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Koongarra

Northern Territory, NT, Australia

Main commodities: U Au
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The Koongarra uranium deposit is located some 225 km east of Darwin in the Alligator Rivers uranium field of the Northern Territory, Australia.

It is interpretted to be an unconformity style deposit which is hosted by the Palaeoproterozoic Cahill Formation which has been overthrust to the north-west onto the Mesoproterozoic Kombolgie (sandstone) Formation over a 60° SE dipping, NE striking thrust that parallels lithological banding in the Cahill Formation and sub-parallels the regional S2 schistosity.

The ore occurs in two discrete orebodies separated along strike by a 100 m wide barren gap.   Both are hosted by a 50 m thick quartz-chlorite schist unit that is found immediately above the 5 to 7 m thick thrust breccia defining the contact with the underlying, younger Kombolgie Formation.   The upper contact of the quartz-chlorite schist is marked by a distinctive 5 to 8 m thick graphite-quartz-chlorite schist, which passes up into a 25 m thick, sulphide rich, graphite-mica-quartz schist unit.   This is in turn overlain by 90 to 100 m of garnet-muscovite-biotite-quartz schist and at least 180 m of muscovite-biotite-quartz-feldspar schist.   Bands up to 15 m thick of amphibolite are found in these latter two hangingwall units.

The main No. 1 orebody has a stike length of 450 m and persists to a depth of 100 m.   Secondary mineralisation is found in the 25 to 30 m thick weathering zone, forming a tongue like fan of ore grade material dispersed down slope to the SE over a lateral width of about 80 m.   Underlying this secondary mineralisation are lenses of primary ore in breccia zones that sub-parallel the thrust and persist to depths of 90 to 100 m in the quartz-chlorite schist. The best primary grade is over a consistent interval several metres thick just below the hangingwall graphite-quartz-chlorite schist.

The No. 2 orebody has a strike length of only 100 m.   The top of the primary mineralisation is 50 m below the surface (hence there is no secondary ore developed), but continues to depths of 250 m.

Primary ore is present as 1 to 10 mm thick uraninite veins and veinlets that cross cut the S2 foliation of brecciated and hydrothermally altered schist hosts.   These vainlets are intimately intergrown with chlorite which forms the matrix to the host breccia, while fine uraninite grains are disseminated in the schist adjacent to the veins.   Chlorite is the main alteration mineral accompanying the ore, while hematite is present in association with the main thrust and in the schists above it.

Resources in the No 1 orebody (Snelling, 1990) are:
    3.453 Mt @ 0.44% U3O8 at a cutoff of 0.02% U3O8, for 15 200 t U3O8, including,
    1.831 Mt @ 0.795% U
3O8 at a cutoff of 0.09% U3O8,
    The reserve also includes 3.11 tonnes of contained Au.

Resources at the end of 2007, as quoted by Areva, 2007, are as follows:
    Measured resource - 0.624 Mt @ 10.55% U, for 6585 T U; plus,
    Indicated resource - 0.188 Mt @ 5.33% U, for 1000 T U;

For detail see the reference(s) listed below.

The most recent source geological information used to prepare this summary was dated: 1990.    
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.


  References & Additional Information
   Selected References:
Beaufort D, Patrier P, Laverret E, Bruneton P and Mondy J  2005 - Clay Alteration Associated with Proterozoic Unconformity-Type Uranium Deposits in the East Alligator Rivers Uranium Field, Northern Territory, Australia: in    Econ. Geol.   v100 pp 515-536
Derome D, Cuney M, Cathelineau M, Fabre C, Dubessy J, Bruneton P, Hubert A  2003 - A detailed fluid inclusion study in silicified breccias from the Kombolgie sandstones (Northern Territory, Australia): inferences for the genesis of middle-Proterozoic unconformity-type uranium deposits: in    J. of Geochemical Exploration   v80 pp 259-275
Foy M F, Pederson C P  1975 - Koongarra uranium deposit: in Knight C L, (Ed.), 1975 Economic Geology of Australia & Papua New Guinea The AusIMM, Melbourne   Mono 5 pp 317-321
Maas R  1989 - Nd-Sr isotope constraints on the age and origin of unconformity-type Uranium deposits in the Alligator Rivers Uranium Field, Northern Territory, Australia: in    Econ. Geol.   v84 pp 64-90
Snelling A A  1990 - Koongarra Uranium deposits: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne   Mono 14, v1 pp 807-812
Wilde A R, Mernagh T P, Bloom M S, Hoffmann C F  1989 - Fluid inclusion evidence on the origin of some Australian unconformity-related Uranium deposits: in    Econ. Geol.   v84 pp 1627-1642


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 takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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