Wiso Basin collaborative SkyTEM survey

Abstract

In July, 2010 Toro Energy conducted a SkyTEM airborne electromagnetic (AEM) survey over EL 27138, covering 1625 km2 approximately 340 km north of Alice Springs. The collaborative geophysical survey between Toro Energy and the NT Department of Resources involved the acquisition, processing and interpretation of approximately 1100 line kilometres (1500m line spacing) of helicopter-borne electromagnetics. The SkyTEM system was preferred because it captures calibrated shallow high-resolution and deep-penetrating EM data that is highly suited to quantitative geological interpretation. Other systems either resolve too deep (VTEM) or too shallow (Tempest). SkyTEM is also quite cost effective for a heliborne system. SkyTEM has proven effective in mapping sandstone packages elsewhere and has been used effectively to target 'roll-front style' uranium mineralisation in Australia and overseas. The Wiso Basin and its structurally-controlled southern margin are poorly understood compared to other areas of the NT, largely because the basin has not attracted the attention of explorers for its mineral economic potential. Existing data consists of two BMR stratigraphic boreholes, a seismic survey, regional gravity and aeromagnetic surveys. The basin is also substantially covered by Tertiary sediments and the eastern extension of the Tanami Desert. Limited historic exploration has been focussed on petroleum systems, analogous with the gas-producing Amadeus Basin. The objective for Toro was to resolve the geometry, depth and thickness of the Wiso Basin sequence and determine its relationship with the adjacent Aileron Province, providing a foundation for future on-ground uranium exploration programs. In addition to helping advance Toro's exploration in this frontier basin, the proposed AEM survey will add substantially to the overall geological understanding of the Wiso Basin and it's juxtaposition with the Arunta Inlier. It will more clearly define the orientation of the basin edge and the architecture of the basin immediately to the north. A sedimentary hosted uranium model, akin to the Angela and Bigrlyi deposits, has not previously been interpreted for in this basin despite many similarities with the Amadeus and Ngalia Basins. The proposed survey will generate architectural information that, in combination with surface geochemical programs like soil-gas, vegetation or mobile metal ion, will point the direction of Toro's future exploratory drilling in the tenement. These techniques are critical for the exploration of sandstone hosted uranium deposits, which are essentially blind to direct detection techniques. The maximum overlap of any historical tenement over the proposed survey area was 25%. Most historical exploration occurred over the southern edge of the proposed survey area and was mainly for base metals and gold with some uranium within the Arunta Complex. Toro Energy are exploring for a completely different style of uranium mineralisation within the Wiso Basin. Main results and conclusions: The southern edge of the Wiso Basin has been mapped by the AEM survey in combination with the available Bonney Well magnetic data. The Hanson River drainage system in the western part of the AEM survey area is seen as a broad deltaic-looking conductive 'fan' extending well out into the basin. The ongoing drainage is much less conductive and more constrained. Within this drainage system, and within the basin, there appears to be a linear east west more resistive zone that may be indicating the position of an active basement fault and The Taylor River drainage system near the eastern edge of the AEM survey is less conductive and possibly shallower than the Hanson River 'fan'.