Fluid Inclusion Gas Research Articles

Determination of methane content in NaCl–H2O fluid inclusions by Raman spectroscopy. Calibration and application to the external part of the Central Alps (Switzerland)

The reconstruction of the entrapment conditions of geological fluids requires determining the volumetric and composition properties of the inclusions containing these fluids. In some cases, the analytical data necessary for PVTX determination cannot be obtained from microthermometry. The quantification of the dissolved gases in aqueous fluid inclusions by Raman spectroscopy, following proper calibration of the instrument and methodology, can provide alternative data. In the present study, the intensity of the Raman signal of the symmetric stretching vibrational mode of methane was calibrated in order to (1) determine CH4 concentration in pure and saline water and (2) quantify the molar fractions of H2O and CH4 in the gas phase. High-pressure optical cell (HPOC), i.e. a pressurization system connected to a silica microcapillary heated on a customized heating–cooling stage, reveals to be much more convenient and accurate than synthetic fluid inclusions. Moreover, a wide range of pressure, temperature, and salinity can be covered by this methodology. Over 1000 measurements were produced to define the calibration curves, covering the ranges in temperature, pressure and salinity of 60–180°C, 30–1000bar, and 0–4mol.kg−1 NaCl, respectively, which corresponds to a CH4 molality up to 0.6mol.kg−1. The CH4 solubility vs. CH4/H2O Raman peak area ratio was fitted by a second-order polynomial curve (R2=0.996). In the gas phase, the molar fraction of H2O vs. Raman peak area ratio is fitted by a straight line (R2=0.990). The calibration was applied to a set of natural fluid inclusions trapped within late quartz Alpine fissure of the external part of the Central Alps (Switzerland). The determination of CH4 concentration in the studied fluids provided valuable insight on conditions of trapping and on the pressure regimes prevailing in this low-grade metamorphic setting.

Provenance and burial history of cement in sandstones of the Northbrook Formation (Carboniferous), western Newfoundland, Canada: A geochemical investigation

The Carboniferous North Brook Formation (western Newfoundland, Canada) consisting of fluvial/lacustrine arkosic litharenites has undergone two cementation cycles. The first cycle comprises chlorite followed by minor quartz and calcite. Mono-phase aqueous fluid inclusions hosted in first-cycle calcite reflect precipitation in a near-surface meteoric diagenetic environment. Chlorite linings and cements generally inhibit precipitation of quartz overgrowths, thus maintaining open pore space until a subsequent cycle when temperatures are within the oil window. The second cycle comprises chlorite followed by calcite which hosts two-phase fluid inclusions with homogenization temperatures ranging from 91.7 to 120.7°C and salinity from 6.3 to 8.4eq. wt.% NaCl. These results suggest conditions in-line with a deep burial environment, and calculated fluid inclusion isochors stipulate a trapping temperature of around 132°C and pressure of 500bar (5km hydrostatic pressure) for these cements. Quantitative fluid inclusion gas analysis further confirms that fluids were sourced from evolved meteoric fluids with fluctuating CO2:CH4:N2 ratios. Manganese analysis confirms an oxidizing environment for the first-cycle calcite cement but a reducing one for the infilling second-cycle cement. Both cements have similar REE signatures, are slightly LREE-depleted, and during migration the fluids were influenced by the sedimentary host rock. Although there is a prominent negative Ce anomaly, there is no Eu anomaly in the cements. The δ13C and δ18O values are mostly in the negative in the calcite cement hosted in the coarse-grained clastics, which were influenced by migrating brines and/or hydrocarbons.In the diagenetic history of this sedimentary basin, the first cementation event is characterized by chlorite, quartz and calcite emplaced under shallow, oxidizing meteoric water conditions and appropriate temperatures. A diagenetic hiatus ensued until the units were more deeply buried. At this stage, a second generation of cement characterized by minor chlorite and major calcite, infilled vugs and voids under higher temperatures equivalent to the upper limit of the oil window and 5km burial depth. The lack of porosity precludes the North Brook Formation from being a petroleum reservoir although limited petroleum may have been sourced during the geologic history.

A new method of reconstituting the P–T conditions of fluid circulation in an accretionary prism (Shimanto, Japan) from microthermometry of methane-bearing aqueous inclusions

In paleo-accretionary prisms and the shallow metamorphic domains of orogens, circulating fluids trapped in inclusions are commonly composed of a mixture of salt water and methane, producing two types of fluid inclusions: methane-bearing aqueous and methane-rich gaseous fluid inclusions. In such geological settings, where multiple stages of deformation, veining and fluid influx are prevalent, textural relationships between aqueous and gaseous inclusions are often ambiguous, preventing the microthermometric determination of fluid trapping pressure and temperature conditions.To assess the P–T conditions of deep circulating fluids from the Hyuga unit of the Shimanto paleo-accretionary prism on Kyushu, Japan, we have developed a new computational code, applicable to the H2O–CH4–NaCl system, which allows the characterization of CH4-bearing aqueous inclusions using only the temperatures of their phase transitions estimated by microthermometry: Tmi, the melting temperature of ice; Thyd, the melting temperature of gas hydrate and Th,aq, homogenization temperature. This thermodynamic modeling calculates the bulk density and composition of aqueous inclusions, as well as their P–T isochoric paths in a P–T diagram with an estimated precision of approximatively 10%.We use this computational tool to reconstruct the entrapment P–T conditions of aqueous inclusions in the Hyuga unit, and we show that these aqueous inclusions cannot be cogenetic with methane gaseous inclusions present in the same rocks. As a result, we propose that pulses of a high-pressure, methane-rich fluid transiently percolated through a rock wetted by a lower-pressure aqueous fluid. By coupling microthermometric results with petrological data, we infer that the exhumation of the Hyuga unit from the peak metamorphic conditions was nearly isothermal and ended up under a very hot geothermal gradient.In subduction or collision zones, modeling aqueous fluid inclusions in the ternary H2O–CH4–NaCl system and not simply in the binary H2O–NaCl is necessary, as the addition of even a small amount of methane to the water raises significantly the isochores to higher pressures. Our new code provides therefore the possibility to estimate precisely the pressure conditions of fluids circulating at depth.

Fluid inclusion and mineralization of Dafulou tin deposit in Dachang metal district, Guangxi, south China

Based on the study of the petrology, mineralogy, structural geology and fluid inclusion of the Dafulou ore deposit in the Dachang ore field, the ore deposit geology and ore-forming fluids were analyzed. It shows that there are five main hydrothermal alteration types in the Dafulou ore district, namely the silicification, carbonate, sericite, pyrite and pyrrhotite. The mineralization types are composed of the stratiform type, interlayer type and stockwork type. The ore textures present as metasomatic texture, euhedral-subhedral granular texture and solid solution texture. The ore structure consists of massive structure, dissemination structure, fine veined structure, stockwork structure and brecciated structure. Four ore types are recognized, namely the disseminated ore, dense massive ore, veinlet ore and brecciated ore. Six types of fluid inclusions are determined, i.e. the single-phase gaseous fluid inclusions, single-phase salt solution fluid inclusions, two-phase vapour-rich fluid inclusions, two-phase liquid-rich fluid inclusions, three-phase CO2-rich fluid inclusions and solid(s)-bearing fluid inclusions, all of which form in three dominant temperature scopes, 120–150, 230–270, 350–460 °C. But, the majority of them form in the high temperature environment (350–460 °C). The tectonism plays an important role in the mineralization, which usually controls the scale, occurrence and shape of the Sn orebody. There are four types of hydrothermal fluid systems, H2O-NaCl-CaCl2, H2O-CaCl2, H2O-NaCl-MgCl2 and H2O-MgCl2. Similar to the other ore deposits in the Dachang ore field, there also exists the multiple source of ore-forming fluids. Overall, the Dafulou ore deposit should be the result of the crust-mantle interaction.

Paleoproterozoic Mississippi Valley Type Pb–Zn mineralization in the Ramah Group, Northern Labrador: Stable isotope, fluid inclusion and quantitative fluid inclusion gas analyses

Mississippi Valley Type (MVT) Pb–Zn sulfide mineralization is common in Phanerozoic rocks but relatively few MVT deposits have been reported from Paleoproterozoic rocks. This study investigates the genesis of numerous Pb–Zn showings in the ca.2.0Ga Ramah Group, northern Labrador. Pb–Zn mineralization is hosted within the Reddick Bight Dolomite Member (RBDM), Ramah Group. The RBDM is characterized by a well developed secondary porosity associated with solution dissolution of tepee structures in the dolomite. Mineralization occurs as open fill in this secondary porosity, with dark-brown sphalerite, galena and pyrite with gangue quartz, dolomite, calcite and feldspar. The presence of blocks of mineralized RBDM in thrust faults indicates that mineralization predates propagation of these faults during the Torngat Orogeny from 1.85 to 1.87Ma.Fluid inclusion analysis of sphalerite has identified H2O–NaCl–CaCl2+CO2±N2±CH4 mineralizing fluids with high salinities (up to 19.4eq.wt.% NaCl+CaCl2) and homogenization temperatures of 104 to 177°C. The presence of significant volatiles in the mineralizing fluids has been confirmed through quantitative fluid inclusion gas analysis of sphalerite, which has recorded 5.9mol% CO2. Fluid inclusion data from quartz suggests high temperature (135 to 231°C), high salinity (up to 20.5eq.wt.% NaCl+CaCl2) fluids with significant volatile contents (quantitative fluid inclusion gas analysis up to 21.5mol% CO2).Carbon isotope data show a decrease in δ13C from host dolomite (−1.3±0.9‰) through pre-ore dolomite (−4.7±1.5‰) to post-ore calcite (−5±1.7‰), indicating an influx of isotopically light hydrocarbon-bearing fluids. The δ34S isotopic ratios range from 8.3 to 11.1‰ for early pyrite mineralization, 23.3 to 31.8‰ for late stage pyrite, 16.7 to 32.9‰ for galena and 23.2 to 33.8‰ for sphalerite. The relatively high δ34S values associated with Pb–Zn mineralization, high fluid temperatures (>175°C) and presence of CO2 fluids indicate ore deposition was associated with thermochemical sulfate reduction. Pb isotope data from galena separates suggests that the Pb was derived from a relatively non-radiogenic source consistent with the Archean basement rocks of the Nain Province.The Pb–Zn mineralization in the RBDM shares many features with classic MVT deposits including geological setting, mineralogy, fluid characteristics and crustal sources for both metals and sulfur. However, MVT mineralization in the RBDM is unusual when compared with Phanerozoic MVT deposits, with elevated fluid temperatures, high CO2 contents of mineralizing fluids and minimum trapping pressures for fluid inclusions corresponding to mineralization depths of >4.5km. Similar characteristics have been described from other Paleoproterozoic MVT deposits (e.g. Pering Zn–Pb deposit, South Africa, Kamarga Pb–Zn deposit, Australia).

ORE GENESIS CONSTRAINTS ON THE IDAHO COBALT BELT FROM FLUID INCLUSION GAS, NOBLE GAS ISOTOPE, AND ION RATIO ANALYSES—A DISCUSSION

Sir: In their paper, “Ore genesis constraints on the Idaho cobalt belt from fluid inclusion gas, noble gas isotope, and ion ratio analyses,” Landis and Hofstra (2012) report on the analysis of hydrogen gas within fluid inclusions using mass spectrometry. They indicate surprisingly high hydrogen contents in fluid inclusions (~25,000 ppm) in this and their other, previous work that they reference. But it is highly unlikely that hydrogen is really that common in geofluids and even less likely that it could remain trapped in fluid inclusions for geological time periods because hydrogen diffuses easily through most materials, including quartz. The laser Raman method for analysis of gas contents of fluid inclusions can also measure hydrogen contents, but such analyses never find the presence of hydrogen within inclusions. The only detection of hydrogen in fluid inclusions by laser Raman that I am aware of was by Dubessy et al. (1988) and the hydrogen was present due to radiolytic dissociation of water within inclusions in a uranium deposit. These contradictions in the measurement of hydrogen in fluid inclusions are most likely a problem within the method of mass spectrometric analysis for hydrogen in aqueous fluids, as occur in fluid …

Source of diagenetic fluids from fluid-inclusion gas ratios

Alteration of marine carbonates, such as those from the Mesoproterozoic and Lower Ordovician, during burial history is carried out by diagenetic fluids that could potentially have different sources. During precipitation diagenetic minerals may trap tiny amounts of those solutions in fluid inclusions, thus providing fossil archives and aliquots that offer valuable record about the origin of fluids. The analysis of various fluid-inclusion gases (e.g., CH4, CO2, N2, He and Ar) may provide reliable information which allows the discrimination among different fluid sources. Generally speaking, the meteoric cements should have N2/Ar ratio around 38 (the value for air-saturated water). However, the gases in inclusions of the current study, trapped by diagenetic carbonates (cements), from independent depositional basins of different ages (Mesoproterozoic, Early Ordovician, and Modern) and locations (Canada, USA, Brazil and Java Sea), have N2/Ar ratios (~92) which match non-magmatic (modified marine or meteoric) fluids. Also, the Ar/He ratios (~3) in the studied fluid inclusions are significantly lower than those of calc-alkaline magmatic fluids (≥20), thus excluding magmatic fluids as a potential source. On the other hand, some N2/Ar and Ar/He ratios of the studied samples approach values reported for basinal fluids from the Hansonburg MVT deposit in New Mexico (68 and 1, respectively), suggesting that both meteoric/mixed marine–meteoric (evolved meteoric) and basinal fluids may be involved during carbonate diagenesis.

Origin of Lower Ordovician dolomites in eastern Laurentia: Controls on porosity and implications from geochemistry

The Catoche Formation of the St. George Group in eastern Laurentia (western Newfoundland) consists of early Ordovician (Arenigian) shallow marine platform carbonates (∼160 m thick), which were extensively dolomitized during the course of their diagenetic history. The dolomites occur as both replacement and pore-filling cements and are a major control on porosity distribution in the formation. The origin and diagenetic history of the Catoche dolomites at Daniel's Harbour (western Newfoundland) were analysed in comparison to equivalent successions at Port au Choix (PaC) and Port au Port Peninsula (PaP) to assay the reservoir potential of these dolomites in eastern Laurentia. Petrographic examination identified at least three generations of dolomites in the Catoche Formation, which are: (1) an early replacement sub- to eu-hedral micritic dolomite (<4 μm–30 μm, D1), (2) eu- to sub-hedral dolomite (70 μm–1 mm) often with cloudy cores and clear rims (D2), and (3) subhedral to anhedral saddle dolomite cement (200 μm–3 mm, D3). The micritic dolomite (D1) exhibits a dull cathodoluminescence (CL) under cathodoluminoscope, whereas dolomite D2 exhibits consistent concentric CL zonation. Some subhedral crystals of D3 appear zoned both in plane polarized light and cathodoluminoscope, otherwise D3 exhibits a dull CL. Stoichiometric dolomite occurs in all three generations with D2 as the dominant dolomite by abundance.The low strontium (47 ± 25 ppm) content coupled with depleted δ18O value of dolomitizing fluids (−10 to −11.2‰ VSMOW) and near-micritic grain size, suggests an early precipitation of dolomite D1 at low temperatures of near-surface conditions from solutions likely formed by mixing of early Ordovician sea and meteoric waters. In contrast, microthermometric measurements of primary two-phase fluid inclusions in dolomite D2 (homogenization temperatures of 102–168 °C with a salinity range of 19.8–25 eq wt% NaCl) and dolomite D3 (homogenization temperatures of 158–190 °C with a salinity range of 20.2–22.2 eq wt% NaCl), suggest that both dolomite generations were generated in mid to deep burial settings from high salinity, low temperature (<200 °C) hydrothermal fluids likely under suboxic conditions. This is consistent with the low Sr concentrations for D2 (36.4 ± 8 ppm) and D3 (38.7 ± 9 ppm), δ18O values of dolomitizing fluids for D2 (+2.1 to +8.1‰, VSMOW) and D3 (+6 to +8.1‰ VSMOW), coupled with Fe contents of D2 (1684 ± 1096 ppm) and D3 (1783.7 ± 618 ppm) as well as the respective Mn (D2 = 131.2 ± 50 and D3 = 197.5 ± 55 ppm) concentrations.ΣREE and shale normalized (REESN) values of Catoche carbonates indicate enrichment in rare earth element (REE) composition of the earliest calcite (C1) relative to those of Arenig seawater, whereas the REESN profiles of the dolomite generations mimic that of calcite C1. The Ce (Ce/Ce*)SN and La (La/La* = Pr/Pr*)SN anomalies of the Catoche dolomites are consistent with precipitation in equilibrium with source fluids in slightly oxic to suboxic conditions whereas Eu (Eu/Eu*)CN anomalies suggest similar source fluids for D2 and D3. Results of fluid inclusion gas analysis are consistent with petrographic features and geochemical compositions and support the exclusion of magmatic fluids during dolomitization. Visual estimates of porosity (ϕ) from thin sections indicate four porous (ϕ = 4–12) horizons. Vugs and intercrystalline pores are two types of porosity associated with the dolomites with the latter being the dominant type and associated mainly with dolomite D2.

Ore Genesis Constraints on the Idaho Cobalt Belt from Fluid Inclusion Gas, Noble Gas Isotope, and Ion Ratio Analyses

The Idaho cobalt belt is a 60-km-long alignment of deposits composed of cobaltite, Co pyrite, chalcopyrite, and gold with anomalous Nb, Y, Be, and rare-earth elements (REEs) in a quartz-biotite-tourmaline gangue hosted in Mesoproterozoic metasedimentary rocks of the Lemhi Group. It is the largest cobalt resource in the United States with historic production from the Blackbird Mine. All of the deposits were deformed and metamorphosed to upper greenschist-lower amphibolite grade in the Cretaceous. They occur near a 1377 Ma anorogenic bimodal plutonic complex. The enhanced solubility of Fe, Co, Cu, and Au as chloride complexes together with gangue biotite rich in Fe and Cl and gangue quartz containing hypersaline inclusions allows that hot saline fluids were involved. The isotopes of B in gangue tourmaline are suggestive of a marine source, whereas those of Pb in ore suggest a U ± Th-enriched source. The ore and gangue minerals in this belt may have trapped components in fluid inclusions that are distinct from those in post-ore minerals and metamorphic minerals. Such components can potentially be identified and distinguished by their relative abundances in contrasting samples. Therefore, we obtained samples of Co and Cu sulfides, gangue quartz, biotite, and tourmaline and post-ore quartz veins as well as Cretaceous metamorphic garnet and determined the gas, noble gas isotope, and ion ratios of fluid inclusion extracts by mass spectrometry and ion chromatography. The most abundant gases present in extracts from each sample type are biased toward the gas-rich population of inclusions trapped during maximum burial and metamorphism. All have CO 2 /CH 4 and N 2 /Ar ratios of evolved crustal fluids, and many yield a range of H 2 -CH 4 -CO 2 -H 2 S equilibration temperatures consistent with the metamorphic grade. Cretaceous garnet and post-ore minerals have high R H and R S values suggestive of reduced sulfidic conditions. Most extracts have anomalous 4 He produced by decay of U and Th and 38 Ar produced by nucleogenic production from 41 K. In contrast, some ore and gangue minerals yield significant SO 2 and have low R H and R S values of a more oxidized fluid. Three extracts from gangue quartz have high helium R/R A values indicative of a mantle source and neon isotope compositions that require nucleogenic production of 22 Ne in fluorite from U ± Th decay. Two extracts from gangue quartz have estimated 40 K/ 40 Ar that permit a Precambrian age. Extracts from gangue quartz in three different ore zones are biased toward the hypersaline population of inclusions and have a tight range of ion ratios (Na, K, NH 4 , Cl, Br, F) suggestive of a single fluid. Their Na, Cl, Br ratios suggest this fluid was a mixture of magmatic and basinal brine. Na-K-Ca temperatures (279°–347°C) are similar to homogenization temperatures of hypersaline inclusions. The high K/Na of the brine may be due to albitization of K silicate minerals in country rocks. Influx of K-rich brines is consistent with the K metasomatism necessary to form gangue biotite with high Cl. An extract from a post-ore quartz vein is distinct and has Na, Cl, Br ratios that resemble metamorphic fluids in Cretaceous silver veins of the Coeur d’Alene district in the Belt Basin. The results show that in some samples, for certain components, it is possible to “see through” the Cretaceous metamorphic overprint. Of great import for genetic models, the volatiles trapped in gangue quartz have 3 He derived from a mantle source and 22 Ne derived from fluorite, both of which may be attributed to nearby ~1377 Ma basalt-rhyolite magmatism. The brine trapped in gangue quartz is a mixture of magmatic fluid and evaporated seawater. The former requires a granitic intrusion that is present in the bimodal intrusive complex, and the latter equatorial paleolatitudes that existed in the Mesoproterozoic. The results permit genetic models involving heat and fluids from the neighboring bimodal plutonic complex and convection of basinal brine in the Lemhi Group. While the inferred fluid sources in the Idaho cobalt belt are similar in many respects to those in iron oxide copper-gold deposits, the fluids were more reduced such that iron was fixed in biotite and tourmaline instead of iron oxides.

Simultaneous measurements of gas isotopic compositions of fluid inclusion gases (N2, CH4, CO2) using continuous‐flow isotope ratio mass spectrometry

Simultaneous measurements of gas isotopic compositions of fluid inclusion gases (N₂, CH₄, CO₂) using continuous‐flow isotope ratio mass spectrometry

Composition and evolution of crustal, geothermal and hydrothermal fluids interpreted using quantitative fluid inclusion gas analysis

Quantitative analysis of fluid inclusion volatiles is an underutilized methodology. Fluid inclusion volatiles are analyzed by the incremental crush fast scan method using mass spectrometry. About 100mg of sample is partly and progressively crushed between pauses of 5 and 10min at room temperature while under 10−8Torr vacuum and the released gases are analyzed by dual quadrupole mass spectrometers. The gases routinely reported include H2, He, CH4, H2O, N2, O2, H2S, Ar, CO2, SO2, C2H4, C2H6, C3H6, C3H8, C4H8, C4H10, and benzene. Besides the incremental crush method, fluid inclusion gases may also be analyzed by the bulk cold crush or thermal decrepitation, Raman spectroscopy and gas chromatography.In geothermal systems and hydrothermal ore deposits, fluid inclusion gas data may be used to discriminate fluid sources (meteoric, magmatic), identify processes (boiling, condensation, mixing), constrain redox, correct fluid inclusion isochors, apply gas geothermometry, and provide valuable chemical constraints for fluid–rock equilibria modeling. CO2/CH4 versus N2/Ar plots as well as N2–Ar–He ratios are used to discriminate calc-alkaline magmatic volatiles which have N2/Ar ratios in the 100s to 1000s from meteoric (where the N2/Ar ratio is ~38) and basinal fluids (where Ar/He ratios approach 1). Boiling and condensation have negative and positive slopes respectively on CO2/N2 versus total gas plots. Organic compounds derived by Fischer–Tropsch reactions plot as straight lines on Schulz–Flory (log of concentration versus carbon number) plots whereas boiled volatiles and residual fluids create deflections. Redox is constrained by CO2–CH4–H2 ratios or alkane–alkene ratios provided the temperature is known. Gas geothermometry, similar to the approach applied in geothermal wells, is equally applicable to dissolved fluid inclusion gases with the CO2–CH4–H2 geothermometer potentially useful. Isochors can be corrected using the total partial pressures of all gas species dissolved within homogenized fluid inclusions by multiplying the gas concentration and values for Henry's Law constants. Fluid–rock equilibria modeling is enhanced by knowing the concentration of gases which control redox and a(H2S) which is vital for gold and base metal solubility constraints.The methodology is not limited to geothermal and hydrothermal systems and examples are presented from several geologic systems such as Libyan Desert glass, metamorphic systems, serpentinites, fault fluids, and artificial meteorites, thus demonstrating the versatility and flexibility of the fluid inclusion volatile analysis technique.

Oral Histories in Meteoritics and Planetary Science––XVI: Grenville Turner

Abstract– In this interview, Grenville Turner (Fig. 1) recounts how he became interested in meteorites during postdoctoral research with John Reynolds at the University of California, Berkeley, after completing a DPhil with Ken Mayne at the University of Oxford. At Berkeley, he worked on xenon isotopes with fellow students Bob Pepin and Craig Merrihue, but Reynolds’ insistence that they analyze all the inert gases in their samples meant that they also made important contributions to Ne isotope studies and potassium‐argon dating leading to the Ar‐Ar technique. In 1964, Grenville obtained a teaching position at the University of Sheffield where he developed his own laboratory for inert gas isotope measurements. After the return of samples from the Moon by the Apollo program, he became involved in determining the chronology of volcanism and major impacts on the Moon. In 1988, Grenville and his team moved to the University of Manchester as part of a national reorganization of earth science departments. During the post Apollo years, Grenville’s interest turned to the development of new instrumentation (resonance ionization mass spectrometry and the ion microprobe), and to problems in terrestrial isotope geochemistry, particularly the source of inert gases in fluid inclusions. He received the Leonard Medal of the Meteoritical Society in 1999, and he has also received awards from the Royal Society, the European Association of Geochemistry, and the Royal Astronomical Society. Grenville Turner.image

Mineralogy and fluid inclusion gas chemistry of production well mineral scale deposits at the Dixie Valley geothermal field, USA

AbstractAt the Dixie Valley geothermal field, Nevada, USA, fluid boiling triggered the precipitation of carbonate scale minerals in concentric bands around tubing inserted into production well 28–33. When the tubing was removed, this mineral scale was sampled at 44 depth intervals between the wellhead and 1227 m depth. These samples provide a unique opportunity to evaluate the effects of fluid boiling on the scale mineralogy and geochemistry of the vapor and liquid phase. In this study, the mineralogy of the scale deposits and the composition of the fluid inclusion gases trapped in the mineral scales were analyzed. The scale consists mainly of calcite from 670–1112 m depth and aragonite from 1125 to 1227 m depth, with traces of quartz and Mg‐smectite. Mineral textures, including hopper growth, twinning, and fibrous growth in the aragonite and banded deposits of fine grained calcite crystals, are the result of progressive boiling. The fluid inclusion noncondensable gas was dominated by CO2. However, significant variations in He relative to N2 and Ar provide evidence that the geothermal reservoir consists of mixed source deeply circulating reservoir water and shallow, air saturated meteoric water. Gas analyses for many inclusions also showed higher CH4 and H2 relative to CO2 than measured in gas sampled from this well, other production wells, and fumaroles. These inclusions are interpreted to have trapped CH4‐ and H2‐enriched gas resulting from early stages of boiling.

Geochemical Characteristics of the Fluid Inclusion of the Dafulou Deposits in Guangxi, China

Abstract In this paper, the fluid inclusions study was performed on quartz, sphalerite and calcite from the Sn–polymetallic orebodies of the Dafulou deposit. On the basis of optical observations and microthermometric data, six types of fluid inclusions have been recognized, such as single-phase gaseous fluid inclusions, single-phase salt solution fluid inclusions, two-phase vapour-rich fluid inclusions, two-phase liquid-rich fluid inclusions, three-phase CO2-rich fluid inclusions, solid(s)-bearing fluid inclusions, etc. And it showed that water is the main component, for example the water content of quartz more than 1700 μg/g, ranges from 1717 to 2320 μg/g. The sphalerite has lower content than quartz, only 978 μg/g. The calcite has lowest water content, i.e. 242 μg/g and 324 μg/g respectively. The gas component of inclusions mainly consists of CO2 and H2O. The main cationic consists of Ca2+, secondly Mg2+, K+ and Na+, only little Li+ and NH4+.

The noble gas systematics of late-orogenic H 2O–CO 2 fluids, Mt Isa, Australia

The noble gases (He, Ne, Ar, Kr and Xe) are powerful geochemical tracers because they have distinctive isotopic compositions in the atmosphere, crust and mantle. This study illustrates how noble gases can be used to trace fluid origins in high-temperature metamorphic and mineralising environments; and at the same time provides new information on the composition of noble gases in deeper parts of the crust than have been sampled previously. We report data for H 2O and CO 2 fluid inclusions trapped at greenschist to amphibolite facies metamorphic conditions associated with three different styles of mineralisation and alteration in the Proterozoic Mt Isa Inlier of Australia. Sulphide fluid inclusions are dominated by crustal 4He. However, co-variations in fluid inclusion 20Ne/ 22Ne, 21Ne/ 22Ne, 40Ar/ 36Ar and 136Xe/ 130Xe indicate noble gases were derived from three or more reservoirs. In most cases, the fluid inclusions elemental noble gas ratios (e.g. Ne/Xe) are close to the ranges expected in sedimentary and crystalline rocks. However, the elemental ratios have been modified in some of the samples providing evidence for independent pulses of CO 2, and interaction of CO 2 with high-salinity aqueous fluids. Compositional variation is attributed to mixing of: (i) magmatic fluids (or deeply sourced metamorphic fluids) characterised by basement-derived noble gases with 20Ne/ 22Ne ∼ 8.4, 21Ne/ 22Ne ∼ 0.4, 40Ar/ 36Ar ∼ 40,000 and 136Xe/ 130Xe ∼ 8; (ii) basinal–metamorphic fluids with a narrow range of compositions including near-atmospheric values and (iii) noble gases derived from the meta-sedimentary host-rocks with 20Ne/ 22Ne ∼ 8–9.8, 21Ne/ 22Ne < 0.1, 40Ar/ 36Ar < 2500 and 136Xe/ 130Xe ∼ 2.2. These data provide the strongest geochemical evidence available for the involvement of fluids from two distinct geochemical reservoirs in Mt Isa’s largest ore deposits. In addition the data show how noble gases in fluid inclusions can provide information on fluid origins, the composition of the crust’s major lithologies, fluid–rock interactions and fluid–fluid mixing or immiscibility processes.

Characteristics of Fluid Inclusions and its Significance to the Coaliferous Gas Reservoirs of the Xujiahe Formation in the Central Sichuan Basin, China

In the central Sichuan Basin, the maturity of source rocks in the Xujiahe Formation of the Upper Triassic is not high, with Ro values ranging from 0.8% to 1.2%. However, the gas reservoirs nowadays show characteristics of high gas-oil ratios and low condensate oil content (3.8–91.9 g/m3 on average). There are abundant gas hydrocarbon inclusions developed in the reservoir, with few liquid hydrocarbon inclusions, which indicates that the coal measures gave priority to gas rather than oil. In the fluid inclusion group, the CH4 and C2H6 contents are 79.62–96.42% and about 10% respectively, while the content of C3H8 ranges from 3% to 5%. The carbon isotope values are δ13C1= −44.59 ∼ −39.31‰, δ13C2= −24.82 ∼ −28.05‰, δ13C3= −21.39‰, δ13C4= −22.05 ∼ −20.2‰, δ13Cco2= −9.14 ∼ −13.86‰. The component and isotope compositions of gas in fluid inclusions coincide with those in the reservoirs, indicating that the gas hydrocarbon in the fluid inclusions can represent the residual gas in the reservoirs. The coal-measure source rocks can generate gas all the time during its burial process. The formation of salt-water inclusions associated with the gas inclusions can be divided into three stages. Firstly, the subsidence stage was at 170∼100 Ma, with the temperature of 70∼120°C. Secondly, the deep burial stage was during 100∼60 Ma, with the temperature of 120∼150°C. Thirdly, the uplift stage was at 60∼0 Ma, with the temperature of 90∼120°C. The time range reflected from gas inclusion is very wide, showing that the coal measures gave priority to gas hydrocarbon and can generate and expel gas continuously in a long period.

Characteristics of Gases in Fluid Inclusions from the Nurukawa Kuroko Deposit and Submarine Sulfide Deposits of the Izu-Ogasawara Arc

Characteristics of Gases in Fluid Inclusions from the Nurukawa Kuroko Deposit and Submarine Sulfide Deposits of the Izu-Ogasawara Arc

Inclusions of magmatic fluids: P-V-T-X properties of aqueous salt solutions of various types and petrological implications

The P-V-T-X properties of H2O-salt systems are compared depending on the solubility coefficient of compounds contained in these systems and the presence or absence of critical phenomena in the saturated solutions. Data on synthetic and natural inclusions captured in minerals at elevated temperatures and pressures and employed to discuss the principal features of phase diagrams of the H2O-NaCl system (type I) and H2O-NaF system (type II or P-Q type). It is demonstrated how characteristics of magmatic fluids of various types are manifested during the development of miarolitic pegmatites (Malkhan field in Transbaikalia) and during the crystallization of F-rich ongonitic melts (Ary-Bulak Massif in eastern Transbaikalia). Characteristics of solutions and gas-rich (gaseous) fluid inclusions in quartz phenocrysts from porphyritic ongonites (disappearance of the liquid regardless of its density and the overall salinity near the critical point of water, distinctive features of the dissolution of the crystalline phase, and the ability of the inclusions to withstand heating to 1400°C without decrepitation), and the richness of the fluid-magmatic system as a whole in F suggest that the ongonite melt crystallized in the presence of low-density NaF-bearing fluids of the P-Q type with a minor admixture of chlorides. It is important to identify the type of solutions in the fluid inclusions, because without knowing this type, it is impossible to accurately enough calculate the pressure at the temperatures of inclusion capture. For example, the unwarranted classification of solutions of type II (P-Q) in inclusions with the chloride system results in a significant overestimation of the calculated fluid pressures. A technique is proposed for studying the high-temperature immiscibility region in P-Q systems based on data obtained on gaseous fluid inclusions.

Primary migration and secondary alteration of the Upper Paleozoic gas reservoir in Ordos Basin, China — Application of fluid inclusion gases

The composition of fluid inclusions (FI) often represents the initial geochemical characteristics of palaeo-fluid in reservoir rock. Influence on composition and carbon isotopic composition of gas during primary migration, reservoir-forming and subsequent secondary alterations are discussed through comparing fluid inclusion gas with coal-formed gas and natural gas in present gas reservoirs in the Ordos Basin. The results show that primary migration of gas has significant effect on the molecular but not on the carbon isotopic composition of methane. Migration and diffusion fractionation took place during the secondary migration of gas in Upper Paleozoic gas reservoir according to carbon isotopic composition of methane in Fls. Composition and carbon isotopic composition of natural gas were nearly unchanged after the gas reservoir forming through comparing the FI gases with the natural gas in present gas reservoir.

A gas-chromatograph, continuous flow-isotope ratio mass-spectrometry method for δ13C and δD measurement of complex fluid inclusion volatiles: Examples from the Khibina alkaline igneous complex, northwest Russia and the south Wales coalfields

A new method is described for on-line extraction of complex mixtures of fluid inclusion volatiles for compound specific carbon- and hydrogen-isotope determination by gas-chromatography–continuous flow mass-spectrometry. Reproducibility for multiple aliquots of gas released from single samples and for duplicate samples is generally ≤ ± 0.7‰ for δ 13C measurements of hydrocarbon and CO 2 gases to concentrations as low as 20 nmol and ≤ ± 7‰ for δD measurements of hydrocarbon gases to concentrations as low as 100 nmol. This approach significantly improves upon the detection limits for trace gas analysis in fluid inclusions and enables rapid stable isotope measurements of multiple gas species in a single run. Two examples are evaluated and discussed in their geological context. First, stable isotope results for CH 4, CO 2 and C 2–C 5 fluid inclusion gases hosted in the undersaturated peralkaline igneous complex of Khibina in northwest Russia indicate that CH 4 was the juvenile magmatic gas phase ( δ 13C = − 13 to − 8‰, δD = − 120 to − 50‰). The δ 13C values of the C 2–C 5 hydrocarbons are lower relative to CH 4 (by up to 12‰), confirming their abiogenic origin. The δ 13C values of CO 2 are consistently lower than CH 4 (by up to 9‰) and the δD values of C 2H 6 are 70–100‰ lower than the δD CH 4 values. This pattern indicates that the CO 2 and higher hydrocarbons were generated during sub-solidus, kinetic CH 4-oxidation fractionation and polymerisation reactions. Second, CH 4, CO 2 and C 2H 6 fluid inclusion gases were analysed from quartz veins associated with anthracite from the Nant Helen mine in the south Wales coalfields. The δ 13C values of CH 4 (− 27.9 ± 0.1‰), CO 2 (− 3.1 ± 0.8‰) and C 2H 6 (− 20.7 ± 0.1‰) are typical of mature thermogenic coal-associated natural gases, as is the δD CH 4 values (− 148 ± 1‰). Assuming equilibrium, the Δ 13C CO 2–CH 4 value (+ 24.8‰) suggests that temperatures may have reached ∼ 300 °C in the anthracite zone.