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Gold rushes to build a gold mine

* 21 October 2006
* From New Scientist Print Edition.

RARE they may be, but it appears some gold deposits form with surprising alacrity.

At least half of all known deposits formed when hot, pressurised water that had picked up gold elsewhere in the crust fizzled through rock to deposit the metal in veins. It was not clear, though, how concentrated the gold in the water usually is or how quickly deposits can form.

To find out, Stuart Simmons and Kevin Brown from the University of Auckland in New Zealand studied an active deposit at Ladolam on Lihir Island, Papua New Guinea. "It's the only known gold deposit being hosted by the hydrothermal system in which it formed," says Simmons.

They sampled water from up to 1.5 kilometres underground and measured the concentration of gold and the speed at which it is being pushed through the rocks.

From this, they estimate that the 1300 tonnes of gold in the Ladolam deposit built up within about 55,000 years - the blink of an eye in geological terms (Science, vol 314, p 288). Simmons says a better understanding of how deposits form should make them easier to find.
From issue 2574 of New Scientist magazine, 21 October 2006, page 17