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Fluid mixing and boiling during latest stage orogenic gold mineralization at Brusson, NW Italian Alps

Type of publication Peer-reviewed
Publikationsform Contribution to book (peer-reviewed)
Publication date 2010
Author Lambrecht G. Diamond L.W.,
Project Genesis of orogenic gold deposits
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Contribution to book (peer-reviewed)

Book Water-Rock Interaction
Editor , Birkle & Torres-Alvarado
Publisher Taylor & Francis Group, London
Page(s) 211 - 214
ISBN 978-0-415-60426-0
Title of proceedings Water-Rock Interaction

Abstract

The orogenic gold deposit at Brusson, NW Italian Alps, consists of quartz-carbonate- sulphide veins, which are known to have formed from a CO2–H2O–NaCl hydrothermal fluid. Our recent discovery of an aqueous type of fluid inclusion, previously unknown at this location, raises the question of which processes triggered gold deposition. New petrographic evidence and fluid inclusion analyses show that the aqueous inclusions represent pore waters from the local wall rocks. These pore waters seeped into the vein structures and mixed with the main ore-bearing fluid, which at that time happened to be boiling. However, timing constraints suggest that this mixing event played no part in gold deposition. All the observations of gold and associated fluid inclusions suggest that cooling, wall-rock reactions and boiling of the main carbonic fluid were the principal causes of gold deposition. The aqueous inclusions simply record a lull in hydrothermal activity between gold-deposition events.
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