Senior consents planner Shay McDonald said the company’s plans to compensate for the harm it could cause a rare native moth were inappropriate.
The gold mine’s expansion would cause "a high level of effect" on tussock grassland, lizards, invertebrates and some birds, including the New Zealand falcon (kārearea), Ms McDonald said.
It would cause "a very high level of adverse effect" on ephemeral wetlands in the project area, which were considered critically endangered natural ecosystems.
Ms McDonald’s notification report said Oceana Gold was seeking 34 new or replacement consents, as well as variations to 20 existing consents, after the company found that expanding some areas of its present operation and revisiting areas that were previously mined over the past three decades could extend the life of the mine to 2030.
In 2010 the company applied for and received 55 resource consents that allowed it to extend operations beyond the original expected closure in 2012 of the mine that straddles the Dunedin and Waitaki districts.
Without the proposed expansion, the mine was due to begin scaling back operations and begin rehabilitations this year and next.
The company had applied to the regional council and the Dunedin city and Waitaki district councils for consent and requested its application be publicly notified, she said.
The Macraes mine, 30km northwest of Palmerston, is the largest gold mine in New Zealand, and since it was commissioned in 1990, has produced more than 5million ounces of gold, application documents said.
Ms McDonald said there was a good level of agreement between the company and e3 Scientific managing director Glenn Davis who audited its ecological impact management plan.
However, she agreed with Mr Davis that the characterisation by the company of it having "generally low or very low" adverse effects on its surrounds was not appropriate.
Her finding was instead the project as a whole would have "a high level of adverse ecological effect, with some exceptions where a lower level of effects is expected".
She went on to say the company’s consultant appeared to get the "effects management hierarchy" wrong and incorrectly prioritised remedying a negative effect rather than minimising it.
Further, Ms McDonald raised a "fundamental issue" with the company’s plan to compensate for the damage it would do to the habitat of the moth Orocrambus sophistes, a threatened species.
The company had proposed to salvage the moth’s "host plant" to investigate opportunities for habitat recreation in a protected site outside the mining operation’s footprint.
But as set out in various statutory documents, ecological compensation such as what was proposed was not appropriate for vulnerable indigenous biodiversity.
"The applicant should give further consideration to these matters," Ms McDonald said.
Forest & Bird Otago-Southland regional conservation manager Chelsea McGaw said the environmental organisation was "very concerned" the proposed expansion would have adverse effects on nature, "even after efforts are made to minimise and mitigate".
"Of particular concern is the effect on the threatened moth Orocrambus sophistes, potentially thousands of lizards and the complete removal of ephemeral wetlands."
The wetlands were critically endangered natural ecosystems, inhabited by 128 indigenous plant species — including 14 rare species.
They provided habitat for 11 indigenous bird species, including one threatened and two at-risk species.
"This is yet another case of where economic gain is being prioritised over nature, and the true value of biodiversity is not being considered or protected," she said.
