EL 282, report on 1973 Investigations

Abstract

The basic aims of the 1973 field season were to evaluate anomalies defined by earlier work and to assess the regional potential of the Exploration Licence. All anomalous areas were, therefore, mapped in detail where this had not previously been done and investigated by auger and/or percussion drilling. In the more regional studies the main emphasis was on geological mapping backed up by reconnaissance auger traverses in areas of poor exposure. Much of the earlier efforts were directed towards detailed examination of possible structural traps close to the Kombolgie Formation/Lower Proterozoic unconformity. However, increasing knowledge of the geology at the new uranium discoveries in the Alligator Rivers region had suggested proximity to the Nanambu Complex margins and the presence of a favourable lithological unit termed 'Koolpin Equivalent' by current BMR workers were also favourable factors in ore localisation. Efforts were therefore made to identify these and trace them along strike. Extensive geochemicals arrlpling cf stream sediments and auger cuttings were carried out in conjunction with the geological work. 1. The diamond drilling programme carried out at the Koongarra No 2 orebody has indicated that economic grades of uranium mineralisation persist to a depth of at least 600 feet. The deposit does, however have a fairly limited strike length and grades are much lower than those at the Koongarra No 1 orebody. The deposit should be regarded as an underground mining proposition rather than an open pit proposition, 2. The diamond drilling programme at the Koongarra No l Orebody has not indicated any significant occurrence of ore grade material at depths below those encountered last year, 3. Field mapping and diamond drilling at Koongarra have shown that the Koongarra Reverse Fault consists of at least two and probably several sub-parallel fault planes. These exert a strong controlling influence on the distribution of uranium mineralisation, 4. A strong lithological control on uranium mineralisation, is suggested by field investigations at Koongarra, the adjacent areas and the other new uranium discoveries in the Alligator Rivers area. The mineralisation is accompanied by an intense chloritic alteration of the host rocks. Work carried out this year has confirmed that the margins of Mt Brockman are highly prospective. At Koongarra North deep percussion drilling has indicated sub-economic uranium mineralisation and Koongarra type lithologies and alteration. West of Koongarra suitable hosts may occur southeast of dolomitic rocks intersected in percussion holes. At Anomaly F, drilling has indicated dolomitic lithologies which are probably the equivalent of those at the Ranger No 1 orebody. Prospecting has failed to locate any economic mineralisation away from the Mt Brockman Outlier. Regional investigations have, however, outlined prospective zones within 'Koolpin Equivalent? rocks close to the Nanambu and Mt Partridge contacts. Several anomalies defined in these areas by reconnaissance augering, stream sediment sampling and recent flying require detailed investigation during the coming season.