Deep drillhole electromagnetic surveys for nickel/copper sulphides at Sudbury, Canada

Abstract

Drillhole electromagnetic surveys have been successfully used in the Sudbury Igneous Complex to detect and define further occurrences of nickel/copper sulphides. This style of mineralisation is extremely conductive and deposits have been detected at distances up to 300 m from the drillhole. This paper gives several examples of step-response (Utem) data from a number of Inco's mines within the Complex. They show that the system can provide information on the location, geometry and quality of mineralisation of very deep, excellent conductors. The examples also show the complexity of the data when several conductors are present and the problems that can occur if the drillhole geometry and/or transmitter loop locations are not properly determined. Responses from in-mine culture; eg, railways, may also mislead. DHEM surveys are now routinely used in and around Inco's Sudbury mines to explore for further occurrences of ore and to help define the extent of partially outlined mineralisation.