Report on 1975 Field Operations in Areas Adjacent to Jabiluka Uranium Deposits

Abstract

Areas to the north and south of the Jabiluka uranium deposits were investigated by the Commission during 1975. The two areas investigated total 4,399 ha and adjoin Special Mining Lease Application 6lA. The areas are situated at the edge of outliers of the Kombolgie Formation and are marginal to the Magela Mass of the Nanambu Complex. Alluvial and colluvial cover are extensive, the exploration program was directed at determining the presence or otherwise of the favourable beds of the Cahill Formation and assessing the uranium potential of the areas. A surveyed grid was established for control purposes and a geological map of the areas was completed. Radiometric and magnetic surveys were conducted. In the northern area track Etch, soil geochemical and biogeochemical surveys were also conducted. An auger drilling program was commenced late in the season but was discontinued because of the onset of the 'wet' season after only three holes were drilled. Over most of the northern area there is an extensive alluvial and colluvial cover which masks the underlying rocks. It is considered that in the southwest corner there are rocks of the Nanambu Complex indicated by the presence of gneiss in cuttings from the collars of two of Pancontinental?s percussion holes and a group of apparently anomalous Track Etch results which are attributed to the higher background of the Nanambu Complex. In the central and northern portion there is a relatively thin (less than 50 m) layer of sandstone which is interpreted as being Kombolgie Formation downfaulted to the west of the outliers. Below the Kombolgie Formation it is postulated that there are units of the favourable Cahill Formation. This interpretation is based on an intersection of muscovite schist in Pancontinental's auger hole AT 5, the regional geology, the magnetic survey and the structural geology of the Jabiluka deposits. The structure is considered to be influenced by strong east-trending cross folds - a synform through the north of the area and an antiform between the area and the Jabiluka deposit, with the Jabiluka deposit situated on the southern limb of the antiform. The plunges of the folds are likely to be gentle and the style of folding is likely to be open. Photolineainents and linear magnetic trends indicate that faulting is likely to complicate the fold structure.