Project

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Equilibrium between silicate melts and H-O-C-S-Cl magmatic volatiles: a key to understand volcanic eruptions and ore deposit genesis

Applicant Zajacz Zoltán
Number 136857
Funding scheme Ambizione
Research institution Institut für Geochemie und Petrologie ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Geochemistry
Start/End 01.11.2011 - 31.12.2013
Approved amount 303'901.00
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Lay Summary (English)

Lead
Lay summary

The exsolution of a volatile phase from silicate melts in magma chambers underneath arc volcanoes is an essential process in the formation of hydrothermal ore deposits of numerous economically important elements (e.g. Au, Cu, Mo) and the main driving force for explosive volcanic activity. Such volatiles are generally water-rich, but also contain CO2 and various sulfur (S) and chlorine (Cl) species in significant concentrations. These two latter elements play the most important role in metal-complexation in hydrothermal solutions. Furthermore, their concentrations in degassed magmatic volatiles are indicators of magma chamber processes.

This project aims at constructing a thermodynamic model that is able to predict the composition of the volatile phase exsolving from various silicate melts under upper crustal conditions. High pressure-temperature experiments in cold-seal pressure vessels and piston cylinder apparatus will be conducted to explore the pressure, temperature and compositional dependence of the volatile/melt partition coefficients of S and Cl. Furthermore, in situ and ex situ Raman and X-Ray Absorption Near Edge Structure (XANES) spectroscopy will be applied to determine the oxidation state and speciation of S and Cl in the silicate melt and the volatile phase. The experimental results will be understood with the help of classical Molecular Dynamics simulations and ab initio quantum chemical calculations of the structural environment of S and Cl in both phases, and the thermodynamic properties of the identified species.

The results of this project will improve our capability to predict the composition of volatiles exsolving from magmas and increase the efficiency of ore deposit exploration and volcanic eruption forecasting.

Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Solubility and partitioning behavior of Au, Cu, Ag and reduced S in magmas
Zajacz Zoltan, Candela Philip, Piccoli Philip, Sanchez-Valle Carmen, Walle Markus (2013), Solubility and partitioning behavior of Au, Cu, Ag and reduced S in magmas, in Geochimica et Cosmochimica Acta, 112, 288-304.
The partitioning of sulfur and chlorine between andesite melts and magmatic volatiles and the exchange coefficients of major cations
Zajacz Zoltan, Candela Philip, Piccoli Philip, Sanchez-Valle Carmen (2012), The partitioning of sulfur and chlorine between andesite melts and magmatic volatiles and the exchange coefficients of major cations, in Geochimica et Cosmochimica Acta, 89, 81-101.

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
Invited seminar presentation at the Geosciences Environment Toulouse, University of Toulouse Individual talk 24.09.2013 Toulouse, France Zajacz Zoltán;
Goldschmidt Conference 2013 Talk given at a conference 25.08.2013 Florence, Italy Zajacz Zoltán;
Goldschmidt Conference 2013 Talk given at a conference 25.08.2013 Florence, Italy Zajacz Zoltán;
IAVCEI 2013 Meeting Talk given at a conference 20.07.2013 Kagoshima, Japan Zajacz Zoltán;
ECROFI XXII Meeting Talk given at a conference 07.06.2013 Antalya, Turkey Zajacz Zoltán;
Gordon Research Conference on the Geochemistry of Mineral Deposits Talk given at a conference 15.07.2012 Andover, MA, United States of America Zajacz Zoltán;
Goldschmidt Conference Talk given at a conference 24.06.2012 Montreal, Canada Zajacz Zoltán;
Experimental Mineralogy Petrology Geochemistry Meeting 2012 Talk given at a conference 04.03.2012 Kiel, Germany Zajacz Zoltán;


Abstract

The solubility of volatile elements (H, C, O, S, Cl) in silicate melts have been in the main focus of research in the past decades due to their important role in igneous petrogenesis, volcanic activity and ore deposit formation. Despite that large amount of existing experimental data, the speciation of oxidized S (S6+) and Cl in the silicate melt is still poorly known. Furthermore it is yet to be understood how various S, Cl and CO2 species interact in the silicate melt structure, as it may significantly affect their solubilities, and therefore the composition the volatile phase exsolving from the silicate melt. The research proposed here focuses on filling these gaps of knowledge. We will use an interdisciplinary approach to obtain information on the speciation of S and Cl in silicate melts. This will comprise experimental investigation of solubilities in systems with stepwise increasing complexity, spectroscopic studies (Raman, XANES, FTIR), ab initio quantum chemical calculation of the geometries and thermodynamic properties of plausible species, and classical molecular dynamics simulations of volatile solubilities. Furthermore, systematic sets of experiments will be conducted on a wide variety of natural melt compositions to explore the dependence of volatile/melt partition coefficients of S and Cl on pressure, temperature and melt composition. Our experiments will address conditions relevant for magma chambers and conduits underneath volcanoes (25-400 MPa, 750-1300 oC). All investigations are oriented towards facilitating the construction of an accurate thermodynamic model that predicts the equilibrium composition of multicomponent silicate melts and volatile phases.A doctoral student will focus on the investigation of the partitioning of volatile and metallic elements in silicate melt-vapor-brine systems at relatively low pressures (25-125 MPa) with the purpose of understanding syn- and preeruptive evolution of the volatile phase in magma reservoirs and volcanic conduits. Her/his research will also include a field component tracking the presence of residual brines or salt melts in freshly erupted volcanic rocks, which may also lead to development of new tools to understand eruption dynamics.
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