Geophysics for Sediment Hosted Copper and Gold Mineralisation, The Role of 3DIP

Abstract

Sediment hosted copper mineralisation involves redox precipitation of copper sulphides where oxidised basinal fluids interact with in situ organic material or migrated hydrocarbons. This is a common process in sedimentary basins so it is important to find fast and cost-efficient methods for their exploration. Airborne magnetic/ electromagnetic and ground gravity and electrical resistivity-induced polarisation (IP) methods are commonly used to explore for these types of deposits. The application of IP methods can be utilised as a direct targeting tool in the sediment hosted environment. Multichannel receivers, large transmitters, improvements in processing capacity has led to more confidence in inversion results and the recent popularity of the 3D IP technique. Examples of the application of large 3D IP surveys for sediment hosted copper deposits from Zambia and Alaska show that high grade copper mineralisation is associated with an IP response. Sedimentary textures associated with mineralisation compromise the inductive conductivity and resistivity response (anisotropy). An integrated exploration approach using geology, geochemistry and geophysics helps alleviate pursuing responses from digenetic pyrite, graphitic shales and specular haematite.