bluuebunny/crossref_metadata_2025_split huggingface dataset:
Preferred orientation of experimentally deformed pyrite measured by means of rieutron diffraction
Authors: Siemes H. , Zilles D. , Cox S. F. , Merz P. , Schäfer W. , Will G. , Schaeben H. , Kunze K. 
Published: December 2006

AbstractNeutron diffraction texture goniometry indicates that naturally deformed polycrystalline pyrite ores from Mt. Lyell (Tasmania) and Degtiarka (Ural Mountains) have weak lattice preferred orientations. During experimental deformation involving dislocation flow at elevated temperatures and pressures, these initial fabrics have been modified to produce new lattice preferred orientations.Polycrystalline pyrite form Mt. Lyell (B-1) has an initial <111> - fibre texture perpendicular to a grain-size layering. After 24% shortening perpendicular to the <111> - fibre axis at 700°C a new, but weak <100> texture has developed parallel to the shortening axis. The Degtiarka pyrite (PN-6) initially has two weak fibre components. The somewhat stronger component is a <100>-fibre texture, similar to that in the experimentally deformed B-1 pyrite. The other one is a <111> - fibre texture similar to the intital B-1 preferred orientation. After 30% shortening oblique to both initial fibre axes at 600°C weak <110>- and <111>-fibre textures have developed. The experimentally produced fabrics have developed during deformation involving dislocation flow, dynamic recrystallisation and some microcracking. Intergranular sliding may also have been involved. Differences between lattice preferred orientations developed in the 600°C and 700°C experiments are interpreted to indicate a change in the dominant flow mechanism with changing temperature.In comparison with other cubic minerals that have been deformed experimentally by dislocation flow mechanisms, the pyrite shows an unusually weak preferred orientation which can be detected only by means of neutron diffraction texture goniometry.
Deformation textures in pyrite from the Vangorda Pb-Zn-Ag deposit, Yukon, Canada
Authors: Brown D. , McClay K. R. 
Published: December 2006

AbstractThe Vangorda Pb-Zn-Ag orebody is a 7.1 M tonne, polydeformed stratiform massive sulphide deposit in the Anvil mining district, Yukon, Canada. Five sulphide lithofacies have been identified within the desposit with a typical mineralogy of pyrite, sphalerite, galena, and barite. Pyrrhotite-sphaleritemagnetite assembalges are locally developed. Etched polished sections of massive pyrite ores display relict primary depositional pyrite textures such as colloform growth zoning and spheroidal/framboidal features. A wide variety of brittle deformation, ductile deformation, and annealing textures have been identified. Brittle deformation textures include thin zones of intense cataclasis, grain indentation and axial cracking, and grain boundary sliding features. Ductile deformation textures include strong preferred grain shape orientations, dislocation textures, grain boundary migration, dynamic recrystallisation and pressure solution textures. Post deformational annealing has produced grain growth with lobate grain boundaries, 120° triple junctions and idioblastic pyrite porphyroblasts. The distribution of deformation textures within the Vangorda orebody suggests strong strain partitioning along fold limbs and fault/shear zones, it is postulated that focussed fluid flow in these zones had significant effects on the deformation of these pyritic ores.
A supposed sövite from Oldoinyo Lengai, Tanzania: result of extreme alteration of alkali carbonatite lava
Authors: Dawson J. B. 
Published: December 2006

AbstractA calcite-rich block in nephelinitic agglomerate at Oldoinyo Lengai comprises Sr-calcite, apatite, fluorite, a Ba-Mn oxide akin to romanrchite, and a distinctive Mn-Fe spinel. Formerly reported as sövite, on textural, mineralogical and stable isotope grounds it is now re-interpreted as a highly-altered natrocarbonatite lava. An implication of this study is that natrocarbonatite is not just a modern phenomenon, but has been extruded from Oldoinyo Lengai for at least around 1250 years.
Mineral chemistry and reaction textures in metabasites from the Eastern Ghats belt, India and their implications
Authors: Dasgupta Somnath , Sengupta Pulak , Mondal A. , Fukuoka M. 
Published: December 2006

AbstractThree types of mafic granulites, namely two pyroxene-plagioclase granutite (MG), two pyroxeneplagioclase-garnet granulite (GMG) and spinel-olivine-plagioclase-two pyroxene granulite (SMG) are exposed at Sunkarimetta, Eastern Ghats belt, India. The marie granulites exhibit a foliation concordant with that in associated granulite facies quartzofeldspathic gneisses. Textural characteristics and mineral chemical data suggest the following mineral reactions: olivine + plagioclase = spinel + orthopyroxene + clinopyroxene (SMG), orthopyroxene + plagioclase = garnet + quartz (GMG), clinopyroxene + plagioclase = garnet + quartz (GMG) and plagioclase + hemoilmenite + quartz = garnet + ilmenite + 02 (GMG). Geothermobarometry indicates maximum P-T conditions of metamorphism at c. 8.5 kbar, 950°C The marie granulites later suffered nearly isobaric cooling to c. 7.5 kbar, 750°C Bulk compositional characteristics suggest that SMG is of cumulate origin. The protoliths of the mafic granulites, emplaced at c. 32 km depth, are probably responsible for thermal perturbation causing granulite facies metamorphism of the enclosing rocks.
Crystal structure of KBSi3O8 isostructural with danburite
Authors: Kimata Mitsuyoshi 
Published: December 2006

AbstractThe crystal structure of KBSi3O8 (orthorhombic, Pnam, with a = 8.683(1), b = 9.253(1), c = 8.272(1) Å,, V = 664.4(1) Å3, Z = 4) has been determined by the direct method applied to 3- dimensional rcflection data. The structure of a microcrystal with the dimensions 20 × 29 × 37 μm was refined to an unweightcd residual of R = 0.031 using 386 non-zero structure amplitudes. KBSi3O8 adopts a structure essentially different from recdmergneritc NaBSi3O8, with the low albite (NaAlSi3O8) structure, and isotypic with danburite CaB2Si2Os which has the same topology as paracelsian BaAl2Si2O8. The chenfical relationship between this sample and danburitc gives insight into a new coupled substitution; K+ + Si4+ = Ca2+ + B3+ in the extraframework and tetrahedral sites. The present occupancy refinement revealed partial disordering of B and Si atoms which jointly reside in two kinds of general equivalent points, T(1) and T(2) sites. Thus the expanded crystal-chemical formula can be written in the form K(B0.44Si0.56)2(B0.06Si0.94)2O8The systematic trend among crystalline compounds with the M+T3+T4+3O8 formula suggests that they exist in one of four structural types; the feldspar structures with T3+/T4+ ordered and/or disordered forms, and the paracelsian and the hollandite structures.
Cr-Zr-armalcolite-bearing lamproites of Cancarix, SE Spain
Authors: Contini Simona , Venturelli Gianpiero , Toscani Lorenzo , Capedri Silvio , Barbieri Mario 
Published: December 2006

AbstractLamproites with high MgO, high SiO2affinity are abundant only in SE Spain where the Cancarix outcrop (in the province of Albacete) occurs. The rocks of Cancarix are peralkaline, saturated to oversaturated in silica, very high in K2O, Th and LREE. The mineralogy and petrography show some variations which depend on the conditions of emplacement and rate of cooling of the magma. The following phases may be present: olivine, phlogopite, K-amphibole, clinopyroxene, sanidine, orthopyroxene, apatite, and, in minor amounts, Cr-spinel, minerals of the pseudobrookite group, ilmenite, roedderite, dalyite, carbonate, analcime (probably pseudomorphous on leucite), a silica phase, rutile, pyrochlore (?), britholite (?) and glass. The lamproites of Cancarix contain Cr-Zrarmalcolite, which is typical of lunar basalts and which has been found also in kimberlites. The composition of early magmatic spinel and the occurrence of Cr-Zr-armalcolite indicate low oxygen fugacity for the primitive magma and related mantle source, in agreement with recent experimental data on lamproitic systems. The redox conditions changed during crystallisation, leading to increase of the Fe3+/Fe2+ratio in the system. During the later stages of crystallisation, the residual melts/fluids were depleted in alumina and enriched in several components, e.g. Na, Zr, Fe, REE, C1, etc. stabilising Na-Fe-clinopyroxene, dalyte, arfvedsonitic rims around K-richterite and other alumina-free phases which, on a chemical basis, have been identified as britholite and pyrochlore. Rough comparison with experimental systems and the geochemistry of the rocks suggests that the magma was generated at shallow depth (≪20 kbar) in the lithospheric mantle, which, after early depletion, underwent strong enrichment in many 'incompatible' elements.
Non-equilibrium highly anisometric crystals and whiskers of galena
Authors: Bonev I. K. 
Published: December 2006

AbstractUnusual irregular galena crystals and whiskers were found in close proximity in some druse cavities from the Gradishtc hydrothcrmal lead-zinc deposit in the Madan ore district, Bulgaria. The following crystal forms were observed: (1) straight thin [110] whiskers and thicker needles; (2) kinked whiskers; (3) curvilinear whiskers; (4) complex tortuous whiskers composed of segments with varying directions—[110], [100], [211], (5) thicker irregular elongated crystals. Combinations of these forms occur also. The detailed SEM study shows that all these formations are single crystals of extreme anisometricity, bounded by octahedral and cubic faces as well as by stepped surfaces of these forms. Surface structures such as longitudinal grooves, jagged edges, striations, pits, etc., are abundant.It is assumed that these highly non-equilibrium crystals with large surface areas were formed through rapid directed growth from highly supersaturated solutions under a diffusional regime. Such special environments arose in the ore veins as a result of tectonic shocks leading locally to a drastic volume increase and P and T decrease in the solutions.
Crystal structure of paralaurionite and its OD relationships with laurionite
Authors: Merlino S. , Pasero M. , Perchiazzi N. 
Published: December 2006

AbstractThe crystal structure of the rare lead hydroxychloride paralaurionite [PbCI(OH), monoclinic, space group C2/m,a= 10.865(4),b= 4.006(2),c= 7.233(3) Å, β = 117.24(4)°] has been refined to R = 0.062, Rw= 0.048. Its Order-Disorder (OD) character and its OD relationships with the orthorhombic polytpe of PbCI(OH), laurionite, are discussed. Laurionite and paralaurionite represent the two MDO structures within a family of OD structures built up by two different kinds of layers. The structures of paralaurionite and laurionite are compared thoroughly. The first coordination of the various atoms in the two polytypes is the same, however, remarkable differences exist in the connection between adjacent Pb-centred polyhedra.
Metamorphic fluids and gold
Authors: Neil Phillips G. 
Published: December 2006

AbstractLow-salinity fluids (T > 200°C reduced S, modest CO2) and high geothermal gradients are common to many gold deposits and provinces. In contrast, host rocks, hosting structures, depth of formation (in the crust during deposition), subsequent metamorphic overprint, alteration mineralogy and isotopic signatures can vary dramatically within single deposits or provinces. Gold deposits with co-product base metals are an exception to the above comments, and probably relate to saline fluids.The low salinity fluids inferred for major gold-only deposits are not easily explained by seawater, basinal brines, meteoric fluid or common magmatic processes. In contrast, metamorphic devolatilisation of mafic/greywacke rocks is one effective way to produce low-salinity metamorphic fluids with characteristics matching the gold fluids. Such an origin also explains the link to geothermal gradients.The transition from chlorite—albite—carbonate assemblages to amphibole-plagioclase assemblages (commonly greenschist—amphibolite facies boundary) involves considerable loss of metamorphic fluid whose composition is buffered by the mineral assemblage, and is a function of P and T. This low salinity, H2O-CO2 fluid is evolved at T > 400°C commonly carries reduced sulphur, and may contain Au complexed with this sulphur. This auriferous fluid is likely to mix with other fluid types during times of elevated temperature, especially magmatic fluids at depth, and upper crustal fluids at higher levels.Gold deposits in Archaean greenstone belts exhibit good evidence of low salinity, H2O-CO2 fluids of T > 300°C these include examples from Canada, Australia, Brazil, Zimbabwe, India, and South Africa. Turbidite-hosted (slate-belt) deposits exhibit similar evidence for such fluids but commonly with appreciable CH4; the Victoria and Juneau (Alaska) goldfields are examples. The Witwatersrand goldfields also show evidence of low salinity, H2O-CO2 fluids carrying reduced sulphur and gold, but their distribution and timing are not well established. Epithermal (sensu lato) gold deposits have evidence for low salinity fluids carrying Au and S, but are much more diverse in character than those from the previously mentioned gold provinces: this probably arises from mixing of several fluid types at high crustal levels. Together these four types of gold provinces account for over 80% of the primary gold mined to date.
Post-metamorphic gold-quartz veins from N.W. Italy: the composition and origin of the ore fluid
Authors: Yardley B. W. D. , Banks D. A. , Bottrell S. H. , Diamond L. W. 
Published: December 2006

AbstractMulti-element crush-leach analysis of H2O-CO2 inclusion fluids from a suite of six vein samples from gold-quartz veins in the Brusson district demonstrates that their solute chemistry (c. 5 wt.% NaCl equivalent) is dominated by sodium chloride with lesser amounts of calcium bicarbonate, potassium chloride and sodium bicarbonate. The samples have been analysed both for gas species (CO2, H2O, N2 and H2S) and for Na, K, Li, Rb, Ca, Mg, Sr, Ba, Fe, Mn, Zn, Pb, Cu, Al, As, B, SO42−, F, Cl, Br and I. The fluids contain appreciable H2S (>10−3 molal), which correlates with the contents of As, CO2 and B. Concentrations of many cations remain similar irrespective of wall rock, but there is evidence of leaching of Li, and possibly I, from some wall rocks. Large variations in the K-content of the fluid may result from precipitation of sericite. The bicarbonate concentrations in the fluids, estimated from charge imbalance, are substantially less than their total CO2 content when trapped as single phase fluids, indicating a low pH. Sulphate : sulphide ratios suggest relatively reducing conditions, which is consistent with Fe concentrations significantly greater than Mn.The gold-quartz veins formed as H2O-CO2 fluids of modest salinity and very uniform composition ascended from depth. Halogen ratios of the fluids are consistent with an ultimate origin for these fluids from deep-penetrating surface or connate waters although such a model requires extremely low fluid : rock ratios, to account for the hydrogen isotope composition of many similar deposits. There is as yet insufficient reference data to use halogen ratios as a rigorous test for the alternative model of an origin for the fluid by metamorphic devolatilisation.
Late-kinematic gold mineralisation during regional uplift and the role of nitrogen: an example from the La Codosera area, W. Spain
Authors: Dee S. J. , Roberts S. 
Published: December 2006

AbstractVein formation occurred throughout a deformation sequence which involved early transpressive ductile deformation through to late-kinematic transpressive brittle structures which host a series of gold prospects. Fluid inclusion data from (S1) fabric parallel veins associated with early deformation suggest that a low-salinity aqueous fluid, with a mean salinity of 6.4 wt.%, was present during peak metamorphism, Pelite mineralogy and isochores constrain peak metamorphism to the lowermost part of the upper greenschist facies at 325 to 425°C and 1.4 to 3.4 kbar.Fluid inclusion data from auriferous and barren late-kinematic quartz veins, both containing unmixing assemblages of aqueo-carbonic inclusions with low salinities of ≈2.7 wt.% NaCl equiv., indicate unmixing occurred at 300°C and 1.5 kbar.Volatiles (CO2, N2, CH4) are observed in all the late-kinematic veins. The N2 contents of veins with elevated gold grades are typically higher than those with low gold grades. N2 reaches 8.7 mole% in a vein with 0.49−4.6 p.p.m. Au compared to <1 mole% in a vein with <0.05 p.p.m. Au. The CH4 content of late kinematic veins is generally less than 1 mole% and shows no relative enrichment in mineralised veins. The generation of N2 in the mineralising fluid most likely results from interaction of fluid with the ammonium ion, NH4+, in micas and feldspars. This interaction could take place either at source, due to metamorphic devolatisation reactions, or along those structures which acted as fluid conduits due to fluid-rock interaction.
Xenocrystic richterite in an olivine-nephelinite: destabilisation and diffusion phenomena
Authors: Wagner Christiane , Mokhtari Abdelkader , Velde Danielle 
Published: December 2006

AbstractA partly destabilised Na-richterite has been found in an olivine-nephelinite from Morocco. The riehterite crystal (600 × 420 μm) is surrounded by a reaction zone (400-700 μm) of K- and Si-rich glass containing small (<50 μm) olivine (Fo80-83%) and endiopside crystals. Outwards, another zone is formed of normal magmatic minerals and circumscribes the original crystal, indicating that the destabilisation event took place at the end of the crystallisation sequence. Estimated ascent time of about 100 hours would have completely decomposed an isolated richterite crystal, which suggests that the amphibole was originally included in a xenolith. A mass-balance calculation shows that the fichterite isovolumic decomposition was accompanied by exchanges with the magma. The loss of Na from the reaction zone and the gain of AI from the magma allowed the precipitation of an analcime-rich zone observed around the destabilised amphibole and the concentration of K in the reaction zone glass. Compositional variations, Fe and Ti increase and Mg, Ca and F decrease at the richterite edge are interpreted as the result of a diffusion process. No alkali gradients are observed. The diffusion phenomenon lasted less than 100 hours and ceased to be operative at a temperature of 900-950°C i.e. just below the solidus temperature. Diffusion coefficients for the amphibole are proposed: e.g 10−9 cm2 s−1 for K2O and 10−10 for FeO at 900°C
The origins of contrasting zoning patterns in hyalophane from olivine leucitites, Northeast China
Authors: Zhang Ming , Suddaby Paul , Thompson Robert N. , Dungan Michael A. 
Published: December 2006

AbstractOlivine (ol) leucitite lavas from Northeast China contain hyalophanes with contrasting Ba-zoning patterns. The hyalophanes occur: (1) in a magmatic inclusion (DZ2n), consisting of barian-titanian phlogopite + hyalophane + leucite + sodalite, and (2) as a mantle surrounding a sanidine megacryst (DZ19). Hyalophanes contain 4.6-20.2 mol.% celsian (Cn). The DZ2n hyalophane is normally zoned with respect to Ba (decreasing Ba toward rim), whereas the hyalophane mantle of megacryst DZ19 is reversely zoned. DZ2n probably crystallised from an extensively evolved (>80 wt.% crystallisation) potassic melt derived from a primitive magma chemically similar to the host, at relatively low temperatures and pressures (e.g. T-720°C P∼2 kbar). Competition with barian-titanian phlogopite for Ba, and limited Ba supply from the residual melt are the main cause for the normal Ba zonation. Sanidine megacryst DZ19 originated as a high P-T product (e.g. T > 950°C P > 15 kbar) of an evolved leucite (lc) basanite/trachybasalt genetically related to ol-leucitites. Subsequently, it was incorporated into the host ol-leucititic magma at which point it was partially resorbed and then mantled by hyalophane. An increase in KBaaf/liq values with decreasing temperature and pressure and cocrystallisation of the hyalophane mantle with Ba-free phases may have caused the unusual reverse zonation.
The influence of secondary alteration on the ammonium content of granites, exemplified by the Rosses complex of Donegal
Authors: Hall A. 
Published: December 2006

AbstractAmmonium analyses of representative rocks from the Rosses granite complex (Ireland) and their constituent mineral show that any variation of magmatic origin has been completely obscured by pervasive hydrothermal alteration. The altered rocks are strongly enriched in the ammonium ion, most of which is held by chloritized biotite and sericitized plagioclase. The present ammonium content of the Rosses granites averages 13 ppm, but the original ammonium content of the magmas is estimated to have been less than 5 ppm. Potassium feldspars may preserve a better record of the original magmatic ammonium content than the whole rocks or the biotites.
57Fe-Mössbauer investigation on garnets from the Ivrea-Verbano Zone
Authors: Quartieri Simona , Artioli Gilberto , Deriu Antonio , Lottici Pier Paolo , Antonioli Gianni 
Published: December 2006

AbstractA Mössbauer investigation has been carried out on garnets from the Ivrea-Verbano zone and the results are compared with those obtained on the same samples by X-ray absorption spectroscopy (XAS). The problem addressed is the precise structural characterisation of the local environment of iron in garnets with Fe/Ca ratio variable between ∼3.0 and ∼18.0. Ferric iron is octahedrally coordinated and ferrous iron is in the dodecahedral site in all the samples. Mössbauer results are in agreement with those obtained by XAS and show that, at least in the compositional range of the garnets examined (0.1-0.5 calcium atoms p.f.u.), the iron environment is not significantly modified by the larger calcium cations sharing the same dodecahedral site. It is confirmed that the Mössbauer technique is more sensitive than XAS in detecting low percentages of iron, especially when the cation is present in more than one oxidation state and coordination number.
Some aspects of the crystal-chemistry of apatites
Authors: Liu Yu , Comodi Paola 
Published: December 2006

AbstractTwenty-four apatite (Ap) samples mainly from carbonatite and alkaline rocks were studied by electron microprobe, IR spectroscopy and X-ray powder diffraction. The crystal structures of six were refined using single crystal X-ray diffraction data to R = 1.7-2.5%. The generally high Si content of Ap from carbonatite and alkaline rock has been related to the presence of characteristic Si-O absorptions in IR spectra. Bands, whose intensities change with Si content, were observed at 520, 650, 930 and 1160 cm-1. The IR absorption features of v3 CO3 mode of Ap from carbonatite are different from those of v3 CO3 mode of Ap from sedimentary rock. This phenomenon is probably due to the different effects of F and OH on the CO3 substitution for PO4. The structural refinements yield more information on the CO3=PO4 substitution, which is now supported also by the geometrical evolution of the tetrahedron with increasing CO3 content: the tetrahedral size decreases and the angle distortion increases with C-content. It is likely that the triangular planar CO3 group is disordered on the four faces of PO43-tetrahedron. It was observed also that Ap from early-stage carbonatite is OH-dominant with considerable LREE, Si, CO3 and negligible Mn, Fe, Mg, K, S and C1 contents. They have high Sr/Mn, Si/S and C/S ratios.