Regional mineral exploration targeting for gold and nickel deposits using crustal electrical conductivity variations determined using the magnetotelluric method

Abstract

Current ideas on regional prospectivity analysis emphasize the importance of major fault structures and in particular (palaeo) suture zones within and between cratonic blocks. These features represent deep penetrating zones of enhanced permeability encouraging the passage of potentially mineralizing brines and melts. Such features have been linked with the occurrence of several different types of deposit, notably nickel-sulfide and gold deposits. Detection of such geological features requires mapping variations in physical properties at lower crustal and mantle depths. As part of a study on regional prospectivity, magnetotelluric (MT) surveys have been completed in several prospective Proterozoic and Archean terrains in Western Australia (Kimberley Craton and surrounding orogenic belts, Musgrave Province, Capricorn Orogen, Yilgarn Craton). . These data, which have been interpreted in association with potential field, seismic, geological and geochemical data, demonstrate that MT surveys can be used to identify features indicative of regional-scale prospectivity based on variations in the electrical conductivity of the crust and upper mantle. For example, a survey in the southern Yilgarn Craton has identified lateral changes in deep crust and upper mantle conductivity structure consistent with palaeo-cratonic boundaries inferred from studies using isotope geochemistry. The MT data allow the boundaries to be accurately located; the isotopic results being limited by the spatial distribution of outcrops of suitable lithotypes. The survey areas in Western Australia are geographically remote and often environmentally and culturally significant. MT surveys represent a comparatively cheap means of evaluating regional prospectivity, whilst causing minimal cultural and environmental disturbance. It is argued that MT data comprise useful pre-competitive data type and that Governments should consider this type of survey as a complement to the more common potential field surveys.