Geophysics in Gold Exploration: Application to Greenstone Belt Gold Deposits

The use of geophysical methods in exploration for greenstone belt gold deposits is as an indirect tool. These methods assist the exploration effort by mapping structures, lithologies, and alteration effects that may be related to mineralization. By using deposit models, and with knowledge of the deposit characteristics that are important for providing measurable physical property contrasts, an effective exploration program may be designed. Structures at all scales, especially shear zones and faults, play a major part in localizing greenstone gold deposits. Airborne and ground geophysical techniques of all types can playa major role in defining structures, and are particularly Important where extensive cover exists. The magnetic, remote sensing, gamma-ray and electromagnetic methods are the most applicable and often are used in combination. Geophysical methods also play an important role in the mapping of lithologies. Greenstone belt gold may occur in a wide variety of rock types so that multiple techniques are more effective at separation of the variety of lithologies within greenstone terranes. However, magnetic methods are used most often, because magnetic mafic units are often favored hosts. Typically, alteration haloes around these deposits are small so detailed ground and borehole methods are most appropriate for their detection. The best geophysical targets provided by alteration processes are due to sulfidation and potassium metasomatism, which provide targets for electrical or gamma-ray method., respectively. However, much research ramains to be done to better define geophysical characteristics of these deposits, and especially of alteration haloes.