Analysis Of Bulk Composition Research Articles

Investigation on Oil Physical States of Hybrid Shale Oil System: A Case Study on Cretaceous Second White Speckled Shale Formation from Highwood River Outcrop, Southern Alberta

Nine samples collected from the Upper Cretaceous Second White Speckled Shale Formation at the Highwood River outcrop in southern Alberta were geochemically characterized for their oil contents, physical states, and chemical compositions. Cold extraction was performed on 8–10 mm and 2–5 mm chips sequentially to obtain the first and second extractable organic matter (EOM-1 and EOM-2), while Soxhlet extraction was performed on powder from previously extracted chips to obtain the third extract (EOM-3). EOM-1 can be roughly regarded as free oil and EOM-2 is weakly adsorbed on mineral surfaces, while EOM-3 may represent the oil strongly adsorbed on kerogen. While both extraction yields and Rock-Eval pyrolysates differed from their original values due to the evaporative loss during outcropping, there was a generally positive correlation between the total EOM and total oil derived from Rock-Eval pyrolysis. EOM-1 was linearly correlated with Rock-Eval S1, while the extractable S2 content was well correlated with the loss of TOC, suggesting that TOC content was the main constraint for adsorbed oils. A bulk composition analysis illustrated that EOM-1 contained more saturated hydrocarbons, while EOM-3 was enriched in resins and asphaltenes. More detailed fractionation between the free and adsorbed oils was demonstrated by molecular compositions of each extract using quantitative GC-MS analysis. Lower-molecular-weight n-alkanes and smaller-ring-number aromatic compounds were preferentially concentrated in EOM-1 as compared to their higher-molecular or greater-ring-number counterparts and vice versa for EOM-3. Fractionation between isoprenoids and adjacent eluted n-alkanes, isomers of steranes, hopanes, alkylnaphthalenes, alkylphenanthrenes and alkyldibenzothiophenes was insignificant, suggesting no allogenic charge from deep strata. Strong chemical fractionation between saturated and aromatic hydrocarbon fractions was observed with EOM-1 apparently enriched in n-alkanes, while EOM-3 retained more aromatic hydrocarbons. However, the difference between free and adsorbed state oils was less dramatic than the variation from shales and siltstones. Lithological heterogeneities controlled both the amount and composition of retained fluids. Oil that resided in shales (source rock) behaved more similar to the EOM-3, with diffusive expulsion leading to the release of discrete molecules from a more adsorbed or occluded phase to a more free phase in siltstones with more connected pores and/or fractures (reservoir). Under current technical conditions, only the free oil can flow and will be the recoverable resource. Therefore, the highest potential can be expected from intervals adjacent to organic-rich beds. The compositional variations due to expulsion and primary migration from source rocks to reservoirs illustrated in the present study will contribute to a better understanding of the distribution of hydrocarbons generated and stored within the shale plays.

A landmark for local communities. Compositional analysis of the early Iron Age sanctuary at Polizzello Mountain (Sicily, Italy)

With this study we provide the compositional characterization of archaeological ceramics from the earliest phases of the indigenous sanctuary located on top of Polizzello Mountain, in Central Sicily (Italy). The site represents a remarkable evidence of the Late Bronze Age (LBA) - Early Iron Age (EIA) transition on the island, and it is characterized by the striking occurrence of material offerings in the form of ritually fragmented and highly standardized objects. The presence of multiple structures and the frequent evidence of dining activities, has led to the idea that the hilltop represented an important landmark for local indigenous communities across the landscape of Central Sicily. To test such hypothesis, bulk compositional analysis was used for the ceramics from the EIA levels of the sanctuary at Polizzello Mountain. Sixty-eight diagnostic specimens were analyzed via Instrumental Neutron Activation Analysis (INAA) to discriminate among distinct pottery groups according to the composition of their paste. The outcomes show little but clear compositional variations between three main pottery groups, which likely reflect the geographic background of the communities gathering at the sanctuary.

Sintered nanocomposites ZrO2-WC obtained with field assisted hot pressing

In the paper, the research results o nanostructural composite ZrO2 – WC obtained with modified Field Assisted Sintering is described. Hot pressing processes were performed at different sintering temperatures using mixtures of different proportions of tungsten monocarbide, such as 10 wt%, 20 wt%., 30 wt%. Sintering process activated by alternating current provided good results in short time of 2 min at pressure 30 MPa and temperature 1350 °C. Reduced temperature and shorter sintering time prevented grains from growth, ensuring enhanced mechanical properties of the composite. The test campaign included analysis of shrinkage process and respective porosity of obtained composite, analysis of bulk material structure, especially dimensions and composition of grains, as well as analysis of mechanical properties, such as microhardness and fracture toughness. Analysis of wear resistance was performed in real work conditions, comparing the nozzles made from different materials working in an abrasive waterjet machining system. Even though the mechanical properties of the sintered ZrO2 – WC material was comparable to the other reported methods and compositions, the proposed modified Field Assisted method consumed much less energy and time. The most remarkable result was obtained for wear resistance, where the tested nozzle worked almost two times longer than the ones available in the market.

Effects of Basicity and Al2O3 Content on the Chemistry of Phases in Iron Ore Sinter Containing ZnO

The effects of basicity and Al2O3 content on the chemistry of phases in iron ore sinter containing ZnO were investigated by Rietveld analysis of the X-ray diffraction (XRD) patterns. Bulk composition analysis was carried out using inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and wet-chemical analysis. The composition of each phase was investigated using a scanning electron microscope-energy dispersive X-ray analyzer (SEM-EDX). It was found that ZnO exists in the franklinite and the silicoferrite of calcium and aluminum (SFCA) phases. With increasing ZnO content, the phase fraction of the franklinite increased, while the fraction of SFCA slightly increased. When ZnO content was fixed at 1 wt pct and basicity increased, the fraction of franklinite decreased and that of SFCA increased. Here, the solubility of ZnO in the SFCA increased. As the Al2O3 content increased, the fraction of franklinite decreased and that of SFCA increased, while ZnO content in the SFCA did not change significantly.

Simulated solar photocatalytic ozonation of contaminants of emerging concern and effluent organic matter in secondary effluents by a reusable magnetic catalyst

A magnetic TiO2/Fe3O4/activated carbon composite was used as a photocatalyst for the removal of contaminants of emerging concern (CECs) and effluent organic matter (EfOM) of real and simulated effluents from municipal wastewater treatment plants (MWWTPs). While the catalyst showed limited activity under simulated solar irradiation in the absence of ozone, the CECs were completely eliminated and dissolved organic carbon (DOC) removal efficiencies reached up to more than 75% by simulated solar photocatalytic ozonation. The effects of EfOM (0–30 mg·L−1 DOC), carbonate/bicarbonate (0–60 mg·L−1 IC) and PO4-P (0–3.5 mg·L−1) concentrations of the secondary effluent on the photocatalytic activity was studied. Both EfOM and carbonate/bicarbonate concentration accelerated the DOC removal in single ozonation experiments (i.e., absence of catalyst and radiation) due to the presence of initiators of the hydroxyl radical chain, the formation of secondary oxidants (i.e., hydrogen peroxide and carbonate radical) and the buffering capacity of the effluent. However, the interaction of EfOM and carbonate/bicarbonate with the catalyst brought about a decrease of its photocatalytic activity. Phosphates, in the concentration range studied, did not influence appreciably the catalytic activity. The reusability of the catalyst was evaluated through eight consecutive simulated solar phototacalytic ozonation runs. Samples of fresh and reused catalysts were examined by bulk composition analysis, N2 adsorption-desorption isotherms, XRD, XPS, SQUID magnetometry and the pHPZC. Despite some changes in the porous structure and the fixation of some oxygen groups on the carbon surface as a result of ozonation, the catalyst showed good stability and the oxidation efficiency was maintained through runs.

Surface layer investigation of dual ion beam sputtered Cu2ZnSn(S,Se)4 thin film for open circuit voltage improvement

We present surface analysis of Cu2ZnSn(S,Se)4 (CZTSSe) thin films deposited on Mo/glass substrates. X-ray photoelectron and energy dispersive x-ray spectroscopy has been performed on CZTSSe thin-film solar cell absorbers for surface and bulk compositional analysis, respectively. It is observed that the surface of the CZTSSe absorber is Cu deficient. For further verification of Cu deficiency, spectroscopic ellipsometry has been used to determine the extinction coefficient of CZTSSe thin films with Cu variation. The surface layer has a higher bandgap of 1.79 eV in reference to the bulk film bandgap of 1.5 eV. This surface bandgap increase is beneficial for solar cell performance. The thin film with a Cu deficient surface has a noticeably higher open circuit voltage of 562 mV using a very thin absorber layer of 300 nm in thickness. The open circuit voltage for the Cu deficient surface is 25% higher than that of the Cu rich surface. This analysis gives an understanding into the significance of surface layer engineering for photovoltaic device.

Characteristics and Origin of Solid Bitumen in Glutenites: A Case Study from the Baikouquan Formation Reservoirs of the Mahu Sag in the Junggar Basin, China

Solid bitumen was identified in the pore spaces of the Triassic Baikouquan Formation glutenite reservoir in the Mahu Sag of the Junggar Basin, northwestern China. Optical microscopy, scanning electron microscopy, and organic geochemical techniques were used to characterize solid bitumen and determine its source and origin. Rock core observations as well as optical microscopy, scanning electron microscopy, and energy spectrum analyses show that the reservoir pores are filled with isotropic solid bitumen. Biomarker geochemistry indicates that the solid bitumen is early mature to mature and formed in a reductive lacustrine environment with saline water. Oil–source correlation suggests that the solid bitumen was sourced from the low-early mature Fengcheng Formation shale. Bulk composition, alkane composition, and terpane analyses indicate that the solid bitumen did not experience oxidation or biodegradation. Geothermal evolution of the Baikouquan Formation confirms that thermal alteration is not effective for bitumen formation. On the basis of the comprehensive analysis, the solid bitumen was formed from early mature crude oil by high pressure and moderate temperatures.

Indium Mineralization in the Yejiwei Sn‐Polymetallic Deposit of the Shizhuyuan Orefield, Southern Hunan, China

AbstractThe Yejiwei deposit, which is located in the southern Hunan W–Sn–Pb–Zn Metallogenic Belt in south China, is a large‐scale porphyry–skarn–veinlet‐type deposit containing 806 t In. Mineralization occurs as porphyry‐type Sn (stockworks), skarn‐type Sn–Cu, marble‐hosted‐type Sn–Cu (veinlet), and vein‐type Pb–Zn ores. Thirty‐five ore samples were collected from the Yejiwei deposit for bulk and mineral chemical composition, microscopic observation and electron microprobe analyses. The porphyry‐type Sn ores contain variable amounts of In (2.3–76 ppm; mean of 17.4 ppm) with local In enrichment (226 ppm) and 1000 × In/Zn values are 3.8–52.4. The skarn‐type Cu–Sn ore is richest in In (12.3–214 ppm; mean of 114 ppm), and 1000 × In/Zn values are 2.4–117. In contrast, the In content of the marble‐hosted‐type Cu–Sn ores is relatively low (7.4–34.9 ppm; mean of 20.3 ppm), and 1000 × In/Zn is in the range of 0.61–5.5, and the vein‐type Pb–Zn ores in the external zone contain the lowest In contents (7.2–17.0 ppm; mean of 12.1 ppm) with 1000 × In/Zn values of 0.07–0.09. The ore minerals in the deposit include pyrite, pyrrhotite, cassiterite, and In‐bearing minerals of sphalerite, chalcopyrite, and stannite. Although only trace amounts of sphalerite are hosted in the porphyry ores, the sphalerite contains the highest In content (0.27–10.1 wt.% In) in the deposit. We observed the highest In contents of all In‐bearing sphalerite reported in China. The In contents of sphalerite in the skarn‐type ore range from 0.15 to 0.56 wt.%, whereas the marble‐hosted‐, and vein‐type ores have lower In contents (0.00–0.04, and 0.03–0.06 wt.%, respectively). The In resources of the Yejiwei deposit are mainly hosted in skarn ores of the No. 31 and No. 32 orebodies. The genesis of In in the Yejiwei deposit was closely related to the shallow intrusive environment of related igneous rocks. As W–Sn–Mo–Bi–Cu–Pb–Zn–Ag mineralization is widespread in south Hunan, this study would suggest a focus on skarn‐type Sn–Zn deposits for the future prospecting of In resources.

Design and pharmaceutical applications of a low-flow-rate single-nozzle impactor

A new low-flow-rate (0.5L/min) single-nozzle impactor for the concentration of dilute aerosol particles with selected pharmaceutical applications is described in this paper. The impactor can be configured up to 11 stages with a wide range of cutoff diameters from 0.6μm to 21.1μm, enabling convenient sampling of inhalable drug particles from inhalation devices and drug production processes. Its unique single-nozzle design and removable impaction plate allow direct sample transfer for subsequent compositional, morphological, solid-state, and other analysis. Agreement between the measured size distribution of fluticasone propionate particles actuated from commercial pMDI Flixotide® 250 Evohaler® and reported data in the literature verified that the impactor stages have accurate cutoff diameters as designed. The multi-stage configuration of the impactor allows rapid separation of polydisperse aerosol particles into different size classes for further characterization. Overlapping of the Raman spectra of the double-component powders from the Seretide® 250 pMDI collected using two different methods demonstrated the applicability of the impactor for a representative sampling of multi-component aerosol particles for bulk composition analysis. A time-dependent and size-dependent stability study was conducted consuming only a single sample canister with 80mg of amorphous indomethacin particles suspended in HFA-134a. It was found that amorphous indomethacin particles converted to the γ crystalline polymorph upon storage at 45°C and that the crystallization rate is strongly size dependent. With its highly effective aerosol collection capability and accurate cutoff diameters for aerosol classification, the impactor will have various applications in the pharmaceutical industry.

Induced wettability and surface-volume correlation of composition for bovine bone derived hydroxyapatite particles

Hydroxyapatite powders characteristics need to be determined both for quality control purposes and for a proper control of microstructural features of bone reconstruction products. This study combines bulk morphological and compositional analysis methods (XRF, SEM-EDS, FT-IR) with surface-related methods (XPS, contact angle measurements) in order to correlate the characteristics of hydroxyapatite powders derived from bovine bone for its use in medical applications. An experimental approach for correlating the surface and volume composition was designed based on the analysis depth of each spectral method involved in the study. Next, the influences of powder particle size and forming method on the contact angle between water drops and ceramic surface were evaluated for identifying suitable strategies of tuning hydroxyapatite’s wettability. The results revealed a preferential arrangement of chemical elements at the surface of hydroxyapatite particles which could induce a favourable material behaviour in terms of sinterability and biological performance.

Sedimentary microfacies and organic geochemical characterization of mudstones in the Keluke Formation in northeastern Qaidam, China

During the Early Carboniferous, the northeastern Qaidam Basin probably formed in an active continental margin setting. Due to marine regression after the late Early Carboniferous, the marginal shelf began to receive more terrestrial clastic sediments, and alternating occurrence of carbonates and siliciclastics characterized this region. Consequently, shales or mudstones with considerable thickness were deposited in the Upper Carboniferous, especially in the Keluke Formation. In order to illuminate a more accurate sedimentary environment of shales and further evaluate the shale gas potential, multidisciplinary traditional methods were conducted including rock core examinations and laboratory analysis. Results reveal that the sedimentary microfacies of shales in the Keluke Formation can be divided into the upper shoreface, the lower shoreface, and the upper to transition offshore. These microfacies developed on a homoclinal carbonate ramp with a gentle slope. The thickest succession of mudstone develops in the lower shoreface, which is a counterpart with the lagoonal setting of a stationary hydraulic system. The quartz content of shale samples ranges from 30% to 66% and clay minerals from 24% to 43% by bulk compositional analysis, which indicates the content of brittle minerals and shales fissility to some extent. The total organic carbon content ranges from 0.5% to 7.6% by weight, with an average value of 2.69% in ZK1‐1 and 1.11% in ZK3‐2, indicating abundant organic matter richness. The kerogen is mainly of type II, which indicates that source for the organic matter is a mixture of higher terrestrial plants and acquatic organisms. The vitrinite reflectance ranges from 1.22% to 1.55%, indicating a moderate to high thermal maturity. Three types of pores are recognized in the shales, including organic pores, intrapartical pores, and interparticle pores. The significance of this work emphasizes two aspects. First, it gives a more detailed classification of sedimentary environment of the mudstone succession; second, it acquires the preliminary subsurface data regarding to the shale gas potential evaluation.

Characteristics and Behavior of Hydrothermal Fluids for Gold Mineralization at the Hishikari Deposits, Kyushu, Japan

AbstractThe Hishikari gold–silver deposits in southern Kyushu, Japan, are low‐sulfidation vein‐type epithermal deposits. Bulk composition analysis, fluid inclusion microthermometry and quantitative gas composition analysis on the basis of the crush‐fast scan (CFS) method were conducted to elucidate characteristics and behavior of hydrothermal fluids responsible for the gold mineralization of the Hishikari deposits. Quartz vein samples were collected from widely scattered locations of ore veins: Zuisen‐6, ‐3, ‐1 (Main deposit), Keisen‐2 and Shosen‐5 (Sanjin deposit), and Seisen‐8 (Yamada deposit) between −70 and 64 ML (mine meter level). The samples are composed mainly of quartz and adularia, and ore minerals of electrum, pyrargyrite, pyrite and/or stibnite, having an average bulk Ag/Au weight ratio of 0.54. Fluid inclusions in quartz and adularia are two‐phase liquid–vapor, and their trapping temperatures and salinities are ca. 190–220 °C and 1.5–2.7 wt.% NaCl eq., respectively. The salinity is highest with an average 2.4 wt.% NaCl eq. of the fluid inclusions from the deepest level (Zuisen‐6 vein at −70 ML), while the fluid inclusion salinities from other samples are relatively low less than ca. 2.0 wt.% NaCl eq. Parallel‐ and lattice‐bladed quartz occur in a number of veins, suggesting fluid boiling during the vein formation.Gases of fluid inclusions are composed mainly of H2O (93.4–99.8 mol%) and CO2 (0.15–6.2 mol%), N2 (0.007–0.96 mol%), Ar (0.0001–0.0047 mol%), CH4 (0.002–0.048 mol%), H2S (0.0004–0.0028 mol%), H2 (0–0.074 mol%) and He (0.0002–0.0011 mol%). CO2, N2 and Ar contents of the fluid inclusions are elevated in the samples collected from deep levels, while H2O, H2S and He contents are elevated in those from shallow levels. The Ar/He, CO2/CH4 and N2/Ar ratios of fluid inclusion gas indicate a systematic transition from magmatic to meteoric signatures in order from deep to shallow levels. The CO2/N2 ratio and volatiles contents are positively correlated suggesting condensation in relatively high Au‐grade quartz vein samples (19.5–27.7 ppm Au), while negative correlations suggest boiling with volatile contents less than 1% are indicative of low Au‐grade quartz vein samples (0.14 to 0.18 ppm Au). The elevated CO2 contents observed in the Zuisen veins are signatures of the deeply circulating hydrothermal fluid with a magmatic contribution. Due to intermittent boiling of hydrothermal fluid, CO2 and H2S were partitioned into the vapor phase in deeper portions and condensed into the steam‐heated meteoric water in shallower portions. The signatures of both meteoric and magmatic fluids in fluid inclusion gas compositions were detected in the samples collected near the unconformity between Shimanto Supergroup (shale and sandstone) and Hishikari Lower Andesite. This suggests that a mixing of the deeply circulating hydrothermal fluids with the steam‐heated meteoric water took place near the unconformity, and it was one of the mechanisms to have precipitated gold.

Macro-Raman spectroscopy for bulk composition and homogeneity analysis of multi-component pharmaceutical powders

A new macro-Raman system equipped with a motorized translational sample stage and low-frequency shift capabilities was developed for bulk composition and homogeneity analysis of multi-component pharmaceutical powders. Different sampling methods including single spot and scanning measurement were compared. It was found that increasing sample volumes significantly improved the precision of quantitative composition analysis, especially for poorly mixed powders. The multi-pass cavity of the macro-Raman system increased effective sample volumes by 20 times from the sample volume defined by the collection optics, i.e., from 0.02μL to about 0.4μL. A stochastic model simulating the random sampling process of polydisperse microparticles was used to predict the sampling errors for a specific sample volume. Comparison of fluticasone propionate mass fractions of the commercial products Flixotide® 250 and Seretide® 500 simulated for different sampling volumes with experimentally measured compositions verified that the effective sample volume of a single point macro-Raman measurement in the multi-pass cavity of this instrument was between 0.3μL and 0.5μL. The macro-Raman system was also successfully used for blend uniformity analysis. It was concluded that demixing occurred in the binary mixture of l-leucine and d-mannitol from the observation that the sampling errors indicated by the standard deviations of measured leucine mass fractions increased during mixing, and the standard deviation values were all larger than the theoretical lower limit determined by the simulation. Since sample volume was shown to have a significant impact on measured homogeneity characteristics, it was concluded that powder homogeneity analysis results, i.e., the mean of individual test results and absolute and relative standard deviations, must be presented together with the effective sample volumes of the applied testing techniques for any measurement of powder homogeneity to be fully meaningful.

Integrating comprehensive two-dimensional gas chromatography and downhole fluid analysis to validate a spill-fill sequence of reservoirs with variations of biodegradation, water washing and thermal maturity

Optimization of production depends heavily on crude oil composition and its variation within and across multiple reservoirs. In particular, asphaltene content has enormous impact on crude oil viscosity and the economic value of reservoir fluids. Thus, it is important to understand the primary controls on crude oil composition and asphaltene distributions in reservoirs. This paper examines a complex oilfield in the North Sea that contains seven separate reservoirs. The crude oil is believed to have spilled from deeper into shallower reservoirs during reservoir charging. In-situ asphaltene content is measured by downhole fluid analysis (DFA) and is generally consistent with a spill-fill sequence in reservoir charging. Detailed compositional analysis of crude oil samples by comprehensive two-dimensional gas chromatography (GC×GC) was used to determine the extent of water washing, biodegradation and thermal maturity among the reservoirs. Increased biodegradation and water washing in the shallower reservoirs is consistent with a spill-fill sequence. Aromatic and alkylated aromatic compounds decrease according to a combination of water solubility and susceptibility to biodegradation in the shallower reservoirs. Four thermal maturity biomarker ratios show that the shallower reservoirs contain less mature oil, consistent with a spill-fill sequence. The combination of DFA for bulk compositional analysis and GC×GC for detailed compositional analysis combined with geochemical interpretation is an effective tool to unravel complex oilfield scenarios.

Terminal particle from Stardust track 130: Probable Al-rich chondrule fragment from comet Wild 2

A 4×6μm terminal particle from Stardust track 130, named Bidi, is composed of a refractory assemblage of Fo97 olivine, Al- and Ti-bearing clinopyroxene and anorthite feldspar (An97). Mineralogically, Bidi resembles a number of components found in primitive chondritic meteorites including Al-rich chondrules, plagioclase-bearing type I ferromagnesian chondrules and amoeboid olivine aggregates (AOAs). Measured widths of augite/pigeonite lamellae in the clinopyroxene indicate fast cooling rates suggesting that Bidi is more likely to be a chondrule fragment than an AOA. Bulk element concentrations, including an Al2O3 content of 10.2wt%, further suggests that Bidi is more akin to Al-rich rather than ferromagnesian chondrules. This is supported by high anorthite content of the plagioclase feldspar, overall bulk composition and petrogenetic analysis using a cosmochemical Al2O3–Ca2SiO4–Mg2SiO4 phase diagram. Measured minor element abundances of individual minerals in Bidi generally support an Al-rich chondrule origin but are not definitive between any of the object types. Oxygen isotope ratios obtained from olivine (+minor high-Ca pyroxene)fall between the TF and CCAM lines and overlap similar minerals from chondrules in primitive chondrites but are generally distinct from pristine AOA minerals. Oxygen isotope ratios are similar to some minerals from both Al-rich and type I ferromagnesian chondrules in unequilibrated carbonaceous, enstatite and ordinary chondrites. Although no single piece of evidence uniquely identifies Bidi as a particular object type, the preponderance of data, including mineral assemblage, bulk composition, mineral chemistry, inferred cooling rates and oxygen isotope ratios, suggest that Bidi is more closely matched to Al-rich chondrules than AOAs or plagioclase-bearing type I ferromagnesian chondrules and likely originated in a chondrule-forming region in the inner solar system.

The Tafassasset primitive achondrite: Insights into initial stages of planetary differentiation

Tafassasset is an exceptional meteorite that has been linked to both the CR chondrites and the primitive achondrites. Because previous evidence suggests it might be a primitive achondrite from a known chondrite type, we have undertaken a study of the petrology, geochemistry, and formation history of the meteorite. Tafassasset is predominantly FeO-rich olivine (∼58%) yet contains abundant Fe,Ni-metal (∼10vol.%) and sulfide (∼3vol.%). Other phases include high- and low-Ca pyroxene, plagioclase, chromite, and phosphate. It has a recrystallized texture, containing equigranular grains that often meet at 120° triple junctions. There are no relict chondrules in the thin sections examined, although they have been reported previously. Electron microprobe analyses reveal homogeneous olivine (Fa28.6), both low-and high-Ca pyroxene (Fs23.6Wo3.7 and Fs12.2Wo39.3±1), a range of plagioclase composition (An23–47), Fe,Ni-metal (with 5.3–36.6wt.% Ni and 0.1–0.8wt.% Co), troilite, chromite, and Ca–phosphate. Bulk composition analyses reveal two chips depleted in refractory lithophile and some siderophile elements compared to CI chondrites. Exceptions are enrichments in Fe, Ni and Co. A third chip is essentially chondritic in bulk composition. Different stones of the meteorite have slightly different oxygen isotope composition, yet all lie in the CR chondrite trend with one in the acapulcoite–lodranite field. Thermodynamic calculations show that Tafassasset equilibrated at a temperature above the Fe,Ni–FeS eutectic and at an oxygen fugacity of ∼IW-1. The texture, heterogeneous distribution of mineral phases, plagioclase composition, two-mineral closure temperatures, and bulk composition all provide evidence that Tafassasset partially melted on its parent body. A comparison with the CR chondrites, the brachinites, and two anomalous achondrites indicates that Tafassasset is most similar to ungrouped primitive achondrites Lewis Cliff (LEW) 88763 and Divnoe, and to the brachinites in overall petrography, modal mineralogy, mineral compositions, oxidation state, and bulk composition. The comparison also excludes the possibility that Tafassasset formed by partial melting of a CR chondrite. Tafassasset is a primitive achondrite and likely evolved on a parent body that experienced incomplete melting, never reached isotopic homogeneity, and was from the same oxygen isotopic reservoir as the CR chondrite parent body.

Mechanisms of trace metal enrichment in submarine, methane-derived carbonate chimneys from the Gulf of Cadiz

Methane oxidation and sulphate reduction are the key processes driving the precipitation of carbonates and iron sulphides in methane-seeps under anaerobic conditions. These carbonates incorporate trace metals from several sources, such as dissolved species in seawater and the surrounding sediments. Thus, it is possible to infer significant information about the development of methane-derived carbonates from their bulk composition. However, post-depositional processes change relative trace metal concentrations and mask this information. In order to study mechanisms of trace metal accumulation despite interference from these post-depositional processes, we examined submarine carbonate chimneys from different sites on the seafloor of the Gulf of Cadiz using analysis of bulk composition and electron microprobe composition of carbonates, detrital minerals, authigenic pyrite, and iron oxyhydroxides. Positive correlations between Si, Al, Ca and Fe and trace element contents and electron microprobe results suggest that the main processes of trace metal incorporation into chimneys are: (1) inclusion and cementation of sediment material into the chimneys (Ti, Zr, Rb, Cr and some rare earth elements); (2) substitution of Ca in microcrystalline carbonates (Ba, Sr); and (3) assimilation into authigenic pyrite (Mo, Co, Ni, Pb, As, Zn, V and U), a process enhanced by bacterial sulphate reduction and development of framboidal textures. We also calculated several redox indices to evaluate the effects of exposure to oxygenated waters on the composition of chimneys. Ni/Co and V/Cr ratios, EF Mo/EF U and the mean and standard deviation of iron mineral sizes pointed to oxygen-rich settings. Geochemical compositions of selected minerals and positive correlations between trace metals and representative indices can be used to determine the source and enrichment mechanism of trace metals in authigenic carbonates developed in methane-seeps as a consequence of anaerobic oxidation of methane.

Geochemical and mineralogical control on the mobility of arsenic in a waste rock pile at Dlouhá Ves, Czech Republic

A waste rock pile with initial high sulfide (10–20 wt.%) and low carbonate content (1–2 wt.%) located at Dlouhá Ves in the Czech Republic has been investigated in two profiles (excavation and outcrop) using powder X-ray diffraction, electron microprobe analysis, bulk composition analysis and Mössbauer spectroscopy. The mobility of arsenic and other contaminants was evaluated by leaching experiments. The primary source of the arsenic was arsenopyrite, which was significantly oxidized in both profiles. The principal As-bearing phase at the excavation profile was goethite, located at the top of the profile, and minerals of the jarosite group which were found down to its base. Melanterite, rich in copper and zinc, was found in a sulfide-rich, lower part of the profile together with anglesite. At the outcrop profile, minerals of the jarosite–beudantite group, scorodite and kaňkite prevail and no Fe(II)-minerals were found. The paste pH was lower at the excavation profile (minimum about 1.9) than at the outcrop profile (minimum of about 2.8). Processes in the pile are affected by the pyrite/arsenopyrite ratio, where high pyrite content decreases the As/S ratio and results in the formation of jarosite group minerals and low pH conditions. Where arsenopyrite predominates, sulphides are coated by scorodite and other Fe–As phases like schwertmannite, which limit their further oxidation. Arsenic concentrations released during the leaching experiments were generally low; maximum amounts (up to 0.56 ppm) were released from horizons with jarosite and arsenopyrite. In contrast, minimum amounts of arsenic were released from horizons with beudantite and scorodite. Melanterite found at the excavation profile was fully soluble, releasing copper and zinc into the solution. Differences between both profiles are caused especially by the different degrees of water flow through the pile material and the limited penetration of oxygen into the deep parts of the excavation profile. It seems that beudantite and scorodite represent a long-term option for immobilization of arsenic, but arsenic stored in jarosite can be mobilized relatively easily. Highly soluble Fe(II) minerals such as melanterite may represent an environmental problem. However, potential mineralogical transformations and stability of arsenic in beudantite group minerals have yet to be evaluated.

Metamorphic evolution of sapphirine- and orthoamphibole-cordierite-bearing gneiss, Okanogan dome, Washington, USA

Gneiss domes are commonly cored by quartzofeldspathic rocks that provide little information about the pressure–temperature–fluid history of the domes. Three northern Cordilleran migmatite domes (Thor-Odin and Valhalla/Passmore, British Columbia, Canada; Okanogan, Washington, USA), however, contain Mg–Al-rich orthoamphibole-cordierite gneiss as layers and lenses that record metamorphic conditions and pressure–temperature (P–T) path information not preserved in the host migmatite. These Mg–Al-rich rocks are therefore a valuable archive of metamorphic conditions during dome evolution, although refractory rocks such as these commonly contain reaction textures that may complicate the calculation of metamorphic conditions. In the Okanogan dome, Mg–Al-rich layers are part of the Tunk Creek unit, which occurs at the periphery of an underlying migmatite domain. Bulk compositional layers (mm- to m-scale) consist of gedrite-dominated, hornblende-dominated and biotite-bearing layers that contain variable amounts of gedrite, hornblende, anorthite, cordierite, spinel, sapphirine, corundum, kyanite, biotite and/or staurolite. The presence of different compositional layers (some with reaction textures, some without) allows systematic analysis of metamorphic history by a combined petrographic and phase equilibrium analysis. Gedrite-dominated layers containing relict kyanite preserve evidence of the highest-P conditions; symplectitic and coronal reaction textures around kyanite indicate decompression at high temperature. Gedrite-dominated layers lacking these reaction textures contain layers of sapphirine and spinel in apparent textural equilibrium and record a later high-T–low-P part of the path. Phase equilibria (pseudosection) analysis for layers that lack reaction textures indicates metamorphic conditions of 720–750 °C at a range of pressures (>8 to <4 kbar) following decompression. Elevated crustal temperatures and concordant structural fabrics in the Tunk Creek unit and underlying migmatite domain suggest that the calculated P–T conditions recorded in Tunk Creek rocks were coeval with anatexis, extension, and dome formation in Palaeocene–Eocene time. In contrast to orthoamphibole-cordierite gneiss in the other Cordilleran domes, the Tunk Creek unit occurs as a discontinuous km-scale layer rather than as smaller (m-scale) pods, is more calcic, and lacks garnet. In addition, kyanite did not transform to sillimanite, and spinel commonly occurs as a blocky matrix phase in addition to vermicules in symplectite. These differences, along with the compositional layering, allow an analysis of bulk composition v. tectonic (P–T path) controls on mineral assemblages and textures. Pseudosection modelling of different layers in the Tunk Creek unit provides a basis for understanding the metamorphic history of these texturally complex, refractory rocks and their host gneiss domes, and other such rocks in similar tectonic settings.

Combining biomarker and bulk compositional gradient analysis to assess reservoir connectivity

Hydraulic connectivity of petroleum reservoirs represents one of the biggest uncertainties for both oil production and petroleum system studies. Here, a geochemical analysis involving bulk and detailed measures of crude oil composition is shown to constrain connectivity more tightly than possible with conventional methods. Three crude oils from different depths in a single well exhibit large gradients in viscosity, density and asphaltene content. The oils were collected with a wireline sampling tool to provide samples from well-defined locations and relatively free of contamination from drilling fluid; the known provenance of the samples minimizes uncertainties in analysis. The detailed chemical composition of almost the entire crude oil was determined by use of comprehensive two-dimensional gas chromatography (GC×GC) to interrogate the non-polar fraction and negative ion electrospray ionization Fourier transform-ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) to interrogate the polar fraction. The simultaneous presence of 25-norhopanes and mildly altered normal and isoprenoid alkanes was detected, suggesting that the reservoir experienced multiple charges and contains a mixture of oils biodegraded to different extents. The gradient in asphaltene concentration is explained by an equilibrium model considering only gravitational segregation of asphaltene nanoaggregates; this grading can be responsible for the observed variation in viscosity. Combining the analyses affords a consistent picture of a connected reservoir in which the observed viscosity variation originates from gravitational segregation of asphaltene nanoaggregates in a crude oil with high asphaltene concentration resulting from multiple charges, including one charge that suffered severe biodegradation. Observation of these gradients having appropriate magnitudes suggests good reservoir connectivity with greater confidence than possible with traditional techniques alone.