Episodic modes of operation in hydrothermal gold systems: Part I. Deformation, mineral reactions and chaos

Abstract

AbstractEpisodic fluctuations in fluid pressure and temperature are characteristic of the behaviour of orogenic gold systems and are commonly attributed to processes external to the system, such as seismic events and associated adiabatic fault valve or suction pump/piston behaviour; any temperature changes are attributed to the adiabatic nature of the process. Such processes are commonly associated with fluctuations in fluid pressure with little, if any, changes in temperature. We describe aseismic, non-adiabatic processes internal to the hydrothermal system that lead to episodic modes of temperature and fluid pressure behaviour and the deposition of gold. These gold deposition processes are essentially controlled by localized changes in temperature; such temperature-dependent gold deposition processes are normally thought of as inconsequential. We propose that internal episodic behaviour is fundamental in hydrothermal mineralizing systems associated with orogenic gold deposits. Importantly, the time period for these hydrothermal events appears to be small relative to metamorphic systems, with 1–2 myr as an upper limit. This has important ramifications for rates of heat production and for the resultant kinetics of mineral reactions during alteration and mineralization. We explore these systems as non-linear, non-equilibrium dynamic, open flow systems.