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Bigrlyi |
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Northern Territory, NT, Australia |
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U V
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The Bigrlyi uranium deposit comprises seven uraninite and carnotite lenses distributed over a strike length of 11 km in the northern Ngalia Basin, 345 km WNW of Alice Springs in the Northern Territory, Australia.
The Ngalia Basin is a 300x70 km elongate intracratonic depression/basin filled with 7500 m of Neoproterozoic and younger sediments surrounded by pre-Neoproterozoic crystalline basement which include gneisses, granite and quartzite, the assumed source of both the basin sediments and the uranium.
The Neoproterozoic sandstones and dolomites are overlain by around 20 m of probable Ordovician sandstones, another 90 m of Ordovician to Devonian sandstone, siltstone and shale and by approximately a 1 km thickness of Devonian to Carboniferous sediments known as the Mount Eclipse Sandstone.
The Mount Eclipse Sandstone is the host to mineralisation. It has been divided into 8 units from H at the base to A at the top. Unit H the lowermost unit comprises a 10 to 30 m thick basal boulder conglomerate. Units G upwards to Unit E, varies from 65 to 395 m in thickness and consist of fine to medium micaceous sandstone dolomite, quartz sandstone, pebble sandstone and arkosic sandstone. The overlying Units D and C both host the significant strata-bound uranium mineralisation at Bigrlyi. Unit D is from 10 to 100 m thick and consists of medium-grained grey and red, feldspathic sandstone, and contains uranium mineralisation at several locations. Unit C, which is the principal host for uranium mineralisation at Bigrlyi, ranges from 20 to 200 m in thickness and consists of medium to coarse-grained white to grey feldspathic sandstone, with shale clasts, abundant carbonaceous debris, pyrite and, rarely, pebbles. The matrix is composed of chlorite and fine mica with carbonate cement. Carbonaceous material is present as disseminated flecks of graphite or rare coaly stringers. Shale bands and beds are similar in appearance to the shale clasts and are also carbonaceous, graphitic and pyritic. Uranium mineralisation is predominantly concentrated towards the base of this unit, close to the contact with unit D. Some mineralisation is also in unit B. In outcrop, Unit C is pale yellow, brown to yellow, brown and white with feldspar component frequently kaolinised.
At the surface the uranium mineralisation occirs as carnotite, while at depth and below the water table, it is present as uraninite and montroseite (VO(OH)). The uraninite has an maximum grain size of 1 mm although individual grains commonly occur as blotchy aggregates of around 1 cm in diameter, giving the host a black sooty appearance in some intervals. The sooty appearance is enhanced by the presence of the black montroseite and the associated organic detritus. In high-grade mineralised intervals the feldspars are commonly a bright orange colour in association with red and reddish brown enclosing rocks. Gangue minerals are predominantly quartz with accessory to significant orthoclase, kaolin and/or chlorite, muscovite and calcite. Trace amounts of zircon, goethite, ilmenite, pseudorutile, chromite, ferrosilite, pyrite, marcasite and garnet are also present.
The ore occurs as disseminations and patches within the host sandstone in seven, typically pitching, generally steep dipping and narrow, tabular bodies, averaging around 5 m in true thickness. Ore is always intimately associated with carbonaceous matter. Two of the larger bodies dips at 65 to 80° S and have dimensions of 160 m in length, 90 m down dip and 4 m thick with an average grade of 4.19 kg/t U3O8, and 370 m long x 150 m down dip and 3.8 m thick with 3.53 kg/t U3O8 respectively. The latter pitches at 18° to the west. Weathering extends to around 25 m below surface. These deposits also carry appreciable vanadium, although the uranium and vanadium peaks seldom coincide.
Measured and indicated resources in 1987 were - 0.808 Mt @ 3.43 kg/t U3O8 for 2770 t of contained U3O8.
2000 t of this is in the two deposits whose dimensions are given above.
Resources in 2006 were quoted by Paladin Resources as follows, using a 0.1% U3O8 cutoff grade in 5 deposit of the known 16 mineralised occurrences:
Indicated resource - 1.05 Mt @ 0.23% U3O8, 0.22% V2O5 for 2450 t U3O8
Inferred resource - 0.78 Mt @ 0.17% U3O8, 0.22% V2O5 for 1340 t U3O8.
In March 2007 the resources had become, also a 0.1% U3O8 cutoff grade (Paladin Energy, 2008):
Indicated resource - 1.94 Mt @ 0.17% U3O8 for 3250 t U3O8
Inferred resource - 2.59 Mt @ 0.13% U3O8 for 3260 t U3O8.
For detail consult the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 2006.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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Fidler R W, Pope G J, Ivanac J F 1990 - Bigrlyi Uranium deposit: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne Mono 14, v2 pp 1135-1138
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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