A new survey design for 3D IP inversion modelling at Copper Hill

Abstract

The Copper Hill prospect is a well known porphyry copper/gold system. Investigation of geochemical assay data and gradient array IP data suggest that grid northwest and grid northeast structural directions have considerable control over mineralisation. Previous drilling has been oblique to these directions. The sulphide rich mineralisation zones have moderate to strong IP responses. The intention of Golden Cross Resources Ltd, as tenement holders, was to verify the main trends and locations of possible extensions to mineralisation. A 3D inversion of IP data is a suitable approach to the problem of mapping the sulphide horizons in detail. The primary aim of the survey was to gather sufficient IP/resistivity data over an area 1.2km by 1km to generate a reasonably detailed 3D-inversion model for Copper Hill. Based on the knowledge that the data was to be processed in a 3D-inversion program, a modification of the pole-dipole IP survey geometry was used. The new array design resulted in fast collection of a large quantity of data. The high data redundancy inherent in the design allowed for editing prior to inversion. 3D inversion results highlighted the three dimensionality of sulphides zones at Copper Hill. Zones of high IP response are concentrated along northwest and north trending structures forming an annular zone terminating at depth. A cost effective broad scale and detailed IP survey was successfully accomplished.