The Miduk porphyry Cu deposit,Kerman, Iran: A geochemical analysis of the potassic zone including halogen element systematics related to Cu mineralization processes

Miduk hypogene and supergene porphyry Cu–Mo mineralization occurs within the Miocene porphyritic quartz–diorite and host Eocene plagioclase–hornblende phyric andesitic pyroclastic and flow sequence. Both the host rocks were extensively altered by hydrothermal fluids to dominantly potassic, phyllic, and argillic with interstitial to distal propylitic types.     

Iron(III) accumulations in inland saline waterways,Hunter Valley,Australia: Mineralogy,micromorphology and pore-water geochemistry

Discharge of Fe(II)-rich groundwaters into surface-waters results in the accumulation of Fe(III)-minerals in salinized sand-bed waterways of the Hunter Valley, Australia. The objective of this study was to characterise the mineralogy, micromorphology and pore-water geochemistry of these Fe(III) accumulations. Pore-waters had a circumneutral pH (6.2–7.2), were sub-oxic to oxic (Eh 59–453 mV), and had dissolved Fe(II) concentrations up to 81.6 mg L⁻¹. X-ray diffraction (XRD) on natural and acid-ammonium-oxalate (AAO) extracted samples indicated a dominance of 2-line ferrihydrite in most samples, with lesser amounts of goethite, lepidocrocite, quartz, and alumino-silicate clays. The majority of Fe in the samples was bound in the AAO extractable fraction (Fe^Ox) relative to the Na-dithionite extractable fraction (Fe^Di), with generally high Fe^Ox:Fe^Di ratios (0.52–0.92). The presence of nano-crystalline 2-line ferrihydrite (Fe₅HO₃·4H₂O) with lesser amounts of goethite (α-FeOOH) was confirmed by scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (EDX), and transmission electron microscopy (TEM) coupled with selected area electron diffraction (SAED). In addition, it was found that lepidocrocite (γ-FeOOH), which occurred as nanoparticles as little as ∼5 lattice spacings thick perpendicular to the (0 2 0) lattice plane, was also present in the studied Fe(III) deposits. Overall, the results highlight the complex variability in the crystallinity and particle-size of Fe(III)-minerals which form via oxidation of Fe(II)-rich groundwaters in sand-bed streams. This variability may be attributed to: (1) divergent precipitation conditions influencing the Fe(II) oxidation rate and the associated supply and hydrolysis of the Fe(III) ion, (2) the effect of interfering compounds, and (3) the influence of bacteria, especially Leptothrix ochracea.     

Cretaceous and Tertiary terrane accretion in the Cordillera Occidental of the Andes of Ecuador

New field, geochronological, geochemical and biostratigraphical data indicate that the central and northern parts of the Cordillera Occidental of the Andes of Ecuador comprise two terranes. The older (Pallatanga) terrane consists of an early to late (?) Cretaceous oceanic plateau suite, late Cretaceous marine turbidites derived from an unknown basaltic to andesitic volcanic source, and a tectonic mélange of probable late Cretaceous age. The younger (Macuchi) terrane consists of a volcanosedimentary island arc sequence, derived from a basaltic to andesitic source. A previously unidentified, regionally important dextral shear zone named the Chimbo-Toachi shear zone separates the two terranes. Regional evidence suggests that the Pallatanga terrane was accreted to the continental margin (the already accreted Cordillera Real) in Campanian times, producing a tectonic mélange in the suture zone. The Macuchi terrane was accreted to the Pallatanga terrane along the Chimbo-Toachi shear zone during the late Eocene, probably in a dextral shear regime. The correlation of Cretaceous rocks and accretionary events in the Cordillera Occidental of Ecuador and Colombia remains problematical, but the late Eocene event is recognised along the northern Andean margin.     

Microphytobenthos: The ecological role of the “secret garden” of unvegetated,shallow-water marine habitats. II. role in sediment stability and shallow-water food webs

The microphytobenthos form an important component of all shallow-water ecosystems where enough light reaches the sediment surface to support appreciable primary production. Although less conspicuous than macroalgae or vascular plants, the microphytobenthos can contribute significantly to primary production and can modify habitat characteristics. The microphytobenthos alter sediment properties (e.g., erodibility) both directly, in the extreme forming a mat or scum on the sediment surface, and indirectly by modifying the activities of benthic infauna (e.g., pelletization, burrowing, tube building, and sediment tracking). Carbon dioxide fixed by the microphytobenthos supports higher, grazing trophic levels. These include deposit-feeding and suspension-feeding macrofauna as well as meiofauna and microfauna. Quantitative relations between the feeding and growth rates of macrofauna and the abundance of microphytobenthos and suspended organic matter (i.e., functional responses) are reviewed. Given the current state of knowledge of the direct and indirect interactions involving trophic dynamics, sediment properties, and benthic microalgae, we argue for reductionist studies of particular interactions as distinct entities. This is a prerequisite for the emergence of a comprehensive picture of unvegetated ecosystems and the ability to predict their responses to man’s activities. *** DIRECT SUPPORT *** A01BY074 00005     

Some applications of paleoecology to the management of tidal marshes

The shallow-water habitat is under increasing environmental pressures from accelerated sea-level rise and continual urban sprawl and will require well-informed management decisions to maintain its health into the future. One of the keys to the effective management of the shallow-water habitat is understanding the processes responsible for its development. Paleoecology has the potential to provide much insight into the development of the system, particularly when the impacts of accelerated sea-level rise on vegetation and sedimentation dynamics in tidal marshes is being considered. For example, a paleoecological comparison of tidal salt marshes to tidal freshwater marshes shows that rates of development will dictate the system's response to accelerated sea-level rise, with tidal freshwater marshes capable of transgressing landward more rapidly than their saline counterparts. Such information implies that management of the adjacent uplands is as important to the future of the system as management of the marsh itself. Therefore, it is important to consult paleoecological research when management strategies are being considered. *** DIRECT SUPPORT *** A01BY074 00010     

On the breakdown of zircon upon “dry” thermal annealing

Zircon samples without and with secondary chemical alteration from diverse sources were subjected to heat treatment at 1400 °C for 96 h. Resulting new phases and textures suggest that decomposition of zircon into component oxides occurred in all experiments to various degrees. The crucible material was found to have a strong influence on the extent of breakdown, especially in the case of altered starting materials. In this study the progressive stages of the breakdown of zircon grains are described. The factors that may govern the decomposition are discussed, including radiation damage, secondary alteration and external reaction conditions (sample container, atmosphere). Alumina crucibles should generally be avoided in dry annealing of zircon, to minimise uncontrolled breakdown into oxides.     

A chemical and thermodynamic model of oil generation in hydrocarbon source rocks

Thermodynamic calculations and Gibbs free energy minimization computer experiments strongly support the hypothesis that kerogen maturation and oil generation are inevitable consequences of oxidation/reduction disproportionation reactions caused by prograde metamorphism of hydrocarbon source rocks with increasing depth of burial.These experiments indicate that oxygen and hydrogen are conserved in the process.Accordingly, if water is stable and present in the source rock at temperatures ?25 but ?100 °C along a typical US Gulf Coast geotherm, immature (reduced) kerogen with a given atomic hydrogen to carbon ratio (H/C) melts incongruently with increasing temperature and depth of burial to produce a metastable equilibrium phase assemblage consisting of naphthenic/biomarker-rich crude oil, a type-II/III kerogen with an atomic hydrogen/carbon ratio (H/C) of ∼1, and water. Hence, this incongruent melting process promotes diagenetic reaction of detritus in the source rock to form authigenic mineral assemblages.However, in the water-absent region of the system CHO (which is extensive), any water initially present or subsequently entering the source rock is consumed by reaction with the most mature kerogen with the lowest H/C it encounters to form CO₂ gas and a new kerogen with higher H/C and O/C, both of which are in metastable equilibrium with one another.This hydrolytic disproportionation process progressively increases both the concentration of the solute in the aqueous phase, and the oil generation potential of the source rock; i.e., the new kerogen can then produce more crude oil.Petroleum is generated with increasing temperature and depth of burial of hydrocarbon source rocks in which water is not stable in the system CHO by a series of irreversible disproportionation reactions in which kerogens with higher (H/C)s melt incongruently to produce metastable equilibrium assemblages consisting of crude oil, CO₂ gas, and a more mature (oxidized) kerogen with a lower H/C which in turn melts incongruently with further burial to produce more crude oil, CO₂ gas, and a kerogen with a lower H/C and so forth.The petroleum generated in the process progresses from heavy naphthenic crude oils at low temperatures to mature petroleum at ∼150 °C. For example, the results of Computer Experiment 27 (see below) indicate that the overall incongruent melting reaction in the water-absent region of the system C-H-O at 150 °C and a depth of ∼4.3 km of an immature type-II/III kerogen with a bulk composition represented by C₂₉₂H₂₈₈O_12(c) to produce a mature (oxidized) kerogen represented by C₁₂₈H₆₈O_7(c), together with a typical crude oil with an average metastable equilibrium composition corresponding to C_8.8H_16.9 (C_8.8H_16.9(l)) and CO₂ gas (CO_2(g)) can be described by writing

(A)     

A morphological, sedimentological and geophysical investigation of the Woore Moraine, Shropshire, England

The Bar Hill-Whitchurch-Wrexham Morainic Complex is a large-scale glacial landform thought to represent either the maximum extent or the re-advance of the British-Irish Ice Sheet during the Late Devensian. The origin of the moraine remains uncertain as its key characteristics have not been studied in detail due to a lack of exposures from which its large-scale structure can be determined. The development of new technologies has enabled detailed examination of the topography and internal structure of such large-scale landforms. This paper describes a multi-disciplinary approach involving digital geomorphological mapping using enhanced resolution NextMAP™ digital surface models, geophysical imaging (electrical resistivity tomography) and conventional sedimentological analyses. This combination of techniques is useful for elucidating the origin of a large glacial landform in a region of poor exposure. Digital elevation models such as NextMAP™ offer an efficient and accurate method for landform-mapping, whilst electrical resistivity tomography was able to map the major constituent sediments of the moraine, which had in turn been identified in the single exposure available. Additional geophysical techniques should however be applied to provide further structural data and thereby enable a more detailed interpretation of the moraine's internal structure. Preliminary findings indicate that the moraine is a glaciotectonic landform composed of diamicton and glaciofluvial sediments, an origin consistent with recent suggestions that the Cheshire Plain contained an active ice lobe during the last glacial maximum.     

ISIS IR: The first infrared fibre-fed spectrograph

ISIS IR is the first attempt to use fibre optics for near infrared spectroscopy (1.8m). It is a field spectrograph (2D spectroscopy), and can work at various resolving powers (up to 25000). It can be transported anywhere, and soon it will be used at CFHT with one NICMOS 3-based camera.Département d'Astrophysique Extragalactique et de Cosmologie