Repeated reactivation of clogged permeable pathways in epithermal gold deposits: Kestanelik epithermal vein system, NW Turkey

This study presents a detailed study of the dimensions, geometry, textures and breccias of a well-exposed epithermal vein system, the Kestanelik gold deposit in the Biga Peninsula, NW Turkey and investigates the permeability enhancement mechanisms in epithermal gold deposits. Here mineralisation is associated with quartz veins up to 13.6 m thick. Vein textures and breccia components indicate repeated sealing and subsequent brecciation of wall rock and pre-existing vein infill. Field and petrographic analyses characterize E-W trending veins as left lateral faults, whilst NE- SW trending veins are extensional (Mode I) fractures. Cataclasite and tectonic breccia of wall rocks and early quartz, hydrothermal crackle breccias, and matrix supported chaotic breccias of pre- existing vein infill, all of which are cemented by late iron-oxide-bearing quartz, indicate that co- seismic rupturing and hydraulic fracturing are two major permeability enhancement mechanisms. In addition, transient variations in local stress direction, caused by syn-mineralisation dyke intrusion, may have enhanced permeability on mis-oriented surfaces and at locations where the dip changes. This study emphasizes the importance of understanding structural geology and kinematics as controls on the location of boiling and mineralisation mechanisms in epithermal gold deposits.