The licence covering the Mt Deans Project (P63/2063) was granted in September quarter 2019. The lease was subject to an earn-in JV with Lithium Australia NL which expired in mid 2020, resulting in the Project reverting to Aruma 100%. Aruma holds a positive view of the lithium, tantalum and REE potential of the Project 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 190km north of the Esperance port, 170km south of Kalgoorlie and approximately 10km south of the mining town of Norseman (below).

Image module

Mt Deans Lithium-Tantalite Project, 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.

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 (below).

Image module

The 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

Image module

Table 1: Locations of Aruma’s rock samples

In addition, Aruma conducted a limited rock chip sampling program which delivered exceptionally high-grade 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 below.

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.

Image module

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

Image module

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 4.5km by 1.5km trending north, north-west (as discussed in Amit Eliyahu’s University of Western Australia thesis on the Mt Deans pegmatites). The pegmatites range from 500m to 2,000m in length and 0.3m to 7.5m thick, with some 20m 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’ 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.