04-10-2012, 03:25 PM
MINERAL SANDS
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Nature and Occurrence
Mineral sands are sand-sized occurrences of detrital minerals of high specific gravity (heavy minerals), including such minerals as rutile, zircon, ilmenite, magnetite, kyanite, sillimanite, monazite, xenotime, chromite, tourmaline, garnet and staurolite. These heavy minerals (Table 23) typically have a specific gravity greater than 2.9, are chemically stable, resistant to abrasion and commonly able, with the notable exception of ilmenite, to withstand diagenetic alteration (Baker 1962; Force 1991).
Although heavy minerals form as accessory minerals in many igneous and metamorphic rocks, nearly all major economic deposits of these minerals, principally rutile, zircon and ilmenite, occur as detrital accumulations in young (Pliocene or younger)
shoreline or beach placer deposits (Force 1991). Fluvial accumulations of these minerals are not globally significant. The potential for alluvial placer deposits of diamonds, sapphires and magnetite in New South Wales are not considered in this.
Deposit Types
The geological processes that are responsible for the development of commercially significant deposits of titanium and zircon minerals are as follows (Force 1991; Harben & Kužvart 1996; Roy 1999; Roy et al. 2000).
• The accumulation (magmatic segregations) of
dense oxide-rich liquids in cooling magmas
of the anorthosite–ferrodiorite suite, in alkali intrusive deposits, skarns and as relict TiO2 in titanium-rich rocks.
• The concentration of heavy minerals in a range of coastal sedimentary environments — dominated by aeolian, wave and tidal processes. Heavy minerals also occur in fluvial placers but they are (globally) relatively insignificant. Although the concentration mechanism at the site of deposition is initially mechanical, diagenetic processes may alter the primary mineralogy and grainsize.
New South Wales Occurrences
Beach placers in coastal dunes of Pleistocene and Holocene age have been the traditional source of mineral sands in New South Wales. Numerous deposits occur (or occurred) between Gosford and Tweed Heads (Figure 18). Available resources, however, are now almost entirely depleted or are not available for extraction owing to environmental restrictions. Remaining deposits are small and of variable quality. Although offshore sediments at several localities were found to contain heavy minerals, only minor deposits were defined (Whitehouse 2007). Their economic potential depends not only on their original concentration of heavy minerals, but also on those beach deposits surviving intense reworking that occurred during ensuing marine transgressions.
The Murray Basin (Figure 18) has the potential to become one of the world’s major mineral sands provinces (Whitehouse et al. 1999). Intensive exploration in recent years has identified numerous coarse-grained beach placer deposits with economic potential associated with the Pliocene Loxton-Parilla Sands. Many of the deposits are associated with northeast–southwest topographic ridges — the Neckarboo and Iona Ridges are probably the most important — that appear to be structural blocks that developed in response to growth faulting (Roy & Whitehouse 2003).
Applications
About 95% of all titanium-bearing mineral sand products are used in the titanium dioxide pigment industry (Harben & Kužvart 1996). Titanium dioxide is used predominantly as an opaque white pigment to impart whiteness, brightness and opacity. Titanium dioxide pigment is the premier white pigment and is used in UV-resistant paint and plastics, high-quality paper, rubber, ceramics, fabric, toothpaste, soap, cosmetics, food and sunscreens. Other important properties of titanium dioxide include its chemical inertness, resistance to UV degradation and thermal stability over a wide range of temperatures.