Geophysical methods can be used effectively to map the extent of alluvial channels and runs and to obtain a cost-effective solution together with drilling. The geophysical survey is often initially conducted to provide targets for drilling and to have a quick initial overview of the extent and positions of the gravel channels. A technique such as gravity works very well where the underlying bedrock is dolomite and a pothole type alluvial deposit is present.
The nature of kimberlites and its strong geophysical signature makes it a very attractive target for mapping with a range of geophysical techniques. Potential targets are usually identified from airborne geophysical surveys or site investigations, and ground geophysical methods can then be employed to characterize the pipe and to confirm its presence. Kimberlites usually have a strong magnetic signature and it thus suitable for mapping with magnetics, although the magnetic signature can be reduced by weathering, making the target magnetically invisible. Gravity is also a very good method for mapping kimberlite pipes due to the low density caused by the preferentially weathered kimberlite. A combination of the gravity and magnetic techniques is recommended for general exploration and characterization of kimberlite pipes.
Mineralization is often controlled by geological structures and zones of weakness such as geological contacts, faults, fractures zones and dykes. Mapping and understanding of the structural geology is critical for development of a mineralization model and to effectively plan an exploration programme. Geophysical surveys such as magnetics and gravity are often used to map dykes and faults to assist in the mapping of the structural geology with magnetic being a relatively low-cost geophysical exercise and relatively large areas can be covered at reasonable costs.
Massive and Disseminated Sulphides
Geophysical surveys offer a very attractive exploration tool for the mapping of massive and disseminated sulphides. These targets are characterized by the presence of high chargeabilities (disseminated sulphides) and high conductivity (massive sulphides) which can be mapped using a combination of Induced Polarization (IP) and Electromagnetic Techniques. Global Geophysical uses the IRIS system (ELREC Pro and VIP4000 transmitter) for IP surveys and the MaxMin system for frequency domain EM investigations.
Underground Mining: Roof Integrity Investigations
Ground Penetrating Radar (GPR) offers a very efficient method of investigating shallow roof conditions in the underground mining industry for rock engineering and safety concerns. Features such as dome planes, disseminated layers, chrome triplets, and other zones/planes of weakness can be imaged rapidly and efficiently with minimal data processing. About 8 systems are currently being used by various Chrome and Platinum mines in South Africa with data being collected and processed by the Rock Engineering personnel on the mines. Open Ground Resources provide training and technical support and sales of these systems in collaboration with Red Dog Scientific Services which is the GSSI system representative in Africa.