Anomalously Metal-Rich Fluids Form Hydrothermal Ore Deposits

Wilkinson, Jamie J.; Stoffell, Barry; Wilkinson, CC; Jeffries, Teresa; Appold, Martin S.

doi:10.1126/science.1164436

Cited by 157 publications

(69 citation statements)

References 25 publications

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“…The large enhancement by S − 3 of the fluid transport capacities for Au, coupled with the efficient Au precipitation triggered by S − 3 breakdown, implies that far smaller but more concentrated amounts of fluid than previously thought (39,41) are responsible for economic gold deposition at high temperatures. This conclusion offers previously unidentified insights into magmatic and metamorphic ore fluid dynamics that appears to be similar to that for sedimentary rock-hosted base-metal deposits whose formation would occur by periodic injections of anomalously metal-rich batches of fluids during short ore-forming events (40). A smaller amount of S − 3 -bearing fluid would imply a smaller volume of the magma source necessary for an economic gold deposit.…”

Section: Discussion and Geological And Metallogenic Applicationsmentioning

confidence: 65%

“…A smaller amount of S − 3 -bearing fluid would imply a smaller volume of the magma source necessary for an economic gold deposit. Furthermore, modern conceptual models of ore deposits require an exceptionally fortuitous combination of Au-rich sources such as Au preconcentration in magmatic sulfides (3,41,42) or sedimentary pyrite (7,8), sustained and focused hydrothermal fluid flow (38,39), and tectonic and other geochemical triggers of an efficient precipitation mechanism (39)(40)(41)(42), all acting in unison to form an economic gold deposit from typically part-per-billion levels of Au concentrations as hydrogen sulfide or chloride complexes in the fluid and silicate melt. The existence of gold-trisulfur ion species with large capacities to extract, transfer, and precipitate gold reduces these requirements and shortens by up to 10-100 times the duration needed to form a given deposit from a much smaller magma or rock source.…”

Section: Discussion and Geological And Metallogenic Applicationsmentioning

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.

118

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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 Applicationsmentioning

confidence: 65%

Section: Discussion and Geological And Metallogenic Applicationsmentioning

confidence: 99%

Sulfur radical species form gold deposits on Earth

Pokrovski

Kokh

Guillaume

et al. 2015

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

118

View full text Add to dashboard Cite

show abstract

“…This could either be by derivation of fluids (or melts) from a pre-enriched source (the source rock paradigm, e.g. 46 ); or by unusually efficient extraction from an un-enriched source 4 . The alternative argument, that large deposits are rare because they require the random coincidence of multiple, coincident, not atypical factors 26,71 -the "perfect storm" of ore formation -is hard to disprove, but does not satisfactorily explain the clustering of deposits in certain belts and at certain periods of time.…”

Section: Episodicity and Rarity Of Ore Formationmentioning

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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“…It is also the basis for the more advanced techniques such as laser ablation ICP--MS that are providing fundamental new insights into metal transport and deposition from ore--forming fluids (e.g. Audetat et al, 1998Audetat et al, , 2008Heinrich et al, 1999;Ulrich et al, 1999;Wilkinson et al, 2009;Kouzmanov and Pokrovski, 2012).…”

Section: Introductionmentioning

confidence: 99%

“…Audetat et al, 1998Audetat et al, , 2008Heinrich et al, 1999;Ulrich et al, 1999;Wilkinson et al, 2009;Kouzmanov and Pokrovski, 2012).…”

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confidence: 99%

Metastable Freezing: A New Method for the Estimation of Salinity in Aqueous Fluid Inclusions

Wilkinson

2017

Economic Geology

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On cooling during microthermometry, fluid inclusions invariably supercool before freezing under disequilibrium (metastable) conditions to form ice and hydrates. Measurements of fluid inclusions from the Irish Zn--Pb hydrothermal system reveal a strong linear correlation (R 2 = 0.968) between final ice melting temperature (TmI) and metastable freezing temperature (Tmf) of the form: TmI = 0.563 Tmf + 22.7 (+1.5/--3.5) The relationship is shown to be independent of heating--freezing stage model, host mineral, and largely of inclusion size, but is affected by the presence of CO2 and by cooling rate. The correlation shows that metastable freezing is predictable and in fact, in small droplets of pure solution, occurs at a well--defined, salinity--dependent temperature referred to as the homogeneous freezing point. This relationship allows salinity to be estimated in fluid inclusions where the optical recognition of final ice melting is not possible due to small inclusion size or cloudy samples, or where inclusions go into a metastable, vapor--absent, state because of collapse of the bubble on freezing. Using a cooling rate of 50°C/min, inclusion salinity is given by:Salinity (wt% NaCl equivalent) = --69.7 --2.617Tmf --0.02603Tmf 2 --0.0000994Tmf 3 The homogeneous freezing point is controlled by an equilibrium thermodynamic property related to the activity of water. In small droplets of pure solution, as approximated by fluid inclusions, freezing will occur when the water activity is 0.305 above that of the stable ice melting condition at the same temperature, independent of solute type. "Early" metastable freezing, at a temperature above the homogeneous freezing point may occur in very large inclusions, or those containing "seed" particles or CO2. In such cases, the salinity will be underestimated by the equation above. Introduction Fluid inclusion microthermometry has been long established as the only direct method for constraining the properties of paleofluids in the Earth's crust (e.g. Roedder, 1967a). In particular, the ability to constrain fluid density, trapping temperature and pressure, solute and volatile contents has provided many important tests of genetic models for hydrothermal ore formation (Roedder and Bodnar, 1997). It is also the basis for the more advanced techniques such as laser ablation ICP--MS that are providing fundamental new insights into metal transport and deposition from ore--forming fluids (e.g. Audetat et al., 1998Audetat et al., , 2008Heinrich et al., 1999;Ulrich et al., 1999;Wilkinson et al., 2009;Kouzmanov and Pokrovski, 2012).The basic principles of microthermometry by which fluid inclusions are investigated using a heating--freezing stage are well established (e.g. Roedder, 1984;Shepherd et al., 1985). Total homogenisation temperatures, typically by liquid--vapor homogenisation, can provide minimum constraints on trapping pressure and temperature. Measurements of halite, hydrate and ice melting temperatures can be used to estimate fluid salinity, assuming simple model systems...

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Anomalously Metal-Rich Fluids Form Hydrothermal Ore Deposits

Cited by 157 publications

References 25 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

Metastable Freezing: A New Method for the Estimation of Salinity in Aqueous Fluid Inclusions

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