A number of steps should be carried out before commencing any first-phase drilling of a prospect, these are:
- Map the surface outcrop around the drill hole in as detailed a scale as possible (preferably 1:1,000 or better) before drilling commences. Ideally, the scale of core logging and surface mapping should be comparable, but the lower density of geological information available on surface means that the surface map is usually compiled at a smaller scale.
- Draw a geological section along the line of the proposed hole. If there is any significant surface relief then the section should show this with a vertical accuracy of at least a metre.4 If existing topographic data are not sufficiently accurate to draw the profile, then a special topographic survey of the section line should be undertaken.
- Plot on to the section the trace of the proposed hole (and data from any existing holes on the section) and all known surface geology along with geochemistry and geophysics data. If necessary, project the data along strike so that it lies on the section.
- From the section, make predictions on the expected down-hole intersections of important geological elements.
- These predictions should be written down, along with a brief drill hole justification statement. This practice forces the project geologist to think about the important questions: “Why am I drilling this hole?” and “What do I expect to find?” Apart from this, a hole justification statement such as this keeps the geologist honest when the actual hole results become known.
