Mesothermal gold deposits of southernAlaska and Westland, New Zealand have both formed at the seaward edge of
major collisional zones in the Pacific basin. In Alaska, production of large fluid volumes
correlates in time with the addition of heat into the lower parts of the
accreted terranes in the late stages of collisional orogeny. This heat was
critical for driving both the metamorphic reactions that released the large
volumes of fluid that carried the gold, and the contemporaneous widespread
anatexis and magmatism. In Alaska's Chugach
terrane, this heat as produced by subduction of a spreading ridge beneath the
North America continental margin in the Eocene.
The resulting products were the S-type granites and gold-bearing veins. The
similar widespread S-type plutonism and gold veining in Westland's Buller terrane
suggest that a similar tectonic event could have triggered ore formation along
the southeastern edge of Gondwanaland. Based on the Alaskan model, a Devonian or
Early Carboniferous age is favoured for high volume metamorphogenic fluid
generation and gold vein formation in Westland.