NZ Orphan mine site taken into care

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Tanya Piejus (New Zealand)

One of New Zealand’s most contaminated sites, the Tui Mine near Te Aroha, is to be cleaned up. The New Zealand budget for 2007 confirmed that NZ$9.88 million was available for the two-year project.

The orphan mine site sits on the western flank of Mount Te Aroha, one of Waikato’s highest peaks. In Maori legend, the spirit of Te Mamoe, son of a Bay of Plenty chief, caused a stream of crystal water to flow from the heart of the mountain. However, that stream has become blighted by acid and metals from the abandoned mine workings and is now almost devoid of life.

Fig. 1. Polluted water at Tui Mine

Tui Mine’s story began in 1967. Norpac Mining Ltd opened it in order to extract metals, including copper, lead and zinc. The mine prospered and the company found several thousand ounces of gold and silver among the ore.  However, unacceptable levels of mercury in the ore soon proved to be the mine’s undoing. The company buying the ore pulled out in 1973 and, two years later, Norpac went into liquidation. Tui Mine was abandoned.

Mining equipment was removed for reuse at other sites or was sold for scrap. Left behind was a large pile of larger ore pieces, along with sand-sized crushed ore (tailings). This was dammed to prevent it slipping down the mountainside but, through neglect, the tailings dam became unstable. In 1980, the Hauraki Catchment Board had to build a gravel embankment to stop the tailings slipping onto property further down the mountain.

Fig. 2. Tui Mine.

Over the last 30 years, little progress has been made in dealing with Tui Mine’s toxic legacy that flows into the Waihou River from its tailings and shafts. However, the future for the mine looks brighter now. The Ministry for the Environment, in partnership with local government, provided money to stabilise the dam in 2006. And, thanks to the 2007 New Zealand government budget, money has been set aside to start a major clean-up operation.

“There will clearly need to be a considerable amount of public consultation and detailed planning required before work actually starts,” says Dennis Crequer, special projects manager at Environment Waikato.

The clean-up will involve reconstructing the tailings dam to remove any risk of it slipping down the mountainside. A cap will be put on the tailings deposit to stop acid and metals washing out. Finally, the horizontal shafts into the old underground mine workings will be flooded and sealed. In fact, work has already started on the remediation design.  The next step will be to obtain resource and building consent from the local authorities.

Fig. 3. Tailings dam at Tui Mine.

When the clean-up is complete, locals and visitors to Mount Te Aroha will be able to safely enjoy its unscarred natural beauty and Te Mamoe’s stream of crystal water can flow once again.

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