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Tumas |
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Namibia |
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U
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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 Tumas Project includes the Tumas 1, Tumas 2, Tumas 3, Tumas 1 East and Tubas Red Sand/Calcrete orebodies and is located ~80 km ESE of the coastal town of Swakopmund in Namibia, and ~80 km ENE of the Seaport of Walvis Bay (#Location: 22° 53' 28"S, 14° 58' 10"E).
The Tumas Project area is located within the Namib Naukluft National Park in the Erongo Region of Namibia.
The Tumas palaeo-channel was explored separately by Anglo American and Falconbridge from the mid-1970s to the early 1980s. Falconbridge outlined uranium mineralisation in the Oryx Area (now Tumas 3) whilst Anglo American drilled the Tubas Red Sand mineralisation. In 2006, Reptile Mineral Resources and Exploration (Pty) Limited acquired tenure over the Project. In 2008, Deep Yellow Namibia (Pty) Ltd, acquired Reptile Mineral Resources. In late 2016, Deep Yellow re-evaluated all previous drill and geophysical data to generate a new geological model and exploration strategy targeting the prospective Tumas palaeochannel for substantial resource increases. Drilling in 2017 and 2018 concentrated on Tumas 3 resulting in a maiden calcrete Inferred Mineral Resource of 15014 tonnes of contained U308 at 378 ppm U308. An in-house scoping study in 2019 provided encouraging results and was followed by a Prefeasibility Study in 2020/21. The PFS resulted in a maiden ore reserve of 40 Mt @ 344 ppm U308 for an 11.5 year mine life. Reserves have since been expanded to 30 527 tonnes of U308. In September 2023, following the release of the Tumas DFS Re-Costing Study, the Namibian Ministry of Mines and Energy issued a mining licence for the Tumas Project, allowing the project to progress towards production.
The Tumas Project palaeochannel/calcrete-type uranium deposits are located on the coastal plain of the Namib Desert, between the Great Escarpment in the east and the Atlantic coast in the west. The deposits are associated with a fluviatile environment within palaeo-valleys of ancient rivers that flowed westwards from the Great Escarpment between 88 Ma in the Upper Cretaceous and 25 Ma in the Lower Tertiary. The catchment of the headwaters of these ancient rivers, immediately above the Great Escarpment, includes the Rössing and Husab hard rock uranium deposits, which are located 30 to 40 km to the north to NE of the mineralised Tumas palaeo-channel, whilst the Langer Heinrich calcrete hosted uranium deposit is on a tributary palaeo-channel that flows into the Tumas system.
Uranium mineralisation occurs as carnotite, a secondary uranium-vanadium mineral, hosted by Late Cretaceous to Cenozoic fluvial sediments occupying narrow and steep-sided palaeo-channels. The simplified Cenozoic sequence includes from top to bottom, scree, sand, gravel, gypcrete, various intercalated calcareous sand and calcrete horizons, discordantly overlying Damaran age folded sequences of meta-volcanic and meta-sedimentary rocks (as described later in this record). The host to mineralisation vary from hard, carbonate-cemented sandstones and conglomerates (calcrete) to poorly consolidated and friable sands.
All of the uranium mineralisation is secondary in nature, and is hosted by 'calcretised' channel fill sediments which mainly comprise poorly sorted polymictic gravels and conglomerates that locally grade to clayey and/or silty facies with only minor sands and silts. Fine-grained calcite-cemented sandstone occurs locally at the bottom and lower edges of the palaeo-channel. The detrital components are mainly sub-angular quartz and feldspar granules with abundant debris of surrounding basement rocks, e.g., mica schists, meta-quartzites and granites. Calcrete bodies are interbedded with porous gravel units throughout the sedimentary column.
Two principal calcrete types have been recognised, namely a: i). pale to dark brown and hard, and i). white to 'whitish' and commonly chalky variety. Other minor types are darker, including a dark reddish brown to pale red, very hard, fine-grained calcrete.
The Tumas Project comprises from east to west, the Tumas 1 East, Tumas 1, Tumas 2 and Tumas 3 orebodies.
The Tumas 1 East zone is in the most easterly section of the mineralised Tumas palaeo-channel, and varies from 100 to 400 m in width, increasing in depth from east to west from 10 to 20 m, with mineralisation found from surface to the channel base. It includes tributary channels to the north and south of the main channel.
The Tumas 1 section of the deposit is relatively shallow, up to a maximum of 15 to 20 m depth and narrow, up to 200 m wide. It lies directly to the west of Tumas 1 East and continues west, cutting through a barrier bar of the NE striking Tinkas Formation, before bending to the NNW to become the Tumas 2 zone. Two fining up mineralised sequences are evident, with in both cases, higher-grade mineralisation found at the transition between underlying cross-stratified coarser and locally calcretised deposits, and overlying planar horizontal laminated silty sandy grit.
The Tumas 2 zone follows a NNW trend and its depth gradually increases to slightly over 40 m towards it's northern end. The palaeo-channel varies from 200 to 500 m in width, although the +100 ppm U308 equivalent mineralisation is generally a lot more patchy than at Tumas 1 and 3. The base of the sequence is composed of calcite-cemented, matrix-supported, sandy conglomerates and grits with abundant angular to subangular clasts of mica-schist and quartzite derived from the surrounding bedrock, intercalated with lesser lenses of silty to sandy grit. The 15 m thick upper part of the sequence is moderate reddish to light brown in colour and comprises crudely stratified, less calcareous and more oxidised sediments, whilst the top of the sequence is predominantly planar horizontal laminated silty to clayey sand which locally can be gritty. Higher grade uranium mineralisation occurs at the contact of the upper and lower sequence.
Within the Tumas 3 zone, the Palaeo-channel turns to flow to the WNW, and includes 40 to 60 m of palaeochannel fill overlying the basement 'Namib Unconformity Surface'. This palaeo-surface is characterised in part by steeply incised palaeo-channels, carved deeply into the folded and metamorphosed Damara sequence that underlies the 'unconformity'. The palaeochannel can reach up to 1.5 km in width, and other mineralised palaeo-channel tributaries join the main channel from both the east and south. The Tumas 3 zone is characterised by at least two vertically stacked sedimentary cycles of fining-upward sequences, each composed of coarse conglomerates at the base, especially at the bedrock contacts, followed by gravels, sand and clays with calcrete layers developed towards their tops. Uranium mineralisation is confined to calcrete layers in both cycles. Uranium is precipitated as carnotite close to the palaeo-channel floor and its edges, at the contact with the Proterozoic bedrock and sporadically occurs in more silty gravels of the upper sequence below the upper calcrete. In general, higher uranium grades appear to be linked to the confluence of sub-channels, where they preferentially occur above island channel-bars and flood plains on the palaeo-channel sides. The top calcrete unit hosts the main deposit extending across those basement islands.
Carnotite is preferentially precipitated where there are physical basement barriers constricting the flow of groundwater, and by chemical barriers where bedrock marble is in contact with the palaeochannel fill. The basement sequence in the project area is largely Neoproterozoic Late Cryogenian to Late Ediacaran in age, belonging to the Nosib-Swakop Group. The principal units, as exposed from east to west, comprise the:
• Donkerhoek Granite - mainly to the east of Tumas 1 East;
• Kuiseb Formation - biotite schist with white and grey marble bands and breccia, and spotted hornblende-bearing calc-silicate rock, which largely underlies Tumas 1 East;
• Tinkas Member - a marble rich sequence of alternating calc-silicate rocks, para-amphibolite, marble and mica-quartz schists that underlies Tumas 1;
• Etusis Formation - feldspathic quartzite, meta-arkose and meta-conglomerates which forms the western margin of the Tinkas Member in the north;
• Salem Granite - that forms the intrusive western margin of the Tinkas Member in the south, and the southern limit of the Etusis Formation to its north;
• Karibib Formation - layered marble, phyllites and amphibole schist which occurs as a 'V-shaped inlier', with a NW-SE arm within the Etusis Formation to the north and another that trends east-west following the contact with the Salem Granite to the west. Tumas 2 and 3 partly overlie this inlier.
All of these sequences are strongly metamorphosed, and have undergone isoclinal folding and been stacked as overthrust sheets. Strike is generally NE-SW to NNE-SSW, with mostly steep dips. Three different folding events are observed.
The basement topography of this sequence is irregular with numerous ridges and troughs that generally trend NE-SW.
Four mineralisation types have been recognised within the Tumas-Tubas palaeochannel based on the host rock. These are calcrete, gypcrete, red sand and basement. The calcrete-type mineralisation contains most of the uranium. It ranges from sand to granule size, with ~30% comprising pebbles with a maximum 6.4 cm diameter. The only uranium-bearing mineral of economic importance is carnotite [K2(UO2)2V2O8•3(H2O)], in which the uranium/vanadium ratio is 4.5:1. Detailed analysis shows that minor vanadium is also contained in iron oxide and titanium minerals. The calcrete mineralisation contains, on average, 3 to 4 wt.% clay minerals, predominantly illite and the magnesium-bearing palygorskite. A small portion of uranium behaves refractorily as it occurs as submicron-sized carnotite inclusions in calcite.
Only gypcrete and sulphate bearing calcrete are known to have direct adverse affect on the leaching efficiency under alkaline conditions. Gypcrete is a palaeochannel sediment with >0.35 wt.% total sulphur (equivalent to 1.58 wt.% bassanite). Gypcrete occurs a thin, discontinuous layer, a few metres below the surface and generally defines the upper limit of uranium mineralisation. It is only mineralised with uranium in a few locations and is likely to make up only a very small portion of the total resource.
NOTE: There is no mention in sources studied of reductants within the host nor any oxidation front. The bulk of mineralisation is associated with calcrete or 'calcretised' course clastic sedimentary rocks.
Reserves and Resources
As at October, 2021, the JORC compliant Probable Ore Reserve at Tumas was, with a 150 ppm U308 cut-off (Deep Yellow Tumas Definitive Feasibility Study, 2023);
Tumas 3 - 44.9 Mt @ 414 ppm U308;
Tumas 1 East - 29.5 Mt @ 266 ppm U308;
Tumas 1 and Tumas 2 - 13.9 Mt @ 292 ppm U308;
TOTAL - 88.4 Mt @ 345 ppm U308 for 30 527 tonnes of U308.
As at February, 2023, the JORC compliant Mineral Resource at Tumas was, with a 100 ppm U308 cut-off (Deep Yellow Tumas Definitive Feasibility Study, 2023);
Tumas 3
Indicated Resource - 78.0 Mt @ 320 ppm U308;
Inferred Resource - 10.4 Mt @ 219 ppm U308;
Tumas 1 East
Indicated Resource - 36.3 Mt @ 245 ppm U308;
Inferred Resource - 19.4 Mt @ 216 ppm U308;
Tumas 1 and Tumas 2
Indicated Resource - 54.1 Mt @ 203 ppm U308;
Inferred Resource - 2.4 Mt @ 206 ppm U308;
TOTAL TUMAS
Indicated Resource - 168.3 Mt @ 266 ppm U308;
Inferred Resource - 32.2 Mt @ 216 ppm U308;
Indicated+Inferred Resource - 200.5 Mt @ 258 ppm U308 for 51 710 tonnes of contained U308.
TUBAS
Indicated Resource - 10.0 Mt @ 187 ppm U308;
Inferred Resource - 24.0 Mt @ 163 ppm U308;
Indicated+Inferred Resource - 34.0 Mt @ 170 ppm U308 for 5760 tonnes of contained U308.
The information in this description is largely drawn from: Ausenco Services Pty Ltd, 2023 - Tumas Definitive Feasibility Study, Chapter 1 - Executice Sumary, prepared for Deep Yellow Limited, 106p.
The most recent source geological information used to prepare this decription was dated: 2023.
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.
Tumas
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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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