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Westmoreland - Redtree, Junnagunna, Huarabagoo
Queensland, Qld, Australia
Main commodities: U

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The Westmoreland district comprises at least 50 uranium prospects of various sizes and grades, the most significant of which are Redtree, Junnagunna and Huarabagoo. The district is located in far north western Queensland, Australia, close to the border with the Northern Territory, 200 km south of the Gulf of Carpentaria coast and 900 km NNW of Mount Isa.

The sandstone hosted Westmoreland district deposits lie on the southern margin of the large intracratonic Palaeo- to Mesoproterozoic McArthur Basin which hosts the unconformity-related Jabiluka, Ranger, Nabarlek and Koongarra deposits of the Alligator Rivers uranium field on its northern end.   While the known uranium deposits in the Alligator Rivers district are hosted by amphibolite and granulite facies metasedimentary schists, the majority of those in the Westmoreland field are within undeformed sandstones.

Collectively, the three main Westmoreland deposits have an inferred resource of approximately 15.6 Mt @ 1.18% U308 for a contained resource of 17900 tonnes of U308.

The McArthur Basin was filled by a 5 to 10 km thick sequence of mostly unmetamorphosed sedimentary and volcanic rocks deposited between around 1800 and 1575 Ma. The ~1850 Ma Murphy tectonic ridge and the 1890 to 1820 Ma Pine Creek inlier define the southern and northern extent of this basin, respectively. The oldest sediments of the McArthur basin in the Westmoreland district unconformably overlie and onlap the ~1850 Ma Cliffdale Volcanics, the Scrutton Volcanics, and the Urapunga Granite. The basal Westmoreland Conglomerate and the overlying Seigal Volcanics of the southern McArthur Basin are part of the ~1800 to 1750 Ma Leichhardt superbasin which incorporates the lower 1000 to 4000 m thick Tawallah Group of proximal to distal fluvial conglomeratic sandstones, mafic volcanics and well-sorted marine and aeolian sediments.

The up to 1800 m thick Westmoreland Conglomerate is subdivided into five upward-fining units, each comprising proximal fluvial deposits typical of debris flows, alluvial fans, and braided river systems that are overlain by medium- to coarse-grained, well-sorted sandstone. Breaks in sedimentation are indicated by angular unconformities or disconformities, with each cycle of pebble or boulder conglomerate generally defining the beginning of the next unit. Cobbles and coarse sand grains within the basal conglomerate are predominantly reworked quartz veins, chert and clasts of felsic to mafic volcanic rocks that appear to have been derived from the Murphy tectonic ridge or similar basement rocks from the north.

The Seigal Volcanics, which are generally <20 m thick at Westmoreland, conformably overlie the Westmoreland Conglomerate. They are predominantly composed of basaltic lava flows and are strongly altered to chlorite, illite, Fe-oxides and rarely quartz and plagioclase.

Aphyric, medium-grained dolerite dykes cut the Westmoreland Conglomerate and basement units of the Murphy inlier in northeast-trending structures that likely reflect zones of weakness in the underlying basement. One of these, the Redtree dyke, has a geochemistry consistent with that of the Seigal Volcanics, suggesting that the dykes may have been feeders for these lava flows.

The Redtree uranium deposit flanks the Redtree dyke zone immediately to the north of the northwest-trending Namalangi fault. It comprises stratabound and discordant uranium mineralisation with grades ranging from 0.15 to >2% U
308 in four lenses. Stratabound mineralisation is up to 15 m (locally up to 30 m) in thickness and is hosted entirely within the fourth unit of the Westmoreland Conglomerate below the Seigal Volcanics. Vertically discordant mineralisation is found in the Westmoreland Conglomerate and dolerite belonging to the Redtree dyke zone.

The Junnagunna uranium deposit occurs at a fault intersection west of the Redtree dyke zone and south of the northwest-trending Cliffdale fault. Uranium is predominantly found as flatlying, 0.5 to 10 m thick bodies, again concentrated within the fourth unit of the Westmoreland Conglomerate, immediately below the Seigal Volcanics. Grades range from ~0.3 to 1% U
308. Minor discordant mineralisation occurs within the Westmoreland Conglomerate adjacent to the Redtree dyke.

Uranium mineralisation in these deposits comprises uraninite with hematite and illite within zones of chlorite alteration that formed prior to the uraninite during peak diagenesis. Illite crystallinity suggests a temperature of formation of the uraninite-illite-hematite assemblage of 200° ±50°C, while
40Ar/39Ar and 207Pb/206Pb dating of the uraninite indicates the mineralisation formed at between 1655 ±83 and 1606 ±80 Ma, coincident with major tectonic events in northern Australia. Further, it appears the mineralisation was later remobilised between 1150 and 850 Ma.

The most recent source geological information used to prepare this decription was dated: 2005.    
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:
Ahmad, M., Dunster, J.N. and Munson, T.J.,  2013 - McArthur Basin: in Ahmad M and Munson TJ (compilers)  Geology and mineral resources of the Northern Territory Northern Territory Geological Survey   Special Publication 5 pp. 15:1-15:72
Hills J H and Thakur V K,  1975 - Westmoreland Uranium Deposits: in Knight C L, (Ed.), 1975 Economic Geology of Australia & Papua New Guinea The AusIMM, Melbourne   Mono 5 pp 343-347
Polito P A, Kyser T K, Rheinberger G and Southgate P N,  2005 - A Paragenetic and Isotopic Study of the Proterozoic Westmoreland Uranium Deposits, Southern McArthur Basin, Northern Territory, Australia: in    Econ. Geol.   v100 pp 1243-1260
Polito, P.A., Kyser, T.K. and Jackson, M.J.,  2006 - The Role of Sandstone Diagenesis and Aquifer Evolution in the Formation of Uranium and Zinc-Lead Deposits, Southern McArthur Basin, Northern Territory, Australia: in    Econ. Geol.   v.101, pp. 1189-1209.

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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