Bringing geophysics into the mine: radio attenuation imaging and mine geology

Abstract

Recent work using radio wave frequencies to define ore shape between boreholes shows promise for changing the way mine geologists evaluate a deposit. Traditionally, orebody evaluation at an advanced exploration site or a mine involves three distinct tiers of information, exploration drilling (>200 m borehole separation), follow-up drilling (40 m to 100 m separation), and in-fill drilling (<20 m). The inexact nature of ore definition at the follow-up and in-fill stages inevitably results in poor mine design or dilution. This has been shown to have a significant cost to any operation. The clear incentive is to improve evaluation techniques by using high resolution sensing methods between physical intersections. A new geophysical technique using comparative radio wave attentuation values from cross-borehole measurements and advanced tomographic imaging procedures has been applied at a number of mine sites in Australia. Radio wave attentuation is a function of the host medium conductivity. Conductive ore will attenuate the signal more than resistive host rock. These variations in signal attenuation may be expressed in the form of a tomographic image for analysis. This paper evaluates results from controlled experimentation at the Broken Hill and Osborne deposits and reviews the likely future role for radio imaging at metalliferous mine sites. It is suggested that the clear role for radio scanning is particularly in the follow-up stage of drilling (40 m to 100 m). The integration of the images into mine planning packages, as an input to geostatistics and as a visualisation aid for mine planners and geologists is likely to improve the accuracy of ore definition and overall metal recovery at individual mine sites.