Core Drilling

In 1663, the Swiss engineer M. Leskot designed a tube with a diamond set face, for drilling in the Mount Cenis tunnel, where the rock was too hard for conventional tools. The intention was to explore rock quality ahead of the tunnel face, and warn miners of possible rock falls.

This was the accidental birth of core drilling, a technique now very widely used within the mining industry. Core drilling is carried out is special drillings , using e hollow drill string with an impregnated diamond cutting bit to resist wear while drilling hard rock. The crown-shaped diamond bit cuts a cylindrical core of the rock, which is caught and retained in a double tube core-barrel.

A core-catcher is embedded in, or just above, the diamond bit, to make sure that the core does not fall out of the tube. In order to retrieve the core, the core-barrel is taken to surface, either by pulling up the complete drill string or, if the appropriate equipment is being used, by pulling up only the inner tube of the core-barrel with the special fishing device run inside the drill string at the and of a thin steel wire.

The core is an intact of the underground geology, which can be examined thoroughly by the geologist to determine the exact nature of the rock and any mineralization. Samples of special interest are sent to a laboratory for analysis to reveal any metal contents. Cores from exploration drilling are stored in special boxes, and kept in archives for a long period of time. Boxes are marked to identify from which hole, and at what depth, the sample was taken. The information gathered by core drilling is important, and represent substantial capital investment.

Traditionally, core drilling was a very arduous job, and more operator-friendly equipment, was very slow, and the cost per drilled metre was often prohibitive. Atlas Copco Craelius pioneered several techniques to reduce manual work, increase efficiency and cut the cost per drilled metre. Over the years, the company developed thin walled core barrels, diamond impregnated bits, aluminium drill rods, fast rotating hydraulic rigs, mechanical rod handling, and, more recently, partly or totally computer-controlled rigs. Core drilling has always been the most powerful tool in mineral exploration. Now that it has become much cheaper, faster and easier, it is being used more widely.

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