Abstract - Faults are important structures in the formation of many mineral deposits, often acting as conduits for ore-forming fluids
and sometimes providing, or generating, the bounding structures to associated mineralizing sites. Using 3-D analysis and modeling of the Lisheen
and Silvermines deposits within the Irish ore field, we investigate the geometry of normal fault systems and their implications on the origin and
nature of associated deposits. These Irish-type deposits are carbonate hosted and developed within the hanging walls of normal faults arising from
an Early Carboniferous episode of north-south rifting, with relatively limited amounts of later deformation. Structural analysis of high-quality
mine datasets indicates that fault segmentation is ubiquitous with left-stepping segments arising from north-south stretching developed above
generally ENE-NE-trending fault arrays, which are subparallel to older Caledonian penetrative fabrics and structure within underlying Silurian
and Ordovician rocks. Fault segments occur on different scales and have a profound impact on structural evolution, with larger scale segments and
intervening relay ramps defining distinct orebodies within deposits and smaller scale segments and relays potentially providing paths for upfault
fluid flow. The difference in behavior is attributed to the integrity of associated relay ramps where intact ramps represent orebody-bounding
structures, and smaller breached ramps provide enhanced associated hydraulic properties and act as vertical conduits. Hanging-wall deformation along
the rheological boundary between host-rock limestones and underlying shales has an important control on the localization of earlier dolomitization
and/or brecciation and later mineralization adjacent to this contact, and on the migration pathways for basinal brines and mineralizing fluids.
Economic Geology, 114, 93-116, doi: 10.5382/ECONGEO.2019.4621.