Quarrying & Mining

By Jenny Baker

Aerial shot of tailings ponds – the decommissioned pond is at the centre, the pond still in use is to the right

Opencast mining and flourishing protected species may sound like an unlikely combination – yet focused environmentally sustainable planning and long-term vision make for strange bedfellows.

Waihi-based Mar tha Mine site progressive rehabilitation is achieving good results. The rehabilitation plan covers all the conditions of owner Newmont Waihi Gold’s (NWG) mining licence and resource consents, as well as several initiatives coming from the
mining team.

These team members know they will not live to see the kauri trees they are planting on the mine premises mature . . . but watching the new colonies of endangered bird species – dabchicks and dotterels prospering on the rehabilitation site gives them more
than enough satisfaction.

Mine manager, Glen Grindlay says progressive, closure, and post closure rehabilitation of the modern Martha Mine has always been a major part of mine planning and proposals. “We had complete rehabilitation concept plans well before commencement of the mine’s construction in 1987.

“In the process we benefited from the advice and skill of a range of experts. Each year we prepare a rehabilitation and closure plan that details progressive work and work that remains to be done on closure,” he says.

Closure planning has four aspects – cultural, environmental, financial, and social. “We do all four together and progressively to ensure we meet our targets and allow for a seamless transition from operations to post-closure,” Mr Grindlay says.

The rehabilitation plan has two objectives. The first is to ensure the site and any structures on it, including the pit slopes and vegetation, will remain stable in the long term. The second is that the quality of surface water discharge or groundwater from the site will not adversely affect aquatic life or other Waihi water resources users.

The rehabilitation plan consists of five main projects. The first is turning the open pit into a 29-hectare, 200-metre-deep productive lake in the years following the mine’s closure. The area around it is already in the process of transforming to a communal park with walkways, lookouts, interpretative stations and lake access.

The second main project is revegetating the pit slopes once operations are finished. Progressive rehabilitation work has been very successful. The third main project consists of rehabilitating waste rock embankments. Some have been progressively rehabilitated to pasture since 1991 and are performing well. Pastures are dotted with native trees and shrubs that now provide a food source and nesting shelter for birds and prevent tracking by
cattle.

The fourth is rehabilitating the two tailings ponds. The first tailings pond was decommissioned in 2004. “Once tailings deposition ceases, we monitor and treat the water quality of the tailing ponds until dischargeable water quality is achieved, which according to our model takes three to four years. When that happens, we will remove the decant system and allow the pond to rise in a controlled manner.

“Tailings consolidation also deepens the pond. At this point it will be able to support a range of aquatic organisms including plants, insect larvae and waterfowl. In support of this, outlet structures will be constructed to allow fish passage between the ponds and the river,” Mr Grindlay says.

The decommissioned pond currently contains only rainwater, and rehabilitation is in progress. The second tailings pond is still in use. A variety of bird species frequent the NWG tailings ponds all year round.

Birdwatchers will find black swans, pied shags, pied stilts, plovers, silver eyes, skylarks, sparrows, swallows, yellowhammers, goldfinches, seagulls, harrier hawks, herons, and a range of duck species, including paradise ducks.

And then there are the New Zealand dabchick (Weweia) and New Zealand Dotterel (Tuturiwhatu)– both New Zealand natives, both protected, and both spending part of their year at the mine site.

In 1995 Ma r t h a Mine workers observed Tuturiwhatu, an endangered species, nesting on the waste rock embankment’s haul road. NWG contacted the Department of Conservation and entered into the Dotterel Watch Partnership, funded by NWG, soon after. Waihi is the only known inland Tuturiwhatu nesting site in the country.

The past three seasons saw 300 chicks fledged all over the Coromandel – good progress since 2004, when there were only about 1500 birds in the country.

The fifth project is to remove buildings and plant from the area, backfill the crusher slot, cover the present surface facilities with soil and recontour them where required, then afforest them with native plants and trees.

Re-establishing vegetation is being done in several ways. Started in 1995, the ten-year Bridge to Bridge Riparian Planting Project involved fencing and planting around 5km riparian margins of the Ohinemuri River and tributaries between the Golden Valley Road and the Coronation (SH2) bridges. The project established 200,000 native plants at a cost of $2 million. Maintenance in these areas continues.

NWG has supported the construction and maintenance of public walkways in the Waihi area through funding and in-kind contributions. One of these walkways, built by NWG, runs partly alongside the riparian planting project areas, to provide access to the summit of Black Hill. Walkway establishment around the pit, which will eventually include lookouts and amenities such as car parks and a boat ramp, is progressing well.

Rehabilitation of the site also included planting about 3,500 kauri trees at a cost of more than $100,000– not including planting and maintenance. NWG started its KauriBank project in 2003 in recognition of the historic loss of kauri trees through mining and forestry
activities around the Waihi area in the late 1800s and early 1900s.

The aim of the project is to plant one kauri for each person/year spent in the modern mine. Each grove of trees planted is counted and entered into a KauriBank register, map and aerial
photograph. The database is updated regularly as the growth of each grove of trees
is monitored.

Following the closure and post-closure period a charitable body, the Martha Trust, will take title to the rehabilitated mining land, including the lake and the rehabilitated tailings storage
area, and maintain it for public use. Interest from a sum of money NWG will hand over to Trust will cover expenses and provide necessary insurance cover.

“Martha Mine and the Waihi community come a long way. Some team members have been associated with the mine for two or three generations. It’s only fitting that Martha, once the lifeblood of Waihi, is turning into a model recreational area for its community,” Mr Grindlay says.

The Waihi tailings ponds are a birdwatcher’s paradise