FAULT DAMAGE AS THE PRIMARY CONDUIT OF FLUID COMMUNICATION AND THE SOFT-LINKAGE OF FLUID RESERVOIRS

Here I demonstrate that faults can soft-link with hydrothermal fluid reservoirs by triggering fault damage. Indeed fault damage may be a more important conduit for fluid migration in the Earth's crust than large-scale faults and shear zones. We use an example from the North Carlin trend, where gold mineralization around the large-scale Post-Genesis Fault has an enigmatic distribution - wide, scallops of mineralization at shallow depths in the footwall, contrasting with narrow deep ore envelopes in the step-over and tip zones. Small-scale faults are ubiquitous within the gold field but only a subset are associated with mineralization, sometimes at distances >2 km from the Post-Genesis fault. We find Coulomb failure static stress changes, from slip events on the Post-Genesis Fault, correspond with the distribution of mineralization in three-dimensions. The Post-Genesis Fault segments, 5-7 km long, had the ability to activate subpopulations of the damage network from surface to 12 km, and transiently enhance permeability during earthquake or creep events. Independent analyses support this conclusion, with nanoSIMS mapping of gold in pyrite and apatite fission track thermochronology both indicating mineralization occurred in discrete, short duration, pulse-like events. The implications of this study are far-reaching. For example, faults pose a risk to the integrity of storage reservoirs for radioactive waste and CO₂, even when not directly linked to those reservoirs. Risks only begin to decrease at distances greater than 1 equivalent fault length from the reservoirs.