Diamond Core Drilling

Diamond core drilling  utilizes an annular diamond-impregnated drill bit attached to the end of hollow drill rods to cut a cylindrical core of solid rock. The diamonds used are fine to micro fine industrial grade diamonds. They are set within a matrix of varying hardness, from brass to high-grade steel. Matrix hardness, diamond size and dosing can be varied according to the rock which must be cut. Holes within the bit allow water to be delivered to the cutting face. This provides three essential functions; lubrication, cooling, and removal of drill cuttings from the hole.

Diamond drilling is much slower than reverse circulation (RC) drilling due to the hardness of the ground being drilled. Drilling of 1200 to 1800 meters is common and at these depths, ground is mainly hard rock.

Core samples are retrieved via the use of a core tube, a hollow tube lowered inside the rod string by a winch cable until it stops inside the core barrel. As the core is drilled, the core lifter slides over the core as it is cut. An overshot attached to the end of the winch cable is lowered inside the rod string and locks on to the backend, located on the top end of the core tube. The winch is retracted, pulling the core tube to the surface. The core does not drop out the inside of the lifter tube when lifted because a "core lifter spring," located at the bottom of the tube allows the core to move inside the tube but not fall out.

Once the core tube is removed from the hole, the core sample is then removed from the tube and catalogued. The driller's assistant unscrews the core tube using tube clamps, then each part of the core tube is taken and the core is shaken out (or pumped out in triple tube drilling) into core trays. The core is washed, measured and broken into smaller pieces using a hammer to make it fit into the sample trays. Once catalogued, the core trays are retrieved by geologists who then analyze the core and determine if the drill site is a good location to expand future mining operations.

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Last modified: 11/21/07