In exploration the first steps are remote sensing which gives an...

In exploration the first steps are remote sensing which gives an indication of potential.
Next step is ground work which starts with surface sampling... this confirms the potential.
Drilling is a major step up from the previous two both in cost and outcome. (It is not called the rotary truth detector for nothing!!)

The first drill programme will be based on the remote sensing data and surface mapping. The drill holes are targeted at the most likely targets... but they are still just targets at this point. When (usually if) mineralisation is hit by a drill hole, and further drilling (based on this new information) is able to define a resource (as opposed to simply mineralisation)... that first drill hole is the key that transformed exploration potential into a resource. It is known as the "discovery hole".

* It should be noted that the discovery hole was guided by significant previous work and was not just a stab in the dark that "discovered" a resource.