bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cryptic variations of minor elements Al, Cr, Ti and Mn in Lower and Critical Zone orthopyroxenes of the Western Bushveld Complex
Authors: Eales H. V. , Teigler B. , Maier W. D. 
Published: December 2006

AbstractCompositional variations with respect to minor elements A1, Cr, Ti and Mn, and major elements Fe and Mg, in orthopyroxenes along ca. 160 km of strike of the Lower (LZ), Lower Critical (LCZ) and Upper Critical (UCZ) Zones are reviewed on the basis of 1900 analyses by electron microprobe. AI increases with stratigraphic height and declining Mg/(Mg + Fe2) ratios (hereafter MMF ratios) through the LZ and LCZ, reaching peak values close to the base of the UCZ, where the first cumulus plagioclase appears in the succession. Above this, Al contents decline as MMF ratios decline. Through the same interval, subdued increase in Ti occurs through >1000 m of ultramafic cumulates, but this increase accelerates within the ca. 450 m UCZ sequence. Mn increases linearly with declining MMF ratios through the entire succession, Cr levels are highest in orthopyroxenes of the ultramafic LZ and LCZ, and olivine norites of the UCZ, but decline in more evolved norites and associated anorthosites of the UCZ.This pattern of cryptic variations, displayed by a thick succession of cumulates, is consistent with the model of Bence and Papike (1972) and Grove and Bence (1977) for basaltic rocks, which links the levels of minor elements in pyroxenes with entry of plagioclase into the paragenesis.
Gatehouseite, a new manganese hydroxy phosphate from Iron Monarch, South Australia
Authors: Pring A. , Birch W. D. 
Published: December 2006

AbstractGatehouseite is a new manganese hydroxy phosphate from Iron Monarch, South Australia. The new mineral occurs as radiating clusters of pale yellow, and yellow to pale brownish orange bladed crystals up to 100 ~tm in length. The crystals are elongated along [010] and the principal forms are {102}, {110} and {001}. Gatehouseite also occurs as overgrowths on prismatic arsenoclasite crystals. Associated with gatehouseite are baryte, shigaite, manganoan ferroan calcite, hausmannite and hematite. Gatehouseite appears to have formed at low temperature by the interaction of phosphorus-rich fluids on hausmannite in carbonate-rich fractures in the hematite ore. Electron microprobe analysis yielded: MnO 64.42, FeO 0.19, CuO 0.03, ZnO 0.03, PbO 0.05, Al2O3 0.10, P2O5 22.18, V2O5 0.38, As2O5 3.58, H2O (6.44%). These data gave an empirical formula of Mn5.09Fe0.01Al0.01(P1.75As0.17-V0.02)∑1.94O8(OH)4.00, calculated on the basis of 12 oxygen atoms. The simplified formula is Mn5(PO4)2(OH)4. The mineral is transparent with a pale yellow streak, an adamantine lustre and an estimated Mohs hardness of 4. The crystals exhibit a distinct cleavage on {010} and have a splintery fracture. The strongest lines in the X-ray powder pattern are (dobs, Iobs, hkl) 4.48 (10) (004); 4.03 (10) (104); 2.900 (100) (11.5); 2.853 (70) (106); 2.801 (50) (021); 2.702 (80) (303); 2.022 (15) (322); 1.608(15) (330). These data were indexed on an orthorhombic cell, with a = 9.097(2), b = 5.693(2), c = 18.002(10) Å and a volume of 932.4(8) Å3; the space group is probably P212121. For Z = 4 and using the empirical formula, the calculated density is 3.74 g/cm3. Optical properties could not be determined in full; two refractive indices are 1.74(1) and 1.76(1) (white light); pleochroism is distinct from brown to near colourless. The crystals are length slow with parallel extinction. The name is for Dr. Bryan Michael Kenneth Cummings Gatehouse (1932-), crystal chemist of Monash University, Melbourne, Australia.
Sulphidation in the Witwatersrand Goldfields: evidence from the Middelvlei Reef
Authors: Myers Russell E. , Zhou Taihe , Neil Phillips G. 
Published: December 2006

AbstractThere is extensive textural evidence for sulphidation in the Middelvlei Reef of the Carletonville Goldfield, South Africa. Secondary iron sulphides have replaced sand- and pebble-sized elasts in conglomerate, as well as matrix material in both conglomerate and quartzite. Within the Middelvlei Reef there is a close correspondence between the intensity of sulphidation and areas of greater modal muscovite, and there is less sulphidation where chloritoid dominates. Both pyrite and minor pyrrhotite are widespread. The timing of the sulphidation appears to be post-depositional but the relative importance of diagenetic and syn-metamorphic processes cannot be determined using textural criteria. The absence of retrograde effects suggests that sulphidation occurred prior to or during peak metamorphism. The distribution and intensity of sulphidation and phyllosilicate alteration indicate that these processes may be more significant in the Witwatersrand than has generally been thought. These processes should be considered in all future genetic models.
Nature and evolution of metamorphic fluids associated with turbidite-hosted gold deposits: Hill End goldfield, NSW, Australia
Authors: Seccombe P. K. , Ju J. , Andrew A. S. , Gulson B. L. , Mizon K. J. 
Published: December 2006

AbstractThe Hill goldfield, NSW, Australia, is an example of a syntectonic, slate-belt gold deposit formed in a multiply deformed, Late Silurian slate-metagreywacke turbidite sequence. Gold is confined to bedding-parallel veins and discordant leader veins composed of as many as four generations of quartz, accompanied by phyllosilicates, carbonates and minor sulphides. Vein formation and gold deposition was apparently synchronous with Early Carboniferous metamorphism and deformation. Homogenisation temperatures (Th) for fluid inclusions in vein quartz demonstrate five groupings in the temperature intervals 350-280°C 280-250°C 250-190°C 190-150°C and 150-110°C corresponding to a variety of primary and secondary inclusions developed during four periods of vein quartz deposition under a generally declining temperature regime. Inclusion fluids are characterised by a low salinity of around 0.1 to 3.6 wt. % NaCl equivalent. The dominant gas phase present in the inclusion fluids varies from N2 in the early stages of the paragenesis, through CH 4 during the main episode of gold deposition, to CO2- rich fluids associated with late-stage mineralisation. δ18O values for vein quartz (range 15.1-17.1‰) and vein carbonate (range 11.3-13.4‰) are typical of metamorphic mineralisation. δD composition of hydrous minerals and inclusion fluids (range −53 to −138‰) suggest an influx of meteoric water in the later mineralising fluids. This conclusion is supported by δ13C data for vein calcite (range −2.5 to −9.7%0). δ34S composition of vein pyrrhotite and pyrite ranges from 6.9 to 7.8‰ early in the paragenesis, to lighter values (around 4.2 to 5.8%0) accompanying late gold deposition from more oxidising fluids. Sulphur isotope data imply a sulphur source from underlying turbidites and an increase in fluid oxidation state during mineralisation . Lead isotope measurements on vein pyrite, arseno py rite, galena and gold are characterised by two isotope populations with 207Pb/206Pb ratios of 0.862 and 0.860, which define two discrete mineralising events during vein formation. Consistency between data from vein minerals and lead isotope signatures for potential source rocks indicate that lead was derived from the sedimentary pile.
Calcite and carbocernaite exsolution and cotectic textures in a Sr,REE-rich carbonatite dyke from Rajasthan, India
Authors: Wall F. , Le Bas M. J. , Srivastava R. K. 
Published: December 2006

AbstractA carbonatite dyke from the Sarnu-Dandali alkaline complex, Rajasthan, India, contains a remarkable suite of rare earth, strontium-rich minerals with spectacular primary textures.Sr, Mn-rich calcite in the outer 5 mm of the dyke contains exsolved lamellae of carbocernaite, (Ca,Na)(Sr,Ce,Ba)(CO3)2, orientated parallel to its twin and cleavage planes. The amount of exsolved carbocernaite increases away from the dyke margin as the Sr content of the calcite increases to a maximum 13 wt.%. Sr levels as high as this in calcite have previously been recorded only in experimental work. The carbocernaite exsolution suggests that Sr-rich calcium carbonate can be a host for major amounts ofREEin carbonatite magma.Separated by a sharp internal boundary, is a complex possibly cotectic intergrowth of carbocernaite and Sr-rich calcite with late Ca-rich strontianite (19 wt.% CaO). Other minerals in the dyke include baryte, pyrrhotite, alabandite, sphalerite and occasional bastnäsite-(La) and thorite. Bands of late britholite-(Ce) traverse the dyke.The host rock for the dyke is fenitized melanephelinite which is itself traversed by narrow, <1 mm, carbonatite veins beleived to predate the carbonatite dyke. Allanite, britholite-(Ce) and rare monazite-(Ce), developed at the boundary between the carbonatite dyke and the fenite, may have been produced by a reaction between the dyke and the wall rock, or may be related to the later britholite mineralisation.The textures and mineral compositions indicate primary crystallisation. They are unique amongst rare earth-rich carbonatites which are usually late-stage phenomena with signs of secondary alteration.Comparison with experimental data available for the calcite-strontianite system suggests conditions of 500°C and 2 kbar for coexisting Sr-rich calcite and Ca-rich strontianite. A smaller scale intergrowth of calcite containing only 2.9 wt.% SrO and coexisting Ca-strontianite may correspond to a further unmixing at 350°C and 2 kbar. Since no experimental data are available for a calcite-carbocernaitestrontianite system, mineral chemistries and the interpreted sequence of crystallisation have been used to construct a hypothetical phase diagram.
Rare earth element patterns of carbonado and yakutite: evidence for their crustal origin
Authors: Shibata Ken , Kamioka Hikari , Kaminsky Felix V. , Koptil Vassili I. , Svisero Darcy P. 
Published: December 2006

AbstractCarbonado and yakutite are both porous aggregates of polycrystalline micrometre-size diamond, with very different characters from those of monocrystalline diamond. The genesis of carbonado is very controversial, whereas yakutite is thought to have been formed by meteorite impact. Neutron activation analyses of trace elements in carbonado and yakutite indicate that their rare earth element (REE) abundance patterns have common characteristics: heavy REEs are not much depleted and a negative Eu anomaly is observed. These patterns are quite different from those of kimberlite and monocrystalline diamond and are similar to those of crustal materials such as shale, supporting the hypothesis of a crustal origin for carbonado and yakutite.
Five-fold symmetry in chrysotile asbestos revealed by transmission electron microscopy
Authors: Cressey Barbara A. , Whittaker Eric J. W. 
Published: December 2006

AbstractThe structure of chrysotile, an important asbestos mineral, consists of layers curled concentrically or spirally into tubes. Published transmission electron microscope (TEM) images suggest that successive layers are generally stacked out of register with one another. However, a lattice model can be constructed in such a way that each layer can be stacked in register with the next, five times around the circumference, so that the structure exhibits a global 5-fold symmetry. We report here TEM observations confirming that chrysotile asbestos can form crystals with this structure, the first observation of five-fold symmetry in a natural crystalline material.
Ferroelastic phase transition in SrAl2Si2O8 feldspar at elevated pressure
Authors: McGuinn M. D. , Redfern S. A. T. 
Published: December 2006

AbstractSynthetic end-member strontium feldspar (SrAl2Si2O8) has been studied in a diamond-anvil cell at elevated pressures up to 10.3 GPa using energy-dispersive X-ray powder diffraction. Cell parameters have been refined between ambient pressure and 6 GPa. SrAl2Si2O8 undergoes a ferroelastic phase transition from the ambient pressure monoclinic space group I2/c to the high-pressure triclinic space group I at 3.2 ± 0.4 GPa. The transition appears to be first-order and the ferroelastic and co-elastic components of the spontaneous strain tensor have been calculated.
Transitional granulite-eclogite facies metamorphism of basic supracrustal rocks in a shear zone complex in the Precambrian shield of south India
Authors: Mukhopadhyay Biswajit , Bose Mihir K. 
Published: December 2006

AbstractThe phase petrology of two bodies of basic granulites occurring in association with supracrustal sequences within a dextral oblique-slip shear complex in the high-grade terrain of south India, have been studied. Some metabasites are characterized by garnet + clinopyroxene assemblages such as Grt + Cpx + PI ± Hbl ± Opx ± Qtz + Fe-Ti oxide(s) which are high-pressure granulites (garnet-clinopyroxene subfacies) transitional between the intermediate-pressure granulites (orthopyroxene-plagioclase subfacies) and eclogite. Mineralogical characteristics suggest that metamorphic conditions did not reach the eclogite facies but certainly approached that level. Close spatial association of the garnetiferous varieties with garnet-free assemblages (Opx + Hbl + Pl ± Cpx) and intimate juxtaposition of anhydrous and hydrous assemblages indicate a complex interplay of variable μH2O and bulk composition, especially αSiO2. Due to variable and low closure temperature of Fe-Mg exchange reactions between coexisting pyroxene and garnet, reliable estimation of peak temperatures during this near eclogite-facies metamorphism is problematic. A combination of a garnet-clinopyroxene barometer and various temperature estimates suggestsP-Tconditions of 875 ± 25°C and 8 ± 1 kbar for the Mettuppalaiyam samples and 900 ± 50°C and 14 ± 2 kbar for the Kanjamalai samples. Bulk rock chemical differences in terms of SiO2-content can account for the development of similar mineral assemblages along a near adiabatic metamorphic gradient between these two localities. These assemblages represent some of the highest grade granulite facies rocks in south India. The high-pressure granulites are notin situsamples of ancient lower continental crust, but low-pressure protoliths buried at depth. Textural features suggest that the high-pressure garnet-clinopyroxene subfacies rocks evolved from an amphibolitic assemblage by formation of garnet at the expense of hornblende and plagioclase and this high-pressure assemblage underwent an isothermal decompression indicating a clockwiseP-T-tpath resulting from crustal thickening and exhumation. A later isobaric cooling, possibly accompanying shearing and high H2O influx (aH2O≈0.78) gave rise to the coexisting orthopyroxeneplagioclase subfacies rocks (intermediate pressure granulites).
Mineralogic reaction zones at a calc-silicate/metapelite interface: an example of trace element mobility in a metamorphic environment
Authors: Owen J. V. , Dostal J. , Church B. N. 
Published: December 2006

AbstractMetasomatic interaction on a cm scale between calc-silicate pods and the enclosing sillimanite + biotite + tourmaline gneiss at Partridge Breast Lake, northern Manitoba, Canada, led to the development of an inner (by calc-silicate rock), hornblende-rich reaction zone and an outer, biotite-rich zone. The boundary between the reaction zones is interpreted as the original calc-silicate/metapelite interface. Compared with its metapelitic protolith, the biotite zone shows a two- to twenty-fold depletion in the concentrations of incompatible trace elements (notably the light rare earths, U, Th, Nb, Ta, Zr and Hf). In contrast, the relative concentrations of trace elements remained nearly constant during the mineralogical transformation of the calc-silicate rock to the hornblende zone. The depletion of trace elements in the biotite zone is attributed to the dissolution of accessory phases (e.g. monazite). Although stable at the metamorphic conditions (∼600–650°C at ∼ 4.5 kbar) prevalent during metasomatism, Mg-rich tourmaline is absent in the biotite zone, suggesting that either the pH or composition (e.g. the (Al + Si)/(Ca + Mg + Fe) ratio) of the aqueous fluid phase was inappropriate for the preservation of this mineral.
A cobalt-rich spinel inclusion in a sapphire from Bo Ploi, Thailand
Authors: Guo Jingfeng , Griffin W. L. , O'Reilly S. Y. 
Published: December 2006

AbstractCobalt-rich spinel is found as a ∼200 µm inclusion, together with a glassy phase, in a gem-quality blue sapphire from Bo Ploi, Thailand. This is the first reported natural occurrence of such a spinel. Its composition is directly analogous with that of cochromite, a previously reported rare cobalt-rich chromite. The compositional ranges for the cobalt-rich spinel, obtained using electron microprobe and proton microprobe (methods described below), are Al2O3 48.18–61.27 %, CoO 19.7–22.84 %, Cr2O3 0–12.28 %, FeO 8.64–9.67 %, MgO 6.04–6.89, TiO2 0.49–0.73 %, Ni 2251–2532 p.p.m., Zn 335–371 p.p.m., Mn < 177–849 p.p.m., Ga 113–153 p.p.m., Nb 24–1252 p.p.m., Zr <4–167 p.p.m., Sn 22–428 p.p.m., As <4–56 p.p.m., Sr <4–59 p.p.m., Ag 13–64 p.p.m. Transition elements decrease in abundance from core to rim of the spinel while the other elements increase. Crystal chemical considerations suggest that a vacancy-creating substitution mechanism may be operative in the cobalt-rich spinel despite the small scale, i.e. 3Co2+ = 2Al3+ + [4]□. The glassy phase coexisting with the spinel is likely to be the product of heating by the host basaltic magma. The mode of occurrence of the cobalt-rich spinel prevents further physical investigation. This unusual spinel is considered to be the result of a complex magma mixing process in the lower crust.
Mg-Al yttrian zirconolite in a partially melted sapphirine granulite, Vestfold Hills, East Antarctica
Authors: Harley Simon L. 
Published: December 2006

AbstractA new compositional variety of zirconolite characterized by high Mg, Al, Y2O3 and REE, and low Fe is described from a sapphirine granulite xenolith entrained in an intrusive norite body which was emplaced into the late Archaean (2520–2480 Ma) Vestfold Hills high-grade terrain during the early Proterozoic. The zirconolite, and similarly Mg-Al rich perrierite-(Ce), formed as a result of sanidinite facies partial melting of the particularly magnesian and aluminous sapphirine granulite xenolith during its incorporation into the c. 1170°C basic magma at c. 2240 Ma. The high REE compared to Al cations require that a previously unrecognized coupled substitution:occurs in this zirconolite. Full chemical analyses are presented for zirconolite and perrierite from this unique occurrence.
Staringite discredited
Authors: Groat Lee A. , Putnis Andrew , Kissin Stephen A. , Scott Ercit T. , Hawthorne Frank C. , Gaines Richard V. 
Published: December 2006

AbstractDetailed examination of ‘staringite’ by X-ray precession photography and high-resolution transmission electron microscopy shows it to consist of a sub-microscopic intergrowth of cassiterite and tapiolite. ‘Staringite’ is discredited as a valid mineral species.
Hyalotekite from reedmergnerite-bearing peralkaline pegmatite, Dara-i-Pioz, Tajikistan and from Mn skarn, Långban, Värmland, Sweden: a new look at an old mineral
Authors: Grew Edward S. , Yates Martin G. , Belakovskiy Dimitriy I. , Rouse Roland C. , Su Shu-Chun , Marquez Nicholas 
Published: December 2006

AbstractIn specimens of Mn skarn from the type locality of Långban, hyalotekite, (Ba,Pb,K)4Ca2−(Si,B,Be)12O28F, occurs in a matrix consisting mostly of aegirine (⩽22 mol.% CaMnSi2O6), andradite (⩽27 mol.% Mn3Fe2Si3O12), hematite, pectolite, quartz, calcite, baryte, barylite, and hedyphane. Melanotekite, plumbian taramellite, ferrian K-feldspar (to 6.5 wt.% Fe2O3), rhodonite, a talc-like mineral, apophyllite, and several Pb-As-Sb-O minerals are found in trace amounts. In a single specimen of reedmergnerite-microcline pegmatite from Dara-i-Pioz, hyalotekite occurs in close association with microcline. Other accessory minerals are albite, aegirine, pyrochlore, eudialyte, and polylithionite. The optical constants for hyalotekite from Långban and Dara-i-Pioz are, respectively, α = 1.656, 1.646, β = 1.659–1.660, 1.649, γ = 1.670–1.671, 1.659 (all ± 0.002), 2Vγ (mcas) = 57.2–60.5 ± 0.5°, 57.0 ± 1.1°(λ = 589 nm). Cell parameters of the Dara-i-Pioz hyalotekite for a body-centred triclinic cell are: a = 11.284(2), b = 10.930(1), c = 10.272(8) Å, α = 90.35(2)°, β = 90.11(3)°, γ = 89.98(1)°. Electron and ion microprobe data show that Långban hyalotekite is heterogeneous even within a given sample; the most important substitutions are Pb = Ba, K and coupled B = Si and B = Be. Minor constituents include Mn in the Långban hyalotekite and Na in the Dara-i-Pioz hyalotekite, which also differs in its significantly higher Ba/Pb ratio. Conditions suggested for hyalotekite formation at Långban and Dara-i-Pioz are P ⩽ 4 kbar, T ⩾ 500°C, silica saturation, peralkalinity, and relatively high oxygen fugacities and low sulphur fugacities. These temperatures must have been sufficiently high to allow for miscibility of Pb with Ba (and K) despite the lone pair of electrons of Pb2+.
Mineralogy of the near-surface expression of Au-As-Cu mineralization in an arid environment
Authors: Bogoch R. , Shirav M. , Gilat A. , Halicz L. 
Published: December 2006

AbstractIn the arid, Late Precambrian terrain of southern Israel, a complex suite of minerals and amorphous species were deposited in host gneiss from fluids under near-neutral conditions within 1 m of the surface. The morphology of secondary gold appears to relate to its host mineral (skeletal-dendritic with quartz; multi-faceted crystals with arsenates; spherical droplets with iron oxide). The gold is very fine-grained, and was most likely complexed as a thiosulphate.Three amorphous phases are present (iron oxide, chrysocolla, Cu-Mn-(Fe-As) silicate). At least in part, gold and baryte appear to have crystallized out of a metal-Fe-oxide gel. Other minerals, including apatite, anglesite, and conichalcite, may have grown from appropriate crystallites present in the gel.The conichalcite occurs mainly as bladed to acicular radial spherulites. In the presence of lead, a solid solution phase between duftite and conichalcite (‘Pb-conichalcite’) was formed.
Picritic basalts from the Palaeocene lava field of west-central Skye, Scotland: evidence for parental magma compositions
Authors: Bell Brian R. , Williamson Ian T. 
Published: December 2006

AbstractMineral chemistry and whole-rock compositional data are reported for two lavas of picritic basalt from the Palaeocene lava field of west-central Skye, Scotland. Whole-rock compositions for both flows plot on Thompson's (1982) 9 kbar cotectic for olivine + plagioclase + clinopyroxene + liquid. Both flows contain highly forsteritic olivine phenocrysts (c. Fo89), which enclose early-precipitated crystals of chrome-spinel (Al2O3: c. 25 wt.%; Cr2O3: c. 36 wt.%; FeO + Fe2O3: c. 20 wt.%; MgO: c. 15 wt.%). The olivine compositions indicate equilibrium with picritic basalt magma compositions, as represented by the whole-rock compositions of both lavas. A high-pressure origin for the chrome-spinels is suspected on the basis of their textural association and aluminous composition. Compositional comparisons between the whole-rock and mineral chemistry characteristics of both flows and a picritic basalt chill facies of the temporally- and spatially-associated Rum Igneous Complex suggests that similar parental magmas were involved.