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  • 1
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    CRYPTIC VARIATION OF CHROMITE CHEMISTRY, PLATINUM GROUP ELEMENT AND PLATINUM GROUP MINERAL DISTRIBUTION IN THE UG-2 CHROMITITE: AN EXAMPLE FROM THE KAREE MINE, WESTERN BUSHVELD COMPLEX, SOUTH AFRICA (2014)
    Society of Economic Geologists (SEG)
    Details
    Publication Date: 2014-02-07
    Description: The UG-2 chromitite of the Bushveld Complex in South Africa contains the world’s largest resources of platinum group elements (PGEs). However, only limited work has been conducted on the fine-scale chemical variation of chromite, and the distribution of PGEs and platinum group minerals (PGMs) within the UG-2. In the present study, one drill core (155 cm long) covering the sequence of the UG-2 chromitite at the Karee mine in the western Bushveld Complex was studied in detail. Geochemically, Pt correlates well with Pd, but not with Ni, Cu, and S, and Pt and Pd show high concentrations at the bottom and in the center of the main UG-2 layer. The mineral chemistry of chromite is characterized by distinct cryptic variation, leading to the division of the UG-2 sequence into 10 distinct sublayers. From bottom to top (with exception of the basal sublayer), each sublayer is defined by an upward decrease of Mg# combined with increases of Cr# and TiO 2 . It is proposed that these trends reflect magmatic differentiation of individual chromitite entities, which coalesced to form a massive chromitite seam. Sulfides (pentlandite, chalcopyrite) interstitial to chromite grains are rare, and associated PGM grains are mainly Pt-Fe alloy, laurite, and cooperite-braggite. The PGEs are bimodally distributed in the UG-2. Platinum and the IPGE (Os, Ir, Ru) are dominantly present as discrete PGMs, whereas large proportions of Pd and Rh are hosted in the crystal lattice of pentlandite. Palladium and rhodium contents of pentlandite reach a maxima of 2.2 wt % Pd and 3.0 wt % Rh. The present data suggest that a succession of chromitite sublayers formed due to magmatic differentiation and segregated sequentially on top of each other, finally forming a massive chromitite seam. Contemporaneously with chromite segregation, PGE-rich magmatic sulfides segregated with chromite grains, but large proportions of these sulfides were subsequently removed mainly by reaction of sulfide with chromite, thereby upgrading the PGE contents of the remaining sulfides. Upon cooling, the PGE-bearing sulfide droplets recrystallized, leading to a bimodal distribution of the PGEs in the UG-2. The bulk of the Pd and Rh is hosted in pentlandite, whereas Pt and the IPGEs, apparently incompatible in the remaining sulfides, formed a distinct suite of discrete PGMs.
    Print ISSN: 0361-0128
    Topics: Geosciences
    Published by Society of Economic Geologists (SEG)
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  • 2
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    Control of kinetic properties of AMPA receptor channels by nuclear RNA editing (1994)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1994-12-09
    Description: AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptor channels mediate the fast component of excitatory postsynaptic currents in the central nervous system. Site-selective nuclear RNA editing controls the calcium permeability of these channels, and RNA editing at a second site is shown here to affect the kinetic aspects of these channels in rat brain. In three of the four AMPA receptor subunits (GluR-B, -C, and -D), intronic elements determine a codon switch (AGA, arginine, to GGA, glycine) in the primary transcripts in a position termed the R/G site, which immediately precedes the alternatively spliced modules "flip" and "flop." The extent of editing at this site progresses with brain development in a manner specific for subunit and splice form, and edited channels possess faster recovery rates from desensitization.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Lomeli, H -- Mosbacher, J -- Melcher, T -- Hoger, T -- Geiger, J R -- Kuner, T -- Monyer, H -- Higuchi, M -- Bach, A -- Seeburg, P H -- New York, N.Y. -- Science. 1994 Dec 9;266(5191):1709-13.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Laboratory of Molecular Neuroendocrinology, University of Heidelberg, Germany.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/7992055" target="_blank"〉PubMed〈/a〉
    Keywords: Alternative Splicing ; Amino Acid Sequence ; Animals ; Base Sequence ; Brain/embryology/*metabolism ; Cell Nucleus/metabolism ; Exons ; Glutamic Acid/pharmacology ; Glycine/genetics ; Introns ; Kinetics ; Membrane Potentials ; Molecular Sequence Data ; Oocytes ; PC12 Cells ; Patch-Clamp Techniques ; *RNA Editing ; Rats ; Rats, Wistar ; Receptors, AMPA/*genetics/*metabolism ; Recombinant Proteins/metabolism ; Xenopus
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 3
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    Detrital Platinum-Group Minerals and Gold In Placers of Southeastern Samar Island, Philippines (2017)
    Mineralogical Association of Canada
    Details
    Publication Date: 2017-07-08
    Description: The present work provides a comprehensive description of the assemblage of detrital platinum-group minerals (PGM) and gold found in the Llorente river and its tributaries draining the area west of the town of Llorente in southeastern Samar, Philippines. Altogether, 610 grains of detrital PGM were studied by reflected light and scanning electron microscopy, and 464 quantitative electron-microprobe compositions were obtained from 265 grains of PGM in polished sections. The concentrates are dominated by grains of gold, followed by accessory PGM grains. The assemblage of detrital PGM is composed of mainly monophase grains of Os-Ir-Ru-(Pt) alloys (41.3%), Pt-Fe alloys and platinum (together 40.5%), laurite–erlichmanite (16.6%), and rare other PGM (1.6%). Grain sizes of the PGM range from ~50 μm up to 2–3 mm; median sizes are 250 μm for Pt-Fe and Os-Ir-Ru alloy grains, and 420 μm for laurite–erlichmanite grains. Gold grains are commonly silver-rich and display leached outer zones of Ag-poor gold. Grain sizes range from ~50 μm to 6.8 mm (median about 400–500 μm). Notable is the presence of rare tetraauricupride. Both the regional bedrock geology and the distinct PGM assemblage indicate that the PGM originated from Alpine-type ophiolite rocks, probably chromitites, which are common in the study area drained by the Llorente river and its tributaries in the Eastern Bicol-Eastern Mindanao ophiolite belt of Samar. Gold and tetraauricupride may originate from diverse sources. Rare inclusions of tellurides and chalcopyrite in detrital gold grains suggest epithermal gold vein deposits or gold-bearing porphyry copper mineralization as sources of the gold, whereas the tetraauricupride grains may originate from hydrothermal mineralization, different from the gold lode deposits, in mafic/ultramafic rocks of the ophiolite belt.
    Print ISSN: 0008-4476
    Topics: Geosciences
    Published by Mineralogical Association of Canada
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  • 4
    Electronic Resource
    Electronic Resource
    Tryptophan mutants of human C5a anaphylatoxin: A fluorescence anisotropy decay and energy transfer study
    Amsterdam : Elsevier
    Biophysical Chemistry 46 (1993), S. 237-248 
    Details
    ISSN: 0301-4622
    Keywords: C5a mutants (biosynthetic analogues) ; Comparison with NMR structure ; Complement peptide C5a ; Fluorescence energy transfer ; Time-resolved fluorescence
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0301-4622(93)80017-D
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    Paper (German National Licenses)
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  • 5
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    Relative abundance of subunit mRNAs determines gating and Ca2+ permeability of AMPA receptors in principal neurons and interneurons in rat CNS (1995)
    Cell Press
    Details
    Publication Date: 1995-07-01
    Print ISSN: 0896-6273
    Electronic ISSN: 1097-4199
    Topics: Biology , Medicine
    Published by Cell Press
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