Reverse circulation drilling is the drilling of sample holes to determine the sufficient presence or value of minerals for mining, e.g. coal, gold, iron ore, platinum and diamonds. Reverse Circulation drilling uses rods with inner and outer tubes. The drill cuttings are returned to surface inside the rods. Larger rigs and machinery are used and depths of up to 250 meters can be obtained. RC drilling ideally produces dry rock chips. Reverse circulation is achieved by blowing air down the rod whilst drilling, the pressure creates a lift and the cuttings are brought up the inner tube which is inside each rod. It reaches the deflector box at the top of the drill string then moves through a sample hose which is attached to the top of the cyclone.
The drill cuttings travel around the inside of the cyclone until they fall through an opening at the bottom and are collected in a sample bag. Samples may be split using a riffle splitter. For any drill hole there will be a large number of sample bags, each one marked to record the location and drilling depth that the sample was obtained.
The samples are later sent to a laboratory and analysed for mineral content.