Different Drilling methods- Useful reminder20 Sep 2023 21:44
> Auger
Auger drilling is the baby of the different types of drilling. It is done by rotating a helical screw into the ground with the earth being lifted up the borehole by the blade of the screw. They range in size from small hand-held units to somewhat larger ones mounted on small vehicles. Auger drilling can only really be used where the ground is soft but it is both cheap and fast, making it suitable for its main use as an initial geochemical reconnaissance technique.
> Rotary air blast
Moving up to the next size, we have rotary air blast (RAB) drilling, which is the most common shallow drilling method. This uses a piston-driven “hammer” to drive the drill bit into the rock, creating rock fragments, or “chips”, that are lifted to the surface by compressed air. it may produce lower quality samples due to the way that the rock chips are blown up the borehole.
> Aircore
Aircore drilling is preferred over RAB as it tends to provide more representative, or accurate, samples. It uses a three-bladed steel or tungsten drill bit with a hollow drill rod to penetrate the weathered layer of loose soil and rock fragments.
Once drilling is complete, compressed air is injected into the space between the inner tube and drill rod’s inner wall to flush the cuttings to the surface.This makes samples from aircore drilling less prone to contamination, though it is generally slower and more costly than RAB. Aircore is also unable to cut through fresh rock.
> Reverse circulation
Moving on to the big guns, reverse circulation, or RC drilling as it is more commonly known, is a popular technique for mineral exploration. Like RAB, RC drilling uses a piston-driven “hammer” to drive a tungsten-steel bit into the rock, though the use of larger rigs and machinery allows holes to be drilled much deeper. RC drilling is slower and costlier than the previous types of drilling, but it is cheaper than the next and final type of drilling.
> Diamond
The most expensive form of drilling is diamond drilling, which uses a diamond-impregnated drill bit attached to hollow drill rods to extract a continuous cylinder of rock. Despite its cost, diamond drilling has several advantages over RC drilling. It is capable of drilling down to several kilometres in depth, it can penetrate hard rock and it returns the most accurate samples, as its core samples can show the actual veins of a mineral and their precise location in the ground.
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