Drilling into an undersea volcano has enabled New Zealand scientists to work out how mineral deposits rich in copper and gold form on the seafloor.
With demand for copper expected to explode, and as electric vehicle maker Tesla warns of upcoming shortages, it’s thought the New Zealand research could help identify new deposits of the metal now uplifted on land, but which were once formed on the seafloor.
The research was carried out on about 225 metres of core recovered from the Brothers undersea volcano in the Kermadec Arc, about 400km northeast of the Bay of Plenty coast. The drilling was done by an international team on board the research drilling ship JOIDES Resolution in a $US15 million project last year.
GNS Science said research led by its scientists strongly indicated the metallic minerals deposited on the seafloor originally came from deep within the volcano.
First very salty, super-hot metal-rich fluids were expelled from magma within the volcano, but were too dense to make it all the way to the seafloor.
Later, when seawater was able to get into the volcano it was heated by hot rocks and magma, and interacted with the metal-rich brines, bringing them closer to the seafloor and even expelling them on the seafloor.
At that point the fluid containing the brines mixed with surrounding much colder seawater and formed the black smoker chimneys that could be seen at Brothers.
“These fluids, pregnant with metals, have come back up to the seafloor,” GNS research geologist Dr Cornel de Ronde said. “They reach temperatures up to 320 degrees Celsius. When 320C mixes with ambient sea water – that’s about 4C – you get these incredible chemical reactions, and the massive sulphide deposits literally grow as chimneys.”
Some of the chimneys at Brothers were 20 metres high and were full of metals – copper, zinc and some gold, de Ronde said. He is lead author of a paper about the research published in the journal Geology.
“This is an important advance in the understanding of the way deposits rich in copper and gold are formed on the seafloor at tectonic plate boundaries around the world. Copper and gold and other critical metals are being formed continuously at Brothers.”
“These fluids, pregnant with metals, have come back up to the seafloor,” GNS research geologist Dr Cornel de Ronde said. “They reach temperatures up to 320 degrees Celsius. When 320C mixes with ambient sea water – that’s about 4C – you get these incredible chemical reactions, and the massive sulphide deposits literally grow as chimneys.”
Some of the chimneys at Brothers were 20 metres high and were full of metals – copper, zinc and some gold, de Ronde said. He is lead author of a paper about the research published in the journal Geology.
“This is an important advance in the understanding of the way deposits rich in copper and gold are formed on the seafloor at tectonic plate boundaries around the world. Copper and gold and other critical metals are being formed continuously at Brothers.”
In some places, deposits that had originally been on the seafloor were uplifted and were now on land. The research findings could help identify the location of such copper deposits.
“For example, looking in some uplifted areas like Papua New Guinea, or Chile, you might find massive sulphide deposits, so you know they were formed on the seafloor,” de Ronde said. However from this research, conceivably the source of the metals, including a big copper deposit, could be in the rock layers below the massive sulphide deposit.
He emphasised the work done at Brothers was research, and was not about mining offshore New Zealand. And that what was happening at Brothers was a modern day analog of how the deposits may have formed in the geologic past, and could be an indication of how to look for them in areas that were now uplifted seafloor.
“Metals like copper are considered to be critical as we move into a low carbon-footprint society. We want to have more electric cars and solar panels and wind turbines and all of those require enormous amounts of metals, including copper,” de Ronde said.
Brothers volcano started out as a stratovolcano like Mt Taranaki, then later collapsed into a caldera. Taupō is a massive example of a caldera, while White Island has a small caldera about 1km across. Brothers is about 3km across.
A new cone about the size of Mt Eden has grown up inside the caldera at Brothers, since the volcano collapsed.
Researchers had drilled into the new cone growing up in the centre of the volcano, and discovered the metal-rich brines at depth, de Ronde said. The cone was a recent version of what had happened at the Brothers previously, when it was a large stratovolcano, before it collapsed.
“If you collapse the top of that volcano you effectively provide pathways for fluids to enter the inner workings of the volcano and ‘mine’ those brines that contain lots of metals,” de Ronde said.
If the volcano hadn’t collapsed, the brines and metals would stay trapped inside and never make it to the seafloor.
