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That has taken an almost literal twist at OceanaGold’s gold mining operation at Macraes.
University of Otago geology department researchers have collaborated with the mine’s environmental adviser for operations James Skurupey, and neighbouring farmers to determine the feasibility of using mine water for irrigation.
Macraes is the country’s largest active gold-producing mine with more than five million ounces produced since 1990.
Geo-ecology research team project leader Dr Cathy Rufaut said short-term results from samples taken from rainfall that seeped through waste, mined Otago schist rock, and then pooled in gullies, showed the water contained elements such as calcium, magnesium, sulphur and nitrogen, as well as pH 7-8 levels and a low metal content.
Mine water was being applied to test paddocks on private land owned by the mining operation and leased to local farmers.
To date, results showed increased nutrients in soil receiving mine water, with an increased plant uptake, and it had the potential to both feed and water paddocks and revegetated areas, Dr Rufaut said.
When applied at a suitable rate, there should be no run-off into adjacent streams, she said.
Prior to the trial launch in 2018, researchers used data from a previous study by Emeritus Prof Dave Craw to find out how and why mine water contained the elements, where it came from, and whether the composition changed over time and at different sites.
OceanaGold gave them access to the operation’s extensive water testing database so researchers could extract mine water chemistry patterns over several decades.
"One of the more intriguing findings was that lime, gypsum, and epsom salts were naturally forming from the mine water, as saturated elements fell out of the solution during evaporative conditions."
The data gathering includes regular measurements of irrigated and non-irrigated soil, bacteria, pasture, and stream quality, as well as surrounding native tussocks and shrubs, to identify how the paddock system changes in response to mine water seasonal applications.
Regular field samples were analysed by Hill Laboratories to generate nutrient and bacteria profiles.
Technicians in the geology department used specialised instruments as well as drones to capture visual changes to the paddocks and surrounds.
"The mine water requires long-term management and if we can show that irrigation [using that water] is beneficial to pasture and is not affecting the downstream creeks and rivers, then it will be a win-win for the farmers and the mine," she said.
The collaboration showed there were potential benefits for all parties and the environment.
"It is a great example of sustainability at work in Otago."
The trial is expected to finish by the end of 2021.