Boulder tracing and geological mapping of the bedrockReverse circulation (RC) drilling or percussion drilling
RC-drilling can be compared to diamond drilling, with respect to the size of the drill rig, and at which stage of exploration it is used. As opposed to diamond drilling, which is only based on rotation, RC-drilling involves percussion drilling (rotation and crushing). RC-drilling can be carried out with or without water. The principle is that pressurized air, pumped down the drill, blows up liberated fragments of rock, which are called rock-chips or drill rock-chips (figure 8). For each drilled metre, the rock chips are collected in large sacks. These samples are recorded and a smaller, but representative portion of the sample is then sent for analysis of the metal content. RC-drilling is generally faster and somewhat cheaper than diamond drilling. A larger hole (10-20 cm in diameter) is drilled using the RC-technique, and usually means that a larger sample size is obtained per drilled metre, about 45 kg. The length of the holes generally varies from 10 to 100 metres.
Fig 8. Schematic diagram for RC-drilling that shows the flow of pressurized air and the rock fragments (chips).