New Zealand Journal of Geology and Geophysics abstracts
The mercury and silver contents of gold in quartz vein deposits,
Otago Schist, New Zealand
D. J. MacKenzie
D. Craw
Geology Department
University of Otago
P.O. Box 56
Dunedin, New Zealand
dave.craw@stonebow.otago.ac.nz
Abstract 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. Almost all Hg-bearing gold occurs in east Otago vein systems,
and Hg-free gold occurs in central and northwest Otago vein systems,
irrespective of host terrane. One Central Otago mineralised zone has up
to 1.7 wt% Hg in the gold. Au-Ag alloy (3–8 wt% Ag) is typical for gold
found in most Torlesse-hosted vein deposits, and Au-Ag-Hg alloys with
1–4 wt% Hg are found in vein material from the Torlesse-hosted
Hyde-Macraes Shear Zone. Au-Ag-Hg alloy (3–8 wt% Ag, 2–8 wt% Hg) is
found in many Caples-hosted vein deposits. There is no relationship
between depth of vein emplacement and Hg content of gold, as both high
and low Hg gold are found in shallow-formed (<2 km) and
deep-formed (>6 km) deposits. There is no spatial relationship
between Hg-bearing gold and cinnabar-bearing veins that occur in Caples
Terrane rocks on the southern edge of the schist belt. Mercury-bearing
placer gold in eastern Southland may have been derived from erosion of
east Otago veins. The source of Hg-bearing placer gold in northern
Southland is unknown as yet.
Keywords gold; mercury; silver; veins; Otago
Schist; Caples Terrane; Torlesse Terrane
G04019; Received 30 April 2004; accepted 29 November 2004; Online
publication date 25 May 2005
New Zealand Journal of Geology & Geophysics, 2005, Vol. 48:
265–278
0028–8306/05/4802–0265© The Royal Society of New Zealand 2005
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