The Rhyolite Ridge lithium-boron project is a greenfield project located in southern Nevada, US. Credit: ioneer.
The definitive feasibility study (DFS) completed in April 2020 validated Rhyolite Ridge as a world-class resource. Credit: Sibanye-Stillwater.
The Rhyolite Ridge ore is readily leachable and does not require major crushing and milling. Credit: Sibanye-Stillwater.

The Rhyolite Ridge lithium-boron project is a large-scale, greenfield open-pit project proposed to be developed in southern Nevada, US, by ioneer, an emerging company focused on lithium minerals production.

A definitive feasibility study (DFS) for the Rhyolite Ridge lithium-boron project was completed in April 2020. It indicated the potential for an open-pit lithium mining operation with an estimated capital investment of $785.4m.

The project will have an average annual production of 22,340t of lithium carbonate (Li₂CO₃) in the first three years, 21,951t of LiOH over the remaining mine life, and 174,378 tonnes per annum (tpa) of boric acid (H₃BO₃) over its lifespan. The total mine life is expected to be 26 years.

Multinational precious metals mining company Sibanye-Stillwater reached an agreement with ioneer to establish a joint venture (JV) for the development of the lithium-boron project in September 2021. The agreement will allow Sibanye-Stillwater to acquire a 50% interest in the JV by investing $490m in the project. ioneer will retain the remaining 50% and be responsible for the development and operation of the mine.

The company reached an agreement for the placement of shares to Sibanye-Stillwater. The proceeds from the placement will be used to meet the project’s capital requirement and medium-term working capital needs.

Construction works are expected to commence during the second half (H2) of 2022, following the completion of necessary permits and financing agreements. The first product shipment from the project is expected in H2 2024.

Rhyolite Ridge lithium-boron project location and geology

The Rhyolite Ridge project will be developed on a portion of land in Esmeralda County in the Silver Peak Range, approximately 20km north-east of Dyer, Nevada. The deposit is situated within the Basin and Range Province, which is dominated by horst and graben normal faulting.

The project area features tertiary volcanic rocks characterised by a sequence of interlayered sedimentary and volcanic rocks. Folded and faulted metasedimentary basement rocks from the Precambrian-Paleozoic era are overlain by the tertiary volcanic rocks.

Mineralisation and reserves of the Rhyolite Ridge project

The mineralisation at the Rhyolite Ridge project is hosted in lacustrine (lake) beds which envelop the Rhyolite Ridge Tuff and Argentite Canyon volcanic rocks aged more than six million years.

The lacustrine section within the Cave Spring formation hosts three members, of which the middle member is bounded by gritstones, bearing anomalous lithium in its upper half.

The proven and probable mineral reserves at the Rhyolite lithium-boron project were estimated at 60.2 million tonnes (Mt) grading 1,797 parts per million (ppm) of lithium and 15,418ppm of boron, as of April 2020.

Mining methods at Rhyolite Ridge lithium-boron project

The Rhyolite Ridge lithium-boron project will be mined employing an open-pit mining method using conventional drill-and-blast, and load-and-haul. Ore will be transported to the nearby ore processing stockpile and then fed to the crushing plant.

The project will be developed in two stages, with stage one involving the development of a starter pit in the southwestern part of the ore body to supply ore feed for the initial 4.5 years of the project. The ore in the stage one mining area is more exposed at the surface and has 15% higher lithium grades compared to the average grade for the deposit.

Stage two will involve the development of the greater pit to facilitate a larger mining area. It will support the operation of the mine for another 21 years through expansions to the south and east, as well as further to the north of the deposit.

The mining fleet in the initial operation will include automated haul trucks to reduce operating costs and accidents at the mine site. A high-precision global positioning system (GPS) and real-time analytics will support the operations of the mining fleet.

Mineral processing at the Ridge lithium-boron project

The processing facility will be an environment-friendly plant with measures to reduce the emissions of greenhouse gases and harmful pollutants into the atmosphere. The overall recovery is estimated to be 85% Li₂CO₃, 95% lithium hydroxide (LiOH), and 79% H₃BO₃.

The readily leachable property of the Rhyolite Ridge ore eliminates the need for major crushing and milling to achieve high lithium and boron extraction rates. The ore will be crushed to less than 20mm before being conveyed and stacked directly into the leaching vats.

A series of seven vats operating in a counter-current configuration will be used to sequentially leach the ore for three days with diluted sulphuric acid. A displacement wash will be used to remove valuable interstitial lithium and boron in the solution.

The vat leach or pregnant leach solution (PLS) will be cooled in a crystalliser to produce H₃BO₃ crystals. Centrifuges will be used to separate the crystals, which will be purified through recrystallisation.

The resultant solution from the crystallisation of H₃BO₃ will be treated for the removal of aluminium and other impure elements, before being sent to a four-stage evaporator circuit where up to 70% of water content will be removed. Lithium will also be concentrated in the evaporator circuit for further processing in the Li₂CO₃ circuit.

The Li₂CO₃ circuit will employ the precipitation method to remove the remaining magnesium from the solution. The process will also liberate Li₂CO₃, which will be filtered, washed and dried to produce technical-grade Li₂CO₃.

Off-take agreements of the Rhyolite Ridge project

The project envisions selling Li₂CO₃ as a technical-grade product at 99% purity during the initial three years of operation and lithium hydroxide (LiOH) at a 99.5% purity from the fourth year.

A binding off-take agreement was signed with Chinese boron company Dalian Jinma Boron Technology (Jinma) in December 2019. The agreement allows Jinma to procure 105,000tpa of H₃BO₃ from the project for five years.

ioneer signed two separate agreements with Kintamani Resources and Boron Bazar for the supply of H₃BO₃ in May 2020.

The company also reached an agreement with South Korean lithium battery specialist EcoPro Innovation for the supply of up to 7,000tpa of Li₂CO₃ for three years.

Infrastructure details at the lithium-boron project

A sulphuric acid plant with a capacity of 3,500 tonnes per day (tpd) will be constructed at the project site to produce commercial-grade (98.5%) sulphuric acid, which will be used for the vat leaching process.

The Rhyolite Ridge project will receive electricity from a 35.2MW on-site steam power plant, which will use steam produced from the waste heat boiler in the sulphuric acid plant to generate electricity.

A 13.8kV substation near the steam generator will distribute power to the project. A new heavy haul road will be built to facilitate the transportation of the ore from the quarry to the stockpile area.

Key players involved

Multinational engineering and construction company Fluor was engaged to prepare the DFS for the project. It is also the engineering, procurement, and construction management (EPCM) contractor for the project.

Canadian engineering firm SNC-Lavalin is responsible to provide engineering and procurement services for both the power plant and sulphuric acid plant.

The mine and haul road design were completed by consulting and design services company Golder Associates. Local engineering consultant Kappes, Cassiday & Associates (KCA) was selected to provide baseline metallurgical test work for vat leaching.

Global technology provider DuPont Clean Technologies was contracted to provide its MECS® sulphuric acid technology for the project. EM Strategies, NewFields, and Trinity were appointed to provide environmental permitting oversight and prepare permit applications.

Global automation solutions provider Emerson supported the DFS by providing control systems architecture and budget pricing. EnviroMINE and NewFields prepared the geotechnical report for the project.

Kemetco was awarded the contract to build a pilot plant for the project in March 2019. Mining equipment supplier Caterpillar was named as the exclusive heavy equipment partner for the project in October 2020.

Danish firm FLSmidth received a contract to supply major engineering and equipment, including crushing and material handling equipment, as well as lithium carbonate and boric acid dryers, in July 2021.

An engineering and equipment supply contract was awarded to water and wastewater treatment solutions provider Veolia Water Technologies for the supply of evaporation, crystallisation, and dewatering equipment, in August 2021.