Alteration and Ore Distribution in the Proterozoic Mines Series, Tenke-Fungurume Cu–Co District, Democratic Republic of Congo

Miner Deposita (2012) 47:501–519 DOI 10.1007/s00126-011-0391-2

ARTICLE

Alteration and ore distribution in the Proterozoic Mines Series, Tenke-Fungurume Cu–Co district, Democratic Republic of Congo

I. Fay & M. D. Barton

Received: 2 March 2011 /Accepted: 1 November 2011 /Published online: 27 November 2011 # Springer-Verlag 2011

Abstract Two sediment-hosted stratiform Cu–Co deposits Fungurume results both from original hypogene lithology- in the Tenke-Fungurume district of the Central African and contact-related precipitation and from supergene oxida- Copperbelt were examined to evaluate the alteration history tion, transport, and Cu–Co decoupling. The supergene fluid of the ore-hosting Mines Series and its implications for ore flow also redistributed gangue minerals such as dolomite, distribution and processing. Core logging and petrography, which has an economically important influence on the focused on lithology and timing relationships, outlined a processing costs of supergene ores. complex alteration sequence whose earliest features include formation of anhydrite nodules and laths, followed by Keywords Mines Series . Sediment-hosted deposits . Ore precipitation of dolomite. Later alteration episodes include distribution . Gangue acid consumption . Central African at least two silica introductions, accompanied by or Copperbelt alternating with two dolomite introductions into the existing gangue assemblages. One introduction of Cu–Co sulfides accompanied the last episode of dolomite alteration, over- Introduction printing an earlier generation of ore whose gangue association was unidentifiable. Sulfides and some carbo- The African Copperbelt, an arcuate band of Neoproterozoic nates were subsequently modified by supergene oxidation, sedimentary and metasedimentary rocks extending across the transport, and reprecipitation to 100–200 m depth. Present- southeastern Democratic Republic of Congo into northern day ore distribution resulted from these successive process- Zambia (Fig. 1a, b), contains some of the world’smost es. Ore is concentrated in two shale-dominated units on important but least-understood sources of copper and cobalt either side of a cavernous silicified dolomite, which is (Hitzman et al. 2005;Selleyetal.2005). Recent rejuvenation interpreted as the main conduit for the mineralizing fluids. of large-scale mining in the Congolese deposits has brought Sulfide ores precipitated at the redox or sulfidation contacts with it renewed need for research, particularly studies of the between this dolomite and the shales. Later, supergene fluids ore-bearing “Mines Series”. These strata host most of the dissolved and moved some of the metals, redepositing them as DRC’s (Democratic Republic of Congo) large, high-grade oxides and carbonates. Solubility differences between Cu and copper and cobalt deposits, but determining their timing and Co in supergene conditions caused them to precipitate their lithological relationships to ore and to later events has separately. Thus, modern ore distribution at Tenke- challenged researchers since the 1930s. The still-ongoing, 80-year debate over the origin of the ores (e.g., Bateman 1930;Darnley1960;Mendelsohn1961;Bartholoméetal. Editorial handling: H. Frimmel 1972;Annels1974; Selley et al. 2005) is one example of the : I. Fay (*) M. D. Barton capacity of the Mines Series to perplex and intrigue Department of Geosciences and Institute for Mineral Resources, geologists who study its deposits. University of Arizona, Although the origin of mineralization remains a key 1040 East Fourth Street, Building #77, Tucson, AZ 85721-0077, USA topic, others are also critical for mining interests in the e-mail: [email protected] DRC, especially ore distribution. Like the origin question, 502 Miner Deposita (2012) 47:501–519 this has been much studied and yet remains poorly McMoRan. In spite of its economic importance, published understood (e.g., Bain 1960; Dewaele et al. 2006). Many work on the Tenke-Fungurume district is limited to authors have attempted to quantify ore distribution patterns, Oosterbosch’s(1951) study of its sulfide mineralogy. The but have generally restricted their work to the deposit or present paper is intended to characterize the relationships district scale (e.g., Oosterbosch 1951; Bartholomé 1974; among stratigraphy, hydrothermal alteration, and distribu- Garlick 1989; El Desouky et al. 2010). This is partly because tion of hypogene and supergene ore minerals within two ore distribution in the Copperbelt is as much the result of deposits (Mambilima and Kansalawile) selected for their supergene alteration as it is of original ore precipitation structural simplicity and their wide variety of ore types, patterns, rendering it complex, difficult to characterize, and grades, and gangue mineralogy (Fig. 2). challenging to mineral exploration (e.g., Decrée et al. 2010). Field work involved detailed logging of 2,215 m of drill This project focused on two deposits in the Tenke- core at a 1:50 scale, supplemented by reconnaissance Fungurume district in the Democratic Republic of Congo surface observations along the cross section lines, in nearby (Fig. 1). Tenke-Fungurume contains one of the larger deposits, and elsewhere in outcrops of the upper Roan copper–cobalt resources in the African Copperbelt, with a stratigraphy. Samples collected for study were examined in reported reserve of 119 Mt of 2.64% Cu and 0.35% Co ore hand specimen and by petrographic examination of 37 (Freeport-McMoRan, 2009); one of the deposits within it polished thin sections. X-ray diffraction and Raman has recently been put into production by Freeport- spectroscopy were used to identify unknown minerals.

Fig. 1 Location maps for the Tenke-Fungurume district. a Simplified pattern of the Mines Series outcrops in the eastern Tenke-Fungurume structural map of southern Africa, modified from Kampunzu and district. Note that all orientation markings are schematic; dip, though Cailteux (1999). b Map of the Central African Copperbelt, modified not precisely measured, typically ranges from 30° to 60° from Kampunzu and Cailteux (1999). c Simplified depiction of the Miner Deposita (2012) 47:501–519 503

Fig. 2 Geologic maps and cross sections of the Mambilima and Kansalawile deposit in plan view (left) and cross section along the Kansalawile deposits. Top, the Mambilima deposit in plan view (left) 700 NE line (right). Dip angles marked on plan maps vary between and cross section along the 418300 line (right). Bottom,the 30° and 50°; precise measurements were not made

Geologic framework the Congo and Kalahari cratons of southern Africa (Selley et al. 2005;Fig.1). Following accumulation of these clastic to Regional context evaporitic sedimentary rocks in an extensional basin, compressional tectonism led to extensive deformation and related The African Copperbelt is hosted in the Neoproterozoic low- to moderate-grade metamorphism, particularly in the Katangan succession, a thick sedimentary sequence between Zambian area of the Copperbelt (Unrug 1988; Kampunzu and 504 Miner Deposita (2012) 47:501–519

Cailteux 1999). Nodules and laths pseudomorphing anhydrite (2003) also consider the Copperbelt a species of gigabreccia, indicate that the climate was arid during sedimentation but include the RAT among the clast material rather than the (Kirkham 1989;Muchezetal.2008). matrix and invoke salt tectonics as a mechanism for the Sedimentation in the basin was cyclical, beginning around deformation and northward movement. Even the date of the 880 Ma and alternating between carbonate- and clastic- Lufilian orogeny is disputed: 545–515 Ma (Porada and dominated layers (Annels 1984, 1989;Lefebvre1989; Porada Berhorst 2000), 750–600 Ma (Kampunzu and Cailteux and Berhorst 2000;Masteretal.2005). After deposition of 1999), or 650–600 Ma (Jackson et al. 2003). Metamorphism the Roan Supergroup, the lowest Katangan unit, sedimenta- accompanied deformation, with metamorphic grade decreas- tion continued in a separate basin, the northeast-trending ing from south to north (Selley et al. 2005). The Tenke- Kundelungu Aulacogen (Unrug 1988; Kampunzu and Fungurume district, located on the northern, outer fringe of Cailteux 1999; Porada and Berhorst 2000). The Lower and the arc, underwent only diagenesis and metasomatism, Upper Kundelungu Supergroups, also consisting of carbo- although tectonic deformation was extensive enough to fold nates and clastics, were deposited there (Fig. 3). and fault the district into the complex arrangements visible in After deposition, the Lufilian orogeny transported large plan view (Fig. 1c). Mambilima and Kansalawile are located rafts of the Katangan sediments to the north, eventually on the anticlinal segment of a syncline-anticline pair with generating the Copperbelt of today. The details of this north-dipping axial planes (Fig. 2). movement and deformation are the subject of much debate, hinging on the nature of the lowest Roan unit, the Roches Stratigraphy of the Mines Series Argilo-Talqueuses (RAT). Wendorff (2000)suggeststhatitis a synorogenic olistostrome comprising the matrix for the The stratigraphy in the Mines Series at Tenke-Fungurume is megabreccia that is the Copperbelt. In response, Kampunzu shown in Figs. 3 and 4. At the base is the RAT (Roches et al. (2005) propose that the RAT is a normal sedimentary Argilo-Talqueuses=clay–talc rocks). At Tenke-Fungurume, unit, formed in the same basin as the overlying Mines Series it has three subunits: an argillite–dolomite crackle breccia and in a normal lithostratigraphic relation to it. Jackson et al. (Woodcock and Mort 2008) of unknown thickness, overlain

Fig. 3 Simplified stratigraphic column of the Katangan Succession, modified from Cailteux et al. (1994), with inset (right) showing the Mines Series at Mambilima and Kansalawile. See text for meaning of abbreviations for rock units Miner Deposita (2012) 47:501–519 505

units; both consist of laminated shales and dolomites with the proportion of shale increasing upward, with total thickness typically 8–15 m. Together with the uppermost RAT, they comprise the “Lower Orebody” and host Cu–Co ores in veins, laminations, and nodules, locally reaching 15% Cu. Above them is the RSC (Roches Siliceuses Cellulaires=cellular [algal] siliceous rocks), originally an algal dolomite but everywhere intensely altered to a mixture of silica and dolomite. Mineralization renders it economic in some places, although Cu grade does not typically exceed 2–3%. The RSC is 20–25 m thick and is overlain by the SDB (Schistes Dolomitiques de Base=basal dolomitic shales), a well-laminated, iron-oxide-rich shale unit forming the “Upper Orebody”, sometimes called the “Black Ore Mineralized Zone”. About 10 m thick, its upper contact with the SDS (Schistes Dolomitiques Superieures=upper dolomitic shales) is marked by the appearance of sand in the shale. The SDS is composed of shales, dolomitic sandstones, and dolomites, as is the unit above it, the CMN (Calcaire a Minerai Noire=Black Ore Limestone).

The Mines Series and mineralization in the Tenke-Fungurume district

In the Tenke-Fungurume district, the Mines Series exhibits some spatial variation in lithology. The proportion of carbonate to siliciclastic material varies with rock type and alteration, with carbonates comprising up to 75% of some intervals and almost none of others; in general, clastics dominate in eastern Mambilima and the proportion of carbonates increases westward and from south to north. All the economic mineralization occurs within the Mines Fig. 4 Rocks of the Mines Series. a SDS shale. b SDS dolomitic sandstone, showing fluid oscillation banding. c Chalcocite-bearing Series. Ore is present in all the strata in varying amounts, but SDB shale. d Fe oxide-rich SDB shale with dolomitic and silicic the highest grades occur in the Upper and Lower Orebodies. alteration. e The RSC with dolomite partially dissolved within a Other units can also be mineralized; however, mineralization siliceous fabric. f Silicified dolomite in the RSC, showing its correlates strongly with lithology and most ore occurs in the characteristic near-surface cavernous fabric. g The RSC with silica, dolomite, cobaltoan dolomite (pink), and chalcocite with minor aforementioned zones. These high-grade zones are localized, oxidation. h Laminated shale-dolomite from the RSF, with malachite normally with sharply defined upper and lower boundaries. veinlets and dolomitic alteration. i Laminated shale-dolomite in the Much of the ore occur within a topography-controlled DStrat with dolomitic alteration, including a broad vein with dolomite weathered zone whose lower boundary varies from 50 crystals. j A contorted laminated dolomite in the DStrat with coarse, partially oxidized chalcocite grains. k The argillic sandstone of the to >100 m below the surface. Within this zone, the uppermost RAT. l The DStrat with dolomite veining and chalcocite. a dominant ore minerals are malachite and heterogenite KASA0006, 47.0 m; b KASA0037, 71.5 m; c MAMB0001, 297.5 m; d (CoOOH), with accessory chrysocolla. Chalcocite, minor MAMB0031, 128.1 m; e KASA0006, 77.8 m; f KASA0069, 26.7 m; g carrollite (CuCo S ), cobaltoan dolomite, and spheroco- KASA0033, 127.7 m; h MAMB0061, 96.9 m; i KASA0037, 195 m; j 2 4 KASA0006, 79.2 m; k MAMB0061, 108.1 m; l KASA0033, 142.2 m baltite (CoCO3)aremixedinwiththembelowthe weathered zone. The proportion of oxide and carbonate ore to mixed and (rare) sulfide ore is generally >10:1 in the eastern by a meter-thick polymict conglomerate or breccia of well- sections of Mambilima and decreases to the west. rounded argillite clasts, and on top a 5–10-m-thick sandstone with a distinctive yellow-brown clay matrix. Stratigraphy and lithology The total thickness of the RAT is unknown. Above it are the DStrat (Dolomites Stratifiées=stratified dolomites) and Twelve major rock types—reflecting combinations of RSF (Roches Siliceuses Feuilletées=fissile siliceous rocks) original rock types with the often texture-destructive effects 506 Miner Deposita (2012) 47:501–519 of alteration—were identified in hand specimen and logged preferred orientation of the grains of their host rock; where at Mambilima and Kansalawile (Table 1, Fig. 4). Figures 5 the rock shows no such fabric, their orientation is random. In and 6 show their distribution across the deposits and the the DStrat of Mambilima, some of the laths are aligned into main loci of alteration. Figure 7 shows the distribution of thin (<0.6 cm) bands, although those in between bands are metal grades in Mambilima and Kansalawile and the scarcer and show no preferred alignment. The similarity in relationship of the highest-grade zones to contacts between orientation of laths with the alignment of grains in the rock these rock types. suggests that they formed early. Sandstones, shales, dolomites, and their combinations Nodules of silica and/or dolomite also occur, primarily in comprise the major rock types. Sandstones generally the DStrat. These are normally ellipsoidal, elongate parallel consist of quartz grains in a matrix of dolomite or clay. to bedding, and measure approximately 2–3 cm on the Only one type of sandstone, the yellow-brown argillaceous major axis. The laminations of the rock bend around them facies unique to the uppermost RAT, can host significant (Fig. 8b). In contrast to the laths, the nodules are quantities of ore, normally in dolomite or malachite veins. cryptocrystalline. Shales, distinguished by their well-laminated appearance White dolomite veins parallel to sedimentary lamination and tendency to contain obvious iron oxides, can host high commonly exhibit “toothbrush” textures, with elongate grades of sulfide and oxide ore and range from relatively dolomite crystals perpendicular to vein margins (Fig. 9d). unaltered to pervasively dolomitized. Dolomitized shale is These veins are discontinuous, rarely more than 5 cm in recognized by hardness, cohesion, and extensive dolomite length. They are found in the DStrat, RSF, SDB, SDS, and veining. Shales can also occur finely interlaminated with CMN and occur in dolomite-altered rocks, mostly shales. dolomites, a combination especially liable to host ore and Laths, in particular, are commonly preserved even where which makes up most of the Lower Orebody. Dolomites, dolomite has been completely replaced by silica. In thin where not interleaved with the shales, occur as massive, section, they have sharp boundaries; as with the nodules, stylolitic rock, most commonly in the RSC and CMN, and the laminations in the rock bend smoothly around the edges are generally barren. Other rock types present include a of the veins, indicating an early formation. polymict conglomerate of well-rounded argillic clasts, overlying an argillite-dolomite crackle breccia in the RAT; Alteration features massive, largely unmineralized claystones; and limestones, limey shales, and various mixtures of limestone and Later dolomite, silica, and sulfides are found overprinting dolomite. None of these is a significant ore host. textural features of the host rocks and their diagenetic minerals at Tenke-Fungurume. These superimposed events Post-deposition features involve multiple episodes of alteration and related metal deposition. Their mineralogy, texture, and timing are Hand specimen and petrographic examination revealed a described here, followed by an outline of their spatial number of features useful in determining the nature and order distribution. Other alteration types described elsewhere in of alteration events. Carbonate minerals were distinguished by the Copperbelt, such as assemblages with hydrothermal reaction with 10% HCl; dolomite was ubiquitous, calcite albite or K-feldspar (e.g., Darnley 1960; Selley et al. 2005; scarce. There was no evidence found for magnesite or Fe-rich Sutton and Maynard 2005), were searched for in thin carbonates. These observations, detailed below, were used to section and hand sample, but have not been found in the construct a paragenetic sequence. Mines Series in this study, even in the clastic rocks where they might have been expected. Early features Petrographic examination shows evidence for multiple, separate episodes of dolomite formation. At least Some strata, particularly the DStrat and SDB, show features one early generation of dolomite has been replaced by whose relationship to their host rocks suggest they formed quartz. These rhomb-shaped quartz crystals have inclu- prior to lithification. These include nodules, laths, and sions of dolomite and are overgrown by euhedral “toothbrush” veins. dolomite crystals (Fig. 8c–f). In some cases, the quartz Laths and nodules of quartz and dolomite likely represent has replaced only the rims of the dolomite crystals early-formed anhydrite (e.g., Warren 2006). Polycrystalline, (Fig. 8e–f). Many of these rims are themselves overgrown rectangular laths of quartz and dolomite are common in the by dolomite, indicating that the introduction of silica Mines Series, mostly in the DStrat and more rarely in the occurred between two episodes of dolomitic alteration. RAT, RSF, and RSC (Fig. 8a). Possible laths were also The dolomite and quartz appear to overprint the rock, observed in the SDB and SDS. Some contain small cutting through laminations and including microscopic inclusions of anhydrite. The laths are aligned with the fragments of rock material. ie eoia(02 47:501 (2012) Deposita Miner – 519

Table 1 Rock types present in the Mines Series at Mambilima and Kansalawile, Tenke-Fungurume district

Lithology Found in Features Mineralogy Ore

Crackle breccia RAT Reddish-purple argillite crackle breccia with white dolomite veins Clays+dolomite±specularite None Polymict RAT Breccia or conglomerate supported by well-rounded argillite clasts Clays±dolomite±specularite Rare malachite or cobaltoan from 0.3 to 10 cm, unsorted, in dolomite or clay matrix dolomite Claystone CMN, SDS, RAT Soft, unlaminated red claystone with occasional quartz grains Clays+quartz+Fe oxides None Dolomite DStrat, RSF, CMN, Well-laminated, most commonly gray with white dolomite veins Dolomite±dolomitic shales Chalcocite; major ore host in SDS and nodules in DStrat and RSF; massive gray and blue with RSF and DStrat stylolites in SDS and CMN Laminated dolomite and shale DStrat, RSF Well-laminated, fissile when unaltered, in a variety of colors Clays+dolomite±silica Malachite, heterogenite, chalcocite, chrysocolla Chlorite+quartz+talc DStrat Soft, white rock easily mistaken for clay, commonly interlaminated Chlorite+quartz+talc±dolomite Malachite when interlaminated with dolomite with dolomite Shale SDB, SDS, CMN Gray or red, well-laminated shale, with extensive iron oxide staining Clays+muscovite±quartz± Malachite, heterogenite dolomite Quartzose sandstone RAT, SDS, CMN Fine to medium–coarse grains in clay or dolomitic matrix Qtz+clays±dolomite Rare malachite and heterogenite Argillic sandstone RAT Yellow-brown to gray-green argillite with some fine quartz grains Clays+quartz±dolomite Malachite Silica[dolomite] RSC White and gray cavernous silica with abundant oxides Silica+Fe oxides Malachite, minor heterogenite Silica[dolomite]+dolomite RSC Very dense, hard rock with obvious coarse dolomite crystals Silica+dolomite±Fe oxides Malachite, cobaltoan dolomite, spherocobaltite Carbonates SDS, CMN Mixed limestone, dolomite, and carbonaceous clays Calcite+dolomite+clays+Fe oxides None 507 508 Miner Deposita (2012) 47:501–519

Fig. 5 South–north cross sections showing the distribution of data; their inferred extents are traced in dashed lines. Note that these lithological types in Mambilima, with lines denoting the uppermost traces show only the extant alteration minerals, not those removed or occurrences of dolomite (blue) and sulfides (orange) and, where overprinted by later events. Drill holes in MAMB417550E section (left to possible, the lower bound of Cu–Co oxide occurrence (green); in right): MAMB0031, MAMB0061, MAMB0001; in MAMB418300E MAMB417550E, oxides persist to the lowest depth drilled. Areas of (left to right): MAMB0045, MAMB0008, MAMB0044 moderate to strong alteration are shown to the left of the lithological

There is evidence for multiple generations of silica as and relatively unaltered rocks tend to be sharp rather than well as of dolomite. Widespread silica alteration in the RSC gradational. and RSF left textures such as in Fig. 8g–h, clearly showing The effects of alteration were not limited to gangue fan-shaped brown chalcedony crosscut by silica veinlets, minerals. Sulfide assemblages at Mambilima and Kansalawile chalcedony fans nucleating on top of colloform chalcedony, are of two types (Fig. 9a–b). One consists almost entirely of and chalcedony fans crosscut by quartz crystals. The coarse (<5 mm) chalcocite crystals with only slight alter- crosscutting relationships among the various forms of silica ation. This type occurs below the main supergene zone (50– indicate at least two generations of silica precipitation. The 100 m depth), in association with euhedral dolomite crystals extent of silica addition varies from stratum to stratum, but and with toothbrush veins. The other includes both chalco- the total amount of silica is substantially less than the cite and lesser amounts of carrollite and displays complex quantity of added dolomite, except in the pervasively replacement and alteration textures, some involving super- silicified RSC. Boundaries between silicified, dolomitized, gene goethite and hematite. It appears from samples like the Miner Deposita (2012) 47:501–519 509

Fig. 6 South–north cross sections showing the distribution of extents are traced in dashed lines. Note that these traces show only the lithological types in Kansalawile, with lines denoting the uppermost extant alteration minerals, not those removed or overprinted by later occurrences of dolomite (blue) and sulfides (orange) and the lowest events. Drill holes in KASA1200NE (left to right): KASA0069, occurrence of oxide ores (green). Areas of moderate to strong KASA0018, KASA0019, KASA0037; in KASA700NE section (left alteration are shown to the left of the lithological data; their inferred to right): KASA0070, KASA0006, KASA0007, KASA0033

one in Fig. 9b that the carrollite preceded the chalcocite Sequence of events which partially replaced it. This type has no recognized gangue association. A few grains of other, partly oxidized Figure 10 summarizes the temporal sequence of features sulfide minerals, mostly bornite and chalcopyrite, were observed within the Mines Series at Mambilima and discovered deep in Mambilima and Kansalawile. Because of Kansalawile. Crosscutting, inclusion, and replacement their scarcity, little was learned of their distribution or timing. relationships suggest that the formation of evaporites and Supergene minerals, particularly goethite and hematite, initial dolomitization—with dolomite crystals probably exist throughout Mambilima and Kansalawile, varying in replacing original calcite—in the Mines Series occurred appearance from concretions and fine disseminated grains during or shortly after sedimentation. A subsequent influx at the surface to thin rims surrounding otherwise intact of silica, preceded or accompanied by the dissolution of sulfides at depth. Oxide and carbonate ore minerals such as some of the dolomite, created a silica-rich groundmass and malachite, chrysocolla, and heterogenite occur disseminat- lined void spaces with colloform brown chalcedony ed, in veins, and in dissolution cavities left by former (Fig. 8g–h). The first, carrollitic Cu and Co sulfides likely dolomite and sulfide crystals in the supergene zone. Lower precipitated at that time (Fig. 9b). The formation of down, below the zone of dolomite dissolution, spheroco- chalcedony was followed by the introduction of more baltite (CoCO3) and cobaltoan dolomite are present in dolomite, which created coarse crystals whose rhombic veinlets and around the edges of dolomite crystals, outlines and remaining fragments are still visible in the particularly in the RSC’s silicified dolomites. Sulfides shape of the silica that replaced them (Fig. 8c–f). This appear lower down and coexist with veins of spherocobal- replacement quartz was overgrown by a third and last tite and cobaltoan dolomite. generation of dolomite, distinguished by its euhedral 510 Miner Deposita (2012) 47:501–519

Fig. 7 Series of cross sections showing areas of high metal grades in holes, Cu and Co occurrences to the left, separated by a dashed line. the Kansalawile and Mambilima deposits and their correspondence The Mambilima 418300E section is not pictured due to its lack of with lithological contacts. Lithology is shown to the right of the drill significant mineralization appearance and accompanied by a second period of sulfide but only for about 50 m in Kansalawile. Likewise, the deposition, this one almost entirely chalcocite. This complete oxidation of sulfides extends to >150 m depth in sequence is seen throughout the two deposits, suggesting Mambilima and <50 m in Kansalawile, although partial that the events were widespread. oxidation persists at much greater depths in both deposits. Supergene processes extensively redistributed minerals The intensity and character of alteration also vary among after the major hypogene alteration events. Near the different strata, probably a consequence of differences in surface, almost all of the remaining dolomite was dissolved porosity, permeability, and chemical properties. For in- and the sulfides oxidized by circulating fluids, which stance, the shales of the SDB are less prone than the RSC precipitated metal oxides and carbonates into the cavities unit either to accommodate alteration or to preserve its left by dolomite dissolution. traces. Therefore, alteration events that profoundly changed This series of events applies to both deposits, although with the mineralogy throughout the RSC limited their effects to some local variations in the extent and depth of alteration veining in the SDB and likely did even less to modify other, processes. In Mambilima, dolomite dissolution and metal less porous units. Only in the RSC is the full paragenetic oxidation and transport went deeper and were more pervasive sequence of Fig. 10 found; the SDB, RSF, and DStrat show than in Kansalawile. For instance, the 100% removal of fragments of the sequence of events, but either were not dolomite occurs for the top 100 m of the Mambilima deposit, affected by some of them or failed to preserve evidence of Miner Deposita (2012) 47:501–519 511

Fig. 8 Examples of the complex textures at Mambilima and Kansalawile. a Silicified laths after early anhydrite, in cross- polarized transmitted light; b laminations in silicified DStrat (outlined in black) deforming smoothly around them in hand sample; c and d rhomb-shaped quartz crystals with dolomite inclusions are overgrown by euhedral dolomite crystals. Both quartz and dolomite cut across chalcedony fans. Cross- polarized transmitted light. e and f Quartz rims marking the locations of former dolomite crystals are overgrown by later dolomite. Cross-polarized transmitted light. g and h Chalcedony nucleating on top of earlier chalcedony. Cross-polarized transmitted light. All samples except for (b) come from below the surficial no-dolomite zone. a MAMB0044, 151.0 m depth; b MAMB0045, 33.9 m; c–d KASA0019, 107.8 m; e MAMB0001, 297.5 m; f: KASA0019, 107.8 m; g: MAMB0001, 297.5 m; h: MAMB0001, 191.2 m

them. However, there was no observed correlation between below. The connection between metal distribution and siliciclastic/carbonate ratio and alteration style; the clastic- stratigraphy is already well established, as shown by the dominated eastern and the carbonate-richer western parts of the prevalence of the terms Upper Orebody and Lower Ore- study area appear to have been equally affected by the same body, but metal distribution is also related to lithology and styles of alteration. This homogeneity and the wide extent and to contacts between different types of rock (Fig. 7). thoroughness of the alteration suggest that the fluids came from Particularly favorable ore hosts are those contacts which an external source rather than originating within the rocks, for mark substantial changes in rock characteristics, such as instance by silica release from mineral reactions. porosity and rheology. Two types of contact-related high- grade zones exist: those bounded by lithological contacts Distribution of diagenetic features, alteration, and those localized at them and not extending significant and mineralization distances into the surrounding rock. Using the Lower Orebody as an example of the first The distribution of some of the post-depositional features type, grade extends throughout the DStrat and RSF, two observed in this study is related to the stratigraphy; the lithologically similar units (Fig. 7). Ore grade does not distribution of others is related to topography. change significantly across the internal contact between Features whose distributions correlate with stratigraphy the two strata, where laminated dolomites give way to include siliceous alteration and metal distribution. Figures 5 laminated shale-dolomites, but decreases precipitously and 6 show that silicic alteration is concentrated in the across the boundary separating laminated shale-dolomite RSC, with significant overlap into the strata above and and the massive, cavernous silicified dolomite of the RSC. 512 Miner Deposita (2012) 47:501–519

Fig. 9 Illustration of selected features of the hypogene and supergene void spaces marking former dolomite sites, some of which are mineralogy in Mambilima and Kansalawile. a and b show evidence partially filled in by malachite or other metal oxides and carbonates for two generations of sulfide ore mineralization, chalcocite surround- (f–j). Mineral abbreviations: Brackets surround replaced mineral site, ing earlier carrollite (reflected light). Such sulfides were later oxidized e.g., Sil[dol]=silica replacing dolomite. a MAMB0001, 297.5 m through supergene fluid circulation, either in situ (c) or with additional depth; b KASA0033, 140 m; c KASA0033, 139.2 m; d KASA0033, transport, leaving behind iron oxide boxwork (d and e). d also shows 110.5 m; e KASA0037, 177.2 m; f KASA0018, 60.0 m; g rock laminations deforming smoothly around a “toothbrush” dolomite KASA0007, 116.6 m; h MAMB0031, 98 m; i MAMB0061, 89 m; j vein in shale, indicating early formation of the dolomite. Supergene KASA0070, 34.4 m fluids also dissolved dolomite, leaving behind high-silica rocks with

A high-grade zone of the second variety is found at the contact The mineralization in both types of these lithology- and of the RSC’s silicified dolomite and the laminated shale in the contact-related high-grade zones can be sulfide, oxide and SDB, where heterogenite commonly occurs in high concen- carbonate, or mixed. However, most of the sulfides trations and extends into the neighboring rock only in fractures. observed in Mambilima and Kansalawile were chalcocite Miner Deposita (2012) 47:501–519 513

Fig. 10 Inferred sequence of events in the Mines Series at Mambilima and Kansalawile. The timing of the first sulfide precipitation event is uncertain; the dotted line shows its estimated position in the paragenetic sequence

whose origin(s), hypogene or supergene, have not been Interpretation and discussion settled. Determining whether hypogene ores at Tenke- Fungurume followed this distribution scheme is a subject Alteration history for future work. Other high-grade zones occur in lithologically homo- The sequence of events discussed above and portrayed in geneous intervals and do not appear to be bounded by, Fig. 10 summarizes the features observed in thin sections and coincident with, or otherwise related to, changes in hand samples. The complex intergrowth, overgrowth, and lithology. Several examples of this type are found in the replacement textures of dolomite and silica can only have high-Cu spots within the RSC of Kansalawile (Fig. 7). been formed by multiple generations of alteration, beginning They occur only above a line about 50–70 m below the with the formation of anhydrite laths and nodules prior to full land surface and parallel to it, and the ore consists lithification of the Mines Series sediments. The first episode exclusively of oxides and carbonates in veins and cavity of dolomitic alteration is also considered pre-lithification, but fillings (e.g., Fig. 9c). In Kansalawile, these contact- the two subsequent generations of silica and the two unrelated high-grade zones are exclusively Cu-rich; in additional dolomite influxes that alternated with them show Mambilima, some are rich in Cu and some in Co, but in very no evidence of occurring before lithification. few cases are ores of the two metals found together, i.e., high- Alteration changed the physical as well as the litholog- Cu zones tend to be low-Co zones and vice versa. No such ical characteristics of the Mines Series rocks. Some dichotomy exists in the high-grade zones associated with evidence for this is obvious in much of the chalcedony lithological contacts. observed in thin sections (e.g., Fig. 8), which exhibits the This separation of Cu from Co at shallow depths is most clear “wall-lining” textures characteristic of chalcedony pronounced immediately below the surface. In six of the 15 precipitating on the borders of an existing void (Graetsch et drill holes logged, percentage of Co is elevated to 0.2% al. 1987). Even today the strata show a wide range in and, in one case, to 0.3%, for the 1–2 m at the collars. This permeability: the RSC contains cavities up to 10 cm in is similar to the “cobalt capping” described by Decrée et al. diameter where dolomite has been dissolved, whereas the (2010), and along with the above-mentioned tendency for shales above and below have little or no visible void space. supergene Cu and Co minerals to occur in separate high- At greater depths, where dolomite persists in the RSC, the grade zones near the surface, supports their suggestion of cavities are minor to nonexistent. Thus, alteration affects oxidation-induced decoupling. not only composition but permeability and is likely to have Topography, not lithology, exerts the most obvious exercised a similar control in the past. control on the distribution of dolomite and sulfides. Ore paragenesis is as complicated as events in the Both minerals are absent from all rocks above the gangue. As the textures in Fig. 9 illustrate, at least two marked lines in Figs. 5 and 6, but both left traces of their generations of sulfides precipitated in the main ore former presence there. The cavities, some of them rhomb- horizons. Judging by their overgrowth relationships, the shaped (Fig. 9e–h), found in rocks near the surface older sulfide was at least partially carrollite, while the indicate that dolomite was originally there but was younger, overgrowing phase was almost entirely chalco- dissolved. Boxwork filled with metal oxides (Fig. 9c–d) cite. The earlier sulfide phase has no clear gangue shows that sulfides were likewise present but have been association, but the younger, coarser-grained chalcocite oxidized. Although the original distribution of dolomite is commonly found in veins of dolomite from the last and sulfides was unconnected with modern topography, dolomitic alteration event. Both sulfide types show the distribution of areas where they were dissolved shows extensive oxidation in all shallow occurrences, and astrongrelationshiptoit. sulfides are not found at all within >50 m of the surface. 514 Miner Deposita (2012) 47:501–519

These interpretations are generally similar to those existing multiphase model of sulfide precipitation (e.g., developed by other authors working on other deposits, Cailteux et al. 2005; Selley et al. 2005; Hitzman et al. 2005; and fit in with the current understanding of ore-forming Dewaele et al. 2006; Muchez et al. 2008, 2010; El Desouky processes and paragenesis in the Copperbelt. Existing et al. 2009, 2010; Haest and Muchez 2011). The association literature on gangue alteration is regrettably scarce, but of the chalcocite with the last dolomitic influx in the Dewaele et al. (2006) also found multiple generations of gangue corresponds to the findings of Dewaele et al. dolomite bracketing an interval of silicic alteration at (2006) at Kamoto and Musonoi. The heavy supergene Kamoto and Musonoi, although without distinguishing alteration of the Mambilima and Kansalawile deposits multiple episodes in the silica. unfortunately precludes more extensive study of sulfide The far more extensive body of work on ore paragenesis paragenesis. has evolved with the decades of Copperbelt research, but the current metallogenetic models center around multiple Distribution and evolution of mineralization phases of sulfide deposition followed by late supergene reworking (e.g., Bartholomé et al. 1972; Bartholomé 1974; The present distribution pattern of Cu and Co at Mambi- Selley et al. 2005; Hitzman et al. 2005). The existence of lima and Kansalawile is in fact a combination of two multiple phases is generally agreed, although their number, distinct patterns, each created by a different process. The timing, and other details remain controversial and vary first comprised the deposition of sulfides and was con- between Zambian and Congolese deposits (Haest and trolled by the lithology—both original and alteration—of Muchez 2011). Whether the first episode of sulfide precip- the rocks, generating the original Upper and Lower itation was partly syngenetic and continued into the early Orebodies. The second, superimposed much later, consisted diagenetic stage (e.g., Cailteux et al. 2005), solely diagenetic of the supergene alteration that remobilized the metals and and pre-Lufilian (Dewaele et al. 2006; El Desouky et al. redistributed them close to the surface. Much of the ore 2009), or solely diagenetic and synorogenic (e.g., Sillitoe et remained in the two main orebodies as oxides and al. 2010, Haest and Muchez 2011) is one such debate; carbonates, but extensive fluid flow moved some of it into another concerns its tectonic drivers, whether extensional (e. other units, particularly the RSC. Figure 11 schematically g., Muchez et al. 2010) or compressional (e.g., Sillitoe et al. represents both. 2010). Controversy also surrounds subsequent ore-forming The first pattern of distribution was a consequence of episodes, which may have involved addition of new ore (e. lithology and, more specifically, of lithological contrast. g., Brems et al. 2009), remobilization of old (e.g., Sillitoe et According to current and historical understanding of al. 2010, El Desouky et al. 2010), or both (e.g., El Desouky sediment-hosted Cu deposits, several factors govern the et al. 2009; Haest and Muchez 2011), and which may have precipitation of sulfide ore (e.g., Bartholomé 1974; Kirkham numbered one (Dewaele et al. 2006; El Desouky et al. 2009, 1989; Selley et al. 2005). The two most likely to be 2010; Haest and Muchez 2011) or two (Brems et al. 2009), important at Tenke-Fungurume are redox state and the not including minor late-stage remobilization (e.g., Dewaele availability of reduced sulfur (Kirkham 1989), both of which et al. 2006). Understandably, most authors simply allude to depend on the lithology of the rock. The precipitation of the existence of multiple sulfide phases without specifying sulfides at redox boundaries, where a metalliferous oxic their number. However, there is some consensus on the brine meets a reservoir of reduced sulfur, offers a plausible importance of evaporite-derived mineralizing fluids. Most of cause for the relationship of ore concentrations to the the sulfides are thought to have precipitated from fluids of contacts between shale-dominated strata and a silica– high salinity and moderate temperature (100–180°C and 9– dolomite unit (Bartholomé et al. 1972;Bartholomé1974; 22 wt.% NaCl eq. according to Annels 1989;80–192°C and Rose 1989). Similar ore occurrence patterns have been 8.4–18.4 wt.% NaCl eq. according to Dewaele et al. 2006; documented in other Copperbelt deposits by Garlick (1989); 8–18 wt.% NaCl eq. according to Muchez et al. 2008;115– he and Mendelsohn (1989) also noted that sulfide mineral- 220°C and 11.3–20.9 wt.% NaCl eq. according to El ization occurs in the silica–dolomite unit only in small shale Desouky et al. 2009). A second diagenetic sulfide stage was intercalations between algal mounds. Permeability may have the result of hotter, more saline fluids (197–425°C according been another significant factor, with the relatively imperme- to Annels 1989; >200°C according to Cailteux et al. 2005; able shale-dominated units hindering fluid circulation for 270–385°C, 35–45.5 wt.% NaCl eq. according to El long enough to enable more extensive ore-precipitating Desouky et al. 2009). reactions there than in the more hydraulically open strata. The two generations of sulfide ore distinguished at Although this hypothesis is difficult to test, it is not unlikely Mambilima and Kansalawile are consistent with this that lithology exerted a physical control on mineralization general framework. The existence of carrollite partly through permeability as well as the obvious chemical replaced by chalcocite (Fig. 9) is a common feature of the controls of redox state and sulfur availability. Miner Deposita (2012) 47:501–519 515

Fig. 11 Schematic representa- tion of fluid circulation and ore precipitation and movement at Tenke-Fungurume; timing of the deformation of the Mines Series relative to hypogene mineralization is uncertain. a shows the initial sulfide precipitation at lithologic boundaries that likely represented redox boundaries or sulfide sources; b depicts oxidation and selective redistri- bution of Cu and Co, as oxide and carbonate ores, by post-deformation supergene processes

This model fits the occurrence patterns observed at Grade decreases precipitously in the lithologically homoge- Mambilima and Kansalawile, with the RSC as the fluid neous uppermost RAT, where this contrast-induced perme- conduit and the RSF–DStrat and SDB providing shale-rich ability vanishes. Beyond these observations, however, this hosts for ore precipitation (Fig. 11a;Oosterbosch1951; remains a hypothesis and difficult to confirm. Annels 1989; S. Castro-Reino, personal communication This original sulfide ore distribution was overprinted by the 2009). Permeability can be generated by dissolution of second, generated during supergene alteration controlled by the dolomite, which petrographic evidence (detailed above) modern land surface. Sulfide ores were oxidized, remobilized, suggests has happened repeatedly throughout the unit’s and reprecipitated in oxide and carbonate ore concentrations history. This permeability, and the dolomite-silica composi- unrelated to lithological contacts (Fig. 11b). This conclusion is tion of the RSC, would make it a poor sulfur reservoir but a supported by their restriction to a near-surface zone and the fine aqueduct; the opposite is true of the ore-hosting strata. late timing apparent from their relationships to other minerals. There is also a potentially instructive difference in the ore Their monometallic nature—either Cu-rich or Co-rich, but not mineralization of the Lower and Upper Orebodies, reflecting both—likely reflects the greater solubility of Cu in supergene the lithological differences between the laminated dolomite- fluids and resulting tendency to separate the two metals (Rose shale of the RSF/DStrat and the shale of the SDB (Fig. 7). In 1989; Katsikopoulos et al. 2008;Decréeetal.2010). The the Upper Orebody grades are high at the contact of the RSC occurrence of the monometallic, high-grade zones is erratic; and the homogeneous SDB shales but can drop off sharply in they are possibly related to faults, joints and other zones of the absence of fracturing. In contrast, the high-grade zone enhanced permeability as seen in many deposits, but bear no that begins near the RSF-RSC contact continues throughout systematic relationship to lithology (Bateman 1930;P. the alternating shale and dolomite laminations of the RSF Mambwe, personal comm. 2009). and DStrat. The lithological contrast of shale and dolomite, with consequent differences in rheology, could cause the Metallurgical considerations: gangue acid consumption shale and dolomite laminations to separate under strain, increasing permeability and making the RSF and DStrat Like those at many other oxide- and carbonate-rich deposits, more susceptible to pervasive mineralization than the SDB. the Tenke-Fungurume ores are leached with acid to recover 516 Miner Deposita (2012) 47:501–519 the metals. Consequently, acid is a major expense in ore silicified rocks tend to have low GAC values, whereas processing and abundant acid-consuming gangue minerals heavily dolomitized areas, particularly those units with high can render even rich deposits uneconomic by raising the original carbonate, exhibit the highest GAC values. This processing costs. Understanding the factors that lead to high example illustrates the applicability of lithological analyses wastage of acid on nonmetallic gangue minerals (“GAC”,or of Mines Series strata for more than standard mineral gangue acid consumption) was one motivation for this study. exploration. Petrography and direct measurements of acid consumption show that dolomite is the only acid-consuming gangue Comparison with other deposits in the Copperbelt mineral present in significant quantities in the ore zones at Tenke-Fungurume. Because of its dependence on dolomite, Previous work has established that although local differences GAC is correlated with lithology and alteration type exist, the Mines Series deposits in the Copperbelt are (Fig. 12). Most notably, it is low in the upper 50–100 m remarkably uniform over long spatial distances (Bartholomé below the land surface, where supergene processes re- 1974;Cailteuxetal.1994). These differences, long noticed, moved most or all dolomite. Below that level, the GAC have been summarized by Hitzman et al. (2005), Selley et al. values reflect the intensity of dolomitic alteration and the (2005), and Cailteux et al. (2005), among others. Some amount of carbonate present in the original rock. Strongly pertinent features have been summarized in Table 2.

Fig. 12 Gangue acid consumption of samples (in kilogram per tonne estimated using %Cu values for the entire assay interval around the H2SO4 equivalent) and their locations, correlated with lithology and sample, some over-correction occurred. Blue dashed lines show the alteration data from Figs. 5 and 6. Negative numbers are due to elevation of the highest dolomite occurrences observed and are copied corrections for Cu carbonates’ acid consumption; since this was from Figs. 5 and 6 Miner Deposita (2012) 47:501–519 517

The Mines Series deposits are similar to one another ; mostly because they result from similar processes acting on ; 1989 ) similar rocks in the same stratigraphic units. Although the ; Sutton and 2009 2009 2006 2006 host rocks vary locally in the proportions of carbonate and 2005 2006 2005

) siliciclastic material, all rock types fall within a relatively 2005 narrow range of compositions which do not change much 1989 over distance (Bartholomé 1974; Cailteux et al. 2005). The Lower Orebody is hosted in laminated dolomites and Dewaele et al. Maynard Selley et al. El Desouky et al. Dewaele et al. this study El Desouky et al. McGowan et al. interlaminated shales and dolomites, and the Upper Ore- body in dolomite-bearing shales, all the 350 km along strike from Kolwezi to Kambove (Cailteux et al. 2005). Lithology does change across strike, from southern reef to northern supratidal facies (Lefebvre 1989), and with it varies the average Co:Cu ratio of the deposits, from an average of 1:57 in the south to 1:13 in the north (Cailteux et al. 2005). enrichment transport, enrichment and bedding planes local enrichment OxidationOxidation Annels ( Sweeney and Binda Oxidation, leaching, Higher temperatures of alteration are generally agreed upon for the more southerly Zambian deposits, perhaps because of their proximal position in the Lufilian arc (Hitzman et al. 2005). As discussed above, the multi-stage diagenetic model for ore mineralization is now agreed for the Mines Series deposits on both sides of the Copperbelt, and debate is mostly confined to its details. Mambilima and Kansalawile fit well within this geolog- microcline minor zircon, tourmaline, rutile chlorite ical and metallogenic framework: similar to other Con- Dolomite and silica added Oxidation and Dolomite and silica added Leaching, oxidation± Dolomite and silica added+Carbonate, albite, Oxidation chlorite, in fractures +Dolomite, quartz, feldspars; golese deposits, they differ in detail from the Zambian ones (Table 2). Like Kamoto, Musonoi, and Luiswishi, carbonates and siliciclastics are present in subequal to equal proportions. Evidence of early anhydrite abounds at all deposits, though no traces were found at Mambilima and Kansalawile of the gypsum discovered at Kamoto, Musonoi, early dolomite dolomite early dolomite carbonate early carbonate and Luiswishi. At all five deposits, post-evaporite alteration Anhydrite, gypsum, Anhydrite, gypsum, Anhydrite, early Anhydrite, clays, Evaporites +Dolomite, quartz, sericite, phases are mostly dolomite and silica. At Mambilima and Kansalawile, as at Kamoto and Musonoi, the last episode of dolomite addition corresponds to the second sulfide precipi-

sulfide tation, although the mineral identities differ. The sulfide

” assemblage observed at Mambilima and Kansalawile consists mostly of chalcocite, with some carrollite and phases one+remobilization one+remobilization remobilization phase syn- to post-Lufilian Several “ Two sulfide phases, or Two sulfide phases Anhydrite, early chalcopyrite; however, the heavy supergene overprint precludes proper study of the sulfides and may contribute to the difference from the sulfides of Kamoto and Musonoi, which Dewaele et al. (2006) describe as clastic Two sulfide phases, or ≥ carrollite, bornite, digenite, and chalcocite, with chalcopyrite conspicuously absent from the main orebodies. This and clastics and clastic difference may also be a reflection of the variability of sulfide mineralization types within the same strata, emphasized by Cailteux et al. (2005) and used by them as evidence that sulfide zonation is not controlled by the Katanga Subequal carbonate lithological characteristics of the host rock. However, all the deposits show evidence for multiple generations of sulfide mineralization, despite the diversity of composi- Comparison of alteration and mineralization in selected deposits of the Copperbelt tions. Mambilima and Kansalawile are consistent with the general multiphase model for the formation of the Kansalawile – Mufulira Zambia Clastics>carbonates Two sulfide phases Anhydrite +Dolomite, calcite, quartz Oxidation Cailteux et al. ( KamotoMusonoiLuiswishi Katanga Carbonate Katanga Katanga Subequal carbonates Table 2 DepositMambilima and Place Lithology Mineralization type Diagenesis Alteration types Supergene features Source ChambishiKonkola Zambia Clastics>carbonates One sulfide Zambia phase+ Clastics>carbonates One diagenetic sulfide Nchanga Zambia Clastics>carbonatesMines Two sulfide phases, Series Cu Co deposits. 518 Miner Deposita (2012) 47:501–519

Differences with Zambian deposits are more pro- Sergio Castro-Reino, Linda Dufek, and Pascal Mambwe for their nounced. Far more carbonates exist in the gangue in scientific assistance during the project. Further financial support was provided by a grant to HIF from the Society of Economic Geologists Mambilima and Kansalawile than in the Zambian deposits. and by Science Foundation Arizona through the University of Arizona None of the hydrothermal feldspars reported from Zambian Institute for Mineral Resources. Thesis committee members Eric orebodies were observed in this study. Seedorff and Jon Patchett provided helpful guidance and comments. Unlike gangue alteration, supergene alteration is fairly Another committee member, Frank Mazdab, deserves special thanks for helping with the petrographic work and designing the titration uniform on both sides of the Copperbelt. It caused experiments. We also thank Bob Downs and Dave Bish for help with extensive oxidation close to the surface and, in some mineral characterization, and the reviewers for their helpful comments locations, variable leaching and enrichment. Separation of and suggestions. Cu from Co and the formation of Cu-poor “cobalt caps” is one geochemical side effect of this, recorded at several References deposits (Decrée et al. 2010) and noticeable, though not as well developed, at Mambilima and Kansalawile. Annels AE (1974) Some aspects of the stratiform ore deposits of the Zambian Copperbelt and their genetic significance. In: Bartholomé P (ed) Gisements stratiformes et provinces cuprifères: Liège. Société Géologique de Belgique, Belgium, pp 235–254 Summary and conclusions Annels AE (1984) The geotectonic environment of Zambian copper- cobalt mineralization. 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DR Congo: Mineralium but are not identical to them, and illustrate the need for a Deposita 45:621–629 broader synthesis of regional patterns in alteration and Dewaele S, Muchez P, Vets J, Fernandez-Alonzo M, Tack L (2006) Multiphase origin of the Cu-Co ore deposits in the western part mineralization. of the Lufilian fold-and-thrust belt, Katanga (Democratic Repub- lic of Congo). J Afr Earth Sci 46:455–469 Acknowledgments This research, which comprised the first author’s El Desouky HA, Muchez P, Cailteux J (2009) Two Cu-Co sulfide phases MS thesis, has been supported by Freeport-McMoRan Copper & Gold and contrasting fluid systems in the Katanga Copperbelt. Demo- and its Congolese subsidiary, Tenke-Fungurume Mine. 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