Archaean BIF-hosted gold, Mount Morgans, Western Australia: a geophysical case history

Abstract

The Mount Morgans Archaean gold deposit is hosted by banded iron-formation and has produced over 25 t of gold to date. The gold is associated with sulphides which have replaced magnetite. Aeromagnetic data covering the Mount Morgans deposit show a variably depleted magnetic effect caused by the replacement of magnetite by non-magnetic minerals, chiefly pyrite. Coincident with the magnetic effect is a conductive response recorded using airborne e1ectromagnetics. The likely source of this conductivity anomaly is the weathering profile. The main ground geophysical surveys over the deposit are magnetics and 50 m dipole?dipole induced polarisation. The induced polarisation detected a chargeability anomaly associated with the sulphide mineralisation and a conductive response associated with the weathering of sheared rocks. Surveys of magnetometric resistivity and very low-frequency electromagnetics have been conducted over the Mount Morgans North resource, a similar but smaller gold resource located on the BIF ridge north of the main Mount Morgans deposit. The responses observed over this resource confirm the conductive and chargeable nature of the sulphide mineralisation associated with the gold.