Remobilisation features and structural control on ore grade distribution at the Konkola stratiform Cu–Co ore deposit, Zambia

K. Torremans, J. Gauquie, A.J. Boyce, C.D. Barrie, S. Dewaele, O. Sikazwe, Ph. Muchez
2013 Journal of African Earth Sciences  
28 The Konkola deposit is a high grade stratiform Cu-Co ore deposit in the Central African Copperbelt in 29 Zambia. Economic mineralisation is confined to the Ore Shale Formation, part of the Neoproterozoic 30 metasedimentary rocks of the Katanga Supergroup. Petrographic study reveals that the copper-cobalt 31 ore minerals are disseminated within the host rock, sometimes concentrated along bedding planes, 32 often associated with dolomitic bands or clustered in cemented lenses and in
more » ... s and in layer-parallel and 33 irregular veins. The hypogene sulphide mineralogy consists predominantly of chalcopyrite, bornite and 34 chalcocite. Based upon relationships with metamorphic biotite, vein sulphides and most of the 35 sulphides in cemented lenses were precipitated during or after biotite zone greenschist facies 36 metamorphism. New δ 34 S values of sulphides from the Konkola deposit are presented. The sulphur 37 isotope values range from -8.7‰ to +1.4‰ V-CDT for chalcopyrite from all mineralising phases and 38 from -4.4‰ to +2.0‰ V-CDT for secondary chalcocite. Similarities in δ 34 S for sulphides from different 39 vein generations, earlier sulphides and secondary chalcocite can be explained by (re)mobilisation of S 40 from earlier formed sulphide phases, an interpretation strongly supported by the petrographic 41 evidence. Deep supergene enrichment and leaching occurs up to a km in depth, predominantly in the 42 form of secondary chalcocite, goethite and malachite and is often associated with zones of high 43 permeability. Detailed distribution maps of total copper and total cobalt contents of the Ore Shale 44 formation show a close relationship between structural features and higher copper and lower cobalt 45 contents, relative to other areas of the mine. Structural features include the Kirilabombwe anticline and 46 fault zones along the axial plane and two fault zones in the southern limb of the anticline. Cobalt and 47 copper behave differently in relation to these structural features. These structures are interpreted to 48 have played a significant role in (re)mobilisation and concentration of the metals, in agreement with 49 observations made elsewhere in the Zambian Copperbelt. between Zambia and the Democratic Republic of Congo (Fig. 1) . Throughout the years, different 54 metallogenetic models have been proposed for the ore deposits in the Central African Copperbelt (for 55 reviews see Cailteux et al., 2005; El Desouky et al., 2010; Selley et al., 2005) . Several recent studies 56 agree that most of the high grade Cu-Co deposits formed via a multiphase system with several early to 57 late diagenetic and synorogenic mineralisation and mobilisation stages (Cailteux et al., 2005; Haest 58 and Muchez, 2011; Muchez et al., 2010; Selley et al., 2005). However, to date this model is not yet 59 generally accepted (Sillitoe et al., 2010). 60 The Konkola deposit has been the subject of intensive research in the past. Several authors have 61 investigated the local geology, petrology and the type and occurrence of mineralisation as well as 62 indications for the sedimentological and palaeo-environment at Konkola (e.g. Fleischer et al., 1976;
doi:10.1016/j.jafrearsci.2012.10.005 fatcat:b77zinhkwne4vg624rji7dtikm