There are 14 nationally significant eco-systems, habitats, or species on the plateau, which Mr Anderson said was also a natural refuge from predators.
The conservationist lawyers argued that the proposed coal processing plant site coincided with a "patch'' where snail densities are particularly high.
If the mine got the green light, a 500ha 'Denniston Permanent Protection Order' was suggested by Bathurst as a form of compensation.
But it's a proposal rejected by Forest & Bird.
It shunned many of the proposed management conditions that went with the mine's consent, saying there are "unachievable''.
"Consequences of the proposal will include the local and possible national extinction of critically endangered species, and the destruction of one of the best known populations of P. patrickensis (carnivorous land snail),'' Mr Anderson said.
"The witnesses agreed that there will be poor outcomes for flora and fauna.
"The rehabilitation proposed ... will not effectively mitigate these effects.''
A 35-year pest and predator control scheme offered by the mine company was "unlikely to offset the losses'' brought about by mining, he said, and would not add to work already being done by the Department of Conservation.
Quentin Davies, lawyer for West Coast Environmental Network which brought the appeal alongside Forest & Bird, said the economic benefits of the project have been overstated.
Bathurst's assertion that the mine would generate up to 225 jobs was not proven by evidence during the hearing, he said.
And he argued that local underground miners would not necessarily be immediately employed at the new open-cast operation because they have different skill sets.
Mr Davies also claimed that estimates of how much coal could be extracted were "overly optimistic''.
West Coast Regional Council and Buller District Council granted mine consents earlier this year.
Lawyer Hans van der Wal today said Buller District plans "clearly demonstrates'' provision for mining, as long as it's not at the expense of its legal sustainability requirements under the Resource Management Act.
Environmentally responsible rehabilitation techniques would have to be applied to adhere to the mining permit, he said.
Bathurst counsel Jo Appleyard say the Escarpment Mine Project represented a "significant and compelling'' opportunity to bring economic and social benefits to the Buller District, the West Coast, and even wider New Zealand.
Environmentalists' concerns were offset by the mine's comprehensive mitigation package, which the mining group say would "deliver a net gain to overall flora and fauna''.
Bathurst was confident in the economic viability of the mine, having done extensive drilling since the acquisition of the intellectual property.
The mine also backed predictions that 225 mining jobs would be created, with another 251 jobs being generated indirectly.
A decision from Environment Court Judge Laurie Newhook, and commissioners Carron Blom and Russell Howie, will be released early next year.
They could either uphold the appeal, let the mine go ahead as planned with basic consent conditions, or give the green light with additional detailed conditions.
