Lode gold deposits of the Western and Eastern provinces,
South Island,
New Zealand
, formed as a part of the
Cordilleran-style tectonism during Tasman/Tahua and Rangitata orogenesis along
the Paleozoic-middle Mesozoic southern Gondwanan margin. These deposits, hosted
by lower grade greenschist facies sedimentary rock sequences of the Buller,
Takaka, Torlesse, and Caples terranes, universally show geological features that
are consistent with the orogenic gold deposit model, and genetic features are
generally suggestive of a metamorphic origin, with the possible exception of a
magmatic fluid source for the mineralisation at Sams Creek. However, ore fluid
chemistry in Mesozoic deposits of the Eastern province, particularly the low
concentration of non-aqueous volatiles and the very dilute nature of the fluids,
is uncharacteristic of most orogenic gold deposits; this must be explained by
either a unique fluid source or fluid type, which we believe unlikely, or an
unrecognised significance of relatively rare gas-rich fluid inclusions in the
deposits. Absolute age data for gold deposits in both provinces remain
equivocal, thus hindering definition of the exact temporal relationship between
ore formation and terrane accretion, regional metamorphism, and magmatic arc
emplacement. Mercury and antimony occurrences in subgreenschist grade parts of
the Haast Schist may target the upper levels of unrecognised orogenic gold
deposits. If low-grade, high-tonnage intrusion-related gold systems occur on the
South Island, then they are most likely to be
discovered in association with the small molybdenite-, scheelite-, or
cassiterite-bearing quartz stockworks spatially related to the Karamea and
Median batholiths.