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

It is shownthat the first-order control on the distribution of gold mineralization in
the northern 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, 0.3–0.9kmand >1 kmrespectively). Static stress change calculations
indicate the fault system had the ability to induce damage, enhance permeability
and tap fluids as deep as 15 km.