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Published 22 May 2018

Gold in the hills: New issue of New Zealand Journal of Geology and Geophysics released

Frasers Pit, Macraes gold mine

An article discussing geology around the formation of New Zealand's largest active gold mine published in the new issue of New Zealand Journal of Geology and Geophysics vol/iss 61/2.

The new issue of New Zealand Journal of Geology and Geophysics vol/iss 61/2 is now available at Taylor and Francis Online.

One of the featured articles in the new issue Extensional deformation along the Footwall Fault below the Hyde-Macraes Shear Zone, Otago Schist, New Zealand authored by Nick Mortimer FRSNZ, Uwe Ring, Christoph Butz and Matthias Bernet, reflects a multi-national effort of scientists from different countries collaborating to discuss structures across the Footwall Fault, directly underneath the Hyde-Macraes Shear Zone in the Otago Shist. 

The Macraes gold deposit is the largest active gold mine in New Zealand and has produced more than 1.8 million ounces of gold since its opening 28 years ago. The mine is situated near a small township and is about 100 km west of Dunedin city in the Waitaki district of East Otago.

hyde macraes shear zone

Image from the University of Otago's Department of Geology

The Hyde-Macraes shear zone at Macraes appears as slightly darker rocks within the Otago Schist of the area, it is a very subtle feature which can be hard to detect in natural rocky outcrops. The darker colour of the rock in the shear zone is partly due to graphite/carbon that was added to the Otago Schist during the same hydrothermal processes that introduced the gold into the rock.

The Footwall Fault cut across the gold-laden zone during the middle Cretaceous period, at the same time that the Waihemo Fault Zone started. The normal fault motion and its associated erosion of the landscape exposed the gold zone at Macraes and made opencast and underground mining for gold there possible. The normal fault movement and the suggested accompanying formation of the steeper Waihemo Fault is discussed in further detail in Extensional deformation along the Footwall Fault below the Hyde-Macraes Shear Zone, Otago Schist .

One of the authors, Dr Nick Mortimer is a newly minted Fellow of Royal Society Te Apārangi and has played a key role in exploring, revealing and promoting the continent of Zealandia. The foundation for this has been his multifaceted work on the older crystalline rocks of on-land New Zealand, including their relationships with Australia and Antarctica.

The article is available open-access in the New Zealand Journey of Geology and Geophysics Vol/iss 61/2.