Stability of AuCl2− from 25 to 1000 °C at Pressures to 5000 bar and Consequences for Hydrothermal Gold Mobilization

Зотов, А. В.; Kuz'min, N. N.; Reukov, Vladimir L.; Тагиров, Б. Р.

doi:10.3390/min8070286

Cited by 25 publications

(25 citation statements)

References 32 publications

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“…The thermodynamic modeling was carried out using the Gibbs free energy minimization algorithm implemented in the HCh program (version 4.5 for Windows) 60,61 . Thermodynamic data for Au aqueous complexes were adopted from the study of 62 , with the exception of data for gold dichloride complex, AuCl 2 -, that was adopted from the recent study of 63 . Data for minerals and other aqueous species are from the SUPCRT database 64 .…”

Section: Laser Ablation Icp-ms Of Fluid Inclusions and Quartz The Chmentioning

confidence: 99%

Exceptional Concentrations of Gold Nanoparticles in 1,7 Ga Fluid Inclusions From the Kola Superdeep Borehole, Northwest Russia

Prokofiev

Banks

Lobanov

et al. 2020

Sci Rep

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In the drill core of the Kola super-deep borehole (SG-3, 12,262 m depth) gold-bearing rocks of Archaean age have been located at depths of 9,500 to 11,000 m. In veins, between 9,052 and 10,744 m, within this gold zone, quartz contains fluid inclusions with gold nanoparticles. There are 4 types of fluid inclusions (1) gas inclusions of dense CO 2 , (2) liquid-vapor two-phase aqueous inclusions, (3) three-phase inclusions with NaCl daughter crystals, and (4) CO 2-aqueous inclusions. In all inclusion types, there are extremely high concentrations of gold. The highest gold concentrations were found in the type 3 and 4 fluid inclusions with an average concentration of c. 750 ppm and may be as high as 6,000 ppm. The presence of gold as nanoparticles in the solutions of these fluid inclusions was determined by optical and spectroscopic methods. We suggest that these fluids could be a precursor of "orogenic gold fluids" which, at the gold concentrations determined, would reduce the requirements for large volumes of metamorphic fluids to form orogenic ore deposits. Further, as nanoparticles, gold could be transported in larger amounts than in true solution.

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Section: Laser Ablation Icp-ms Of Fluid Inclusions and Quartz The Chmentioning

confidence: 99%

Exceptional Concentrations of Gold Nanoparticles in 1,7 Ga Fluid Inclusions From the Kola Superdeep Borehole, Northwest Russia

Prokofiev

Banks

Lobanov

et al. 2020

Sci Rep

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show abstract

“…- [59] ( Figure 13). As the temperature decreases, the dominant role of chloride complex is replaced by hydrosulfide AuHS 0 (scenario 1) or hydroxide AuOH 0 complexes (scenario 2) [60].…”

Section: Results Of Thermodynamic Modelingmentioning

confidence: 99%

Formation of Au-Bearing Antigorite Serpentinites and Magnetite Ores at the Massif of Ophiolite Ultramafic Rocks: Thermodynamic Modeling

et al. 2019

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We constructed thermodynamic models of the formation of two types of gold-ore mineralization at the Kagan ultramafic massif in the Southern Urals (Russia). The first type of gold-mineralization is widely spread at the massif in the tectonic zones of schistose serpentinites containing typically ≤ 0.1 ppm Au. The second type of gold-ore mineralization is represented by veined massive, streaky and impregnated magnetite ores in contact with serpentinites. It contains to 5 vol.% sulfides and 0.2–1.2 ppm Au. Our thermodynamic calculations explain the formation of two types of gold-ore mineralization in the bedrocks of ultramafic massifs. Metamorphic water, which is the result of the dehydration of early serpentinites (middle Riphean) during high-temperature regional metamorphism (700 °C, 10 kbar) (late Precambrian), is considered as the source of ore-bearing fluid in the models. The metasomatic interaction of metamorphic fluid with serpentinites is responsible for the gold-poor mineralization of the 1st type at T = 450–250 °C and P = 2.5–0.5 kbar. The hydrothermal gold-rich mineralization of the 2nd type was formed during mixing of metamorphic and meteoric fluids at T = 500–400 °C and P = 2–3 kbar and discharge of mixed fluid in the open space of cracks in serpentinites. The model calculations showed that the dominant forms of gold transport in fluids with pH = 3–5 are AuCl2− complexes (≥450 °C) and, as the temperature decreases, AuHS0, or AuOH0. Mineral associations obtained in model calculations are in general similar to the observed natural types of gold mineralization.

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“…Depending on the composition of hydrothermal solution and the evolution of its physicochemical parameters, the forms of metal complexes change during transfer and deposition of ore elements (Figure 9). In the suggested model, gold in the fluid (Figure 9a) in the first reservoir (700 °C) is mainly represented by chloride complex AuCl2 − [29]. Thereafter, when the fluid was transported to the next reservoirs and the temperature decreased, its amount decreased significantly: at 450 °C, the main gold-bearing complex is hydroxocomplex AuOH 0 in the presence of small amounts of Au(HS)2 − and AuHS 0 [30], and at 300 °C, the role of gold sulfide complexes increased drastically [29].…”

Section: Fluid Composition and Forms Of Transfer And Deposition Of Aumentioning

confidence: 99%

Physicochemical Model of Formation of Gold-Bearing Magnetite-Chlorite-Carbonate Rocks at the Karabash Ultramafic Massif (Southern Urals, Russia)

et al. 2018

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Abstract:We present a physicochemical model for the formation of magnetite-chlorite-carbonate rocks with copper gold in the Karabash ultramafic massif in the Southern Urals, Russia. The model was constructed based on the formation geotectonics of the Karabash massif, features of spatial distribution of metasomatically altered rocks in their central part, geochemical characteristics and mineral composition of altered ultramafic rocks, data on the pressure and temperature conditions of formation, and composition of the ore-forming fluids. Magnetite-chlorite-carbonate rocks were formed by the hydrothermal filling of the free space, whereas chloritolites were formed by the metasomatism of the serpentinites. As the source of the petrogenic and ore components, we considered rocks (serpentinites, gabbro, and limestones), deep magmatogenic fluids, probably mixed with metamorphogenic fluids released during dehydration and deserpentinization of rocks in the lower crust, and meteoric waters. The model supports the involvement of sodium chloride-carbon dioxide fluids extracting ore components (Au, Ag, and Cu) from deep-seated rocks and characterized by the ratio of ore elements corresponding to Clarke values in ultramafic rocks. The model calculations show that copper gold can also be deposited during serpentinization of deep-seated olivine-rich rocks and ore fluids raised by the tectonic flow to a higher hypsometric level. The results of our research allow predicting copper gold-rich ore occurrences in ultramafic massifs.

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Stability of AuCl2− from 25 to 1000 °C at Pressures to 5000 bar and Consequences for Hydrothermal Gold Mobilization

Cited by 25 publications

References 32 publications

Exceptional Concentrations of Gold Nanoparticles in 1,7 Ga Fluid Inclusions From the Kola Superdeep Borehole, Northwest Russia

Exceptional Concentrations of Gold Nanoparticles in 1,7 Ga Fluid Inclusions From the Kola Superdeep Borehole, Northwest Russia

Formation of Au-Bearing Antigorite Serpentinites and Magnetite Ores at the Massif of Ophiolite Ultramafic Rocks: Thermodynamic Modeling

Physicochemical Model of Formation of Gold-Bearing Magnetite-Chlorite-Carbonate Rocks at the Karabash Ultramafic Massif (Southern Urals, Russia)

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