Principles involved in mobilization and remobilization

Abstract Many orebodies result from appropriate combinations of fluid flow, chemical environment, pressure, temperature, and rock structure, within the context of mobilization and possibly remobilization. This is largely because solid-state diffusion is too slow to allow transport of materials over distances in the order of kilometres within appropriate time-frames. Advective mass transport, involving large fluid/rock ratios, is the only viable mechanism of solution transfer that satisfies distance/time-frame requirements. Despite removal of metal species from a source region and their emplacement in otherwise barren rock being influenced by transport mechanism and fluid chemistry, it is the porosity and permeability (mechanical and chemical) of source region and emplacement site, and the need for focussed flow, that are fundamental to forming ore concentrations and constitute important exploration guides. Thee processes and recognition of mechanically enhanced permeability are related to crack-seal vein systems, critical vein systems, subcritical joints and vein breccias. The only significant differences between the basic principles of mobilization and remobilization are the lesser need for focussing of circulating fluids, and the local role of solid-state remobilization in highly ductile massive sulphide. By definition, the chemical environment associated with fluid-state mobilization and remobilization must differ from that of previous deposition; and this generally means that the associated metamorphic conditions will differ.