Episodic modes of operation in hydrothermal gold systems; Part II; A model for gold deposition
Episodic modes of operation in hydrothermal gold systems; Part II; A model for gold deposition (in Characterization of ore-forming systems from geological, geochemical and geophysical studies, K. Gessner (editor), T. G. Blenkinsop (editor) and Peter Sorjonen-Ward (editor))
Special Publication - Geological Society of London (April 2018) 453 (1): 147-164
- chemical reactions
- deposition
- enrichment
- equilibrium
- fluid flow
- fluid pressure
- gold ores
- hydrothermal alteration
- metal ores
- metasomatism
- mineral deposits, genesis
- mineralization
- models
- numerical models
- ore grade
- ore-forming fluids
- P-T conditions
- solubility
- solutions
- structural controls
- volatilization
Coupling between the physical processes intrinsic to a hydrothermal system can lead to episodic and chaotic behaviour. Such behaviour includes variations in both space and time of the temperature, fluid pressure and activity of H (sub 2) S, which result in the deposition of alteration mineral assemblages, zoned pyrite and gold; these variations are multifractal. In particular, the coupling of deformation and simultaneous endothermic and exothermic reactions with fluid flow leads to the highly localized deposition of gold. We discuss the physical and chemical mechanisms for such episodic and localization behaviour and explore the non-linear dynamic reasons why such mechanisms are recorded in the multifractal paragenetic sequence and deformation history. The synchronization of intrinsic episodicity as described here and extrinsic forcing induced by episodic seismicity provides another mechanism for enhancing the yield of gold deposition processes and hence the grade of orogenic gold deposits.
