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1.
M. Deb 《Mineralium Deposita》1986,21(4):313-321
The sulfur isotope composition of 86 sulfide minerals from the Middle Proterozoic, metamorphosed, stratiform, sediment-hosted Zn-Pb-CU sulfide deposits of Dariba and Sindeswar Kalan located within the Rajpura-Dariba belt in Rajasthan, NW India, have been determined. In addition, 16 carbonaceous and 2 carbonate rock samples from the ore zone have been analyzed for their Ctot and Corg contents and carbon isotope compositions. The sulfur isotope compositions range from 9.1 to –6.7 (mean value of 1.9). Increasing 34S values stratigraphically upward are observed, particularly for pyrite and pyrrhotite suggesting a syngenetic origin for the sulfur. No marked lateral isotopic variations or isotopic variation in minerals from successive laminae in banded ore samples occur. Fractionation of sulfur isotopes between coexisting sulfides suggests that the original isotopic pattern was basically preserved during the amphibolite-facies metamorphism suffered by the deposits. Corg in carbonaceous rocks ranges 0.5–9.3 wt%, with 13C values between –21 and –31 (mean of –25.4) in keeping with the biogenic derivation of the carbon. Recrystallized dolostones have 13C values close to –14.4Geological evidence and isotopic features are consistant with the following genetic scheme: (a) base-metal ores along the belt formed from geothermal emanations carrying H2S, produced by the chemical reduction of seawater sulfates and leaching of mafic volcanics, in a semiclosed (with respect to SO4), shallow-water, rift-related basin with high biological activity; (b) pyrite and pyrrhotite formed diagenetically by bacterial reduction of sulfate in pore seawater in a system open to H2S, thus bringing about the gradual enrichment of 34S in these minerals stratigraphically upward; and (c) northward in the belt, at Sindeswar Kalan, the basin of ore deposition was relatively more open.  相似文献   

2.
The isotopic composition of oxygen and carbon was studied in accessory carbonates and quartz separated from salts in Upper Devonian halogenous formations of the Pripyat Trough (Belorus). It is established that isotopic characteristics vary in a wide range. Values of 18O vary in the following range (SMOW): from 18.2 to 29.2 in calcites, from 15.7 to 32.5 in dolomites, and from 17.4 to 27.2 in quartz. Values of 13C range from –13.4 to 1.4 in calcites and from –11.1 to 1.7 in dolomites (PDB). Results obtained indicate highly variable isotope-geochemical conditions of sedimentation and early diagenesis during the formation of evaporitic sediments. Accessory minerals were repeatedly formed in a wide temperature range and probably at various stages of the lithogenesis.  相似文献   

3.
The Tallberg deposit is situated in the Skellefte District in northern Sweden. It is a Palaeoproterozoic equivalent of Phanerozoic poryphyry-type deposits. The mineralization is situated within the Jörn granitoid complex and is associated with intrusive quartz-feldspar porphyries. The granitoids are coeval with mainly felsic volcanic rocks hosting several massive sulphide deposits. The alteration is generally of a mixed phyllic-propylitic type, but areas or zones associated with high gold grades exhibit phyllic alteration. Ore minerals are pyrite, chalcopyrite, sphalerite, magnetite, and trace amounts of molybdenite. In this stable isotope study, quartz, sericite, and chlorite from the alteration zones were sampled. The magmatic quartz has a 18O composition of + 6.2 to +6.7 whereas the quartz in the hydrothermal alteration zones have values ranging from +7.5 to +10.6. The calculated temperatures for this fractionation range from 430° to 520°C. The sericites have 18O ranging from +4.6 to +8.2 (average +6.6) and D -31 to -54 (average -41). Chlorites range from 18O +4.2 to +7.7 and D from –34 to –44. The range of 34S of 11 pyrite samples is +3.8 to +5.5 with an average of +4.6 ± 0.5, suggesting a relatively homogeneous sulphur source, probably of magmatic origin. Modelling waters in equilibrium with the minerals indicates early magmatic fluids with 18O of 6.5. This fluid mixed with a low 18O and high D fluid, which is tentatively identified as seawater. The 18O signature of sericite and chlorite also indicates significant water-rock exchange, explaining the positive 18O values for the waters in equilibrium with the hydrated minerals.  相似文献   

4.
Zusmmenfassung Die Ergebnisse der Schwefelisotopenanalysen von sechs Sulfid- und vier Sulfatmineralproben von Bleiberg/Kreuth (Österreich) variieren von –6,9 bis –25,9 34S in den Sulfiden und von +14,8 bis +18,9 34S in den Sulfaten. Die große Variationsbreite der Schwefelisotopen und die Bevorzugung des leichten Schwefels deutet vermutlich auf bakterielle Prozesse der Sulfidfällung. Die Sulfatschwefel fallen in den Bereich der Schwefelisotopenzusammensetzung des mesozoischen (postskytischen) Meerwassers.
Determination of the sulfur isotopic composition in some sulfide and sulfate minerals of the lead zinc deposit, Bleiberg/Kreuth, Carinthia
Summary Results of sulfur isotope analyses on 6 sulfides and 4 sulfates from Bleiberg/Kreuth (Austria) range from –6.9 to –25.9 34S (in sulfides) and from +14.8 to +18.9 34S (in sulfates). A large range of sulfide sulfur isotope fractionation with appreciable light sulfur probably indicates a bacterial sulfur source in sulfide precipiation. The sulfate sulfur plots in the range of Mesozoic (post-Skytian) seawater sulfur isotopic composition.
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5.
A systematic study of the auriferous quartz veins of the Val-dOr vein field, Abitibi, Quebec, Canada, demonstrates that the C, O, S isotope composition of silicate, carbonate, borate, oxide, tungstate and sulphide minerals have a range in composition comparable to that previously determined for the whole Superior Province. The oxygen isotope composition of quartz from early quartz–carbonate auriferous veins ranges from 9.4 to 14.4 whereas later quartz-tourmaline-carbonate veins have 18Oquartz values ranging from 9.2 to 13.8 . Quartz-carbonate veins have carbonate (18O: 6.9–12.5 ; 13C: –6.2– –1.9 ) and pyrite (34S: 1.2 and 1.9 ) isotope compositions comparable to those of quartz-tourmaline-carbonate veins (18O: 7.9–11.7 ; 13C: –8.0 – –2.4 ; 34S: 0.6–6.0 ). 18Oquartz values in quartz-tourmaline-carbonate veins have a variance comparable to analytical uncertainty at the scale of one locality, irrespective of the type of structure, the texture of the quartz or its position along strike, across strike or down-dip a vein. In contrast, the oxygen isotope composition of quartz in quartz-tourmaline-carbonate veins displays a regional distribution with higher 18O values in the south-central part of the vein field near the Cadillac Tectonic Zone, and which 18O values decrease regularly towards the north. Another zone of high 18O values in the northeast corner of the region and along the trace of the Senneville Fault is separated by a valley of lower 18O values from the higher values near the Cadillac Tectonic Zone. Oxygen isotope isopleths cut across lithological contacts and tectonic structures. This regional pattern in quartz-tourmaline-carbonate veins is interpreted to be a product of reaction with country rocks and mixing between (1) a deep-seated hydrothermal fluid of metamorphic origin with minimum 18O=8.5 , 13C=0.6 and 34S=–0.4 , and (2) a supracrustal fluid, most likely Archean seawater with a long history of water-rock exchange and with maximum 18O=3.9 , 13 C=–5.6 and 34S=5.0 .  相似文献   

6.
The isotopic composition of carbon and oxygen was studied in carbonate concentrations with different compositions (calcite, dolomite, and siderite) from Jurassic, Cretaceous, and Tertiary terrigenous deposits of the Northern Caucasus. Wide variations in the isotopic composition (from 41.4 to 18.1 for 13C and from 11.7 to 33.5 for 18O) point to different formation conditions in the early diagenesis zone and the later catagenesis zone.  相似文献   

7.
Preliminary studies have been made on the distributions of oxygen and sulphur isotopes in the Rosebery, Mount Farrell, and Mount Lyell ores. These ores lie in Cambrian geosynclinal volcanic rocks in West Tasmania. At each locality the sulphur of the sulphide minerals has a distinctive degree of enrichment in 34S in relation to sulphur in meteorites and a narrow range of 34S values. The dominant ore at Mount Lyell (mainly pyrite-chalcopyrite) has an average 34S value of +7.0, the main lode at Rosebery (pyrite-sphalerite-galenachalcopyrite) averages +10.9, and the Mount Farrell ore (galena-sphalerite) averages +14.1. The degree of enrichment does not appear to be related to local, near-surface geological factors. Other ores of geosynclinal volcanic type with similar mineralogy also show narrow ranges in 34S and varying enrichments in 34S. Barite from a concordant sulphide-barite-carbonate lode at Rosebery has an average 34S of +38.1 and an average 18O of +10.7. Barite from veins at Mount Lyell has an average 34S of +25.3 and an average 18O of +10.6.
Die Verteilung von Sauerstoff- und Schwefel-Isotopen in den Erzkörpern von Rosebery, Mount Farrell und Mount Lyell wurde untersucht. Die Erzkörper sind in kambrische, geosynklinale vulkanische Gesteine Westtasmaniens eingebettet. An jeder dieser Lagerstätten zeigt der Schwefel der Sulfiderze einen charakteristischen Anreicherungsgrad an 34S im Verhältnis zum Meteoritenschwefel und einen eng begrenzten Bereich der 34S-Werte. Die Erze des Mount Lyell-Lagers (hauptsächlich Pyrit-Chalkopyrit) zeigen überwiegend einen 34S-Durchschnittswert von +7.0, das Hauptlager von Rosebery (Pyrit-Sphalerit-Galenit-Chalkopyrit) +10.9, und des Mount Farrell-Erz (Galenit-Sphalerit) +14.1. Der Anreicherungsgrad scheint nicht mit den lokalen geologischen Faktoren verbunden zu sein. Auch andere Erzkörper geosynklinaler vulkanischer Art von ähnlicher mineralogischer Struktur zeigen eng begrenzte 34S-Werte und 34S-Anreicherungsvariationen. Der Baryt des konkordant aufgebauten Sulfid-Baryt-Carbonat-Lagers bei Rosebery hat einen 34S-Durchschnitt von +38.1 und einen 18O-Durchschnitt von +10.7. Der Baryt aus den Erzgängen von Mount Lyell ist durch einen 34S-Durchschnitt von +25.3 und einen 18O-Durchschnitt von +10.6 charakterisiert.
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8.
Further support for the view that mineralization at Mount Isa comprises two separate events is provided by 34S/32S measurement. Isotopic exchange between sulphides in lead-zinc-silver ores appears to have been promoted locally during metamorphism, whereas isotopic disequilibrium persists in the copper ores. These isotopic data are explained by a model in which sedimentary deposition of lead, zinc and silver was succeeded by the post-metamorphic emplacement of copper. Past biological activity is inferred from the occurrence of low concentrations of organic carbon with 13C values ranging from –21 to –26 PDB. Carbonate contents, expressed as carbon, vary from <0.1% to 10.9%. The 13C and 18O values for the carbonates are relatively constant at –4.4±1.1 and –17.6±1.1 PDB respectively. These values are interpreted as reflecting isotopic changes induced in original marine carbonates by isotopic exchange during lower greenschist metamorphism.  相似文献   

9.
Sulfur isotope analyses were made on 14 alunites from volcanic and sedimentary rocks widely different in chemistry and age from southern Tuscany and northern Latium, central Italy. The 34S values range from +0.7 to +9.6, and appear not to be related to the nature of the host rock. Geological and isotopic evidence suggests that all the alunites formed by supergenic oxidation of sulfides. Sulfides occurring with alunites in the volcanic rocks of Latium can be divided into an isotopically light group of probably magmatic origin (34S=–1.5 to +3.4) and a heavy one with 34S=+6.0 to +10.3, tentatively interpreted as deposited by hydrothermal fluids that leached sulfides of similar 34S/32S from the deep basement. Such an interpretation is consistent with recent studies indicating that in the perityrrhenian belt of Latium exists a continuation, at depth, of the Tuscan stratigraphic series, rich in sulfides with 34 from +6 to +12.  相似文献   

10.
Emerald deposits in Swat, northwestern Pakistan, occurring in talc-magnesite and quartz-magnesite assemblages, have been investigated through stable isotope studies. Isotopic analyses were performed on a total of seven emeralds, associated quartz (seven samples), fuchsite (three samples) and tourmaline (two samples) from the Mingora emerald mines. The oxygen isotopic composition ( 18O SMOW) of emeralds shows a strong enrichment in18O and is remarkably uniform at + 15.6 ± 0.4 (1,n = 7). Each of the two components of water in emerald (channel and inclusion) has a different range of hydrogen isotopic composition: the channel waters being distinctly isotopically heavier (D = –51 to –32 SMOW) than the other inclusion waters (D = –96 to –70 SMOW). Similarly the oxygen isotopic compositions of tourmaline and fuchsite are relatively constant ( 18O = + 13 to + 14 SMOW) and show enrichment in18O. The 18O values of quartz, ranging from + 15.1 to + 19.1 SMOW, are also high (+ 16.9 ± 1.4 1, n = 7). The meanD of channel waters measured from emerald (–42 ± 6.6 SMOW) and that of fluid calculated from hydrous mineralsDcalculated (–47 ± 7.1 SMOW) are consistent with both metamorphic and magmatic origin. However, the close similarity between the measuredD values of the hydroxyl hydrogen in fuchsite (–74 to –6 SMOW) and tourmaline (–84 and –69 SMOW) with pegmatitic muscovite and tourmaline suggests that the mineralization was probably caused by modified (18O-enriched) hydrothermal solutions derived from an S-type granitic magma. The variation in the carbon and oxygen isotopic composition of magnesite, locally associated with emerald mineralization, is also very restricted ( 13 –3.2 ± 0.7%, PDB; 18O + 17.9 ± 1.27 SMOW). On the basis of the isotopic composition of fluid ( 13C –1.8 ± 0.7 PDB; 18O + 13.6 ± 1.2 SMOW calculated for the 250-550 °C temperature), it is proposed that the Swat magnesites formed due to the carbonation of previously serpentinized ultramafic rocks by a CO2-bearing fluid of metamorphic origin.  相似文献   

11.
We have studied the oxygen isotopic composition of rocks from a 100 km transect through the central Superior province of Ontario, representing progressively the shallower terrains of the Kapuskasing structural zone (KSZ), the Wawa gneiss terrane (WGT), and the Michipicoten greenstone belt (MGB). These rocks range in age from 2.76 to 2.60 Ga, and correspond to a section through approximately 20 km of crustal thickness. Equivalent lithologic types have similar range of 18O values at each crustal level: tonalitic to granodioritic rocks: 6.4 to 9.5; dioritic and anorthositic rocks: 5.5 to 7.6; mafic gneisses: group 1 (majority): 5.7 to 7.1; group 2: 8.1 to 9.5. 18O values exhibit a remarkable correlation with SiO2 values, similar to that observed in unaltered plutonic rocks of equivalent composition. Paragneisses have significantly higher 18O values: 9.3 to 12.2. Low-grade metavolcanic and metasedimentary rocks of the MGB are 18O-enriched compared to their high-grade equivalents in the KSZ and WGT: 7.4 to 13.3 for mafic to felsic metavolcanic rocks; 11.4 to 14.7 for clastic metasediments. Coexisting minerals exhibit 18O-fractionation consistent with equilibrium, but corresponding to uniform isotopic temperatures about 553 to 584°C across the entire transect, lower than the inferred metamorphic temperatures in the highest-grade (KSZ) terrane. The lack of distinctive isotopic differences between equivalent rock types in the KSZ, WGT and MGB suggests that there is no significant gradient in 18O with depth in the crust. The majority of mafic gneisses (group 1) appear to have been emplaced either as subaerial extrusives, intrusive sills, or, less likely, as submarine extrusives that were hydrothermally altered at high temperatures. The less abundant group 2 mafic rocks have the 18O values typical of greenstones that were altered at low temperature by seawater, and isotopically resemble low-grade rocks in the Michipicoten and Abitibi belts. In general, no major changes in whole-rock isotopic composition appear to have occurred during granulite facies metamorphism, implying limited flux of water or CO2. The continuous linear gradient in 18O versus SiO2 in the high-grade rocks cannot be due to differentiation of a mafic source magma. A model involving an association between mantle-derived mafic magma and 18O-enriched crustal materials is more consistent with the oxygen isotopic and the REE data.McMaster Isotopic, Nuclear and Geochemical Studies Group Publication 163; LITHOPROBE Publication 168.  相似文献   

12.
Isotopic compositions of carbon and oxygen are studied in different (rhodochrosite, calcareous-rhodochrosite, and chlorite–rhodochrosite) types of manganese carbonate ores from the Usa deposit (Kuznetskii Alatau). The 13C value varies from –18.4 to –0.7, while the 18O value ranges between 18.4 and 23.0. Host rocks are characterized by higher values of 13C (–1.9 to 1.0) and 18O (21.2 to 24.3). The obtained isotope data suggest an active participation of oxidized organic carbon in the formation of manganese carbonates. Manganese carbonate ores of the deposit are probably related to metasomatic processes.  相似文献   

13.
In Riphean mudstones of the Yudoma–Maya Trough (southeastern Siberian Platform), which underwent deep catagenetic and metagenetic transformations, 18O values range from 11.2 to 18.9 (18Oaver= 14.4), which are 5–7 lower than those in similar Cenozoic rocks. The isotopic shift is caused by postsedimentary alterations at temperatures up to 200°C under the influence of a moderate influx of metamorphogenic solutions and relative geochemical insulation of rock formations from each other. Within separate formations, we have revealed a distinct positive correlation between 18O and SiO2, which is typical for thermodynamically ordered metamorphic rocks composed of minerals in isotopic equilibrium.  相似文献   

14.
The pre-Cenozoic geology at Candelaria, Nevada comprises four main lithologic units: the basement consists of Ordovician cherts of the Palmetto complex; this is overlain unconformably by Permo-Triassic marine clastic sediments (Diablo and Candelaria Formations); these are structurally overlain by a serpentinitehosted tectonic mélange (Pickhandle/Golconda allochthon); all these units are cut by three Mesozoic felsic dike systems. Bulk-mineable silver-base metal ores occur as stratabound sheets of vein stockwork/disseminated sulphide mineralisation within structurally favourable zones along the base of the Pickhandle allochthon (i.e. Pickhandle thrust and overlying ultramafics/mafics) and within the fissile, calcareous and phosphatic black shales at the base of the Candelaria Formation (lower Candelaria shear). The most prominent felsic dike system — a suite of Early Jurassic granodiorite porphyries — exhibits close spatial, alteration and geochemical associations with the silver mineralisation. Disseminated pyrites from the bulk-mineable ores exhibit a 34S range from — 0.3 to + 12.1 (mean 34S = +6.4 ± 3.5, 1, n = 17) and two sphalerites have 34S of + 5.9 and + 8.7 These data support a felsic magmatic source for sulphur in the ores, consistent with their proximal position in relation to the porphyries. However, a minor contribution of sulphur from diagenetic pyrite in the host Candelaria sediments (mean 34S = — 14.0) cannot be ruled out. Sulphur in late, localised barite veins ( 34S = + 17.3 and + 17.7) probably originated from a sedimentary/seawater source, in the form of bedded barite within the Palmetto basement ( 34S = + 18.9). Quartz veins from the ores have mean 18O = + 15.9 ± 0.8 (1, n = 10), which is consistent, over the best estimate temperature range of the mineralisation (360°–460°C), with deposition from 18O-enriched magmatic-hydrothermal fluids (calculated 18O fluid = + 9.4 to + 13.9). Such enrichment probably occurred through isotopic exchange with the basement cherts during fluid ascent from a source pluton. Whole rock data for a propylitised porphyry ( 18O = + 14.2, D = — 65) support a magmatic fluid source. However, D results for fluid inclusions from several vein samples (mean = — 108 ± 14, 1, n = 6) and for other dike and sediment whole rocks (mean = — 110 ± 13, 1, n = 5) reveal the influence of meteoric waters. The timing of meteoric fluid incursion is unresolved, but possibilities include late-mineralisation groundwater flooding during cooling of the Early Jurassic progenitor porphyry system and/or meteoric fluid circulation driven by Late Cretaceous plutonism.  相似文献   

15.
Sulfur and carbon isotope data are presented of 15 granulite samples from the Furua Complex, southern Tanzania, in which scapolite is a primary and major rock-forming constituent (up to 30 vol%). From these data, the isotopic composition is deduced of the sulfate and carbonate group in the scapolite structure. Subsequently, the composition and origin is discussed of the volatile species that are present in the deep crustal environment in which these scapolites formed.The 34S-values show a narrow range from 0.3 to 3.6, consistent with a deep-seated (mantle) origin of the sulfur; the mean value of 1.9 is slightly higher than usually found in rocks of assumed mantle provenance. The results of the carbon isotope analyses are more difficult to interpret; they suggest that the granulites contain two different carbon components with different isotopic compositions. Firstly, one component, liberated by phosphoric acid at room temperature, has 13Cvalues between –3.8 and –11.2 and a mean value of –6.7. This carbon component is assumed to occur as finely dispersed, submicroscopic carbonate inclusions. The second carbon fraction is liberated by phosphoric acid treatment at temperatures between 200 and 400° C and has considerably lower 13Cvalues with a mean value of –14.1 This seems to represent the carbon isotope composition in the scapolite structure. Such low 13C-values do not agree with the generally accepted value of –7 for juvenile carbon, but they are comparable to those found in early, primary carbonic inclusions from various granulite regions. It is argued that these low 13C-values are typical for granulite-facies metamorphism and that they may characterize an important fluid phase of the lower crust.  相似文献   

16.
Summary The stable isotope geochemistry of native gold-bearing quartz veins contained within low-grade metasedimentary strata in the central Canadian Rocky Mountains, British Columbia is examined. The data augment previous geological and geochemical studies.Vein pyrite 34S values cluster between + 14.2 and + 16.3 (CDT). Coeval galenas exhibit 34S values between + 11.4 and 13.3. Pyrite-galena geothermometry reveals a mean temperature of mineralization of 300 ± 43°C. Comparison of 34S values for the vein pyrites, with values for pyrite porphyroblasts in country rocks suggests that vein sulfur was probably derived from the host rocks.18O(SMOW) values of host quartzites and pelites cluster between + 12.0 and + 13.5, and + 9.5 and + 10.5, respectively. Auriferous vein quartz exhibits 18O values between + 13.0 and + 15.0. Veins were likely deposited from fluids undergoing post-peak metamorphic cooling.Vein inclusion fluids exhibit values between –105 and –124 (SMOW). Combined O-H-isotope data are most compatible with a source fluid involving chemically- and isotopically-evolved meteoric waters.The critical role of H-isotope data in the evaluation of source fluids for such mesothermal gold lodes is stressed. The paucity of H-isotope data pertaining to the study of lode gold deposits in similar low-grade metasedimentary domains suggests that the involvement of meteoric waters may at times be overlooked.
Der Ursprung metamorphogener Gold-Ganglagerstätten: Bedeutung stabiler Isotopendaten aus den zentralen Rocky Mountains, Kanada
Zusammenfassung Die vorliegende Arbeit befaßt sich mit der Untersuchung der Geochemie stabiler Isotope goldführender Quarzgänge in schwach metamorphen Sedimenten der zentralen Rocky Mountains in Britisch Kolumbien, Kanada. Die Resultate ergänzen früher publizierte geologische und geochemische Daten.Die 34S-Werte von Gang-Pyrit liegen zwischen + 14.2 und + 16.3 (CDT); gleichzeitig gebildeter Bleiglanz hat 34S-Werte von + 11.4 bis + 13.3. Die Isotopengeothermo metrie des Pyrits und Bleiglanzes ergibt eine mittlere Mineralisationstemperatur von 300°C + 43° für diese beiden Minerale. Vergleiche der 8345-Werte des Gang-Pyrits mit denen von Pyrit-Porphyroblasten des Nebengesteins lassen für die Gang-Pyrite eine Herkunft des Schwefels aus dem Nebengestein als wahrscheinlich erscheinen.Die 18O-Werte von Quarziten und Peliten, die als Nebengesteine auftreten, streuen von + 12.0 bis + 13.5 (SMOW), beziehungweise von +9.5 bis + 10.5 Quarz goldführender Gänge hat 18O-Werte, die zwischen + 13.0 und + 15.0 (SMOW) liegen. Er wurde als Gangfüllung wahrscheinlich bei sinkenden Temperaturen aus post metamorphen wäßrigen Lösungen abgesetzt.Flüssigkeitseinschlüsse von Gangmineralien zeigen D-Werte von -105 bis -124 (SMOW). Die H-O-Isotope sind deshalb ein Hinweis dafür, daß als mineralisierende Lösungen isotopisch veränderte meteorische Wässer in Betracht zu ziehen sind. Bei der Deutung der Herkunft der mineralisierenden wäßrigen Lösungen von mesothermalen Goldgängen muß die Kenntnis der H-Isotope als kritisch betrachtet werden. Die Seltenheit mit der H-Isotopendaten dieses Lagerstättentyps in der Literatur diskutiert werden, dürfte ein wesentlicher Grund dafür sein, daß die Rolle meteorischer Wässer bei der Genese mesothermaler, in Metasedimenten liegender Goldgänge, vielfach übersehen wurde.

With 4 Figures  相似文献   

17.
Stibnite mineralisation in the antimony province of New England can be divided into Central type ores (veins of stibnite + quartz ± berthierite) and Peripheral type ores of stibnite + quartz + native antimony ± berthierite. The Central stibnites have 34SCDT values of –5±2 (1) which may represent equilibrium precipitation from mantle sulfur at about 200°C. Peripheral stibnites have 34S values between 0 and –25, with a large group at 0±2. They represent precipitation from a limited supply of mantle sulfur and the acquisition of sedimentary sulfur. We consider that the different ore types were produced from distinct ore solutions derived from two immiscible melts. These originated in the deep mantle, were mobilised by tectonic activity and supplied the antimony and most of the sulfur to the ores.  相似文献   

18.
For the first time 18O and 13C values from carbonates and D values of individual n-alkanes were used to reconstruct palaeohydrological conditions in a lagoon at the southern margin of the Central European Zechstein Basin (CEZB). A 12-m core covering the complete Ca2 interval and adjacent anhydrites (A1 and A2) was analyzed for 18O and 13C values of dolomitized carbonates and D values of individual n-alkanes. 18Ocarb values (+2 to +5 vs. VPDB) were strongly influenced by evaporation and temporal freshwater input into the lagoon. The 13Ccarb values (–1 to +4 vs. VPDB) were controlled mainly by changes in primary production. Both isotopic ratios show an inverse relationship throughout most of the core, contradicting diagenetic alteration, since 13Ccarb values are not altered significantly during dolomitization. Assuming a temperature range of 35–40 °C in the lagoon, 18Ocarb values of +2.5 to +8 (vs. VSMOW) for the lagoonal water can be reconstructed. The lagoon may have desiccated twice during the Ca2 interval, as indicated by very high 18Ocarb and low 13Ccarb values, coinciding with increasing amount of anhydrite in the analyzed sample. These events seem to reflect not just local but a regional intra-Ca2 cyclicity. Measured D values of the short-chain n-alkanes, namely n-C16 and n-C18 which are widely used as indicators for photosynthetic bacterial and algal input, reflect the isotopic composition of the lagoonal water. Assuming constant fractionation during incorporation of hydrogen into lipids of –160, an average D value of +70 (vs. VSMOW) can be reconstructed for the lagoonal water, accounting for very arid conditions. The long-chain n-alkanes n-C27, n-C28, n-C29 and n-C30, thought to be derived from the leaf waxes of terrestrial higher plants, were shown to be depleted in D relative to the short-chain alkanes, therefore indicating a different hydrogen source. Terrestrial plants in arid areas mainly use water supplied by precipitation. By using a smaller fractionation of –120 due to evaporation processes in the leaves, reconstructed values vary between –74 and –9 (vs. VSMOW). These values are not indicating extremely arid conditions, implying that the long-chain n-alkanes were transported trough wind and/or rivers into the lagoon at the Zechstein Sea coast. Dwater values, reconstructed using the n-C16 alkane and 18O water values, independently reconstructed on the same sample using the temperature dependant fractionation for dolomites are good agreement and suggest high amounts of evaporation affecting the coastal lagoon. Altogether, our results indicate that hydrogen isotopic ratios of n-alkanes give information on their origin and are a useful proxy for palaeoclimatic reconstruction.  相似文献   

19.
In this paper, we present boron isotope analyses of variably degassed rhyolitic glasses from Long Valley, California. The following results indicate that pre-eruptive boron isotopic signatures were preserved in degassed glasses: (1) averaged secondary ionization mass spectrometry (SIMS) measurements of H2O-rich (~3 wt%) melt inclusions from late erupted Bishop Tuff pumice are indistinguishable from positive thermal ionization mass spectrometry (PTIMS) analysis of vesiculated groundmass glass (11B=+5.0±0.9 and +5.4±5, respectively); (2) SIMS spot-analyses on H2O-poor obsidian (~0.15 wt% H2O) from younger Glass Mountain Dome YA (average 11B=+5.2±1.0) overlap with compositionally similar late Bishop Tuff melt inclusions; and (3) four variably degassed obsidian samples from the 0.6 ka Mono Craters (H2O between 0.74 and 0.10 wt%) are homogeneous with regard to boron (average 11B=+3.2±0.8, MSWD=0.4). Insignificant variations in 11B between early and late Bishop Tuff melt inclusion glasses agree with published experimental data that predict minor 11B depletion in hydrous melts undergoing gas-saturated fractional crystallization. Melt inclusions from two crystal-rich post-caldera lavas (Deer Mountain and South Deadman Dome) are comparatively boron-rich (max. 90 ppm B) and have lower 11B values (average 11B=+2.2±0.8 and –0.4±1.0 ) that are in strong contrast to the boron isotopic composition of post-caldera crystal-poor rhyolites (27 ppm B; 11B=+5.7±0.8). These variations in 11B are too large to be caused by pre-eruptive degassing. Instead, we favor assimilation of 11B depleted low-temperature hydrothermally altered intrusive rocks subsequent to fresh rhyolite recharge.Editorial responsibility: J. HoefsAn erratum to this article can be found at  相似文献   

20.
Oxygen and carbon isotope compositions were determined for calcites from the Green Tuff formations of Miocene age in Japan. Values of 18O from 24 calcites in altered rocks from 5 districts range from –2 to +16SMOW, in most cases from 0 to +8SMOW. The low 18O values rule out the possibility of their low-temperature origin or any significant contribution of magmatic fluid in the calcite precipitation. These values, coupled with their mineral assemblages, suggest that the calcites formed from meteoric hydrothermal solutions which caused propylitic alteration after the submarine strata became emergent.Values of 13C from the calcites show a wide variation from –17 to 0PDB. Calcites from different districts have different ranges of 13C values, indicating that there was no homogeneous reservoir of carbon at the time the calcite formed, and that the carbon had local sources. Carbon isotopic compositions of calcite within ore deposits in the Green Tuff formations range from –19 to 0PDB, similar to those of calcite in the altered rocks in the same district, suggesting that the carbon in ore calcites was likely supplied from the surrounding rocks through activity of meteoric hydrothermal solutions.  相似文献   

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