Diamond Core Drilling: Theory, Mechanisms and Applications

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.

Drill Structure

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 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.

Rotary and Wire Line Diamond Drilling

There are two primary types of diamond drilling, which include rotary drilling and wire line drilling. Rotary drilling is used primarily for bore hole drilling, whereas wire line drilling is used for solid core sampling.

There five standard tube sizes associated with wire line drilling:

  • AQ (Hole diameter: 48mm)
  • BQ (60mm)
  • NQ (75.5mm)
  • HQ (96mm)
  • PQ (122.6mm)

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.

A drill bit with industrial diamond cutters in a matrix. Image Credits: sandia.gov

Core Extraction

To extract 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.

Applications

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.

Major Diamond Core Drilling Locations

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.

Health and Safety

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 heat stroke.

Companies Involved In Diamond Core Drilling

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:

Contract Drilling Companies

  • KATI: A Scandinavian company with over thirty years’ experience, KATI specializes in ore prospecting.
  • LESEDI: Based in South Africa, LESEDI use continuous coring for mining exploration.
  • G&O: A North American company with over forty years’ experience in mining exploration in some of the harshest environments on the planet.
  • Layne: This global water management, construction and drilling company has emerged as a key player in the international diamond core drilling market.
  • Diamond Coring: A Chicago-based company with more than twenty years’ experience with providing specialized contractor services for concrete sawing and drilling purposes.
  • Godbe Drilling LLC: This company typically operates in both the United States and Mexico, and is known for having one of the best safety and cost-effective programs in the industry.

Diamond Drill Manufacturers

  • Geodrilling Bits MFR: The company supplies a wide range of diamond drilling equipment, such as reaming shells and PDC bits.
  • Safari Diamond Bits: The leading Canadian manufacture of diamond drill bits using innovative alloys.
  • Spencer Drill Supply: The leading drilling supplier in northern Mexico, specializing in tools and spare parts including core barrel and diamond bits.
  • CS Unitec, Inc.: This Connecticut-based manufacturer is best known for producing concrete drills, including diamond core drills and rotary hammer drills.
  • Dynatech: Ohio-based manufacturer and distributer of diamond core drills, including bits.

Sources and Further Reading

This article was updated on the 6th May, 2019.

G.P. Thomas

Written by

G.P. Thomas

Gary graduated from the University of Manchester with a first-class honours degree in Geochemistry and a Masters in Earth Sciences. After working in the Australian mining industry, Gary decided to hang up his geology boots and turn his hand to writing. When he isn't developing topical and informative content, Gary can usually be found playing his beloved guitar, or watching Aston Villa FC snatch defeat from the jaws of victory.

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Comments

  1. marvin french marvin french United States says:

    I worked for long year drilling now known as boart longyear. also a major force in the north America mining area what about them

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