New Zealand Journal of Geology and Geophysics abstracts

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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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