Episodic mineralising fluid injection through chemical shear zones

Abstract

The nature of the geological mechanisms allowing mineralising fluids to flow from depth and form localized mineral deposits is uncertain and a matter of debate. Traditional assumptions of fluids travelling through highly permeable faults raise interesting questions about the existence of highly permeable faults at depths below the brittle-ductile transition, for example. A recent model of multi-physics oscillation can explain the behaviour of impermeable shear zones in such environments, under specific conditions where temperature sensitive endothermal reactions trigger in-situ release of fluids that lubricate the fault and lead to their reactivation. The response of such systems can be of various nature, including slow creep, one-off reactivation events, or episodic reactivation events during which the permeability increases by several orders of magnitudes and allows fluids from depth to flow upwards. In this contribution, we review briefly the previous studies on this chemo-mechanical oscillator and place the findings in the context of mineral exploration. We extend the parameter sensitivity analysis to the main two dimensionless parameters controlling the chemical reactions, the Arrhenius and Damköhler numbers, to understand how they affect the location of episodic slip instabilities in the global parameter space. We show that lower values of the Damköhler number reduce the range of Gruntfest values in which the oscillator operates and we propose some fitting relationships between the main parameters in various interesting areas of the parameter space.