MIP test survey over the HYC deposit in McArthur River Area, N.T.

Abstract

A test survey using the magnetic induced polarization (MIP) method was executed over the HYC sulfide deposit in the McArthur River area of the Northern Territory, Australia in September, 1992. The survey conducted by the Metal Mining Agency of Japan (MMAJ) using Scintrex equipment and personnel, was planned to define the MIP response over the huge stratified sulphide deposit and to compare the results with other geophysical data (including conventional IP) compiled since discovery in 1955. For current flow parallel to strike of the HYC deposit, a strong MIP anomaly was observed, providing accurate interpretation of depth and dip direction of the ore horizon and the upper pyritic shale-siltstone member. The MIP anomaly was in good agreement with the conventional electrical IP data collected with pole-dipole array. On the other hand, current flow perpendicular to strike produced no MIP anomaly. This result is consistent with the theory of MIP, indicating that the exploration programme must take account of regional geology and structures. Petrophysical study of drillcores showed the strongest IP source to be the ore horizon containing abundant sulphides. The upper pyritic shale-siltstone member also contains a considerable amount of sulphide and gives a significant IP effect. The MIP test survey verified the HYC orebody as a target for both electrical and magnetic IP methods, and MIP is suggested as a viable prospecting technique for similar base-metal targets in the region.