Textural and structural characteristics of the Kestanelik epithermal vein system, NW Turkey : implications for permeability enhancement mechanisms and gold exploration in epithermal systems

• Main Author: Gülyüz, Nilay
• Published: University of Strathclyde 2017
• Subjects: 624
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.736861

It has long been known that faults and fracture provide a critical role in multiphase epithermal mineralization, however the mechanisms of permeability enhancement after a conduit becomes sealed up over time has been less well studied. The research in this thesis investigates the vein-scale permeability enhancement mechanisms in epithermal gold deposits through a detailed study of geology, dimensions, geometry, textures and breccias of the well-exposed Kestanelik gold deposit (NW Turkey). New mapping of the deposit and its host rocks show that the Late Eocene mineralization is associated with regional Cenozoic calc-alkaline magmatism. Vein textures and breccia components indicate repeated sealing and subsequent brecciation of wall rock and pre-existing vein infill. Kinematic analyses together with macroscopic and petrographic analyses of vein textures characterize E-W trending veins as left lateral faults, whilst NE-SW trending veins are extensional (Mode I) fractures. Although two phases of mineralization were picked up from E-W trending veins, at least three were determined from NE-SW trending veins. Cataclasite and tectonic breccia of wall rocks and early quartz, hydrothermal crackle breccias, and cement supported chaotic breccias of pre-existing vein infill, all of which are cemented by late-stage quartz, indicate that coseismic rupturing and hydraulic fracturing are two major permeability enhancement mechanisms. Faults were reactivated along the vein footwall-wall rock contact, while extensional veins were opened along their either margin. Transient local stress variation also has the potential to enhance permeability on mis-oriented surfaces and at locations where the dip changes. Constructed 3D vein geometries show subsurface vein bends are more favorable structural locations for gold to precipitate than smooth, planar segments, and the host rock schist host the majority of gold. This study emphasizes the importance of detailed structural and textural studies for gold exploration and 3D orebody modelling.