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1.
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   

2.
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   

3.
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   

4.
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   

5.
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   

6.
Zusammenfassung Zur Bestimmung der O18-Werte von Sulfaten wird BaSO4 mit Kohlenstoff reduziert und das gewonnene CO2 massenspektrometrisch gemessen. Das sehr einfache Reduktionsverfahren erlaubt eine Meßgenauigkeit von 0,4 relativ zur SMOW-Skala.Eine kombinierte Schwefel- und Sauerstoffisotopenanalyse von Gips bzw. Anhydrit sollte Einzelheiten über Entstehung und Herkunft dieser Sulfate erkennen lassen. Am Beispiel eines Kupferschieferprofiles wird gezeigt, daß durch eine derartige Analyse primäre Restsulfate von sekundär zu Sulfaten aufoxidierten Sulfiden unterschieden werden können. Die sekundären Sulfate sind durch relativ leichten Sauerstoff (O18=+4)gekennzeichnet und an S34 verarmt (S34–23), was auf den Zusammenhang mit den durch bakterielle Reduktion gebildeten Kupferschiefersulfiden schließen läßt (Einzelheiten vgl. Marowsky, 1969). Die primären Restsulfate sind dagegen an O18 und S34 angereichert. Die von Lloyd (1968) gefundene Korrelation zwischen der Anreicherung von schwerem Schwefel und schwerem Sauerstoff in dem verbleibenden Sulfat bei bakterieller Sulfatreduktion konnte bestätigt werden.
Sulfur and oxygen isotope studies of sulfates from the Permian Kupferschiefer
The oxygen isotopic composition of sulfates has been determined in CO2 by mass spectrometry after reduction of BaSO4 with carbon. The experimental procedure with a precision of 0.4 in the scale relative to SMOW is described in some detail. It is a problem to distinguish between primary and secondary gypsum or anhydrite in argillaceous sediments. A combined analysis of sulfur and oxygen of the sulfates mentioned is applied for getting evidence on the origin of these sulfates. Samples of a Permian Kupferschiefer profile show that primary residual sulfates from closed systems can be distinguished from secondary sulfates formed from oxidized sulfides. These secondary sulfates are characterized by relatively light oxygen (O18+4 relative to SMOW) and sulfur (S34-23), which is due to their origin from sulfides of bacterially reduced sulfates. The primary residual sulfates are enriched in O18 and S34. The correlation of heavy sulfur with heavy oxygen during bacterial reduction of sulfates (Lloyd, 1968) could be confirmed.

Die massenspektrometrischen Messungen wurden von der Deutschen Forschungsgemeinschaft durch die Einrichtung des Zentrallabors für Geochemie der Isotope an der Universität Göttingen ermöglicht. Herrn Prof. Dr. K. H. Wedepohl und den Mitarbeitern des Zentrallabors danke ich für wertvolle Ratschläge und Diskussionsbereitschaft.  相似文献   

7.
Peak metamorphic temperatures for the coesite-pyrope-bearing whiteschists from the Dora Maira Massif, western Alps were determined with oxygen isotope thermometry. The 18O(smow) values of the quartz (after coesite) (18O=8.1 to 8.6, n=6), phengite (6.2 to 6.4, n=3), kyanite (6.1, n=2), garnet (5.5 to 5.8, n=9), ellenbergerite (6.3, n=1) and rutile (3.3 to 3.6, n=3) reflect isotopic equilibrium. Temperature estimates based on quartz-garnet-rutile fractionation are 700–750 °C. Minimum pressures are 31–32 kb based on the pressure-sensitive reaction pyrope + coesite = kyanite + enstatite. In order to stabilize pyrope and coesite by the temperature-sensitive dehydration reaction talc+kyanite=pyrope+coesite+H2O, the a(H2O) must be reduced to 0.4–0.75 at 700–750 °C. The reduced a(H2O) cannot be due to dilution by CO2, as pyrope is not stable at X(CO2)>0.02 (T=750 °C; P=30 kb). In the absence of a more exotic fluid diluent (e.g. CH4 or N2), a melt phase is required. Granite solidus temperatures are 680 °C/30 kb at a(H2O)=1.0 and are calculated to be 70°C higher at a(H2O)=0.7, consistent with this hypothesis. Kyanite-jadeite-quartz bands may represent a relict melt phase. Peak P-T-f(H2O) estimates for the whiteschist are 34±2 kb, 700–750 °C and 0.4–0.75. The oxygen isotope fractionation between quartz (18O=11.6) and garnet (18O=8.7) in the surrounding orthognesiss is identical to that in the coesitebearing unit, suggesting that the two units shared a common, final metamorphic history. Hydrogen isotope measurements were made on primary talc and phengite (D(SMOW)=-27 to-32), on secondary talc and chlorite rite after pyrope (D=-39 to -44) and on the surrounding biotite (D=-64) and phengite (D=-44) gneiss. All phases appear to be in nearequilibrium. The very high D values for the primary hydrous phases is consistent with an initial oceanicderived/connate fluid source. The fluid source for the retrograde talc+chlorite after pyrope may be fluids evolved locally during retrograde melt crystallization. The similar D, but dissimilar 18O values of the coesite bearing whiteschists and hosting orthogneiss suggest that the two were in hydrogen isotope equilibrium, but not oxygen isotope equilibrium. The unusual hydrogen and oxygen isotope compositions of the coesite-bearing unit can be explained as the result of metasomatism from slab-derived fluids at depth.  相似文献   

8.
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   

9.
Graphite occurs in two distinct textural varieties in syntectonic granitoids of the New Hampshire Plutonic Series and in associated metasedimentary wall rocks. Textural characteristics indicate that coarse graphite flakes were present at an early stage of crystallization of the igneous rocks and thus may represent xenocrystic material assimilated from the wall rocks. The range of 13C values determined for flake graphite in the igneous rocks (–26.5 to –13.8) overlaps the range for flake graphite in the wall rocks (–26.0 to –16.7), and spatial correlation of some 13C values in the plutons and wall rocks supports the assimilation mechanism. The textures of fine-grained irregular aggregates or spherulites of graphite, on the other hand, indicate that they formed along with secondary hydrous silicates and carbonates during retrograde reactions between the primary silicates and a carbon-bearing aqueous fluid phase. Relative to coexisting flake graphite, spherulitic graphite shows isotopic shifts ranging from 1.9 higher to 1.4 lower in both igneous and metasedimentary samples.The observed isotopic shifts and the association of spherulitic graphite with hydrous silicates are explained by dehydration of C-O-H fluids initially on or near the graphite saturation boundary. Hydration of silicates causes dehydration of the fluid and drives the fluid composition to the graphite saturation surface. Continued dehydration of the fluid then requires coprecipitation of secondary graphite and hydrous silicates and drives the fluid toward either higher or lower CO2/CH4 depending upon the inital bulk composition. Isotopic shifts in graphite formed at successive reaction stages are explained by fractionation of 13C between secondary graphite and the evolving fluid because 13C is preferentially concentrated into CO2 relative to CH4.Epigenetic graphite in two vein deposits assiciated with the contacts of these igneous rocks is generally enriched in 13C (–15.7 to –11.6) relative to both the igneous and wall-rock 13C values. Values of 13C vary by up to 3.4 within veins, with samples taken only 3 cm apart differing by 2.0 These variations in 13C correlate with textural evidence showing sequential deposition of different generations of graphite in the veins from fluids which differed in proportions of carbon species or isotopic composition (or both).  相似文献   

10.
The Ordovician volcano-sedimentary succession of Erquy (northern Brittany) is made of immature sediments thermally metamorphosed at the contact of intruding basic sills. Pillow lavas constitute the upper part of the sequence. The trace element geochemistry of sills and pillow lavas suggests that they were derived from a tholeiitic source located beneath a passive margin. This volcanic sequence was metamorphosed under low to moderate greenschist facies conditions. In this study the direction and amplitude of chemical and isotopic fluxes in the basalt-sediment-water system were established and the oxygen and hydrogen isotope compositions of the aqueous fluid that reacted with the volcanic rocks were characterized. Cationic thermometry on chlorites and isotopic thermometry on plagioclase-chlorite pairs indicate closure metamorphic temperatures in the range 200–250°C for the basaltic sills. Stable isotope compositions of iron-rich chlorites (18O-5.5; D from-60 to-50) and plagioclases (18O from +9 to +10) reveal that the source of the fluid was certainly seawater. The 18O variations within the sills are strongly correlated with the rate of progress of the main metamorphic reaction:clinopyroxene+plagioclase+ilmenite chlorite+albite+epidote+quartz+sphene that produced major element mobility at the scale of the volcanosedimentary sequence. Calculation of elemental fluxes by mass balance combined with oxygen isotopic compositions of basalts shows that the highest water-rock ratios (1) were at sill-sediment boundaries and within pillow lavas at the top of the pile. The volcanosedimentary sequence of Erquy was a net sink for Na and a source for Ca. No Mg uptake could be detected whereas the hydrothermal alteration of the sediments released Fe, Si, and K trapped by the volcanic rocks. The 18O value of the fluid reacting with sills appears to have shifted no more than +4 after percolation at low temperature through immature sediments (18O12). The Erquy volcano-sedimentary sequence represents a marine hydrothermal system dominated by low-temperature exchange which allowed a general 18O-enrichment of the volcanic rocks and a 18O-depletion of sediments.  相似文献   

11.
The Mount Lofty Ranges comprises interlayered marbles, metapsammites, and metapelites that underwent regional metamorphism during the Delamarian Orogeny at 470–515 Ma. Peak metamorphic conditions increased from lowermost biotite grade (350–400°C) to migmatite grade (700°C) over 50–55 km parallel to the lithological strike of the rocks. With increasing metamorphic grade, 18O values of normal metapelites decrease from 14–16 to as low as 9.0, while 18O values of calcite in normal marbles decrease from 22–24 to as low as 13.2 These isotopic changes are far greater than can be accounted for by devolatilisation, implying widespread fluid-rock interaction. Contact metamorphism appears not to have affected the terrain, suggesting that fluid flow occurred during regional metamorphism. Down-temperature fluid flow from synmetamorphic granite plutons (18O=8.4–8.6) that occur at the highest metamorphic grades is unlikely to explain the resetting of oxygen isotopes because: (a) there is a paucity of skarns at granite-metasediment contacts; (b) the marbles generally do not contain low-XCO2 mineral assemblages; (c) there is insufficient granite to provide the required volumes of water; (d) the marbles and metapelites retain a several permil difference in 18O values, even at high metamorphic grades. The oxygen isotope resetting may be accounted for by along-strike up-temperature fluid flow during regional metamorphism with time-integrated fluid fluxes of up to 5x109 moles/m2 (105 m3/m2). If fluid flow occurred over 105–106 years, estimated intrinsic permeabilities are 10-20 to 10-16m2. Variations in 18O at individual outcrops suggest that time-integrated fluid fluxes and intrinsic permeabilities may locally have varied by at least an order of magnitude. A general increase in XCO2 values of marble assemblages with metamorphic grade is also consistent with the up-temperature fluid-flow model. Fluids in the metapelites may have been derived from these rocks by devolatilisation at low metamorphic grades; however, fluids in the marbles were probably derived in part from the surrounding siliceous rocks. The marble-metapelite boundaries preserve steep gradients in both 18O and XCO2 values, suggesting that across-strike fluid fluxes were much lower than those parallel to strike. Up-temperature fluid flow may also have formed orthoamphibole rocks and caused melting of the metapelites at high grades.This paper is a contribution to IGCP Project 304 Lower Crustal Processes  相似文献   

12.
Oxygen-isotope compositions have been measured for whole-rock and mineral samples of host and hydrothermally altered rocks from three massive sulfide deposits, Centennial (CL), Spruce Point (SP), and Anderson Lake (AL), in the Flin Flon — Snow Lake belt, Manitoba. Wholerock 18O values of felsic metavolcanic, host rocks (+8.5 to +16.1) are higher than those of altered rocks from the three deposits. The 18O values of altered rocks are lower in the chlorite zone and muscovite zone-I (CL=+ 5.3; SP=+5.4 to +8.3; AL= +3.7 to +5.9) than in the gradational zone (CL= +9.9 to +11.7; SP= +8.4 to +9.8; AL= + 6.6 to +7.7). Muscovite schist (Muscovite Zone-II) enveloping the Anderson Lake ore body has 18O values of +7.2 to +8.3. Quartz, biotite, muscovite, and chlorite separated from the altered rocks have lower 18O values compared to the same minerals separated from the host rocks. However, isotopic fractionation between mineral-pairs is generally similar in both host and altered rocks.It is interpreted that differences in the oxygen-isotope compositions of the altered and host rocks were produced prior to metamorphism, during hydrothermal alteration related to ore-deposition. Isotopic homogenization during metamorphism occurred on a grain-to-grain scale, over no more than a few meters. The whole-rock 18O values did not change significantly during metamorphism. The generally lower 18O values of altered rocks, the Cu-rich nature of the ore and the occurrence of the muscovite zone-II at Anderson Lake are consistent with the presence of higher temperature hydrothermal fluids at Anderson Lake than at the Centennial and Spruce Point deposits.  相似文献   

13.
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   

14.
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.
  相似文献   

15.
Dalradian metamorphic rocks, Lower Ordovician meta-igneous rocks (MGS) and Caledonian granites of the Connemara complex in SW Connemara all show intense retrograde alteration. Alteration primarily involves sericitization and saussuritization of plagioclase, the alteration of biotite and hornblende to chlorite and the formation of secondary epidote. The alteration is associated with sealed microcracks in all rocks and planes of secondary fluid inclusions in quartz where it occurs, and was the result of a phase of fluid influx into these rocks. In hand specimen K-feldspar becomes progressively reddened with increasing alteration. Mineralogical alteration in the MGS and Caledonian granites took place at temperatures 275±15°C and in the MGS Pfluid is estimated to be 1.5 kbar during alteration. The °D values of alteration phases are:-18 to-29 (fluid inclusions),-47 to-61 (chlorites) and-11 to-31 (epidotes). Chlorite 18O values are +0.2 to +4.3, while 18O values for quartz-K-feldspar pairs show both positively sloped (MGS) and highly unusual negatively sloped (Caledonian granites) arrays, diverging from the normal magmatic field on a - plot. The stable isotope data show that the fluid that caused retrogression continued to be present in most rocks until temperatures fell to 200–140°C. The retrograde fluid had D -20 to-30 in all lithologies, but the fluid 18O varied both spatially and temporally within the range-4 to +7. The fO2 of the fluid that deposited the epidotes in the MGS varied with its 18O value, with the most 18O-depleted fluid being the most oxidizing. The D values, together with low (<0) 18O values for the retrograde fluid in some lithologies indicate that this fluid was of meteoric origin. This meteoric fluid was probably responsible for the alteration in all lithologies during a single phase of fluid infiltration. The variation in retrograde fluid 18O values is attributed to the effects of variable oxygen isotope shifting of this meteoric fluid by fluid-rock interaction. Infiltration of meteoric fluid into this area was most likely accomplished by convection of pore fluids around the heat anomaly of the Galway granite soon after intrusion at 400 Ma. However convective circulation of meteoric water and mineralogical alteration could possible have occurred considerably later.  相似文献   

16.
Zusammenfassung Die Schwefelisotopenzusammensetzung von sulfidischen Erzmineralen und Baryten der unterdevonischen schichtgebundenen Bleiglanz-Zinkblende-Baryt-Erzvorkommen des Grazer Paläozoikums (Ostalpen, Österreich) wurde untersucht. Zur Analyse gelangten 64 Proben von etwa 15 Lokalitäten. Die Schwefelisotopenverteilung zeigt Ähnlichkeiten mit anderen an das Devon gebundenen schwerspatführenden Lagerstätten. Die Baryte ergaben 34S-Werte von +23, 1 bis +27, 8, die dem Meerwassersulfat devonischen Alters entsprechen. Die untersuchten Galenite variieren von +2, 4 bis +6, 9 und die Sphalerite von +3, 3 bis +9, 1. Die Werte der Pyrite zeigen einen großen Streubereich (–27, 4 bis +37, 6). Eine massive buntmetallarme Pyritvererzung fällt durch sehr schweren Schwefel auf. Späte Mineralisationsphasen der Sulfide tendieren gleichfalls zur Anreicherung des schweren Schwefels.
The sulphur isotope compositions of 64 samples of sulphide minerals and barites from the strata-bound Lower Devonian ore deposits of the Paleozoic Complex of Graz in the Eastern Alps (Austria) have been investigated. The 34S-values of galenites and sphalerites show only small variations in the range of +2, 4 up to +6, 9 for PbS and +3, 3 up to +9, 1 for ZnS indicating abiogenic origin. Later remobilized sulphide minerals show a tendency to heavier sulphur. The deposition of pyrites is influenced partly by bacteriogenic processes (–27, 4 up to +37, 6). The enrichment of heavier sulphur characterizes massive pyrite mineralisations being poor on base metals. The sulphur isotope compositions of barites (+23, 1 up to 27, 8) correspond to Devonian sea water sulphate. An ore free barite characterized by increased strontium concentration shows heavier sulphur (+29, 6) than barites from ore beds.

Derzeit Oberste Bergbehörde, Bundesministerium für Handel, Gewerbe und Industrie (Wien)  相似文献   

17.
Polished ore samples from the world-class Bleiberg lead-zinc deposit in Austria were studied by Field Emission Scanning Electron Microscopy (FESEM) at magnifications in the range of 105–106. The zinc ore shows nano-sized sphalerite filaments and spherules which are morphologically similar to recent biofilms of sulphate-reducing bacteria. The activity of sulphate-reducing bacteria is suggested by a large 34S difference of ~40 between coeval seawater sulphate (+16 ) and sulphide sulphur (< –25 ) in the Bleiberg ores, and by variable sulphur valences. Peloids of sphalerite, Zn-bearing calcite and pyrite have features typical of bacterial colonies. Combined with geological and mineralogical evidence, a significant role of bacteria during ore deposition at Bleiberg is likely.Eugen F. Stumpfl deceasedEditorial handling: B. Lehmann  相似文献   

18.
Hydrothermally-altered mesozonal synmetamorphic granitic rocks from Maine have whole-rock 18O (SMOW) values 10.7 to 13.8. Constituent quartz, feldspar, and muscovite have 18O in the range 12.4 to 15.2, 10.0 to 13.2, and 11.1 to 12.0, respectively. Mean values of Q–F ( 18Oquartz– 18Ofeldspar)=2.4 and Q–M ( 18Oquartz– 18Omuscovite)=3.3 are remarkably uniform (standard deviations of both are 0.2). Measured Q–F and Q–M values demonstrate that the isotopic compositions of the minerals are altered from primary magmatic 18O values but that the minerals closely approached oxygen isotope exchange equilibrium at subsolidus temperatures. Analyzed muscovites have D (SMOW) values in the range –65 to –82.Feldspars in the granitic rocks are mineralogically altered to either (a) muscovite+calcite, (b) muscovite+calcite+epidote, (c) muscovite+epidote, or (d) muscovite only. A consistent relation exists between the assemblage of secondary minerals and the oxygen isotope composition of whole rocks, quartz, and feldspar. Rocks with assemblage (a) have whole-rock 18O>12.1 and contain quartz and feldspar with 18O>13.8 and >11.4, respectively. Rocks with assemblages (b), (c), and (d) have whole-rock 18O<11.4 and contain quartz and feldspar with 18O< 13.1 and <11.0, respectively. The correlation suggests that the mineralogical alteration of the rocks was closely coupled to their isotopic alteration.Three mineral thermometers in altered granite suggest that the hydrothermal event occurred in the temperature range 400°–150° C, 100°–150° C below the peak metamorphic temperature inferred for country rocks immediately adjacent to the plutons. Calculations of mineral-fluid equilibria indicate that samples with assemblage (a) coexisted during the event with CO2-H2O fluids of and 18O=10.8 to 12.2 while samples with assemblages (b), (c), or (d) coexisted with fluids of and 18O=9.4 to 10.1. Compositional variations of the hydrothermal fluids were highly correlated: fluids enriched in CO2 were also enriched in 18O. Because CO2 was added to the granites during hydrothermal alteration and because fluids enriched in CO2 were enriched in 18O, some or all of the variation in 18O of altered granites may have been caused by addition of 18O to the rocks during the hydrothermal event. The source of both the CO2 and 18O could have been high-18O metasedimentary country rocks. The inferred change in isotopic composition of the granites is consistent with depletion of the metacarbonate rocks in 18O close to the plutons and with large volumes of fluid that were inferred from petrologic data to have infiltrated the metacarbonate rocks during metamorphism.A close approach of minerals to oxygen isotope exchange equilibrium in altered mesozonal rocks from Maine is in marked contrast to hydrothermally-altered epizonal granites whose mineral commonly show large departures from oxygen isotope exchange equilibrium. The difference in oxygen isotope systematics between altered epizonal granites and altered mesozonal granites closely parallels a differences between their mineralogical systematics. Both differences demonstrate the important control that depth exerts on the products of hydrothermal alteration. Deeper hydrothermal events occur at higher temperature and are longer-lived. Minerals and fluid have sufficient time to closely approach both isotope exchange and heterogeneous chemical equilibrium. Shallower hydrothermal events occur at lower temperatures and are shorter-lived. Generally there is insufficient time for fluid to closely approach equilibrium with all minerals.  相似文献   

19.
Summary Pervasive hydrothermal alteration zones in quartz-feldspar porphyry domes underly all massive sulfide lenses in the D-68 Zone Cu-Zn deposit, Noranda. Alteration pipes are mineralogically zoned and contain chloritic cores consisting of stringer sulfides, enveloped by sericitic haloes. Silicified rocks are found locally.Alteration took place at nearly constant volume. Na depletion, and K enrichment relative to the least altered rocks, are found in all alteration zones. Fe and Mg have been added to the chloritic zone and subtracted in the sericitic and silicic zones. Ca and Si are enriched mainly in the silicic zone. Al, Ti and Zr were the least mobile of the elements studied.Whole-rock 18O values vary from +5.6 to +6.2 per mil in chloritized rocks, +5.8 to + 7.3 per mil in sericitized rocks and + 7.2 to + 8.3 per mil in silicified rocks. D values for two chloritized samples are – 63 and – 70 per mil whereas in two sericitized samples they are close to –62 per mil. Quartz from the chlorite alteration zone is isotopically heavier (18O = 8.6 per mil) than that from the sericite alteration zone (18O = 6.4 per mil), suggesting equilibration with different hydrothermal fluid or different temperature of alteration. Assuming an alteration temperature of 300° + 50°C the fluid in equilibrium with quartz and chlorite had 18O and D values of about 1.5 ± 2.0 per mil and –23 ± 5 per mil, respectively. The fluid in equilibrium with quartz and sericite had 18O and D values of about –0.5 ± 2 per mil and –30 ± 5 per mil, respectively. On the basis of isotopic data, seawater was probably the major constituent of the hydrothermal fluids.
Hydrothermale Umwandlung und Sauerstoff-Wasserstoff-Isotopengeochemie der Zone D-68 Cu-Zn Derberz Sulfidlagerstätte, Noranda District, Quebec, Canada
Zusammenfassung Hydrothermale Umwandlungszonen in porphyrischen Quarz-Feldspat Gesteinskörpern liegen unterhalb von Derberz Sulfidlinsen in der D-68 Zone Cu-Zn Lagerstätte, Noranda. Umgewandelte pipes sind mineralogisch zoniert; sie enthalten aus Sulfiden bestehende chloritische Kerne, die von sericitischen Höfen umhüllt werden. Lokal treten silicifizierte Gesteine auf.Die Umwandlung ging bei annähernd konstantem Volumen vor sich. Na-Verarmung und K-Anreicherung, bezogen auf die am wenigsten umgewandelten Gesteine, liegen in allen Umwandlungszonen vor. Fe und Mg wurden der Chloritzone zugeführt, in den Sericit- und Si-Zonen abgeführt. Ca und Si sind vor allem in der Si-Zone angereichert. Al, Ti und Zr waren von den untersuchten Elementen am wenigsten mobil.Gesamtgesteins-18O Werte variieren von +5,6 bis +6,2 in den chloritisierten Gesteinen, von +5,8 bis 7,3 in sericitisierten Gesteinen und von +7,2 bis +8,3 in den silicifizierten Gesteinen. Die D Werte für zwei chloritisierte Proben betragen –63 und –70, in zwei sericitisierten Proben liegen sie hingegen nahe bei –62. Quarz von der Chlorit-Umwandlungszone ist isotopisch schwerer (18O = 8,6) als von der Sericit-Umwandlungszone (18O = 6.4), was eine Gleichgewichtseinstellung mit verschiedenen hydrothermalen Lösungen oder eine verschiedene Umwandlungstemperatur nahelegt. Bei einer angenommenen Umwandlungstemperatur von 300 ± 50°C, hatte die im Gleichgewicht mit Quarz und Chlorit stehende Lösung 18O und D Werte von etwa 1,5 ± 2 bzw. –23 + 5. Die im Gleichgewicht mit Quarz und Sericit befindliche Lösung hatte 18O und D Werte von etwa –0,5 ± 2%o bzw. –30 ± 5. Aufgrund der Isotopendaten war wahrscheinlich Meerwasser der Hauptbestandteil der hydrothermalen Lösungen.

With 7 Figures  相似文献   

20.
Zusammenfassung Die S-Isotopenverteilung wurde an 67 Sulfid- und 17 Barytproben aus der Blei-Zink-Erzlagerstätte Grund untersucht. Die 34S-Werte der Zinkblende der Mineralisationsphase II liegen im Westfeld-Erzmittel I und in den östlich anschließenden Erzmitteln zwischen +4 und +6, in dem am weitesten westlich liegenden Westfeld-Erzmittel II zwischen +6 und +10. Die Werte für Bleiglanz der Mineralisationsphase II sind +2 bis +4 bzw. +4 bis +7. Die Sulfide der Mineralisationsphase III haben allgemein niedrigere -Werte. Koexistierende Sulfide zeigen eine deutliche Fraktionierung, wobei stets ZnS > PbS ist; die Differenz beträgt in der Mineralisationsphase II im Mittel 1,8, in der Phase III 3. Dies deutet auf niedrigere Bildungstemperatur der Minerale der Phase III hin. Zur genetischen Deutung der beobachteten -Abnahme beim Übergang zur Mineralisationsphase II werden vier Modelle diskutiert. Baryte zeigen innerhalb der Lagerstätte recht einheitliche 34S-Werte zwischen +11 und +14,5%. Diese Einheitlichkeit wird durch den Einfluß deszendenter Zechstein-Lösungen erklärt.
34S-values are given for 67 sulfide and 16 barite specimens from the Pb-Zn-deposit Grund (Harz mountains, W-Germany). In the central part of the deposit the sulfide 's of the first major mineralization (phase II) range from: ZnS +4 to +6 and PbS +2 to +4. The sulfides of the second major mineralization (phase III) are depleted in 34S and range from: ZnS +2 to +4, PbS –1,4 to 3. The sulfides at the western end of the vein system are heavier; the phase II minerals ranging from: ZnS +6 to 10 and PbS +4 to 7. The mean -difference between co-existing ZnS and PbS in phase II is 1,8, in phase III 3. This indicates lowering of temperature of formation for the phase III ore. Four models have been set up in order to explain the observed -variation. Barites with rather uniform 's from +11 to +14,5 are probably affected by descendent solutions from overlying sulfate sediments of Permian age.
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