There is always a trade-off between speed, cost, necessary sample quality, sample amount, logistics, and environmental factors when choosing the best approach or combination of procedures (see Table 1). Although RAB drilling and augering offer relatively little geological knowledge, they are quick and inexpensive, making them suitable primarily as geochemical reconnaissance techniques for gathering samples beneath shallow overburden areas [1].
Table 1: Comparison of exploration drilling methods.
| Drill type | Indications | Advantages | Disadvantages |
| Hand auger | Geochemical sampling in upper few meters of unconsolidated material | Hand portable and operable. Uncontaminated sample. Cheap | Poor penetration |
| Power auger (post-hole digger) | Geochemical sampling in upper few metres of unconsolidated material | Small lightweight machine – vehicle mounted or hand operated. Quick, cheap | Poor penetration (better than hand auger). Sample contamination |
| Rotary air blast (RAB) | Geochemical sampling to base of regolith. Ideal regolith sampling tool | Large sample volume. No site preparation needed. Quick and relatively cheap. Some rock chip geological data | Poor penetration of hard rocks. Sample contamination. Limited depth. No structural data |
| Air core | Geochemical sampling where good characterisation of bedrock required | Small rock core return. Minimal contamination. Relatively quick and cheap. Can penetrate heavy clay/mud | Small sample size |
| Reverse circulation (RC) | Geochemical sampling hard and soft rocks to 200 m + Ore body proving above water table | Uncontaminated large volume sample. Rock chip geological data. Relatively quick and cheap cf. diamond | Large heavy rig may need access preparation. Limited structural data. Poor orientation control |
| Diamond | Ore targeting and proving to 1,000 m + High quality sample. Geological/structural understanding | Maximises geological information. Uncontaminated, undisturbed high-recovery sample. Accurate hole positioning/control | Some site preparation required. Water supply required. Relatively small sample size. Slow. Expensive |
Reference
[1] R. Marjoribanks, Geological Methods in Mineral Exploration and Mining. Berlin, Heidelberg: Springer, 2010. doi: 10.1007/978-3-540-74375-0.
