In-Situ Resistivity Measurements of Veins in Epithermal Gold Mines Near Waihi

Abstract

Detailed DC resistivity measurements using a variety of electrode arrays have recently been conducted across known epithemal vein deposits near Waihi (namely Golden Cross and Martha Hill Pit), in order to improve our understanding of the geophysical signatures associated with these types of ore bodies. The measured resistivity values vary widely from more than ohm-m within massive quartz veins to less than 30 ohm-m in flanking pods of intense clay alteration. A vector gradient-array traverse across the Martha Pit shows a good correlation between resistive structures and gold-enriched veins. Strong deflectionsin the azimuth of the electric field are associated with obliquely intersected veins. At the Golden Cross Mine, dipole-dipoledata show anomalously strong induced polarisation responses and the gradient array data show a very strong deflection in the azimuth of the electric field. Further interpretation of these observations, together with 2-D modelling and property measurements,is expected to assist future planning and interpretation of geophysical borehole logging and surface-based exploration surveys of similar epithermal prospects.