- Leach results provide an economic pathway for Rhyolite Ridge to become a significant near-term producer of lithium and boron through a low-cost acid-leach flowsheet using established technologies and processes.
- Recoveries of 98% for lithium and 99% for boron from acid-leach testwork.
- Acid consumption of 296kg per tonne of ore for both metals, well below the pre-test target range of 350-450kg.
- Work has commenced to optimise the processing flowsheet.
- Pre-Feasibility Study due for completion in late 2017.
- Global has exercised its option to acquire 100% ownership of the Rhyolite Ridge Project with no residual interest or royalties to the previous owners.
Global's Managing Director, Bernard Rowe commented: "The acid-leach results exceed our expectations and demonstrate that Rhyolite Ridge mineralisation is amenable to low-cost acid-leaching to extract lithium and boron. The combination of high recoveries and low acid consumption from the testwork indicates the likelihood of favourable economics."
Company Chairman, James D. Calaway commented "Our processing team, headed by Silvio Bertolli and Peter Ehren, working with Hazen Research and SGS Minerals, have made significant progress in uncovering and understanding the unique properties of this deposit, and then applying this knowledge to design what is a simple processing flowsheet. These latest results confirm our view that we have an economic pathway to make the Rhyolite Ridge resource into a significant, near-term producer of lithium and boron in America."
The current work program is evaluating a simple process route involving crushing, grinding and flotation followed by acid leaching to extract lithium and boron from the high-grade Li-B (Searlesite) Indicated and Inferred Resource at South Basin (65Mt at 1.0% Li2CO3 and 9.1% H3BO3). The process will allow for the on-site production of lithium carbonate/hydroxide and boric acid. Testwork is being undertaken by Hazen Research in Colorado, USA and SGS Minerals in Ontario, Canada under the supervision of Silvio Bertolli and Peter Ehren.
Acid is a major cost in the proposed flowsheet and the reduction in acid consumption has been a major focus of the work. Low acid consumption will have a significant positive effect on the economics of the deposit.
Key findings from the program are:
- High grade Li-B rich mineralisation occurs in thick (20-30m), consistent and flat lying sedimentary layers within the deposit. Mineralogical and geochemical continuity is very high across the deposit including between outcrop and at depth in drill core.
- The rocks are dominated by the minerals searlesite (B-bearing), sepiolite (Li-bearing), K-feldspar and calcite/dolomite.
- Calcite and dolomite (acid consuming carbonate minerals) can be removed prior to leaching via reverse flotation with recoveries for lithium and boron above 95%.
- Lithium and boron can be leached using sulphuric acid with high recoveries (98% for Li and 99% for B) and low acid consumption (296kg per tonne of ore).
Acid Leach Results
The acid leach testwork was conducted on samples collected from outcrop and diamond drill hole SBHC12 from within the South Basin Mineral Resource and considered to be representative of the high-grade Li-B searlesite mineralisation across the Resource. Carbonate minerals were removed from the de-slimed samples by reverse flotation prior to acid leaching.
Concentrates from flotation (containing 5% CO3) were leached with sulphuric acid at a controlled and maintained acidity and temperature, and 25% solids over a 4-hour period. Results show recoveries of up to 98% for lithium and 99% for boron. Acid consumed during the test was measured at up to 353kg per tonne of feed (flotation concentrate) which equates to 296kg per tonne of raw ore.
A comparative leach test performed on whole ore (no flotation, containing 17% CO3) showed a 57% greater acid consumption for similar recoveries (98% Li, 93% B).
Test results have confirmed that boron is easily and completely leached at low acid levels and ambient temperatures, while lithium requires higher temperatures (50-80oC) and increased acidity. This should readily allow for separation of boron from lithium early in the process. The results also confirm the viability of using a reverse-flotation technique for decreasing the cost of acid during leaching. This circuit will be optimized to achieve the highest carbonate rejection at acceptable lithium and boron recoveries.
Future Work Program
With the results obtained, the Company will focus on optimizing the front-end process conditions. Future work will include additional carbonate flotation and leaching tests in order to arrive at optimal design conditions for these process steps. Additionally, future tests will involve work in brine concentration and crystallization of boric acid, brine purification, and lithium carbonate precipitation tests. The work will provide the preliminary design criteria for the design of the process facility at Rhyolite Ridge and the basis for a pre-feasibility study to be completed late 2017.
1. Optimisation of the flotation and acid leach process steps
2. Leaching lock-cycle tests to provide design data
3. Production of brine for crystallisation testwork
4. Production of boric acid, lithium sulphate, lithium carbonate or lithium hydroxide
Exercise of Option for 100% of Rhyolite Ridge
Global Geoscience has exercised the option to purchase 100% ownership interest in the Rhyolite Ridge Project. Under the terms of the agreement, upon exercise of the option Global must pay the owner US$200,000 cash and US$1,500,000 in Global shares (subject to a 6-month voluntary escrow period). The number of Global shares to be issued will be determined using the 30-trading day VWAP for Global shares (15 trading days on either side of the notice date) and an exchange rate of A$1:US$0.75.
About Rhyolite Ridge Lithium-Boron Project
Rhyolite Ridge is a lithium-boron deposit located in southern Nevada and is 100% owned by Global Geoscience. The project consists of two sedimentary basins located four kilometres apart: South Basin (9 km2) and North Basin (20 km2). South Basin includes an Indicated and Inferred Resource of 3.4 million tonnes of lithium carbonate and 11.3 million tonnes of boric acid, making it one of the largest lithium and boron deposits in North America. The Resource is open in most directions and is likely to increase in size with additional drilling. North Basin hosts thick, shallow lithium-boron mineralisation drilled by wide-spaced holes that are not yet sufficient to estimate a Resource.
The South Basin Indicated and Inferred Resource contains a high-grade Li-B zone referred to as the Searlesite Zone and comprising 65Mt at 1.0% Li2CO3 and 9.1% H3BO3 for a total of 650,000 tonnes of lithium carbonate and 5.9 million tonnes of boric acid.
The mineralisation is hosted within shallow, flat-lying sedimentary rocks, representing a potential third source of lithium. Lithium-boron mineralisation occurs with the mineral searlesite - an acid-leachable sodium boro-silicate mineral.
Rhyolite Ridge is located close to existing infrastructure and is 25km west of Albermarle's Silver Peak lithium mine and 340km by paved road from the Tesla Gigafactory. It has the potential to be a strategic, long-life, low-cost and reliable source of lithium and boron.
To view tables and figures, please visit:
About Global Geoscience Limited
Global Geoscience Limited (ASX:GSC) is a Sydney-based mineral exploration company specialising in greenfield exploration and mineral discovery. The Company's main focus is for copper, gold and silver on its mostly 100%-owned projects in Nevada and Arizona in the United States, and Peru in South America.
Global Geoscience Limited