oa Heterogeneous Fault Zone Structure and Related Flow Localization Within Limestones

High quality outcrop and mine data for normal faults within limestone sequences are used to highlight the inherently heterogenous nature of fault rock and fault zone structure. This heterogeneity is attributed to fault-related segmentation and refraction compounded by progressive breaching of segment boundaries (i.e. relays) and the removal of fault surface asperities with increasing displacement. Relay breaching and fault linkage is responsible for rapid changes in fault zone structure, with the generation of high fracture densities and increased host rock brecciation. Recent work on classic Zn-Pb Irish mineral deposits, hosted within Carboniferous limestones, suggests that the accentuated deformation associated with relay breaching and related fault bends is responsible for the creation of sub-vertical zones of high permeability which act as conduits for upward flow of mineralizing fluids from underlying basement rocks. These zones of enhanced permeability occur on a range of scales, most often below the limit of hydrocarbon and mineral exploration datasets. This talk considers the potential implications of the strongly heterogeneous nature of fault zone structure and related flow, for a variety of application areas, including hydrocarbon exploration/production and CO2 storage.