Martha Mine, Waihi, New Zealand
Figure 2: The Martha Mine operated by Newmont at Waihi in the Hauraki goldfields, North Island, New Zealand. View from the public viewing platform, looking east towards the coastal hills.

Gold Deposits of New Zealand

Gold was one of New Zealand’s first industries. What is less known, and somewhat at odds with the countries “clean green” image, is that there are still are a number of commercial gold mines in the country. There is continual debate and some tension between a pro-development government and well-organised and vocal conservation lobby which also includes many Maori (indigenous) interests.

It has been estimated that New Zealand’s gold resources may be worth  over NZ$45 million (US$ 35 million). Current production is around 13,000kg/year comparable to the production of Surinam or Venezuela. By comparison, neighbouring Australia produces about 260,000kg annually.

Today there are three main gold producing areas in New Zealand; Macraes and Reefton areas in the South Island and the Waihi area in the North Island (Figure 1).

New Zealand Gold Deposits

Figure 1: Major gold producing areas of New Zealand; Macraes, Reefton and Waihi. Major cities are also labelled.

Waihi Gold Mines

The Waihi gold deposits are low sulphide epithermal gold-silver veins with associated volcanic breccias. The gold veins are hosted within a fine-grained volcanic rock, andesite, aged between 3 and 12 million years ago (Ma), during the Pliocene and Miocene.

In the Waihi area, Newmont Waihi Gold Limited, which is a wholly-owned subsidiary of the American Newmont Mining Corporation, , operates the Martha open pit together with the Favona and Trio underground mines. Correnso, a new underground mine, is expected to be commissioned in 2015. Production is estimated to continue until 2021.

Under Martha Hill at Waihi existed numerous closely spaced gold-bearing quartz veins. These were mined via underground shafts from the 1880’s to 1952. These historic workings have been incorporated into a modern open pit (Figure 2). The Martha open pit mine has been in operation since 1988. In total, some, 8 million ounces of gold has been extracted from the Martha mines, including historic production.

The development of an open pit mine under the town of Waihi has been a major public relations exercise for Newmont over the life of the mine and beyond. The town of Waihi and the wider Coromandel area is well-known for its natural beauty, and is predominantly Department of Conservation reserve. There are ongoing “robust” discussions between those who dislike the reality of noise and blasting in in a mining town, and those who appreciate the economic benefits and jobs the company creates in the community. Newmont reportedly plans to convert the open pit into a lake for recreational purposes.

Martha Mine, Waihi, New Zealand

Figure 2: The Martha Mine operated by Newmont at Waihi in the Hauraki goldfields, North Island, New Zealand. View from the public viewing platform, looking east towards the coastal hills.

At Mount Karangahake, just to the west of Waihi, is the historic underground Talisman Mine , now poised for redevelopment. A deposit with similar geology to Martha, at Talisman, the high grade veins are not as closely spaced as those in the Martha Mine, so the mine is likely to be lower grade. The existing mine comprises 16 levels of drives (Figure 3).

New Talisman Gold Mines Limited, a New Zealand company, plans to recommence underground mining operations from Level 8, in the not too distant future. As most of the mine is under Department of Conservation land, the company will be operating under strict environmental regulations. The company has an inferred resource of 205,000 ounces of gold at a grade of 6.9 g/t Au. Historically, 1 million ounces of gold was extracted from the immediate area.

Karangahake Mine, New Zealand

Figure 3: The Talisman Mine is an historic mine within the interior of Mount Karangahake, near Waihi. It has been extensively mined from 16 levels of drives. The company New Talisman Gold Mines Limited plans to recommence underground mining operations from Level 8.

Macraes and Reefton Mines

The Globe Progress open pit at Reefton, as well as the Frasers open pit and underground mines at Macraes, are owned and operated by Oceana Gold Corporation, an Australian company.

Both the Macraes and Reefton gold deposits are mesothermal and were formed at deeper levels, with correspondingly higher temperatures and pressures, than the epithermal deposits of Waihi. The two deposits are however located in quite different environments. The Macraes deposits are in the Haast Schist, while at Reefton rocks of the the Buller Terrane.

The deposits at Macraes are located in  a north-west striking belt of metamorphic rocks of the Haast Schist. The gold deposits occur within the 30km-long Hyde-Macraes Shear Zone, developed within the schist 145-200 million years ago, during the Jurassic period.

Macraes is New Zealand’s largest gold producing area. It is located only 100km north of the city of Dunedin. Mine employees live and commute to work from either Dunedin, Palmerston or a few who live in the local town of Macraes Flat. The mine is located on a plateau at an elevation of greater than 500m above sea level. In winter snowfalls are common, and can block the main access road. When this happens, mine workers are ferried to the Macraes mine site using four wheel drive vehicles.

Exploring for gold in the exposed Otago region of New Zealand can be difficult at times due to the ever changing weather. Thick snow cover can make it almost impossible to carry out field exploration activities, except for drilling (Figure 4). While at other times, howling north-westerly gales, blowing for days on end, make for tough work conditions.

Macraes has been in production since 1990, with a total of 3 million ounces of gold poured during this time. In 2012, 169,609 ounces of gold was produced at an average grade of 1.29 g/t. Current resources comprise 4.55 million ounces of gold (Moz Au) with reserves of 1.41 Moz Au. It is estimated that gold will continue to be produced at Macraes until 2019, however this end date is continually being extended as new discoveries are made in the area.

Macraes Mining, New Zealand

Figure 4: The Macraes operation in the Otago region of New Zealand after a winter snow fall. The tailings dam is visible in the far distance.

Near the township of Reefton is the Globe Progress open pit. Commissioned in 2007, mining has been along a major regional shear and its offshoots within weakly metamorphosed Ordovician age rocks (443-490 Ma) of the Buller Terrane. The Reefton mine, as it is also called, currently has resources of 1.2 Moz gold, with reserves of 0.37 Moz gold. In 2012, 63,000 oz of gold was produced at a grade of 1.56 grams per tonne (g/t). Concentrated ore is railed to Palmerston, just north of Dunedin, and then trucked to the processing plant at Macraes where the gold is extracted.

Oceana Gold, recently announced that the Reefton mine will cease production in mid-2015, due to recent drops in the price of gold.

Companies Referenced:

Further Reading:

 

About David Tilley

Dr. David Tilley has a wealth of experience in the minerals industry, federal government and academia. Early in his career from 1991 to 1998 he was a PhD scholar, research associate and associate lecturer at the Australian National University, in Canberra. During this time, he lectured geology, mineralogy and field mapping techniques and studied the weathering of minerals and the formation of bauxite. From 1999 to 2005, he was a resources and energy policy writer within the Australian Government. Since 2006, he has worked as an exploration geologist for a number of exploration and mining companies in Australia and New Zealand.