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1.
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   

2.
Stable isotope compositions have been determined for serpentinites from between Davos (Arosa-Platta nappe, Switzerland) and the Valmalenco (Italy). D and 18O values (–120 to –60 and 6–10, respectively) in the Arosa-Platta nappe indicate that serpentinization took place on the continent at relatively low temperatures in the presence of limited amounts of metamorphic fluids that contained a component of meteoric water. One sample of chrysotile has a 18O value of 13 providing evidence of high W/R ratios and low formation temperature of lizardite-chrysotile in this area. In contrast, relatively high D values (–42 to –34) and low 18O values (4.4–7.4) for serpentine in the eastern part of the Valmalenco suggest a serpentinization process that took place at moderate temperatures in fluids that were dominated by ocean water. The antigorite in the Valmalenco is the first reported example of continental antigorite with an ocean water signature. An amphibole sample from a metasomatically overprinted contact zone to metasediments (D=-36) indicates that the metasomatic event also took place in the presence of ocean water. Lower D values (–93 to –60) of serpentines in the western part of the Valmalenco suggest a different alteration history possibly influenced by fluids associated with contact metamorphism. Low water/rock ratios during regional metamorphism (and metasomatism) have to be assumed for both regions.  相似文献   

3.
Boron isotope variations in nature: a synthesis   总被引：9，自引：0，他引：9  
The large relative mass difference between the two stable isotopes of boron, 10B and 11B, and the high geochemical reactivity of boron lead to significant isotope fractionation by natural processes. Published 11B values (relative to the NBS SRM-951 standard) span a wide range of 90. The lowest 11B values around — 30 are reported for non-marine evaporite minerals and certain tourmalines. The most 11B-enriched reservoir known to date are brines from Australian salt lakes and the Dead Sea of Israel with 11B values up to +59. Dissolved boron in present-day seawater has a constant world-wide 11B value of + 39.5. In this paper, available 11B data of a variety of natural fluid and solid samples from different geological environments are compiled and some of the most relevant aspects, including possible tracer applications of boron-isotope geochemistry, are summarized.
Résumé La grande différence relative de masse entre les isotopes stables du bore, 10B et 11B, et la grande réactivité geochimique du bore ont pour conséquence un fractionnement isotopique naturel important. Les valeurs de 11B publiées (par rapport au standard NBS SRM-951) varient de 90. Les valeurs de 11B les plus basses (–30) correspondent aux evaporites non-marines et à certaines tourmalines. Le réservoir le plus enrichi en 11B est représenté par les saumures des lacs salés d' Australie et par la Mer Morte en Israël, qui ont des valuers de 11B allent jusqu'à + 59. L'eau de mer a une valeur de 11B mondialement constante de + 39.5. Des valeurs de 11B des solutions naturelles ainsi que des roches et minéraux de différentes origines, publiées jusqu'à présent, sont présentées ici. En outre quelques aspects importants concernant la géochimie des isotopes du bore y compris quelques applications sont exposés.
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4.
Sea water basalt interaction in spilites from the Iberian Pyrite Belt   总被引：2，自引：0，他引：2  
Low grade hydrothermally metamorphosed mafic rocks from the Iberian Pyrite Belt are enriched in 18O relative to the oxygen isotopic ratio of fresh basalt (+6.5±1). The observed 18O whole rock values range from +0.87 to +15.71 corresponding to positive isotopic shifts of +5 to +10, thus requiring isotopic exchange with fluids under conditions of high water:rock ratios at low temperatures. The lowest 18O observed corresponds to an albitized dolerite still and is compatible with independent geochemical data suggesting lower water: rock ratios for the alteration of these rocks.The isotope data are consistent with the hypothesis that the spilites from the Pyrite Belt were produced by interaction of basaltic material with sea water.Significant leaching of transition metals from the mafic rocks during alteration coupled with available sulphur isotopic data for the sulphide ores also suggest that sea water may have played an important role in the formation of ore deposits in the Iberian Pyrite Belt.  相似文献   

5.
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   

6.
In closed magma systems SiO2 approximately measures differentiation progress and oxygen isotopes can seem to obey Rayleigh fractionation only as a consequence of the behaviour of SiO2. The main role of 18O is as a sensitive indicator of contamination, either at the start of differentiation ( 18Oinit) or as a proportion of fractionation in AFC. Plots of 18O vs SiO2-allow to determine initial 18O values for different sequences for source comparison. For NBS-28=9.60, the 18O at 48% SiO2-varies between a high 6.4 for Kiglapait (Kalamarides 1984), 5.9 for Transhimalaya, 5.8 for Hachijo-Jima (Matsuhisa 1979), 5.6 for Koloula (Chivas et al. 1982) and a low 5.3 for the Darran Complex, New Zealand. The Transhimalayan batholiths (Gangdese belt) were emplaced in the Ladakh-Lhasa terrane, between the present-day Banggong-Nujiang, and Indus-Yarlung Tsangbo suture zones, after its accretion to Eurasia. The gradient of the least contaminated continuous ( 18O vs SiO2-igneous trend line is similar to that of Koloula, and AFC calculations suggest a low secondary assimilation rate of less than 0.05 times the rate of crystallisation. Outliers enriched in 18O are frequent in the Lhasa, and apparently rare in the Ladakh transsect. Low- 18O (5.0–0) granitoids and andesites on the Lhasa-Yangbajain axis are the result of present day or recent near-surface geothermal activity; their quartzes still trace the granitoids to the Transhimalaya 18O trend line, but the distribution of low total rock or feldspar 18O values could be a guide to more recent heat flow and thermally marked tectonic lineaments. Two ignimbrites from Maqiang show hardly any 18O-contamination by crustal material.  相似文献   

7.
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   

8.
The 620 M.y.-old in Hihaou (In Zize) magmatic complex located at the north-western boundary of the Archaean In Ouzzal block (western Ahaggar), is composed of massive alkaline rhyo-ignimbrites and rhyolitic domes, which are intruded by a granophyric and granitic body. The whole is preserved in a cauldron structure. Extrusive rocks are strongly 18O-depleted, with -values as low as –1.5/SMOW, while granophyres are less depleted (minimum -18O value=+2.0/SMOW. The granite has values around + 6/SMOW. D/H compositions are rather low, with D–90 to –110/SMOW. Isotopic zoning of quartz phenocrysts, 18O/16O fractionation among coexisting phases, and heterogeneity of the whole-rock -18O values, suggest that the volcanic rocks have interacted with meteoric water after the eruption. Several mechanisms of isotopic alteration are discussed. The hydrothermal alteration does not seem to have been controlled by the granitic intrusion, but rather seems to have followed the deposition of thick pyroclastic deposits on permeable arkosic sandstones and fluvio-glacial conglomerates. Pervasive circulation of water through the cooling volcanic deposits could have produced the observed 18O depletion.  相似文献   

9.
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   

10.
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   

11.
Zusammenfassung In den DSDP-Legs 1, 11, 13, 17, 25, 27, 32, 36, 41, 43, 44, 50 und 62 wurden die Unterkreide-Foraminiferen biostratigraphisch, taxonomisch und paläoökologisch bearbeitet. Eine Übersicht zeigt die in Leg 1–80 erbohrte Unterkreide und ihre Foraminiferen-Bearbeitungen.Im Nordatlantik fehlen regional ab dem Oberen Tithonium im Verlaufe einer Regression und der sie begleitenden Schichtlücken bis in das Valanginium charakteristische Foraminiferenfaunen. In Gebieten ohne Schwarzschiefer-Bedingungen setzen im Valanginium-Barremium mäßig reichhaltige bis sehr spärliche Mikrofaunen mitPraedorothia ouachensis (Sigal) der gleichnamigen Zone ein (Valanginium-Hauterivium). Hauterivium-Aptium gliedern sich in dieGavelinella barremiana-, dieGaudryina dividens- und dieConorotalites aptiensis- Zone.Wo im Albium nicht das ausgedehnte Schwarzschiefer-Milieu herrschte, findet man eine kosmopolitische Fauna aus agglutinierten und kalkschaligen Foraminiferen derPseudoclavulina gaultina- Zone. Für das höhere Albium und Cenomanium wurde dieGavelinella cenomanica- Zone ausgeschieden. Von biostratigraphischer Bedeutung sind im Berriasium-Albium die GattungenPraedorothia, Gaudryina, Pseudoclavulina, von den Kalkschalern nur wenige skulptierte Arten der Nodosariiden (Citharina, Lenticulina) sowieGavelinella, Conorotalites, Pleurostomella, Valvulineria undOsangularia. Die vonMoullade (1984) begründeten Zonen vom Berriasium-Albium der Tethys und des DSDP sind wegen der großen stratigraphischen Reichweite der verwendeten Foraminiferenarten nicht überall anwendbar.Im Indischen Ozean lassen die wenigen, bisher bekannten »australen« Foraminiferenfunde aus dem Neokom von Site 261 mit überwiegend primitiven agglutinierenden Formen eine genaue Datierung kaum zu. Die Kalkschaler sind meist aufgelöst oder auch umgelagert. Man ordnet sie dem Bereich des kühleren Wassers zu.Im Pazifischen Ozean sind die meisten Mikrofaunen wegen der geringen Kerngewinne, Verunreinigungen oder primärer Foraminiferenarmut (Schwarzschiefer) biostratigraphisch und paläoökologisch kaum verwertbar. Erst im Albium findet sich — wie im Atlantik — eine etwas reichhaltigere Kalk- und Sandschalerfauna mit wichtigen Arten derPseudoclavulina gaultina- Zone. Da außerGavelinella cenomanica (Brotzen) keine andere benthonische Foraminiferenart neu einsetzt, wird die Grenze zum Cenomanium in der Regel mit planktonischen Foraminiferen gezogen.Im Albium fallen die einheitlichen, kosmopolitischen Foraminiferenfaunen ohne ausgeprägte Faunenprovinzen auf.
From the DSDP Legs 1, 11, 13, 17, 25, 27, 32, 36, 41, 43, 44, 50, and 62 the Lower Cretaceous foraminifers have been investigated for biostratigraphical, taxonomical, and palaeoecological purposes. An overview of the cored Lower Cretaceous sections of Leg 1–80 is given.In the Northern Atlantic Ocean characteristic foraminiferal faunas are missing from the Upper Tithonian to the Valanginian due to a marked regression which caused hiatuses. In areas without black shale conditions Valanginian to Barremian medium rich to poor microfaunas withPraedorothia ouachensis (Sigal) of thePraedorothia ouachensis Zone (Valanginian-Hauterivian). The Hauterivian-Aptian interval is characterized by zones ofGavelinella barremiana,Gaudryina dividens, andConorotalites aptiensis. During the Albian a world-wide fauna consisting of agglutinated and calcareous foraminifers of thePseudoclavulina gaultina Zone is established in areas lacking the wide-spread black-shale conditions. The Upper Albian and the Cenomanian are represented by theGavelinella cenomanica Zone. Some ornamented species of the nodosariids (Citharina, Lenticulina), Gavelinella, Conorotalites, Pleurostomella, Valvulineria, andOsangularia are of some importance for the biostratigraphy of the Berriasian-Albian interval. The Berriasian to Albian zones introduced for the Tethys and the DSDP byMoullade (1984) could only be of some local importance due to the long stratigraphical range of the foraminiferal species used.In the Indian Ocean an exact stratigraphical age cannot be assigned to the few Neocomian foraminiferal faunas of a cooler sea water (Site 261). These faunas mainly contain primitive agglutinated foraminifers, because in most cases the calcareous tests are dissolved or redeposited.In the Pacific Ocean most of the Berriasian to Aptian microfaunas are of minor biostratigraphical and palaeoecological importance for reasons of poor core recoveries, contaminations or original foraminiferal poverty (black shales). Since the Albian there are somewhat higher-diverse faunas of calcareous and agglutinated foraminifers with index species of thePseudoclavulina gaultina Zone. As a rule, the boundary Albian/Cenomanian is set by means of planktonic foraminifers because no other foraminifer has its first appearance datum during this interval, exceptGavelinella cenomanica.During the Albian very uniform, world-wide foraminiferal faunas without a marked provincialism are obvious.
Résumé Dans les Legs DSDP 1, 11, 13, 17, 25, 27, 32, 36, 41, 43, 44, 50 et 62, les foraminifères du Crétacé inférieur ont été étudiés aux points de vue biostratigraphique, taxonomique et paléoécologique. La note présente une vue d'ensemble de la section d'âge crétacé inférieur du Leg 1–80.Dans l'Atlantique nord, les faunes caractéristiques de foraminifères sont absentes depuis le Tithonique supérieur jusqu'au Valanginien, en raison d'une régression importante et des lacunes qui en résultent. Dans les régions dépourvues de milieux à shales noirs, on rencontre une microfaune, pauvre à moyennement riche, valanginienne à barrémienne, àPraedorothia ouachensis (Sigal), appartenant à la Zone àPraedorothia ouachensis. L'intervalle Hauterivien-Aptien est caractérisé par les Zones àGavelinella barremiana, Gaudryina dividens et Conorotalites aptiensis. Au cours de l'Albien une faune d'extension mondiale de foraminifères agglutinés et calcaires appartenant à la Zone àPseudoclavu-lina gaultina, s'est établie dans les aires où ne règnaient pas les conditions de formation de shales noirs. L'Albien supérieur et le Cénomanien sont représentés par la Zone àGavelinella cenomanica. Dans l'intervalle Berriasien-Albien, un rôle biostratigraphique de quelque importance est joué par quelques espèces de Nodosariides à coquilles ornementées (Citharina, Lenticulina) ainsi queGavelinella, Conorotalites, Pleurostomella, Valvulineria et Osangularia. Les zones établies parMoullade (1984) pour le Berriasien-Albien de la Téthys et du DSDP ne sont pas partout utilisables, en raison de l'extension verticale trop grande des foraminifères utilisés.Dans l'Océan Indien, un âge exact ne peut être assigné aux faunes de foraminifères néocomiennes considérées jusqu'ici comme «australes» (site 261): ces faunes renferment surtout des formes agglutinées primitives, car les tests calcaires ont été généralement dissous ou remaniés.Dans l'Océan Pacifique, la plupart des microfaunes berriasiennes à aptiennes sont de faible intérêt biostratigraphique et paléo-écologique, en raison des mauvais rendements des carottes, de contaminations ou de leur pauvreté originelle (facies des shales noirs). A partir de l'Albien, on trouve une faune plus diversifiée de foraminifères agglutinés et calcaires, comportant des espèces caractéristiques de la Zone àPseudoclavulina gaultina. Comme d'ordinaire, la limite Albiencénomanien est définie par les foraminifères planctoniques, aucun autre foraminifère n'apparaissant dans cet intervalle, saufGavelinella cenomanica.A l'Albien, la faune de foraminifères est uniforme à l'échelle mondiale, sans distinction de provinces.
, 1, 11, 13, 17, 25, 27, 32, 36, 41, 43, 44, 50 62 DSDP, , . , 1–80 . . , , - Praedorothia ouachensis (Sigal) — . : Gavelinella barremiana, Gaudryina dividens Conorotalites aptiensis,, , , Pseudoclavulina gaultina. Gavelinella ni. - Praedorothia, Gaudryina, Pseudoclavulina, (Citharina, Lenticulina), Gavelinella, Conorotalites, Pleurostomella, Valvulineria Osangularia. , moullade (1984) - , .. , , . .: 261, , «», . . , . , . . , - - , , ( ). , , , Pseudoclavulina gaultina. T. . Gavelinella ni (brotzen) , , , . .
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12.
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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13.
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   

14.
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   

15.
Summary A set of 354 sulphur isotope data from the Bleiberg deposit, the type deposit of Alpine low temperature carbonate hosted Pb–Zn deposits (APT deposits), is critically evaluated applying statistical methods. The sulphur isotope patterns vary significantly among the ore horizons. This suggests a long lasting and polyphase mineralisation system. The sulphur isotope composition of barite corresponds to that of Carnian seawater (i.e. 16 34S). The 34S values of the iron sulphides correspond to data from sedimentary iron sulphides. Pb and Zn sulphides are characterized by three normally distributed 34S populations with mean values of –6 to –8, –13 to –18, and –25 to –29. Heavy sulphur (>–10 34S) indicates contribution of sulphide sulphur from epigenetic-hydrothermal fluids, whereas light sulphide sulphur (<–21 34S) was produced by sulphur – reducing bacteria. The intermediate population is explained by mixing of sulphur derived from these two sources. Other sources of local importance, however, can not be excluded. The isotope populations correspond only partly to the paragenetic ore stages. The sulphur isotope patterns in the APT deposits are regionally different. Data from other low-temperature sediment-hosted Pb–Zn deposits support the proposed interpretation. A comparison demonstrates that the sulphur isotope patterns of APT deposits correspond to patterns of the Irish type deposits, but are different to those of Mississippi Valley type deposits.Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1007/s00710-004-0071-3  相似文献   

16.
The Loon Lake pluton in the Grenville province of Southeastern Ontario consists of a quartz monzonite rim surrounding a monzonite core containing inclusions of gneiss, gabbro and diorite. The pluton was emplaced in amphibolite facies Apsley gneiss, amphibolite and marble. Abnormally high 18O values are observed in all igneous rock types: quartz monzonite (8.9–13.9), monzonite (8.9–9.7), diorite-gabbro (8.0–9.3). High 18O contents are attributable to interaction between pluton and country rocks, through either isotopic exchange or direct mixing of mobilizate anatectically produced in the contact aureole of the pluton.The Apsley gneiss displays a 18O range from 8.3 to 16.9. There is no difference in 18O distribution between rocks inside and outside the contact aureole, although intermineral isotopic fractionations in the aureole are smaller than those outside. A chemical composition discriminant function that distinguishes rocks of igneous origin (DF>0) from sedimentary (DF<0) is inversely correlated with 18O of the gneisses, indicating that low 18O values are inherited from a silicic volcanic protolith. Al2O3/Na2O, an index of maturity of sediments, increases with 18O for the DF<0 group but is almost constant for the DF>0 group over a 18O range from 8.3 to 13.4. The DF<0 group is inferred to have formed from a series of clastic sediments of varying degree of weathering or maturity; the DF>0 group formed either from tuffs partially altered to zeolites, or from hydrated volcanic flows or ignimbrites.  相似文献   

17.
Sulfur isotope ratios have been determined in 27 selected volcanic rocks from Iceland together with their whole rock chemistry. The 34S of analyzed basalts ranges from –2.0 to +0.4 with an average value of –0.8 Tholeiitic and alkaline rocks exhibit little difference in 34S values but the intermediate and acid rocks analyzed have higher 34S values up to +4.2 It is suggested that the overall variation in sulfur isotope composition of the basalts is caused by degassing. The small range of the 34S values and its similarity to other oceanic and continental basalts, suggest that the depleted mantle is homogeneous in its sulfur isotope composition. The 34S of the depleted mantle is estimated to be within the range for undegassed oceanic basalts, –0.5 to +1.0  相似文献   

18.
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   

19.
The S-isotopic compositions of sulfide deposits from Steinmann, granitoid and felsic volcanic associations have been examined. Ores of Steinmann association have 34S values close to zero per mil (34S=+0.3±3.1) it appears they are of mantle origin. Isotopically, ores of granitoid association regularly show a variable enrichment in 32S relative to meteoritic (34S=–2.7±3.3). The composition is in accord with an upper mantle/lower crustal source. Two stratiform accumulations of felsic volcanic association show a narrow spread of 34S values (+0.2 to 2.4); a mantle origin for the sulfur in these deposits is favored. In contrast, vein, stockwork and cement ores are moderately enriched in 32S relative to meteoritic (34S=–4.0±6.4). These ores are polygenetic; sulfur and metals appear to have been leached from local country rocks where volcanogenic and biogenic sulfur predominate.  相似文献   

20.
Sulfur isotope abundance data for minerals of the historically important alunite deposits of the Tolfa district indicate (1) compositional similarity between sulfates and sulfides (mean S34 values of +5.54 and +6.34 permil respectively), (2) negligible fractionation factors (0.995 to 1.004) for sulfate-sulfide mineral pairs, (3) two distinct sulfide isotopic populations characterized by pyrite (+8.34 permil) and marcasite (–1.05 permil) and with associated alunite displaying a covariant isotopic shift, and (4) possible contamination of the hydrothermal system by evaporite sulfate (+25.1 permil) because hypogene pyrite, galena, and cinnabar are enriched in S34 (+6.1 to +10.3 permil). We suggest that alunite, barite, and possibly marcasite are of supergene origin and that the sulfate-sulfur was derived from the surficial oxidation of sulfides. Our conclusion is compatible with the geologic evidence and confirms the supergene hypothesis for the genesis of Tolfa alunites proposed by Fuchs and De Launay (1893) and De Launay (1906; 1913).
Zusammenfassung Die Schwefel-Isotopen-Häufigkeiten von Mineralen der historisch wichtigen Alunit-Vorkommen des Gebietes um Tolfa zeigen (1) eine große Ähnlichkeit der Isotopen-Zusammensetzungen zwischen Sulfaten und Sulfiden (Mittelwerte für S34 von +5,54 bzw. +6,34), (2) höchstens sehr geringe Fraktionierungs-Faktoren (0,995 bis 1,004) für Mineralpaare von Sulfat und Sulfid, (3) zwei verschiedene Gruppen von Isotopenverhältnissen bei den Sulfiden, und zwar für Pyrit (+8,34) und Markasit (–1,05), wobei der jeweils begleitende Alunit ähnliche Unterschiede aufweist, und (4) eine mögliche Beeinflussung des hydrothermalen Systems durch Sulfat aus Salzlagerstätten (+25,1), weil hypogener Pyrit, Galenit und Zinnober eine Anreicherung von S34 zeigen (+6,1 bis +10,3). Wir nehmen an, daß Alunit, Baryt und möglicherweise auch Markasit supergen gebildet wurden, und daß der Sulfat-Schwefel durch die Oxydation von Sulfiden an der Erdoberfläche entstand. Unsere Schlußfolgerung ist mit den geologischen Befunden vereinbar und bestätigt die supergene Hypothese für die Bildung der Alunitvorkommen von Tolfa, wie sie von Fuchs und De Launay (1893) und De Launay (1906; 1913) vertreten wurde.
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