Querying potential field inversions for signatures of chemical alteration: an example from Cobar, NSW

Abstract

Major metal resources, predominantly gold and base metals, are hosted in the Cobar region, in the Central Lachlan Orogen of NSW, (Figure 1). The Predictive Mineral Discovery Cooperative Research Centre (pmd*CRC) T11 Cobar project was a two-year, one-on-one project between the pmd*CRC, NSW DPI and five mining companies in the Cobar region: CBH Resources Ltd., Cobar Management Pty Ltd., Peak Gold Mines, Triako Resources Ltd. and Tritton Resources Ltd. The aim of the Cobar project was to undertake a 3D mineral system analysis of the Cobar region, using the ?5 Questions? framework (Price and Stoker, 2002; Barnicoat, 2007): 1. What are the geodynamic and pressure-temperature histories of the system? 2. What is the architecture of the mineral system? 3. What and where are the fluid reservoirs for the mineral system? 4. What are the fluid flow drivers and pathways? 5. What are the metal (and sulphur) transport and deposition mechanisms? The answers to the ?5 Questions? of mineral systems provide the entire context of a mineral system. This context is exceedingly important, as it provides information on all of the processes that result in the formation of mineral deposits. This paper will discuss how 3D geological maps and potential field 3D inversions can be used for regional exploration targeting by querying for signatures of alteration. The volume of interest for this study is 40 km east-west, 50 km north-south and 16 km deep. The model is discretised into cubic cells of side length 250 m³. Inversions were performed using grav3d and mag3d (Li and Oldenburg, 1998a and 1996 respectively). Before inversion, an inverse model based regional-residual separation (Li and Oldenburg, 1998b) was performed. In the terms of the ?5 Questions? approach, this paper predominantly addresses question 4, although the results also addresses questions 2 and 5.