The drilling of boreholes from the surface or from underground workings, to seek and locate coal or mineral deposits and to establish geological structure. Exploratory drilling is frequently done from underground workings, the holes being drilled upward, horizontally, or downward as required. For underground drilling, roller bits, diamond crowns, or tungsten-carbide bits may be used and can be coring or noncoring. Rotary boring is the predominant method for exploratory work from the surface, particularly where cores of significant deposits are required.