Geotechnical drilling, what we used to call mineral exploration, or just mineral ex, is quite different from normal water well drilling. Sure, we drill a hole in the ground, but the methods and objectives are very different. Usually, it’s done in hard rock, but instead of a hammer making fine cuttings, most of them are cored, so the geologist can see what the formation looks like in situ. Core bits require cooling and lubrication, so fluid circulation is required. Usually, the pump is quite different than the normal pump on a water well rig. High pressure is required to overcome friction in the pipe and core barrel, and large volumes are not usually called for, so a small, high-pressure triplex pump is used. A lot of the time, the driller won’t even get returns to surface. As long as the bit stays cool, it’ll drill. Outside cuttings are chased into vugs, or cracks in the rock.
I was once on a job in central Slovakia, in the largest volcanic caldera in Europe. Not as big as the Yellowstone caldera, but still about 25 miles across. The customer had bought a mineral lease on most of the area, and hired us to explore and find what he had bought! We had a new track-mounted, Korean rig that could angle drill, and a portable mud system (that I built), so we could go just about anywhere and drill just about anything, which was good because the geologists just marked dots on the map and expected us to drill there. They never went to look at site conditions, and part of the contract stipulated that the pristine forest be disturbed as little as possible. These constraints made for some interesting locations.