Sulfur concentration at sulfide saturation (SCSS) in magmatic silicate melts

Liu, Yanan; Samaha, Naji-Tom; Baker, Don R.

doi:10.1016/j.gca.2007.01.004

Cited by 221 publications

(179 citation statements)

References 49 publications

(130 reference statements)

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“…ΔNNO: difference between log fO2 of the charge and log fO2 of the Ni-NiO equilibrium at the same pressure and temperature. log fS2 in sulfur-bearing charges was calculated from the expression of Liu et al (2007). ΔFFS: difference between log fS2 of the charge and log fS2 of the iron-pyrrhotite equilibrium at the same pressure and temperature.…”

Section: Discussionmentioning

confidence: 99%

“…The fugacity of sulfur (fS 2 ) was calculated from the expression of Liu et al (2007) which considers T, fO 2 , and the mole fraction of FeO in melt, and includes a correction term for pressure:…”

Section: Analytical Data Processingmentioning

confidence: 99%

“…According to Liu et al (2007), their equation reliably estimates fS 2 to within an uncertainty of 0.7 log units.…”

Section: Analytical Data Processingmentioning

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: Discussionmentioning

confidence: 99%

Section: Analytical Data Processingmentioning

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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show abstract

“…The same settings were used for the analysis of silicate glass. They are similar to those used by Liu et al (2007) and Wallace & Carmichael (1992). Astimex standards were used for calibration: pyrite for S, hematite for Fe, chalcopyrite for Cu, and pentlandite for Ni.…”

Section: Sampling and Analytical Methodsmentioning

confidence: 99%

Textural Variations in Morb Sulfide Droplets Due to Differences in Crystallization History

Patten¹,

Barnes²,

Mathez³

2012

The Canadian Mineralogist

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Sulfide droplets from fresh Mid-Ocean-Ridge Basalt (MORB) glasses show different textures. Some are fine-grained droplets consist of Monosulfide Solid Solution (Mss) and Intermediate Solid Solution (Iss) micrometric intergrowths with pentlandite at the Mss-Iss interface and disseminated Fe-oxide grains; other droplets display a characteristic "zoned" texture consisting of segregated massive grains of Mss and Iss, with euhedral Fe-oxides and pentlandite occuring as equant grains and as flame-shaped domains in the Mss formed by exsolutions. The difference in the textures implies a difference in the crystallization history of the sulfide droplets. These different textures are observed in droplets that are only millimeters apart in the same sample, and thus had an identical cooling history. Therefore, some other factors controlled the textural development. There is relationship between the size and the texture of the droplets. The larger sulfide droplets tend to have zoned textures and the smaller ones fine-grained textures. We propose that the latter have experienced greater undercooling before crystallization. The reason for the delay in crystallization could be that, in the small sulfide droplets, large stable grains with low surface to volume ratio cannot form, which results in higher effective solubility of the Mss. Due to the high degree of undercooling in the small droplets, there were numerous nucleation sites and the diffusion rates of the crystal components in the liquid were lower, leading to fine-grained Mss-Iss intergrowths. In contrast, larger droplets with lower effective solubility of Mss began to crystallize at higher temperature, and thus had fewer nucleation sites, higher diffusion rates, and more time for sulfide differentiation.

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“…Using the model of Liu et al (2007), we calculated the sulphur content at sulphide saturation for our melt inclusions. According to this model, almost all the inclusions Table 6 Intrinsic variables calculated using a range of models (Andersen and Lindsley 1988;Beattie 1993;Ghiorso and Evans 2008;Harrison and Watson 1984;Papale et al 2006;Putirka 2005;Putirka et al 2003Putirka et al , 2007Sisson and Grove 1993;Spencer and Lindsley 1981) Oxide formulae recalculated according to Stormer (1983).…”

Section: Evidence From Melt Inclusion Compositionsmentioning

confidence: 99%

The 2011 eruption of Nabro volcano, Eritrea: perspectives on magmatic processes from melt inclusions

Donovan

Blundy

Oppenheimer

et al. 2017

Contrib Mineral Petrol

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The 2011 eruption of Nabro volcano, Eritrea, produced one of the largest volcanic sulphur inputs to the atmosphere since the 1991 eruption of Mt. Pinatubo, yet has received comparatively little scientific attention. Nabro forms part of an off-axis alignment, broadly perpendicular to the Afar Rift, and has a history of large-magnitude explosive silicic eruptions, as well as smaller more mafic ones. Here, we present and analyse extensive petrological data obtained from samples of trachybasaltic tephra erupted during the 2011 eruption to assess the pre-eruptive magma storage system and explain the large sulphur emission. We show that the eruption involved two texturally distinct batches of magma, one of which was more primitive and richer in sulphur than the other, which was higher in water (up to 2.5 wt%). Modelling of the degassing and crystallisation histories demonstrates that the more primitive magma rose rapidly from depth and experienced degassing crystallisation, while the other experienced isobaric cooling in the crust at around 5 km depth. Interaction between the two batches occurred shortly before the eruption. The eruption itself was likely triggered by recharge-induced destabilisation of vertically extensive mush zone under the volcano. This could potentially account for the large volume of sulphur released. Some of the melt inclusions are volatile undersaturated, and suggest that the original water content of the magma was around 1.3 wt%, which is relatively high for an intraplate setting, but consistent with seismic studies of the Afar plume. This eruption was smaller than some geological eruptions at Nabro, but provides important insights into the plumbing systems and dynamics of off-axis volcanoes in Afar.

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Sulfur concentration at sulfide saturation (SCSS) in magmatic silicate melts

Cited by 221 publications

References 49 publications

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

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

Textural Variations in Morb Sulfide Droplets Due to Differences in Crystallization History

The 2011 eruption of Nabro volcano, Eritrea: perspectives on magmatic processes from melt inclusions

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