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Views: 74 Author: Site Editor Publish Time: 2023-01-31 Origin: Site
Diamond drilling has revolutionised the mining industry and has directly led to the discovery of many mineable ore bodies that would otherwise not have been exploited. Prior to the introduction of mainstream diamond drilling, mining still relied heavily on finding outcrops of rock, with little information available on the concentration of ore below the surface. Diamond drilling allows solid cylindrical rocks (cores) to be removed from deep within the earth.
The term diamond core drilling is derived from the 'diamond drill bit' used in this process. This drill bit consists of a set of small, industrial grade diamonds set in a metallic, soft matrix. As the ground is drilled, this matrix is worn down and more diamonds are exposed.
The diamond bit is then attached to a drill pipe which is approximately 10 feet in length. Further sections of pipe can be attached to the top of the drill pipe, allowing greater depths to be drilled as required. The number of drill pipes attached to the top of the drill pipe will therefore determine the depth that can be drilled. Inside the drill pipe, a core tube is attached to the cable by a locking mechanism. The cable is used to lift the core tube to the surface to facilitate the removal of the solid core.
There are two main types of diamond drilling, including rotary and wireline drilling. Rotary drilling is primarily used for drilling, while wireline drilling is used for solid core sampling.
These are the five standard pipe sizes associated with wireline drilling.
AQ (hole size: 48 mm)
BQ (60 mm)
NQ (75.5 mm)
HQ (96 mm)
PQ (122.6 mm)
The size of drill bit used for wireline drilling depends on the required core diameter and the depth of drilling. For example, wider pipe diameters will require more power to drive the drill.
Extracting the core
To extract the core, the drill stem turns the diamond bit and spins it into the ground. As the bit is drilled through the rock, the solid rock is carried into a circular opening at the end of the bit and into the core tube, where it can then be recovered as it builds up at the surface. Once the core has been recovered at the surface it is broken up along natural fractures and stored in the core tray awaiting analysis. A standard core tray can hold around 10 feet of core.
To keep the drill moving smoothly through the rock, the bit must be well lubricated with water to prevent overheating or sticking. For optimum core extraction, the driller must listen to the drill bit to assess subsurface conditions. To ensure that drilling remains efficient, speed, pressure and water circulation must be strictly monitored. Sometimes when drilling in high fracture zones, overheating can occur as the bit gets stuck. This problem is usually counteracted by injecting mud or sawdust to plug the fractures in the rock.
