bluuebunny/crossref_metadata_2025 huggingface dataset:
Replacement phenomena in tantalum minerals from rare-metal pegmatites in South Africa and Namibia
Authors: Baldwin Joy R.
Published: December 2006

Manganotantalite replacement by (1) microlite and (2) ferrotantalite, and changes in composition of uranoan microlite from rare-metal pegmatites in South Africa and Namibia have been investigated with the electron microprobe. A uranmicrolite from Karibib, Namibia contained 14.35% UO2, 1.03% PbO, 56.12% Ta2O5, 13.18% Nb2O5, 0.58% Fe2O3, 6.87% CaO, 0.54% SrO, 0.59% MnO, 0.86% Na2O and 0.47% F. Analyses along traverses across a 1.3 mm uranoan microlite, Tantalite Valley, Namibia, revealed two essentially distinct compositions: a more hydrated rim area of 200 µm radius containing 7% higher Ta2O5, 10% lower CaO and 1.3% lower F than a main central area of slightly variable composition. Back-scattered electron images reveal zoning and distinctive subspheroidal structures. New data and structural features are given for radioactive uranoan microlite from Namaqualand, South Africa. These crystals contain remnants of a bismuth phase and are in various stages of replacement. In the microlites replacing manganotantalite, the microlite reflects the composition of the replaced mineral. At Rubicon Mine, Karibib, a narrow marginal zone of mangantantalite is replaced by ferrotantalite along cleavages; a zone of intermediate composition is apparent. Detailed traverses have been completed across all of these crystals.
EXAFS and XANES spectroscopy study of the oxidation and deprotonation of biotite
Authors: Güttler Bernd , Niemann Wilhelm , Redfern Simon A. T.
Published: December 2006

The coupled thermal oxidation and deprotonation in air of iron-rich biotite (FeO + Fe2O3= 34%) has been investigated by EXAFS and XANES spectroscopy at the Fe-Kedge and by XANES spectroscopy at the Ti-Kedge. Samples annealed for 5 h at temperatures between 250° to 600°C have been studied. Distortions mainly of the Fe-Fe correlation within the octahedral layers are reflected in increasing Debye-Waller factors of the Fe-Fe correlation peak proportional to the annealing temperature. Unchanged Fe-O nearest-neighbour and Fe-Fe next-nearest-neighbour coordination numbers show that these distortions, nonetheless, do not change the structural topology of the octahedral layers. A model is introduced to demonstrate that increasing distortions are compatible with the expected heterogenous deprotonation mechanism in biotite. Titanium occurs in octahedral coordination. It was found to be unaffected by the coupled oxidation/deprotonation process. Both the coordination number and the valence state stay constant during the annealing process, in spite of dramatic changes of the Fe2+/Fe3+ratio. Thermally activated hopping conduction involving Ti according to Fe2+Ti4+→ Fe3+Ti3+is, therefore, not a significant process during thermal deprotonation and oxidation in biotite.
The crystal structure of manganoan kilchoanite, Ca2.33Mn0.67Si2O7: a site-preference rule for the substitution of Mn for Ca
Authors: Kimata Mitsuyoshi
Published: December 2006

The crystal structure of a Mn-bearing kilchoanite, Ca2.33Mn0.67Si2O7, orthorhombic,I2cm, a= 11.356(2),b= 5.007(1),c= 21.817(1)Å, Z = 8, was refined using single-crystal X-ray data to anRvalue of 3.1% for 1725 unique reflections. It is isostructural with kilchoanite, Ca3Si2O7, and shows a partial disorder of Mn and Ca over the four octahedral sites. On a basis of occupancy refinement, theM3 site (〈M3-O〉 = 2.307 Å) contains 0.508Ca and 0.492Mn, and theM4 site (〈M4-O〉 = 2.346 Å) contains 0.822Ca and 0.178Mn, whereas theM1 andM2 sites (〈M1-O〉 = 2.538 Å, (〈M2-O〉 = 2.380 Å) are occupied only by Ca. Substitution of Mn cations for Ca can be interpreted as taking place on the following sites in preferential order: (1) the smaller Ca site; (2) the less distorted Ca site; (3) the Ca site showing a loss in neutrality of formal electrostatic valence. A statistical survey of Si-O-Si angles observed in silicates containing [Si2O7] groups confirms that these angles become smaller with an increase in the coordination number of the bridging oxygen. Oversaturation of electrostatic bond-strength to the bridging oxygen in some groups of the crystal structures with two tetrahedra sharing a vertex (pyro-anion,), which is caused by increase in the coordination number of the bridging oxygen and/or byTcations with larger charge than 4+, results in longerT-Obrbonds length and in smallerT-Obr-Tangles.
S-type granite formation in the Dalradian rocks of Connemara, W. Ireland
Authors: Ahmed-Said Y. , Leake B. E.
Published: December 2006

The vicinity of the 490 Ma Cashel gabbroic intrusion experienced pressures of about 4.05 ± 0.2 kbar and temperatures in excess of 850 °C. These conditions caused intense hornfelsing and partial melting of the surrounding Dalradian metasediments. From the study of the progressively changed composition of the aureole hornfelses it is deduced that elements were fractionated into the melts as follows: Si>K>Na>Ca>Mn>Al>Fe>Mg and Rb>Ba>Sr>Ga>Cr,Ni,Co. This order of fractionation, which is the opposite to that in magmatic crystallization, provides a detailed picture of the mode of interaction between a mantle derived basic magma and mid-crustal rocks, illustrating how one type of S-type granite can be produced. The rare earth elements (REE) were both removed and fractionated but Eu largely remained in the crystal fractions giving increasing positive Eu anomalies with rising partial melting and these trends can be explained by the extraction of a granitic melt from the hornfelses. Fission track mapping of U is used to study the behaviour of U within the aureole and the metamorphic recrystallization of detrital brown zircon to pink new zircon. The S-type Cashel microgranite sill is shown to have been derived by anatexis from the Dalradian rocks, to have preserved the Sr isotope ratios of the metasediments at 490 Ma, and not to be of the same composition as the leucosomes in the metasediments.
Mineralogical evolution of fayalite-bearing rapakivi granites from the Prins Christians Sund pluton, South Greenland
Authors: T. N. Harrison  , I. Parsons  , Brown P. E.
Published: December 2006

The Prins Christians Sund rapakivi granite pluton in South Greenland is a member of the early Proterozoic ‘Rapakivi Suite’ and is emplaced into early Proterozoic Ketilidian migmatites. The pluton is composed predominantly of black or dark brown monzonites and quartz monzonites (collectively, rapakivi granites), although a localised white facies is developed adjacent to metasedimentary xenoliths. The back rapakivi granites are extremely fresh and have an anhydrous primary mafic mineralogy of olivine and orthopyroxene, with rare inverted pigeonite and clinopyroxene; minor amounts of biotite and amphibole occur in most fayalite-bearing rapakivi granites. Feldspars in these rocks are black and non-turbid. The white rapakivi granites have a wholly hydrous mafic silicate assemblage and turbid, white or cream-coloured feldspars. Electron microprobe analyses of the mafic silicates in the black rapakivi granites show that they are Fe-rich, comprising fayalite (Fa93−96.5), orthopyroxene (Fs77−81), ferro-pargasitic and ferro-edenitic hornblende (Fe/(Fe + Mg) = 0.72−0.93), and biotite (Fe/(Fe + Mg) = 0.77−0.88). Both biotite and amphibole crystallised subsolidus, and often adopt symplectic morphologies. Biotite has formed in response to a fayalite-consuming reaction at temperatures below 650–700°C and fO2, of 10−16.5 to 10−17.5 bars, and continued to grow under reducing conditions below the QFM buffer to temperatures below 450–500°C. Orthopyroxene formed in response to a low-pressure fayalite-consuming reaction in the melt. The correlation of black, pristine feldspar with anhydrous mafic silicates, and of turbid feldspar with hydrous phases suggests either that the feldspars reflect the anhydrous nature of the parent magma, or more likely that the mafic mineralogy of the white rapakivi granites is secondary.
Manganian andalusite from Manbazar, Purulia District, West Bengal, India
Authors: Acharyya K. S. , Mukherjee S. , Basu Abhijit
Published: December 2006

Manganian andalusite occurs abundantly as porphyroblasts in manganiferous metasediments subjected to contact metamorphism under hornblende hornfels facies at the contact of a picrodolerite dyke near Manbazar, Purulia District, India. The Mn2O3content of andalusite varies from 13.2% to 19.17%, corresponding to 14.8 and 21.14 mole per cent of ‘Mn2SiO5’ respectively. Based on the analysis showing maximum amount of Mn2O3in andalusite, the mineral formula may be represented as follows:

Other minerals in the assemblage are muscovite, manganophyllite, spessartine, piemontite, quartz, braunite, hematite and rutile. The manganian andalusite is completely fresh and appears to have formed at the expense of spessartine, piemontite and braunite during contact metamorphism. The manganian andalusite probably formed at about 600°C at around 3 kbar pressure. This is another rare example of andalusite with very high Mn2O3(and Fe2O3) as well as that of an occurrence of abundant manganian andalusite.
A hydrated barium silicate in unmetamorphosed sedimentary rocks of central North Greenland
Authors: Jakobsen U. H.
Published: December 2006

A new occurrence of barium silicates has been found in unmetamorphosed sedimentary rocks of central North Greenland. Two different barium minerals have been identified, the Ba-feldspar hyalophane, and an unknown and hitherto undescribed hydrated Ba-silicate with an anhydrous chemical composition identical to cymrite but with about 4 moles of water in the mineral structure. Both silicates are found in a black organic-rich chert sequence in close association with baryte. No replacement textures are observed between the three Ba-minerals.

The hydrated Ba-silicate in the unmetamorphosed rock sequence of the Navarana Fjord area is considered to represent a member in a sequence of Ba-silicates from the unknown Ba-silicate with four H2O in the structure (BaAl2Si2O8·4H2O), through cymrite with one H2O (BaAl2Si2O2O8·H2O) to celsian with none (BaAl2Si2O8). This sequence might reflect the continuous release of water during prograde diagenesis and metamorphism. The association between chert and Ba minerals in the sedimentary rocks of the Navarana Fjord area is believed to reflect an addition of silica and barium by hydrothermal solutions.
A potassium-rich zeolite in soil development on Danian chalk
Authors: Nørnberg P
Published: December 2006

A zeolite found in a soil profile developed in Danian chalk was studied. The results showed that it is a heulandite, temperature-stable to above 600°C with a Si/Al ratio of 2.88 and almost completely K-exchanged. The mineral probably formed under burial diagenetic conditions in the chalk formation.
Fluid migration during contact metamorphism: the use of oriented fluid inclusion trails for a time/space reconstruction
Authors: Cathelineau M. , Lespinasse M. , Bastoul A. M. , Bernard C. , Leroy J.
Published: December 2006

Microthermometric characteristics of metamorphic to hydrothermal fluids and microfracturing were studied in a contact zone between metamorphic series and peraluminous granites, located in the southern part of the Mont Lozère pluton (Massif Central, France). Four major stages of fluid production or migration have been recognized: (1) N2-CH4 (±CO2)-rich fluids related to the metamorphism of the C-bearing shales, occurring as fluid inclusion along the quartz grain boundaries; (2) CO2-CH4-H2O vapours or liquids, with homogenization temperatures of 400 ± 20 and 350 ± 50°C respectively, related to the first hydrothermal stage produced by the late peraluminuous intrusions; (3) aqueous fluids having low salinities and Th in the range 150–330°C; (4) low-temperature aqueous fluids.

It is shown that the percolation of hydrothermal fluids occurs through a dense set of microfissures on a microscopic scale. The different stages of fluid percolation have been investigated by relating the deformational events to the observed fracturing. The nature of the hydrothermal fluid has been deduced by studying the trails of fluid inclusions. Analysis of the relationships of the fluid inclusion trails (F.I.T.) with structures associated with plastic deformation show that their propagation is independent of the intracrystalline anisotropies. Combined studies of their orientation in space and their microthermometric characteristics show that: (1) according to the direction, several generations of fluids are distinguished within each sample on the basis of their physical-chemical characteristics; they correspond to different stages of the hydrothermal activity and to different directions of micro-crack opening; (2) in bulk isotropic media (granite), fluid inclusion trails are essentially mode I cracks which can be used as excellent markers of paleostress fields; however, in bulk anisotropic media (quartz lenses in mica schists) the migration directions of the fluids are mostly dependent on the local reorientations of the stress fields.

The study of the contact zone between granites and a metamorphic series submitted to local abnormal heat flows shows that fluid characteristics are significantly different in the two environments. Migration of carbonic fluids from mica schists towards granites occurred but is relatively limited, whilst aqueous fluids mixed in variable amounts with carbonic fluids in the metamorphic zone.
Evolution of a metamorphic fluid during progressive metamorphism in the Joroinen-Sulkava area, southeastern Finland, as indicated by fluid inclusions
Authors: Poutiainen Matti
Published: December 2006

Fluid inclusions in the progressively metamorphosed rocks of the Joroinen-Sulkava area, located in the south-eastern end of the Raahe-Ladoga zone near the Archaean-Proterozoic boundary, southeastern Finland, fall into four main categories: (1) H2O-rich, (2) CO2-rich, (3) mixed H2O-CO2and (4) CH4-N2inclusions. The samples were collected from quartz veins associated with different deformation phases (D2-D4) and from metapelites. The progressive stage of metamorphism took place mainly during the D2deformation. The age of metamorphism and D2deformation becomes younger with increase in metamorphic grade from amphibolite to granulite facies.

Regional distribution of the different fluid types indicates a change in fluid regime from H2O to CO2-dominant during the progressive stage of the metamorphism. H2O entered preferentially into the anatectic melt. The possibility of CO2infiltration from deeper crust can not be excluded, because granulite facies rocks occur most probably below the lower grade zones. A zone enriched in CH4-N2fluids is located near the lineament zones caused by the D3deformation. This fluid type dominates the Au-bearing D2–D3quartz lenses in the K-feldspar-sillimanite zone. Density data of early CO2inclusions in combination with estimates of metamorphic temperatures (645–750°C) in the different metamorphic zones indicate a pressure range of 3.0–4.5 kbar, which is consistent with data derived from mineral geobarometry. The diversity of fluid types encountered in the D2–D4quartz veins are a result of the passage of different fluids through veins at different times without re-equilibrating with the wall rocks. However, it is supposed that the CH4-N2fluid is derived from a CO2-rich fluid with XCH4⩽ 0.4 by re-equilibration during its passage through the rocks.
Characterization of hydrocarbon fluid inclusions by infra-red and fluorescence microspectrometry
Authors: Guilhaumou Nicole , Szydlowskii Nathalie , Pradier Bernard
Published: December 2006

Liquid-hydrocarbon-bearing fluid inclusions have often been described associated with petroleum occurrences and diagenetic sediments. Infra-red microspectrometry allows characterization of fluid inclusions greater than 20 µm by establishing the presence of aliphatic and aromatic hydrocarbons as well as associated H2O, CO2 and CH4. Semi-quantitative analyses have been made by focussing on gaseous and liquid phases separately. Some CH2/CH3 and CO2/CH4 ratios have been determined by this method.

Fluorescence microspectrometry permits precise measurements of the fluorescence emission spectrum of chromophore-bearing organic phases (essentially aromatic hydrocarbons) in fluid inclusions greater than 10 µm. Such a spectrum is a function of both the gross composition of the trapped oil and its thermal history.

Both of these methods lead to the in situ characterization of hydrocarbon fluid inclusions. They are useful in providing a quantifiable distinction between different oil generations trapped during mineral growth in diagenetic and epigenetic minerals.
Chemical variation in micas from the Cairngorm pluton, Scotland
Authors: Harrison T. N.
Published: December 2006

Electron microprobe analyses of micas from the Cairngorm pluton in the Eastern Grampian Highlands of Scotland show extensive compositional variation in biotite, despite a lack of chemical variation in the host granite. Biotite has high Fe/(Fe + Mg) (0.6–0.85) and Alvi (0.6–2.1 a.f.u.), and enrichment trends in these two parameters are attributable to the Al-Tschermak and dioctahedral-trioctahedral substitutions, the latter becoming dominant with increasing Alvi content. Ti content is low (0.2–0.4 a.f.u.), and is largely controlled by a Tschermak-type substitution. Biotite is also unusually rich in Mn (up to 2.57 wt. % MnO), which increases with both Alvi and Fe/(Fe+Mg). F contents generally range between 0.55 and 2.05 wt.% All compositional variation in biotite can be attributed to the extensive development of a fluid phase during the late-magmatic and subsolidus evolution of the pluton. The presence of an abundant fluid phase has resulted in the alteration of biotite to muscovite, which has occurred in response to de-stabilization of the biotite as octahedral R2+ cations are lost in favour of Al. Extreme build-up of this fluid phase has resulted in the crystallization of muscovite as a late, interstitial primary phase. Both primary and replacive muscovite have Fe/(Fe+Mg) > 0.50, 15–36 mol. % celadonite and <1 mol. %paragonite.
Connellite: stability relationships with other secondary copper minerals
Authors: Pollard A. M. , Thomas R. G. , Williams P. A.
Published: December 2006

The stability of synthetic connellite has been determined at 298.2K (25 °C) and 105 Pa, using solution methods. For the reaction 1/37{62H+(aq) + Cu37Cl8(SO4)2(OH)62.8H2O(s) ⇌ Cu2+(aq) + 8Cl−(aq) + 2SO42−(aq) + 70H2O(l)}, log KH+ is equal to 6.44(2). This result has been used in turn to calculate a value for ΔfG°(1/37Cu37Cl8(SO4)2(OH)62.8H2O, s, 298.2K) of −423.7±6.6 kJ mol−1. During the synthesis of connellite, claringbullite sometimes forms as a metastable phase. This solid recrystallizes to connellite if kept in contact with the reaction solution. The results have been used to construct an equilibrium model for the formation of connellite in relation to other common secondary copper (II) minerals. Connellite crystallizes from solution over an appreciable range of conditions. This result is consistent with the observed widespread occurrence of connellite, though as a very minor phase, in the oxidized zones of cupriferous sulfide ores.
Transparent bright blue Cu-bearing tourmalines from Paraiba, Brazil
Authors: Henn Ulrich , Bank Hermann , Bank Francisco Hermann , Platen Hilmar Von , Hofmeister Wolfgang
Published: December 2006

Physical, crystal-chemical and absorption spectroscopical properties of blue tourmalines from a new occurrence in the State of Paraiba, Brazil, are described. Refractive indices, birefringence and specific gravity have been determined as ne = 1.615–1.620, no = 1.632–1.640, Δn=−0.017 to −0.020 and 3.04–3.07g/cm3. Microprobe analyses proved the samples to be elbaites, which are relatively Mn-rich and contain 2.1 wt. % CuO and 0.5 wt. % Bi2O3. Lattice constants are ao = 15.854(4) and co = 7.102(1) Å. The blue colour is due to pleochroic absorption bands of Cu2+ and Mn3+ with maxima at 700 and 520 nm respectively.
Zirconium and niobium-bearing ilmenites from the Igaliko dyke swarm, South Greenland
Authors: Pearce N. J. G.
Published: December 2006

Ilmenites from alkaline basic dykes in the Gardar province, south Greenland have Zr contents up to 3850ppm and Nb contents up to 1030ppm. These elements substitute for Ti in the octahedral site. These are amongst the highest recorded Zr and Nb contents for ilmenites, giving distribution coefficients (Kdilmenite/matrix) for Zr up to 11.6 and Nb up to 70.3. Fractionation of ilmenite may thus have a dramatic effect on residual Zr and Nb contents. These effects are discussed in relation to the use of trace element tectonomagmatic discrimination diagrams.
The crystal structure of kamchatkite, a new naturally occurring oxychloride sulphate of potassium and copper
Authors: Varaksina T. V. , Fundamensky V. S. , Filatov S.K. , Vergasova L. P.
Published: December 2006

The crystal structure of the new mineral kamchatkite, a= 9.741(5), b= 12.858(6), c=7.001(3)Å, space group Pna21, Z = 4, has been determined through direct methods using 1430 intensities and refined to a final discrepancy index R = 0.055. It contains (SO4) tetrahedra and Cu octahedra interconnected by oxygen atoms to form an electrostatically neutral three-dimensional arrangement of formula Cu3O[SO4]2 which contains channels parallel to [001]. The channels are not empty but house KCl molecules.
Metallogenetic significance of a North Pennine springwater
Authors: Manning D. A. C. , Strutt D. W.
Published: December 2006

The occurrence is reported of a saline spring water from Weardale, which compositionally closely resembles other saline waters derived from the Carnmenellis granite, southwest England. The total dissolved solutes achieve approximately 38 000 mg/L, and alkali geothermometers suggest equilibration temperatures of approximately 150°C, equivalent to a depth of 4 km. Using Na, K and Li it is possible to compare the composition of the spring water with those of other spring waters derived from Carboniferous sequences adjacent to the North Pennine Orefield and with published data for fluid inclusions from North Pennine fluorite. These compositional parameters suggest that the ancient mineralizing fluids resemble modern Carboniferous sediment-derived waters and contain a relatively minor component of granite-derived water. Data for Br and Cl indicate that a significant component of the present day Weardale spring waters was probably ultimately derived from organic-rich sedimentary sequences while data for K, Na and Li indicate the importance of a component derived from a permeable granite aquifer. The Weardale springwaters continue to have ‘mineralizing’ potential, in view of the possibility that they may have precipitated quartz or chalcedony during their ascent.
Kornerupine breakdown reactions in paragneisses from southern Madagascar
Authors: Ackermand Dietrich , Windley Brian F. , Razafiniparany Andriantefison H.
Published: December 2006

Kornerupine-rich layers up to several centimetres thick with minor sillimanite, spinel, Fe oxide and ilmenite occur in a diopsidite in sillimanite-cordierite gneiss south of Beraketa (24°27′S, 46°48′E), southern Madagascar. Kornerupine, sillimanite, spinel and hematite grains up to 1 mm across have mutual polygonal boundaries indicating textural equilibrium at their crystallisation. Kornerupine has XMg 0.67–0.80 and 0.9 to 2.6 wt.% B2O3. Sillimanite contains up to 2.0 wt.% Fe2O3. Spinel is essentially (Mg,Fe2+) Al2O4 with an XMg range of 0.29–0.40 and exsolution lamellae of Fe oxide. Textural relations demonstrate two limited reactions, each confined to areas less than 500 µm across: (1) Kornerupine and spinel reacted along grain contacts to form very fine-grained tourmaline, corundum and chlorite. The replacing phases are symmetrically zoned with a central tourmaline and hematite, bordered by an aggregate of chlorite, tourmaline and corundum, followed outwards by a rim of chlorite against the kornerupine and spinel. (2) Within kornerupine grains, zoned, round aggregates consist of very fine-grained chlorite, tourmaline and corundum of different composition than in (1). They define the terminal reaction of kornerupine breakdown.

Geothermobarometry indicates that the early kornerupine-bearing assemblage was stable at 7.0 kbar and 700 °C. This P-T point lies close to the retrograde, nearly isothermal trajectory defined independently by nearby sapphirine-bearing assemblages. The fine-grained aggregates formed most likely during further cooling, or by increasing water fugacity.
Barstowite, 3PbCl2.PbCO3.H2O, a new mineral from Bounds Cliff, St Endellion, Cornwall
Authors: Stanley C. J. , Jones G. C. , Hart A. D. , Keller P. , Lloyd D.
Published: December 2006

Barstowite, ideally 3PbCl2.PbCO3.H2O is a new mineral from a lead-antimony vein at the south-western end of Bounds Cliff, St Endellion, Cornwall. It occurs as very small (0.2–0.5 mm) subparallel elongate intergrown crystals which form aggregates (up to 3 mm) containing minor inclusions of galena and jamesonite. Other associated minerals are quartz, dolomite, phosgenite, cerussite, sphalerite, pyrite and chalcopyrite. Barstowite is colourless to white and is transparent with an adamantine lustre and white streak. It is brittle, has an imperfect prismatic cleavage, and an uneven fracture. Low reflecting, barstowite has a moderate bireflectance from grey to dark grey in hue and weak to moderate anisotropy. Internal reflections (colourless) are abundant. Measured reflectance values in air and oil are tabulated. Colour values relative to the CIE illuminant C for R1 and R2 in air respectively are: Y% 12.9, 13.3; λd 477, 476; Pe% 3.5, 3.7. VHN100 111 (range 108–117); calculated Mohs hardness is 3. Infrared spectra of barstowite, phosgenite and cerussite are compared.

X-ray studies show that barstowite is monoclinic with space group P21/m and a 4.218(2), b 9.180(2), c 16.673(4) Å, β 91.49(3)°. It has a cell volume of 645.38 Å3 with Z = 2. Dcalc. is 5.76 g/cm3, Dmeas. is 5.71 g/cm3. The strongest six lines of the X-ray powder pattern are [d in Å (I) (hkl)] 4.02 (10) (022); 2.296(8) (040; ; 106); 2.377(6) (007; 026); 4.16(5) (004); 2.108(4) (200); 3.79(3) (014). The name is for the late Richard William Barstow, the Cornish mineral dealer.
Coexisting glasses occurring as inclusions in leucite from lamproites: examples of silicate liquid immiscibility in ultrapotassic magmas
Authors: Mitchell Roger H.
Published: December 2006

Inclusions occurring in leucites from the Oscar and Zirkel Mesa leucite lamproites consist of high (>10 wt.%) and low (<4 wt.%) K2O discrete glass phases which are interpreted to have resulted from silicate liquid immiscibility. Both glasses are quartz-normative and rich in Ti, Fe, Mg, Ca and Ba and poor in Al. The high-K glass is strongly peralkaline. Neither of the glasses have compositions representative of any known lamproites. These inclusions represent the first described examples of silicate-silicate immiscibility shown by glass in alkaline rocks.
The geochemistry and tectonic setting of the Demirköy pluton of the Srednogorie–Istranca granitoid chain, NW Turkey
Authors: Aykol A. , Tokel S.
Published: December 2006

The chain of Late Subhercynian granitoids can be traced along the Srednogorie-Istranca-Pontid belt. The Demirköy pluton outcrops in the Istranca segment. The rocks of the pluton range from diorite through grandiorite to perthite granite with granodiorite predominating. On the basis of 25 chemical analyses, the intrusive setting of the granitoid has been investigated. Calcic to calc-alkaline and peraluminous to metaluminous character indicate a subduction-related origin. Low to moderate concentrations of the large-ion lithophiles (LIL), high field strength elements (HFS), light rare earth elements (La, Ce) and low HFS/LIL ratios indicate a mantle-derived magma with subduction-related enrichment. Trace element discrimination diagrams such as Rb/Zr-Nb, Rb/Zr-Y, Rb-SiO2 and Rb-(Nb + Y), are particularly indicative of normal arc-setting for the samples.

The Demirköy granitoid is chemically indistinguishable from the Upper Cretaceous granitoids of Strednogorie to the west and the Pontids to the east. This extensive maximum of plutonism can be considered as a time marker in the northern Tethys subduction system.
Oscillatory zoning in metamorphic minerals: an indicator of infiltration metasomatism
Authors: Yardley B. W. D. , Rochelle C. A. , Barnicoat A. C. , Lloyd G. E.
Published: December 2006

Examples of oscillatory zoning in metamorphic minerals, imaged using a Back-Scattered Electron Detector on the SEM, are described from a series of contrasting environments. These are a prehnite vein sampled by drilling in the Mirvalles geothermal field, Costa Rica, a pyroxene vein developed in a regional metamorphic shear zone in the Yilgarn block, Western Australia, and a bedded metasomatic diopside rock from regionally metamorphosed metasediments in Connemara, Ireland. In each case the formation of oscillatory zoning can be ascribed to mineral growth under supersaturated conditions due to fluid infiltration. Oscillations can be related in the first example to periodic episodes of pressure release and boiling in the geothermal field, but in the regional metamorphic examples actualistic models are harder to define. The development of oscillatory zoning is likely to be a characteristic feature of infiltration metasomatism and can be used as a criterion in the recognition of metasomatic mineral growth in metamorphic rocks outside the vein environment.
Porphyroblast textural sector-zoning and matrix displacement
Authors: Rice A. H. N. , Mitchell J. I.
Published: December 2006

There is an association between the development of cleavage domes, a texture reflecting the displacement of insoluble matrix grains by porphyroblasts growing under a bulk hydrostatic stress, and textural sector-zoning. This has been found in garnet, staurolite, chiastolite, pyrite and possibly emerald porphyroblasts. Sector-zoned porphyroblasts form by lineage growth normal to the crystal faces. This causes several distinctive textures (type 1 inclusions and type 2 intergrowths, inclusion bands, growth prongs), all of which are directly or indirectly related to displacement growth. Graphite or other carbonaceous material is ubiquitous in samples showing textural sector-zoning.
Modification of antiphase domain sizes in omphacite by dislocation glide and creep mechanisms and its petrological consequences
Authors: van Roermund H. L. M. , Lardeaux J. M.
Published: December 2006

A T.E.M. study of omphacites from the western Italian Alps (Sesia Lanzo Zone and Monviso eclogites) has revealed a bimodal size distribution of antiphase domains: (a) 250–350 Å, (b) ≥ 2500 Å. In addition observed dislocation substructures and ‘large-scale’ antiphase domains are intimately interconnected.

A model is presented that can explain modification of the antiphase domain sizes by the interplay of cooling/growth and dislocation glide and/or creep mechanisms. Subsequent coarsening of the modified antiphase domains is inferred to be the result of surface free-energy processes. The model clearly illustrates that only the ‘relatively undeformed’ areas containing the small-scale antiphase domains can be used for thermometric methods.
Banded sphalerite from the North Pennine Orefield
Authors: More A. P. , Vaughan D. J. , Ashworth J. R.
Published: December 2006

Optical microscopy of doubly polished thin sections of North Pennine sphalerite has revealed a range of previously unrecognised textures for the Alston Block mineralisation. Delicate growth zoning, interrupted by numerous solution disconformities, was seen in transmitted light. Two principal varieties of growth-banded sphalerite are recognised; the earlier (Type 1) is characterised by the development of thin opaque bands. Type 2 has colour bands between yellow and brown, correlated with iron content. In Type 1, iron levels (up to 3 wt.%) are not sufficient to account for the observed opacity. Ultra-violet and infra-red techniques failed to detect any organic inclusions. Electron microscopy revealed locally high concentrations of sub-micrometre inclusions, both beam-stable and beam-unstable, and a variety of growth-related crystal defects.

Fluid inclusion thermometry in both sphalerite varieties and the accompanying quartz gangue implies a saline mineralising fluid (20–25 wt.% equiv. NaCl) at a relatively low temperature (100° to 140°C). Tubular inclusions are conspicuous. A deformation-induced lamelliform optical anisotropy is superimposed on a growth-related grid-iron anisotropy. Growth band offset is apparent where the deformation fabric cross-cuts the growth banding. Deformation on {111} twin and slip planes was indicated by electron microscopy.
The ore textures of the Neves-Corvo volcanogenic massive sulphides and their implications for ore beneficiation
Authors: Gaspar O. , Pinto A.
Published: December 2006

The Neves-Corvo mine opened officially in December 1988 and it is already the biggest producer of copper in the Iberian Pyrite Belt (IPB). Tin production started in 1990. The ore deposits of the IPB are related to felsic submarine volcanism which developed during the lower Tournaisian to the middle Visean. At the end of the first phase of Hercynian deformation in the middle Westphalian, the ore deposits were affected by low-pressure metamorphism producing schistosity and prehenite-pumpellyite greenschist facies assemblages in the volcanogenic sediments of the IPB.

The unique nature of the mineralogy of the Neves-Corvo deposit compared with other IPB deposits is mainly a result of the introduction of later Cu-rich hydrothermal solutions to the primitive ore pile and the presence of tin mineralisation. The cupriferous ores are rich in tetrahedrite-tennantite, stannite, kesterite, stannoidite and mawsonite.

Cassiterite occurs in Neves-Corvo: (a) as thin layers of euhedral crystals in cupriferous ores, partially replaced by chalcopyrite; (b) in the schistosity of a banded black shale chalcopyrite hanging wall formation; (c) as metre-sized lenses of massive cassiterite overlying the cupriferous ores.

The ore textures at Neves-Corvo are complex, due to intergrowths of fine colloform pyrite with the base metal minerals. Because of the low grade of metamorphism, colloform, geopetal and soft-sediment diagenetic features are preserved in the ‘complex ores’. These ‘complex ores’ have contents of 0.5% Cu, 1% Pb and 5.5% Zn. In copper-rich ores (7.9% Cu and 1.4% Zn), replacement of the primary ore by chalcopyrite has obliterated most of these textures and produced fine chalcopyrite-tetrahedrite-pyrite intergrowths. The textures clearly indicate the genesis of these ores but they impose a practical problem in recovery of the metals. There is no clear correlation between these textures and the ore classification used at the mine, but an understanding of the textures is vital since the ‘complex ores’ require fine grinding to achieve liberation and the fine grinding adversely affects the froth flotation processing of the ore.

The implications of the complex sulphide textures for ore beneficiation have been studied using reflected light microscopy, with determination of modal analyses and grain-size distributions of free particles and middlings from concentrates and tailings.

The outcome of a one-year intensive study is that the ore microscopy laboratory at the mine now produces daily information about the textures of the feed ores so that metallurgical engineers can optimise the performance of the ore dressing plant.
Mineralogical and textural evolution of the economic manganese mineralisation in western Rhodope massif, N. Greece
Authors: Nimfopoulos M. K. , Pattrick R. A. D.
Published: December 2006

The western Rhodope massif contains a significant number of ‘battery grade’ Mn-oxide deposits which are best developed in the area near Kato Nevrokopi, Drama district, N. Greece. Economic Mn-oxide ore concentrations are confined to fault zones and related karsts in marbles. The mineralisation has formed by weathering of hydrothermal veins that were genetically related to Oligocene magmatism.

At Kato Nevrokopi, progressive and continuous weathering of primary, hydrothermal veins of rhodochrosite, mixed sulphide, quartz and ‘black calcite’ (calcite and todorokite) has resulted in the formation of the assemblage MnO-gel-(amorphous Mn-oxide)-todorokite-azurite-goethite-cerussite in the veins and the assemblage MnO-gel-nsutite-chalcophanite-birnessite-cryptomelane-pyrolusite and malachite and amorphous Fe-oxides in karstic cavities.

The fs2 and fO2 of the hydrothermal fluids increased with time. The breakdown of the hypogene Mn-carbonate was aided by the production of an acidic fluid due to the oxidation of sulphides. Precipitation of the supergene ores was caused by neutralisation of the fluids due to reaction with the host marble and to mixing of relatively reduced fluids with oxygenated surface water in a fluctuation water table regime. Zinc was also mobile during weathering and became concentrated in the intermediate Mn-oxides, effectively stabilising their structures. The mineral paragenesis records the progressive oxidation of the ore and the appearance of less hydrated Mn-oxides, low in alkalis and alkaline earths.
Textural evolution of W-Cu-Sn-bearing hydrothermal veins at Minas da Panasqueira, Portugal
Authors: Foxford K. A. , Nicholson R. , Polya D. A.
Published: December 2006

Combined structural and textural studies of the quartz veins of the Panasqueira W-Cu-Sn deposit of central Portugal have revealed the presence of coeval forms of crack-seal and cavity-fill mineral textures. The textures result from the dilational and infilling histories of brittle fractures produced within the host rock by the intrusion of pressurised fluids. Crack-seal textures were produced wherever or whenever crystal growth rates matched or were greater than fracture dilation rates, whereas cavity-fill textures developed wherever or whenever dilation rates were quicker than those of crystal growth. Rates of dilation within the blade-like fissures were naturally lowest at the edges, where types of crack-seal textures were produced, and highest in the cores, where cavity-fill texture formed. During propagation the linkage of adjacent echelon blades, by the rupture of the host-rock straps (bridges) between them, enhanced dilation rates and led to the widespread development of cavity-fill textures. Within the composite fissures so produced, environments in which types of crack-seal textures could form were restricted to the fissure margins and to areas where the tensile strain was sympathetically shared between closely spaced fissures. Textures and minerals characteristic of each fracture environment were able to form simultaneously within the fracture system.
Cathodoluminescence and growth of cassiterite in the composite lodes at South Crofty Mine, Cornwall, England
Authors: Farmer C. B. , Searl A. , Halls C.
Published: December 2006

The cathodoluminescence (CL) of cassiterite (SnO2) from the paragenetic sequence in the lodes at South Crofty Mines has been used in the interpretation of the processes which govern mineral deposition. Luminescence is controlled by the substitution of Ti, Fe and W for Sn in the cassiterite lattice. Ti and W behave as luminescence activators whereas Fe quenches luminescence. The observed colours and intensity of the luminescence are believed to result from the interplay between these effects. Successive generations of cassiterite formed during the separate stages of paragenetic evolution show different luminescence colours. These are believed to reflect changes in bulk composition of the fluid, which is indicated by the systematic variation in the composition of tourmaline in the associated gangue.

CL also reveals details of growth and deformation in individual crystals. Growth textures observed in CL are broad concentric growth banding, oscillatory zoning and sector zoning. Sector boundaries often show a zig-zag form which is indicative of competitive growth of adjacent crystal faces. Interpretation of CL textures is used to support the hypothesis that cassiterite growth took place under two main regimes. These are, firstly, conditions in which fluid pressure decreased abruptly when tectonic reactivation caused dilation of parts of the lode fracture system and secondly, conditions of sustained hydraulic pressure within fractured vein fill. In tectonically induced fractures the crystals are stubby, have non-equivalent growth faces and are commonly tetragonal bipyramidal forms in which sector zoning is invariably present. In hydraulic fractures crystals take a predominantly tetragonal prismatic form. Thus, it is believed that growth under these contrasting conditions leads to distinctive morphology and zoning in cassiterite, providing a basis for typomorphic characterisation.
Conversion of nepheline to sodalite during subsolidus processes in alkaline rocks
Authors: Finch Adrian A.
Published: December 2006

Cathodoluminescence (CL) petrography of nepheline syenites of the Igaliko complex, Gardar province, South Greenland shows that sodalites possess embayed contacts against nepheline, and have formed by a process of metasomatic replacement. This texture is demonstrated clearly by CL, since sodalite luminesces bright orange and nepheline is poorly luminescent. The transformation from nepheline to sodalite results in a volume change which leads to a network of fractures in which deep-blue luminescent fluorite is precipitated. Fluorite is formed since the chlorination process involved in the transformation causes localised reductions of the salinity of the fluid and therefore a decrease in the solubility of fluorite. Sodalite-fluorite textures observed using CL allow sodalites of secondary origin in alkaline igneous rocks to be identified.

Nephelines and sodalites, when observed using scanning electron microscopy, possess small micropores. By analogy with recent work on alkali feldspars, pervasive alteration of nephelines may occur by fluid flow assisted by a permeable micropore network.
Vanadian allanite-(La) and Vanadian allanite-(Ce) from the Hemlo gold deposit, Ontario, Canada
Authors: Pan Yuanming , Fleet Michael E.
Published: December 2006

Allanite-(La) (containing up to 7.80 wt.% V2O3 and with La/ΣREE and La/Ce atomic ratios up to 0.54 and 1.45, respectively) and allanite-(Ce) (up to 8.46 wt.% V2O3) occur in close association with vanadian muscovite, barian tomichite and vanadian titanite in the main ore zone of the Hemlo gold deposit, Ontario, Canada. Allanite-(Ce) generally occurs as a minor constituent in cross-cutting veins or along foliation planes, whereas allanite-(La) invariably occurs in direct contact with titanite. The high V concentrations in the allanites from Hemlo are readily attributable to an adequate local source of this element, and are most likely controlled mainly by a simple substitution of V for Al in octahedral coordination. Vanadian allanite-(La) and vanadian allanite-(Ce), without any systematic differences in other constituents, are clearly distinct in REE composition, in respect to both the relative concentrations of La and Ce and abundances of other REE. The formation of both allanites (Ce- and La-rich) indicates very localised remobilisation and concentration of REE during a late hydrothermal alteration. The unusual REE composition of vanadian allanite-(La) directly reflects partitioning of REE with coexisting titanite, and the formation of this unusual phase may be attributable to replacement of earlier titanite with redistribution of REE in the solid state.
On the poikilitic nature of Jabal Al Hasawinah eudialyte
Authors: Oun Khaled M.
Published: December 2006

Poikilitic eudialyte outcrops in a strongly peralkaline phonolithic cumulo-dome in Jabal Al Hasawinah, Libya. Textural relationships reveal that the eudialyte has formed at a very late stage of the rock petrogenesis. Electron microprobe analyses confirm its volatile (hydrous) nature and low REE content.
Mg-rich dumortierite in cordierite-orthoamphibole-bearing rocks from the high-grade Bamble Sector, south Norway
Authors: Visser Diederik , Senior Antony
Published: December 2006

Dumortierite is described from several occurrences of cordierite-orthoamphibole-bearing rocks in the upper-amphibolite facies area of the Bamble Sector, south Norway. Dumortierite occurs with chlorite, muscovite and quartz in late M4 alteration zones or aggregates after M3, peak-metamorphic cordierite and garnet and early M4 vein-cordierite, and intergrown with or replacing orthoamphibole. Late M4P-T conditions, which are interpreted as conditions of dumortierite formation, are estimated from the associated late M4 kyanite-andalusite-chlorite-quartz assemblage and Mg-Fe exchange geothermometry to be 500 ± 50 °C and 3–4 kbar. Retrogression of M3 mineral assemblages is initiated by influx of fluids with XCO2 of 0.3–0.4 during early M4 followed by more water-rich fluids during late M4. Late M4 fluids may show local variations in alkalis and boron. The dumortierites are the most Mg-rich (2.23–3.42 wt. % MgO) ever reported, and contain 0.00–2.05 wt.% TiO2, 0.00–1.08 wt.% Fe2O3, 29.62–32.42 wt.% SiO2 and 55.20–59.71 wt.% Al2O3. Al is the most likely substituent for Si, which shows a minor deficiency at the tetrahedral sites in most dumortierites. The major variations in the mineral chemistry can be described by the coupled substitutions Mg + Ti = 2AlVI, 3Mg = 2AlVI and possibly Mg + H = AlVI. Favoured by low ƒO2 prevailing conditions a significant part of total iron in dumortierites at one locality is present as Fe2+ giving evidence for the Fe2+ + SiIV = AlIV + AlVI tschermakite substitution. FeMg−1 substitution is considered to be limited. Ti-rich dumortierites coexist with rutile, ilmenite or titaniferous magnetite. The development of dumortierite from orthoamphibole correlates with an observed decrease of Al, Mg and Na and increase of Si and Fe in orthoamphibole towards dumortierite.
A new method for measuring the crystallinity index of quartz by infrared spectroscopy
Authors: Shoval S. , Ginott Y. , Nathan Y.
Published: December 2006

A new method for measuring the crystallinity index of quartz is presented. It is based on the measurement of the intensity of the first derivative of the infrared absorption spectrum at the shoulder at c. 1145 cm−1. The results correlate well with X-ray and D.T.A. crystallinity measurements.
Fluid inclusion and stable isotope evidence for the origin of mineralizing fluids in south-west England
Authors: Alderton D. H. M. , Harmon R. S.
Published: December 2006

The oxygen and hydrogen isotope composition of hydrothermal fluids associated with the Variscan granites of southwest England has been inferred from analysis of various silicate minerals (predominantly quartz) and by direct analysis of fluid inclusions within quartz and fluorite. These data have been combined with the results of a fluid inclusion study to develop a model for the origin and evolution of hydrothermal fluids in the region. Magmatic fluids expelled from the granites had compositions in the range δD = −65 to −15‰, and δ18O = 9 to 13‰. Respective temperature, salinity, fluid δD, and fluid δ18O values for the (i) early Sn-W mineralization, (ii) later Cu-Pb-Zn sulphide mineralization, and (iii) latest ‘crosscourse’ Pb-Zn-F mineralization are: (i) 230–400 °C, 5–15 wt.% NaCl equiv., −39 to −16‰, and 7.0 to 11.2‰, (ii) 220–300 °C mostly 2–8 wt.% NaCl equiv., −41 to −9‰, and 2.3 to 8.1‰, and (iii) 110–150 °C 22–26 wt.% NaCl equiv., −45 to +2‰, and −1.8 to +5.5‰. These data highlight the important role of both magmatic fluids exsolved from the crystallizing granite, and basinal brines circulating within restricted fracture systems.