Reynolds Range Collaborative Tempest Survey

Abstract

A Tempest airborne electromagnetic survey of 911 line kilometres (1500m line spacing) covering 1,247 sq km was completed as per the 50 percent NT Government funded Reynolds Range Collaborative Tempest Survey. The survey area covers a large proportion of Toro Energy's EL 26987, EL 27301 and EL 29396, which are situated on the northern edge of the Reynolds Range, comprising Arunta Block, possible Georgina Basin and thin Tertiary cover. The objective was to refine the geological understanding in the area to assist in exploration drillhole targeting for uranium mineralisation. The Tempest system was utilised because it captures calibrated shallow high-resolution EM data that is highly suited to quantitative geological interpretation of palaeochannel settings, which is more cost effective than helicopter-borne systems. Tempest has proven effective in mapping sandstone packages elsewhere and has been used effectively to target 'roll-front style' uranium mineralisation in Australia and overseas. Main results and conclusions: A combination of AEM and regional magnetic data provides evidence for extensions of the Georgina Basin into the survey area from the east, with thicknesses greater than predicted previously by the NTGS; The large linear (NW-trending) magnetic feature in the centre of the survey area may be a younger mafic intrusive body than the Georgina Basin, perhaps correlating to the Antrim Volcanics to the northwest; A large palaeodrainage network is evident as a broad sinuous conductive 'plume', which emanates southeast of the survey area in the Reynolds Ranges, and propagates northward across the flat landscape overlying the Georgina Basin and Arunta Complex. This palaeochannel was probably deposited in the Tertiary and is now providing a conduit for northward dispersion of saline groundwater; The surrounding sand plain is much less conductive and is interpreted to be a similar thickness sequence as the palaeochannel, but comprised of less permeable sands with fresher groundwater; Below this drainage system, within the Georgina Basin, there appears to be a series of linear northwest oriented faults that may have controlled deposition and subsequent basin inversion and hydrocarbon leakage; and The modern drainage systems, including the Lander River, are not reflected in the subsurface electromagnetic data, indicating that the underlying palaeochannels are of an older generation when the depositional environment and setting were different to today.