A new sulphur isotopic study of some Iberian Pyrite Belt deposits: evidence of a textural control on sulphur isotope composition

The sulphide deposits of the Iberian Pyrite Belt (IPB) represent an ore province of global importance. Our study presents 113 new sulphur isotope analyses from deposits selected to represent the textural spectrum of ores. Measured ³⁴S values range from −26 to +10‰ mostly for massive and stockwork ores, in agreement with data previously published. In situ laser ³⁴S analyses reveals a close correlation of ³⁴S with texture. Primary diagenetic textures are dominated by relatively low ³⁴S (−8‰ to −2‰), whereas stockwork feeder textures are dominated by higher ³⁴S (∼+3‰ to +5‰). Intermediate textures (mainly coarse textures in stratiform zones) have intermediate ³⁴S, although they are mostly dominated by the high ³⁴S component. Rare barite has a homogeneous ³⁴S around +18‰, which is consistent with direct derivation from Lower Carboniferous seawater sulphate. A dual source of sulphide sulphur in the IPB deposits has been considered. A hydrothermal source, derived from reduction of coeval seawater sulphate in the convective systems, is represented by sulphide in the feeder zones. Here variations in ³⁴S are caused by variations in the extent of the sulphate reduction, which governs the SO₄:H₂S ratio. The second end-member was derived from the bacterial reduction of coeval seawater sulphate at or near the surface, as reflected in the primary textures. A distinct geographical variation in ³⁴S and texture from SW (more bacteriogenic and primary textures) to NE (more hydrothermal textures and ³⁴S) which reflects a variation in the relative input of each source was likely controlled by local geological environments. Given that the sulphur isotope characteristics of the IPB deposits are unlike most VMS and Kuroko deposits, and noting the dominance of a mixed reduced sedimentary and volcanic environment, we suggest that the IPB could represent an ore style which is intermediate between volcanic and sedimentary hosted massive sulphide types. Received: 8 October 1997 / Accepted: 14 May 1998     

Genesis of upper proterozoic stratabound copper mineralization,Kapunda, South Australia

Chalcopyrite-rich bedded and vein mineralization at Kapunda occurs in two locally developed dolosiltstone units within a sequence of generally darker-coloured, finer-grained calcmudstones and siltstones. The Mine Series accumulated in shallow water to supratidal, sabkha-like environments; there is no evidence for igneous activity in the region. Isotope data for bedded sulphides are characteristic of biological sulphate reduction in a restricted basin. It is likely that iron sulphides were produced initially, and that copper was introduced subsequently in mildly oxidizing, highly saline groundwaters, the influence of which is seen in the ¹³C-¹⁸O correlation for dolomite in the mineralized siltstones. Isotopic data support derivation of the veins from their host sediments, and this appears to have occurred before lithification.     

蓟县中上元古界典型剖面锶同位素组成特征及其地层意义

笔者在地矿部同位素开放研究实验室资助下，对长城系、蓟县系、青白口系等各系界线及各地层组之间，进行了锶同位素组成测定，并探讨地层剖面系级之间及层内87Sr/86Sr 同位素组成可能的变化及其地层意义。为追朔地层形成时间和演化历史，乃至为全球元古宙地层划分对比提供新的依据，填被我国在锶同位素地层学研究领导域的空白。     

Oxygen isotope study of a Precambrian banded iron-formation,Hamersley Range,Western Australia

Oxygen isotope ratios were determined for quartz, magnetite, ankerite, siderite, riebeckite, hematite and talc in samples of banded iron-formation from the Dales Gorge Member of the Brockman Iron Formation and for quartz, dolomite and calcite in samples of the Wittenoom Dolomite and Duck Creek Dolomite Formations, all from the Hamersley Range area of Western Australia. Additionally, in order to interpret the measured isotope ratios, isotopic fractionations for oxygen between quartz, siderite and magnetite and between these minerals and water as a function of temperature were calculated, using a combination of spectroscopic and thermodynamic data and constraints set by experimental determinations of the fractionations.The Dales Gorge Member was found to have undergone isotopic exchange between minerals at a temperature estimated on the basis of the isotopic fractionations to be above 270°C and probably less than 310°C, during burial metamorphism. At these temperatures quartz and the carbonates were almost completely equilibrated with one another, while hematite apparently underwent negligible exchange. Magnetite may have undergone exchange in some samples but not others, as a result of permeability variations, or it may have been as resistant to exchange as hematite. Riebeckite, and probably talc as well, were also subject to exchange, but to a lesser degree or on a smaller scale than quartz and the carbonates. Hematite formed at temperatures of 140°C or below. Magnetite appears to have formed at temperatures above 140°C, and possibly over a range of temperatures between about 180 and 300°C.The Wittenoom Dolomite and Duck Creek Dolomite samples show apparent lack of equilibrium, due to incomplete exchange or to retrograde effects. A chert from the Wittenoom Dolomite, along with two samples from the Marra Mamba Iron Formation, with δ¹⁸O values of + 24%. can be considered to set a lower limit of about ?11%. on the δ¹⁸O value of the ocean 2.2 × 10⁹ yr ago. Internal fractionations in the Wittenoom Dolomite chert sample may be interpreted as yielding an upper limit on this oceanic δ¹⁸O value of ? 3.5%.     

Strontium isotope composition of the lower proterozoic carbonate concretions: The Zaonega Formation,Southeast Karelia

The middle part of the volcanosedimentary Zaonega Formation of the Ludikovian Suprahorizon (approximately 2.0 Ga) includes large carbonates concretions and lenses in shungite layers. Carbonate lenses and concretions are primarily elongated and flattened, and their thickness varies from tens of centimeters to a few meters. Some lenses retain relicts of lamination. Concretions are composed of calcite or dolomite. They contain abundant organic matter, as well as mica, talc, chlorite, quartz, and pyrite crystals. The calcite concretions contain some dolomite admixture (Mg/Ca = 0.011?0.045) and differ from sedimentary limestones by a low Fe/Mn value (0.3–2.1). The Sr content is as much as 385–505 μg/g in most samples and is low (86 μg/g) only in one sample. The Rb-Sr systematics of carbonate concretions was studied with the stepwise dissolution procedure, which included processing with the ammonium acetate solution (AMA fraction) to partially remove the secondary carbonate material, with dissolution of the residue in acetic acid (ACA fraction). In individual calcite samples, discrepancy between the measured ⁸⁷Sr/⁸⁶Sr values in the AMA and ACA calcite fractions shows a variation range of 0.0008–0.0033. The initial ⁸⁷Sr/⁸⁶Sr ratio in the ACA fractions of the studied samples varies from 0.7053 to 0.7162. The ratio shows a positive correlation with Mg/Ca and the proportion of siliciclastic admixture and negative correlation with the Mn content. The concretions were formed when the sediments subsided, probably, during the transition from a zone with “mild” reductive conditions to zones with active sulfate reduction and methanogenesis. In the sulfate reduction zone, where most pyrite-bearing concretions were formed, the sediment was not geochemically exchaged with the bottom water and was evolved into a closed or semiclosed system. Processes of diagenesis in this zone promoted the release of the radiogenic ⁸⁷Sr from the associated siliciclastic minerals, resulting in growth of the initial ⁸⁷Sr/⁸⁶Sr in concretions up to 0.7108–0.7162. Some calcite concretions, which lacked pyrite (or contained its minimal amount) were likely formed in a thin surficial sediment layer located above the sulfate reduction zone. Therefore, they precipitated Sr in isotope equilibrium with Sr of the bottom water. However, large concretions and carbonate lenses with an insignificant siliciclastic admixture could retain the signature of early diagenesis or even sedimentation. The initial ⁸⁷Sr/⁸⁶Sr ratio in one of such samples with the siliciclastic admixture of 6.2% makes it possible to estimate the maximal value of this ratio (0.7053) in the Ludikovian paleobasin.     

Fluid inclusion and sulphur isotope evidence for syntectonic mineralisation at the Elura mine,southeastern Australia

Fluid inclusion and sulphur isotope data for the discordant, metasediment-hosted massive sulphide deposit at Elura are consistent with a syntectonic origin of the orebodies. Thermometric and laser Raman microprobe analyses indicate that two-phase, primary fluid inclusions are low salinity and H₂O-CO₂-CH₄ types. Inclusion fluids from quartz in ore yield homogenisation temperatures (T_h) ranging from 298 ° to 354 °C (mean 320 °C). They are likely to have been trapped close to the solvus of the H₂O-CO₂-(CH₄-NaCl) system and thus should give temperatures of the mineralising fluid. An additional, low T_h population of later fluid inclusions is recognised in quartz from ore and syntectonic extension veins in the adjacent wallrock. T_h's for these low CO₂bearing inclusions range from 150 to 231 °C (mean 190 °C), and should be considerably lower than true trapping temperatures. Sulphur isotopic composition (³⁴S) of pyrite, sphalerite, pyrrhotite and galena ranges from 4.7 to 12.6% and indicates a sulphur source from underlying Cobar Supergroup metasediments. An average temperature of 275 °C from the sphalerite-galena sulphur isotopic thermometer suggests isotopic re-equilibration below peak metamorphic temperatures.     

Some new lead isotope determinations from the proterozoic sulfide ores of central Sweden

Lead isotope determinations were made on galenas from three strata-bound sulfide ores in the early Proterozoic (Svecokarelian) Bergslagen district of central Sweden and four epigenetic deposits in the Älvdalen and Vansbro districts in the early to middle Proterozoic post-Svecokarelian belt. The leads from the strata-bound Bergslagen deposits show exceptional isotopic homogeneity over large areas. Their isotopic composition suggests the existence of a pre-Svecokarelian crust in the district and is consistent with exhalative-sedimentary ore formation in an active continental margin environment. The Vansbro and Älvdalen leads display constant compositions within each district, but marked divergence between the districts. Their compositions preclude derivation exclusively from recycled Svecokarelian lead and suggest a substantial lead contribution from a mantle-like source. The difference between model ages and geologic ages for many of the deposits, with a small but significant excess of radiogenic lead, suggests a significant deviation of the Fennoscandian Shield from conventional global lead evolution models.     

Geochemistry and geochronology of proterozoic tholeiite dykes of east antarctica: evidence for mantle metasomatism

Two episodes of tholeiite dyke emplacement have been identified in Archaean high-grade metamorphics of the Napier Complex in Enderby Land. Middle Proterozoic Amundsen dykes are typical continental tholeiites and most of the chemical variation in individual suites can be explained in terms of different degrees of partial melting and low-pressure crystal fractionation. Group I Amundsen tholeiites were derived from a relatively homogeneous source region 1,190±200 m.y. ago, whereas that of the group II Amundsen tholeiites was chemically and isotopically heterogeneous. Group II dykes have various degrees of enrichment in incompatible elements, and commonly show normalised trace element abundance patterns with negative Nb anomalies. These features imply variable metasomatism of the source region by a volatile-rich fluid phase (rather than a melt of any observed igneous composition) enriched in K, Rb, Ba, Th, and possibly La and Ce.Early Proterozoic (2,350±48 m.y.) tholeiites were emplaced at considerable depths in the crust during the waning stages of granulite-facies metamorphism and include a high-Mg suite of possible komatiitic affinity, ranging in composition from hypersthene-rich tholeiite (norite) to quartz-rich tholeiite. They tend to have higher ratios of highly to moderately incompatible elements (e.g., K/Zr, K/Ce), and larger Nb anomalies (i.e., higher K/Nb) compared with middle Proterozoic tholeiites, suggesting derivation from more enriched source regions. Isotopic data are not compatible with significant crustal contamination, but constrain source metasomatism to a time immediately before emplacement. Metasomatism of the source region of the much younger group I tholeiites may have been contemporaneous with that of the high-Mg suite.     

Carbon-sulphur-iron-variations and sulphur isotope patterns of Silurian Graptolite Shales

ABSTRACT Black shale horizons (Graptolithenschiefer) in Silurian and Lower Devonian strata of the Franconian-Thuringian Highlands (Frankenwald-Thüringer Wald) of Germany have high metal concentrations (e.g. U,V,Mo). Organic carbon, sulphur and iron contents, degree of pyritization (DOP) and sulphur isotope ratios from the Lower Graptolite Shales, along with faunal and sedimentological evidence show that the depositional environment was anoxic. Although some data (e.g. C/S plots) do not suggest completely euxinic conditions, the DOP versus C plot indicates a Black Sea-type environment. From the sulphur isotope data the environment fluctuated between'open'and'closed'with respect to sulphate supply, with higher carbon contents reflecting an increased bacterial reduction of the available sulphate. Diagenetic effects were responsible for somewhat unusual plots of C/S ratios, though iron availability may have been influential.     

Genesis of post-collisional granitoids and basement nature of the Junggar Terrane, NW China: Nd–Sr isotope and trace element evidence

The post-collisional magmatism of the Junggar Terrane is characterized by intrusion of large amounts of granitoids and minor basic/ultrabasic rocks. The granitoids comprise two magmatic suites: calc-alkaline and alkaline, which were emplaced contemporaneously at about 294 Ma. The calc-alkaline rocks are typically sodium-rich (Na₂O/K₂O=1.1–3.5) and metaluminous (A/NK >1.0, A/CNK=0.78–1.04). They show mildly fractionated REE patterns ((La/Yb)_N<15) and spidergrams with strong depletion of Nb, Ti and, to a lesser extent, Sr. The alkaline granites have high contents of SiO₂ (75–78%), alkalis, Nb, HREE, Y, Sn, F and high FeO/MgO ratios and huge Sr and Eu depletion in the spidergrams. Moreover, they display characteristic tetrad REE patterns and non-CHARAC trace element behaviour. The two rock suites have similar initial Nd and Sr isotopic compositions, with _Nd(T) in the range +5.2 to +7.1 and I_Sr mostly in the range 0.7031–0.7041. This points to a predominance of juvenile components in their sources. The calc-alkaline rocks are most probably derived by dehydration-melting of a basic lower crust leaving behind a granulite residue. The process was probably triggered by underplating of mantle-derived basic magmas in an extensional regime. The alkaline granites are considered to have formed by differentiation of the calc-alkaline granitoids. Our study argues for a juvenile continental crust for the basement of the Junggar terrane, which is likely dominated by early Paleozoic oceanic crust and arc complex that were deeply buried during the late Paleozoic subduction and accretion.     

The effect of Rayleigh degassing of magma on sulphur isotope composition: a quantitative evaluation

The effect of Rayleigh distillation by outgassing of SO₂ and H₂O on the isotopic composition of sulphur remaining in silicate melts is quantitatively modelled. A threshold mole fraction of sulphur in the sulphide component of the melts is reckoned as being critically important in shifting the δ³⁴S value of degassed melts with respect to the original magmas. During the outgassing, melts above the threshold are depleted in ³⁴S, whereas melts below the threshold are enriched in ³⁴S. In particular, the outgassing of SO₂ above the sulphide threshold can produce large negative δ³⁴S values in the degassed melts, whereas the outgassing of H₂S below the threshold will strongly drive the δ³⁴S value of the melts in the positive direction. The correlation between δ³⁴S value and sulphur content of total sulphur in the solidified rocks is indicative of the Rayleigh-type degassing.     

Genesis and evolution of subduction-zone andesites: evidence from melt inclusions

Andesite magmatism plays a major role in continental crustal growth, but its subduction-zone origin and evolution is still a hotly debated topic. Compared with whole-rock analyses, melt inclusions (MIs) can provide important direct information on the processes of magma evolution. In this article, we synthesize data for melt inclusions hosted by phenocrysts in andesites, extracted from the GEOROC global compilation. These data show that melt inclusions entrapped by different phenocrysts have distinct compositions: olivine-hosted melt inclusions have basalt and basaltic andesite compositions, whereas melt inclusions in clinopyroxene and othopyroxene are mainly dacitic to rhyolitic. Hornblende-hosted melt inclusions have rhyolite composition. The compositions of melt inclusions entrapped by plagioclase are scattered, spanning from andesite to rhyolite. On the basis of the compositional data, we propose a mixing model for the genesis of the andesite, and a two-chamber mechanism to account for the evolution of the andesite. First, andesite melt is generated in the lower chamber by mixing of a basaltic melt derived from the mantle and emplaced in the lower crust with a felsic melt resulting from partial melting of crustal rocks. Olivine and minor plagioclase likely crystallize in the lower magma chamber. Secondly, the andesite melt ascends into the upper chamber where other phenocrysts crystallize. According to SiO₂-MgO diagrams of the MIs, evolution of the andesite in the upper chamber can be subdivided into two distinct stages. The early stage (I) is characterized by a phenocrystal assemblage of clinopyroxene + othopyroxene + plagioclase, whereas the late stage (II) is dominated by crystallization of plagioclase + hornblende.     

A steady-state model for sulphur isotope fractionation in bacterial reduction processes

A model is developed to explain the isotope fractionation effects produced in laboratory experiments involving the reduction of sulphate to hydrogen sulphide by the bacterium Desulfovibrio desulfuricans. The approach differs from previous ones in its use of zero-order kinetics to describe the uptake of sulphate by the bacterium. Expressions are developed which relate the overall isotope effects produced by the bacterium to the ratios of backward to forward flows between its internal sulphur reservoirs. Other applications of this type of model are discussed, including the differences of isotopic composition between sulphate and hydrogen sulphide in the Black Sea and an unusual isotope effect observed in the course of bacterial nitrate reduction.     

Geographical trends of carbon and sulphur isotope abundances in human kidney stones

$\text{δ}{}^{13}\text{C}$ values and $\text{δ}{}^{34}\text{S}$ values in human kidney stones range from ?24 to ?10 and ?10 to + 20 %., respectively, and depend upon geographical location. Although the distributions overlap, the mean $\text{δ}{}^{13}\text{C}$ values in oxalate stones from North America become less negative with decreasing latitude. For Mexico and Hawaii, the distributions appear to be bimodal. Uric acid stones are generally enriched in ¹³C by up to 7%. in comparison to oxalates from the same location, whereas cystine stones tend to span the ranges of both stone types. The geographical trends can be explained by the relative proportions of dietary carbon derived ultimately from plants undergoing various established photosynthetic mechanisms (C₃, C₄, CAM). The differences among the various major stone types may reflect isotope fractionation during biochemical conversions.Exogenic oxalates and uric acid are considered to have little role in precipitating the respective minerals. Whereas, the currently available C isotope data support this contention, more data are desirable, particularly for ingested oxalates. In contrast, S isotope data provide strong evidence that cystine stones are derived from ingested organo-S compounds and bear no relation to inorganic sulphate consumed by the individual. In turn, these organic-S compounds were probably derived from sulphate in the hydrosphere at lower levels in the food chain, e.g., by bacterial assimilation.     

The sulphur isotope systematics of the Taolin lead-zinc ore deposit,China

Sulphur isotope data from coexisting sulphides and sulphates from the Taolin Pb-Zn ore deposit have been used to estimate the temperatures of sulphur mineral precipitation. The data indicate that sulphide was the dominant sulphur species in solution at high temperatures and that sulphate was dominant at low temperatures. Also the data show that the δ³⁴S value of total sulphur in solution was close to zero at high temperatures (~325°C) but had high positive values (+15%.) at low temperatures (~250°C). We interpret this phenomenon in terms of the effects of mineral precipitation on the isotopic composition of the solution. The increase in the δ³⁴S value of total sulphur with decreasing temperature was brought about by the removal from the system, by precipitation, of isotopically light sulphides.     

Tectonic systems and the deposition of iron-formation

The iron-formation group of chemically precipitated cherty iron-rich sediments ranges in age from Early Precambrian to Recent and is composed of a variety of lithological facies. Iron-formations are classified as Lake Superior and Algoma types to emphasize the contrasting conditions in the spectrum of sedimentary-tectonic environments in which they formed. Thick stratigraphic units of Lake Superior type iron-formation, which form the most extensive iron ranges of the world, are part of sedimentary-tectonic systems that developed along the margins of cratons or continental platforms and were deposited over extended periods of time under relatively stable tectonic conditions. The Algoma type iron-formations were deposited with volcanic rocks and greywacke in various tectonic-volcanic systems, formed under more dynamic tectonic conditions, but are otherwise comparable to present day spreading ridges on the ocean floor. The thick sequences of Lake Superior type iron-formation deposited between 2.7 and 2.0 Ga form part of major sedimentary-tectonic systems that extended along the margins of continents. Direct biogenic factors and the composition of the atmosphere probably had only limited influence on the precipitation of these chemical sediments.     

Petrology, chronology and isotope geochemistry of the proterozoic amphibolites from Xiangshan, central Jiangxi province, China

On the basis of a comprehensive study on the petrology,trace elements and isotopic geochemistry of the Xiangshan amphibolites,we suggest that the protoliths of the amphibolites were basalts formed in an island-arc tectonic setting.The basaltic magma was derived from a slightly depleted mantle source with a small amount of crustal contamination.Assemblage of the rock-froming minerals indicates that these amphibolites underwent a low-grade metamorphism of amphibolite facies.According to the formation age(1113Ma) and subsequent metamophic age(726.6Ma) of the basalts aw well as the geological and gochemical features of these amphibolites,a tectonic model of Proterozoic oceanic island-arc setting is proposed for central Jiangxi.     

Isotopic evidence of middle proterozoic magmatism from bombay high field: Implications to crustal evolution of western offshore of India

Precambrian granitic basement rocks obtained from well BH-36 of Bombay High Field, western offshore of India has been studied both by Rb-Sr and K-Ar dating methods. Seven basement samples chosen from two cores have yielded whole rock Rb-Sr isochron age of 1446 ± 67 Ma with an initial⁸⁷Sr/⁸⁶Sr ratio of 0.7062 ± 0.0012. This age has been interpreted as the formation/emplacement time of the granite. Two biotite fractions of different grain size separated from a sample CC6B2T have yielded Rb-Sr mineral isochron age of 1385 ± 21 Ma. However, these fractions when studied by K-Ar dating method have yielded slightly higher but mutually consistent ages of 1458 ± 43 Ma and 1465 ± 43 Ma, respectively. Further, two biotites separated from additional samples CC5B9T and CC6B3B have yielded K-Ar ages of 1452 ± 42 Ma and 1425 ± 40 Ma with an overall mean age of 1438 ± 19 Ma. This mean K-Ar age is indistinguishable from whole rock Rb-Sr isochron as well as mineral isochron age within experimental error. The similarity in the whole rock and biotite ages obtained by different isotopic methods suggests that no thermal disturbance has occurred in these rocks after their emplacement/formation around 1450 Ma ago. The present study provides the evidence for the existence of an important Middle Proterozoic magmatic event around 1400-1450 Ma on the western offshore of India which, hitherto, was thought to be mainly confined to the eastern Ghats, Satpura and Delhi fold belt of India. This finding may have an important bearing on the reconstruction of Proterozoic crustal evolution of western Indian shield.     

The Pechenga Ni-Cu deposits, Russia: Data on PGE and Au distribution and sulphur isotope compositions

Summary The Early Proterozoic Ni-Cu deposits of the Pechenga ore field, located in the northwestern part of Russia, are associated with gabbro-wehrlite intrusions which are cogenetic with ferropicritic volcanics. The total PGE content of the ores and Ni-bearing ultramafics varies widely, showing a positive correlation with sulphur content, and reaching 2-3 ppm in the massive and breccia ores. Barren intrusions and sulphide-free ultramafic lithologies of the ore-bearing intrusions, as well as ferropicritic volcanics, have low PGE contents and are depleted in noble metals relative to Ni and Cu. Accommodation of PGE in sulphides and PGE depletion in low-sulphur ultramafic rocks are consistent with a magmatic model, implying partitioning of PGE from silicate melt to sulphides and indicating sulphide saturation and separation of the immiscible sulphide liquid at an early stage of the magma's history, prior to ferropicrite eruption and gabbro-wehrlite emplacement.A juvenile sulphur source for a number of Ni-Cu ore deposits and prospects (Kaula, Kotselvaara, Kammikivi, Sputnik-Verkhnee, Yuzhnoe) and barren intrusions is indicated by uniform ³⁴S values, ranging from c.-1.0 to +2.5. In contrast, ores associated with the large intrusive bodies (Pilgujärvi, Kierdzhipor), characterised by ³⁴S values ranging from c.1 to 7, are contaminated by crustal sulphur from the host metasedimentary rocks. This contamination apparently occured during magma ascent through the host sulphide-rich shales.Metamorphic hydrothermal alteration of the rocks led to remobilisation of the sulphide ores. Au was leached from massive and breccia ores and redeposited as native gold in zones of talc-carbonate alteration and stringer sulphides. Sedimentary sulphur from the host metasedimentary rocks has been introduced into the stringer zone Ni-Cu mineralisation and zones of talc-carbonate alteration by metamorphic fluids.Zusammenfassung Die altproterozoischen Kupfer-Nickel-Lagerstätten von Pechenga (Petsamo) in Nordwest-Russland sind mit Gabbro-Wehrlit Intrusionen assoziiert. Diese wiederum sind co-genetisch mit ferropikritischen Vulkaniten. Der gesamte PGE-Gehalt der Erze und Nickel-führender Ultramafite variiert beträchtlich und zeigt eine positive Korrelation mit dem Schwefelgehalt. PGE-Gehalte erreichen bis zu 2-3 ppm in den massiven und in den Breckzien-Erzen. Erzfreie Intrusionen und Sulfid-freie ultramafische Lithologien der erzführenden Intrusionen, sowohl wie auch ferropikritische Vulkanite haben niedrige PGE-Gehalte und sind, relativ zu Nickel und Kupfer, an Edelmetallen verarmt. Der Einbau von PGE in Sulfiden, sowie PGE-Abreicherung in schwefelarmen ultramafischen Gesteinen entsprechen einem magmatischen Modell. Dieses impliziert eine Fraktionierung von PGE aus der Silikatschmelze in Sulfide. Es weist weiterhin auf Sulfid-Sättigung und Abtrennung der Sulfidschmelze zu einem frühen Studium der magmatischen Entwicklung, vor der Ferropikrit-Eruption und vor der Platznahme der Gabbro-Wehrlite, hin.Eine juvenile Schwefelquelle für eine Anzahl von Nickel-Kupfer-Erzlagerstätten und Prospekten (Kaul, Kotselvaara, Kammikivi, Sputnik-Verkhnee, Yuzhnoe) und erzfreie Intrusionen wird durch gleichförmige ³⁴S-Werte bewiesen, die von ca. 1,0 bis 2,5% reichen. Im Gegensatz dazu sind Erze, die mit den großen Intrusiv-Körpern (Pilgujärvi, Kierdzhipor), assoziiert sind, durch ³⁴S-Werte von 1 bis 7% charakterisiert; letztere sind durch krustalen Schwefel aus den umgebenden metasedimentären Gesteinen kontaminiert. Diese Kontamination fand offensichtlich während des Magmenaufstieges durch die sulfidreichen Schiefer statt.Metamorphe hydrothermale Alteration der Gesteine führte zur Remobilisation der Sulfiderze. Gold wurde aus massiven und Breckzien-Erzen herausgelöst und als gediegenes Gold in Zonen von Talk-Karbonat-Alteration und stringer-Sulfiden abgesetzt. Sedimentärer Schwefel aus den metasedimentären Wirtsgesteinen ist in die stringer Nickel-Kupfer-Mineralisation und in Zonen von Talk-Karbonat-Alteration durch metamorphe Fluide zugeführt worden.

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Die Nickel-Kupfer-Lagerstätten von Pechenga, Rußland: PGE- und Au-Verteilung und Schwefelisotopen

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With 8 Figures     

Contents and sulphur isotope composition of trace sulphate and sulphide in various rock types

The in vacuo Kiba extraction technique for trace sulphate and sulphide has been extended to a variety of rocks including some altered granites provided by the Canadian Nuclear Fuel Waste Management Programme. Although the technique requires considerable development, it shows promise for determining the redox conditions, temperature, and the sulphur isotope composition of dissolved species in fluids involved in initial mineralization and subsequent alteration processes. This may in turn be used to identify sources of sulphur in fluids and provide information about long term weathering of resistant rocks. Preliminary concentration and sulphur isotope data for altered granite samples from the Underground Research Laboratory, Whiteshell, Manitoba suggest that sulphur of other than igneous origin is minor or absent.