2.3 Exploring for coal
Early miners would have found it easy to trace the distinctive black colour of coal along an outcrop (for example, a coastline or river valley), and surface trenches were used to locate less obvious outcrops. However, tracing an outcrop underground was problematical as the only means of exploration was by digging costly trial shafts. The development of exploratory steam-powered drilling in the early 19th century improved matters, but it was not until the mid- to late- 20th century that more advanced techniques made it possible to significantly reduce the uncertainties associated with estimating the size of a coalfield.
Modern exploration techniques are aimed at accurately assessing the location, quality and quantity of coal in a coalfield. In order to achieve this there are three broad categories of tools available to geologists: mapping, geophysical methods and drilling. They are considered here in the order in which they are likely to be employed.