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Shinkolobwe |
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Katanga, Dem. Rep. Congo |
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U Co PGE PGM Pt Pd Ni
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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.
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The Shinkolobwe uranium deposit is located ~20 km WSW of Likasi, ~20 km SSW of Kambove, ~110 km NW of Lubumbashi and ~120 km ESE of Kolwezi in Katanga province of the Democratic Republic of Congo. It falls within the extensive Central African Copperbelt (#Location: 11° 2' 56"S, 26° 33' 1"E).
Pre-European copper workings were known at Shinkolobwe prior to the earliest recorded prospecting activity for copper by Tanganyika Concessions Ltd in the early 20th Century. Uranium was discovered over the deposit in 1915 by Robert Richard Sharp. Following geological investigations, mining operations were commenced in 1921 by Union Minière du Haut Katanga to produce radium. Mining continued until suspended in 1936, and the mine closed and was allowed to flood in 1939. Over this initial period of mining, ~100 000 tonnes of radioactive material were extracted from both open pit and underground workings to depths of ~55 and ~75 m below surface respectively. During this period, the deposit was exploited for radium, with uranium ore stockpiled.
Between 1942 and 1944, about 30 000 tonnes of uranium ore from stockpiles were sold to the US Army for use in the Manhattan Project to develop an atomic bomb. This included an initial 1200 tonnes of 65% U3O8 direct shipping ore that had been stored in New York, USA, a further 1000 tonnes at a similar grade and another 2000 tonnes of 20% U3O8 in stockpiles at the mine.
Open pit operations resumed in 1944, and underground in 1945, and continued until officially closing in 2004, principally for uranium. Sporadic artisanal working has taken place subsequently, mainly for cobalt and copper.
Geological Setting
Shinkolobwe, along with other similar uranium bearing deposits, such as Swambo, Menda and Kalongwe define an inner, southern flank to the Katangan/Congolese section of the Central African Copperbelt. Of these deposits, only Shinkolobwe has yielded significant quantities of uranium, with a production of >50 000 tonnes of U3O8.
For details of the regional setting, stratigraphy and metallogeny of the Central African Copperbelt and the Shinkolobwe deposit, see the separate Central African Copperbelt - Congolese/Katangan Copperbelt record.
Like many of the Cu-Co deposits of the Congolese section of the Copperbelt, Shinkolobwe is hosted by mega-fragments of a Roan Group mega-breccia. It is located towards the centre of a ~15 km long, arcuate, WSW-ESE to east-west elongated, fault bounded window of Roan mega-breccia that varies from <500 to >1500 m in width.
The stratigraphic sequence at Shinkolobwe, is as follows, from the base, according to Derriks and Vaes (1956), modified to be consistent with current nomenclature:
Roan Group
R.A.T. (Roches Argilleuses Talceuse) Subgroup - (R-1) purple/lilac coloured dolomitic and chloritic brecciated siltstone and dolostone that is >200 m thick (Heinrich, 1958; François and Coussement, unpub., 1990), and an upper 10 m of sandy dolomitic schists (Derriks and Vaes, 1956).
Mines Subgroup, (R-2) comprising,
• Kamoto Formation, (R-2.1.) subdivided into,
- R.A.T. Grises, (R-2.1.1) 0.5 to 2 m thick - grey, chloritic and dolomitic siltstone;
- D.Strat., (Dolomies Stratified), (R-2.1.2a) - commencing with ~2 m of blackish, phaneroblastic magnesite and/or siliceous dolomite, overlain by a further 2 m of nodular, quartz-bearing, stratified, grey, magnesite, or stratified siliceous dolostone;
- R.S.F., (Roches Siliceuses Feuilletées), (R-2.1.2b) - 5 m of fine grained, well stratified magnesite, with or without interstratified chert;
- R.S.C., (Roches Siliceuses Cellulaires), (R-2.1.3) - 0 to 20 m of silicified massive collenia stromatolitic dolostone, with abundant cavities in the weathered zone from dissolution of carbonates between silicified fractures;
• S.D., (Schistes Dolomitiques) Formation, (R-2.2.), which is ~30 m thick, composed of,
- 10 m of grey, stratified, crystalline, magnesium-rich dolostone;
- 5 m of light grey micaceous shale, with pyritic lenses;
- 3 m of dark grey micaceous dolomitic shale;
- 7 m of light grey micaceous dolomitic shale;
- 4 m of dark grey micaceous shale.
• Kambove Formation or C.M.N., (Calcaire á Mineral Noir), (R-2.3) divided into,
- Lower C.M.N., (R-2.3.1), composed of a lower
Acicular dolomite unit, which is ~25 m thick, and in turn subdivided into,
a lower 10 m of stylolitic magnesium-rich dolostone and beige-grey dolostone with silica concretions; overlain by
5 m of magnesium-rich dolostone, with interbedded grey shales and black needles of magnetite;
4 m of stratified, magnesium-rich and muscovite-bearing dolostone; and the uppermost
4 m of grey-beige, stratified, magnesium-rich dolostone;
Acicular dolostone unit, which is up to 130 m thick, and subdivided into,
a lower 7 m of grey, stratified micaceous magnesite; overlain by
35 m of light grey, irregularly stratified, siliceous magnesite, with blackish joints;
45 m of granular white magnesite; and the uppermost
28 m of greyish, poorly stratified crystalline magnesite;
Siliceous-talcose dolostone unit, which is ~60 m thick, and subdivided into,
a lower 18 m of variably stratified talcose dolostone with lenticular chert; overlain by
20 m of purplish dolomitic and argillaceous to sandy chert with pseudo-oolitic dolomite crystalloblasts;
7 m of lilac to pink, stratified, talcose dolomitic quartzite with occassional silica nodules;
11 m of light grey stylolitic crystalline dolomite; capped by
1 m of light grey banded dolostone.
- Upper C.M.N., (R-2.3.2), which is >75 m thick and composed of
a lower suite of variably stratified greyish-beige and bluish-grey argillaceous and argillaceous-sandy dolostone,
dolomitic quartzite and siliceous dolostone occurring as 1 to 5 m, and up to 9 m thick beds over a thickness of 24 m;
1 m of dark grey, argillaceous, talcose shale, with rounded magnesite crystalloblasts;
1 m of light coloured, irregularly stratified, silicified sandstone and conglomerate;
5 m of light bluish-grey, weakly stratified, silicified dolostone;
3 m of brecciated, silicified dolostone;
2 m of dolomitic, chloritic shale;
6 m of pink, crystalline dolostone;
3 m of white, high magnesium, crystalloblastic dolostone;
3 m of variably stratified talcose dolostone;
13 m of crystalline, magnesium-rich dolostone;
1 m of fine-grained greenish, argillaceous dolomitic quartzite, overlain by 2 m of crystalline, magnesium-rich dolostone;
and further greenish dolostone and fine grained sand.
Dipeta Subgroup, (R-3), which is either absent or only very thin at Shinkolobwe. It is possible that some rocks mapped as C.M.N., between the Mines Subgroup and Grand Conglomérat, may instead belong to the R.G.S. Formation of the Dipeta Subgroup (Derriks and Vaes, 1956).
Mwashya Subgroup, (R-4), which is not observed in the immediate Shinkolobwe area, or is not differentiated from the overlying Grand Conglomérat., although it does appear on the western margin of the Roan window, ~10 km to the west.
Nguba Group
• Grand Conglomérat (or Mwale Formation), (Ng-1.1) - which comprises a ~120 m thickness of predominantly diamictite, but is only poorly developed in the immediate Shinkolobwe deposit area, although it redevelops further to the west;
• Kaponda Formation, (Ng-1.2) - ~60 m of grey-green, well stratified, platy argillaceous shale;
• Kakontwe Formation, (Ng-1.3) - lenticular development of calcareous rocks and dolostones;
• ~900 m of grey argillaceous shale and lilac, pink or red, poorly stratified intraformational conglomerate;
• a ~1650 m suite that comprises,
- well stratified, light coloured, ripple-marked argillaceous or argillaceous-sandy shale;
- fine-grained, thinly stratified to platy or massive, grey argillaceous or sandy shale, with ripple marks, cross-bedding and silica concretions;
- bluish-grey or greenish, well stratified to massive siliceous sandstone;
Kundelungu Group
• Petit Conglomérat (or Kyandamu Formation), (Ku-1.1) - which comprises a ~60 m thickness of predominantly diamictite, that is bluish-grey and argillaceous to varying degrees. In outcrop it is light coloured, calcareous, often limonitic, with only rare quartz fragments;
• Several metres of banded, brown, silicified rock, which when fresh is a pink calcareous rock;
• Several metres of poorly to well stratified, argillaceous, slightly sandy, micaceous and pyritic shale, with interstratified, massive, bluish-grey, siliceous sandstone.
Structure
The generally east-west trending, elongate Roan mega-breccia window that hosts the Shinkolobwe deposit represents the core of a thrusted, complex, north-vergent, overturned antiform, bounded by north-vergent reverse faults. The Roan mega-breccia is overlain to the south, across the south-bounding reverse Shinkolobwe Fault, by rocks of the Nguba Group. To the north the bounding fault limiting the Roan mega-breccia, transgresses the Kundelungu to Nguba groups contact, from west to east respectively.
Between, and adjacent to, the faulted margins of the window, shallow synclinal cores and rafts of Nguba and Kundelungu groups rocks are found overlying the Roan Mega-breccia.
The mega-breccia within the window is composed of mega-fragments (or écailles) of coherent Mines Subgroup rocks that varies from a few metres to as much as 2 km in length, and up to 400 m thick, within a matrix of generally brecciated fine dolomitic sandstone to siltstone, and assorted tectonic breccia.
Mineralisation
The main Shinkolobwe deposit occurs within a plan area of ~400 x ~150 m, and to a depth of >250 m, although uranium grades begin to decline below 220 m. Within this area, three main blocks of host Mines Subgroup rocks are exposed at surface, distributed within a groundmass of R.A.T. and related breccias. A similar fourth block occurs at depth.
To the north, the mineralised area is separated from Nguba and Kundelungu groups rocks by north-dipping east-west and offsetting north-south faults. The southern contact is marked by south dipping NE-SW and east-west faults, whilst a NNW-SSE fault breccia marks the western margin. All three mineralised blocks have an east-west alignment, and are overturned, with an average dip of 60°N. The northern block diminishes with depth and pinches out against the northern bounding fault. Where the three blocks overlap, there is a steeply plunging, pipe-like, brown clay breccia containing fragments of both Mines Subgroup and Nguba and Kundelungu groups rocks.
At the surface, uranium mineralisation is concentrated in the S.D. Formation, occurring as discontinuous veins that follow stratification, fractures and cavities, and secondary faults, but not the major clay-talc filled faults that bound the mineralised zone. Individual veins extend from a few metres to 10 m in length. Locally mineralisation is also disseminated. Within the deposit, mineralisation also spreads from the S.D., through the cavities of the weathered R.S.C. into the R.S.F.
Uranium is commonly closely associated with cobalt and nickel, as well as gold and palladium, and in addition to the veins described above, occurs in association with Co-Ni vein mineralisation. However, the Co-Ni mineralisation persists to greater depths, beyond the uranium zone, which diminishes downward.
Secondary uranium minerals are dominant to a depth of ~57 m, where the brightly coloured uranium-bearing veins pass into black masses of uraninite (UO2). In the oxide zone, the host rocks are generally silicified and cavernous, passing down into compact dolostones in the hypogene zone, where deeper intervals of secondary mineralisation may still be sporadically encountered in fault zones. The first sulphide bearing veins are evident at a depth of ~79 m, containing cattierite (CoS2), nickel-cattierite ([CoNi]S2), vaesite (NiS2), cobalt-vaesite ([NiCo]S2) and siegenite ([Ni,Co]3S4; nickel bearing linnaeite). Locally, up to 19% Se produces selenium-vaesite and selenium-seigenite.
The bulk of the cattierite is developed distal to the main uranium mineralisation, often in the C.M.N., and is never accompanied by uraninite. It is accompanied by pyrite below 57 m, and is replaced by siegenite at shallower depths. Carrollite is rare to absent at Shinkolobwe.
In contrast, vaesite occurs as disseminations in the lower Mines Subgroup, and is characteristic of the uraninite zone below 79 m. It is associated with pyrite, siegenite, minor chalcopyrite and associated digenite, covellite and bornite, with some molybdenite. The latter is found in small quantities throughout the deposit, but is particularly associated with uraninite, and occurs as large, high grade pockets in a number of locations within the deposit.
Chalcopyrite is almost always present in the zone of uranium mineralisation, but is rarely found in association with cattierite. It is possibly the only early copper mineral, with associated bornite, digenite and covellite being developed later.
Native gold is frequently found in the uraninite, where it occurs as thin coatings and rods, and with sulphides. It also replaces vaesite veinlets.
In the oxide zone, the majority of the secondary minerals occur only as in situ replacement of primary uraninite, forming compact yellow, orange or red masses, with microscopic crystals of seconadry minerals. There is only minor transport from veins to cavities, usually forming torbernite (Cu[UO2]2[PO4]2•12H2O) and metatorbernite, but also kasolite (Pb[UO2][SiO4]•H2O), renardite (Pb[UO2]4[PO4]2[OH]4•H2O), saléite (Mg[UO2]2[PO4]2•10H2O), sklodowskite (Mg[UO2]2[HSiO4]2•5H2O), uranophane (Ca[UO2]2[HSiO4]2•5H2O) and soddyite ([UO2]2SiO4•2H2O).
Three main types of supergene ores are recognised (Heinrich, 1958):
• Black ore - mainly comprising hydrous oxides, becquerelite (Ca[UO2]2O4[OH]6•8H2O) and ianthinite ([UO2]•5[UO3]•10[H2O]; which alters to becquerelite), lesser schoepite ([UO2]8O2[OH]12•12H2O) and curite (Pb3[UO2]8O8[OH]6•3H2O), relict uraninite and minor sklodowskite and uranophane.
• Yellow-orange ore - which contains little or no becquerelite or relict uraninite. Curite is very common and frequently predominates. Schoepite is common, with lesser soddylite and kasolite, while uranophane is more abundant than in the black ores. This ore replaces black ore. Yellow to yellow-greenish variants are chiefly composed of schoepite with soddylite and uranophane. Orange versions mainly comprise curite with soddylite or uranophane. Red to red-orange variants contain curite alone, or curite + kasolite.
• Zoned or striped ore - chiefly composed of phosphates, with brown stripes of parsonite (Pb2[UO2][PO4]2•2H2O); yellow dewindtite (H2Pb3[UO2]2[PO4]4O4•12H2O) and green torbenite.
Between the 57 and 79 m levels there is a change in secondary minerals, with uranophane dominating.
The paragenetic sequence as defined by Derriks and Vaes (1956) is as follows: Magnesite → uraninite-pyrite → molybdenite-monazite-chlorite-Se and Te minerals (since replaced by Co-Ni sulphides) → quartz-cattierite-vaesite → fracturing and dolomitisation → chalcopyrite → transformation of cattierite-vaesite to siegenite (with the release of native gold) and chalcopyrite to bornite-digenite-covellite-umangite → supergene minerals.
U-Pb dating of uraninite from U-Mo-Co-Ni-Cu ore from Shinkolobwe returned ages of 670±20 Ma and 620±20 Ma (Cahen et al., 1971, and references therein).
Geological images yet to be prepared
The bulk of this summary has been drawn from Derriks and Vaes (1956) and Heinrich (1958).
The most recent source geological information used to prepare this decription was dated: 1993.
Record last updated: 15/1/2016
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.
Shinkolobwe
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Derriks, J.J. and Vaes, J.F., 1956 - The Shinkolobwe uranium deposits: current status of our geological and metallogenic knowledge: in Proceedings of the International Conference on the Peaceful Uses of Atomic Energy, Geneva, 8 to 20 August, 1955, United Nations, New York, v.6, Geology of Uranium and Thorium, pp. 94-128
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