Lithological and structural controls on the form and setting of vein stockwork orebodies at the Mount Charlotte gold deposit, Kalgoorlie

The Mount Charlotte quartz vein gold deposit comprises a series of steeply plunging, pipelike Vein stock-work orebodies in massive metagabbro. The ore bodies are strata bound to the most differentiated unit of the host sill an d are typically adjacent to major steeply dipping faults that cut the sill. The stockworks have two sets of veins with a dihedral angle of about 50 de grees that developed as hydraulic fractures, filled simultaneously, and are generally approximately equally developed. Veins crosscut major faults and parallel minor faults of two sets but are cut along reactivated fault surf aces. The fault sets were inactive during mineralization and are neither ve ined nor are loci of zones of intense alteration. Rare faults of a third se t are in part veined and are loci of zones of mineralization. Two interpret ations of the stress regime during Vein formation are based on different mo dels of fracture formation. For both stress regimes, the major fault sets a re relatively unfavorably oriented for slip or dilation, and predicted move ment Vectors do not Gt fault-plane lineations. The lack of fault activity d uring ore fluid flow promoted formation of vein stockworks at Mount Charlot te rather than shear zone or fault-hosted veins. Fluid flow paths and orebo dy siting are controlled by stress-guide effects due to the rheology of the host gabbro, and by the three-dimensional geometry of impermeable faults a nd of fault-bounded blocks of rock.