The Mt Deans Lithium Tantalum Project

The Mt Deans lease (P63/2063) was granted in September quarter 2019. The lease was subject to an earn-in JV with Lithium Australia NL which ceased in mid 2020, with the lease reverting to 100% Aruma. Aruma holds a positive view of the lithium tantalum REE potential of the lease area with previous work having identified swarm pegmatites over 1km in length.

The Mt Deans Project covers an area of 1.44km2 in the Mt Deans pegmatite field, which is part of the Eastern Goldfields Terrane of the Yilgarn Craton. The Project is located approximately 190 kilometres north of the Esperance port, 170km south of Kalgoorlie and approximately 10 kilometres south of the mining town of Norseman (Figure 1).

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Figure 1: Mt Deans Lithium-Tantalite Project area, with pegmatites and projected cauldron

The geology at Mt Deans presents as potentially analogous to that of Liontown Resources’ (ASX: LTR) world-class Kathleen Valley Lithium-Tantalum Project in the Mid-West region of WA, where the lithium mineralisation is hosted within spodumene-bearing pegmatites.

Details of Proposed Drill Program

Aruma’s first phase of drilling at Mt Deans will target the junction of known pegmatites within the Project area as the possible cauldron target. The drilling is designed to test for spodumene and other lithium minerals, plus tantalum, tin and rare earth minerals.

The Mount Deans pegmatite field covers an area of 6 kilometres north-to-south and 4 kilometres in extension east-to-west, and comprises multiple individual pegmatite sheets and lenses. It is Archaean in age and hosted in the north-south trending Dundas Hill greenstone belt.

Aruma plans to drill an initial 12 RC holes in the first phase of drilling at the Mt Deans Project, to a maximum hole depth of 200 metres and with drill holes spaced approximately 120 metres apart, to intersect the possible cauldron or pegmatite chamber (Figure 2).

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Figure 2: Mt Deans Lithium-Tantalite drill section with pegmatites and projected cauldron with the planned holes (From Tantalum Australia Operations Pty Ltd Annual Report 2002 (A65809)).

Project Background and Opportunity

The Mt Deans Project sits within WA’s lithium corridor in south-east WA, which hosts multiple significant hard-rock lithium projects. Previous work at the Project area from 2002, undertaken by Tantalum Australia Ops Pty Ltd, identified swarm pegmatites within the lease over a 1.5km strike length.

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Table 1: Locations of Aruma’s rock samples

In addition, Aruma conducted a limited rock chip sampling program which delivered exceptionally high lithium and tantalum results, with lithium (lithium oxide – Li2O) grades of up to 2.1% and tantalum (tantalum pentoxide – Ta2O5) of up to 556ppm in sample AR003. These compare favourably with similar deposits. Strongly anomalous rare earth results were also reported from the rock chip sampling program, as detailed in Tables 2 and 3.

In the formation of pegmatites from their associated granite, proximal pegmatites are the least evolved and poorly mineralised, containing only the general rock-forming minerals. More distal and evolved pegmatites may include beryl and columbite; tantalite and lithium aluminosilicates; and pollucite in the most evolved pegmatites. The lithium-rich or spodumene-dominated pegmatites may occur beneath the micaceous lithium minerals lepidolite-zinnwaldite zones seen at Mt Deans.

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Table 2: Assays results of Aruma’s rock samples (Assay Report 1560.0/1611047)  

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Table 3: Assays from Mt Deans rock samples results, with assays converted to oxide values     

The Mt Deans area has a swarm of 71 recognised pegmatites covering 4.5 by 1.5 kilometres trending north north-west (as discussed in Amit Eliyahu’s University of Western Australia thesis on the Mt Deans pegmatites). The pegmatites range from 500 to 2,000 metres in length and 0.3-7.5 metres thick, with a few 20 metres thick.

The pegmatites have an upper portion quartz-poor, feldspar-rich marginal layer, which is where most of the cassiterite and tantalum is found. The pegmatites in the project area are considered later (deeper) and are suggested to be closer to a main ‘cauldron’ or ‘chamber’ (Figure 2) that may host spodumene-rich material, potentially suitable for direct shipping.

A prime example of this style of deposit is Liontown Resources’ (ASX: LTR) Buldania and Kathleen Valley lithium deposits, where finger-like thin, steep pegmatites coalesce into a thick spodumene zone at shallow depth.

Aruma managing director Peter Schwann said;

“Aruma is of the view that the previous lithium results plus the high-grade tantalum and rare earth elements results, together with the infrastructure advantages afforded by the Project’s location make Mt Deans a highly exciting lithium exploration opportunity. We look forward to commencing our first pass drilling program at the Project as soon as the PoW is granted.”