Geological and 40Ar/39Ar geochronological constraints on the timing of quartz vein formation in Meguma Group lode-gold deposits, Nova Scotia

The results of geological and 40Ar/39Ar geochronological investigations of several gold districts hosted by the Meguma Group are presented. Observations at both the macro- (deposit to ore zone) and micro- (hand sample to thin section) scale indicate that quartz vein formation followed major Acadian folding and metamorphism (ca. 400 ±10 Ma) and was broadly coincident with mafic-felsic magmatism at ca. 370 Ma. 40Ar/39Ar analyses of vein-fill mica and amphibole from the Beaver Dam, Moose River, Fifteen Mile Stream, Upper Seal Harbour and Caribou deposits indicate ages of ca. 380 Ma to ca. 362 Ma. The age data are interpreted to reflect discrete hydrothermal events with rapid cooling following crystallization of vein constituents. The age data do not reflect either variable amounts of resetting by later granitic intrusions or diachronous cooling. Genetic models that interpret the generation of the auriferous quartz veins as either before or during major Acadian folding are considered to be inconsistent with the present results. Instead, a model is favored that interprets quartz vein formation in the context of continued transpression of the Meguma Terrane following regional folding and metamorphism. RÉSUMÉ On présente les résultats d'études géologiques et géochronologiques [40Ar/39Ar] effectuées dans plusieurs districts aurifères au sein du Groupe de Meguma. Des observations tant macroscopiques (du gite à la zone de minéral) que microscopiques (de l'échantillon à la lame mince) indiquent que la formation des veines de quartz suivit un métamorphisme et un plissement majeurs acadiens (env. 400 ± 10 Ma) et coiincida d'une facon générale avec unmagmatisme mafique à felsique vers 370 Ma. Des analyses 40Ar/39Ar effectuées sur des micas et des amphiboles de remplissages de veine provenant des gites de Beaver Dam, Moose River, Fifteen Mile Stream, Upper Seal Harbour et Caribou révèlent des âges aux environs de 380 à 362 Ma. On interprète ces données d 'âge comme le reflet d'épisodes hydrothèrmaux distincts avec un refroidissement rapide suite à la cristallisation des constituants filoniens. Ces données ne reflètent ni un degré variable de remise à ziro par des intrusions granitiques ultérieures, ni un refroidissement diachrone. On considere que les modèles genetiques interprétant la formation des veines de quartz auriferes comme precedent ou ayant eu lieu pendant le plissement majeur acadien, sont en contradiction avec les resultats actuels. En leur lieu, on favorise un modèle qui interprète la formation des veines de quartz dans le contexte d'une transpression continue de la Lanière de Méguma à la suite d'un plissement et d'un métamorphisme régionaux. [Traduit par le journal

The CO\u3csub\u3e2\u3c/sub\u3e Concentration of Air Trapped in Greenland Ice Sheet Project 2 Ice Formed During Periods of Rapid Climate Change

The CO2 content of air occluded in Greenland Ice Sheet Project 2 (GISP2) ice formed over two separate intervals of rapidly changing climate, centered at approximately 46 and 63 kyr B. P., is as much as 90 ppm more during warm periods (interstadials) than during cold periods (stadials). These CO2 variations are superimposed on changes in annual layer thickness and δ18O of the ice and do not show the 200- to 700-year offsets which would be expected for concurrent variations in the atmosphere and the ice. The CO2 concentrations during the stadials are similar to the atmospheric values recorded by Antarctic ice of the same age, so processes occurring in the ice after bubble enclosure must be enriching the air trapped in GISP2 ice formed during the interstadials. This conclusion is supported by Ca content and electrical conductivity measurements of the ice, which show that adequate carbonate is present to produce these enrichments and that CO2 content is high only when the electrical conductivity (a proxy for H+ concentration) is high. High-resolution mapping of one 4-cm section of ice shows a 200-ppm increase in the CO2 content of the trapped air, from approximately 275 to 475 ppm. Analyses of the total inorganic carbon of ice from both the LGM and Holocene show that most of the Ca in the ice is from CaCO3 and that the δ13CO2 approaches that of soil and marine carbonates. These results show that the CO2 record preserved in ice can be altered by in situ decarbonation reactions and that only ice containing either abundant carbonate or essentially no carbonate contains a reliable record of paleoatmospheric CO2

Environmental regulation in transition: Policy officials’ views of regulatory instruments and their mapping to environmental risks

This study re-analysed 14 semi-structured interviews with policy officials from the UK Department for Environment, Food and Rural Affairs (Defra) to explore the use of a variety of regulatory instruments and different levels of risk across 14 policy domains and 18 separately named risks. Interviews took place within a policy environment of a better regulation agenda and of broader regulatory reform. Of 619 (n) coded references to 5 categories of regulatory instrument, ‘command and control’ regulation (n = 257) and support mechanisms (n = 118) dominated the discussions, with a preference for ‘command and control’ cited in 8 of the policy domains. A framing analysis revealed officials' views on instrument effectiveness, including for sub-categories of the 5 key instruments. Views were mixed, though notably positive for economic instruments including taxation, fiscal instruments and information provision. An overlap analysis explored officials' mapping of public environmental risks to instrument types suited to their management. While officials frequently cite risk concepts generally within discussions, the extent of overlap for risks of specific significance was low across all risks. Only ‘command and control’ was mapped to risks of moderate significance in likelihood and impact severity. These results show that policy makers still prefer ‘command and control’ approaches when a certainty of outcome is sought and that alternative means are sought for lower risk situations. The detailed reasons for selection, including the mapping of certain instruments to specific risk characteristics, is still developing

Radiative absorption enhancements by black carbon controlled by particle-to-particle heterogeneity in composition.

Black carbon (BC) absorbs solar radiation, leading to a strong but uncertain warming effect on climate. A key challenge in modeling and quantifying BC's radiative effect on climate is predicting enhancements in light absorption that result from internal mixing between BC and other aerosol components. Modeling and laboratory studies show that BC, when mixed with other aerosol components, absorbs more strongly than pure, uncoated BC; however, some ambient observations suggest more variable and weaker absorption enhancement. We show that the lower-than-expected enhancements in ambient measurements result from a combination of two factors. First, the often used spherical, concentric core-shell approximation generally overestimates the absorption by BC. Second, and more importantly, inadequate consideration of heterogeneity in particle-to-particle composition engenders substantial overestimation in absorption by the total particle population, with greater heterogeneity associated with larger model-measurement differences. We show that accounting for these two effects-variability in per-particle composition and deviations from the core-shell approximation-reconciles absorption enhancement predictions with laboratory and field observations and resolves the apparent discrepancy. Furthermore, our consistent model framework provides a path forward for improving predictions of BC's radiative effect on climate

In search of phylogenetic congruence between molecular and morphological data in bryozoans with extreme adult skeletal heteromorphy

peerreview_statement: The publishing and review policy for this title is described in its Aims & Scope. aims_and_scope_url: http://www.tandfonline.com/action/journalInformation?show=aimsScope&journalCode=tsab20© Crown Copyright 2015. This document is the author's final accepted/submitted version of the journal article. You are advised to consult the publisher's version if you wish to cite from it

Supercritical antisolvent precipitation of amorphous copper–zinc georgeite and acetate precursors for the preparation of ambient‐pressure water‐gas‐shift copper/zinc oxide catalysts

A series of copper-zinc acetate and zincian georgeite precursors have been produced by supercritical CO2 anti-solvent (SAS) precipitation as precursors to Cu/ZnO catalysts for the water gas shift (WGS) reaction. The amorphous materials were prepared by varying the water/ethanol volumetric ratio in the initial metal acetate solutions. Water addition promoted georgeite formation at the expense of mixed metal acetates, which are formed in the absence of the water co-solvent. Optimum SAS precipitation occurs without water to give high surface areas, whilst a high water content gives inferior surface areas and copper-zinc segregation. Calcination of the acetates is exothermic, producing a mixture of metal oxides with high crystallinity. However, thermal decomposition of zincian georgeite resulted in highly dispersed CuO and ZnO crystallites with poor structural order. The georgeite-derived catalysts give superior WGS performance in comparison to the acetate-derived catalysts, which is attributed to enhanced copper-zinc interactions that originate from the precursor

The effect of sodium species on methanol synthesis and water-gas shift Cu/ZnO catalysts: utilising high purity zincian georgeite

The effect of sodium species on the physical and catalytic properties of Cu/ZnO catalysts derived from zincian georgeite has been investigated. Catalysts prepared with <100 ppm to 2.1 wt% Na+, using a supercritical CO2 antisolvent technique, were characterised and tested for the low temperature water–gas shift reaction and also CO2 hydrogenation to methanol. It was found that zincian georgeite catalyst precursor stability was dependent on the Na+ concentration, with the 2.1 wt% Na+-containing sample uncontrollably ageing to malachite and sodium zinc carbonate. Samples with lower Na+ contents (<100–2500 ppm) remained as the amorphous zincian georgeite phase, which on calcination and reduction resulted in similar CuO/Cu particle sizes and Cu surface areas. The aged 2.1 wt% Na+ containing sample, after calcination and reduction, was found to comprise of larger CuO crystallites and a lower Cu surface area. However, calcination of the high Na+ sample immediately after precipitation (before ageing) resulted in a comparable CuO/Cu particle size to the lower (<100–2500 ppm) Na+ containing samples, but with a lower Cu surface area, which indicates that Na+ species block Cu sites. Activity of the catalysts for the water–gas shift reaction and methanol yields in the methanol synthesis reaction correlated with Na+ content, suggesting that Na+ directly poisons the catalyst. In situ XRD analysis showed that the ZnO crystallite size and consequently Cu crystallite size increased dramatically in the presence of water in a syn-gas reaction mixture, showing that stabilisation of nanocrystalline ZnO is required. Sodium species have a moderate effect on ZnO and Cu crystallite growth rate, with lower Na+ content resulting in slightly reduced rates of growth under reaction conditions

A well-conserved Plasmodium falciparum var gene shows an unusual stage-specific transcript pattern

The var multicopy gene family encodes Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) variant antigens, which, through their ability to adhere to a variety of host receptors, are thought to be important virulence factors. The predominant expression of a single cytoadherent PfEMP1 type on an infected red blood cell, and the switching between different PfEMP1 types to evade host protective antibody responses, are processes thought to be controlled at the transcriptional level. Contradictory data have been published on the timing of var gene transcription. Reverse transcription-polymerase chain reaction (RT-PCR) data suggested that transcription of the predominant var gene occurs in the later (pigmented trophozoite) stages, whereas Northern blot data indicated such transcripts only in early (ring) stages. We investigated this discrepancy by Northern blot, with probes covering a diverse var gene repertoire. We confirm that almost all var transcript types were detected only in ring stages. However, one type, the well-conserved varCSA transcript, was present constitutively in different laboratory parasites and does not appear to undergo antigenic variation. Although varCSA has been shown to encode a chondroitin sulphate A (CSA)-binding PfEMP1, we find that the presence of full-length varCSA transcripts does not correlate with the CSA-binding phenotype

The preparation of large surface area lanthanum based perovskite supports for AuPt nanoparticles: tuning the glycerol oxidation reaction pathway by switching the perovskite B site

Gold and gold alloys, in the form of supported nanoparticles, have been shown over the last three decades to be highly effective oxidation catalysts. Mixed metal oxide perovskites, with their high structural tolerance, are ideal for investigating how changes in the chemical composition of supports affect the catalysts' properties, while retaining similar surface areas, morphologies and metal co-ordinations. However, a significant disadvantage of using perovskites as supports is their high crystallinity and small surface area. We report the use of a supercritical carbon dioxide anti-solvent precipitation methodology to prepare large surface area lanthanum based perovskites, making the deposition of 1 wt% AuPt nanoparticles feasible. These catalysts were used for the selective oxidation of glycerol. By changing the elemental composition of the perovskite B site, we dramatically altered the reaction pathway between a sequential oxidation route to glyceric or tartronic acid and a dehydration reaction pathway to lactic acid. Selectivity profiles were correlated to reported oxygen adsorption capacities of the perovskite supports and also to changes in the AuPt nanoparticle morphologies. Extended time on line analysis using the best oxidation catalyst (AuPt/LaMnO3) produced an exceptionally high tartronic acid yield. LaMnO3 produced from alternative preparation methods was found to have lower activities, but gave comparable selectivity profiles to that produced using the supercritical carbon dioxide anti-solvent precipitation methodology

Calcitization of aragonitic bryozoans in Cenozoic tropical carbonates from East Kalimantan, Indonesia

© The Author(s) 2016. Open Access. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The file attached is the published version of the article