Exploration geology can be done near existing mines or in areas where there is no evidence of previous mining, however all work must be conducted within mining leases managed by KCGM. KCGM’s mining leases extend 10km north and 20km south of Kalgoorlie.
Exploration geologists use many different types of data to determine where gold may be found. The data sets can be very large and complex and require computers to process the data and to display it in a form that can be analysed. A large array of sophisticated geological, geochemical and geophysical technology is available to geologists so that they may add to their understanding of the rocks below the surface.
Exploration may start with looking at aerial photographs, published geological maps and reports written by previous geologists working in the area. When a favourable area has been selected, a more detailed geological map may be made or samples of soil or rock may be taken to see if there is gold content, or the content of other elements that indicate the presence of gold.
Ground or air geophysical surveys may be conducted to measure variations in the magnetic and electrical properties of the rocks or mineralisation below the surface.
Once geologists have assessed and analysed all these data sets a first pass drilling program may be done to determine the gold content below ground. A reverse air blast (RAB) drill rig drills to depths of up to 100m into the weathered rock profile. It is a relatively cheap drilling method and can be used to cover large areas. Once an area of anomalous gold values has been outlined with the RAB rig a reverse circulation (RC) drill rig is used to collect deeper samples at depths of up to 800m. A diamond drill rig can also be used and can drill to depths of 1000m or more. A diamond rig is expensive to operate but produces cylindrical cores that provide valuable information about the rock and gold mineralisation.
If gold mineralisation is located additional drilling is undertaken until the shape and size of the orebody is known. A large amount of data must be compiled on the orebody before it can be mined. This work is then completed by Resource Definition geologists.
If drilling fails to locate sufficient gold mineralisation for mining the area is rehabilitated back to how it was prior to the commencement of exploration activities. This involves the removal of drill hole collars, back-filling of holes and scarification of the drill site so that plants can regrow.