Final Report - West Arunta Carbonatite Search: Regional-Scale Gravity Program

Abstract

GSW Resources' (GSWR) West Arunta Carbonatite Search Project is located on granted titles EL 33042 and EL 33043, which form part of GSWR's larger critical-metals-prospective West Arunta project area under Group Report GR597. The underexplored West Arunta region is part of the Proterozoic Aileron Province of central Australia and comprises a distinctive magnetic-gravity belt of about 350km east-west extent that straddles the NT-WA border (the 'West Arunta Magnetic Gravity Belt' or WAMGB). As noted in the recent NTGS publication Critical Minerals in the Northern Territory 2025: High-grade niobium resources, including the globally significant Luni deposit, have been discovered in carbonatite complexes of the Aileron Province in Western Australia with high potential for further discoveries to extend into western regions of the Northern Territory. GSWR is focussed on exploration for mineralised carbonatites, analogous to the recent WA1 Resources Ltd (WA1) and Encounter Resources Ltd (ENR) discoveries in the western WAMGB, as well as other intrusive bodies with Cu-Au potential. Because much of the basement in the WAMGB is under cover, the WA1/ENR discoveries utilised high-resolution magnetic and gravity data to target concealed carbonatite intrusive bodies and associated cogenetic lamprophyres, which are typically located within and adjacent to crustal-scale structural corridors. In the 2024 season GSWR completed a high-resolution (100m-spaced) aerial magnetic and radiometric survey for 22,185 line-kms over its West Arunta project area that substantially improved the previous wide-spaced regional survey. Interpretation of the new magnetic imagery reveals strong similarities with the WA1/ENR carbonatite-prospective basement terrain across the WA border including the presence of crustal-scale fault zones within variably magnetic basement dominated by the ca 1.85Ga Lander Rock Formation and the ca 1.77Ga Carrington Suite. A first-pass analysis of the high-resolution 2024 magnetic imagery identified numerous potential carbonatite targets plus other likely intrusion-related magnetic features. However, the existing open-file, 4-km-spaced regional gravity grid was of insufficient resolution for target refinement. Therefore, under Round 18 of the Collaborations Program, GSWR proposed the acquisition of an enhanced ground gravity grid at 400m station-spacing over an area of 840km2 (maximum extents 60km east-west and 22km north-south). The Carbonatite Search project area represents the assessed most prospective part of GSWR's tenement package based on magnetic-structural interpretations, the likelihood of relatively shallow (less than approx. 50m) regolith cover and the proximity of lamprophyre dykes as an indicator of potential carbonatitic magmatism. The project objective is to create a high-quality, high-resolution integrated magnetic-gravity geophysical dataset for target identification, refinement and later drill-test prioritisation. The gravity program was approved for collaborative funding in May 2025 and the field program commenced on 1st September 2025. The program ran for seven weeks with two ATV-assisted gravity crews operating for most of the period. A total of 5,305 ground gravity stations, including selected in-fill stations over anomalies, were acquired at an average rate of 120 stations per day. A total of 238 repeat readings representing 4.5% of the survey were acquired for quality control purposes. The final data was assessed by GSWR's geophysical consultants and judged to be of high quality. The consultants provided various filtered imagery and interpretive products to assist with target picking, prioritisation and modelling. More than one hundred magnetic-gravity targets of interest were identified in the 840km2 project area. The targets include Luni 'look-a-like' anomalies such as target RY15, which is a ~3 mGal gravity and variably magnetic anomaly of 2.5km x 0.8km extent, closely similar in both scale and geophysical character to WA1's mineralised Luni carbonatite body. The gravity program included the collection of complementary soil geochemical samples at selected station sites for assay by the Ultrafine method, with collaborative funding provided under the Innovative Targeting scheme. Results of the geochemical program will be provided separately.