Reverse Circulation (RC) Drilling: The Australian Legacy
Reverse Circulation (RC) Drilling, a technique that has become a standard in many mining operations around the globe, has its roots in Australia. Developed in the 1970s, this drilling method was conceived as a solution to the challenges faced when using open hole techniques in iron ore and mineral sands exploration. Today, it’s a fundamental part of various operations, from mineral exploration to water well drilling and geothermal drilling
The Birth of RC Drilling
The genesis of RC drilling is linked to the Australian mining industry. In 1972, Bruce Metzke and John Humphries, two Australian innovators, adapted drill rods from the US oil industry to create the first RC drill rods. This marked the birth of a drilling method that would revolutionise the mining industry.
Understanding the RC Drill Rig
The RC drill rig is usually a large apparatus that requires ample space not just for the rig itself but also for the supporting vehicles and the pit for collecting waste. The drill cuttings are transferred to the surface inside the drill rods, linked together to create a ‘drill string’. Drill bits attached to the end of the hammer are made from tungsten-steel and are around 13-20cm in diameter. These bits also have metal nodules attached at the end to enable cutting through particularly tough rock.
Most RC drilling uses dual-tube drill rods, with one tube nested inside another. The overlap of tubes inside the rod provides a path for drilled rock to travel from the ground to the surface. These inner tubes can be sealed together, allowing the RC drill to sample remarkable depths, often around 500m.
The Modern Variation: Centre Sample Drilling
A modern variation of RC drilling known as ‘centre sample’ drilling has also emerged. In this method, a central hammer with a hollow centre allows the sample to directly enter the drill pipe, eliminating the need for the sample to travel past the hammer.
The Process of Sample Extraction
RC drilling produces dry chips of the drilled rock as samples. The hammer acts as a pneumatic piston, pushing a tungsten-steel drill bit onto the rock to break it up. The rock chips are dried out using an air compressor before they reach the surface. Water is often used down the hole to cool the drill bit, reduce dust, and assist with the transportation of sample bits to the surface.
Analysing Samples in RC Drilling
Once the sample reaches the surface, an exploration geologist analyses and logs the sample to determine the prospective mineralisation within the drilled body. A representative sample is taken, sieved to remove excess dust, washed, dried, and then the weight percentage of the desired minerals is noted. These samples are then stored in plastic cutting boxes for further chemical analysis offsite.
Challenges in RC Drilling
RC drilling comes with its challenges. Drill bits can wear down, and rods, which are quite expensive, can get stuck in the ground. Recovering these rods can be time-consuming and can potentially set a project back by weeks. To combat this, many companies consistently re-grind the tungsten nodules off the drill bit.
Applications of RC Drilling
RC drilling is commonly used in various stages of mine development. Being cheaper than diamond core drilling, it is often preferred in the first stage of exploration mining to delineate a potentially extractable ore body. It is also used consistently during in-pit grade control and the development stage of an ore body.
Health and Safety Measures in RC Drilling
Operating large mining equipment, including RC drilling rigs, comes with inherent risks. Personal Protective Equipment (PPE), including hearing protection, gloves, goggles, suitable footwear, and dust masks, must be worn at all times.
Key Players in RC Drilling
Several drilling contractors specialise in RC drilling, including Castle Drilling, Midnight Sun Drilling Co. Ltd., SBD Group, Leon Marsh Drilling, and Atlas Copco. These companies have contributed significantly to enhancing RC drilling machinery and selling drill rigs across the world.
RC drilling, with its origins in Australia, has shaped the mining industry in significant ways, allowing for efficient and effective extraction of mineral samples. With continuous advancements in technology, this drilling method is set to become even more prominent in the future.