Mineral sands contain suites of economically important minerals of high specific gravity known as ‘heavy minerals’. These include minerals rich in titanium, zirconium and rare earth elements that are found in very low concentrations in a variety of igneous and metamorphic rocks. However, because they are chemically and physically resistant to weathering and have a high specific gravity, they tend to accumulate in placer deposits in river channels and along coastlines.
Beach sands contain the most important accumulations of heavy minerals. Wave action deposits sand on beaches and the heavy minerals are concentrated when backwash carries lighter minerals such as quartz back into the sea. Onshore winds that preferentially blow lighter grains inland can also concentrate heavy minerals at the front of coastal dunes. Old (fossil) shorelines, known as strandlines, which occur some distance inland, can also be a source of heavy minerals.
The principal heavy minerals of commercial interest are rutile, zircon, ilmenite and leucoxene.
Rutile (titanium dioxide, TiO2) is a red to black, naturally occurring mineral with a theoretical TiO2 content of 100%, but impurities such as Fe2O3 and Cr2O2 commonly reduce this to 93–95%.
About 90% of world titanium mineral production is used to manufacture white titanium dioxide pigment. Titanium dioxide is the premier white 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 lead carbonate pigments, and as a pigment in plastics, paper and latex rubber. Because it is non-toxic it is also used in cosmetics and pharmaceuticals.
About 6% of mined rutile is used to manufacture titanium metal, a light, strong and corrosion-resistant metal used in the manufacture of aircraft, spacecraft and medical prostheses. Minor uses of TiO2 include welding rod coatings, sand blasting and water filtration.
Zircon (ZrSiO4), a colourless to off-white mineral, is the world's major source of zirconium products. Zircon is extremely refractory, with a melting point of over 2430ºC. Zircon is used in foundry sand moulds, molten metal moulds, and for continuous steel casting nozzles. Finely ground zircon is used in ceramic glazes and specialised ceramics such as porcelain used in electrical equipment. A range of hard, tough zirconia-based engineering refractories has been developed for uses such as extrusion dyes and engine parts.
Ilmenite (FeTiO3) is black and opaque when fresh, but typically undergoes some weathering and iron removal, so that TiO2 contents are between 45% and 65%. Ilmenite is mined for extraction of titanium dioxide.
Leucoxene is the name given to highly altered ilmenite. Grains are brown or grey with a waxy lustre and TiO2 content of 68%.
Victoria's Murray Basin contains several world-class heavy mineral sands deposits. Additional deposits are located in the Gippsland Basin.
- GSV TR2012/1 - Heavy Mineral Sands in the Murray Basin of Victoria
- GSV UR2011/2 - Heavy Mineral Sands in Victoria
- Industrial minerals and rocks of Victoria - Geological Survey of Victoria Report 102
- Geological History of Victoria
- Victoria's Minerals, Petroleum and Extractives Industries - Statistical Review
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