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Leading Practice Mining Acts Review | Central Eyre Iron Project mining lease approved

state_kaolin_smKaolin (hydrated aluminium silicate, Al2Si2O5(OH)4) is the most important of the industrial clays in terms of both consumption and value. Properties of fine particle size, platy shape, inertness, non-toxicity, and high brightness and whiteness make it a most versatile mineral, with applications in a wide variety of industries. The largest single market, taking ~40% of production, is the paper industry where kaolin is used to fill the spaces between cellulose fibres, and as a coating agent to produce high gloss paper with good printability. Other uses include clay-based ceramics and refractories, white cement, fibreglass, and fillers and extenders in rubber, paint, plastic and adhesives. Numerous minor uses include pesticide and herbicide carriers, zeolite manufacture, catalyst supports, pharmaceuticals and cosmetics.

Commercial kaolin resources are found as sedimentary deposits and as weathering or hydrothermal alteration products of rocks containing a high proportion of alumino-silicate minerals.

World resources of all clays are extremely large. World production was 37 Mt, with the largest exporters being United Kingdom, United States and Brazil. Recent Australian production has declined from ~360 000 t/year in 1990–91 to 250 000 t in 1997–98, due mainly to closure of Comalco’s Weipa kaolin operation in 1996.

South Australian production in 2013 was 3,400 tonne from Birwood and was used for white cement manufacture and filler applications in paint and plastics.

Eyre Peninsula 

Exploration and resource drilling on north-western Eyre Peninsula has outlined very large kaolin-(halloysite) resources in the Poochera district, including the Careys Well, Karcultaby South, Tootla, Tomney, and Condooringie Well deposits. Of these, weathered Hiltaba Suite granite in the Carey Well area, 15 km southwest of Poochera, has returned the highest quality kaolin, with a resource of 16.3 Mt of “bright white” kaolin identified. Testwork from samples from all deposits has confirmed that kaolin from all deposits is pure, and exceptionally white, and has potential for use in high value kaolin markets. There is potential to considerably expand the resource size throughout Eyre Peninsula. 

Mount Lofty Ranges

Small, high-grade kaolin deposits are mined at Williamstown and Birdwood, 40 km northeast of Adelaide. Other deposits in weathered Adelaidean rocks have been mined at Bradbury and Woodside, and in weathered Cambrian schist at Cromer.

kaolin_williamstown

Williamstown kaolin. Fibrous 
sillimanite partly replaced by
kaolinite which pseudomorphs the acicular habit of sillmanite.
kaolin_birdwood
Birwood kaolin. Coarse vermicular crystal of stacked kaolinite platelets.
The Williamstown deposits, currently operated by Unimin Australia Ltd, have been mined since the early 1900s as a source of kaolinite, mixed sillimanite–kaolinite (‘kaosil’), sillimanite and kyanite used mainly in the manufacture of refractories and insulators. The orebodies are metasomatic pods of massive fibrous sillimanite and coarse crystalline kyanite which have been largely altered to kaolinite by hydrothermal fluids. These are contained within an 800 m wide shear zone of highly deformed schist, gneiss and quartzite. Age of the rocks is uncertain, but they are most probably basal Burra Group equivalents of upper Aldgate Sandstone and Woolshed Flat Shale of Adelaidean age. Three orebodies have been mined; the largest is a 60 by 25 m pipe-like body which plunges steeply and extends for more than 100 m. Remaining ore reserves in these very unusual deposits are limited and production is restricted to a few thousand tonnes per year. 

Birdwood 

During the 1870s, high-grade kaolin masses were encountered during underground mining and prospecting for gold north of Birdwood township. Since 1886, kaolin has been mined on a small scale for ceramics, refractory bricks, industrial fillers, and cement manufacture. Kaolin formed by deep weathering of a 30 m thick quartz–biotite schist unit at the top of the Adelaidean Saddleworth Formation. The bulk of the ore is pale yellow to white sandy kaolin used in general cement manufacture. High-grade zones comprise masses of almost pure kaolin up to 50 m wide, 30 m deep and ~100 m long. Variable and unpredictable iron-oxide-stained patches dictate selective mining to produce white kaolin which is used in white cement manufacture by Adelaide Brighton Cement Ltd at Angaston and for filler applications.

Other deposits

Other kaolin deposits in weathered Adelaidean sedimentary rocks have been mined at Woocalla (north of Port Augusta) and Booleroo Centre (southeast of Port Augusta).

Sedimentary kaolin

In the Adelaide region, sedimentary kaolin was deposited in river channels and lakes draining into a much larger Gulf St Vincent which formed in early Tertiary times. The clay deposits typically form thin lenses in the Middle Eocene North Maslin Sand and comprise poorly crystalline kaolinite with variable amounts of quartz silt. The clay is moderately plastic, classed as a semi-ball clay, and gives a pale greyish or orange-pink colour when fired. It is used extensively in brick clay blends and has found limited use in the manufacture of ceramics and refractories. Largest deposits are at Golden Grove, with indicated resources of 15 Mt, and much smaller deposits are at One Tree Hill, Sandy Creek and McLaren Vale.

Additional Reading

Barnes, L.C., 1990. Williamstown kaolin–sillimanite–mica deposits. In: Hughes, F.E. (Ed.), Geology of the mineral deposits of Australia and Papua New Guinea. Australasian Institute of Mining and Metallurgy. Monograph Series, 14:1163-1166.

Ferris, G.M., 1993. Review of exploration for kaolin in the Kimba area, Eyre Peninsula, South AustraliaSouth Australia. Department of Mines and Energy. Report Book, 93/37.

Ferris, G.M. and Keeling, J.L., 1993. Review of exploration for kaolin near Poochera, northern Eyre Peninsula, South AustraliaSouth Australia. Department of Mines and Energy. Report Book, 93/18.

Keeling, J.L., 1993. Birdwood kaolin deposits. In: 10th International Clay Conference, Adelaide, 1993. Field Guide, F3:6-14.

Keeling, J.L., Barnes, L.C. and Conor, C.H.H., 1993. Williamstown kaolin–sillimanite–mica deposits. In: 10th International Clay Conference, Adelaide, 1993. Field Guide, F3:15-21.

Keeling, J.L., Self, P.G., McClure, S.G., Raven, M.D. and Milnes, A.R., 1992. Characterisation of kaolin samples from the Mount Hope deposit.Mines and Energy Review, South Australia, 158:21-26.