Mining methods vary across Iluka’s operations. Dry mining operations use scrapers to collect and transport ore to concentrator plants. Dry mining is suitable where deposits are shallow, contain hard bands of rock or are in a series of unconnected ore bodies. Dredge mining, or wet mining, is best suited to ore reserves below the water table. Dredges mine in artificial ponds, pumping ore in slurry form to a floating concentrator. The ore is washed through spirals that use gravity to separate the heavy mineral sands from the lighter quartz and clay.
Mine planning uses the latest technology to model the geology of the ore body from information supplied by survey and exploration drilling and sampling. From the ore body model an economic evaluation is undertaken using 3D-optimisation software to determine the most economic mine design taking into consideration:
- the amount of overburden that must be removed to access the ore;
- the concentration of target minerals;
- the presence of clay and rock;
- any land use restrictions; and
- the desired post mining land use and rehabilitation requirements.
Mining sequences
When rehabilitation studies and requirements are complete, the land is cleared and any millable timber harvested. Topsoil and subsoil are stripped and stockpiled for re-spreading during rehabilitation.
Mining utilises either a dry or wet mining technique. All of Iluka’s mining operations involve dry mining. CRL’s operations in North Stradbroke, Queensland, utilise a wet mining or dredging technique. Iluka typically uses contracted mining operators.
Dry mining utilises scrapers to collect and transport the ore to a nearby road hopper. The road hopper (and associated plant) is towed forward as the mine face advances to maintain an optimum haul cycle.
At the hopper the ore is screened to remove debris, which is returned to the pit, and then transported to a concentrator plant either via a pipeline or overland conveyor.
Dredge mining, or wet mining, is employed where the ore body extends below the water table. The dredge sits in an artificial pond and moves through the ore body as the mine face advances with the ore being pumped to a floating concentrator plant in tow.
Both wet and dry mining techniques utilise wet concentrator plants to produce a high grade of heavy mineral concentrate (about 98 per cent heavy mineral content). The ore is washed through a series of spiral separators that use gravity to separate the heavy mineral sands from the lighter quartz and clay.
Water used in the process is recycled into a clean water dam with any extra water requirements made up from pit dewatering or rainfall.
Sand residue from the concentration process is pumped through a pipeline to the mine pit and discharged via a monitor or cyclone stacker. The sand is re-contoured before overburden and topsoil replacement, and is then ready for rehabilitation.