Our success depends upon a constant supply of world class mineral deposits. They must represent resources capable of being economically extracted, and we obtain them either through our own exploration or by the acquisition of mineral deposits found by others.
Types of exploration
The two main types of exploration are greenfield and brownfield.
- Brownfield, around mine or near-mine, exploration, is focused on the discovery of resources close to existing operations. This can expand existing holdings and known reserves and add value to the business relatively quickly
- Greenfield exploration focuses on identifying entirely new or previously unrecognised mineral deposits. Our global exploration activity for 2011 focused on greenfields exploration across a number of mature and frontier locations.
With much of the world having had at least a surface examination, it is becoming harder to find mineral deposits. Exploration techniques therefore focus on finding buried or hidden deposits. This requires sophisticated geochemical, geophysical and remote sensing tools to indicate anomalies due to hidden mineralisation. Collected data is then evaluated by experienced geoscientists, using advanced computer hardware and 2D and 3D software.
Today’s mineral exploration programmes also demand appropriate hand specimen, hand lens and field geology skills.
Aircraft, helicopters and high altitude earth orbiting satellites are used to map geological structures, rock units and rock alteration to identify sites for mineralisation. Subtle changes in surface rock alteration can now be mapped remotely from space, and sites targeted for ground follow-up.
Geophysical surveys can also be conducted from fixed-wing aircraft, helicopters and airships, providing a relatively rapid method of collecting magnetic, electromagnetic, gravimetric and radiometric data over wide areas.
Identified anomalies can suggest surface/near surface mineralisation or deeper and hidden deposits. These require more detailed ground follow-up involving additional geophysical surveys. Media such as stream and lake sediments, rocks, soils and overburden, vegetation and even soil gases can be sampled for geochemical anomaly detection.
Detailed ground surveys provide sufficient information and physical parameters to be able to position test and exploratory trenches, pits or drill holes.
Various drilling techniques are used, but all provide real evidence of mineralisation. Drill holes are laid out in lines or grid patterns depending on the target depth and geometry, and provide rock chips or continuous rock core down through the target.
Following initial discovery, a mineralised target is then investigated by more detailed ground surveys and drilling which defines the:
- grade variation
- and likely economic value of the discovery
If successful, the discovery is subjected to further technical, financial and commercial evaluation and a decision taken on mining and exploiting the economic ore deposit.