Scientists Map Colville Ridge Seafloor Off New Zealand

Scientists have returned from a three-week mission to map the seafloor of the Colville Ridge, northeast of Auckland, as part of a long-term programme to survey regions within New Zealand’s offshore territory considered prospective for seafloor minerals.

The voyage over the middle part of the Colville Ridge was led by GNS Science in collaboration with Oregon State University. It took place on NIWA’s deepwater research ship Tangaroa and was funded by the Ministry of Business Innovation and Employment.

The area of seafloor mapped was just over 20,000km2 , equivalent to the size of Israel, GNS Science noted.

Combined with a similar survey of the southern part of the Colville Ridge in 2013, GNS Science has now mapped almost 38,000km2 of what was previously unmapped New Zealand territory.

A key finding during the voyage were seafloor rocks that had been ‘hydrothermally altered’.

This means hot fluids containing dissolved elements such as silica had once passed through them.

Often these same fluids carry dissolved metals that, on mixing with cold seawater, precipitate out and accumulate on the seafloor, GNS Science explained.

Voyage leader, Cornel de Ronde of GNS Science, said the find indicated that parts of the submerged Colville Ridge, which is estimated to cover about 100,000km2 , could be prospective for metallic minerals such as copper and gold.

“This find is a real bonus as our mission was to produce a detailed bathymetric map of the area, backed up by gravity and magnetic measurements,” Dr de Ronde said.

The shallowest point on the new map is 390m below the surface, and the deepest is 3,730m.

“A dominant feature of the area we surveyed is a large mountain chain that when viewed from the northwest looks almost like an alligator snaking its way towards Auckland.

“We believe this survey will show that the Colville Ridge and Kermadec Ridge were once joined and they rifted apart at some unknown time in the past.”

The older Colville Ridge and neighbouring Kermadec Ridge have formed as a result of subduction of the Pacific tectonic plate. Both ridges stretch northeast from New Zealand toward Fiji and Tonga respectively.

Scientists now plan to review the gravity and magnetic data and analyse the rocks they recovered from the seafloor. This will tell them more about how and when the Colville Ridge formed and when the two ridges rifted apart.

Dr de Ronde said it was amazing to think that so little was known about the Colville Ridge.

“The southern end of this large geological feature lies within 500km of New Zealand’s largest city, and yet prior to this mapping expedition and the one we completed in 2013, we knew almost nothing about it.”

There were four or five major ridge features in New Zealand’s offshore territory and until now Colville was arguably the least known of them, Dr de Ronde added.

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