Heavy mineral resources in South Australia
- Jacinth-Ambrosia Mineral Sand Project
They include economically important minerals rich in titanium, zirconium and rare earths. These minerals occur in very low concentrations in a variety of igneous and metamorphic rocks, but being chemically and physically resistant to weathering, and having comparatively high specific gravity, they tend to accumulate in placer deposits in river channels or along coastal shorelines.
Beach sands contain the most important accumulations of these minerals; wave action deposits sand on the beach, and the heavy minerals are concentrated when backwash carries some of the lighter minerals such as quartz back into the sea. Onshore winds which preferentially blow lighter grains inland can lead to higher concentrations of heavy minerals at the front of coastal dunes. Old ‘fossil’ shorelines known as strandlines can now be found some distance inland.
The principal heavy minerals of commercial interest are rutile, ilmenite, leucoxene and zircon:
- Rutile (TiO2) is a red to black, naturally occurring titanium dioxide with a theoretical TiO2 content of 100%, but impurities such as Fe2O3 and Cr2O2 reduce this to 93–95%. World production, in 2013 was 0.77 Mt with the main producers being Australia (58%) and South Africa (16%).
- Ilmenite (FeTiO3) is black and opaque when fresh, but has typically undergone some weathering and iron removal, so TiO2 contents are between 45 and 65%. World production, in 2013 was 6.79 Mt with the main producers being Australia (14%), China (14%) and South Africa (15%).
- Leucoxene is the name given to highly altered ilmenite. Grains are brown or grey with a waxy lustre and TiO2 content of 68%.
- Zircon (ZrSiO4), a colourless to off-white mineral, is the world’s major source of zirconium products. World production, in 2013 was 1.44 Mt with the main producers being Australia (42%) and South Africa (25%).
About 90% of the world’s titanium mineral production is used in the manufacture of white titanium dioxide pigment. TiO2 is the premier pigment, having high refractive index (opacity), whiteness, brightness, thermal stability and chemical inertness. It is used extensively in the paint industry where it has replaced old-fashioned lead carbonate pigments, and as a pigment in plastics, paper, and latex rubber. Because it is non-toxic it is used in cosmetics and pharmaceuticals. About 6% is used to manufacture titanium metal, a light, strong, corrosion-resistant metal used in aircraft, spacecraft and medical prostheses. Minor TiO2 uses include welding rod coatings, sand blasting and water filtration.
Zircon is extremely refractory, having a melting point of over 2430ºC. High-purity zirconia such as that used in synthetic cubic zirconia gemstones melts at over 2700ºC. Zircon is used in foundry sand moulds, molten metal moulds and continuous steel casting nozzles. Finely ground zircon is used in ceramic glazes and specialised ceramics such as electrical porcelain. A range of hard, tough zirconia-based engineering refractories has been developed for uses such as extrusion dyes and engine parts.
Australia is a major producer of heavy minerals. During 1998, deposits in Western Australia, New South Wales and Queensland supplied 0.25 Mt or 58% of the world’s rutile concentrate, 2.4 Mt of ilmenite (27%), and 0.40 Mt of zircon (40%; ABARE Australian Commodity Statistics).
South Australian deposits
Exploration has highlighted the prospectivity of the Murray and Eucla Basins.
The Early Pliocene Loxton Sand and overlying Parilla Sand formations have been the target of mineral sand exploration in the Murray Basin. During the 1980s one of the world’s largest accumulations of heavy minerals was delineated by drilling in the basin near Horsham in Western Victoria (Murray Basin strandlines). The WIM 150 deposit is a sheet-like accumulation formed in an offshore environment. Grain sizes are very fine, typically around 50 µm (0.05 mm), which is about a quarter of that in many producing deposits. Despite initial optimism, the deposit proved difficult to beneficiate, and has not been mined commercially. More recent exploration has focused on the search for coarser strandline deposits amenable to beneficiation using conventional techniques.
In 1986–87, Aberfoyle Resources Ltd drilled the Mindarie, Perponda and Mercunda prospects near Karoonda in South Australia, where heavy minerals have accumulated in northwest–southeast-trending Pliocene strandlines. A renewed phase of exploration commenced in 1998, with Murray Basin Minerals NL defining 11 mineralised strandlines in the Karoonda area (Strandlines in the Karoonda-Mindarie area). In September 2000, the company announced the results of a first-stage feasibility study based on a resource of 65.6 Mt containing 3.3% heavy minerals using a 1.32% heavy mineral cutoff. This includes a mineral inventory, adjusted for likely mining losses and dilution, of 32.8 Mt at 4.2% heavy minerals. The mineral assemblage is predominantly ilmenite with significant zircon, rutile and leucoxene.
Marine transgression during the Late Eocene or Early Oligocene was a major period of dune building which formed the Ooldea, Barton and Paling Ranges from sediments deposited by the rivers draining into the basin from the north. Heavy minerals, comprising predominantly ilmenite and zircon, are present within the Middle Eocene Hampton Sandstone and Ooldea Sand, the main dune-forming units. The best prospect outlined was Immarna, with two heavy mineral strandlines. Representative bulk samples showed the upper strandline in Ooldea Sand to contain 2.77% heavy minerals, and the lower strandline in Hampton Sandstone to have 0.94%. Heavy mineral assemblages are dominated by ilmenite (86 and 66% respectively) and zircon (11 and 26% respectively). The Immarna deposit remains undeveloped and is currently held by North Ltd.
BHP outlined several low-grade anomalous zones within the Ooldea Range, but mineralisation was generally located 20–40 m below the surface, rendering the deposits uneconomic.
Drilling for construction sand along the eastern margin of the Golden Grove Embayment by the former Department of Mines in 1975 discovered heavy minerals within lacustrine sand of the Middle Eocene North Maslin Sand. The mineral suite comprises rutile, zircon, ilmenite and monazite sourced from Adelaidean quartzite, slate, schist and pegmatite, and Barossa Complex schist, gneiss and pegmatite. The resource is inferred to contain approximately 26 000 t of ilmenite and altered ilmenite, 39 000 t of rutile and 32 000 t of zircon. This modest resource may eventually be exploited, but a mining plan will need to be devised which is compatible with construction sand extraction.
Kangaroo IslandThe only site of heavy mineral mining in South Australia was Morrison Beach on the north coast of Kangaroo Island where 1200 t of rutile and 190 t of zircon were mined by Minoil Services Pty Ltd between 1971 and 1976 (Morris, 1986). Heavy minerals were derived from Kanmantoo Group metasediments which crop out along the northwest and west coast of the island.
Ferris, G.M., 1994. Review of heavy mineral sand exploration in South Australia — the Eucla Basin. South Australia. Department of Mines and Energy. Report Book, 94/22.
Ferris, G.M. and Hayball, A.J., 1993. Review of heavy mineral sand exploration in South Australia. South Australia. Department of Mines and Energy. Report Book, 93/27.
Morris, B.J., 1986. Reconnaissance sampling for heavy mineral sands, Kangaroo Island. South Australia. Department of Mines and Energy. Report Book, 86/31.
Stewart, R. (Ed.), 1999. Murray Basin mineral sands. Extended abstracts of papers presented at a conference in Mildura, 21–23 April 1999. Australian Institute of Geoscientists. Bulletin, 26.