Platinum-group element distribution in base-metal sulfides of the Merensky Reef from the eastern and western Bushveld Complex, South Africa

Base-metal sulfides in magmatic Ni-Cu-PGE deposits are important carriers of platinum-group elements (PGE). The distribution and concentrations of PGE in pentlandite, pyrrhotite, chalcopyrite, and pyrite were determined in samples from the mineralized portion of four Merensky Reef intersections from the eastern and western Bushveld Complex. Electron microprobe analysis was used for major elements, and in situ laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) for trace elements (PGE, Ag, and Au). Whole rock trace element analyses were performed on representative samples to obtain mineralogical balances. In Merensky Reef samples from the western Bushveld, both Pt and Pd are mainly concentrated in the upper chromitite stringer and its immediate vicinity. Samples from the eastern Bushveld reveal more complex distribution patterns. In situ LA-ICP-MS analyses of PGE in sulfides reveal that pentlandite carries distinctly elevated PGE contents, whereas pyrrhotite and chalcopyrite only contain very low PGE concentrations. Pentlandite is the principal host of Pd and Rh in the ores. Palladium and Rh concentrations in pentlandite reach up to 700 and 130 ppm, respectively, in the samples from the eastern Bushveld, and up to 1,750 ppm Pd and up to 1,000 ppm Rh in samples from the western Bushveld. Only traces of Pt are present in the base-metal sulfides (BMS). Pyrrhotite contains significant though generally low amounts of Ru, Os, and Ir, but hardly any Pd or Rh. Chalcopyrite contains most of the Ag but carries only extremely low PGE concentrations. Mass balance calculations performed on the Merensky Reef samples reveal that in general, pentlandite in the feldspathic pyroxenite and the pegmatoidal feldspathic pyroxenite hosts up to 100 % of the Pd and Rh and smaller amounts (10–40 %) of the Os, Ir, and Ru. Chalcopyrite and pyrrhotite usually contain less than 10 % of the whole rock PGE. The remaining PGE concentrations, and especially most of the Pt (up to 100 %), are present in the form of discrete platinum-group minerals such as cooperite/braggite, sperrylite, moncheite, and isoferroplatinum. Distribution patterns of whole rock Cu, Ni, and S versus whole rock Pd and Pt show commonly distinct offsets. The general sequence of “offset patterns” of PGE and BMS maxima, in the order from bottom to top, is Pd in pentlandite?→?Pd in whole rock?→?(Cu, Ni, and S). The relationship is not that straightforward in general; some of the reef sequences studied only partially show similar trends or are more complex. In general, however, the highest Pd concentrations in pentlandite appear to be related to the earliest, volumetrically rather small sulfide liquids at the base of the Merensky Reef sequence. A possible explanation for the offset patterns may be Rayleigh fractionation.     

The stable aryl hydrocarbon receptor agonist potency of United Kingdom Continental Shelf (UKCS) offshore produced water effluents

The in vitro aryl hydrocarbon receptor (AhR) agonist potency of offshore produced water effluents, collected from the United Kingdom Continental Shelf, was determined using the dioxin responsive (DR)-chemically activated luciferase expression (CALUX) assay. Octadecylsilane (C18) solid phase extraction (SPE) extracts of produced water were exposed to DR-CALUX cells for 24 h in order to investigate the contribution in potency from compounds that are stable to metabolism by the CALUX cells during exposure. The stable AhR agonist potency determined over 24 h was highly variable and ranged from 1 to 430 ng TCDD TEQ_CALUX l⁻¹. These data reflect the highly variable composition of produced water discharges from different production fields. It is recommended that further work be performed to characterise the full range of stable dioxin like AhR agonists present in offshore produced water discharges using techniques such as bioassay-directed analysis.     

Paleoenvironmental analysis of a middle Wisconsinan biota site, southwestern Virginia, U.S.A.

The Ratcliff Site in southwestern Virginia lies in a small second-order stream valley filled with approximately 3.5 m of organic-rich deposits that contain bones of mammoth, mastodon, deer (or antelope), logs, and plant macrofossils. Radiocarbon analyses indicate the age of the organic-rich sediment ranges from > 44,000 to 29,100 ¹⁴C yr BP, a time period with no fossil remains reported in this region of the Appalachians. Analyses of field observations, textural data, organic carbon content, and plant macrofossils indicate that the organic-rich sediments contain interbedded standing-water and debris-flow deposits. Up to 6 m of oxidized debris-flow sediments bury the organic-rich sediments. The presence of Rubus parviflorus (Thimble Berry) throughout the deposit indicates the site had a boreal environment from > 44,000 to 29,100 ¹⁴C yr BP. Plant macrofossil evidence indicates the uplands had stands of spruce/jack-pine forests while the valley contained ponds and associated wetlands. Three debris flows occurred at the site between approximately 38,000 and 29,000 ¹⁴C yr BP, suggesting a recurrence interval for major storms of approximately 3000 yr, even though the apparent stability of the boreal environment implies a climate not conducive to catastrophic rainstorms. This conflicting combination of features suggests that during the middle Wisconsinan this area experienced generally cool climates, dominated by polar air masses, but was punctuated by relatively brief warm periods marked by incursions of tropical air masses.     

A review of applications of microwave radiometry to oceanography

The thermal microwave radiation from the ocean surface as seen from space is a function of the surface temperature and wind speed and is modified by liquid water and water vapor in the intervening atmosphere. Further, if the ocean surface is frozen, the emissivity is drastically increased and the effect of the intervening atmosphere is generally negligible. The emissivity of first-year ice is somewhat larger than that of multi-year ice.The data from the Electrically Scanning Microwave Radiometers (ESMR's) on the Nimbus-5 and —6 satellites operating at wavelengths of 1.55 cm and 8 mm, respectively, can be interpreted in terms of rain rate, ice coverage and first-year versus multi-year ice determination. The rain-rate data are being used to establish a climatology of rainfall over the oceans. The ice data are being used by the United States Navy in support of international scientific efforts in the Antactic region. Both ice and rain data sets have been generated for the Global Atmospheric Research Project Data Systems Test.It is possible, by making multifrequency measurements, to separate the surface and atmospheric effects and to make useful measurements of sea surface temperature, surface wind speed, and atmospheric parameters along with improved measurements of rain and ice.     

The resin sealed column (RESECO) setup for flow-through experiments on solid rocks under high temperature and high pore pressure conditions

Hydrogeology Journal - High-pressure flow-through experiments on solid rock samples are commonly conducted with experimental setups using a confining pressure to restrict the flow to the rock....     

Hydrocarbons in bivalve mollusks of Port Valdez, Alaska: Consequences of five years' permitted discharge

Petroleum hydrocarbons were investigated in Mytilus edulis and Macoma balthica at six intertidal sites in Port Valdez, Alaska after three to five years of oil terminal operation. Information about the concentrations of total hydrocarbons, unresolved complex mixture, normal alkanes, isoprenoids, olefins, hopanes and polycyclic aromatic hyrocarbons shows that petroleum accumulation in these bivalve mollusks is greatest at the Valdez municipal boat harbor and a crude oil terminal which has been permitted to discharge 170 kg oil day⁻¹. Accumulation two- to ten-fold less were observed at 3 km from the terminal and boat harbor. The temporal trends in petroleum hydrocarbon concentrations in M. edulis and M. balthica reflect the effects of selective retention and depuration of different hydrocarbon classes as well as variation in hydrocarbon sources. It is not clear whether the petroleum concentrations in Port Valdez bivalves had reached steady state by 1982, the final sampling time reported here.     

Decomposition of Hudson estuary macrophytes: Photosynthetic pigment transformations and decay constants

Plant pigment decay constants were determined for four macrophytes collected from the Hudson Estuary.Typha angustifolia andScirpus fluviatilis were used as representatives of emergent aquatic vegetation (EAV), andPotamogeton sp. andVallisneria americana were used to represent submerged aquatic vegetation (SAV). Litter bags were maintained in an environmental chamber in the dark for 104 d. The fastest rate of total mass loss was in the SAVV. americana and slowest in the EAVT. angustifolia. Changes in carotenoid and chloropigment concentration resulting from microbial and meiofaunal heterotrophy in each of the macrophytes were quantified using reverse-phase, high-performance liquid chromatography (RP-HPLC) techniques. Chlorophyllc and the carotenoid, fucoxanthin, provided useful biomarkers in determining the presence of epiphytic diatom growth, which only occurred on the SAV. The highest concentrations of phaeophorbidea, commonly used as an indication of metazoan grazing, were found in the SAVV. americana. Low concentrations of phaeophorbidea in the SAVPotamogeton sp. indicate inefficient use of this SAV by meiofaunal grazers. Lutein decayed slower than all other carotenoids in both EAV and SAV. Microcosm studies such as this are necessary to further understand the mechanisms and kinetics of photosynthetic pigment transformations in natural systems.     

Effect of spatial resolution on regionalization of hydrological model parameters

Lack of availability of historical data series is one of the major hindrances in hydrological modelling. Regionalization of hydrological model parameters is one of the solutions to obtain the parameters for ungauged basins. Recently, lots of methodologies have been developed. They can be categorized as model calibration then fitting regression between model parameters and catchments characteristics, using some kind of transfer function. The aim of this study was to compare different regionalization methods as well as to look how the spatial resolution affects regionalization. In this study, a modified Lipschitz and monotony condition was used for regionalization. To identify the effect of the model resolution, the parameters of a distributed and semi‐distributed version of the Hydrologiska Byråns Vattenbalansavdelning (HBV) model were regionalized. The study was conducted at the upper Neckar catchment of southwest Germany. It has been found that the combination of Lipschitz and monotony condition has performed reasonably. It has been seen that the distributed model structure has outperformed the semi‐distributed model structure. It shows under present data conditions that higher model resolution can describe processes of ungauged basins reasonably. Copyright © 2011 John Wiley & Sons, Ltd.