Project 540 - Gold-Bearing Hydrothermal Fluids of Oregenic Deposits
This project considers orogenic gold deposits, one of the most relevant mineral resources of the world market. Orogenic deposits are vein networks generated by syntectonic flow of hydrothermal fluids through large sections of active continental margins of late Archean to Tertiary age. Veins are made of quartz-carbonate-sulfide assemblages, and are located within high-dilatancy areas of narrow, steeply dipping shear zones. Because hydrothermal fluid flow controls how Au is transported and deposited within the vein networks, knowledge of the physical and chemical properties of the ore fluid at the time of vein formation is one of the strategic components of a genetic model. Such properties have been constrained after decades of academic and industrial research, but work is still in progress considering that the actual genetic models do not allow for effective exploration strategies.
This project proposes a multi-technique study of fluid inclusions to implement the fundamental knowledge on the composition of Au-transporting hydrothermal fluids by considering the following analytical strategy:
- Petrographic identification of co-genetic inclusions related to Au deposition
- Spindle-stage measurements of the liquid/vapor ratio in the fluid inclusions
- Microthermometric determination of phase transitions
- Laser Ablation-ICP-Mass Spectrometry of single representative fluid inclusions to determine the concentration of Au and other major and trace chemical components in the ore fluid
- Raman spectroscopy to determine nature and composition of the vapor phase; SEM and X-ray diffraction analysis of all the minerals that make the assemblages of the Au-bearing veins.
This data set has never been compiled systematically at a global scale, and data from LA-ICP-MS is scarce. Therefore, this study defines a comprehensive and quantitative approach to the study of fluid inclusions in orogenic gold deposits, hopefully providing answers to fundamental questions like the effects of post-entrapment re-equilibration of fluid inclusions in the determination of the ore fluid properties, and the significance of microchemical analyses of fluid inclusions from this tectonically-active environment. These data represent fundamental ingredients of working genetic models. The participants to this project carry out leading research in the field of orogenic gold deposits. Following a spirit of trans-national cooperative research, this project would involve ore deposit geologists from 12 countries making available the new techniques of fluid inclusion analysis. In the first year of the project, we will focus on the set up of a template data set from a small number of well-studied deposits from the Superior Province of Canada and from the Yilgarn Block of W Australia, in order to test the feasibility of this strategy. The results of this part of the project will be presented in international meetings and published in international journals. After this feasibility test, work will concentrate on fluid inclusions from deposits located worldwide, e.g. in Morocco (Central Anti Atlas), Bohemian Massive (Krasna Hora), Chile (North Coastal Range), India (South Indian Shield), China (Jiaodong Peninsula), Russia (Eastern Transbaykalia, Siberia; Ural region), and Australia.
This project will establish a benchmark approach to the study of fluid inclusions applicable in metamorphic rocks, as all deposits reflect regional fluid flow in tectonically unroofed orogenic belts. Therefore, support to this study of the chemistry of hydrothermal fluids would not be just be applicable to the evaluation of global gold resources, but also would provide a potential step towards a rationale use of fluid inclusion data for effective and sustainable Earth resource valuation.