Chemical composition of the Tertiary black shales of West Sabah, East Malaysia

The X-ray fluorescence and ICP methods were used to analyze 60 outcrop samples of black shale, of which 15 were collected from Belait, 15 from the Setap Shale, 15 from Temburong, and 15 from the Trusmadi formations. The average compositions of the shales from the study area are 64.62%, 63.95%, 62.32%, 63.84% SiO2, 1.84%, 2.14%, 2.04%, 1.99% MgO, 2.55%, 3.12%, 2.89%, 2.72% K2O, 0.32%, 0.30%, 0.32%, 0.53% CaO, 5.86%, 6.06%, 7.14%, 6.60% Fe2O3, 207×10^-6, 180×10^-6, 213×10^-6, 200×10^-6 Rb, and 56×10^-6, 49×10^-6, 50×10^-6, 32×10^-6 Sr for the Setap Shale, Temburong, Belait and Trusmadi samples, respectively. The high Rb/Sr ratios of 3.8, 3.7, 4.2, and 6.1 are attributed to the lowest contents of Sr due to reducing conditions prevailing. The high Rb/K ratio sug- gests either brackish marine or rapid deposition that prevented equilibrium between Rb and K in the shales and marine waters.     

Ferric-ferrous ratios,H2O contents and D/H ratios of phlogopite and biotite from lavas of different tectonic regimes

 Complete chemical analyses, including ferric and ferrous iron, H₂O contents and δD values for 16 phlogopite and biotite and 2 hornblende separates are presented. Samples were obtained from volcanic rocks from four localities: (1) phlogopite phenocrysts from minette lavas from the western Mexico continental arc, (2) biotite and hornblende phenocrysts from andesite lavas from Mono Basin, California, (3) phlogopite and biotite from clinopyroxenite nodules entrained in potassic lavas from the East African Rift, Uganda, and (4) phlogopite phenocrysts from a wyomingite lava in the Leucite Hills, Wyoming. The Fe₂O₃ contents in the micas range from 0.8 to 10.5 wt%, corresponding to 0.09 to 1.15 Fe³⁺ per formula unit (pfu). Water contents vary from 1.6 to 3.0 wt%, corresponding to 1.58 to 3.04 OH pfu, significantly less than would be expected for a site fully occupied by hydroxyl. Cation- and anion-based normalization procedures provide accurate mineral formulae with respect to most cations and anions, but are unable to generate accurate estimates of Fe³⁺/Fe^T, and overestimate OH at the expense of O on the hydroxyl site. These inaccuracies are present despite acceptable adjusted totals and stoichiometric calculated site occupancies. The phlogopite and biotite phenocrysts in arc-related lavas from western Mexico and eastern California have the highest Fe³⁺/Fe^T ratios (56–87%), reflecting high magmatic oxygen fugacities (ΔNNO = +2 to +5), in contrast to those from Uganda (25–40%) and the Leucite Hills (23%). There is no correlation between the OH content and the Fe³⁺/Fe^T ratio in the micas. Values of KMg/Fe²⁺D (± 2σ errors) were calculated for three phlogopite-olivine pairs (0.12 ± 0.12, 0.26 ± 0.14, 0.09 ± 0.12), two biotite-hornblende pairs (0.73 ± 0.08 and 1.22 ± 0.10) and a single phlogopite-augite pair (1.15 ± 0.12). Values of KF/OHD for two biotite and hornblende pairs could not be determined without significant error because of the extremely low F contents (< 0.2 wt%) of the four phases. The δD values obtained in this study encompass a large range (−137 to −43‰). The phlogopite and biotite separates from Uganda have δD values of −70 to −49‰, which overlap those believed to represent “primary” mantle. There is a larger range in δD values (−137 to −43‰) for phlogopite phenocrysts from western Mexico minette lavas, although their range in δ¹⁸O values (5.2–6.2‰) is consistent with “normal” mantle. It is unlikely, therefore, that the variable δD values reflect heterogeneity in the mantle source region of the minette magmas. Nor can the extremely low δD values reflect degassing of H₂ or H₂O since almost 100% loss of dissolved water in the magma is required, an unrealistic scenario given the stability of the hydrous phenocrysts. The very low δD values of the Mascota minette phlogopites require that the hydrogen be introduced from an external source (e.g., meteoric water). Whatever the process responsible for the observed hydrogen isotope composition, it had no effect on the δ¹⁸O value, f _{O 2}, a _{H 2O} or bulk composition of the host magmas. Received: 5 January 1995 / Accepted: 19 March 1996     

Multistage Carbonatization and Mineral Geochemistry of a Skarn—type Copper Deposit at Tongshan ,Guichi

The Tongshan copper deposit at Guichi can be considered as a skarn-type copper deposit. Multi-stage carbonatization was well developed in the skarn zone and copper-bearing orebodies. Mineralogy, mineral chemistry and stable isotope data allow it to be divided into five stages: (1) carbonatization of single calcite crystals in the skarn stage; (2) calcite carbonatization in the oxide stage; (3) carbonatization in the early sulfide stage; (4) carbonatization in the late sulfide stage; and (5) carbonatization in the post-sulfide stage. Carbonatization in the early sulfide stage is, among other things, closely related to copper mineralization and is one of the alteration indicators of copper mineralization of this type. C. O, Rb and Sr isotopic studies indicate that the calcites of skarn and oxide stages were formed from hydrothermal solutions predominated by magmatic water, and those of sulfide stage were formed from hydrothermal solutions mainly involving heated meteoric water. The former was formed in the environment wherefO ₂ (fO ₂ < 10⁻³³ and 10⁻³³< fO₂>10⁻³⁶)(pH = 7–8) is high as compared with the latter (10⁻³⁵< fO₂< 10⁻³⁸; pH = 5–7).     

Crystal-chemical and energetic systematics of wadeite-type phases A2BSi3O9 (A = K, Cs; B = Si, Ti, Zr)

Wadeite K₂ZrSi₃O₉ and its analogues K₂TiSi₃O₉ and Cs₂ZrSi₃O₉, synthesized by high-temperature solid-state sintering, have been investigated using powder X-ray diffraction coupled with Rietveld analysis and high-temperature oxide melt solution calorimetry. The crystal chemistry and energetics of these phases, together with K₂Si^VISi₃ ^IVO₉, a high-pressure wadeite analogue containing both tetrahedral and octahedral Si, are discussed in term of ionic substitutions. As the size of the octahedral framework cation increases, Si⁴⁺ → Ti⁴⁺ → Zr⁴⁺, the cell parameter c increases at a much higher rate than a. In contrast, increasing the interstitial alkali cation size (K⁺ → Cs⁺) results in a higher rate of increase in a compared with c. This behavior can be attributed to framework distortion around the interstitial cation. The enthalpies of formation from the constituent oxides (ΔH_f,ox⁰) and from the elements (ΔH_f,el⁰) have been determined from drop-solution calorimetry into 2PbO·B₂O₃ solvent at 975 K. The obtained values (in kJ/mol) are as follows: ΔH_f,ox⁰ (K₂TiSi₃O₉) = −355.8 ± 3.0, ΔH_f,el⁰ (K₂TiSi₃O₉) = −4395.1 ± 4.8, ΔH_f,ox⁰ (K₂ZrSi₃O₉) = −374.3 ± 3.3, ΔH_f,el⁰ (K₂ZrSi₃O₉) = −4569.9 ± 5.0, ΔH_f,ox⁰ (Cs₂ZrSi₃O₉) = −396.6 ± 4.4, and ΔH_f,el⁰ (Cs₂ZrSi₃O₉) = −4575.0 ± 5.5. The enthalpies of formation for K₂Si^VISi₃ ^IVO₉ were calculated from its drop-solution enthalpy of an earlier study (Akaogi et al. 2004), and the obtained ΔH_f,ox⁰ (K₂SiSi₃O₉) = −319.7 ± 3.4 and ΔH_f,el⁰ (K₂SiSi₃O₉) = −4288.7 ± 5.1 kJ/mol. With increasing the size of the octahedral framework cation or of the interstitial alkali cation, the formation enthalpies become more exothermic. This trend is consistent with the general behavior of increasing energetic stability with decreasing ionic potential (z/r) seen in many oxide and silicate systems. Further, increasing the size of the octahedral framework cation appears to induce more rapid increase in stability than increasing the interstitial alkali cation size, suggesting that framework cations play a more dominant role in wadeite stability.     

Large calcite and bulk-rock volume loss in metacarbonate xenoliths from the Quérigut massif (French Pyrenees)

Chemical mass transfer was quantified in a metacarbonate xenolith enclosed within the granodiorite of the Quérigut massif (Pyrenees, France). Mass balance calculations suggest a strong decrease of CaO, SrO and CO₂ contents (up to −90%), correlated with a decrease of modal calcite content as the contact is approached. Most other chemical elements behave immobile during metasomatism. They are therefore passively enriched. Only a small increase of SiO₂, Al₂O₃ and Fe₂O₃ contents occurs in the immediate vicinity of the contact. Hence, in this study, skarn formation is characterized by the lack of large chemical element influx from the granitoid protolith. A large decrease of the initial carbonate volume (up to −86%) resulted from a combination of decarbonation reactions and loss of CaO and CO₂. The resulting volume change has potentially important consequences for the interpretation of stable isotope profiles: the isotope alteration could have occured over greater distances than those observed today.     

Primary production in Long Island sound

Daily and annual integrated rates of primary productivity and community respiration were calculated using physiological parameters measured in oxygen-based photosynthesis-irradiance (P-I) incubations at 8 stations throughout central and western Long Island Sound (cwLIS) during the summer and autumn of 2002 and 2003 and the late spring of 2003. Each calculation takes into account actual variations in incident irradiance over the day and underwater irradiance and standing stock with depth. Annual peak rates, ±95% confidence interval of propagated uncertainty in each measurement, of gross primary production (GPP, 1,730±610 mmol O₂ m⁻² d⁻¹), community respiration (R_c, 1,660±270 mmol O₂ m⁻² d⁻¹), and net community production (NCP, 1,160±1,100 mmol O₂ m⁻² d⁻¹) occurred during summer at the western end of the Sound. Lowest rates of GPP (4±11 mmol O₂ m⁻² d⁻¹), R_c (−50±300 mmol O₂ m⁻² d⁻¹), and NCP (−1,250±270 mmol O₂ m⁻² d⁻¹) occurred during late autumn-early winter at the outer sampled stations. These large ranges in rates of GPP, R_c, and NCP throughout the photic zone of cwLIS are attributed to seasonal and spatial variability. Algal respiration (R_a) was estimated to consume an average of 5% to 52% of GPP, using a literature-based ratio of R_a:R_c. From this range, we established that the estimated R_a accounts for approximately half of GPP, and was used to estimate daily net primary production (NPP), which ranged from 2 to 870 mmol O₂ m⁻² d⁻¹ throughout cwLIS during the study. Annual NPP averaged 40±8 mol O₂ m⁻² yr⁻¹ for all sampled stations, which more than doubled along the main axis of the Sound, from 32±14 mol O₂ m⁻² yr⁻¹ at an eastern station to 82±25 mol O₂ m⁻² yr⁻¹ at the western-most station. These spatial gradients in productivity parallel nitrogen loads along the main axis of the Sound. Daily integrals of productivity were used to test and formulate a simple, robust biomass-light model for the prediction of phytoplankton production in Long Island Sound, and the slope of the relationship was consistent with reports for other systems.     

Estimation of methane emission from whole waste landfill site using correlation between flux and ground temperature

A methodology to estimate a methane emission in a waste landfill site was developed. The methane flux at a waste landfill site in summer, autumn, and winter was within the following ranges: from −1.3×10⁻² to 16, from −6.4×10⁻² to 7.5, and from −1.6×10⁻³ to 1.5×10⁻² g-CH₄ m⁻² h⁻¹, respectively. In those seasons, the mean methane emission rate and coefficient of variation were 1.1 g-CH₄ m⁻² h⁻¹ ±290%, 0.57 g-CH₄ m⁻² h⁻¹ ±347%, and 5.4×10⁻² g-CH₄ m⁻² h⁻¹ ±370%, respectively. These results simultaneously showed that fluctuations of methane emission from the landfill surface were both of spatial and temporal variability. In each season, an exponential relationship was observed between the methane flux density and the ground temperature. Total methane emissions were estimated to be 5.7×10⁻², 7.1×10⁻³, and 1.7×10⁻³ g-CH₄ m⁻² h⁻¹ in the summer, autumn, and winter surveys, respectively, using a temperature surrogated-kriging method. The results of this study would improve upon the labor-intensive closed-chamber method, and could be a more practical way to estimate methane emissions from waste landfills.     

Thermal expansion of gehlenite, Ca2Al[AlSiO7], and the related aluminates LnCaAl[Al2O7] with Ln = Tb, Sm

The thermal expansion of gehlenite, Ca₂Al[AlSiO₇], (up to T=830 K), TbCaAl[Al₂O₇] (up to T=1100 K) and SmCaAl[Al₂O₇] (up to T=1024 K) has been determined. All compounds are of the melilite structure type with space group Thermal expansion data were obtained from in situ X-ray powder diffraction experiments in-house and at HASYLAB at the Deutsches Elektronen Synchrotron (DESY) in Hamburg (Germany). The thermal expansion coefficients for gehlenite were found to be: α₁=7.2(4)×10⁻⁶×K⁻¹+3.6(7)×10⁻⁹ΔT×K⁻² and α₃=15.0(1)×10⁻⁶×K⁻¹. For TbCaAl[Al₂O₇] the respective values are: α₁=7.0(2)×10⁻⁶×K⁻¹+2.0(2)×10⁻⁹ΔT×K⁻² and α₃=8.5(2)×10⁻⁶×K⁻¹+2.0(3)×10⁻⁹ΔT×K⁻², and the thermal expansion coefficients for SmCaAl[Al₂O₇] are: α₁=6.9(2)×10⁻⁶×K⁻¹+1.7(2)×10⁻⁹ΔT×K⁻² and α₃=9.344(5)×10⁻⁶×K⁻¹. The expansion mechanisms of the three compounds are explained in terms of structural trends obtained from Rietveld refinements of the crystal structures of the compounds against the powder diffraction patterns. No structural phase transitions have been observed. While gehlenite behaves like a ‘proper’ layer structure, the aluminates show increased framework structure behavior. This is most probably explained by stronger coulombic interactions between the tetrahedral conformation and the layer-bridging cations due to the coupled substitution (Ca²⁺+Si⁴⁺)–(Ln ³⁺+Al³⁺) in the melilite-type structure. This article has been mistakenly published twice. The first and original version of it is available at .     

Geochemistry and mineralization age of magnesian skarn-type iron deposits of the Janggun mine, Republic of Korea

The Janggun iron deposits, Republic of␣Korea, occur as lens-shaped magnesian skarn, magnetite and base-metal sulfide orebodies developed in the Cambrian Janggun Limestone Formation. Mineralization stage of the deposits can be divided into two separate events. The skarn stage (107 Ma) consists of magnetite, pyrrhotite, base-metal sulfides, carbonates and magnesian skarn minerals. The hydrothermal stage (70 Ma) consists of base-metal sulfides, native bismuth, bismuthinite, tetrahedrite, boulangerite, bournonite and stannite. Mineral assemblages, chemical compositions and thermodynamic considerations indicate that formation temperatures, −log fs₂ and −log fo₂ values of ore fluids from the skarn stage were 433 to 345 °C, 8.1 to 9.7 bar and 29.4 to 31.6 bar, and the hydrothermal stage was 245 to 315 °C, 10.4 to 13.2 bar and 33.6 to 35.4 bar, respectively. Thermochemical considerations indicate that the XCO₂ during magnesian skarnization ranged from 0.06 to 0.09, and the activity of H⁺ presumably decreased when the fluids equilibrated with host dolomitic limestone which resulted in a pH change from about 6.1 to 7.8, and decreases in fo₂ and fs₂. The δ³⁴S values of ore sulfides have a wide range from 3.2 to 11.6 ‰ (CDT). Calculated ³⁴SH_{2 S} values of ore fluids are 2.9 to 5.4 ‰ (skarn stage) and 8.7 to 13.5 ‰ (hydrothermal stage). These are interpreted to represent an initial deep-seated, igneous source of sulfur which gave way to influence of oxidized sedimentary sulfur to hydrothermal stage. The δ¹³C values of carbonates in ores range from −4.6 to −2.5 ‰ (PDB). It is likely that carbon in the ore fluids was a mixture of deep-seated magmatic carbon and dissolved carbon of dolomitic limestone. The δ¹⁸OH_{2 O} and δD values (SMOW) of water in the ore fluids were 14.7 to 1.8 and −85 to −73 ‰ during the skarn stage and 11.1 to −0.2 and −87 to −80 ‰ in the hydrothermal stage. Received: 5 March 1997 / Accepted: 28 August 1997     

Geochemistry characterization of groundwater in an agricultural area of Razan,Hamadan, Iran

This study was conducted to evaluate factors regulating groundwater quality in an area with agriculture as main use. Thirty groundwater samples have been collected from Razan area (Hamadan, Iran) for hydrochemical investigations to understand the sources of dissolved ions and assess the chemical quality of the groundwater. The chemical compositions of the groundwater are dominated by Na⁺, Ca²⁺, HCO₃ ⁻, Cl⁻ and SO₄ ²⁻, which have been derived largely from natural chemical weathering of carbonate, gypsum and anthropogenic activities of fertilizer’s source. The production of SO₄ ²⁻ has multiple origins, mainly from dissolution of sulphate minerals, oxidation of sulphide minerals and anthropogenic sources. The major anthropogenic components in the groundwater include Na⁺, Cl⁻, SO₄ ²⁻ and NO₃ ⁻, with Cl⁻ and NO₃ ⁻ being the main contributors to groundwater pollution in Razan area.     

Fluid inclusion and stable isotope evidence for the genesis of quartz-scheelite veins, Metaggitsi area, central Chalkidiki Peninsula, N. Greece

Scheelite mineralization accompanied by muscovite and albite, and traces of Mo-stolzite and stolzite occurs in epigenetic quartz vein systems hosted by two-mica gneissic schists, and locally amphibolites, of the Paleozoic or older Vertiskos Formation, in the Metaggitsi area, central Chalkidiki, N Greece. Three types of primary fluid inclusions coexist in quartz and scheelite: type 1, the most abundant, consists of mixed H₂O-CO₂ inclusions with highly variable (20–90 vol.%) CO₂ contents and salinities between 0.2 and 8.3 equivalent weight % NaCl. Densities range from 0.79 to 0.99 g/cc; type 1 inclusions contain also traces (<2 mol%) of CH₄. Type 2 inclusions are nearly 100 vol.% liquid CO_2, with traces of CH₄, and densities between 0.75 and 0.88 g/cc. Type 3 inclusions, the least abundant, contain an aqueous liquid of low salinity (0.5 to 8.5 equivalent weight% NaCl) with 10–30 vol.% H₂O gas infrequently containing also small amounts of CO₂ (<2 mol%); densities range from 0.72 to 0.99 g/cc. The wide range of coexisting fluid inclusion compositions is interpreted as a result of fluid immiscibility during entrapment. Immiscibility is documented by the partitioning of CH₄ and CO₂, into gas-rich (CO₂-rich) type 1 inclusions, and the conformity of end-member compositions trapped in type 1 inclusions to chemical equilibrium fractionation at the minimum measured homogenization temperatures, and calculated homogenization pressures. Minimum measured homogenization temperatures of aqueous and gas-rich type 1 inclusions of 220°–250 °C, either to the H₂O, or to the CO₂ phase, is considered the best estimate of temperature of formation of the veins, and temperature of scheelite deposition. Corresponding fluid pressures were between 1.2 and 2.6 kbar. Oxygen fugacities during mineralization varied from 10⁻³⁵ to 10⁻³¹ bar and were slightly above the synthetic Ni-NiO buffer values. The fluid inclusion data combined with δ¹⁸O water values of 3 to 6 per mil (SMOW) and δ¹³C CO₂₋ fluid of −1.2 to +4.3 per mil (PDB), together with geologic data, indicate generation of mineralizing fluids primarily by late- to post-metamorphic devolatilization reactions. Received: 8 April 1997 / Accepted: 8 July 1997     

Calorimetric study of perovskite solid solutions in the CaSiO3–CaGeO3 system

 Enthalpies of drop solution (ΔH _drop-sol) of CaGeO₃, Ca(Si_0.1Ge_0.9)O₃, Ca(Si_0.2Ge_0.8)O₃, Ca(Si_0.3Ge_0.7)O₃ perovskite solid solutions and CaSiO₃ wollastonite were measured by high-temperature calorimetry using molten 2PbO · B₂O₃ solvent at 974 K. The obtained values were extrapolated linearly to the CaSiO₃ end member to give ΔH _drop-sol of CaSiO₃ perovskite of 0.2 ± 4.4 kJ mol⁻¹. The difference in ΔH _drop-sol between CaSiO₃, wollastonite, and perovskite gives a transformation enthalpy (wo → pv) of 104.4 ± 4.4 kJ mol⁻¹. The formation enthalpy of CaSiO₃ perovskite was determined as 14.8 ± 4.4 kJ mol⁻¹ from lime + quartz or −22.2 ± 4.5 kJ mol⁻¹ from lime + stishovite. A comparison of lattice energies among A²⁺B⁴⁺O₃ perovskites suggests that amorphization during decompression may be due to the destabilizing effect on CaSiO₃ perovskite from a large nonelectrostatic energy (repulsion energy) at atmospheric pressure. By using the formation enthalpy for CaSiO₃ perovskite, phase boundaries between β-Ca₂SiO₄ + CaSi₂O₅ and CaSiO₃ perovskite were calculated thermodynamically utilizing two different reference points [where ΔG(P,T )=0] as the measured phase boundary. The calculations suggest that the phase equilibrium boundary occurs between 11.5 and 12.5 GPa around 1500 K. Its slope is still not well constrained. Received: 20 September 2000 / Accepted: 17 January 2001     

Epidotisation of diorites at Al Hadah,Saudi Arabia: Fluid influx into cooling plutons

Diorite plutons at Al Hadah Saudi Arabia, which constitute part of the pan-African magmatic sequence (ca. 600 Ma), exhibit extensive development of epidote. The epidote alteration is concentrated along veins and dyke margins, and is characterised by transformation of plagioclase (Ab 67)+hornblende+biotite+quartz to epidote+hornblende+tremolite−actinolite+plagioclase (Ab 99)±quartz. The reactions involve addition of CaO and total Fe₂O₃, depletion of MgO, Na₂O and K₂O, with variable gains or losses of SiO₂. Epidotised alteration products are hydrated and oxidised relative to the diorite precursor. The whole rock δ¹⁸O of fresh diorite is + 8.2‰ to + 8.8‰, whereas epidote domains have δ¹⁸O whole rock of +9.8‰ to +10.48‰ and negative Δ¹⁸O_{quartz-plagioclase}, implying oxygen isotope exchange with fluids at low temperatures. Epidotisation is considered to have accompanied influx of fluids into plutons during cooling and contraction. The fluids were probably deep formation waters with relatively high Ca²⁺/Na⁺ ratios, moving up thermal gradient.     

The effect of chemical composition and oxygen fugacity on the electrical conductivity of dry and hydrous garnet at high temperatures and pressures

The in situ electrical conductivity of hydrous garnet samples (Py₂₀Alm₇₆Grs₄–Py₇₃Alm₁₄Grs₁₃) was determined at pressures of 1.0–4.0 GPa and temperatures of 873–1273 K in the YJ-3000t apparatus using a Solartron-1260 impedance/gain-phase analyzer for various chemical compositions and oxygen fugacities. The oxygen fugacity was controlled by five solid-state oxygen buffers (Fe₂O₃ + Fe₃O₄, Ni + NiO, Fe + Fe₃O₄, Fe + FeO, and Mo + MoO₂). Experimental results indicate that within a frequency range from 10⁻² to 10⁶ Hz, electrical conductivity is strongly dependent on signal frequency. Electrical conductivity shows an Arrhenius increase with temperature. At 2.0 GPa, the electrical conductivity of anhydrous garnet single crystals with various chemical compositions (Py₂₀Alm₇₆Grs₄, Py₃₀Alm₆₇Grs₃, Py₅₆Alm₄₃Grs₁, and Py₇₃Alm₁₄Grs₁₃) decreases with increasing pyrope component (Py). With increasing oxygen fugacity, the electrical conductivity of dry Py₇₃Alm₁₄Grs₁₃ garnet single crystal shows an increase, whereas that of a hydrous sample with 465 ppm water shows a decrease, both following a power law (exponents of 0.061 and −0.071, respectively). With increasing pressure, the electrical conductivity of this hydrous garnet increases, along with the pre-exponential factors, and the activation energy and activation volume of hydrous samples are 0.7731 ± 0.0041 eV and −1.4 ± 0.15 cm³/mol, respectively. The results show that small hopping polarons ( \textFe_\textMg ^· ) \left( {{\text{Fe}}_{\text{Mg}}^{ \cdot } } \right) and protons ( \textH ^· {\text{H}}^{ \cdot } ) are the dominant conduction mechanisms for dry and wet garnet single crystals, respectively. Based on these results and the effective medium theory, we established the electrical conductivity of an eclogite model with different mineral contents at high temperatures and high pressures, thereby providing constraints on the inversion of field magnetotelluric sounding results in future studies.     

Chemical composition of rock-forming minerals in gold-related granitoid intrusions,southwestern New Brunswick,Canada: implications for crystallization conditions,volatile exsolution,and fluorine-chlorine activity

Chemical composition of rock-forming minerals in Appalachian Siluro-Devonian granitoid intrusions, southwestern New Brunswick, was systematically determined by electron microprobe. The mineral chemical data together with petrographic examination was used to test magmatic equilibration and to constrain crystallization conditions, volatile exsolution, and fluorine-chlorine activity of fluids associated with these intrusions. Mineralogical distinction between Late Silurian to Early Devonian granodioritic to monzogranitic series (GMS) and Late Devonian granitic series (GS) rocks is evident, although both are subsolvus I-type to evolved I-type granitoids. Oxidized to reduced GMS rocks consist of quartz, plagioclase (An>10), K-feldspar, biotite, apatite, titanite, zircon, monazite, ± hornblende, ± pyroxene, ± magnetite, ± ilmenite, and ± sulfide. GS rocks comprise quartz, K-feldspar, plagioclase (An<10), mica group minerals, zircon, monazite, apatite, sulfide, ± ilmente, ± magnetite, ± topaz, ± columbite, and ± xenotime. Inter-intrusion and intra-intrusion variations in mineral chemistry are interpreted to reflect petrogenetic processes (e.g., assimilation and fractional crystallization) during granitoid evolution. Although magmatic equilibration among rock-forming minerals are disturbed by subsolidus hydrothermal processes, GMS rocks appear to have higher magmatic temperatures, variable levels of emplacement, a range of (i.e., reduced intrusions 10^−16.7∼10^−13.4 and oxidized intrusions 10^−14.0∼10^−10.5 bars), and relatively low f _HF/f _HCl ratios (10^−3.0∼10^−1.0) in exsolved fluids, compared to GS rocks. Reduced GMS intrusions bear higher gold potential and thus may be prospective targets for intrusion-related gold systems. Electronic Supplementary Material Supplementary material is available for this article at     

Thermal expansion of gehlenite, Ca2Al[AlSiO7], and the related aluminates LnCaAl[Al2O7] with Ln=Tb, Sm

The thermal expansion of gehlenite, Ca₂Al[AlSiO₇], (up to T=830 K), TbCaAl[Al₂O₇] (up to T=1,100 K) and SmCaAl[Al₂O₇] (up to T=1,024 K) has been determined. All compounds are of the melilite structure type with space group Thermal expansion data was obtained from in situ X-ray powder diffraction experiments in-house and at HASYLAB at the Deutsches Elektronen Synchrotron (DESY) in Hamburg (Germany). The thermal expansion coefficients for gehlenite were found to be: α₁=7.2(4)×10⁻⁶ K⁻¹+3.6(7)×10⁻⁹ΔT K⁻² and α₃=15.0(1)×10⁻⁶ K⁻¹. For TbCaAl[Al₂O₇] the respective values are: α₁=7.0(2)×10⁻⁶ K⁻¹+2.0(2)×10⁻⁹ΔT K⁻² and α₃=8.5(2)×10⁻⁶ K⁻¹+2.0(3)×10⁻⁹ΔT K⁻², and the thermal expansion coefficients for SmCaAl[Al₂O₇] are: α₁=6.9(2)× 10⁻⁶ K⁻¹+1.7(2)×10⁻⁹ΔT K⁻² and α₃=9.344(5)×10⁻⁶ K⁻¹. The expansion-mechanisms of the three compounds are explained in terms of structural trends obtained from Rietveld refinements of the crystal structures of the compounds against the powder diffraction patterns. No structural phase transitions have been observed. While gehlenite behaves like a ’proper’ layer structure, the aluminates show increased framework structure behaviour. This is most probably explained by stronger coulombic interactions between the tetrahedral conformation and the layer-bridging cations due to the coupled substitution (Ca²⁺+Si⁴⁺)-(Ln ³⁺+Al³⁺) in the melilite-type structure. Electronic Supplementary Material Supplementary material is available for this article at     

Transport properties of low-sanidine single-crystals, glasses and melts at high temperature

Thermal diffusivity (D) was measured using laser-flash analysis from oriented single-crystal low-sanidine (K_0.92Na_0.08Al_0.99Fe³⁺ _0.005Si_2.95O₈), and three glasses near KAlSi₃O₈. Viscosity measurements of the three supercooled liquids, in the range 10^6.8 to 10^12.3 Pa s, confirm near-Arrhenian behavior, varying subtly with composition. For crystal and glass, D decreases with T, approaching a constant near 1,000 K: D _sat ∼ 0.65 ± 0.3 mm² s⁻¹ for bulk crystal and ∼0.53 ± 0.03 mm² s⁻¹ for the glass. A rapid decrease near 1,400 K is consistent with crossing the glass transition. Melt behavior is approximated by D = 0.475 ± 0.01 mm² s⁻¹. Thermal conductivity (k _lat) of glass, calculated using previous heat capacity (C _P) and new density data, increases with T because C _P strongly increases with T. For melt, k _lat reaches a plateau near 1.45 W m⁻¹ K⁻¹, and is always below k _lat of the crystal. Melting of potassium feldspars impedes heat transport, providing positive thermal feedback that may promote further melting in continental crust.     

Interaction of model F-bearing silicic melt with chloride fluid,uraninite, and columbite at 750°C and 1000–2000 bar and its implications for estimation of the ore-forming capability of the upper crustal magma chamber beneath the Strel’tsovka caldera,eastern Transbaikalia

The experimental study of an F-bearing silicic melt—U, Nb, Ta minerals—chloride-fluoride fluid system is focused on ascertaining the origin of uranium deposits spatially related to intraplate silicic volcanism. The first series of experiments on uranium solubility in silicic melts close in composition to ore-bearing rhyolite of the unique Strel’tsovka Mo-U ore field has been performed in order to determine more precisely the ore genesis. As starting solid phases, model homogeneous glass of the chemical composition (wt %) 72.18 SiO₂, 12.19 Al₂O₃, 1.02 FeO, 0.20 MgO, 0.33 CaO, 4.78 Na₂O, 3.82 K₂O, 1.44 Li₂O, and 2.4 F (LiF, NaF, KF, CaF₂, MgF₂); synthetic UO₂ and UO₃·0.33H₂O; and natural columbite were used. The starting solutions contained 1.0 m Cl and 10⁻² m F. The runs were conducted in a gas vessel at a pressure of 1000 bar and in a high-pressure hydrothermal vessel at 2000 bar. The O₂ (H₂) fugacity was set by Ni-NiO, Co-CoO, Fe₃O₄-Fe₂O₃, and Cu-Cu₂O buffers. The equilibrium between melt and solution for major elements is reached during the first day, whereas 5–7 days are required for ore elements (U, Nb, Ta) to come into equilibrium. The solubility of Nb and especially Ta in Cl-F solutions equilibrated with F-bearing melt is extremely low. The solubility of U is much higher (10⁻⁴−10⁻⁵ mol/kg H₂O). The energy dispersive spectroscopy of run products allowed us to establish that columbite dissolved incongruently with formation of U- and F-bearing pyrochlores. The performed experiments have shown that a silicic melt close to the rhyolitic magma of the Strel’tsovka caldera in composition is not able to generate postmagmatic ore-forming solutions containing more than 10⁻⁶−10⁻⁵ mol U/kg H₂O under the relatively low pressure necessary for the existence of the first type of fluid. The amount of uranium that could have precipitated from this fluid in the zone of ore deposition is estimated at 216–9000 t. This estimate is two orders of magnitude lower than the total uranium resources of the deposits localized in the Strel’tsovka caldera. Thus, the upper crustal silicic magma chamber hardly was a source of uranium for Mo-U deposits of the Strel’tsovka ore field.     

Thermodynamic functions of eskolaite Cr<Subscript>2</Subscript>O<Subscript>3</Subscript>(c) at 0–1800 K

The heat capacity of eskolaite Cr₂O₃(c) was determined by adiabatic vacuum calorimetry at 11.99–355.83 K and by differential calorimetry at 320–480 K. Experimental data of the authors and data compiled from the literature were applied to calculate the heat capacity, entropy, and the enthalpy change of Cr₂O₃ within the temperature range of 0–1800 K. These functions have the following values at 298.15 K: C _p ⁰ (298.15) = 121.5 ± 0.2 J K⁻¹mol⁻¹, S ⁰(298.15) = 80.95 ± 0.14 J K⁻¹mol⁻¹, and H ⁰(298.15)-H ⁰(0) = 15.30±0.02 kJ mol⁻¹. Data were obtained on the transitions from the antiferromagnetic to paramagnetic states at 228–457 K; it was determined that this transition has the following parameters: Neel temperature T _N = 307 K, Δ _tr S = 6.11 ± 0.12 J K⁻¹mol⁻¹ and δ _tr H = 1.87 ± 0.04 kJ mol⁻¹.     

The nature of the stability of an incommensurate 3D structural modulation in Baikal lazurite: Experimental data at 550°C

The nature of the stability of an incommensurate 3D modulation (ITM) in the structure of Baikal lazurite was evaluated using the methods of experimental geochemistry and X-ray photoelectron spectroscopy. It was shown that ITM with a period of 4.6a is preserved in the lazurite structure at 550°C almost without changes within the time interval from t = 100 h to at least 2000 h, although its initial (t = 0) development was not restored. In contrast to higher temperatures (≥ 600°C), the activities of gas species have no significant influence on the process of modulation release, except for the region of low O₂, S₂, and SO₂ fugacities, where the type of modulation changes, and the monosulfide ion appears in the lazurite composition. At T = 550°C and probably at lower temperatures, SO₂ fugacity ceases to be the critical parameter of ITM existence. The ordered state of polysulfide and sulfate clusters corresponding to the ITM period of Baikal cubic lazurite is stable at T = 550°C and is an example of forced equilibrium. It develops in response to a crystal chemical event occurring at a temperature of T _x within 600–550°C and is related to the thermal compression of the structure resulting in the isolation of structural cages containing clusters with different states of sulfur. Their mutual interaction, which leads to the rapid release of the modulation at higher temperatures owing to the equalizing of cluster sizes in the cages, ceases. As a result, the proportions of reduced (S₂²⁻, and S _x ²⁻) and oxidized (SO₄²⁻, So₃²⁻, and S₂O₃²⁻ sulfur species show negligible variations, and there is only partial reduction of sulfate to sulfite and thiosulfate. Lazurite samples with disulfide and polysulfide ions behave similarly, which suggests that an important condition for the preservation of ITM is the presence of sulfur-bearing anions with different sizes rather than particular sulfur species in structural cages. The degree of ordering in the distribution of clusters attained at T _x remains unchanged owing to the development of forced equilibrium maintained by the energy balance between framework deformation and cluster ordering. Natural lazurite with an ITM structure could not form at temperatures higher than T _x , i.e., above 550–600°C