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  • 1
    Monograph available for loan
    Monograph available for loan
    Magmatic processes and plate tectonics (1993)
    London : The Geological Society
    Associated volumes
    Details Availability
    Call number: 9/M 95.0254
    In: Geological Society special publication
    Description / Table of Contents: This volume is a collection of papers to celebrate the life and work of Professor lan Gass. The research themes cover many of the subjects which most interested him, especially processes operating in oceanic crust. The introductory papers examine evolution of magmas from mantle melting to eruption. A central section concerns ophiolite complexes. Several papers focus on different aspects of the Troodos ophiolite complex in Cyprus, where lan first recognized that sheeted dykes within the ophiolite sequence must have formed in an oceanic spreading environment. In addition, ophiolites ,are reviewed and examined in terms of tectonics, magmatic and mantle textures, metallogenesis and hydrothermal alteration. A further section concentrates on tectonics and the genesis of magmas associated with collision and subduction. This contrasts with continental rifting and the effects of mantle plumes. This collection of papers covers a broad range of topics from processes in the mantle to those in the oceanic crust. The volume will be of interest to all scientists concerned with igneous processes and global tectonics.
    Type of Medium: Monograph available for loan
    Pages: IX, 526 S. , Ill., graph. Darst., Kt.
    ISBN: 090331794X
    Series Statement: Geological Society special publication 76
    URL: http://sp.lyellcollection.org/content/76/1
    Classification:
    Petrology, Petrography
    Language: English
    Note: Mantle and Magmatic Processes --- George P. L. Walker: Basaltic-volcano systems / Geological Society, London, Special Publications, 76:3-38, doi:10.1144/GSL.SP.1993.076.01.01 --- M. J. O’Hara: Trace element geochemical effects of imperfect crystal-liquid separation / Geological Society, London, Special Publications, 76:39-59, doi:10.1144/GSL.SP.1993.076.01.02 --- Alexander R. McBirney: Differentiated rocks of the Galapagos hotspot / Geological Society, London, Special Publications, 76:61-69, doi:10.1144/GSL.SP.1993.076.01.03 --- Martin A. Menzies, Weiming Fan, and Ming Zhang: Palaeozoic and Cenozoic lithoprobes and the loss of 〉120 km of Archaean lithosphere, Sino-Korean craton, China / Geological Society, London, Special Publications, 76:71-81, doi:10.1144/GSL.SP.1993.076.01.04 --- Ophiolites and Oceanic Crust --- Alastair Robertson and Costas Xenophontos: Development of concepts concerning the Troodos ophiolite and adjacent units in Cyprus / Geological Society, London, Special Publications, 76:85-119, doi:10.1144/GSL.SP.1993.076.01.05 --- Dorothee Dietrich and Sara Spencer: Spreading-induced faulting and fracturing of oceanic crust: examples from the Sheeted Dyke Complex of the Troodos ophiolite, Cyprus / Geological Society, London, Special Publications, 76:121-139, doi:10.1144/GSL.SP.1993.076.01.06 --- C. J. MacLeod and B. J. Murton: Structure and tectonic evolution of the Southern Troodos Transform Fault Zone, Cyprus / Geological Society, London, Special Publications, 76:141-176, doi:10.1144/GSL.SP.1993.076.01.07 --- J. Malpas, T. Calon, and G. Squires: The development of a late Cretaceous microplate suture zone in SW Cyprus / Geological Society, London, Special Publications, 76:177-195, doi:10.1144/GSL.SP.1993.076.01.08 --- A. W. Shelton: Troodos revisited: the Mount Olympus gravity anomaly / Geological Society, London, Special Publications, 76:197-212, doi:10.1144/GSL.SP.1993.076.01.09 --- Alan G. Smith: Tectonic significance of the Hellenic-Dinaric ophiolites / Geological Society, London, Special Publications, 76:213-243, doi:10.1144/GSL.SP.1993.076.01.10 --- I. D. Bartholomew: The interaction and geometries of diapiric uprise centres along mid-ocean ridges — evidence from mantle fabric studies of ophiolite complexes / Geological Society, London, Special Publications, 76:245-256, doi:10.1144/GSL.SP.1993.076.01.11 --- Stephen Roberts and Christopher Neary: Petrogenesis of ophiolitic chromitite / Geological Society, London, Special Publications, 76:257-272, doi:10.1144/GSL.SP.1993.076.01.12 --- H. M. Prichard and R. A. Lord: An overview of the PGE concentrations in the Shetland ophiolite complex / Geological Society, London, Special Publications, 76:273-294, doi:10.1144/GSL.SP.1993.076.01.13 --- H. Elderfield, R. A. Mills, and M. D. Rudnicki: Geochemical and thermal fluxes, high-temperature venting and diffuse flow from mid-ocean ridge hydrothermal systems: the TAG hydrothermal field, Mid-Atlantic Ridge 26°N / Geological Society, London, Special Publications, 76:295-307, doi:10.1144/GSL.SP.1993.076.01.14 --- Martin A. Menzies, Andrew Long, Gerry Ingram, Matthew Tatnell, and David Janecky: MORB peridotite-sea water interaction: experimental constraints on the behaviour of trace elements, 87Sr/86Sr and 143Nd/144Nd ratios / Geological Society, London, Special Publications, 76:309-322, doi:10.1144/GSL.SP.1993.076.01.15 --- Tectonics and Convergent Margins --- J. F. Dewey, P. D. Ryan, and T. B. Andersen: Orogenic uplift and collapse, crustal thickness, fabrics and metamorphic phase changes: the role of eclogites / Geological Society, London, Special Publications, 76:325-343, doi:10.1144/GSL.SP.1993.076.01.16 --- Robert M. Shackleton: Tectonics of the Mozambique Belt in East Africa / Geological Society, London, Special Publications, 76:345-362, doi:10.1144/GSL.SP.1993.076.01.17 --- N. B. W. Harris, C. J. Hawkesworth, and A. G. Tindle: The growth of continental crust during the Late Proterozoic: geochemical evidence from the Arabian Shield / Geological Society, London, Special Publications, 76:363-371, doi:10.1144/GSL.SP.1993.076.01.18 --- Julian A. Pearce and Ian J. Parkinson: Trace element models for mantle melting: application to volcanic arc petrogenesis / Geological Society, London, Special Publications, 76:373-403, doi:10.1144/GSL.SP.1993.076.01.19 --- Peter J. Wyllie and Michael B. Wolf: Amphibolite dehydration-melting: sorting out the solidus / Geological Society, London, Special Publications, 76:405-416, doi:10.1144/GSL.SP.1993.076.01.20 --- Claudio Vita-Finzi: Evaluating Late Quaternary uplift in Greece and Cyprus / Geological Society, London, Special Publications, 76:417-424, doi:10.1144/GSL.SP.1993.076.01.21 --- Continental Rifting --- Ray Macdonald and Brian G. J. Upton: The Proterozoic Gardar rift zone, south Greenland: comparisons with the East African Rift System / Geological Society, London, Special Publications, 76:427-442, doi:10.1144/GSL.SP.1993.076.01.22 --- K. G. Cox, N. Charnley, R. C. O. Gill, and K. A. Parish: Alkali basalts from Shuqra, Yemen: magmas generated in the crust-mantle transition zone? / Geological Society, London, Special Publications, 76:443-453, doi:10.1144/GSL.SP.1993.076.01.23 --- N. W. Rogers: The isotope and trace element geochemistry of basalts from the volcanic islands of the southern Red Sea / Geological Society, London, Special Publications, 76:455-467, doi:10.1144/GSL.SP.1993.076.01.24 --- Jon M. Davis, Wolfgang E. Elston, and Chris J. Hawkesworth: Basic and intermediate volcanism of the Mogollon-Datil volcanic field: implications for mid-Tertiary tectonic transitions in southwestern New Mexico, USA / Geological Society, London, Special Publications, 76:469-488, doi:10.1144/GSL.SP.1993.076.01.25 --- George P. L. Walker: Re-evaluation of inclined intrusive sheets and dykes in the Cuillins volcano, Isle of Skye / Geological Society, London, Special Publications, 76:489-497, doi:10.1144/GSL.SP.1993.076.01.26 --- Analytical Techniques --- Philip J. Potts, Chris J. Hawkesworth, Peter van Calsteren, and Ian P. Wright: Advances in analytical technology and its influence on the development of modern inorganic geochemistry: a historical perspective / Geological Society, London, Special Publications, 76:501-520, doi:10.1144/GSL.SP.1993.076.01.27
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  • 2
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    Magmatic Processes and Plate Tectonics (1993)
    London : The Geological Society
    Details
    Keywords: Magmatismus ; Plattentektonik ; Magmatism ; Plate tectonics ; Volcanism
    Description / Table of Contents: Mantle and Magmatic Processes --- George P. L. Walker: Basaltic-volcano systems / Geological Society, London, Special Publications, 76:3-38, doi:10.1144/GSL.SP.1993.076.01.01 --- M. J. O’Hara: Trace element geochemical effects of imperfect crystal-liquid separation / Geological Society, London, Special Publications, 76:39-59, doi:10.1144/GSL.SP.1993.076.01.02 --- Alexander R. McBirney: Differentiated rocks of the Galapagos hotspot / Geological Society, London, Special Publications, 76:61-69, doi:10.1144/GSL.SP.1993.076.01.03 --- Martin A. Menzies, Weiming Fan, and Ming Zhang: Palaeozoic and Cenozoic lithoprobes and the loss of 〉120 km of Archaean lithosphere, Sino-Korean craton, China / Geological Society, London, Special Publications, 76:71-81, doi:10.1144/GSL.SP.1993.076.01.04 --- Ophiolites and Oceanic Crust --- Alastair Robertson and Costas Xenophontos: Development of concepts concerning the Troodos ophiolite and adjacent units in Cyprus / Geological Society, London, Special Publications, 76:85-119, doi:10.1144/GSL.SP.1993.076.01.05 --- Dorothee Dietrich and Sara Spencer: Spreading-induced faulting and fracturing of oceanic crust: examples from the Sheeted Dyke Complex of the Troodos ophiolite, Cyprus / Geological Society, London, Special Publications, 76:121-139, doi:10.1144/GSL.SP.1993.076.01.06 --- C. J. MacLeod and B. J. Murton: Structure and tectonic evolution of the Southern Troodos Transform Fault Zone, Cyprus / Geological Society, London, Special Publications, 76:141-176, doi:10.1144/GSL.SP.1993.076.01.07 --- J. Malpas, T. Calon, and G. Squires: The development of a late Cretaceous microplate suture zone in SW Cyprus / Geological Society, London, Special Publications, 76:177-195, doi:10.1144/GSL.SP.1993.076.01.08 --- A. W. Shelton: Troodos revisited: the Mount Olympus gravity anomaly / Geological Society, London, Special Publications, 76:197-212, doi:10.1144/GSL.SP.1993.076.01.09 --- Alan G. Smith: Tectonic significance of the Hellenic-Dinaric ophiolites / Geological Society, London, Special Publications, 76:213-243, doi:10.1144/GSL.SP.1993.076.01.10 --- I. D. Bartholomew: The interaction and geometries of diapiric uprise centres along mid-ocean ridges — evidence from mantle fabric studies of ophiolite complexes / Geological Society, London, Special Publications, 76:245-256, doi:10.1144/GSL.SP.1993.076.01.11 --- Stephen Roberts and Christopher Neary: Petrogenesis of ophiolitic chromitite / Geological Society, London, Special Publications, 76:257-272, doi:10.1144/GSL.SP.1993.076.01.12 --- H. M. Prichard and R. A. Lord: An overview of the PGE concentrations in the Shetland ophiolite complex / Geological Society, London, Special Publications, 76:273-294, doi:10.1144/GSL.SP.1993.076.01.13 --- H. Elderfield, R. A. Mills, and M. D. Rudnicki: Geochemical and thermal fluxes, high-temperature venting and diffuse flow from mid-ocean ridge hydrothermal systems: the TAG hydrothermal field, Mid-Atlantic Ridge 26°N / Geological Society, London, Special Publications, 76:295-307, doi:10.1144/GSL.SP.1993.076.01.14 --- Martin A. Menzies, Andrew Long, Gerry Ingram, Matthew Tatnell, and David Janecky: MORB peridotite-sea water interaction: experimental constraints on the behaviour of trace elements, 87Sr/86Sr and 143Nd/144Nd ratios / Geological Society, London, Special Publications, 76:309-322, doi:10.1144/GSL.SP.1993.076.01.15 --- Tectonics and Convergent Margins --- J. F. Dewey, P. D. Ryan, and T. B. Andersen: Orogenic uplift and collapse, crustal thickness, fabrics and metamorphic phase changes: the role of eclogites / Geological Society, London, Special Publications, 76:325-343, doi:10.1144/GSL.SP.1993.076.01.16 --- Robert M. Shackleton: Tectonics of the Mozambique Belt in East Africa / Geological Society, London, Special Publications, 76:345-362, doi:10.1144/GSL.SP.1993.076.01.17 --- N. B. W. Harris, C. J. Hawkesworth, and A. G. Tindle: The growth of continental crust during the Late Proterozoic: geochemical evidence from the Arabian Shield / Geological Society, London, Special Publications, 76:363-371, doi:10.1144/GSL.SP.1993.076.01.18 --- Julian A. Pearce and Ian J. Parkinson: Trace element models for mantle melting: application to volcanic arc petrogenesis / Geological Society, London, Special Publications, 76:373-403, doi:10.1144/GSL.SP.1993.076.01.19 --- Peter J. Wyllie and Michael B. Wolf: Amphibolite dehydration-melting: sorting out the solidus / Geological Society, London, Special Publications, 76:405-416, doi:10.1144/GSL.SP.1993.076.01.20 --- Claudio Vita-Finzi: Evaluating Late Quaternary uplift in Greece and Cyprus / Geological Society, London, Special Publications, 76:417-424, doi:10.1144/GSL.SP.1993.076.01.21 --- Continental Rifting --- Ray Macdonald and Brian G. J. Upton: The Proterozoic Gardar rift zone, south Greenland: comparisons with the East African Rift System / Geological Society, London, Special Publications, 76:427-442, doi:10.1144/GSL.SP.1993.076.01.22 --- K. G. Cox, N. Charnley, R. C. O. Gill, and K. A. Parish: Alkali basalts from Shuqra, Yemen: magmas generated in the crust-mantle transition zone? / Geological Society, London, Special Publications, 76:443-453, doi:10.1144/GSL.SP.1993.076.01.23 --- N. W. Rogers: The isotope and trace element geochemistry of basalts from the volcanic islands of the southern Red Sea / Geological Society, London, Special Publications, 76:455-467, doi:10.1144/GSL.SP.1993.076.01.24 --- Jon M. Davis, Wolfgang E. Elston, and Chris J. Hawkesworth: Basic and intermediate volcanism of the Mogollon-Datil volcanic field: implications for mid-Tertiary tectonic transitions in southwestern New Mexico, USA / Geological Society, London, Special Publications, 76:469-488, doi:10.1144/GSL.SP.1993.076.01.25 --- George P. L. Walker: Re-evaluation of inclined intrusive sheets and dykes in the Cuillins volcano, Isle of Skye / Geological Society, London, Special Publications, 76:489-497, doi:10.1144/GSL.SP.1993.076.01.26 --- Analytical Techniques --- Philip J. Potts, Chris J. Hawkesworth, Peter van Calsteren, and Ian P. Wright: Advances in analytical technology and its influence on the development of modern inorganic geochemistry: a historical perspective / Geological Society, London, Special Publications, 76:501-520, doi:10.1144/GSL.SP.1993.076.01.27
    Pages: Online-Ressource (IX, 526 Seiten) , Illustrationen, Diagramme, Karten
    ISBN: 090331794X
    URL: http://sp.lyellcollection.org/content/76/1
    Language: English
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  • 3
    Electronic Resource
    Electronic Resource
    Petrology and mineralogy of dredged gabbro from Gettysburg Bank, eastern Atlantic (1982)
    Springer
    Contributions to mineralogy and petrology 79 (1982), S. 46-55 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Gabbros have been dredged from Gettysburg Bank, 110 km west of Portugal on the Azores/Gibraltar fracture zone. Primary minerals in olivine, pyroxene and brown hornblende gabbros are partially replaced by metamorphic minerals. Igneous textures are inhomogeneously overprinted by a granular polyhedral deformation and a cataclastic deformation. Amphiboles show characteristics which indicate a transition from crystallisation in a magma chamber to formation of amphibole in solid gabbro under metasomatic conditions. Of the amphiboles analysed, chlorine was present in the green amphiboles but below 0.05% in the brown suggesting the penetration of sea water after the formation of the brown amphibole but during the formation of the green.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00376960
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  • 4
    Electronic Resource
    Electronic Resource
    A petrographie study of the process of serpentinisation in ophiolites and the ocean crust (1979)
    Springer
    Contributions to mineralogy and petrology 68 (1979), S. 231-241 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The process of serpentinisation is illustrated by 17 samples showing different degrees of serpentinisation chosen from a large number of peridotites and serpentinites from the ocean floor and from ophiolite complexes. Observations of textural relationships were made by optical and scanning electron microscope. Mineral identification was confirmed by X-ray diffraction. Of the serpentine polymorphs, lizardite forms during early stages of serpentinisation and displays a characteristically platy morphology. Olivine and pyroxene are replaced by lizardite until no olivine remains. At this stage chrysotile begins to crystallise as fine fibres characteristically filling veins and actually replacing lizardite throughout the rock. Antigorite is confined to sheared surfaces and is rare in the ocean floor forming the latest polymorph. Both ocean floor and ophiolite samples show well developed mesh textures in hand specimen, while a much smaller web network of serpentine occurs on some ocean floor samples. Serpentines from ophiolites show two morphological types of lizardite which may have formed at different temperatures.
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    URL: http://dx.doi.org/10.1007/BF00371544
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  • 5
    Electronic Resource
    Electronic Resource
    Irarsite-hollingworthite solid-solution series and other associated Ru-, Os-, Ir-, and Rh-bearing PGM's from the Shetland ophiolite complex (1987)
    Springer
    Mineralium deposita 22 (1987), S. 178-184 
    Details
    ISSN: 1432-1866
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Pure end and intermediate members of the irarsite-hollingworthite solid-solution series occur in the Shetland ophiolite complex. Hollingworthite frequently rims irarsite. Their compositions are unusually Pt poor, compared with analyses of these minerals from elswhere, suggesting the existence of a Pt-poor environment during their formation. Ir-Sb-S and Rh-Sb-S have been identified as inclusions within irarsite. Ir-Sb-S and Rh-Sb-S together with Rh-Ni-Sb are thought to be new platinum-group minerals (PGM's) in ophiolite complexes. Two types of laurite are present. An Os-rich (up to 22% Os) variety is entirely enclosed by chromite, whereas an Os-free variety is located in the silicate matrix interstitial to the chromite. Laurites in the rims of chromite grains are Os-free but contain tiny inclusions of native osmium. It is suggested that either the availability of Os decreased during crystallisation of the laurites or that Os has been removed from laurites not totally enclosed by chromite. In a few cases laurite is surrounded by a ruthenian pentlandite containing up to 12% Ru.
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    URL: http://dx.doi.org/10.1007/BF00206607
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  • 6
    Electronic Resource
    Electronic Resource
    Book reviews (1995)
    Springer
    Mineralium deposita 30 (1995), S. 332-334 
    Details
    ISSN: 1432-1866
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00196370
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  • 7
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    THE FIRST REPORT OF PLATINUM-GROUP MINERALS IN MAGNETITE-BEARING GABBRO, FREETOWN LAYERED COMPLEX, SIERRA LEONE: OCCURRENCES AND GENESIS (2013)
    Mineralogical Association of Canada
    Details
    Publication Date: 2013-10-17
    Description: Platinum-group minerals (PGM) have been located in magnetite-bearing gabbroic rocks of the Freetown Layered Complex, Sierra Leone for the first time. The PGM occurrences described here are from four stratiform layers characterized by a local, more primitive, composition of the associated silicate minerals and elevated platinum-group elements (PGE) and base metal assays. The uppermost layer (Horizon B) is the best exposed; the three lower layers are currently known only from single outcrops. Platinum-group minerals are irregularly distributed through these layers. Altered PGE arsenides and antimonides, possibly derived from sperrylite (PtAs 2 ) and "mertieite" [Pd 8 (Sb,As) 3 to Pd 11 (Sb,As) 4 ], occur in the lowest known PGE-enriched layer (Horizon M). Cooperite (PtS) and Pt-Fe alloys were observed in a higher layer (Horizon D). Pd-Cu alloys including nielsenite (PdCu 3 ) are unique to the next stratigraphically higher PGM-bearing layer (Horizon C). The uppermost layer (Horizon B) contains the most PGM. Pt-Fe alloy (usually Pt 3 Fe) is by far the most abundant PGM and cooperite is a significant component of the assemblage. Bowieite [(Pt,Ir,Rh) 2 S 3 ], tulameenite (Pt 2 CuFe), and laurite (RuS 2 ) have also been found in this horizon. Cooperite occurs in a late magmatic, high Ca-amphibole (cannilloite) which has formed interstitially to plagioclase and between plagioclase and olivine at a depth of about 20 km. The cooperite is often attached to rounded magnetite grains within the amphibole. Where cooperite is located at the edge of the amphibole or in interstitial locations it has been altered to Pt-Fe alloy. Platinum-group minerals sometimes occur near the margin of sulfides, mainly chalcopyrite and minor pentlandite. The entire PGM assemblage is found mainly interstitial to olivine, pyroxene, and plagioclase, often at the edge of amphibole or in interstitial sites associated with amphibole, chlorite, or quartz. Many of the PGM grains are less than 1 micron in size, with a few in the 2–4 micron range; the largest example is a grain of Pt-Fe alloy that measures 9 by 6 microns. The PGM described here from the rocks are three orders of magnitude smaller than the eluvial and alluvial PGM of the Freetown complex, which are predominantly Pt-Fe alloys, laurite, erlichmanite (OsS 2 ), and Os-Ir alloys. The large eluvial and alluvial PGM might be derived from a horizon containing coarse-grained mineralization, but no vestige of such a horizon has yet been discovered. Previous studies of this area have suggested that secondary remobilization of the PGE has occurred, leading to the growth of large secondary PGM. The primary PGE-mineralization associated with magnetite and Cu-rich sulfide mineralization maybe due to late sulfur saturation in the magma after Ni has been removed by being incorporated into earlier olivine. The presence of digenite, native copper, and nielsenite indicates a low sulfur fugacity, possibly due to oxidation. The four distinctive PGM-bearing horizons are the result of separate injections of magma. The silicate compositions, the minor element content, the PGM mineral assemblage, and the Cu/Pd ratios of the rocks of the PGM-bearing horizons demonstrate that these four magma pulses are compositionally distinct.
    Print ISSN: 0008-4476
    Topics: Geosciences
    Published by Mineralogical Association of Canada
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  • 8
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    Geochemical Variations Within Podiform Chromitite Deposits in the Shetland Ophiolite: Implications for Petrogenesis and PGE Concentration (2014)
    Society of Economic Geologists (SEG)
    Details
    Publication Date: 2014-11-26
    Description: The Shetland ophiolite, located to the northeast of the Scottish mainland, contains podiform chromitites. Two of these are known to host extremely anomalous PGE concentrations. The chromitite at Cliff is enriched in Pt, Pd, and Rh PGE (PPGE) and the Harold’s Grave chromitite is enriched in Ir, Ru, and Os PGE (IPGE). Analysis of multiple samples of chromitite from chromite quarry spoil tips and surrounding chromite-bearing dunite and chromite-bearing harzburgite has revealed that there are links between the chromite geochemistry and the PGE. Both Cliff and Harold’s Grave have a characteristic chromite geochemistry, which distinguishes them from the other PGE-poor chromitites. The IPGE-rich Harold’s Grave chromite contains elevated trace elements (TiO 2 , V 2 O 5 , and Zn), lower Mg#, and a lower Fe 3+ /Fe 2+ ratio than in the other chromitite deposits. This suggests formation from a more reduced magma that favors the concentration of IPGE in chromitite. It is proposed that the IPGE have been concentrated to such enriched and consistent concentrations due to large throughput of magma, leaving an unusually large dunite envelope that surrounds a rather small concentration of chromitite. The geochemistry of the Harold’s Grave deposit suggests formation from a mid-ocean ridge basalt (MORB)/island-arc tholeiite-type magma. There is a range of chromite compositions at Cliff that suggests formation of the chromitite from a variety of mantle melts from mantle of variable composition. PPGE-rich Cliff chromite has a lower Cr# combined with a higher TiO 2 than the other chromite in chromitites at Cliff. It is suggested that a more island-arc tholeiite-type magma formed these PPGE-rich chromitites compared to a more boninitic magma that formed the other chromitites at Cliff. This island-arc tholeiite-type magma was closer to sulfur saturation than the boninitic magma and reached sulfur saturation, producing the very PPGE-rich chromite at Cliff.
    Print ISSN: 0361-0128
    Topics: Geosciences
    Published by Society of Economic Geologists (SEG)
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  • 9
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    The Distribution of PGE and the Role of Arsenic as a Collector of PGE in the Spotted Quoll Nickel Ore Deposit in the Forrestania Greenstone Belt, Western Australia (2013)
    Society of Economic Geologists (SEG)
    Details
    Publication Date: 2013-11-05
    Description: The Spotted Quoll PGE-bearing Ni deposit in the Forrestania greenstone belt in the Archean Yilgarn block in Western Australia is a komatiite-associated massive sulfide orebody tectonically displaced from its original host. The brecciated ore contains clasts of quartz and garnet schist and is located along a shear zone overlain by banded iron formation (BIF) and underlain by BIF and quartz-biotite metasediments. The deformation of the ore has destroyed its magmatic textures and it has been sheared and recrystallized at amphibolite facies. Then the deformed ore has been subjected to a hydrothermal event that concentrated the PGE with Au and As, often at the edge of the Ni ore. The PGE are distributed between PGM and in solid solution in Ni sulfarsenides, and Pd also occurs in pentlandite. The PGM include sudburyite (PdSb), sperrylite (PtAs 2 ), and irarsite (IrAsS). All six PGE and minor Au are hosted in gersdorffite (NiAsS). Two generations of gersdorffite have been recognized. A higher temperature magmatic euhedral Co-rich gersdorffite encloses Ir-, Pt- and Rh-bearing PGM surrounded by halos of Rh-, Ir-, and Os-rich gersdorffite. A lower temperature Ni-rich gersdorffite forms anhedral grains and rims on grains of nickeline (NiAs). In this low-temperature gersdorffite PGE are concentrated toward the mineral edges. Sudburyite and gold occur associated predominantly with nickeline. The PGE and gold are now predominantly associated with sulfarsenides that are the controlling factor for their distribution.
    Print ISSN: 0361-0128
    Topics: Geosciences
    Published by Society of Economic Geologists (SEG)
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  • 10
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    Mineralogy and Geochemistry of Cu-Rich Ores from the McCreedy East Ni-Cu-PGE Deposit (Sudbury, Canada): Implications for the Behavior of Platinum Group and Chalcophile Elements at the End of Crystallization of a Sulfide Liquid (2013)
    Society of Economic Geologists (SEG)
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    Publication Date: 2013-12-22
    Description: Copper-rich massive sulfides are an important source of Pt and Pd in magmatic Ni-Cu-platinum group element ore deposits. At the McCreedy East deposit, Sudbury, they constitute a classic magmatic assemblage of chalcopyrite, cubanite ± pentlandite, located in sharp-walled footwall veins. These Cu-rich ores represent the subsolidus (〈600°C) exsolution products of intermediate solid solution (ISS) that crystallized (950°–800°C) from a highly fractionated sulfide liquid rich in Pt, Pd, Ag, As, Bi, Cd, Pb, Se, Sn, Te, and Zn. Laser ablation-inductively coupled plasma-mass spectrometry and scanning electron microscope analyses have revealed the distribution of platinum group elements (PGE) and trace elements in these ores, which is important for a better understanding of the petrogenesis of Cu-rich sulfide deposits and to improve PGE extraction. Chalcopyrite and cubanite are the dominant hosts of Se and Sn, with Co in pentlandite. Lead is hosted by galena and Zn and Cd by sphalerite, with only a small proportion of these elements present at trace level in ISS (now equally distributed between chalcopyrite and cubanite). Platinum, Pd, Au, As, Bi, and Te, however, are not concentrated in the base metal sulfides and are accounted for almost entirely by the platinum group mineral assemblage, which is dominated by Pt-Pd-Bi-Te phases, such as michenerite [(Pt,Pd)BiTe] and froodite [PdBi 2 ], with minor sperrylite [PtAs 2 ] and Sn-bearing platinum group minerals (PGM), such as niggliite [PtSn], paolovite [Pd 2 Sn], and an unnamed Pt-Sn-Te phase. The PGM form complex, composite grains hosted at the grain boundaries of the base metal sulfides. They typically comprise a core of Sn- or As-bearing PGM (stable at higher temperatures) hosted in Bi-Te-PGM (lower temperatures), which are commonly surrounded by accessory tellurides (Ag, Bi, Pb bearing) and sulfides (galena, sphalerite, and stannite [Cu 2 FeSnS 4 ]). Primary chloride minerals such as cottunite [PbCl 2 ] and ferropyrosmalite [(Fe,Mn) 8 Si 6 O 15 (OH,Cl) 10 ] also form composite grains with hessite [Ag 2 Te] and galena. In contrast to much of the previous work at Sudbury, which has invoked the role of late-magmatic and/or hydrothermal fluids in the collection of precious metals, we show that, in this case, PGM in Cu-rich ore have a magmatic origin. Due to the incompatibility of Pt, Pd, Bi, and Te during the crystallization of ISS, these elements became concentrated in a small volume of late-stage S-bearing melt trapped between intermediate solid solutions. A sequence of PGM, followed by accessory tellurides and sulfides, crystallized from this late-stage melt and formed composite grains. Toward the end of crystallization, the small amount of Cl that was soluble in the sulfide liquid crystallized as primary chloride minerals at low temperatures (〈500°C), either from the late-stage melt or from an exsolved Cl-rich late-magmatic fluid. Some of the primary PGM have been partially altered by Cl-rich fluids (late magmatic and/or hydrothermal) that leached Bi in preference to Pd to form an unnamed Pd-Bi-O-Cl phase. Many PGM also show scalloped edges and truncated grain boundaries, indicating partial corrosion and dissolution, most likely by late-magmatic/hydrothermal fluids that probably remobilized and deposited PGE in the footwall surrounding the veins.
    Print ISSN: 0361-0128
    Topics: Geosciences
    Published by Society of Economic Geologists (SEG)
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