Rare Seafloor Chimney Cut Up for Science

Rare Seafloor Chimney Cut Up for Science

Scientists have sliced up a rare 2.5m-tall seafloor chimney to find out its age and the concentrations of the metallic minerals it contains. It is thought to be one of the largest chimneys recovered from the seafloor.

The chimney was sent to GNS Science for analysis by Canadian-registered company Nautilus Minerals. It was recovered from the Lau Basin in Tongan waters in 2008 by Nautilus’ exploration partner Teck Cominco. Nautilus has numerous prospecting licences in Tongan waters and has applied for a licence to prospect for seafloor minerals in New Zealand waters, northeast of the North Island.

The chimney was recovered from the seafloor using a remotely operated vehicle (ROV) at a depth of 1,470m, and then winched to the surface by a crane during Teck’s 2008 exploration voyage to Tonga.

This week the chimney, believed to weigh in excess of 1,000kg, was sliced lengthwise into three sections by a large diamond-tipped circular saw, which is normally used for cutting concrete.

The middle piece will be kept for analysis and one of the outer pieces will be returned to Nautilus. Negotiations are underway to see if the third piece can go on permanent public display in Wellington.

Researchers at GNS Science will undertake the geochemical analysis and age-dating with assistance from the University of Tasmania and the University of Ottawa.

"What is remarkable about this chimney, aside from its obvious large size, is the fact it was recovered more-or-less intact,” said Marine Geologist at GNS Science, Cornel de Ronde.

"Cutting the chimney open has revealed a really complex interior, with no dominant orifice where the fluids would have flowed. The centre of the chimney is largely in-filled by copper-rich minerals,” Dr de Ronde said.

Being able to view the interior of the chimney enabled scientists to piece together its growth history.

"We see a central area dominated by copper-rich minerals, and outer zone of zinc-rich minerals and an exterior made up of mostly silica and barium-rich minerals."

The last episode of fluid activity deposited minor arsenic (yellow), antimony (red) and probably mercury (purple) rich minerals in the cavities. This zonation reflected a range of fluid temperatures from around 300°C down to probably less than 150°C, Dr de Ronde said.

While it was pumping hot mineral-rich fluids into the ocean, an assortment of microscopic fauna might have lived on the chimney's exterior. However, Dr de Ronde said it appeared the chimney had been 'extinct' for some years before it was sampled.

Results from the analysis will help scientists understand submarine hydrothermal systems and their associated mineral deposits, Dr de Ronde said. The chimney is presently housed at GNS Science in Lower Hutt.

"The chimney was collected from a field of dozens of inactive chimneys and active black smokers.

“A significant amount of the copper mined on land was originally formed as mineral deposits on the seafloor, such as this one."

Submarine mineral exploration companies mostly use ROVs to sample small quantities of rock from the seafloor during exploration. It was extremely rare for a chimney of this size to be collected from the seafloor during exploration, due to its weight being around 1,000kg.

Nautilus is the first company to commercially explore the ocean floor for polymetallic seafloor massive sulphide deposits and is currently developing its first project. The Company's main focus is the Solwara 1 Project, which is located in the territorial waters of Papua New Guinea in the western Pacific Ocean. The Company has exploration permits in the territorial waters of Papua New Guinea, Solomon Islands and Tonga.

ENDS

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