Multifrequency Turam measurements over a sulfide deposit

Abstract

A six‐frequency electromagnetic (EM) system has been developed and used for a Turam‐type survey over the sulfide deposit of Mailaram copper belt in Andhra Pradesh, India. Turam field strength ratio (FSR) and phase difference (PD) are measured in the range 84 to 2688 Hz. Sulfides in this belt occur as thin concentrated lodes which grade into disseminations. Soil covers a major part of the area. Interpretation of the results is carried out using a thin sheet model in free space. However, an attempt has been made to account for finite resistivity of the normal ground by computing Turam response of a conducting half‐space appropriate for the area and subtracting the same from the observed response. The results of the survey confirm the known advantage of the Turam method, viz., its greater depth of investigation compared to a method like Slingram. The normal ground at Mailaram is only mildly conducting so that the free‐air approximation is valid at low frequencies. A correction for the finite resistivity of the ground is required only at high frequencies. However, the limitation of a single‐body interpretation scheme for the bedrock conductor is well brought out by the results.