CONTENT and DESCRIPTIONS OF ORE DEPOSITS
Porter GeoConsultancy, in association with the Australian Association of Exploration Geophysicists (ASEG), continued its International Study Tour series of professional development courses by visiting a representative selection of the major uranium deposits & ore styles across Australia, in South Australia, the Northern Territory and Queensland.
- palaeo-channel sandstone roll front deposit, South Australia,
Olympic Dam - IOCGU style deposit, South Australia,
Northern Australia Uranium - classroom & field workshop, Northern Territory,
Ranger & Jabiluka - unconformity style deposits, Northern Territory,
Westmoreland - Sandstone hosted, associated
with basic dykes, NT/NW Queensland,
Ben Lomond - caldera-volcanic hosted deposit, East Queensland - visit cancelled.
The tour commenced in Adelaide, South Australia on the morning of Thursday 26 February and ended in Mt Isa, Queensland on the evening of Tuesday 3 March, 2009. Participants were able to take any 2 or more days, up to the full tour, as suited their interests or availability.
The main components of the itinerary were:
NOTE: Geological visits were requested to all of these deposits, and formal approvals received.
The Uranium 2009 International Study Tour was designed as a post conference field trip to ASEG 09, the 20th International Geophysical Conference and Exhibition organised by the Australian Society of Exploration Geophysicists (ASEG) and
Petroleum Exploration Society of Australia (PESA), held in Adelaide, South Australia from 22 to 25 February, 2009. Although discounts were offered to conference delegates, the tour was also open to non-delegates.
The tour included the following deposits and workshops:
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Honeymoon ...................... Thursday 26 February, 2009.
The Honeymoon in situ leach uranium deposit is located around 400 km NE of Adelaide, approximately 75 km NW of Broken Hill, over 150 km SE of Beverley and 30 km NE of exposed Mesoproterozoic basement of the the Olary Ranges.
It lies below and almost flat featureless plain of low sand dunes separated by shallow drainage depressions. It is one of a series of deposits in the southern part of the Frome Embayment, within the Yarramba Channel that drains the Palaeo to Mesoproterozoic Benagerie Ridge and Willyama Complex which contain the uranium rich Crocker Well and Mundi Mundi granites. The Yarramba Palaeochannel comprises three subhorizontal permeable sand layers (the upper, middle and basal aquifers). The aquifers are separated by clay layers, with the potential uranium mineralisation occurring in the basal sand unit. The aquifers contain water of distinctly different qualities which indicates that mixing of groundwater between the aquifers does not occur. The channel was incised into Proterozoic and Cretaceous basement for 155 km and contains around 55 m of poorly consolidated Eocene sediments representing an upward fining sequence of braided stream deposition, culminating in Miocene to Pliocene pyritic clay units. The more permeable beds have been oxidised to orange and yellow-brown colours, whereas where the permeability is lower sediments remain reduced.
The source of Honeymoon's uranium is considered to have been derived from both chemical and mechanical weathering of a high-level granite located approximately two kilometres to the south of the deposit.
Mineralisation in the channel is generally at the interface between the oxidised permeable sands and the reduced clays and silts containing carbonaceous material. The majority of mineralisation is located near the confluence with a major tributary entering the Yarramba Palaeovalley from the south and is also associated with a topographical high in the channel floor. The Honeymoon mineralisation is concentrated at the convex edge of a major bend in the palaeochannel and occurs within coarse grained, pyritic basal sand where it pinches out between the overlying reduced clays and the basement of the channel floor. Mineralisation extends along this pinch-out for around 900 m, is around 450 m wide and averages 4.3 m in thickness at a depth of 110 m. It occurs as microscopic coffinite in the upper basal sand, closely associated with pyrite and humic matter.
This physical setting in association with extremely fine grained, acid soluble uranium mineralogy of uraninite, coffinite and uranium phosphates, makes the ore amenability to in situ recovery mining
The resource delineated in 1990 (Curtis et al., 1990) was 3 400 tonnes of contained U3O8 at a grade of 0.157% U3O8. In 2000, the resource was quoted as 6800 t of contained U (IAEG, 2001). In 2007, the indicated mineral resource at Honeymoon was 1.2 Mt @ 0.24% U3O8 over an average thickness of 1.7 m, containing 2900 t of recoverable U3O8 (Uranium 1, 2008). The Indicated mineral resource estimate according to each sand unit has been calculated from drill intercepts of 0.4 metre minimum thickness and 0.03% U3O8 minimum grade up to 1 metre of internal dilution. An economic grade thickness cut-off of 0.1m% U3O8 has been applied.
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Olympic Dam ...................... Friday 27 September, 2009.
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Travelling from Adelaide to Darwin ...................... am Saturday 28 February, 2009.
The Olympic Dam copper-gold-uranium-REE ore deposit is located some 550 km NNW of Adelaide and 275 km NNW of Port Augusta, in northern South Australia (#Location: 30° 26' 24"S, 136° 53' 22"E).
Olympic Dam and all of the other significant known IOCG mineralised systems of the Mesoarchaean to Mesoproterozoic Gawler Craton are hosted within Palaeo- to Mesoproterozoic rocks, and are distributed along the eastern rim of the currently preserved craton to define the Olympic IOCG Province (Skirrow et al., 2007). Olympic Dam lies below the Neoproterozoic Stuart Shelf, where >300 m of flat lying, barren, Neoproterozoic to lower Palaeozoic sedimentary rocks unconformably overlie both the craton and the ore deposit. Some 75 km to the east, this cover sequence expands over the major NNW trending Torrens Hinge Zone at the edge of the craton, into the thick succession of the north-south aligned Neoproterozoic Adelaide Geosyncline rift basin, that masks the mid- to late-Palaeoproterozoic suture between the Gawler craton and Palaeo- to Mesoproterozoic Curnamona Province to the east.
The oldest basement rocks in the Gawler craton are Meso- to Neoarchaean gneisses (to the west) and metasedimentary and meta-volcanosedimentary rocks, and deformed granites correlated with the Palaeoproterozoic 1.96 to 1.85 Ga Hutchison Group, the 1.79 to 1.74 Ga Wallaroo Group, and the 1.85 to 1.69 Ga Lincoln Complex (Donington Suite) granitoids, respectively. These rocks are intruded by the widespread Mesoproterozoic A- and I-type granitoids of the ~1.59 Ga Hiltaba Suite (with the former dominating in the Olympic IOCG Province) and are overlain by comagmatic bimodal volcanic rocks of the areally extensive Gawler Range Volcanics (GRV).
Mineralisation at Olympic Dam is hosted by the 50 km2 Olympic Dam Breccia Complex (ODBC) that is developed within the Mesoproterozoic (1600 to 1585 Ma) Roxby Downs Granite. The Roxby Downs Granite is a pink to red coloured, undeformed, unmetamorphosed, coarse to medium grained, quartz-poor syenogranite with A-type affinities that is petrologically and petrochemically similar to granitoids of the Hiltaba Suite. Other lithologies within the ODBC comprise a variety of granite- to hematite-rich breccias, sedimentary facies, felsic/mafic/ultramafic dykes, volcaniclastic units, basalts and their altered/mineralised equivalents. The ODBC and the surrounding Roxby Downs Granite form a local basement high on a broader regional basement uplift.
Within the overall alteration envelope, the distribution of mineralisation and alteration exhibits a downward and outward zonation, while the ODBC correspondingly comprises a downward narrowing, funnel-shaped body of fractured, brecciated and hydrothermally altered granite which has resulted in a great variety of granitic, hematitic and siliceous breccias. The complex has a conical, downward tapering, central "core" of barren, but intensely altered hematite-quartz-breccia, passing outwards through concentrically zoned breccia types, including heterolithic hematite breccias (with clasts dominantly of granite and recycled hematite breccias, and domains where abundant sedimentary and volcaniclastics rocks predominate locally), to monoclastic granite breccias with a magnetite/hematite matrix, to weak incipient microfracturing of the RDG on the outer margins. A halo of weakly altered and brecciated granite extends out approximately 5 to 7 km from the core in all directions to an indistinct and gradational margin with the host granite. This progression represents an outward decrease in the degree of brecciation and intensity of iron metasomatism away from the core of the complex. The quantity of recycled hematite breccia, GRV and sedimentary rock clasts within the heterolithic hematite breccias decreases from shallow to deep levels (Ehrig, 2010; McPhie et al., 2010). The areal extent of more intensely hematite altered breccias within the complex is >5 km in a NW-SE direction, up to 3 km across, and is known to extend to a depth of at least 1400 m.
The development of the ODBC, which shows textural evidence of polycyclic alteration and brecciation events, can be considered as having formed by the progressive hydrothermal brecciation and iron metasomatism of the host granite. In detail, alteration assemblages are highly variable with complex mineral distribution patterns resulting from the polycyclic nature of the hydrothermal activity. Never-the-less, there are systematic patterns of alteration that are recognised across the deposit as a whole, and at the scale of individual breccia zones, with the degree of alteration intensity being directly related to the amount of brecciation.
The bulk of the mineralisation within the Olympic Dam deposit is associated with an assemblage of hematite-sericite-fluorite-barite-chalcopyrite-bornite-chalcocite (djurleite), the outer margin of which largely corresponds to the limits of the ODBC, where a deeper magnetite-carbonate-chlorite-pyrite±chalcopyrite zone marks the transition to the more regional magnetite-K feldspar±actinolite±carbonate assemblage (Ehrig, 2010). No associated sodic metasomatism has been observed.
The better mineralisation and strongest alteration outside of the barren core corresponds to the best-developed hematite-granite breccias. The concentric, moderate to steeply inward dipping breccia zones of the ODBC are cut by a convoluted, but overall roughly horizontal, ~50 m thick layer characterised by chalcocite and bornite, ~100 to 200 m below the unconformity with the overlying Neoproterozoic cover sequence. Both the upper and lower margins of this zone are mappable. Above the upper margin, sulphides are rare and little copper mineralisation is found in the same hematitic breccias. The lower margin marks a rapid transition to chalcopyrite, which decreases in copper grade downwards, corresponding to an increase in the pyrite:chalcopyrite ratio. While this zone is largely horizontal, as it approaches the central barren core it steepens markedly, but is still evident at depths of >1 km below the Neoproterozoic unconformity (Reeve et al., 1990; Reynolds, 2000; Ehrig, 2010). The geometry of this mineral zonation, strongly suggest interaction between upwelling and downward percolating fluids. For all fluids related to hematite alteration, fluid inclusion homogenisation temperatures are mostly between 150 and 300°C and salinities range from ~1 to ~23% NaCl equiv. (Knutson et al., 1992;
Oreskes and Einaudi, 1992; Bastrakov et al., 2007).
The higher grade underground resource occurs as up to 150 separate bodies distributed within an annular zone up to 4 km in diameter surrounding the central barren hematite-quartz breccia. These bodies correspond to the overlap of the flat-lying chalcocite-bornite layer and the steeper, inwardly dipping ring of hematite-granite breccias.
The principal copper-bearing minerals are chalcopyrite, bornite, chalcocite (djurleite-digenite), which on the basis of Nd isotopic data, textural and geochemical features appear to have precipitated cogenetically. Minor native copper and other copper-bearing minerals are locally observed. The main uranium mineral is uraninite (pitchblende), with lesser coffinite and brannerite. Minor gold and silver is intimately associated with the copper sulphides. The main REE-bearing mineral is bastnaesite. Copper ore minerals occur as disseminated grains, veinlets and fragments within the breccia zones. Massive ore is rare.
At the end of 1989, after commencing mining operations in mid-1988, reported resources and reserves (Reeve et al., 1990) amounted to:
Measured + indicated resource = 450 Mt @ 2.5% Cu, 0.6 g/t Au, 6.0 g/t Ag, 0.8 kg/tonne U3O8,
Inferred resource = 2000 Mt @ 1.6% Cu, 0.6 g/t Au, 3.5 g/t Ag, 0.6 kg/tonne U3O8,
Proved reserve = 13 Mt @ 3.0% Cu, 0.3 g/t Au, 10.2 g/t Ag, 1.1 kg/tonne U3O8,
Proved gold reserve = 2.3 Mt @ 1.6% Cu, 3.6 g/t Au, 2.9 g/t Ag, 0.3 kg/tonne U3O8.
At December 2004, published (BHP Billiton, 2005) reserves and resources were:
Proved+probable reserves totalled 761 Mt @ 1.5% Cu, 0.5 g/t Au, 0.5 kg/tonne U3O8,
within a total resource of 3810 Mt @ 1.1% Cu, 0.5 g/t Au, 0.4 kg/tonne U3O8.
At 30 June 2012, the published resources (BHP Billiton, September, 2012) amounted to:
Measured resource = 1474 Mt @ 1.03% Cu, 0.35 g/t Au, 1.95 g/t Ag, 0.30 kg/tonne U3O8,
Indicated resource = 4843 Mt @ 0.84% Cu, 0.34 g/t Au, 1.50 g/t Ag, 0.27 kg/tonne U3O8,
Inferred resource = 3259 Mt @ 0.70% Cu, 0.25 g/t Au, 0.98 g/t Ag, 0.23 kg/tonne U3O8,
Total resource = 9576 Mt @ 0.82% Cu, 0.31 g/t Au, 1.39 g/t Ag, 0.26 kg/tonne U3O8.
This resource includes a total proved + probable reserve of:
629 Mt @ 1.76% Cu, 0.73 g/t Au, 3.36 g/t Ag, 0.57 kg/tonne U3O8.
At the same date, the separate non-sulphide gold resource was 364 Mt @ 0.75 g/t Au, comprising:
Measured resource = 73 Mt @ 0.85 g/t Au; Indicated resource = 255 Mt @ 0.73 g/t Au; Inferred resource = 36 Mt @ 0.70 g/t Au.
At 30 June 2015, the published resources (BHP Billiton Annual Report, 2015) amounted to:
Measured resource = 1.330 Gt @ 0.96% Cu, 0.40 g/t Au, 2.0 g/t Ag, 0.29 kg/tonne U3O8,
Indicated resource = 4.610 Gt @ 0.79% Cu, 0.32 g/t Au, 1.0 g/t Ag, 0.24 kg/tonne U3O8,
Inferred resource = 4.120 Gt @ 0.71% Cu, 0.24 g/t Au, 1.0 g/t Ag, 0.25 kg/tonne U3O8,
Total resource = 10.060 Gt @ 0.78% Cu, 0.30 g/t Au, 1.0 g/t Ag, 0.25 kg/tonne U3O8.
This resource includes a total proved + probable reserve of:
484 Mt @ 1.95% Cu, 0.74 g/t Au, 4.0 g/t Ag, 0.59 kg/tonne U3O8.
Stockpile - 44 Mt @ 0.99% Cu, 0.51 g/t Au, 2.0 g/t Ag, 0.37 kg/tonne U3O8.
At 30 June 2015, a separate non-sulphide gold resource was 283 Mt @ 0.84 g/t Au, which was not reported in 2015.
At 30 June 2017, the published resources (BHP Annual Report, 2017) amounted to:
Measured resource = 1.460 Gt @ 0.96% Cu, 0.41 g/t Au, 2.0 g/t Ag, 0.30 kg/tonne U3O8,
Indicated resource = 4.680 Gt @ 0.79% Cu, 0.34 g/t Au, 1.0 g/t Ag, 0.25 kg/tonne U3O8,
Inferred resource = 3.920 Gt @ 0.71% Cu, 0.28 g/t Au, 1.0 g/t Ag, 0.24 kg/tonne U3O8,
Total resource = 10.100 Gt @ 0.78% Cu, 0.33 g/t Au, 1.0 g/t Ag, 0.25 kg/tonne U3O8.
This resource includes a total proved + probable reserve of:
508 Mt @ 1.99% Cu, 0.72 g/t Au, 4.0 g/t Ag, 0.58 kg/tonne U3O8.
Low grade Stockpile - 37 Mt @ 1.13% Cu, 0.51 g/t Au, 3.0 g/t Ag, 0.36 kg/tonne U3O8.
Production in 2011-12 totalled 192 600 tonnes of Cu, 3.66 t Au, 28.21 t Ag, 3885 tonnes U3O8.
Production in 2014-15 totalled 124 500 tonnes of Cu, 3.26 t Au, 22.52 t Ag, 3144 tonnes U3O8.
The mine is owned and operated by a subsidiary of BHP Billiton Ltd.
Northern Australia Uranium Classroom Workshop, Darwin ................ pm, Saturday 28 February, 2009.
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Pine Creek Orogen Field Workshop ................ Sunday 1 March, 2009.
A classroom and field workshop led by experts is planned to provide an overview of the setting, geology, distribution, geophysical expression and controls on ore in the major Alligator Rivers uranium province. Emphasis will be on the major unconformity style deposits, but will also include details of other styles of uranium mineralisation and ore found within the province.
The field workshop will be concentrated in the Rum Jungle area of the Pine Creek Orogen, where there are good exposures of mineralised, but less metamorphosed, equivalents of the Archaean and Paleoproterozoic sequences that host the unconformity style uranium deposits of the eastern part of the Orogen in the Ranger/Jabiluka area.
Ranger & Jabiluka ................ Monday 2 March, 2009.
Ranger is an operating mine, while Jabiluka is undeveloped.
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The Ranger unconformity-style uranium deposit is located in the Alligator Rivers uranium field, some 250 km east of Darwin in the Northern Territory, Australia (#Location: 12° 41 'S, 132° 55'E).
The Ranger deposits are located in the north-eastern part of the Paleoproterozoic Pine Creek Geosyncline which overlies Archaean basement. The Paleoproterozoic comprises the 2470 to 1800 Ma basement Nanambu Complex granite, gneiss and schists. The overlying Cahill Formation comprises a lower unit which consists of quartz-schist, mica-schist, para-amphibolite, calc-silicate and carbonate with a regional northerly strike and dip of 15 to 40°E. An upper unit represented elsewhere has been eroded in the region around Ranger and the lower Cahill Formation is unconformably overlain by the Mesoproterozoic (~1650 Ma) Kombolgie Formation of the McArthur Basin. The Kombolgie Formation is made up of a lower and upper sandstone separated by the Nungbalgarri Volcanic Member.
In the main ranger string of deposits, the stratigraphy is as follows, from the base (Kendall, 1990):
Footwall sequence which is part of the Nanambu Complex, comrpising a variable mixture os schist, gneiss, micro-gneiss and granitic rocks, which in the main No. 1 mine has been altered chloritised and sericitised gneisses and schists laterally and vertically away from the orebody.
Lower Mine sequence - a thick sequence of interbedded carbonates, schists and cherts. The carbonates, which are up to 300 m thick, ranges in composition from magnesite to dolomite, are divided into a lower and upper unit separated by the lenticule schist unit. The lower carbonate is essentially magnesian marble. The schist consists of quartz, chlorite and sericite. The upper carbonate is an impure dolomite with interbedded chlorite schist. Below the mineralised zone of No. 1 Orebody the Lower Mine Sequence thins to <100 m, with the upper carbonate and some of the lower having been silicified to produce a jasperoid chert. Some of the lower carbonate has been replaced by massive chlorite. Uranium mineralisation in the Lower Mine Sequence is restricted to the zones of chlorite alteration and the lenticule schist.
Upper Mine sequence - comprises a 500 m thick sequence of quartz-feldspar-biotite schists, micro-gneisses (altered to quartz-chlorite schist) and irregular carbonates. Discrete carbonate bands are found within the unit, originally believed to have been black shales. The graphitic schists in the central disturbed zone contain high grade uranium mineralisation. Away from the disturbed zone there is no apparent association between graphite and uranium.
Hanging wall sequence - a group of micaceous quartz-feldspar schists with intercalated amphibolitic units and garnetiferous horizons, the basal 50 m of which contain finely disseminated magnetite.
Intrusives - in the mine area are largely pegmatite and dolerite dykes. The dolerite dykes, believed to be part of the Oenpelli Dolerite, are thought to have intruded during, or just after mineralisation.
The Lower and Upper Mine and Hanging wall sequences all belong to the Cahill Formation and are unconformably over lain by the Kombolgie Formation.
There are two main orebodies. The No 1 Orebody is localised in a discrete basin shaped structure formed by the dissolution of carbonate and thinning of the host unit. It is represented by two different grade populations. The first averages 1% U3O8 and occurs as four parallel vein or reef structures within the Upper Mine Sequence recognisable by intense brecciation and chloritisation. The second averages 0.15% U3O8 and includes patchy mineralisation in the Lower Mine Sequence and as lower grade halos surrounding the veins within the Upper Mine Sequence. The No. 1 orebody was mined out in the early 1990's.
The No 3 Orebody occurs as a thin 2 to 3 m thick, shallow dipping high grade (up to 8% U3O8) body of mineralisation against a 5 to 10 m thick chert unit developed at the Lower Mine Sequence to Upper Mine Sequence boundary, accompanied by intense brecciation. Above this zone in the Upper Mine Sequence there is a wider zone of weakly brecciated chloritic schisthosting mineralisation that averages 0.15% U3O8. The remainder of the Upper Mine Sequence is not brecciated, is weakly chloritised and contains finely disseminated pitchblende. There is no evidence of carbonate dissolution at this orebody.
Gold is present as a zone of up to 1 g/t Au in the higher grade uranium mineralisation, while 0.5 g/t Au is an average for the remainder of the uranium mineralised Upper Mine Sequence.
Uranium mineralisation is principally present as pitchblende, is intimately associated with chloritisation and occurs as sooty smudges on joint planes and foliations. Secondary uranium minerals saleeite, sklodowskite, gummite and metatorbenite are common in the oxidised zone.
Since the commencement of mining in 1981 to 1989, 19 400 t of U3O8 were produced from the original reserve of 52 000 tonnes in the No. 1 and No. 3 Orebodies.
In 1990 the No 3 Orebody had reserves of 35 Mt @ 0.2% U3O8 for 70 000 t of U3O8 (Browne, 1990).
In December 2008, the remaining reserves and resources at Ranger were (ERA Media Release, Jan. 2009):
Proved + probable reserves (0.06% U3O8 cut-off) - 30.19 Mt @ 0.23% U3O8 = 43 996 tonnes of U3O8 plus, in addition to the reserves,
Measured + indicated + inferred resources (0.02% U3O8 cut-off) - 128.26 Mt @ 0.09% U3O8 = 115 368 t U3O8.
Ranger 68 is 20 km NNW of Ranger 1 and comprises 1.5 Mt @ 0.357% U3O8 at a cutoff of 0.1% U3O8 for over 5000 tonnes of contained U3O8. All mineralisation is hosted by the Cahill Formation, which is essentially a chloritised and sericitised schist, gneiss and micro-gneiss with intercalated thin carbonates and local amphibolitic gneiss, overlying a massive carbonate unit. The schist contains coarse breccias that host the bulk of the mineralisation which occurs as sooty pitchblende, with sooty chalcocite in the same breccias. Most of the Cahill Formation above the deposit is unconformably overlain by up to 90 m of Cretaceous Bathurst Island Formation conglomerate and sandstone.
The Jabiluka uranium deposit is located approximately 230 km east of Darwin in the Alligator Rivers uranium field of the Northern Territory, Australia, some 25 km north of the Ranger mine (#Location: 12° 30'S, 132° 55'E).
The Jabiluka deposits are located in the north-eastern part of the Paleoproterozoic Pine Creek Geosyncline which overlies Archaean basement. The Paleoproterozoic comprises the 2470 to 1800 Ma basement Nanambu Complex granitic gneiss and biotite schists. Regionally, this complex is unconformably overlain by the Paleoproterozoic Kakadu Group conglomerate, sandstone and arkose, although in the Alligator Rivers area, the overlying Cahill Formation lies directly on the Nanambu Complex. In the Jabiluka area, the Cahill Formation comprises three units, i). a lower unit composed of carbonate, generally dolomite or magnesite; ii). a middle unit which hosts the bulk of the mineralisation which consists of graphitic pelitic schist, semi-pelitic schist and minor carbonate; and iii). the upper unit which is more psammitic and includes quartz-muscovite schist and amphibolite.
The Cahill Formation is conformably overlain by the dominantly clastic Mourlangie Schist psammitic schist, carbonates and quartzite. All of these rocks are cut by the 1870 Ma Zamu dolerite prior to regional deformation and metamorphism of the Pine Creek Geosyncline between 1870 and 1800 Ma. Four phases of deformation are recorded, the most intense being D2 which produced isoclinal recumbent folds with a flat lying foliation sub-parallel to lithological layering and low angle thrust faults. F2 folds were refolded by D2 and D3. These deformations were followed by three post-orogenic igneous events, prior to deposition of the main Mesoproterozoic sequence, namely: i). the felsic volcanics and tuffs of the 1760 Ma Edith River Volcanics in the south; ii). the 1750 Ma granitic pegmatites throughout the Alligator Rivers area; and iii). the 1690 Ma Oenpelli Dolerite.
Following a period of erosion, the preceding rocks were unconformably overlain by Mesoproterozoic Kombolgie Formation of the McArthur Basin which is preserved as a flat lying sequence of sandstone with minor shale and conglomerate and two volcanic units. The lower and thicker of the volcanic units is the up to 250 m thick, predominantly basaltic Nungbalgarri Volcanic Member which is about 300 m above the base of the formation and has been dated at ~1650 Ma. Post Kombolgie structure is characterised by gentle warping and NW striking strike slip faults, associated with reactivation of earlier low angle reverse faults which follow preferred layers in the Paleoproterozoic and in places follow the unconformity and pass into the overlying sandstones. The Kombolgie Formation is cut by 1370 basic and 1320 Ma phonolitic dykes and overlain by the sandstones and conglomerates of the Cretaceous Bathurst Island Formation.
Within the immediate Jabiluka area, the host Cahill Formation is locally exposed as a window through the Kombolgie Formation hosting the Jabiluka I deposit, truncated to the west by down-faulted Kombolgie sandstones across the north-south trending Rowntree Fault. To the east the Jabiluka I mineralisation fades out, but reappears 500 m further east by Jabiluka II which is entirely concealed below 20 to 200 m of Kombolgie Formation. The Cahill formation dips to the south from near horizontal to near vertical below the unconformity in the deposit area and when the stratigraphy compared to the regional sequence appears to be overturned, interpreted to represent the lower limb of a recumbent fold.
The nearest Nanambu Complex rocks are quartz-feldspar-biotite gneisses 3 km to the south of the deposit, which are directly overlain by the Kombolgie Formation. Within 600 m of the deposit the Complex rocks are faulted out against carbonates of the Cahill Formation below the unconformity.
Jabiluka I and II are unconformity style deposit hosted by carbonaceous schists and brecciated, bedded carbonates of the Paleoproterozoic Cahill Formation. In detail the deposits are contained within a set of up to nine bands of alternating mineralised and barren schists, which have been variously interpreted as a stratigraphic sequence, or structural repetition of a simpler succession by folding or faulting. The mineralised intervals are characterised by brecciation and chloritisation and contain quartz, sericite and graphite, while the barren intervals tend to contain coarse shiny muscovite flakes, and are often porphyroblastics schists with muscovite after garnet. Outside of the ore zone these barren and mineralised bands are apparently equivalent to a thicker sequence of bedded carbonate which towards the ore thins drastically or is replaced by cryptocrystalline silica, hematite and apatite ('cherts'). Fragments of this chert are found in chlorite cemented breccia in the ore zone.
In the immediate deposit area the Kombolgie Formation comprises a alternating medium- and coarse-grained (locally to conglomerate) quartz sandstone unit with an onlapping unconformable contact above the Cahill Formation basement ridge. Hematite and chlorite at the unconformity have been attributed to a pre-Kombolgie regolith development or to post-Kombolgie alteration. Hematite and chlorite alteration is extensively developed within the Kombolgie Formation.
The mineralisation at Jabiluka I is confined to a single unit within the Cahill Formation, the 'main mine sequence', while at Jabiluka II around 75% of the resource is within the same unit. Ore is also found within the overlying 'upper graphite sequence' (separated from the 'main mine sequence' by the barren 'hangingwall sequence'), and in the 'lower mine sequence 1' and 'lower mine sequence 2', separated from each other and the overlying 'main mine sequence' by barren bands. The 'main mine sequence' is higher grade at Jabiluka II with 0.51% U3O8 compared to the overall geological average of 0.39% U3O8 for the deposit. Ore is almost entirely below the unconformity, within the Cahill Formation.
The primary mineralisation is uraninite, with minor coffinite, brannerite and organo-uranium minerals. It occurs in three main forms: i). in breccias, representing the bulk of the resource, where uraninite commonly occurs as infillings occupying voids and cementing clasts; ii). in veins adjacent to the breccias which cut across schistosity; and iii). as fine grained, low grade uraninite disseminations in schistose host rocks adjacent to the breccias and veins. Sulphides generally only amount to a few percent of the hosts, although up to 10% pyrite can occur in graphitic zones. Galena and chalcopyrite with quartz and/or dolomite is found in fractures cutting uraninite veins.
Mineralisation related alteration forms a zone parallel to the unconformity with the overlying Kombolgie Formation and decreases intensity downwards and is characterised by chlorite and quartz with Mg marble in the Cahill Formation also and is dated at 1600 to 1300 Ma. An outer, ealry phase zone is apparently represented by iron rich chlorite and anatase replacing metamorphic biotite and white mica after feldspar. Within a few metres of the unconformity, or adjacent to breccias, more intense clay-sized magnesian-aluminium rich chlorite and phengitic (celadonite) mica is developed. Veins of chlorite and white mica are also found up to 300 m above the unconformity within the Kombolgie Formation.
Gold mineralisation is found as a discrete zone in the western half of Jabiluka II in association with graphitic horizons accompanied by high grade uranium (averaging 0.8% U3O8). Like the uranium the bulk of the gold (52%) is hosted by the the 'main mine sequence', lesser amounts in the 'upper graphite sequence' (17%), the 'lower mine sequence 1' and 'lower mine sequence 2', while 22% is in the 'barren' 'hangingwall schist' without accompanying uranium. The gold occurs as 10 to 100 µm native gold in uraninite and in cross-cutting veinlets. Un-economic traces of Pd correlate with Au and U.
Jabiluka II has an E-W strike length of 1000 m and a down dip extent of 500 m.
Resource and reserves in 1986 (Hancock, et al., 1990) were:
Jabiluka I - 1.3 Mt @ 0.25% U3O8
Jabiluka II - 52 Mt @ 0.39% U3O8.
Jabiluka II includes - 1.1 Mt @ 10.7 g/t Au
Jabiluka II reserves included 207 000 t U3O8
In December 2008, the reserves and resources at Jabiluka were (ERA Media Release, Jan. 2009):
Proved + probable reserves (0.20% U3O8 cut-off) - 13.8 Mt @ 0.49% U3O8 = 67 700 tonnes of U3O8 plus, in addition to the reserves,
Measured + indicated + inferred resources (0.20% U3O8 cut-off) - 15.44 Mt @ 0.48% U3O8 = 73 940 t U3O8.
Westmoreland ................ Tuesday 3 March, 2009.
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, 130 km south of Burketown near the Gulf of Carpentaria coast and 350 km NNW of Mount Isa.
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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.
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 thickTawallah 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% U308 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% U308. 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.
Rheinberger, et al. (1998) reported that collectively, the three main Westmoreland deposits had an:
inferred resource of approximately 15.6 Mt @ 0.118% U308 for a contained resource of 17 900 tonnes of U308.
In October 2006, Mining Associates of Australia reported at Westmoreland:
indicated resources - 8.0 Mt @ 0.088% U308, for 7100 t U308 plus
inferred resources - 16.0 Mt @ 0.094% U308, for 14 800 t U308.
Ben Lomond ................ Visit, scheduled for Wednesday 4 March, 2009, cancelled by the host for project operational reasons beyond the control of PGC
The Ben Lomond uranium deposit is associated with Late Palaeozoic felsic intrusives and volcanics in north-eastern Queensland, Australia. Ben Lomond lies towards the north-western margin of the Townsville-Bowen volcanic field, in the overlap with the more northerly Newcastle Range-Featherbed volcanic field. The similar Maureen deposit is located towards the western margin of the latter field. Ben Lomond is some 50 km WSW of the city of Townsville, while Maureen is a further 340 km to the NW (see the separate Maureen record).
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The summaries above were prepared by T M (Mike) Porter from a wide range of sources, both published and un-published. Most of these sources are listed on the "Tour Literature Collection" soon to be available from the Uranium 2009 Tour options page.
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.
The Ben Lomond uranium-molybdenum-zinc deposit is located in the Hervey Range, North Queensland, Australia, approximately 50 km WSW of Townsville. It occurs within a fault-bounded block of Carboniferous calc-alkaline volcanics of the St James Volcanics,predominantly rhyolitic tuffs and lavas, which are part of the Glenrock Group. These overlie the Late Devonian to Early Carboniferous Keelbottom Group sediments and older basement sedimentary and volcanic rocks of the Paleoproterozoic Argentine Metamorphics. The St James Volcanics are unconformably overlain by andesitic and basaltic lavas and pyroclastics of the Upper Andesite Member. These are in turn unconformably followed by the Early Carboniferous Watershed North Rhyolite (previously known as the Cattle Creek Group), a crystal-rich to lithic-rich rhyolitic ignimbrite which is at least 400 m thick and is thought to have been deposited in a cauldron subsidence event.
In the immediate vicinity of the deposit, the youngest non-intrusive rocks are pyritic carbonaceous shales and sandstones of the Late Carboniferous Insolvency Gully Formation, which unconformably overlies both the St James Volcanics and Watershed North Rhyolite. The Insolvency Gully Formation is intruded by the Late Carboniferous to Early Permian Speed Creek Granite.
The St James Volcanic sequence has been subdivided into the following units, from the stratigraphic top to bottom:
i). Host unit, comprising from the top to base, the following sub-units: coarse grained quartz feldspar porphyry dyke; coarsely porphyritic, chloritic, flow banded rhyolite; maroon siltstone and tuffaceous sandstone with minor conglomerate and quartzite (the “Black Tuff Formation”); coarsely porphyritic dacite; rhyolite with siderite patches; porphyritic rhyolite; porphyritic lapilli tuff with rare fiamme; ppebbly porphyritic lapilli tuff with rare fiamme; coarse agglomerate; rhyolite; coarse porphyritic dacite; pebbly tuffaceous sandstone and siltstone; lapilli tuff; and porphyritic flow banded rhyolite,
ii). Flow-banded rhyolite,
iii). Welded tuffs and ash flows with local sedimentary intercalations,
iv). Basic-intermediate lava flows and pyroclastics with minor intercalated sediments,
v). Lahars of dacitic to rhyolitic composition.
The unconformably overlying lensoid Upper Andesite Member and the Watershed North Rhyolite which have been subdivided into the following units from the top:
i). Ignimbrite with classic fiamme texture,
ii). Lapilli tuffs, ignimbrites and minor vitric tuff,
iii). Lapilli tuffs and ignimbrites with subordinate crystal lithic tuffs,
iv). Ash flow tuffs with abundant shards and ejecta,
v). Welded tuffs and lapilli tuffs,
vi). Vitric tuffs and ignimbrites,
vii). Rhyolitic airfall tuffs, grading into coarse ignimbrites then lithic/vitric tuffs,
viii). Upper Andesite Member – Andesitic basalt flows.
The host volcanic units appear to have undergone at least two stages of pre-mineralisation alteration. The first was associated with cooling of the thick volcanic pile, while the second was the result of later convective hydrothermal activity associated with the shallow intrusion of the Pall Mall adamellite. The later hydrothermal activity produced tourmaline and dumortierite that preceded uranium-molybdenum-zinc mineralisation of the Ben Lomond deposit in the rhyolitic welded tuff at the top of the St. James volcanics.
The uranium-molybdenum mineralisation at Ben Lomond and its associated alteration halo, occurs within a strongly sheared east-west striking, steeply south dipping zone sub-parallel to the axial plane of a shallow plunging syncline, outcropping on the northern flank of Ben Lomond East Ridge. It has a shallow eastward plunges beneath the unconformably overlying Watershed North Rhyolite, and dips at 75°S, with a maximum width of 150 m, with an upper limit a few metres below the St James Volcanics/Watershed North Rhyolite unconformity. The mineralisation extends down dip for some 90 m overall, although the best grades are developed from 10 to 50 m below the unconformity. Within the overall mineralised envelope, a resource was initially, delineated over a 750 m strike length, although mineralisation and alteration continues below 100 to 400 m of Watershed North Rhyolite cover, for at least another kilometre.
The uranium-molybdenum mineralisation occurs as primary vein fillings of a complex system of steeply dipping fracture-infill veins, subordinate stockworks and brecciated zones, and as disseminations in the adjacent wallrock, The strongest grades are within subvertical vein filled structures, some with sharp contacts, although the majority have wispy diffuse contacts where the uranium minerals are disseminated through the wall rock immediately adjacent to the vein system. Veins are typically lenticular and discontinuous both along strike and down dip. The veins form a discontinuous swarm with individual veins rarely exceeding 200 m in length and 1 to 2 m in thickness. They are densely packed in the main zone of mineralisation such that higher grades persist over broad widths despite the intervening barren material between the veins. The vein zone is surrounded by an envelope of alteration, with a close relationship between uranium grade and
the presence of haematite and quartz.
The hypogene mineralisation comprises a simple assemblage of pitchblende, coffinite, molybdenite and jordisite, with minor accompanying pyrite and arsenopyrite and trace marcasite, galena, sphalerite and chalcopyrite. The main gangue within the veins include fine grained quartz with subordinate sericite, chlorite and tourmaline, all of which also occur as disseminations in the wallrock.
The mineralised zone is characterised by strong silicic and hematitic alteration within the wallrock with associated peripheral chlorite and pervasive dolomite. In the west of the mineralised zone, where there is no capping of Watershed North Rhyolite, the depth of weathering ranges from a few to 30 m or more, generally from 15 to 20 m. The base of oxidation is gradational and typically sub-parallel to the topography, passing down into the underlying hypogene zone. Within the zone of oxidation, sporadic secondary accumulations of mineralisation occur, with the most common uranium minerals being umohoite and iriginite. In the eastern portion of the mineralised zone, where the mineralised zone passes below the Watershed North Rhyolite, oxidation is absent.
Deposit summary based on Vigar & Jones, (2005).
The estimated resource has been quoted by AAEC (McKay 1982) as 1.93 Mt @ 0.217% U for 4200 t of contained U.
Resources in July 2008 were quoted by Mega Uranium Ltd, 2008, at:
Indicated resource - 1.33 Mt @ 0.27% U3
O8 for 3597 t U3
Inferred resource - 0.60 Mt @ 0.21% U3
O8 for 1275 t U3
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T M (Mike) Porter, of Porter GeoConsultancy
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