The development and distribution of gold placers in Otago -
Southland is related primarily to the evolution and architecture of three
distinctly different drainage networks that developed during and since Gondwana
breakup:

Late-Gondwana - Pre-marine;

Middle Tertiary Post-marine; and

Modern.
Late Gondwana - Pre-marine drainage was dominantly
recti-linear and controlled by normal faults and sedimentary basins formed
before or during Gondwana breakup. Placers formed dominantly in 2nd order
transverse drainages with primary sources in their catchments. This drainage
network was progressively destroyed by inundation and burial by marine strata
during Late Cretaceous - Middle Tertiary marine transgression that ultimately
covered most of New Zealand.
Middle Tertiary Post-marine drainage evolved on and incised the newly emergent
low-relief landscape during regional marine regression driven by development of
the present plate boundary through South
Island. Most of Central Otago was drained into Southland and to the
southern coast via a large braided river system with an extensive network of
tributaries in its Central Otago reach.
East Otago was drained by several smaller
systems. Placers formed dominantly in proximal and medial reaches of 1st and 2nd
order drainages with primary or pre-existing placers in their catchments. This
drainage network was destroyed by inundation and burial of the Central Otago
reach of the major system by lacustrine strata following tectonic damning of its
middle reach by range uplift and development of a lake complex that covered
>5000km2 of Central Otago. The Modern drainage network evolved from the
Middle Tertiary network through complex response, firstly to uplift of
NW-trending and NE-trending ranges throughout the region since the Late Miocene,
and secondly to the effects of major Pleistocene glacial advances in West Otago. Placers formed in alluvial fans at range
margins, proximal and medial pre-glacial fluvial systems and glacial outwash
sequences. Evolution of each of these drainage networks has been accompanied by widespread sedimentary recycling of alluvial
gold from older to younger placers, augmented locally by input of first-cycle
gold derived from erosion of primary sources in the repeatedly exhumed basement
rocks.