Fault-induced damage controlling the formation of carlin-type ore deposits

Paper Abstract: It is shown that the first-order control on the distribution of gold mineralization in thenorthern Carlin Trend was fluid migration through fault-related damage networks, triggered by slip events on the Post-Genesis fault system. This fault system consists of two segments ~5-7 km in length, linked at a stepover across a large granodiorite intrusion. In the footwall of the system a wall-damage zone consists of steep, small-displacement faults spatially associated with mineralization. Many wall-damage zone structures formed on pre-existing planes of weakness (e.g. dike margins, folded bedding planes and pre-existing faults). In active fault systems, the static stress changes that occur around an earthquake can be calculated using Stress Transfer Modelling (STM) and used to understand the distribution of aftershock fracturing on damage zone structures - the critical parameter being positive changes in Coulomb failure stress. In this study, STM was applied to model hypothetical slip events on the Post and Genesis fault segments. The distribution of stress change matches the distribution of gold mineralization, with broad, shallow scallops of mineralization occurring in the footwalls of the Post and Genesis fault segments, whereas mineralization at the tips of the fault system, the stepover and the hangingwall is deeper (~0.7-0.9 km, 0.3-0.9 km and >1 km respectively). Static stress change calculations indicate the fault system had the ability to induce damage, enhance permeability and tap fluids as deep as 15 km.