The
Favona adularia-sericite epithermal Au-Ag deposit is located at the southern end
of the Hauraki Goldfield, about one kilometre southeast of the world-class
Martha deposit. The deposit occurs in Late Miocene andesitic lava flows and
local dacitic tuffs of the Waipupu Formation. In some places,
post-mineralisation ash fall and ignimbrite, up to 50 m thick, cover mineralised
rocks and andesite. We collected soils samples from 110 sites along eight
traverses over Favona, and from three regional lines: two south of Favona, and
one north of Favona.

Analyses of soils
identify prominent enhanced concentrations of Au, Ag, and Hg, and lower
enrichments of Sb and As. At Favona, Au and Ag appear to be highly anomalous in
areas over mineralisation with Au concentrations greater than 100 ppb and Ag
concentrations greater than 1000 ppb, whereas background concentrations are
approximately 5 ppb and 50 ppb respectively. The background concentrations of Hg
in soils are approximately 100 - 200 ppb, but in mineralised areas, Hg generally
exceeds 200 ppb, and some soils contain greater than 600 ppb. Antimony shows
enrichments, although weak, above known veins and As locally shows some
enrichment above areas of known mineralisation. Therefore, soil sampling at
Favona defines geochemical anomalies that correlate with the position of known
mineralisation at depth. Thus, there is strong empirical support for the use of
Au, Ag and Hg, and possibly Sb and As geochemistry to identify mineralised
trends associated with buried deposits at other epithermal
prospects.