Catherine Delahunty, chairwoman of Coromandel Watchdog of Hauraki, said she believed the legal decision supported a narrow consideration of 'jobs only' when assessing whether an overseas company should have the right to buy land for a tailings facility.
The High Court ruling would not deter her organisation, she said.
"Of course we are disappointed in this decision but we are proud we challenged the Labour ministers for their failure to protect our environment. "
OceanaGold Waihi operation acting general manager Dan Calderwood welcomed the decision, saying the company is free to continue with its plans for farmland east of Waihi.
"When the company purchased the Waihi operation in 2015, the mine had a life of less than three years remaining," Mr Calderwood said. "We made a commitment then to extend the life of the mine and support the economic benefits it brings to the region."
He said a third tailings impoundment will contribute to the company's ability to sustain the industry in Waihi.
Since 2015 the company has invested $108.1 million in exploration in the region and will invest around $50m in coming years.
"The decision made this week allows us to extend that commitment by targeting decades of additional, responsible mining."
Some business owners have raised concerns about the expansion's impact as more areas of urban streets are swallowed up for the expansion, questioning why there has not been an offer of compensation similar to those offered to residents for disruption caused by vibration, dust and noise.
Mayor Adams said he understood that people have concerns.
"It's a difficult one, I get where people have their concerns, and [Minister] Eugenie [Sage] had her concerns about productive dairy land.
"We're also hearing the dairy industry has impacts on the environment as well, and the Government is trying to diversify on dairy land. While the Government still has mineral extraction as a permitted activity in New Zealand, they need to be an enabler as much as they can while making sure all the environmental impacts are taken care of."
Ms Delahunty said the High Court decision "rejects our argument that the national benefit of a project must include a proper assessment of any detriments as well as positives".
"Eugenie Sage made a wise decision citing risks from toxic waste, climate change effects and the lack of longer-term economic benefits to the region. We welcomed that decision as a recognition that assessing benefits obviously means assessing detriments.
"We have no regrets that we stood up for the public interest in this matter as there were strongly differing views between ministers and debate over how the Overseas Investment Act should be interpreted.
Background
• May 3, 2019 OceanaGold's application to purchase farmland to the east of Waihi on which to construct a third tailings storage facility was declined.
• On October 8, 2019 it was announced that the company's re-application for permission to purchase the land had been successful.
• A Judicial Review of this decision made by the Government was subsequently sought by a local group.
• The decision handed down on September 9, 2020 upholding the October 2019 decision allows the company to advance planning for additional tailings storage.
