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1.
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   

2.
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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3.
Mo mineralization within the Galway Granite at Mace Head and Murvey, Connemara, western Ireland, has many features of classic porphyry Mo deposits including a chemically evolved I-type granite host, associated K- and Si-rich alteration, quartz vein(Mace Head) and granite-hosted (Murvey) molybdenite, chalcopyrite, pyrite and magnetite mineralization and a gangue assemblage which includes quartz, muscovite and K-feldspar. Most fluid inclusions in quartz veins homogenize in the range 100–350°C and have a salinity of 1–13 eq. wt.% NaCl. They display Th-salinity covariation consistent with a hypothesis of dilution of magmatic water by influx of meteoric water. CO2-bearing inclusions in an intensely mineralized vein at Mace Head provide an estimated minimum trapping temperature and pressure for the mineralizing fluid of 355°C and 1.2 kb and are interpreted to represent a H2O-CO2 fluid, weakly enriched in Mo, produced in a magma chamber by decompression-activated unmixing from a dense Mo-bearing NaCl-H2O-CO2 fluid. 34S values of most sulphides range from c. 0 at Murvey to 3–4 at Mace Head and are consistent with a magmatic origin. Most quartz vein samples have 18O of 9–10.3 and were precipitated from a hydrothermal fluid with 18O of 4.6–6.7. Some have 18O of 6–7 and reflect introduction of meteoric water along vein margins. Quartz-muscovite oxygen isotope geothermometry combined with fluid inclusion data indicate precipitation of mineralized veins in the temperature range 360–450°C and between 1 and 2 kb. Whole rock granite samples display a clear 18O-D trend towards the composition of Connemara meteoric waters. The mineralization is interpreted as having been produced by highlyfractionated granite magma; meteoric water interaction postdates the main mineralizing event. The differences between the Mace Head and Murvey mineralizations reflect trapping of migrating mineralizing fluid in structural traps at Mace Head and precipitation of mineralization in the granite itself at Murvey.  相似文献   

4.
The 18O and D values in mud-volcanic waters of the Taman Peninsula and Kakhetia vary from +0.7 to +10.0 and from –37 to –13 , respectively. These values increase as the Greater Caucasus is approached. The increase in 18O and D also positively correlates with fluid generation temperatures based on hydrochemical geothermometers. This is accompanied by changes in the chemical composition of waters, in which contents of alkali metals, HCO– 3 ion, and boron increase, while the content of halogen ions (Cl, Br, J) decreases. Changes in the isotopic composition of water are also accompanied by the increase of 13 in methane and decrease of 11 B in clays. Analysis of formal models of the evolution of isotopic composition of mud-volcanic waters showed that mud volcanoes are recharged by freshened water from the Maikop paleobasin with an inferred isotopic composition of D –40 and 18 O –6. Based on this assumption, the 18O and D values observed in mud-volcanic waters can be explained not only by processes of distillation and condensation in a closed system, but also by combined processes of isotopic reequilibration in the water-illite-methane system.Translated from Litologiya i Poleznye Iskopaemye, No. 2, 2005, pp. 143–158.Original Russian Text Copyright © 2005 by Lavrushin, Dubinina, Avdeenko.  相似文献   

5.
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   

6.
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   

7.
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   

8.
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   

9.
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   

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.
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   

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.
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   

14.
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   

15.
Late Hercynian U-bearing carbonate veins within the metamorphic complex of La Lauzière are characterized by two parageneses. The first is dominated by dolomite or ankerite and the second by calcite and pitchblende. Fluids trapped in the dolomites and ankerites at 350–400° C are saline waters (20 to 15 wt % eq. NaCl) with D –34 to –49. In the calcite they are less saline (17 to 8 wt % eq. NaCl) and trapped at 300–350° C with D –50 to –65. All fluids contain trace N2, CO2 and probably CH4. The carbonates have 13C –8 to –14. and derived their carbon from organic matter. Evolution of the physico-chemical conditions from dolomite (ankerite) to calcite deposition was progressive.H and O-isotope studies indicate the involvement of two externally derived fluids during vein development. A D-rich ( –35) low fO2, saline fluid is interpreted to have come from underlying sediments and entered the hotter overlying metamorphic slab and mixed with more oxidizing and less saline U bearing meteoric waters during regional uplift. This evidence for a sedimentary formation water source for the deep fluid implies that the metamorphic complex overthrusted sedimentary formations during the Late-Hercynian.  相似文献   

16.
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   

17.
This paper deals with barite from stratiform, karst, and vein deposits hosted within Lower Paleozoic rocks of the Iglesiente-Sulcis mining district in southwestern Sardinia. For comparison sulfates from mine waters are studied. Stratiform barite displays 34S=28.8–32.1, 18O=12.7–15.6, and 87Sr/86Sr=0.7087, in keeping with an essentially Cambrian marine origin of both sulfate and strontium. Epigenetic barite from post-Hercynian karst and vein deposits is indistinguishable for both sulfur and oxygen isotopes with 34S=15.3–26.4 and 18O=6.6–12.5; 87Sr/86Sr ratios vary 0.7094–0.7140. These results and the microthermometric and salinity data from fluid inclusions concur in suggesting that barite formed at the site of mineralization by oxidation of reduced sulfur from Cambrian-Ordovician sulfide ores in warm, sometimes hot solutions consisting of dilute water and saline brine with different 18O values. The relative proportion of the two types of water may have largely varied within a given deposit during the mineralization. In the karst barite Sr was essentially provided by carbonate host rocks, whereas both carbonate and Lower Paleozoic shale host rocks should have been important sources for Sr of the vein barite. Finally, 34S data of dissolved sulfate provide further support for the mixed seawater-meteoric water composition of mine waters from the Iglesiente area.  相似文献   

18.
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   

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.
Chemistry dependence of D of chlorites is inferred from data for natural chlorites. D of water equilibrated with those chlorites is estimated to be –2–8.  相似文献   

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