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11

Electronic Resource

Dolomitization and the mineralization of the Marl Slate (N. E. England) (1978)

Turner, P. ; Vaughan, D. J. ; Whitehouse, K. I.

Springer

Mineralium deposita 13 (1978), S. 245-258

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ISSN: 1432-1866

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Notes: Abstract The Marl Slate, the English equivalent of the Kupferschiefer, has been studied with particular reference to the relationships between dolomitization and the origin of the metal sulphides. Dolomite occurs as: 1) discontinuous lenses of ferroan dolomicrite, 2) micronodules of finely crystalline dolospar in association with length-slow chalcedony and 3) discrete laminae of ferroan or non-ferroan dolospar. The ferroan dolomicrite has excess CaCO3, and is more abundant in the lower, sapropelic facies of the Marl Slate. It is considered to have formed by the penecontemporaneous alteration of calcium carbonate under hypersaline conditions. Small micronodules (typically about 0.3 mm in diameter) are also more abundant in the sapropelic Marl Slate. These frequently contain cores of length-slow chalcedony (quartzine) fibres and sometimes quartz megacrysts. Textural observations clearly indicate that this silica is of authigenic origin and the dolomite/chalcedony micronodules are interpreted as diagenetic replacements of a calcium sulphate mineral such as anhydrite. The discrete laminae of finely crystalline dolospar are often inter-laminated with calcite in the upper part of the Marl Slate. This dolomite is also calcium rich and represents a replacement, possibly of anhydrite, during a later phase of diagenesis. Metal sulphides occur in two distinct forms: as disseminated framboidal pyrite and as discrete lenses of pyrite, chalcopyrite, galena, sphalerite and rarer sulphides. The framboidal pyrite originated during early diagenesis by reaction of sulphide, produced by reduction of sulphate by organic material and micro-organisms, with iron also released in the reducing environment. The sulphide lenses are often in intimate association with dolospar, length-slow chalcedony and authigenic quartz megacrysts. This indicates that the lenses were produced during diagenesis by the reduction and replacement of calcium sulphate (anhydrite). Various sources, such as co-precipitation with dolomite precursors and the underlying Yellow Sands, may have supplied metals which were mobilized and transported by connate brines as diagenesis progressed.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00204646

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12

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Diagenetic processes and the mineralization in the triassic of Central England (1983)

Holmes, I. ; Chambers, A. D. ; Ixer, R. A. ; [et al.]

Springer

Mineralium deposita 18 (1983), S. 365-377

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ISSN: 1432-1866

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Notes: Abstract Continental red beds are the host rocks of a characteristic style of mineralization which suggests a genetic link between red bed formation and ore formation. Samples of unmineralized and mineralized Triassic sediments from Central England have been studied sedimentologically, petrographically and geochemically with the aim of clarifying this link which may provide valuable guides for exploration. On the basis of sedimentological and petrographic observations it is suggested that these red beds were formed as a result of diagenetic alteration whereby detrital silicates and oxides are progressively dissolved and the iron released is deposited as hematite. A model for mineralization is proposed involving the release of trace metals from detrital minerals during diagenesis, their retention in saline interstitial solutions, migration to suitable sites of precipitation and deposition by reaction with trapped hydrocarbons or reduced sulphur.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00206485

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13

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Conditions of ore mineral formation in certain Zambian Copperbelt deposits with special reference to the role of cobalt (1983)

Annels, A. E. ; Vaughan, D. J. ; Craig, J. R.

Springer

Mineralium deposita 18 (1983), S. 71-88

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ISSN: 1432-1866

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Notes: Abstract Studies of the compositions of coexisting sulphide assemblages from certain Zambian Copperbelt deposits and of their textural relations and host rock environments have been undertaken by routine microscopy and using electron microprobe analysis. Special attention has been paid to sulphide assemblages containing cobalt. Using experimental data on the systems Cu-Co-S, Cu-Fe-Co-S and on sulphidation equilibria, together with the available information on equilibria involving gangue minerals and some new calculations, an attempt has been made to define the chemical conditions of ore formation and/or re-equilibration in several deposits (Baluba, Chibuluma West and Chibuluma, Chambeshi S.E.). If a re-equilibration temperature of 300°C is assumed the range of aS2 prevailing during final formation of the assemblages was of the order 10−7 – 10−9 atm, more rarely dropping to 10−11 – 10−12 atm. If magnetite is present, and this is considered very unlikely in most cases, aO2 may have reached as high as 10−35 atm but it is generally likely to have been around 10−50 atm or even lower. Values of aCO2 are assumed to have been of the order of 10−0.5 atm. Detailed studies of drill hole samples from the Chambeshi S.E. deposit suggest an important link between the petrology of the host rocks and the sulphide mineral chemistry. In particular, the control exerted on sulphide composition by aS2 may have been related to the availability of sulphate in the form of diagenetic anhydrite or in sulphate-rich interstitial waters. The distinctive distribution of cobalt in the ores appears related to the distribution of amphibolite bodies and in turn to rift fault systems in the Basement which allowed upward movement of fluids enriched in magmatically derived cobalt.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00206696

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14

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Oxidation state and electronic configuration determination of copper in tetrahedrite group minerals by L-edge X-ray absorption spectroscopy (1993)

Pattrick, R. A. D. ; Laan, G. ; Vaughan, D. J. ; [et al.]

Springer

Physics and chemistry of minerals 20 (1993), S. 395-401

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ISSN: 1432-2021

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology , Geosciences , Physics

Notes: Abstract L-edge X-ray absorption spectroscopy employing a synchrotron radiation source has been used to study the electronic structure and valency of Cu in the chemically and structurally complex tetrahedrite group of minerals. Mechanical mixtures of Cu2+O and Cu+FeS2 were used to estimate the relative cross sections of Cu2+ and Cu+; the absorption of Cu2+ at 931 eV is 25 times greater than that of Cu+ at 945 eV. Using this calibration, Cu2+/Cu ratios were found to vary from 0.00 to 0.054 in the tetrahedrite samples studied; the highest proportion of Cu2+ occurs in synthetic tetrahedrites with a composition close to Cu12Sb4S13. This study reveals the utility of the technique for determining the valence state of copper in complex minerals, allowing the crystal chemistry to be more fully characterised.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00203108

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15

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The electronic structures of the pyrite-type disulphides (MS2, where M = Mn, Fe, Co, Ni, Cu, Zn) and the bulk properties of pyrite from local density approximation (LDA) band structure calculations (1993)

Temmerman, W. M. ; Durham, P. J. ; Vaughan, D. J.

Springer

Physics and chemistry of minerals 20 (1993), S. 248-254

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ISSN: 1432-2021

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology , Geosciences , Physics

Notes: Abstract A local density approximation (LDA) band structure method, the Linear Muffin-Tin Orbital Atomic Sphere Approximation (LMTO-ASA) method has been used to calculate the electronic structures of the pyrite-type disulphides (MS2, where M = Mn, Fe, Co, Ni, Cu, Zn). The total density of states has been calculated for 10 eV above and below the Fermi Level, along with the separate contributions from metal and sulphur and shows that the metal d band occurs above the sulphur p bands in MnS2, FeS2, CoS2 and NiS2, whereas in CuS2, the d band passes through the sulphur p band and in ZnS2, it lies below the sulphur p band. Substantial hybridization of the metal d states with the sulphur states occurs. FeS2 is calculated to be a semiconductor with a direct band gap of 0.64 eV in good agreement with experiment. The calculated local densities of states have been used in turn to calculate X-ray photoelectron spectra and Bremsstrahlung Isochromat spectra for this series of compounds, and these also show reasonable agreement with experimental data. A particular strength of the LMTO-ASA method is the ability to calculate and predict certain bulk properties of solids of interest in mineral physics. This has enabled the first reasonably accurate calculations of the total energy of the valence electrons of the system for pyrite (FeS2), given as — 345.885 rydbergs per unit cell, and the equilibrium unit cell volume which is within 3.3% of that determined experimentally. A theoretical pressure vs. volume curve for pyrite was also calculated along with values for the bulk modulus. However, our calculations predict a bulk modulus of 6.75 Mbar which is too high by a factor of 4.6 due to the simplifying assumption of a uniform scaling of interatomic distances on compression.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00208138

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16

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Pyrite, marcasite, and arsenopyrite type minerals: Crystal chemical and structural principles (1981)

Tossell, J. A. ; Vaughan, D. J. ; Burdett, J. K.

Springer

Physics and chemistry of minerals 7 (1981), S. 177-184

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ISSN: 1432-2021

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology , Geosciences , Physics

Notes: Abstract Quantitative molecular orbital (MO) calculations and qualitative perturbational MO arguments are used to interpret the spectra and structure of transition metal dichalcogenides and related compounds. Competition between pyrite (FeS2), marcasite (FeS2) and loellingite (FeAs2) structure types is explained in terms of the number of electrons occupying a set of MO's obtained from the mixing of dianion (A 2) orbitals and metal (M) dσ orbitals. Direct metal-metal d orbital interaction is argued to be small. Attention is focused upon the M - A - M angles which differ substantially among the three structure types as a consequence of varying numbers of electrons in orbitals which closely resemble the pπ* orbitals of the dianions. Variations in M - A and A - A distances can also be understood in terms of the occupations of this set of MO's. Disulfide valence region photo-emission spectra are interpreted in terms of calculations on MS6 and S6 molecular clusters. M3d orbitals are found to progressively approach the S3p orbitals with increasing atomic number of M from Fe to Ni. For CuS2 comparison of calculation and experiment supports an approximate electron configuration of Cu+1 S 2 −1 .

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00307263

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17

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Investigation of Fe structural environments in “leucite”-type framework silicates using a combination of Mössbauer and X-ray absorption spectroscopies (1994)

England, K. E. R. ; Henderson, C. M. B. ; Charnock, J. ; [et al.]

Springer

Hyperfine interactions 91 (1994), S. 709-714

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ISSN: 1572-9540

Source: Springer Online Journal Archives 1860-2000

Topics: Physics

Notes: Abstract Synthetic iron-containing leucite-type phases have been studied using57Fe Mössbauer spectroscopy in combination with X-ray absorption spectroscopy (XAFS and XANES). The Mössbauer and XAS data confirm that both Fe2+ and Fe3+ occupy tetrahedrally coordinated framework sites in the synthetic phases. In addition, information on Fe2+/Fe3+ ratios, cation site occupancies and first shell bond lengths has also been obtained.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02064595

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18

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The use of coupling agents to enhance the performance of aramid reinforced composites (1978)

Vaughan, D. J.

Stamford, Conn. [u.a.] : Wiley-Blackwell

Polymer Engineering and Science 18 (1978), S. 167-169

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ISSN: 0032-3888

Keywords: Chemistry ; Chemical Engineering

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics

Notes: In view of the organic nature of aramid fiber and its ability to be combined with a number of polymer systems, fabric woven from that fiber has previously been used in an unfinished or scoured stale. However, this has resulted in a marked lack of adherence at the fiber-resin interface that has considerably reduced compressive values in the composite; this is particularly evident when the composite is exposed to adverse aqueous environments. In order to overcome what appears to be the major deficiency in this fiber, a series of coupling agents has been developed which, when used in conjunction with a number of commercial resin systems, shows a marked improvement in interlaminar adhesion. The paper outlines the problem of using untreated fiber and establishes the area of responsibility for initial failure. It then shows how the correct use of coupling agents has overcome the interfacial adhesion problem and has enhanced the performance of aramid fiber reinforced composites.

Additional Material: 7 Ill.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1002/pen.760180214

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19

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The {micro}2M project on quantifying the effects of biofilm growth on hydraulic properties of natural porous media and on sorption equilibria: an overview (2007)

Brydie, J. R. ; Wogelius, R. A. ; Merrifield, C. M. ; [et al.]

In: Geological Society Special Publication 249: 131-144.

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Publication Date: 2007-10-08

Description: The physical and chemical effects of bacterial biofilm formation upon hydraulic conductivity, mineral-solution interactions and the formation of biogenic mineral precipitates have been studied over a wide range of scales, from microscopic to macroscopic. Several novel pieces of equipment have been designed, constructed and commissioned in order to measure the physical effects of biofilms upon fluid flow through fractures and porous media, the overall effects of biofilm formation upon mineral surface reactivity, and the imaging and identification of mineral precipitates formed due to the presence of biofilm and bacterial cell surface polymers on a quartz surface. This paper presents an overview of key experimental methods and selected results; further experimental information is being published elsewhere. Biofilm formation with quartz sand in artificial groundwater resulted in a two orders of magnitude reduction in hydraulic conductivity under bench-scale constant head conditions. However, under quasi-environmental conditions within macroscopic centrifuge experiments, a reduction of 21% was measured, revealing differences in measurements and, hence, the value of the macroscopic experimental work in scaling from micro to macro. In-situ microscopic evaluation of biofilms within simulated quartz rock fractures and in porous media reveal only a small percentage of the biomass to be in direct contact with the mineral surface, allowing mineral chemistry to be predominantly controlled by mineral surface reactivity, rather than by a diffusion-limited mineral-biofilm-solution interface. This is true even when a mineral surface is apparently completely covered by biofilm. The alteration of mineral surface drastically increases the kinetics of surface-coordinated trace metal precipitate formation by providing nucleation sites upon extracellular biopolymers and cell wall polymers. Over geological time-scales, these processes, particularly the formation of thermodynamically stable pore-blocking mineral precipitates, are envisaged to markedly change the flow paths, flow rates and interaction of migrating geofluids (water, petroleum, ore-forming solutions) with minerals and rocks.

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