Ingress of magmatic Ni-Cu sulphide liquid into surrounding brittle rocks: physical & structural controls

Field observations and theoretical considerations suggest that dense magmatic sulphide liquids are injected into and/or passively infiltrate surrounding wall rocks late in the emplacement history of intrusion-hosted magmatic ore systems. Using analogies with other engineering and mineral systems, we evaluate the structural and physical controls on the ingress of sulphide liquid into brittle host rocks. Gravity-driven infiltration of sulphide liquid out of the host igneous intrusion into country rock may be analogous to the behaviour of dense immiscible fluids in groundwater systems (Dense Non Aqueous Phase Liquids; DNAPL), which is controlled by the body force of the liquid itself. Downward penetration of sulphide liquid into micro-fractures may occur once a sufficient thickness of sulphide, known as the critical accumulation height, is reached in the overlying intrusion. Upward and lateral injection of sulphide liquid is a similar process to the behaviour of crustal hydrothermal fluids, where active deformation, fluid pressure and host-rock anisotropy play critical roles. Such physical controls must be considered and integrated with well-established petro-geochemical concepts in order to better understand the genesis of magmatic Ni-Cu-PGE sulphide deposits.