Stress-Controlled Hydrothermal Fluid Flow in Basement Greywacke, Kuaotunu, Coromandel Peninsula, New Zealand

Abstract

A hydrothermal system extends into well-exposed basement greywacke at Kuaotunu, the northem-most of the major Hauraki Goldfields. Stress-controlled structural permeability in a predominantly extensional tectonic regime has governed hydrothermal fluid flow in the greywacke. Localised dilatation has occurred as a consequence of two modes of brittle failure: extension perpendicular to the least principal stress, and extensional-shear to the directions of principal stress. Changes in the dip of normal faults, linkage structures between closely-spaced parallel faults, and fault reactivation of suitably oriented bedding planes have focussed fluid into remarkably localised conduits..