Katanga, Dem. Rep. Congo
Super Porphyry Cu and Au|
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The Etoile and Ruashi copper-cobalt deposits are 3.5 km apart, ~5 km east and NE of Lubumbashi, in the Katanga province of the Democratic Republic of Congo and are part of the extensive Congolese Copperbelt (#Location: Etoile - 11° 38' 9"S, 27° 34' 53"E; Ruashi - 11° 37' 8"S, 24° 32' 46"E).
The first recorded exploration in the Lubumbashi district was by Tanganyika Concessions Limited in 1907. Etoile and the three Ruashi deposits (Ruashi I, II and III) were discovered in 1911 and 1919 respectively by Union Miniére du Haut-Katanga. Intermittent mining took place at Etoile from 1911 to 1926, 1935 to 1946 and 1953 to 1964, and at Ruashi in 1919, 1932 to 1935 and 1960 to 1963. Activity at Ruashi was mainly restricted to limited to prospect drives and crosscuts for sampling purposes, although Union Miniére mined the very high grade (>7% Cu) oxide cap. These and high grade Cu oxides (>5% Cu) from Etoile were selectively mined and processed as direct feed to the Union Miniére smelter at Lubumbashi.
In 1967, Ruashi and Etoile and the other mines of Union Miniére were nationalised to become part of the state-owned mining company, Gécamines, which undertook geological reserve estimates by the 1980s and then mined both deposits. Due to a lack of reinvestment, Gécamines production declined from 450 000 tpa Cu and 10 000 tpa Co, to 30 000 tpa Cu and 4000 tpa Co during the early 1990s. Privatisation of the Ruashi operation commenced in 1996, followed by an evaluation of Ruashi and Etoile stockpiles by JCI Projects Ltd in 1997. In 2000, Cobalt Metals Company Ltd (CMC) acquired the rights to exploit the Ruashi deposit and the Ruashi and Etoile stockpiles under an agreement with Gécamines and undertook scoping studies. Ruashi Mining, owned by CMC (55%) and Gécamines (45%), was registered in the DRC in 2003 for the purpose of continued exploitation of the deposits. After a series of financial deals, the ownership of Ruashi Mining became 80% Ruashi Holdings and 20% Gécamines, with the ownership of Ruashi Holdings being 100% Metorex by 2007. In January 2012, Metorex became a wholly owned subsidiary of the Jinchuan Group of China.
In 2005, the resources in the stockpiles was assessed as Ruashi -1.5 Mt @ 1.84% Cu and 0.34% Co; Etoile:1.7 Mt @ 1.88% Cu and 0.35% Co. Open pit mining commenced at Ruashi I in October 2007 and treatment of ore from the mine and stockpiles began at new SX-EW Cu and Co plants in 2008 and 2009 respectively.
For details of the regional setting and stratigraphy see the separate Central African Copperbelt - Congolese/Katangan Copperbelt record.
The Etoile and Ruashi deposits are situated along the NW-SE trending, 24 x 2 km, recumbent Etoile-Luiswishi antiformal structure, that also hosts the Luiswishi-Lukuni deposits on its northwestern extremity, 24 km from Ruashi. The flanks of this antiform comprise sedimentary rocks of the Nguba and Kundelungu groups, while the core is occupied by the Mines and R.A.T. subgroups of the Roan Group. The NE vergent antiform is bounded on its northeastern flank by a longitudinal, SW-dipping overthrust which causes the Roan Group rocks to override the clastic and carbonate rocks of both the Nguba and Kundelungu groups. A second longitudinal fault to the west, brings the Mwashia Subgroup carbonaceous and dolomitic argillites into contact with the underlying mineralised lower section of the Mines Subgroup. This results in the mineralised Mines Subgroup rocks occurring as a strip flanked on both margins across faults by younger rocks, the Kundelungu (and locally Nguba Group) to the NE and the Mwashia Subgroup and Nguba Group to the SW (Pelletier 1964).
Within the core of the antiformal structure, between the bounding thrusts, the core of R.A.T. and Mines subgroup rocks form a synform, with Ruashi and Etoille are on the southwestern and northeastern limbs of the structure respectively.
The geology and mineralisation of the Etoile deposits can be summarised as follows, from the stratigraphic base:
Roches Argillo Talqueuses Lilas, or R.A.T. Lilas - is represented by layered albite-rich, pink to lilac, chloritic, dolomitic siltstones containing colourless tourmaline inclusions. It is devoid of copper and passes from a white, massive, slightly quartzose dolostone, which becomes enriched in hematite upwards, where it takes a dark ochre shade to locally dark lilac. It contains ankerite, a little white mica and euhedral apatite. At Etoile, the R.A.T. Lilas is in thrust contact with structurally underlying younger Kundelungu Group rocks.
R.A.T. Grises - in the northern part of the Etoile mine area, this better developed than usual, nearly 7 m thick, and very homogeneous. It was previously known as the M.V., the couches á Minerai Vert (or Green Ore Horizon). At the base, the rocks are well laminated and tectonically disturbed and broken. The unit comprises a green siliceous rock with aligned chalcedonic lenses impregnating a fine iron oxide and separated by felted green chlorite (clinochlore) 'riddled' with siliceous "pellets" up to 0.5 mm in diameter. Sheaves of fibrous zeolite, sometimes abundant, are developed within the chloritic matrix. Silica is locally recrystallised to form a network of quartz veining, with apatite inclusions and a little coarse dolomite and leucoxene. Locally, the silica is replaced by the dolomite. No detrital quartz and feldspar has been observed.
Mineralisation occurs as thin bands of chalcocite in the chlorite matrix, often intimately interwoven with lenses of cuprite. In the siliceous lenses, chalcocite with cuprite has been identified. Goethite is abundant and there is sometimes a thin crust of cobalt sulphide peripheral to the copper sulphides. Copper mineralisation is abruptly terminated by an underlying, ~1 m thick breccia zone, composed of angular to rounded clasts of massive grey dolomite, a little quartz and abundant hematitic dolomite, with minor feldspathic debris. This band is developed in the top of the underlying R.A.T. Lilas and forms the base of the R.A.T. Grises (Lefebvre & Cailteux, 1975).
Dolomies Stratified, D.Strat. - is 2 to 3 m thick and hosts the main ore zone. It is predominantly a widely stratified, grey to beige, silicified dolostone. The base of the unit is marked by a transition from the R.A.T. Grises comprising 20 cm of contorted clear, massive, siliceous rock.
Under the microscope, the D.Strat. is composed of a very fine mosaic of dolomite and only minor quartz. The dolomite has been silicified to form a complex chalcedonic assemblage enclosing partially digested spherulites. Coarser quartz-rich crystals overgrow the chalcedony, and contain abundant inclusions of dolomite, apatite and colourless tourmaline (Lefebvre & Cailteux, 1975).
Mineralisation includes fine, subidiomorphic disseminations of linnaeite/carrolite, which also occurs in fractures where it is coarser and more abundant, and is closely associated with chalcopyrite. Chalcopyrite is more restricted, limited to certain layers, accompanied by minor bornite exsolutions. Chalcocite also occurs in this bed as spots with fine inclusions and peripheral light crustings of cobalt sulphide.
To the east of the deposit, the D.Strat. is divided into two distinct beds:
• The lower is a cream or pink layered dolostone containing medium grained quartz with fine inclusions of dolomite, and is characterised by the absence of nodules and the presence of minor talc. Within coarser interbeds, up to 2 mm haloes of microcline, with abundant inclusions of dolomite, quartz, mica, apatite and idiomorphic rutile, surround cores of pyrite or copper sulphide. The feldspar is commonly altered to a simple aggregate of finely crystallised illite and montmorillonite. Where not altered, fractures developed within the microcline are filled with dolomite.
• The upper bed comprises ~2 m of well stratified, black, fine grained, carbonaceous, dolostone, with detrital quartz and muscovite. It contains large, dark, ellipsoidal nodules whose growth distorts the bedding planes both above and below. The nodules are composed of silica, that has been overprinted by intense silicification and coarse dolomite recrystallisation accompanied by the deposition of euhedral linnaeite/carrolite, with very little associated chalcopyrite. The cobalt sulphide is riddled with inclusions of dolomite and chert, but is overprinted, in turn, by a final dolomitic phase deposited in the fractured sulphides. Mineralisation is predominantly found in the inner periphery of the nodules. Minor chalcopyrite is found as fine inclusions in both quartz and linnaeite, and on the margin of the latter, and is transformed successively into 'normal' covellite, blaubleibender covellite and digenite. Finally, a second generation of cobalt sulphide encrusted all of the preceding (Lefebvre & Cailteux, 1975).
Roches Siliceuses Feuilletées, R.S.F. - is <4 m thick, and has a transitional contact with the underlying D. Strat., represented by a 50 cm interval of banded rock that is almost entirely composed of hematite, in part altered to goethite. These iron oxides invade the rock as a fine network of veins cutting finely crystallised cherty or chalcedonic rock that contains abundant small greenish chlorite flakes and granular leucoxene clusters with rare remnant white mica and dispersed recrystallised rutile. The basal 20 cm of the unit above the transition, contains abundant fracture controlled chalcocite (djurleite) surrounding remnant inclusions of digenite, chalcopyrite and fine cobalt sulphide grains. Goethite is abundant in voids containing residual chalcopyrite. This mineralised zone and underlying transition has been interpreted as supergene. It has a sharp upper boundary, and is dark and more massive than the overlying section of the unit, with an oolitic texture and ghosts of nodules in a recrystallised cherty to chalcedonic matrix. The remainder of the unit is characterised by thin layering and is a dark and strongly carbonaceous, intensely silicified and recrystallised dolomite. It contains coarse, euhedral apatite, colourless, finely crystalline tourmaline, and cryptocrystalline white mica with a composition similar to illite and montmorillonite, as well as lesser euhedral grains of monazite and rutile needles. Mineralisation is rare, occurring as patchy covellite, chalcopyrite and linnaeite. The contact with the overlying R.S.C. is abrupt, marked by the sudden disappearance of fine stratification, although otherwise the two units are petrographically similar.
Roches Siliceuses Cellulaires, R.S.C. - comprises a massive, grey, coarsely recrystallised dolomite, with frequent macrocrysts of black dolomite. The dolomite is commonly formed after cryptozoon stromatolitic bioherms, with interstices filled by strongly carbonaceous pelitic material and detrital muscovite. In addition to the strong dolomitisation, the rock has been silicified, locally so intensely that it approaches a quartzite in composition, and has associated fine apatite and rutile. Primary mineralisation is rare and patchy, and comprises covellite, chalcopyrite and linnaeite/carrolite, with digenite, similar to that described below in the S.D.B (Lefebvre & Cailteux, 1975).
Schistes Dolomitiques Basal, S.D.B. - which is 5 to 6 m thick, is composed of medium grained and finely stratified dolomitic rocks, with irregular, stratification, accentuated by the presence of organic material. It is rich in white detrital mica which is chaotically distributed and is not feldspathic. Quartz, which is abundant but irregularly distributed, is regarded as likely diagenetic, and is rich in dolomite inclusions. Detrital ilmenite is common and tends to be altered to leucoxene-rutile. Abundant nodules, generally <1 cm in diameter, occur throughout the entire section, but increase towards the top of the unit, bending the stratification, both above and below, as they grow. These have an irregular shape and are often deformed, and are composed of coarse, recrystallised anhedral dolomite and quartz, frequently with associated nested and poikilitic chalcopyrite and linnaeiite/carrolite towards the peripheries. At Etoile, the S.D.B. is usually mineralised throughout by very finely disseminated pyrite. Where the nodules are enriched in chalcopyrite-linnaeite/carrolite, chalcopyrite replaces pyrite in the enclosing rock, surrounded by a halo of fine supergene copper sulphides (covellite and digenite), with a fine crust of cobalt sulphide. The chalcopyrite and carrolite overgrows the pyrite. Chalcopyrite and carrolite overgrows pyrite, while carrolite formed after chalcopyrite. Fine veinlets of dolomite, with minor quartz, crosscut the dolomitic rocks, and contain chalcopyrite-linnaeite/carrolite, which accompany and surround quartz and pyrite where the veins cut dolomitic beds. Locally framboid-like bornite occurs, possibly replacing pyrite. Although Cu and Co sulphides are frequently observed, the mineralisation rarely contains >1% Cu (Lefebvre & Cailteux, 1975).
Black Ore Mineralised Zone, B.O.M.Z. - is marked by the appearance of a large quantity of dolomite associated with recrystalised quartz, and by the disappearance of microcline, partially offset by traces of albite. It is ~10 m thick and occurs as a poorly stratified, well crystallised dolomite. The dolomite is sub-idiomorphic and shows growth zones, along which opaque minerals are developed. The more pelitic sections contain carbon, scaly detrital quartz and fine white mica flakes. Sub-idiomorphic pyrite was apparently recrystallised from framboids and contains very fine inclusions of chalcopyrite and galena (Lefebvre & Cailteux, 1975).
Schistes Dolomitiques Supérieur, S.D.S. - is ~10 m thick, and consists of an alternation of pure dolostones and dolomite-poor, feldspar-rich and micaceous sandy pelites to sandstones. Detrital tourmaline, mica and K-feldspar are observed in these rocks. The quartz, in places, occurs as regular chalcedonic bands, the feldspars occur as microcline halos surrounding K feldspar and quartz, muscovite replaces biotite, and abundant ilmenite. The development of framboidal pyrite is associated with the alteration of ilmenite to leucoxene and leucoxene-rutile (Lefebvre and Cailteux, 1975).
Calcaire á Mineral Noir, C.M.N. - is >45 m in thickness and occurs above a thin organic-rich, carbonate poor and silica rich pelitic sandstone horizon at the top of the S.D.S. In contrast to the compositionally well banded nature of the S.D.S., it has a predominantly dolomitic nature. It is generally composed of light-coloured bands of impure dolostone alternating with dark coloured bands of feldspathic dolomitic mudstones containing quartz and detrital biotite. The upper part is mainly an Mg-rich, light coloured and very talcose dolostone (Lefebvre & Cailteux, 1975).
The total package from CMN to R.A.T. Grises is ~120 m thick, contained within structurally disrupted NW-SE elongated breccia and fault-bounded tectonic fragments, or 'écailles', within the Roan megabreccia that forms the core of the Etoile-Luiswishi antiform.
The deposit is cut by a series of faults that are occupied by breccias made of R.A.T Lilas, R.A.T. Grises and other lithologies, both longitudinal and transverse to the stratigraphy. The faults at the contact between the Mines Subgroup and the enveloping Kundelungu and Nguba groups rocks are barren. Faults of other sets are either barren or represent mineral coated fractures, attesting to multistage fracturing. Kipata (2013) recognised 5 fault sets:
• Large, barren faults delimiting the fault-bound tectonic fragments (écailles), sometimes hosting only black-oxide coatings, silica and pink crystals. A few fractures are covered with malachite, chrysocolla and carbonates along reactivated bedding planes. These structures are mostly observed in the R.G.S. unit of the hanging wall.
• The second set comprises parallel fault planes enveloping a transverse fault zone dominated by en echelon sigmoidal fractures of the third set, and also includes barren fractures and faults. This set was initiated under a NE-SW compressional stress, and are mostly bedding-oblique structures.
• The third set comprises conjugate fractures and faults with malachite and chrysocolla coating, observed at the faulted contact between the R.S.F and R.S.C units. They correspond to a normal faulting stress regime, with a radial extension component, and include some reactivated bedding-oblique faults.
• Set 4 includes barren faults covered by black oxides which displace the mineralised fractures of the preceding stage, and mark a NE-SW compressional stress. Its fractures, mostly east-west, belong to large bedding-orthogonal fault related folds characterised by flexural slip.
• The last set was formed by reactivated bedding planes with black-oxides and corresponds to a NE-SW extension.
Ore is found over 1.4 km of strike, and extends to a depth of >250 m. It occurs in two discrete orebodies. The Upper ore body is oxidised and enriched, occurring as an enlarged supergene cap ~60 m thick, extending from the R.A.T. Grises to R.S.C.. It overlies the inclined, stratabound sulphide deposit of the Lower orebody which is hosted by the R.A.T. Grises, D.Strat. and basal R.S.F., as described above.
Cobalt and copper mineralisation is hosted by the R.S.F. and D.Strat. units of the Mines Subgroup subgroup between the Etoile and Ruashi III deposits. The strike length of the orebody at Etoile Extension is just over 300 m and the width near surface is approximately 100 to 150 m. While the deposit has relatively low copper mineralisation, cobalt grades are consistent with those of the Etoile and Ruashi mines.
Resource and production figures include:
Etoile as at 31 July 2012 (Shalina Resources, 2012)
Measured + indicated resources,
Etoile oxides - 2.015 Mt @ 2.88% Cu, 0.67% Co,
Etoile mixed - 3.618 Mt @ 2.09% Cu, 0.32% Co,
Etoile sulphides - 11.766 Mt @ 2.58% Cu, 0.29% Co,
Stockpiles - 0.887 Mt @ 2.49% Cu, 0.68% Co,
HMS rejects - 3.203 Mt @ 1.89% Cu, 0.50% Co,
Mufunta extensions - 0.858 Mt @ 1.34% Cu,
Subtotal - 22.347 Mt @ 2.39% Cu, 0.37% Co.
Etoile oxides - 0.107 Mt @ 4.49% Cu,1.07% Co,
Etoile mixed - 0.128 Mt @ 4.86% Cu, 0.41% Co,
Etoile sulphides - 0.0244 Mt @ 3.39% Cu, 0.35% Co,
HMS rejects - 3.203 Mt @ 1.89% Cu, 0.50% Co,
Mufunta extensions - 0.363 Mt @ 2.03% Cu.
Etoile Extension - 3.170 Mt @ 0.31% Cu, 0.66% Co.
Subtotal - 3.792 Mt @ 0.76% Cu, 0.60% Co
TOTAL Measured + indicated + inferred resources, July 2012 - 26.14 Mt @ 2.14% Cu, 0.40% Co (Shalina Resources, 2012);
TOTAL Production + resources - 29.698 Mt @ 4.32% Cu, 0.31% Co (USGS Scientific Investigations Report 2010-5090-J, 2010);
Included as a separate item in the Etoile resources listed above.
The Ruashi deposit is located on the southwestern limb of the NW-SE trending Etoile-Luiswishi antiform hosted by the same sequence as Etoile, as described above. The three orebodies, Ruashi I, II and III are aligned and elongated parallel to the same NW-SE trend, both as a cluster and individually, and are distributed over a ~2 km interval.
Ruashi I, the largest of the three, is located to the northwest, with a total lateral NW-SE extent of ~900 m, and 350 m across strike. The oxide zone extends to a depth of ~130 m below the surface, whilst sulphide mineralisation has been intersected to depths of >300 m. The orebody is terminated by a brecciated shear zone on both its north-western and south-eastern margins. Some open pit and underground mining was undertaken on the orebody in the 1920s and 1930s.
Ruashi II, is a smaller fragment, with a length of ~200 m, and width of ~250 m across strike, and is terminated by listric shear zones to both the NW and SE, whilst a flat lying thrust terminates the ore body at depth. Ruashi I and II are separated by a gap of ~200 m of brecciated Nguba Group strata.
Ruashi III, is the most south-easterly of the three deposits, and has a length of ~650 m and a cross strike width of >200 m. Unlike the other two deposits, it is concealed by 30 m to 80 m of cover rocks. It comprises a high grade cobalt "cap" at a depth of ~12 m, overlying a low grade copper zone in the west. The deposit is structurally controlled within a complex fold structure. Malachite mineralisation has been intersected to depths of 300 m on the eastern margin of the ore-body.
Historic mining focussed on near surface malachite and chrysocolla-rich oxide copper, occurring as an irregular, 30 to 60 m thick supergene mineralisation blanket in near surface saprolitic rock, overlying, but more extensive than the primary sulphide mineralisation. This oxide mineralisation is hosted within all lithologies from the R.A.T. Grises to the C.M.N., being well developed in the latter, but not in the overlying R.G.S. of the Dipeta Subgroup. In addition to malachite and chrysocolla, oxide copper minerals include, native copper, cuprite, cornetite and azurite. Other oxide minerals include magnetite and specularite. The dominant cobalt mineral in the oxide zone is heterogenite. Trace amounts of oxidised uranium have also been recorded but are very uncommon.
The sulphide zone is dominated by chalcopyrite and digenite (up to 96%), with only minor bornite. Cobalt sulphides are linnaeite/carrollite, irregularly distributed in intimate association with the copper sulphides, and sporadic abnormal concentrations. Very high cobalt grades may occur in veins dominated by cobalto-calcite. Disseminated pyrite is found in all the units of the Mines Subgroup, occurring as small amorphous masses in the R.A.T. Grises. Abundant pyrite occurs in the graphitic shales of the SDS zone. Chalcocite together with malachite occurs below the water table in the transition zone as replacement rims on primary bornite and chalcopyrite sulphides. Cobalt sulphides generally decrease with depth beyond the transition zone.
Resource and production figures include:
Total resources - 43 Mt @ 2.97% Cu, 0.46% Co, including
proved + probable reserves - 31.9 Mt @ 3.5% Cu, 0.35% Co (Metorex, 2009);
Production + resources - 45.844 Mt @ 2.81% Cu, 0.25% Co (USGS Scientific Investigations Report 2010-5090-J, 2010);
Remaining mineral resources at 30 June, 2013 (SRK report to Metorex, 2013) were:
Measured resource - 0.7 Mt @ 4.71% Cu, 0.26% Co,
Indicated resource - 18.6 Mt @ 2.15% Cu, 0.38% Co,
Inferred resource - 14.0 Mt @ 2.08% Cu, 0.21% Co,
TOTAL remaining resource - 33.3 Mt @ 2.18% Cu, 0.30% Co
The Ruashi description is based on details in "A competent person's report and valuation report on the mineral assets of Metorex (Pty) Ltd in the Democratic Republic of Congo and the Republic of Zambia", prepared for Metorex (Pty) Ltd in June 2013 by SRK Consulting (South Africa) (Pty) Ltd.
The most recent source geological information used to prepare this summary was dated: 2013.
Record last updated: 17/12/2015
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.
Lefebvre, J.J. and Cailteux, J., 1975 - Volcanisme et mineralisations diagenetiques dans le gisement de L etoile, Shaba, Zaire: in Annales de la Societe Geologique de Belgique, (In French, Abstract in English) v.98, pp. 177-195|
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