Hydrothermal Alteration at the Karangahake Epithermal Au-Ag Deposit, Hauraki Goldfield, New Zealand

摘要

The Karangahake deposit is the third largest gold producer in the Hauraki goldfield, Coromandel, New Zealand. Production was mainly from the Maria and Welcome/Crown veins that were mined over a strike length of >1,300 m and vertical interval of 700 m. The veins are hosted in andesite that is strongly altered over an area of approximately 4.2 × 2.7 km. By using petrography, qualitative and quantitative X-ray diffraction (XRD), and automated mineralogy from a scanning electron microscope (SEM), hydrothermal alteration has been characterized in detail for surface rocks exposed along the Ohinemuri and Waitawheta rivers and along the underground Keillors crosscut, which links the Maria and Welcome/Crown veins. The chemistry of hydrothermally altered rocks was analyzed using portable X-ray fluorescence (pXRF). The automated mineralogy reveals alteration mineral occurrences, abundances, and some textural relationships that are not as apparent from conventional studies.