Drilling tech for mineral exploration
Cautious optimism of a recovery for the mineral exploration sector is a good time for a primer on mineral drilling techniques
Last updated 12/14/2018 at 5:24am
Whilst the mining industry continues to shift on several levels, mineral exploration is still very much needed in determining where new mineral deposits are located.
Technology has helped mineral exploration techniques evolve from a time consuming endeavor marked by unreliable sample quality and a high environmental impact, to a highly efficient process with lower environment impact and consistent grade control for accurate sampling, eliminating the need for multiple samples being taken at one spot. As an added bonus for a parent company and its investors, mineral exploration is also becoming more cost effective as technology provides increasingly better ways to obtain samples.
With industry professionals being cautiously optimistic of mining industry growth due to the political climate and worldwide industry changes, it is worth looking at the drilling technologies available to mineral exploration companies.
Before any mining is done, drilling is performed to gather detailed information of what is occurring under the surface level of the earth.
The size of the equipment (or rig) and the method will be highly determined by the terrain, type of rock, and information needed from the drilling. Other factors that come to play are available resources, ease of access, and the cost or budget of the operation.
Traditional drilling methods have been shallow drilling, deep drilling, and diamond drilling. Within those, there are different types of drilling methods, including the widely popular reverse circulation drilling, although it is a newer method of obtaining samples.
In this category, there are two popular types used: auger drilling and air drilling.
Auger drilling is done with a hand powered auger or through an auger mounted on a small vehicle. This method is highly portable, comparable to a jackhammer, and similar to the post hole digger used for fencing.
Air drilling contains two main sub-types; aircore drilling and rotary airblast (RAB). Both methods utilize a small or utility type truck with a mounted drill rig and an accompanying air compressor on the vehicle or towed. There is almost no site preparation with air drilling at the shallow level, allowing it to be completed easily in under a days' time of work. Rock chips (fragments) are lifted to the surface via compressed air being forced down the drilled hole to lift them to the surface.
Within the deep drilling umbrella, there are air drilling, diamond drilling, or rotary mud drilling.
Air drilling at the deep level is usually done by one of the two main types- open hole percussion or reverse circulation drilling (RC) with both using comparable equipment to water bore drilling.
Open hole percussion is low on the expense side and doesn't require highly skilled labor. A specialized drill bit is used in a similar manner to a jackhammer and compressed air is used to bring the loosened rock chips to the surface.
Once again, the equipment is conveniently mounted on a truck with the added need for a couple of support vehicles. However, this is still an easily performed method of getting samples. Unfortunately, samples obtained from the open-air percussion method aren't always the best samples as they aren't free from contamination.
The rock obtained at depth may have pieces of other rocks from further up the hole, making the sample an inaccurate representative of the minerals at the bottom.
Reverse circulation drilling
Reverse circulation drilling is comparable to open hole percussion with one major difference; the use of dual drill rods.
The outer drill rod has a hollow interior, allowing the samples to travel back to the surface via compressed air (the same as other methods) but without the chance of contamination as the rock chips are protected within the tube. This makes the samples a true representation of what is at the bottom of the drilling site and allows for more precise location of mineral deposits.
Reverse circulation drilling allows for quick sample retrieval, easy in and out of equipment compared to other methods, and removes a lot of the guesswork of mineral location. There is also the added benefit of versatility in rough conditions; less water is needed and due to the speed of the drilling, less time spent on site which can eliminate the need for extra equipment.
Diamond drilling differs from the methods explained so far in that it doesn't take samples of rock chips.
Instead, sample of the rock core are brought up in a cylinder instead of chips. This requires far more equipment and demands a much higher labour skill level as it is more involved. Diamond drilling is one of the older methods of obtaining samples - yet is capable of drilling to great depths. In fact, so much as many kilometers or miles deep in some cases.
As mentioned, it is also equipment intensive, needing more equipment to be transferred to the location, along with a need to access water to keep drill bits and machinery cool. Since it is so involved, there is quite a bit more site prep needed and usually requires several days to complete due to its slower nature. As far as the rehabilitation of the site, where the other methods are fairly easy to rehab, a diamond drilling site is more complicated.
Rotary mud drilling
Rotary mud drilling isn't as widely used as the other methods and is mostly needed for the deep drilling needed in coal exploration.
It requires more equipment and skilled labor, since the drilling is more involved with the ability of underground directional drilling to specific targets. It is also more time intensive, with around the clock drilling performed over a time period of several weeks to months.
Where the other methods used compressed air to bring the rock pieces to the surface, rotary mud drilling uses water and fluids for both drill bit lubrication while also bringing the chips to the surface. Obviously, this also limits the usage of this method to places with high water access. Similar to diamond drilling, there will also be more site preparation, support vehicles, and rehabilitation needs.
There are several ways to obtain samples in mineral exploration that allow for a range of terrain and needs. Pre-surveying the site will help make the choice that fits the best for each company and individual sample requirement.
About the Author: Ben Howard is a third-year mechanical engineering student at the University of Western Australia specializing in mining sector and drilling technologies. Practical experience ranges from mineral exploration techniques, different drilling methods and testing for mining engineering firms in Perth, Australia.