The Wharekirauponga (WKP)
epithermal gold-silver deposit is located about 10 km north of Waihi in the
Hauraki Goldfield east of Auckland. WKP is notable for its sheeted to
stockwork quartz veins hosted in rhyolitic rocks, that have attracted
exploration interest as a low grade, bulk tonnage exploration target.
Exploration between 1978 and 1993 included 23 diamond drill holes totalling 5505
m. The mineralisation occurs in a rhyolite dome complex (Miocene), consisting of
flow-banded rhyolite and rhyolitic pyroclastic rocks, with minor andesite. Fifty
four drill core samples were collected from six exploration drill holes and
analysed by semiquantitative XRD techniques. Hydrothermal alteration of the
rhyolitic and andesitic rocks has developed secondary mineral assemblages of
quartz, adularia, albite, chlorite, illite, sericite, interlayered
illite-smectite, carbonate, halloysite and pyrite. The main zone of
mineralisation is characterised by quartzadularia alteration, which grades
oiItward to quartz-clay (illite, local halloysite and/or interlayered
illite-smectite) alteration. Propylitic alteration is present at the southern
end of the drilled area of the prospect. Depth-related changes in mineralogy
include a decrease in illite and appearance and increase in quantity of chlorite
with increasing depth, and the localisation of halloysite and interlayered
illite-smectite in the shallow parts of some drill holes.