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1.
The Katanga Copperbelt is the Congolese part of the well-known Central African Copperbelt, the largest sediment-hosted stratiform Cu–Co province on Earth. Petrographic examination of borehole samples from the Kamoto and Luiswishi mines in the Katanga Copperbelt recognized two generations of hypogene Cu–Co sulfides and associated gangue minerals (dolomite and quartz). The first generation is characterized by fine-grained Cu–Co sulfides and quartz replacing dolomite. The second generation is paragenetically later and characterized by coarse-grained Cu–Co sulfides and quartz overgrown and partly replaced by dolomite. Fluid inclusion microthermometric data were collected from two different types of fluid inclusions: type-I fluid inclusions (liquid + vapor) in the quartz of the first generation and type-II fluid inclusions (liquid + vapor + halite) in the quartz of the second generation. The microthermometric analyses indicate that the fluids represented by type-I and type-II fluid inclusions had very different temperatures and salinities and were not in thermal equilibrium with the host rock.Petrographic and microthermometric data indicate the presence of at least two main hypogene Cu–Co sulfide phases in the Katanga Copperbelt. The first is an early diagenetic typical stratiform phase, which produced fine-grained sulfides that are disseminated in the host rock and frequently concentrated in nodules and lenticular layers. This phase is related to a hydrothermal fluid with a moderate temperature (115 to 220 °C, or less if reequilibration of inclusions has occurred) and salinity (11.3 to 20.9 wt.% NaCl equiv.). The second hypogene Cu–Co phase produced syn-orogenic coarse-grained sulfides, which also occur disseminated in the host rock but mainly concentrated in a distinct type of stratiform nodules and layers and in stratabound veins and tectonic breccia cement. This second phase is related to a hydrothermal fluid with high temperature (270 to 385 °C) and salinity (35 to 45.5 wt.% NaCl equiv.).A review of available microthermometric and ore geochronological data of the Copperbelt in both the Democratic Republic of Congo and Zambia supports the regional presence of the two Cu–Co phases proposed in our study. Future geochemical analyses in the Copperbelt should take into account the presence of, at least, these two Cu–Co phases, their contrasting fluid systems and the possible overprint of the first phase by the second one.  相似文献   

2.
The Lufilian foreland is a triangular-shaped area located in the SE of the Democratic Republic of Congo and to the NE of the Lufilian arc, which hosts the well-known Central African Copperbelt. The Lufilian foreland recently became an interesting area with several vein-type (e.g., Dikulushi) and stratiform (e.g., Lufukwe and Mwitapile) copper occurrences. The Lufilian foreland stratiform Cu mineralization is, to date, observed in sandstone rock units belonging to the Nguba and Kundelungu Groups (Katanga Supergroup).The Mwitapile sandstone-hosted stratiform Cu prospect is located in the north eastern part of the Lufilian foreland. The host rock for the Cu mineralization is the Sonta Sandstone of the Ngule Subgroup (Kundelungu Group). A combined remote sensing, petrographic and fluid inclusion microthermometric analysis was performed at Mwitapile and compared with similar analysis previously carried out at Lufukwe to present a metallogenic model for the Mwitapile- and Lufukwe-type stratiform copper deposits. Interpretation of ETM+ satellite images for the Mwitapile prospect and the surrounding areas indicate the absence of NE–SW or ENE–WSW faults, similar to those observed controlling the mineralization at Lufukwe. Faults with these orientations are, however, present to the NW, W, SW and E of the Mwitapile prospect. At Mwitapile, the Sonta Sandstone host rock is intensely compacted, arkosic to calcareous with high silica cementation (first generation of authigenic quartz overgrowths). In the Sonta Sandstone, feldspar and calcite are present in disseminated, banded and nodular forms. Intense dissolution of these minerals caused the presence of disseminated rectangular, pipe-like and nodular dissolution cavities. Sulfide mineralization is mainly concentrated in these cavities. The hypogene sulfide minerals consist of two generations of pyrite, chalcopyrite, bornite and chalcocite, separated by a second generation of authigenic quartz overgrowth. The hypogene sulfide minerals are replaced by supergene digenite and covellite. Fluid inclusion microthermometry on the first authigenic quartz phase indicates silica precipitation from an H2O–NaCl–CaCl2 fluid with a minimum temperature between 111 and 182 °C and a salinity between 22.0 and 25.5 wt.% CaCl2 equiv. Microthermometry on the second authigenic quartz overgrowths and in secondary trails related to the mineralization indicate that the mineralizing fluid is characterized by variable temperatures (Th = 120 to 280 °C) and salinities (2.4 to 19.8 wt.% NaCl equiv.) and by a general trend of increasing temperatures with increasing salinities.Comparison between Mwitapile and Lufukwe indicates that the stratiform Cu mineralization in the two deposits is controlled by similar sedimentary, diagenetic and structural factors and likely formed from a similar mineralizing fluid. A post-orogenic timing is proposed for the mineralization in both deposits. The main mineralization controlling factors are grain size, clay and pyrobitumen content, the amount and degree of feldspar and/or calcite dissolution and the presence of NE–SW to ENE–WSW faults. The data support a post-orogenic fluid-mixing model for the Mwitapile- and Lufukwe-type sandstone-hosted stratiform Cu deposits, in which the mineralization is related to the mixing between a Cu-rich hydrothermal fluid, with a temperature up to 280 °C and a maximum salinity of 19.8 wt.% NaCl equiv., with a colder low salinity reducing fluid present in the sandstone host rock. The mineralizing fluid likely migrated upwards to the sandstone source rocks along NE–SW to ENE–WSW orientated faults. At Lufukwe, the highest copper grades at surface outcrops and boreholes were found along and near to these faults. At Mwitapile, where such faults are 2 to 3 km away, the Cu grades are much lower than at Lufukwe. Copper precipitation was possibly promoted by reduction from pre-existing hydrocarbons and non-copper sulfides and by the decrease in fluid salinity and temperature during mixing. Based on this research, new Cu prospects were proposed at Lufukwe and Mwitapile and a set of recommendations for further Cu exploration in the Lufilian foreland is presented.  相似文献   

3.
The Neoproterozoic central African Copperbelt is one of the greatest sediment-hosted stratiform Cu–Co provinces in the world, totalling 140 Mt copper and 6 Mt cobalt and including several world-class deposits (10 Mt copper). The origin of Cu–Co mineralisation in this province remains speculative, with the debate centred around syngenetic–diagenetic and hydrothermal-diagenetic hypotheses.The regional distribution of metals indicates that most of the cobalt-rich copper deposits are hosted in dolomites and dolomitic shales forming allochthonous units exposed in Congo and known as Congolese facies of the Katangan sedimentary succession (average Co:Cu = 1:13). The highest Co:Cu ratio (up to 3:1) occurs in ore deposits located along the southern structural block of the Lufilian Arc. The predominantly siliciclastic Zambian facies, exposed in Zambia and in SE Congo, forms para-autochthonous sedimentary units hosting ore deposits characterized by lower a Co:Cu ratio (average 1:57). Transitional lithofacies in Zambia (e.g. Baluba, Mindola) and in Congo (e.g. Lubembe) indicate a gradual transition in the Katangan basin during the deposition of laterally correlative clastic and carbonate sedimentary rocks exposed in Zambia and in Congo, and are marked by Co:Cu ratios in the range 1:15.The main Cu–Co orebodies occur at the base of the Mines/Musoshi Subgroup, which is characterized by evaporitic intertidal–supratidal sedimentary rocks. All additional lenticular orebodies known in the upper part of the Mines/Musoshi Subgroup are hosted in similar sedimentary rocks, suggesting highly favourable conditions for the ore genesis in particular sedimentary environments. Pre-lithification sedimentary structures affecting disseminated sulphides indicate that metals were deposited before compaction and consolidation of the host sediment.The ore parageneses indicate several generations of sulphides marking syngenetic, early diagenetic and late diagenetic processes. Sulphur isotopic data on sulphides suggest the derivation of sulphur essentially from the bacterial reduction of seawater sulphates. The mineralizing brines were generated from sea water in sabkhas or hypersaline lagoons during the deposition of the host rocks. Changes of Eh–pH and salinity probably were critical for concentrating copper–cobalt and nickel mineralisation. Compressional tectonic and related metamorphic processes and supergene enrichment have played variable roles in the remobilisation and upgrading of the primary mineralisation.There is no evidence to support models assuming that metals originated from: (1) Katangan igneous rocks and related hydrothermal processes or; (2) leaching of red beds underlying the orebodies. The metal sources are pre-Katangan continental rocks, especially the Palaeoproterozoic low-grade porphyry copper deposits known in the Bangweulu block and subsidiary Cu–Co–Ni deposits/occurrences in the Archaean rocks of the Zimbabwe craton. These two sources contain low grade ore deposits portraying the peculiar metal association (Cu, Co, Ni, U, Cr, Au, Ag, PGE) recorded in the Katangan sediment-hosted ore deposits. Metals were transported into the basin dissolved in water.The stratiform deposits of Congo and Zambia display features indicating that syngenetic and early diagenetic processes controlled the formation of the Neoproterozoic Copperbelt of central Africa.  相似文献   

4.
New age data on detrital zircons and micas are presented from key units within the Neoproterozoic Katanga Supergroup, which hosts the major stratiform Cu–Co deposits of the Central African Copperbelt. Detrital zircon ages indicate a mainly Palaeoproterozoic (between 2081 ± 28 and 1836 ± 26 Ma) provenance for the Katanga basin, derived from the Lufubu Metamorphic Complex of the Kafue Anticline and the Bangweulu Block to the north of the outcrop belt. Detrital zircons and clasts from the Grand Conglomerat glacial diamictite indicate a source from the Palaeoproterozoic metavolcanic porphyries and granitoids of Luina Dome region, which was a basement high during Nguba Group deposition. Minor zircons of Mesoproterozoic age may have been derived from the Kibaran belt. Finally, 40Ar/39Ar age data from detrital muscovites from Biano Group siltstones give a maximum age of sedimentation of 573 Ma, strongly supporting previous models that the Biano Group was deposited in a foreland basin of the Lufilian Orogen.  相似文献   

5.
鲁苏西铜钴矿床位于刚果(金)加丹加铜钴矿带,是该区域典型层控铜钴矿床。该矿床的矿石类型依据氧化程度可分为硫化矿和氧化矿。野外地质观察和区域资料分析表明,硫化矿的成矿期可分为成岩早期和造山期,矿石矿物为黄铜矿、斑铜矿、硫铜钴矿和辉铜矿。氧化矿主要为铜钴硫化物在富水表生环境下淋滤而成。矿床的同位素数据分析表明:该矿床成岩期的硫化物为以生物还原作用为主,硫源来自元古宙海水,碳源以海相无机碳为主,放射性锶同位素与基底物质有关;造山期硫化物生成以热化学还原作用为主,成矿流体来自蒸发盐的溶解,硫源来自早期硫化物再活化和蒸发盐溶解,碳氧同位素表明成矿流体与围岩发生了强烈的缓冲反应。综合分析表明,蒸发相的海水为鲁苏西铜钴矿富集和成岩早期成矿提供了有利条件,造山期改造和表生期氧化对矿床品位的富集影响明显。  相似文献   

6.
The Kundelungu foreland, north of the Lufilian arc in the Democratic Republic of Congo, contains a number of various vein-type and stratiform copper mineralisations. The geodynamic context and metallogenesis of these mineral occurrences remain enigmatic. Currently, the vein-type Cu–Ag ore deposit at Dikulushi is the most significant deposit in the region. Mineralisation at Dikulushi comprises two major styles: 1) a polysulphide assemblage (Zn–Pb–Fe–Cu–As) within brecciated rocks along an anticlinal closure; and 2) a vein-hosted Cu–Ag assemblage. Petrographic and fluid inclusion studies indicate that the early Zn–Pb–Fe–Cu–As assemblage formed from a high-salinity Ca–Na–Cl fluid of modest temperature (135–172 °C). The later, economically more significant vein-related Cu–Ag mineralisation formed from intermediate salinity, lower temperature (46–82 °C) Na–Cl fluids. Weathering of the sulphide minerals resulted in a supergene enrichment with the formation of secondary Cu-minerals.  相似文献   

7.
The Lufilian arc of Central Africa (also called Katangan belt or Copperbelt) is a zone of low to highgrade metasedimentary (and subsidiary igneous) rocks of Neoproterozoic age hosting highgrade CuCoU and PbZn mineralizations. The Lufilian arc is located between the Congo and Kalahari cratons and defines a structure which is convex to the north. Three major phases of deformation characterize the construction of the Lufilian arc. The first phase (D1) called the “Kolwezian phase” developed folds and thrust sheets with a northward transport direction. D1 deformation occurred in the Lufilian arc between ca. 800 and 710 Ma, with a peak in the range 790–750 Ma. It is here correlated with the main deformation in the Zambezi belt. Southward-verging folds with the same trends as the D1 structures were previously linked to a second tectonic event named Kundelunguian phase of the Lufilian orogeny. We show in this paper that they are backfolds developed during D1 along Katangan ramps and especially along the Kibaran foreland. The second phase (D2) of the Lufilian orogeny is the “Monwezi phase” including several large leftlateral strikeslip faults which have been activated successively. During this deformation phase, the eastern block of the belt rotated clockwise, giving the present day NWSE trend of D1 structures in this part of the Lufilian arc, and generating its convex geometry. The Mwembeshi dislocation, the major transcurrent shear zone separating the Zambezi and Lufilian arc, was mostly active during the D2 deformation phase. D2 deformation occurred between ca. 690 and 540 Ma. Such a long time interval is attributed to the migration of strikeslip faults developed sequentially from south to north, and probably to a slow convergence velocity during the collision between the Congo and Kalahari cratons. The third phase (D3) of the Lufilian orogeny is a late event called the “Chilatembo phase”, marked by structures transverse to the trends of the Lufilian arc. This deformation and the post-D2′ uppermost Kundelungu sequence (Ks3 Plateaux Group), are younger than 540 Ma and probably early Paleozoic.  相似文献   

8.
中非卢菲里安地区以铜钴资源闻名于世,同时也赋存一定的铀矿资源。铀成矿作用分别与大陆裂谷及盆地成岩期（876~823 Ma）、早期洋盆形成或大陆碰撞期（720~652 Ma）、卢菲里安变质高峰期（550~530 Ma）相对应。受区域构造活动影响形成的多期次热流体,从基底及加丹加超群富铀岩石萃取铀元素并在构造发育的区域富集成矿为其主要的成矿模式,其变质基底或班委乌卢基底可能提供了铀物质来源,热流体为载体,断裂及穹窿构造则提供通道与空间。含铀矿体多受地层及构造双重控制,围岩褐铁矿化及方柱石化对找矿具有指示意义。研究区内铀矿成矿条件较好,下罗安群受断裂及逆冲推覆构造影响强烈且蚀变较为发育的区域为有利的找矿前景区。  相似文献   

9.
Luiswishi is a Congo-type Neoproterozoic sediment-hosted stratiform Cu–Co ore deposit of the Central Africa Copperbelt, located northwest of Lubumbashi (DRC). The ores form two main Cu–Co orebodies hosted by the Mines Subgroup, one in the lower part of the Kamoto Formation and the other at the base of the Dolomitic Shales Formation. Sulphides occur essentially as early parallel layers of chalcopyrite and carrolite, and secondarily as late stockwork sulphides cross-cutting the bedding and the early sulphide generation. Both types of stratiform and stockwork chalcopyrite and carrolite were systematically analyzed for sulphur isotopes, along the lithostratigraphic succession of the Mine Series. The quite similar δ34S values of stratiform sulphides and late stockwork sulphides suggest an in situ recrystallization or a slight remobilization of stockwork sulphides without attainment of isotopic equilibrium between different sulphide phases (chalcopyrite and carrolite). The distribution of δ34S values (−14.4‰ to +17.5‰) combined with the lithology indicates a strong stratigraphic control of the sulphur isotope signature, supporting bacterial sulphate reduction during early diagenesis of the host sediments, in a shallow marine to lacustrine environment. Petrological features combined with sulphur isotopic data of sulphides at Luiswishi and previous results on nodules of anhydrite in the Mine Series indicate a dominant seawater/lacustrine origin for sulphates, precluding a possible hydrothermal participation. The high positive δ34S values of sulphides in the lower orebody at Luiswishi, hosted in massive chloritic–dolomitic siltite (known as Grey R.A.T.), fine-grained stratified dolostone (D.Strat.) and silicified-stromatolitic dolomites alternating with chloritic–dolomitic silty beds (R.S.F.), suggest that they were probably deposited during a period of regression in a basin cut off from seawater. The variations of δ34S values (i.e. the decrease of δ34S values from the Kamoto Formation to the overlying Dolomitic Shales and then the slight increase from S.D.2d to S.D.3a and S.D.3b members) are in perfect agreement with the inferred lithological and transgressive–regressive evolution of the ore-hosting sedimentary rocks [Cailteux, J., 1994. Lithostratigraphy of the Neoproterozoic Shaba-type (Zaire) Roan Supergroup and metallogenesis of associated stratiform mineralization. In: Kampunzu A.B., Lubala, R.T. (Eds.), Neoproterozoic Belts of Zambia, Zaire and Namibia. Journal of African Earth Sciences 19, 279–301].  相似文献   

10.
Stratabound epigenetic sulphide Zn–Pb–Cu ore deposits of the Central African Copperbelt in the Democratic Republic of Congo and Zambia are mostly hosted in deformed shallow marine platform carbonates and associated sedimentary rocks of the Neoproterozoic Katanga Supergroup. Economic orebodies, that also contain variable amounts of minor Cd, Co, Ge, Ag, Re, As, Mo, Ga, and V, occur mainly as irregular pipe-like bodies associated with collapse breccias and faults as well as lenticular bodies subparallel to bedding. Kipushi and Kabwe in the Democratic Republic of the Congo and Zambia, respectively, are the major examples of carbonate-hosted Zn–Pb–Cu mined deposits with important by-products of Ge, Cd, Ag and V in the Lufilian Arc, a major metallogenic province famous for its world-class sediment-hosted stratiform Cu–Co deposits. The carbonate-hosted deposits range in age from Neoproterozoic to early Palaeozoic (680 to 450 Ma). The formation of the relatively older Neoproterozoic deposits is probably related to early collision events during the Lufilian Orogeny, whereas the younger Palaeozoic deposits may be related to post-collisional processes of ore formation. Fluid inclusion and stable isotope data indicate that hydrothermal metal-bearing fluids evolved from formation brines during basin evolution and later tectonogenesis. Ore fluid migration occurred mainly along major thrust zones and other structural discontinuities such as karsts, breccias and faults within the Katangan cover rocks, resulting in ore deposition within favourable structures and reactive carbonates of the Katangan Supergroup.  相似文献   

11.
The Dikulushi Cu–Ag vein-type deposit is located on the Kundelungu Plateau, in the southeastern part of the Democratic Republic of Congo (D.R.C.). The Kundelungu Plateau is situated to the north of the Lufilian Arc that hosts the world-class stratiform Cu–Co deposits of the Central African Copperbelt. A combined petrographic, fluid inclusion and stable isotope study revealed that the mineralisation at Dikulushi developed during two spatially and temporally distinct mineralising episodes. An early Cu–Pb–Zn–Fe mineralisation took place during the Lufilian Orogeny in a zone of crosscutting EW- and NE-oriented faults and consists of a sequence of sulphides that precipitated from moderate-temperature, saline H2O–NaCl–CaCl2-rich fluids. These fluids interacted extensively with the country rocks. Sulphur was probably derived from thermochemical reduction of Neoproterozoic seawater sulphate. Undeformed, post-orogenic Cu–Ag mineralisation remobilised the upper part of the Cu–Pb–Zn–Fe mineralisation in an oxidising environment along reactivated and newly formed NE-oriented faults in the eastern part of the deposit. This mineralisation is dominated by massive Ag-rich chalcocite that precipitated from low-temperature H2O–NaCl–KCl fluids, generated by mixing of moderate- and low-saline fluids. The same evolution in mineralisation assemblages and types of mineralising fluids is observed in three other Cu deposits on the Kundelungu Plateau. Therefore, the recognition of two distinct types of (vein-type) mineralisation in the study area has a profound impact on the exploration in the Kundelungu Plateau region. The identification of a Cu–Ag type mineralisation at the surface could imply the presence of a Cu–Pb–Zn–Fe mineralisation at depth.  相似文献   

12.
The Lufilian Belt is of geological significance and economic importance due to rich CuCo mineralisation in the Katanga Province of the Democratic Republic of Congo and the Copperbelt of Zambia. Though thorough exploration has yielded much information on the mines districts, the understanding of the belt as a whole appears, to some extent, historically charged and confused. In the first part of this article, basic knowledge and assumptions are reviewed and existing models critically assessed. Results include recognition of standard lithostratigraphies of the Katanga Supergroup comprising the Roan, Mwashia, Lower and Upper Kudelungu Groups in the Copperbelt and Katanga, a lower limit for the onset of deposition at about 880 Ma, and a major orogenetic event involving northeast directed thrusting (Lufilian Orogeny) at 560-550 Ma. The depositional history of the Lufilian Belt was controlled by continental rifting leading to formation of a passive continental margin. Continental rifting related to the dispersal of Rodinia began ca 880 Ma ago and was accompanied by magmatism (Kafue rhyolites: 879 Ma; Nchanga Granite: 877 Ma; Lusaka Granite: 865 Ma). Differential subsidence of the northwestward propagating rift soon allowed invasion by the sea advancing from the southeast, and subsequent development of marine rift-basin and platform domains. The standard stratigraphies for the Roan Group are restricted to the platform domain that bordered the rift-basin on its northeastern side. This domain included the Domes region of the Lufilian Belt and extended southeastwards into the northern Zambezi Belt. The platform was differentiated into a carbonate platform (barrier) represented by the Bancroft Subgroup (previously ‘Upper Roan’) in Zambia and Kambove Dolomite Formation in Katanga and a lagoon-basin (lower Kitwe Subgroup/Zambia; Dolomitic Shale Formation/Katanga) with mudflats (R.A.T. Subgroup/Katanga) and a siliciclastic margin towards the hinterland. The mineralised horizons of the ‘Ore Formation’ in Zambia and ‘Series des Mines’ in Katanga are related to temporarily anoxic conditions prevailing in the Roan Lagoon-Basin which had a southwest-northeast extent of ca 400 km. The lagoon-basin was subsequently filled by clastics derived from mainly northeastern sources (upper Kitwe Subgroup/Zambia; Dipeta Subgroup/Katanga).Possibly due to continental rupture in the southeastern, more advanced, segment of the rift and concomitant differential movement in the rupturing plate, the Kundelungu Basin started to open during deposition of the Mwashia Group. Opening of the extensional basin was accompanied by rifting, rapid subsidence of the affected platform segment and widespread mafic magmatism, which lasted until deposition of the Lower Kundelungu Group. The elevated margins of the rapidly subsiding Kundelungu Basin offered favourable conditions for inland glaciation during the Sturtian-Rapitan global glaciation epoch. The diamictites of the Grand Conglomát are thus dated at ca 750 Ma.Tectonogenesis in the Lufilian and Zambezi Belts is related to ca 560-550 Ma collision of the ‘Angola-Kalahari Plate’ (comprising the Kalahari Craton and southwestern part of the Congo Craton) and the ‘Congo-Tanzania Plate’ (comprising the remaining part of the Congo Craton) along a southeast-northwest trending suture linking up the southern Mozambique Belt with the West Congo Belt. Collision was accompanied by northeast directed thrusting involving deep crustal detachments and forward-propagating thrust faults that developed in platform and slope deposits below a high level thrust. In the Domes region, the platform sequence was detached from its basement and displaced for ca 150 km into the External Fold-Thrust Belt of Katanga. The large displacement was enhanced by fluids liberated from evaporite-rich mudflat deposits of the R.A.T. Subgroup.In the Zambezi Belt, northeast directed thrusting was succeeded by southwest directed backfolding and backthrusting, due to greater shortening or thickening of the thrust wedge. The Mwembeshi Shear Zone accommodated greater shortening in the Zambezi Belt relative to the Lufilian Belt by sinistral transcurrent movement. The Mwembeshi Shear Zone is a reactivated pre-existing zone of weakness in the lithosphere of possibly Palæoproterozoic age. There is no evidence of Neoproterozoic collision along this zone in the Lufilian Belt/Zambezi Belt domain.  相似文献   

13.
Sediment-hosted base metal sulfide deposits in the Otavi Mountain Land occur in most stratigraphic units of the Neoproterozoic Damara Supergroup, including the basal Nosib Group, the middle Otavi Group and the uppermost Mulden Group. Deposits like Tsumeb (Pb–Cu–Zn–Ge), Kombat (Cu–Pb–Zn), Berg Aukas (Zn–Pb–V), Abenab West (Pb–Zn–V) all occur in Otavi Group dolostones, whereas siliciclastic and metavolcanic rocks host Cu–(Ag) or Cu–(Au) mineralization, respectively. The Tsumeb deposit appears to have been concentrated after the peak of the Damara orogeny at around 530 Ma as indicated by radiometric age data.Volcanic hosted Cu–(Au) deposits (Neuwerk and Askevold) in the Askevold Formation may be related to ore forming processes during continental rifting around 746 Ma. The timing of carbonate-hosted Pb–Zn deposits in the Abenab Subgroup at Berg Aukas and Abenab is not well constrained, but the stable (S, O, C) and Pb isotope as well as the ore fluid characteristics are similar to the Tsumeb-type ores. Regional scale ore fluid migration typical of MVT deposits is indicated by the presence of Pb–Zn occurrences over 2500 km2 within stratabound breccias of the Elandshoek Formation. Mulden Group siliciclastic rocks host the relatively young stratiform Cu–(Ag) Tschudi resource, which is comparable to Copperbelt-type sulfide ores.  相似文献   

14.
The Neoproterozoic Katangan R.A.T. (“Roches Argilo-Talqueuses”) Subgroup is a sedimentary sequence composed of red massive to irregularly bedded terrigenous-dolomitic rocks occurring at the base of the Katangan succession in Congo. Red R.A.T. is rarely exposed in a continuous section because it was affected by a major layer-parallel décollement during the Lufilian thrusting. However, in a number of thrust sheets, Red R.A.T. is in conformable sedimentary contact with Grey R.A.T which forms the base of the Mines Subgroup. Apart from the colour difference reflecting distinct depositional redox conditions, lithological, petrographical and geochemical features of Red and Grey R.A.T. are similar. A continuous sedimentary transition between these two lithological units is shown by the occurrence of variegated to yellowish R.A.T. The D. Strat. “Dolomies Stratifiées” formation of the Mines Subgroup conformably overlies the Grey R.A.T. In addition, a transitional gradation between Grey R.A.T. and D. Strat. occurs in most Cu–Co mines in Katanga and is marked by interbedding of Grey R.A.T.-type and D. Strat.-type layers or by a progressive petrographic and lithologic transition from R.A.T. to D. Strat. Thus, there is an unquestionable sedimentary transition between Grey R.A.T. and D. Strat. and between Grey R.A.T. and Red R.A.T.The R.A.T. Subgroup stratigraphically underlies the Mines Subgroup and therefore R.A.T. cannot be comprised of syn-orogenic sediments deposited upon the Kundelungu (formerly “Upper Kundelungu”) Group as suggested by Wendorff (2000). As a consequence, the Grey R.A.T. Cu–Co mineralisation definitely is part of the Mines Subgroup Lower Orebody, and does not represent a distinct generation of stratiform Cu–Co sulphide mineralisation younger than the Roan orebodies.  相似文献   

15.
The sediment-hosted stratiform Cu–Co mineralization of the Luiswishi and Kamoto deposits in the Katangan Copperbelt is hosted by the Neoproterozoic Mines Subgroup. Two main hypogene Cu–Co sulfide mineralization stages and associated gangue minerals (dolomite and quartz) are distinguished. The first is an early diagenetic, typical stratiform mineralization with fine-grained minerals, whereas the second is a multistage syn-orogenic stratiform to stratabound mineralization with coarse-grained minerals. For both stages, the main hypogene Cu–Co sulfide minerals are chalcopyrite, bornite, carrollite, and chalcocite. These minerals are in many places replaced by supergene sulfides (e.g., digenite and covellite), especially near the surface, and are completely oxidized in the weathered superficial zone and in surface outcrops, with malachite, heterogenite, chrysocolla, and azurite as the main oxidation products. The hypogene sulfides of the first Cu–Co stage display δ34S values (−10.3‰ to +3.1‰ Vienna Canyon Diablo Troilite (V-CDT)), which partly overlap with the δ34S signature of framboidal pyrites (−28.7‰ to 4.2‰ V-CDT) and have ∆34SSO4-Sulfides in the range of 14.4‰ to 27.8‰. This fractionation is consistent with bacterial sulfate reduction (BSR). The hypogene sulfides of the second Cu–Co stage display δ34S signatures that are either similar (−13.1‰ to +5.2‰ V-CDT) to the δ34S values of the sulfides of the first Cu–Co stage or comparable (+18.6‰ to +21.0‰ V-CDT) to the δ34S of Neoproterozoic seawater. This indicates that the sulfides of the second stage obtained their sulfur by both remobilization from early diagenetic sulfides and from thermochemical sulfate reduction (TSR). The carbon (−9.9‰ to −1.4‰ Vienna Pee Dee Belemnite (V-PDB)) and oxygen (−14.3‰ to −7.7‰ V-PDB) isotope signatures of dolomites associated with the first Cu–Co stage are in agreement with the interpretation that these dolomites are by-products of BSR. The carbon (−8.6‰ to +0.3‰ V-PDB) and oxygen (−24.0‰ to −10.3‰ V-PDB) isotope signatures of dolomites associated with the second Cu–Co stage are mostly similar to the δ13C (−7.1‰ to +1.3‰ V-PDB) and δ18O (−14.5‰ to −7.2‰ V-PDB) of the host rock and of the dolomites of the first Cu–Co stage. This indicates that the dolomites of the second Cu–Co stage precipitated from a high-temperature, host rock-buffered fluid, possibly under the influence of TSR. The dolomites associated with the first Cu–Co stage are characterized by significantly radiogenic Sr isotope signatures (0.70987 to 0.73576) that show a good correspondence with the Sr isotope signatures of the granitic basement rocks at an age of ca. 816 Ma. This indicates that the mineralizing fluid of the first Cu–Co stage has most likely leached radiogenic Sr and Cu–Co metals by interaction with the underlying basement rocks and/or with arenitic sedimentary rocks derived from such a basement. In contrast, the Sr isotope signatures (0.70883 to 0.71215) of the dolomites associated with the second stage show a good correspondence with the 87Sr/86Sr ratios (0.70723 to 0.70927) of poorly mineralized/barren host rocks at ca. 590 Ma. This indicates that the fluid of the second Cu–Co stage was likely a remobilizing fluid that significantly interacted with the country rocks and possibly did not mobilize additional metals from the basement rocks.  相似文献   

16.
The Lufilian arc is an orogenic belt in central Africa that extends between Zambia and the Democratic Republic of Congo (DRC) and deforms the Neoproterozoic-Lower Palaeozoic metasedimentary succession of the Katanga Supergroup. The arc contains thick bodies of fragmental rocks that include blocks reaching several kilometres in size. Some megablocks contain Cu and Cu–Co-mineralised Katangan strata. These coarse clastic rocks, called the Katangan megabreccias, have traditionally been interpreted in the DRC as tectonic breccias formed during Lufilian orogenesis due to friction underneath Katangan nappes. In mid-90th, several occurrences in Zambia have been interpreted in the same manner. Prominent among them is an occurrence at Mufulira, considered by previous workers as a ≈1000 m thick tectonic friction breccia containing a Cu–Co-mineralised megablock.This paper presents new results pertaining to the lower stratigraphic interval of the Katanga Supergroup at Mufulira and represented by the Roan Group and the succeeding Mwashya Subgroup of the Guba Group. The interval interpreted in the past as tectonic Roan megabreccia appears to be an almost intact sedimentary succession, the lower part of which consists of Roan Group carbonate rocks with siliciclastic intercalations containing several interbeds of matrix-supported conglomerate. A Cu–Co-mineralised interval is not an allochthonous block but a part of the stratigraphic succession underlain and overlain by conglomerate beds, which were considered in the past as tectonic friction breccias. The overlying megabreccia is a syn-rift sedimentary olistostrome succession that rests upon the Roan strata with a subtle local unconformity. The olistostrome succession consists of three complexes typified by matrix-supported debris-flow conglomerates with Roan clasts. Some of the conglomerate beds pass upwards to normally graded turbidite layers and are accompanied by solitary slump beds. The three conglomeratic assemblages are separated by two intervals of sedimentary breccia composed of allochthonous Roan blocks interpreted as mass-wasting debris redeposited into the basin by high-volume sediment-gravity flows. Sedimentary features are the primary characteristics of the conglomerate interbeds in the Roan succession and of the overlying megabreccia (olistostrome) sequence. Both lithological associations are slightly sheared and brecciated in places, but stratigraphic continuity is retained throughout their succession. The olistostrome is deformed by an open fold, the upper limb of which is truncated by and involved in a shear zone that extends upwards into Mwashya Subgroup strata thrust above.Based on the sedimentary genesis of the megabreccia, local tectonostratigraphic relations and correlation with the succession present in the Kafue anticline to the west, the Mwashya Subgroup, formerly considered as a twofold unit, is redefined here as a three-part succession. The lower Mwashya consists of an olistostrome complex defined as the Mufulira Formation, the middle Mwashya (formerly lower Mwashya) is a mixed succession of siliciclastic and carbonate strata locally containing silicified ooids and tuff interbeds, and the term upper Mwashya is retained for a succession of black shales with varying proportions of siltstone and sandstone interlayers. The sedimentary genesis and stratigraphic relations of the megabreccia at Mufulira imply that the position and tectonostratigraphic context of the Katangan Cu and Cu–Co orebodies hosted in megablocks associated with fragmental rocks, which were in the past interpreted as tectonic friction breccias, need to be critically re-assessed in the whole Lufilian arc.  相似文献   

17.
The Konkola deposit is a high grade stratiform Cu–Co ore deposit in the Central African Copperbelt in Zambia. Economic mineralisation is confined to the Ore Shale formation, part of the Neoproterozoic metasedimentary rocks of the Katanga Supergroup. Petrographic study reveals that the copper–cobalt ore minerals are disseminated within the host rock, sometimes concentrated along bedding planes, often associated with dolomitic bands or clustered in cemented lenses and in layer-parallel and irregular veins. The hypogene sulphide mineralogy consists predominantly of chalcopyrite, bornite and chalcocite. Based upon relationships with metamorphic biotite, vein sulphides and most of the sulphides in cemented lenses were precipitated during or after biotite zone greenschist facies metamorphism. New δ34S values of sulphides from the Konkola deposit are presented. The sulphur isotope values range from −8.7‰ to +1.4‰ V-CDT for chalcopyrite from all mineralising phases and from −4.4‰ to +2.0‰ V-CDT for secondary chalcocite. Similarities in δ34S for sulphides from different vein generations, earlier sulphides and secondary chalcocite can be explained by (re)mobilisation of S from earlier formed sulphide phases, an interpretation strongly supported by the petrographic evidence. Deep supergene enrichment and leaching occurs up to a km in depth, predominantly in the form of secondary chalcocite, goethite and malachite and is often associated with zones of high permeability. Detailed distribution maps of total copper and total cobalt contents of the Ore Shale formation show a close relationship between structural features and higher copper and lower cobalt contents, relative to other areas of the mine. Structural features include the Kirilabombwe anticline and fault zones along the axial plane and two fault zones in the southern limb of the anticline. Cobalt and copper behave differently in relation to these structural features. These structures are interpreted to have played a significant role in (re)mobilisation and concentration of the metals, in agreement with observations made elsewhere in the Zambian Copperbelt.  相似文献   

18.
The Pan-African Lufilian orogenic belt hosts world-class Cu deposits. In the Congolese Copperbelt (DRC), Cu(–Co) deposits, are mostly hosted within evaporitic and siliciclastic Neoproterozoic metasedimentary rocks (Mines Subgroup) and are interpreted as syn- to late-diagenetic deposits. In this paper, we present new data on Cu(–U) deposit hosted in metamorphic rocks of the internal zone of the Lufilian belt known as the Western Zambian Copperbelt in which a primary Cu mineralization is overprinted by a second syn-metamorphic Cu mineralizing event. This mineralizing event is synchronous with the Pan-African metamorphism affecting both the pre-Katanga basement and the Katanga metasedimentary sequence. Cu(–U) occurrences in the Western Zambian Copperbelt are hosted by kyanite-micaschists metamorphosed in the upper amphibolite facies.Mineral inclusions of graphite, micas and sulfides in kyanite porphyroblasts of the Cu-bearing kyanite-micaschists in the Lumwana Cu deposit point to a sedimentary protolith with relics of an inherited Cu stock. Based on petrologic, microstructural and geochronological evidence, we propose that this initial Cu-stock was remobilized during the Pan-African orogeny. Graphite, micas and sulfides preserved in a first generation of kyanite poikiloblasts (Ky1) define an inherited S0/1 foliation developed during the prograde part of the P–T path (D1 deformation-metamorphic stage) reaching HP–MT metamorphic conditions.Remobilization during the retrograde part of the P–T path is evidenced by chalcopyrite–pyrrhotite and chalcopyrite–bornite delineating a steep-dipping S2 schistosity and by chalcopyrite and bornite delineating a shallow-dipping S3 schistosity associated with top to the south kinematic criteria. This retrograde path is coeval with ductile deformation in the kyanite field as evidenced by a second generation of synkinematic kyanite porphyroblasts (Ky2) transposed in the S3 schistosity (Ky2–3), and is marked by progressive cooling from ca. 620 °C down to 580 °C (rutile geothermometry). Syn-S2–3 metamorphic monazite grains yield U–Th–Pb ages ranging from ca. 540 to 500 Ma.Final retrogression and remobilization of Cu is marked by recrystallization of the sulfides in top to the north C3 shear bands associated with rutile crystals yielding temperatures from ca. 610 to 540 °C. This final remobilization is younger than ca. 500 Ma (youngest U–Th–Pb age on syn-S3 recrystallized monazite). These data are consistent with successive Cu remobilization for more than 40 Ma during Pan-African reworking of sediment-hosted deposits either from the basement of the Katanga sedimentary sequence or from the Katanga sequence itself marked by burial (D1), syn-orogenic exhumation (D2), and post-orogenic exhumation during gravitational collapse (D3).  相似文献   

19.
Fundamental evidence from world-class stratiform copper deposits repeatedly indicates that they originated by a two-stage mineralization process: a syn-diagenetic enrichment of the host sediment in iron sulfide, followed by a sub-surface addition of copper during early diagenesis of the sediment. In contrast to the previously favored syngenetic hypothesis, which suggested an open equilibration between atmosphere, hydrosphere, biosphere and upper lithosphere during mineralization, the two-stage model implies that only the initial deposition of iron sulfides should take place with open exchanges between the upper “spheres”. The sub-surface emplacement of copper should occur in relative isolation from surface environments and, therefore, the occurrence and distribution of stratiform copper deposits through time and space should not be used to make direct interpretations of contemporaneous conditions in the upper “spheres”.  相似文献   

20.
卢菲利安弧形构造带由泛非运动引起,该带由南往北可进一步划分为加丹加高地、复向斜带、穹隆区、外部褶皱逆冲带和前陆带等5个单元。泛非运动期间,卢菲利安弧经历了3个不同的构造变形阶段。文章对中非铜钴成矿带的地层层序进行了合理划分,将中非铜钴成矿带中的矿床类型划分为6种,最著名的为矿山亚群中的层状铜钴矿床,次为恩古巴群中以碳酸盐岩为容矿岩石的锌铅铜银矿床;总结了成矿带中矿床的时空分布规律,认为矿床受地层、岩性、构造和表生氧化作用的联合控制。  相似文献   

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