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1.
The recovery of magnesium from magnesite tailings in aqueous hydrochloric acid solutions by acid leaching was studied in a batch reactor using hydrochloric acid solutions. Subsequent, production of magnesium chloride hexahydrate (MgCl2.6H2O) from leaching solution was also investigated. The effects of temperature, acid concentration, solid-to-liquid ratio, particle size and stirring speed on the leaching process were investigated. The pseudo-second-order reaction model seemed to be appropriate for the magnesium leaching. The activation energy of the leaching process was estimated to be 62.4 kJ mol− 1. Finally, MgCl2.6H2O in a purity of 91% was produced by evaporation of leaching solution obtained at a temperature of 40 °C, 1.0 M acid, solid-to-liquid ratio of 10 g/L, particle size of 100 µm, stirring speed of 1250 rpm and leaching time of 60 min.  相似文献   

2.
The 1.27 Ga old Ivigtut (Ivittuut) intrusion in South Greenland is world-famous for its hydrothermal cryolite deposit [Na3AlF6] situated within a strongly metasomatised A-type granite stock. This detailed fluid inclusion study characterises the fluid present during the formation of the cryolite deposit and thermodynamic modelling allows to constrain its formation conditions.Microthermometry revealed three different types of inclusions: (1) pure CO2, (2) aqueous-carbonic and (3) saline-aqueous inclusions. Melting temperatures range between − 23 and − 15 °C for type 2 and from − 15 to − 10 °C for type 3 inclusions. Most inclusions homogenise between 110 and 150 °C into the liquid.Stable isotope compositions of CO2 and H2O were measured from crushed inclusions in quartz, cryolite, fluorite and siderite. The δ13C values of about − 5‰ PDB are typical of mantle-derived magmas. The differences between δ18O of CO2 (+ 21 to + 42‰ VSMOW) and δ18O of H2O (− 1 to − 21.7‰ VSMOW) suggest low-temperature isotope exchange. δD (H2O) ranges from − 19 to − 144‰ VSMOW. The isotopic composition of inclusion water closely follows the meteoric water line and is comparable to Canadian Shield brines. Ion chromatography revealed the fluid's predominance in Na, Cl and F. Cl/Br ratios range between 56 and 110 and may imply intensive fluid–rock interaction with the host granite.Isochores deduced from microthermometry in conjunction with estimates for the solidification of the Ivigtut granite suggest a formation pressure of approximately 1–1.5 kbar for the fluid inclusions. Formation temperatures of different types of fluid inclusions vary between 100 and 400 °C. Thermodynamic modelling of phase assemblages and the extraordinary high concentration in F (and Na) may indicate that the cryolite body and its associated fluid inclusions could have formed during the continuous transition from a volatile-rich melt to a solute-rich fluid.  相似文献   

3.
Ilmenite separated from beach sands of Bangladesh was oxidized for 1 h at 950 °C and then reduced in charcoal for 4 h at 1050 °C. This was followed by leaching in 5% to 15% hydrochloric acid solution in temperature range of 30 to 75 °C for periods of up to 2 h. The results were compared with those obtained by leaching of ilmenite reduced without oxidizing. Oxidation prior to reduction of the ilmenite was found to increase both the extent and the rate of leaching. The residual iron contents after leaching were also found to be lower than that obtained for non-oxidized samples. The kinetic data of leaching of ilmenite reduced after oxidation was found to follow first order reaction model, i.e., G(α) = − ln(1 − α) up to an α value of 0.5 (i.e. up to 50% reduction) and then changed to spherical model, i.e., G(α) = [1 − (1 − α)]3. On the other hand, leaching of ilmenite reduced without oxidizing was found to follow the Ginstling-Brounshtein reaction, i.e., G(α) = 1 − (2/3)α − (1 − α)2/3 throughout the leaching process. Oxidation of ilmenite prior to reduction was also found to have decreased the activation energy of leaching from 43 kJ/mol, found for samples leached after reduction without oxidizing, to 30 kJ/mol.  相似文献   

4.
Study on the kinetics of iron oxide leaching by oxalic acid   总被引：2，自引：0，他引：2  
The presence of iron oxides in clay or silica raw materials is detrimental to the manufacturing of high quality ceramics. Although iron has been traditionally removed by physical mineral processing, acid washing has been tested as it is more effective, especially for extremely low iron (of less than 0.1% w/w). However, inorganic acids such as sulphuric or hydrochloric acids easily contaminate the clay products with SO42− and Cl−, and therefore should be avoided as much as possible. On the other hand, if oxalic acid is used, any acid left behind will be destroyed during the firing of the ceramic products. The characteristics of dissolution of iron oxides were therefore investigated in this study.The dissolution of iron oxides in oxalic acid was found to be very slow at temperatures within the range 25–60 °C, but its rate increases rapidly above 90 °C. The dissolution rate also increases with increasing oxalate concentration at the constant pH values set within the optimum range of pH2.5–3.0. At this optimum pH, the dissolution of fine pure hematite (Fe2O3) (105–140 μm) follows a diffusion-controlled shrinking core model. The rate expression expressed as 1 − (2 / 3)x − (1 − x)2 / 3 where x is a fraction of iron dissolution was found to be proportional to [oxalate]1.5.The addition of magnetite to the leach liquor at 10% w/w hematite was found to enhance the dissolution rate dramatically. Such addition of magnetite allows coarser hematite in the range 0.5–1.4 mm to be leached at a reasonable rate.  相似文献   

5.
The Central African Belt in the Nkambe area, northwestern Cameroon represents a collisional zone between the Saharan metacraton and the Congo craton during the Pan-African orogeny, and exposes a variety of granitoids including foliated and massive biotite monzogranites in syn- and post-kinematic settings. Foliated and massive biotite monzogranites have almost identical high-K calc-alkaline compositions, with 73–67 wt.% SiO2, 17–13 wt.% Al2O3, 2.1–0.9 wt.% CaO, 4.4–2.7 wt.% Na2O and 6.3–4.4 wt.% K2O. High concentrations of Rb (264–96 ppm), Sr (976–117 ppm), Ba (3680–490 ppm) and Zr (494–99 ppm), with low concentrations of Y (mostly< 20 ppm with a range 54–6) and Nb (up to 24 ppm) suggest that the monzogranites intruded in collisional and post-collisional settings. The Sr/Y ratio ranges from 25 to 89. K, Rb and Ba resided in a single major phase such as K-feldspar in the source. Garnet was present in the source and remained as restite at the site of magma generation. This high K2O and Sr/Y granitic magma was generated by partial melting of a granitic protolith under high-pressure and H2O undersaturated conditions where garnet coexists with K-feldspar, albitic plagioclase. CHIME (chemical Th–U-total Pb isochron method) dating of zircon yields ages of 569 ± 12–558 ± 24 Ma for the foliated biotite monzogranite and 533 ± 12–524 ± 28 Ma for the massive biotite monzogranite indicating that the collision forming the Central African Belt continued in to Ediacaran (ca 560 Ma).  相似文献   

6.
Hydrometallurgical processing of spent hydrodesulphurisation (HDS) catalyst for the recovery of molybdenum using sodium carbonate and hydrogen peroxide mixtures was investigated. The results indicated that the recovery of molybdenum was largely dependent on the concentrations of Na2CO3 and H2O2 in the reaction medium, which controls the acidity of the leach liquor and carry over of impurities such as Al, Ni, P, Si and V. Leaching process was exothermic and leaching efficiency of molybdenum decreased with increasing solid to liquid ratio. Large scale leaching of spent catalyst, under optimum conditions: 20% pulp density, 85 g/L Na2CO3, 10 vol.% H2O2 and 1 h reaction, resulted a leaching efficiency of 84% Mo. The obtained leach liquor contained (g/L): Mo — 22.0, Ni — 0.015 and Al — 0.82, P — 1.1, Si — 0.094 and minor quantities of V — 8 mg/L, As and Co — < 1 mg/L. Recovery of Mo from leach solution as MoO3 of 97.30% purity was achieved by ammonium molybdate precipitation method.  相似文献   

7.
The crustal structure of the Dabie orogen was reconstructed by a combined study of U–Pb ages, Hf and O isotope compositions of zircons from granitic gneiss from North Dabie, the largest lithotectonic unit in the orogen. The results were deciphered from metamorphic history to protolith origin with respect to continental subduction and exhumation. Zircon U–Pb dating provides consistent ages of 751 ± 7 Ma for protolith crystallization, and two group ages of 213 ± 4 to 245 ± 17 Ma and 126 ± 4 to 131 ± 36 Ma for regional metamorphism. Majority of zircon Hf isotope analyses displays negative εHf(t) values of − 5.1 to − 2.9 with crust Hf model ages of 1.84 to 1.99 Ga, indicating protolith origin from reworking of middle Paleoproterozoic crust. The remaining analyses exhibit positive εHf(t) values of 5.3 to 14.5 with mantle Hf model ages of 0.74 to 1.11 Ga, suggesting prompt reworking of Late Mesoproterozoic to Early Neoproterozoic juvenile crust. Zircon O isotope analyses yield δ18O values of − 3.26 to 2.79‰, indicating differential involvement of meteoric water in protolith magma by remelting of hydrothermally altered low δ18O rocks. North Dabie shares the same age of Neoproterozoic low δ18O protolith with Central Dabie experiencing the Triassic UHP metamorphism, but it was significantly reworked at Early Cretaceous in association with contemporaneous magma emplacement. The Rodinia breakup at about 750 Ma would lead to not only the reworking of juvenile crust in an active rift zone for bimodal protolith of Central Dabie, but also reworking of ancient crust in an arc-continent collision zone for the North Dabie protolith. The spatial difference in the metamorphic age (Triassic vs. Cretaceous) between the northern and southern parts of North Dabie suggests intra-crustal detachment during the continental subduction. Furthermore, the Dabie orogen would have a three-layer structure prior to the Early Cretaceous magmatism: Central Dabie in the upper, North Dabie in the middle, and the source region of Cretaceous magmas in the lower.  相似文献   

8.
This study presents an investigation of the purification of a raw diatomite by acid leaching conducted in hot solution (75 °C and 5 M HCl) for long periods up to 240 h, evaluates the use of these purified powders in the fabrication of porous materials, and examines their porosities. The treatment for 1 h increased the specific surface area of diatomite from 189 m2/g to 222 m2/g, but the SiO2 content of 78.66% was still low. Material leached for a relatively short time shows an amorphous phase with quartz and plagioclase phases and the plagioclase is removable at longer leaching times during which no disruptive effect on the fine microscopic pores of the particles was observed. Thus, the diatomite based powders have potential use in the fabrication of porous coating as a membrane-separating layer: sintering at a relatively high temperature (1300 °C) still showed a significantly high apparent porosity of 48%.  相似文献   

9.
The Banded Hematite Jasper Formation within the Iron Ore Supergroup of the Singhbhum Craton in eastern India comprises fine alternating layers of jasper and specularite. It was deposited at 3000 Ma and deformed by a mobile episode at 2700 Ma. Hematite pigment (<1 μm) mixed with cryptocrystalline silica and specularite (> 10 μm) is chiefly responsible for red to brown rhythmic bands in the hematite jasper facies although thermomagnetic study also shows that minor amounts (1–2%) of magnetite are present. Palaeomagnetic study identifies a dual polarity remanence resident in hematite (D/I = 283/60°, α95 = 12°) which predates deformation. Studies of the fabric of magnetic susceptibility and rock magnetic results suggest a diagenetic origin for this magnetisation with the hematite formed from oxidation of primary magnetite. The palaeopole (32°E, 24°N, dp/dm = 14/18°) records the earliest post-metamorphic magnetisation event in the Orissa Craton. A minimum apparent polar wander motion of the Orissa-Singhbhum craton of through 80° is identified during Late Archaean times (2900-2600 Ma).  相似文献   

10.
Boehmite-rich coal of Pennsylvanian age was discovered earlier at the Heidaigou Surface Mine, Jungar Coalfield, Inner Mongolia, China. This paper reports new results on 29 bench samples of the no. 6 coal from a drill core from the adjacent Haerwusu Surface Mine, and provides new insights into the origin of the minerals and elements present. The results show that the proportion of inertinite in the no. 6 coal is higher than in other Late Paleozoic coals in northern China. Based on mineral proportions (boehmite to kaolinite ratio) and major element concentrations in the coal benches of the drill core, the no. 6 coal may be divided into five sections (I to V). Major minerals in Sections I and V are kaolinite. Sections II and IV are mainly kaolinite with a trace of boehmite, and Section III is high in boehmite. The boehmite is derived from bauxite in the weathered surface (Benxi Formation) in the sediment-source region. The no. 6 coal is rich in Al2O3 (8.89%), TiO2 (0.47%), Li (116 μg/g), F (286 μg/g), Ga (18 μg/g), Se (6.1 μg/g), Sr (350 μg/g), Zr (268 μg/g), REEs (172 μg/g), Pb (30 μg/g), and Th (17 μg/g). The elements are classified into five associations by cluster analysis, i.e. Groups A, B, C, D, and E. Group A (ash–SiO2–Al2O3–Na2O–Li) and Group B (REE–Sc–In–Y–K2O–Rb–Zr–Hf–Cs–U–P2O5–Sr–Ba–Ge) are strongly correlated with ash yield and mainly have an inorganic affinity. The elements that are negatively or less strongly correlated with ash yield (with exceptions of Fe2O3, Be, V, and Ni) are grouped in the remaining three associations: Group C, Se–Pb–Hg–Th–TiO2–Bi–Nb–Ta–Cd–Sn; Group D, Co–Mo–Tl–Be–Ni–Sb–MgO–Re–Ga–W–Zn–V–Cr–F–Cu; and Group E, S–As–CaO–MnO–Fe2O3. Aluminum is mainly distributed in boehmite, followed by kaolinite. The high correlation coefficients of the Li–ash, Li–Al2O3, and Li–SiO2 pairs indicate that Li is related to the aluminosilicates in the coal. The boehmite-rich coal is high in gallium and F, which occur in boehmite and the organic matter. Selenium and Pb are mainly in epigenetic clausthalite fillings in fractures. The abundant rare earth elements in the coal benches were supplied from two sources: the bauxite on the weathered surface of the Benxi Formation and from adjacent partings by groundwater leaching during diagenesis. The light rare earth elements (LREEs) are more easily leached from the partings and incorporated into the organic matter than the heavy REEs, leading to a higher ratio of LREEs to HREEs in the coal benches than in the overlying partings.  相似文献   

11.
Experimental studies concerning the dissolved air flotation (DAF) of fine (dp < 100 μm) quartz particles, using two different flotation cells (setups), are presented. Pure and well characterised quartz samples were treated with a commercial amine as collector prior to flotation and bubbles were characterised by the LTM-BSizer technique. Bubble size distribution showed 71% (by volume) and 94% (by number) of the bubbles having sizes (db) lower than 100 μm (i.e. microbubbles). The Sauter and arithmetic mean diameters were 79 μm and 56 μm, respectively, for the bubbles generated at 300 kPa (gauge) saturation pressure (after 30 minute saturation time). Quartz particle size distribution (obtained by laser diffraction) showed a volume-moment diameter of 13 μm. The Rosin–Rammler–Bennett, Gates–Gaudin–Schumann and log-normal distribution functions were well fitted (R2 > 0.96) to the bubble size distribution and quartz particle size distribution data. Values of total quartz recovery ranging from 6% to 53% (by mass) were obtained for the DAF experiments under different collector concentrations (up to 2 mg g− 1), with an optimal collector concentration found at 1 mg g− 1. These results are significant considering that 27% (by volume) of the quartz particles are ultrafine (dp < 5 μm), demonstrating the widely-known efficiency of DAF to remove small particles when applied in the field of water and wastewater treatment. The true flotation behaviour, as a function of particle diameter (dp), exhibits a local minimum when particles are approximately 3–5 μm in size. The results contribute to the discussion in the literature about the existence of such a minimum, which is generally interpreted as a change in the mechanism of particle collection from convection (collision) to diffusion at lower particle sizes.  相似文献   

12.
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.  相似文献   

13.
The primary occurrence of ruby in the Mogok area, northern Myanmar is exclusively found in marble along with spinel–forsterite-bearing marble and phlogopite–graphite marble. These marble units are enclosed within banded biotite–garnet–sillimanite–oligoclase gneisses. Samples of these marbles collected for C–O stable isotope analysis show two trends of δ13C–δ18O variation resulting most likely from fluid–rock interactions. Ruby-bearing marble and phlogopite–graphite marble follow a trend with coupled C–O depletion, whereas spinel–forsterite-bearing marble follows a δ18O depletion trend with relatively constant δ13C values. Ruby formation might have resulted from CO2-rich fluid–rock interaction, while spinel–forsterite-bearing marble was genetically related to CO2-poor fluid–rock interaction. Both fluids may have arisen from external sources. Based on graphite Raman spectral thermometry, the estimated temperature for phlogopite–graphite marble, and probably ruby-bearing marble, was lower than 607 °C, and for spinel–forsterite-bearing marble, lower than 710 °C. Contrasting C/O diffusion between graphite/ruby/spinel/forsterite and calcite, local variations of isotopic compositions of newly formed minerals as a result of non-pervasive fluid infiltration, and open-system isotopic disturbance during cooling may have affected C-/O-isotopic fractionations between minerals. The estimated high formation temperatures for ruby and spinel/forsterite imply that the parental fluids may have been related to nearby igneous intrusions and/or metamorphic processes. Whether these two types of fluid were genetically related is unclear based on the present data.  相似文献   

14.
Cleats and fractures in southwestern Indiana coal seams are often filled with authigenic kaolinite and/or calcite. Carbon- and oxygen-stable isotope ratios of kaolinite, calcite, and coalbed CO2 were evaluated in combination with measured values and published estimates of δ18O of coalbed paleowaters that had been present at the time of mineralization. δ18Omineral and δ18Owater values jointly constrain the paleotemperature of mineralization. The isotopic evidence and the thermal and tectonic history of this part of the Illinois Basin led to the conclusion that maximum burial and heat-sterilization of coal seams approximately 272 Ma ago was followed by advective heat redistribution and concurrent precipitation of kaolinite in cleats at a burial depth of < 1600 m at  78 ± 5 °C. Post-Paleozoic uplift, the development of a second generation of cleats, and subsequent precipitation of calcite occurred at shallower burial depth between  500 to  1300 m at a lower temperature of 43 ± 6 °C. The available paleowater in coalbeds was likely ocean water and/or tropical meteoric water with a δ18Owater  − 1.25‰ versus VSMOW. Inoculation of coalbeds with methanogenic CO2-reducing microbes occurred at an even later time, because modern microbially influenced 13C-enriched coalbed CO2 (i.e., the isotopically fractionated residue of microbial CO2 reduction) is out of isotopic equilibrium with 13C-depleted calcite in cleats.  相似文献   

15.
The Oroscocha Quaternary volcano, in the Inner Arc Domain of the Andean Cordillera (southern Peru), emitted peraluminous rhyolites and trachydacites that entrained decimetric to millimetric lamprophyric blobs. These latter show kersantite modal compositions (equal proportion of groundmass plagioclase and K-feldspar) and potassic bulk-rock compositions (1<K2O/Na2O<2; 6.7–7.2 wt.% CaO). Kersantite blobs have shapes and microstructures consistent with an origin from a mixing process between mafic potassic melts and rhyolitic melts. Both melts did exchange their phenocrysts during the mixing process. In addition to index minerals of lamprophyres (Ba–Ti–phlogopite, F-rich apatite, andesine and Ca-rich sanidine), the groundmass of kersantite blobs displays essenite-rich diopside (up to 22 mol%), Ti-poor magnetite microlites, Ti-poor hematite microlites and a series of Ca–Ti–Zr- and REE-rich accessory minerals that have never been reported from lamprophyres. Titanite [up to 5.3 wt.% ZrO2 and 5.2 wt.% (Y2O3 + REE2O3)] and Zr- and Ca-rich perrierite (up to 7.2 wt.% ZrO2 and 10.8 wt.% CaO) predate LREE- and iron-rich zirconolite and Fe-, Ti-, Hf-, Nb- and Ce-rich baddeleyite (up to 5.3 wt.% Fe2O3, 3.2 wt.% TiO2, 1.5 wt.% HfO2, 1.2 wt.% Nb2O5, 0.25 wt.% CeO2) in the crystallization order of the groundmass. Isomorphic substitutions suggest iron to occur as Fe3+ in all the accessory phases. This feature, the essenitic substitution in the clinopyroxene and the occurrence of hematite microlites, all indicate a drastic increase of the oxygen fugacity (from FMQ − 1 to FMQ + 5 log units) well above the HM synthetic buffer within a narrow temperature range (1100–1000 °C). Such a late-magmatic oxidation is ascribed to assimilation of water from the felsic melts during magma mixing, followed by rapid degassing and water dissociation during eruption of host felsic lavas. Thus, magma mixing involving felsic melt end-members provides a mechanism for mafic potassic melts to be oxidized beyond the HM synthetic buffer curve.  相似文献   

16.
Cinnabar (α-HgS) and metacinnabar (β-HgS) dissolved at environmentally significant rates in oxygenated slurry experiments simulating a low-flow fluvial system. Based on SO42− production, cinnabar dissolution rates were 2.64 to 6.16 μmol (SO42−) m− 2 day− 1, and metacinnabar dissolution rates were 1.20 to 1.90 μmol (SO42−) m− 2 day− 1. Monodentate-bound thiosulfate (S2O32−) was identified as an oxidation product on the HgS surface by ATR-IR spectroscopy based on strong infrared absorption bands in the 1140–1145 cm− 1 and 1006–1014 cm− 1 regions. The presence of sulfide oxidation intermediates on the HgS surface indicates that SO42− concentration underestimates α-HgS and β-HgS dissolution in this setting. Mercury release rates during dissolution were more than two orders of magnitude less than SO42− production, but were significant: 0.47 mg (Hg) m− 2 y− 1 from cinnabar [6.45 nmol (Hg) m− 2 day− 1], and 0.17 mg (Hg) m− 2 y− 1 from metacinnabar [2.29 nmol (Hg) m− 2 day− 1]. The Hg mobilized during α-HgS and β-HgS dissolution is sufficient to form natural Au–Hg amalgam in downstream placer settings. The proportion of mercury that is not remobilized during α-HgS and β-HgS dissolution likely adsorbs to the dissolving mercuric sulfide. Adsorption of Hg2+ to cinnabar was detected in situ by anodic stripping voltammetry using a cinnabar-modified carbon paste electrode following accumulation of Hg2+ on the electrode at open circuit potential.  相似文献   

17.
The Changkeng Au and Fuwang Ag deposits represent an economically significant and distinct member of the Au–Ag deposit association in China. The two deposits are immediately adjacent, but the Au and Ag orebodies separated from each other. Ores in the Au deposit, located at the upper stratigraphic section and in the southern parts of the orefield, contain low Ag contents (< 11 ppm); the Ag orebodies, in the lower stratigraphic section, are Au-poor (< 0.2 ppm). Changkeng is hosted in brecciated cherts and jasperoidal quartz and is characterized by disseminated ore minerals. Fuwang, hosted in the Lower Carboniferous Zimenqiao group bioclastic limestone, has vein and veinlet mineralization associated with alteration comprised of quartz, carbonate, sericite, and sulfides. Homogenization temperatures of fluid inclusions from quartz veinlets in the Changkeng and Fuwang deposits are in the range of 210 ± 80 °C and 230 ± 50 °C, respectively. Salinities of fluid inclusions from the two deposits range from 1.6 to 7.3 wt.% and 1.6 to 2.6 wt.% equiv. NaCl, respectively. The δDH2O, δ18OH2O, δ13CCO2 and 3He/4He values of the fluid inclusions from the Changkeng deposit range from − 80‰ to − 30‰, − 7.8‰ to − 3.0‰, − 16.6‰ to − 17.0‰ and 0.0100 to 0.0054 Ra, respectively. The δDH2O, δ18OH2O, δ13CCO2 and 3He/4He values of fluid inclusions from the Fuwang deposit range from − 59‰ to − 45‰, − 0.9‰ to 4.1‰, − 6.7‰ to − 0.6‰ and 0.5930 to 0.8357 Ra, respectively. The δDH2O, δ18OH2O, δ13CCO2 and 3He/4He values of the fluid inclusions suggest the ore fluids of the Changkeng Au-ore come from the meteoric water and the ore fluids of the Fuwang Ag-ore are derived from mixing of magmatic water and meteoric water. The two deposits also show different Pb-isotopic signatures. The Changkeng deposit has Pb isotope ratios (206Pb/204Pb: 18.580 to 19.251, 207Pb/204Pb: 15.672 to 15.801, 208Pb/204Pb: 38.700 to 39.104) similar to those (206Pb/204Pb: 18.578 to 19.433, 207Pb/204Pb: 15.640 to 15.775, 208Pb/204Pb: 38.925 to 39.920) of its host rocks and different from those (206Pb/204Pb: 18.820 to 18.891, 207Pb/204Pb: 15.848 to 15.914, 208Pb/204Pb: 39.579 to 39.786) of the Fuwang deposit. The different signatures indicate different sources of ore-forming material. Rb–Sr isochron age (68 ± 6 Ma) and 40Ar–39Ar age (64.3 ± 0.1 Ma) of the ore-related quartz veins from the Ag deposit indicate that the Fuwang deposit formed during the Cenozoic Himalayan tectonomagmatic event. Crosscutting relationships suggests that Au-ore predates Ag-ore. The adjacent Changkeng and Fuwang deposits could, however, represent a single evolved hydrothermal system. The ore fluids initially deposited Au in the brecciated siliceous rocks, and then mixing with the magmatic water resulted in Ag deposition within fracture zones in the limestone. The deposits are alternatively the product of the superposition of two different geological events. Age evidence for the Fuwang deposit, together with the Xiqiaoshan Tertiary volcanic-hosted Ag deposit in the same area, indicates that the Pacific Coastal Volcanic Belt in the South China Fold Belt has greater potential for Himalayan precious metal mineralization than previous realized.  相似文献   

18.
Ambient-temperature environments in which dissolved silica and U(VI) are present may lack the conditions necessary to readily form crystalline uranyl-silicate phases; however amorphous phases, as defined by the absence of well-defined Bragg reflections in powder X-ray diffraction patterns, are kinetically favored when solution saturation levels are appropriate. Such amorphous uranyl-silicates may be related to the crystalline phases predicted to be thermodynamically stable and influence the mobility of U in the environment. To investigate amorphous uranyl-silicates and their relation to crystalline phases we precipitated solids from solutions containing 0.05 M UO2(ClO4)2 and 0.1 M Na2SiO3 adjusted to pH values from 2.2 to 9 and allowed the precipitates to age in their mother liquors for approximately 6 weeks at 22 °C. We compared the chemical composition, X-ray diffraction patterns, and Fourier transform infrared spectra of the precipitates to those of the crystalline phases predicted by thermodynamic modeling. The precipitates were amorphous with U:Si ratios of 0.8 ± 0.1. Their FTIR spectra revealed changes in the UO22+ and SiO44− vibrations as a function of pH that are consistent with a shift in mid-range structural linkages from those similar to soddyite to those more like Na-boltwoodite. Structural H2O, OH, and SiO3OH3− vibrations do not change as a function of pH and are consistent with a mixture of soddyite-like and Na-boltwoodite-like features. Six weeks of aging at ambient temperature is enough time for the precipitate structures to rearrange and adopt mid-range structural linkages characteristic of crystalline phases predicted by thermodynamic modeling.  相似文献   

19.
Aggregates composed of olivine and magnesiowüstite have been deformed to large strains at high pressure and temperature to investigate stress and strain partitioning, phase segregation and possible localization of deformation in a polyphase material. Samples with 20 vol.% of natural olivine and 80 vol.% of (Mg0.7Fe0.3)O were synthesized and deformed in a gas-medium torsion apparatus at temperatures of 1127 °C and 1250 °C, a confining pressure of 300 MPa and constant angular displacement rates equivalent to constant shear strain rates of 1–3.3 × 10− 4 s− 1. The samples deformed homogeneously to total shear strains of up to γ  15. During constant strain rate measurements the flow stress remained approximately stable at 1250 °C while it progressively decreased after the initial yield stress at the lower temperature. Mechanical data, microstructures and textures indicate that both phases were deforming in the dislocation creep regime. The weaker component, magnesiowüstite, controlled the rheological behavior of the bulk material and accommodated most of the strain. Deformation and dynamic recrystallization lead to grain refinement and to textures that were not previously observed in pure magnesiowüstite and may have developed due to the presence of the second phase. At 1127 °C, olivine grains behaved as semi-rigid inclusions rotating in a viscous matrix. At 1250 °C, some olivine grains remained largely undeformed while deformation and recrystallization of other grains oriented for a-slip on (010) resulted in a weak foliation and a texture typical for pure dry olivine aggregates. Both a-slip and c-slip on (010) were activated in olivine even though the nominal stresses were up to 2 orders of magnitude lower than those needed to activate these slip systems in pure olivine at the same conditions.  相似文献   

20.
The Cobre–Babilonia vein system formed during a single major hydrothermal stage and is part of the Taxco district in Guerrero, southern Mexico. Homogenization and ice melting temperatures range from 160 to 290 °C and from − 11.6 to − 0.5 °C, respectively. We determined an approximate thermal gradient of 17 to 20 °C per 100 m using fluid inclusions. A thermal peak marked by the 290 °C isotherm is interpreted as a major feeder channel to the veins. The highest content of Zn + Pb in ore coincides with the 220 and 240 °C isotherms. Salinities of mineralizing fluids range from 0.8 to 15.6 wt.% NaCl equiv, and are distributed in two populations that can be related with barren or ore-bearing vein sections, with 0.8 to 6 wt.% NaCl equiv and 7 to 15.6 wt.% NaCl equiv, respectively. δ13C and δ18O water values from calcite from the Cobre–Babilonia vein system and the Esperanza Vieja and Guadalupe mantos range − 5.4‰ to − 10.4‰ and 9.9‰ to 13.4‰, respectively. δ34S values range from 0‰ to 3.2‰ and − 0.7‰ to − 4.3‰ in sphalerite, − 4‰ to 0.9‰ in pyrite, and − 1.4‰ to − 5.5‰ in galena. Both fluid inclusion and stable isotope data are compatible with magmatic and meteoric sources for mineralizing fluids. Also, sulfur isotope compositions suggest both magmatic and sedimentary sources for sulfur.  相似文献   

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