bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractUranium-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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractIn 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

AbstractAlmandine- 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

AbstractGraphitic, 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

AbstractProterozoic 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

AbstractCarbonates 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

AbstractAn 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

AbstractNew 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.
Distribution of the ammonium ion in pegmatites, aplites and their minerals from central northern Portugal
Authors: Hall A. , Neiva A. M. R. 
Published: December 2006

AbstractThe ammonium content of pegmatites, aplites and granites from Alijó-Sanfins, northern Portugal, averages 162, 109 and 159 ppm respectively. There is no systematic difference in the NH4/K ratio between these rocks, and the variation in their ammonium content is mainly due to variations in the amount of potassium minerals they contain. The K-feldspars have higher NH4+ contents than the muscovites, but lower NH4/K ratios. The preference of NH4+ for micas rather than feldspars is not as great as that shown by rubidium. The ammonium content of pegmatites in general is highly variable, and is largely determined by the nature of the granites with which they are associated.
Precious and base metal selenide mineralization at Hope's Nose, Torquay, Devon
Authors: Stanley C. J. , Criddle A. J. , Lloyd D. 
Published: December 2006

AbstractPrecious and base metal selenide minerals have been identified in gold-bearing carbonate veins cutting Middle Devonian limestones of the Torquay Limestone Group at Hope's Nose, Torquay. The selenide assemblage consists of clausthalite (PbSe), tiemannite (HgSe), klockmannite (CuSe), umangite (Cu3Se2), tyrrellite (Cu,Co,Ni)3Se4, trustedtite (Ni3Se4), penroseite (NiSe2), naumannite (Ag2Se), eucairite (AgCuSe) and fischesserite (Ag3AuSe2), only clausthalite having previously been reported from Britain. They are associated with palladian gold, gold, hematite, and accessory pyrite and chalcopyrite in a gangue consisting predominantly of calcite; alteration products include cerussite, malachite, aragonite and goethite.The relative abundance of Au, Ag, Hg and Se is a characteristic feature in the uppermost parts of some precious metal ‘epithermal’ systems. The occurrence at Hope's Nose is related to both structural and lithological factors: a deep-seated NW-SE structural lineament, the Lundy-Sticklepath-Lustleigh-Torquay fault; local thrusting, and to an association of basic-intermediate igneous rocks with a sedimentary sequence including carbonaceous shales and limestones. The mineralization is considered to be post-Variscan, probably Permo-Triassic in age.
Optical absorption spectroscopy of doped materials: the P213-P212121 phase transition in K2(Cd0.98Co0.02)2(SO4)3
Authors: Percival M. J. L. 
Published: December 2006

AbstractThe use of optical absorption spectroscopy for the study of the changes in local distortions during phase transformations is discussed, with particular reference to the P213-P212121 transition in K2Co2(SO4)3 langbeinite. In order to extend this technique to the study of cobalt-doped cadmium langbeinite, K2Cd2(SO4)3, the consequences of the doping with regard to site occupancies and low signal strength are discussed, and some details of data modelling are considered. The problem of modelling the spectrum of Finero sapphirine is taken as an example, and it is shown that even simple and evidently inadequate models can provide useful information.The results of optical spectroscopic investigation of the P213-P212121 transition in K2(Cd0.98Co0.02)2(SO4)3 langbeinite are presented. The trigonal splitting of the spin allowed 4T1g(F)-4T1g(P) transition has been determined, and shows a linear increase with increasing temperature in the high temperature cubic phase, and a constant value in the low temperature phase. This is in good agreement with previous structural work on this material, and it is concluded that optical spectroscopy of doped materials can provide useful information about site distortions.
Overcoming the problems of high-resolution transmission electron microscopy of biogenic aragonite
Authors: Ness S. E. , Haywick D. W. , Cuff C. 
Published: December 2006

AbstractHigh-resolution transmission electron microscopy of biogenic carbonate minerals is hampered by a lack of stability during exposure to the electron beam. However, aragonite in bivalve shells may be successfully imaged using a modification of the ‘minimal-exposure technique’ of Williams and Fisher (1970). Diffraction patterns taken before and after beam exposure indicate that the aragonite remained stable during imaging. The procedure described here should prove useful for further studies of the ultrastructure and/or the diagenesis of biogenic carbonate minerals.
Damaraite, a new lead oxychloride mineral from the Kombat mine, Namibia (South West Africa)
Authors: Criddle A. J. , Keller P. , Stanley C. J. , Innes J. 
Published: December 2006

AbstractDamaraite, ideally 3PbO.PbCl2, is a new mineral which occurs with jacobsite, hausmannite, hematophanite, native copper, an unnamed Pb-Mo oxychloride, calcite, and baryte, in specimens from the Asis West section of the Kombat mine, Namibia (South West Africa). Damaraite is colourless and transparent with a white streak, and adamantine lustre. It is brittle with an irregular to subconchoidal fracture and a cleavage on (010). The mineral has a low reflectance, a weak bireflectance, barely discernible reflectance pleochroism, from grey to slightly bluish grey in some sections, and is weakly anisotropic. Reflectance data in air and in oil are tabulated. Colour values relative to the CIE illuminant C for the most strongly bireflectant grain are, for R1 and R2 respectively:It has a VHN50 of 148 (range 145–154) with a calculated Mohs hardness of 3. X-ray powder diffraction studies give the following parameters refined from the powder data: orthorhombic; space group Pma2, Pmam or P21am; a 15.104(1), b 6.891(1), c 5.806 (1)Å; V is 604.3 (4)Å3 and Z = 3. Dcalc 7.84 g/cm3. The strongest six lines of the powder pattern are [d in Å (I) (hkl)]: 2.902 (10) (121,002); 2.766 (10) (510,221); 2.877 (9) (411); 3.164 (6) (401); 3.135 (6) (220); 1.747 (b) (313,721,531). The name is for the Damara sequence which hosts the Kombat deposit.