Diamond drilling has revolutionized the mining industry and directly resulted in the discovery of many minable orebodies that would otherwise have gone untapped. Before the introduction of mainstream diamond drilling, mining was still primarily dependent on finding outcrops of rock, with little information available about ore concentrations below the surface. Diamond drilling allows for the removal of solid cylinders of rock (core) from deep within the earth.
The term diamond core drilling comes from the ‘diamond bit’ drill used during this process. This drill bit is made up of a group of small, industrial-grade diamonds set into a metallic, soft matrix. As the ground is drilled this matrix will wear away and expose more diamonds.
The diamond bit is then attached to a drill rod which measures to about 10 feet in length. More sections of the pipe can be attached to the top of the drill rod, allowing greater depths to be drilled as needed. Therefore, the number of rods attached to the top of the drill rod will determine the depth that can be drilled. Within the drill rod, a core tube is attached to a cable by a latching mechanism. The core tube is lifted to the surface using the cable to allow for the removal of the solid core.
There are two primary types of diamond drilling, which include rotary drilling and wireline drilling. Rotary drilling is used primarily for borehole drilling, whereas wireline drilling is used for solid core sampling.
These five standard tube sizes associated with wireline drilling:
The drill size used during wireline drilling depends on the desired core diameter and the depth of drilling. For example, a wider tube diameter will require more power to drive the drilling.
A drill bit with industrial diamond cutters in a matrix. Image Credit: sandia.gov
To extract the core, the drill rod rotates the diamond bit and spins it into the ground. As the drill bit bores through the rock, solid rock is taken into the circular opening at the end of the bit, into the core tube, and can then be recovered at the surface as it piles up. Once the core is recovered at the surface it is broken along natural fractures and stored in core trays to await analysis. A standard core tray can hold around 10 feet of core.
To keep the drill moving through the rock smoothly, the drill must be well lubricated with water in order to prevent overheating or sticking. For optimum core extraction, the driller must listen to the drill to evaluate subsurface conditions. To ensure that drilling remains efficient, the rotation speed, pressure and water circulation must be strictly monitored. Sometimes when drilling in highly fractured zones, overheating can occur due to a stuck bit. This issue is usually counteracted by the injection of mud or sawdust to plug fractures in the rock.
Core Rig Animation
Diamond core finds its primary function in the exploration mining sector. It is usually one of the last stages of exploration, during which the orebody is delineated in three dimensions. This will determine whether the prospect is economically viable. Using a diamond drill rig, long vertical sections of core can be extracted from deep in the ground which can then be analyzed at the surface by geologists.
The core can then be analyzed using a wide range of petrologic, structural, and mineralogical techniques to determine whether the potential mining site is economically viable. Extracted core is first washed and macroscopic features are logged by an exploration geologist. The core is then cut and representative samples are sent for chemical analysis.
An increasing amount of exploratory wells are being drilled into by exploration companies around the world. As energy demand continues to rise, the number of these wells is also expected to increase. Currently, the most prevalent geographies in which diamond core drilling takes place includes various locations in North America, Asia Pacific, the Middle East, and Europe.
Mine sites always have inherent safety risks and diamond drilling rigs are no exception. While operating a diamond drill rig, the appropriate personal protective equipment (PPE) must be worn at all times, of which typically includes steel toe cap boots, hearing protectors, gloves and goggles.
When approaching an active drill rig, care must be taken to catch the drillers’ attention before stepping into the work area, as not to surprise the operator.
Furthermore, as diamond drilling is primarily an exploration technique, the conditions in which it is carried out are often harsh and so due diligence needs to be taken whilst in these environments. For example, if working in desert conditions, enough water and shelter must be provided for the drillers to prevent dehydration and heatstroke.
Diamond core drilling is an extremely important and profitable sector of the mining industry. There are many different areas of the business, from drill bit manufacturing to companies contracted to undertake the drilling. Here are just a few examples:
This article was updated on the 6th May, 2019.
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