Platinum-group element mineralisation in the Unst ophiolite, Shetland

The ophiolitic basic and ultrabasic rocks of the island of Unst, Shetland comprise a sequence of harzburgites, dunites, clinopyroxene-rich cumulates, and gabbro, within tectonic blocks that have been thrust over a migmatite complex during the Laxer Palaeozoic. Concentrations of chromite are found in the harzburgite and dunite, and to a small extent in the pyroxene cumulate rocks. They occur as disseminations, sometimes forming millimetre scale layers, and as more massive schlieren and pods of chromitite. Five alteration or hydrothermal events have been recognised in the ultrabasic rocks. These comprise early pervasive serpentinisation, later fracture controlled serpentinisation, veining and pervasive carbonation, minor late serpentine veining and talc-carbonate alteration controlled by fault zones. Exploration for platinum group element (PGE) mineralisation uas carried out using a combination of drainage, overburden and rock sampling. Analyses of PGE were obtained by fire assay followed by either neutron activation analysis or flameless atomic absorption spectrometry, and up to 20 other elements Here determined by X-ray fluoresence analysis. Panned concentrate samples were taken from 73 drainage sites distributed throughout the complex. Ir, the only PGE determined in all samples, showed a greater concentration in samples derived from the harzburgite unit than those from other units. Lox amplitude anomalies are present in three discrete areas in the harzburgite but the maximum level of 210 ppb Ir is associated with a sample derived from a prominent N-S zone of faulting and hydrothermal activity markedly discordant to the regional trend of layering in the harzburgite and dunite. This discordant zone, which extends for at least 7 km, is also marked by samples containing enrichments in Fe, Co, Ni, Cu and As. The highest Cr levels are associated with an area in the north of the harzburgite with no previous history of chromite working but where many locally derived pieces of chromitite float have been discovered. Relatively high Cr levels are also associated nith the area of dunite containing the greatest concentration of visible chromite and old norkings. A technique of collecting panned heavy mineral concentrates from overburden samples was adopted as a reconnaissance exploration technique after orientation sampling in the harzburgite unit at Cliff, an area with high PGE levels in chromitite and associated dunite. Systematic sampling in the Cliff area outlined a zone of coincident Pd, Pt and Rh enrichment near to but separate from the chromite workings knorrn to be enriched in PGE. In contrast the distribution of Ru was entirely different with scattered lon amplitude anomalous zones and a maximum anomaly 300m from the chromite-rich zone. Reconnaissance lines were sampled at other locations within the harzburgite, dunite and cumulate units. Lore amplitude Pd and Pt anomalies were detected xithin the dunite unit, especially in 'a traverse across the trace of the prominent N-S fault zone at Helliers Uater, adjacent to the outcrop of the cumulate unit. In general the overburden data suggest some association between PGE enrichment and enhanced levels of Ni relative to typical silicate levels apparent when expressed as the ratio Ni/MgC. Rock samples Here collected from all parts of the complex, including most of the main chromitite workings. Very high levels of all PGE occur in samples of chromitite, chromite-rich dunite and dunite from the Cliff area, with a strong positive intercorrelation between all PGE. The proportions of the various PGE are very similar to those present in deposits in major layered basic/ultrabasic complexes like Bushveld and Stillwater, irith strong relative enrichment in Pd and Pt. These PGE proportions are completely different from the Ru-Ir-0s dominant assemblage typical of ophiolitic rocks. Associated with high levels of PGE are enrichments in Ni, Cu, As, Sb and Te. There is no correlation rrith Cr and some samples of chromitite from the Cliff area contain only background levels of PGE. High to moderate levels of PGE with the same proportions of elements as the Cliff samples also occur in samples of chromitite and serpentinised dunite from the dunite unit and in samples of pyroxenite from the cumulate unit, In contrast PGE-rich samples of chromitite from the harzburgite unit near Harold's Grave have entirely different proportions of PGE with Ru and Ir in greatest abundance. This PGE distribution is similar to that in some background samples of harzburgite and closely resembles the pattern found in typical ophiolites. The PGE in the Harold's Grave samples do not exhibit the Ni enhancement noted in the Cliff PGE mineralisation. In samples from the Cliff area the platinum-group minerals (PGM) sperrylite, stibiopalladinite, hollingnorthite, laurite and possibly irarsite have been identified, mostly as grains less than 10 microns in size. In chromite-rich rocks these minerals occur Rithin chlorite haloes around chromite, in the blackened altered rims of chromite grains and in interstitial Ni-rich serpentine/carbonate intergroxths in association with pentlandite, orcellite and other Ni sulphides and arsenides, sometimes spatially related to chlorite-carbonate-magnetite veins. They also occur as fine grains Rithin magnetite rims around chromite and in magnetite or carbonate veins in dunite. The Ni sulphide/arsenide assemblage associated Rith the PGH is characteristic of serpentinisation at temperatures less than 500'C, Rell belox the range of magmatic conditions. A hydrothermal origin for the PGE mineralisation is proposed, probably related to the second phase of serpentinisation. This involved the redistribution of Ni accompanied by the introduction of As, Sb and Te probably with a StrUCtUral Control. Pre-existing concentrations of chromite may have acted as a precipitation barrier causing rich PGH deposition in the alteration haloes around chromite grains. Continuous borehole or trench sections through mineralised zones are required to assess the economic significance of the PGE mineralisation. Nevertheless the high levels of PGE attained and the evidence of xidespread occurrence of the Cliff-type PGE enrichment are favourable indications. The PGE enrichments found in the cumulate complex are of potential interest as they may originally have been of magmatic origin. Larger tonnage targets may therefore be present in this unit compared Rith the likely size of structurally-controlled mineralisation elswhere in the complex

A preliminary report on the mineralogy of the Tundulu and Songwe carbonatite complexes, Malawi

A group of samples from the Tundulu and Songwe carbonatite complexes in Malawi, supplied by Dr. Appleton, have been studied by various mineralogical techniques. The aim was to characterise them and assess their Usefulness as direct application fertilizers and sources of rare earth metals. A brief summary 9f the results obtained so far is given here and a full report will be made when the work is complete. Polished thin sections were made from 17 samples. These were examined on the optical microscope and 7 were analysed on the electron microprobe. This examination showed that there were three main rock types, apatite rocks, ferruginous carbonatites and calcite carbonatites(sovites) and the following report discusses them under theses broad headings

Discussion of ‘Silicified serpentinite – a residuum of a Tertiary palaeo-weathering surface in the United Arab Emirates’

Alicja M. Lacinska and Michael T. Styles reply: We appreciate the comment by C. R. M. Butt on the publication by Lacinska & Styles (2013) on the silicified serpentinites described from the Hajar Mountains in the United Arab Emirates. This comment is based on his very extensive knowledge of laterites and regoliths from ancient shield areas around the world; the degree to which this knowledge is directly applicable to the rocks formed at the margins of a recently uplifted mountain range, as described in the original paper, is debatable

An assessment of global resources of rocks as suitable raw materials for carbon capture and storage by mineralisation

Carbon capture and storage by mineralisation (CCSM) is a method proposed for capturing CO2 by reacting it with magnesium in ultramafic rocks to form carbonate minerals and silica. Large quantities of magnesium silicate rocks are required for this process and to demonstrate the feasibility, and adequately plan for the development and supply of mineral resources, their locations and quantities must be known. This study attempts to globally define the spatial extent and quantity of resources that could be used for the CCSM processes and to assess, if based on resources, this could be a viable, widely applicable CO2 sequestration process. It has been estimated that around 90 teratonnes of material is available. This is sufficient to capture global CO2 emissions for over 700 years at current levels of output and highlights the enormous resource. Even if only a small part is utilised, it could make a significant impact on CO2 reduction. The majority of the resource is contained within ophiolitic rocks. The study further attempts to split CCSM resources into altered (serpentine-rich rocks) and unaltered (olivine-rich rocks) due to the different processing requirements for these rock types. Carbon capture and storage by mineralisation is likely to be of most use in areas with no access to underground geological CO2 storage or for small operations where underground storage is not practical. This study demonstrates that substantial resources are available and their supply is unlikely to be a constraint

UK export performance research - review and implications

Previous research on export performance has been criticized for being a mosaic of autonomous endeavours and for a lack of theoretical development. Building upon extant models of export performance, and a review and analysis of research on export performance in the UK for the period 1990-2005, an integrated model of export performance is developed and theoretical explanations of export performance are put forward. It is suggested that a multi-theory approach to explaining export performance is viable. Management and policy implications for the UK emerging from the review and synthesis of the literature and the integrated model are discussed

First observation of the decay Bˉs0→D0K∗0\bar{B}^0_s \to D^0 K^{*0} and a measurement of the ratio of branching fractions B(Bˉs0→D0K∗0)B(Bˉ0→D0ρ0)\frac{{\cal B}(\bar{B}^0_s \to D^0 K^{*0})}{{\cal B}(\bar{B}^0 \to D^0 \rho^0)}

The first observation of the decay $\bar{B}^0_s \to D^0 K^{*0}$ using $pp$ data collected by the LHCb detector at a centre-of-mass energy of 7 TeV, corresponding to an integrated luminosity of 36 pb$^{-1}$, is reported. A signal of $34.4 \pm 6.8$ events is obtained and the absence of signal is rejected with a statistical significance of more than nine standard deviations. The $\bar{B}^0_s \to D^0 K^{*0}$ branching fraction is measured relative to that of $\bar{B}^0 \to D^0 \rho^0$: $\frac{{\cal B}(\bar{B}^0_s \to D^0 K^{*0})}{{\cal B}(\bar{B}^0 \to D^0 \rho^0)} = 1.48 \pm 0.34 \pm 0.15 \pm 0.12$, where the first uncertainty is statistical, the second systematic and the third is due to the uncertainty on the ratio of the $B^0$ and $B^0_s$ hadronisation fractions.Comment: 10 pages, 3 figures, submitted to Phys. Lett. B; ISSN 0370-269

Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector

A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results

Jet size dependence of single jet suppression in lead-lead collisions at sqrt(s(NN)) = 2.76 TeV with the ATLAS detector at the LHC

Measurements of inclusive jet suppression in heavy ion collisions at the LHC provide direct sensitivity to the physics of jet quenching. In a sample of lead-lead collisions at sqrt(s) = 2.76 TeV corresponding to an integrated luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with a calorimeter over the pseudorapidity interval |eta| < 2.1 and over the transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the anti-kt algorithm with values for the distance parameter that determines the nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of the jet yield is characterized by the jet "central-to-peripheral ratio," Rcp. Jet production is found to be suppressed by approximately a factor of two in the 10% most central collisions relative to peripheral collisions. Rcp varies smoothly with centrality as characterized by the number of participating nucleons. The observed suppression is only weakly dependent on jet radius and transverse momentum. These results provide the first direct measurement of inclusive jet suppression in heavy ion collisions and complement previous measurements of dijet transverse energy imbalance at the LHC.Comment: 15 pages plus author list (30 pages total), 8 figures, 2 tables, submitted to Physics Letters B. All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2011-02