Round 16 Resourcing the Territory Initiative Tanami North Gravity Survey Final Report

Abstract

The Tanami North gravity proposal is aimed at providing detailed gravity data over an area which has only regional 4km x 4km gravity data. A recent detailed ground gravity survey at the Hyperion deposit highlighted several structural trends which host mineralisation which are not evident within the detailed aeromagnetic data. Prodigy Gold NL ('Prodigy') believes that the proposed gravity survey will assist in the basement interpretation and potentially highlight structural zones which may not be evident within the magnetic data and may highlight areas worthy of drilling where surface sampling and previous hallow drilling may be ineffective in targeting gold mineralisation within the Tanami Group. The area has been mapped and interpreted by multiple geologists and methods from the NTGS, Acacia Resources, Ord River Resources, ABM Resources, and Prodigy Gold. Lithologies identified over the area belong to the favourable Killi Killi Fm and Nanny Goat Volcanics, and unfavourable Birrindudu Group and Antrim Plateau basalt. ABM Resources and Prodigy Gold did extensive ME sampling (at surface from drill spoils and from drilling) at Hyperion and surrounding prospects and interpreted the extensive presence of the Mt Charles and Killi Killi Formations. Drilling at Tregony and recent field work conducted by Prodigy Gold in 2020-2021 has highlighted the presence of strongly foliated micaceous sandstone thought to be from the Killi Killi Formation. Therefore, the geology over much of the project area is interpreted to be similar to that to the Hyperion area; consisting of a sequence of basaltic flows, with interflow sediments, conformably overlain by the Killi Killi Formation, which is in part covered by the Birrindudu Group and Antrim plateau basalt. The favourable units have been deformed by at least three phases of deformation resulting in folding, thrusting and structural repetition of those units. Several phases of post mineralisation faulting are recognised and likely to be present, potentially offsetting mineralisation. Syn and post orogenic granitic rocks have intruded the sequences; little are known about those in the Tregony area, but they can be broadly categorised as either strongly magnetic or weakly magnetic. A series of structural trends were interpreted in the area from multiple geologists using different data sets. The latest regional interpretation was integrated with earlier detailed company interpretations (Ord River Resources, Prodigy Gold) and three trends stand out. A main N-trending Crusade - Tregony - Suplejack Fault/Corridor, a NW-trending fault splay off the main corridor consisting of the PhD Fault and sub parallels, and a series of obliquely trending E-W favourable conjugates and post mineralisation brittle faults. It is interpreted that the older, favourable Mt Charles Formation has been fault over the Killi Killi Formation by a series of thrust faults. Detailed aeromagnetic interpretation over the Tregony and surrounding prospects outlined N-S trending magnetic bedding interpreted to represent stratiform mafic intrusive rocks. The bedding shows evidence for thrust repetition and NE-SW / NW-SE / sub-E-W strike-slip fault offset. The interpretation outlined the presence of the Tregony shear running N-S, on the eastern side of the mineralisation. Detailed mapping of outcropping quartz veins outlines a dominant N-S trend. The Tregony shear was subsequently mapped, and it seems to follow the western boundary between the interbedded sediments and the haematitic shale. The previous NTGS-Prodigy collaborative geophysics program succeeded in trailing aground gravity survey at the Hyperion Deposit to image the stratigraphic sequence. The surveys successfully imaged both the Tanami Group lithologies and the overlying cover sequence. The data collected is comparable to that of the quality of magnetic data. In magnetically quiet areas, it has been possible to image additional stratigraphic units and the method has been able to image the controlling Au-bearing structures that only occur as subtle features in the magnetics.