bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Sulphur Isotope Study of Iron Sulphides in the Late Precambrian Dalradian Easdale Slate Formation, Argyll, Scotland
Authors: Hall A. J. , Boyce A. J. , Fallick A. E. 
Published: December 2006

AbstractPyritic slates from the late Precambrian, Middle Dalradian Argyll Group Easdale Slate Formation, contain mainly quartz, muscovite and chlorite with variable amounts of dolomite, albite and paragonite. Slates from Easdale Island and Cuan Ferry contain pyrite porphyroblasts with δ34S = + 12 to + 16‰. The pyrite grew during a post-tectonic retrogressive event at the expense ofpyrrhotine which formed during the main regional metamorphism of the Grampian orogeny by reduction of diagenetic pyrite. Slate from Oban contains abundant diagenetic framboidal pyrite and small syn-tectonic pyrite porphyroblasts with δ34S = +22‰. This pyrite was not all reduced to pyrrhotine on metamorphism so there was little retrogressive growth of pyrite. Metamorphism appears to have homogenized local (cm scale at least) isotopic inhomogeneities and preserved an average seawater-sulphate-sulphide isotopic fractionation value. Middle Dalradian seawater-sulphate had a δ34S value of about + 35‰, so the small fractionations are appropriate for bacteriogenic reduction in bituminous sediments, the heavier sulphide in the case of the Oban slate indicating more rapid reduction of sulphate. Lower Dalradian Appin Group, Ballachulish slate contains pyrite with δ34S = +15±2‰ and is best interpreted as forming in the same manner as the Easdale slates of Easdale Island and Cuan Ferry; the sharp increase in late Precambrian ocean-sulphate sulphur isotope signature from +15 to > +30‰ therefore occurred by Lower Dalradian Appin Group times.
Zirconium-rich Sodic Pyroxenes in Felsic Volcanics from the Warrumbungle Volcano, Central New South Wales, Australia
Authors: Duggan M. B. 
Published: December 2006

AbstractSoda-rich pyroxenes in felsic rocks from the Warrumbungle Volcano, central New South Wales, contain up to 14.5 wt. % ZrO2, which is more than double the previously reported maximum ZrO2in pyroxene. Zr is believed to enter aegirine as the component Na(Fe2+,Mn,Mg)0.5Zr0.5Si2O6via the coupled substitution: (Fe2+,Mn,Mg)VI+ZrVI= 2(Fe3+)VI. This component exceeds 50 mol. % in some analyses.Pronounced pyroxene Zr-enrichment is restricted to rocks in which sodic amphibole is the major ferromagnesian mineral, with pyroxene only a minor late-stage phase. The Zr-rich pyroxenes resulted from a combination of host lava peralkalinity, low oxygen fugacity, rapid disequilibrium crystallization and low mobility of the Zr ion. These factors collectively led to the development of interstitial Zr-enriched microdomains in the felsic hosts during their final stages of crystallization.
Compositional Variation in Wolframites from the Barroca Grande Mine, Portugal: Evidence for Fault-Controlled Ore Formation
Authors: Polya D. A. 
Published: December 2006

AbstractThe major and trace element composition of over 40 wolframites from the Barroca Grande mine of the Panasqueira W-Sn-Cu quartz-vein hosted orebody have been determined by electron probe microanalysis.The hübnerite content of wolframite is largely uniform (12 to 20 mol. %) throughout most of the mine, suggesting relative uniformity in composition of the main stage ore-forming fluids. However, wolframites show a striking pattern of enrichment in niobium adjacent to major sub-vertical fault zones. Typical wolframite Nb2O5 contents are below 1000 ppm, whilst values greater than 1000, 2000 and 4000 ppm are generally only found in wolframites less than 50, 30, and 10 metres respectively from major sub-vertical faults. This strongly suggests that some of these fault zones acted as major pathways for hydrothermal fluid migration during ore formation. The idea that the greisened cupola at Panasqueira was the sole major pathway for fluid movement is discounted.
Xenocrysts in Eocene Camptonites from Taourirt, Northern Morocco
Authors: Mokhtari Abdelkader , Velde Danielle 
Published: December 2006

AbstractA study of xenocrystic material included in 57 Ma igneous rocks that outcrop in the Taourirt area of north-east Morocco has been made. The mineralogy of the host rocks is essentially clinopyroxene, rare olivine, titanomagnetite and either kaersutite or biotite. Feldspars (plagioclase and alkali feldspar) and nepheline are usually altered. Accessories may include haüyne, perovskite and ferriannite-rich annite. The complex xenocrystic assemblage includes various types of clinopyroxene, amphiboles, micas of differing compositions and various types of spinel. These inclusions did not dissolve in the melt and, as a consequence, the residual (alkali-rich) mineralogical assemblage is not modified. Their abundance is such that they may not significantly affect the major element compositions, but they may strongly influence the levels of certain trace elements such as Cr and Ni.
Mineral Chemistry of Leucitites from Visoke Volcano (Virunga Range, Rwanda): Petrogenetic Implications
Authors: Marcelot G. , Rançon J. Ph. 
Published: December 2006

AbstractThe Visoke complex is one of the main Quaternary volcanic centres of the Virunga Range, located north of lake Kivu. Mineralogical (microprobe) data are given for two representative leucitite lavas; one sample contains a complex coarse-grained xenolith (phlogopite, diopside, leucite, titanomagnetite, perovskite and apatite) and megacrysts of pyroxene, phlogopite and olivine scattered in fine-grained leucite-rich host lava. Compared with the typical leucite-dominated, low-pressure phenocryst assemblage of the two samples studied, the chemical trends of ferromagnesian crystals suggest an earlier igneous event (high-pressure phenomenon) strongly related to the leucite-bearing magma suite.
Metamorphism of the Palaeozoic Cinco Villas Massif (Basque Pyrenees): Illite Crystallinity and Graphitization Degree
Authors: Pesquera A. , Velasco F. 
Published: December 2006

AbstractThe degree of metamorphism affecting the Devonian-Carboniferous rocks of the Palaeozoic Cinco Villas massif has been studied by (a) petrographic techniques, (b) illite crystallinity, and (c) degree of graphitization of the carbonaceous material. Some mineralogical differences have been found between the Devonian and Carboniferous rocks; paragonite and mixed-layer paragonite/muscovite, typical of anchimetamorphic areas, appear in the Devonian but are not found in the Carboniferous rocks. These are characterized by the local appearance of chloritoid, garnet, amphibole, epidote, andalusite and biotite, and the generalized presence of muscovite/chlorite. Illite crystallinity shows a metamorphic zonation (anchizone epizone) towards the granitic Aya massif, and a concentric pattern around the intrusive body.The optical analysis shows that the first effects of the regional metamorphism began before the D2deformation, reaching its paroxysm during this phase and continuing afterwards. The degree of graphitization evolves progressively with metamorphism, and this fact is reflected in an exponential relationship betweend(002)and crystallinity Lc(002). The similarity in the degree of graphitization between homologous materials within and outside the Aya aureole suggests a similar kinetic factor for both the thermal and regional metamorphisms, or a similar duration time. This fact, as well as the distribution and relationship between the deformation and recrystallization of the minerals, suggests a syn-plutonic regional metamorphism developed at low pressures, in accordance with the value of theb0parameter for the white micas, and probably a maximum temperature of about 500°C.
The Significance of Almandine Garnets in the Lundy and Dartmoor Granites
Authors: Stone Maurice 
Published: December 2006

AbstractAlmandine garnets in the cordierite-bearing granite of Sweltor Quarry, Dartmoor, contain < 10 mol. % of the spessartine end-member, whilst those in the Lundy granite have c. 10 mol. % spessartine. Experimental work indicates that such compositions can grow in equilibrium with siliceous melts at depths of 18–25 km. This evidence, reaction rims, lack of marked zoning and comparison with garnets in other siliceous calc-alkaline siliceous rocks point to a genesis involving partial melting of the ‘local’ lower crust. A restite origin rather than direct crystallization from magma is favoured but the evidence is equivocal. The Dartmoor granite (Hercynian) is a typical peraluminous late- to post-tectonic S-type granite. The S-type character of the Lundy (Tertiary) granite is revealed by the occurrence of garnet and topaz together with biotite enriched in Rb, Cs and F, despite its close association with Tertiary basic magmatism in an anorogenic setting.
Magmatic Garnets in the Cairngorm Granite, Scotland
Authors: Harrison T. N. 
Published: December 2006

AbstractSmall, euhedral Mn-rich garnets (32–52 mol. % spessartine) from the Cairngorm granite, Eastern Grampian Highlands, Scotland, are considered to be of magmatic origin and have not been derived from the assimilation of metasedimentary material, despite their occurrence largely at the margins of the pluton. Similar garnets also occur in a late cross-cutting aplite sheet. The garnets in the granite crystallized early in the sequence and are thought to have formed in response to the ponding of Mn-rich fluids against the wall of the pluton. This Mn enrichment of the fluid phase continued throughout the evolution of the pluton, resulting in Mn-rich biotites and opaque oxides and the localized crystallization of Mn-rich garnets in aplite. Garnet contains up to 1.67 wt. % Y, but has not played a major role in the geochemical evolution of the Cairngorm granite, which has high SiO2 (72–77%) and is enriched in Y and HREE. Chemical analyses of garnets, biotites and rocks are given.
Cathodoluminescence Colours of α-Quartz
Authors: Ramseyer K. , Baumann J. , Matter A. , Mullis J. 
Published: December 2006

AbstractA new cathodoluminescence-microscope has been developed with a considerably improved detection limit. Time-dependent luminescence intensity changes observed during electron bombardment enabled the recognition of short-lived, long-lived, and brown luminescence colour types in α-quartz.Short-lived bottle-green or blue luminescence colours with zones of non-luminescing bands are very common in authigenic quartz overgrowths, fracture fillings or idiomorphic vein crystals. Dark brown, short-lived yellow or pink colours are often found in quartz replacing sulphate minerals. Quartz from tectonically active regions commonly exhibits a brown luminescence colour. A red luminescence colour is typical for quartz crystallized close to a volcanic dyke or sill.The causes of these different and previously poorly understood luminescence colours were investigated using heat treatment, electron bombardment and electrodiffusion. Both natural and induced brown luminescence colours reflect the presence of lattice defects (nonbonding Si-O) due to twinning, mechanical deformation, particle bombardment or extremely rapid growth. The bottle-green and blue linearly polarized luminescence colour, characterized by a plane of polarization parallel to the c-axis, both depend on the presence of interstitial cations. The yellow and red luminescence colours in α-quartz both exhibit a plane of polarization perpendicular to the c-axis and appear to be related to the presence of trace elements in an oxidizing solution and to ferric iron respectively.
The Chemistry of Formation of Some Secondary Arsenate Minerals of Cu(II), Zn(II) and Pb(II)
Authors: Magalhães M. Clara F. , Pedrosa de Jesus Julio D. , Williams Peter A. 
Published: December 2006

AbstractSolution studies have been carried out on natural and synthetic arsenate minerals, which are often found in the oxide zones of base metal orebodies. Solubility products and free energy of formation data have been derived for the minerals olivenite, cornubite, clinoclase, adamite, legrandite, euchroite, duftite, conichalcite, austinite, bayldonite, and schultenite at 298.2 K (25 °C). The data have been used in turn to construct stability field diagrams illustrating the chemical conditions under which the various species may crystallize from aqueous solution. This equilibrium model is then compared with several natural occurrences of the arsenate suites and it is demonstrated that it can be used to explain a number of observed paragenetic sequences. Descriptions of solution conditions which describe the stabilities of the arsenate minerals with respect to more commonly found secondary minerals of Pb(II), Cu(II), and Zn(II) involve more complex calculations and estimates of the likely levels of various dissolved species, but it is shown how these may be taken into account in the development of a more complex equilibrium model.
Ion microprobe analysis—a review of geological applications
Authors: Reed S. J. B. 
Published: December 2006

AbstractIn ion microprobe analysis the specimen is bombarded with a focussed ion beam a few µm in diameter and the secondary ions produced are accelerated into the entrance slit of a mass spectrometer. An outline of the salient features of the instrument is given here, together with an account of the methods used for quantitative elemental and isotopic analysis.The major part of this paper consists of a comprehensive account of the geological applications of ion microprobe analysis. These include elemental analysis, especially for trace elements (down to sub-ppm levels in many cases) and light elements (H-F) which are beyond the scope of the electron microprobe. The other main area of geological interest is isotopic analysis, where the ion microprobe has the advantage over conventional mass spectrometry of being capable of in situ analysis of selected points on polished sections, obviating the need for laborious specimen preparation, and enabling spatially-resolved data to be obtained, with a resolution of a few µm. The ion microprobe has been especially successful in U-Pb zircon dating and the study of isotope anomalies in meteorites. Other significant applications include diffusion and stable isotope studies.
A Pan-African zincian staurolite imprint on Namaqua quartz–gahnite–sillimanite assemblages
Authors: Moore J. M. , Reid A. M. 
Published: December 2006

AbstractQuartz-gahnite-sillimanite asssemblages are described from a supracrustal enclave at Kraaifontein, 45 km south-west of Springbok in the Namaqualand Metamorphic Complex, South Africa. The assemblage formed by prograde reaction in the granulite facies zone during the 1100 Ma Namaqua event, possibly as the result of desulphidation of sphalerite. Subsequent lower-amphibolite-facies retrogression occurred in close proximity to shear zones during an early Pan-African metamorphic event at 700 Ma. Zincian staurolite formed as overgrowths on gahnite in a hydration reaction involving the consumption of gahnite, quartz, and sillimanite. Compositional zoning to more zinc-rich rims in gahnite at Kraaifontein is unrelated to the retrograde reaction, but is interpreted as a result of changing conditions during the prograde Namaqua event.
A barian bannisterite from Japan
Authors: Matsubara S. , Kato A. 
Published: December 2006

AbstractChemical analyses of bannisterite from the Kamo mine, Toba City, Mie Prefecture, Japan, give Ba : Ca = 69:31–55:45, yielding the ideal formula with Ba > Ca, i.e. (Ba,Ca)(K,H3O)(Mn2+ · Mg,Fe2+)21 (Si,Al)32(O,OH)92 · nH2O, where Ba > Ca, Mn2+ > Mg, Fe2+,Si ≫ Al, and O > OH. The unit cell parameters calculated after the indexing of the X-ray powder pattern are: a = 22.95, b = 16.52, c = 25.66 Å, β = 94.2°. It occurs as dark brown veinlets cutting massive caryopilite-rhodochrosite ore, which is also cut by veinlets of manganoan chlorite (Mn/(Mg + Mn + Fe) = c. 0.30–0.39) with minor barian orthoclase (Ba/(K+ Ba) = 0.05 ∼ 0.06).
Zirconium-bearing amphiboles from the Igaliko Dyke Swarm, South Greenland
Authors: Pearce N. J. G. 
Published: December 2006

AbstractSodic-calcic and alkali amphiboles from benmoreitic members of the Igaliko Dyke Swarm contain up to 4.13 wt. % ZrO2. It is proposed that Zr enters the amphiboles by a coupled substitution of(where C = octahedral site and T = tetrahedral site) to produce the richest Zr-bearing amphiboles so far identified, with compositions ranging up toThese amphiboles crystallize at a late stage from magmas which were Zr-rich, highly peralkaline and hydrous, with an fo2 close to the synthetic QMF buffer. The incorporation of Zr in to the amphibole is a consequence of the failure of other Zr-bearing phases (such as zircon, baddeleyite, eudialyte) to crystallize.
BBonding in minerals: the application of PAX (photoelectron and X-ray) spectroscopy to the direct determination of electronic structure
Authors: Urch David S. 
Published: December 2006

AbstractX-ray photoelectron spectroscopy can be used to measure the ionization energies of electrons in both valence band and core orbitals. As core vacancies are the initial states for X-ray emission, a knowledge of their energies for all atoms in a mineral enables all the X-ray spectra to be placed on a common energy scale. X-ray spectra are atom specific and are governed by the dipole selection rule. Thus the individual bonding roles of the different atoms are revealed by the fine structure of valence X-ray peaks (i.e. peaks which result from electron transitions between valence band orbitals and core vacancies). The juxtaposition of such spectra enables the composition of the molecular orbitals that make up the chemical bonds of a mineral to be determined.Examples of this approach to the direct determination of electronic structure are given for silica, forsterite, brucite, and pyrite. Multi-electron effects and developments involving anisotropic X-ray emission from single crystals are also discussed.
Studies of the orthoamphiboles. IV. Mössbauer spectra of anthophyllites and gedrites
Authors: Law Anthony D. 
Published: December 2006

AbstractFitted Mössbauer spectra are presented for a set of anthophyllites and gedrites. Despite their complexity it is possible to obtain fits for gedrite spectra and the Mössbauer parameters are consistent with results for anthophyllites from this and previous studies. At least three doublets are required to fit the Fe2+ absorption in gedrites; there is no single model at present to explain the behaviour of the spectra. Fe3+ absorption is also resolved.
EXAFS and Mössbauer spectroscopic study of Febearing tetrahedrites
Authors: Charnock J. M. , Garner C. D. , Pattrick R. A. D. , Vaughan D. J. 
Published: December 2006

AbstractEXAFS and Mössbauer data on synthetic silver-rich tetrahedrite, (Cu, Ag)10+xFe2−xSb4S13, reveal the presence of Fe2+and Fe3+the former occupying trigonal planar sites and the latter tetrahedral sites. There is also a clear relationship between increased silver substitution and an increase in Fe2+. The amount of Fe3+incorporated in the synthetic tetrahedrites is proportional to the excess of Cu+(Cu + Ag > 10 atoms) in the mineral, thus maintaining a charge balance. The iron in the natural tetrahedrites and the tennantite examined is mainly tetrahedrally co-ordinated Fe2+.
Luminescence spectroscopy of Mn2+rock-forming carbonates
Authors: Walker G. , Abumere O. E. , Kamaluddin B. 
Published: December 2006

AbstractCathodoluminescence emission spectra and luminescence excitation spectra of Mn2+in calcites, dolomites, magnesites, a manganocalcite and a rhodochrosite have been measured at both room temperature and 77 K. Ligand-field parameters have been calculated from the excitation spectra which reflect the size of the metal cation site in which the Mn2+ion resides. The technique of luminescence excitation spectra has enabled the absorption profile of Mn2+in Mg and Ca sites in dolomite to be separately determined. The variation of the distribution of Mn2+between Mg and Ca sites in dolomites is demonstrated and discussed in terms of a simple model. It is concluded that the distribution of Mn2+in dolomites may well provide information about its conditions of formation and/or subsequent alteration.
Arsenopyrite: a spectroscopic investigation of altered surfaces
Authors: Richardson S. , Vaughan D. J. 
Published: December 2006

AbstractSurfaces of a natural sample of arsenopyrite (FeAsS) were oxidized by a range of inorganic oxidants, and the resultant surface alteration products studied using various spectroscopic techniques. The oxidants used were air during heating to relatively low temperatures (150°C), steam, ammonium hydroxide, hydrogen peroxide, and sulphuric acid. Electrochemical oxidation in water was also undertaken. X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and spectral reflectance measurements, were used to characterize the surface compositions. New data are proposed for the binding energies of core electrons in arsenopyrite based on the fitted XPS spectra: 706.9 eV for the Fe 2p3/2 level, 161.2 eV for the S 2p level, and 40.7eV for the As 3d level. Spectroscopic analyses of the surfaces following oxidation indicated a range of iron oxides and hydroxides (Fe1−xO, Fe3O4, Fe2O3, FeOOH and Fe(OH)3), arsenic oxides (As2O3 and As2O5), sulphur and iron sulphates (FeSO4, Fe2(SO4)3). The relative proportions of the different phases present in the surface layer are related to the strength of the oxidant employed and, where relevant, the Eh/pH conditions prevalent during oxidation. The conclusions regarding the nature of the oxidation of arsenopyrite are discussed in relation to arsenopyrite extraction by flotation and leaching, and the breakdown of arsenopyrite in natural systems.
Infrared spectra of synthetic almandine–grossular and almandine–pyrope garnet solid solutions: evidence for equivalent site behaviour
Authors: Geiger C. A. , Winkler B. , Langer K. 
Published: December 2006

AbstractThe infrared (IR) spectra of almandine-grossular and almandine-pyrope garnet solid solutions have been measured using the powder method. Frequency shifts of a band related to internal vibrations associated with the 8-co-ordinate dodecahedral site are nonlinear in almandine-grossular garnets and mimic the form of its molar volume of mixing curve. Almandine-pyrope solid solutions have nearly ideal molar volumes of mixing and the frequency shift of this same 8-co-ordinate site-related band is linear. The IR data support the empirically based crystal chemical model of Equivalent Site (ES) behaviour (Newton and Wood, 1980). The IR spectra give no indication of long-range ordering between Ca and Fe2+ in garnet, but thermodynamic calculations involving Ca-poor garnets might be affected by small volume or short-range ordering anomalies.
High-resolution silicon Kβ X-ray spectra and crystal structure
Authors: Purton J. , Urch D. S. 
Published: December 2006

AbstractHigh-resolution X-ray emission spectra (XES) are presented for minerals with a variety of structures. The participation of the Si 3p orbitals in bonding is influenced by the local structure around the silicon atom. In orthosilicates the distortion of the SiO44--tetrahedron influences both peak-width and the intensity of the high-energy shoulder of the Si-Kβ spectrum. In minerals containing Si-O-Si bonds there is mixing of the Si 3s and 3p orbitals giving rise to a peak on the low-energy side of the main Si-Kβ peak. When combined with X-ray photoelectron spectra (XPS), a complete molecular orbital picture of bonding can be established.
Magnesian ilmenite in picritic basalts from the Karoo Province, South Africa
Authors: Cawthorn R. Grant , Bristow John W. , Groves David I. 
Published: December 2006

AbstractSome picritic lavas from near the base of the volcanic succession in the Lebombo region of the Karoo Province contain phenocrysts of olivine and skeletal microphenocrysts of ilmenite, the latter indicating rapid crystallization from the magma. These ilmenite grains contain up to 6% MgO. The near-liquidus crystallization and the high MgO content of the ilmenite are highly anomalous for ilmenite in tholeiitic rocks. These features reflect the atypical nature (high MgO and TiO2) of the parental magma and/or highly reduced conditions of crystallization.