Annual report for EL 4500 Mt Douglas North period ending 27-12-1985

Abstract

During the 1985 field season CEGEA carried out a uranium exploration programme on EL 4500 under an agreement with ACGH. A detailed airborne gamma-ray spectrometer and magnetometer survey was completed and the data are presently being processed. Total count radiometric traversing was carried out along the Kombolgie Formation/Lower Proterozoic unconformity of the Mt Douglas outlier. A weakly radioactive kaolin bearing horizon was discovered close to the boundary of the EL on the western escarpment. The radioactivity was due to thorium. At the northern end of the kaolin zone a highly radioactive boulder was found. The source of the boulder could not be traced. The radioactivity in it is due to highly anomalous thorium. Anomalous tin, strontium and zirconium was also reported. Petrography and SEN studies suggested that the main thorium mineral was thorite, a thorium silicate which often contains uranium. Uranium values reported were less than 40 ppm U. Also lead values are low, around 70ppm Pb. It is possible that uranium has been leached from this thorite and redeposited in favourable underlying traps e.g. the unconformity. However if the thorite is a detrital, then uranium and lead were probably leached front it during erosion and transport. Rock chip sampling located a small, narrow zinc bearing ironstone north of Mt Harris but outside the EL. Reconnaissance gravel sampling was carried out for diamonds, micro diamonds and indicator minerals. Two samples reported traces of gold and sulphides and accessory to trace cassiterite. Airphoto and Landsat interpretation showed the presence of a circular feature around 3km diameter to the north east of Mount Douglas. It may be an intrusive or an astroblembe. The Kombolgie Formation was subdivided into 3 units based on kaolin content and corresponding airphoto tonal differences. It is thought that the rocks mapped as Kombolgie Formation at Mount Douglas may be equivalent to the El Sherana Group. This inference is based on the extensive and pervasive silicification and folding present in these rocks.