闪锌矿中单个流体包裹体成分LA-ICP-MS分析及其指示意义：以南岭新田岭钨矿床为例

单个流体包裹体成分LA-ICP-MS分析在精准示踪成矿物质来源和精细刻画成矿过程方面具有独特优势,但已有研究主要聚焦于透明的脉石矿物中的流体包裹体,对用于矿石矿物较少,二者之间有何异同特别是谁更能代表成矿流体组成目前研究薄弱。闪锌矿是岩浆热液矿床和MVT型矿床中常见的矿石矿物,其通常发育流体包裹体并在透射光下具有透明-半透明特征,是研究流体包裹体较为理想的矿石矿物。文章选择南岭新田岭钨矿硫化物阶段的闪锌矿及共生石英为研究对象,开展流体包裹体成分LA-ICP-MS对比分析。分析结果显示,闪锌矿和石英中的流体包裹体组成存在较大差异,前者异常富Cu、Ag和Sn等金属元素,后者富Li、B、Na、K、Rb、Sr、Cs和Pb等元素。结合闪锌矿本身微量元素特征,文章认为元素Cu、Ag和Sn的超常富集与其从寄主矿物扩散进入流体包裹体有关。在基于大离子亲石元素的流体成因类型判别图中,闪锌矿和石英中的流体包裹体组成均能有效示踪成矿流体来源,但后者示踪效果更好。总体而言,共生石英中流体包裹体组成可能更能代表成矿流体组成,闪锌矿因其莫氏硬度较低、金属元素含量高等原因,元素易发生后期扩散/改变,流体包裹体组成可能不能代表真实流体信息。在研究矿石矿物流体包裹体时,需谨慎对待某些元素的超常富集。综合研究脉石矿物流体包裹体和矿石矿物本身元素组成是成矿流体研究更准确的手段。     

Trace Element Determination of Single Fluid Inclusions in Quartz by Laser Ablation ICP-MS

Single fluid inclusions in quartz from a Pb-Zn-Ag carbonate replacement deposit were selected for trace element determination by laser ablation ICP-MS. Spikes in element intensities were noted between first breached fluids versus subsequent analyses, suggesting that accurate element concentrations may not be determined in smaller fluid inclusions when only one analysis is obtained before the fluid is exhausted. Elemental concentrations in the fluid inclusions were determined by external standardisation using solutions sealed in microcapillary tubes. Standards and single natural inclusion analyses give repeatabilities (%RSD) of ˜ 20% for Rb and Sr. Rubidium and strontium concentrations range from 0.56-5.07 μg ml^-1 and 1.12-27.4 μg ml^-1, respectively, whereas Zn and Ag are below detection limits (< 10 ng ml^-1). The results suggest that nearly all Zn and Ag are removed by the time hydrothermal fluids precipitate gangue minerals.     

Advances in lithium analysis in solids by means of laser-induced breakdown spectroscopy: an exploratory study

Lithium is an important geochemical tracer for fluids or solids. However, because the electron microprobe cannot detect Li, variations of Li abundance at the micrometric scale are most often estimated from bulk analyses. In this study, the Li intense emission line at 670.706 nm in optical emission spectroscopy was used to perfect the analysis of Li at the micrometric scale by means of laser-induced breakdown spectroscopy (LIBS). To estimate lithium content for different geological materials, LIBS calibration of the emission line at 670.706 nm was achieved by use of synthetic glasses and natural minerals. The detection limit for this method is ∼5 ppm Li. Three applications to geological materials show the potential of LIBS for lithium determination, namely for Li-bearing minerals, melt inclusions, quartz, and associated fluid inclusions.For spodumene and petalite from granite pegmatite dikes (Portugal), the Li₂O concentrations are 7.6 ± 1.6 wt% and 6.3 ± 1.3 wt%, respectively, by use of LIBS. These values agree with ion microprobe analyses, bulk analyses, or both. For eucryptite crystals, the Li concentrations are scattered because grain size is smaller than the LIBS spatial resolution (6 to 8 μm). Lithium concentrations of melt inclusions from the Streltsovka U deposit (Siberia) are in the range of 2 to 6.2 wt% (Li₂O) for Li-rich daughter minerals. Lithium estimations on silicate glasses display values between 90 and 400 ppm.Lithium was also analyzed as a trace element in quartz. Transverse profiles were performed in hydrothermal barren quartz veins from the Spanish Central System (Sierra de Guadarrama). The highest Li concentrations (250 to 370 ppm) were found in specific growth bands in conjunction with the observed variation in optical cathodoluminescence intensity. Considering the fluid inclusion analysis, the source of fluid responsible to the Li enrichment in quartz is probably high-salinity fluids derived from sedimentary basins.     

X-ray imaging of uranium in individual fluid inclusions

The spatial distribution of major (K, Ca, Mn, Fe) and trace elements (Ti, Cr, Cu, As, Br, Rb, Sr, Zr, Pb, Th, U) were determined in individual fluid inclusions from quartz veins of the Streltsov uranium deposit, Russia, using synchrotron radiation X-ray fluorescence (SXRF). The analyses were performed on the beamline ID-22 Micro-FID (Fluorescence, Imaging, Diffraction) of the European Synchrotron Research Facility (ESRF, Grenoble, France). Fluorescence X-ray maps of single fluid inclusions show a relatively homogeneous distribution of most elements throughout the inclusion, whereas Fe and, to a lesser extent, Sr display highly localized count rates. This observation argues for the presence of minute, optically invisible, compounds that are precipitated inside the inclusion. Simple model calculations indicate that relatively diluted solutions (10–100 ppm U) trapped at geologically relevant temperatures (e.g. 250 °C) would precipitate submicron sized particles. These particles would be highly reactive to the photon flux but not necessarily visible under the microscope. These results indicate that third-generation synchrotron light source can be a powerful technique to study the physical processes undergone by the fluid. When combined with chemical data, this technique can help to clarify fluid transport properties in natural systems.     

Mobility and H2O loss from fluid inclusions in natural quartz crystals

Petrographic observations on quartz crystals from the Mole Granite (Australia) and other localities shed new light on the mechanisms of post-entrapment modification of fluid inclusions. These modifications include migration away from pseudosecondary trails, changes in fluid salinity and density, shape distortion and the formation of “sweat-haloes” around strongly deformed inclusions. Increases in fluid salinity, which usually are associated with inclusion migration, indicate water-losses of up to 50%. However, LA-ICP-MS-analysis of unmobilized and mobilized inclusions of the same trail reveals basically unchanged ratios of major – and trace element cations, with the exception of Li, which seems to be incorporated into the crystal lattice during migration. Despite the fact that all these modifications are closely related to deformation processes, they occur not only in mechanically deformed quartz, but also in free-standing crystals. In the latter samples, stress has been generated internally as a result of brazil-twinned growth and compositional zonation. These observations and their interpretation leads to a list of practical criteria that should help in differentiating between reliable and suspect fluid inclusions in other samples. Received: 17 November 1998 / Accepted: 16 April 1999     

Analysis of individual fluid inclusions using synchrotron X-ray fluorescence microprobe: progress toward calibration for trace elements

A critical problem for conducting quantitative analysis of individual fluid inclusions using Synchrotron X-Ray Fluorescence (SXRF) technique relates to the standardization and the calibration of the X-ray spectra. In this study, different approaches have been tested for calibration purposes: (a) the use of chlorine when Cl content can be estimated either from melting point depressions of undersaturated fluid inclusions or from saturation limits for halite-bearing fluid inclusions, (b) the use of calcium from synthetic fluid inclusions of known CaCl₂ content as an external standard. SXRF analysis was performed on individual fluid inclusions from the Chivor and Guali emerald deposits, Columbia. These well-known samples contain a single fluid inclusion population for which detailed crush-leach analyses are available, thus providing a relevant compositional reference frame. Concentration estimates were also compared to Particle Induced X-ray Emission (PIXE) analysis carried out independently on the same fluid inclusions.Results of the calibration tests indicate that major (Cl, K, Ca, Fe, Mn) and trace element (Cu, Zn, As, Br, Rb, Sr, Ba, Pb) concentration estimates can be performed without precise knowledge of the analytical volume and the inclusion’s 3D geometry. Although the standard deviation of the SXRF results can be relatively high depending on the calibration mode used, mean concentration estimates for most elements are in good agreement with PIXE and crush-leach analysis. Elemental distributions within single fluid inclusions were also established. Associated correlation diagrams argue for the homogeneous distribution of most elements in the fluid inclusion. In contrast, Br shows a bimodal distribution interpreted to reflect a significant enrichment of the vapor portion of the inclusion fluid.     

REE in fluid inclusions of quartz from gold deposits of north-eastern Russia

Inductively coupled plasma-mass spectrometry (ICP-MS) has been used to determine rare earth element concentrations in aqueous solutions extracted from fluid inclusions. Quartz has been sampled from ores of three major types of polygenic gold hydrothermal systems of North-Eastern Russia: (1) gold-quartz-sulphide (Au-Q, Nezhdaninsk); (2) gold-antimony (Au-Sb, Sarylakh) and (3) intrusion-related gold-bismuth-siderite-polysulphide (Au-Bi-Sid, Arkachan) large deposits located in terrigenous rocks of the Verkhoyansk fold belt. The total concentration of REE in the fluid inclusions is not high (up to 52 ppm). The contribution of LREE dominates in REE balance (??LREE/??HREE=7.4?C112.1). The chondrite-normalized REE patterns of inclusion fluids for the Au-Q and Au-Bi-Sid deposits are characterized by LREE enrichment with a positive or negative Eu anomaly. REE patterns for the regenerated quartz from Au-Sb deposits are characterized by pronounced differentiation between light and heavy lanthanides in fluid inclusions. Significant total REE concentration decreasing (on 1?C2 order) from early to late stages of Nezhdaninsk and Arkachan deposits is revealed. The positive correlations of total REE concentrations with Rb, Cs, Li and B contents in fluid inclusions are shown. The REE distribution in fluid inclusions can be used as indicators of the contribution of magmatic fluid in the hydrothermal system.     

Synthetic fluid inclusions. XV. TEM investigation of plastic flow associated with reequilibration of fluid inclusions in natural quartz

The nature and abundance of dislocations in quartz surrounding fluid inclusions were studied to obtain a better understanding of processes associated with fluid inclusion reequilibration. Synthetic fluid inclusions containing 10 wt% NaCl aqueous solution were formed in three samples at 700 °C and 5 kbar. One of the samples was quenched along an isochore to serve as a reference sample. The other two samples were quenched along a P-T path that generated internal pressures in excess of the confining pressure. The two samples were held at the final reequilibration P-T conditions of 625 °C and 2 kbar for 30 and 180 days, respectively. Following the experiments, microstructures associated with fluid inclusions were examined with the TEM. Quartz in healed fractures in the reference sample that was quenched isochorically shows a moderate dislocation activity. Quartz adjacent to reequilibrated fluid inclusions in the other two samples, however, showed a marked increase in dislocation activity compared to the un-reequilibrated sample. Deformation of the inclusion walls occurred anisotropically by expansion of mobile dislocations in their slip systems. Dislocation expansion was controlled by glide in the rhombohedral planes {1 0 1 1} that was restricted to narrow zones (≤3 μm) in the immediate vicinity of the fluid inclusion walls outside of the healed fracture plane. These plastic zones were observed after both short term (30 days) and long term (180 days) experiments and are attributed to hydrolytic weakening of quartz around fluid inclusions owing to diffusion of water into the quartz matrix during the experiment. The close spatial association of submicroscopic water bubbles with dislocations, and the rarity of water bubbles in the reference sample, show clearly that in both the 30 and 180 day experiments reequilibration involves water loss from the fluid inclusions. Our results indicate that synthetic fluid inclusions in this study recover (chemically and volumetrically), even at relatively fast experimental loading rates, such that internal stresses never reach the point of brittle failure. The driving force for fluid inclusion deformation involves two related mechanisms: plastic deformation of hydrolytically weakened wet quartz in the healed fracture, and water leakage associated with preexisting and strain-induced dislocations. Received: 5 May 1998 / Accepted: 10 February 2000     

Compositional characteristics of fluid inclusions as exploration tool for Au-mineralization at Larafella, Burkina Faso

The Larafella Au-prospect (Burkina Faso) lies within dacitic rocks of the Palaeoproterozoic Birimian greenstone belts. Gold mineralization is intimately associated with zones of cataclastic deformation. Whilst the lode-vein mineralization is closely associated with CO₂-rich fluid inclusions, the barren quartz veins are characterized by H₂O ± salt-bearing inclusions. Geochemical studies on the immediate wall-rock of the quartz veins have shown an increase of As in zones of gold enrichment, while alteration overprints such as carbonatization and chloritization cannot be correlated unequivocally with Au-mineralization. Consequently, fluid inclusion studies of quartz veins and As-anomalies constitute important exploration tools for mesothermal gold mineralization, since Au-rich zones can be distinguished from Au-depleted zones.     

Silicate and salt melts in the genesis of the industrial’noe tin deposit: Evidence from inclusions in minerals

The data obtained on melt and fluid inclusions in minerals of granites, metasomatic rocks, and veins with tin ore mineralization at the Industrial’noe deposit in the southern part of the Omsukchan trough, northeastern Russia, indicate that the melt from which the quartz of the granites crystallized contained globules of salt melts. Silicate melt inclusions were used to determine the principal parameters of the magmatic melts that formed the granites, which had temperatures at 760–1020°C, were under pressures of 0.3–3.6 kbar, and had densities of 2.11–2.60 g/cm³ and water concentrations of 1.7–7.0 wt %. The results obtained on the fluid inclusions testify that the parameters of the mineral-forming fluids broadly varied and corresponded to temperatures at 920–275°C, pressures 0.1–3.1 kbar, densities of 0.70–1.90 g/cm³, and salinities of 4.0–75.0 wt % equiv. NaCl. Electron microprobe analyses of the glasses of twelve homogenized inclusions show concentrations of major components typical of an acid magmatic melt (wt %, average): 73.2% SiO₂, 15.3% Al₂O₃, 1.3% FeO, 0.6% CaO, 3.1% Na₂O, and 4.5% K₂O at elevated concentrations of Cl (up to 0.51 wt %, average 0.31 wt %). The concentrations and distribution of some elements (Cl, K, Ca, Mn, Fe, Cu, Zn, Pb, As, Br, Rb, Sr, and Sn) in polyphase salt globules in quartz from both the granites and a mineralized miarolitic cavity in granite were assayed by micro-PIXE (proton-induced X-ray emission). Analyses of eight salt globules in quartz from the granites point to high concentrations (average, wt %) of Cl (27.5), Fe (9.7), Cu (7.2), Mn (1.1), Zn (0.66), Pb (0.37) and (average, ppm) As (2020), Rb (1850), Sr (1090), and Br (990). The salt globules in the miarolitic quartz are rich in (average of 29 globules, wt %) Cl (25.0), Fe (5.4), Mn (1.0), Zn (0.50), Pb (0.24) and (ppm) Rb (810), Sn (540), and Br (470). The synthesis of all data obtained on melt and fluid inclusions in minerals from the Industrial’noe deposit suggest that the genesis of the tin ore mineralization was related to the crystallization of acid magmatic melts. Original Russian Text@ V.B. Naumov, V.S. Kamenetsky, 2006, published in Geokhimiya, 2006, No. 12, pp. 1279–1289.     

High-density CO2 inclusions in the Colorado Front Range

A fluid density in an inclusion is commonly observed to be too low for the P-T estimates for the postulated time of trapping, and is generally attributed to a fluid loss during the uplift process. It is more difficult to explain a fluid density which is too high. In the 1700 m.y. Front Range migmatites, such high densities occur in some of CO₂ inclusions which were deduced to have formed during the migmatization episode. The peak P-T estimates for migmatization in the Front Range are 4–6 kb and 650°–700° C (in sillimanite field) but pressures required to form the most dense inclusions are >7.6 kb (in kyanite field). The high density is not likely to be a relic of a higher pressure condition earlier than the main migmatization episode for the following reasons: (a) no kyanite (or any other relic high pressure phase) has been found in the Precambrian Front Range; (b) the high density inclusions are rare in zones with least signs of deformation and melting (paleosomes and quartz inclusions within feldspar grains) which instead contain relatively undisturbed early inclusions; (c) high density inclusions with Th <–30° C are associated with heavily altered plagioclase caused by hydrothermal activity which was a late event in leucosome formation. Further, there is evidence for post-entrapment change(s) in density: an intragranular trail in quartz contains CO₂ inclusions that exhibit almost the whole range in Th (–40 to +24° C) as displayed by the entire population of the early CO₂ inclusions (–66 to +30° C). The density of an inclusion in the trail is not related to inclusion size but to the position of the inclusion relative to apparent micro-shear zones crossing the CO₂ trail. A change to a higher density (=a smaller volume) could have resulted from an initially isobaric cooling path which intersects CO₂ isochores with increasingly higher densities. Additional excess pressure may have resulted from overthrusting. However, because high density inclusions occur selectively in the zones in which plagioclase shows alteration indicating a high and because there is a correlation between shear zones and high density inclusions, it is postulated that local hydrolytic weakening of quartz was necessary for the decrease of inclusion volume which occurred during deformation. The localized deformation may also result in an excess pressure. However, the introduction of a small amount of H₂O into these inclusions as a possible cause of high density inclusions cannot be ruled out.     

Trace element incorporation into quartz: A combined study by ICP-MS, electron spin resonance, cathodoluminescence, capillary ion analysis, and gas chromatography

Pegmatite quartz from different occurrences in Norway and Namibia was investigated by a combination of ICP-MS, Electron Spin Resonance (ESR), Capillary Ion Analysis (CIA) and Gas Chromatography (GC) to quantify trace elements in very low concentrations and to determine their position in the quartz structure.The studied quartz samples show similar geochemical characteristics with low contents of most trace elements. Remarkable are the elevated concentrations of Al (36-636 ppm), Ti (1.6-25.2 ppm), Ge (1.0-7.1 ppm), Na (5.2 to >50 ppm), K (1.6 to >100 ppm) and Li (2.1-165.6 ppm). These elements are preferentially incorporated into the quartz lattice on substitutional (Al, Ti, Ge) and interstitial (Li, Na, K) positions. Li⁺ was found to be the main charge compensating ion for Al, Ge and Ti, whereas some ppm of Na and K may also be hosted by fluid inclusions. Ti may be incorporated as substitutional ion for Si or bound on mineral microinclusions (rutile). The results of the ESR measurements show that there may be a redistribution of alkali ions during irradiation. The diamagnetic [AlO₄/M⁺]⁰ center transforms into the paramagnetic [AlO₄]⁰ center, whilst the compensating ions diffuse away and may be captured by the diamagnetic precursor centers of [GeO₄]⁰ and [TiO₄]⁰ to form paramagnetic centers ([TiO₄/Li⁺]⁰, [GeO₄/Li⁺]⁰).In general, fluid inclusions in pegmatite quartz can be classified as H₂O-CO₂-NaCl type inclusions with water as the predominant volatile. Among the main elements hosted by fluid inclusions in quartz are Na, K, NH₄, Ca, Mg and the anionic complexes Cl⁻, NO₃⁻, HCO₃⁻ and SO₄²⁻. Gas analysis of trapped fluids shows volatile components in the following order of abundance: H₂O > CO₂ > N₂(+) ≥ CH₄ > COS > C₂ and C₃ hydrocarbons. Additionally, traces of Co, Ni, Zn, Pb, and Cu were detected by CIA in fluid inclusions of some samples. There are indications that the REE and Rb are also bound in fluid inclusions, however, the concentrations of these elements are too low to be measured by CIA. Assuming that the REE preferentially occur in fluid inclusions, the typical chondrite normalized REE distribution patterns with tetrad effects and a distinct negative Eu anomaly would reflect the composition of the mineralizing fluid.For a number of elements, especially those with extremely low concentrations, the “type” of incorporation in quartz could not directly be determined. We conclude that these ions either are too large to substitute for the small Si⁴⁺ ion or they are not soluble in the mineralizing fluids to be hosted by fluid inclusions. Some of these elements, which are concentrated in the specific mineralization of certain pegmatites, are not present in elevated concentrations in the paragenetic pegmatite quartz itself. This was observed, for instance, for Be, Cs and Rb in the Li (Be-Cs-Rb) pegmatites of Rubicon or for Nb and Ta for Nb-Ta bearing pegmatites from Norway. It may be concluded that the concentrations of these trace elements in quartz do not reflect the mineralization and that these elements thus, cannot be used as petrogenetic indicator.     

The behavior of trace elements during the chemical evolution of the H2O-, B-, and F-rich granite–pegmatite–hydrothermal system at Ehrenfriedersdorf, Germany: a SXRF study of melt and fluid inclusions

Detailed melt and fluid inclusion studies in quartz hosts from the Variscan Ehrenfriedersdorf complex revealed that ongoing fractional crystallization of the highly evolved H₂O-, B-, and F-rich granite magma produced a pegmatite melt, which started to separate into two immiscible phases at about 720°C, 100 MPa. With cooling and further chemical evolution, the immiscibilty field expanded. Two conjugate melts, a peraluminous one and a peralkaline one, coexisted down to temperatures of about 490°C. Additionally, high-salinity brine exsolved throughout the pegmatitic stage, along with low-density vapor. Towards lower temperatures, a hydrothermal system gradually developed. Boiling processes occurred between 450 and 400°C, increasing the salinities of hydrothermal fluids at this stage. Below, the late hydrothermal stage is dominated by low-salinity fluids. Using a combination of synchrotron radiation-induced X-ray fluorescence analysis and Raman spectroscopy, the concentration of trace elements (Mn, Fe, Zn, As, Sb, Rb, Cs, Sr, Zr, Nb, Ta, Ag, Sn, Ta, W, rare earth elements (REE), and Cu) was determined in 52 melt and 8 fluid inclusions that are representative of distinct stages from 720°C down to 380°C. Homogenization temperatures and water contents of both melt and fluid inclusions are used to estimate trapping temperatures, thus revealing the evolutionary stage during the process. Trace elements are partitioned in different proportions between the two pegmatite melts, high-salinity brines and exsolving vapors. Concentrations are strongly shifted by co ncomitant crystallization and precipitation of ore-forming minerals. For example, pegmatite melts at the initial stage (700°C) have about 1,600 ppm of Sn. Concentrations in both melts decrease towards lower temperatures due to the crystallization of cassiterite between 650 and 550°C. Tin is preferentially fractionated into the peralkaline melt by a factor of 2–3. While the last pegmatite melts are low in Sn (64 ppm at 500°C), early hydrothermal fluids become again enriched with about 800 ppm of Sn at the boiling stage. A sudden drop in late hydrothermal fluids (23 ppm of Sn at 370°C) results from precipitation of another cassiterite generation between 400 and 370°C. Zinc concentrations in peraluminous melts are low (some tens of parts per million) and are not correlated with temperature. In coexisting peralkaline melts and high-T brines, they are higher by a factor of 2–3. Zinc continuously increases in hydrothermal fluids (3,000 ppm at 400°C), where the precipitation of sphalerite starts. The main removal of Zn from the fluid system occurs at lower temperatures. Similarly, melt and fluid inclusion concentrations of many other trace elements directly reflect the crystallization and precipitation history of minerals at distinctive temperatures or temperature windows.     

Application of a new Raman microprobe spectrometer to nondestructive analysis of sulfate and other ions in individual phases in fluid inclusions in minerals

Rosascoet al. (1975), reported the first successful application of laser-excited Raman spectroscopy for the identification and nondestructive partial analysis of individual solid, liquid, and gaseous phases in selected fluid inclusions. We report here the results of the application of a new instrument, based on back-scattering, that eliminates many of the previous stringent sample limitations and hence greatly expands the range of applicability of Raman spectroscopy to fluid inclusions.Fluid inclusions in many porphyry copper deposits contain 5–10 μm ‘daughter’ crystals thought to be anhydrite but too small for identification by the previous Raman technique. Using the new instrument, we have verified that such daughter crystals in quartz from Bingham, Utah, are anhydrite. They may form by leakage of hydrogen causing internal autooxidation of sulfide ion. Daughter crystals were also examined in apatite (Durango, Mexico) and emerald (Muzo, Colombia).Valid analyses of sulfur species in solution in small fluid inclusions from ore deposits would be valuable, but are generally impossible by conventional methods. We present a calibration procedure for analyses for SO₄^2? in such inclusions from Bingham, Utah (12,000 ± 4000 ppm) and Creede, Colo. (probably < 500 ppm). A fetid Brazilian quartz, originally thought to contain liquid H₂S, is shown to contain only HS^? in major amounts.     

Preferential water loss from synthetic fluid inclusions

A fundamental question in most fluid inclusion studies is whether inclusions behave as compositionally closed systems after trapping, and, thus, represent samples of the fluid phase(s) present in the system at the time of their formation. This question was addressed in high-temperature laboratory experiments with synthetic fluid inclusions in quartz and it was found that at 825°C the inclusions exhibited open-system behavior with respect to water. Synthetic salt-water fluid inclusions in quartz were reequilibrated for 12 hours to 35 days at 825° C in a dry argon atmosphere under 1.5 kbar confining pressure. These conditions created initial internal overpressures (P _int> P _conf) of 1.5–4 kbar in the inclusions and differential water fugacities in the same sense i.e., fH₂OfH₂O. After 108 hours of reequilibration, preferential water loss had resulted in salinity increases as large as 22 wt% salt (e.g., from 57 to 79 wt% NaCl, as determined from measured temperatures of salt dissolution). Also, following reequilibration, a strong inverse correlation between salinity and inclusion volume was observed, and this trend became more pronounced with increasing reequilibration time. These observations, together with a lack of evidence for selective H₂O removal via hydration reactions, suggest that water loss occurred by a diffusion-related mechanism. Fluxes of 4x10^-11 g/cm²-s and diffusion coefficients on the order of 10^-9 cm²/s are calculated for water loss from the inclusions. The calculated H₂O diffusion coefficient is consistent with the determination of Blacic (1981) derived from hydrolytic weakening experiments, but is much larger than the value obtained by Giletti and Yund (1984) for volume diffusion of oxygen in isotope exchange experiments. These observations suggest that the mechanism of water loss from our synthetic fluid inclusions may have been pipe diffusion along dislocations, subgrain boundaries or other structural defects rather than bulk volume diffusion.The results of this study are relevant to the interpretation of fluid inclusions in quartz from several natural high-temperature environments where water fugacities of included and ambient fluids are known to have evolved along separate paths over geologic time.     

Dawsonite as a daughter mineral in hydrothermal fluid inclusions

Traces of dawsonite (NaAlCO₃(OH)₂) are extremely common as a daughter product in fluid inclusions in gold-quartz veins and altered wallrock of the Oriental mine, Alleghany district, California. A very similar daughter salt occurs in hydrothermal inclusions in quartz from 19 other mining localities of worldwide distribution.Vein fluids of the Oriental mine were probably CO₂-rich sodium bicarbonate brines that contained at least 1 weight percent dissolved aluminum. These fluids precipitated quartz and oligoclase in the veins and adjacent altered rocks. The precipitation of dawsonite rather than albite or oligoclase in the cooled inclusion brines suggests either that sodic plagioclase gives way to dawsonite plus quartz as the stable pair at low temperatures or that the dawsonite is a metastable daughter mineral. The rarity of dawsonite as a separate vein mineral or alteration product at the Oriental mine and elsewhere is attributed to its high solubility under normal conditions of mineralization.Dawsonite contributes 190 ppm or more to the aluminum content of some Oriental mine quartz. Large errors would result if the dawsonite were overlooked and the aluminum geothermometer of Dennen et al. (1970) were applied to this quartz. The combination of high primary inclusion filling temperatures and very low aluminum contents of optically clear quartz indicate that major revisions are needed in the published thermometer curve.     

Synthetic fluid inclusions - VI. Quantitative evaluation of the decrepitation behaviour of fluid inclusions in quartz at one atmosphere confining pressure

ABSTRACT The decrepitation behaviour of fluid inclusions in quartz at one atmosphere confining pressure has been evaluated using pure H₂O synthetic inclusions formed by healing fractures in natural quartz. Three different modes of non-elastic deformation, referred to as stretching, leakage or partial decrepitation, and total decrepitation have been observed. The internal pressure required to initiate non-elastic deformation is inversely related to inclusion size according to the equation: internal pressure (kbar) = 4.26 D^-0.423 where D is the inclusion diameter in microns. Regularly shaped inclusions require a higher internal pressure to initiate non-elastic deformation than do irregularly shaped inclusions of similar size. Heating inclusions through the α/β quartz inversion results in mechanical instability in the quartz crystal and leads to mass decrepitation of inclusions owing to structural mismatches generated by pressure gradients in the quartz around each inclusion. Long-term heating experiments (∼2 years) suggest that the internal pressure required to initiate non-elastic deformation does not decrease significantly with time and indicates that short-lived thermal fluctuations in natural systems should not alter the inclusion density and homogenization temperature. Inclusions that do exhibit decreased density (higher homogenization temperature) are, however, always accompanied by a change in shape from irregular to that of a negative crystal. Observations of this study are consistent with elasticity theory related to fracture generation and propagation around inclusions in minerals. These results indicate that an inclusion will not be influenced by a neighbouring inclusion, or other defect in the host phase, as long as the distance between the two is >2–4 diameters of the larger of the two inclusions.     

流体包裹体中Sr同位素的激光剥蚀多接收等离子体质谱原位微区分析

本文研究了用激光剥蚀多接收等离子体质谱（LA-MC-ICPMS）技术原位微区分析包裹体中Sr同位素的分析方法。5、10、16和30μm剥蚀序列进行包裹体的Sr同位素组成分析结果表明,包裹体中Sr同位素比值和Rb含量明显高于与包裹体接触的方解石矿物,从大个体包裹体（大于2μm）可获得较准确的Sr同位素组成（精密度为0.08%）。由于87Rb的含量只能通过85Rb计算而来,有限包裹体分析信号而导致的Sr同位素分析精度较传统的化学方法略差,因此本方法不能得到包裹体中的Rb-Sr年龄。     

藏东玉龙斑岩铜矿床多期流体演化与成矿的流体包裹体证据

通过对王龙斑岩铜矿石英斑晶、辉钼矿石英脉中流体包裹体岩相学、包裹体显微测温分析、包裹体成分的激光拉曼探针分析及包裹体中子矿物的扫描电镜/能谱分析,发现矿化斑岩石英斑晶中发育多期流体包裹体。斑晶中除流体包裹体外尚可见少量熔体包裹体,与斑岩期矿化有关的成矿流体以中高温(200～537℃)、高盐度(29.6～44.7 wt%NaCleq)为特征,与粘土化蚀变有关的流体包裹体以低温、富 Ca 为特征,不同气相充填度的气液两相包裹体与高盐度含子矿物多相包裹体共存,且具有相似的均一温度,显示不混溶流体包裹体特征。温度、压力降低引起的流体不混溶是造成斑岩型矿化矿质沉淀的主要因素,斑岩期流体与浅成低温热液期流体形成于统一的流体系统,为同源演化结果。