New Zealand Journal of Geology & Geophysics abstracts
Golden Bar gold deposit as an extension of the Hyde-Macraes Shear
Zone, east Otago, New Zealand
P. Jones
D. Craw*
R. J. Norris
Geology Department
University of Otago
PO Box 56
Dunedin 9054, New Zealand
*Corresponding author: dave.craw@stonebow.otago.ac.nz
Abstract The Golden Bar gold mine pit near
Macraes, east
Otago, was developed in Textural Zone (TZ) 3 of the Otago Schist, at
least 100 m structurally up-section from the Hyde-Macraes Shear Zone.
This study tests the hypothesis that the Golden Bar mineralised zone
was an extension of the major Hyde-Macraes Shear Zone mineralisation
system. The Golden Bar rocks have been extensively, but subtly,
hydrothermally altered. Principal hydrothermal alteration effects are
replacement of titanite by rutile, replacement of epidote by siderite
and kaolinite, and addition of pyrite. Mineralised (gold-bearing) rocks
within this hydrothermal alteration zone are volumetrically minor and
include micaceous schist with disseminated pyrite and arsenopyrite,
silicified micaceous schist, and quartz veins. The structurally lowest
mineralised rocks occur in a well-defined foliation-parallel zone of
black sheared rocks with abundant hydrothermal graphite and sulfide
minerals. The top of the mineralised zone is defined by a duplex shear
zone, c. 10 m thick, containing abundant silicified and
sulfide-bearing schist that has been deformed into an imbricate stack.
Between the lower shear and the upper duplex zone, shallow-dipping
thick (metre scale) mineralised extensional quartz veins cut across
schist foliation and extend for up to 60 m laterally. The Golden Bar
mineralised rocks were emplaced during contractional deformation and
this resulted in WNW-directed thrusting that controlled the formation
of ore-grade zones. The deformation and mineralisation style at Golden
Bar is essentially identical to that of the Hyde-Macraes Shear Zone
that structurally underlies the Golden Bar zone. This inferred
relationship between the Hyde-Macraes Shear Zone and Golden Bar
mineralisation extends the overall structural thickness of this
gold-bearing deformation zone to >250 m.
Keywords Otago Schist; mesothermal gold;
orogenic gold;
hydrothermal alteration; structure; duplex; thrust
G07009 ; Online publication date 1 August 2007; Received 4 May 2007;
accepted 13 July 2007
New Zealand Journal of Geology & Geophysics, 2007, Vol. 50:
271–281
0028–8306/07/5003–0271 © The Royal Society of New Zealand 2007
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