New mapping and drilling associated with gold exploration has elucidated the structural and lithological controls on hydrothermal gold systems in the White River area. The Paleozoic basement consists of a sequence of amphibolite facies clastic metasedimentary and meta-igneous rocks that host lower grade ultramafic rocks, some magmatically and some tectonically emplaced during the Late Triassic – Early Jurassic. Mapped ultramafic bodies show close congruence with published airborne magnetic anomalies. All of these rocks are cut by brittle normal faults and fractures, and dykes correlated with middle Cretaceous to early Tertiary extension-related intrusive rocks. Gold mineralization associated with these fractures is strongly controlled by host rock types. Two main rock types, felsic gneiss and quartzite, are preferentially fractured and hydrothermally altered. Other rock types are only weakly fractured and locally altered. In particular, ultramafic bodies and micaceous lithologies locally impeded fluid flow.
