Walker River Airborne Gravity Gradiometry (AGG) survey

Abstract

Late Paleoproterozoic rocks in northwest Queensland and the Northern Territory host world-class stratiform sediment-hosted Zn-Pb-Ag deposits. These orebodies occur in intracontinental rift or rifted margin (marine) basins. Host rocks to these deposits are carbonaceous and/or pyritic black and grey (dolomitic) siltstone, mudstone and shale, often with a significant clastic carbonate (dolomite) component. The same lithologies occur within the McArthur Basin which hosts the world class HYC deposit and the Walker River Project, ~300 km to the north. Mineralisation at HYC is in part controlled by the Batten Fault Zone, a prominent north-south aligned eastward-deepening half-graben (aka the Batten Fault Trough). The Walker Fault Trough, a north continuation of the Batten Fault Trough, hosts the Walker River Project. The lithological and structural settings for the Walker River Project are thought by NTGS and Geoscience Australia to be analogous to the HYC deposit. Economic stratiform sediment-hosted Zn-Pb-Ag deposits are often associated with recognisable residual gravity responses, either directly related to mineralisation or associated pyritic sediments. Gravity is therefore a primary exploration tool. Government gravity stations have been acquired over the project area at roughly a 4 km density and due to land access restrictions, only one 'exploration' gravity survey has been conducted on the project since the discovery of the Walker Gossan in 1972 (2.7% Pb from rock chip). The 2016 gravity survey consisted of 160 stations acquired on six widely spaced traverses at 100 m spacing. Despite these limitations three unexplained gravity and/or soils geochemical anomalies were identified in structurally favourable locations. The Walker River AGG survey (Figure 1) over the highly prospective project area has expedited the geological knowledge and the exploration potential of the area. Several targets of interest have been identified from the AGG survey. Due to the short survey duration, the airborne survey minimised the impact to the local community and negate the need for extensive ground gravity surveys (to acquire the equivalent coverage) and the precursor archaeological clearance campaign/s. Discussions with local communities over access to AGG features of interest will commence shortly.