exploration geophysics

exploration geophysics Exploration geophysics is the application of geophysical techniques to mineral exploration. A range of methods is available, usually grouped according to the physical property to which they respond (Table 1). The choice of the appropriate method for each application is therefore important. In some instances, geophysical methods cannot be used to sense a deposit directly, but are used indirectly to detect characteristic features that may be associated with it, or just to determine the geological structure of the prospect. It is therefore common for a mixture of methods to be applied. Cost is important, and so cheaper methods tend to be used for preliminary surveys and more expensive ones kept for later refinement.

Many of the methods have been adapted for airborne, marine, and borehole surveys. Many are finding increasing application in environmental surveys.

Table 1. Methods of exploration geophysics

Method	Sensed property	Relative cost	Typical targets
Gravity	Density, mass	Moderate	Regional and local structure
			Ore bodies with large density contrasts (e.g. chromite, salt)
			Estimating total reserves
			Detecting cavities
Magnetic	Magnetic susceptibility; natural remanent magnetization	Cheap	Regional and local structure
			Magnetic ore bodies (e.g. magnetite)
			Ferrous metal deposits
Electromagnetic	Electrical conductivity	Cheap to moderate	Regional and local structure
			Conducting ore bodies
			Groundwater exploration
			Contaminated groundwater
Electrical	Electrical conductivity; electrical potential	Moderate	Local structure
			Conducting (or resistive) and electrically charged ores;
			Groundwater and water table
			Contaminated groundwater
Radioactive	Natural or induced radioactivity	Moderate	Radioactive minerals
			Clay and other lithologies
Seismic refraction and reflection	Seismic velocity; acoustic impedance	High	Regional and local structure
			Hydrocarbons

Roger Searle