Controls on gold solubility in arc magmas: An experimental study at 1000°C and 4kbar

Jégo, Sébastien; Pichavant, Michel; Mavrogenes, John

doi:10.1016/j.gca.2010.01.012

Cited by 43 publications

(37 citation statements)

References 101 publications

(150 reference statements)

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“…In Fig. 3a, melt Au contents are plotted versus oxygen fugacity and compared with data from previous studies at 0.4 GPa (Jégo et al, 2010), 0.2 GPa (Botcharnikov et al 2011), and ambient pressure/high temperature (Borisov and Palme, 1996). All new data plot as a cluster at fO 2~N NO, showing no particular variation with fO 2 .…”

Section: Sulfur Concentrations In S-bearing Glassesmentioning

confidence: 83%

“…Nevertheless, Borisov and Palme (1996) report Au solubility values from ~300 to 2000 ppb in anhydrous haplobasaltic S-free melt at 1 atm and 1300-1400˚C, and suggest that gold dissolution is dependent on the oxidation state by involving Au 2 O species. Jégo et al (2010) report much lower solubility values (30-240 ppb Au) in S-free dacitic compositions at 4 kbar and 1000˚C, but also show an increase of melt Au contents with fO 2 in a way consistent with the dissolution of gold as both Au 1+ and Au 3+ species. In presence of 5 sulfur, Simon et al (2007) report gold solubility values up to 1100 ppb in Cl-bearing haplogranitic melt at ~NNO (800°C, 1-1.5 kbar) and Jugo et al (2005) give evidence for a solubility on the order of ~500 ppb in anhydrous basaltic melt (1300°C, 10 kbar) in reducing conditions, while a solubility value of ~800 ppb is reported by Bezmen et al (1994) in the Bushveld Complex melt (1300°C, 4 kbar, ~NNO).…”

Section: Introductionmentioning

confidence: 79%

“…They are both dacitic in composition, one being representative of a typical adakite (Bal2) whereas the other one stands for an intermediate adakite (Pin Dac) according to the definition of Jégo et al (2005) (a summary of this adakite classification is given in Jégo et al, 2010). Recent (< 20 Ma) magmatism in the North Luzon arc is linked to the current subduction of the South China Sea plate along the Manila Trench, and includes a range of arc rocks (Sajona and Maury, 1998;Prouteau et al, 2000;Bellon and Yumul, 2001;Jégo et al, 2005).…”

Section: Starting Materialsmentioning

confidence: 99%

“…The selected starting rocks are samples of this recent magmatic episode in North Luzon. Their respective sampling location and geochemical characteristics (major and trace elements) are described in detail by Jégo et al (2010) Field Strength Elements (HFSE) and Heavy Rare Earth Elements (HREE), the HREE and yttrium (Y) contents are significantly lower in Bal2 than in PinDac, consistent with a more extensive fractionation of these elements by garnet during adakite genesis (e.g., Defant and Drummond, 1990;Sen and Dunn, 1994), as evidenced by the very high Sr/Y ratio of Bal2 (197.8) compared with the relatively low one of PinDac (42.4).…”

Section: Starting Materialsmentioning

confidence: 99%

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Is gold solubility subject to pressure variations in ascending arc magmas?

Jégo

Nakamura

Kimura

et al. 2016

Geochimica et Cosmochimica Acta

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Magmas play a key role in the genesis of epithermal and porphyry ore deposits, notably by providing the bulk of ore metals to the hydrothermal fluid phase. It has been long shown that the formation of major deposits requires a multi-stage process, including the concentration of metals in silicate melts at depth and their transfer into the exsolved ore fluid in more superficial environments. Both aspects have been intensively studied for most of noble metals in subsurface conditions, whereas the effect of pressure on the concentration (i.e., solubility) of those metals in magmas ascending from the sublithospheric mantle to the shallow arc crust has been quite neglected. Here, we present new experimental data aiming to constrain the processes of gold (Au) dissolution in subduction-linked magmas along a range of depth. We have conducted hydrous melting experiments on two dacitic/adakitic magmas at 0.9 and 1.4GPa and ~1000°C in an end-loaded piston cylinder apparatus, under fO 2 conditions close to NNO as measured by solid Co-Pd-O sensors. Experimental charges were carried out in pure Au containers, the latter serving as the source of gold, in presence of variable amounts of H 2 O and, for half of the charges, with elemental sulfur (S) so as to reach sulfide saturation. Au concentrations in melt quenched to glass were determined by LA-ICPMS. When compared to previous data obtained at lower pressures and variable redox conditions, our results show that in both S-free and sulfide-saturated systems pressure has no direct, detectable effect on melt Au solubility. Nevertheless, pressure has a strong, negative effect on sulfur solubility. Since gold dissolution is closely related to the behaviour of sulfur in reducing and moderately oxidizing conditions, pressure has therefore a significant but indirect effect on Au solubility.The present study confirms that Au dissolution is mainly controlled by fO 2 in S-free melts and 3 by a complex interplay of fO 2 and melt S 2-concentration in sulfide-saturated melts, at given temperature. In addition, we propose that the transition from sulfide (S 2-) to sulfate (S 6+ ) species in melt is shifted towards more oxidizing conditions when pressure and the degree of melt polymerization increase. If this is true, this may have important consequences during mantle melting and magma ascent. In particular, if mantle melting occurred in moderately oxidizing conditions, a small degree of partial melting would allow the primary melts to become Au-enriched but the relatively high pressure would move the sulfide-sulfate transition to more oxidizing conditions, making the primary melts saturated with sulfide phases that would sequester gold from the melt. During magma ascent, the decreasing pressure would favour the destabilization of sulfides and the release of gold to the silicate melt. However, at shallow levels, decreasing pressure, magma evolution, and varying redox conditions would be continuously competing to concentrate or fractionate gold.

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Section: Sulfur Concentrations In S-bearing Glassesmentioning

confidence: 83%

Section: Introductionmentioning

confidence: 79%

Section: Starting Materialsmentioning

confidence: 99%

Section: Starting Materialsmentioning

confidence: 99%

See 2 more Smart Citations

Is gold solubility subject to pressure variations in ascending arc magmas?

Jégo

Nakamura

Kimura

et al. 2016

Geochimica et Cosmochimica Acta

Self Cite

View full text Add to dashboard Cite

show abstract

“…Concentrations of sulphur range from a few hundred to a few thousand parts per million 3,4 . When placed in the upper crust, the majority of magmas soon saturate with an immiscible sulphide melt that hosts numerous economically interesting elements, such as copper, nickel, gold and the platinum-group elements 5 . According to the classic mechanism of magmatic sulphide ore formation 6 , sulphide melts readily settle out of the main molten body of magma because they are much denser than the surrounding silicate melt.…”

Section: Introductionmentioning

confidence: 99%