Ravensthorpe, Western Australia
Lithium Australia NL (‘LIT’) holds 100% equity in the Ravensthorpe lithium project, located 420 kilometres (‘km’) southeast of Perth. The project consists of a single Exploration Licence, 74/543, covering a structural corridor 20 km long. Lithium mineralisation in the LIT tenure is hosted by the Cocanarup pegmatite swarm, which lies within the same geological sequence as the Mt Cattlin lithium mine of Galaxy Resources Limited, 18 km to the north (see Figure 1).
Several large pegmatites were already identified from historical exploration, while recent fieldwork has greatly enhanced the project’s potential through the discovery of additional, and substantial, pegmatite units. The Horseshoe pegmatite is estimated to contain an Exploration Target of between 525,000 tonnes (‘t’) and 1,281,000 t at a grade of between 0.8% and 1.2% lithium oxide (‘Li2O’).
A recently excavated costean has revealed lithium mineralisation that includes spodumene, lepidolite and elbaite, all of which can be processed with LIT’s 100% owned SiLeach® process.
Although a drilling programme undertaken in July 2017 (see photos below) confirmed the geological and structural setting of the Horseshoe pegmatite, it failed to intersect economic lithium grades. The programme was abbreviated due to wet conditions. Drilling is due to recommence following further trenching across the pegmatites to better understand the distribution of the mineralisation.
E74/543 covers a belt of Archaean greenstones hosting numerous occurrences of copper, gold and zinc. The greenstones are draped around granitoids, the late-stage, volatile phases of which discordantly intrude the greenstones. These late-stage intrusive phases, which solidified as pegmatites, have concentrated the lithium and rare metals.
The regional mineralisation potential is well demonstrated by the occurrences of lithium pegmatites at Mt Cattlin, as well as sporadic production from other pegmatites within the area, which have been exploited for rare metals. E74/543 contains a significant proportion of the Cocanarup Pegmatite Field, discovered in 1900. The licence includes pegmatites named Quarry, Horseshoe and Eastern. Previous exploration identified lepidolite at Horseshoe (see Figure 2), zinnwaldite at Eastern, and lepidolite, beryl and tantalite at Quarry.
The maiden drilling programme, designed to test the Horseshoe pegmatite, has been completed. Twenty-six reverse circulation drill holes ranging in depth from 19 metres (‘m’) to 72 m, totaling 959 m were drilled in July 2017.
That drilling confirmed the Horseshoe pegmatite as a relatively flat, sheet-like body with a true thickness ranging from 15 m to 25 m. The continuation of the pegmatite to the west of the surface expression is open, and the lithium minerals spodumene and lepidolite were identified in the drill chips.
Assays failed to define any economic lithium mineralisation. Trenches across the pegmatite clearly show that the main lithium-bearing minerals, lepidolite and spodumene, are irregularly distributed and tend to form discrete veins and pods. More costeans are planned prior to any further drilling at Horseshoe, to better quantify the nature of the mineralisation.
Wet weather, which adversely affected drill rig access, prematurely terminated the recent drilling campaign, which will resume when ground conditions improve later in the year. Initially the focus of that drilling will be other pegmatites in the suite, commencing with Deep Purple, a lepidolite pegmatite located east of the Horseshoe pegmatite.