Dem. Rep. Congo

Main commodities: Cu Ag
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The Dikulushi copper-silver deposit is located to the west of Lake Mweru, some 300 km northeast of Lubumbashi in the Katanga Province of the Democratic Republic of the Congo (DRC).

It lies near the north-eastern margin of the triangular Kundelungu Plateau, which is bordered by the Mesoproterozoic Kibaran Belt to the north-west, the Paleoproterozoic Bangweulu block in Zambia to the east, and the Lufilian arc to the south. As such it is ~250 km NE of the main Central African Copperbelt.

For a full description of the setting, geology and mineralisation of the Central African Copperbelt and Kundelungu Plateau (or Kundelungu Gulf Foreland), see the Zambian Copperbelt and Congolese/Katangan Copperbelt records.

The Neoproterozoic sediments of both the Lufilian Arc and the Kundelungu Plateau region belong to the Katanga Supergroup, which comprises an ~7 km thick sequence that can be sub-divided into the Roan, Nguba and Kundelungu Groups, separated by two regionally recognisable diamictite horizons.

The Roan Group, which is exposed in the Lufilian arc, is divided into four subgroups, namely: i). the R.A.T. Subgroup (the "roches argilo-talqueuses") which consists of hematite-rich siliciclastic formations; ii). the Mines Subgroup, a carbonate unit, that hosts the richest stratabound Cu-Co mineralisation of the Cupriferous Arc in the DRC, occurring mainly at two distinct stratigraphic positions. iii). the overlying Dipeta Subgroup, which consists of argillaceous and siliciclastic beds, interlayered with carbonate beds, and volcaniclastic units at the top. iv). the Mwashya Subgroup, composed of carbonaceous or dolomitic shale, siltstone, sandstone and conglomeratic beds.

The Nguba Group, commences with: i). the Grand Conglomérat a diamictite, which is exposed in the core of the regional Lufukwe anticline and thickens toward the south; ii). the Muombe Subgroup, which overlies the Grand Conglomérat and contains a mixture of shale and dolomite in the south and a lateral facies that grades into sandstone and siltstone in the north; iii). the overlying Bunkeya Subgroup, consists of detrital lithologies with a thick package of dolomitic shale and fine sand layers in the south, and a relatively thin package of arkose layers to the north.

The Kundelungu Group commences with the i). Gombela Subgroup, the base of which is defined by a transition from the underlying sequence into the second diamictite of the sequence, the Petit Conglomérat or Kyandamu Formation, which is exposed in the core of the Kiaka anticline. The Petit Conglomérat is overlain by the Lusele Formation, which commences with the "Calcaire Rose" a continuous, thin (around 5 m thick) carbonate layer. Toward the top of the Gombela Subgroup becomes more detrital, grading into alternating greenish or purple-grey, finely bedded dolomitic shale, and massive or coarsely bedded carbonatic siltstone from the Kanianga Formation, capped by the Lubudi Formationwhich consists of 3 to 10 m thick pink limestone beds containing occasional oolites, alternating with sandy carbonate beds. The overlying ii). Ngule Subgroup commences with interbedded pelites and sandstones from the Mongwe and Kiubo Formations, with characteristic sedimentary structures including cross-bedding and intra-formational conglomerates).
The 550 to 510 Ma Lufilian orogeny produced folding and thrusting, reflected by gentle anticlines, such as the Lufukwe, Kiaka and Kabangu anticlines within the Kundelungu Plateau region. These anticlines may be the surface expression of duplex development above detachments at depth, and are unconformably overlain by the iii). Biano Subgroup, which consists of a molasse sequence of arkose, sandstone, sandy shale and conglomerate deposited over the entire Kundelungu Plateau region during the Lufilian orogeny.

The main lithologic units within the Dikulushi mine area all belong to the Katanga Supergroup, as do the breccia clasts, and comprise:
i). The Carbonate unit is only exposed over a small, NW-SE trending area in the far western corner of the mine, and consists of a clast-supported breccia with angular red dolomite fragments of varying sizes in a fine-grained red matrix made up of quartz grains cemented by dolomite. This unit has been assigned to the Lubudi Formation, at the top of the Gombela Subgroup.
ii). The Shale unit, which consists of ductile, deformed red shale, with some green diagenetic spots and bands, and contains fragments of red mica-rich sandstone, greenish basalt, grey-brown stromatolitic dolomite and stromatolitic chert, that range from a few cm to 2 m across. This unit trends NW-SE parallel to the Carbonate unit to the south-west.
iii). The Sandstone unit occupies the bulk of the mine area, occurring to the east of the other lithologies, mainly composed of massive red sandstone beds with a mean bed thickness around 1 m, with cross laminations, wave ripples, conglomerate-filled channels and some thin intercalated red shale layers. The observed lithological variability and sedimentary structures of this unit strongly resemble the Mongwe Formation at the base of the Ngule Subgroup.
iv). The Breccia unit, which separates the Siltstone and Sandstone units, and contains fragments ranging in size from a few tens of cm up to 30 m of a). red sandstone that is commonly altered to a grey or green color, b). grey, sometimes brecciated carbonate, c). a breccia with cm sized chert fragments and a sandy matrix, and d). greenish basalt. The exposed surfaces of all of these fragment types are covered with slickensides, while the matrix between the different fragments is a grey-green altered shale with a dense cleavage and a brown shale that underwent a ductile deformation and has almost no cleavage. The Breccia unit is composed of lithologies derived from the Carbonate, Sandstone and Shale units.

The mineralised units in the Dikulushi mine are stratigraphically above the Roan Group hosts of the major deposits of the Central African Copperbelt.

North-east trending, bedding parallel faults are concentrated in the western sector of the mine area, close to the contact between the Breccia and Sandstone units, and in the central part of the mine. Those faults in the western sector contain a clay rich fault gauge with slickensides on their bounding surfaces indicating a dominant oblique-slip movement, while their centres are filled with calcite. These faults, which are largely concentrated around the hinge zones of kink folds, are surrounded by a zone of green alteration.

The Main Fault Zone which extends across the open pit from the NE trending zone in the west, trends ENE-WSW overall and is around 100 m in width. The north-western margin of the Main Fault Zone is represented by the arcuate east-west to NE-SW trending Main Fault and the NE-SW trending Northern Fault which coalesces with the former fault in the eastern part of the mine. The south-eastern margin of the main fault zone is represented by the NE-SW trending Southern Fault. Three other major fault directions are recognized in the mine area, namely Group 1 trending NNW-SSE, Group 2 which are east-west and Group 3 that trend ENE-WSW to NNE-SSW trends.

Alteration, in the form of grey sandstone or associated green altered clay, is essential bedding parallel, from the Sandstone unit in the hangingwall in the south-east, to the footwall to the north-west and is restricted to the north-east oriented main fault zone. This alteration is folded by the kink-folds. Complete grey-green alteration is observed in the central part of the Main Fault Zone and within the sandstone at its contact with the Breccia Unit outside of the Main Fault Zone, although this gradually diminished to the east in conjunction with the disappearance of mineralisation. Neither the Carbonate nor the Shale units are altered, while within the breccia, alteration is confined to sandstone clasts which are grey-green in ib colour.

The Dikulushi ore deposit is situated on the north-eastern nose of a regional doubly plunging anticline, where a major NE-SW trending fault zone fault intersects the contact between the Mongwe Formation and an underlying carbonate unit (the Lubudi Formation); this intersection is considered to be a key control on the location of ore.

The main orebody is oriented overall in an ENE direction, dips at 70°SE, and is restricted to a 20 to 50 m wide zone zone centred on the Main Fault and the Northern fault. Disseminated mineralisation occurs in the hanging wall of the main orebody, associated with a fracture zone that parallels the Main and the Northern faults and is beleived to have been the feeder zone. A second southeast-dipping zone of mineralisation occurs around 50 m in the footwall of the main orebody and is open at depth. The strike length of the main orebody is approximately 250 m.

The mineralogy of the ore is variable. Mineralisation within the Breccia unit at the surface, both in the Main and Southern Fault, is characterised by bornite, while a galena + sphalerite assemblage occurs in the hanging wall of the Main Fault Zone, near the contact with the Breccia unit, following Group 2 faults. At depth, this part of the mineralisation is restricted to the Main Fault in the western and central parts of the mine, and changes to an assemblage of chalcopyrite, bornite and chalcocite, with minor arsenopyrite, pyrite, sphalerite, tennantite and galena. This Cu-Pb-Zn-Fe mineralisation is predominantly developed along Group 3 faults that are crosscut by Group 2 faults, all of which have associated drag folding. In the central and eastern parts of the mine, the central part of the Main Fault contains massive Ag-rich chalcocite that is controlled by Group 3 faults and surrounds remnant bornite mineralisation at depth. These Group 3 mineralised faults dislocate the kink folds and some of the drag folds that are associated with faulting. At depths of more than around 100 m, the Southern fault only contains chalcocite.

At the surface, supergene mineralisation comprises malachite, chrysocolla and azurite, with varying amounts of malachite present to the deepest levels mined (approximately 100 m below the surface). Chrysocolla only dominates over malachite in the central part of the mine, where it occurs in massive sandstones of the Sandstone unit. Azurite is less widespread and is only observed along the Northern fault.

Reserves at the end of 2006 were estimated at 1.94 Mt @ 8.5% Cu, 226 g/t Ag (Haest, et al., 2007).

Reserves and resources quoted by Anvil Mining, 2007, include:
  Proved reserve - 0.481 Mt @ 6% Cu, 180 g/t Ag,
  Measured + indicated resource - 0.783 Mt @ 7.6% Cu, 180 g/t Ag,
  Inferred resource - 1.07 Mt @ 6.8% Cu, 169 g/t Ag,

The mine was established in 2002. Production in 2006 totalled:   0.607 Mt of ore @ 5.41% Cu, to recover 25 456 t Cu and 67.6 t Ag. 3.281 Mt of waste were removed.

The most recent source geological information used to prepare this summary was dated: 2008.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.

  References & Additional Information
   Selected References:
Haest M, Muchez P, Dewaele S, Franey N and Tyler  R,  2007 - Structural Control on the Dikulushi Cu-Ag Deposit, Katanga, Democratic Republic of Congo: in    Econ. Geol.   v102 pp 1321-1333
Haest M, Muchez P, Petit JCJ and Vanhaecke F,   2009 - Cu Isotope Ratio Variations in the Dikulushi Cu-Ag Deposit, DRC: of Primary Origin or Induced by Supergene Reworking: in    Econ. Geol.   v104 pp. 1055-1064
Haest, M. and Muchez, P.,  2011 - Stratiform and vein-type deposits in the Pan-African orogen in central and southern Africa: evidence for multiphase mineralisation: in    Geologica Belgica   v.14, pp. 23-44,
Haest, M., Muchez, P., Dewaele, S., Boyce, A.J., von Quadt, A. and Schneider, J.,  2009 - Petrographic, fluid inclusion and isotopic study of the Dikulushi Cu-Ag deposit, Katanga (D.R.C.): implications for exploration: in    Mineralium Deposita   v.44, pp. 505-522.
Van Wilderode J, El Desouky H A, Elburg M A, Vanhaecke F and Muchez P,  2014 - Metal sources for the Katanga Copperbelt deposits (DRC): insights from Sr and Nd isotope ratios: in    Geologica Belgica   v.17 pp. 137-147

Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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