The Geophysical Characteristics of the Trilogy Massive Sulphide Deposit, Ravensthorpe, Western Australia

The Trilogy deposit is a polymetallic massive sulphide deposit hosted within the conductive graphitic phyllites of the Proterozoic Mount Barren metasediments. There are two different styles of mineralisation, Pb-Zn massive style mineralisation and Cu-Au stringer style mineralisation, contained within a silicified envelope that hosts the mineralisation. Petrophysical samples were taken and geophysical surveys conducted to characterise the response of the massive sulphide system to help define an exploration model. Gravity, ultra-detailed airborne magnetics and radiometrics, airborne time domain electromagnetics (EM) and ground time domain EM have all been conducted over the deposit. The gravity outlined the position of the massive Pb-Zn mineralisation. A radiometric low around the surface projection of the silicified zone was evident in the airborne radiometrics. There was no response from the deposit recorded in the airborne magnetics. There is a subtle airborne EM anomaly over the known mineralisation, but the ground EM better defines its location and EM response. The airborne EM anomaly produced by the deposit was small compared with the response of the conductive phyllites elsewhere in the region. Geophysical exploration may aid in the search for additional sulphide mineralisation in the area. The combination of airborne EM with followup detailed gravity and ground EM have proven to be the most effective geophysical methods in locating Trilogy style mineralisation in the Mount Barren basin.