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Maureen

Queensland, Qld, Australia

Main commodities: U F Mo
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The Maureen uranium deposit is associated with Late Palaeozoic felsic intrusives and volcanics in north-eastern Queensland, Australia.   It is located towards the western margin of the Newcastle Range-Featherbed volcanic field.   Ben Lomond is some 50 km WSW of the city of Townsville, while Maureen is a further 340 km to the NW of the similar Ben Lomond deposit (which is 50 km west of Townsville - see the separate "Ben Lomond"  record), 280 km SW of the city of Cairns and 35 km NNW of Georgetown.

These deposits are the biggest of a large number of uranium-fluorine-molybdenum occurrences and radiometric anomalies that are associated with the extensive late Palaeozoic continental felsic volcanics and related intrusives of the Coastal Range Igneous Province that overlie and intrude the Georgetown-Coen Province of north-eastern Queensland and Cape Yorke Peninsular.

The Georgetown-Coen Province comprises the Georgetown, Einsaleigh and Gilberton Inliers, which are composed of variably deformed and metamorphosed Paleo- to Mesoproterozoic meta-sediments (from older calc-silicate gneisses, to andalusite-sillimanite-cordierite-mica-schists and quartzites, to younger, less metamorphosed mudstones, sandstones, shales and carbonaceous shales) and meta-volcanics (gabbros, dolerites and basalts low in the pile, to andesites and extensive rhyolites at the top), intruded by Mesoproterozoic granitoids.

The Proterozoic sequences are divided into the up to 15 000 m thick sequence of metamorphosed shallow water peltic to psammitic sediments and lesser mafic volcanics that comprise the Paleoproterozoic Etheridge Group, separated from the overlying early Mesoproterozoic Langlovale Group by the 1570 ±20 Ma Ewamin orogenic event. The Langlovale group, which is an at least 3000 m thick sequence of fluviatile to shallow marine psammites and pelites, and the coeval ~1550 Ma trondhjemite intrusives, were terminated by the 1470 ±20 Ma Jana Orogeny with associate S-type anatectic granitoids. These were unconformaby followed by the up to 2500 m thick, late Mesoproterozoic Croydon Volcanic Group, comprising early basaltic andesites followed by extensive rhyolites, and coeval S-type granitoids of the Forsayth Supersuite. These volcanics and intrusives were unconformably ovelain by the late Proterozoic to early Palaeozoic fluviatile sediments of the Inorunie Group.

These inliers are separated, overlain and intruded by Cambro-Ordovician, Siluro-Devonian, Carboniferous and Permian igneous rocks. The Cambro-Ordovician are laregly found to the south of the Georgetown Inlier, itself in the south, and include the Mt Windsor and Balcooma submarine to sub-aerial volcanics and volcaniclastics, which are largely felsics and comprise a sequence that is up to 7000 m thick.

The up to 100 to 150 km wide and 1000 km long, Siluro-Devonian Cape Yorke Plutonic Belt extends along the eastern margin of the Georgetown-Coen Province, along its faulted margin with the Palaeolzoic the thick Palaeozoic monotonous greywacke-shale sedimentary pile of the Hodgkinson Basin to the east. The most common rock type in this belt is biotite ± hornblende granodiorite occurring as composite, but not zoned batholiths, that are strongly discordant, foliated, sheared and intrude high grade metamorphcs with noobvious contact aureoles.

The Carboniferous and Permian igeous rocks of the Coastal Range Igneous Province extensively overprint the Georgetown-Coen Province and the sediments of the Hodgkinson Basin. The Carboniferous is largely represented by continental, welded rhyolitic ignimbrites, with minor more mafic components. The ignimbrite-dominated sequences are generally basinal and associated with concentric (ring) and/or linear fracture intrusive systems, many of which represent partial, single or composite cauldron collapse structures. The associated magma chambers are exposed as granitic batholiths. Extrusive rocks of the Newcastle Range-Featherbed volcanic field and intrusive equivalents are variably fractionated I-type in character. In many areas these have been divided into two suites, one predominantly dacitic to andesitic, the other, which is volumatrically dominant, of rhyolitic (or granitic) composition. Isotopic ratios suggest the intermediate suite was derived from old mantle, while the more acid suite were derived by anatectic reworking of Proterozoic basement rocks by invading mantle derived mafic magmas.

Early Permian igneous rocks are more widely distributed than the preceeding Carboniferous igneous complexes. In the Georgetown-Coen Province, the individual centres of igneous activity are characteristically thinner, less extensive and more heterogeneous than the underlying Carboniferous, with the intermediate to basic suites being relatively more voluminous. Thes volcanic sequences rest unconformably on Upper Devonian to Lower Carboniferous clastic sediments and Proterozoic basement, with much of the Carboniferous ignimbrite having been eroded. The Permian extrusives were deposited within broadly basinal structures, without associated concentric fracture system intrusives. The intrusives are dominantly sub-volcanic and of limited areal extent. Only to the east of the Georgetown-Coen Province did these basinal sediments overlap with more voluminous, felsic ignimbrite dominated volcanism with major cauldron subsidence, as exemplified by the Featherbed Volcanic Group. The Permian structural trend is predominantly NW, in contrast to the northerly structures of the Carboniferous. As in the Carboniferous, there are two suites represented, namely basaltic to andesitic and highly felsic rhyolitic rocks. The former suite is taken to represent an isotopically evolved mantle source, with the felsic suite being A-type derived from a depleted crustal source. There are also isolated putons of variably fractionated and zoned I-type granodiorite to granite with no preserved extrusive equivalents.

Maureen

The Maureen deposit lies towards the north-western margin of the Georgetown Inlier, which is bounded to the north-west by Mesozoic sedimentary cover of the Carpentaria Lowlands. The Inlier is composed of a diverse range of rocks, including Mesoproterozoic to early Palaeozoic metamorphic rocks and granites and late Palaeozoic volcanic rocks and related granites, overlain by scattered remnants of Mesozoic sedimentary rocks, and in the east by Cainozoic basalt. The older basement consists of Mesoproterozoic continental sediments of the Etheridge Group, which have been progressively deformed and metamorphosed from low-grade in the west to granulite facies in the east. Late Ordovician to Devonian deformation and metamorphism up to amphibolite grade, was followed by granitoid emplacement. A further orogenic cycle commenced in the Carboniferous with the intrusion of felsic magmas and eroded preserved remnants of coeval volcanic and subvolcanic complexes.

From the Late Carboniferous to the Early Permian the Georgetown Inlier underwent widespread subsidence accompanied by the out-pouring of massive volumes of welded crystal-rich rhyolitic ignimbrites from large cauldron structures. These include the Galloway Volcanic Group and the Maureen Volcanic Group and coeval granitic intrusives, with numerous associated uranium (±fluorine and molybdenum) occurrences.

From the Middle to Late Jurassic, widespread intra-cratonic down-warping occurred. Initially, a series of isolated basins formed, with fluvial and lacustrine sedimentation. As down-warping continued, the basins coalesced and a blanket of sand, the fluviatile Late Devonian to Early Carboniferous Gilbert River Formation, was deposited over most of the Gulf region on an irregular palaeo-topography in fans and braided streams. These sediments are not folded, although flexures are evident resulting from drapes over basement structures and differential compaction. In the Maureen area, the Gilbert River Formation is characterized by immature and poorly sorted epiclastic sedimentary rocks, mainly quartzose to feldspathic sandstone and polymictic conglomerate, with subordinate mudstone and siltstone and minor nodular limestones and volcaniclastic material. They were overlain by regionally extensive ignimbrite-dominated volcanic and extrusive rocks, with the major eruption of felsic extrusives being during the Late Carboniferous to Early Permian, represented in the Georgetown region by the Newcastle Range Volcanic Group, which outcrops over an area >2500 sq km to the east of Georgetown. The Newcastle Range Volcanic Group is predominantly composed of ignimbrites to welded ash-flow tuffs, with minor lavas, unwelded pyroclastics and rare sedimentary rocks. The primary eruptive rocks were almost exclusively deposited in a sub-aerial variety and range in composition from rhyolite to andesite, and possibly very rare basalt, 85 to 90% rhyolitic rocks and 5 to 10% dacitic rocks, with andesites making up the remainder. Volcaniclastic rocks at the base contain lenses of plant fossil-bearing arenaceous limestone, probably deposited in a restricted lacustrine environment, while other minor sedimentary rocks intercalated within the volcanics are either of fluviatile, shallow lacustrine, or mass-flow origin.

The Maureen Volcanic Group outcrops over an area of around 80 sq. km, around 30 km north of Georgetown on the northern margin of the Georgetown Inlier, passing below the Mesozoic and younger sediments of the Carpentaria and Karumba Basins to the north. It has not been dated (2006), but is possibly early Permian in age, and is a separate structural and lithological entity concordantly to paraconformably overlying the main mass of the Newcastle Range Volcanic Group. It is distinct from the almost adjacent Galloway Volcanics which are part of the Newcastle Range Volcanic Group, being distinctly bimodal and includes, or overlies, a considerable thicknesses of sedimentary rocks. The most common lithologies are crystal-poor to -rich, commonly lithic clast-rich, rhyolitic ignimbrites, partly brecciated rhyolite lava, quartz sandstone to siltstone, fine vitric tuff and augite andesite, with minor dacitic andesite at the top of the sequence, dacite lava and coarse volcanogenic rudite.

In the immediate vicinity of the Maureen deposit, the Mesoproterozoic basement Etheridge Group is represented by the Lane Creek Formation which comprises mainly mica schists with some quartzite and calc-silicate rocks, after protoliths of laminated, highly carbonaceous mudstone and siltstone, interbedded with pale grey to white mudstone and siltstone which were locally calcareous, with rare thin limestone and dolomitic beds. In areas of amphibolite grade metamorphism there are andalusite and cordierite porphyroblasts, and locally developments of amphibolite and migmatite. These rocks are unconformably overlain by a gently west dipping basal conglomerate of the Late Devonian to Early Carboniferous Gilberton Formation. Some 98% of the uranium at Maureen is hosted by the lower part of the Gilberton Formation, with only 2% in the underlying basement. The Gilberton Formation is overlain by the un-mineralised volcanics of Maureen Group. The local sequence is as follows, from the top down:

Maureen Volcanic Group, of Late Carboniferous to Early Permian age - the Ironhurst Formation, including the Ant Hill Andesite Member and the Womblealla Rhyolite Member, has been identified at Maureen. These rocks are dominantly basaltic andesite; dacite; rhyolitic volcanic rudite and lutite; crystal-poor rhyolitic ignimbrite; rhyolite, and sub-lithic to quartzose arenite and siltstone. The overall thickness of the Ironhurst Formation varies from 350 to 600 m, while the distinctive Ant Hill Andesite Member varies from 50 to 120 m in thickness. Locally the Group has been informally subdivided into:
    “Upper volcanics” - Ignimbrites and agglomerates; Agglomerates, basalts, tuffs, rhyodacites and rhyolitic ignimbrite;
    “Basalt sediments” - Tuffs; Bioclastic limestone; Siltstone with minor sandstone.
Gilberton Formation, of Late Devonian to Early Carboniferous age - 400 m thick, consisting primarily of a rhythmic sequence of rapidly alternating coarse, conglomeratic sandstones, with coarse, medium and fine-grained sandstone interbeds, together with arkose, siltstones, hematitic siltstones and shales, carbonaceous shales and some rhyolite flows, sub-divided as follows
    Unit 6 - Rhyolite; Oolitic siltstones; Chocolate siltstones; Fine-grained sandstones and siltstones; Fine to medium-grained sandstones; Coarse-grained and pebbly sandstone.
    Unit 7, the thinnest, but most consistent unit, averaging around 12 m in thickness - Rhyolite; Chocolate siltstones; Fine-grained sandstones and siltstones; Fine to medium-grained sandstones; Coarse-grained and pebbly sandstone.
    Unit 8, has an average thickness of 40 m and contains a thin band of elliptical spherulites, possibly of algal origin, that provides a useful marker horizon - Rhyolite; Chocolate siltstones;Fine-grained sandstones and siltstones; Fine to medium-grained sandstones; Coarse-grained and pebbly sandstone.
    Unit 9, lies unconformably on the basement and is extremely variable in thickness, ranging from 10 to 50 m, due to the uneven basement surface as well as some syn-depositional faulting. A well-developed carbonaceous shale horizon occurs near the base in some areas. It comprises - Chocolate siltstones; Fine-grained sandstones and siltstones; Fine to medium-grained sandstones; Coarse-grained and pebbly sandstone.
    Unconformity
Etheridge Group - Robertson River Sub-Group
    Lane Creek Formation - Graphitic schist, quartz mica schist, graphitic quartzite, quartzite, amphibolite, pegmatite and quartz veins.

Around 98% of the uranium mineralisation at Maureen is restricted to units 7 to 9 inclusive, and is strongly controlled by sedimentary features, being hosted mainly by conglomerate, sandstone and rhyolitic volcanic rocks, with the remaining 2% found within the underlying metamorphic basement.

The upper Palaeozoic sediments and volcanics have an overall dip of ~25°W, with minor local variations, cut by numerous faults and shears which dominantly trend east-west, corresponding to zones of outcropping silicification, often accompanied by uranium and fluorite mineralisation. These structures appear to exert a significant control on the distribution of the best mineralisation. Vertical and lateral displacement across these structures is usually no more than a few metres, with a maximum of 8 m. An extensive, 54° trending normal fault with maximum vertical displacement of 45 m, disrupts the main zone of mineralisation on the southern margin of a basement high.

Complex uranium and molybdenum phosphates occur as groundmass replacement, selective replacement of clasts, fracture filling and occasionally as complete replacement of clays. From the surface down to about 75 m depth, dispersion of the U-F-Mo minerals is extensive, strongly influenced by the permeability in the coarser sediments, and by the chemical composition of the finer sediments. At depth, the mineralised zones narrow, and appear to be confined to zones of deformation, accompanied by strong hydrothermal alteration. A correlation between uraninite and carbonaceous material is indicated in the primary zone, while arsenopyrite is widespread in the sediments but absent in the basement. The best uranium values occur in tabular elongate bodies (“mantos”) associated with abundant fluorite and lesser molybdenum. These mantos dip at about 20°, are elongated along the bedding planes and are enclosed within generally tabular zones of weaker U-F-Mo mineralisation which 'bulk-up' to form coherent tabular bodies with three-dimensional continuity and economic grades.
Deposit summary based on Jones, 2006).

The estimated resource has been quoted by GeoScience Australia (2001) as 2.383 Mt @ 0.123% U3O8 for 2940 t of contained U3O8.

Resources in July 2008 were quoted by Mega Uranium Ltd, 2008, at:
    Indicated resource - 3.124 Mt @ 0.09% U
3O8, 0.06% Mo for 2709 t U3O8
    Inferred resource - 0.154 Mt @ 0.11% U
3O8, 0.10% Mo for 173 t U3O8

The most recent source geological information used to prepare this summary 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.


  References & Additional Information
   Selected References:
Hurtig N C, Heinrich C A, Driesner T, Herrmann W, Wall V and Mathison I,  2014 - Fluid Evolution and Uranium (-Mo-F) Mineralization at the Maureen Deposit (Queensland, Australia): Unconformity-Related Hydrothermal Ore Formation with a Source in the Volcanic Cover Sequence: in    Econ. Geol.   v.109 pp. 737-773
Jones D  2006 - Technical Report for Mega Uranium Ltd on the Georgetown Project (Maureen Deposit), North Queensland, Australia (excerpt): in    Publicly available report to Mega Uranium    18p


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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