Journal
JOURNAL OF STRUCTURAL GEOLOGY
Volume 58, Issue -, Pages 108-121Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jsg.2013.11.006
Keywords
Magmatic-to-hydrothermal transition; Pluton dynamics; Strain localization; Granite roof; Mechanical instabilities; Reduced intrusion-related gold deposit; Variscan; NW Spain; Boboras granite; Brues gold deposit
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Funding
- CNRS
- BRGM through the National Research Group on Ore Deposits (GDR) [2458]
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Structural controls are critical during magmatic-to-hydrothermal transition in the formation of intrusion-related gold deposits. They may explain why only some parts of intrusions are mineralized and why only very few intrusions host large deposits. Moreover, most of these gold deposits postdate peak regional metamorphism and were formed in zones of relatively low strain. Indeed, the efficiency of structural gold traps is highest along favourably oriented intrusion/host-rock contacts where mechanical instability maintains high permeability in the cracked thermal aureole. This may be reinforced by melt injections from an underlying root zone. We present a structural analysis of the deformation features of a granite-pluton roof; large-scale dykes and a network of gold veins are intensively developed in this roof, recording a succession of mechanical instabilities. Our gravity survey underlines the presence of a pluton feeder zone located just beneath the mineralized network. It is argued that interferences between regional stress and melt injection in the feeder zone favoured the development of the network by strain located close to the granite roof. This stresses the role of mechanical instabilities triggered by the combined effects of regional stress and melt dynamics in determining the location and size of this type of gold deposit. (C) 2013 Elsevier Ltd. All rights reserved.
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