Boulder tracing and geological mapping of the bedrockDiamond drilling
Diamond drilling is often the last step in exploration. An interesting area has, with the help of geological mapping, ground geophysical surveys and/or shallow drilling and bedrock chip sampling, been identified and needs to be investigated further.
A drill rig is driven to the drill site. The best available route is selected, preferably on a hard ground and in consultation with the landowner. Certain areas, for example wetlands, can only be drilled during the winter, when the ground is frozen. Sometimes the snow is packed down by driving, for example, a snowmobile along the transport route before the drill rig is positioned at the drill site. Usually, one or several holes are drilled, which are approximately 46 to 56 mm in diameter and to depths of up to several hundred metres. Water is required for the drilling and is taken from nearby water systems or drill holes, or is transported to the drill site in a tank. In certain cases, trees are cut down, to position the drill rig.
The drill bit, which is covered with small diamonds, cuts a cylindrical drill core out of the rock. When the core tube is full, it is taken up and emptied. The drill cores are placed in special boxes and transported to a drill core archive for geological logging and sampling. The mineralised parts of the drill core are sent to a laboratory where the metal content is analysed.
Diamond drilling is an expensive but necessary exploration method. A drill hole costs generally between SEK 500 and 1000 per meter. The drill bit contains small industrial diamonds and each bit costs around SEK 3,500 - 4,000. Depending on the rock properties, a drill bit can cut through different lengths, from 10 to 100 m before it is worn down.
Fig 7. Example of diamond drill rig.