This study provides quantitative data on vein distributions within seven selected epithermal systems, four deposits hosted
predominantly in rhyolitic rocks: Ohui, Wharekirauponga, Neavesville and Komata, and three major deposits mainly
hosted in andesite: Martha Hill, Golden Cross and Karangahake. The technique of fractal analysis was used to help
quantify vein distribution patterns. The fractal dimensions (D) obtained are related to the number of veins per metre,
the degree of vein clustering, and vein thickness. An increase in any of these tends to increase the fractal dimension.
It is the relative relationship of these parameters that is important for the characterisation of vein distributions, and the
comparison of different deposits. Within the same systems, the rhyolites are characterised by lower vein thickness and
vein density, but have a higher degree of vein clustering compared to the andesites. Sections that are deeper and more
centrally located within the epithermal system and/or close to major structures, tend to have a greater degree of vein
clustering, higher average vein thickness and density, and higher thickness to density ratios. This depth control is most
pronounced in epithermal gold-silver systems because they have formed at shallow crustal levels where physico-chemical
conditions change drastically both vertically and laterally. In addition to lithological and structural control at vein scale,
deposit scale structure is of great importance in the deposition of economic mineralisation. Large open vein structures
capable of sustaining high fluxes of hydrothermal fluid, favourable for the formation of large, high-grade gold deposits,
are best developed in andesite sequences.