Ocean clues may yield new mineral discoveries
BRAD COLLIS Note
Melbourne, Victoria, Australia,
Received January 8, 2001; published January 9, 2002
Keywords: Bismarck Sea, geology, hyperthermophile, Kidd Creek, ocean floor, ore, Vanuatu, volcanic vent
Scientific exploration of volcanic activity on the deep ocean floor is about to rewrite the rules of terrestrial geology, giving mining companies a chance to re-explore many areas previously passed over.
In nature, valuable metals commonly form chemical compounds with sulfur or oxygen, producing sulfides or oxides, respectively. It is these compounds, or ores, that are mined and processed to extract precious metals including copper and gold.
Sulfide deposits were found in volcanic vents in the Bismarck Sea off Papua New Guinea in 1991, and in deep crevices in the Pacific Ocean near Vanuatu in September 2001. The discovery of this type of deposit, which is like the ore deposits found at Broken Hill, Australia and Kidd Creek, Canada, indicates that such deposits may be found in geological settings not previously considered as possible sources. The scientist who initiated the research program, Dr. Ray Binns from the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Australia, says the discoveries mean that geologists can now re-explore continents with fresh eyes.
Dr. Ray Binns with a fragile sample of iron oxides dredged from Vanuatu's ocean floor. The material is a good indicator of proximity to valuable sulfide minerals.
When mineral deposits in the Bismarck Sea were examined in the early 1990s, they were found to be formed from submarine hot springs spewing volcanic fluids, the mineral load of which precipitated upon contact with the cold sea water. For scientists, it was a chance to step back tens of millions of years in time.
"We were able to collect samples of newly born deposit and even the fluids from which they formed, and study the chemical and physical factors that govern where an ore body is going to develop, how rich it might be, and how bigthe underlying scientific issues that are fundamental to successful mineral exploration," said Binns. "Until now, companies have used information collected when mining places like Broken Hill to search for similar ore depositswhat you might call the 'look-alike principle.' But we are now finding that by watching ores in the process of being formed on today's ocean floor we can improve on that procedure. In other words, we have new conceptual frameworks with which to judge and measure what we have been used to seeing on land."
Dr. Ray Binns (left) and Dr. Tim McConachy (right) assembling equipment to be lowered on a cable to detect and sample plumes of mineral particles in the seawater column above volcanic hot springs on the ocean floor. This is the first step in exploration for sites of mineral formation in the deep ocean.
The Vanuatu team, led by Dr. Tim McConachy, a principal research scientist with CSIRO, and including the head of geology at the Australian National University, Professor Richard Arculus, had decided to probe 2 km into a basin that Japanese researchers had suggested was filled with sediment. It was hoped that the sediment might either contain minerals representing a modern analog of known terrestrial ore bodies, or, like the Bismarck Sea discoveries, provide a new framework for terrestrial exploration. The latter proved to be the case, but not in the way that the Australian researchers had expected. Instead of sediment, they found signs of ongoing volcanic activity.
Rock samples brought to the surface revealed fresh movements in the earth's crust, caused by the Australian tectonic plate being pushed down under the Pacific plate. The consequence of this movement is a volcanic arc behind which crevices are opening, disgorging the earth's molten innards onto the ocean floor. This suggested the exciting possibility that the deep Vanuatu basin was a new geological setting for sulfide ores.
The discovery has sent an undercurrent of anticipation through the minerals exploration sector because it promises to equip the industry with a new suite of tactical and information tools on which to base future exploration decisions. The notion that most of the world's prospective areas have been thoroughly explored has been turned on its head.
"These discoveries have made us all realize that our previous geological interpretations were far too narrow," said McConachy. "The new signals we are seeing in the ocean environment will help us understand many terrestrial puzzles, and they convey a clear message to geologists not to give up just because their geology is different to what might be considered desirable according to conventional thinking."
McConachy stated that the next task will be to study the geological processes in these ocean floor environments more closely so that detailed guidelines can be extrapolated for geologists to use on land. He emphasized that the value of the deep ocean deposits lies in their role as natural laboratories in which ore formation can be studied as it happens, and that they are not potential sub-sea mines, although this possibility would arise if a large enough deposit were found.
The head of CSIRO Mining and Exploration, Professor Neil Phillips, said that the ore-forming processes occurring today on the Pacific seafloor are believed to be very similar to the processes that led to the formation of massive copper-zinc ore bodies in eastern Canada 2700 million years ago, exemplified by the highly profitable Kidd Creek mine.
"Very similar rocks to those at Kidd Creek also form in the southern half of Western Australia; in fact, the rocks are of similar age and similar type and both areas contain major gold deposits. The one big difference is that Western Australia has few copper-zinc deposits and none to match Kidd Creek; or, if present, they have not been discovered yet. But understanding how copper and zinc form on the seafloor today will help geologists predict where ancient deposits may be hidden in the vast expanse of the west."
The ocean floor research has also led to another scientific spin-off: the recovery of microbes living in the hot volcanic fluidsa hostile, deep ocean environment that has no light and little oxygen and is under massive water pressure. These microbesbacteria and archaea called "hyperthermophiles"were first discovered near the Galapagos Islands in the late 1970s and, for Australian researchers, have opened up the possibility of a new generation of clean "bio-mining."
Ray Binns explained that microbes are already used by companies to "pre-treat" ores prior to extraction of gold and other valuable metals. For example, the microbes can oxidize minerals like pyrite (an iron sulfide), which makes the very fine gold particles locked inside more accessible to cyanide, which leaches them out.
However, currently-employed "biomining" processes operate under relatively cool conditions. Their efficiency would be greatly improved, providing an alternative to conventional mineral processing technology and the undesirable emissions associated with it, if they could be made to work at higher temperatures. Microbes collected from sub-sea volcanoes might do just this, given that they are adapted to life at near-boiling temperatures.
The discovery of the microbes in such hostile ocean floor environments has also thrown new light onto the origins of life on earth, and onto the possibilities of life on other planets.
About the Author
Brad Collis runs a freelance writing and editing business, specializing in science, technology and the environment. Aside from 25 years in journalism, he is the author of several books including SNOWY - The Making of Modern Australia, which is the prime reference for the history of Australia's Snowy Mountains Hydro-Electric Scheme, and Fields of Discovery, the history of the Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australia's leading science institution.
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