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Scientists slice rare deep-sea mineralised chimney in half - 03/04/2001

Scientists in Wellington have sliced a rare deep-sea volcanic growth in half in a bid to find out more about submarine hydrothermal systems and their associated mineral deposits.

Cornel de Ronde holding sliced 'black smoker chimney'

The rare marine growth - known as a black smoker chimney - was given to Institute of Geological & Nuclear Sciences Limited minerals geologist Cornel de Ronde after an American research submersible, Alvin, accidentally knocked it over while investigating hydrothermal vent sites on the East Pacific Rise 3500km west of Chile.

Dr de Ronde, as a specialist minerals geologist, was invited to participate in the series of scientific dives by Alvin, which is owned by the US Navy and operated by Woods Hole Oceanographic Institute, based in Massachusetts.

The dives were jointly funded by the US National Science Foundation and the National Oceanographic and Atmospheric Administration, based in Seattle. After the black smoker was knocked over at a depth of 2.6km, the crew of Alvin brought it to the surface and gave it to Dr de Ronde to study.

" Fewer than a dozen black smoker chimneys of this size have been retrieved, and this is one of the biggest and best preserved ever recovered. There are only a handful of submarines in the world suitably equipped to recover chimneys from such depths," Dr de Ronde said.The mineral-packed chimney stands 1.2m tall and weighed 70kg when wet.

Allcutt Concrete Cutters Limited, of Upper Hutt near Wellington, cut the chimney in half with a large circular diamond-encrusted saw.

10The cleaved chimney revealed glittering metallic crystals inside as well as a passage through which hot hydrothermal fluid used to travel. Fauna that live on the exterior of chimneys include bacteria and other micro-organisms. Further along the food chain are tube worms, crabs, shrimp, and squid.

These life forms thrive in an alien world of no light, extremely high temperature and high pressure, high acidity, little oxygen, and a cocktail of chemicals that would be poisonous to mammals.

" It's one of the most extreme environments we know on Earth. Scientists are discovering new species associated with black smokers all the time,'' Dr de Ronde said.

Some scientists believe that these organisms may be similar to the first life forms on Earth. Gaining knowledge about these organisms may help shed light on the way life evolved.

Chimney saw

" The capacity of these organisms to live happily in these extreme environments surprises even the most sceptical of scientists. We've learnt never to underestimate the ability of micro-organisms to adapt to the harshest conditions.

" On the ocean floor, hydrothermal fluids containing dissolved minerals course through the centre of the chimney at temperatures between 350 and 400 degrees celsius. As the fluid exits the chimney and meets cold seawater, the dissolved minerals precipitate out forming dark billowing clouds. Thus the term "black smoker". About 95 percent of the minerals drift off in the "smoke" and later fall to the ocean floor. Only 5 percent form the metal-rich deposits on and around the chimneys.

Dr de Ronde's chimney is packed with sulphides of iron, lead, zinc, copper and possibly silver. Scientific names for the main mineral components are chalcopyrite, sphalerite, and galena. Gold is rare in chimneys from the East Pacific Rise because it is not present in the host volcanic rock. However, similar chimneys on the seafloor northeast of New Zealand do contain gold.

" There's a marked difference in chemistry between arc-related hydrothermal vents and vents located above spreading ridges such the East Pacific Rise. One of the distinguishing features of the mineralisation associated with vents of the Kermadec arc, north of New Zealand, is that they contain relatively high concentrations of gold and silver."

Chimney

He plans to date the chimney's layers to find out when it formed and how quickly it grew. He will also analyse the chemistry of the different mineral zones to determine the physical and chemical conditions under which the chimney formed. This will help in understanding the formation of these mineral deposits, hydrothermal systems in general, and the physico-chemical conditions under which vent-related animals live.

Dr de Ronde has offered one half of the chimney to the Museum of New Zealand, Te Papa, in Wellington, where it may form part of a deep-sea display. He believes the chimney is probably less than 10 years old because it was not seen in an earlier dive to the same spot in 1994.

" We have video footage of this particular site from a series of dives in 1994 and this chimney is nowhere to be seen."Once a chimney is removed, a new structure grows in its place commonly at a rate of a centimeter a day .

John Callan
Communications Manager
Institute of Geological & Nuclear Sciences Limited
Ph: 04-570-1444 (w)

Chimney