The study points to the huge untapped potential in boiling acidic water containing precious metals.
The study points to the huge untapped potential in boiling acidic water containing precious metals.
NZ geothermal systems could yield millions of dollars in precious metals, say scientists.
Our picture-postcard hot springs aren't just natural treasures - they're also treasure chests laden with silver and gold, scientists say.
New research has estimated that the geothermal systems that heat our bubbling hot pools could yield the country millions of dollars worth of byproduced precious metals.
The study, just published in the international journal Geothermics, points to the huge untapped potential of up to 18 large reservoirs of boiling acidic water in the Taupo Volcanic Zone, that contain large amounts of precious metals.
The metals were being naturally deposited in these vast pockets as the water - heated to scalding temperatures of up to 300C by magma below - dissolved surrounding rock.
The researchers estimated how a single well drilled beneath Rotokawa Power Station, near Taupo, could yield up to $4.1 million of gold each year, while wells there and at nearby Mokai Power Station could annually produce up to $5.5 million of silver.
Study co-author Dr Julie Rowland, a structural geologist at Auckland University, said it was already known that these underground reservoirs carried gold in small volumes.
Scientists are exploring how high-value minerals can be recovered from waste geothermal fluids.
"The amazing thing about geothermal production is that it creates what we think is one of the key processes for depositing gold, and that's boiling.
"So you've got fluid that's carrying gold focused into little pipes with big flows - and that adds up to quite a considerable volume of water over the lifetime of a production well."
The big challenge, she said, was to extract the gold from the fluid without interrupting geothermal production.
"At the moment, it's certainly a lot easier to go somewhere where mother nature has already done the concentrating and condensing, and you can just dig it up."
But a solution could soon be found by a joint project between GNS Science and Auckland University, which was exploring how high-value minerals could be stripped from waste geothermal fluids before power companies injected them back in the ground near their plants.
The government-funded "Waste to Wealth" programme sought to identify cost-effective ways to extract precious minerals such as lithium, gold and silver, and scientists estimated many thousands of tonnes of metallic minerals were being reinjected each year.
As for legal rights to the resources, a recent study found that, under the Resource Management Act, regional councils had jurisdiction over materials in water. Holders of water permits allocated under the act had rights to the water and materials within it.
A Treaty of Waitangi claim for rights of geothermal minerals was also possible, but neither the Treaty nor its principles was directly enforceable in New Zealand law.
Te Arawa kaumatua Dr Toby Curtis was aware of the potential worth of the minerals, but because the situation remained unclear, could not speculate on whether his iwi would consider any claim.
"If it can be guaranteed that environment will not be unduly affected, there could be a view of pursuing the issue in terms of the value that it could bring to the community ... but at this stage, I don't know."
Dr Rowland said while New Zealand wasn't the only country blessed with geothermal resources, which provide about 13 per cent of our electricity supply, the country could boast a great depth of knowledge of the processes that create them.
"This means we've got an incredible landscape for understanding the link between the active hydrothermal system and ore-grade mineralisation currently giving us this gold and silver. So if there's a place to find out what the connection is, it's here."
