Geochemical characterisation, provenance, source and depositional environment of ‘Roches Argilo-Talqueuses’ (RAT) and Mines Subgroups sedimentary rocks in the Neoproterozoic Katangan Belt (Congo): Lithostratigraphic implications

The chemical characteristics of sedimentary rocks provide important clues to their provenance and depositional environments. Chemical analyses of 192 samples of Katangan sedimentary rocks from Kolwezi, Kambove–Kabolela and Luiswishi in the central African Copperbelt (Katanga, Congo) are used to constrain (1) the source and depositional environment of RAT and Mines Subgroup sedimentary rocks and (2) the geochemical relations between the rocks from these units and the debate on the lithostratigraphic position of the RAT Subgroup within the Katangan sedimentary succession. The geochemical data indicate that RAT, D. Strat., RSF and RSC are extremely poor in alkalis and very rich in MgO. SD are richer in alkalis, especially K₂O. Geochemical characteristics of RAT and Mines Subgroups sedimentary rocks indicate deposition under an evaporitic environment that evolved from oxidizing (Red RAT) to reducing (Grey RAT and Mines Subgroup) conditions. There is no chemical difference between RAT and fine-grained clastic rocks from the lower part of the Mines Subgroup. The geochemical data preclude the genetic model that RAT are syn-orogenic sedimentary rocks originating from Mines Group rocks by erosion and gravity-induced fragmentation in front of advancing nappes.     

Genesis of sediment-hosted stratiform copper–cobalt deposits, central African Copperbelt

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.     

The Neoproterozoic Mwashya–Kansuki sedimentary rock succession in the central African Copperbelt, its Cu–Co mineralisation, and regional correlations

Rocks of the Neoproterozoic Mwashya Subgroup (former Upper Mwashya) form the uppermost sedimentary unit of the Roan Group. Based on new field and drill hole observations, the Mwashya is subdivided into three formations: (1) Kamoya, characterized by dolomitic silty shales/siltstones/sandstones and containing a regional marker (the “Conglomerate de Mwashya” bed or complex); (2) Kafubu, formed by finely bedded black carbonaceous shales; and (3) Kanzadi, marked by feldspathic sandstones. Rocks of the Mwashya Subgroup are overlain by the Sturtian age Grand Conglomérat diamictite (equivalent to the Varianto/Brazil and Chuos/Namibia diamictites), and conformably overlie rocks of the Kansuki Formation (former Lower Mwashya), a carbonate unit containing volcaniclastic beds. New geochemical data confirm the continental rift context of this magmatism, which is contemporaneous with rift-related volcanism of the Askevold Formation (Nosib Group, Namibia). A gradational lithological transition between rocks of the Kansuki and the underlying Kanwangungu Formations, and similar petrological composition of these two formations, support the hypothesis that the Kansuki is the uppermost unit of the carbonate-dominated Dipeta/Kanwangungu sequence, and does not form part of the Mwashya Subgroup. Base metal deposits, mostly hosted in rocks of the Kansuki Formation, include weakly disseminated early-stage low-grade Cu–Co mineralisation, which was reworked and enriched, or initially deposited, by metamorphic fluids associated with the Lufilian orogenic event.     

Sulphur isotope constraints on formation conditions of the Luiswishi ore deposit, Democratic Republic of Congo (DRC)

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].     

Sedimentary genesis and lithostratigraphy of Neoproterozoic megabreccia from Mufulira, Copperbelt of Zambia

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.     

Revision of the stratigraphical position of the ‘Roches Argilo-Talqueuses’ (R.A.T.) in the neoproterozoic Katangan belt,south Congo

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.     

Metallogenesis of the Carajás Mineral Province, Southern Amazon Craton, Brazil: Varying styles of Archean through Paleoproterozoic to Neoproterozoic base- and precious-metal mineralisation

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.     

Santa Bárbara Formation (Early Paleozoic, Caçapava do Sul, southern Brazil): Petrographic and Sm–Nd isotopic provenance parameters

Integrated petrographic and Sm–Nd isotopic data were applied in order to constrain the provenance of the Early Paleozoic Santa Bárbara Formation, Sul-rio-grandense Shield, southern Brazil. This unit comprises continental sandstones, conglomerates and siltstones deposited under semi-arid climate in a rift or pull-apart basin. Samples were collected within a stratigraphic framework composed of three sequences, in which the two basal ones present northeastwards paleoflow, and the third one marks the inversion of basin filling. Samples from sequence I show, in the south, a strong influence of intermediate volcanic (Hilário Formation) sources, and a significant increase in quartz and metamorphic fragments upsection. In the northern deposits, there is a possible influence of juvenile units (Cambaí/Vacacaí), and a more significant input of Paleoproterozoic-sourced sedimentary rocks (e.g. Maricá Formation) upsection. Samples collected from the topmost deposits of sequence II present a clear increase in the amount of volcanic fragments (mostly acidic), reflecting denudation of the “Caçapava high”. Data obtained in sequence III (Pedra do Segredo) show a progressive decrease in quartz content and a significant increase in feldspathic, plutonic fragments. A more evolved phase of denudation of the “Caçapava high”, exposing leucogranitoids of the Caçapava do Sul complex, is proposed for this interval.     

Lithostratigraphy, basin development, base metal deposits, and regional correlations of the Neoproterozoic Nguba and Kundelungu rock successions, central African Copperbelt

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.     

Zircon ages of high-grade gneisses in the Eastern Erzgebirge (Central European Variscides)—constraints on origin of the rocks and Precambrian to Ordovician magmatic events in the Variscan foldbelt

This study is an attempt to unravel the tectono-metamorphic history of high-grade metamorphic rocks in the Eastern Erzgebirge region. Metamorphism has strongly disturbed the primary petrological genetic characteristics of the rocks. We compare geological, geochemical, and petrological data, and zircon populations as well as isotope and geochronological data for the major gneiss units of the Eastern Erzgebirge; (1) coarse- to medium-grained “Inner Grey Gneiss”, (2) fine-grained “Outer Grey Gneiss”, and (3) “Red Gneiss”. The Inner and Outer Grey Gneiss units (MP–MT overprinted) have very similar geochemical and mineralogical compositions, but they contain different zircon populations. The Inner Grey Gneiss is found to be of primary igneous origin as documented by the presence of long-prismatic, oscillatory zoned zircons (540 Ma) and relics of granitic textures. Geochemical and isotope data classify the igneous precursor as a S-type granite. In contrast, Outer Grey Gneiss samples are free of long-prismatic zircons and contain zircons with signs of mechanical rounding through sedimentary transport. Geochemical data indicate greywackes as main previous precursor. The most euhedral zircons are zoned and document Neoproterozoic (ca. 575 Ma) source rocks eroded to form these greywackes. U–Pb-SHRIMP measurements revealed three further ancient sources, which zircons survived in both the Inner and Outer Grey Gneiss: Neoproterozoic (600–700 Ma), Paleoproterozoic (2100–2200 Ma), and Archaean (2700–2800 Ma). These results point to absence of Grenvillian type sources and derivation of the crust from the West African Craton. The granite magma of the Inner Grey Gneiss was probably derived through in situ melting of the Outer Grey Gneiss sedimentary protolith as indicated by geological relationships, similar geochemical composition, similar Nd model ages, and inherited zircon ages. Red Gneiss occurs as separate bodies within fine- and medium-grained grey gneisses of the gneiss–eclogite zone (HP–HT overprinted). In comparison to Grey Gneisses, the Red Gneiss clearly differs in geochemical composition by lower contents of refractory elements. Rocks contain long-prismatic zircons (480–500 Ma) with oscillatory zonation indicating an igneous precursor for Red Gneiss protoliths. Geochemical data display obvious characteristics of S-type granites derived through partial melting from deeper crustal source rocks. The obtained time marks of magmatic activity (ca. 575 Ma, ca. 540 Ma, ca. 500–480 Ma) of the Eastern Erzgebirge are compared with adjacent units of the Saxothuringian zone. In all these units, similar time marks and geochemical pattern of igneous rocks prove a similar tectono-metamorphic evolution during Neoproterozoic–Ordovician time.     

Rôles respectifs de l''advection et de la décantation sur la ride médio-atlantique (40° à 50°N)

Coring at 45 sites in the North Atlantic permitted to determine flux velocity and chemical composition of pelagic sediments. Piston cores were used to carry out a comparative study between the post-glacial period (10,000 yr. B.P. until present) and last glacial period (75,000–10,000 yr. B.P.). Special attention has been paid to the Mid-Atlantic Ridges-Azores-Iceland area, where an enrichment of chemical elements was observed with regards to “regional ocean ground noise”, perceived on an isolated seamount of the abyssal plain.This “ground noise” characterized by the presence of Pb, Rb, U, Th, illite and chlorite, is associated to a settling vertical flux since the surface brought by surface currents and wind transport since the North American shield: sediments, here, are continental soil erosion products.The ridge is clearly enriched by Ba, Br, Fe, Ti, Mn, Cu, Ni, Co and As. Ba and Br are mostly associated with planktonic carbonates. Part of Ba may be linked to the ridge's activity. Basalt weathering on the ridge supplies a part of Fe in excess. Hydrothermal activity may account for Mn, Cu, Co, Ni and As enrichment. Most of the excess observed may be explained by intrusion of advective inputs from erosion Icelandic products (Fe, Ti, Cu, Ta, Sc and smectites), probably transported by Norwegian bottom currents.Advective flux (Icelandic-Faeroan basaltic materials) and flux linked to submarine ridge activity represent 30% of inorganic sedimentation. Vertical flux (North American continental-derived terrigenous materials) represent 70% of inorganic sedimentation. These percentages are very similar to those which were calculated for the Pacific.

Résumé

Les vitesses d'accumulation (flux) et les compositions chimiques ont été déterminées pour des sédiments pélagiques, dans 45 sites de l'océan Atlantique Nord. Les échantillons, prélevés par carottage Kullenberg, ont permis de réaliser une étude comparative de la période post-glaciaire (10.000 ans B.P. à nos jours) et du dernier glaciaire (75.000–10.000 ans B.P.). Notre attention s'est portée particulièrement sur la dorsale médioatlantique Açores-Islande où l'on observe des enrichissements en éléments chimiques par rapport au “bruit de fond océanique régional” appréhendé sur un dôme isolé dans la plaine abyssale.À ce bruit de fond, caractérisé par Pb, Rb, U, Th, illite et chlorite, est associé un flux vertical mis en place par décantation depuis la surface, apporté par le vent et les courants de surface depuis le craton nord-américain; il s'agit des produits d'érosion des sols continentaux.L'enrichissement de la dorsale est net pour Ba, Br, Fe, Ti, Mn, Cu, Ni, Co et As.Ba et Br précipite en grande partie avec les carbonates planctoniques. Une partie de Ba peut être associée à l'activité de la ride. L'altération des basaltes de la ride fournit une partie du Fe en excès. L'activité hydrothermale peut expliquer les enrichissements en Mn, Cu, Co, Ni et As.L'essentiel de l'excès observé est expliqué par un apport advectif de produits d'érosion de l'Islande (Fe, Ti, Cu, Ta, Sc et smectites). Leur vecteur serait le courant de fond de la mer de Norvège.Le flux advectif (matériaux basaltiques islando-faeroan) et le flux liéà l'activité sousmarine de la dorsale représenterait 29% de la sédimentation inorganique.Le flux vertical (matériaux continentaux terrigènes nord-américain) représenterait 71% de la sédimentation inorganique. Ces chiffres sont très proches de ceux qui ont été évalués dans le Pacifique.     

Lherzolites and the western “Chainons bearnais” (French Pyrenees): Structural and paleogeographical pattern

Field observations of the “Chaînons béarnais”, in the area of Oloron-Sainte-Marie, reveal two families of units: The first one contains a well developed Jurassic-Cretaceous series, it structurally underlies the second one. The second one contains a thin Jurassic-Cretaceous series, deposited on a basement including metamorphic Paleozoic terrain and lherzolites. The structural arrangement, as well as the sedimentological characteristics, suggests a southern origin for these highest units.The tectonic association between metamorphic and ultrabasic rocks of the basement was probably formed during the Hercynian orogeny, or in a Late Hercynian period. However, it clearly predates fossiliferous sediments attributed to the Callovo-Oxfordian (Pic de Saraillé, Lourdios) or still undated terrains presenting a typical Triassic facies (Tos de la Coustette, Lourdios).     

Un nouveau critere de sens de mise en place dans une caisse filonienne: Le “pincement” des mineraux aux epontes : Orientation des minéraux dans un magma en écoulement

The flow of a magma into a dike, sill, laccolite, pipe or batholith leads to a preferential orientation of crystals in the magma. A study by computer simulation has brought to light certain types of fabric for oblate and prolate minerals in the case of a plane deformation, on the one hand by pure shear, and on the other hand by simple shear. Theoretical and practical studies suggest a new method for determining the direction of injection (“injection axis”) in a dike, based on the angular relations of minerals near the walls.New developments are proposed on the relations between plane and linear flow-lines, on the distinction between “apparent flow-lines” and the transport-plane of the magma (“real flow-lines”) and on the amount of magma deformation.

Résumé

La mise en place d'un magma dans une caisse filonienne (ou dans des sills, dykes, laccolites, batholites, etc.) s'accompagne d'une orientation préférentielle des minéraux déjà formés. Une étude par simulation sur ordinateur a mis en évidence certains types de fabrique pour les minéraux phylliteux et les minéraux aciculaires dans le cas d'une déformation plane, d'une part par aplatissement pur et d'autre part, par cisaillement simple.En application théorique puis pratique, un nouveau critère de sens de mise en place (axe d'injection) dans une caisse filonienne est défini: le pincement des minéraux aux épontes; en effet, à chacune d'elles, les fluidalités apparentes, observées sur les minéraux, font un angle avec la paroi du filon.Des développements nouveaux sont proposés concernant les relations entre fluidalités planaire et linéaire, la distinction entre fluidalité apparente et plan de transport du magma (fluidalité réelle), le taux de déformation subi par le magma,....     

Petrographic,fluid inclusion and isotopic study of the Dikulushi Cu–Ag deposit,Katanga (D.R.C.): implications for exploration

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.     

La ligne du Tonale (Alpes centrales et orientales): sens de décrochement et prolongements

This work discusses the state of knowledge (mainly tectonic and geophysical data) about the Tonale line and other “peri-Adriatic” lines in the Central and Eastern Alps. The chain is here cut into a mosaic of independent blocs, separated by faults with basic injections in some places. The Tonale fault had a dextral movement in Oligo-Miocene times; it is connected with the Austrian “Thermenlinie”, and not to the Pusteria—Gail line. An attempt at chronology is presented.

Résumé

Ce travail fait le point des connassiances, principalement tectoniques et géophysiques, sur la linge du Tonale et les accidents “péri-adriatiques” récents des Alpes centrales et Orientales. Dans cette région, la chaine est découpée en une mosaïque de blocs indépendants, séparés par des accidents injectés ça et là de masses basiques. L'accident du Tonale, Qui a joué en décrochement dextre à l'Oligo-Miocéne, est relié à la Thermenlinie d'Autriche Et non à la linge Pusteria—Gail. Un essai de chronologie est présenté.     

Tectonic Evolution of the Lufilian Arc (Central Africa Copper Belt) During Neoproterozoic Pan African Orogenesis

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-D_2′ uppermost Kundelungu sequence (Ks3 Plateaux Group), are younger than 540 Ma and probably early Paleozoic.     

Genesis of sediment-hosted stratiform copper–cobalt mineralization at Luiswishi and Kamoto, Katanga Copperbelt (Democratic Republic of Congo)

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 ∆³⁴S_SO4-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.     

Changement de faunes de bryozoaires dans le Valanginien supérieur des Alpes-de-Haute-Provence. Parallélisme avec la crise observée dans le Jura à la même époque

Dans le Valanginien supérieur (Marnes à Toxaster et Grande Lumachelle) des Alpes-de-Haute-Provence, la succession de deux faunes de bryozoaires est observée. Parmi les causes du changement de faune, le remplacement d'un fond vaseux en eau calme (Marnes à Toxaster) par un fond sableux coquillier en eau assez agitée (Grande Lumachelle) est certainement important. Cependant, ces modifications résultent elles-mêmes d'événements plus généraux.Le changement de faune peut être comparé à celui qui intervient dans le Jura au début de la zone à Trinodosum. La faune des Marnes à Toxaster (zone à Verrucosum) montre certaines des espèces caractéristiques de la “faune 1” du Jura et, de plus, les deux mêmes espèces dominantes. Le milieu de vasière des Marnes à Toxaster, opposé à celui de plate-forme carbonatée du Jura, entraîne seulement un appauvrissement spécifique. Quant à la faune de la grande Lumachelle, elle est absolument semblable à la “faune 2” récoltée dans les Marnes à bryozoaires et le Calcaire à Alectryonia du Jura.Ce parallélisme des deux faunes avec celles du Jura, malgré les différences de faciès sédimentaire, montre que le changement de faune, maintenant reconnu sur près de 400 km, résulte d'une même cause principale. Ainsi, l'hypothèse d'un refroidissement que j'ai proposée pour le Jura semble pouvoir être étendue à la Provence.The change of bryozoan fauna in the upper Valanginian of the Alpes-de-Haute-Provence. Parallelism with the crisis observed in the Jura at the same time.In the upper Valanginian (Marnes à Toxaster and Grande Lumachelle) of the Alpes-de-Haute-Provence, the succession of two bryozoan faunas is observed. Among the reasons for the change of fauna, the replacement of a muddy bottom in calm water (Marnes à Toxaster) by a sandy-shelly bottom in rather agitated water (Grande Lumachelle) is certainly important, but these modifications are the result of more general events. The change of fauna could be compared with the one that took place at the beginning of the Trinodosum Zone in the Jura. The fauna of the Marnes à Toxaster (Verrucosum Zone) shows some characteristic species of the “faune 1” of the Jura and, moreover, the same two dominating species. The muddy basin environment of the Marnes à Toxaster, unlike the carbonate platform environment in the Jura, involves only a specific impoverishment. As for the fauna of the Grande Lumachelle, it is totally identical to the “faune 2” found in the Marnes à bryozoaires and the Calcaire à Alectryonia of the Jura.This parallelism of the two faunas with those of the Jura, in spite of the differences of sedimentary facies, shows the change of the fauna now observed over about 400 km, has the same principal cause. Thus it seems possible to extend the cooling hypothesis I have proposed for the Jura, to Provence.     

Répartition et utilisation stratigraphique des Bryozoaires du crétacé moyen (Aptien-Coniacien)

Bien que la durée stratigraphique de la plupart des Bryozoaires crétacés ne soit pas exacterment connue, beaucoup d'espèces caractérisent assez bien les différents étages. Au Crétacé inférieur, dont la faune bryozoologique est plus pauvre que celle du Crétacé supérieur, ce sont les Cyclostomata qui dominent encore, comme au Jurassique. A l'Aptien, citons Chisma, mais aussi Ceata, Meliceritites et Laterocavea apparus au Barrémien. La faune de l'Albien, un peu appauvrie et peu connue, n'a fourni que quelques genres nouveaux encroûtants de Cheilostomata anasca (Rhammatopora, Wilbertopora).Au Cénomanien commence l'explosion des Bryozoaires. Les Cheilostomata les plus anciennes, les Cribrimorpha, les genres “Biflustra”, Cellarinidra, Quadricellaria, Onychocella, “Rhagasostoma”, Stichomicropora, Aechmella et un grand nombre de Cyclostomata (Crisisina, Heterocrisina, Fascipora, Spirentalophora, Marssoniella, Amphimarssoniella, Umbrellina, Exidmonea, Corymbopora, Desmopora, Discocytis, Supercytis, Truncatulipora, etc.) apparaissent. Le Turonien est caractérisé par les genres Cyclostomes (Reticrisina, Bicavea, Homoeosolen), les Cheilostomes (Tylopora, Euritina, Fusicellaria, Reptolunulites) et par de nombreuses Cribrimorpha.Onychocella nerei et Membranipora perincerta sont caractéristiques du Coniacien où l'on trouve aussi les Lunulites et Pavolunulites. Le Coniacien, plus riche en espéces que le Turonien, contient de très nombreux genres et espèces qui se poursuivent dans les étages plus élevés (Santonien-Maastrichtien).This paper deals with the distribution and stratigraphic value of Mid-Cretaceous Bryozoa (Aptian-Coniacian). Research on Cretaceous bryozoa has been neglected during the last decades and knowledge of the stratigraphical range of many Upper Cretaceous genera and species is based mainly on the personal experience of the present author. Accordingly, the range of most species is not exactly known, and the results of these investigations are only preliminary. Many cyclostomate genera (such as Stomatopora, Proboscina, Diastopora, Berenicea and Entalophora) lack easy identifiable specific characteristics, and all the other genera which can be recognized only by their rare ovicells (gonozoids) (such as Plagioecia, Diaperoecia, Microecia, Mecynoecia, Spiropora, Heteropora or Ceriopora, Reptomulticava, Lichenopora and many others) are not particularly suitable as guide-fossils. On the other hand, many characteristic new species have not yet been described.The bryozoa of the Lower Cretaceous are similar to those of the Jurassic. Both are characterized by the absolute predominance of the Cyclostomata and a few very rare primitive Cheilostomata belonging to the encrusting membranimorph Anasca.The Barremo-Aptian fauna, known mainly from England (Faringdon, Berkshire) and eastern and southern France, is characterized by the first Eleidae (Meliceritidae) with Meliceritites and Foricula, the first Ceidae, Clausidae and Horneridae with Siphodictyum and Laterocavea, Chisma furcillatum is known only from the Aptian. Cheilostomata are rare and are represented solely by encrusting membranimorph genera (Rhammotopora, “Membranipora”). The poor Albian bryozoan fauna, although similar to that of the Aptian, is characterized by the appearance of primitive uniserial cheilostomate genera such as (?) Pyriporopsis, Charixa and the genus Wilbertopora. Erect precenomanian Cheilostomata are not known. Albian Bryozoa are little-known and relatively rare.Within the Cenomanian (the plenus-zone included) many new cyclostomate genera Fascipora, Umbrellina, Siphoniotyphlus, Crisisina, Heterocrisina, Discofascigera, Corymbopora, Marssoniella, Amphimarssoniella, Discocytis, Discotruncatulipora, Truncatulipora, Desmepora, Exidmonea, Meliceritella and numerous cheilostomate genera besides “Membranipora” mainly Aechmella, Onychocella, Stichomicropora and several cribrimorphs appear for the first time. The Cenomanian is also characterized by the first erect cheilostomate species such as Onychocella, “Biflustra” or “Vincularia” and the oldest articulated or radicelled cheilostomes (Cellarinidra, Quadricellaria).During the Turonian (excluding the plenus-zone), which is less abundant in Bryozoa than the Cenomanian, the cheilostomes increase (common genera are Onychocella, Euritina, “Rhagasostoma”, bilamellar membranimorphs and cribrimorphs, mainly Rhabdopora) and the first primitive Lunulitidae (Reptolunulites) occur. Among the cyclostomes, represented by numerous species of Meliceritites, Semielea, Foricula, Truncatulipora, Clausa, Petalopora, Heteropora and the first representatives of Homoesolen, Reticrisina, Tervia and Bicavea appear.Within the Coniacian, rich faunas are known from France and England. Although the Cyclostomata are still dominant until the Santonian, considerable progress in the evolution of the Cheilostomata was made mainly by the development of the onychocellids, the erect membranimorphs and the radiation of the different cribrimorph families and genera. The oldest free-living Lunulitidae with Lunulites and Pavolunulites are recorded from the Coniacian. Among the Cyclostomata, the appearance of the genera Diplosolen, Clypeina, Crisina, Filicrisina, Sulcocava, Ditaxia, Pachyteichopora and Cytis is noteworthy. The Coniacian bryozoan fauna is closely related to that of the Santonian and has clearly an Upper Cretaceous character.I refer to the text for comments on single species which may be supposed to be useful as guide-fossils for the Aptian-Coniacian stages.     

Anhydrite pseudomorphs and the origin of stratiform Cu–Co ores in the Katangan Copperbelt (Democratic Republic of Congo)

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.