosilicate mineral, searlesite (up to 30,000 parts per million [ppm] boron) – as well as lithium in mixed illite-smectite layers (about 1,500 to 2,500 ppm lithium). This marl is composed of very fine grained, intimately mingled searlesite, smectite, illite, potassium feldspar, and carbonate. The searlesite zone is capped by about 12 meters of smectite-rich marl with relatively high lithium values (commonly 2,000 to 2,500 ppm). The grade and thickness of this middle member are laterally uniform and continuous over a distance of at least 3 kilometers north to south.

The Cave Spring Formation hosts the ore zones of interest for the project, designated as follows:
- M5 – 13-meter-thick lithium claystone layer to be removed and separately stockpiled for possible future processing.
- B5 – 18-meter-thick upper ore zone of high-grade lithium-boron ore making up most of the ore planned for extraction.
- L6 – 40-meter-thick lower ore zone of lower-grade lithium-boron ore zone.

Underlying layer are sedimentary and volcanic rocks of the Silver Peak Formation.

Development of the Rhyolite Ridge quarry will occur in two stages:

- Quarry Stage 1 – Starter Pit. An initial starter pit will be developed in the southwestern part of the ore body to supply ore for the first 4.5 years of the project. In this area, lithium grades are 15% higher than the average grade for the deposit and the ore is more exposed at surface.

- Quarry Stage 2. Development of the greater pit will start once the environmental permits for this development have been granted. The Stage 2 pit design will facilitate a larger mining area to be maintained, aiding the efficiency of the operation for another 21 years (there will be an overlap of Stage 1 and Stage 2 ore mined during years 4 and 5). Stage 2 will involve expansion to the south and east. Finally, mining will progress to the north of the deposit. The Stage 2 pit requires prestripping to begin in year 4.

The mining operations will consist of a conventional drill-and-blast, load-and-haul operation. Ore will be trucked from the mine quarry to the nearby ore processing stockpile over a new heavy haul road. The ore will be reclaimed by a loader and fed to the crushing plant.

The open-pit mining operations are scheduled nominally for 350 days per year. It was assumed that 15 days per year will be lost due to unscheduled delays such as weather conditions. The open-pit equipment will operate 24 hours a day in two 12-hour working shifts.

The key parameters for the corresponding mine plan and mine schedule are as follows:
- Minimize initial overburden prestripping.
- Minimize mine disturbance area during the first 3 years (through starter pit operations).
- Target mining of higher grade lithium ore at the beginning of the project.
- Achieve 2.5 million metric tons per annum ore production.
- Maintain high-grade ore feed to the plant during the initial phases of the mine life.

IONEER will capitalize on current mining advances to enhance project performance including:

- Haul Truck Automation. IONEER will become the first greenfield site in the United States to use automated haul trucks in the initial operation. This has shown to have several advantages in operating and capital costs in addition to minimizing safety incidents.

- Mining Selectivity. To minimize the effects of loss and dilution in the mining operation, an accurate geologic model, high-precision GPS (global positioning system), competent operators, and a fleet management system (FMS) will be used. Specifically, an integrated, GPS-guided bucket system, such as Caterpillar’s (CAT) MineStar Terrain package, will allow excavator and wheel loader operators to know in real time what type of material is being loaded.

In-pit dewatering will be necessary in all stages of quarry progression to maintain a dry, stable floor, as the lower hydraulic conductivity Cave Springs formation provides a barrier to groundwater flow in the quarry.

Dewatering rates are predicted to range from 15 to 27 cubic meters per hour. A minimum of one dewatering area will be maintained at all times in the lowest area of the pit floor. This water will be pumped out of the quarry using dewatering pumps where it will be sent to the process circuit for reuse. Stormwater controls will be constructed around the perimeter of the pit, before the quarrying process begins in the respective area, to limit the quantity of water in the pit. Between production years 4 and 9, there may be two entirely separate mining areas in two separate pits, in which case two dewatering areas will be used, one for each pit.

The quarry lake mentioned above is expected to form in the quarry after dewatering ceases. For evaluating quarry lake impacts, three scenarios were simulated: a base case (expected); scenario that simulated the quarry lake refilling with a higher hydraulic conductivity; and another with a lower hydraulic conductivity. In all cases, the quarry lake is predicted to stabilize below the local, pre-mining groundwater elevation, resulting in a long-term stable hydraulic sink around the quarry.

ORE SIZING
Blended ore is transported by belt conveyor to the primary and secondary sizers where the coarse ore particles are crushed to less than 20 mm. The crushed ore is conveyed and stacked directly into the leaching vats. A unique property of the Rhyolite Ridge ore is that large particles are readily leachable and do not require expensive size reduction and milling to achieve high lithium and boron extraction rates.

The Rhyolite Ridge process is expected to produce quality products at an overall recovery of 85% for lithium carbonate, 95% for the lithium hydroxide circuit, and 79% for boric acid, excellent yields for these products, particularly lithium.

The Rhyolite Ridge process plant general layout consists of the main unit operations described below:

VAT LEACHING
The vat leaching process uses a series of 7 vats where crushed ore is sequentially leached for 3 days with diluted sulphuric acid. The vats operate in a counter-current configuration, made possible by the unique Rhyolite Ridge ore particles remaining largely intact and free-draining during the leach process. Counter-current leaching minimizes the overall leaching time and acid consumption. The spent ore undergoes a displacement wash to remove valuable interstitial lithium and boron in solution. The spent ore is free draining, allowing the vat to be emptied of solution and produces a residue material that is s ........