THE SIGNIFICANCE OF LINEAR TRENDS AND CLUSTERS OF FAULT-RELATED MESOTHERMAL LODE GOLD MINERALIZATION

Gold deposits from the Laverton region, Western Australia, form both linear trends and cluster-like distributions in map view, associated with regional-scale shear zone systems. Clusters of deposits are common, and they form 5 ‚àöv= 5 km domains, spaced every 15 to 20 km. In contrast, there is also a linear trend of mineralization that can be traced continuously for ~20 km along a shear zone. In detail, mineralization is found in a range of different rock types and is hosted in fault-shear zone networks that are smaller than the adjacent regionalscale shear zones by several orders of magnitude. A mixture of different fault types comprise these mineralized fault-shear networks often within the same gold field, although thrust and reverse faults are a common component of the richer deposits (e.g., Sunrise Dam, Wallaby, Granny Smith). The seismogenic behavior of fault systems during mineralization can explain these observations, illustrated by simple stress transfer models that show the location of aftershock distributions around different fault types. Strike-slip ruptures on regional-scale structures can repeatedly trigger restricted clusters of aftershocks. These aftershock clusters describe vertical, pipe-like domains in three dimensions. In contrast, regional-scale thrust or reverse ruptures trigger continuous, more diffuse domains of aftershocks along the full strike of the rupture. Thus ruptures along regional strike-slip structures are able to trigger ruptures on preexisting thrust faultsshears at the deposit scale. When they do so, the thrust aftershocks generate a vertical domain of elevated permeability over the depth of the crust, where the individual flow paths are likely to be highly tortuous, increasing the potential for fluid-rock interaction or fluid mixing. The existence of linear trends and cluster-like distributions of deposits at Laverton may be consistent with two different ages of mineralization in this gold camp. The results also show that distributions of deposits provide an indication of the kinematics of the regional fault systems that they relate to, and that stress transfer modeling is a simple, non-computationally demanding technique that is easily adapted to exploration for fault-related mineral deposits.