Report on 1976 investigations for EL 123 South Alligator Valley

Abstract

This report summarises exploration activities completed during 1976 in Exploration Licence No. 123 (EL 123). The work carried out in this area was part of a reconnaissance geological programme carried out in the area from Saddle Ridge to Dinner Creek. For practical purposes the area mapped was divided into two; (A) Dinner Creek to Coronation Hill, (B) Coronation Hill to Saddle Ridge. Area A was wholly within EL 119 whilst area B straddled the boundary between EL 119 and EL 123. Area A and B were situated within the central portion of the South Alligator river valley. The sinuous river channel wound between steep ridges of Lower and Middle Proterozoic rocks and was surrounded by a narrow flood alluvium zone. Tributary streams of the South Alligator River rose in the escarpment country, to both the east and the west of the River, and had deeply incised stream beds consequent of the steep gradients from escarpment to local river base levels. At the Southern end of the Scinto Plateau vertical cliff faces of Kombolgie Sandstone were present. Access to the mapped area was via the main El Sherana to Sleisbeck road, but within this area access was made along river flood plains or areas of low relief. A four wheel drive vehicle was essential for cross country access. Mapping in area A was by informal traversing with photographic control. In area B mapping was carried out using compass and pace controlled traversing at 100 and 125 yard spacing with photographic plotting of the traverse end points. This programme was carried out in a one month period during September and October 1976.

Scintrex Scintillometer BGS-1S No. 309165 was used to take readings of gamma ray intensities. Its use in area A was as continuous monitor on the informal traverses,, anomalous areas were selected by visual comparison of assessed background and anomalous reading. In area B scintillometer readings were taken every 25 yards along the traverse lines, zones between reading station were continuously monitored and spot values noted. No further work was warranted in Area A, 2) Numerous untested situations were seen to exist in Area B, these need further investigation. A suggested programme was set out in Section 3 of this report, 3) The majority of possible mineral locations were thought to exist within Lower Proterozoic rocks close to the Middle Proterozoic unconformity and in arenaceous units of the Lower portion of the Middle Proterozoic succession. Groundwater movements and chemical/structural interfaces were considered the important elementsfor uranium emplacement, 4) Analogy with East Alligator River Deposits was not strong except possibly at the meta-shale anomaly zone found to the east of Pul Pal Hill. This radiometric anomaly was found in the middle greensehist facies metamorphic equivalent of Koolpin Formation at the sedimentary

facies transition from Limestone to Cherty Ferruginous Siltstone, 5) No potential was envisaged for the development of economic concentration of base metals. Recommendations - Work on the 35 leases pegged in November 1976 was recommended as follows; (i) Meta Shale anomaly east of Pul Pul Hill - Detailed geological mapping, soil and rock chip geochemical, radiometric and Track Etch radon surveys. Close attention should be paid to alteration/metamorphism, detailed structure and its relationship to radiometrics and geochemistry, the relationship of the anomaly to limestones and the source of radioactivity. Petrological samples would be needed to study metamorphism, alteration and mineralization, (ii) South east extremity of Scirito Plateau to south east side of Pul Put Hill - Selective Track Etch radon, geochemical and radiometric sampling of structural zones, porous Middle Proterozoic units, scree slopes and scree toe zones. A sample spacing of approximately 100 metres was envisaged but distribution would of course be irregular. More detailed geological mapping and radiometric coverage was envisaged. Accurate magnetometer and radiometric work could possibly delimit the zones of oxidation within the breccia. A magnetometer orientation survey would be of paramount importance in evaluation of the applicability of the technique to this situation. Use of this method should await the outcome of the measurement of radon dispersion from Breccia areas, (iii) Radiometric anomalies at the Gimbat fence line N. W. of the Gimbat access road. - Detailed radiometrics and geology to delimit the anomaly zones and detailed soil geochemical sampling of the anomalous areas, (iv) Saddle Ridge North East and the strike faulting zone north west from the prospect - Track Etch radon, radiometric, geological and geochemical surveys along the fault structures NW of the North East prospect and within scree dispersing from the faulted zone. Geological evaluation of the North East prospect with a view to determining the structural setting and its relationship to mineralization.