bluuebunny/crossref_metadata_2025 huggingface dataset:
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

X-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

Fitted 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

EXAFS 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

Cathodoluminescence 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

Surfaces 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

The 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

High-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

Some 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.
Re-examination of kirwanite: a ferri-ferro-hornblende from Co. Down, Northern Ireland
Authors: Nawaz Rab , Ryback George
Published: December 2006

X-ray powder, optical, infrared, and chemical data suggest that kirwanite is an amphibole of composition (Na,K)0.10Ca1.80(Fe2+,Mn)3.10Mg0.79Fe1.143+Al0.78Si7.18O22(OH)2 and thus corresponds to ferri-ferro-hornblende (Leake, 1978). The type locality, originally given as the NE coast of Ireland, is most likely Dunmore Head, Co. Down. Kirwanite occurs in the groundmass and the vesicles of variolitic andesite dykes of the Mourne dyke swarm. Thomson's original analysis of kirwanite was probably made on a mixture and the name should not be used for an amphibole species.
Non-metamict uranoan pyrochlore and uranpyrochlore from tuff near Ndale, Fort Portal area, Uganda
Authors: Hogarth D. D. , Horne J. E. T.
Published: December 2006

A thin (100 m) cover of flat-lying, Recent, calcite-rich tuff at Ndale near Fort Portal, Uganda, unconformably overlies steeply dipping Precambrian metamorphic rocks. It is locally radioactive owing to uranium-rich pyrochlore minerals and lesser amounts of zircon, monazite, titanite, and an unidentified thorium phosphate. In one concentrate, four grains of uranpyrochlore and one grain of uranoan pyrochlore showed a positive linear correlation of Ti with U, and negative linear correlations of Ti with Na, F and Sr. Ta remained high and relatively constant [11 anal., ave. 14.5 (0.6)% Ta2O5]. In the same concentrate the composition of a separate grain of uranoan pyrochlore did not plot on these lines and Ta was comparatively low [2 anal., ave. 4.5 (0.3)% Ta2O5]. The data suggest two separate paths of differentiation. However, zoned grains were not observed. Unit cells were cubic with a = 10.351 ± 0.002 Å for a grain with 12.9% UO2tot and 10.333 ± 0.002 Å for a grain with 26.6% UO2tot. On heating in air the cell size decreased, possibly due to oxidation of U4+. The crystalline nature of these minerals can be attributed to a very young (4000–5000 yr) geological age.
Petrology and geothermometry of the Little Michiru Complex, Malawi
Authors: Morel S. W.
Published: December 2006

The Little Michiru complex is a composite intrusion of pyroxenite and pyroxene syenite which is located at the boundary between amphibolite and granulite facies gneisses in the Shire rift valley. Pyroxene and feldspar chemistry shows that the intrusion consolidated from two magmatic fractions, one a pyroxenite cumulate that equilibrated at 870–1000 °C, the other a partly anatectic pyroxene syenite magma which metasomatized the surrounding gneisses during granulite-facies metamorphism and equilibrated at a temperature of 730–830 °C at 7 kbar.
Yimengite of K–Ti metasomatic origin in kimberlitic rocks from Venezuela
Authors: Nixon Peter H. , Condliffe Eric
Published: December 2006

This second recorded occurrence of yimengite, K(Cr, Ti, Fe, Mg, Al)12O19, is in a Precambrian kimberlitic sill in the Guaniamo District of Bolivar Province, Venezuela. The paragenesis is similar to that of the type area in Shandong Province, China, where the mineral is in kimberlite dykes. At both localities the yimengite is a K, Ti-bearing metasomatic product of chromium-rich spinel. In the Venezuela rocks the spinels are of the type occurring both as diamond inclusions and as a component of diamond-related Cr-rich garnet harzburgite mantle xenoliths. Yimengite contains significant amounts of barium (up to 3.4wt.% BaO) and is thus transitional to the recently described mineral hawthorneite, Ba(Cr, Ti, Fe, Mg)12O19. Both members are part of a suite of titanate minerals found in kimberlites and their inclusions which has been described by Haggerty and coworkers; they formed as a result of mantle metasomatism generated by K- and Ba-rich fluids. In Venezuela, metasomatism of this type would appear to be deeper than that usually recorded, namely in the basal lithosphere. The metasomatizing fluids are derived from the underlying, more oxygenated asthenosphere. The host kimberlitic rocks are not significantly enriched in K and Ba, but these elements are concentrated in later micaceous dykes which are conjectured to have been generated within similar metasomatized mantle.
On the reported presence of potassium in clinopyroxene from potassium-rich lavas: a transmission electron microscope study
Authors: Mellini M. , Cundari A.
Published: December 2006

Titanian aegirine in a pegmatoid differentiate from leucitite sensu stricto (i.e. without modal plagioclase) was found to contain significant K (up to 0.07K atoms per formula unit; 0.11 wt.% K2O) by electron probe microanalysis. A transmission electron microscope study showed that this pyroxene contained a lamellar amorphous phase and other more irregular, amorphous domains where K and Al are concentrated. The microstructures suggest that the aegirine-amorphous phase system did not achieve textural equilibrium. Also, the chemistry of this phase is variable, particularly in Ca and Mg, suggesting lack of chemical equilibrium within the liquid from which the phase derived. The average composition of the latter approaches that of the coexisting K-richterite and is interpreted as trapped residual liquid, i.e. glass, from pyroxene crystallization which failed to develop a crystalline amphibole. In view of the extensive stability of richterite coexisting with pyroxene to high pressure, the reported occurrence of ‘K-bearing pyroxene’ may not be considered as a homogeneous K-bearing phase and a predictable potassium carrier in the petrogenesis of K-rich rocks like leucitites and lamproites.
Ternary feldspars: two-feldspar assemblages at P(H2O) = 5 kbar
Authors: Jones Rhian H.
Published: December 2006

In a study of the liquidus surface in the silica-undersaturated part of the system Q-An-Ne-Ks at P(H2O) = 5 kbar, several two-feldspar plus liquid assemblages were obtained. The compositions of the feldspars were determined by electron microprobe analysis. The products of short runs (one or two days) consisted of fine intergrowths of two feldspars which may have crystallized during the heating period, or in the early stages of the run. Runs of four days were of sufficient length to coarsen these intergrowths such that individual euhedral crystals could be observed. However, analyses of the feldspar crystals from the longer runs showed a greater amount of ternary solid solution than expected. This may be attributed to the persistence of a small quantity of the second feldspar intergrown in the crystals. The slope of the tie-line joining one of the inferred pairs has been shown to be reproducible for gel and crystalline starting materials, hence the slopes of the tie-lines are believed to represent their equilibrium slopes.
The chemical stability of mimetite and distribution coefficients for pyromorphite–mimetite solid-solutions
Authors: Inegbenebor Adedayo I. , Thomas John H. , Williams Peter A.
Published: December 2006

The equilibrium solubility of mimetite has been determined in aqueous solution at 298.2K. For the reaction Pb5(ASO4)3Cl(s,mimetite)+6H+(aq)⇌5Pb2+(aq)+3H2AsO4−(aq)+Cl−(aq) at this temperature log KH+, extrapolated to zero ionic strength, is equal to −27.9(4). This value is equal, within experimental error, to that corresponding to pyromorphite, Pb5(PO4)3Cl, derived from the literature, and redetermined here under analogous conditions. Distribution coefficients in terms of both HXO42− and H2XO4−(aq) ions (X = P,As) have also been determined for solid phases of the pyromorphite-mimetite solid solution series containing from 5 to 95 mol. % mimetite. Although the two end-members are isostructural without being strictly isomorphous, the solid solution series behaves ideally over the whole compositional range; that is, the composition of the solid phase reflects the ratio of arsenate to phosphate species in aqueous solution at pH values corresponding to naturally-occurring aqueous solutions generally associated with the oxidized zones of base metal orebodies. Some relationships between mimetite and other secondary lead(II) and copper(II) arsenate minerals have been explored.
Thermal decomposition of Li8(Al6Si6O24)Cl2
Authors: Taylor D.
Published: December 2006

Li8(Al6Si6O24)Cl2, a synthetic member of the sodalite family (Henderson and Taylor, 1977), was prepared by heating natural sodalite, Na8(Al- 6Si6O24)Cl2 (from Låven, Norway), in molten LiC1 at 800 °C for 2h, washing uncombined LiC1 from the product and drying at 110 °C Chemical analyses of the natural sodalite and the Li-sodalite are given in Table 1. The cell edge of the Lisodalite was 8.4476(9) Å (Si as internal standard: a = 5.43065/Å at 25 °C in good agreement with literature values (Henderson and Taylor, 1977).
A calcian analcime-bytownite intergrowth in basalt, from Skye, Scotland, and calcian analcime relationships
Authors: Livingstone A.
Published: December 2006

Within a reyerite-tobermorite (11 Å) amygdale assemblage in olivine basalt blocks, near Drynock, Skye, is a porcellaneous material which either lines or completely fills the amygdales (Livingstone, 1988). Electron-probe microanalysis combined with back-scattered electron imaging identifies individual components of the porcellaneous material as calcian analcime and bytownite, (An74-79). Back-scattered electron imaging reveals a second generation analcime pervading the calcian analcime-bytownite intergrowth and forming patches and discrete veinlets (Fig. 1A).
Unit cell dimensions of the hydrated aluminium phosphate–sulphate minerals sanjuanite, kribergite, and hotsonite
Authors: De Bruiyn H. , Beukes G. J. , Van Der Westhuizen W. A. , Tordiffe E. A. W.
Published: December 2006

AT the time when the hydrated aluminium phosphate-sulphate hotsonite (Beukes et al., 1984a) and its equally rare relative zaherite (Beukes et al., 1984b; De Bruiyn et al., 1985) were discovered near Pofadder, South Africa, very little was known about the unit cells of the other two hydrated aluminium phosphate-sulphate minerals sanjuanite and kribergite, originally described by De Abeledo et al. (1968) from Argentina and Sweden, respectively. Although the Powder Diffraction file (PDF) contains the X-ray diffraction patterns for sanjuanite and kribergite (PDF 20-47 and 20-48 respectively), they had not been indexed nor have their unit cell parameters been calculated thus far.
Niobian K–Ba–V titanates from micaceous kimberlite, Star mine, Orange Free State, South Africa
Authors: Mitchell Roger H. , Meyer Henry O. A.
Published: December 2006

Compositional data are presented for Nb-Ba-K-V titanates from micaceous kimberlite (Star mine, S. Africa). These data significantly extend the previously known range of solid solutions in naturally occurring members of the hollandite group. Two distinct suites of crystals occur. One is a suite of primary groundmass prismatic crystals that are Ba-K-V-rich and represent solid-solutions from the priderite series towards mannardite. The second suite consists of anhedral xenocrysts that are Ba-free. In this suite relatively Nb-rich varieties (>4.0% Nb2O5) represent solid-solution towards a niobian-bearing potassian analogue of mannardite, whereas relative Nb-poor (<3.0% Nb2O5) varieties are Nb-bearing vanadian priderites. These hollandite-group minerals have compositions that differ significantly from priderites found in lamproites.
Holtite, (Si2.25Sb0.75)B [Al6(Al0.43Ta0.27□0.30) O15 (O,OH)2.25]: crystal structure and crystal chemistry
Authors: Hoskins B. F. , Mumme W. G. , Pryce M. W.
Published: December 2006

Holtite, (Si2.25Sb0.75)B[Al6(Al0.43Ta0.27□0.30)O15(O,OH)2.25], is orthorhombic a = 4.6914(5), b = 11.896(2), c = 20.383(4)Å, space group Pnma. Full-matrix least-squares refinement yielded a final R = 0.030, for 1664 reflections with I ⩾ 3σ(I). Its crystal structure is closely related to that of dumortierite, but with the difference that extensive substitution of Si by Sb occurs in holtite. SbO3 triangular pyramids replace the SiO4 tetrahedra arranged around the inside edge of the hexagonally shaped tunnels which are the feature of the dumortierite and holtite structures. Associated with these replacements is the replacement of Al by Ta in the octahedral site centred in these tunnels, and the development of vacancies in this metal site and its attached oxygens.
Time-dependent Landau theory for order/disorder processes in minerals
Authors: Carpenter M. A. , Salje E.
Published: December 2006

Recent advances in the use of time-dependent order parameter theory to describe the kinetics of order/disorder transitions are reviewed. The time dependence of a macroscopic order parameter,Q, follows, to a good approximation:

For systems in which the order parameter has a long correlation length (large ξ) and is not conserved (small ξC), the Ginzburg-Landau equation provides a general kinetic solution:

Specific rate laws can be derived from this general solution depending on whether the crystals remain homogeneous with respect to the order parameter,Q. The advantages of the overall approach are, firstly, that it does not depend on the detailed structure of the material being examined; secondly, that the order parameter can be followed experimentally through its relationship with other properties, such as spontaneous strain, excess entropy, intensities of superlattice reflections, etc.; and, finally, that conventional Landau expansions inQmay be used to describe the thermodynamic driving forces.

For a simple second-order transition in crystals which remain homogeneous inQthe rate law is:

If the free energy of activation varies with the state of order of the crystal, this becomes:

Simplifying assumptions can be introduced into the mathematics, or the integrals can be solved numerically. For crystals which remain homogeneous, the simplest solution valid only over small deviations from equilibrium is:

For crystals which develop heterogeneities inQ, the rate laws change significantly and we find as an extreme case:

where theAcoefficient may be temperature dependent.

Experimental data available for a limited number of minerals (omphacite, anorthite, albite, cordierite and nepheline) are used to demonstrate the practical implications of the overall approach. As anticipated from the theory, modulated structures commonly develop during kinetic experiments, the observed rate laws depend on whether the critical point of the ordering is located at the centre or boundary of the Brillouin zone, and the rate laws for ordering and disordering can be quite different. The importance of different length scales, not only in the different techniques for characterizing states of order (IR, NMR, calorimetry, X-ray diffraction, etc.) but also for interpreting observed mechanisms and rate laws, is also outlined.

Use of the order parameter in Landau expansions and in Ginzburg-Landau rate laws provides, in principle, a means of predicting the equilibrium and non-equilibrium evolution of minerals in nature.
Lead isotope and trace element variation in Tenerife pumices: evidence for recycling within an ocean island volcano
Authors: Wolff J. A. , Palacz Z. A.
Published: December 2006

Three voluminous Quaternary phonolitic pumice fall deposits erupted from the compositionally-zoned Tenerife magma chamber exhibit variability in Sr and Pb isotope ratios. It has been previously argued that the Sr isotope variations are due to syn-eruptive interaction between magma and hydrothermal fluids (Palacz and Wolff, 1989). Pb compositions are not correlated with Sr, and are believed to reflect magmatic values. Pb isotope ratios exhibit regular variation with degree of fractionation, and one zoned deposit is heterogeneous in Pb. The highest values seem to characterize the most fractionated upper parts of the zoned system. This is unlikely to be a consequence of magmatic recharge. Isotopic and trace element behaviour is instead consistent with combined assimilation and fractional crystalliza- tion, involving the recycling of material containing relatively radiogenic Pb, from within the volcanic edifice. Assimilation of sediment intercalated within the submarine portion of the pile is ruled out by the isotopic data. The most probable contaminant is a felsic igneous rock. Early trachytes reported by Sun (1980) have the required Pb isotope compositions and may approximately represent the assimilant.
An apparatus for the study of fast precipitation reactions
Authors: Rickard David
Published: December 2006

An apparatus is described for the measurement of the rates of fast precipitation reactions. It consists of a T-tube, where reactants are added to the arms of the T, mixed rapidly at the junction, and the rates of disappearance of reactants or appearance of products are measured along the stem of the T. The geometry of the system results in a steady state being established in the apparatus, enabling detailed analysis of reaction progress. The apparatus has been used to investigate the kinetics and mechanism of iron sulphide precipitation reactions. It has enabled measurements to be made with relatively high precision and good accuracy of the first 130 ms of reaction time.
Bernardite, a new thallium arsenic sulphosalt from Allchar, Macedonia, with a determination of the crystal structure
Authors: Pašava J. , Pertlik F. , Stumpfl E. F. , Zemann J.
Published: December 2006

The new mineral bernardite has been identified on one specimen from Allchar, Macedonia, Yugoslavia, together with orpiment and realgar. It forms black crystals, the size of which may exceed 1 mm. The streak is deep red; on an arbitrarily oriented section R(589nm) ranges from 23.8 to 24.7% in air, from 10.2 to 11.6% in oil. Microprobe analyses together with an X-ray structure analysis suggest the ideal formula TlAs5S8, with a possible replacement of As by Sb up to 15 wt. %. Monoclinic; a 15.647(4), b 8.038(3), c 10.750(3) Å, β 91.27(3)°; space group P21/c; Z = 4; R = 0.049, wR = 0.036 for 2410 reflections. The atomic arrangement consists of a 3-dimensional As5S8 framework with eight-coordinated T1 in its holes. The mineral is named for Doc. Dr Jan H. Bernard, Prague, Czechoslovakia.
Fluid and mineral inclusions in corundum from gem gravels in Sri Lanka
Authors: de Maesschalck A. A. , Oen I. S.
Published: December 2006

Mineral and fluid inclusions were studied in seven gem corundums from gravels of three areas in Sri Lanka. All fluid inclusions are pure CO2. Microthermometry results on primary fluid inclusions suggest formation of corundum under granulite facies metamorphism (>630°C, 5.5 kbar). Secondary fluid inclusions indicate different retrograde events of post-metamorphic cooling and uplift for different source areas.
Deerite from Ile de Groix, Brittany, France
Authors: Dudek K. , Kienast J. R.
Published: December 2006

Deerite has been found in layers of Fe-rich metasediments, metamorphosed under conditions of blueschist to eclogite facies (T = ca. 480°C). Geochemical comparisons with other deerites described in the literature show that the Ile de Groix deerites most closely resemble the Mn-poor, alpine type, and Sifnos deerites. The P-T conditions of the Ile de Groix metamorphism do not conform with the stability field of deerite. In the assemblages examined here deerite seems to be a relic from earlier stages of prograde metamorphism.
Mn-silicate skarns from the Gåsborn area, West Bergslagen, central Sweden
Authors: Damman Arend H.
Published: December 2006

In the Gåsborn area, West Bergslagen, central Sweden, Mn-silicate-magnetite-jacobsite skarns were formed as the result of three successive processes. (1) Deposition of exhalative-sedimentary manganiferous iron-ore-bearing sediments together with cherts and volcanics. (2) Intrusion of a synvolcanic anorogenic granite and some slightly younger gabbros and tonalites: under influence of these intrusives the manganiferous iron-ore-bearing sediments were metamorphosed into (a) rhodonite(I)-magnetite-pyrophanite-garnet assemblages; (b) (manganiferous) hedenbergite(I)-allanite-titanite-garnet-magnetite assemblages; (c) tephroite-jacobsite-pyrophanite-garnet assemblages and (d) magnetite-bearing quartzites. (3) Release of hydrothermal fluids from the granite and subsequent alteration of the above assemblages into metasomatic infiltration skarns, consisting of rhodonite(II), garnet, hedenbergite(II), biotite, actinolite or edenite (with up to 20.11 wt.% MnO), chlorite, bementite, fluorite, helvite, rhodochrosite, hematite, rutile and accessory galena, sphalerite, wittichenite, aikinite, pyrrhotite, chalcopyrite and pyrite.

The maximum temperature (T) and pressure (P) during contact metamorphism are estimated at 550°C and 1.0 kbar respectively. The fluid under influence of which the metasomatic infiltration skarns were formed was relatively rich in Fe, Cl and F and carried little or no Mg and Mn.

During early diagenesis (beginning of stage 2) fo2 was between the hematite/magnetite (hm/mt) and the hausmannite + hematite = jacobsite buffers (h + m = j). During stage 2, with increasing T, fo2 changed from above to below hm/mt. Magnetite and jacobsite at some distance from the hydrothermal veins from which the metasomatic skarn-forming fluids were released, were altered during stage 3 into hematite. Magnetite in, and close to the hydrothermal veins was not altered to hematite, implying an increase in fo2 to above hm/mt with increasing distance from these veins.
The cyclic unit beneath the UG1 chromitite (UGIFW unit) at RPM Union Section Platinum Mine—Rosetta Stone of the Bushveld Upper Critical Zone?
Authors: Eales H. V. , de Klerk W. J. , Butcher A. R.
Published: December 2006

The UG1 Footwall unit is a layered pyroxenite-norite-leuconorite-anorthosite sequence between the Middle Group 4 and Upper Group 1 chromitites of the Upper Critical Zone, and is c. 300 m thick at Rustenburg Platinum Mines, Union Section, where it shows an oscillatory fluctuation in whole-rock Mg/(Mg + Fe), Cr/Co, Ni/V and Fe/Ti ratios with stratigraphic height. This permits subdivision into 8 sub-cycles which match a subdivision based on cyclical variations in orthopyroxene and feldspar compositions. Constituent pyroxene grains of pyroxenites, norites and leuconorites alike contain rounded and embayed plagioclase inclusions in abundance. Sr-isotope disequilibrium prevails in some samples between the orthopyroxene and feldspar populations. Chemical and isotopic data support a model of pulsatory injection of limited volumes of a more primitive, mafic liquid into a resident column of depleted residua, from which sodic labradorite and Mg-poor bronzite were crystallizing. The depleted liquid is equated with the supernatant liquid residuum of buried cumulates (Sric. 0.7054) and the primitive liquid with magma parental to the UG1-UG2 lineage (Sri ⩾ 0.7068). The increase in leucocratic character of the 300 m column, with height, is attributed to the rising of low-density liquids enriched in the components of feldspar during separation of the pyroxenites. Deposition of the UG1 chromitite layers is attributed to mixing of a major influx of primitive liquid with a feldspathic residuum at the top of the UG1 Footwall unit. There is no evidence to indicate the participation of a discrete A-type liquid (Irvine and Sharpe, 1982) in this process.
Indium-bearing chalcopyrite and sphalerite from the Gåsborn area, West Bergslagen, central Sweden
Authors: Kieft Kees , Damman Arend H.
Published: December 2006

In the Gåsborn area, West Bergslagen, central Sweden, Fe-rich, indium-bearing (0.1–2.0wt.% In) sphalerite is replaced by Fe-poor sphalerite containing minute inclusions of chalcopyrite, roquesite and an unnamed In-Zn-rich phase. Fe-rich, In-bearing sphalerite is primary; indium occurs as a roquesite molecule in solid solution. Fe-poor sphalerite, roquesite, chalcopyrite and the unnamed In-Zn-rich phase were formed from In-bearing sphalerite by secondary processes, characterized by the so-called ‘chalcopyrite disease’.
The origin of sapphires: U–Pb dating of zircon inclusions sheds new light
Authors: Coenraads Robert R. , Lin Sutherland F. , Kinny Peter D.
Published: December 2006

Uranium-lead isotope dating of two zircon inclusions in sapphires from the Central Province, NSW. gives ages of 35.9 ± 1.9 and 33.7 ± 2.1 million years (Ma). These ages fall within the range of basalt potassium-argon ages of 19 to 38Ma and zircon fission track ages of 2 to 49Ma for the timing of volcanism of the Central Province, NSW. These data, combined with the observation that corundum is found associated with many alkali basaltic provinces, indicate a genetic link between the growth of large corundum crystals and the processes involved in alkali basaltic magma generation. The reported failure of experimental attempts to grow corundum from a corundum-bearing basaltic composition, and more significantly, the abundance of incompatible elements such as U, Th, Zr, Nb and Ta in inclusion minerals indicate that the crystallization process is not simple. Corundum and the other minerals found as its inclusions (zircon, columbite, thorite, uranium pyrochlore, alkali feldspar etc.) could not have crystallized from most basaltic compositions. A more complex process must occur in which crystallization takes place when there are high proportions of incompatible elements and volatiles in the melt. These crystallization products are then carried to the surface by upward movement of later magmas. The extent of this process presumably determines whether a particular basaltic province carries sufficient corundum to be worked into economic concentrations of sapphire.
CO2 fluid inclusions in ultramafic xenoliths from the Iblean Plateau, Sicily, Italy
Authors: De Vivo B. , Lima A. , Scribano V.
Published: December 2006

The Iblean Plateau (Southeastern Sicily, Italy) consists of a thick Meso-Cenozoic carbonate sequence with interbedded volcanic horizons (alkaline and tholeiitic basalts). The alkaline basalts contain ultramafic (peridotites and pyroxenites) and mafic xenoliths. The peridotites are spinel-bearing lherzolites and lherzolitic harzburgites, with porphyroblastic to protogranular texture. Pyroxenites consist of Cr-diopside-bearing and Al-augite-bearing websterites. The mineral chemistry of the nodules indicates temperatures between 700 and 1050°C.

Fluid inclusions containing CO2 and (sometimes) various proportions of silicate glass have been studied in olivine, orthopyroxene and clinopyroxene. The secondary inclusions occur as trails of CO2-rich inclusions, often cross-cutting deformation lamellae. The few primary inclusions, generally empty, show clear evidence of decrepitation. Of the 390 inclusions examined, 97% homogenized to the liquid phase (Th → L = −43.9 to +30.9°C); 3% homogenized to the vapour phase (Th → V = + 20.5 to +30.3°C, yelding CO2 densities in the range 0.20–1.13 g/cm3. Assuming a trapping temperature of 1100°C, the corresponding trapping pressure for a pure CO2 system lies in the range 0.6–11.0 kbar, i.e. a depth of ∼2.2 to 42 km.

The majority of CO2 trapping events in the xenoliths occurred from 2.2 to 11.0 kbar, with no major trapping events at pressures less than 2.3 kbar, indicating the absence of a shallow magma reservoir below the Iblean Plateau.
Silicate melt inclusions from a mildly peralkaline granite in the Oslo paleorift, Norway
Authors: Hansteen T. H. , Lustenhouwer W. J.
Published: December 2006

The mildy peralkaline Eikeren-Skrim granite belongs to the Permian magmatic province of the Oslo rift, south-east Norway. Euhedral quartz crystals from the abundant miarolitic cavities contain primary inclusions of partly crytallized silicate melts and coexisting primary, aqueous fluid inclusions. Micro-thermometric measurements give maximum estimates for the granite solidus of 685–705°C. Quenched silicate melt inclusions are not peralkaline, have normative Or/Ab weight ratios of 1.15–1.44 (compared to 0.49–0.80 in whole-rock samples) and F and Cl contents of 0.1 and 0.21–0.65 wt. %, respectively. Coexisting magmatic fluid inclusions are highly enriched in Na, Cl, S and to some extent K. These chemical characteristics are the results of late-magmatic melt-mineral-fluid interaction in the miarolitic cavities.
Chronology and orientation of N2–CH4, CO2-H2O, and H2O-rich fluid-inclusion trails in intrametamorphic quartz veins from the Cuiabá gold district, Brazil
Authors: de Alvarenga C. J. S. , Cathelineau M. , Dubessy J.
Published: December 2006

The upper Proterozoic Cuiabá group of Mato Grosso, Brazil, is composed of low-grade clastic meta-sediments which have been folded by several successive tectonic events. Three generations of quartz veins are associated with the structural evolution of this area. The first veins are deformed by the main tectonic phases and show a complex deformational patterns. The second set is parallel to the cleavage and was formed syntectonically during the main folding phase, whilst the last quartz veins are related to a later stage of deformation. A systematic study of fluid inclusions in relation with a statistical study of microstructural markers (fluid inclusion trails, opened microcracks) was carried out on quartz veins from three localities. On the basis of microthermometric studies and Raman spectrometry analysis, four differents types of fluids have been distinguished, each trapped in specific fluid inclusion trails: (i) CO2-rich liquids and vapours (Lc, Vc) at Casa de Pedra, (ii) Lc and Vc inclusions with variable amounts of CO2, CH4, N2 in the vapour phase at BR-70, (iii) CH2-N2-rich vapours (Vn-m), and (iv) aqueous inclusions (L) with variable salinities representing the last fluid generations at all localities.

At Casa de Pedra and BR-70, most fluids are observed within the three generations of quartz veins, indicating an important fluid circulation associated with the last phase of brittle deformation. Fluid inclusions of type (iii) and (iv) are oriented along several well defined directions. The study shows the importance of integrated microstructural and fluid-inclusion studies for understanding the geometry and chronology of fluid circulation.
Multiphase methane-rich fluid inclusions in gold-bearing quartz as illustrated at Pontal (Goias, Brazil)
Authors: Guilhaumou N. , Santos M. , Touray J. C. , Beny C. , Dardenne M.
Published: December 2006

In the Pontal auriferous lode, dominant saccharoidal quartz is associated with oligoclase, biotite, hornblende, tremolite-actinolite, sulphides (less than 2%), and disseminated native gold. Four main types of fluid inclusion have been distinguished based on their habit, distribution and spatial relation-ship with gold particles. Type S are primary multiphase large sized (100 to 200 µm) inclusions with homogenization temperatures (V + L → L) between 350 and 450°C. They contain siderite and/or calcite and graphite-like microcrystals as daughter phases. Commonly associated with these inclusions are tiny (50 to 100 µm) solid inclusions of biotite or actinolite. In most of these inclusions, only CH4 has been detected in the vapour phase. However some noticeable exceptions were observed (CO2/CH4 ratio near 0.85). Type C inclusions are later than gold and occur disseminated in quartz or along trails that crosscut quartz grain boundaries. They may contain nahcolite daughter crystals. CO2/CH4 ratios range from 0.0 to 0.5. Homogenization temperatures vary from 150 to 300°C. Type V are mainly gaseous CH4-H2O inclusions. They may occur as small-sized inclusions directly associated with gold particles. Type L are aqueous two-phase inclusions of late secondary origin.

The scattering of the CO2/CH4 ratios could be related to fluctuations of the oxygen fugacity that triggered gold precipitation at the time of trapping. These variations of fO2 with time could reflect unbuffered fluid-rock interaction with respect to redox conditions during quartz deposition.

Finally, gold deposition is interpreted to have occurred at elevated temperature (500°C) and pressure, compatible with boundary conditions between greenschist and amphibolites facies.
Contrasting garnet parageneses in a composite Grenvillian granitoid pluton, Newfoundland
Authors: Victor Owen J. , Marr Robert A.
Published: December 2006

Almandine- and grossular-rich garnet occurs as both a coronitic and non-coronitic phase in ferruginous, Grenvillian (c. 1050 Ma) granitoid rocks of the composite Potato Hill pluton of the Long Range Inlier, Newfoundland. The country rock includes garnetiferous gneiss, but garnets in the pluton are compositionally distinct (higher Ca and Mn, lower Mg), so none are interpreted as xenocrysts from the Long Range gneiss complex.

Coronal garnet, quartz and hornblende separate primary pyroxene, ilmenite and hornblende from feldspar in two-pyroxene charnockite. Balanced mass-transfer reactions based on microprobe data and modes for the pyroxene-centred corona structures suggest that corona sites gained Fe and lost Na. The flux of Fe apparently controlled corona growth in the charnockite. The corona structures are attributed to subsolidus cooling of the pluton rather than to a metamorphic overprint because the coronas are obliterated in high strain zones cutting the charnockite. Temperature of formation is constrained at c. 775–630°C by two-pyroxene and garnet-hornblende thermometry. Compositionally-similar coronas in rare, Fe-rich enderbite of the Long Range gneiss complex probably formed during cooling after early, high-grade metamorphism or following the regional emplacement of the Grenvillian plutons.

Non-coronitic garnets occur in equigranular and megacrystic hornblende-biotite granite. Garnets in the equigranular granite are large, well-formed, and in some instances are associated with compositional layering of probable igneous origin. These garnets are enriched in grossular (XCa = 0.28), and are therefore interpreted as phenocrysts crystallized at high pressure (>9 kbar?). They would nevertheless have been stabilized to lower pressures by their moderate spessartine content (XMn = 0.13).

Garnets in foliated megacrystic granite form tiny crystals depleted in Fe and Mg, and enriched in Mn and Ca, and in these respects are similar to garnet in deformed charnockite. These garnets are therefore interpreted to have formed (or re-equilibrated) during the late Grenvillian deformation. Garnet is absent in relatively magnesian Grenvillian granites (bulk XFe2+ = 0.50–0.85) elsewhere in the inlier. The restriction of garnet to the Potato Hill pluton (bulk XFe2+ = 0.88–0.94) therefore testifies to bulk compositional controls on the formation of both magmatic and subsolidus garnet in this intrusion.
High chromium and vanadium in andalusite, phengite and retrogressive margarite in contact metamorphosed Ba-rich black slate from the Abercrombie Beds, New South Wales, Australia
Authors: Morand Vincent J.
Published: December 2006

Graphitic, quartz-rich black slate within the Late Ordovician Abercrombie Beds, Lachlan Fold Belt, southeast Australia, has undergone contact metamorphism adjacent to the Siluro-Devonian Wyangala Batholith. This produced porphyroblasts of andalusite and cordierite, and smaller grains of pale green phengitic mica. Later regional metamorphism caused complete retrogression of cordierite and partial retrogression of andalusite, with margarite replacing some andalusite.

The aluminous minerals andalusite, margarite and phengite all contain V and Cr substituting for Al. Andalusite has up to 1.39% V2O3and 1.09% Cr2O3, margarite has up to 1.07% V2O3and 0.37% Cr2O3, and phengitic mica has up to 6.93% V2O3and 1.52% Cr2O3. This mica also has BaO contents of up to 1.96%.

Chemical analyses reveal very high SiO2contents for these rocks (about 89%), carbon contents of about 2%, and extremely low CaO, FeO, MgO and Na2O. Although V and Cr are prominent in aluminous minerals, their concentrations in the rock are only about average for black shales. However, Ba values range from 2000 to 6000 p.p.m., well above average for black shales. It is suggested that V and Cr probably precipitated from sea water, but Ba may have been concentrated by planktonic organisms such as radiolaria.
Chemistry and phase petrology of amphiboles and orthoamphibole–cordierite rocks, Old Woman Mountains, SE California, USA
Authors: Stoddard Edward F. , Miller Calvin F.
Published: December 2006

Proterozoic amphibolites from Sweetwater Wash, in the Old Woman Mountains of southeastern California, contain a variety of mineral assemblages dominated by the low-Ca amphiboles anthophyllite, gedrite, and cummingtonite. Their Mg- and Al-rich, Ca-poor bulk compositions suggest that the amphibolites represent basalts that were altered prior to metamorphism. In addition to amphiboles, mineral assemblages include cordierite, biotite, garnet, Ca-rich plagioclase, and ilmenite ± rutile. Corundum, staurolite, and spinel occur locally in Al-rich enclaves associated with cordierite. Orthoamphiboles commonly exhibit complex microstructures, including twinning, intergrowths, and apparent exsolution; spot analyses show an unusually large range of chemical compositions, even within a single thin section, in several cases extending across the crest of the solvus in the orthoamphibole system. Ionic substitution within the orthoamphibole series was dominated by the Mg-tschermakitic and edenitic exchange reactions. The amphibolites are thought to have been subjected to metamorphic temperatures above the orthoamphibole solvus during both the Proterozoic and the Cretaceous. Cretaceous metamorphism was followed closely by rapid uplift and denudation, which may be responsible for the exsolution and range of compositions of the orthoamphiboles.
Carbonates of the magnesite–siderite series from four carbonatite complexes
Authors: Buckley H. A. , Woolley A. R.
Published: December 2006

Carbonates of the magnesite-siderite series have been found and analysed in carbonatites from the Lueshe, Newania, Kangankunde, and Chipman Lake complexes. This series has been represented until now only by a few X-ray identifications of magnesite and three published analyses of siderite and breunnerite (magnesian siderite). Most of the siderite identified in carbonatites in the past has proved to be ankerite, but the new data define the complete solid-solution series from magnesite to siderite. They occur together with dolomite and ankerite and in one rock with calcite. The magnesites, ferroan magnesites and some magnesian siderites may be metasomatic/hydrothermal in origin but magnesian siderite from Chipman Lake appears to have crystallized in the two-phase calcite + siderite field in the subsolidus CaCO3-MgCO3-FeCO3 system. Textural evidence in Newania carbonatites indicates that ferroan magnesite, which co-exists with ankerite, is a primary liquidus phase and it is proposed that the Newania carbonatite evolved directly from a Ca-poor, Mg-rich carbonatitic liquid generated by partial melting of phlogopite-carbonate peridotite in the mantle at pressures >32 kbar.
Dufrenite in iron-formation on the Kangnas farm, Aggeneys district, Bushmanland, South Africa
Authors: Van Der Westhuizen W. A. , de Bruiyn H. , Beukes G. J. , Strydom D.
Published: December 2006

An occurrence of yellowish green to green dufrenite in iron-formation from Proterozoic metamorphites on Kangnas farm near Aggeneys, Bushmanland, South Africa is described. The mineral formed by reaction between iron oxides and hydroxides and a phosphate, probably apatite. It was identified by its characteristic X-ray diffraction pattern, but microprobe analyses presented here indicate that the chemical compositions are extremely variable.
The Lundy granite: a geochemical and petrogenetic comparison with Hercynian and Tertiary granites
Authors: Stone Maurice
Published: December 2006

New chemical data show that the two main granite types (G1 and G2) cannot be discriminated, but that microgranite sheets/dykes (G3) are significantly different and more evolved, largely as a result of biotite, accessory mineral, and plagioclase fractionation. The Lundy granite is similar to other Tertiary granites of Scotland and Ireland, in age, setting, possible high-temperature mineralogy, relationship to basic magmatism, and REE patterns. These features and a highly evolved chemistry suggest derivation from an unexposed more ‘primitive’ granite that, in turn, had a basaltic parentage. However, similarities with the nearby S-type Hercynian granites, such as high aluminium saturation index (and normative corundum), high trace alkali, Nb, and F contents, low Zr, and high initial Sr ratio suggest a significant crustal component. The problem is resolved by proposing either mixing of silicic magma derived by strong fractionation of basaltic magma with anatectic magma from a pelitic/semi-pelitic crustal source, or fractionation of basaltic magma heavily contaminated by assimilated crustal material. Both origins would yield the high REE contents and fiat REE patterns of a ‘primitive’ granite magma. Fractionation, perhaps of hornblende initially, and later, of biotite and accessory minerals together with feldspars, would produce the small volume of highly fractionated Lundy granite.