Impact of sulfur on the fate of metals of high economic value in geological fluids
Participants du GET: Gleb Pokrovski (coordinateur), Damien Guillaume, Nicolas Jacquemet, Pascal Gisquet, Alain Castillo, Anastassia Borisova, Maria Kokh (thèse de doctorat 2012-2016)
Equipes-partenaires: Géoressources (Nancy), INEEL/ FAME (Grenoble), ENS/ IMPMC (Paris)
Quantifying the impact of sulfur and carbon on the extraction, transport and concentration of metals as economic deposits:
Although sulfur and carbon are the two major constituents of the fluids circulating in the deep of our planet, their role on the transfers and concentration of economically critical metals remains virtually unknown. To fill this large gap of Geochemistry and Metallogeny, our project aims the following objectives:
– to obtain pioneering data on the tenors, partitioning and chemical forms (speciation) of metals of high technological value (Au, Cu, Pt, Mo) in model water-salt-CO2-sulfur systems under controlled laboratory conditions representative of those in the Earth’s crust;
– to study the identity and stability of sulfur chemical forms in such systems;
– to elucidate the molecular structure and physical-chemical properties of the major natural solvents (water-salt-CO2);
– to develop original analytical tools for characterizing the properties and composition of high-temperature high-pressure natural fluids carrying sulfur, carbon, gold and associated metals.
The achievement of these objectives would allow a far better quantification of metal and volatile transfers across the lithosphere, a deep understanding of the mechanisms controlling the formation and distribution of metal deposits, and, in the near future, an improvement of ore exploration and extraction procedures.
An interdisciplinary approach combining experiments, in situ analyses and modeling, applied to high-temperature high-pressure fluids:
Geological fluids operating at depth are not accessible to direct observation and leave very little trace on their passage. Their final products, which are rocks and minerals, brought to the Earth’s surface and cooled down over geological times, may not adequately reflect the composition and properties of the deep fluids by which they have been formed. The only mean to access the fluids under ‘extreme’ conditions is to use in situ experimental and analytical methods coupled with theoretical models. In this project we have developed and set up the following original methods:
– new hydrothermal reactors coupled to different analytical techniques for measuring metal tenors and mineral solubilities in fluids and vapors enriched in sulfur, CO2 and salt at high temperatures and pressures;
– methods of synthesis and analyses of fluid inclusions opening the possibility to study, by in situ Raman spectroscopy, the chemical speciation of sulfur in natural fluids;
– molecular and thermodynamic models for characterizing the structure and transport properties of S- and CO2-bearing fluids;
– in situ micro-analytical methods (laser ablation coupled with mass spectrometry) for quantifying gold tenors in both synthetic and natural fluid inclusions;
Such an interdisciplinary approach, bringing together geochemistry, ore deposit geology, physics and chemistry, has never been applied so far for studies of deep geological fluids and processes of metal resources formation on Earth.
Major results:
– We have developed and validated an ensemble of new experiments (solubity methods in hydrothermal reactor; fluid inclusions synthesis), analytical (laser ablation ICPMS, atomic emission ICP), in situ spectroscopic (Raman and X-ray Absorption synchrotron-based spectroscopies), and theoretical (molecular dynamics and thermodynamics) methods for studying metals and volatiles in high-temperature high-pressure fluids. These innovative approaches and techniques, which may now be applied in a variety of domains in geochemistry, physical chemistry and material science, have allowed us to obtain the following major results in the framework of this project.
– We have demonstrated the existence of new sulfur chemical forms, the radical S3- and S2- ions, and generated the first thermodynamic data for these species, which appear to be stable in geological fluids across the Earth’s crust.
– These ions have strong capacities for binding gold thereby increasing dramatically the mobility of this noble metal, which has always been considered to be the most inert metal of the Periodic table; this discovery revolutionizes our present understanding of gold deposit formation on Earth and opens new perspectives for exploration of new resources and ore processing.
– We have revealed, for the first time, the molecular and thermodynamic properties of the major geological solvent H2O-CO2 at elevated temperatures and pressures, and we have found a combined effect of CO2, salt and sulfur on the mobility of metals such as Au, Fe, Cu, Mo and Pt in the fluids and on metal distribution and zonation in the principal types of ore deposits.
Overview of scientific production:
In total 12 peer-reviewed articles (from which 3 book chapters) have been published in rang A journals and special publication series, together with 30 abstracts/communications at international meetings (from which 9 keynote or invited presentations), 6 articles are currently submitted or in preparation (see section E for details). The impact of our publications (by group) is resumed below.
– Pokrovski et al. (2015) PNAS112, 13484. The discovery of a major impact of the trisulfur radical ion S3- on the extraction, transport and precipitation of gold; these findings revolutionize the current models of the formation of gold and associated metal deposits and open new doors for ore treatment and nanotechnology. Since its publication in November 2015, our article has generated 15 press releases and articles in general public journals, 1 radio news (France Inter) and 1 TV show (France 2).
– Pokrovski et Dubessy (2015) EPSL411, 298; Jacquemet et al. (2014) Amer Miner99, 1109. Systematic identification and quantitative characterization of the S3- et S2- radical ions in geological fluids.
– Kokh et al. (2016a) GCA187, 311; Kokh et al. (2016b) GCA, submitted after moderate revisions. Findings of a combined effect of sulfur (H2S), salt (Cl) and carbon (CO2) on metal transport and precipitation by CO2-rich fluids.
– Kouzmanov & Pokrovski (2012)SEG Spec Pub16, 573; Pokrovski et al. (2014)GSL Spec Pub402, 7; Pokrovski et al. (2013)RiMG76, 165. These three exhaustive reviews may serve as references on the phenomena related to the transport, fractionation and precipitation of metals by magmatic-hydrothermal fluids, before the discovery of the effect of sulfur radical ions.
– Da Silva-Cadoux et al. (2012) JCP 136, 044515; Louvel et al. (2015) JML 205, 54. First in situ studies of the molecular properties and structure (hydrogen bonding, clustering, density fluctuations) of supercritical H2O and H2O-CO2 solvents.
– Pokrovski et al. (2013) GCA 106, 501; Jonchière et al. JCP in prep. Coupling of synchrotron spectroscopy data with molecular dynamic simulations to reveal the identity and structure of complexes that carry metals in salt- and CO2-rich fluids.
– Kokh et al. (2016a) GCA187, 311; Kokh et al. (2016b) GCA, submitted after moderate revisions. Findings of a combined effect of sulfur (H2S), salt (Cl) and carbon (CO2) on metal transport and precipitation by CO2-rich fluids.
– Kouzmanov & Pokrovski (2012)SEG Spec Pub16, 573; Pokrovski et al. (2014)GSL Spec Pub402, 7; Pokrovski et al. (2013)RiMG76, 165. These three exhaustive reviews may serve as references on the phenomena related to the transport, fractionation and precipitation of metals by magmatic-hydrothermal fluids, before the discovery of the effect of sulfur radical ions.
– Da Silva-Cadoux et al. (2012) JCP 136, 044515; Louvel et al. (2015) JML 205, 54. First in situ studies of the molecular properties and structure (hydrogen bonding, clustering, density fluctuations) of supercritical H2O and H2O-CO2 solvents.
– Pokrovski et al. (2013) GCA 106, 501; Jonchière et al. JCP in prep. Coupling of synchrotron spectroscopy data with molecular dynamic simulations to reveal the identity and structure of complexes that carry metals in salt- and CO2-rich fluids.
Publucations:
Articles:
Da Silva-Cadoux C., Hazemann J.L., Testemale D. Proux O., Rochas C. (2012) Influence of monovalent ions on density fluctuations in hydrothermal aqueous solutions by small angle X-ray scattering.Journal of Chemical Physics136(4), pp. 044515.
Pokrovski G.S., Roux J., Ferlat G., Jonchiere R., Seitsonen A.P., Vuilleumier R., Hazemann J.-L. (2013) Silver in geological fluids from in situ X-ray absorption spectroscopy and first-principles molecular dynamics.Geochimica et Cosmochimica Acta106, 501-523.
Jacquemet N., Guillaume D., Zwick A., Pokrovski G.S. (2014) In situ Raman spectroscopy identification of the S3- ion in S-rich hydrothermal fluids from synthetic fluid inclusions.American Mineralogist99, 1109-1118.
Pokrovski G.S. (2014) Use and misuse of chemical reactions and aqueous species distribution diagrams for interpreting metal transport and deposition in porphyry copper systems: Comment on Sun et al. (2013) “The link between reduced porphyry copper deposits and oxidized magmas”, Geochim. Cosmochim. Acta 103, 263–275. Geochimica et Cosmochimica Acta126, 635-638.Pokrovski G.S., Dubessy J. (2015) Stability and abundance of the trisulfur radical ion S3- in hydrothermal fluids.Earth & Planetary Science Letters411, 298-309.
Louvel M., Bordage A., Da Silva-Cadoux C., Testemale D., Lahera E., Del Net W., Geaymond O., Dubessy J., Argoud R., Hazemann J.-L. (2015) A high-pressure high-temperature setup for in situ Raman spectroscopy of supercritical fluids.Journal of Molecular Liquids205, 54-60.
Pokrovski G.S., Dubessy J. (2015) Stability and abundance of the trisulfur radical ion S3-in hydrothermal fluids.Earth and Planetary Science Letters 411, 298-309.
Pokrovski G.S., Kokh M.A., Guillaume D., Borisova A.Y., Gisquet P., Hazemann J.-L., Lahera E., Del Net W., Proux O., Testemale D., Haigis V., Jonchière R., Seitsonen, A.P., Ferlat G., Vuilleumier R., Saitta A.M., Boiron M.-C., Dubessy J. (2015) Sulfur radical species form gold deposits on Earth.Proceedings of National Academy of Science (PNAS)112, 13484-13489.
Kokh M.A., Lopez M., Gisquet P., Lanzanova A., Candaudap F., Besson P., Pokrovski G.S. (2016a) Combined effect of carbon dioxide and sulfur on vapor-liquid partitioning of metals in hydrothermal systems.Geochimica et Cosmochimica Acta187, 311-333.
Kokh M.A., Akinfiev N.N., Pokrovski G.S., Salvi S., Guillaume D. (2016b) The role of carbon dioxide in the transport and fractionation of metals by geological fluids.Geochimica et Cosmochimica Acta, accepted pending revisions.
Book Chapters:
Kouzmanov K., Pokrovski G.S. (2012) Hydrothermal controls on metal distribution in Cu(-Au-Mo) porphyry systems. In: ‘Geology and Genesis of Geology and Genesis of Major Copper Deposits and Districts of the World: A Tribute to Richard H. Sillitoe’ (eds. J.W. Hedenquist, M. Harris, and F. Camus).Society of Economic Geologists Special Publication,16, 573-618.
Pokrovski G.S., Akinfiev N.N., Borisova A.Y., Zotov A.V., Kouzmanov K. (2013) Gold speciation and transport in geological fluids: insights from experiments and physical-chemical modeling. Book chapter in:Geological Society of London Special Publication“Gold-transporting fluids in the Earth’s crust”, eds. P. Girofalo, J. Ripley,402, 9-70.
Pokrovski G.S., Borisova A.Y., Bychkov A.Y. (2013) Speciation and transport of metals and metalloids in geological vapors.Chapter in Reviews in Mineralogy & Geochemistry 76, 165-218.
Vulgarisation articles, press releases
Pokrovski G.S.(2015) De nouvelles espèces soufrées découvertes dans les fluides géologiques. Nouvelles de l’INSU 234, 16 Janvier 2015: http://www.insu.cnrs.fr/node/5152
Pokrovski G.S.(2015) Resolving the enigmas of gold deposit formation using X-ray absorption spectroscopy.Highlights ESRF 2015, Matter at Extremes, p. 94-95.
http://www.insu.cnrs.fr/node/5491 La formation des gisements d’or enfin expliquée, Nouvelles de l’INSU 13 octobre 2015