The
Rise & Shine Shear Zone is a shallow-dipping Cretaceous late metamorphic
shear zone formed in a compressional environment. The Shotover mineralised
system is dominated by normal faults with well-defined vein systems that cut
across Miocene schist folds and faults related to the inception of the Alpine
Fault. Despite the geological differences between these mineralisation systems,
they share many common features of hydrothermal alteration that have resulted in
disseminated gold in altered sheared schist. The most distinctive feature of
both systems is the abundant ankeritic carbonate that has formed from
decomposition of metamorphic chlorite. Excess iron from this alteration reaction
combined with hydrothermal sulphur to form sulphides that host the disseminated
gold. The chlorite decomposition reaction was reversed in the latter stages of
both mineralisation systems, and this was accompanied by further gold
emplacement in the Rise & Shine system.

Both
alteration systems involved initial decomposition of metamorphic albite,
followed by deposition of albite as a vein mineral in the latter stages. The
fluid flow that yielded the disseminated gold was controlled by microshears that
pervade host schists, in strong contrast to many Otago Schist vein systems where
host rock alteration is absent. The ankeritic alteration in the Shotover and
Rise & Shine mineralised systems has increased the volume of mineralised
rock, and may have made suitable targets for large-tonnage, low grade gold
deposits.