1979 Summary Report on Joint Venture Areas in the South Alligator River Valley Northern Territory Australia

Abstract

The report covers work during 1979 of the South Alligator Joint Venture, including detailed reviews of previous work by SAJV and United Uranium NL since the 1960s. Prospects reviewed include: High Priority Areas:

Window I,

Skull II,

Saddle Ridge,

Sleisbeck. Medium Priority Areas:

Palette,

Window II,

Coronation Hill. Low priority areas:

Anomaly 3-171,

Rockhole Reverse Fault Extension,

Anomaly 105 &110. High Priority Areas

Window I: A NW trending topo depression 13km long by up to 2km wide. A window of Lower Proterozoic rocks exposed through the Kombolgie Formation with a faulted contact on its SW side and a depositional contact on the NE side. Lower Proterozoic rocks are Fisher Creek Siltstone intruded by Zamu dolerite. Dolerites are chloritised, sericitised and carbonatised near the SW bounding fault. The unconformity surface lies close to the floor of the depression. Drillhole (W1/DDH3) samples assayed 0.02% - 0.224% U3O8. Follow up of drilling of zones anomalous in radon uranium and base metals is strongly recommended .

Skull II: The prospect occurs on the NE slope of Scinto Plateau 6.5 km SE of El Sherana Camp. It was a radiometric anomaly, tested in 1961 by a BMR SP survey and at least 11 shallow percussion drill holes, which contained subeconomic values of uranium in the altered Koolpin Formation. The Koolpin Formation in the prospect is in faulted contact (NW-SE) with Kombolgie Formation. There is an intersection with a set of NE-SW lineations in the vicinity of the prospect. Anomalous Rn, Pb, and U3O8 was shown in 1977 soil sampling. 700m of additional drill testing is recommended.

Saddle Ridge: This small abandoned uranium mine (1960) is located on a topographic saddle on the SE corner of the Scinto Plateau. It was discovered by UUNL prospectors and showed secondary uranium minerals at surface. BMR completed shallow diamond drilling with disappointing results, but subsequent UUNL percussion drilling was more successful (0.34%U3O8 over width of 1.83m), and in 1960, 60 to 82 tons of U3O8 were extracted from 29,900 tons of open pit ore, of entirely secondary U minerals. Later deep drilling indicated primary mineralisation of potentially economic grades and widths below the mined zone, and anomalous Rn and radiometrics confirm that not all mineralisation has been removed. Additional drilling (550m) is recommended, as well as relogging and assaying of remaining core is also recommended. Noranda Australia Limited remapped the area and during radiometric surveys detected values of uranium 50 times background on Scinto Breccia and within Koolpin Formation shales.

Sleisbeck: Sleisbeck lies in a 70 x 30km window of exposed Lower Proterozoic metasediments and intrusives surrounded by Middle Proterozoic Edith River Volcanics and Kombolgie Formation, in the headwaters of the Katherine River. the Lower Proterozoic metasediments strike east- west, dip steeply to the north, and are described as meta- shales, siltstones, and cherts, of upper greenschist to lower amphibolite facies. These are variably chloritic, carbonatitic and slightly carbonaceous if unaltered. They are considered to belong to the Masson Formation in the more recent work. At or near the unconformity, siliceous breccias are present and the uranium mineralisation worked by NAUC occurred on the contact between the siliceous breccias and surrounding metasediments. The report recommends follow up of INPUT conductors revealed in the 1979 survey, with a radon survey, with concurrent soil geochemical and spectrometer survey, particularly in areas where faulting is indicated by the airborne magnetic survey. It was mined between 1954-1957and produced approximately 3.0 tons of U3O8 at a grade of 0.4% U3O8.

Palette: The deposit is located on the NE side of Scinto Plateau, in and around a faulted contact between Koolpin Formation carbonaceous shales and a sandstone unit within the Edith River Volcanics. It operated from 1958 to 1963 and produced 118 tons of U3O8 with an average grade of 2.45%. Most ore was obtained from very rich pods. Gold was sometimes found in separate shoots from the uranium ore. Some mercury has also been recovered from Palette, and Coloradoite (HgTe) has been recorded, as has chalcopyrite. There does not appear to have been much exploration for extensions of the mineralisation at depth, and this is recommended in the report.

Window II: the prospect is a 6km long east- west section of the steep sided valley which lies at the headwaters of the north- flowing Barramundie Creek and south- flowing Koolpin Creek, and the gorge extending to the north west. The floor of the valley is dolerite (Oenpelli Dolerite?) with overlying Kombolgie Formation sandstone forming the valley walls. There is evidence that the sandstone is downfaulted against the dolerite on the south side of the valley. The northern contact is a nonconformity. Anomalous total count radiometrics were found in 1972 and subsequent strem sediments sample draining the valley floor assayed 17ppm U3O8 and 57 ppm Th. However, follow up program could not substantiate it.. It is suspected that the anomalous results may be due to Th rather than U, possibly from monazite derived from basal Kombolgie Formation conglomerates. A programme to resolve this issue is recommended.

Coronation Hill: The mine area is located on the NE slopes of Coronation Hill, and mineralisation appears to have been deposited in a diatreme breccia containing fragments of Koolpin Formation carbonaceous shales, and intrusive quartz porphyry. The diatreme pierces Middle Proterozoic basic volcanics, and is in turn cut by quartz feldspar porphyry. U mineralisation is said to be localised around the Carbonaceous shale fragments, while, U/ Au mineralisation and Au mineralisation may be concentrated in the quartz porphyry and on its contact with the basic volcanic host rock. Uranium occurrs as both primary sooty pitchblende and uranyl prhosphates. Drill hole CH-DDH3 drilled beneath the old workings in 1976, showed the existence of more widespread mineralisation, particularly of Au, at Coronation Hill, and could be regarded as the 'discovery hole' for the gold mineralisation. the report urges further mapping, sampling and assaying of existing core, followed by additional drilling.

Low- priority targets Anomaly 3-171, the Rockhole Reverse Fault Extension, and Anomaly 105 & 110 are briefly described and limited work proposed. The report contains the following Appendices:

Appx 1: Descriptions of El Sherana and Rockhole mine areas

Appx 2: Selected bibliography

Appx 3: Summarised contents of Noranda Australia reports on South Alligator Joint Venture

Appx 4: Petrological Examination of 33 samples from the South Alligator River Region, NT, by Lowder Geoscience

Appx 5: Interpretation Report Airborne Electromagnetic survey Barringer 'INPUT' System of the Sleisbeck Area, NT, for Utah Development Company (83-296) by T. Whiting.