Report on 1976 investigations on EL 281

Abstract

Airborne radiometric surveys of the original Prospecting Authority were flown in 1968 and 1970. Part of the area was again covered by an airborne radiometric survey in 1973. Ground investigations, consisting of detailed geological mapping and radiometric surveying of the anomalous areas, commenced in 1969 and these continued through the subsequent field seasons. Several of the anomalies were drilled. A programme of regional mapping was continued each year and in order to augment the information available from outcrops a series of auger holes was drilled in areas covered by alluvium. A stream sediment sampling programme was also carried out during 1973 and 1974.

At the conclusion of 1973 several strong uranium emitters had been identified in the Cooinda area, but they appeared to be dispersive features. The geology in this area was considered to be essentially similar to that at the Ranger Uranium Deposits and the catchment area was investigated in 1974 by a detailed 'Track Etch' radon survey and by extensive auger drilling. These programmes were extended over a larger area in 1975 and a Turam electromagnetic survey was carried out. Several of the most prospective areas were drilled. The Ten Mile Creek North Prospect (originally known as West Jim Jim), was found late in 1974. Geological mapping and surface radiometric and Turam electromagnetic surveys were carried out in

1975. The main effort in 1976 was directed towards a final general assessment of the Cooinda Area with a view to taking out mineral leases over any highly prospective areas prior to the expiry of the Exploration Licence. Detailed mapping, ground radiometric and, radon monitor surveys and a ground magnetic survey were carried out and several prospective areas were percussion drilled. Nothing was discovered which warranted the taking out of leases. The Ten Mile Creek North prospect was further investigated by detailed mapping, ground magnetic and ground radiometric surveys over the area of Gold Mining Lease Applications Nos. 120A to 137A. Extensive radiometric and radon anomalies in the Cooinda area occur over rocks thought to be equivalent to the host rocks at the Ranger Deposits. The anomalies tested are all related to superficial features such as laterite or organic material in swamps, or to underground water. Most of the anomalies occur over the major aquifer in the area, and are probably caused by minor concentrations, in favourable surficial deposits, of radioactive material leached from rocks with high background radioactivity. Exhaustive auger and percussion drilling of the most prospective anomalies of all types has not given any indication of uranium mineralization and despite the favourable lithological environment, it seems most unlikely that economic mineralization occurs in the Cooinda area. The area is to be relinquished. Detailed mapping completed at Ten Mile Creek North will facilitate interpretation of future geophysical results with the aim of siting possible drill holes to the best advantage. The area of interest is protected by Gold Mining Lease Applications Nos. 120A to l37A. Further percussion drilling was carried out just outside the EL boundary near Anomaly 77 by the South Alligator Joint Venture. No significant mineralization was found, and this part of the Exploration Licence (Area A) is to be allowed to lapse.