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Group Metallogenesis of stratiform copper deposits in the Lufilian orogen, Democratic Republic Congo.

Researcher: El Desouky Hamdy
Promotor: Prof. Dr. PH. MUCHEZ, K.U.Leuven, Geodynamics & Geofluids Research Group
Co-promotor:  
Funding:  

 

Keywords:
 

 

Research abstract:
 

 

Introduction and Regional Geologic Setting:
 

The sediment-hosted stratiform copper deposits form a large diverse class of deposits that include some of the richest and largest copper deposits in the world (e.g., White Pine and deposits in the Central African Copperbelt). They account for approximately 20 to 25 % of the world’s copper production and reserves and they also form an important source of cobalt, silver, uranium, lead and gold. They are defined as stratiform disseminations of native copper and copper sulfides in a variety of reducing sedimentary rocks, including black shale, sandstone and carbonates (Kirkham, 1989).

The central African Copperbelt stretches on both sides of the border between Zambia and Democratic Republic of Congo (Cailteux et al., 2005). It hosts one of the world’s greatest concentrations of stratiform copper–cobalt deposits, representing more than half of the world’s mineable cobalt and includes several world-class Cu–Co deposits each containing ≥ 10Mt copper. Total copper hosted in the Katangan basin of Central Africa is close to 200 Mt if sub-economic (Cu ≥ 1 wt.%) occurrences are included (Cailteux et al., 2005). The Congolese part of the Central African Copperbelt (the Katanga Copperbelt) can be divided into two main parts. The first part is a north-directed fold-and-thrust belt well known as the ‘‘Lufilian Arc’’, located between the Congo and Kalahari cratons. It is more than 150 km wide and stretches for 700 km from Mwinilunga in the west (e.g. Brock, 1961; Steven, 2000) to Kolwezi in the northwest, up to Luanshya (previously Roan Antelope) and Lonshi in the southeast of the belt. The second part is a triangular-shaped area well known as the “Lufilian foreland” located to the north of the Lufilian fold-and-thrust belt. This foreland is the northward extension of the Central African Copperbelt.

The Lufilian Arc is part of an extensive network of Neoproterozoic to early Palaeozoic (Pan African) orogenic belts that cut across central and southern Africa. In contrast to other components of this network, the Lufilian Arc has two unique characteristics, namely its arcuate shape, and its major copper–cobalt deposits within deformed Katangan strata. The Lufilian foreland consists largely of tabular metasedimentary rocks of Neoproterozoic age belonging to the Katangan supergroup. Numerous explanations exist for the origin of the Lufilian foreland. According to Kampunzu and Cailteux (1999), the Lufilian foreland is a Neoproterozoic continental depression where mostly clastic sediments were deposited, while Porada and Berhorst (2000) proposed an intracratonic rift origin. At the eastern border of the Lufilian foreland a series of NNW-SSE trending anticlines are located (e.g. the Kiaka and Lufukwe anticlines). These folds are overlain by the uppermost Kundelungu sub-horizontal formations of the "Plateaux" subgroup (Kampunzu and Cailteux 1999).

The Katangan Supergroup, which covers the Lufilian arc and foreland and hosts the stratiform copper mineralizations, is ~5-10 km thick and commonly sub-divided into three groups: Roan, Nguba and Kundelungu, based on the regional occurrence of two diamictites. The lower diamictite is called “Grand Conglomérat” at the base of the Nguba group and the upper diamictite is called “Petit Conglomérat” at the base of the Kundelungu group (Cailteux et al., 2005). The Roan group is mainly composed of dolomites and dolomitic siltstones, while the Nguba and Kundelungu groups are composed of clastic sedimentary rocks with few carbonate units. The Katangan supergroup is deformed during a major orogenic event well known as the Lufilian Orogeny with its maximum at ~560-550 Ma (Porada and Berhorst, 2000).

kat_strat  

The stratiform copper-cobalt deposits in the Lufilian arc are generally characterised by two major orebodies hosted in the Mines subgroup of the Roan group, the ‘‘lower’’ and ‘‘upper’’ orebodies, totalling 15–55 m cumulative thickness (average: 20–25 m). The lower orebody host-rocks include: (1) a massive chloritic dolomitic siltite known as Grey R.A.T. (‘‘Roches Argilo-Talqueuses’’); (2) a fine-grained stratified dolostone (D.Strat. ‘‘Dolomie Stratifie´e’’); (3) silicified stromatolitic dolomites forming laminites alternating with thin chloritic–dolomitic silty beds (R.S.F. ‘‘Roches Siliceuses Feuillete´es’’). The Upper Orebody host-rocks include: (1) the basal Dolomitic Shales (S.D.B., ‘‘Shales Dolomitiques de Base’’ also called S.D.1a); (2) an overlying coarse grained impure dolostone (B.O.M.Z., ‘‘Black Ore Mineralised Zone’’ also called S.D.1b) which is sometimes missing in the succession (e.g. in the Kambove area). A generally ‘‘barren’’ reef-type stromatolitic dolomite (R.S.C., ‘‘Roches Siliceuses Cellulaires’’) occurs between the two orebodies (Cailteux et al., 2005).

Although copper production from the Lufilian arc goes back to several decades, copper production from the Lufilian foreland is still in its very early stages. The Dikulushi mine, a sediment-hosted vein-type high-grade low tonnage Cu-Ag ore deposit (Dewaele et al., 2006), is the first producing copper mine from the Lufilian foreland. Since exploration of this mine, mining companies (e.g. Anvil Mining Congo) started to give much more attention to the copper potential of the Lufilian foreland, hence some copper prospects were proposed, including the Kinkumbi prospect at the Lufukwe anticline. Although copper mineralization in the Lufilian arc is mainly concentrated in Roan sediments (Mines subgroup) (Cailteux et al. 2005; Selley et al., 2005) and always associated with cobalt, up to date the observed copper mineralizations in the Lufilian foreland are only observed in Nguba (e.g. Lufukwe) and Kundelungu sediments (e.g. Dikulushi; Dewaele et al., 2006) and in both, copper is mainly associated with silver not cobalt.

The research carried out in the Central African Copperbelt during the last decades was mainly concentrated on investigating its geology and the possible mineral occurrences and origin of the stratiform copper-cobalt deposits hosted the Mines subgroup. Despite the large number of publications coming out from this research, up to date there is no agreement about the origin of the stratiform copper deposits hosted in the Mines subgroup (e.g. Dewaele et al., in press). Further more up to date there is no published information on the sediment-hosted stratiform copper deposits of the Lufilian foreland. Hence the geodynamic context and metallogenesis of the stratiform copper deposits in the Lufilian orogen (arc and foreland) remains enigmatic. This situation makes both the Lufilian arc and the Lufilian foreland an exciting site for ore deposit research.

 
Objectives
 

The aim of the study is to investigate the geology and metallogenesis of the stratiform copper deposits in the Lufilian orogen, Democratic Republic Congo (DRC). For this purpose four different stratiform copper mineralisations have been selected for careful investigation and comparison.  Two study areas (Kamoto and Luiswishi) are hosted in the Lufilian fold-and-thrust belt (Lufilian Arc). The other two study areas (Lufukwe and Mwatepile) are hosted in the Lufilian foreland. During this 4 years research project structural, petrographic, mineralogical and geochemical methods are applied to investigate the tectonic setting, sedimentology, diagenesis, mineralogy, fluid chemistry and -if possible- geochronology of the stratiform copper deposits.

Methdology
 

The research techniques to be used are fieldwork, transmitted and incident light microscopy, fluid inclusion microthermometry, LA-ICPMS and/or crush leach analysis, stable and radiogenic isotope geochemistry and remote sensing analysis. The data obtained in this basinal analysis approach will be integrated to develop local and general metallogenetic models for these deposits. General and site specific criteria will be proposed for further exploration in the DRC and in similar fold-and-thrust belts worldwide.

Results
 

Lufukwe

Lufukwe is a double plunged anticline situated ~200 km NE of Lubumbashi. The anticline is related to the first deformation phase (D1) of the Lufilian orogeny (Kampunzu and Cailteux, 1999), which caused the major fold-and-thrust deformations throughout the Lufilian arc. The anticline is composed of Neoproterozoic sediments belonging to the Roan, Nguba and Kundelungu groups of the Katangan Supergroup (Kampunzu and Cailteux, 1999). The units have a NNW trend and an easterly vengeance (Cahen, 1954; Cahen et al., 1984). The anticline hosts a sediment-hosted stratiform copper prospect with disseminated copper-silver mineralization concentrated in the lower 10 to 15 m of the Monwezi sandstone (the host-rock; Nguba group).

A combined remote sensing, petrographic and fluid inclusion microthermometric analysis were applied to study the sediment-hosted stratiform copper prospect at Lufukwe. The Monwezi sandstone has been subject to strong compaction and silica cementation (authigenic quartz overgrowths), followed by intense feldspar dissolution, which resulted in a well-developed secondary porosity represented by dissolution cavities. Copper sulfide minerals are mainly concentrated in these cavities and partially replace the detrital grains. The copper mineralization took place in two phases: hypogene (chalcopyrite, bornite and chalcocite) and supergene (digenite, covellite and minor native copper), in addition to malachite and chrysocolla as the main surface oxidation minerals. The research results support a post-orogenic fluid-mixing model in which the mineralization is related to the mixing between two fluids of different salinities and temperatures.

 

 

Mwatepile, Kamoto and Luiswishi

under construction

 

 

References

 

Brock, B.B., 1961. The structural setting of the Copperbelt. In: Mendelsohn, F. (Ed.), The Geology of the Northern Rhodesian Copperbelt. Macdonald, London, pp. 81–89.
Cahen, L., 1954, Geologie du Congo Belge. Editions Vaillant-Carmanne, Liege, Belgium, P. 577.
Cahen, L., Snelling, N. J., Delhal, J., and Vail, J. R., 1984, The Geochronology and Evolution of Africa: Oxford, Clarendon Press, p. 512.
Cailteux, J.L.H., Kampunzu, A.B., Lerouge, C., Kaputo, A.K., and Milesi, J.P., 2005, Genesis of sediment-hosted stratiform copper–cobalt deposits, central African Copperbelt: Journal of African Earth Sciences, v. 42, p. 134–158.
Dewaele, S., Muchez, Ph., Heijlen, W., Boutwood, A., Lemmon, T., and Tyler, R., 2006, Reconstruction of the hydrothermal history of the Cu–Ag vein-type mineralisation at Dikulushi, Kundelungu foreland, Katanga, D.R. Congo: Journal of Geochemical Exploration, v. 89, p. 376–379.
El Desouky, H., Muchez, Ph., Dewaele, S., Boutwood, A. and Tyler, R., 2006, Late diagenetic to post-orogenic origin of the stratiform Cu mineralisation at Lufukwe, Lufilian foreland, Democratic Republic Congo: Conference Abstract, Annual Winter Meeting of the Mineral Deposit Studies Group (MDSG), 4-6 January 2006, Imperial College, London, UK.
El Desouky, H., Muchez, Ph., Dewaele, S., Boutwood, A. and Tyler, R., 2006, Late diagenetic to post-orogenic origin of the stratiform Cu mineralisation at Lufukwe, Lufilian foreland, Democratic Republic Congo: Conference Poster and Abstract, in: Wealth Creation in the Minerals Industry, Conference Proceedings on DVD-ROM, Society of Economic Geologists (SEG) 2006 Conference, 14-16 May 2006, Keystone, Colorado, USA.
El Desouky, H., Muchez, Ph., Dewaele, S., Boutwood, A. and Tyler, R., 2006, The stratiform Cu mineralisation at Lufukwe, Lufilian foreland, Democratic Republic Congo: Conference Abstract, 2nd Geologica Belgica Meeting, 7-8 September 2006, Liege, Belgium.
Kampunzu, A.B., and Cailteux, J., 1999. Tectonic evolution of the Lufilian Arc during Neoproterozoic pan African orogenesis: Gondwana Research, v. 2, p. 401–421.
Kirkham, R.V., 1989, Distribution, settings and genesis of sediment-hosted stratiform copper deposits: Geological Association of Canada Special Paper 36, p. 3-38.
Porada, H., and Berhorst, V., 2000. Towards a new understanding of the Neoproterozoic-Early Palaeozoic Lufilian and northern Zambezi belts in Zambia and the Democratic Republic of Congo. Journal of African Earth Sciences 30, 727–771.
Selley, D., Broughton, D., Scott, R., Hitzman, M., Bull, S., Large, R., McGoldrick, P., Croaker, M., Pollington, N., and Barra, F., 2005, A new look at the geology of the Zambian Copperbelt, in Hedenquist, J. W., Thompson, J.F.H., Goldfarb, R. J., and Richards, J.P, eds., Economic Geology 100th Anniversary Volume, p. 965-1000.
Steven, N.M., 2000. A Shaba-type Cu–Co(–Ni) deposit at Luamata, West of the Kapompo Dome, northwestern Zambia. Exploration Mining Geology 9, 277–287.
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