Distribution of Gold, Palladium, Platinum, Rhodium, Ruthenium, and Iridium in Leg 115 Hotspot Basalts: Implications for Magmatic Processes

Greenough, John D.; Fryer, Brian J.

doi:10.2973/odp.proc.sr.115.128.1991

Cited by 14 publications

(14 citation statements)

References 45 publications

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“…It is therefore important to emphasize that none of the primary characteristics of average MORB with respect to PGE inventory and Re-Os systematics, except the initial 187 Os/ 188 Os, have been fundamentally changed by hydrothermal alteration. This conclusion confirms results from a PGE study on altered ocean island basalts from the Réunion hot spot, recovered during ODP Leg 115 [Greenough and Fryer, 1990]. The majority of the 504B basalts are offset by $0.05 toward higher 187 Os/ 188 Os relative to a 6.75 Myr reference isochron with depleted upper mantle initial ratios, indicative of early addition of minor amounts (<10% of the total crustal inventory) of hydrogenous Os (Figure 2).…”

Section: Discussionsupporting

confidence: 85%

Rhenium‐osmium isotope systematics and platinum group element concentrations in oceanic crust from DSDP/ODP Sites 504 and 417/418

Peucker‐Ehrenbrink

Bach

Hart

et al. 2003

Geochem Geophys Geosyst

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[1] Rhenium, Os, 187 Os/ 188 Os, Ir, Ru, Pt, and Pd analyses of 43 samples from DSDP/ODP Hole 504B in the eastern equatorial Pacific crust with an age of $6.7 Myr are used to calculate the composition of a composite section through the upper oceanic crust. Weighted average Re (1526 pg/g), Os (21 pg/g), 187 Os/ 188 Os (0.213), 187 Re/ 188 Os (353), initial 187 Os/ 188 Os (0.173), Ir (9 pg/g), Pt (304 pg/g), and Pd (265 pg/g) are similar to a composite sample from DSDP Sites 417/418 in the western Atlantic with an age of $120 Myr (2153 pg Re/g, 33 pg Os/g, 187 Os/ 188 Os = 1.042 ± 0.016, 187 Re/ 188 Os = 349; 187 Os/ 188 Os i = 0.344, 25 pg Ir/g, 698 pg Ru/g, 804 pg Pt/g, and 2001 pg Pd/g). These sections complement existing data for ODP Site 735B (11-12 Myr) and, combined, provide the best available information on Re-PGE-Os isotope systematics of the upper and middle oceanic crust. Weighted average Os concentrations for samples from the volcanic zone, the transition zone with stockwork mineralization, and the sheeted dike complex decrease from 30 pg/g to 18 pg/g. Rhenium concentrations are highest in the transition zone (3867 pg/g), leading to 187 Re/ 188 Os of 885, compared to values of 178 for the volcanic zone and 393 for the sheeted dike complex. The present-day and initial 187 Os/ 188 Os are highest in the transition zone (0.329 and 0.230, respectively). This zone also has the highest average Pt (899 pg/g) and Pd (523 pg/g) concentrations. Of all lithologic units, breccias are most enriched in Re (4874 pg/g) and depleted in Os (8 pg/g), Ir (3 pg/g), Pt (131 pg/g), and Pd (173 pg/g) and have the most radiogenic present-day and initial 187 Os/ 188 Os (0.710 and 0.324, respectively). We contend that this is indicative of intense alteration, loss of PGE, and early addition of hydrogenous Os. Pillow lavas and massive flows and dikes of the volcanic zone and the sheeted dike complex are also affected by additions of hydrogenous Os, causing superchonditic initial 187 Os/ 188 Os. The weighted average Os/Ir of 2.4 for the entire core is significantly higher than values reported for mantle peridotites and estimates of the upper mantle and most likely indicates fractionation during melting and melt extraction or intracrustal differentiation rather than differential mobility of Os and Ir during alteration. Addition of hydrogenous Re to altered oceanic crust, although locally important, does not increase the Re concentration of oceanic crust by more than a few percent. The magnitude of mantlederived Os loss to seawater cannot be reliably estimated from our data, but a steady state mass balance of hydrogenous Os indicates that the average loss cannot exceed 10% of the crustal inventory. Similarly, average addition of hydrogenous Os does not exceed 10% of the primary crustal inventory. This, however, leads to a significant increase in 187 Os/ 188 Os from depleted upper mantle values to $0.17. The characteristic fractionated PGE pattern and 187 Re/ 188 Os of fresh MORB are not fundamentally changed during hydrothermal a...

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Section: Discussionsupporting

confidence: 85%

Rhenium‐osmium isotope systematics and platinum group element concentrations in oceanic crust from DSDP/ODP Sites 504 and 417/418

Peucker‐Ehrenbrink

Bach

Hart

et al. 2003

Geochem Geophys Geosyst

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“…The global upper mantle contains 1.5 ppb Au (e.g., Mitchell and Keays, 1981;Lorand et al, 1999;McInnes et al, 1999;Borisov and Palme, 2000), but in Archean greenstones and modern oceanic basalts, typical background Au contents are 0.7-2 ppb (Meyer and Saager, 1985;Greenough and Fryer, 1990;Togashi and Terashima, 1997). Loucks and Mavrogenes (1999) report solubility values of 29 and 167 ppm Au at 0.37 GPa and 625°C in supercritical hydrothermal brines equilibrated with pyrrhotite + magnetite.…”

Section: Implications For the Gold Budget Of Arc Magmasmentioning

confidence: 97%

Gold solubility in arc magmas: Experimental determination of the effect of sulfur at 1000 °C and 0.4 GPa

Jégo

Pichavant

2012

Geochimica et Cosmochimica Acta

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To investigate the behaviour of gold in sulfur-bearing hydrous intermediate calc-alkaline melts under different redox states typical of subduction-zone settings, we have determined the solubility of Au at 0.4 GPa and 1000°C for three dacitic magmas (two adakites and one calc-alkaline composition) from the North-Luzon Arc (Philippines). The experiments were performed over an oxygen fugacity (fO 2 ) range corresponding to reducing ($NNOÀ1), moderately oxidizing ($NNO+1.5) and strongly oxidizing (PNNO+3) conditions as measured by solid Ni-Pd-O sensors. They were carried out in gold containers, serving also as the source of gold, in presence of variable amounts of H 2 O and $1 wt.% of elemental sulfur (S). Concentrations of Au in glasses were determined by laser-ablation inductively-coupled plasma mass spectrometry (LA-ICPMS). Gold solubility in S-bearing melts is drastically enhanced compared to S-free melts, by up to two orders of magnitude. In addition, very high gold solubilities are reached under reducing conditions (

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“…Platinum-group elements (PGE: Os, Ir, Ru, Rh, Pt, Pd) are important as petrogenetic tracers in the study of Earth's accretion history, core-mantle interaction, and mantle differentiation processes (Greenough and Fryer, 1990;Fryer and Greenough, 1992;Rehkämper et al, 1997;Brandon et al, 1999;Brü gmann et al, 2000;Puchtel and Humayun, 2000;Righter and Drake, 2000;Brandon and Walker, 2005;Lightfoot and Keays, 2005;Becker et al, 2006;Maier et al, 2009;Savard et al, 2010). They are also potential pathfinders for Ni-Cu mineralization (Brü gmann et al, 2000;Lightfoot and Keays, 2005;Fiorentini et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

Ruthenium in komatiitic chromite

Locmelis

Pearson

Barnes

et al. 2011

Geochimica et Cosmochimica Acta

107

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Distribution of Gold, Palladium, Platinum, Rhodium, Ruthenium, and Iridium in Leg 115 Hotspot Basalts: Implications for Magmatic Processes

Cited by 14 publications

References 45 publications

Rhenium‐osmium isotope systematics and platinum group element concentrations in oceanic crust from DSDP/ODP Sites 504 and 417/418

Rhenium‐osmium isotope systematics and platinum group element concentrations in oceanic crust from DSDP/ODP Sites 504 and 417/418

Gold solubility in arc magmas: Experimental determination of the effect of sulfur at 1000 °C and 0.4 GPa

Ruthenium in komatiitic chromite

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