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1.
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   

2.
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   

3.
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   

4.
The outer sector of the Neoproterozoic Katangan Orogen of Central Africa is characterised by nappes thrust northwards, toward the foreland region, the major part of which occurs in the Democratic Republic of Congo (DRC). The rocks called R.A.T. (‘Roches Argilo-Talqueuses’) are terrigenous clastics traditionally considered as the oldest stratigraphical interval of these allochthonous units. They are correlated with the terrigenous clastic sediments at the base of the autochthonous Katangan succession in Zambia to the south, which were deposited at the opening stage of the Katangan Rift Basin. The lower interval of the R.A.T. represents red beds, whereas the upper one was deposited in anoxic conditions. Therefore, they are called red and grey R.A.T., respectively. This paper presents stratigraphic, structural and geochemical arguments against the traditional stratigraphical view and demonstrates that the R.A.T. rocks are younger than previously considered. They are interpreted here as synorogenic sediments of the Katangan foreland basin.Olistostromes with R.A.T. olistoliths, which occur either interbedded within ‘normal’ R.A.T. sediments or overlie angular unconformities, testify to pronounced tectonic movements and palæotopography of the basin in which the R.A.T. sediments were deposited. The provenance of other olistoliths implies that, contrary to the previous views, the R.A.T. olistostromes are younger than the overlying rock complexes and the contact between the two is tectonic. Clastic dykes of the incompetent R.A.T. lithologies injected into the overlying competent units suggest that the former were partly unconsolidated sediments over-ridden by the Katangan nappes. Plots of the geochemical compositions point to two distinct tectonosedimentary cycles and two types of sources, each related to a different stage of orogen evolution. The terrigenous materials of the Katangan autochthonous strata (Roan and Kundelungu Groups) and correlative allochthonous units are derived from basement granitic and metamorphic rocks eroded during the opening of the Katagan rift basin. By contrast, the R.A.T. rocks are related to the closure of the basin. Their provenance is from the orogenic source-the Katangan nappes advancing towards the foreland region in the north.The autochthonous Roan Group rocks in Zambia and their allochthonous correlatives in DRC contain one of the richest Cu-Co deposits known. In accord with the previous correlation, the CuCo mineralisation in the grey R.A.T. rocks was considered of the same age as the Zambian deposits. However, the results presented in this paper imply that the grey R.A.T. deposits represent a second generation of mineralisation in the Katangan belt, younger than the Roan Group orebodies. The R.A.T. Cu-Co mineralisation is related to the anoxic stage of the foreland basin, and the advancing nappes containing Roan-correlative orebodies acted as the sources of the metals. In conclusion, points pertaining to the revision of stratigraphical classification of the Katangan Supergroup are proposed.  相似文献   

5.
The Itacaiúnas Belt of the highly mineralised Carajás Mineral Province comprises ca. 2.75 Ga volcanic rocks overlain by sedimentary sequences of ca. 2.68 Ga age, that represent an intracratonic basin rather than a greenstone belt. Rocks are generally at low strain and low metamorphic grade, but are often highly deformed and at amphibolite facies grade adjacent to the Cinzento Strike Slip System. The Province has been long recognised for its giant enriched iron and manganese deposits, but over the past 20 years has been increasingly acknowledged as one of the most important Cu–Au and Au–PGE provinces globally, with deposits extending along an approximately 150 km long WNW-trending zone about 60 km wide centred on the Carajás Fault. The larger deposits (approx. 200–1000 Mt @ 0.95–1.4% Cu and 0.3–0.85 g/t Au) are classic Fe-oxide Cu–Au deposits that include Salobo, Igarapé Bahia–Alemão, Cristalino and Sossego. They are largely hosted in the lower volcanic sequences and basement gneisses as pipe- or ring-like mineralised, generally breccia bodies that are strongly Fe- and LREE-enriched, commonly with anomalous Co and U, and quartz- and sulfur-deficient. Iron oxides and Fe-rich carbonates and/or silicates are invariably present. Rhenium–Os dating of molybdenite at Salobo and SHRIMP Pb–Pb dating of hydrothermal monazite at Igarapé-Bahia indicate ages of ca. 2.57 Ga for mineralisation, indistinguishable from ages of poorly-exposed Archean alkalic and A-type intrusions in the Itacaiúnas Belt, strongly implicating a deep magmatic connection.A group of smaller, commonly supergene-enriched Cu–Au deposits (generally < 50 Mt @ < 2% Cu and < 1 g/t Au in hypogene ore), with enrichment in granitophile elements such as W, Sn and Bi, spatially overlap the Archean Fe-oxide Cu–Au deposits. These include the Breves, Águas Claras, Gameleira and Estrela deposits which are largely hosted by the upper sedimentary sequence as greisen-to ring-like or stockwork bodies. They generally lack abundant Fe-oxides, are quartz-bearing and contain more S-rich Cu–Fe sulfides than the Fe-oxide Cu–Au deposits, although Cento e Dezoito (118) appears to be a transitional type of deposit. Precise Pb–Pb in hydrothermal phosphate dating of the Breves and Cento e Dezoito deposits indicate ages of 1872 ± 7 Ma and 1868 ± 7 Ma, respectively, indistinguishable from Pb–Pb ages of zircons from adjacent A-type granites and associated dykes which range from 1874 ± 2 Ma to 1883 ± 2 Ma, with 1878 ± 8 Ma the age of intrusions at Breves. An unpublished Ar/Ar age for hydrothermal biotite at Estrela is indistinguishable, and a Sm–Nd isochron age for Gameleira is also similar, although somewhat younger. The geochronological data, combined with geological constraints and ore-element associations, strongly implicate a magmatic connection for these deposits.The highly anomalous, hydrothermal Serra Pelada Au–PGE deposit lies at the north-eastern edge of the Province within the same fault corridor as the Archean and Paleoproterozoic Cu–Au deposits, and like the Cu–Au deposits is LREE enriched. It appears to have formed from highly oxidising ore fluids that were neutralised by dolomites and reduced by carbonaceous shales in the upper sedimentary succession within the hinge of a reclined synform. The imprecise Pb–Pb in hydrothermal phosphate age of 1861 ± 45 Ma, combined with an Ar/Ar age of hydrothermal biotite of 1882 ± 3 Ma, are indistinguishable from a Pb–Pb in zircon age of 1883 ± 2 Ma for the adjacent Cigano A-type granite and indistinguishable from the age of the Paleoproterozoic Cu–Au deposits. Again a magmatic connection is indicated, particularly as there is no other credible heat or fluid source at that time.Finally, there is minor Au–(Cu) mineralisation associated with the Formiga Granite whose age is probably ca. 600 Ma, although there is little new zircon growth during crystallisation of the granite. This granite is probably related to the adjacent Neoproterozoic (900–600 Ma) Araguaia Fold Belt, formed as part of the Brasiliano Orogeny.Thus, there are two major and one minor period of Cu–Au mineralisation in the Carajás Mineral Province. The two major events display strong REE enrichment and strongly enhanced LREE. There is a trend from strongly Fe-rich, low-SiO2 and low-S deposits to quartz-bearing and more S-rich systems with time. There cannot be significant connate or basinal fluid (commonly invoked in the genesis of Fe-oxide Cu–Au deposits) involved as all host rocks were metamorphosed well before mineralisation: some host rocks are at mid- to high-amphibolite facies. The two major periods of mineralisation correspond to two periods of alkalic to A-type magmatism at ca. 2.57 Ga and ca. 1.88 Ga, and a magmatic association is compelling.The giant to world-class late Archean Fe-oxide Cu–Au deposits show the least obvious association with deep-seated alkaline bodies as shown at Palabora, South Africa, and implied at Olympic Dam, South Australia. The smaller Paleoproterozoic Cu–Au–W–Sn–Bi deposits and Au–PGE deposit show a more obvious relationship to more fractionated A-type granites, and the Neoproterozoic Au–(Cu) deposit to crustally-derived magmas. The available data suggest that magmas and ore fluids were derived from long-lived metasomatised lithosphere and lower crust beneath the eastern margin of the Amazon Craton in a tectonic setting similar to that of other large Precambrian Fe-oxide Cu–Au deposits.  相似文献   

6.
With a reserve of  200 Mt ore grading 6.08% Zn and 1.29% Pb (i.e., a metal reserve of  15 Mt) hosted in Cretaceous and Tertiary terrestrial rocks, the Jinding deposit is the largest Zn–Pb deposit in China, and also the youngest sediment-hosted super giant Zn–Pb deposit in the world. The deposit mainly occurs in the Jinding dome structure as tabular orebodies within breccia-bearing sandstones of the Palaeocene Yunlong Formation (autochthonous) and in the overlying sandstones of the Early Cretaceous Jingxing Formation (allochthonous). The deposit is not stratiform and no exhalative sedimentary rocks have been observed. The occurrence of the orebodies, presence of hangingwall alteration, and replacement and open-space filling textures all indicate an epigenetic origin. Formation of the Jinding Zn–Pb deposit is related to a period of major continental crust movement during the collision of the Indian and Eurasian Plates. The westward thrusts and dome structure were successively developed in the Palaeocene sedimentary rocks in the ore district, and Zn–Pb mineralisation appears to have taken place in the early stage of the doming processes.The study of fluid inclusions in sphalerite and associated gangue minerals (quartz, celestine, calcite and gypsum) shows that homogenisation temperatures ranged from 54 to 309 °C and cluster around 110 to 150 °C, with salinities of 1.6 to 18.0 wt.% NaCl equiv. Inert gas isotope studies from inclusions in ore- and gangue-minerals reveal 2.0 to 15.6% mantle He, 53% mantle Ne and a considerable amount of mantle Xe in the ore-forming fluids. The Pb-isotope composition of ores shows that the metal is mainly of mantle origin, mixed with a lesser amount of crustal lead. The widely variable and negative δ34S values of Jinding sulphides suggest that thermo-chemical or bacterial sulphate reduction produced reduced sulphur for deposition of the Zn–Pb sulphides. The mixing of a mantle-sourced fluid enriched in metals and CO2 with reduced sulphide-bearing saline formation water in a structural–lithologic trap may have been the key mechanism for the formation of the Jinding deposit.The Jinding deposit differs from known major types of sediment-hosted Zn–Pb deposits in the world, including sandstone-type (SST), Mississippi Valley type (MVT) and sedimentary-exhalative (SEDEX). Although the fine-grained ore texture and high Zn/Pb ratios are similar to those in SEDEX deposits, the Jinding deposit lacks any exhalative sedimentary rocks. Like MVT deposits, Jinding is characterised by simple mineralogy, epigenetic features and involvement of basinal brines in mineralisation, but its host rocks are mainly sandstones and breccia-bearing sandstones. The Jinding deposit is also different from SST deposits with its high Zn/Pb ratios, among other characteristics. Most importantly, the Jinding deposit was formed in an intracontinental terrestrial basin with an active tectonic history in relation to plate collision, and mantle-sourced fluids and metals played a major role in ore formation, which is not the case for SEDEX, MVT, and SST. We propose that Jinding represents a new type of sediment-hosted Zn–Pb deposit, named the ‘Jinding type’.  相似文献   

7.
A multiphase origin of the Cu–Co ores in the western part of the Lufilian fold-and-thrust belt in Central Africa is proposed based on literature, satellite image interpretations and petrographic and fluid inclusion analyses on samples from the stratiform mineralization of Kamoto and Musonoi (DR Congo). The various mineral occurrences in the Katanga Copperbelt can be classified in distinct categories: stratiform, supergene enrichment and vein-type. The stratiform mineralization form the largest group and can be found mainly in Lower Roan (R-2) rocks, which can be identified as ridges on satellite imagery. Ore deposits outside the R-2 occur along lineaments and result often from supergene enrichment.The main phase of the stratiform mineralization in the Katanga Copperbelt occurred during diagenesis preceding the Lufilian orogeny. Petrographic observation identified various mineralizing phases, which played a role in the formation of these stratiform mineralization. Mineralization started during early diagenesis, but mainly occurred during further burial. After the formation of early diagenetic pyrite, the circulation of diagenetic Cu–Co-rich fluids resulted in the formation of the main mineralization. Preliminary microthermometric investigation of primary inclusions in authigenic quartz, associated with the main stage of stratiform mineralization, indicates that an H2O–NaCl fluid with a minimum temperature between 80 and 195 °C and a salinity between 8.4 and 18.4 eq. wt% NaCl circulated during the main phase of mineralization.Numerous faults and fractures formed during the Lufilian orogeny cut the stratiform mineralization. They are, however, at Kamoto and Musonoi only associated with minor sulphides. Supergene alteration along faults and fractures resulted in an enrichment of the mineralization, with the formation of secondary Cu-oxides, -carbonates and -silicates.The importance of the interaction of various processes for the formation of economic Cu–Co ore deposits is confirmed by the straightforward relationship on satellite imagery between the location of economic mineral occurrences and faults, which acted as pathway for descending waters that caused the supergene enrichment and upgrading of the primary mineralization.  相似文献   

8.
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   

9.
The Central African Copperbelt lies within the Lufilian orogenic belt, in the border region between the Democratic Republic of Congo (DRC) and Zambia. A Sr and Nd isotope study was performed on gangue carbonates associated with multiphase mineralisation at the Zambian Konkola and Nkana deposits. Comparison with isotopic signatures of basement rocks provides new insights into the likely metal source(s) for the Cu–Co mineralisation. At least three mineralisation phases can be identified with respect to the Lufilian orogeny. Gangue carbonates of the first, pre- to syn-kinematic mineralisation phase in both deposits have Sr and Nd isotopic compositions that correspond to felsic rocks of the Domes Region, a tectonic zone in the Zambian part of the Lufilian Belt where basement rocks crop out. However, the isotopic signatures from both deposits differ. This can be attributed to local variation in isotopic composition of the basement below the deposits. Radiogenic isotope ratios suggest that subsequent, syn-kinematic mineralisation at both sites occurred due to the remobilisation of precursor ore. Petrographic evidence indicates that the third, late-kinematic mineralisation phase at Nkana resulted from a renewed input of metals with a mafic affinity (e.g. Co, Ni). However, Sr and Nd isotope ratios resemble those of the earlier mineralisation phases and do not reflect a change in source composition. Nonetheless, comparison with the isotopic signatures of the Co-poor Konkola deposit and Co-rich stratiform deposits in the DRC might indicate a mafic component in the Nkana metal source. Calculated mixed isotopic compositions support such a mafic component.  相似文献   

10.
Lead isotope ratios of galena from the carbonate-hosted massive sulphide deposits of Kabwe (Pb-Zn) and Tsumeb (Pb-Zn-Cu) in Zambia and Namibia, respectively, have been measured and found to be homogeneous and characteristic of upper crustal source rocks. Kabwe galena has average isotope ratios of 206/204Pb = 17.997 ± 0.007, 207/204Pb = 15.713 ± 0.010 and 208/204Pb = 38.410 ± 0.033. Tsumeb galena has slightly higher 206/204Pb (18.112 ± 0.035) and slightly lower 207/204Pb (15.674 ± 0.016) and 208/204Pb (38.276 ± 0.073) ratios than Kabwe galena. The isotopic differences are attributed to local differences in the age and composition of the respective source rocks for Kabwe and Tsumeb. The homogeneity of the ore lead in the two epigenetic deposits suggests lead sources of uniform isotopic composition or, alternatively, thorough mixing of lead derived from sources with relatively similar isotopic compositions. Both deposits have relatively high 238U/204Pb ratios of 10.31 and 10.09 for Kabwe and Tsumeb galenas, respectively. These isotope ratios are considered to be typical of the upper continental crust in the Damaran-Lufilian orogenic belt, as also indicated by basement rocks and Cu-Co sulphides in stratiform Katangan metasediments which have a mean μ-value of 10.25 ± 0.12 in the Copperbelt region of Zambia and the Democratic Republic of Congo (formerly Zaire). The 232Th/204Pb isotope ratios of 43.08 and 40.42 for Kabwe and Tsumeb suggest Th-enriched source regions with 232Th/235U (κ-values) of 4.18 and 4.01, respectively. Model isotopic ages determined for the Kabwe (680 Ma) and Tsumeb (530 Ma) deposits indicate that the timing of the mineralisation was probably related to phases of orogenic activity associated with the Pan-African Lufilian and Damaran orogenies, respectively. Galena from the carbonate-hosted Kipushi Cu-Pb-Zn massive sulphide deposit in the Congo also has homogeneous lead isotope ratios, but its isotopic composition is comparable to that of the average global lead evolution curve for conformable massive sulphide deposits. The μ (9.84) and κ (3.69) values indicate a significant mantle component, and the isotopic age of the Kipushi deposit (456 Ma) suggests that the emplacement of the mineralisation was related to a post-tectonic phase of igneous activity in the Lufilian belt. The isotope ratios (206/204Pb, 207/204Pb, 208/204Pb) of the three deposits are markedly different from the heterogeneous lead ratios of the Katangan Cu-Co stratiform mineralisation of the Copperbelt as well as those of the volcanogenic Nampundwe massive pyrite deposit in the Zambezi belt which typically define radiogenic linear trends on lead-lead plots. The host-rock dolomite of the Kabwe deposit also has homogeneous lead isotope ratios identical to the ore galena. This observation indicates contamination of the Kabwe Dolomite Formation with ore lead during mineralisation. Received: 8 September 1997 / Accepted: 21 August 1998  相似文献   

11.
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   

12.
张东红 《地质与勘探》2013,49(3):577-588
沉积型铜矿作为重要的铜矿类型之一,一直是工业界找矿和开发的重点。中非铜(-钴)矿带是世界著名的巨型沉积型铜矿带之一。赞比亚谦比希铜矿是我国企业在非洲矿业开发的成功典范项目,其矿体分布和产状严格受新元古代加丹加超群的下罗恩组地层控制,含矿岩石为下罗恩组下部的含矿泥质页岩、砂岩。本文通过对谦比希铜矿的矿床地质特征、成矿地质背景、成岩-成矿规律的详细研究,揭示了其含矿地层和矿体明显受古沉积环境、基底形态的控制;成岩-成矿过程经历了海侵-海退过程,沉积古地理环境为滨浅海蒸发背景。赞比亚铜带省和西北省拥有巨大的资源和找矿潜力,未来必将吸引更多投资。  相似文献   

13.
The South Australian portion of the Willyama Inliers hosts a diversity of small sulphide and uranium deposits and numerous outcropping gossans. This fact, together with geological similarities to the adjacent Broken Hill Block has led to extensive exploration. A broad classification distinguishes two main types of sulphide mineralisation: 1) stratiform iron sulphide-dominated (±Cu, Zn, Co) deposits which occur widespread within specific stratigraphic intervals, and stratabound occurrences of syn-depositional to diagenetic origin which show some structural control; 2) syn-tectonic to post-peak metamorphic replacement and vein-type deposits (Fe-Cu-Au and Cu-Zn-Pb), which are hosted by fractures and within faults and shear zones. These occurrences show no stratigraphic control and are not spatially related to type 1 mineralisation. Late-stage deposits also differ from stratiform/stratabound mineralisation in their texture, mineral assemblage and geochemical composition. Much of the sulphide mineralisation in the Olary Block has been interpreted as resulting from rift-associated syn- to diagenetic processes, such as hot spring exhalations and base metal precipitation along reduction-oxidation interfaces. Subsequent granitic intrusive, high grade metamorphic and multiphase deformation events would have induced remobilisation and redeposition of sulphides in a variety of epigenetic modes. However, a detailed petrographic and geochemical study of sulphide mineralisation in the Olary Block demonstrates that due to the lack of abundant pervasive fluids, translocation and modification of preexisting sulphides were restricted to less than a few centimetres. Instead, widespread syn-tectonic to epigenetic (i.e., post-peak metamorphic) mobilisation of ore constituents occurred to form retrograde sulphide mineralisation as well as multiple generations of late-stage vein deposits. These epigenetic deposits are genetically unrelated to synsedimentary and diagenetic occurrences, an aspect of significance for exploration in the Olary Block. Temporal separation of peak metamorphism in deeper crustal levels from its occurrence in shallow levels, periodic tectonic disturbances and repeated seismic pumping are processes believed to have resulted in intermittent mobilisation of ore constituents from a deep-seated metasedimentary reservoir.  相似文献   

14.
The Neoproterozoic Katangan Supergroup comprises a thick sedimentary rock succession subdivided into the Roan, Nguba, and Kundelungu Groups, from bottom to top. Deposition of both Nguba and Kundelungu Groups began with diamictites, the Mwale/Grand Conglomérat and Kyandamu/Petit Conglomérat Formations, respectively, correlated with the 750 Ma Sturtian and (supposedly) 620 Ma Marinoan/Varanger glacial events. The Kaponda, Kakontwe, Kipushi and Lusele Formations are interpreted as cap-carbonates overlying the diamictites. Petrographical features of the Nguba and Kundelungu siliciclastic rocks indicate a proximal facies in the northern areas and a basin open to the south. The carbonate deposits increase southward in the Nguba basin. In the southern region, the Kyandamu Formation contains clasts from the underlying rocks, indicating an exhumation and erosion of these rocks to the south of the basin. It is inferred that this formation deposited in a foreland basin, dating the inversion from extensional to compressional tectonics, and the northward thrusting. Sampwe and Biano sedimentary rocks were deposited in the northernmost foreland basin at the end of the thrusting. The Zn–Pb–Cu and Cu–Ag–Au epigenetic, hypogene deposits occurring in Nguba carbonates and Kundelungu clastic rocks probably originate from hydrothermal resetting and remobilization of pre-existing stratiform base metal mineralisations in the Roan Group.  相似文献   

15.
The stratiform Cu–Co ore mineralisation in the Katangan Copperbelt consists of dispersed sulphides and sulphides in nodules and lenses, which are often pseudomorphs after evaporites. Two types of pseudomorphs can be distinguished in the nodules and lenses. In type 1 examples, dolomite precipitated first and was subsequently replaced by Cu–Co sulphides and authigenic quartz, whereas in type 2 examples, authigenic quartz and Cu–Co sulphides precipitated prior to dolomite and are coarse-grained. The sulphur isotopic composition of the copper–cobalt sulphides in the type 1 pseudomorphs is between −10.3 and 3.1‰ relative to the Vienna Canyon Diablo Troilite, indicating that the sulphide component was derived from bacterial sulphate reduction (BSR). The generation of during this process caused the precipitation and replacement of anhydrite by dolomite. A second product of BSR is the generation of H2S, resulting in the precipitation of Cu–Co sulphides from the mineralising fluids. Initial sulphide precipitation occurred along the rim of the pseudomorphs and continued towards the core. Precipitation of authigenic quartz was most likely induced by a pH decrease during sulphide precipitation. Fluid inclusion data from quartz indicate the presence of a high-salinity (8–18 eq. wt.% NaCl) fluid, possibly derived from evaporated seawater which migrated through the deep subsurface. 87Sr/86Sr ratios of dolomite in type 1 nodules range between 0.71012 and 0.73576, significantly more radiogenic than the strontium isotopic composition of Neoproterozoic marine carbonates (87Sr/86Sr = 0.7056–0.7087). This suggests intense interaction with siliciclastic sedimentary rocks and/or the granitic basement. The low carbon isotopic composition of the dolomite in the pseudomorphs (−7.02 and −9.93‰ relative to the Vienna Pee Dee Belemnite, V-PDB) compared to the host rock dolomite (−4.90 and +1.31‰ V-PDB) resulted from the oxidation of organic matter during BSR.  相似文献   

16.
Most ore-forming characteristics of the Langshan-Zha‘ertaishan hydrothermal exhalation belt, which consists of the Dongshengmiao, Huogeqi, Tanyaokou and Jiashengpan large-superlarge Zn-Pb-Cu-Fe sulfide deposits, are most similar to those of Mesoproterozoic SEDEX-type provinces of the world. The characteristics include: (1) All deposits of this type in the belt occur in third-order fault-basins in the Langshan-Zha‘ertaishan aulacogen along the northern margin of the North China Platform; (2) these deposits with all their orebodies hosted in the Mesoproterozoic impure dolomite-marble and carbonaceous phyllite (or schists) have an apparent stratabound nature; ores display laminated and banded structures, showing clear depositional features; (3) there is some evidence of syn-sedimentary faulting, which to a certain extent accounts for the temporal and spatial distribution and the size of the orebodies in all deposits and the formation of intrabed conglomerates and breccias; (4) they show lateral and vertical zonation of sulfides; (5) The Cu/(Pb Zn Cu) ratio of the large and thick Pb Zn Cu orebodies gradually decreases from bottom to top; and (6) barite is interbedded with pyrites and sometimes with sphalerite. However, some characteristics such as the Co/Ni radio of the pyrites, the volcanism, for example, of the Langshan-Zha‘ertalshan metallogenic belt, are different from those of the typical SEDEX deposits of the world. The meta-basic volcanic rock in Huogeqi, the sodic bimodal volcanic rocks in the Dongshengmiao and potassic bimodal-volcanic rocks with blastoporphyfitic and blasto-glomeroporphyritic texture as well as blasto-amygdaloidal structure in the Tanyaokou deposits have been discovered in the only ore-bearing second formation of the Langshan Group in the past 10 years. The metallogeny of some deposits hosted in the Langshan Group is closely related to syn-sedimentary volcanism based on the following facts: most of the lead isotopes in sphalerite, galena, pyrite, pyrrhotite and chalcopyrite plot on both sides of the line for the mantle or between the lines for the mantle and lower crust in the lead isotope composition diagram; cobalt content of some pyrites samples is much higher than the nickel content (Co/Ni= 11.91-12.19). Some volcanic blocks and debris have been picked out from some pyritic and pyrrhotitic ores. All Zn-Pb-Cu-Fe sulfide orebodies in these deposits occur in the strata overlying metamorphic volcanic rocks in the only ore-bearing second formation. In the Jiashengpan deposit that lacks syn-sedimentary volcanic rocks in the host succession only Pb and Zn ores occur without Cu ore, but in the Dongshengmiao, Tanyaokou and Huogeqi deposits with syn-sedimentary volcanic rocks in the host succession Cu ores occur. This indicates a relatively higher ore-forming temperature. The process of synsedimentary volcanic eruption directly supplied some ore-forming elements, and resulted in secular geothermal anomaly favorable for the circulation of a submarine convective hydrothermal system, which accounts for the precipitation of deep mineralizing fluids exhaling into anoxidic basins along the syn-sedimentary fault system in the Langshan-Zha‘ertai rift. The Dongshengmiao, Tanyaokou, and Huogeqi deposits hosted in the Langshan Group appear to be a transitional type of mineral deposit between SEDEX and VMS-types but with a bias towards SEDEX, while the Jiashengpan deposit hosted in the Zha‘ertai Group is of a characteristic SEDEX type. This evidence, together with other new discoveries of Mesoproterozoic volcanic rocks and the features of lithogeny and metallogeny of the Bayun Obo deposit in the neighborhood emphasize the diversity, complexity and uniqueness of the Mesoproterozoic Langshan-Zha‘ertal-Bayun Obo ore belt.  相似文献   

17.
The Huize Zn–Pb–(Ag) district, in the Sichuan–Yunnan–Guizhou Zn–Pb–(Ag) metallogenic region, contains significant high-grade, Zn–Pb–(Ag) deposits. The total metal reserve of Zn and Pb exceeds 5 Mt. The district has the following geological characteristics: (1) high ore grade (Zn + Pb ≥ 25 wt.%); (2) enrichment in Ag and a range of other trace elements (Ge, In, Ga, Cd, and Tl), with galena, sphalerite, and pyrite being the major carriers of Ag, Ge, Cd and Tl; (3) ore distribution controlled by both structural and lithological features; (4) simple and limited wall-rock alteration; (5) mineral zonation within the orebodies; and (6) the presence of evaporite layers in the ore-hosting wall rocks of the Early Carboniferous Baizuo Formation and the underlying basement.Fluid-inclusion and isotope geochemical data indicate that the ore fluid has homogenisation temperatures of 165–220 °C, and salinities of 6.6–12 wt.% NaCl equiv., and that the ore-forming fluids and metals were predominantly derived from the Kunyang Group basement rocks and the evaporite-bearing rocks of the cover strata. Ores were deposited along favourable, specific ore-controlling structures. The new laboratory and field studies indicate that the Huize Zn–Pb–(Ag) district is not a carbonate-replacement deposit containing massive sulphides, but rather the deposits can be designated as deformed, carbonate-hosted, MVT-type deposits. Detailed study of the deposits has provided new clues to the localisation of concealed orebodies in the Huize Zn–Pb–(Ag) district and of the potential for similar carbonate-hosted sulphide deposits elsewhere in NE Yunnan Province, as well as the Sichuan–Yunnan–Guizhou Zn–Pb–(Ag) metallogenic region.  相似文献   

18.
The Rhodope Massif in southern Bulgaria and northern Greece hosts a range of Pb–Zn–Ag, Cu–Mo and Au–Ag deposits in high-grade metamorphic, continental sedimentary and igneous rocks. Following a protracted thrusting history as part of the Alpine–Himalayan collision, major late orogenic extension led to the formation of metamorphic core complexes, block faulting, sedimentary basin formation, acid to basic magmatism and hydrothermal activity within a relatively short period of time during the Early Tertiary. Large vein and carbonate replacement Pb–Zn deposits hosted by high-grade metamorphic rocks in the Central Rhodopean Dome (e.g., the Madan ore field) are spatially associated with low-angle detachment faults as well as local silicic dyke swarms and/or ignimbrites. Ore formation is essentially synchronous with post-extensional dome uplift and magmatism, which has a dominant crustal magma component according to Pb and Sr isotope data. Intermediate- and high-sulphidation Pb–Zn–Ag–Au deposits and minor porphyry Cu–Mo mineralization in the Eastern Rhodopes are predominantly hosted by veins in shoshonitic to high-K calc-alkaline volcanic rocks of closely similar age. Base-metal-poor, high-grade gold deposits of low sulphidation character occurring in continental sedimentary rocks of synextensional basins (e.g., Ada Tepe) show a close spatial and temporal relation to detachment faulting prior and during metamorphic core complex formation. Their formation predates local magmatism but may involve fluids from deep mantle magmas.The change in geochemical signatures of Palaeogene magmatic rocks, from predominantly silicic types in the Central Rhodopes to strongly fractionated shoshonitic (Bulgaria) to calc-alkaline and high-K calc-alkaline (Greece) magmas in the Eastern Rhodopes, coincides with the enrichment in Cu and Au relative to Pb and Zn of the associated ore deposits. This trend also correlates with a decrease in the radiogenic Pb and Sr isotope components of the magmatic rocks from west to east, reflecting a reduced crustal contamination of mantle magmas, which in turn correlates with a decreasing crustal thickness that can be observed today. Hydrogen and oxygen isotopic compositions of the related hydrothermal systems show a concomitant increase of magmatic relative to meteoric fluids, from the Pb–Zn–Ag deposits of the Central Rhodopes to the magmatic rock-hosted polymetallic gold deposits of the Eastern Rhodopes.  相似文献   

19.
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   

20.
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   

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