Additional report on 1972-73 investigations within final relinquished area for EL 123

Abstract

Anomaly 2J was delineated during the Noranda interpretation of the data from the airborne radiometric and magnetic survey conducted by CRD during 1970. Initial field investigations of the area consisted of radiometric gridding, geological mapping and sampling. These investigations indicated the presence of weak uranium mineralisation at the surface. Subsequently a total of 1,285 feet of rotary percussion drilling was carried out and within the limits of this type of drilling interesting uranium mineralisation was intersected at depth. The area has now become a high priority target for further investigation during 1973. Surface geological mapping of Anomaly 2J showed that the area of interest was contained in shales and siltstones of the Masson Formation. These rocks strike north-west to south-east and locally are thought to dip steeply to the south-west. Approximately 350 feet from the centre of the anomaly3 to the north-west the Coirwong Greywacke crops out as a dominant ridge. To the south-west approximately 600 feet from the centre of the anomaly sub-outcrop of Stag Creek Volcanics was found. A north-easterly trending fault zone is thought to limit the anomaly to the north-west. Radiometric gridding showed a strong anomaly, greater than 25 micro-Roentgens per hour (uR/hr) with a maximum of 100 uR/hr, over an area of 200 feet in length following a small creek. The strongest part of the anomaly showed a distinct uranium residual when traversed with a spectrometer. Several surface samples were taken and assayed for uranium. This confirmed the presence of uranium. Little outcrop of the Masson Formation can be found in the was interpreted as a zone of mineralisation striking north-west to south-east and bounded on the north-west by a fault. It was thought to be exposed by the dissection of the scree slope from the Coirwong Greywacke by a small stream. This interpretation was then tested by a small rotary percussion drilling programme. Rotary percussion drilling was carried out by Mitchell Drilling Contractors of Brisbane1 with a Mayhew 1000 rig mounted on a Foden tandem truck. Drilling commenced on the 12th of December and finished on the 16th of December. Two samples were taken from each five foot interval. One sample was dispatched to Geochemical and Mineralogical Laboratories (N. T.) PLy. Ltd., Darwin where fluorometric analysis for uranium was conducted. Some of these samples. were also sent to Sydney for colorimetric uranium and thorium analyses. The second sample was used for lithological and gamma spectrometer logging and when this was completed each sample was panned to examine the heave mineral content. The collars of all the vertical rotary percussion drill holes were surveyed using a Brunton Compass and tape. All elevations are referred to a datum, the collar of RDH1, selected as 300 feet. Rotary percussion drilling showed that the Masson Formation consists of siltstones and quartz sandstones. The sequence is characterised by thin quartz veins parallel and sub-parallel to the bedding. All drill holes intersected at depth a fine -grained dark-green rock, containing chlorite, epidote and minor pyrite, which is very similar to the Stag Creek Volcanics. The ranging depths of intersection of this greenstone can be explained by two faults trending north-easterly and north-south. The greenstone is usually brecciated for the first 10 to 20 feet of the intersection. Its top surface appears to be near flat -lying with a shallow dip to the south-west. Uranium mineralisation appears to die off in this rock type, with the possible exception of RDH 5 where 35 feet assayed 1.3 lbs U308 /short ton. Anomaly 2J - Percussion drill sections. The maximum assay recorded over a five feet sample interval was 19.6 lbs U308/short ton. A total of 233 samples were assayed for U3O8 and the results are summarised in the company report.