High resolution X-ray computed tomography studies of Grasberg porphyry Cu-Au ores,Papua, Indonesia     

J. Richard Kyle  Alison S. Mote  Richard A. Ketcham 《Mineralium Deposita》2008,43(5):519-532

High-resolution X-ray computed tomography (HRXCT) provides unique information of the geological and metallurgical significance for gold and related ore minerals in the supergiant Grasberg porphyry Cu–Au deposit. Digital radiographs have proved to be an effective means of screening samples for the presence of gold for HRXCT studies. Digital radiograph effectiveness is limited by the thickness of samples (typically to ≤2 cm), as well as the associated minerals. Thus, preselecting samples for gold studies using HRXCT is most effective using digital radiographs combined with assay information. Differentiating between metallic mineral grains with relatively small differences in density, e.g., bornite (5.1 g/cm³) from chalcopyrite (4.2 g/cm³), is relatively straightforward for isolated monominerallic grains or composites in a similar lower-density matrix, but difficulties are encountered with the interpretation of typical intergrown ore minerals. X-ray beam-hardening artifacts lead to inconsistency in attenuation determination, both within and among slice images, complicating quantitative processing. However, differentiation of chalcopyrite and bornite has been successful in smaller-diameter (≤22-mm) cores of Grasberg ores. Small-diameter (≤10 mm) cores of the Grasberg stockwork Cu–Au ore were analyzed using HRXCT methods scanned at the minimum spacing currently available (7.5 μm), and data reduction protocols using the Blob3D program were modified to improve the quantification of grain sizes and shapes. Grains as small as 6.5 μm have been identified. All of these grains are in direct contact with chalcopyrite, providing support for gold distribution in porphyry copper systems being a result of exsolution from copper sulfides. HRXCT scanning (±digital radiography) precisely defines the in situ location of mineral grains of interest within a sample, which then can be studied in conventional petrographic sections, and other types of analytical studies conducted, e.g., gold trace element geochemistry.  相似文献   

Occurrence and turnover of DMSP and DMS in deep waters of the Ross Sea,Antarctica     

Alison N. Rellinger  Ronald P. Kiene  Daniela A. del Valle  David J. Kieber  Doris Slezak  Hyakubun Harada  John Bisgrove  Jordan Brinkley 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(5):686-702

High concentrations of the phytoplankton metabolite dimethylsulfoniopropionate (DMSP) and its degradation product dimethylsulfide (DMS) are associated with blooms of Phaeocystis antarctica in the Ross Sea, Antarctica. Episodic and rapid vertical export of Phaeocystis biomass to deep water has been reported for the Ross Sea, therefore we examined the distribution and microbial consumption rates of DMSP and DMS throughout the sub-euphotic water column. Total DMSP (dissolved+particulate; DMSPt) was present at 0.5–22 nM at depths between 70 and 690 m during both the early bloom (November) and the late bloom (January). Sub-euphotic peaks of DMSP were sometimes associated with mid-water temperature maxima, and elevated DMSP below 70 m was found mainly in water masses characterized as Modified Circumpolar Deep Water or Antarctic Shelf Water. Overall, 50–94% of the integrated water-column DMSPt was found below the euphotic zone. At one station during the early bloom, local maxima of DMSPt (14 nM) and DMS (20 nM) were observed between 113 and 240 m and these maxima corresponded with high chlorophyll a concentrations, P. antarctica cell numbers, and Fv/Fm (the quantum yield of photosystem II). During the late bloom, a sub-euphotic maximum of DMSPt (15.8 nM) at 250 m cooccurred with peaks of chlorophyll a concentration, DMSP lyase activity, bacterial production and dissolved DMSP consumption rates. DMSP turnover contributed ～12% of the bacterial carbon demand between 200 and 400 m. DMS concentrations peaked at 286 m but the maximum concentration (0.42 nM) was far lower than observed during the early bloom, probably because of relatively rapid biological consumption of DMS (1–3 turnovers per day) which, in turn, contributed to elevated dissolved dimethylsulfoxide (DMSO) concentrations. Relatively stable DMSPt distributions at some sites suggest that rapid sinking of Phaeocystis biomass is probably not the major mechanism responsible for mesopelagic DMSP accumulations. Rather, subduction of near-surface water masses, lateral advective transport or trapping of slowly sinking P. antarctica biomass in intermediate water masses are more likely mechanisms. We found that a culture of P. antarctica maintained cellular integrity during 34 days of darkness, therefore the presence of intact cells (and DMSP) at depth can be explained even under a slow sinking/advection scenario. Whatever the mechanism, the large pools of DMSP and DMS below the euphotic zone suggest that export exerts a control on potential DMS emission from the surface waters of the Ross Sea.  相似文献   

Thinking Space: Ten Truths about Australia's Rush to Mine and the Mining Workforce     

Alison McIntosh 《The Australian geographer》2012,43(4):331-337

  相似文献   

Climate change scenarios and long term projections     

Warwick J. McKibbin  David Pearce  Alison Stegman 《Climatic change》2009,97(1-2):23-47

Predictions of future temperature increases depend critically on the projections of future greenhouse gas emissions. Yet there is a vigorous debate about how these projections should be undertaken. This paper explores a range of methodological issues surrounding projecting greenhouse emissions over the next century. It points out that understanding future emissions requires a framework that deals with the sources of economic growth and allows for endogenous structural change. It also explores the role of convergence assumptions and the “Castles and Henderson Critique” of the Special Report on Emission Scenarios (SRES) regarding use of Market Exchange Rates (MERs) rather than Purchasing Power Parity exchange rates (PPPs) to benchmark income differentials in the world economy. In the G-Cubed multi-country model, we show that emission projections based on convergence assumptions defined in MER terms, are 40% higher by 2100 than emissions generated using a PPP comparison of income differentials between economies. We support the argument presented by Castles and Henderson, that the use of MERs in the SRES represents a serious analytical error. It is not clear what this means for the SRES projections because the SRES is not transparent in its assumptions. In the G-Cubed model, the error leads to considerably higher emissions projections.  相似文献   

Spin vectors in the Koronis family: II. Additional clustered spins, and one stray     

Stephen M. Slivan  Richard P. Binzel  Mikko Kaasalainen  Andrew N. Hock  Alison J. Klesman  Laura J. Eckelman  Robert D. Stephens 《Icarus》2009,200(2):514-530

We recorded 101 new rotation lightcurves of five Koronis family members, and then combined the new observations with previous data to determine the objects' sidereal rotation periods, spin vector orientations, and model shape solutions. The observing program was tailored specifically for spin vector analyses by determining single-apparition Lumme–Bowell solar phase coefficients, and by measuring synodic rotation periods precisely enough to unambiguously count the rotations between two consecutive oppositions, which is a prerequisite for identifying the correct sidereal period. The new data make possible first pole and shape determinations for (263) Dresda, (462) Eriphyla, and (1289) Kutaïssi, and they improve the models for (277) Elvira and (534) Nassovia, two objects previously studied by Slivan et al. [Slivan, S.M., Binzel, R.P., Crespo da Silva, L.D., Kaasalainen, M., Lyndaker, M.M., Kr?o, M., 2003. Icarus 162, 285–307]. Our results increase the number of Koronis family spin vectors reported in the literature to fourteen, a sample which now includes the seven largest family members. The spin properties of Eriphyla (rotation period , spin vector obliquity ε=51°) and Kutaïssi (P=3.62 h, ε=165°) are consistent with the markedly nonrandom distribution reported by Slivan [Slivan, S.M., 2002. Nature 419, 49–51], and explained by Vokrouhlický et al. [Vokrouhlický, D., Nesvorný, D., Bottke, W.F., 2003. Nature 425, 147–151] as the result of the effects of thermal “YORP” torques combined with solar and planetary gravitational torques. Dresda (P=16.81 h, ε=16°) is the first prograde Koronis member whose spin obliquity and spin rate significantly differ from the clustered spin properties previously found for other prograde Koronis members; nevertheless, its spin vector is consistent with several of the spin evolution possibilities that were identified in the YORP modeling.  相似文献   

Polarization at 4430Å     

Alison Kelly 《Astrophysics and Space Science》1971,13(1):211-218

The wavelength dependence of polarization in the region of the interstellar absorption band at 4430 Å is investigated theoretically by variation of the relevant parameters over a wide range. Comparison is made with observations, and the suggestion that the 4430 Å band is produced by impurities in a silicate matrix is found to be not inconsistent.  相似文献   

Histopathological observations on liver,kidney and gonad of plaice (Pleuronectes platessa) taken from the Mersey estuary     

Simpson MG  Walker P  Helm A  Leah R 《Marine environmental research》2002,54(3-5):543-546

The Mersey estuary is the most contaminated estuary in British waters. Detailed studies are underway on the pathology of flounder (Platichthys flesus) from the Mersey and on flounder from the nearby, but less contaminated, Dee estuary. Flounder breed offshore but spend a lot of time in the estuaries, penetrating into freshwater. These flatfish are in close contact with sediments and will be exposed to exenobiotic stored in the sediments. Plaice (Pleuronectes platessa) are flatfish which enter the Mersey with the tidal flow but spend less time in the estuary than flounder and are less likely to show evidence of pollutant exposure. Over 20 plaice were collected from the Mersey. Samples of the liver, kidney and gonad were fixed in 10% formal saline, processed into paraffin wax and 5 microm sections cut and stained with haematoxylin and eosin. Liver changes consisted of variable amounts of glycogen/lipid storage product, minor perivenular and perivascular fibrosis, and helminth parasitisation. No tumours or foci of cellular alteration, necrosis and inflammation were seen. In the gonad only changes consistent with normal gonadal cycling was seen. These studies provide evidence that plaice show little or no evidence of toxic pathological damage resulting from their stay in the estuary.  相似文献   

The pressure and temperature stability limits of lawsonite: implications for H2O recycling in subduction zones     

Alison R. Pawley 《Contributions to Mineralogy and Petrology》1994,118(1):99-108

The stability relations of lawsonite, CaAl₂Si₂O₇(OH)₂H₂O, have been investigated at pressures of 6 to 14 GPa and temperatures of 740 to 1150°C in a multi-anvil apparatus. Experiments used the bulk composition lawsonite+H₂O to determine the maximum stability of lawsonite. Lawsonite is stable on its own bulk composition to a pressure of 13.5 GPa at 800°C, and between 6.5 and 12 GPa at 1000°C. Its composition does not change with pressure or temperature. All lawsonite reactions have grossular, vapour and two other phases in the system Al₂O₃-SiO₂-H₂O (ASH) on their high-temperature side. A Schreinemakers analysis of the ASH phases was used to relate the reactions to each other. At the lowest pressures studied lawsonite breaks down to grossular+kyanite+coesite+vapour in a reaction passing through 980°C at 6 GPa and 1070°C at 9 GPa. Above 9 GPa the reactions coesite=stishovite and kyanite+vapour=topaz-OH are crossed. The maximum thermal stability of lawsonite is at 1080°C, at 9.4 GPa. At higher pressures the lawsonite breakdown reactions have negative slopes. The reaction lawsonite=grossular+topaz-OH+stishovite+vapour passes through 1070°C at 10 GPa and 1010°C at 12 GPa. At 14 GPa, 740–840°C, lawsonite is unstable relative to the assemblage grossular+diaspore+vapour+a hydrous phase with an Al:Si ratio of 1:1. Oxide totals in electron microprobe analyses suggest that the composition of this phase is AlSiO₃(OH). Two experiments on the bulk composition lawsonite+pyrope [Mg₃Al₂Si₃O₁₂] show that at 10 GPa the reaction lawsonite=Gr-Py_ss+topaz-OH+stishovite+vapour is displaced down temperature from the end-member reaction by 200°C for a garnet composition of Gr₂₀Py₈₀. Calculations suggest similar temperature displacements for reaction between lawsonite and Gr-Py-Alm garnets of compositions likely to occur in high-pressure eclogites. Temperatures in subduction zones remain relatively low to considerable depth, and therefore slab P-T paths can be within the stability field of lawsonite from the conditions of its crystallisation in blueschists and eclogites, up to pressures of at least 10 GPa. Lawsonite contains 11.5 wt% H₂O, which when released may trigger partial melting of the slab or mantle, or be incorporated in hydrous phases such as the aluminosilicates synthesised here. These phases may then transport H₂O to an even greater depth in the mantle.  相似文献   

Factors that influence water exchange in spring-fed tidal canals     

Alison M. Fox  William T. Haller  Kurt D. Getsinger 《Estuaries and Coasts》1991,14(4):404-413

Environmental factors that influenced the rates of water exchange in a series of tidal, dead-end canals in Crystal River, Florida, were investigated by measuring the rates of dilution of the fluorescent dye Rhodamine WT. Water temperature regime was the most influential of these factors, with type of tidal cycle (spring or neap) and density of submersed vegetation (dominated byHydrilla verticillata) only affecting dye dilution rates in winter treatments. Dye half-lives were shortest in the summer (12–24 h), longest in the fall and spring (60–120 h), and most sensitive to water temperature patterns in the winter (26–60 h). These data provide useful information relating to the timing of hydrilla management using aquatic herbicides in spring-fed tidal systems. A mechanism is proposed that relates the canal water temperatures to tidal water movement and outputs from the adjacent Three Sisters Springs.  相似文献   

A new approach to detecting vegetation and land-use change using high-resolution lipid biomarker records in stalagmites   总被引：2，自引：0，他引：2  

Alison J. Blyth  Asfawossen Asrat  Andy Baker  Pauline Gulliver  Melanie J. Leng  Dominique Genty 《Quaternary Research》2007,68(3):314-324

A hundred-year stalagmite lipid biomarker record from Mechara, southeastern Ethiopia, is presented. The record has been recovered at a 10-yr temporal resolution, marking the first time this has been achieved in stalagmite biomarker work and providing the first opportunity to investigate the relationship between stalagmite lipid records and hydrological transport lags, a vital issue in interpreting palaeoenvironmental signals. Preserved plant-derived n-alkanes and n-alkanols show clear changes in composition over time, relating to known land-use changes in the area, particularly the expansion of agriculture in the early twentieth century. The level of environmental detail provided by this technique, combined with the long-term chronological framework offered by stalagmites, holds significant promise for the investigation of early human environments and their associated climatic and anthropogenic controls.  相似文献