Forest & Bird believes it has a good chance of stopping a coal mining plan in its tracks.
The High Court has released its decision on an appeal against the Environment Court's interim decision on Bathurst Resources plans to create a mine on Buller's Denniston Plateau.
The appeal relates to whether mitigation considerations relating to adverse effects on the environment are enough to be considered a biodiversity offset.
Justice John Fogarty finds that the Environment Court will have to keep the considerations separate, meaning Forest & Bird has been partially successful in its appeal.
Top of the South field officer Debs Martin says winning this point was critical to the 'finely balanced' case and she hopes it will shift the judge's balance in favour of protecting the area.
The case will be back before the Environment Court next week.