Geologic Setting and Relevant Exploration Features of the Jabiluka Uranium Deposits

CIM Bulletin, Vol. 70, No. 788, 1977

M. R. Hegge, Senior Geologist, Pancontinental Mining Limited, Sydney, N.S.W., Australia

The Jabiluka One and Two uranium deposits occur in Lower Proterozoic metasediments of the Cahill Formation, which is part of the Pine Creek Geosyncline in the East Alligator River area, Nothern Territory. The Jabiluka One deposit coincides with a "window" through un-conformably overlying Middle Proterozoic sandstone of the Kombolgie Formation; Jabiluka Two is completely covered by that sandstone. The observed part of the Cahill Formation exhibits four horizons which are favourable hosts for uranium -mineralization. These have been folded into an east-southeast-striking, gently plunging, open asymmetric syncline-anticline structure. The host rocks are mainly chlorite and/or graphite schists and their brecciated equivalents which have undergone, initial regional prograde metamorphism to the amphibolite fades, then retrograde metamorphism to the greenschist fades. Mineralization consists of pitchblende, mainly filling open spaces and to a lesser extent in disseminated form. Chlorite, pyrite and quartz are commonly associated with the uranium mineralization. A portion of the Jabiluka Two deposit contains economic concentrations of gold. Structural preparation with low-pressure conditions at these sites appears to be the most significant ore control. Genetic hypotheses favour initial deposition in Lower Proterozoic sediments, followed by remobilization during later orogenic events. The deposits bear a marked similarity to some pitchblende deposits in central Canada.
Keywords: Mineral deposits, Uranium deposits, Jabiluka uranium deposits, Exploration, Australia, Stratigraphy, Petrology, Alteration, Metallogenesis.