Rise and Shine shear zone, Central Otago, New Zealand

Author:

Cox, Luke (Luke Lavington)

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Abstract:

The Rise and Shine Shear Zone (RSSZ) is a predominantly brittle late metamorphic structure striking NW to W and dipping 30-40° to the N or NE. The shear zone hosts quartz-gold mineralisation and extends at least 16km across the Dunstan Range. The shear zone is on average -21m in width (intrashear zone) and is bounded by a mainhanging wall and footwall shear. This shear package juxtaposes TZ Ill Torlesse terrane schist in the hanging wall against TZ IV Torlesse terrane schist in the footwall. The textural zone IV intrashear zone hosts N-NE and S-SW dipping normal shears that are synthetic and antithetic to the main hanging wall and footwall shears and formed coevally with them. The shear zone cuts regional D3 structures and parallels in three dimensions D4 and D5 planar structures. Steeply east to south-east dipping Cenozoic reverse faults related to the uplift of the Dunstan Range cut, but do not laterally offset the RSSZ in at least three locations. The RSSZ has a top to north direction of movement. Gold mineralisation occurred under greenschist facies conditions and was coeval with the inception of the main footwall shear and prior to the normal fault juxtaposition of textural zone Ill and textural zone IV schist. Gold is also concentrated in the minor N-NE and S-SW dipping normal shears. Later north striking and steeply east dipping faults also host gold. The schists that are altered by the RSSZ, i.e. the intrashear zone and diffuse zones above the main hanging wall shear are enriched in AI, K, Ca and Fe, Cr and As relative to the host schist. A positive correlation exists between the concentration of arsenic and the concentration of neodymium, niobium, thorium and uranium within gold mineralised schists. Fluid inclusions within the mineralised quartz homogenise at a modal temperature of 133 °C. A pressure correction of 2-4kbar, typical of greenschist facies conditions yields a true trapping temperature of 300 ± 50°C . Stable carbon and oxygen isotope analysis indicate the mineralising fluids of the RSSZ have a metamorphic origin. Although the RSSZ and the Hyde-Macraes Shear Zone formed broadly over the same period, the lack of unequivocal evidence for thrusting on the RSSZ means that the RSSZ is unlikely to be the western continuation of the Hyde-Macraes Shear Zone.

Thesis description:

114 leaves : ill. (some col.), maps (some col., 1 folded) ; 30 cm.

Department:

OU geology Identifier:

2003Cox

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Location (WKT, WGS84):

POLYGON ((169.563204474343223 -45.000637646504998,169.472362805457522 -44.995720821790677,169.454384825594019 -44.985159979197768,169.392269634504061 -44.93212312453548,169.429349424213655 -44.934361777101124,169.464637980020001 -44.957611547275853,169.56196997426224 -44.962373096255774,169.563204474343223 -45.000637646504998))

Files

http://download.otagogeology.org.nz/temp/Abstracts/2003Cox.pdf

Collection

Citation

Cox, Luke (Luke Lavington), “Rise and Shine shear zone, Central Otago, New Zealand ,” Otago Geology Theses, accessed May 22, 2024, https://theses.otagogeology.org.nz/items/show/407.

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