Geologists search for surface minerals through visual examination, whereas geophysicists identify underground mineral deposits by detecting rock alterations beneath the surface. Geochemistry is also used to analyze samples of soil, rock, and water. These methods are supplemented by aerial or satellite photography and combined with historical maps and literature to develop detailed maps of surface and underground rock formations.
Drilling is used to search for mineral occurrences or clues in the rocks that may lead to mineral deposits. The information gathered during this stage may or may not lead to a discovery of valuable minerals.
Drilling penetrates deep into the ground and brings up samples of whatever it finds on its way. If there is any mineralization at given points far beneath the surface, drilling can give a straightforward answer and can quantify its presence at that particular point.
There are two main methods of exploratory drilling. Core drilling, yields a solid cylinder shaped sample of the ground at an exact depth. Percussion drilling, or Reverse Circulation (RC) drilling yields a crushed sample, comprising cuttings from a fairly well determined depth in the hole. Beyond that, the drill hole itself can provide a complementary amount of information, particularly by logging using devices to detect physical anomalies, similar to the geophysical surveys mentioned above.