Surface Exploration (also called Diamond Drilling or Contract Drilling) is when a mining company has done some prospecting and found indications of significant ore bodies. They hire a contract drilling company to bore through the earth and retrieve long cylinders of rock (called core samples) which are then sent to an assay firm who determines the percentages of whatever ores are found in the rock sample. If there are large percentages of an ore that is important to the global market (and therefore valuable and worth mining) the mining company may do full scale mining at that site.
The name diamond drilling comes from the drill bits that are used (not what they are drilling for!). The bits are doughnut shaped and embedded with industrial diamonds which are tough enough to grind through the earth’s rock. (Industrial diamonds are grey and unattractive).