Monday, April 25, 2016

Millions of dollars’ worth of gold and silver found beneath volcanoes

The intense heat and acidic water welling up from reservoirs deep underground are causing gold and silver to leach out of the surrounding rocks and accumulate in the water. At a few sites, like Champagne Pool close to Lake Taupo in New Zealand's North Island, (pictured) the rich deposits form around the pools themselves
  • In New Zealand, deep reservoirs teem with precious metals
  • They say magma is heating the water and causing metals to accumulate
  • It could trigger one of the most perilous gold rushes in human history.

There’s gold in them thar volcanoes. Geoscientists have uncovered a mother lode of gold- and silver-enriched water in reservoirs inside a series of New Zealand volcanoes.

A shallow glob of magma heats water in the Taupo Volcanic Zone from below. The scalding water breaks down nearby rock and becomes loaded with dissolved metals such as gold and silver.

While subsurface rocks contain modest amounts of gold, researchers identified six water reservoirs hundreds of meters deep that brim with bling. Gold concentrations in the water topped 20 parts per billion and silver concentrations reached 2,000 or more parts per billion. Geoscientist Stuart Simmons of the University of Utah in Salt Lake City and colleagues report their findings in a paper to be published in Geothermics.

Tapping one of these water reservoirs could yield as much as $2.71 million of gold and $3.6 million of silver annually, the researchers estimate. Hopeful prospectors should note, however, that safe extraction may require the development of new mining technologies to avoid interfering with a way people are already tapping into the volcanoes' riches: by converting their heat into electricity.

The researchers say chloride rich water forms in underground reservoirs and get heated to temperatures of up to 752°F (400°C). The intense heat and chemistry of the water in these reservoirs causes gold and silver to move from the surrounding rocks and magma into the water.

At a few locations where the water bubbles to the surface in hot springs high concentrations of gold and silver can be found around their scalding pools. While the rocks beneath the surface also contain some gold and silver, the researchers say the concentrations in the water reservoirs are higher.

They found gold concentrations topped 20 parts per billion and silver reached 2,000 parts per billion. From the Rotokawa reservoir alone they estimate they could obtain 150lbs of gold a year. Writing in the journal the researchers said: 'Precious metals deposit at the surface in a few hot springs, including the Ohaaki Pool at Broadlands–Ohaaki and Sinter Flat at Rotokawa..

'However, because it is in a tourist thermal area, the Champagne Pool at Waiotapu is probably the best known, and active deposition has occurred for more than 70 years. The striking orange and yellow precipitates that line the pool contain As, Hg, S, Sb, and Tl, plus very high concentrations of Au and Ag.'

Credit: S.F. Simmons et al. Gold and silver resources in Taupo Volcanic Zone geothermal systems 
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