The mining industry and mineral exploration involves drilling to discover subsurface conditions. Over the years, there has been many advances in drilling technologies and techniques in the various sectors; however, in the mining sector there have been no significant advances. Generally, mineral exploration involves percussion and/or rotary drilling to produce rock chips and samples of core for evaluation by the geological team and mining engineers.
Drilling is used to obtain detailed subsurface information. This allows the mine to gather sufficient data on mineralogy in the rock formations to resource the mine and have an expected life span. In addition to the mineralogy information gathered, significant geological information is also collected which allows the mining engineers to effectively build the mining model to ensure the safety of the mine and all of its employees and contractors.
There are three primary techniques that can be used for mineral exploration. Selecting the appropriate technique will depend on several factors including cost, the environment, type of equipment required, and the skill and knowledge of those involved. We will focus on Reverse Circulation Air Percussion drilling.
Reverse circulation drilling is more expensive than rotary air blasting. It also requires more equipment and greater operating skills. Although there is an increase in costs, RC drilling results in greater sample accuracy and recovery, making it a more popular form of mining exploration. It is the most common drilling technique used for mining exploration.
RC drilling is a form of percussion drilling. With RC drilling, a dual wall drill rod is utilized. Air is injected between the annulus of the two tubes. The air exits the drill string behind the bit. The air and cuttings are forced across the face of the bit and back up inside of the inner tube which is sealed using O-rings and seated in the outer tube using a circlip. From there, the air and cuttings travel back to the surface out to the top of the rotary head through a deflector elbow along a discharge hose to the cyclone. At the face of the bit, the air is prevented from rising the annulus with a collar or shroud.
The rock is fragmented into chips using a piston that delivers rapid impacts to the drill stem, transferring energy to the drill bit. These blows to the rock are delivered by the bit, while a rotational device makes sure that the bit hits a new rock surface with each blow at a rate of 90 rpm. A feed force is applied to maintain rock/bit contact. Compressed air (950cfm & 24 bar) is used to remove or flush the drill cutting from the hole, advancing the hole depth efficiently.
