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Magnetized and unmagnetized Nd16Fe76B8 sintered magnets were exposed to hydrogen environment. Hydrogen absorption, desorption, and temperature variation for the magnetized and unmagnetized magnets were measured by hydrogen differential thermal analyzer. It is found that hydrogen decrepitation for magnetized NdFeB magnets, both isotropic and anisotropic, was delayed compared with that for unmagnetized magnets. It is suggested that magnetization may play a role on hydrogen decrepitation for sintered Nd–Fe–B magnets.

Hydrogen decrepitation of Sm 2 Fe 17 followed by treatment in ammonia produces interstitial nitrides with nitrogen concentrations greater than three per formula unit. Measurements of the lattice parameters and magnetic properties are consistent with interstitial nitrogen occupation of the 9e and either the 3b or 18g sites. The effect of the extra nitrogen on the iron sublattice is to reduce the overall moment, particularly of the 18h sites. The magnetocrystalline anisotropy constants K 1 and K 2 indicate a significant decrease in the easy-axis character compared to Sm 2 Fe 17 N 3 material.

Anisotropic NdFeB powder was prepared from mechanically alloyed and hot deformed magnets using hydrogen decrepitation. After hydrogen desorption the material becomes very friable. The powder particles show similar anisotropic behaviour as the original dic-upset material. Values of ( BH ) max = 81 kJ/m 3 were obtained for textured resin bonded magnets with a coercivity of about μ oJ H c = 1.6 T and a measured density of 5.4 g/cm 3 .

[1] I made measurements of the permanent strain of thermal expansion, compressional wave velocity, and density of microcracks of Inada granite, which was subjected to slow and homogeneous temperature change under atmospheric pressure. The permanent strain implying the cumulative amount of newly generated microcracks and the opening of preexisting microcracks appeared distinctly at a temperature between 100° and 125°C and increased almost exponentially in the range from 200°C to immediately before the temperature of α-β transition in quartz (573°C) as the peak temperature of the thermal cycle was elevated. At 600°C, the strain increased further. The density of the microcracks was heightened as the peak temperature increased. Moreover, the said trend coincided with that of the crack density parameter estimated from the compressional wave velocity. At the same time, the maximum width of the microcracks, which was determined by microscopic observation, and the average width increment of the microcracks, calculated from the permanent strain and microcrack density, showed a similar trend. Using the mercury intrusion porosimetry method, the average width increment of the microcracks coincided with the equivalent width of the microcracks measured. There are two causes of thermally induced microcracking: the mismatching of the coefficients of thermal expansion between the adjacent mineral grains and the decrepitation of the fluid inclusions. The density of the fluid inclusion microcracks showed a remarkable increase starting from the peak temperature of 300°C. At temperatures equal to or higher than 400°C, the fluid inclusion microcracks accounted for approximately 35% of all the intragranular cracks.

Quadrupole mass spectrometer (QMS) is an instrument for effectively determining gaseous composition of fluid inclusion. The gaseous component is extracted from inclusions with thermal decrepitation method and then determined with the sensitive QMS instrument. The method is characterized by high sensitivity and high accuracy with the relative standard deviation (RSD, n = 6) of less than 3%. It has been successfully used for analyzing fluid inclusions. The analytical results meet the requirement of geological study.

Quartz, as the most ubiquitously occurring mineral, was chosen for investigations of the acoustic emission upon heating. Various samples from a wide range of conditions of formation were analyzed in the frequency range of 400–10 000 Hz with a high‐resolution decrepitometer. The acoustic emission patterns showed a variation of 5000–80 000 total signals over the entire temperature range of 90 °C‐610 °C (1‐cm3 sample, grainsize fraction 250–500 μm). Microthermometric investigations of the sound‐emitting processes and correlation with microcrack patterns determined by scanning electron microscopy (SEM) showed that various sources contribute to the sometimes vehement noise production. Stress built up because of thermal anisotropy causes the formation of microcracks along inter‐ and intragranular grain boundaries over most of the observed temperature range. Accumulation of signals from the decrepitation of fluid inclusions reveals information about the conditions of formation and subsequent alterations of the i...

Linear elastic fracture mechanics quantitatively relates the driving stress of fracture propagation to the material properties of the fractured solid and may be used to model the decrepitation (fracturing) of fluid inclusions under the influence of internal pressure. Existing experimental data on decrepitation can be explained by the methods of fracture mechanics. The decrepitation pressure vs. size relation may therefore be predicted for fluid inclusions in minerals that have not been the subject of quantitative decrepitation studies. It may be possible to determine the fracture toughness of minerals by decrepitation studies utilizing synthetic fluid inclusions.

Fluid inclusions break, or decrepitate, when the fluid pressure exceeds the least principal lithostatic stress by a critical amount. After decrepitation, excess fluid pressure is relaxed, resulting in crack arrest; subsequently, crack healing may occur. Existing models of decrepitation do not adequately explain several experimentally observed phenomena. We developed a linear elastic fracture mechanics model to analyze new data on decrepitation and crack arrest in San Carlos olivine, compared the model with previous fluid inclusion investigations, and used it to interpret some natural decrepitation microstructures. The common experimental observation that smaller inclusions may sustain higher internal fluid pressures without decrepitating may be rationalized by assuming that flaws associated with the inclusion scale with the inclusion size. According to the model, the length of the crack formed by decrepitation depends on the lithostatic pressure at the initiation of cracking, the initial sizes of the flaw and the inclusion, and the critical stress intensity factor. Further experiments show that microcracks in San Carlos olivine heal within several days at 1280 to 1400°C; healing rates depend on the crack geometry, temperature, and chemistry of the buffering gas. The regression distance of the crack tip during healing can be related to time through a power law with exponent n = 0.6. Chemical changes which become apparent after extremely long heat-treatments significantly affect the healing rates. Many of the inclusions in the San Carlos xenoliths stretched, decrepitated, and finally healed during uplift. The crack arrest model indicates that completely healed cracks had an initial fluid pressure of the order of 1 GPa. Using the crack arrest model and the healing kinetics, we estimate the ascent rate of these xenoliths to be between 0.001 and 0.1 m/s.

Further developments in the analysis of fluid inclusion decrepitates by inductively-coupled plasma emission spectroscopy (ICP) are outlined. Decrepitates from samples of quartz have been analysed and give useful results. As several mechanisms of transfer of material into the plasma are feasible it is important that the temperature of heating should be restricted to the temperature range of decreptiation. However, contamination by silicate phases in the quartz appears to be of little significance. Reproducibility in our analyses is usually better than 30% (relative standard deviation, RSD) and most of this appears to be due to heterogeneity in the abundance of fluid inclusions. We have been able to estimate the ore metal content of some hydrothermal fluids from SW England and have obtained values in the range one hundred to a few thousand parts per million for some elements (Cu, Pb, Zn, Sn and B). Because of the sensitivity of the method we feel that its greatest potential is in the field of routine mineral exploration, and we have had considerable success in this application.

Means of extracting and quantitatively analyzing volatiles in fluid inclusions have been studied and details of the methods developed are presented. Thermal decrepitation is the preferred method to open inclusions because experiments indicate that this method yields more accurate measurements of the sulphur-species gases and water. Two assemblages of inclusion species have repeatedly been detected in inclusions from mineral deposits. A CO 2 -dominated assemblage typically has been measured in inclusions from porphyry-type deposits. A CO 2 N 2 C n H n assemblage is typical of inclusion volatiles from sediment-hosted and epithermal deposits. The probable source of N 2 and organic compounds is biologic material which is consistent with a crustal source for the ore solutions. Inclusion volatiles from most ore deposits have 1–3 mole% gaseous species. However, levels of 5–15% have been measured in assemblages of vapor-dominant and liquid dominant inclusions from epithermal deposits. The interpretation is that vapor-dominant inclusions are rich in gaseous species. This implies that the indicated “boiling” of the ore solutions was not strictly aqueous boiling but more an unmixing of the gaseous components. Analytical data on volatiles in fluid inclusions have been used to calculate f O 2 , f S 2 , f CO 2 and pH of ore fluids, and these values agree with values calculated from other data. Data on gases in fluid inclusions have also been used to estimate trapping pressure and study paragenesis.

Fluid inclusions in minerals provide a source of geologically significant fluids. A new computerized mass spectrometric technique for analyzing volatiles in individual inclusions has been developed. The inclusions are opened by decrepitation in vacuum, and the computer recognizes the abrupt rise in pressure and controls the mass spectrometer. This scans continuously from 1 to 65 amu every 25 ms, which is within the time constraints of a bursting inclusion. The peak height for each mass in each spectrum is measured and stored along with the background data. Data are reduced after analysis. Each mass number is assigned its own attenuation factor by the computer in a preliminary analysis. This permits the determination of trace components down to 1 part in 10,000. With this system it is possible to analyze up to 225 inclusions in 1 h using a 10-mg sample of quartz, calcite, plagioclase, pyroxene, galena, or other mineral.

Acoustic emissions recorded during slow heating of rocks at 1 atm have generally been attributed to intergranular stresses generated by differences in thermal expansion coefficients and elastic moduli of neighboring grains. These experiments have considered only the solid phases in analysis of the results, and little attention has been given to the role of intragranular or grain boundary fluid inclusions in initiating or facilitating fracturing. In principle, fluid inclusions may be thought of as a special case in which the “ neighboring grains” are fluids rather than the usual solid mineral phases. The major differences are that (1) the number of inclusions per unit volume is usually 10 2 to 10 6 times greater than the number of mineral grains in that same volume and that (2) the volume increase with temperature for most fluids is 1–2 orders of magnitude greater than for minerals. Thus, when fluid inclusion “grains” are considered, the absolute number of grain-to-grain contacts in a given sample volume is several orders of magnitude greater than if the inclusions are not considered. Further, the magnitude of the stresses between any two adjacent grains may be much higher if one of the “grains” is a fluid inclusion, owing to the larger coefficient of thermal expansion of the fluid relative to a solid phase. As a result, substantial overpressures may be generated at the fluid inclusion “grain”-mineral grain contact, during heating experiments. These overpressures result in brittle failure when the stress around the inclusion exceeds the local strength of the host crystal. In fluid inclusion terminology, this fracturing event is referred to as decrepitation. Samples of Westerly granite and Sioux quartzite were heated at 2° C/min in a gas-flow stage in order to determine the decrepitation profiles (number of decrepitations as a function of temperature) of these rocks. Decrepitation was monitored visually during heating experiments, and was evidenced by the explosive loss of fluids from the inclusion during a fracturing event. Decrepitation produces microfractures which originate at decrepitated fluid inclusions and propagate outward into the surrounding mineral. Four different types of inclusions, based on room temperature phase ratios and distribution within the host phase, were noted in Westerly granite. Type (1) inclusions contain a single aqueous liquid, type (2) are two-phase, liquid-rich inclusions, type (3) are mostly one-phase fluid inclusions that occur in dense clusters in plagioclase and type (4) are two-phase, moderate-density, H 2 O-CO 2 -“salt” inclusions. Type (5) inclusions are one-phase, aqueous liquid inclusions observed in Sioux quartzite. Fluid inclusions in Westerly granite decrepitate between 75° and 573° C with peaks at 275–300°C and 400–450°C. Type (4) inclusions in Westerly granite tend to decrepitate at lower temperatures (75–300°C) than other inclusion types. Initial fracturing of the quartz host surrounding type (1) inclusions (primary decrepitation) generally occurs over the range 100–400°C and the fractures continue to propogate through the quartz (secondary decrepitation) during further heating from 400° to 573°C. Fluid inclusions in Sioux quartzite decrepitate between 188° and 573°C with a broad maximum at 250–450°C. Primary decrepitation generally occurs at 200–450°C while secondary decrepitation occurs at 350°–573°C in Sioux quartzite. Some small inclusions in both samples do not decrepitate until the quartz α-β transition temperature (573°C) is reached. Decrepitation profiles determined in this study display many similarities and differences when compared to previously published acoustic emission profiles of Westerly granite and Sioux quartzite. Owing to fundamental differences in the techniques used to measure acoustic emission and decrepitation, and the potentially different energies associated with the two events, it is unclear whether decrepitating fluid inclusions are recorded during acoustic emission studies. However, if decrepitating fluid inclusions are being recorded during acoustic emission measurements, then our results suggest that: (1) decrepitation contributes more to low temperature portions of acoustic emission profiles than to high temperature portions for both Sioux quartzite and Westerly granite; (2) compared to Westerly granite, a larger percentage of acoustic emissions in the low temperature decrepitation profile of Sioux quartzite is due to fluid inclusions; (3) decrepitating fluid inclusions, not stresses generated by solid-solid interactions, cause the majority of intragranular fracturing in quartz below the temperature of the α-β transition in both these rocks.

The Proterozoic high-level anorogenic (A-type) Ostra Hojden granite and associated hydrothermal veins and skarns from the Gasborn area, W. Bergslagen, central Sweden, contain aqueous, CO2-rich (gaseous) and mixed aqueous-gaseous fluid inclusions. The oldest aqueous inclusions are highly saline (32–40 wt.% NaCl eq.). The oldest gaseous inclusions are CO2-rich with, locally, minor amounts of N2 and CH4. Aqueous inclusions become less saline and CO2-rich inclusions become less dense and loose their N2 and CH4 content, going from older to younger generations. Large quantities of mixed aqueous-gaseous inclusions only occur in hydrothermal veins in marble. δ 13C values of around − 1.6% of CO2 in these inclusions suggest that they were formed by heterogeneous trapping of an aqueous fluid and CO2 was derived from the surrounding marble. Many of the oldest aqueous and mixed aqueous-gaseous inclusins are decrepitated and surrounded by trails and fields of less dense, younger inclusions formed during and after decrepitation. The maximal fluid pressure and temperature are estimated at about 4 kbar and approximately 560°C, respectively. The lithostatic pressure is estimated at < 1.0 kbar, indicating that hydrothermal vein formation resulted from hydrostatic overpressuring of fluids expelled from the cooling granite.

Fluorite and quartz samples from Oseja (Oviedo, Spain) and Sierra de Lujar (Granada, Spain) contain multiphase fluid inclusions with two immiscible liquids, a gas and a solid phase at room temperature. Studies by Raman scattering microspectrometry permitted: 1. (a) An unambiguous identification of native sulphur daughter solid. 2. (b) Determination of CO 2 H 2 S molar ratios in the gas phase and in the two liquids (aqueous solution and a mixture of liquefied CO2 and H2S). 3. (c) In H2S-rich inclusions, identification of a H2S hydrate (probably the clathrate H2S · 5.75 H2O), observed at low temperature. A check of internal consistency is given by the comparison of the theoretical ( CO 2 H 2 S ) gas ( CO 2 H 2 S ) water ratio (value = 3) and the observed ratio (mean value = 3.3). Homogenization of the gas and (CO2 + H2S) liquid occurs generally in the liquid phase. In the Lujar samples it occurs between +24° and 38°C and there is a fair correlation with H2S content. In the Oseja samples it occurs between +27° and +48°C, and the trend with composition is not clear. H2S hydrate was observed during some freezing runs in fluorite from Oseja and CO2 hydrate in samples from Sierra de Lujar. Because of decrepitation, total homogenization was observed only in small inclusions of the quartz from Lujar at above 300°C. The temperature of total homogenization corresponds to the vanishing of the sulphur droplet, which determines the paleofugacity of S2 in the fluid (10−3.6 bar). The main equilibria describing the composition of the fluid inclusions before total homogenization are the following: 1. (a) 2S /af S2 (buffering fS2) 2. (b) H 2 S + 1 2 O 2 /af H 2 O + 1 2 S 2 (buffering fO2). An example of calculation is given at +250°C. One may see that inclusions are just outside the graphite field and that CH 4 CO 2 is very low which explains that methane was not detected by Raman scattering microspectrometry. The origin of the sulphur-rich fluid at Sierra de Lujar is presently poorly understood. It could result from diagenetic processes, similar to those responsible for deposition of sulphur ores in the neighbouring Sierra de Gador.

Mass spectrometric analyses of phenocrysts, containing glass-vapor inclusions quenched in glassy rims of tholeiitic submarine pillow basalts from spreading centers and Hawaii, indicate that water released from the inclusions upon thermal decrepitation is much less than is released from equivalent volumes of the matrix glass enclosing the same phenocrysts. If water released represents water quenched in the two types of glass (inclusion and matrix) at the time of eruption, then the inclusions contained far less water than the magma surrounding the phenocrysts. Such a condition is consistent with a water depleted source mass for the basalts and an influx of water into the melt after inclusion formation but before quenching at the ocean floor. Glass-vapor inclusions within phenocrysts in tholeiitic pillow basalts from the Marianas Interarc Basin released abundant water even though the adjacent matrix glasses contain only 50% more water than Hawaiian matrix glasses. Water contents of matrix glasses from the Marianas pillow rims are very close to experimental saturation values. In contrast, matrix glasses from MORs and Hawaii are distinctly below water saturation. Vesicles in these glasses are most reasonably accounted for by a CO2-dominated vapor phase, because CO2 contents of those basalt glasses closely approximate experimental solubility limits. Glass-vapor inclusions in phenocrysts from the same pillows appear to contain more CO2 than adjacent matrix glasses, implying that a CO2-dominated vapor developed and outgassed prior to eruption and after inclusion formation. Water influx and CO2 degassing combine to make the CO2(CO2 + H2O) ratio of seafloor basalt glasses a minimum value for the magma source mass. The sulfur content of the inclusion glasses is normally very similar to that of the enclosing matrix glass.

Scanning electron microscopy and energy dispersive analysis of fluid inclusion decrepitates in sparry dolomite cements associated with sphalerite mineralization in the Mascot-Jefferson City Missis- sippi Valley-type district of East Tennessee show a markedly lower NaJCa ratio than those in dolomites unassociated with ore. The exploration potential of this variation in fluid inclusion chemistry has been evaluated by analyzing inclusion decrepitates from white sparry dolomite along a 150 m traverse in the New Market West mine area. The traverse extends from the central portion of a large domal collapse- breccia orebody with greater than 3% Zn, into the dolomite-veined, but unmineralized Knox Group limestones. Ratios of Na/Ca as low as 0.8--1.2 were common in dolomite-hosted decrepitates from the high-grade collapse ores. This anomalous decrepitate chemistry was not observed in sparry dolomites less than 12 m from the margins of the breccia bodies where Na/Ca ratios ranged from 1.8 to 3.6. Dolomite cements in IDly grade (

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.

Trace components in fluid inclusions from the Aberfoyle tin-tungsten deposit in Tasmania, Australia, were examined by thermal decrepitation-mass spectrometry. The technique involves the decrepitation of fluid inclusions by stepwise heating in the source of a mass spectrometer. In addition to water, other species identified were carbon dioxide and hydrocarbons. Detailed analysis of these hydrocarbons showed that they ranged in carbon number from C1 up to at least C33 and probably comprised, in part, biological marker compounds, previously unreported in such high-temperature environments. Their presence suggests that the fluid responsible for mineralisation was not entirely magmatic but contained a non-magmatic component evolved through fluid-rock interaction in the sedimentary country rocks.

The RbSr whole-rock age of the Bayerischer Pfahl, a 150 km long, hydrothermally quartz-filled system of en echelon tension gashes and feather joints, is given as 247 ± 21 Ma with an initial Sr isotopic ratio of 0.7133 ± 0.0009. The mean Sr isotopic ratio for minerals from the Nabburg—Wolsendorf mineral district — at the northern end of the Pfahl zone — is 0.7135 ± 0.0007. The concordance in Sr isotopic ratios (at the time of the Lower Triassic) points to a genetic relationship for the mineral-precipitating solutions in the two areas and which must have been homogeneous over a distance of at least 90 km with respect to Sr isotopes. The Sr isotope composition of the quartz- and fluorite/barite mineralisation is not in contradiction to the model of “tectonic pumping” for the Pfahl. The age of the mineralisation of the Pfahl quartz of 247 ± 21 Ma is thought to be connected to the development of continental rifting systems related to the beginning of the opening of the North Atlantic. A by-product of this work is that decrepitation/leaching experiments cannot be used to study the chemical compositions of fluid inclusions.

The volatiles (CO 2 and H 2 O) from the inclusions in fluorite crystals from seven sites of the Mikhalkovo ore deposit were determined. Vacuum heating up to the decrepitation temperature (400°C) was used to extract the volatiles and they were later analysed mass-spectrometrically. The salinity of the mineral-forming solutions (⩽1%) was evaluated using freezing temperature data. On the basis of the analytical results and some geological data, and assuming an equilibrium state between hydrothermal solutions and carbonate, the pH-values of the fluorite-forming media were calculated. In the acidity of the solution vs. temperature plot, the points from the seven ore sites delineate the crystallization field of the Mikhalkovo fluorites. The different crystal habits pertain to different regions of this field.

A large number of fluid inclusions are observed in quartz contained in Au ores. A study of the geochemistry of inclusions from the Linglong Au deposit in Shandong Province shows that ore-forming temperature and pressure, frequency of appearance for critical inclusion, and saline halo of the main Au-bearing veins 108 and 51 increase in the direction of Linglong Fault. We concluded accordingly, that: (1) the Linglong Fault was a conduit structure for mineralization and will form a favourable place for prospecting where the fault intersects a host structure trending east-northeast; (2) distinct differences in geochemical characteristics are present in relation to the fluid inclusions contained in Au-bearing quartz veins and barren quartz veins, with the former having higher homogenization temperatures, appearing frequency for critical inclusion, content of CO2, H2 and CH4, and molar concentration ratio of (H2 + CH4) to CO2, than those of the latter; (3) decrepitation curves for the two sorts of quartz veins have obviously different characteristics; and (4) geochemical characteristics of fluid inclusions present in the quartz of quartz-vein-type Au ore deposits demonstrate that its metallogenetic pressure, salinity, and decrepitation temperature all increased progressively towards the deeper part of the quartz vein, approximating those of altered-rock-type Au ore deposits. We already know of some Au mines where quartz-vein-type Au ore deposits are turned at depth into altered-rock-type Au ore deposits. Therefore, attention should be paid to prospecting for altered-rock-type Au ore deposits below the quartz-vein-type. From this study, we believe that the geochemical study of fluid inclusions in minerals is a new and useful exploration approach, which should be further explored and used.

The evolution of fluid inclusions in synthetic quartz up to decrepitation was followed in situ by X-ray topography. Fluid inclusions could be distinguished from dislocations above the homogenization temperature because of a contrast enhancement of X-ray topographs.

Inductively coupled plasma atomic emission spectrometry (ICP) has been used to investigate the composition of fluid inclusions in samples of pegmatite topaz from Malaysia and carbonatite apatite from Kenya. In this preliminary study we describe a method whereby material ejected from the sample during decrepitation at elevated temperatures is transferred to the plasma by a stream of Ar. Up to 40 elements can be determined simultaneously in the resulting decrepitate. The method is rapid and permits the determination of a number of important elements which, in conventional fluid inclusion isolates, are present in a concentration so low that there are problems of detection even with sensitive methods such as ICP. A further advantage of the ICP-linked decreptiation method is the small sample size (∼ 0.5 g) normally required. Comparison of results obtained by the proposed method and the ICP analysis of leachates for the same sample shows that most elements give higher values of X Na by the decrepitation method. Possible explanations for this difference include: (1) selectivity of decrepitation as a means of nebulishing inclusion contents; (2) hydrolysis and precipitation or adsorption of metal ions during the leaching method; and (3) extraction of Na + ions from the host mineral during leaching. Regardless of these differences on-line decrepitation is a highly efficient method of nebulishing inclusion fluids for introduction into the plasma, and the method has considerable potential as a routine means of analysing inclusions.

A method for the determination of reduced sulfur species in inclusion fluids is described. Inclusion fluids are released by decrepitation in a nitrogen stream, the sulfur species are trapped in a 0.1 M NaOH solution and subsequently determined fluorometrically. Method blanks are low (ca. 3 ng S) compared to yields from vein quartz samples (80-6,700 ng S); the detection limit for reduced S is effectively set by this blank and corresponds to ca. 20 ppm S in the original inclusion fluid for a typical 0.5-g sample yielding a total of 1 mg of volatiles. The method is sensitive to S present as H 2 S or COS but not CS 2 or SO 2 .Analyses of inclusion fluids from unmineralized feeder veins in the Dolgellau gold belt, north Wales, indicate that Au(HS) (super -) 2 predominated over AuCl (super -) 2 as the major gold-transporting complex.

The stability of carbon saturated manganese-iron alloys was studied by means of simulated decrepitation tests, and it was found that the product must contain a minimum of about 5 wt pct iron to be stable during storage. By means of several experimental techniques it was shown that the structure of the carbide phase present in carbon saturated ferromanganese determines whether the alloy is stable. Below the critical iron content of about 5 wt pct, the carbide phase is Hāgg carbide (MnFe)5C2, whereas above about 5 wt pct iron the carbide phase is cementite (MnFe)3C. The role of iron is to stabilize the cementite phase. Experiments with the synthetic manganese carbides, Mn5C2 and Mn3C, showed that the former reacts readily with water whereas the latter is stable.

The decrepitometric method of fluid inclusion study is based on the analysis of acoustic emissions associated with the breaking of fluid inclusions during the heating of mineral grains. The decrepitation behaviour of a mineral depends on its mechanical characteristics, the inclusion size distribution and the composition and density of the inclusion fluid. Where the size of the inclusions is greater than some critical dimension, which depends on the mineral (∼ 15 μm for quartz), there appears to be a broad correlation between the actual fluid inclusion populations and the decrepitometric populations. For such samples containing inclusion fluids with 0–25 wt.% NaCl and low gas content, corrections in the range − 75 ± 20°C to the means of Gaussians fitted to the decrepitometric data give good estimations of the mean temperatures of homogenization of the inclusion populations. For other inclusion size distributions and fluid compositions, particularly if the fluid contains a high gas content, the relationships between the temperatures of homogenization and decrepitation are less precise and estimated homogenization temperatures may not be particularly meaningful. Nevertheless samples may still be compared and classified on the basis of selected peak parameters derived from curve fitting. The decrepigram may therefore serve to “fingerprint” veins of different generations. The present procedures are compared and contrasted with those previously used by other workers.

P-T conditions inferred from fluid inclusions in metamorphic rocks often disagree with the values predicted from mineral equilibria calculations. These observations suggest that inclusions formed during early stages of regional metamorphism continue to re-equilibrate during burial and subsequent uplift in response to differential pressure. P-T conditions accompanying burial and uplift were experimentally simulated by initially forming pure H2O inclusions in quartz at elevated temperatures and pressures, and then re-equilibrating the inclusions in the presence of a 20 wt% NaCl solution such that final confining pressures ranged from 5 kbar above to 4 kbar below the initial internal pressure of the inclusions at the temperature of re-equilibration. In all samples re-equilibrated at confining pressures below the internal pressure, some inclusions were formed that had compositions of 20 wt% NaCl and densities in accord with the final P-T conditions. Additionally, some inclusions were observed to contain fluids of intermediate salinities (between 0 and 20 wt% NaCl). Densities of these inclusions were also consistent with formation at the re-equilibration P-T conditions. The remainder of the fluid inclusions observed in these samples contained pure H2O and their homogenization temperatures corresponded to densities intermediate between the initial and final P-T conditions. In short-term experiments (7 days) where the initial internal overpressure exceeded 1 kbar, no inclusions were found that contained the original density and none were found to have totally re-equilibrated. Instead, most H2O inclusions re-equilibrated until their internal pressures were between ∼750 and 1500 bars above the confining pressure, regardless of the initial pressure differential. In a long-term experiment (52 days), inclusions re-equilibrated at a lower confining pressure than the initial internal pressure displayed homogenization temperatures corresponding to a range in final internal pressures between 0 kbar (i.e. total re-equilibration) and 1.2 kbar above the confining pressure. In experiments where the confining pressure during re-equilibration exceeded the initial internal pressure, densities of pure H2O inclusions increased to values intermediate between the initial and final P-T conditions. Additionally, these inclusions were generally surrounded by a three-dimensional halo of smaller inclusions, also of intermediate density, resulting in a texture similar to that previously ascribed to decrepitation from internal overpressure. In extreme cases where confining pressures were 4–5 kbar above the initial pressure, the parent inclusion almost completely closed leaving only the three-dimensional array of small (5 μm) inclusions, the outline of which may be several times the volume of the original inclusion. Groups of such inclusions closely resemble textures commonly observed in medium- to high-grade metamorphic rocks. Inclusions containing 10 and 42 wt% NaCl solutions trapped at 600 °c and 3 kbar were re-equilibrated at 600 °c and 1 kbar for 5 days in dry argon to evaluate the importance of H2O diffusion as a mechanism of lowering the inclusion bulk density. Salinities of re-equilibrated inclusions obtained from freezing point depressions and halite dissolution temperatures indicate that original compositions were preserved. Density changes similar to those previously described were noted in these experiments, in inclusions showing no visible microfractures. Therefore, density variations observed in inclusions in this study, re-equilibrated under rapid deformation conditions, are considered to result from a change in the inclusion volume, without significant loss of contents by diffusion or leakage.

Mantle-derived xenoliths of spinel lherzolite, spinel pyroxenite, garnet pyroxenite and wehrlite from Bullenmerri and Gnotuk maars, southwestern Victoria, Australia contain up to 3 vol.% of fluids trapped at high pressures. The fluid-filled cavities range in size from fluid inclusions (1–100 μm) up to vugs 11/2 cm across, lined with euhedral high-pressure phases. The larger cavities form an integral part of the mosaic microstructure. Microthermometry and Raman laser microprobe analysis show that the fluids are dominantly CO2. Small isolated inclusions may have densities ≥1.19 g/cm3, but most inclusions show microstructural evidence of partial decrepitation during eruption, and these have lower fluid densities. Mass-spectrometric analysis of gases released by crushing or heating shows the presence of He, N2, Ar, H2S, COs and SO2 in small quantities; these may explain the small freezing-point depressions observed in some inclusions. Petrographic, SEM and microprobe studies show that the trapped fluids have reacted with the cavity walls (in clinopyroxene grains) to produce secondary amphiboles and carbonates. The trapped CO2 thus represents only a small residual proportion of an original volatile phase, which has undergone at least two stages of modification — first by equilibration with spinel lherzolite to form amphibole (±mica±apatite), then by limited reaction with the walls of the fluid inclusions. The inferred original fluid was a CO2-H2O mixture, with significant contents of (at least) Cl and sulfur species. Generation of this fluid phase in the garnet-peridotite stability field, followed by its migration to the spinel peridotite stability field, would provide an efficient mechanism for metasomatic enrichment of the upper mantle in LIL elements. This migration could involve either a volatile flux or transport in small volumes of silicate melt that crystallize in the spinel peridotite field. These observations suggest that some portions of the subcontinental upper mantle contain large reservoirs of free fluid CO2, which may be liberated during episodes of rifting or magmatism, to induce granulite-facies metamorphism of the lower crust.

A suite of coarsely crystalline samples of crinoidal limestone adjacent to a PbS-CaF2-CaCO3 vein in the North Pennine orefield (Greenhow Rake) was analysed by three independent methods [Inductively Coupled Plasma emission spectroscopy (ICP), Mass Spectrometry (MS) and Gas Chromatography (GC)], in order to determine the nature and origin of trace elements and volatiles released on heating and thermal decrepitation, to establish whether fluid inclusions from the host limestone differed in composition from those within the vein, and to assess the value of the results obtained for mineral exploration. The ICP method gave reproducible results for Ca, Na and K, and significant values for Pb and Zn. Na and K correlate with H2O levels determined by MS/volumetric analysis, suggesting their coexistence within fluid inclusions. No such correlation was found for Pb and Zn, suggesting that these elements were derived by volatilisation, perhaps from traces of galena and sphalerite. Methane showed no correlation with H2O and a source other than aqueous fluid inclusions is thought probable for this volatile.The vein calcite showed much lower K/Na fluid ratios (0.05 cf 0.1–0.2), than the limestones. The limestone-hosted fluids occur predominantly in crinoid ossicles and are believed to represent early pre-mineralisation fluids, unrelated to those associated with veining. Combined ICP and MS techniques may be of value in investigating samples where fluid inclusions are too small for microthermometric and optical analysis.

Basic technique for the extraction and isotopic analysis of fluid inclusions in halite was investigated using synthetic single crystals of halite and three natural halite samples from China. Vacuum ball-mill, vacuum decrepitation and vacuum melting methods were examined for the extraction of fluid inclusions. Results of analyses on δD and δ18O of the water in fluid inclusions extracted by the ball-mill method from synthetic single crystals agreed with those of the mother solution from which the single crystals were formed. Although the δ18O value of the water extracted by the melting method agrees well with that of the mother solution, the δD value was about 7‰ more negative than that of the mother solution. There was a great difference in both δD and δ18O of the water extracted by the two methods applied to the identical natural halite samples; the melting method gave consistently more negative values for both δD and δ18O compared with those by the ball-mill method. The difference was interpreted as a result of the hydrolysis of NaCI with H2O combined with the formation of oxides of alkaline-earth elements in brine inclusions in natural halite samples in the process of the melting method. Although the melting method has an advantage of complete recovery of volatiles in halite samples, the chemical and isotopic compositions of volatiles can not be retained owing to a variety of thermal reactions which occur at high temperatures. It was concluded that the ball-mill method is much superior to the melting method in order to obtain isotopic and chemical information on fluid inclusions in halite, though the recovery of fluid inclusions by the ball-mill method is not 100%, and high concentrations of Mg2+ and Ca2+ in fluid inclusions require correction for the δD and δ18O values of the water.

Models for the formation of crustal granulites, which include the metamorphism of anhydrous lithologies1,2, the extraction of hygroscopic granite melts3,4 and fluxing by CO25–7 constrain the thermal and geochemical evolution of the lower crust and its interaction with mantle-derived volatiles. Here we present abundances and carbon isotope compositions of CO2 in fluid inclusions in quartz and garnet from gneiss–granulite pairs from the incipient char-nockite quarries of southern India, determined by a stepped combustion/thermal decrepitation carbon–extraction technique, which quantifies problematic sample contamination and allows precise lithological control. The results show that the CO2 in incipient charnockite is more abundant and isotopically heavier than the CO2 in associated gneiss, providing evidence for the influx of CO2-rich fluids during their formation. The inferred carbon isotope compositions of these fluids are consistent with a mantle source, and at Ponmudi, the isotopic composition of coexisting graphite and CO2 implies fluid/rock volume ratios in excess of 0.15.

Besides sodium and potassium, manganese and iron were found in significant amounts. The results confirm that the base metal and silver transporting capability of some early magmatic fluids is considerable. Chloride complexes were the most favorable species for transporting silver and base metals. An electron probe in the energy dispersive mode was used to analyze the precipitates formed upon the decrepitation of fluid inclusions.--Modified journal abstract.

The quaternary oxides Ba 2 YCu 3 O 6.5+ x , Ba 2 GdCu 3 O 6.5+ x and Li 8 Mg 4 Cu 12 O 20+ x with constant 2:1:3 ratio of metal atoms can be treated as pseudobinary oxides MO z with variable oxygen content at octahedral interstitial sites of bcc M=Ba 2 YCu 3 , Ba 2 G dCu 3 or fcc M=Li 8 Mg 4 Cu 12 derivative structure. Some properties of interstitial oxides are similar as in interstitial hydrides: Order-disorder transitions, metastable phases, spinodal decomposition, decrepitation, void formation, corrosion.

Abundance ratios of major and minor elements in single fluid inclusions from the synmetamorphic copper deposit at Mount Isa (Queensland, Australia) have been estimated by electron microprobe analyses of salt residues liberated by thermal decrepitation. X-ray intensity ratios were calibrated using thin mixed-salt standards. Measured cation ratios are within ±20% of the values in the parent fluid inclusion, provided that decrepitation can be achieved below 400°C. Wave-length dispersive spectrometry (WDS) used here is less accurate for major salt components, but more sensitive for minor elements, than energy dispersive spectrometry (EDS) used recently by Haynes and Kesler (1987). Results demonstrate the advantage of the single-inclusion method for studying paragenetically complex ore samples containing several generations of inclusions. Microprobe analyses could be assigned to single fluid inclusions or small groups of inclusions, which were texturally interpreted as primary and secondary, and which were characterized by microthermometric measurements prior to decrepitation. In favourable cases, the combination of microthermometry and microprobe analysis allowed estimation of absolute cation concentrations in individual fluid inclusions. Syntectonic metasomatism at Mount Isa involved highly calcic brines with major KCl and AlCl3 in early dolomitic alteration preceding copper mineralization. Compositionally similar fluids were again trapped on cracks postdating mineralization. The main stage of copper mineralization was deposited by a NaCl-dominated brine with a composition of about 2 m (mol/kg) NaCl, 0.2 m KCl, 0.01 m each of S (as HS− + H2S) and AlCl3, and with MgCl2 and FeCl2 near or below their respective detection limits of 0.002 and 0.01 m.

The major element chemical composition of inclusion fluids from Mississippi Valley-type deposits has been evaluated semiquantitatively using scanning electron microscopy and energy dispersive analysis of individual inclusion decrepitates in ore and gangue minerals. The volcano-shaped decrepitates are produced by heating polished plates above the decrepitation temperature of the inclusions, forcing the enclosed fluids to the surface where the nonvolatile components precipitate. Energy dispersive analyses of these precipitates, here called decrepitates, are expressed in cation and anion weight ratios and carry errors of + or - 10 percent.Application of this technique to fluid inclusions in sphalerite and dolomite from the Mascot-Jefferson City zinc district of East Tennessee and the Pine Point lead-zinc district of the Northwest Territories reveals that fluids attending sulfide deposition in both districts are dominantly Na-Ca chloride brines. Subordinate but significant amounts of K, Mg, and locally Sr and Fe are also present. CaCl 2 /(CaCl 2 + NaCl) weight ratios vary greatly among the samples from both deposits but are consistently lower (0.1-0.3) in gangue dolomites not associated with sulfides than in sphalerite and ore-stage dolomite (0.2-0.6 at East Tennessee; 0.4-0.8 at Pine Point). Although Cl is the only significant anion detected in the East Tennessee analyses, a significant proportion of decrepitates from sphalerite and ore-associated dolomite at Pine Point contain appreciable S, occasionally in amounts equal to or exceeding Cl.Mass balance calculations show that the increase in the CaCl 2 /(CaCl 2 + NaCl) ratio in decrepitates associated with ore from both districts cannot result simply from limestone dissolution at the site of brecciation and mineralization. Instead, they appear to require either fluid mixing or a chemical evolution of the fluids entering the carbonate host rocks. The presence of significant Ca and S together in the Pine Point fluid inclusions and the absence of daughter anhydrite requires that most S was reduced, which lends support to mixing models involving metal-rich brines and sulfur-rich waters in ore formation in that district. Further, the presence of excess S in ore-stage decrepitates from Pine Point suggests that sulfide de-position there was limited by the amount of metal-rich brine entering the H 2 S-rich barrier reef complex. In contrast, the lack of detectable sulfur in the decrepitates from Mascot-Jefferson City ores suggests that mineralization there may have been limited by the availability of S, but does not permit selection between mixing and fluid evoluton as a cause of ore deposition.

In this article, the application of the hydrogen decrepitation (HD) process to the production of rare earth containing permanent magnets is discussed. It is shown that the HD process can be applied successfully to the production of SmCo 5 − , Sm 2 (Co, Fe, Cu, Zr) 17 − and Nd 2 Fe 14 B-type magnets. The particular HD conditions for each category of permanent magnet are described. The characteristics of the HD powder of all three alloy types are compared with those of the normal milled material and it is seen that significant advantages accrue from the use of the HD powder.

Burlinson, K., Dubessy, J.C., Hladky, G. and Wilkins, R.W.T., 1983. The use of fluid inclusion decrepitometry to distinguish mineralized and barren quartz veins in the Aberfoyle tin-tungsten mine area. Tasmania. In: G.R. Parslow (Editor), Geochemical Exploration 1982. J. Geochem. Explor., 19: 319–333. In the Aberfoyle Sn/W district of N.E. Tasmania, mineralization is in quartz veins associated with Devonian granite. The host rocks to the mineralization are folded Silurian quartzites, greywackes and shales and these also contain abundant pre-mineralization quartz veins which can be difficult to distinguish from irregularly mineralized ore veins on geological criteria, especially in drill core. It was found that the decrepitation characteristics of the quartz, chiefly the intensity ratio of high and low temperature peaks, which are developed in all decrepigrams, enable a distinction between the two generations of veins to be readily made. The differences between the fluid inclusions in the two generations of veins are relatively subtle, however it seems clear that “CO2-rich” inclusions having a wide range of composition and density are the main source of decrepitation events and that the major differences in decrepitation behaviour can be correlated with differences in average homogenization temperature of these inclusions. Even those ore veins which have undergone moderate ductile deformation have the typical signature of their origin. The decrepitation results are supported by analyses of inclusion gases by Raman microprobe. These analyses differentiate a third group of veins which are possibly unmineralized veins belonging to a separate hydrothermal system.

The present work has shown that hydrogen decrepitation of a 2:17-type Sm (Co0.673 Cu0.080Fe0.222Zr0.025)8.92 alloy is a very rapid and convenient means of producing powdered material for the production of polymer-bonded permanent magnets. The magnets made from the hydrogen decrepitated powder (average particle size ∼100μm) exhibited improved demagnetization loop shapes, higher intrinsic coercivities and improved elevated temperature stability when compared with the magnets produced from the standard milled powder material (average particle size ∼40μm). These differences in properties have been related to the differences in the character of the powders produced by the two methods of decrepitation.

A high-pressure heating-freezing stage constructed at our laboratory permits continuous microscopic observations of fluid inclusions during experimental runs in pressure-temperature paths (patent No. 85.025.12). Conditions currently attainable are − 180° to + 450°C and 1 to 900 bar. Runs were performed on fluid inclusions in fluorite to study the mechanism of stretching and deformation of the cavities by overheating under confining pressure. Confining pressures of 200, 410 and 620 bar were applied on aqueous (H2O, 15 eq.wt.% NaCl) cogenetic secondary inclusions and hydrocarbon primary inclusions, having volumes between 103 and 105μm3 in Tunisian fluorite from Djebel Guebli. In most cases leakage (deformation with loss of content, sometimes observed at 1 bar) was avoided under confining pressure and stretching (yielding with volume change) is the main mechanism observed. Combining our experiments with the law of stretching at 1 bar, we have tried to derive an empirical law of the pressure effect: P I s =P I s1 +KPc (mean value of K=07) Confining pressures permit to reach very high temperatures of stretching. The values of internal pressure at the stretching temperatures calculated from the isochore curves of the H2ONaCl system are between 850 and 1100 bar. The values of ΔTh increase regularly with the amount of overheating ΔToh; on the curves ΔTh = f(ΔToh) we observed two parts: in the first part, the value of Th is constant, that means that the internal pressure is not sufficient to induce a deformation of the mineral; and in the second part, the function increases in relation to plastic deformations of the mineral; the latter deformations are a function of the temperature. When an external overpressure is applied on a preliminary stretched inclusion, we observed a decrease of the new homogenization temperature (Th), that means a decrease of the inclusion volume. This reversible effect could be related to a mechanism of relaxation of the deformation. We have observed that decrepitation of fluid inclusions could also occur by rapid releasing of pressure as well as by overheating. This should be taken into account for interpretation of experiments in blind autoclaves. Those observations could be explained by a microfracturing effect connected with dislocations in a matrix with elasto-plastic deformation under change of temperature, and the possibility of strain relaxation.

A decrepitation instrument has been constructed which provides rapid, reliable and fully automated analyses and it has been used to analyse some 3 000 samples to evaluate the application of decrepitation data in mineral exploration. Monomineralic samples of 0.5 g of crushed, sieved grains are analysed and extensive studies have been done using magnetite, pyrite, galena, carbonates and quartz. Quartz vein samples often show three or more distinct decrepitation peaks. A peak at 570 °C is related to the weakening of quartz during the alpha to beta phase transition, which facilitates the decrepitation of inclusions. A low temperature peak (below 300 °C) is due to the presence of gas-rich inclusions (the most common gas being CO2), while the intermediate temperature peak is due to primary inclusions. Pyrite and quartz of hydrothermal origin usually give strong decrepitation responses whereas sedimentary pyrite or low temperature cherts give negligible decrepitation. Carbonate samples give very intense decrepitation up to their thermal decomposition temperatures, at which point the decrepitation suddenly ceases. Because of the speed and low cost of the analyses, the technique is useful for exploration projects and for scanning and selecting samples prior to conventional microthermometric studies., Un instrument de décrépitation a été construit qui fournit des analyses rapides, sûres et complètement automatisées. Il a été employé pour analyser quelque 3 000 échantillons afin d'évaluer l'application de cette méthode à la prospection minière. Les échantillons monominéraux de 0,5 g de grains broyés et criblés sont analysés ; des études ont été faites employant magnétite, pyrite, galène, carbonates et quartz. Les échantillons des filons de quartz montrent souvent au moins trois pics distincts de décrépitation. Un pic à 570 °C est lié à l'adoucissement du quartz lors de la transition de phase α-β, qui favorise la décrépitation des inclusions. Un pic à une température inférieure à 300 °C est causé par la présence d'inclusions riches en gaz (le plus commun étant CO2) et le pic de température intermédiaire est causé par les inclusions primaires. Pyrite et quartz d'origine hydrothermale donnent normalement des réponses de décrépitation fortes, alors que la pyrite sédimentaire ou le chert de basse température donnent une décrépitation négligeable. Les échantillons de carbonate donnent une décrépitation très intense jusqu'à leur température de décomposition thermique, à laquelle la décrépitation cesse soudainement. Par sa vitesse et son faible coût, la technique est utile pour les projets de prospection et pour la sélection des échantillons en vue d'études microthermométriques conventionnelles., Burlinson Kingsley. An instrument for fluid inclusion decrepitometry and examples of its application. In: Bulletin de Minéralogie, volume 111, 3-4, 1988. Inclusions fluides. IXth symposium on fluid inclusions. University of Oporto – May 1987.

A sample of powdered mineral is heated in an electric furnace with a constant rate of increase in temperature. By means of a sensible microphone the frequency of the decrepitation against temperature is recorded. The interpretation of the delivered curve serves to indicate approximate temperature of deposition for the tested mineral. An original filtering system is utilised to reduce or to eliminate noise interference in microphonic signals and to facilitate the interpretation., Un échantillon de minéral pulvérisé est chauffé dans un four à température régulièrement croissante. A l'aide d'un microphone sensible on enregistre la fréquence de décrépitation en fonction de la température. L'interprétation de la courbe obtenue permet d'avoir la température approchée de dépôt du minéral. Un dispositif de filtrage original est utilisé pour réduire ou éliminer les bruits parasites des signaux microphoniques et facilite l'interprétation., Pulou Raymond, Baudracco-Gritti Célestine. Un enregistreur décrépitométrique à filtrage électronique. In: Bulletin de Minéralogie, volume 101, 4, 1978. pp. 402-405.

The effects of feldspar and mica contamination on the analyses of fluid inclusion contents, in quartz from granitic rocks, are evaluated when the fluid inclusions are analysed by the decrepitation-inductively coupled plasma emission spectroscopy (D-ICP) method.

Volatile ratios (primarily of H2O and CO2) in individual silicate melt (glass) inclusions in minerals have been analyzed using laser volatilization and mass spectrometry. A Nd-glass laser was used to produce 50-micrometer diameter pits in silicate melt inclusions. Released volatiles were analyzed directly with a computer-controlled quadrupole mass spectrometer. The detection limits for CO2 and H2O were on the order of 3 x 10(-14) and 3 x 10(-13) moles, respectively. The reproducibility for CO2/H2O was better than +/- 9%. The total range of volatile ratios from vitreous silicate glass inclusions contained in a suite of Galapagos lavas were: 0.018 to 1.193 for CO2/H2O; 0.002 to 0.758 for CO/H2O; 0 to 0.454 for CH4/H2O; and 0 to 0.432 for Ar/H2O. The mean CO2/H2O from the propagating rift (0.245 +/- 0.068) silicate glass inclusions is significantly lower than that of the actively failing rift (0.641 +/- 0.241); this difference probably reflects different degrees of degassing during magmatic histories for the two regions. Relatively undifferentiated failing rift magmas must have relatively short crustal residence times prior to eruption and, therefore, have not undergone significant degassing of CO2, as would appear to be the case for the more highly fractionated propagating rift magmas. The laser-mass spectrometric system described herein has the ability to act as a point-source probing device that can differentiate between the various volatile sites in minerals and rocks (as well as synthetic materials) on a micrometer scale.

Kesler, S.E., Haynes, P.S., Creech, M.Z. and Gorman, J.A., 1986. Application of fluid inclusion and rock-gas analysis in mineral exploration. In: C.E. Nichols (Editor), Exploration for Ore Deposits of the North American Cordillera. J. Geochem. Explor., 25: 201--215. Gases are known to form haloes around presently active geothermal systems and might be useful in exploration for older, extinct hydrothermal systems. Gases from such extinct hydrothermal systems can be liberated for analysis from fluid inclusions in hydrothermal minerals by thermal decrepitation or they can be desorbed from alteration mineral surfaces by heating. The most abundant of these gases, besides HsO, are usually CO2, CH4, CO and N s. We have used a gas chromatograph to analyze these gases in fluid inclusions in jasperoid around the Pueblo Viejo gold-silver deposit, in vein minerals from the Creede silver-lead-zinc deposit, and from clays in the alteration cap overlying veins at Creede to test for gas haloes useful in exploration. At Pueblo Viejo CO s abundances in the jasperoid range from less than 1 mole percent (with respect to the system CH4-CO 2CO-N2-H20 ) in the ore zone to as much as 6 mole percent in surrounding, barren jasperoid. Fluid inclusion analyses at Creede suggest that a drop in the CO 2 content of the fluid may relate to ore deposition and clay directly above veins has large amounts of adsorbed CO s . These results suggest that primary gas abundances exhibit patterns in and around hydrothermal ore deposits that can be used in mineral exploration.

Strong discrepancies between densities of the fluids trapped in fluid inclusions (F.I.) and P-Tp couples deduced from other geological considerations are common. So, it was decided to test experimentally the possible F.I. re-equilibrations when bringing the host crystal in P-Tp conditions, different from trapping conditions. Runs were conducted on synthetic quartz in a gas apparatus and in a Griggs solid medium apparatus. The following modifications of the F.I. were observed: 1. (1) drastic shape changes of the primary F.I., and appearance of clusters or trails of small secondary inclusions sometimes related to a crack 2. (2) lowering of the fluid densities. Such a re-equilibration is a decrepitation phenomenon: first, hydraulic fracturing, then sealing of the cracks with appearance of secondary inclusions. When using the gas apparatus, the new measured densities are in very good accordance with the nominal P-Tp conditions. When using the solid-medium apparatus, the new densities are surprisingly low relative to the nominal P-T conditions, probably due to a strongly anisotropic stress state in the apparatus.

The numerous small (1–3 μ) gaseous and liquid inclusions in granite minerals were extracted from the samples by grinding in vacuum at normal temperature. This procedure is quantitative, contrary to the separation by decrepitation at high temperatures and also avoids the higher possibility of reactions inherent to the latter method. A description is given of the vacuum ball-mill that grinds the mineral particles (grain size: 1–2 mm) in a closed and evacuated container. The ball-mill and the balls show no noticeable gas development. This was tested by trial runs with optically pure quartz. In the course of the development of this procedure, the origin of the large amounts of nitrogen (up to 1 ml NTP/g mineral) found in former gas-extracts from minerals ground in vacuum ( Elinson 1949 and 1956) was cleared. Samples of 0.5 to 1 g are sufficient for this method of extraction in combination with a vacuum-apparatus of the type used by Wahler (1955) for the determination of partial pressures. The samples were taken from four postorogenetic hercynian granites and their pegmatites, from the Black Forest and the Vosges. Their inclusions could be expected to be mainly of primary origin. Furthermore two other granites, a pegmatite, two samples of olivine from nodules in basalt and a cyanite were examined. The following amounts of gases (in mm 3 NTP/g) were found in the minerals of the young granites: H 2 10–150, CO 2 0–40, CO 0–4, N 2 1–8 and in the minerals of the pegmatites: H 2 2–60, CO 2 0–20, CO 0–2, N 2 1–9, CH 4 0–2, C 2 H 6 traces. The amounts in the olivines were noticeably lower. It was found that most of the hydrogen, at any rate in biotite, is not contained in inclusions but dissolved in the mineral. A critical discussion of the results of former CO 2 determinations, together with own experimental data, shows that the large amounts of CO 2 found by Khitarov and Rengarten (1956) and most of those found in this investigation originate from carbonates. It is shown that traces of carbonates in samples of hard silicate minerals are mostly decomposed not only by heating but also by grinding in vacuum. Thus, no known method is accurate in the selective analysis of free carbon dioxide in small inclusions. The experiments demonstrate that carbon monoxide also is generated from carbonates in amounts comparable to the total amounts found. Thus, the above values for free CO 2 and CO are upper limits. The actual amounts can be lower by magnitudes. It was found that CO 2 in the examined granite quartzes is mainly bound to Ca in carbonates. The water contents in the inclusions of all the samples were also determined in the vaccuum apparatus (10–6300 mm 3 NTP/g). The dissolved chloride and sulfate anions were determined chemically. The dissolved cations K + , Na + and Ca ++ were also determined in most of the granite and pegmatite quartzes, in the olivines and in the sample of cyanite. The main and definite components of the inclusions in most of the examined granites and pegmatites are a quite concentrated solution of salts and nitrogen as gaseous phase.

A NEW METHOD OF REFRACTIONATION IS PRESENTED WHICH ENABLES ANALYSIS OF WET-SIEVED DRIED AGGREGATES GIVING WATER-STABLE AGGREGATE-SIZE DISTRIBUTION IN THE DRY STATE. SOIL AGGREGATES HEATED TO VERY HIGH TEMPERATURES ARE DISINTEGRATED AND HAVE LOWER WATER STABILITY (THAN THE OPTIMUM VALUE OF AGGREGATION AND WATER STABILITY), DUE TO THE PHENOMENON OF SELF-INDUCED SHATTERING (AUTOPHORETIC DISPERSION), WHICH CAN BE COMPARED TO DESICCATION, DECREPITATION, OR INCIPIENT FUSION. EFFECT OF HEAT ON SOILS CAN NOW BE CLASSIFIED AS FOLLOWS: (1) INITIAL SHRINKAGE AT VERY LOW HEATING TEMPERATURE, (2) LOOSE-PAIR FORMATION, RESULTING IN INSTANTANEOUS REHYDRATION OF THE SEMIHYDRATED AGGREGATES, AND HENCE, DECREASED WATER STABILITY, (3) COLLAPSE OF THE CLAY STRUCTURE, FOLLOWED BY AGGREGATION AND HIGH WATER STABILITY, (4) AN OPTIMUM TEMPERATURE OF HEATING AT WHICH AGGREGATION AND WATER STABILITY ARE BOTH AT A MAXIMUM, AND (5) THE DISINTEGRATION THAT TAKES PLACE AT HIGH TEMPERATURES OF HEATING AND RESULTS IN DECREASED WATER STABILITY, DUE TO AUTOPHORETIC SHATTERING OF THE SOIL AGGREGATES IN CONTACT WITH WATER BECAUSE OF ABSORPTIVE INTERACTIONS.

It has been found by the writers that, in the majority of cases, the decrepigraphs of quartz have a form similar to that shown in Fig., 3, which has three inflexion points where the rate of decrepitation increases suddenly., From microscopic observation of the heated samples of quartz, it has been interpreted that the popping at the first peak in the curve is produced by the breaking out of liquid inclusions., The third peak shows the cracking of crystals caused by the existence of cleavage and parting, volume change followed by transition, anisotropy of thermal conductivity and expansion, presence of solid inclusions, or lattice imperfections., And the second peak may be observed as superposition of the above-mentioned two kinds of sound., From these results, it has been found that, as the inflexion point at the beginning of the first peak can be taken to represent the temperature of complete filling of the inclusions with an allowance for possible overshoot, the decrepitation method may be used for measuring temperature of forming the inclusions instead of the heating stage-microscope method., However, in some cases when liquid inclusions are scarcely found in the sample, or when the sound produced by the breaking out of the liquid inclusion is too low to be detected, the inflexion point at the beginning of the second peak or the third peak may be in danger of being mistaken for that of the first peak.