The partitioning behavior of As and Au in S-free and S-bearing magmatic assemblages

Simon, Adam C.; Pettke, Thomas; Candela, Philip A.; Piccoli, Philip M.; Heinrich, Christoph A.

doi:10.1016/j.gca.2007.01.005

Cited by 92 publications

(65 citation statements)

References 103 publications

(154 reference statements)

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“…No Au-nuggets were found in any charge, similarly to Zajacz et al (2012) but contrary to most of previous gold solubility studies in presence of sulfur (e.g., Franck et al, 2002;Simon et al, 2007;Botcharnikov et al, 2010;Jégo et al, 2010;Jégo and Pichavant, 2012), in spite of similar quench rates and comparable Au solubility data. The absence of Au-nuggets could thus be related to the physical state of the system, i.e., a possible supercritical phase at high pressure.…”

Section: Attainment Of Equilibriumcontrasting

confidence: 95%

“…In S-bearing charges, a vapour phase is considered to be systematically present even if the melt is strictly-speaking H 2 Oundersaturated (aH 2 O <1) under the experimental conditions: this is due to the relatively low solubility of S in silicate melts that systematically induces -besides the formation of a S-rich mineral phase at sulfide saturation (i.e., pyrrhotite) -the formation of a S-rich vapour phase (containing mainly H 2 S + SO 2 + S 2 + H 2 O) at equilibrium, whatever the aH 2 O value calculated in the corresponding S-free system (see section 3.4.4). Then, the presence of a vapour phase may lead to significant partitioning of gold from liquid to vapour (e.g., Ulrich et al, 1999;Sun et al, 2004;Simon et al, 2007;Zajacz et al 2010;2012). Given the amount of H 2 O initially loaded in the capsules, the calculated melt H 2 O contents, and the approximate mass of the silicate charges, this vapour phase is present in very low amounts (probably less than a couple wt% of the total charge).…”

Section: Experimental Products and Compositionsmentioning

confidence: 99%

“…The ability of the melt to homogenize with respect to Au can be tested by considering the amount of time required for Au to diffuse through the melt at run conditions. Calculation of the diffusion distance of gold can be performed by assuming that the diffusivity of Au (taken as Au 1+ ) is intermediate between that of the univalent metals Na and Cs (Simon et al, 2007). Thus, at 1000°C and for 6 wt% H 2 O in the melt, a gold diffusivity of ~ 10 -10 m 2 /s is obtained from Watson (1994).…”

Section: Attainment Of Equilibriummentioning

confidence: 99%

“…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). 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.…”

Section: Introductionmentioning

confidence: 95%

“…Most of previous studies focusing on the behavior of gold in silicate melts aimed to determine the partitioning of gold between silicate liquid and sulfide phases (e.g., Bezmen et al, 1994;Fleet et al, 1996Fleet et al, , 1999Crocket et al, 1997;Jugo et al, 1999;Simon et al, 2007; 2008; Bell et al, 2009). Even though these experimental studies quantify the solubility of gold in the melt, the reported melt gold concentrations depend on the starting composition of the metal-doped sulfides.…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

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: Attainment Of Equilibriumcontrasting

confidence: 95%

Section: Experimental Products and Compositionsmentioning

confidence: 99%

Section: Attainment Of Equilibriummentioning

confidence: 99%

Section: Introductionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

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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Amphibole perspective to unravel the rhyolite as a potential fertile source for the Yonaguni Knoll IV hydrothermal system in the southwestern Okinawa Trough

Chen

Zeng

et al. 2019

Geological Journal

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Yonaguni Knoll IV is an active seafloor hydrothermal system containing massive Zn-Pb sulfides located in the southwestern OkinawaTrough. Previous research has suggested that the metal elements Zn and Pb were dominantly derived from the local volcanic rocks via water-rock interactions. However, it is not known whether or why the volcanic rocks are rich in these metals. Here, we performed a detailed in situ analysis of the major and trace elements in amphiboles in the rhyolite from the hydrothermal field to decipher the physical-chemical conditions of the silicic magma, including temperature (T), pressure (P), oxygen fugacity (fO 2 ), volatile contents (Cl, H 2 O) and metal contents (Pb, Zn), and investigate the behavior of the metals (Zn and Pb) during melt evolution. Our results show that the amphiboles are euhedral calcic magnesiohornblende and are in equilibrium with the hydrous and oxidized host rhyolitic melt characterized by high H 2 O melt (~5.8-6.5 wt.%), fO 2 (NNO +0.1 to +0.6) and SiO 2 melt (~71.73-72.62 wt.%) values at 761-797°C and 102-137 MPa, corresponding to an approximate depth of 3.9-5.2 km. In addition, the rare earth element (REE) patterns of the melt reconstructed from the amphiboles are analogous to those of cold-wetoxidized rhyolites. Thus, the amphiboles crystallized in a cold-wet-oxidized shallow silicic magma chamber. The high oxygen fugacity is inferred to have favored sulfur and metal enrichment in the melt. The most abundant metal in the amphiboles is Zn (237-294 ppm), and the concentrations of Pb are much lower (0.86-3.32 ppm), suggesting that Zn preferentially entered the amphibole and that Pb was retained in the melt. The Cl content of the amphiboles ranges from 0.11 to 0.25 wt.%, and accordingly, the Cl melt content estimated from the amphiboles varies from 0.15 to 0.28 wt. %. The low (Cl/H 2 O) melt ratios, which are <0.05 (i.e.,~0.02-0.04), suggest that the melt exsolved an H 2 O-rich vapor rather than a hydrosaline fluid with insufficient Cl to transport metals (e.g., Pb and Zn) into the vapor phase during degassing both in the magma chamber and during ascent. The lack of exsolved hydrosaline fluid and the high oxidation conditions resulted in the metal elements Pb and Zn remaining dissolved in the rhyolitic melt and/or partitioning into crystalline minerals upon eruption. Thus, the large volumes of rhyolitic magma that intruded into the upper crust of the Yonaguni Knoll IV hydrothermal field are a potential fertile source of these elements via leaching by heated seawater.

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Sulphide geochemistry of the superlarge Tiegelongnan Cu (Au) deposit in Tibet, China: Implication for the mineralization process

Lin

Wang

et al. 2021

Geological Journal

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The Tiegelongnan deposit in central Tibet presents a typical high‐sulfidation porphyry Cu (Au) mineralization system. Optical microscopy, scanning electron microscopy–energy dispersive spectrometry (SEM–EDS), and laser ablation inductively coupled plasma mass spectrometry (LA–ICPMS) were used to understand the mineralization processes. The advanced argillic alteration zone directly contacts the phyllic alteration zone, which is linked to the Early Cretaceous porphyritic intrusions. In this study, the spatial distributions of chief copper sulphides with variable gangue minerals are illustrated. The deep inner phyllic zone typically produced an end‐member assemblage of chalcopyrite–sericite (±dolomite), which trended upwards to produce more bornite–sericite (±siderite ± magnesite), and subsequently, the advanced argillic alteration yielded the representative end‐member assemblage of tennantite–alunite ± (aluminium‐phosphate‐sulphate, namely, APS, ±kaolinite). In the phyllic–advanced argillic transition zone, intensive covellite precipitation with the widespread occurrence of sericite–kaolinite (±APS) assemblage is proposed as an important feature in this study, which is mainly produced on the southwest side of the ore‐body centre. The typical co‐occurrence of chalcopyrite with dolomite at great depths indicates that it was related to a gently acidic fluid containing CO2; however, the pervasive tennantite–alunite association present at shallower levels suggests that fluids with SO2 were mainly involved and produced stronger acidic conditions. Acidic fluids are demonstrated to highly accelerate water‐rock alteration. Trace element analyses of the copper sulphides reflect that Au concentrations of bornite and tennantite are higher than chalcopyrite and covellite and present small signal variations. Moreover, comparing the presence of micron‐sized Au‐telluride in tennantite under advanced argillic alteration with the nano‐sized native gold in bornite resulting from phyllic alteration suggests that to a certain extent, Au enrichment is affected by the shift of more Te contents in fluid towards shallower levels, which could promote Au precipitation. Additionally, the Se contents of the selected samples were typically concentrated in chalcopyrite, bornite, and covellite, which yielded contents an order of magnitude greater than those in tennantite, indicating the intimate hydrothermal origin of the first three sulphides. Overall, the sulphide–gangue mineral associations and their copper sulphide geochemistry indicate that the hypogene–chalcopyrite of low Au contents from the phyllic zone closely corresponds to the action of gentle acidic fluids with CO2, while more acidic fluids with SO2 are involved in the formation of supergene tennantite with relatively high values of Au and Te in the advanced argillic alteration.

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The partitioning behavior of As and Au in S-free and S-bearing magmatic assemblages

Cited by 92 publications

References 103 publications

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

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

Amphibole perspective to unravel the rhyolite as a potential fertile source for the Yonaguni Knoll IV hydrothermal system in the southwestern Okinawa Trough

Sulphide geochemistry of the superlarge Tiegelongnan Cu (Au) deposit in Tibet, China: Implication for the mineralization process

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