University of Otago geology Emeritus Prof Daphne Lee said it was rare to have a site such as the prehistoric volcanic crater near Middlemarch that "gives so much" to science.
Emeritus Prof Lee, along with other researchers, was barred from the site near Middlemarch in 2019 as it became embroiled in a mining controversy.
The site was later bought by the Dunedin City Council to be preserved for environmental and scientific purposes, and last year’s return to Foulden Maar had been an exciting one, she said.
Emeritus Prof Lee returned to the site with a small group of scientists who were in the city for last year’s Geoscience Society of New Zealand conference in November.
"We were just going to see what the site looked like," she said.
"I hadn’t been there for almost five years, so I had no idea what I was going to see.
"I took this group of scientists with me, and before we set off, I said, ‘Look, we might not be able to find anything, so don’t get your hopes up.’
"But actually, even though there’s only a small part of the site visible at the moment, it was yielding nicely preserved material and, as I say, an ant that we’d never found before."
Most of the insects found at Foulden Maar were "pretty small", she said.
"They’re little black shiny dots.
"So, in just a few hours, something completely new to science turns up.
"This has happened for the last 15 years or so since we’ve been working there.
"Probably every visit we’ve made, something that nobody has ever seen before in the scientific world has come to light."
Even in a global context, it was "a very, very exciting and interesting scientific place".
The DCC in November granted researchers resource consent and now a group of 20 scientists, students and support staff are permitted to access the site once a month and excavate 0.5cu m a month for up to five years.
Emeritus Prof Lee said the ant that researchers found six weeks ago might not make it into a formal scientific publication for another year or two.
Finds quite often required collaboration with scientists from other parts of the world, she said.
Work done over the last few years from material collected more than five years ago was now being published.
Two more papers mentioning Foulden Maar and its discoveries came out in the last week of 2024.
One was on a new genus and species of fossil plant, called "Old Gold" because its leaves always looked golden when researchers collected them.
Another paper summarised the findings made over the past 20 years within the context of maar lakes from France, Germany, Tanzania, New Zealand, Spain and had a broad range of academics involved, she said.
Foulden Maar was the result of a volcanic eruption 23 million years ago.
Once a lake was created in the crater, sediment started accumulating at the rate of about less than half a millimetre a year, and it carried on accumulating for about 130,000 years, at least, Emeritus Prof Lee said.
"Each layer formed like a blanket on the bottom of the lake, and we can cut through them and count them.
"And so every layer represents a year in the distant past and we can actually see the climate changes through that 130,000 years.
"And that’s exceptionally rare."
