Dunedin Mayor Dave Cull has made a new submission on Plaman Resources' application to the Overseas Investment Office to buy 340ha of farmland surrounding its diatomite mine at Foulden Maar.
Mr Cull had already asked for an earlier letter sent by him supporting the application and another co-signed by Dunedin City Council chief executive Sue Bidrose to be set aside.
He has now asked for those letters to be revoked.
Since the last letter was sent, the council has adopted a resolution which recognises the significance of the maar and supports its preservation.
Based on the advice given to the council by University of Otago geologist Associate Prof Daphne Lee, it was clear the sale of the land to Plaman was at odds with the desire by the city to protect the maar, Mr Cull said.
Losing access to such a nationally and internationally scientific site would be a huge loss, he said.
Both the Geoscience Society of New Zealand and the University of Otago have also made submissions on the application which support full or a significant preservation of the site from mining.