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

Jégo, Sébastien; Pichavant, Michel

doi:10.1016/j.gca.2012.01.027

Cited by 49 publications

(42 citation statements)

References 92 publications

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“…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). Those three solubility values are noticeably lower than those obtained by Jégo and Pichavant (2012) in dacitic compositions (1000°C, 4 kbar), which range from 1200 to 4250 ppb Au at ~NNO-1 and from 865 to 2400 ppb at ~NNO+1.5, depending mainly on the melt S content. Jugo et al (1999) also report high gold solubility values, i.e., ~ 4 ± 2 ppm in hydrous haplogranitic melt (850°C, 1 kbar) in moderately oxidizing conditions (~NNO±0.5).…”

Section: Introductioncontrasting

confidence: 61%

“…Recently, Botcharnikov et al (2010) presented the first experimental Au solubility data in S-bearing hydrous intermediate (i.e., andesitic) silicate melts around NNO. Similarly to Jégo and Pichavant (2012), the data reported in Botcharnikov et al (2010) suggest a positive correlation between the concentrations of Au and S dissolved in the melt under reducing/moderately oxidizing conditions. However, Botcharnikov et al (2010) show significantly lower Au solubility values (from 300 to 2500 ppb) compared to Jégo and Pichavant (2012), and Zajacz et al (2012;2013) also report similarly lower Au concentrations (from 220-1550 ppb Au and from ~60-3200 ppb Au, respectively) in reducing to moderately oxidizing conditions at 1000°C and 2 kbar.…”

Section: Introductionmentioning

confidence: 57%

“…Similarly to Jégo and Pichavant (2012), the data reported in Botcharnikov et al (2010) suggest a positive correlation between the concentrations of Au and S dissolved in the melt under reducing/moderately oxidizing conditions. However, Botcharnikov et al (2010) show significantly lower Au solubility values (from 300 to 2500 ppb) compared to Jégo and Pichavant (2012), and Zajacz et al (2012;2013) also report similarly lower Au concentrations (from 220-1550 ppb Au and from ~60-3200 ppb Au, respectively) in reducing to moderately oxidizing conditions at 1000°C and 2 kbar. Nevertheless, another study by Botcharnikov et al (2011) reports much higher gold concentrations (from 250 to 8000 ppb Au) in basaltic to andesitic melts over an fO 2 range going from NNO-1 to ~NNO+2, which emphasize the role of fO 2 in controlling the incorporation of gold in melt.…”

Section: Introductionmentioning

confidence: 57%

“…Nevertheless, another study by Botcharnikov et al (2011) reports much higher gold concentrations (from 250 to 8000 ppb Au) in basaltic to andesitic melts over an fO 2 range going from NNO-1 to ~NNO+2, which emphasize the role of fO 2 in controlling the incorporation of gold in melt. Under more oxidizing conditions (fO 2 ≥ NNO+3), Jégo and Pichavant (2012) show that gold dissolution is much less effective -with solubility values around 600 ppb Au -and seems independent on the melt S content, yet very high. Thus, the 6 respective effects of the oxidation state and the presence of sulfur on gold solubility are partly understood so far, contrarily to the influence of pressure and temperature.…”

Section: Introductionmentioning

confidence: 94%

“…Table 2), but in S-bearing runs all charges are vapor-saturated even if aH 2 O < 1 (owing to the formation of a fluid phase induced by the sole presence of sulfur in the system; cf. Jégo and Pichavant, 2012). In every experiment, one additional Au capsule containing the fO 2 sensors (see below) was placed together with the two sample capsules in the sample cell of the apparatus.…”

Section: Experimental Chargesmentioning

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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