Electrical imaging of peridotite weathering mantles as a complementary tool for nickel ore exploration in New Caledonia

Abstract

The first 2-D electrical resistivity tomography (ERT) survey on the well explored (for Nickel ore) lateritic mantle of a new Caledonian ultramafic massif shows a good fit between the geoelectrical sections and the core loggings. Data collected along several 1 km long profiles, with 10 m electrode spacing to reach about 100 m penetration depth, are reliable and the preliminary interpretation of resistivity models indicates: well-defined geoelectrical layers with significant resistivity contrast; a very good fit of the above layers with the various units of a weathering mantle, i.e. ferricrete, saprolite and bedrock; the suspected geometry of horizons, deduced from core logs, is better defined by the continuous ERT imaging; a transverse (section to section) continuity of saprolite troughs and bedrock ridges along N140° strike, which is the main structural feature of Tiebaghi ultramafic massif. 2D Electrical Resistivity Tomography appears to be an appropriate geophysical method to investigate the structure of weathering mantles of ultramafic massifs in New Caledonia. It should become a useful complementary tool to locate favourable zones, i.e. the saprolite horizon where Ni accumulation can be found, or, at least, to economize on drillings.