Petrogenesis of sulphide-bearing reaction zones in the Coolac ultramafic belt,New South Wales,Australia

The Coolac ultramafic belt consists dominantly of variably serpentinised harzburgite and contains a diversity of tectonic inclusions. Reaction zones of chlorite-, talc- and Ca-Al silicate-rich rocks are commonly developed between serpentinites and either tectonic inclusions or country rocks. The chlorite-and talc-rich parts of the reaction zones typically contain sparsely disseminated to rarely massive Cu- and Fe-bearing sulphides, variable sphalerite, and minor Ni- (-Co-Fe) sulphides, arsenides and sulpharsenides, Pb and Bi minerals. The reaction zones have formed concomitantly with the serpentinisation of the harzburgite at temperatures of 100°–350°C and at pressures of <6 kb. Migration of Ca, Al, Ti, V, Sc, Cu and Zn has occurred from the ultramafic rocks to the reaction zones. The sulphur content of the ultramafic rocks increased during serpentinisation, but decreased markedly in the final stage of the process owing possibly to rising oxygen fugacity. The availability of sulphur during serpentinisation may have enabled sulphide minerals to form from the concentration of base metals in the reaction zones.

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Zusammenfassung Der ultrabasische Gürtel von Coolac besteht vorwiegend aus unterschiedlich serpentinisiertem Harzburgit und weist mannigfaltige tektonische Einschlüsse auf. Reaktionszonen Chlorit-, Talk-, und Ca-Al-Silikat-reicher Gesteine sind gewöhnlich entwickelt im Kontaktbereich zwischen serpentinisiertem Harzburgit und entweder tektonischen Einschlüssen oder Gesteinen der Umgebung. Die Chlorit- und Talk-reichen Partien der Reaktionszone enthalten typischerweise fein verteilte, seltene Konzentrationen von Cu- und Feführenden Sulphiden, mit wechselndem Zinkblendegehalt, und untergeordnet Ni(-Co-Fe) Sulphide, Arsenide und Schwefel-haltige Arsenide, sowie Pb-und Bi-haltige Mineralien. Die Reaktionszonen entstanden zusammen mit der Serpentinisierung des Harzburgits bei Temperaturen von 100°–350°C und unter einem Druck von <6 Kb. Migration von Ca, Al, Ti, V, Sc, Cu und Zn verlief von den ultrabasischen Gesteinen zu den Reaktionszonen. Der Schwefelgehalt der ultrabasischen Gesteine nahm während der Serpentinisierung zu, verringerte sich jedoch auffällig im letzten Stadium des Prozesses, möglicherweise wegen der zunehmenden Verflüchtigung des Sauerstoffes. Das Angebot von Schwefel während der Serpentinisierung mag der Grund für die Bildung von Sulphiden aus Schwermetallkonzentration in den Reaktionszonen gewesen sein.

     

Zinc-lead skarn deposits at Leadville, New South Wales, Australia, and their distinction from volcanic-hosted massive sulphides

Exploration of Zn-rich sulphide deposits at Leadville, northern Lachlan Fold Belt, New South Wales, for over two decades has been largely on the premise that the mineralisation represents felsic volcanic-hosted massive sulphides (VHMS). Deposits are hosted by ?Silurian felsic metavolcanic, psammopelitic and calcareous metasedimentary rocks which have been intruded by the late Carboniferous I-type Gulgong Granite. Evidence for an epigenetic replacement (skarn) origin of the deposits, rather than representing metamorphosed volcanogenic massive sulphides, includes the proximity of evolved granitic intrusives and reactive carbonate rocks, a skarn mineral assemblage (with characteristic prograde and retrograde stages), lack of textural or lithological indications of an exhalative origin, and gossan and sulphide compositions consistent with Zn-Pb skarns and atypical of Lachlan Fold Belt VHMS deposits. Furthermore, sulphide lead isotope ratios are significantly more radiogenic than signatures for VHMS deposits in the Lachlan Fold Belt. Carbonate δ¹³C and δ¹⁸O and sulphide δ³⁴S values are consistent with the interaction of magmatic hydrothermal fluids with Palaeozoic carbonate rocks and a largely magmatic source of sulphur. It is concluded that the Leadville deposits are of skarn type, genetically related to the Gulgong Granite.     

Sedimentation processes in an impoundment,Union lake,New Jersey

A small (3 75 km²) impoundment. Union Lake, on the Maurice River in southern New Jersey contains fine-grained sediment and organic material being transported through the surface water system Sedimentation is slow and rates calculated from¹³⁷Cs-dated cores indicate a decrease through time from 2 6 mm/yr to 0 57 mm/yr Sediment from shallow areas (<3 m) consists of winnowed preimpoundment fluvial sand, whereas sediment from deeper areas (>3 m) is dy composed of diatoms, organic matter, and silt- and clay-sized mineral grains Sediment distribution is controlled by water moving from the river entrance southward toward the outlet and by wind-generated water motion from shallow areas fringing the shore toward deeper portions of the impoundment     

Making sound inferences from geomagnetic sounding

We examine the nonlinear inverse problem of electromagnetic induction to recover electrical conductivity. As this is an ill-posed problem based on inaccurate data, there is a critical need to find the reliable features of the models of electrical conductivity. We present a method for obtaining bounds on Earth’s average conductivity that all conductivity profiles must obey. Our method is based completely on optimization theory for an all-at-once approach to inverting frequency-domain electromagnetic data. The forward modeling equations are constraints in an optimization problem solving for the electric fields and the conductivity simultaneously. There is no regularization required to solve the problem. The computational framework easily allows additional inequality constraints to be imposed, allowing us to further narrow the bounds. We draw conclusions from a global geomagnetic depth sounding data set and compare with laboratory results, inferring temperature and water content through published Boltzmann-Arrhenius conductivity models. If the upper mantle is assumed to be volatile free we find it has an average temperature of 1409-1539 ° C. For the top 1000 km of the lower mantle, we find an average temperature of 1849-2008 ° C. These are in agreement with generally accepted mantle temperatures. Our conclusions about water content of the transition zone disagree with previous research. With our bounds on conductivity, we calculate a transition zone consisting entirely of Wadsleyite has <0.27  wt.% water and as we add in a fraction of Ringwoodite, the upper bound on water content decreases proportionally. This water content is less than the 0.4 wt.% water required for melt or pooling at the 410 km seismic discontinuity.     

The six capacities of community resilience: evidence from three small Texas communities impacted by Hurricane Harvey

This article builds upon disaster scholarship that suggests community resilience is driven by six capacities: social, economic, physical, human, institutional, and environmental. Together, these capacities constitute a conceptual framework that can be used to investigate and assess community resilience. While recent scholarship has provided insights into how resilience operates in large communities, there remain questions about whether this conceptual framework is appropriate for the study of resilience in small communities. To narrow this knowledge gap, we conducted interviews with twenty-six subjects from three small Texas communities affected by Hurricane Harvey: City of Dickinson; City of Port Aransas; and Town of Refugio. Analysis of the interview data confirms that the six capacities of resilience provide an appropriate framework for the investigation of resilience in small communities. Given the complex and dynamic nature of community resilience, the findings also suggest that it is unlikely policymakers will be able to develop a unified policy solution for hazard events that is appropriate for all communities. Rather, policymakers need to consider community-based resilience solutions, driven by local strengths and weaknesses, that facilitate the reduction of risks associated with hazard events.

     

Adaptive Delta Management for flood risk and resilience in Dordrecht,The Netherlands

Many countries across the world are experiencing strict austerity measures due to the economic crisis. As a consequence, public financing for stand-alone adaptation to flooding and drought will become scarcer in the (near) future, and this hampers the pursuit of resilience (i.e. the ability to remain functioning under a range of hazard magnitudes). In such times, key challenges for adaptation are further complicated by weaker investment dynamics and an increased tendency to ‘work in silos’. These are: to minimise regret with respect to maladaptation, which results from over- or under-investment in water hazard management; to exploit the opportunities for mainstreaming adaptation to flooding and drought into other investment agendas; and to deliver multiple benefits for society and the economy, such as increased biodiversity, liveability and competitiveness. These common challenges drive the best way in which to adapt to uncertain climate and socio-economic changes. In the Netherlands, the Delta Programme has developed and applied a structured and well-defined approach (called Adaptive Delta Management) for including and acting upon uncertainty around these future changes. This approach allows for greater transparency to decision-makers and stakeholders, because it adheres to four specific steps for strategy development. This paper presents the current understanding of Adaptive Delta Management and an illustration of the approach for the management of flood risk and resilience in Dordrecht. It examines the added value and limitations of Adaptive Delta Management concerning its application in the context of the Delta Programme, with a specific emphasis on the lessons learned from Dordrecht.

     

Multi-instrument remote and in situ observations of the Erebus Volcano (Antarctica) lava lake in 2005: A comparison with the Pele lava lake on the jovian moon Io

The stable, persistent, active lava lake at Erebus volcano (Ross Island, Antarctica) provides an excellent thermal target for analysis of spacecraft observations, and for testing new technology. In the austral summer of 2005 visible and infrared observations of the Erebus lava lake were obtained with sensors on three space vehicles Terra (ASTER, MODIS), Aqua (MODIS) and EO-1 (Hyperion, ALI). Contemporaneous ground-based observations were obtained with hand-held infrared cameras. This allowed a quantitative comparison of the thermal data obtained from different instruments, and of the analytical techniques used to analyze the data, both with and without the constraints imposed by ground-truth. From the thermal camera data, in December 2005 the main Erebus lava lake (Ray Lake) had an area of ≈ 820 m². Surface colour temperatures ranged from 575 K to 1090 K, with a broad peak in the distribution from 730 K to 850 K. Total heat loss was estimated at 23.5 MW. The flux density was ≈ 29 kW m^− 2. Mass flux was estimated at 64 to 93 kg s^− 1. The best correlation between thermal emission and emitting area was obtained with ASTER, which has the best combination of spatial resolution and wavelength coverage, especially in the thermal infrared. The high surface temperature of the lava lake means that Hyperion data are for the most part saturated. Uncertainties, introduced by the need to remove incident sunlight cause the thermal emission from the Hyperion data to be a factor of about two greater than that measured by hand-held thermal camera. MODIS also over-estimated thermal output from the lava lake by the same factor of two because it was detecting reflected sunlight from the rest of the pixel area. The measurement of the detailed temperature distribution on the surface of an active terrestrial lava lake will allow testing of thermal emission models used to interpret remote-sensing data of volcanism on Io, where no such ground-truth exists. Although the Erebus lava lake is four orders of magnitude smaller than the lava lake at Pele on Io, the shape of the integrated thermal emission spectra are similar. Thermal emission from this style of effusive volcanism appears to be invariant. Excess thermal emission in most Pele spectra (compared to Erebus) at short wavelengths (< 3 μm) is most likely due to disruption of the surface on the lava lake by escaping volatiles.     

Comparing the behaviour of spherical beads and natural grains in bedload mixtures

It is common to use idealised materials to study the dynamics of granular transport in fluid flows, but the impact of this choice upon sediment behaviour has not been extensively explored. To tackle this research gap, two experiments were undertaken to explore the influence of a finer grain input to a channelized coarser granular flow driven by a shallow fluid flow. The first set of runs was undertaken using spherical glass beads, and the second set with natural fluvial sediment. The transport system approximates a narrow slice through the bedload at the bottom of a river. In the runs with natural grains, the infiltration of fine sediment into the bed was similar to the spherical glass beads, but with reduced infiltration capacity. We ascribe this behaviour to irregular and variable pore shapes and sizes in the natural material. The behaviour of the bedload in the natural material runs matched that of the bead runs only when the feed contained a high content of fines. When the feed contained a low content of fines the transport of natural grains was more complex, including the emergence of migrating collections of grains. However, the overall changes in bed and water slope due to the finer grain input were comparable in both sets of experiments. We conclude that artificial, idealised materials qualitatively represent sedimentary phenomena, but that quantitative differences in the outcomes must be expected. © 2020 John Wiley & Sons, Ltd.     

Spatial distribution and filtering efficiency of Daphnia in a deep subtropical reservoir

Studies of Daphnia distribution and function could help people manage and protect water quality. We investigated how spatial distribution and filtering efficiency of Daphnia in the transition and lacustrine zones of the Nanwan Reservoir (China). Samplings were conducted seasonally for 2 years from six sites in the reservoir. Daphnia abundance and biomass were significantly higher in the lacustrine zone than in the transition zone. Similar composition and biomass of edible phytoplankton were found in the two zones, suggesting that food quantity could not explain high Daphnia distribution in the lacustrine zone. The variations of water velocity and food quality could help explaining Daphnia patchy distribution in the reservoir. On the one hand, rapid water velocity can cause the Daphnia decrement in the transition zone. On the other hand, the ratio of particulate organic carbon (POC) to chlorophyll a (chl a) concentration was significantly higher in the transition zone, indicating more allochthonous material constituted the food source for Daphnia. The lower quality food likely suppressed Daphnia development in the transition zone. A linear regression between Daphnia abundance and Secchi depth (SD) may suggest a cause-effect relationship where increased filtering efficiency was responsible for increased water clarity to some extent.     

Environmental geochemistry of the Gulf Creek copper mine area, north-eastern New South Wales, Australia

 Past mining and smelting of sulphide ore (pyrite-chalcopyrite-sphalerite) at the abandoned Gulf Creek mine has resulted in a stream highly contaminated by acid mine drainage (pH: 2.2–3.4), as well as degradation of local soil and vegetation. Physical dispersion of secondary metal-bearing minerals from abandoned ore and waste dumps into Gulf Creek and adsorption and coprecipitation of dissolved metals and metalloids in the stream bed cause elevated Ag, As, Cd, Cu, Fe, Pb and Zn values in stream sediments. The bioavailability of individual heavy metals to freshwater organisms changes downstream, however, selective bioaccumulation processes in algae reject readily bioavailable Zn and concentrate less bioavailable Cu. Polluted soils in the vicinity of the mine and smelter sites are subject to continuing soil erosion and either support no vegetation, or a depauperate flora with certain species showing bioaccumulation of metals and resistance to high metal contents. Rehabilitation of disturbed areas should involve covering and sealing sulphidic mine waste or removal of ore and waste dumps, installation of a physical and chemical plant or construction of a wetland environment (plus anoxic lime drains), and import of topsoil and planting of local, metal-tolerant plant species. Received: 17 March 1998 / Accepted: 6 October 1998