Electromagnetic methods applied to exploration for deep nickel sulphides in the Leinster area, Western Australia

Abstract

Nickel-sulphide deposits lying at the base of the regolith usually give strong, readily interpreted, surface time-domain electromagnetic (TEM) anomalies. In the Leinster area of Western Australia much of the prospective stratigraphy has been covered by TEM surveys and the strong anomalies have been drill tested. Deep nickel sulphides may be economic if they occur close to existing mining and processing infrastructure, but targeting the subtle TEM responses of these bodies requires skilful application and interpretation of TEM surveys. Conductive regolith can mask the response of deep nickel-sulphide orebodies to surface TEM systems. IP effects and other geological noise originating in the regolith can make recognition of weak bedrock anomalies difficult. Taking a slingram or out-of-loop reading can minimise regolith effects, and give a better response from sub-vertical bedrock conductors than in-loop readings. Downhole electromagnetic (DHEM) surveys in reconnaissance drill-holes increase the effective penetration depth of TEM, and can assist surface TEM interpretation in a prospect area. Despite weak surface TEM anomalism, DHEM surveys of deep drill-holes can yield precise information about the position and conductivity of nickel sulphide systems.