Paragenesis and structure of high-grade, high-angle, gold veins at Macraes mine in the Hyde Macraes Shear Zone, east Otago
King, Alastair James

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King, A. J. (2018). Paragenesis and structure of high-grade, high-angle, gold veins at Macraes mine in the Hyde Macraes Shear Zone, east Otago (Thesis, Master of Science). University of Otago. Retrieved from http://hdl.handle.net/10523/8476
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http://hdl.handle.net/10523/8476
Abstract:
The Hyde-Macraes Shear Zone (HMSZ) in east Otago is a 25 km long regionalscalestructure that hosts New Zealand’s largest gold mine. OceanaGold (NZ) Ltd.’smine at Macraes has produced over 4 Moz gold from a total resource of > 10 Moz.The HMSZ is a low-angle northeast dipping compressional shear zone hosted inTZ3, Chlorite zone Otago Schist. Gold-scheelite mineralisation along the shearzone initiated in the early Cretaceous during the latter stages of metamorphism andduring exhumation of the schist host rocks through the brittle-ductile transition. Thebulk of material mined at Macraes includes graphite-bearing shears and mineralisedschist with disseminated sulphides. Most of the gold is refractory and containedwithin the sulphides, however, some free gold occurs in quartz veins. The 3 Blackvein is one such gold-bearing vein that is currently being mined in the undergroundworkings below Frasers Pit. This vein is relatively narrow, generally less than 1mwide, contains visible gold and dips steeply, cutting the shear foliation at a highangle. The structural setting and relative timing of this vein is not well constrainedand it is unknown what structural kinematics controlled vein emplacement and howit is related to the main low angle shear. This study aims to place this vein (andothers like it) in structural context with the rest of the shear zone. By mappinghost lithologies, metamorphic structures and vein orientations underground, it isplanned to model the principal stress directions that controlled the vein’s formationand determine whether it is purely an extensional vein or hybrid extensional-shearvein related to lateral ramps. In addition, detailed SEM work on polished sectionswill be used to determine the paragenetic sequence of vein textures and ore mineralsincluding sulphides, scheelite, gold and other accessories within the vein. Thiswill help place the vein in the established paragenetic sequence for the Macraesdeposits.
Date:
2018
Advisor:
MacKenzie, Doug
Degree Name:
Master of Science
Degree Discipline:
Geology
Publisher:
University of Otago
Keywords:
Gold; Structural Geology; Macraes; Paragenesis; 3Black; Hyde Macraes Shear Zone; Otago Gold; Economic Geology
Research Type:
Thesis
Languages:
English
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- Geology [228]
- Thesis - Masters [3415]