Gold and copper in volatile saturated mafic to intermediate magmas: Solubilities, partitioning, and implications for ore deposit formation

Zajacz, Zoltán; Candela, Philip A.; Piccoli, Philip M.; Wälle, Marküs; Sanchez-Valle, Carmen

doi:10.1016/j.gca.2012.05.033

Cited by 120 publications

(57 citation statements)

References 68 publications

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“…4), thus preparing an Auenriched source silicate melt for porphyry deposits. This is in agreement with the association of Au-rich porphyry deposits with oxidized [f O2 of quartz-fayalite-magnetite (QFM)+2 at 900°C] arc magmas (44)(45)(46).…”

Section: Discussion and Geological And Metallogenic Applicationssupporting

confidence: 87%

“…Furthermore, another sulfur radical, the disulfur ion (S − 2 ), suggested to be stable above 500°C in sulfate-sulfide aqueous systems (24), may also strongly bind Au and associated metals in magmatic fluids and, potentially, silicate melts. Noteworthy is that Au solubility measured in silicate melts (44,45) is maximized at the sulfide-sulfate transition, which is also the most favorable redox condition for S − 3 (and S − 2 ) in hydrothermal fluids, as shown in this study. If the sulfur radical species are stable in silicate melts, they may further enhance selective extraction of Au from magmatic iron sulfide (Fig.…”

Section: Discussion and Geological And Metallogenic Applicationssupporting

confidence: 50%

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Sulfur radical species form gold deposits on Earth

Pokrovski

Kokh

Guillaume

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

130

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Current models of the formation and distribution of gold deposits on Earth are based on the long-standing paradigm that hydrogen sulfide and chloride are the ligands responsible for gold mobilization and precipitation by fluids across the lithosphere. Here we challenge this view by demonstrating, using in situ X-ray absorption spectroscopy and solubility measurements, coupled with molecular dynamics and thermodynamic simulations, that sulfur radical species, such as the trisulfur ion S − 3 , form very stable and soluble complexes with Au + in aqueous solution at elevated temperatures (>250°C) and pressures (>100 bar). These species enable extraction, transport, and focused precipitation of gold by sulfur-rich fluids 10-100 times more efficiently than sulfide and chloride only. As a result, S − 3 exerts an important control on the source, concentration, and distribution of gold in its major economic deposits from magmatic, hydrothermal, and metamorphic settings. The growth and decay of S − 3 during the fluid generation and evolution is one of the key factors that determine the fate of gold in the lithosphere.gold | sulfur | ore deposit | hydrothermal fluid | trisulfur ion

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Section: Discussion and Geological And Metallogenic Applicationssupporting

confidence: 87%

Section: Discussion and Geological And Metallogenic Applicationssupporting

confidence: 50%

Sulfur radical species form gold deposits on Earth

Pokrovski

Kokh

Guillaume

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

130

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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: 82%

“…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: 89%

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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“…11) and metals such as the REE, Fe, Cu and Au that it scavenged originallyfrom the silicate melt due to the magmatic temperatures and high salinity of the fluid (Reed et al, 2000;Simon et al, 2004Simon et al, , 2005Simon et al, , 2006Zajacz et al, 2012;Frank et al, 2011;Migdisov et al, 2014;Hurtig and Williams-Jones, 2014). The high Cl content of the fluid facilitates metal-chloride complexes and allows it to transport these metals, some of which exhibit retrograde solubility, i.e.…”

Section: Genetic Link Between Kiruna-type Ioa and Iocg Deposits?mentioning

confidence: 99%

Trace elements in magnetite from massive iron oxide-apatite deposits indicate a combined formation by igneous and magmatic-hydrothermal processes

Knipping

Bilenker

Simon

et al. 2015

Geochimica et Cosmochimica Acta

222

104

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This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. data demonstrate that a saline magmatic-hydrothermal ore fluid will scavenge significant quantities of metals such as Cu and Au from a silicate melt, and when combined with solubility data for Fe, Cu and Au, it is plausible that the magmatic-hydrothermal ore fluid that continues to ascend from the IOA depositional environment can retain sufficient concentrations of these metals to form iron oxide copper-gold (IOCG) deposits at lateral and/or stratigraphically higher levels in the crust. Notably, this study provides a new discrimination diagram to identify magnetite from Kiruna-type deposits and to distinguish them from IOCG, porphyry and Fe-Ti-V/P deposits, based on low Cr (< 100 ppm) and high V (>500 ppm) concentrations. Trace elements in magnetite from massive iron oxide-apatite deposits indicate a combined formation by igneous and magmatic-hydrothermal processes

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Gold and copper in volatile saturated mafic to intermediate magmas: Solubilities, partitioning, and implications for ore deposit formation

Cited by 120 publications

References 68 publications

Sulfur radical species form gold deposits on Earth

Sulfur radical species form gold deposits on Earth

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

Trace elements in magnetite from massive iron oxide-apatite deposits indicate a combined formation by igneous and magmatic-hydrothermal processes

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