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661.
Liu Hongbing Kong Xiangru Xiaobing Ma Wang Qianshen Yan Yongli Yan Yafen Yang Zhiqiang 《中国科学D辑(英文版)》2001,44(1):64-76
Chemical reactions of plagioclase, biotite and their single minerals, as well as a mineral mixture of (plagioclase+biotite+quartz),
with KCl and (KCl+KHCO3) solutions were carried out at 150–400°C and 50–80 MPa. Experiments show that alkaline fluid promotes plagioclase’s changing
into potash feldspar, while acid fluid helps plagioclase, potash feldspar and biotite alteration form chlorite and sericite.
After chemical reaction the acidity-alkalinity of solutions often changes reversely. It was observed that gold dissolved from
the tube wall and recrystallized on the surfaces of biotite and pyrite. Therefore the transportation and enrichment of gold
are related to the elementary effect of the fluid-mineral interfaces. Fe3+-Fe2+, as an oxidition-reduction agent, and volatile components Cl- and CO2 play important roles in the reaction process 相似文献
662.
Fault-controlled dolomitization at Swan Hills Simonette oil field (Devonian), deep basin west-central Alberta, Canada 总被引:6,自引:0,他引:6
The partly dolomitized Swan Hills Formation (Middle‐Upper Devonian) in the Simonette oil field of west‐central Alberta underwent a complex diagenetic history, which occurred in environments ranging from near surface to deep (>2500 m) burial. Five petrographically and geochemically distinct dolomites that include both cementing and replacive varieties post‐date stylolites in limestones (depths >500 m). These include early planar varieties and later saddle dolomites. Fluid inclusion data from saddle dolomite cements (Th=137–190 °C) suggest that some precipitated at burial temperatures higher than the temperatures indicated by reflectance data (Tpeak=160 °C). Thus, at least some dolomitizing fluids were ‘hydrothermal’. Fluorescence microscopy identified three populations of primary hydrocarbon‐bearing fluid inclusions and confirms that saddle dolomitization overlapped with Upper Cretaceous oil migration. The source of early dolomitizing fluids probably was Devonian or Mississippian seawater that was mixed with a more 87Sr‐rich fluid. Fabric‐destructive and fabric‐preserving dolostones are over 35 m thick in the Swan Hills buildup and basal platform adjacent to faults, thinning to less than 10 cm thick in the buildup between 5 and 8 km away from the faults. This ‘plume‐like’ geometry suggests that early and late dolomitization events were fault controlled. Late diagenetic fluids were, in part, derived from the crystalline basement or Palaeozoic siliciclastic aquifers, based on 87Sr/86Sr values up to 0·7370 from saddle dolomite, calcite and sphalerite cements, and 206Pb/204Pb of 22·86 from galena samples. Flow of dolomitizing and mineralizing fluids occurred during burial greater than 500 m, both vertically along reactivated faults and laterally in the buildup along units that retained primary and/or secondary porosity. 相似文献
663.
Dolomitization of the Waulsortian Limestone (Lower Carboniferous) in the Irish Midlands 总被引:1,自引:0,他引:1
Jay M. Gregg Kevin L. Shelton Aaron W. Johnson Ian D. Somerville & Wayne R. Wright 《Sedimentology》2001,48(4):745-766
The Waulsortian Limestone (Lower Carboniferous) of the southern Irish Midlands is dolomitized pervasively over a much larger region than previous studies have documented. This study indicates a complex, multistage, multiple fluid history for regional dolomitization. Partially and completely dolomitized sections of Waulsortian Limestones are characterized by finely crystalline (0·01–0·3 mm) planar dolomite. Planar replacive dolomite is commonly followed by coarse (≥0·5 mm) nonplanar replacive dolomite, and pervasive void‐filling saddle dolomite cement is frequently associated with Zn–Pb mineralization. Planar dolomite has average δ18O and δ13C values (‰ PDB) of –4·8 and 3·9 respectively. These are lower oxygen and slightly higher carbon isotope values than averages for marine limestones in the Waulsortian (δ18O=–2·2, δ13C=3·7). Mean C and O isotope values of planar replacive dolomite are also distinct from those of nonplanar and saddle dolomite cement (–7·0 and 3·3; –7·4 and 2·4 respectively). Fluid inclusions indicate a complex history involving at least three chemically and thermally distinct fluids during dolomite cementation. The petrography and geochemistry of planar dolomites are consistent with an early diagenetic origin, possibly in equilibrium with modified Carboniferous sea water. Where the Waulsortian was exposed to hydrothermal fluids (70–280 °C), planar dolomite underwent a neomorphic recrystallization to a coarser crystalline, planar and nonplanar dolomite characterized by lower δ18O values. Void‐filling dolomite cement is isotopically similar to nonplanar, replacive dolomite and reflects a similar origin from hydrothermal fluids. This history of multiple stages of dolomitization is significantly more complex than earlier models proposed for the Irish Midlands and provides a framework upon which to test competing models of regional vs. localized fluid flow. 相似文献
664.
Fluid-rock history of granulite facies humite-marbles from Ambasamudram, southern India. 总被引:1,自引:0,他引:1
An extensive humite‐bearing marble horizon within a supracrustal sequence at Ambasamudram, southern India, was studied using petrological and stable isotopic techniques to define its metamorphic history and fluid characteristics. At peak metamorphic temperatures of 775±73°C, based on calcite‐graphite carbon isotope thermometry, the mineral assemblages suggest layer‐by‐layer control of fluid compositions. Clinohumite + calcite‐bearing assemblages suggest XCO2 < 0.4 (at 700°C and 5 kbar), calcite + forsterite + K‐feldspar‐bearing assemblages suggest XCO2>0.9 (at 790°C); and local wollastonite + scapolite + grossular‐bearing zones formed at XCO2 of c. 0.3. Retrograde reaction textures such as scapolite + quartz symplectites after feldspar and calcite and replacement of dolomite + diopside or tremolite+dolomite after calcite+forsterite or calcite+clinohumite are indicative of retrogression under high XCO2 conditions. Calcite preserves late Proterozoic carbon and oxygen isotopic signatures and the marble lacks evidence for extensive retrograde fluid infiltration, while during prograde metamorphism the possible infiltration of aqueous fluids did not produce significant isotopic resetting. Isotopic zonation of calcite and graphite grains was likely produced by localized CO2 fluid infiltration during retrogression. Contrary to the widespread occurrence of humite‐marbles related to retrograde aqueous fluid infiltration, the Ambasamudram humite‐marbles record a prograde‐to‐peak metamorphic humite formation and retrogression under conditions of low XH2O. 相似文献
665.
Abstract: The Dajing Cu–Sn–Ag–Pb–Zn ore deposit, Inner Mongolia of China, is a fissure‐filling hydrothermal ore deposit that occurs within the Upper Permian Linxi group. No magmatic pluton and volcanic rocks outcrop on the surface of the deposit. Most of ore veins show clear‐cut boundary with country rocks. Wallrock alterations that include silicification, carbonation, chlori–tization, and sericitization are generally weak and occur in the close vicinity of ore veins. Mineralization is divided into three stages: (1) cassiterite–arsenopyrite–quartz stage, (2) sulfide stage, and (3) Pb–Zn–Ag–carbonate stage. These mineralization stages have distinct ranges of homogenization temperatures, 290–350C for Stage 1, 260–320C for Stage 2, and 150–250C for Stage 3. However, salinities for Stages 1, 2, and 3 overlap and range between 2.2 and 10.4 wt % NaCl equivalent. The dD values relative to V‐SMOW of inclusion water from quartz are lower than –88% and centered at –100 to –130%. The δ34S values relative to CDT of sulfide ore minerals and δ13C values relative to PDB of carbonate gangue minerals, vary from –0.3 to +2.6%, and from –7.0 to –2.9%, respectively. Integrated isotopic data point to two major contributions to the mineralizing fluid that include a dominant meteoric‐derived water and the other from hypogene magma for sulfur and carbon species. Analyses of inclusion gas and liquid compositions are performed. The H2O and CO2 are the two most abundant gaseous components, whereas SO42‐ and Cl‐, and Na+, Ca2+, and K+ are the major anions and cations, respectively. A linear trend is shown on the gaseous H2O versus CO2 plot. Phase separation is excluded as cause for the trend on the basis of isotope data and fluid inclusion microthermometry. In addition, a weak wallrock alteration does not support fluid‐rock interaction as an efficient mechanism. Hence, the linear H2O–CO2 trend is interpreted in terms of absorption or dilution of CO2–dominant magmatic vapor by meteoric‐derived water. Cooling effects resulting from dilution may have caused precipitation of ore minerals. Major and trace element compositions of regional granites show a high‐K calc–alkaline characteristics and an arc–affinity. Lead isotopic compositions of galena samples from the Dajing deposit exhibit elevated U/Pb and Th/Pb ratios. These characteristics indicate a common source of supra subduction zone mantle wedge for regional granites and metals from the Dajing deposit. 相似文献
666.
Abstract: Synchrotron X-ray fluorescence analyses on individual hypersaline fluid inclusions were tested to using synchrotron source at Tsukuba (KEK), Japan. The XRF instrumentation at KEK meets the purpose of fluid inclusion analysis, nondestructive, multi–element, ppm detection limits, with micro spatial resolution. In practice, however, the quantitative chemical analysis of fluid inclusion requires further considerable data accumulation. Semi-quantitative distribution of elements (mass number > 25) in single fluid inclusion was obtained. 相似文献
667.
Victor B. MAGLAMBAYAN Daizo ISHIYAMA Toshio MIZUTA Osamu MATSUBAYA Yohei ISHIKAWA 《Resource Geology》2001,51(2):107-116
Abstract: The disseminated Au‐Ag telluride Bulawan deposit, Negros island, Philippines, is hosted by dacite porphyry breccia pipes which formed in a Middle Miocene dacite porphyry stock. Electrum and Au‐Ag tellurides occur mostly as grains intergrown with or filling voids between sphalerite, pyrite, chalcopyrite, galena and tennantite. Calcite, quartz and rare dolomite are the principal gangue minerals. Four types of alteration were recognized in the deposit, namely; propylitic, K‐feldspar‐sericitic, sericitic and carbonate alteration. Carbonate alteration is correlatable to the gold deposition stage and occurs mostly along fault zones. The δ18O and δ13C compositions of calcite and dolomite in propylite zone and ore‐stage dacite porphyry breccia were determined. The δ18O values of calcite in propylitized andesite range from +12.2 to +14.7%, and their δ13C values range from ‐6.1 to ‐1.0%. The δ18O values of calcite and dolomite in sericite‐ and carbonate‐altered, mineralized dacite porphyry breccia and dacite porphyry rocks range from +15.1 to +23.1%, and the δ13C values of calcite and dolomite range from ‐3.9 to +0.9%. The δ18O and δ13C values of the hydrothermal fluids were estimated from inferred temperatures of formation on the basis of fluid inclusion microthermometry. The δ18O values of hydrothermal fluid for the propylitic alteration were calculated to be +8.5 ‐ +9.5%, assuming 375°C. On the other hand, the δ18O values of ore solutions for base metal and Au mineralization were computed to be +13.6 ‐ +14.6%, assuming 270°C. The hydrothermal fluids that formed the Bulawan deposit are dilute and 18O‐enriched fluids which reacted with 18O‐ and 13C‐rich wallrocks such as limestone. 相似文献
668.
Based on the knowing geochemical characteristics of wall rock in the Mobin gold deposit and composition of fluid inclusion in ore,water-rock experiments were carried out,important achievements are acquired as following: Gold is mainly derived from the ore-bearing wall rock,i,e.,a series of epimetamorphic clastic gritstone,sandy slate,and tuffaceous slate in the Wuqiang Banxi Formation,Wuqiangxi Group.In thermal system with middle-low temperature chlorine gold may be derived form stable complex ions,so it is quite important in gold metallogenic process.Sulphur and chlorine perform as the major negative ions throughout the gold activation and migration movement.The concentration of sulphur and chlorine ions,pH value and temperature are of deciding significance for gold activation,migration and precipitation. 相似文献
669.
Modeling of dioctahedral 2:1 phyllosilicates by means of transferable empirical potentials 总被引:1,自引:0,他引:1
C. I. Sainz-Diaz A. Hernández-Laguna M. T. Dove 《Physics and Chemistry of Minerals》2001,28(2):130-141
Dioctahedral 2:1 phyllosilicates with different interlayer charge have been studied theoretically by using transferable empirical
interatomic potentials. The crystal structures of pyrophyllite, muscovite, margarite, beidellite, montmorillonite, and different
smectites and illites have been simulated. The interatomic potentials were able to reproduce the experimental structure of
phyllosilicates with high, medium and low interlayer charge. The calculated structures are in agreement with experiment for
the main structural features of the crystal lattice. The effect of the cation substitution in the octahedral and tetrahedral
sheets on the structural features has been also studied. Good linear relationships have been found, and the calculated effects
are consistent with experimental results. Some unknown structural features of the crystal structures of clays are predicted
in this work.
Received: 8 March 2000 / Accepted: 19 September 2000 相似文献
670.
Polarized electronic single crystal spectra of natural Fe2+ ion-bearing oxygen-based minerals, in which ferrous ions enter octahedral sites of different symmetry and distortion (olivine,
cordierite, ortho- and clinopyroxene, amphibole), eightfold sites in garnet (almandine) and clinopyroxene (M2), and tetrahedral
sites in spinel, were studied at temperatures from 300 to ca. 600 K. In the minerals studied, the spin-allowed bands of Fe2+ display rather variable temperature behaviour. In most cases, due to the thermal expansion of the Fe2+-bearing polyhedra, bands shift to lower energies upon increasing temperature, though there are some exceptions to this rule:
in cases of other than sixfold octahedral or close to octahedral coordination, in almandine and spinel the bands shift to
higher energies, which can be explained by an increase in distortions of the Fe2+-bearing polyhedra. Splitting of the excited 5
E
g-level of Fe2+ ions usually, but not always, increases with temperature, reflecting thermally induced increase in distortion of the Fe2+-bearing sites in the minerals studied. Integral intensities of the bands in question do not always obey the general rule,
according to which intensity should increase with temperature, when the 3d
N-centred site is centrosymmetric, or should remain unchanged when the 3d
N site lacks an inversion centre. The experimental results show that the response of the characteristics of absorption bands
such as width, intensity and energy caused by dd transitions of Fe2+ in oxygen-based minerals to increasing temperature is not always uniform and is at variance with expectation. This temperature
dependence cannot be used directly to solve band assignment problems, as earlier proposed in the literature.
Received: 22 December 1999 / Accepted: 30 October 2000 相似文献