Application of complex resistivity survey in an epithermal Au-Ag deposit, South Korea

Electrochemical reactions at the interface between groundwater and sulphides are remarkable. Sulphides in mineralised zones are relatively abundant compared to hydrothermal alteration zones and host rocks. Complex resistivity is a geophysical tool for visualising difference between various subsurface electrochemical reactions. The epithermal Au–Ag mineralisation at Moisan hill (South Korea) occurs in the extensively disseminated pyrite zone, a typical feature of advanced argillic and argillic alteration zones. The epithermal vein at Moisan had a strike length of >500 m horizontally and approximately 300 m vertically and was controlled by the WNW fault zone. In this context, the deposit was subjected to a test bed to demonstrate the applicability of the complex resistivity survey for mineral exploration. To compare complex resistivity results with geological characteristics of epithermal mineralisation, we visualised the complex resistivity survey results and Au–Ag mineralised zones confirmed by drilling cores in three dimensions. The quartz veins of the targets showed high resistivity and a strong phase response; however, both the alteration zones and host rocks showed lower resistivity and a weaker phase response than the target zones. Through a step-by-step clustering analysis, a simple map integrating both kinds of the geophysical models was generated, to identify the boundary between the target and background. Geologic survey and drilling investigations indicate that the target is well-localised in a mineralised zone. The complex resistivity survey is a useful tool for exploring epithermal Au–Ag deposits.