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1.
Chemical and isotope studies of natural CO2 accumulations aid in assessing the chemical effects of CO2 on rock and thus provide a potential for understanding the long-term geochemical processes involved in CO2 geological storage. Several natural CO2 accumulations were discovered during gas and oil exploration in France’s carbogaseous peri-Alpine province (south-eastern France) in the 1960s. One of these, the Montmiral accumulation at a depth of more than 2400 m, is currently being exploited. The chemical composition of the water collected at the wellhead has changed in time and the final salinity exceeds 75 g/L. These changes in time can be explained by assuming that the fraction of the reservoir brine in the recovered brine–CO2–H2O mixture varies, resulting in variable proportions of H2O and brine in the sampled water. The proportions can be estimated in selected samples due to the availability of gas and water flowrate data. These data enabled the reconstruction of the chemical and isotope composition of the brine. The proportions of H2O and brine can also be estimated from isotope (δ2H, δ18O) composition of collected water and δ18O of the sulfates or CO2. The reconstituted brine has a salinity of more than 85 g/L and, according to its Br− content and isotope (δ2H, δ18O, δ34S) composition, originates from an evaporated Triassic seawater that underwent dilution by meteoric water. The reconstitution of the brine’s chemical composition enabled an evaluation of the CO2–water–rock interactions based on: (1) mineral saturation indices; and (2) comparison with initial evaporated Triassic seawater. Dissolution of K- and SO4-containing minerals such as K-feldspar and anhydrite, and precipitation of Ca and Mg containing minerals that are able to trap CO2 (carbonates) are highlighted. The changes in concentration of these elements in the brine, which are attributed to CO2 interactions, illustrate the relevance of monitoring the water quality at future industrial CO2 storage sites.  相似文献   

2.
A. Proyer  E. Mposkos  I. Baziotis  G. Hoinkes 《Lithos》2008,104(1-4):119-130
Four different types of parageneses of the minerals calcite, dolomite, diopside, forsterite, spinel, amphibole (pargasite), (Ti–)clinohumite and phlogopite were observed in calcite–dolomite marbles collected in the Kimi-Complex of the Rhodope Metamorphic Province (RMP). The presence of former aragonite can be inferred from carbonate inclusions, which, in combination with an analysis of phase relations in the simplified system CaO–MgO–Al2O3–SiO2–CO2 (CMAS–CO2) show that the mineral assemblages preserved in these marbles most likely equilibrated at the aragonite–calcite transition, slightly below the coesite stability field, at ca. 720 °C, 25 kbar and aCO2 ~ 0.01. The thermodynamic model predicts that no matter what activity of CO2, garnet has to be present in aluminous calcite–dolomite-marble at UHP conditions.  相似文献   

3.
Larryn W. Diamond   《Lithos》2001,55(1-4):69-99
Aqueous solutions that contain volatile (gas) components are one of the most important types of fluid in the Earth's crust. The record that such fluids have left in the form of fluid inclusions in minerals provides a wealth of insight into the geochemical and petrologic processes in which the fluids participated. This article reviews the systematics of CO2–H2O fluid inclusions as a starting point for interpreting the chemically more complex systems. The phase relations of the binary are described with respect to a qualitative P–T–X model, and isoplethic–isochoric paths through this model are used to explain the equilibrium and non-equilibrium behaviour of fluid inclusions during microthermometric heating and cooling. The P–T–X framework is then used to discuss the various modes of fluid inclusion entrapment, and how the resulting assemblage textures can be used to interpret the P–T conditions, phase states, and evolution paths of the parent solutions. Finally, quantitative methods are reviewed by which bulk molar volume and composition of CO2–H2O fluid inclusions can be determined from microthermometric observations of phase transitions.  相似文献   

4.
The chromites from the alpine type ultramafic intrusive of Sukinda, India, display a typical partly inverse spinel form and occur in two distinct zones: Brown Ore Zone (BOZ) and Grey Ore Zone (GOZ). The host ultramafites are mostly altered and are represented by the serpentinite, tremolite-talc(chlorite) schist, talc-serpentine schist and chlorite rock. The less altered variants are dunite, harzburgite and websterite. A dyke of orthopyroxenite runs through the main ultramafic body.The composition of olivine (Fo92), orthopyroxene (En92–89) and Al2O3 contents of the parental liquid (10.40–11.45%) determined from chromites, suggest that the parent melt is of boninitic affinity. The chemical plot of TiO2 content against cr# of chromites corroborates a boninitic parental melt. The Fe–Mg partitioning in olivine and chromite depicts the temperature for chromitites as 1200 °C. A compositional plot of mg# and cr# suggests crystallization at high pressure conditions, corresponding to the kimberlite xenolith field. From the P–T diagram of pyrolite melting and mineral assemblage, the pressure of crystallization is stipulated to be ≥1.2 GPa. The fO2 values estimated from Fe3+/Cr+Al+Fe3+ ratios range from 10−8.3 to 10−9.3 for the GOZ and 10−7.1 to 10−7.3 for the BOZ. The fO2 values together with the pressure range suggest crystallization at upper mantle conditions. The heterogeneity in chemical composition and fO2 conditions for the GOZ and BOZ could be linked to heterogeneity in the upper mantle.  相似文献   

5.
The isopiestic method has been used to determine the osmotic coefficients of the binary solutions NaBr-H2O (from 0.745 to 5.953 mol kg−1) and KBr-H2O (from 0.741 to 5.683 mol kg−1) at the temperature t = 50 °C. Sodium chloride solutions have been used as isopiestic reference standards. The isopiestic results obtained have been combined with all other experimental thermodynamic quantities available in literature (osmotic coefficients, water activities, bromide mineral’s solubilities) to construct a chemical model that calculates solute and solvent activities and solid-liquid equilibria in the NaBr-H2O, KBr-H2O and Na-K-Br-H2O systems from dilute to high solution concentration within the 0-300 °C temperature range. The Harvie and Weare [Harvie C., and Weare J. (1980) The prediction of mineral solubilities in naturalwaters: the Na-K-Mg-Ca-Cl-SO4-H2O system from zero to high concentration at 25 °C. Geochim. Cosmochim. Acta44, 981-997] solubility modeling approach, incorporating their implementation of the concentration-dependent specific interaction equations of Pitzer [Pitzer K. (1973) Thermodynamics of electrolytes. I. Theoretical basis and general equations. J. Phys. Chem.77, 268-277] is employed. The model for binary systems is validated by comparing activity coefficient predictions with those given in literature, and not used in the parameterization process. Limitations of the mixed solutions model due to data insufficiencies are discussed. This model expands the variable temperature sodium-potassium model of Greenberg and Moller [Greenberg J., and Moller N. (1989) The prediction of mineral solubilities in natural waters: a chemical equilibrium model for the Na-K-Ca-Cl-SO4-H2O system to high concentration from 0 to 250 °C. Geochim. Cosmochim. Acta53, 2503-2518] by evaluating Br− pure electrolyte and mixing solution parameters and the chemical potentials of three bromide solid phases: NaBr-2H2O (cr), NaBr (cr) and KBr (cr).  相似文献   

6.
Stephan Klemme   《Lithos》2004,77(1-4):639-646
The position of the transition from spinel peridotite to garnet peridotite in a simplified chemical composition has been determined experimentally at high pressures and high temperatures. The univariant reaction MgCr2O4+2Mg2Si2O6=Mg3Cr2Si3O12+Mg2SiO4, has a negative slope in P–T space between 1200 °C and 1600 °C. The experimental results, combined with assessed thermodynamic data for MgCr2O4, MgSiO3 and Mg2SiO4 give the entropy and enthalpy of formation of knorringite garnet (Mg3Cr2Si3O12). Thermodynamic calculations in simplified chemical compositions indicate that Cr shifts the garnet-in reaction to much higher pressures than previously anticipated. Moreover, in Cr-bearing systems a pressure–temperature field exists where garnet and spinel coexist. The width of this divariant field strongly depends on the Cr/(Cr+Al) of the system.  相似文献   

7.
We conducted a series of melting experiments in the join forsterite–diopside–leucite under 0.1 and 2.3 GPa and in the join forsterite–leucite–åkermanite under 2.3 GPa to understand paragenetic relationships amongst different types of lamproitic and lamprophyric magmas with K-rich mafic and ultramafic volcanic (kamafugitic) rocks. Both the joins were studied in the presence of excess water. The experimental results of the join forsterite–diopside–leucite at 0.1 GPa show that the five-phase point of forsterite (Fo)ss + diopside (Di)ss + leucite (Lc)ss + liquid (Liq) + vapour (V) (equivalent to ugandite lava) occurs at Fo2Di50Lc48 at 880 ± 5 °C. Phlogopite appears as the last phase at 830 ± 15 °C. The final crystalline assemblage of forsteritess + diopsidess + leucitess + phlogopite is similar to the phenocryst assemblage of missourite lava. Present study suggests that an olivine leucitite (ugandite) can be derived from an olivine italite, a slightly potassic peridotite and a leucitite magma.

A study of the join Fo–Di–Lc [P(H2O) = P(Total)] at 2.3 GPa shows that liquid compositions penetrate the primary phase volumes of forsteritess, phlogopitess, kalsilitess, K-feldsparss and diopsidess. It has the following three five-phase points: 1) one occurring at Fo9Di49Lc42 and 1005 ± 5 °C, where liquid and vapour coexists with forsteritess, phlogopitess and diopsidess (phlogopite-bearing madupite), 2) the second one at Fo4Di50Lc46 and 990 ± 10 °C, where diopsidess, K-feldsparss and phlogopitess coexist with liquid and vapour (pyroxene-bearing minette), and 3) the third one at Fo3Di21Lc76 and 775 ± 5 °C, where phlogopitess, kalsilitess and K-feldsparss are in equilibrium with liquid plus vapour (kalsilite-bearing minette).

The experimental results of the join Fo–Lc–åkermanite (Ak) show that the join 40 penetrates the primary phase volumes of forsteritess, phlogopitess, kalsilite, K-feldsparss, diopsidess and merwinitess. The data indicate the presence of four five-phase points: 1) one occurring at Fo7Lc42Ak51 and 1165 ± 5 °C, where phlogopitess, forsteritess, diopsidess coexists with liquid and vapour (olivine-bearing madupite), 2) the second one at Fo3Lc49Ak48 and 1140 ± 10 °C, where a liquid is in equilibrium with phlogopitess, K-feldsparss, diopsidess and vapour (pyroxene-bearing minette), 3) the third one at Fo18Lc21Ak61 and 1255 ± 10 °C, where merwinitess, forsteritess and diopsidess are in equilibrium with liquid and vapour (merwinite-bearing wherlite), and 4) the fourth one at Fo5Lc73.5Ak21.5 and 770 ± 5 °C, where kalsilitess, phlogopitess and K-feldspar coexist with liquid and vapour (kalsilite-bearing minette). The present data suggest that high pressure heteromorphic equivalent of a katungite magma is represented by a kalsilite-bearing minette, a pyroxene-bearing minette, or an olivine-bearing madupite.  相似文献   


8.
This paper presents the petrographical, mineralogical and geochemical characteristics of the Carlés Cu–Mo–Au ore deposit, located in the Rio Narcea Gold Belt (Cantabrian zone of the Iberian Massif). It is related to a small postkinematic calc-alkaline monzogranite, which intrudes as a cedar-tree laccolith into the upper siliciclastic Furada Formation (late Silurian age) and the Nieva carbonates (early Devonian age). The Carlés deposit consists mainly of a well-developed exoskarn. The exoskarn is mostly calcic skarn made up of early garnet and pyroxene, and later amphibole, magnetite and sulfides. The presence of magnesian skarn has been recorded on the north side of the intrusion (roof of granitoid). Magnesian skarn consists of olivine, which is partially replaced by diopside and phlogopite and spinel. Close to the igneous rock, skarns are overprinted by strong potassic alteration. The ore is related to the skarn retrogradation and post-skarn veining and faulting. The skarn-related ore consists of earlier, uneconomic magnetite and Fe–As sulfide assemblages and economic Cu–Au–Ag (Bi–Te) assemblages on the eastern and western sides of the contact aureole, and uneconomic Mo and subeconomic Fe–As–Cu–Au–Ag on the northern side of the contact. Later subeconomic Fe–As–Sb–(Zn–Sn–Cu–Au–Ag) assemblages crosscut the granitoid, skarn, marbles and mineral associations developed previously, and are related to younger episodes of fracturing and faulting. Fluid inclusions in the first hydrothermal stage consist of an aqueous solution with significant contents of CO2, which reach unmixing conditions as a result of a decrease in P–T conditions. This led to two types of solutions, aqueous solutions of moderate to high salinity and hydrocarbon solutions of low salinity. This unmixing phenomenon controlled the first stage of gold precipitation. During the late hydrothermal activity, primary low-salinity-aqueous-carbonic inclusions with contrasting densities are found. They homogenize into vapor, critical or liquid phase. Homogenization temperatures are practically the same in all inclusions, indicating a boiling phenomenon that could control a new precipitation of gold.  相似文献   

9.
A set of free-drift experiments was undertaken to synthesize carbonates of mixed cation content (Fe, Ca, Mg) from solution at 25 and 70 °C to better understand the relationship between the mineralogy and composition of these phases and the solutions from which they precipitate. Metastable solid solutions formed at 25 °C which are not predicted from the extrapolation of higher temperature equilibrium assemblages; instead, solids formed that were intermediary in chemical composition to known magnesite–siderite and dolomite solid solutions. A calcite–siderite solid solution precipitated at 25 °C, with the percentage of CaCO3 in the solid being proportional to the aqueous Ca/Fe ratio of the solution, while Mg was excluded from the crystal structure except at relatively high aqueous Mg/Ca and Mg/Fe ratios and a low Ca content. Alternatively, at 70 °C Mg was the predominant cation of the solid solutions. These results are compatible with the hypothesis that the relative dehydration energies of Fe, Ca and Mg play an important role in the formation of mixed cation carbonates in nature.  相似文献   

10.
Mathematical models of hydrocarbon formation can be used to simulate the natural evolution of different types of organic matter and to make an overall calculation of the amounts of oil and/or gas produced during this evolution. However, such models do not provide any information on the composition of the hydrocarbons formed or on how they evolve during catagenesis.From the kinetic standpoint, the composition of the hydrocarbons formed can be considered to result from the effect of “primary cracking” reactions having a direct effect on kerogen during its evolution as well as from the effect of “secondary cracking” acting on the hydrocarbons formed.This report gives experimental results concerning the “primary cracking” of Types II and III kerogens and their modelling. For this, the hydrocarbons produced have been grouped into four classes (C1, C2–C5, C6–C15 and C15+). Experimental data corresponding to these different classes were obtained by the pyrolysis of kerogens with temperature programming of 4°C/min with continuous analysis, during heating, of the amount of hydrocarbons corresponding to each of these classes.The kinetic parameters of the model were optimized on the basis of the results obtained. This model represents the first step in the creation of a more sophisticated mathematical model to be capable of simulating the formation of different hydrocarbon classes during the thermal history of sediments. The second step being the adjustment of the kinetic parameters of “secondary cracking”.  相似文献   

11.
The solubility and stability of synthetic grossular were determined at 800 °C and 10 kbar in NaCl-H2O solutions over a large range of salinity. The measurements were made by evaluating the weight losses of grossular, corundum, and wollastonite crystals equilibrated with fluid for up to one week in Pt capsules and a piston-cylinder apparatus. Grossular dissolves congruently over the entire salinity range and displays a large solubility increase of 0.0053 to 0.132 molal Ca3Al2Si3O12 with increasing NaCl mole fraction (XNaCl) from 0 to 0.4. There is thus a solubility enhancement 25 times the pure H2O value over the investigated range, indicating strong solute interaction with NaCl. The Ca3Al2Si3O12 mole fraction versus NaCl mole fraction curve has a broad plateau between XNaCl = 0.2 and 0.4, indicating that the solute products are hydrous; the enhancement effect of NaCl interaction is eventually overtaken by the destabilizing effect of lowering H2O activity. In this respect, the solubility behavior of grossular in NaCl solutions is similar to that of corundum and wollastonite. There is a substantial field of stability of grossular at 800 °C and 10 kbar in the system CaSiO3-Al2O3-H2O-NaCl. At high Al2O3/CaSiO3 bulk compositions the grossular + fluid field is limited by the appearance of corundum. Zoisite appears metastably with corundum in initially pure H2O, but disappears once grossular is nucleated. At XNaCl = 0.3, however, zoisite is stable with corundum and fluid; this is the only departure from the quaternary system encountered in this study. Corundum solubility is very high in solutions containing both NaCl and CaSiO3: Al2O3 molality increases from 0.0013 in initially pure H2O to near 0.15 at XNaCl = 0.4 in CaSiO3-saturated solutions, a >100-fold enhancement. In contrast, addition of Al2O3 to wollastonite-saturated NaCl solutions increases CaSiO3 molality by only 12%. This suggests that at high pH (quench pH is 11-12), the stability of solute Ca chloride and Na-Al ± Si complexes account for high Al2O3 solubility, and that Ca-Al ± Si complexes are minor. The high solubility and basic dissolution reaction of grossular suggest that Al may be a very mobile component in calcareous rocks in the deep crust and upper mantle when migrating saline solutions are present.  相似文献   

12.
The Permian–Jurassic Mahanadi and Pranhita–Godavari Rifts are part of a drainage system that radiated from the Gamburtsev Subglacial Mountains in central Antarctica. From 12 samples we analysed detrital zircons for U–Pb ages, Hf-isotopes, and trace elements to determine the age, rock type and source of the host magma, and TDM model age. Clusters, in decreasing order of abundance, are (1) 820–1000 Ma, host magmas felsic granitoids with alkaline rock, (2) 1500–1700 Ma felsic granitoids, (3) 500 to 700 Ma mafic granitoids with alkaline rock, (4) 2400–2550 Ma granitoids, and (5) 1000–1200 Ma felsic and mafic granitoids, mafic rock, and alkaline rock. TDM ranges from 1.5 to 3.5 Ga. Joint paleoslope measurements and zircon ages indicate that the Eastern Ghats Mobile Belt (EGMB) and lateral belts and conjugate Antarctica are potential provenances. Zircons from the Gondwana Rifts differ from those in other Gondwanaland sandstones in their predominant 820–1000 Ma and 1500–1700 Ma ages (from the EGMB and conjugate Rayner–MacRobertson Belt) that dilute the 500–700 Ma (Pan-Gondwanaland) ages. The 1000–1200 Ma zircons reflect the assembly of Rodinia, the 500–700 Ma ones that of Gondwanaland; the other ages reflect collisions in the region.  相似文献   

13.
The area of the Middle–Lower Yangtze River valley, Eastern China, extending from Wuhan (Hubei province) to western Zhenjiang (Jiangsu province), hosts an important belt of Cu–Au–Mo and Fe deposits. There are two styles of mineralization, i.e., skarn/porphyry/stratabound Cu–Au–Mo–(Fe) deposits and magnetite porphyry deposits in several NNE-trending Cretaceous fault-bound volcanic basins. The origin of both deposit systems is much debated. We dated 11 molybdenite samples from five skarn/porphyry Cu–Au–Mo deposits and 5 molybdenite samples from the Datuanshan stratabound Cu–Au–Mo deposit by ICP-MS Re–Os isotope analysis. Nine samples from the same set were additionally analyzed by NTIMS on Re–Os. Results from the two methods are almost identical. The Re–Os model ages of 16 molybdenite samples range from 134.7 ± 2.3 to 143.7 ± 1.6 Ma (2σ). The model ages of the five samples from the Datuanshan stratabound deposit vary from 138.0 ± 3.2 to 140.8 ± 2.0 Ma, with a mean of 139.3 ± 2.6 Ma; their isochron age is 139.1 ± 2.7 Ma with an initial Os ratio of 0.7 ± 8.1 (MSWD = 0.29). These data indicate that the porphyry/skarn systems and the stratabound deposits have the same age and suggest an origin within the same metallogenic system. Albite 40Ar/39Ar dating of the magnetite porphyry deposits indicates that they formed at 123 to 125 Ma, i.e., 10–20 Ma later. Both mineralization styles characterize transitional geodynamic regimes, i.e., the period around 140 Ma when the main NS-trending compressional regime changed to an EW-trending lithospheric extensional regime, and the period of 125–115 Ma of dramatic EW-trending lithospheric extension.  相似文献   

14.
Geological sequestration of CO2 is one of the options studied to reduce greenhouse gas emissions. Although the feasibility of this concept is proven, apart from literature data on modelling still little is known about the CO2–water–rock interactions induced by CO2-injection.To evaluate the effect of CO2–water–rock interactions on three sandstone aquifers in NE-Belgium an experimental setup was built. Eighteen experiments were performed in which sandstones were exposed to supercritical CO2. CO2–water–rock interactions were deduced from the evolution of aqueous concentrations of 25 species and a thorough characterisation of the sandstones before and after treatment. The results show that dissolution of ankerite/dolomite and Al-silicates could enhance porosity/permeability. The observed precipitation of end-member carbonates could increase storage capacity if it exceeds carbonate dissolution. Precipitation of the latter and of K-rich clays as observed, however, can hamper the injection.  相似文献   

15.
In this paper, the structure of the Al30O8(OH)56(H2O)2618+(Al30) polyoxocation in aqueous solution is investigated, including an exploration of its water-exchange reaction using a supramolecular model. Thirty-one solvent water molecules were explicitly included in the supramolecular model to approximate the influence of the solvent. The calculated results indicated that both the gas-phase and the supramolecular models could correctly reproduce the structure of the Al30 polyoxocation, but the supramolecular model described the structure more accurately. Using the supramolecular model, we calculated the 27Al NMR chemical shifts of various aluminum atoms using HF and GIAO methods, and they compared well to the chemical shifts determined experimentally. The water-exchange reaction of the Al30 polyoxocation could not be simulated with the gas phase model because of a proton-transfer reaction that is induced by the highly positive charge of the Al30 polyoxocation. However, the inclusion of an explicit second solvation sphere lowered the acidity of the coordinated water molecules and allowed simulation of the water exchange reaction.  相似文献   

16.
The prevailing theory for the formation of trona [Na3(CO3)(HCO3) · 2(H2O)] relies on evaporative concentration of water produced by silicate hydrolysis of volcanic rock or volcaniclastic sediments. Given the abundance of closed drainage basins dominated by volcanics, it is puzzling that there are so few trona deposits and present-day lakes that would yield dominantly Na–CO3 minerals upon evaporation. Groundwater in the San Bernardino Basin (southeastern Arizona, USA and northeastern Sonora, Mexico) would yield mainly Na–CO3 minerals upon evaporation, but waters in the surrounding basins would not. Analysis of the chemical evolution of this groundwater shows that the critical difference from the surrounding basins is not lithology, but the injection of magmatic CO2. Many major deposits of trona and Na–CO3-type lakes appear to have had “excess” CO2 input, either from magmatic sources or from the decay of organic matter. It is proposed that, along with the presence of volcanics, addition of “excess” CO2 is an important pre-condition for the formation of trona deposits.  相似文献   

17.
A model for the carbon and sulfur cycles across the Permian–Triassic boundary has been constructed from carbon and sulfur isotopic data. Results indicate a drop in global organic matter burial, the formation of an anoxic deep ocean, and a large drop in atmospheric oxygen over the time span 270 to 240 Ma. Much of these changes were probably due to a drop in terrestrial productivity and preservation and an increase in global aridity.  相似文献   

18.
The metaturbidites of the Palaeoproterozoic Jormua–Outokumpu thrust belt in eastern Finland enclose m- to km-scale ultramafic massifs that are distributed over an area of more than 5000 km2. These bodies, which almost entirely consist of highly depleted mantle peridotites (now metaserpentinites and metaperidotites), are intimately associated with massive to semimassive, polymetallic Cu–Co–Zn–Ni–Ag–Au sulphide deposits that sustained mining in the region between 1913 and 1988. Currently, one deposit (Kylylahti) is proceeding into a definitive feasibility study emphasising the renewed economic interest for Outokumpu-type deposits.The origin of these Outokumpu-type Cu–Co–Zn–Ni–Ag–Au deposits is now re-interpreted to be polygenetic. First, their formation requires deposition of a Cu-rich proto-ore within peridotitic sea floor at  1950 Ma. Close modern analogues to the proto-ore setting include, for example, the Logatchev and Rainbow fields at the Mid-Atlantic Ridge, where venting of high-T–low-pH hydrothermal fluid resulted in accumulations of Cu–Zn–Co–Ag–Au sulphides on serpentinised ultramafic seafloor. Second, the Ni-rich composition of Outokumpu sulphide ores calls for a separate source for nickel: Some 40 Ma after the deposition of the Cu-rich proto-ore – concomitant with the obduction of the ultramafic massifs – disseminated Ni sulphides formed through chemical interaction between obducting peridotite massifs and adjacent black schists. This process was related to listwaenite–birbirite type carbonate–silica alteration at margins of the ultramafic massifs. Due to this alteration, silicate nickel was released from the primary Fe–Mg silicates and redeposited as Ni sulphides in the alteration fringes of the massifs.We propose that syntectonic mixing of these two “end-member” sulphides, i.e., the primary Cu-rich proto-ore and the secondary Ni-sulphide disseminations, resulted in the uncommon metal combination of the Outokumpu-type sulphides. Late tectonic solid-state re-mobilisation, related to the duplexing of the ore by isoclinal folding, upgraded the sulphides into economic deposits.  相似文献   

19.
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20.
Large groundwater resources are found in densely populated lowland areas, which consist often of young unconsolidated and reduced sediments. When anthropogenic activities lead to oxygenation of the aquifer, breakdown of the main reduced fractions, i.e. sedimentary organic matter (SOM) and pyrite, could lead to severe groundwater deterioration such as acidification, heavy metal mobilization, and increased hardness. The characterization of the reactive properties of these sediments is important in predicting groundwater deterioration, but is often complicated by the high degree of heterogeneity of these sediments. In this study, the potential reduction capacity (PRC, based on SOM and pyrite content), the potential buffer capacity (PBC, based on carbonate content), potential acidification capacity (PAC, based on the potential acid production by sulfide oxidation), and the measured reduction capacity (MRC) of five facies, which are typical of the riverine sediments in the Rhine–Meuse delta (The Netherlands) were determined. A universal facies-classification model was used to classify the deposits into more homogeneous sub-units based on lithologic and geogenic properties, with a further sub-division into oxic or anoxic redox environment based upon groundwater data and field observations. The bulk chemical data show strong variation across facies for the median values of PRC (186–9093 mmol O2 kg−1), PBC (17–132 mmol O2 kg−1), and PAC (36–1530 mmol H+ kg−1). The MRC was measured as reactivity to molecular O2 exposure and was 0.5–567.3 mmol O2 kg−1. Steady-state oxidation rates were in the wide range of 0.001–10.355 mmol O2 kg−1 day−1 but were typically about 3–8 times faster in fine facies than in coarse facies. Both the PRC and MRC depend strongly on grain size, but also on the syn/post-depositional environment and redox conditions. The main part of the PRC consists of SOM, but pyrite reactivity is higher than SOM reactivity as shown by the relative depletion of pyrite in oxic subfacies and the preferential oxidation during the oxidation experiments. Some facies are very prone to acidification because the PAC is higher than the PBC, but the oxidation experiments also show that acidification could already start before the PRC is fully exhausted. This study, is one of the few that combines bulk chemical data, groundwater data, and reactivity measurements and shows that a facies-based approach is a practical tool in characterizing the reactivity of heterogeneous deposits.  相似文献   

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