Cape York region, 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 Cobree – are in the Cape York region (see Figure 1) and have a total area of 2,699 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.

Cape York

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 1,380 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.

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

LIT’s Amber project straddles the Gulf Development Road between Georgetown and Mt Garnet. It comprises four contiguous exploration permits (three granted in April 2017) with total area of 994 km² (see Figure 3).

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.

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.

Cobree

With an area of 325 km², the Cobree project is 100 km west of the coastal town of Ingham and 30 km east-northeast of the now abandoned Greenvale nickel mine (see Figure 5). A number of mineral occurrences are recorded within and proximal to the tenement, including tungsten (Wolfram Hill), gold (Claypan Dam, Black Dog Creek and Suprende) and tin (Ugly Corner). Of significance to LIT, however, is the lithium potential of a new type of mineralisation at the Bitumen and Cobree prospects central to EPM26353.

Regionally, the tenement occupies a portion of the Thompson Fold Belt and locally the Camel Creek Sub-province, a mid- to late-Palaeozoic basin containing Ordovician to Devonian sedimentary sequences with minor mafic volcanics and younger Camel Creek-type granitoids. Tenement geology comprises mudstones, quartz and feldspathic sandstones, chert and conglomerates of the Greenvale, Pelican Range, Perry Creek and Kangaroo Hills Formations.

For LIT, the primary zones of interest are the Tertiary iron-stained, cemented manganiferous sands and grits resting unconformably on rocks of the Silurian-aged Greenvale Formation. Topographically, the deposits are located on the flanks of low hills rising some 20 m above the surrounding plains, but the sequence appears to have originally been deposited into channels incised into the older Palaeozoic basement rocks. Structural activity and elevated thermal regimes during the Tertiary period are postulated to have caused the formation of the cemented, manganese-oxide deposits.

The manganese oxide contains the mineral lithiophorite (the name, literally, means ‘lithium bearer’), an oxide of aluminium and manganese. Lithiophorite has an open crystal structure that can accommodate a variety of metal cations, primarily cobalt and nickel, but also rare-earth elements and lithium. LIT was drawn to the area by reports of bulk rock concentrations of up to 0.5% lithium oxide in samples collected in a 1989 field survey of the Bitumen occurrence. However, no subsequent follow-up exploration of any significance occurred.

Neither the petrogenesis nor economic potential of the deposits is well-understood, and no focused exploration on the lithium-bearing manganiferous wads at Bitumen and Cobree has been undertaken. Aerial imagery and digital elevation models will be acquired and used to map the extent of the mineralisation. Detailed surface and trench sampling is also necessary, to provide greater understanding of the likely extent and lithium content of the deposit. Larger samples will be collected and be tested for amenability to treatment using LIT’s Sileach™ processing technology.