Incursion of meteoric waters into the ductile regime in an active orogen

Rapid tectonic uplift on the Alpine Fault, New Zealand, elevates topography, regional geothermal gradients, and the depth to the brittle ductile transition, and drives fluid flow that influences deformation and mineralisation within the orogen. Oxygen and hydrogen stable isotopes, fluid inclusion and Fourier Transform Infrared (FT-IR) analyses of quartz from veins which formed at a wide range of depths, temperatures and deformation regimes identify fluid sources and the depth of penetration of meteoric waters. Most veins formed under brittle conditions and with isotope signatures (δ18OH2O = −9.0 to +8.7‰VSMOW and ‰ ) indicative of progressively rock-equilibrated meteoric waters. Two generations of quartz veins that post-date mylonitic foliation but endured further ductile deformation, and hence formation below the brittle to ductile transition zone ( depth), preserve included hydrothermal fluids with values between −84 and ‰ , indicating formation from meteoric waters. FT-IR analyses of these veins show no evidence of structural hydrogen release, precluding this as a source of low values. In contrast, the oxygen isotopic signal of these fluids has almost completely equilibrated with host rocks (δ18OH2O = +2.3 to +8.7‰). These data show that meteoric waters dominate the fluid phase in the rocks, and there is no stable isotopic requirement for the presence of metamorphic fluids during the precipitation of ductilely deformed quartz veins. This requires the penetration during orogenesis of meteoric waters into and possibly below the brittle to ductile transition zone

A hybrid neural network/rule-based technique for on-line gesture and hand-written character recognition

A technique is presented which combines rule-based and neural network pattern recognition methods in an integrated system in order to perform learning and recognition of hand-written characters and gestures in realtime. The GesRec system is introduced which provides a framework for data acquisition, training, recognition, and gesture-to-speech transcription in a Windows environment. A recognition accuracy of 92.5% was obtained for the hybrid system, compared to 89.6% for the neural network only and 82.7% for rules only. Training and recognition times are given for an able-bodied and a disabled user

A hybrid neural network/rule-based technique for on-line gesture and hand-written character recognition

A technique is presented which combines rule-based and neural network pattern recognition methods in an integrated system in order to perform learning and recognition of hand-written characters and gestures in realtime. The GesRec system is introduced which provides a framework for data acquisition, training, recognition, and gesture-to-speech transcription in a Windows environment. A recognition accuracy of 92.5% was obtained for the hybrid system, compared to 89.6% for the neural network only and 82.7% for rules only. Training and recognition times are given for an able-bodied and a disabled user

Potential sulfur sources for submarine caldera associated mineralization in north-west Wales

In north-west Wales vein mineralization is hosted by the Ordovician Snowdon Volcanic Group, and older sedimentary rocks. Mineralization typically consists of narrow, steeply dipping base metal veins, stockworks, disseminated sulfides and quartz-sulfide cemented breccia zones. Sulfur isotope analyses were carried out on vein sulfides and country rocks to elucidate ore sulfur source/s. The volcanic-hosted and the majority of sedimentary rock-hosted sulfides have delta S-34 from +9.1 to +22.3 parts per thousand, with mean vein delta S-34 of +12.2 +/- 3.7 parts per thousand. The Snowdon Volcanic Group is generally considered to represent a reservoir of isotopically heavy sulphur with mean delta S-34 of +11.7 parts per thousand +/- 4.5 parts per thousand. The sedimentary rock diagenetic sulfides are typically heavier. These values are thus compatible with a typical volcanogenic massive sulfide system, with sulfur originating from a combination of leaching of volcanic host lithologies, and reduction of Ordovician seawater. The delta S-34 ore sulfides from around Snowdon are comparable to those found in Ordovician age volcanogenic massive sulfide deposits globally

Aspects of the geochemistry of zinc: a journey to sphalerite

Our journey to sphalerite begins with a review of the occurrence and behavior of Zn in a wide spectrum of natural fluids. Measured Zn concentrations in crustal fluids vary over at least six orders of magnitude, from around 0.01 to 20,000 ppm (2 wt %). Whist water-rock interaction and boiling influence Zn concentration, the origin of the fluids and in particular their temperature, pH and ligand concentrations are major factors in their capacity to transport Zn. However, in contrast to previous reviews, our compilation shows no significant overall correlation between Zn and Cl concentrations. Fluid chemistry (mainly mCl-, mΣS, pH and fO2) and temperature, and the resultant speciation determine the solubility of Zn and control precipitation of sphalerite. Bisulphide complexes only dominate under relatively high ΣS, low Cl-, and high pH, and are favoured by low temperatures, in most natural systems though chloride complexes dominate. The limited oxidation state of Zn leads to a narrow range of Zn isotope variation in ore systems, with a mean of all published ore-related δ66Zn data around 0.2 ± 0.3 ‰. Nonetheless, kinetic fractionation of Zn isotopes leads to enrichment in 66Zn in residual fluids, following precipitation of sphalerite from hydrothermal fluids. This has resulted, in a wide variety of systems, in a potentially useful exploration vector to feeder zones. We describe the basic crystallography of sphalerite, and show that commonly occurring layered sphalerite, in particular the colloform texture, has the ability to record the extraordinary dynamism of the ore depositional environment through careful petrographic studies followed by in situ laser S isotope and EMPA trace element analyses. Our journey ends in the Galmoy deposit in the Irish orefield, where we show that three distinct ore sulphide-precipitating events and the full isotopic spectrum of the dual ore sulphide source of the Irish-type deposits are recorded across a 2 cm colloform specimen

Synthesis and properties of complexes of vanadium(V) oxide trichloride with nitrogen- and oxygen-donor ligands

Intensely coloured, extremely moisture sensitive complexes [VOCl3(L)] (L = pyridine, quinoline, Ph3PO, Ph3AsO, pyridine N-oxide), [VOCl3(L)(2)] (L=pyridine, Me3PO, pyridine N-oxide), [VOCl3(L-L)] [L-L = 2,2'-bipyridyl, 1,10-phenanthroline, Ph2P(O)CH2P(O)Ph-2, MeOCH2CH2OMe, 15-crown-5 or Me2NCH2CH2NMe2] and [Cl3OV(mu-L-L)VOCl3] [L-L=18crown-6 or Ph2P(O)CH2P(O)Ph-2] have been prepared from VOCl3 and the appropriate ligands in dichloromethane solution. These constitute the first extended series of complexes of vanadium(V) with neutral donor ligands. They have been fully characterised by analysis, IR, UV/Visible and multinuclear (H-1, P-31, V-51) NMR spectroscopy, and their solution behaviour probed as a function of temperature using 51V NMR spectroscopy. Reducing ligands including phosphanes, arsanes, thio- and selenoethers immediately reduce VOC13 to give V-IV or V-III species. Oxygen atom transfer reactions of some of the complexes with Ph3P, Ph3As, Me2Se and Bu2S, leading to the corresponding ligand oxides are also described

Growth controls in colloform sulfide textures

Colloform textures have been described from many of the world's sulfide ore deposits and involve formation of distinct microcrystalline layers. These textures provide information related to sequential stages of ore formation and yet their mechanism and controls of growth are still poorly understood. Samples of colloform sphalerite from the Galmoy Zn-Pb ore body, Ireland and colloform pyrite from Greens Creek, Alaska have been investigated using crystallographic, in-situ S isotope and trace element chemistry analysis. Electron backscatter diffraction (EBSD) results indicate the crystal preferred orientation (CPO) of discrete microcrystalline colloform layers abruptly switch between <100>, <110> and <111> orientations in all of the samples investigated. Examination of the same layers in the Galmoy colloform textures (sphalerite) using in-situ laser S isotope analysis reveals equally striking and abrupt changes in δ³⁴S signature between end-member bacteriogenic (-25‰) and hydrothermal (+10‰) sources. However, there is no correlation between shifting CPO and S isotope signature at Galmoy. The Greens Creek colloform textures (pyrite) preserve a similar, if less dramatic, variation in δ³⁴S signature (-40‰ to -30‰) but again there is no correlation between changing δ³⁴S signature and CPO in discrete layers. Trace element analysis of both suites of colloform samples reveals major changes in trace element sequestration. The variation in trace element abundance however appears to correlate with changes in δ³⁴S signature rather than CPO. At Galmoy Cd and Cl rich layers appear to correspond with a hydrothermal sulfur signature while Sb sequestration at Greens Creek corresponds with a relatively heavy bacteriogenic δ³⁴S (-30‰) signature. While factors such as bacteria induced mineralisation cannot be ruled out, the temperature of the ore forming environment suggests this process is likely to be restricted and therefore not the primary control on CPO changes. In the absence of evidence for alternative mechanisms it is suggested that the most likely factors influencing CPO changes within discrete layers in the colloform textures are temperature and degree of supersaturation

Understanding the fate of iron in a modern temperate estuary: Leirarvogur, Iceland

Fluvial dissolved Fe concentrations decrease upon mixing with seawater, resulting in the formation of Fe-floccules. However, a clear understanding of the fate of these floccules has yet to be established. Assessing how tidal processes affect the formation of Fe-colloids in the Leirárvogur estuary, SW Iceland, is an important step in understanding the formation and potential deposition of estuarine Fe-rich minerals within this estuarine system. The Leirárvogur estuary drains predominately Fe-rich basalt, increasing the likelihood of detecting changes in Fe-phases. Fluvial waters and local lake waters that drain into the estuary were compared and the effects of seasonal changes were considered, in an attempt to understand how varying end-members and external factors play a role in Fe-rich mineral formation. Aqueous and colloidal Fe concentrations were found to be greater towards the head of the Leirárvogur estuary, suggesting that potential Fe-rich minerals and complexes are forming at sites of fluvial input. Increasing suspended colloidal Fe towards the estuary mouth suggests that Fe-colloids are readily transported seaward

Equivalent diffusion coefficient and equivalent diffusion accessible porosity of a stratified porous medium

Diffusion is an important transport process in low permeability media, which play an important role in contamination and remediation of natural environments. The calculation of equivalent diffusion parameters has however not been extensively explored. In this paper, expressions of the equivalent diffusion coefficient and the equivalent diffusion accessible porosity normal to the layering in a layered porous medium are derived based on analytical solutions of the diffusion equation. The expressions show that the equivalent diffusion coefficient changes with time. It is equal to the power average with p = -0.5 for small times and converges to the harmonic average for large times. The equivalent diffusion accessible porosity is the harmonic average of the porosities of the individual layers for all times. The expressions are verified numerically for several test cases