graphite

Graphite
Graphite, the hexagonal crystalline form of carbon, occurs naturally as disseminated crystal flakes in high-grade metamorphic rocks, as veins, and as microcrystalline ‘amorphous’ graphite associated with metamorphosed coal seams. China supplied around one-third of the annual world natural graphite production of ~605 000 t in 1998. The major market for graphite is in the production of heat resistant ‘refractory’ linings where it is added as an important minor component to magnesia or alumina refractories used for lining furnaces and continuous casting equipment for steel production. Other markets include coating foundry moulds, brake linings, batteries, carbon brushes and lubricants.

South Australian Occurrences
Eyre Peninsula

Disseminated flake graphite is widely distributed in metamorphosed Palaeoproterozoic Hutchison Group rocks. On eastern Eyre Peninsula, numerous occurrences have been recorded over a 200 km long zone extending from south of Port Lincoln to Kimba. The largest resources are in the southern portion of this zone, and comprise the Mikkira Graphite Province which contains resources of ~350 Mt at 6–7% graphite inferred from geophysical surveys and the drilling of five prospects. This is the largest reported graphite resource in Australia and includes the Uley Graphite Mine, 18 km west-southwest of Port Lincoln (Fig. 1).

Graphite concentrate being collected from flotation
cells at the Uley Mine, 1993.

Uley was discovered in the 1910s and has been worked intermittently since the late 1920s. Exploration during the 1980s led to reopening the mine in 1986 but a sharp decline in world graphite prices in 1992 saw the operation placed on care and maintenance in 1993. Indicated resources are 2.9 Mt grading 13% graphitic carbon, including 1.5 Mt at 15% graphite. Graphite formed by high-grade metamorphism of carbonaceous sediments of the lower Middleback Subgroup which, at the mine, are tightly folded along the hinge of a regional, north-plunging anticline (Fig. 2). Processing comprised separation of 0.1–2 mm graphite flakes from weathered schist and gneiss by processes of grinding in a rod mill, froth flotation and gravity separation using Wilfley tables. Product from the mine was sold as coarse (+300 µm) and medium flake (+150 µm) in grades 90–94% graphite.

Other graphite resources on Eyre Peninsula have been investigated at Koppio (west of Tumby Bay), Campoona Hill (north of Cleve) and Carpa (west of Cowell). Results of investigations indicate that these resources are generally lower grade in terms of graphite content or flake size when compared to the Uley resources.

Other prospects

High graphite contents have been reported in schist units during gold and base metal exploration in the Olary district. The graphite is typically fine grained and has not been assessed for commercial uses. Occurrences of minor graphite are known from Precambrian rocks of the Mount Lofty Ranges near Woodside, Williamstown and Truro.

Additional Reading
Keeling, J.L., 2000. Uley graphite - a world class resource. MESA Journal, 18:6-11.

McNally, T.C., 1997. Uley graphite deposit. MESA Journal, 5:16-18.

Valentine, J.T., 1994. Graphite in South Australia — a review of production, use and geology. South Australia. Department of Mines and Energy. Report Book, 94/24.