Previous studies of
alluvial gold in Otago and Southland placer deposits have suggested a
gold-mercury association for some deposits derived from Caples Terrane schist,
whereas alluvial deposits on Torlesse Terrane basement typically have no
mercury. A regional study of gold from Otago Schist vein deposits from both
Caples and Torlesse Terranes has revealed the presence of both Au-Ag and
Au-Ag-Hg alloys in both terranes. Au-Ag alloy (3 - 4 wt per cent Ag) is typical
for gold found in most Torlesse vein deposits, and Au-Ag-Hg alloy (3 - 8 wt per
cent Ag, 2 - 8 wt per cent Hg) is found in many Caples vein deposits. Au-Ag-Hg
alloys are not exclusive to the Caples Terrane, however, as Au-Ag-Hg alloys with
up to 4 wt per cent Hg are found in vein material from the Torlesse-hosted,
HydeMacraes Shear Zone. In addition, not all Caples-hosted deposits have a
gold-mercury association; gold grains from the Carrick and Invincible gold
fields have no detectable mercury. The present study characterises gold
compositions from various hard-rock vein deposits and has potential for
determining placer-source relationships.