Blei-Isotopen-Verhältnisse im Raum der alpin-mediterranen Metallogenese

Zusammenfassung Die statistische Bearbeitung der Isotopenverhältnisse von Bleierzen des alpinmediterranen Raumes ergab den von W. E.Petrascheck behaupteten engen genetischen Zusammenhang zwischen den einzelnen metallogenetischen Provinzen des genannten Gebietes. Gleichzeitig weisen die Resultate auf einen engen Zusammenhang der Vererzungen mit der magmatisch-sedimentären Vorgeschichte des untersuchten Gebietes hin. Die alt- und jungpaläozoischen sowie die mesozoischen Vererzungen scheinen eine verhältnismäßig einfache Vorgeschichte zu besitzen; im Känozoikum tritt dagegen eine aus mehr heterogenen Quellen stammende Stoffzufuhr ein.

---

The statistical evaluation of the isotopic composition of ore leads from the Alpine-Mediterranean system seems to support the assumption of W. E.Petrascheck about the presence of a strong genetical connection between the individual metallogenetical provinces in this area. At the same time, the results indicate a strong connection between ore mineralization and the magmatical-sedimentological history of the studied area. The source system of the Early and Late Palaeozoic, as well as of the Mesozoic ores seem to possess a rather simple genetical history; in the Tertiary a supply of ore material from a more heterogeneous source is implied.

---

Résumé L'élaboration statistique des donnés de composition isotopique des mineraus de plomb provenant du système alpin-mediterranéen souligne la liaison génétique étroite entre les unités métallogéniques postulée par W. E.Petrascheck. Les résultats indiquent en même temps des rapports immédiats entre la métallogénie et l'évolution magmatique-sédimentaire de l'endroit. Quant aux minéralisations paléozoiques inférieures et supérieures ainsi que mésozoiques il semble s'agir de phénomènes plus globaux, tandis que les minéraus du Tertiaire relèvent des sources plus complexes.

---

- . - . , .

     

Mineral/melt partitioning of trace elements during hydrous peridotite partial melting

This experimental study examines the mineral/melt partitioning of incompatible trace elements among high-Ca clinopyroxene, garnet, and hydrous silicate melt at upper mantle pressure and temperature conditions. Experiments were performed at pressures of 1.2 and 1.6 GPa and temperatures of 1,185 to 1,370 °C. Experimentally produced silicate melts contain up to 6.3 wt% dissolved H ₂O, and are saturated with an upper mantle peridotite mineral assemblage of olivine+orthopyroxene+clinopyroxene+spinel or garnet. Clinopyroxene/melt and garnet/melt partition coefficients were measured for Li, B, K, Sr, Y, Zr, Nb, and select rare earth elements by secondary ion mass spectrometry. A comparison of our experimental results for trivalent cations (REEs and Y) with the results from calculations carried out using the Wood-Blundy partitioning model indicates that H ₂O dissolved in the silicate melt has a discernible effect on trace element partitioning. Experiments carried out at 1.2 GPa, 1,315 °C and 1.6 GPa, 1,370 °C produced clinopyroxene containing 15.0 and 13.9 wt% CaO, respectively, coexisting with silicate melts containing ~1–2 wt% H ₂O. Partition coefficients measured in these experiments are consistent with the Wood-Blundy model. However, partition coefficients determined in an experiment carried out at 1.2 GPa and 1,185 °C, which produced clinopyroxene containing 19.3 wt% CaO coexisting with a high-H ₂O (6.26±0.10 wt%) silicate melt, are significantly smaller than predicted by the Wood-Blundy model. Accounting for the depolymerized structure of the H ₂O-rich melt eliminates the mismatch between experimental result and model prediction. Therefore, the increased Ca ²⁺ content of clinopyroxene at low-temperature, hydrous conditions does not enhance compatibility to the extent indicated by results from anhydrous experiments, and models used to predict mineral/melt partition coefficients during hydrous peridotite partial melting in the sub-arc mantle must take into account the effects of H ₂O on the structure of silicate melts.     

Local deformation monitoring using GPS in an open pit mine: initial study

High-performance GPS RTK software has been developed within the Geodetic Research Laboratory (GRL) at the University of New Brunswick (UNB). This software was initially designed for gantry crane auto-steering. Due to limitations with classical geodetic deformation monitoring techniques, the Canadian Centre for Geodetic Engineering (CCGE) at UNB has decided to augment its fully automated deformation monitoring system with GPS. As a result, the GRL and CCGE have combined efforts to achieve the required precision. As a first step, tests of the GPS real-time kinematic (RTK) software have been carried out at Highland Valley Copper Mine in British Columbia, Canada. An open-pit mine environment places certain constraints on the achievable accuracies attainable with GPS. Consequently, the software has been modified to meet the needs of this particular project and data have been post-processed for analysis. This paper describes the approach taken at UNB to address high precision requirements in a constrained signal availability environment. Technical and scientific aspects of the UNB software, especially in handling two predominant errors (residual tropospheric zenith delay and multipath) at the mine, are discussed. Results of tests that have been carried out at the mine are presented.     

Isotope Dilution MC-ICP-MS Rare Earth Element Analysis of Geochemical Reference Materials NIST SRM 610, NIST SRM 612, NIST SRM 614, BHVO-2G, BHVO-2, BCR-2G, JB-2, WS-E, W-2, AGV-1 and AGV-2

We present data for the concentrations of eleven rare earth elements (La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Er, Yb, Lu) in eleven international geochemical reference materials obtained by isotope dilution multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS). We have analysed both rock powders and synthetic silicate glasses, and the latter provide precise data to support the use of these as reference materials for in situ trace element determination techniques. Our data also provide precise measurements of the abundance of mono-isotopic Pr in both glasses and powders, which allows more accurate constraints on the anomalous redox-related behaviour of Ce during geochemical processes. All materials were analysed in replicate providing data that typically reproduce to better than one percent. Sm/Nd ratios in all these materials also reproduce to better than 0.2% and are accurate to < 0.2% and can thus be used as calibrants for Sm-Nd geochronology. Our analyses agree well with existing data on these reference materials. In particular, for NIST SRM 610, USGS BHVO-2, AGV-1 and AGV-2, our measured REE abundances are typically within < 2% (and mostly 1%) of REE concentrations previously determined by isotope dilution analysis and thermal ionisation mass spectrometry, consistent with the higher degree of precision and accuracy obtained from isotope dilution techniques. Close agreement of results between basaltic glass reference materials USGS BHVO-2G and BCR-2G and the BHVO-2 and BCR-2 powders from which they were created suggests that little fractionation, concentration or dilution of REE contents occurred during glass manufacture.     

Is there a first-order discontinuity in the lowermost mantle?

In 1983, Lay and Helmberger [Geophys. J. R. Astron. Soc. 75 (1983) 799–837] reported the detection of a precursor to the seismic phase ScS. They attributed this precursor to a sharp seismic discontinuity located several hundred kilometers above the core–mantle boundary. Such a lowermost mantle discontinuity implies the existence of a sharp phase change or a chemical boundary. Precursors to ScS and, less frequently, PcP have since been observed in numerous locations, but are not a global phenomenon. Frequently, PcP precursors are weak or absent when ScS precursors are observed in the same location, and vice versa. There can be significant variations in the amplitude and arrival time of the precursor relative to the main phase. The presence or absence of these precursors has led to speculations about the nature of the lowermost mantle. Here we demonstrate that ScS or PcP precursors may be produced by gradients in seismic wave speed associated with large-scale lowermost mantle heterogeneity. Rather than a phase or chemical boundary with substantial topography, such gradients require lateral variations in temperature and, close to the core–mantle boundary, composition.     

Carbonate alteration of the Upper Mount McRae Shale beneath the martite-microplaty hematite ore deposit at Mount Whaleback, Western Australia

The formation of large martite-microplaty hematite ore deposits in northwest Australia remains a contentious topic in part because important evidence supporting a unifying genetic model has not been observed at all deposits. Carbonate replacement of silica has been found along normal faults below ore at the Mount Tom Price and Giles Mini deposits, which suggests an early hypogene process during ore formation. However, such rocks have not been identified at the largest martite-microplaty hematite deposit, Mount Whaleback. In this study, samples of the Mount McRae Shale are examined for their chemistry, mineralogy and petrography. These samples were collected from several key locations, including an area that immediately underlies ore along the Mount Whaleback fault at Mount Whaleback. Compared to unaltered black Mount McRae Shale from Wittenoom Gorge in the north and altered black and red Mount McRae Shale at Mount Whaleback, reddish-green Mount McRae Shale along the Mount Whaleback fault is greatly enriched in MgO and CaO and depleted in SiO₂. This chemistry arises from significant amounts of fine- to medium-grained ferroan-dolomite and ankerite and cross-cutting chlorite and carbonate veins. The composition is distinct from that produced during regional metamorphism, and most likely represents hydrothermal alteration after metamorphism. The lack of carbonate-rich, silica-poor rocks in the overlying Dales Gorge Member at Mount Whaleback is consistent with pervasive oxidation of most rocks in the region during or after ore genesis, a process that removed carbonates. Although several questions remain unanswered, these results support models that invoke an early hypogene stage during the formation of the martite-microplaty hematite deposits in the Hamersley Province.Editorial Handling: B. Lehmann     

Storm Surges from Extra-Tropical Cyclones

The possible influence of climate change on the tracks of the extra-tropical cyclones as well as storm surges is studied. Two differentdata bases have been used: one for the Great Lakes of North America and the otherfor the German Bight in the North Sea of Europe. For the Great Lakes region,significant east-west and north-south shifts in the tracks of ETC'S with decadal periodicities have been observed. However, there was no trend in the amplitudes of storm surges. The most important result for the Great Lakes is that, depending upon its position relative to the constantly shifting storm tracks, a given location could eitherexperience a major storm surge or could miss out completely.The storm surges in the German Bight in general, and at Cuxhaven in particular, appear to show a slightly increasing trend in the latterpart of the 20th century. However, the most significant result for the German Bightis that the number of storm tides (i.e., multiple peaks in a given storm surge event)definitely has shown an increase in the second half of the 20th century. This increase isinterpreted as due to the influence of meso-scale weather systems embedded in the synoptic scale ETCs.     

On the occurrence of critical levels in solar magnetohydrodynamics

It is shown that the singular behaviour exhibited by a solution of the magnetoatmospheric wave equation for motion in the presence of a horizontal magnetic field is a special case of the valve type critical level discussed by Acheson (1973), with the difference that the valve effect does not strictly occur; waves are captured as they approach the singular level from either side and are neither reflected or transmitted, but constrained to propagate along the field line. This effect is also likely to occur for purely vertical fields. The possible importance of such critical levels to solar physics is discussed.