Underground UHF-EM transillumination : a feasibility study

Abstract

A feasibility study into the use of UHF-EM transillumination measurements in geophysics is presented. The electrical properties and absorption rates of common crustal materials are examined with the goal of identifying specific conditions under which sufficient material penetration at UHF frequencies is available.A prototype 445 MHz continuous-wave transillumination instrument designed for underground use is described. Test surveys, with this instrument, were conducted at the Big Nickel Mine in Sudbury, Ontario, to obtain a number of through-rock absorption rates. Estimated effective resistivities of between 500 and 1500 ohm-metres are determined from the survey data.Effective conductivities and permittivities from AC and DC electrical property measurements on geological samples from the mine site corroborate these transillumination survey results.The results of the field surveys indicate that the UHF-EM transillumination technique is a feasible and useful geophysical method