Geophysical Responses of Devoncourt Prospect - A Granite Hosted IOCG System in North-West Queensland, Australia

In 2019, Rio Tinto Exploration (RTX) identified an IOCG prospect hosted within the Wimberu Granite by drilling a coincident magnetic/gravity anomaly. The drilling intersected widespread IOCG type alteration and Cu mineralization. The potential field response is characterised by two main coincident gravity and magnetic highs. Modelling of magnetics and gravity, constrained to depth of post-Proterozoic cover, show the eastern anomaly can be explained by a coincidently dense and magnetic body in the basement, whilst the western anomaly has a magnetic phase just below the cover with a deeper denser core, currently untested by drilling. Several lines of Offset Dipole-Dipole Induced Polarisation (IP) data were collected, aiming to understand the chargeability response of the drilled IOCG system and detect any ore grade mineralisation in the interpreted alteration zone. The IP survey highlighted two moderate chargeability anomalies, one coincident with the eastern magnetic and gravity anomaly and another 2 km southwest in a magnetically quieter area. While the drilling around eastern magnetic anomaly encountered copper sulphides associated with the IOCG system, the southwestern feature did not yield a comparable amount of sulphides in the Proterozoic basement. Petrophysical analysis from selected holes confirmed the chargeability response from the surface IP survey is likely a combination of magnetite, specular hematite and copper sulphides in the basement, as well as pyrite logged in the base of the cover sequence.