Journal of African Earth Sciences 140 (2018) 76e93

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Journal of African Earth Sciences

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Origin of the megabreccias in the Katanga Copperbelt (D.R.Congo)

* Jacques L.H. Cailteux a, , Philippe Muchez b, Jana De Cuyper b, Stijn Dewaele a, c, Thierry De Putter a a Geodynamics and Mineral Resource Unit, Royal Museum for Central Africa, Leuvensesteenweg 13, 3080 Tervuren, Belgium b KU Leuven, Geodynamics and Geofluids Research Group, Department of Earth and Environmental Sciences, Celestijnenlaan 200E, B-3001 Leuven, Belgium c Mineralogy and Petrology, Department of Geology, Ghent University, Krijgslaan 281 S8, B-9000 Gent, Belgium article info abstract

Article history: The megabreccias in the Katanga part of the Neoproterozoic Central African Copperbelt contain up to Received 17 August 2017 several km-long blocks and fragments of the Mines Subgroup which host most of the stratiform Cu-Co Received in revised form deposits. New observations, particularly on cores from boreholes drilled at Luiswishi indicate three types 8 November 2017 of fracturing: 1) brittle post-folding in the Mines Subgroup; 2) hydraulic; and 3) ductile in soft incom- Accepted 21 December 2017 petent siltstones of the R.A.T. and Dipeta subgroups. These fracturing phases dislocated the Roan suc- Available online 26 December 2017 cession into blocks and fragments and, in particular, clearly showed that there is an evolution from an in situ hydraulic fracturing, to a heterometric brecciation implying some movement and abrasion of the Keywords: fi fl Neoproterozoic fragments. The process points to signi cant compression, and was accompanied by uid expulsion and Katanga supergroup precipitation of dolomite after decompression. Fluid inclusion microthermometry in dolomite grains Luiswishi-Kambove-Kolwezi shows that the fluids were of high salinity and high temperature, suggesting dissolution of evaporites Megabreccia most likely contained in the Roan sedimentary pile. These saline fluids allowed the fluidization of the Petrography breccias, facilitating the displacement of the nappes, pinching out (extrusion-like) megabreccias along Fluid inclusions thrust-faults, and resulting in intrusion of breccias between the blocks or into large fractures. Breccias between the blocks are clearly identified as friction breccias. They contain a fine material, as part of the matrix, resulting from abrasion of the fragments during transportation. Abrasion and attrition explain the rounding of the fragments. A late cementation phase from less saline and lower temperature fluids suggests the addition of meteoric water in the system, and the mixing with the ambient fluids. The minimum burial depth of the meteoric water incursion is estimated at 2.8 km. Such under-saturated fluids may have contributed to the dissolution of residual evaporites and of the evaporitic material from the Kiubo rocks at the base of the nappes, and led to further brecciation, possibly explaining the multi-phase features of the breccia. The megabreccias occur at the base of the thrusts sheets and are marked by thrust-fault zones. Results of the study support a process of formation of the megabreccias related to a fold-and-trust event, and invalidate a syn-orogenic sedimentary origin as an olistostrome formed by subaqueous conglomeratic debris flows and clastic syn-orogenic sediments. They also contradict a pure salt tectonic hypothesis that propose the extrusions and enlargements of allochthonous evaporites-gigabreccia before the Lufilian deformation. However, the model is compatible with a “fluid behaviour” of pressured saline fluids trapped in folds and/or thrust sheets, and resulting from evaporites dissolution at variable depth. © 2018 Elsevier Ltd. All rights reserved.

1. Introduction of the Zambian e Democratic Republic of Congo (hereafter “Congo”) border (Fig. 1). It represents one of the world's largest The Neoproterozoic Katanga Copperbelt (hereafter KCB) forms concentration of sediment-hosted copper-cobalt deposits part of the Central African Copperbelt that stretches on both sides (Demesmaeker et al., 1963; Cailteux et al., 2005b). In the KCB, most of these deposits occur within megabreccias as up to several km- long fragments or blocks and megablocks of the Roan sedimen- tary rocks. The megabreccias are associated with major thrust- * Corresponding author. faults (e.g. at Tenke-Fungurume, Kambove, Luiswishi; Fig. 1). They E-mail address: [email protected] (J.L.H. Cailteux). https://doi.org/10.1016/j.jafrearsci.2017.12.029 1464-343X/© 2018 Elsevier Ltd. All rights reserved. J.L.H. Cailteux et al. / Journal of African Earth Sciences 140 (2018) 76e93 77

Fig. 1. Geological and tectonic map of the Lufilian Arc, Kundelungu Foreland and Kibaran Belt, with structural subdivisions of the Lufilian Arc (modified from Kipata et al., 2013; according to Kampunzu and Cailteux, 1999). KCB ¼ Katanga Copperbelt; ZCB ¼ Zambia Copperbelt. Location of Nzilo (Nzi) and of the Kolwezi (Kol), Tenke-Fungurume (Fun), Kambove (Kam), Luiswishi (Lui), Ruashi-Etoile (ReE) Kipushi (Kip) and Kimpe (Kim) Roan megabreccias. Insert with location of the Neoproterozoic orogenic belts in south-central Africa and major crustal plates. have been explored by surface mapping and studied from drill core small walls and extrusions of evaporite-gigabreccia from mid-Roan data during decades, resulting in a huge database that allowed time on; (3) enlarged evaporitic diapirs between 940 and 850 Ma; robust modelling of these structures and helped to reconstruct the and (4) laterally squeezed diapirs to form salt welds between 850 puzzling stratigraphy of the Roan succession observed from the and 650 Ma when the Lufilian deformation took place. field in the KCB. A third interpretation proposed that the megabreccias represent The origin of the megabreccias has commonly been related to a coarse clastic syn-orogenic sedimentary bodies (conglomerate fold-and-thrust phase of the Lufilian orogeny (Cailteux and complexes) supplied by north-advancing nappes into a foreland Kampunzu, 1995; Kampunzu and Cailteux, 1999), that resulted in basin (Wendorff, 2000, 2003, 2005, 2011). In this hypothesis, the regional detachments and major dislocations affecting the Roan allochthonous “megablocks” of the Roan sequence (“carbonate sedimentary pile (mainly at the base of the R.A.T. and at the top of rocks with Cu-Co mineralization”) are part of olistostromes sourced the Dipeta units). Detachments and dislocations have been attrib- as debris-flow from uplifted regions to the south, whereas the R.A.T. uted to the occurrence of thick argillaceous incompetent beds, and Dipeta subgroups were deposited as continental red beds and abundance of remobilized fluids during initial fragmentation, and marginal marine deposition in a foreland basin at top of the folded evidence of evaporitic components within the Roan succession (e.g. Kundelungu sequence. This sedimentary hypothesis is based upon sabkha facies, pseudomorphs after anhydrite and gypsum, collapse the following arguments: (1) absence of pervasive shearing; (2) breccias of little extension, evaporitic fluids). In this hypothesis, the provenance of clasts from Katangan lithostratigraphic units and megabreccias are interpreted to have been pushed at the base and geochemical signatures; (3) presence of well-rounded pebbles and in front of the north-advancing nappes during thrusting. intercalations of well-sorted conglomerate layers; (4) vertical A second interpretation based on the indications of former changes in clasts provenance reflecting erosion; (5) lateral facies evaporites and on the occurrence of saline springs, evoked firstly by gradients from proximal (south) to distal (north); (6) presence of De Magnee and François (1988), was developed by Jackson et al. debris-flow deposits and turbidites; (7) coarsening-upwards ver- (2003), suggesting the extrusion of allochthonous evaporites in a tical successions; (8) overturned positions of some blocks; and (9) first step and the orogenic shortening in a second step. This hy- soft-sediment injections of incompetent material upwards into pothesis proposes that salt tectonics: (1) began during deposition open fractures in megablocks. of the Roan Supergroup between 1050 and 950 Ma; (2) emplaced This paper focuses on the formation processes of the Katangan 78 J.L.H. Cailteux et al. / Journal of African Earth Sciences 140 (2018) 76e93 megabreccias. The study relates to the Luiswishi megabreccia, but Kundelungu groups, respectively (François, 1987; Batumike et al., also provides data allowing comparisons with megabreccias from 2007; Cailteux et al., 2007). other areas in the KCB, in order to: (1) describe their lithological, Sedimentary rocks of the Roan Group in the KCB traditionally stratigraphic and structural context; (2) characterise the breccias comprise from bottom to top, the R.A.T. (“Roches Argilo-Tal- sensu-strictu by their petrographic and fluid inclusions features; queuses”), Mines, Dipeta and Mwashya subgroups (Table 1). These and (3) tentatively determine the origin and mechanism of their rocks are generally readily distinguished in the entire area, with formation within the general tectonic setting process. some variations of the sedimentary facies from the south to the north. The succession is affected by many structural discontinuities “ ” 2. Geological setting and occur mainly as big fragments (hereafter called blocks or “megablocks”) in the megabreccias, but conformable deposition 2.1. Stratigraphy between R.A.T and Mines, and between Mines and Dipeta, has been locally demonstrated (Cailteux, 1978a, 1994; Cailteux et al., 2005a; The Neoproterozoic Katanga Supergroup sedimentary succes- Kampunzu et al., 2005). The lowest part of the R.A.T. Group has not sion is ~7.5 km thick (François, 1987) and has been deposited un- been observed, and only a basal conglomerate is known in the Nzilo conformably on the Palaeo-to Mesoproterozoic basement. It is area, unconformably overlying the Palaeo-to Mesoproterozoic subdivided into three units, from bottom to top (Table 1): the Roan, basement (Fig. 1). “ ” Nguba and Kundelungu groups. This subdivision is based on the The R.A.T. Subgroup (also called R.A.T. rouges ) consists of occurrence of two diamictites that are regional stratigraphic pinkish to reddish or purple-grey hematitic chlorite-quartz- markers: the Mwale (“Grand Conglomerat ”) and the Kyandamu dolomite rocks, more sandy-silty at the bottom, becoming more (“Petit Conglomerat ”) formations at the base of the Nguba and dolomitic to the upper part, and locally showing sparse evaporitic

Table 1 Lithostratigraphy of the Katangan Supergroup in the KCB (compiled from Cailteux, 1994; Batumike et al., 2007; Cailteux et al., 2007; Kipata et al., 2013); Sturtian and Marinoan ages based on MacGabhann, 2005;mafic volcanics ages related to Kansuki-Mwashya Formations based on Key et al., 2001. Ages and formation temperature of the metallic mineralizations (based on El Desouky et al., 2008; Heijlen et al., 2008; El Desouky et al., 2009; Haest et al., 2009); PO ¼ post-orogenic; SO ¼ syn-orogenic. J.L.H. Cailteux et al. / Journal of African Earth Sciences 140 (2018) 76e93 79 beds or concretions especially to the top (François, 1973; Cailteux, Rodinia Supercontinent break (Buffard, 1988; Kampunzu et al., 1994; Cailteux et al., 2005a). 1991, 1993). This event has a maximum age of ~880 Ma in The overlying Mines Subgroup that hosts the major Cu-Co Zambia, constrained by the intrusion of the Nchanga Granite at stratiform deposits in the KCB, is mostly a reduced carbonate suc- 883 ± 10 Ma in the basement rocks prior to rift-related sedimen- cession that has been deposited in shallow-water/(hyper-) saline tation and magmatism of the Katanga Supergroup (Garlick and tidal flat, reefal or lagoonal environments. It is subdivided into Brummer, 1951; Armstrong et al., 2005; Master et al., 2005). three units, from bottom to top: the Kamoto dolomites, “Shales A convergence between both cratons and related subduction, Dolomitiques”, and Kambove dolomites formations. At the base linked to the amalgamation of the Gondwana Supercontinent, occurs the “R.A.T. Grises”, a greyish-green massive chloritic- started the closure of the basin by inversion from extensional to dolomitic siltstone, similar in composition to the red R.A.T. but compressional tectonics at the end of the Nguba between 650 and contrastingly marked by reducing conditions (Cailteux et al., 600 Ma (Batumike et al., 2007). This convergence led to the 2005a). development of a fold-and-thrust belt that evolved towards the The Dipeta Subgroup consists predominantly of siliciclastic north (De Swardt and Drysdall, 1964; De Swardt et al., 1965; rocks in its lower part with variably dolomitic argillaceous- Coward and Daly, 1984; Daly et al., 1984; Cosy et al., 1992). This feldspathic sandy beds and argillaceous siltstones, overlain by orogenic process detached the Katangan rocks from the basement predominantly whitish to brownish carbonate beds, and by car- (Kroner,€ 1977; Cahen et al., 1984; Kampunzu and Cailteux, 1999) bonates with siliciclastic beds of the Mofya Formation and formed a ~700 km long SE-NW-SW convex system commonly (Oosterbosch, 1950; Cailteux, 1978b). This succession is marked by called “Lufilian Folded Arc” (Fig. 1). In the KCB, the folded and many tectonic discontinuities which makes it difficult to establish a faulted Roan, Nguba, and Kundelungu rocks form huge allochtho- complete stratigraphic continuity between the sequences. It is nous tectonic sheets, thrust over the Mongwe and Kiubo forma- overlain, through a tectonic contact, by the carbonate sequence of tions (Kampunzu and Cailteux, 1999). the Kansuki Formation, that contains widespread mafic volcanics The tectonic contact between the thrust sheets is marked by and related iron beds (Cailteux, 1994; Cailteux et al., 2007). variably extended megabreccias, composed of Mufulira, Cailteux et al., 1994; However, no clear evidence of thick and large bed or remnants of Luamata in northwestern Zambia, Steven, 2000). Within the brec- such massive evaporites, nor of solution-collapse breccia, have cias, the km-size blocks of competent carbonate rocks of the Mines been recognized within the succession. Subgroup are intensely folded, fractured, and partly dislocated. The Mwashya Subgroup is generally conformably overlying the Siltstones of the R.A.T. Subgroup generally occur as discontinuous Kansuki Formation, and comprise three siliciclastic units: the blocks along the flanks of the folded Mines Subgroup, whereas the Kamoya, Kafubu and Kanzadi formations. The Nguba and Kunde- basal sequences of the Dipeta Subgroup occur in the core of the lungu groups are predominantly siliciclastic sedimentary rocks, Mines synclines (e.g. in the Tenke-Fungurume area). The contact marked by the deposition of carbonates at the bottom, and suc- between the Mines Subgroup and the underlying R.A.T. or the ceeding the Mwale and Kyandamu diamictites, respectively overlying Dipeta Subgroup commonly shows fracturing and/or (Batumike et al., 2006, 2007). The basal, up to 1000 m-thick Mwale shearing in weakness zones, i.e. especially where evaporites diamictic Formation conformably succeeds to the Mwashya Sub- occurred (Cailteux, 1978a, 1994; Cailteux and Kampunzu, 1995). group in the Congo south-eastern areas, but is in unconformable A recent kinematic analysis of the tectonic structures in old or succession in the north-western areas after variable erosion of the active mines and outcrops, has allowed the reconstruction of stress Mwashya and Kansuki formations (Cailteux, 1994; Cailteux et al., stages that generated or reactivated the deformations (Kipata et al., 2007). It is interpreted as being related to the 715-680 Ma global 2013). The results indicate a closure of the rift system in three Sturtian glaciation (MacGabhann, 2005). The Kyandamu diamictic compressive stages: (1) brittle folding, faulting and thrusting with a Formation at the base of the Kundelungu succession is supposedly northward transport direction (D1 - the so-called Kolwezian phase correlated to the 635 ± 1.2 Ma Marinoan/Varanger glaciation in of Kampunzu and Cailteux, 1999); (2) constrictional radial Namibia (Hoffmann et al., 2004). compression in the central part of the Arc, that led to bending of the The mostly pelitic Mongwe and mostly sandy Kiubo formations, Arc and to formation of the megabreccias; and (3) predominantly occurring in the upper part of the Kundelungu Group, comprise strike-slip movements affecting the previously folded, faulted and pelites, sandy pelites, sandstones and arkosic sandstones, with a thrust sedimentary rocks (D2 - the Monwezian phase of Kampunzu variable carbonate content. Anhydrite occurs as nodules or thin and Cailteux, 1999), and affecting also the Kundelungu foreland, beds in the Kiubo Formation (François, 1973). This succession is confined between the Bangweulu block and the Kibaran belt. The interpreted as a molasse deposit filling the Kundelungu basin paroxysm of this compressive period is estimated at ~530 Ma (François, 1973; Batumike et al., 2007). A major tectonic disconti- (Porada and Berhorst, 2000; John et al., 2004), corresponding to the nuity ends the Kiubo deposition in the central and southern parts of maximum shortening of the Arc. The final collision was followed by the KCB. The Sampwe Formation is a ~1700 m-thick sequence of a tectonic uplift in central Zambia and rapid erosion which resulted alternating shales and fine sandstones that overlies conformably in deposition of the Biano Subgroup (Barr et al., 1978; Master et al., the Kiubo Formation in the northern part of the KCB (François, 2005). A late-to post-orogenic extensional collapse succeeded 1973; Dumont et al., 1997). compression probably between 530 and 507 Ma, marked by arc- parallel extension and reactivation of earlier compressional and 2.2. Tectonic evolution strike-slip faults (Kipata et al., 2013). The final post-metamorphic cooling ages range from 512 to 470 Ma as determined by KeAr The deposition of the Katanga Supergroup succession is inter- and RbeSr dating of muscovite and biotite from the Domes region preted as a result of the opening of an intracontinental rift basin (Cosy et al., 1992; John et al., 2004). A late folding phase younger between the Congo and Kalahari cratons, which evolved into a than the Permian deposits, corresponding to the D3 - Chilatembo proto-oceanic rift stage with the widening of the basin during the phase is observed in formations of the tabular Biano (Kampunzu 80 J.L.H. Cailteux et al. / Journal of African Earth Sciences 140 (2018) 76e93 and Cailteux, 1999), and affected both the folded Katangan and the The megabreccia of the Luiswishi area contains large-sized Kundelungu foreland (Kipata et al., 2013). (~1 km) blocks or fragments mostly from the R.A.T., Mines, Dipeta and Mwashya subgroups. It contains the major Cu-Co deposits of 3. The megabreccia in the Luiswishi area Luiswishi and Lukuni, the sub-economic oxidized Kiswishi deposit, hosted in Mines Subgroup lithologies, and the sub-economic The geology of the Luiswishi area is based on surface and open Lukuni-C mineralization hosted in brecciated Kansuki Formation pit mapping, and on logging of exploration cores. The total dataset lithologies (Fig. 2). These blocks and fragments are embedded in starts from 1923 and comprises 642 drill holes (more than Roan-derived fragments and breccias containing smaller size 45,500 m-drilled), including 172 holes (14,855 m-drilled) per- (mostly millimetric to metric) fragments of the same lithologies as formed between 1998 and 2007. the blocks and fragments. To the south, the megabreccia is bordered by a faulted and locally incomplete Mwashya Subgroup succession dipping southwards at 60 (Figs. 2 and 3). Rocks of the 3.1. Geological context Mwashya Subgroup and of the Kansuki Formation were locally duplicated or detached as blocks by thrust faulting at the roof of the The Luiswishi mining area is located ~26 km north-west of megabreccia. At the northern border of the megabreccia, sand- Lubumbashi in the south-eastern region of the fold-and-thrust belt. stones of the Kiubo Formation occur as a succession of sharp It belongs to a north-eastern verging fold-and-thrust nappe, antiforms marking the topography of the area with 50 up to 60 m- including: (1) a Mwashya-Nguba-Kundelungu sedimentary pile high hills. The Kiubo Formation is dipping south below the mega- forming a ~10 km wide syncline (named “Lubumbashi Syncline”)to breccia, as indicated by surface observations and some drill holes in the south-west; and (2) a megabreccia outcropping to the north, in the area (Figs. 2 and 3). front of the syncline, making the contact with the underlying Kiubo and Mongwe formations (Table 1; Figs. 2 and 3). This nappe is part of a ~150 km long thrust sheet aligned NW-SE from Kimpe in the SE 3.2. Vertical section through the megabreccia up to Luishia in the NW (Fig. 1). It forms one of the major tectonic zones in the KCB along which several other major megabreccias A 600 m-deep vertical drill-hole (LSW-1302), located on a N-S occur (e.g. Ruashi-Etoile). oriented local cross-section X: þ150, gives a long vertical section

Fig. 2. Geological surface map of the Luiswishi area; position of the blocks and of the Cu-Co deposits in the megabreccia (modified from maps of the Geological Department, Gecamines). Location of Figs. 3 and 4. J.L.H. Cailteux et al. / Journal of African Earth Sciences 140 (2018) 76e93 81

Fig. 3. Cross-section oriented N45E through the thrust nappe at Luiswishi, by the drill hole LSW-1302; position of the Luiswishi and projected Kiswishi deposits; suggested thrust faults. Location of Fig. 4.

3.2.1. R.A.T. blocks-1, 2 & -3 In the upper part of the succession, two blocks belonging to the R-1.3 Formation consist of massive purple-grey to pink dolomitic variably muddy siltstones, that contain locally mm-to cm-size concretions of dolomite (-quartz) pseudomorphs after anhydrite. A third R.A.T. block shows reddish to greyish R.A.T. Subgroup lithologies, comprising the R-1.2 Formation at the top, character- ized by bedded and slightly dolomitic siltstones with mm-to cm- thick coarse to fine sandy beds, and the R-1.1 Formation to the bottom, characterized by banded to fleecy (“moutonne”) mud- dominated bedded siltstones (Fig. 5). Both units are characterized by a variable content of iron and manganese oxides, while the R-1.1 is particularly rich in Mn. Iron occurs as a red hematite pigment, as specular hematite finely distributed in the matrix of the rock, as coarser specular hematite within the R-1.2 sandy beds, or associ- ated with dolomite in concretions or in filled fractures. Occasional red (iron-rich) to discoloured mm-to cm-size oolite/pisolite-like rounded patches are observed (Fig. 5B). Mostly at the bottom of the succession, sudden colour changes occur, i.e. between Fe-rich reddish-brown and pinkish, to discoloured pale yellow, and Mn- rich grey to dark-grey (Fig. 5A, B, C, D). Locally both R-1.1 and R- 1.2 formations contain dolomite (-quartz) pseudomorphs after evaporite in mm-to cm-size concretions (Fig. 5A, C).

3.2.1.1. Monomictic breccias related to R.A.T. blocks. R.A.T. blocks, and particularly m-thick zones at the borders of the blocks, are marked by: (1) frequent variable open hydraulic-like fractures that brook the rocks into fragments and are accompanied by dolomite infilling voids and fractures; and (2) some sheared zones with joints filled by a fine chlorite matrix. The open (hydraulic-like) fractures show an evolution from fractures into monomictic cm-up to dm-size breccias (Fig. 6A, B, C). The latter is characterized by Fig. 4. Vertical section X:þ150 through the megabreccia and the Luiswishi deposit angular to sub-rounded almost similar mm-to dm-size recogniz- along the drill hole LSW-1302; position of the other drill holes. The contour of the able R.A.T. fragments, lack of powder-size fragments, weak blocks are extrapolated on the principle of abrasion and attrition during transportation. displacement of the fragments, and dolomite cementation. Monomictic R.A.T. breccias show also more heterometric mm-to dm-size fragments, variably to well rounded, and locally fluidized through the megabreccia (Figs. 3 and 4). On that section, the rocks along the borders and in between the R.A.T. blocks. They are are affected by supergene oxidation down to 61 m-deep. The suc- commonly called “R.A.T. breccia” in the local geology. cession shows several m-size blocks or megablocks of R.A.T. (R-1), Mines (R-2) and Dipeta (R-3) lithologies, separated by breccias or 3.2.2. Mines block-1 (Luiswishi deposit) brecciated formations (Table 2). The contact with the underlying The Luiswishi Cu-Co deposit consists of large fragments of fol- Mongwe and Kiubo formations has not been reached. ded formations of the Mines Subgroup (R-2) that form an ~1200 m- 82 J.L.H. Cailteux et al. / Journal of African Earth Sciences 140 (2018) 76e93

Table 2 Description of the megabreccia lithologies observed in the 600-m deep hole LSW-1302 drilled on cross-section X: þ150 at Luiswishi.

from - toUNIT LITHOLOGY Dip Style 2.7 - 61.2 purple-grey argillaceous-talcose wheathered rocks (cungs) hydraulic & R-1.3 massive purple-grey to pink dolomic more or less argillaceous siltstone; open fractures sheared 61.2 - 69.8 (R.A.T. block-1) filled by dolomite, locally sheared with fine chlorite in joins fracturing unsorted almost similar mm- to dm-size grey to pinkish sub-angular to sub-rounded monomicic hydraulic 69.8 - 73.5 fragments typical from the above and below R.A.T. 1.3 blocs, in a dolomite cement; weak R-1.3 breccia breccia displacement of the fragments; lack of powder-size fragment R-1.3 massive purple-grey to pink dolomic more or less argillaceous siltstone containing hydraulic 73.5 - 78.4 (R.A.T. block-2) dolomite (-quartz) pseudomorph aer anhydrite cm-size concreons fracturing unsorted almost similar mm- to dm-size grey to pinkish sub-angular to sub-rounded monomicic hydraulic 78.4 - 82.3 fragments typical from the above R.A.T. 1.3 bloc, in a dolomite cement; fragments weakly R-1.3 breccia breccia displaced; lack of powder-size fragments R-2 from top to boom: Dolomic Shales (SD2d, SD3a, SD3b upper units) and Kambove (R-2.3.1 ± 82° (Mines block-1 brile fracturing 82.3 - 158.9 lower unit) Formaons of the southern flank; Kambove, Dolomic Shales, Kamoto and RAT- & or Luiswishi aer folding Grises formaons of the northern flank; axial fault at ± 40°SW ± 32° deposit) polymicc R-1 unsorted mm- to cm-size fragments from R-1.1 & R-1.2 formaons in a brownish dolomite hydraulic & 158.9 - 160.6 & R-2 breccia cement; few R.A.T. Grises fragments at the contact with the R-2 bloc sheared breccia R-1.2 (≥ 19 m-thick): pinkish-red to purple-grey bedded dolomic siltstone with mm- to cm- thick greyish coarse to fine sandy beds; specular hemate or occasional red (iron-rich) mm- 160.6 - 194,6 ± 55° size rounded patches within the sandy beds; dolomite (-quartz) pseudomorph aer evaporite locally in the siltstones hydraulic & R-1.2/1.1 sheared (R.A.T. block-3) R-1.1 (≥ 61 m-thick): to the top, predominantly purple-grey, somemes pinkish-red, foamy bedded, banded or massive argillaceous slightly dolomic siltstones, with occasional red fracturing 194,6 - 290,1 (iron-rich) mm- to cm-size rounded patches; to the boom, reddish-brown to pinkish, pale ± 50° yellow, or grey to dark-grey (Mn-rich) siltstones with "moutonné" bedding; specular hemate and dolomite pseudomorph aer evaporite polymicc R-1 unsorted mm- to mul cm-size fragments from R-1 & R-2.3 (Kambove Fm) lithologies in a sheared 290,1 - 295.4 & R-2 breccia brownish dolomite cement, locally mixed with a pinkish R.A.T. fine matrix breccia R-2 block-2 variably carbonaceous laminated dolomites with laminated stromatolites and microalgal 25° - brile fracturing 295.4 - 381.1 (Kambove Fm) deposions (R-2.3.1.2), massive beds and talcose dolomite beds (R-2.3.1.3) 55° aer folding unsorted mm- to cm-size sub-rounded to sub-angular R-1 (pinkish siltstone), R-3 (greyish- polymicc R- white dolomite and pale greenish siltstone) fragments in a fine greenish matrix of siltstone sheared & 381.1 - 411.5 1 & R-3 or in a whish to brownish dolomite cement; mul m-size blocks of fractured R-1, hydraulic breccias breccia monomicc R-1 breccia and R-3 dolomite and siltstone beds R-1.3 bl.-4 & massive to bedded pinkish to purple-grey dolomic siltstone R.A.T. 1.3 block; variably 55° - Hydraulic 411.5 - 464.4 monomicc intense fracturing filled by whish dolomite; rocks at both upper and lower borders of the 65° breccias c breccia complex

breccias block are discoloured on several m-thickness polymicc unsorted mm- to cm-size mostly sub-rounded fragments of pinkish pale to greenish pale sheared & partly 464.4 - 464.5 R-1 & R-3 discoloured siltstones from R.A.T. and Dipeta Subgroups in a fine matrix of the same polymic hydraulic breccia breccia lithologies and a dolomite cement predominantly massive whish to greyish dolomite showing locally cavies and geodes with 464.5 - 494.2 brownish Fe-carbonate crystals, and alternang with minor dm- to m-size greyish-green brile fracturing R-3.2 (Dipeta) siltstone beds; brile fractured and breccied in dolomite beds; 45°- fractured & bedded to unstructured grey to bluish grey sandy siltstone marked locally by lencular or hydraulic & 494.2 - 579.9 65° sheared block nodular dolomite (-quartz) pseudomorph aer evaporites concreons sheared in predominant greyish green massive siltstone alternang with dm- to m-thick whish siltstones 579.9 - 600.0 dolomite interbeds; shearing zones and breccied rocks or breccias

long and ~260 m-deep, E-W trending and north-verging tight iso- units of the Kambove dolomite Formation; and (2) in the lower clinal synform structure, with an axial plane dipping ~40 SW northern flank a stratigraphically downward succession from the (Cailteux et al., 2003, 2004, Fig. 4). The folded structure was Kambove Formation up to the base of the Kamoto Formation affected by axial and several transversal brittle fault zones that (Table 1). The hinge line of the fold is located within the Kambove fragmented the deposit. The Mines Subgroup in borehole LSW- Formation, that forms the core of the synclinal structure. Mines 1302 comprises: (1) in the upper southern flank, the Shales Dolo- Subgroup rocks are marked by brittle fractures and related brec- mitiques (SD) Formation (from SD2d up to SD3b), followed by basal ciation, filled by dolomite which has been later recrystallized. J.L.H. Cailteux et al. / Journal of African Earth Sciences 140 (2018) 76e93 83

Fig. 5. R.A.T. Subgroup block-3; A (Core 865 at 265.9 m, Box 57), B: (Core 889 at 272.0 m, Box 58), C (Core 894 at 273.4 m, Box 58) and D (Core 903, 275.8 m, Box 59): siltstones of the R.A.T. 1 unit variably reddish (with Fe-rich pigment) and purple-to dark-grey (with Mn-rich pigment); fleecy (moutonne) bedding (B, C, D), occurrences of pseudomorph after evaporite concretions (A, C) and red (iron-rich) to discoloured mm-to cm-size rounded oolite/pisolite-like patches (B).

Fig. 6. R.A.T. block 2 (Cores 429e447, 172.3e177.2 m, Box 35) showing hydraulic fracturing filled by whitish dolomite (A), that evolved into monomictic R.A.T. breccias (B) and into heterometric breccia with variable up to sub-rounded fragments (C). 84 J.L.H. Cailteux et al. / Journal of African Earth Sciences 140 (2018) 76e93

External zones on both flanks are affected by shearing and related greyish to whitish Dipeta dolomites, and greenish Dipeta siltstones; fracturing. A polymictic breccia occurs between the Mines Sub- (2) a fine matrix with R.A.T. and/or Dipeta siltstone like material; group blocks and the underlying R.A.T. block-3, composed of un- and (3) a cement of whitish to greyish, pinkish or brownish dolo- sorted mm-to cm-size fragments from these R.A.T. lithologies in a mite (Fig. 8A and B). The fragments in the breccia are unsorted. brownish dolomite cement. The R.A.T. Grises member occurs as Pyrite porphyroblasts (up to cm-size) occur within the Dipeta mm-to cm-sized fragments along the contact with the Mines block. siltstone fragments. Locally, on other sections, R.A.T. Grises and red-grey-green varie- The breccia complex also contains: (1) a ~7 m-thick Dipeta block gated R.A.T., that contain evaporitic relicts, occur in the transition consisting of predominant whitish to greyish dolomite and pale- between the Mines and R.A.T. subgroups. greenish dolomitic siltstone beds; (2) a ~11 m-thick block of R.A.T. siltstones with m-thick zones of open hydraulic-like fractured 3.2.3. Mines block-2 and related overlying polymictic breccia R.A.T. and related monomictic breccia on both sides of the block; (3) A second block with Mines Subgroup lithologies follows a 2.4 m-thick monomictic R.A.T. breccia block (Fig. 8C); (4) a ~50 m- downward, and comprises the lower R-2.3.1 unit of the Kambove size R.A.T. block-4 at the bottom, composed of massive to bedded Formation. At both margins of the block, the dolomite rocks appear dolomitic R.A.T.-type siltstones, with more or less intense open variably deformed, i.e. sheared and fractured (~1 m-thick zone) hydraulic-like fracturing and several m-thick monomictic breccias with fragments cemented by a whitish dolomite. A polymictic with weakly displaced R.A.T. fragments, cemented by dolomite at breccia forms the transition with the overlying R-1.1/R-1.2 block-3. the upper margin. Rocks at both upper and lower margins of the This breccia shows a variable distribution of pinkish R-1 and block are discoloured over a thickness of several meters. greyish R-2.3.1 fragments, and a hydraulic R.A.T. breccia in the A ~10 cm-thick polymictic breccia with mm-to cm-size dis- damage zone. Fragments are cemented by a brownish to greyish coloured siltstone fragments, mostly sub-rounded, but flattened/ dolomite locally accompanied by a fine matrix of pinkish R.A.T. stretched, more or less oriented parallel to shearing, originating material (Fig. 7A and B). The fragments are irregular, sub-angular to from R.A.T. and Dipeta lithologies, marks the transition between sub-rounded, elongated/stretched and oriented parallel to shear the R.A.T. block-4 and the succeeding Dipeta Subgroup (Fig. 8D). structures (Fig. 7C). The Kambove dolomite fragments most likely Fine siltstone and dolomite grains occur in between the fragments, occur close to the contact with the Mines block. This breccia locally all of them being cemented by a brownish to whitish dolomite. shows discoloured zones and a structure suggesting fluidization (Fig. 7C1 and C2). 3.2.5. Dipeta Subgroup and related breccias Below the polymictic breccia complex, a 135 m-thick succession 3.2.4. Polymictic breccia complex with Dipeta R-3.2 lithologies extends up to the bottom of the hole. A ~83 m-thick polymictic breccia occurs below the Mines block- A first unit comprises predominantly whitish to pale-greyish 2 and consists of: (1) mm-to cm-size sub-angular to well-rounded massive dolomites alternating with dm-to m-size greyish-green elongated fragments of more or less discoloured R.A.T. siltstones, siltstone beds. The carbonate locally shows cavities and

Fig. 7. Polymicitic breccia between the R.A.T. (R-1.1 Formation) of block-3 and the Mines Subgroup block-2 (from 290.3 up to 295.4 m, Boxes 62 & 63). A (Core 971) and B(Core 977): breccia with R.A.T. and Mines fragments, predominantly stretched, and oriented parallel to shearing; hydraulic R.A.T. breccia in the damage zone and possible fluidization of the breccia(A); dolomite cement. C (Core 986): polimictic breccia close to the Mines block-2; irregular pinkish R.A.T. and grey Mines/Kambove (K) fragments, zones discoloured by fluids (DZ) and shearing shown by direction-signs; the structure suggests fluidization. J.L.H. Cailteux et al. / Journal of African Earth Sciences 140 (2018) 76e93 85

Fig. 8. Polimictic breccia complex between Kambove Formation of the Mines block-2 and the Dipeta block. A (Core 1412, 381.2 m, Box 79): polymictic breccia at the contact with the Kambove Formation (K) of the Mines block-2 and the R.A.T. block-4 showing sub-angular to sub-rounded fragments from R.A.T. and Kambove lithologies. B (Core 1556, 410.2 m, Box 83): polymictic breccia with sub-to well-rounded fragments from R.A.T., Kambove and Dipeta lithologies; chaotic orientation of the fragments; fine matrix of Dipeta siltstone like material. C (Core 1539 at 407.6 m, Box 83): hydraulic-fractured monomictic breccia with sub-angular to sub-rounded R.A.T. fragments; white dolomite cement. D (Core 1892, 464.4e464.5 m, Box 92): Polymictic breccia at the contact between R.A.T. block-4 and the succeeding Dipeta Subgroup; mm-to cm-size fragments of pinkish pale to greenish pale siltstones from R.A.T. and Dipeta lithologies, in a matrix of fine siltstone or dolomite grains and an admixture of brownish to whitish dolomite cement. crystallised geodes. The succession is marked by brittle fracturing (Table 2): (1) post-folding rupture in Mines Subgroup competent and by several dm-to m-size monomictic or polymictic breccias rocks; (2) hydraulic; and (3) ductile in R.A.T.-Dipeta soft incompe- with sub-angular to sub-rounded fragments originating from the tent siltstones. surrounding Dipeta dolomites and siltstones, cemented by a The fracturing in R.A.T. and Dipeta rocks shows hydraulic-like whitish to brownish carbonate. The siltstone beds are marked by ruptures, evolving into an in-situ opening of the rocks, and brec- sheared monomicitic breccias with mm-to cm-size more or less ciation with little displacement of the fragments. This mechanism deformed fragments, fine grained siltstone and dolomite matrix, frequently results from an important increase of the fluid pressure and a whitish to brownish dolomite cement. A second Dipeta unit in weakly permeable rocks, followed by a sudden decompression of consists of bedded to massive grey to bluish sandy siltstone char- the fluid that produces a fluid-assisted monomictic breccia (cf. acterised by frequent open hydraulic-like fracturing of the rocks Jebrak, 1992, 1997). Decompression of the fluid could have caused evolving into breccias with sub-angular to sub-rounded fragments ( the precipitation of the dolomite that fills the open fractures and Fig. 9A and B). Both fractures and breccias are cemented by a voids. The increasing rounding and heterometric-size distribution whitish to brownish dolomite. The rock locally contains nodular or of the fragments in these monomictic breccias suggest movement, lenticular dolomite concretions that are interpreted as pseudo- mixing and abrasion (may be with some dissolution). morphs after evaporites ( Fig. 9 B and C). Some siltstone beds show The ductile fracturing, mostly observed within the Dipeta rocks, lustrous surfaces, shearing and locally fracturing that locally clearly indicates sheared zones with monomictic and polymictic evolved into dm-to m-scale monomictic breccias ( Fig. 9 D and E). breccias. The fragments in these zones show an irregular outline These breccias consist of mm-to cm-size sub-angular to sub- and are commonly elongated with an orientation parallel to the rounded Dipeta siltstone fragments embedded in a fine siltstone shearing. matrix, likely produced from abrasion of the rock, and mixed with a The rounding of the fragments in the polymictic breccia is at minor dolomite cement. . The third unit is composed of predomi- least partly interpreted as the result of abrasion during trans- nant greyish-green siltstones alternating with dm-to m-thick portation, a process which also produced the fine material forming whitish dolomite beds. Some zones are marked by sheared to the matrix of the breccia (Jebrak, 1992, 1997). Orientation of the brecciated rocks, and recrystallization of dolomite and dark green fragments is chaotic, and no bedding or fining-upward sequences chlorite. have been observed in these breccias, excluding sedimentation related to fluviatile or marine activity. Such type of breccia is commonly called “friction breccia” (cf. Jebrak, 1992, 1997). 3.2.6. Interpretation In contrast to the incompetent R.A.T. and Dipeta rocks that were Three types of fracturing have been identified at Luiswishi 86 J.L.H. Cailteux et al. / Journal of African Earth Sciences 140 (2018) 76e93

Fig. 9. A (Cores 2326, 2330, Box 106): hydraulic-fractured bluish-grey siltstones of the Dipeta Subgroup evolving into breccia; whitish to brownish dolomite filling the fractures and breccied zones. B & C (Cores 2331 & 2333, Box 106): Dipeta siltstone showing nodular or lenticular dolomite concretions probably pseudomorphs after evaporites. D & E (Core 2174, 520.5 m, Box 101 & Core 2425, 571.7 m, Box 109): Dipeta siltstones fractured into breccia with mm-to cm-size sub-angular to sub-rounded fragments embedded in the same siltstone matrix like material. hydro-fractured and sheared, the competent Mines rocks show solitary inclusions have been identified and distinguished. A remarkable folded structures and post-folded brittle fracturing. microthermometric analysis of the fluid inclusions has been carried with a Linkam MDS heating-cooling stage mounted on an Olympus 4. Petrographic and fluid inclusion studies of breccias and BX51 microscope, at the Department of Earth and Environmental brecciated rocks Sciences of the KU Leuven. The stage is calibrated with synthetic fluid inclusions of CO2,H2O-NaCl, H2O-KCl and H2O, purchased 4.1. Methodology from SYN FLINC. Accuracy of the measurements is within 0.2 C for temperatures below room temperature (20 C) and 1 C for tem- Detailed macroscopic and microscopic description of different peratures above it. breccias and brecciated rocks focussed on 30 core samples from the drillholes LSW-1216 (X:þ100), LSW-1311 (X:þ300) and LSW-1314 4.2. Results (X:þ150; Fig. 4), in order to characterize their fragments, matrix and cement. Among these samples, 15 are brecciated Mines rocks Two major generations of dolomite are observed in the exam- and breccias (monomictic or polymictic) and carbonate-filled ined breccias and brecciated rocks. They cross-cut and thus post- fractures in the Luiswishi deposit, 11 represent brecciated or frac- date dolomitization of the matrix rock. Dolomite-I shows a red, tured R.A.T. and monomictic R.A.T. breccia, and 4 are from poly- orange to yellow luminescence. Dolomite-II has a yellow lumines- mictic R.A.T.-Mines breccias. Staining of samples, by using Alizarin cence and overgrows the first generation, post-dating it (Fig. 10). red and K-Ferrocyanide (Dickens, 1966), revealed that the carbon- Greyish fine-grained dolomite generation-I occurs as: (1) phase ate of the clasts, matrix or cement is an Fe-poor dolomite. Different Ia, probably formed before brecciation within the nodules or con- carbonate cement phases have been further distinguished by cold cretions of evaporitic origin; and (2) phase Ib, probably formed at cathodoluminescence petrography using a Cold Cathodo Lumi- the first stage of brecciation at the border of the rock fragments. nescence Model 8200 Mk II combined with a Nikon microscope and Generation-Ib that constitutes the matrix, has partially been a ProgRes C10 image capturing system. Operational conditions replaced by a coarse-grained white to brownish dolomite were between 9.5 and 10.5 kV and 300e400 mA. generation-II. The transition between dolomite-I and dolomite-II is A fluid inclusion study has been performed on five samples from marked by a phase of fracturing. Based on the colour zonation the LSW-1216 & -1314 drill holes (PM02, -07, -12, -37, -40). Six observed under cathodoluminescence, dolomite-II shows five doubly-polished sections with a thickness between 200 and phases of crystallization (-IIa up to -IIe), and is associated with 300 mm have been prepared from the dolomites cementing the authigenic quartz. A second fracturing event affected dolomite-IIa breccia fragments in the RAT and Mines subgroups. The wafers & -IIb, filled by the next three dolomite phases (II-c up to II-e). were firstly examined during a petrographic study on an Olympus Besides these two dolomite generations, a very fine-grained BX60 microscope. During this study inclusions occurring in fluid greenish to brownish dolomite (III) occurs along dislocating joints inclusion assemblages (sensu Goldstein and Reynolds, 1994)oras within the R.A.T. rocks after a third fracturing event. Dolomite-III J.L.H. Cailteux et al. / Journal of African Earth Sciences 140 (2018) 76e93 87

Fig. 10. First dolomite generation with a red luminescence is overgrown and post-dated by the second dolomite generation with a yellow to light brown luminescence. Sample LS11PM12. probably results from the crushing and recrystallization of Post-fracturing sulfide spots occur as cm-size grains within the dolomite-I and -II during shearing. This dolomite underwent an dolomite-I and -II, filling the fractures of the rocks and breccias. alteration into clay, suggesting an input of Si and Al. This clayey Sulfides do not occur in monomictic R.A.T. breccias. material contains relics of earlier dolomites-I and -II. Fine-grained The fluid inclusions in dolomite generation-I was studied in two clayey material also occurs around recrystallized dolomites-I and brecciated rocks from the Mines Subgroup. They are characterized -II. by an aqueous liquid and a vapour phase and up to two solids can In both monomictic and polymictic Mines breccias, the pre- occur (Fig. 11kA and B). The solids have been identified by their fracturing Cu-Co sulfide mineralization occurs within the Mines habit and reflectance as anhydrite and halite. The vapour phase can fragments as disseminated grains within bedding parallel layers fill 15e20% of the inclusion, anhydrite ~10% and halite 15e20%. The and as larger crystals within the evaporitic nodules or concretions. rather constant filling ratio indicates that the solids are daughter

Fig. 11. A & B: four-phase fluid inclusions in the first dolomite generation cementing the breccia in the Mines Subgroup; 1 vapour, 2 liquid, 3 halite, 4 anhydrite. C & D: two-phase fluid inclusions (liquid and vapour) in the second dolomite generation cementing the breccia in the RAT. 88 J.L.H. Cailteux et al. / Journal of African Earth Sciences 140 (2018) 76e93 minerals and that the inclusions are indeed co-genetic. The size of appears in some originally one-phase inclusions after cooling the the inclusions studied varies between 10 and 30 mm. A total of 90 wafer at 20 C for two weeks. 67 inclusions were measured in fluid inclusions were measured in this dolomite-I. Depending on dolomite-II. The homogenization temperature varies between 91 the amount of solids present, two or three temperatures were and more than 280 C. Freezing of the inclusions took place measured: anhydrite dissolution Ts(CaSO4), halite dissolution around 38 C. The temperature of first melting is observed Ts(NaCl), homogenization (Th) of the liquid and vapour phase, and between 21.1 and 4.2 C; one value reached 25 C. Final decrepitation (Td) of the inclusions. Decrepitation of an inclusion melting of ice mainly occurred between 0.3 and 2.4 C. Four means that it explodes or leaks during heating before homogeni- values plot between 6.3 and 9 C. sation of the inclusions or even before total dissolution of a daughter mineral. Anhydrite dissolution has been measured be- 4.3. Interpretation tween 80 and 180 C and halite dissolution between 72 and 291 C. All inclusions decrepitated before homogenization of the liquid and Since NaCl and CaSO4 are present as solids in the aqueous fluid vapour phase. Decrepitation took place between 200 and more inclusions in dolomite generation-I, the inclusions have a H2O- than 300 C. NaCl-CaSO4 composition. An estimation of the salinity of the in- The fluid inclusions in dolomite generation-II were studied in clusions is based on the dissolution temperature of the halite two samples from the R.A.T. breccias. They consist of one aqueous crystals by using the empirical formula proposed by Sterner et al. liquid phase or of an aqueous liquid and vapour phase (Fig. 11C and (1988) for a simplified H2O-NaCl system. The calculated salinity D). The vapour phase fills ~15% of the inclusion. The size of the varies between 27.5 and 31.1 wt% NaCl with two outliers of 36.3 and inclusions studied varies between 20 and 45 mm. A vapour bubble 37.5 wt% NaCl (Fig. 12A), all values represent a high salinity fluid.

Fig. 12. A: salinity versus decrepitation temperature of the three- and four-phase inclusions in the first dolomite generation recognized in the breccia. B: salinity versus ho- mogenization temperature of the two-phase inclusions in the second dolomite generation present in the breccia. J.L.H. Cailteux et al. / Journal of African Earth Sciences 140 (2018) 76e93 89

The temperature of fluid homogenization could not be measured. conformable stratigraphic transition marked by pseudomorphs However the decrepitation temperatures above 200 C suggest after evaporite concretions has been observed between the R.A.T. relatively high values for this homogenization. (R-1.3) and Mines (R.A.T. Grises) formations (Cailteux, 1978a, 1994; The temperature of first melting between 21.1 and 4.2 Cin Cailteux et al., 2005a). Polymictic breccias occur between blocks of the inclusions of dolomite generation-II indicates the fluid in- different nature, with similar features to those described at clusions have a H2O-NaCl composition. The temperatures observed Luiswishi. above the eutectic of 21.2 C of this system are due to the low The megabreccia overlies the 10e15 southwards dipping Kiubo salinity of most inclusions, and the very small amount of liquid and Mongwe formations with a contact consisting of an up to 1 m- formed at the eutectic temperature. Final melting temperatures of thick polymicitic breccia that contains a mix of mm-to cm-size up ice (Tm-ice) are between -0.3 and -2.4 C, and correspond to a to well-rounded or stretched, Roan and Mongwe-Kiubo fragments, salinity between 0.5 and 4.0 wt% NaCl (Bodnar, 1993). The lower called “breche de fond” by local geologists (François, 1973; Cailteux temperature between -6.3 and -9 C indicate a range of salinity and Kampunzu, 1995). between 9.6 and 12.8 wt% NaCl (Fig. 12B). The homogenization The Kundelungu rocks that underlay the megabreccia are temperatures show a wide range between 91 and 280 C. The fact marked by layer-parallel shearing and brecciated rocks at the that such a wide range even occurs in one assemblage reflects contact with the megabreccia. The northern part of the mega- stretching or leakage of the fluid inclusions. Therefore, a minimum breccia is composed of brecciated Dipeta and Kundelungu rocks. temperature of 91 C could be proposed. In the same area, other comparable megabreccias containing Roan, Nguba and Kundelungu blocks occur along thrust nappe 5. Comparison with other major Katangan megabreccias fronts (e.g. at Kabolela, Kakanda, Kakanda-Ouest) or are pinched out between Nguba-Kundelungu sub-nappes (e.g. at Sesa and 5.1. Kambove area Kamfundwa; François, 2006).

The Kambove megabreccia is part of a more than 100 km long 5.2. Kolwezi area thrust nappe oriented NW-SE in the same tectonic alignment as this of Kimpe-Luiswishi (Fig. 1). It forms a ~6 km long and up to In the Kolwezi area, three nappes of megabreccia occur (Kol- ~2 km wide structure pushed upon the Kiubo and Mongwe for- wezi, the Five-Klippes, and Tombolo), overlying rocks of a folded mations by a Nguba-Kundelungu thrust pile that includes the Kundelungu succession (Figs. 1 and 14). To the northwest, the Mwashya Subgroup and part of the Kansuki Formation at the bot- Katangan rocks are in contact with the SW-NE oriented basement tom (Table 1). The thrust succession is dipping ~35 south and through a basal conglomerate, and has been interpreted as an extends southward as a vast antiform-synform folded structure autochthonous succession (François, 1973, 1987). In this hypothesis, called “Kambove anticline” (François,1987, 2006). This megabreccia these megabreccias are considered as relics of a unique thrust is one of the best explored in the area, especially by deep boreholes nappe, pinched out from the Kansuki fault at the south, and partly drilled up to the basal thrust contact (Fig. 13). It contains up to km- covering the autochthonous Kundelungu-Nguba pile to the north. size folded and fractured megablocks mostly with R.A.T., Mines, However, deep drilling crossing the Mamfwe anticline demon- Dipeta and Mwashya formations lithologies. Hydraulic and post- strated that at least the eastern part of the supposedly autochtho- folding fracturing characterize the R.A.T. and Mines blocks, nous terranes belongs to a thrust nappe (Cailteux, 1991). respectively, both filled by dolomite cement similar to that at The Kolwezi megabreccia is a ~24 km long and up to ~9 km wide Luiswishi (Cailteux, 1978a; Cailteux and Kampunzu, 1995). R.A.T. structure overlying mostly rocks of the Kiubo Formation (Kunde- lithologies and monomictic R.A.T. breccias occur mostly along the lungu Group), and reaching locally a depth up to ~1200 m in contact with basal Mines formations (e.g. for the Kambove-Ouest exploration drill holes. As at Kambove, a polymictic friction breccia Cu-Co deposit). At the Kamoya-Sud-2 deposit, however, a (the so-called “breche de fond”) occurs at the base of the

Fig. 13. Vertical cross section X:0 through the Kambove-Ouest deposit and Kambove megabreccia (modified from Cailteux, 1986); projection of the drill hole KW-240 and sug- gestion of the basal thrust fault. 90 J.L.H. Cailteux et al. / Journal of African Earth Sciences 140 (2018) 76e93

Fig. 14. Geological map of the Kolwezi area (modified from François, 1973, 2006). Thrust fault lines suggested from the current cross sections for the megabreccias at Kolwezi (François, 1973) and the Five-Klippes (Ilunga & Cailteux, in prep.). megabreccia (François, 1973). Underground observations along 6. Discussion mining infrastructures at ~630 m depth below the Kamoto deposit (Kolwezi area) revealed the presence of hundreds of meters poly- The fragments, blocks and megablocks in the megabreccias mictic breccia with Roan and Kundelungu blocks intersecting the derive mainly from the Roan stratigraphy (R.A.T., Mines, Dipeta), Kundelungu rocks, which could represent the roots of the mega- and less commonly from the neighbouring Mwashya-Nguba- breccia (Cailteux in François, 1993). Isohypse lines drawn by the Kundelungu successions. Tectonic ruptures in the stratigraphy underlying formations of the Kundelungu Group and the sub- were attributed to: (1) the contrasting competencies of rocks concentric orientation of the faults network inside the mega- affected by the tectonic deformation and the expulsion of abundant breccia, evidenced by the surface map and cross sections (François, fluids from the incompetent R.A.T. and Dipeta subgroups (Cailteux 1973; Placet, 1976 in Cailteux, 1991), suggest that the Kolwezi and Kampunzu, 1995); and (2) the dissolution of evaporites whose megabreccia has been pinched out along a thrust-fault with a 75 occurrence has been evidenced within the transitional beds be- SW-NE orientation (Fig. 14). The extrapolation of this thrust-fault tween formations of the R.A.T., Mines and Dipeta subgroups, and from the cross sections suggests a lateral strike-slip movement in supposed at the base of the R.A.T. and at the top of the Dipeta agreement with the third (or D2) compressive stage (Kampunzu (Cailteux, 1994; Cailteux and Kampunzu, 1995). The present study and Cailteux, 1999; Kipata et al., 2013). The in-situ pinching out highlights the importance of hydrofracturing in the R.A.T. and hypothesis is supported by recent drilling in the Five-Klippes area Dipeta subgroups, suggesting compression and a related fracturing (Fig. 14), that cross-cut roots of the megabreccia (Ilunga & Cailteux, of the rocks. Compression is also supported by the folding and in prep.). Such a setting is comparable to the structure occurring fracturing of the Mines Subgroup which shows blocks and mega- along the Sesa-Kamfundwa-Shangulowe alignment. Consequently, blocks variably preserved in the megabreccias as synformal or the whole Kundelungu-Nguba pile north of the Kansuki fault antiformal structures. Such evidences of compressive processes do probably forms a folded and dislocated thrust nappe, as in the other not support the olistostrome hypothesis. areas of the folded arc. This interpretation is in agreement with The presence of high salinity fluids within the KCB have been sinistral strikeslip faulting along the basement at the north- observed by several researchers. Pirmolin (1970) already recog- western margin of the Lufilian Arc (Unrug, 1983). nized the presence of high salinity three- and four-phase inclusions As in other areas, the Kolwezi megabreccia contains Cu-Co de- at Kamoto. El Desouky et al. (2009, 2010) described a high salinity posits hosted in folded and brittle-fractured structures of the Mines (>35 eq. wt% NaCl) and high temperature (>270 C) fluid that Subgroup (e.g. Kamoto, Dikuluwe-Mashamba, Musonoï). As indi- caused the syn-orogenic part of the “hydrothermal” Cu-Co miner- cated by the surface map and cross sections (François, 1973), these alization and enrichments. Circulation of these fluids was respon- structures are aligned more or less parallel to the E-W/60 SW-NE sible for the formation of high-grade ore deposits, including orientation of the thrust nappe, and show symmetric stratigraphic Luiswishi, and could have caused the discolouration of the rocks at successions on both sides of the axial zone of the nappe in agree- the margin of the blocks and within the breccias as observed at ment with the in-situ pinching out hypothesis (Placet, 1976 in Luiswishi. These high salinities were also measured on three- and Cailteux, 1991). four-phase inclusions with anhydrite and halite as solids identified J.L.H. Cailteux et al. / Journal of African Earth Sciences 140 (2018) 76e93 91 at room temperature. In addition, the post-orogenic world-class Fungurume, Luiswishi), indicate a non-chaotic displacement that Cu-Zn deposit at Kipushi formed from a high salinity (30e43 wt% could not result from mass gravity flows as explained in the olis- NaCl) and high temperature (190e340 C) fluid (Heijlen et al., tostrome hypothesis. Similarly, the concentric alignment of the 2008). The first generation of dolomite cement recognized in this Mines Subgroup structures in the Kolwezi megabreccia cannot be study, which is mineralized in chalcopyrite, bornite and carrolite, explained by this model. has similar fluid characteristics as the late diagenetic to syn- The polymictic friction breccia “breche de fond” that overlies the orogenic mineralizing fluid studied by El Desouky et al. (2009, Kiubo and Mongwe formations at Kambove and Kolwezi, and 2010). The high temperatures are in agreement with the probably also in other areas, could correspond to the basal thrust- compressive hypothesis, and in contradiction with the olistostrome fault (Fig. 13), while the breccia complex at Luiswishi could indi- model. cate a major thrust-fault within the megabreccia (Fig. 4). Fluid inclusion data suggest that expelled fluids were charged in salts by the dissolution of the evaporitic material occurring within 7. Conclusions the Roan stratigraphy that contributed to trigger the dislocation of this sedimentary pile during the orogenic process. Concordant Results of the present study indicate that the process of for- collapse breccias as those only observed within the Mines Sub- mation of the megabreccias in the KCB is related to the Lufilian fold- group (Cailteux, 1978b; 1994), are part of the folded structures, and and-trust events, and is characterized by brittle fracturing after therefore were probably formed in early stages, before folding and folding, hydraulic fracturing and ductile shearing, that resulted fracturing of the Mines Subgroup. from intense compression at estimated burial depth up to at least The friction breccias between the blocks show that the nature of 2.8 km. This process caused the liberation of the fluids, a mega to the fragments is changing from one place to another, reflecting the fine fragmentation of the rocks, friction and abrasion of the frag- neighbouring blocks. These breccias also support compression ments, and the precipitation of dolomite in the voids after during transportation, being marked by shearing and abrasion of decompression. Formation of the breccias mostly affected the the fragments resulting in production of a fine material that formed R.A.T., Mines and Dipeta (partly evaporitic) rocks, and probably part of the matrix. significant water expulsion occurred in these rocks during The salinity of the second dolomite generation, observed as a compression. Compression-rupture-decompression cycles during late stage of brecciation at Luiswishi, mainly varies between thrusting, and fluidization within the brecciated rocks could also meteoric water (0 wt% NaCl) and sea water (3.6 wt% NaCl). This have contributed to formation of the megabreccias. Fluidization suggests that the ambient high salinity fluids have been diluted by facilitated the transport of the blocks within the megabreccias, the an input of meteoric water. The addition of a low salinity, most pinching out (extrusion-like) of the latter between the Nguba- likely meteoric, water could have caused undersaturation of the Kundelungu sheets and along thrust-faults, and the injection of fluids with respect to the salts and hence their dissolution. The breccias into fractures of the blocks. temperature and depth of the incursion of the meteoric water is The thrusting event post-dated the deposition of the Mongwe difficult to determine due to the stretching and leakage of the fluid and Kiubo formations, that belong to the Katangan pile at the top of inclusions. However, if a minimum temperature of ~90 C, a surface the folded Kundelungu Group and form the basement of the thrust. temperature of 20, an average geothermal gradient of 25 C and The megabreccias form the base of the thrust nappes, and are thermal equilibrium between the host-rock and the fluid are locally marked by a basal thrust-fault (“breche de fond”) and by accepted, the minimum burial depth is calculated at 2.8 km. internal thrust-faults zones. Fluid extrusion and/or fluid dynamics can occur even with The available data and results clearly contradict and invalidate a relatively little evaporites, if these are undergoing increased pres- syn-orogenic sedimentary origin of the megabreccias as olistos- sure, as in a thrust sheet. The fluid behaviour with pressured trome formed by subaqueous conglomeratic debris flows and evaporites exaggerates any structural features, especially if there is clastic syn-orogenic sediments supplied into a foreland basin in an escape outlet for the fluids as it is the case when fracturing and front of north-advancing nappes. brecciation take place. The importance of the expelled fluids and of The model proposed in this work closely associates brecciation the evaporitic dissolution contributed to fluidization of the breccias with the thrust-and-fold events. The major contribution of fluids, into a paste-like consistence, facilitating the displacement of the either expelled during the burial of the sediment series or linked to nappes, pinching out of megabreccias (extrusion-like) along thrust- the dissolution of evaporites, in the brecciation process is recog- faults, and intrusion of the breccias in between the blocks or into nized. At a late stage of the deformation, the downward percolation their fractures. The penetration of meteoric under-saturated fluids of meteoric fluids down to ~2.8 km has further contributed to the at depth in late phases of the deformation/brecciation process, is an fluidization, physical transportation and injection of the breccias in important feature. It may have: (1) contributed to the dissolution of the weakness zones, hence contributing to a multi-phase breccia- residual evaporites, and also of the evaporitic material from the tion scenario. The importance of evaporites in the sedimentary Kiubo rocks at the base of the nappes; (2) led to further fluidization, series prior to its deformation is not yet fully known. However, even physical transportation of previously formed breccia; and (3) if fluidization associated to evaporite-solution is obvious, there is possibly caused late re-brecciation. Solution-collapse breccias after little evidence of salt tectonics/diapirism as proposed by De dissolution of supposed thick and widespread evaporitic material Magnee and François (1988) and Jackson et al. (2003), and partic- related to R.A.T. and Dipeta subgroups as suggested in the salt ularly of evaporite-megabreccia extrusions before the Lufilian tectonics hypothesis, if they occurred, have not been recognized. deformation. Brecciation is here regarded as the result of thrusting, even if there is an obvious contribution of evaporite solution processes in the Acknowledgements fluidization and transportation of the brecciated material, at several stages of the deformation. Gecamines and Forrest Group companies are acknowledged for Transportation of folded and brittle-fractured Mines Subgroup authorization and support in study and sampling of the Luiswishi megablocks as variably preserved synform or antiform structures in cores. We thank Herman Nijs for the careful preparation of the thin the megabreccia, with detached parts mostly displaced over sections and the doubly-polished thick sections, and to Damien generally short distances (from a few up to hundreds meters; e.g. at Delvaux for the updated figure 1. The authors are grateful to Michel 92 J.L.H. Cailteux et al. / Journal of African Earth Sciences 140 (2018) 76e93

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