Report on an Airborne Radiometric and Magnetic Survey, Including Preliminary Ground Inspection.

Abstract

During 1971, GRD flew a widely spaced airborne radiometric survey over the northern margin of the Ngalia Basin. The survey was not successful in locating any new mineralization due to a variety of factors of which, in hindsight, inadequate instrumentation and poor recovery of position by the contractor were the most important. Following the discovery during 1973 of surface carnotite mineralization at the Bigryli Prospect, it became apparent that it was necessary to prospect all outcropping Mt. Eclipse Sandstone. Due to the failure of the 1971 airborne survey and the nature of the mineralization at Bigryli some doubt existed as to the effectiveness of airborne radiometrics over Mt Eclipse Sandstone. To resolve this doubt an orientation survey was flown in late 1973. This survey was successful and it was decided to fly a radiometric and magnetic survey over the areas of outcropping Mt Eclipse Sandstone in the northern Ngalia Basin. This report describes the results of the initial interpretation and preliminary ground follow-up of this survey flown during April 1974. From the 26th to 29th April 1974, a total of 1,850.3 line tan of survey was flown by a Pioneer Aircraft (Vil-AIS) of Aero Services Aust Pty Ltd. The flight lines were recovered on to 1:25,000 mosaics. Maps NT(NC)18 &19 show the flight paths. Radiometric anomalies were selected from examination of the six channel analogue Brush recordings, and the positions and peak heights of these were recorded. All dubious anomalies were checked by reference to the expanded scale Hewlett-Packard recordings of thorium and uranium channels. Where doubt of the validity of the anomaly still existed, the Munroe printouts of the digital data were consulted. From this, a total of 123 anomalies were selected for further study and ground inspection. The anomaly positions were plotted on the 1:25,000 mosaics and maps. Before checking, the positions were transferred to 1:25,000 air photographs, where necessary, by reference to contact prints of the relevant positions of tracking film.