Highlights

• Latest results from ongoing optimisation acid-leach testwork on Rhyolite Ridge lithium-boron mineralisation show that reducing the crush size improves both leach time and recoveries:
  • Column leach time reduced from 41 to 15 days – a 60% reduction
  • Recoveries to solution increased to 97% for lithium and 98% for boron
• Vat leach testwork returned high recoveries of both lithium (92%) and boron (80%)
• Further improvements for vat and column tests likely with ongoing optimisation testwork
• Consultants Amec Foster Wheeler are conducting trade-off studies as part of the Pre-Feasibility Study (PFS) to determine the optimal processing route
• Global’s Rhyolite Ridge is the only lithium deposit in the world that has been demonstrated to be amenable to simple acid leach processing, reinforcing it as a credible alternative to spodumene and brine deposits as a major, low-cost and long-term source of lithium

SYDNEY, Australia, Feb. 20, 2018 (GLOBE NEWSWIRE) -- Australian-based lithium-boron mine developer Global Geoscience Limited (“Global” or the “Company”) (ASX:GSC) today announced the results of further acid-leach testwork at its 100%-owned Rhyolite Ridge Lithium-Boron Project in Nevada, USA. The latest column leach testwork (for heap leach) has shown that 97% of the lithium and 98% of the boron was extracted into solution within 15 days when the feedstock is crushed to minus 38mm.  This represents a 60% reduction in leach time when compared to previous column tests where feedstock was crushed to minus 150mm. 

Global Geoscience’s Managing Director, Bernard Rowe commented:

“In December, we announced the significant breakthrough of Rhyolite Ridge mineralisation being amenable to heap leaching based on the initial column leach testwork. These latest results show a major reduction in column leach times by simply crushing the feedstock to minus 38mm compared to the minus 150mm used for the initial tests. Recoveries to solution also improved to near-maximum levels.

“The unique Rhyolite Ridge mineralogy enables the lithium and boron minerals to be readily dissolved in sulphuric acid – meaning high recoveries and short leach times with acceptable sulphuric acid consumption.

“This testwork has further demonstrated that acid leaching is likely to be a simple, low-cost processing route for this unique lithium-boron mineralisation.

”Our team and Amec Foster Wheeler are now evaluating the range of excellent testwork results obtained to date. This will determine the most favourable processing flowsheet to be progressed in the Rhyolite Ridge PFS.”

Ongoing metallurgical testwork conducted by Hazen Research (Denver) and Kappes Cassiday (Reno) has further demonstrated that simple, low-cost acid leach processes can be used to extract lithium and boron at high recovery rates into a Pregnant Leach Solution (“PLS”).  Lithium and boron can then be removed from the PLS through crystallisation and purification steps to produce lithium carbonate and boric acid at the mine site.

The table below compares the key results announced today (Column 4 and Vat 1) with the key results announced on 12 December 2017 (Columns 2 and 3).

* Vat 1 represents a preliminary vat test and significant increase in boron recovery and decrease in leach time are expected based on the results obtained.

All results to date indicate that the Rhyolite Ridge lithium-boron mineralisation responds extremely well to acid leaching.

In January 2018, Global appointed Amec Foster Wheeler (part of Wood plc) as the engineering and design firm to complete the Rhyolite Ridge Pre-Feasibility Study (“PFS”). The high-grade lithium-boron mineralisation is the focus of the Rhyolite Ridge PFS as it represents potentially the highest value material combined with a low-cost, simple processing route.  This is due to the low-clay, low-carbonate and high-searlesite (boron) content of the rock, which make the mineralisation amenable to low-cost acid leaching at ambient temperature and pressure. The proposed flowsheet will allow for the production of lithium carbonate and boric acid at the mine site.

Since the Rhyolite Ridge lithium-boron mineralisation responds extremely well to acid leaching, Amec Foster Wheeler is currently evaluating various processing flowsheets to determine the best route to proceed with in the PFS. The processing routes being evaluated in this trade-off study include agitation (tank) leaching, vat leaching and heap leaching.

On-going metallurgical testwork is also analyzing various options for the crystallisation and purification process steps.

Column and Vat Leach Testwork

Testwork was conducted on samples collected from outcrop (424750E, 4185750N NAD27 Z11) from within the Rhyolite Ridge Mineral Resource. The samples are considered to be representative of the high-grade lithium-boron mineralisation across the Resource. 

On 12 December 2017, the Company announced column (heap-leach) testwork results for three large samples (150kg to 495kg) crushed to minus 150mm.

The testwork results announced today are for two additional tests:

1. a column test comprising 58kg sample crushed to minus 38mm
2. a vat leach test comprising 150kg sample crushed to minus 150mm

For the column test, the sample was blended with sulphuric acid prior to be loaded into a 20.2cm diameter and 181.6cm tall column.  Dilute sulphuric acid solution was then applied to the top of the column using a continuously drained drip method at a flow rate of 9-12 g/min at ambient temperature.  Recovery rates for lithium and boron were very high, reaching 98% after fifteen days.  This compares very favourably with 41 days to reach 90% for previously announced column tests where the feedstock was crushed to minus 150mm.  The results suggest that finer particle sizes (-38mm) allow a more rapid contact between the acid and the rock resulting in a significantly faster leach time.  Further improvements are anticipated from ongoing testwork.