Relationship between bulk mineralogy and induced polarisation responses in iron oxide-copper-gold and porphyry copper mineralisation, northern Chile

Abstract

We have studied the correlation between bulk mineralogy and induced polarisation (IP) responses in iron oxide-copper-gold (IOCG) and porphyry copper mineralised systems in northern Chile. Twelve drillholes (> 5000 m) that intersect IP sections were mapped and sampled to obtain geological characteristics and to quantify metallic minerals concentration in ore bodies. Geological parameters and modelled geophysical responses (electrical chargeability and resistivity) were compared using qualitative and quantitative criteria.Data analyses show that bulk sulphide concentration is the major factor that explains variations in the IP effect, even for IOCG ore bodies associated with magnetite mineralisation (up to 5 vol. %). Electrical chargeability exhibits a direct, but non-linear proportionality with sulphides content, while no clear trend is observed when chargeability is compared to magnetite concentration. In drillhole segments where macroscopic sulphides were not mapped, but IP results suggested high chargeabilities, petrographic studies revealed at least 1 vol. % of pyrite occurring as micro crystals (< 0.125 mm). The apparent resistivity data do not show any direct relationship with chargeability or sulphide contents.