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Exploration Drilling
Exploration drilling is the first stage of mining. Alcoa’s mining lease covers a large area, and exploration drilling identifies the specific location of ore bodies within the lease that are suitable for mining. Alcoa’s geologists determine the areas, spacing and priorities for the exploration drilling.
Drilling starts at a broad spacing (120 x 120m). Depending on the geological results, further drilling is done on progressively finer grids, down to 15 x 15m. This is only done in confirmed ore bodies, to identify their boundaries and to determine the concentration of alumina and other minerals that affect the refining process. The locations of the drill holes are surveyed very accurately.
All of the exploration drilling is done by vacuum drilling rigs. The rigs are only in operation for 9 months a year. There are usually two people on each rig – a driller and a sampler. A sample is collected every 0.5m down the drill hole, which goes to an average depth of 6m, to the clay layer. The samples are transported to the Kwinana refinery laboratory for chemical analysis.
Environmental considerations
The drill rigs drive through the forest (between the trees) and on forest tracks so they have the potential to spread dieback.
The drill rigs must clean down on entry to dieback-free forest, and the drill bits are cleaned between drill holes. In many areas drilling is only permitted when the soil is dry to reduce the risk of transporting dieback soil.
Driving machines through the forest can damage vegetation. This is why the tractor-mounted drill rigs have been designed to reduce their impact on the environment. The rigs are small compact machines with good ground clearance, large tyres to minimise compaction, and a modified exhaust to minimise fire risk.
The drill holes are only about 10cm wide, however small animals may fall down and become trapped. To prevent this, the holes are plugged with a rock or Banksia cone.
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