Bottom-up exploration: imaging resistivity of a mineral system from source to sink

Abstract

Ore deposits are broadly defined as a geochemical anomaly which has been concentrated from a significantly larger volume source at depth. This requires a mineral system process through which elements in the lower crust or mantle are entrained and moved to the surface. In various locations around the world, the source region of a mineral system has been shown to have a distinct electrical resistivity signature as a result of past magmatic fluid processes which have left a geochemical overprint. This project focuses on the Curnamona Province, a Paleo-Mesoproterozoic craton which extends across South Australia and New South Wales with approximate dimensions of 300 km east-west and 300 km north-south. A previous broadband magnetotelluric (MT) (102 to 0.01 Hz) traverse of 60 stations spaced 2 km apart across the Curnamona Province identified a 2D geophysical signature with a footprint similar to that below the IOCG Olympic Dam deposit in the Gawler Craton. In this project, broadband MT measurements (104 to 0.01 Hz) were collected along four parallel lines of 1 km spaced sites, and with line separation of 5 km to develop the 3D context. We image a discrete low-resistivity zone on three of the lines, and this extends from the surface down to 20 km depth where it is linked to a conductor of 1Ωm. It appears to be bound between two resistive blocks and is not laterally continuous. The outcomes of this model are comparable to pathways across the Gawler Craton. We show a very strong relationship between deep crustal conductors and narrow pathways, inferring a signature which is responding to past magmatic events.