Final report Jabiluka 2 Deposit, EL 12

Abstract

This report covers the drilling programme carried out on the Jabiluka Two deposit on Exploration Licence 12 during the period June 1st to December 3rd, 1973. The work was carried out by Pancontinental Mining Limited as operator of the Pancontinental Mining Limited/Getty Oil Development Company Limited Joint Venture. The Jabiluka Two deposit occurs in the same westerly striking asymmetrically folded succession of Lower Proterozoic metasedimentary rocks as the Jabiluka One deposit. The fold axis dips about 70 north and has an irregular plunge that appears to flatten from the average 7 east plunge at Jabiluka One. The north Limb of the syncline dips about 35 to the south and the south limb is essentially flat. The deposit so far delineated is located in a sandstone valley which extends east of the Jabiluka One deposit. The drilling at Jabiluka Two proved a uranium deposit with indicated in situ ore reserves of 4.5 million metric tons of ore at an average grade of 0.41% U308. A total of 16 holes intersected ore grade mineralisation. The Mine Sequence rocks contain approximately 9% of the uranium ore reserve at Jabiluka Two. About 9% is contained in the Hanging Wall and Footwall Schist Series and the remaining 1% occurs in two separate horizons, one above the Hanging Wall Schist Series and one below the Footwall Schist Series. The Mine Sequence is composed of four stratigraphic members. The top of the Mine Sequence is a graphitic schist which varies in thickness from 1- 3 metres. A second member consists of a chlorite graphite complex which is developed only in the eastern part of the Jabiluka Two deposit. This member reaches a maximum thickness of 60 metres in the north limb of the fold and pinches out completely down dip in the axial plane area. A light coloured series of quartz chlorite muscovite and quartz muscovite chlorite schists occurs below the graphite schist member in the western part of Jabiluka Two and has a variable thickness from 0- 7 metres. This member pinches out completely to the east. The lowest member of the Mine Sequence consists of two separate submembers which occur along the same stratigraphic horizon within the deposit. One is a chlorite breccia with associated dark coloured chlorite and chlorite graphite schists. This submember reaches a maximum thickness of 42 metres. The breccia shows a maximum thickness of 17 metres but pinches up dip where it disappears in the axial plane area. A series of dolomite magnesite bodies and associated dark coloured chlorite and chlorite graphite schists occurs as a submember to the extreme west of Jabiluka Two. The Hanging Wall and the Footwall Schist Series contain approximately 9% of the uranium mineralisation in the Jabiluka Two deposit and consist of quartz chlorite muscovite and quartz muscovite chlorite schists. Two additional uranium horizons are developed at Jabiluka Two. One is in the graphite and associated chlorite graphite breccia that occur above the Hanging Wall Schist Series. The other horizon is developed in the Dolomite Magnesite Complex that occurs below the Footwall Schist Series. A series of pegmatite dykes and, to a much lesser extent, basic dykes cut the metasedimentary succession. The pegmatite dykes are probably premineralisation and appear to have been poor hosts for uranium deposition except where the dykes are chloritized. Where intersected, the basic dykes are not anomalous and their relationship with the uranium mineralisation is unknown. Uranium minerals that occur at Jabiluka Two include pitchblende and uraninite. Minor secondary uranium minerals occur but have not been identified. Accessory minerals include pyrite, galena, chalcopyrite, marcasite, hematite and minor native gold.