The effect of sulfur on vapor–liquid fractionation of metals in hydrothermal systems

Pokrovski, Gleb S.; Borisova, Anastassia Y.; Harrichoury, Jean-Claude

doi:10.1016/j.epsl.2007.11.023

Cited by 193 publications

(152 citation statements)

References 49 publications

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“…This breakdown induces precipitation of a portion of the gold, consistent with numerous observations in different types of deposits where fluid unmixing occurs (29)(30)(31)(32)(33)(34)(35)(36), with the balance constrained by the vapor phase as volatile complexes with hydrogen sulfide (4,17) or chloride (37), depending on the fluid H 2 S and HCl content, acidity, temperature, and depth of the vapor-liquid separation. For example, vapor-liquid partitioning coefficients for Au in S-rich (∼1 wt% S) acidic (pH < 5) systems at 400-500°C are above 1 (17,36), suggesting an important contribution of the vapor phase to Au transport. Once such H 2 S-SO 2 vapor ascends and condenses to liquid below the water critical temperature, S − 3 and its complexes with Au may reform again, along with AuðHSÞ − 2 .…”

Section: Abundance Of Gold-trisulfur Ion Complexes In Hydrothermal Flsupporting

confidence: 54%

“…These fluids, which have created the major part of economic gold resources on Earth (1-4), may carry much higher Au concentrations, of tens to hundreds of parts per million, as reported from rare fluid inclusion analyses (4, 6, 9, 10) and a few laboratory experiments of Au solubility (17)(18)(19)(20). How gold is transported by such fluids remains, however, controversial, and a variety of other species with H 2 S, Cl, As, and alkali metal ligands (3,14,(17)(18)(19)(20) or Au nanoparticles (4,6,12) were suggested. Thus, a consistent picture of Au speciation and transport in deep and hot crustal fluids is lacking, hampering our understanding of geochemical fluxes of gold across the lithosphere and the formation of gold economic resources.…”

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confidence: 99%

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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.

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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: Abundance Of Gold-trisulfur Ion Complexes In Hydrothermal Flsupporting

confidence: 54%

mentioning

confidence: 99%

Sulfur radical species form gold deposits on Earth

Pokrovski

Kokh

Guillaume

et al. 2015

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

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130

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“…Early exsolution of carbonic fluids may have important implications for metal availability in the later stages of porphyry formation. This is because covalently-bonded sulfur complexes of "soft" metals such as copper or gold may be unusually stable in a weakly ionized H 2 O-CO 2 solvent 51 . Such fluids could help to defertilize a melt by stripping it of metals.…”

Section: Ascent Of Magmas and Volatile Saturationmentioning

confidence: 99%

“…High magmatic sulfur solubilities would appear to be a pre-requisite for the formation of giant porphyry and related epithermal deposits because these deposits are, first and foremost, sulfur anomalies. Abundant sulfur is required for the voluminous deposition of the sulfide ore minerals themselves and it can also play a role in complexing with copper and gold to enable hydrothermal transport 51,85 . The problem with high sulfide concentrations in the melt is that this may trigger sulfide saturation, resulting in crystallization of sulfide minerals or, at higher temperatures, production of an immiscible sulfide melt.…”

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confidence: 99%

Triggers for the formation of porphyry ore deposits in magmatic arcs

2013

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Porphyry ore deposits source much of the copper, molybdenum, gold and silver utilized by humankind. They typically form in magmatic arcs above subduction zones via a series of linked processes, beginning with magma generation in the mantle and ending with the precipitation of metals from hydrous fluids in the shallow crust. A hierarchy of four key "triggers" involved in the formation of porphyry deposits is outlined. Trigger 1 (10 2 -10 3 km scale) is a process of cyclic refertilization of magmas in the deep crust. Trigger 2 (10 1 -10 2 km scale) is the process of sulfide saturation in magmas that can both enhance and destroy ore-forming potential. Trigger 3 (10 0 -10 1 km scale) relates to the efficient transfer of metals into hydrothermal fluids exsolving from porphyry magmas. Trigger 4 (~10 0 km scale) identifies processes that lead to the final precipitation of ore minerals. Although all processes are required to a greater or lesser degree, it is argued that trigger 3, as an over-riding mechanism, can best explain the restriction of large deposits to specific arc segments and time periods. Consequently, recognition of the fingerprint of sulfide saturation in igneous rocks may help mineral exploration companies to identify parts of magmatic arcs particularly predisposed to ore formation.Ore deposits are scarce. Their discovery consumes considerable time and resources and only about one in every one thousand prospects explored by companies is eventually developed into a mine. Deposits often occur in clusters and formed within specific time intervals. This non-uniform pattern provides keys to understanding how and why metals accumulate in some places and not in others and its explanation is fundamental for mineral exploration.The most important metalliferous ore deposits are hydrothermal deposits, formed from hot waters circulating in Earth's crust. Such deposits represent a highly efficient trap where fluids were focused into a limited volume of rock, became supersaturated and precipitated ore minerals. In theory, this does not require unusual fluid compositions 1,2 as long as fluid focusing, sufficient fluid flux and efficient precipitation conditions can be maintained. Recently, this paradigm has been challenged by the recognition that ore fluids in sediment-hosted 3-5 , epithermal 6,7 and porphyryrelated [8][9][10] hydrothermal deposits can carry orders of magnitude more metal than previously considered probable, or measured in modern fluid samples. This suggests that our understanding of metal extraction and transport processes is incomplete.Here, this theme is explored by consideration of porphyry ore deposits [11][12][13][14][15] , remarkable geochemical anomalies that can contain up to 1 Gt of sulphur 16 , 200 Mt copper, 2.5 Mt molybdenum and 2600 t gold 17 . The most copper-rich examples include the 4-5 million-year old El Teniente and Rio Blanco-Los Bronces deposits in Central Chile, and the most gold-rich is the 3 million-year old Grasberg deposit in Irian Jaya, Papua New Guinea 17 .Porphyry deposits...

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“…Hydrothermally altered rocks have been extensively studied 3 especially in the context of ore formation, metal enrichment, and mineralization (Aiuppa et al, 2006;Allen and Hahn, 1994;Franzson et al, 2008;Halbach et al, 1993;Horton et al, 2001;Huston et al, 1995;Marques et al, 2010;Martin-Crespo et al, 2004;Ostwald and England, 1977;Pokrovski et al, 2007), but very few have investigated the potential leaching of toxic elements from these rocks when exposed to the environment.…”

Section: Introductionmentioning

confidence: 99%

The roles of pyrite and calcite in the mobilization of arsenic and lead from hydrothermally altered rocks excavated in Hokkaido, Japan

Tabelin¹,

Igarashi²,

Tamoto³

et al. 2012

Journal of Geochemical Exploration

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This paper describes the enrichment of hydrothermally altered volcanic and sedimentary rocks with arsenic (As) and lead (Pb), and the effects of pyrite and calcite on the mobilities and release mechanisms of these toxic elements under oxic and anoxic conditions. Enrichment of the altered rock with As and Pb predominantly occurred in precipitated pyrite grains and not on the alumino-silicate minerals making up the matrix of the rock. Arsenic was incorporated in pyrite grains formed during alteration in both volcanic and sedimentary rocks, but Pb was only found in the pyrite grains of the volcanic rock samples. When in contact with water, altered volcanic rocks had acidic pH while altered sedimentary rocks had alkaline pH. The mobilities of both As and Pb from the altered rocks were enhanced at acidic and alkaline pH and a minimum was observed in the circumneutral pH under both oxic and anoxic conditions. The absence of O 2 retarded the oxidation of pyrite most notably in the alkaline region but not in the acidic and circumneutral pH. The absence of CO 2 increased the pH of samples with significant calcite content but did not affect those containing substantial amounts of pyrite. Increasing the CO 2 also had insignificant effect on the concentrations of As and Pb in the leachate. The mechanisms controlling the mobilization of As and Pb from these rocks like dissolution of soluble secondary minerals, pyrite oxidation and adsorption were all related to pyrite while the pH of the rock when in contact with water was controlled by pyrite and calcite. Thus, excavated waste rocks that have been altered can be grouped based on the relative abundance of pyrite and calcite and their pH when in contact with water.

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The effect of sulfur on vapor–liquid fractionation of metals in hydrothermal systems

Cited by 193 publications

References 49 publications

Sulfur radical species form gold deposits on Earth

Sulfur radical species form gold deposits on Earth

Triggers for the formation of porphyry ore deposits in magmatic arcs

The roles of pyrite and calcite in the mobilization of arsenic and lead from hydrothermally altered rocks excavated in Hokkaido, Japan

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