When assessing a mineral sands deposit, many geological factors need to be taken into account.
These include the:
- percentage of Heavy Mineral (HM) within the ore, or grade;
- make-up of minerals within the HM to establish the Valuable Heavy Mineral (VHM);
- mineral grain size;
- mineral chemistry;
- non-grade characteristics; specifically the:
- ‘oversize’ (amount of coarse material in the sand); and
- ‘fines’ (the fine silts and clays) that are too small to be processed.
Mineral sands deposits occur in two types:
- Strandlines – deposited on ancient beach fronts. These tend to be tens of metres across and several kilometres long. They are typically high grade, coarse grained, and low tonnage.
- WIM deposits – formed just off the beach front and which are typically large tabular deposits. These tend to be several kilometres in each direction and tens of metres thick, typically finer grained and lower grade – but usually much larger than strandline deposits.
The Glenaladale deposit is classified as WIM style deposit. The heavy minerals of interest in mineral sands deposits are typically zircon, rutile, leucoxene and monazite. This group of minerals make up the majority of the VHM component of any mineral sands deposit. Other heavy minerals that have little value such as magnetite and chromite are known as trash minerals (because they have little value and can complicate processing).
In its heavy minerals, the Glenaladale deposit has a very high percentage of VHM and low trash mineralogy – this means the concentrate produced can command a premium price.
Of great importance is the grain size of the deposit. The larger the grain size, the easier the ore is to process. Most mineral sand projects that have been developed to date have been strandline deposits.
For a WIM deposit, the Glenaladale deposit is unusual as the grain size is relatively large. As a result, it has the advantage of being easier to process. Its other attributes include being very low in oversize and having relatively low fines.
The combination of these qualities make the Glenaladale deposit a world class resource - high tonnage, high percentage of VHM, medium grain size, low oversize, and low fines - making the Glenaladale deposit, as Goldilocks would say, just right.