Heavy Metal Monitoring Alligator Rivers Region Uranium Province 1979
E-Publications; E-Books; PublicationNT; Report No. LC82/1
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Report No. LC82/1
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Winds in the region although extremely variable are seen from studies at Jabiru East to be north to north westerly in the wet changing to east to south easterly in the dry. 1.6 Geology The Alligator Rivers Uranium Province lies in the north east corner of the "Pine Creek Geosyncline" with major uranium deposites at Jabiluka, Ranger (1 & 3), Koongarra and Nabarlek. The regional geology is composed of a stratigraphic succession which includes archaean materials. Most of the area is now covered with unconsolidated to semi consolidated sands, gravels and clays of quaternary and tertiary origin periods with lateritesation common. Generally the tertiary deposits are underlain by Mesozoic sediments of fine to medium sandstone and siltstone encompassing the "Bathurst Island" formation. The Mesozoic sediments are underlain by Pre-cambrian geologies. Middle Proterozoic "Nourlangie" schistose and arenaceous sediments of the "Kombolgie" formation overlay lower Proterozoic metasediments (of the "Cahill" and "Koolpin" formations), and have suffered intrusions by dolerites and phonoli tes . The Cahill and Koopin metasediments in turn overlay lower proterozoic to archean granites making up the "Nanambi" formation. It is within the stratabound Cahill metasediments close to the granite complexes that the major uranium mineralization occurs (Masood, 1981). Throughout the Pine Creek geosyncline, uranium is found in sequences containing carbonaceous and carbonate rocks, and this association is thought to indicate that carbon or carbonate rocks may have played an important role in the formation of uranium deposites. (Needham & Stuart-Smith, 1980). Carbon under reducing conditions before or after lithification 'may have fixed uranium from surface or subsurface waters. Uranium may have been localised by absorption onto clays within carbonate rock fractures (Ferguson et a1., 1980) or during the metasomatising of brines by carbonate rich groundwaters (Crick & Muir, 1980). The ore forming processes have taken place over long periods with uranium datings of 1700-900 Ma being reported by Hills & Richards (1976).* Each of the major deposits in the Cahill formation occurs in zones of faulting and brecciation and there has been no significant movement away from this stratabound sequence. (Nedham & Stuart-Smith 1980). Many other metals have been reported in the Uranium Province. All the known gold occurs in association with the uranium mineralisation, with the only economically viable quantity being so far reported at Jabiluka 2. Other minor metals such as lead and zinc occur within the quartz breccia faults of the Nananabu complex west of Mt. Cahill. Tin is found within the Mt. Partridge range and iron in a quartz hematite rock over the Nourlangie schist north of Jim Jim Falls. LNL25 AI0
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