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The diatomite of the crater lake has preserved a fossil treasure trove and a climate record covering 100,000 years from 23 million years ago.
Foulden Maar was to be mined by Plaman Resources, but the foreign-owned company went into receivership last year.
The Dunedin City Council (DCC) then declared its intention last November to buy the 42 hectares owned by the company under the Public Works Act.
The Act gives the council a year to follow through.
But a year has passed and everyone outside the council and the receivers remain in the dark.
A council spokesperson said the process was ongoing.
"We can confirm councillors at last week's council meeting received an update on work to date in relation to Foulden Maar," the council said.
"The Dunedin City Council's valuer is still working on completing a valuation and we are unable to provide further details at this stage."
Receiver Neale Jackson of Calibre Partners said negotiations were confidential and commercially sensitive.
"DCC stated its intention to go through a process that might result in them compulsorily acquiring the land and we're still working through that process with them," he said.
There was nothing further the receivers had to add at this stage, Jackson said.
A report went to councillors a fortnight ago, but was not public and discussed behind closed doors.
Mayor Aaron Hawkins also did not wish to discuss the matter.
University of Otago associate professor Daphne Lee said researchers had not had access to the site since Plaman Resources went into receivership.
"I think the last time we went there with students was April 2019 and I've made several requests since then to go and they have all been refused," Lee said.
It had caused some frustration for the scientific community as scientifically the site was invaluable and unparalleled in New Zealand.
"I keep hoping for good news from the council, to say they've resolved the ownership of the site and the access but I haven't heard anything directly about that for many months now," she said.
Save Foulden Maar spokesperson Andrea Bosshard said it was frustrating to still be in the dark a year on from the council announcing its intention.
"Plaman Resources is the second, possibly the third, company that has gone bust trying to mine Foulden Maar and it is just so indicative that the mining of the site is absolutely not a viable business," she said.
"For us, more importantly, the people of Otago have made it really clear that this site must be preserved for scientific research and not for private profit."
But it was not only the scientific community which had been left in the dark.
The 42 hectare area covered by the mining permit is surrounded by 430 hectares of farmland.
Before going into receivership, Plaman Resources had applied to the Overseas Investment Office to buy the farm so it could mine the diatomite reserves under it.
RNZ understands those farmers had received little communication from the DCC about its plans and the ongoing negotiations.
Strath Taieri Community Board chairperson Barry Williams said the situation was unfair.
"I just can't believe it's taken so long," he said.
"I haven't had an answer. I guess there's been some paperwork that hasn't been done properly - I'm only guessing that, so I don't know. But for council to take so long I really don't think it's fair on the landowner [surrounding the mining site]."
The matter would be discussed at today's community board meeting Williams said.