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Metallogenesis of vein-type Cu-Zn-Pb-Ag ore deposits in the Lufilian fold-and-thrust belt and its foreland (DRC)

Researcher: Drs. Maarten Haest, Geodynamics and Geofluids Research Group, KULeuven
Promotor: Prof. Dr. Philippe Muchez, K.U.Leuven, Geodynamics & Geofluids Research Group, KULeuven
Co-promotor:  
Funding: FLOF-bursaal from the Katholieke Universiteit Leuven

 

Keywords:
Cu-Zn-Pb-Ag vein type deposits, copperbelt, Dikulushi and Kipushi

 

Research abstract:
The PhD study focuses on the metallogenesis of vein-type Cu-Zn-Pb-Ag ore deposits in the Lufilian fold-and-thrust belt and its foreland, with special emphasis on the deposits of Dikulushi in the foreland and Kipushi in the Lufilian belt. A structural and geochemical study of the deposit at Dikulushi has shown that this mineralisation formed during two major phases. The first mineralising phase developed in a complex set of EW and NE-oriented faults that crosscut an anticline to the southwest. The mineralisation is dominated by sphalerite, chalcopyrite and bornite that precipitated from a high salinity fluid at high temperature in a reducing environment. The first mineralising phase at Dikulushi probably took place during a late stage of the Lufilian orogeny. The second mineralising phase is located along NE-oriented faults that cut the previous fault complex. During the second mineralising phase, the Cu-minerals from the first phase were remobilised into massive chalcocite that precipitated at lower temperatures from a medium salinity fluid under more oxidising conditions. The mineralisation at Kipushi is located along a NNE-SSW-oriented fault that also crosscuts an anticline. As such, both mineralisation at Dikulushi and Kipushi have a comparable structural position. From this study a global model for the formation of the different vein-type mineralisation in the Lufilian belt could be proposed. This model could be applicable to other Cu-mineralisation in similar fold-and-thrust belts over the world.

 

Introduction and Regional Geologic Setting:
   

The Katanga province is located in the south-eastern part of the Democratic Republic of the Congo (D.R.C.) and contains part of the Central African Copper belt straddling the border between the D.R.C and Zambia. This belt is the largest and the highest grade sediment-hosted stratiform copper province known on earth. Combined production and reserves total approximately 190Mt of Cu (Hitzman et al., 2005) of which 102Mt are contained in the Congolese part of the belt (i.e. the Lufilian arc, fig. 1), as stratiform or vein-type deposits. The stratiform copper deposits have been the subject of numerous studies since their discovery in the early 1900s (e.g. Cahen, 1954; Garlick and Fleischer, 1972; Kortman, 1972; Bartholomé, 1974; Cailteux, 1974; Lefebvre, 1974; Sweeney et al., 1986; Unrug, 1988; Annels, 1989; Sweeney and Binda, 1994; Hitzman, 2000; Cailteux et al., 2005; Selley et al., 2005; McGowan et al., 2006; Dewaele et al., 2006b). The largest number of stratiform copper deposits occur in the Lufilian arc, in two separate levels of the Mines Subgroup (R2 in fig. 2), which is part of the Roan Supergroup. Only a limited number of stratiform occurrences have been described in the foreland (e.g. Lufukwe, Mwitapile, etc.).

 

Figure 1: Geological map of the southern part of Katanga (Kap: Kapulo; Pw: Pweto; Ka: Kabangu; D: Dikulushi; Ki: Kibala; Lu: Lufukwe anticline; LM: Lake Mweru; LT: Lake Tshangalele; K: Kipushi; Lo: Lombe; Ke: Kengere) (modified after Lepersonne, 1974)

mh_foreland
   
 
    mh_strat_kat

These occurrences occur at higher stratigraphic levels in the Nguba and Kundelungu Supergroups (fig. 2). Stratiform Cu-Co deposits mainly formed pre- to syn-orogenic, while the Zn-Cu-Pb-Ag vein-type deposits are mostly syn- to post-orogenic (e.g. François, 1974; Dewaele et al., 2006b). Vein-type Zn-Cu-Pb-Ag deposits have been described in the Lufilian arc (e.g. Kipushi, Lombe and Kengere) and in the Lufilian foreland (Dikulushi, Kibala and Kapulo) (fig. 1 and fig. 2). The total amount of copper contained in the Katanga vein-type ore bodies is much smaller than in the stratiform deposits. Nevertheless, the Kipushi deposit, which has been mined between 1926 and 1974 is probably one of the richest Cu-Zn-Pb-Cd-Ag-Ge deposits in the world, with reserves that initially totalled around 20 million tons of ore. Furthermore, the initiation of the Dikulushi project in 2002 (Dewaele et al., 2006a) has stimulated the interest in this class of high grade deposits. In the Dikulushi mine, a Cu-Ag ore is mined, with total production and reserves estimated at 1.94Mt, at an average grade of 8.5% Cu and 226g/t of silver (Tassel, 2003). These grades encouraged the exploration of the Lufilian foreland with a still largely unexplored mineralisation potential.

 

 

Figure 2: Simplified stratigraphic column in the Lufilian fold-and-thrust belt, with on the right side the stratigraphic position of some of the mineralisation mentioned in the text (after De Magnée and François, 1988).

 
 
Objectives
 

 

The PhD study focuses on the Cu-Pb-Zn-Ag vein-type deposits in the Lufilian belt and its foreland. The primary objective is to determine the metallogenesis of these deposits. Possible genetic links between these deposits are investigated based on: (1) the structural controls on mineralisation, (2) remote sensing and (3) mineralogical and geochemical analysis. The data obtained will not only be relevant for the Lufilian belt. They may add evidence to the discussion in which evolutionary phase of a sedimentary basin, ore deposits form and which processes are responsible. The product of this research could assist in developing exploration strategies, which is a secondary objective of this study. Apart from this global approach to investigate the problems concerning the formation mechanisms of the different vein-type mineralisation, a more detailed geochemical study will be carried out on the Dikulushi Cu-Ag deposit. The Cu-Ag mineralisation at Dikulushi is characterised by a transition from a reducing to an oxidising environment. Previous research has shown that such a transition is accompanied by a change in the Cu-isotope ratios of the different Cu-rich minerals that precipitated under these physico-chemical conditions. Analysis of the Cu-isotopic ratios in the different Cu-rich minerals could confirm this coeval transition or it could deliver additional parameters that influence the Cu-isotopic ratio.

Methdology
 

 

The Dikulushi Cu-Ag mineralisation has been mined in an open pit since 2002 by Anvil Mining. Open pit mining has halted in 2006 at a depth of 150m and this has produced an excellent 3D exposure of the mineralisation (fig. 3). Thanks to the logistic support from Anvil Mining, two separate field surveys of 5 weeks were performed. During these field surveys the entire quarry was mapped, level by level, with detailed drawings of all levels. These geological maps, combined with detailed structural analysis (i.e. of faults, bends, etc) allowed constraining the structural controls on the mineralisation.

Three Master theses’s focusing on remote sensing analysis of the Lufilian fold-and-thrust belt investigated the Cu-deposits to constrain the localising factors from a more global point of view. The remote sensing analysis is refined for those vein-type deposits that are investigated.
The geochemical study that is currently in progress is based on hand specimens that were collected in the mine and from the bore holes, stored in the exploration camp (fig. 3). A macroscopic and microscopic description of the samples allowed the reconstruction of the paragenesis that was primarily defined in the field. Microthermometry, crush leach analysis, stable and Sr isotope analysis will give us an idea about the source and the evolution of the mineralising fluids. Rb-Sr isotope analysis of the sphalerite that precipitated during the first, more reducing phase of the mineralisation could give us an exact timing of the mineralisation. This geochemical study will be compared with the geochemistry of the vein-type Cu-Pb-Zn deposit of Kipushi.
The Cu isotope ratios of the Cu-minerals from the mineralisation at Dikulushi will be analysed with a MC-ICP-MS that is currently set up at the Universiteit Gent.

 

mh02

Figure 3: The mining site at Dikulushi.

 

References

 

Annels, A. E., 1989, Ore Genesis in the Zambian Copperbelt, with Particular Reference to the Northern Sector of the Chambisi Basin, in Boyle, R. W., Brown, A.C., Jefferson, C.W., Jowett, E.C. and Kirkham, R.V., ed., Special paper, 36, Geological Association of Canada, p. 427-452.
Bartholomé, P., 1974, On the diagenetic formation of ores in sedimentary beds, with special reference to Kamoto, Shaba, Zaire, in Bartholomé, P., ed., Gisements stratiformes et provinces cuprifères: Liège, La Société Géologique de Belgique, p. 203-213.
Cahen, L., 1954, Géologie Du Congo Belge: Liège, H. Vaillant-Carmanne, S. A., 577 p.
Cailteux, J. L. H., 1974, Les sulfures du gisement Cuprifère stratiforme de Musoshi, Shaba, Zaïre, in Bartholomé, P., ed., Gisements stratiformes et provinces cuprifères: Liège, La Société Géologique de Belgique, p. 267-276.
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, P., Heijlen, W., Boutwood, A., Lemmon, T. and  Tyler, R., 2006a, 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.
Dewaele, S., Muchez, P., Vets, J., Fernandez-Alonzo, M. and  Tack, L., 2006b, Multiphase origin of the Cu-Co ore deposits in the western part of the Lufilian fold-and-thrust belt, Katanga (Democratic Republic of Congo): Journal of African Earth Sciences, v. 46, p. 455-469.
François, A., 1974, Stratigraphie, tectonique et minéralisations dans l'arc cuprifère du Shaba (République du Zaïre), in Bartholomé, P., ed., Gisements Stratiformes et Provinces Cuprifères: Liège, La Société Géologique de Belgique, p. 79-101.
Garlick, W. G. and  Fleischer, V. D., 1972, Sedimentary environment of Zambian copper deposition: Geologie en Mijnbouw, v. 51, p. 277-298.
Hitzman, M. W., 2000, Source basins for sediment-hosted stratiform Cu deposits: implications for the structure of the Zambian Copperbelt: Journal of African Earth Sciences, v. 30, p. 855-863.
Hitzman, M. W., Kirkham, R., Broughton, D., Thorson, J. and  Selley, D., 2005, The sediment-hosted stratiform copper ore system: Economic Geology, v. 100, p. 609-642.
Kortman, C. R., 1972, The geology of the Zambia Broken Hill mine, Kabwe: Geologie en Mijnbouw, v. 51, p. 347-356.
Lefebvre, J. J., 1974, Minéralisations cupro-cobaltifères associées aux horizons pyroclastiques situés dans le faisceau superieur de la série de Roan, a Shituru, Shaba, Zaire, in Bartholomé, P., ed., Gisement stratiformes et provinces cuprifères: Liège, La Société Géologique de Belgique.
McGowan, R. R., Roberts, S. and  Boyce, A. J., 2006, Origin of the Nchanga copper-cobalt deposits of the Zambian Copperbelt: Mineralium deposita, v. 40, p. 617-638.
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: Economic Geology, v. 100th anniversary volume, p. 965-1000.
Sweeney, M., Turner, P. and  Vaughan, J., 1986, Stable Isotope and Geochemical Studies of the Role of Early Diagenesis in Ore Formation, Konkola Basin, Zambian Copper Belt: Economic Geology, v. 81, p. 1838-1852.
Sweeney, M. A. and  Binda, P. L., 1994, Some constraints on the formation of the Zambian Copperbelt: Journal of African Earth Sciences, v. 19, p. 303-313.
Tassel, A., 2003, Dikulushi-setting a new benchmark: African Mining, v. 8, p. 24-35.
Unrug, R., 1988, Mineralisation Controls and Source of Metals in the Lufilian Fold Belt, Shaba (Zaïre), Zambia, and Angola: Economic Geology, v. 83, p. 1247-1258.
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