Cape York projects – Queensland
Lithium Australia NL (‘LIT’) has established a substantial ground position in Queensland’s emerging lithium exploration sector. LIT’s three projects there – Cape York, Amber and Croyden – are in the Cape York region (see Figure 1) and have a combined area of almost 5,000 square kilometres (‘km2‘). These highly prospective geological environments in the far north of the state have been identified through a detailed understanding of the geology of the area, as well as open-file data research.
Figure 1: Cape York regional projects.
Cape York project
Extending over a length of 225 km, the five exploration permits that comprise this project are centered about 80 km west of Princess Charlotte Bay and some 350 km northwest of Cairns. With a combined area of 1,375 km2, the tenure was acquired to explore the margins of a leucogranite in a geologically favourable environment for late-stage alteration and pegmatite emplacement.
The geological focus is the historic recording of lepidolite in the Holroyd Group, a metamorphic sequence flanking prospective leucogranite source rocks (see Figure 2). Pegmatites are known in the area and the Geological Survey of Queensland has recorded some prior mining for mica. In addition to the area’s lithium prospectivity, graphite has been identified in the Sugar Bag Creek Quartzite and the George Quartzite, both major components of the metamorphic sequence.
Figure 2: Cape York Project located on the contact between the Holroyd Group and fertile granites.
Because the LIT tenements cover such a large area, early exploration will aim to delineate smaller areas of interest as having potential for lithium mineralisation. Open-file geophysical surveys will be acquired and reprocessed to target potential pegmatite swarms and radiometric signatures that may indicate greisens along the granite margins. Areas of interest will be mapped and sampled and, if results are sufficiently encouraging, drilling programmes will follow, to test the mineralisation at depth.
Amber project
LIT’s Amber project, which straddles the Gulf Development Road between Georgetown and Mt Garnet, comprises 14 exploration permits with a total area of 3,303 km2 (Figure 3).
Figure 3: Amber project locality plan.
The tenure was procured based on tectonic setting and the identification of fertile granitic intrusions (see Figure 4). These ‘leucogranites’ are often the source of lithium mineralisation that may occur in association with tin and tungsten. Although no lithium exploration has been recorded previously, the Amber region shows all the geological hallmarks associated with many predominant lithium provinces worldwide. When all applications are granted, LIT will control some 85% of the reported tin/tungsten mineralisation in the area.
Figure 4: Amber project geology plan with mineral occurrences.
The margins of the leucogranites are thought to be particularly prospective for lithium mineralisation with the development of pegmatites and greisens (highly altered granites) within a complex granitic-volcanic terrain.
Lithium exploration will initially concentrate at the historic recording of pegmatite and greisen hosted tin, tungsten, and fluorite occurrence. Most of these occurrences are related to local shearing and fracturing caused by various S-type granite and late-stage pegmatite emplacement during the Carboniferous
Existing geophysical data will be remodeled to enhance target generation and augment geological evaluation of the region.
Croyden project
With an area of 257 km2, the Croyden project – EPM 26733 – overlies granitic rocks of the Esmeralda Supersuite and the surrounding Croydon Volcanics. The tenement is centered on historic tin workings known as the Stanhills tin field. Between 1900 and 1936 it is estimated that 260 tonnes of cassiterite concentrates were mined from numerous small but high-grade lodes.Previous explorers reported that tin mineralisation is commonly associated with strong alteration of the granitic rocks. These greisen zones are fine-grained and composed principally of quartz and muscovite in approximately equal quantities. The lithium micas zinnwaldite and lepidolite are commonly associated with altered granites, as seen at the famous Cinovec lithium deposit in Germany and, in particular, LIT’s nearby polymetallic Sadisdorf deposit.
There is no record of lithium-focused exploration within the Stanhills tin field and evaluation of the tin potential was largely concluded in the 1960s, with non-economic outcomes. LIT, however, recognises that the Croydon project has the potential to host lithium-rich greisen deposits in highly evolved, rare-metal-enriched plutonic rocks of the Esmerelda granites.