Thermal alteration of coal in the Khasyn coalfield, Magadan region, Russia

The Early Cretaceous coal deposits of the Khasyn coalfield are intruded by Palaeogene diabase dikes. The coal has vitrinite reflectance values of 2.0–2.5% R_o, and characteristics of normal anthracite at some distance from the dikes, but at direct contact with the dike two morphological coal varieties occur: coal inclusions in the diabase dike and dispersed carbonaceous matter within the dike rock. Both types of coaly matter have properties typical of anthracites: strong anisotropy, altered internal structure and high vitrinite reflectance values ranging from 3.8 to 5.5% R_o. The X-ray diffraction measurements of the interplanar spacing d(002) and the crystallite sizes Lc and La show rather similar values for coal inclusions in the dike and dispersed carbonaceous matter. The additional reflection at 3.37 Å, corresponding to semi-graphite admixture, occurs in the coal and carbonaceous matter inside the dike and is absent in the natural coal outside the dike.     

大同煤田接触变质煤的煤岩煤质变化规律

大同煤田石炭-二叠纪煤层中的岩浆岩侵入造就了大量的接触变质煤,降低了煤的利用价值。为了详细探讨岩浆岩体距煤层距离对煤的物理化学性质影响,通过对塔山井田5222巷的辉绿岩岩墙及周围煤层的地质编录、系统采样,及煤样的煤岩学分析、工业分析和元素分析,研究接触变质带的煤岩煤质特征。结果表明：接触变质煤在高温条件下生成各种天然焦微观结构,如镶嵌结构、流动结构、热解碳等;侵入体对煤层的瞬时加热显著提升了热变煤的煤级,镜质体最大反射率由正常煤的0.67%~0.87%增至接触变质煤的0.94%~3.67%;接触变质煤中水分含量和灰分产率显著升高,挥发分产率降低;靠近岩墙的煤样中C含量上升,H、N、O含量下降。综合分析认为,岩墙接触变质作用对煤层的影响范围约4.5 m,即1.25倍岩墙宽度,而严重变质带为1.6 m。研究成果为煤的开采利用评价提供依据。     

A natural example of crystal-plastic deformation enhancing the incorporation of water into quartz

Water content of quartz in and around a greenschist facies mylonitic shear zone located in the western Adirondacks was analyzed by micro-FTIR spectroscopy. The shear zone is within a pegmatitic dike, which cuts across a granitic gneiss. The thickness of the shear zone varies along strike from 15 cm wide and encompassing all of the pegmatite dike at its northern most exposure to 5 cm wide approximately 10 m south, along strike. Microstructures, including quartz ribbons and recrystallized grains, indicate quartz and feldspar within the mylonite underwent dislocation creep. Infrared spectral analysis was carried out using a Nicolet micro-FTIR on mylonitic quartz ribbons, pegmatitic quartz and gneissic quartz. A small aperture size (56 μm by 50 μm) for the IR beam allowed optically clear regions of the quartz grains to be analyzed without any contribution from grain boundaries. The smallest dimension of the quartz ribbons is 0.3 mm, whereas the pegmatitic quartz has a grain size of 3 to 5 cm. Results show mylonitic quartz ribbons contain the most water (320 H:10⁶ Si average, range of 50 to 1120 H:10⁶ Si); pegmatite quartz contains much less water (30 H:10⁶ Si average, range of 20–40 H:10⁶ Si) and the gneissic quartz contained an intermediate amount (200 H:10⁶ Si average, range of 20 to 870 H:10⁶ Si). These data indicate that water was preferentially incorporated into the deformed quartz ribbons.     

The use of numerical simulation in predicting coalbed methane producibility from the Gates coals, Alberta Inner Foothills, Canada: Comparison with Mannville coal CBM production in the Alberta Syncline

Two medium to low volatile bituminous rank coals in the Lower Cretaceous Gates Formation (Mannville equivalent), Inner Foothills of Alberta, were cored as part of a coalbed methane exploration program. The target seams (Seam 4 and Seam 10) were intersected at 652 m and 605 m, respectively. The coals were bright banded, relatively competent and reasonably cleated, with cleat spacing between 5–20 mm. The FMI (Formation Micro-Imaging) log identified two primary fracture directions, corresponding to both face and butt cleats, which were developed almost equally in some coal intervals. The amount of shearing was limited, in spite of the presence of numerous thrust faults and fold structures in the corehole vicinity. Total gas content was high, with an average of 17.7 cm³/g (arb; 568.1 scf/t). An adsorption isotherm of the thick Seam 4 showed gas saturation levels of 90% at in-situ reservoir conditions. Methane content was 92–96% and carbon dioxide levels were less than 2%. Isotopic studies on the methane confirmed the thermogenic origin of the gas, as anticipated based on the coal rank. The coal seams were fracture stimulated using 50/50 nitrogen and fresh water along with 9 to 12 tons of 12/20 mesh sand used as a proppant. It is believed that the coals were not stimulated properly because of the small proppant volume and the complex — and often unpredictable — fracture pattern in coals, particularly in the Inner Foothills region that has high stress anisotropy. An injectivity test showed coal absolute permeability to be less than 1 mD, the skin to be −  2 (indicating a slightly damaged coal) and water saturation in the cleats to be 90%. A four-month production test was conducted; gas rates declined from 930 to 310 m³/d (33 to 11 MCFD) and water rates were low (< 5 BWD). Produced water was saline (TDS was 20,000 mg/L) and high in chloride and bicarbonate ions. Production testing was followed by history matching and numerical simulation, which consisted of numerous vertical and horizontal well development scenarios and other parameters. Simulating multiple parallel horizontal wells in the Gates coals resulted in the highest peak gas production rates, cumulative production and recovery efficiencies, in agreement with public data from the Mannville coals in the deeper part of the Alberta Syncline. The positive effect of constructive interference in depressurizing the coal reservoirs and accelerating gas production over short periods of time was demonstrated. Coal quality data from a nearby underground mine shows that drilling horizontal wellbores in the Gates coals would be challenging because of unfavourable geomechanical properties, such as low cohesion and unconfined compressive strength values, and structural complexity.     

Dike intrusions into bituminous coal, Illinois Basin: H, C, N, O isotopic responses to rapid and brief heating

Unlike long-term heating in subsiding sedimentary basins, the near-instantaneous thermal maturation of sedimentary organic matter near magmatic intrusions is comparable to artificial thermal maturation in the laboratory in terms of short duration and limited extent. This study investigates chemical and H, C, N, O isotopic changes in high volatile bituminous coal near two Illinois dike contacts and compares observed patterns and trends with data from other published studies and from artificial maturation experiments. Our study pioneers in quantifying isotopically exchangeable hydrogen and measuring the D/H (i.e., ²H/¹H) ratio of isotopically non-exchangeable organic hydrogen in kerogen near magmatic contacts. Thermal stress in coal caused a reduction of isotopically exchangeable hydrogen in kerogen from 5% to 6% in unaltered coal to 2-3% at contacts, mostly due to elimination of functional groups (e.g., OH, COOH, NH₂). In contrast to all previously published data on D/H in thermally matured organic matter, the more mature kerogen near the two dike contacts is D-depleted, which is attributed to (i) thermal elimination of D-enriched functional groups, and (ii) thermal drying of hydrologically isolated coal prior to the onset of cracking reactions, thereby precluding D-transfer from relatively D-enriched water into kerogen. Maxima in organic nitrogen concentration and in the atomic N/C ratio of kerogen at a distance of ∼2.5 to ∼3.5 m from the thicker dike indicate that reactive N-compounds had been pyrolytically liberated at high temperature closer to the contact, migrated through the coal seam, and recombined with coal kerogen in a zone of lower temperature. The same principle extends to organic carbon, because a strong δ¹³C_kerogen vs. δ¹⁵N_kerogen correlation across 5.5 m of coal adjacent to the thicker dike indicates that coal was functioning as a flow-through reactor along a dynamic thermal gradient facilitating back-reactions between mobile pyrolysis products from the hot zone as they encounter less hot kerogen. Vein and cell filling carbonate is most abundant in highest rank coals where carbonate δ¹³C_VPDB and δ¹⁸O_VSMOW values are consistent with thermal generation of ¹³C-depleted and ¹⁸O-enriched CO₂ from decarboxylation and pyrolysis of organic matter. Lower background concentrations of ¹³C-enriched carbonate in thermally unaffected coal may be linked to ¹³C-enrichment in residual CO₂ in the process of CO₂ reduction via microbial methanogenesis.Our compilation and comparison of available organic H, C, N isotopic findings on magmatic intrusions result in re-assessments of majors factors influencing isotopic shifts in kerogen during magmatic heating. (i) Thermally induced shifts in organic δD values of kerogen are primarily driven by the availability of water or steam. Hydrologic isolation (e.g., near Illinois dikes) results in organic D-depletion in kerogen, whereas more common hydrologic connectivity results in organic D-enrichment. (ii) Shifts in kerogen (or coal) δ¹³C and δ¹⁵N values are typically small and may follow sinusoidal patterns over short distances from magmatic contacts. Laterally limited sampling strategies may thus result in misleading and non-representative data. (iii) Fluid transport of chemically active, mobile carbon and nitrogen species and recombination reactions with kerogen result in isotopic changes in kerogen that are unrelated to the original, autochthonous part of kerogen.     

Two magma series and associated ore deposit types in the Permian Emeishan large igneous province, SW China

The Late Middle Permian ( 260 Ma) Emeishan large igneous province in SW China contains two magmatic series, one comprising high-Ti basalts and Fe-rich gabbroic and syenitic intrusions, the other low-Ti basalts and mafic–ultramafic intrusions. The Fe-rich gabbros are spatially and temporally associated with syenites. Each series is associated with a distinctive type of mineralization, the first with giant Fe–Ti–V oxide ore deposits such as Panzhihua and Baima, the second with Ni–Cu–(PGE) sulfide deposits such as Jinbaoshan, Limahe and Zhubu. New SHRIMP zircon U–Pb isotopic data yielded 263 ± 3 Ma for the Limahe intrusion, 261 ± 2 Ma for the Zhubu intrusion and 262 ± 2 Ma for a syenitic intrusion. These new age dates, together with previously reported SHRIMP zircon U–Pb ages, suggest that all these intrusions are contemporaneous with the Emeishan flood basalts and formed during a major igneous event at ca. 260 Ma.The oxide-bearing intrusions have higher Al₂O₃, FeO (as total iron) and total alkalis (Na₂O + K₂O) but lower MgO than the sulfide-bearing intrusions. All intrusions are variably enriched in LREE relative to HREE. The oxide-bearing intrusions display positive Nb- and Ti-anomalies and in certain cases negative Zr–Hf anomalies, whereas the sulfide-bearing intrusions have obvious negative Nb- and Ti-anomalies, a feature of crustal contamination. Individual intrusions have relatively small ranges of Nd(t) values. All the intrusions, however, have Nd(t) values ranging from − 3.9 to + 4.6, and initial ⁸⁷Sr/⁸⁶Sr ratios from 0.7039 to 0.7105. The syenites have very low MgO (< 2 wt.%) but highly variable Fe₂O₃ (2.5 to 13 wt.%) with initial ⁸⁷Sr/⁸⁶Sr ratios ranging from 0.7039 to 0.7089. Magmas from both series could have derived by melting of a heterogeneous mantle plume: the high-Ti series from a Fe-rich, more fertile source and the low-Ti series from a Fe-poor, more refractory source. In addition, the low-Ti series underwent significant crustal contamination. The two magma series evolved along different paths that led to distinct mineralization styles.     

Development of the first coal seam gas exploration program in Indonesia: Reservoir properties of the Muaraenim Formation, south Sumatra

The Late Miocene Muaraenim Formation in southern Sumatra contains thick coal sequences, mostly of low rank ranging from lignite to sub-bituminous, and it is believed that these thick low rank coals are the most prospective for the production of coal seam gas (CSG), otherwise known as coalbed methane (CBM), in Indonesia.As part of a major CSG exploration project, gas exploration drilling operations are being undertaken in Rambutan Gasfields in the Muaraenim Formation to characterize the CSG potential of the coals. The first stage of the project, which is described here, was designed to examine the gas reservoir properties with a focus on coal gas storage capacity and compositional properties. Some five CSG exploration boreholes were drilled in the Rambutan Gasfield, south of Palembang. The exploration boreholes were drilled to depths of ~ 1000 m into the Muaraenim Formation. Five major coal seams were intersected by these holes between the depths of 450 and 1000 m. The petrography of coal samples collected from these seams showed that they are vitrinite rich, with vitrinite contents of more than 75% (on a mineral and moisture free basis). Gas contents of up to 5.8 m³/t were measured for the coal samples. The gas desorbed from coal samples contain mainly methane (CH₄) ranging from 80 to 93% and carbon dioxide (CO₂) ranging from 6 to 19%. The composition of the gas released into the production borehole/well is, however, much richer in CH₄ with about 94 to 98% CH₄ and less than 5% CO₂.The initial results of drilling and reservoir characterization studies indicate suitable gas recovery parameters for three of the five coal seams with a total thickness of more than 30 m.     

The pleochroism of a gem-quality enstatite in the region of the OH stretching frequency,with a stereochemical interpretation

Summary The pleochroic behaviour of a gem-quality enstatite from Tanzania was investigated in the region =2500 to 4000 cm^–1. Two sharp absorption bands at =3410 cm^–1 and =3510 cm^–1 are interpreted to be caused by OH stretching vibrations. As their absorption coefficients are considerably larger parallel to [001] (=direction of the silicate chains) than perpendicular to this direction, the OH dipoles have to be oriented approximately parallel to [001]. On this basis, a stereochemical interpretation of the incorporation of the OH groups into the structure is given.

---

Der Pleochroismus eines Enstatits von Edelsteinqualität im Gebiet der OH-Streckfrequenz und seine kristallchemische Interpretation

Zusammenfassung Das pleochroitische Verhalten eines Enstatits von Edelsteinqualität aus Tansania wurde im Bereich =2500 bis 4000 cm^–1 untersucht. Von zwei scharfen Banden bei =3410 cm^–1 und 3510 cm^–1 wird angenommen, daß sie durch OH-Streckschwingungen herrühren. Da ihre Absorptionskoeffizienten parallel zu [001] (=Richtung der Silikatketten) beträchtlich größer sind als senkrecht dazu, müssen die OH-Dipole ungefähr parallel zu [001] liegen. Auf dieser Basis wird der Einbau der OH-Gruppen in die Struktur diskutiert.

---

---

With 3 Figures     

Thermal maturity and organic composition of Pennsylvanian coals and carbonaceous shales, north-central Texas: Implications for coalbed gas potential

Thermal maturity was determined for about 120 core, cuttings, and outcrop samples to investigate the potential for coalbed gas resources in Pennsylvanian strata of north-central Texas. Shallow (< 600 m; 2000 ft) coal and carbonaceous shale cuttings samples from the Middle-Upper Pennsylvanian Strawn, Canyon, and Cisco Groups in Archer and Young Counties on the Eastern Shelf of the Midland basin (northwest and downdip from the outcrop) yielded mean random vitrinite reflectance (R_o) values between about 0.4 and 0.8%. This range of R_o values indicates rank from subbituminous C to high volatile A bituminous in the shallow subsurface, which may be sufficient for early thermogenic gas generation. Near-surface (< 100 m; 300 ft) core and outcrop samples of coal from areas of historical underground coal mining in the region yielded similar R_o values of 0.5 to 0.8%. Carbonaceous shale core samples of Lower Pennsylvanian strata (lower Atoka Group) from two deeper wells (samples from ~ 1650 m; 5400 ft) in Jack and western Wise Counties in the western part of the Fort Worth basin yielded higher R_o values of about 1.0%. Pyrolysis and petrographic data for the lower Atoka samples indicate mixed Type II/Type III organic matter, suggesting generated hydrocarbons may be both gas- and oil-prone. In all other samples, organic material is dominated by Type III organic matter (vitrinite), indicating that generated hydrocarbons should be gas-prone. Individual coal beds are thin at outcrop (< 1 m; 3.3 ft), laterally discontinuous, and moderately high in ash yield and sulfur content. A possible analog for coalbed gas potential in the Pennsylvanian section of north-central Texas occurs on the northeast Oklahoma shelf and in the Cherokee basin of southeastern Kansas, where contemporaneous gas-producing coal beds are similar in thickness, quality, and rank.     

Contact metamorphism of roof pendants at Hope Valley,Alpine County,California, USA

Calcareous hornfelses and marbles all contain calcite+K-feldspar+quartz+sphene±diopside±plagioclase ±scapolite±clinozoisite. In addition, rocks on one side of a fault contain combinations of biotite, amphibole, and muscovite while those on the other side contain combinations of grossular, wollastonite, and axinite. At bars, mineral-fluid equilibria in biotite and amphibole-bearing rocks record T= 440° C and garnet-bearing rocks record T=540° C and Conventional volumetric fluid-rock ratios were calculated using measured progress of prograde decarbonation reactions and the conditions of metamorphism: marbles, 0–0.4; amphibole-bearing hornfelses, 1.0–1.4; garnet-bearing hornfelses, 2.8–6.7. Decarbonation reactions were driven by pervasive infiltration of rock by reactive aqueous fluids. Differences in fluid-rock ratio between interbedded marble and hornfels and lack of correlation between fluid-rock ratio and whole-rock Cl-content, however, argue for channelized fluid flow along lithologic layers. A new analysis of reaction progress allows estimation of time-integrated fluxes for a specified temperature gradient along the direction of flow. Results are: marbles, 0–0.1×10⁵ cm³/cm²; amphibole-bearing hornfelses, 0.8–1.3×10⁵ cm³/cm²; garnet-bearing hornfelses, 1.2–2.5 × 10⁵ cm³/cm². Fluid flowed from regions of low to regions of high temperature. Using a simple thermal model for the area, the duration of contact metamorphism was estimated as 10⁵ years. Assuming the time of fluid flow was the same as the duration of the thermal event, the first measurements of average metamorphic fluxes (q) and permeabilities (k) are: average marbles, q=0–0.3×10^–8 cm/s and k =2×10^–6 darcy; hornfels, q=3–8×10^–8 cm/s and k =20–53×10^–6 darcy. Estimated premeabilities are within the range of values measured for metamorphic rocks in the laboratory. Fluxes, permeabilities, and whole-system fluidrock ratios are similar to those estimated for the Skaergaard hydrothermal system by Norton and Taylor (1979).     

The generation and crystallization conditions of the Proterozoic Harney Peak Leucogranite,Black Hills,South Dakota,USA: Petrologic and geochemical constraints

The mineralogy, petrology and geochemistry of the Proterozoic Harney Peak Granite, Black Hills, South Dakota, were examined in view of experimentally determined phase equilibria applicable to granitic systems in order to place constraints on the progenesis of peraluminous leucogranites and commonly associated rare-element pegmatites. The granite was emplaced at 3–4 kbar as multiple sills and dikes into quartz-mica schists at the culmination of a regional high-temperature, low-pressure metamorphic event. Principally along the periphery of the main pluton and in satellite intrusions, the sills segregated into granite-pegmatite couplets. The major minerals include quartz, K-feldspar, sodic plagioclase and muscovite. Biotite-{Mg No. [Molar MgO/(MgO+FeO)]=0.32-0.38} is the predominant ferromagnesian mineral in the granite's core, whereas at the periphery of the main pluton and in the satellite intrusions tourmaline (Mg No.=0.18–0.48) is the dominant ferromagnesian phase. Almandine-spessartine garnet is also found in the outer intrusions. There is virtually a complete overlap in the wide concentration ranges of SiO₂, CaO, MgO, FeO, Sr, Zr, W of the biotite- and tourmaline-bearing granite suites with no discernable differentiation trends on Harker diagrams, precluding the derivation of one suite from the other by differentiation following emplacement. This is consistent with the oxygen isotope compositions which are 11.5 ± 0.6 for the biotite granites and 13.2 ± 0.8 for the tourmaline granites, suggesting derivation from different sources. The concentrations of TiO₂ and possibly Ba are higher and of MnO and B are lower in the biotite granites. The normative Orthoclase/Albite ratio is extremely variable ranging from 0.26 to 1.65 in the biotite granites to 0.01–1.75 in the tourmaline granites. Very few sample compositions fall near the high-pressure, watersaturated haplogranite minima-eutectic trend, indicating that the granites for the most part are not minimum melts generated under conditions with =1. Instead, most biotite granites are more potassic than the water-saturated minima and eutectics and in analogy with experimentally produced granitic melts, they are best explained by melting at 6 kbar, <1 and temperatures 800°C. Such high temperatures are also indicated by oxygen isotope equilibration among the constituent minerals (Nabelek et al. 1992). Several of the tourmaline granite samples contain virtually no K-feldspar and have oxygen isotope equilibration temperatures 716–775°C. Therefore, they must represent high-temperature accumulations of liquidus minerals crystallized under equilibrium conditions from melts more sodic than the water-saturated haplogranite minima or during fractionation of intruded melts into granite-pegmatite couplets accompanied by volatile-aided differentiation of the alkali elements. The indicated high temperatures, <1, the relatively high TiO₂ and Ba concentrations and the relatively low values of the biotite granites suggest that they were generated by high-extent, biotite-dehydration melting of an immature Archean metasedimentary source. The ascent of the hot melts may have triggered low-extent, muscovite-dehydration melting of schists higher in the crust producing the high-B, low-Ti melts comprising the periphery of the main pluton and the satellite intrusions. Alternatively, the different granite types may be the result of melting of a vertical section of the crust in response to the ascent of a thermal pulse, with the low- biotite granites generated at a deeper, hotter region and the high- tourmaline granites at a higher, cooler region of the crust. The low-Ti and high-B concentrations in the high- melts resulted in the crystallization of tourmaline rather than biotite, which promoted the observed differentiation of the melts into the granitic and pegmatitic layers found along the periphery of the main pluton and the satellite intrusions.     

Petrological, organic geochemical and geochemical characteristics of coal from the Soko mine, Serbia

A petrological, organic geochemical and geochemical study was performed on coal samples from the Soko Mine, Soko Banja basin, Serbia. Ten coal and two carbonaceous clay samples were collected from fresh, working faces in the underground brown coal mine from different parts of the main coal seam. The Lower Miocene, low-rank coal of the Soko Mine is a typical humic coal with huminite concentrations of up to 76.2 vol.%, liptinite less than 14 vol.% and inertinite less than 11 vol.%. Ulminite is the most abundant maceral with variable amounts of densinite and clay minerals. Sporinite and resinite are the most common macerals of the liptinite group. Inertodetrinite is the most abundant maceral of the inertinite group. The mineral-bituminous groundmass identified in some coal samples, and carbonaceous marly clay, indicate sub-aquatic origin and strong bacterial decomposition. The mean random huminite reflectance (ulminite B) for the main coal seam is 0.40 ± 0.05% Rr, which is typical for an immature to early mature stage of organic matter.The extract yields from the coal of the Soko Banja basin ranges from 9413 to 14,096 ppm, in which alkanes constituted 1.0–20.1%, aromatics 1.3–14.7%, asphaltenes 28.1–76.2% and resins 20.2–43.5%. The saturated hydrocarbon fractions included n-C₁₅ to n-C₃₂, with an odd carbon number that predominate in almost all the samples. The contents of n-C₂₇ and n-C₂₉ alkanes are extremely high in some samples, as a contribution of epicuticular waxes from higher plants. Acyclic isoprenoid hydrocarbons are minor constituents in the aliphatic fraction, and the pristane/phytane (Pr/Ph) ratio varies between 0.56 and 3.13, which implies anaerobic to oxic conditions during sedimentation. The most abundant diterpanes were abietane, dehydroabietane and 16α(H)-phyllocladane. In samples from the upper part of the coal seam, diterpanes are the dominant constituents of the alkane fraction. Polycyclic alkanes of the triterpane type are important constituents of alkane fractions. The occurrence of ββ- and αβ-type hopanes from C₂₇ to C₃₁, but without C₂₈, is typical for the Soko Banja coals.The major and trace elements in the coal were analysed using X-ray fluorescence (XRF), and inductively coupled plasma-mass spectrometry (ICP-MS). In comparison with world lignites, using the geometric mean value, the coal from the Soko Banja Basin has a high content of strontium (306.953 mg/kg). Higher values than the world lignites were obtained for Mo (3.614 mg/kg), Ni (8.119 mg/kg), Se (0.884 mg/kg), U (2.642 mg/kg) and W (0.148 mg/kg). Correlation analysis shows inorganic affinity for almost all the major and trace elements, except for S, which has an organic affinity.     

Geochemistry and evolution of ore-forming fluids of the Yueshan Cu–Au skarn- and vein-type deposits, Anhui Province, South China

The Yueshan mineral belt is geotectonically located at the centre of the Changjiang deep fracture zone or depression of the lower Yangtze platform. Two main types of ore deposits occur in the Yueshan orefield: Cu–Au–(Fe) skarn deposits and Cu–Mo–Au–(Pb–Zn) hydrothermal vein-type deposits. Almost all deposits of economic interest are concentrated within and around the eastern and northern branches of the Yueshan dioritic intrusion. In the vicinity of the Zongpu and Wuhen intrusions, there are many Cu–Pb–Zn–Au–(S) vein-type and a few Cu–Fe–(Au) skarn-type occurrences.Fluid inclusion studies show that the ore-forming fluids are characterised by a Cl⁻(S)–Na⁺–K⁺ chemical association. Hydrothermal activity associated with the above two deposit types was related to the Yueshan intrusion. The fluid salinity was high during the mineralisation processes and the fluid also underwent boiling and mixed with meteoric water. In comparison, the hydrothermal activity related to the Zongpu and Wuhen intrusions was characterised by low salinity fluids. Chlorine and sulphur species played an important role in the transport of ore-forming components.Hydrogen- and oxygen-isotope data also suggest that the ore-forming fluids in the Yueshan mineral belt consisted of magmatic water, mixed in various proportions with meteoric water. The enrichment of ore-forming components in the magmatic waters resulted from fluid–melt partitioning. The ore fluids of magmatic origin formed large Cu–Au deposits, whereas ore fluids of mixed magmatic-meteoric origin formed small- to medium-sized deposits.The sulphur isotopic composition of the skarn- and vein-type deposits varies from − 11.3‰ to + 19.2‰ and from + 4.2‰ to + 10.0‰, respectively. These variations do not appear to have been resulted from changes of physicochemical conditions, rather due to compositional variation of sulphur at the source(s) and by water–rock interaction. Complex water–rock interaction between the ore-bearing magmatic fluids and sedimentary wall rocks was responsible for sulphur mixing. Lead and silicon isotopic compositions of the two deposit types and host rocks provide similar indications for the sources and evolution of the ore-forming fluids.Hydrodynamic calculations show that magmatic ore-forming fluids were channelled upwards into faults, fractures and porous media with velocities of 1.4 m/s, 9.8 × 10^− 1 to 9.8 × 10^− 7 m/s and 3.6 × 10^− 7 to 4.6 × 10^− 7 m/s, respectively. A decrease of fluid migration velocity in porous media or tiny fractures in the contact zones between the intrusive rocks and the Triassic sedimentary rocks led to the deposition of the ore-forming components. The major species responsible for Cu transport are deduced to have been CuCl, CuCl₂⁻, CuCl₃²⁻ and CuClOH, whereas Au was transported as Au₂(HS)₂S²⁻, Au(HS)₂⁻, AuHS and AuH₃SiO₄ complexes. Cooling and a decrease in chloride ion concentration caused by fluid boiling and mixing were the principal causes of Cu deposition. Gold deposition was related to decrease of pH, total sulphur concentration and fO₂, which resulted from fluid boiling and mixing.Geological and geochemical characteristics of the two deposit types in the Yueshan mineral belt suggest that there is a close genetic relationship with the dioritic magmatism. Geochronological data show that the magmatic activity and the mineralisation took place between 130 and 136 Ma and represent a continuous process during the Yanshanian time. The cooling of the intrusions and the mineralisation event might have lasted about 6 Ma. The cooling rate of the magmatic intrusions was 80 to 120 °C my^− 1, which permitted sufficient heat supply by magma to the ore-forming system.     

Aenigmatite,sodic pyroxene,arfvedsonite and associated minerals in syenites from Morotu,Sakhalin

Aenigmatite, sodic pyroxene and arfvedsonite occur as interstitial minerals in metaluminous to weakly peralkaline syenite patches in alkali dolerite, Morotu, Sakhalin. Aenigmatite is zoned from Ca, Al, Fe³⁺-rich cores to Ti, Na, Mn, Si-rich rims reflecting the main substitutions Fe²⁺Ti⁴⁺Fe³⁺, NaSiCaAl and Mn²⁺Fe²⁺. Aenigmatite replaces aegirine and ilmenite supporting the existence of a no-oxide field in — T space. In one case aenigmatite has apparently formed by reaction between ilmenite and arfvedsonite. Titanian aegirine (up to 3.0 wt% TiO₂) and Fe-chlorite may replace aenigmatite. Sodic pyroxene occurs as zoned crystals with cores of aegirine-augite rimmed by aegirine and in turn by pale green aegirine containing 93 mol% NaFe³⁺Si₂O₆. Additional substitution of the type NaAlCaFe²⁺ is indicated by significant amounts (up to 6 mol%) of NaAlSi₂O₆. Arfvedsonite is zoned with rims enriched in Na, Fe and depleted in Ca which parallels the variation of these elements in the sodic pyroxenes.The high peralkalinity of the residual liquid from which the mafic phases formed resulted from the early crystallization of microperthite (which makes up the bulk of the syenites) leading to an increase in the Na₂O/(Na₂O+K₂O) and (Na₂O+K₂O)/Al₂O₃ ratios of the remaining interstitial liquid which is also enriched in Ti, Fe, and Mn. Bulk composition of the melt, , temperature and volatile content were all important variables in determining the composition and stability of the peralkaline silicates. in the residual liquid appears to have been buffered by arfvedsonite-aegirine and later by the arfvedsonite-aenigmatite and aenigmatite-aegirine equilibria under conditions of a no-oxide field. An increase in , above that of the alkali buffer reactions, is inferred by an increase of Ti and Mn in aenigmatite rims. The latest postmagmatic vapour crystallization stage of the syenites is marked by extremely low which may have been facilitated by exsolution of a gas phase. Low is supported by the replacement of aenigmatite by titanian aegirine, and the formation of rare Ti-rich garnet with a very low (Ti⁴⁺+Fe³⁺)/(Ti+Fe) ratio of 0.51, associated with leucoxene alteration of ilmenite.     

Distribution of copper, zinc, lead and cadmium concentrations in stream sediments from the Mapocho River in Santiago, Chile

The Mapocho river, which crosses downtown Santiago, is one of the most important rivers in contact with a population of about six million inhabitants. Anthropogenic activities, industrialization, farming activities, transport, urbanization, animal and human excretions, domestic wastes and copper mining have affected the river, contaminating it and its sediments with heavy metals. Concentration and distribution of Cu, Zn, Pb and Cd were studied with the purpose of determining their bioavailability and their relation with the characteristics of the sediments. Freshly deposited seasonal sediments were collected from 0–8 cm depths from 6 locations (S₁ to S₆) along the 30-km long channel length, in the four seasons of year on the following dates: May 2001 (D₁, autumn); August 2001 (D₂, winter); October 2001 (D₃, spring) and January 2002 (D₄, summer). The dried samples were sifted to obtain the < 63-μm sediment fraction, since it has been shown that large amounts of heavy metals are bound in the fine-grained fraction of the sediment. Cu and Zn were analyzed by atomic absorption spectrophotometry and Pb and Cd by square wave anodic stripping voltammetry. The highest concentrations of Cu (2850 μg g^− 1) were found in the northern part of the river (S₁, average D₁–D₄), near the mountains and a copper mine, and then decreased downstream to 209 μg g^− 1 (S₆). Total Zn showed an irregular variation, with higher values at S₁ (1290 μg g^− 1) and high values in some winter sampling (1384 μg g^− 1 S₄, S₅–D₂). Pb showed different trends, increasing from S₁ to S₆ (17 to 61 μg g^− 1), with the highest values in the summer samples (83 μg g^− 1, S₄–S₆, D₄), and total Cd increased slightly from mean values of 0.2 and 0.5 μg g^− 1. Partition into five fractions was made using Tessier's analytical sequential extraction technique; the residue was treated with aqua regia for recovery studies, although this step is not part of the Tessier procedure. The results show that Cu, Zn and Pb in the sediments were dependent on the sampling places along the river, and variation in two years was low (D₁–D₄). The highest values of total organic matter, carbonate and conductivity were found in S₆, which has the smallest size particles, while at S₁ the sediments were predominantly sand and contain larger amounts of silica. Cu associated with carbonate decreased gradually from 58% (1771 μg g^− 1, S₁) to 16% (32 μg g^− 1, S₆); Cu bonded to reducible fraction was almost constant (33% to 37%), and Cu associated with oxidizable fraction increased from 7% (S₁) to 34% (S₆), but copper content was lower (214 to 68 μg g^− 1). Zn had a similar fractionation profile. However, Pb bound to oxidizable fraction did not show significant percent variation along the river (20% to 19%), but the amount bounded was 4 to 12 μg g^− 1. The residual fraction increased from 24% to 41% (5 to 25 μg g^− 1, S₁ to S₆). The distribution of Cd in the sediment was almost independent of the sampling stations and was bound to carbonate, reducible and residual fraction in similar proportion. Cu and Zn at S₁ were mainly bound to carbonates and reducible phases with 91% and 73% (2779 and 965 μg g^− 1, respectively), and with a change in the pH and/or the redox potential of the sediment–water system, these contaminants could easily enter the food chain. In S₆ the amount of Cu and Zn in these phases was 50% and 53% (100 to 313 μg g^− 1, respectively).     

Mechanics of growth of some laccolithic intrusions in the Henry mountains, Utah, I: Field observations, Gilbert's model, physical properties and flow of the magma

The shapes of sills and laccolithic intrusions and associated host rock deformation were studied at several locations on the flanks of the Henry Mountains. Diorite sills range from 0.5 to 10 m in thickness, are less than 1 km² in areal extent, and have blunt terminations. The laccolithic intrusions range from 10 to 200 m in thickness, and from 1 to 3 km² in areal extent. The host rock, principally sandstone and shale, is deformed along closely spaced cataclastic shear planes. This deformation is concentrated at contacts, especially near sill terminations and over laccolith peripheries. The diorite contains plagioclase phenocrysts which are usually sheared in a thin zone adjacent to each contact. Field observations suggest that sills are the forerunners of laccolithic intrusions which form only after magma has spread far enough laterally (greater than about 1 km² in the Henry Mountains) to gain leverage to bend the overburden upward. Further injection of magma results in laccolithic peripheries or terminations with one of three distinct cross-sectional forms: (1) blunt termination of the diorite accompanied by bending and minor faulting of the host rock; (2) termination at a peripheral diorite dike cutting upward across the host rock; or (3) abrupt termination of the diorite against a nearly vertical fault zone.In order to study some of the processes of sill and laccolith intrusion, mechanical models for the driving pressure, physical properties, and flow behavior of the diorite magma are derived and discussed. A static driving pressure (equal to the difference between total magma pressure and lithostatic pressure) of up to 700 bar is estimated. The rheological behavior of the magma in the Henry Mountains is unknown. However, flow behavior is calculated assuming three of the more common models for fluids: Newtonian viscous, pseudoplastic, and Bingham. Suspended crystals probably contributed to the finite strength of the magma (estimated to be at least 10³ dyn/cm² for the Henry Mountains magma) which enables it to support dense zenoliths and also fixes maximum limits on the lengths of sills or dikes. Pressure in magma flowing along tabular intrusions of uniform thickness drops linearly in the flow direction for all three rheological materials. Thickening of tabular intrusions tends to make the pressure drop less rapidly, but pressure drops more rapidly in the tapered region near a termination. Pressure distributions under these and other conditions are derived in order to use them in the models of host rock deformation presented in Part II.     

Supercritical gas sorption on moist coals

The effect of moisture on the CO₂ and CH₄ sorption capacity of three bituminous coals from Australia and China was investigated at 55 °C and at pressures up to 20 MPa. A gravimetric apparatus was used to measure the gas adsorption isotherms of coal with moisture contents ranging from 0 to about 8%. A modified Dubinin–Radushkevich (DR) adsorption model was found to fit the experimental data under all conditions. Moisture adsorption isotherms of these coals were measured at 21 °C. The Guggenheim–Anderson–de Boer (GAB) model was capable of accurately representing the moisture isotherms over the full range of relative pressures.Moist coal had a significantly lower maximum sorption capacity for both CO₂ and CH₄ than dry coal. However, the extent to which the capacity was reduced was dependent upon the rank of the coal. Higher rank coals were less affected by the presence of moisture than low rank coals. All coals exhibited a certain moisture content beyond which further moisture did not affect the sorption capacity. This limiting moisture content was dependent on the rank of the coal and the sorbate gas and, for these coals, corresponded approximately to the equilibrium moisture content that would be attained by exposing the coal to about 40–80% relative humidity. The experimental results indicate that the loss of sorption capacity by the coal in the presence of water can be simply explained by volumetric displacement of the CO₂ and CH₄ by the water. Below the limiting moisture content, the CO₂ sorption capacity reduced by about 7.3 kg t^− 1 for each 1% increase in moisture. For CH₄, sorption capacity was reduced by about 1.8 kg t^− 1 for each 1% increase in moisture.The heat of sorption calculated from the DR model decreased slightly on addition of moisture. One explanation is that water is preferentially attracted to high energy adsorption sites (that have high energy by virtue of their electrostatic nature), expelling CO₂ and CH₄ molecules.     

Petrographic and geochemical effects of sill intrusions on coal and their implications for gas outbursts in the Wolonghu Mine, Huaibei Coalfield, China

Since the early 1980s, fifteen outbursts have occurred in the Huaibei Coalfield of China. These outbursts were reported to be associated with sills. To study the effect of sill intrusions on coal seam and their relationship to methane outbursts, eleven samples from the No. 10 coal seam were taken from the Wolonghu Mine at various distances from a diorite sill. Comparisons were made between unaltered and heat-affected coals using petrographic and chemical data, micropore characteristics, adsorption properties of coal, and gas outburst indexes from field. Approaching the intrusion, vitrinite reflectance levels increased from 2.74% to 5.03%, and the thermal aureole of the sill ~ 60 m (from the sill boundary to sample 9). Three zones along this gradient were identified as corresponding to (1) thermal evolution zone No. 1 (0-5 m from sill), (2) thermal evolution zone No. 2 (5-60 m from sill), and (3) unaltered zone. The methane adsorption capacity of coal samples in the thermal evolution zone No. 2 was generally higher than in the two other zones, and the unaltered zone higher than the thermal evolution zone No. 1. It is concluded that the contact-metamorphism decreased the adsorption capacity of coal and the thermal evolution of sill increased it. The trap effect of sill, combined with the mudstone and siltstone roof and floor of the No. 10 coal seam, provided a seal for the formation of a gas pocket. Abnormally high formation pressures at the No. 10 coal seam led to two outbursts.     

Carbon in silicate liquids: the systems NaAlSi3O8-CO2, CaAl2Si2O8-CO2, and KAlSi3O8-CO2

To further our knowledge of the effects of volatile components on phase relationships in aluminosilicate systems, we determined the vapor saturated solidi of albite, anorthite, and sanidine in the presence of CO₂ vapor. The depression of the temperature of the solidus of albite by CO₂ decreases from 30° C at 10 kbar, to 10° C at 20 kbar, to about 0 at 25 kbar, suggesting that the solubility of CO₂ in NaAlSi₃O₈ liquid in equilibrium with solid albite decreases with increasing pressure and temperature. In contrast, CO₂ lowers the temperature of the solidus of anorthite by 30° C at 14 kbar, and by 70dg C at 25 kbar. This contrasting behavior of albite and anorthite is also reflected in the behavior of melting in the absence of volatile components. Whereas albite melts congruently to a liquid of NaAl-Si₃O₈ composition to pressures of 35 kbar, anorthite melts congruently to only about 10 kbar and, at higher pressures, incongruently to corundum plus a liquid that is enriched in SiO₂ and CaO and depleted in Al₂O₃ relative to CaAl₂Si₂O₈.The tendency toward incongruent melting with increasing pressure in albite and anorthite produces an increase in the activity of SiO₂ component in the liquid ( ). We predict that this increases the ratio of molecular CO₂/CO ₃ ^2– in these liquids, but the experimental results from other workers are mutually contradictory. Because of the positive dP/dT of the albite solidus and the negative dP/dT of the anorthite solidus, we propose that a negative temperature derivative of the solubility of molecular CO₂ in plagioclase liquids may partly explain the decrease in solubility of carbon with increasing pressure in near-solidus NaAlSi₃O₈ liquids, which is in contrast to that in CaAl₂Si₂O₈ liquid. Also, reaction of CO₂ with NaAlSi₃O₈ liquid to form CO ₃ ^2– that is complexed with Na⁺ must be accompanied by a change in Al³⁺ from network-former to network-modifier, as Na⁺ is no longer abailable to charge-balance Al³⁺ in a network-forming role. However, when anorthite melts incongruently to corundum plus a CaO-rich liquid, the complexing of CO ₃ ^2– with the excess Ca²⁺ in the liquid does not require a change in the structural role of aluminum, and it may be more energetically favorable.The depression of the temperature of the solidus of sanidine resulting from the addition of CO₂ increases from 50° C at 5 kbar to 170° C at 15 kbar. In marked contrast to the plagioclase feldspars, sanidine melts incongruently to leucite plus a SiO₂-rich liquid up to the singular point at 15 kbar. Above this pressure, sanidine melts congruently, resulting in a decrease in the with increasing pressure in the interval up to 15 kbar. Above this pressure, the congruent melting of sanidine results in a lower and nearly constant relative to those of albite and anorthite, and CO₂ produces a nearly constant freezing-point depression of about 170° C. Because of the low at pressures above the singular point, we infer that most of the carbon dissolves as CO ₃ ^2– , resulting in a low CO₂/ CO ₃ ^2– , but a high total carbon content.The principles derived from the studies of phase equilibria in these chemically simple systems provide some information on the structural and thermal properties of magmas. We propose that the is an important parameter in controlling the speciation of carbon in these feldspathic liquids, but it certainly is not the only factor, and it may be relatively less significant in more complex compositions. In addition, our phase-equilibria approach does not provide direct thermal and structural information as do calorimetry and spectroscopy, but the latter have been used primarily on glasses (quenched liquids) and cannot be used in situ to derive direct information on liquids at elevated pressures, as can our method. Hopefully, the results of all of these approaches can be integrated to yield useful results.Institute of Geophysics and Planetary Physics, Contribution No. 2744