Platinum-Group Elements in Sulphide Minerals, Platinum-Group Minerals, and Whole-Rocks of the Merensky Reef (Bushveld Complex, South Africa): Implications for the Formation of the Reef

The concentrations of platinum-group elements (PGE), Co, Re,Au and Ag have been determined in the base-metal sulphide (BMS)of a section of the Merensky Reef. In addition we performeddetailed image analysis of the platinum-group minerals (PGM).The aims of the study were to establish: (1) whether the BMSare the principal host of these elements; (2) whether individualelements preferentially partition into a specific BMS; (3) whetherthe concentration of the elements varies with stratigraphy orlithology; (4) what is the proportion of PGE hosted by PGM;(5) whether the PGM and the PGE found in BMS could account forthe complete PGE budget of the whole-rocks. In all lithologies,most of the PGE (65 up to 85%) are hosted by PGM (essentiallyPt–Fe alloy, Pt–Pd sulphide, Pt–Pd bismuthotelluride).Lesser amounts of PGE occur in solid solution within the BMS.In most cases, the PGM occur at the contact between the BMSand silicates or oxides, or are included within the BMS. Pentlanditeis the principal BMS host of all of the PGE, except Pt, andcontains up to 600 ppm combined PGE. It is preferentially enrichedin Pd, Rh and Co. Pyrrhotite contains, Rh, Os, Ir and Ru, butexcludes both Pt and Pd. Chalcopyrite contains very little ofthe PGE, but does concentrate Ag and Cd. Platinum and Au donot partition into any of the BMS. Instead, they occur in theform of PGM and electrum. In the chromitite layers the whole-rockconcentrations of all the PGE except Pd are enriched by a factorof five relative to S, Ni, Cu and Au. This enrichment couldbe attributed to BMS in these layers being richer in PGE thanthe BMS in the silicate layers. However, the PGE content inthe BMS varies only slightly as a function of the stratigraphy.The BMS in the chromitites contain twice as much PGE as theBMS in the silicate rocks, but this is not sufficient to explainthe strong enrichment of PGE in the chromitites. In the lightof our results, we propose that the collection of the PGE occurredin two steps in the chromitites: some PGM formed before sulphidesaturation during chromitite layer formation. The remainingPGE were collected by an immiscible sulphide liquid that percolateddownward until it encountered the chromitite layers. In thesilicate rocks, PGE were collected by only the sulphide liquid. KEY WORDS: Merensky Reef; Rustenburg Platinum Mine; sulphide; platinum-group elements; image analysis; laser ablation ICP-MS     

Researching female sex work: reflections on geographical exclusion, critical methodologies and 'useful' knowledge

Summary Against the backdrop of ongoing debates about the nature of 'critical' geography, this paper considers the importance of intensive, action-oriented and conversational research methodologies in providing a 'Voice' to excluded populations. The distinct contribution of such methods to the understanding of exclusion is illustrated with reference to research on female prostitution, drawing on the author's own experiences as well as those of feminist researchers in health and the social sciences. However, the paper concludes by comparing the emancipatory potential of such qualitative methods with more quantitative approaches, arguing that no one method can be prioritized in the search for 'useful' know.     

What Determines the Distribution of Coastal Hydrobiid Mudsnails Within North-Western Europe?

The three north-west European species of Hydrobia are often partially segregated along salinity gradients and/or sympatric in the nontidal eastern Danish waters and Baltic Sea, but are rarely sympatric and are confined either to nontidal coastal lagoons ( Hydrobia ventrosa and Hydrobia neglecta ) or to the marine/estuarine intertidal zone ( Hydrobia ulvae ) along the macrotidal Atlantic and North Sea coasts. Significant interspecific competition has been found in Danish waters but not elsewhere in the Atlantic and North-Sea Europe. The two nontidal species and H. ulvae also possess contrasting reproductive strategies. The roles of life-history strategy, interspecific competition and between-habitat dispersal in restricting these mudsnails to their differing habitats are evaluated in the light of these and other findings. It is concluded that all are likely to be relevant, especially dispersal in maintaining and interspecific competition in opposing, mixed populations in the Kattegat-Baltic, and life-history strategy in maintaining the lagoonal versus intertidal dichotomy in the rest of north-west Europe. This dichotomy prevents segregation of species along common salinity gradients outside the Baltic region and restricts potential interspecific competition to within lagoons, where H. ulvae is at a recruitment disadvantage.     

Validation and Joint Inversion of Teleseismic Waveforms for Earthquake Source Models Using Deep Ocean Bottom Pressure Records: A Case Study of the 2006 Kuril Megathrust Earthquake

The importance of accurate tsunami simulation has increased since the 2004 Sumatra-Andaman earthquake and the Indian Ocean tsunami that followed it, because it is an important tool for inundation mapping and, potentially, tsunami warning. An important source of uncertainty in tsunami simulations is the source model, which is often estimated from some combination of seismic, geodetic or geological data. A magnitude 8.3 earthquake that occurred in the Kuril subduction zone on 15 November, 2006 resulted in the first teletsunami to be widely recorded by bottom pressure recorders deployed in the northern Pacific Ocean. Because these recordings were unaffected by shallow complicated bathymetry near the coast, this provides a unique opportunity to investigate whether seismic rupture models can be inferred from teleseismic waves with sufficient accuracy to be used to forecast teletsunami. In this study, we estimated the rupture model of the 2006 Kuril earthquake by inverting the teleseimic waves and used that to model the tsunami source. The tsunami propagation was then calculated by solving the linear long-wave equations. We found that the simulated 2006 Kuril tsunami compared very well to the ocean bottom recordings when simultaneously using P and long-period surface waves in the earthquake source process inversion.     

Introduction to “Tsunami Science Four Years After the 2004 Indian Ocean Tsunami, Part I: Modelling and Hazard Assessment”

In this introduction we briefly summarize the 14 contributions to Part I of this special issue on Tsunami Science Four Years after the 2004 Indian Ocean Tsunami. These papers are representative of the new tsunami science being conducted since the occurrence of that tragic event. Most of these were presented at the session: Tsunami Generation and Hazard, of the International Union of Geodesy and Geophysics XXIV General Assembly held at Perugia, Italy, in July of 2007. That session included over one hundred presentations on a wide range of topics in tsunami research. The papers grouped into Part I, and introduced here, cover topics directly related to tsunami mitigation such as numerical modelling, hazard assessment and databases. Part II of this special issue, Observations and Data Analysis, will be published in a subsequent volume of Pure and Applied Geophysics.     

Standing Conference of Astronomy Professors

The Chair Mike Bode and the Secretary Phil Charles bring the minutes of the 13 October 1999 meeting of the Standing Conference of Astronomy Professors, attended by representatives of 11 universities.