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Genesis of orogenic gold deposits

English title Genesis of orogenic gold deposits
Applicant Diamond Larryn W.
Number 132547
Funding scheme Project funding (Div. I-III)
Research institution Institut für Geologie Universität Bern
Institution of higher education University of Berne - BE
Main discipline Geochemistry
Start/End 01.10.2010 - 31.08.2011
Approved amount 66'597.00
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Keywords (5)

Ore deposit; gold; fluid inclusion; thermodynamic modelling; geochemical analysis

Lay Summary (English)

Lead
Lay summary
"Orogenic Gold Deposits" are one of the world's largest sources of mined gold and they are a major target for the exploration industry. Despite abundant research in the past, many of the fundamental processes that form these deposits remain poorly understood. Any advances in understanding would be most timely, as the exploration industry is now highly active in orogenic belts worldwide and it relies on genetic models to guide its field programmes. One of the problematic aspects concerns the mechanisms of transport and precipitation of gold in the specific kinds of geochemical settings that form orogenic deposits. Although the thermodynamic stabilities of aqueous gold-complexes are fairly well known, it is not clear how gold solubility is influenced by reactions between the fluid and the wall rocks of the deposits. Parameters such as fluid fluxes, the duration of the mineralizing events, the role of kinetics and the evolution of permeability are unconstrained. In addition, the relative influences of processes that compete with rock-water reactions, such as the thermal evolution of the hydrothermal system or phase separation (boiling) have not yet been evaluated. In the proposed project we intend to simulate numerically the rock-water interaction in a specific, well-characterized case study at the Fenilia Mine, Brusson, NW Italian Alps. The distribution of gold in the Fenilia mine shows a strong, simple dependency on wall-rock lithology and the abundant fluid inclusions in the vein quartz allow the original composition of the gold-transporting fluid to be reconstructed. Existing data on the fluid inclusions will be expanded by laser-ablation-ICPMS analyses of individual inclusions. Detailed underground mapping and petrographic, mineralogical and porosity analyses will be performed to characterize the wall rocks. The recalculated rock and fluid properties will be used as input for the numerical simulations. By using quantitative, fully coupled reactive-transport models that involve fluid flow, mineral-fluid equilibria and kinetic laws, we intend to investigate the influence on gold precipitation of dynamic factors such as distal versus local buffering of chemical parameters, fluid flow velocities and fluxes, kinetics of rock-water reactions, thermal aspects of rock-water interaction, and the role of phase separation (boiling). The results will be published in journals that are accessible to both the scientific community and the mineral exploration industry.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Name Institute

Publications

Publication
Morphological ripening of fluid inclusions and coupled zone-refining in quartz crystals revealed by cathodoluminescence imaging: Implications for CL-petrography, fluid inclusion analysis and trace-ele
Lambrecht Glenn Diamond Larryn W. (2014), Morphological ripening of fluid inclusions and coupled zone-refining in quartz crystals revealed by cathodoluminescence imaging: Implications for CL-petrography, fluid inclusion analysis and trace-ele, in Geochimica et Cosmochimica Acta, 141, 381-406.
Fluid mixing and boiling during latest stage orogenic gold mineralization at Brusson, NW Italian Alps
Lambrecht G. Diamond L.W. (2010), Fluid mixing and boiling during latest stage orogenic gold mineralization at Brusson, NW Italian Alps, in Birkle & Torres-Alvarado (ed.), Taylor & Francis Group, London, 211-214.

Associated projects

Number Title Start Funding scheme
122177 Genesis of orogenic gold deposits 01.10.2008 Project funding (Div. I-III)

Abstract

"Orogenic Gold Deposits" are one of the world's largest sources of mined gold and they are a major target for the exploration industry. Despite abundant research in the past, many of the fundamental processes of rock-water interaction that form these hydrothermal deposits remain poorly understood. Any advances in understanding would be most timely, as the exploration industry is now highly active in orogenic belts worldwide and it relies on genetic models of this deposit type to guide its field programmes.One of the problematic aspects concerns the mechanisms of transport and precipitation of gold in the specific kinds of hydrothermal systems that form orogenic deposits. Although the thermodynamic stabilities of aqueous gold-complexes are fairly well known, it is not clear how gold solubility is influenced by reactions between the fluid and the wall rocks of the deposits. Parameters such as fluid fluxes, the duration of the mineralizing events, the role of kinetics and the evolution of permeability are unconstrained. In addition, the relative weights of processes that compete with rock-water reactions, such as the thermal evolution of the hydrothermal system or phase separation (boiling) have not yet been evaluated.A principal reason for the slow progress in understanding has been the lack of sophisticated computer models that allow coupled simulation of chemical reactions and fluid flow. A recent generation of codes now offers these capabilities and over the past years we have gained experience in developing and applying them to hydrothermal systems.In this project we are performing numerical simulations of the rock-water interaction in a specific, well-characterized case study at the Fenilia Mine, Brusson, NW Italian Alps. The distribution of gold in the Fenilia mine shows a strong, simple dependency on wall-rock lithology and the abundant fluid inclusions in the vein quartz aid in reconstructing the original composition of the hydrothermal fluid. Existing data on the fluid inclusions have been augmented by new analyses of individual inclusions in spatially and temporally well-constrained samples. Detailed underground mapping and petrographic, mineralogical and porosity analyses are being performed to characterize the wall rocks. The recalculated rock and fluid properties are being used as input for the numerical simulations. By using quantitative, fully coupled reactive-transport models that involve fluid flow, mineral-fluid equilibria and kinetic laws (e.g. FLOTRAN, Lichtner 2007), we are investigating the influence on gold precipitation of dynamic factors such as distal versus local buffering of chemical parameters, fluid flow velocities and fluxes, kinetics of rock-water reactions, thermal aspects of rock-water interaction, and the role of phase separation (boiling).In this proposal we request funding to extend our on-going SNSF project 200021-122177 on "Orogenic Gold Deposits" by one year (1.10.2010-31.9.2011). The project was initially granted for 2 years (1.10.2008-31.9.2010) and a doctoral student (Glenn Lambrecht) is sucessfully carrying out the main part of the research. A further year of support will allow us to achieve the main goals of the study and will allow Mr Lambrecht to complete his doctoral dissertation.
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