electrical

• Electrical surveys involve the placement of two electrodes in the ground and an electric current is passed between them. Two inner electrodes are used to measure the voltage then resistance of the underlying rock is calculated. 
• Good conductors like rocks containing metallic ore minerals will have a lower resistance than other rocks. 
• Water within pore spaces creates a low resistance, due to water being a good conductor. 
• As resistivities are generally large, the current applied cannot travel far so only a few meters below ground service can be measured. 
• As water affects electrical survey readings, the weather is important. Two sets of reading from a wet and dry day may be different. 
• Resistivity measures water table depth and can detect solution feature and voids. It can locate buried alluvial channel, fracture planes and unconformities. 
• Loose sediments are lower resistivity than solid rocks. 
• Electromagnetic surveys are carried out on land or by air, useful for detecting sulphide minerals like chalcopyrite.