Heavy mineral sands ore deposits

2016-11-10

Heavy mineral sands are a class of ore deposit which is an important source of zirconium, titanium, thorium, tungsten, rare earth elements, the industrial minerals diamond, sapphire, garnet, and occasionally precious metals or gemstones.

Heavy mineral sands are placer deposits formed most usually in beach environments by concentration due to the specific gravity of the mineral grains. It is equally likely that some concentrations of heavy minerals (aside from the usual gold placers) exist within streambeds, but most are of a low grade and are relatively small.

The grade of a typical heavy mineral sand ore deposit is usually low. Within the 21st century, the lowest cut-off grades of heavy minerals, as a total heavy mineral (THM) concentrate from the bulk sand, in most ore deposits of this type is around 1% heavy minerals, although several are higher grade.

Of this total heavy mineral concentrate (THM), the components are typically

• Zircon, from 1% of THM to upwards of 50% of THM,
• Ilmenite, generally of 10% to 60% of THM
• Rutile, from 5% to 25% of THM
• Leucoxene, from 1% to 10% of THM
• Trash minerals, typically quartz, magnetite, garnet, chromiteand kyanite, which usually account for the remaining bulk of the THM content
• Slimes, typically minerals as above and heavy clay minerals, too fine to be economically extracted.

Generally, as zircon is the most valuable component and a critical ore component, high-zircon sands are the most valuable. Thereafter, rutile, leucoxene and then ilmenite in terms of value given to the ore. As a generality, typically the valuable components of the THM concentrate rarely exceed 30%.

Being ancient stranded dune systems, the tonnage of most deposits is in excess of several tens of millions of tonnes to several hundred million tonnes. For example; the medium-sized Coburn mineral sands deposit, Western Australia, is 230 million tonnes at 1.1% heavy minerals, and is 13 km long.

The Tormin mine, on the Western Cape of South Africa’s coastline, provides an unique ocean beach feature, which exposes the resource to wave and tidal conditions that result in a natural jigging effect. Large proportions of the quartz and light heavies waste material are removed by the ocean tidal action,resulting in run of mine (ROM) grades as high as 86% heavy mineral concentrate (HMC).