Progress Report and Work Proposal for EL 4895 and EL 4896 Tennant Creek.

Abstract

Exploration carried out during the latter half of 1986 has been designed to provide a regional appreciation of mineralisation and radioactivity within the Tennant Creek Block. A review of company data followed by field reconnaissance has shown that anomalous radioactivity is associated with the mixed greywacke/acid volcaniclastic unit that hosts the 'Tennant Creek ironstone ore bodies, particularly where hematite shale and/or handed iron is Included in the sequence. The strongest anomalies are in fact associated with the zoned, Cu-Au bearing, magnetite-chlorite pipes, although this may be due to sampling prejudice (good sub-surface information is only available from successful mines). Several mines, notably Warrego, Juno, Northern Star and possibly Black Angel, have reported uranium approaching mill grades in the magnetite-chlorite core. Whether uranium has been remobilised and further concentrated in cherts or black shales outside of the magnetite bodies is beyond the scope of the present survey to determine. Two strong airborne radiometric anomalies, identified from CRA's work in the late 70's and early 80's, have been the subject of more detailed mineralisation during the year. The White Ridge and Whindgap anomalies lie within or near the edge of the Warrego Granite, and may be related to hydrothermal or pegmatitic remobilisation of uranium from the granite with deposition in favourable lithologies at the granite edge. At White Ridge, uranium is concentrated in what appears to be a phosphatic, iron rich metasediment over a strike length of about 600 meters and an apparent width of about 40 meters. The rock is weakly magnetic and corresponds to a belt of anomalous surface radioactivity and ROAC-indicated radon. Within this belt, discrete peaks (up to 1500 cps and ROAC No. 400) can be tentatively related to subsurface fracturing. Rock chip samples from poorly-outcropping laterite assay up to 270 ppm uranium. At Windgap, a broad uranium-in-groundwater anomaly previously reported by CRA appears to be related to zones of deep weathering and chloritic alteration along a gravity, airphoto and topographic lineament, at its intersection with the granite-sediment contact. Surface scintillometry gives a poor response, as a rock is covered up by up to 20 meters of tertiary and recent shale and sand. However content from ROAC and vegetation surveys indicate that discrete targets from ROAC No up to 1200 and uranium-in-leaf-ash to 75 ppm) may he defined by these techniques.