High concentrations of gold found in Iceland's geothermal systems

25.02.2016 08:21
Kategorie: News

Amount of gold was at least 10,000 kilogram’s

On Iceland's Reykjanes peninsula, marine scientists found themselves prospecting for gold when they discovered very high concentrations of gold in the seawater. This was an unexpected find, as the gold concentration in seawater is normally extremely low.

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The sea is a gold mine – in the truest sense of the word. Not only does the seabed contain small amounts of gold, the seawater itself carries traces of the substance. In the first half of the 20th century, chemists had hoped to extract gold from the oceans. However, this never materialised, when it was discovered that a litre of seawater contained only a few billionths of a gram of gold.

Nevertheless, scientists have long known that when seawater is heated to more than 300 degrees Celsius, gold can be leached from oceanic rocks, reaching concentrations thousands of times more than in background water. When this heated seawater emerges onto the seafloor at the hot vents (“black smokers”), it can precipitate minerals that are rich in metal, including gold.

In Iceland, marine scientists found very high concentrations of gold in the seawater emerging from geothermal system deep below the Reykjanes Peninsula. It was more than 500,000 times higher than normal seawater, and at least 100 times higher than in typical black smokers in the deep seas.

The measured concentrations are sufficient to form significant gold deposits within the lifetime of the geothermal system,” said lead scientist Mark Hannington, from GEOMAR's Marine Mineral Resources Group.

Publishing their findings in the international journal Nature Geoscience, the scientists from GEOMAR Helmholtz Centre for Ocean Research Kiel, the Icelandic Geosurvey and Kiel University had collected samples from deep geothermal wells where heated seawater from the nearby Mid-Atlantic Ridge is harnessed for electrical power generation. A special titanium sampler was lowered into holes drilled more than two kilometres below sea level. When it was brought back to the surface, it was quenched from 315 degrees Celsius and the deep liquids were recovered for analysis in special mass-spectrometry labs at the Institute of Geosciences (CAU) at Kiel University.

The researchers estimate the amount of gold to be at least 10,000 kilogram’s. According to Hannington, “typical mid-ocean ridge hydrothermal systems cannot reproduce the very high concentrations of gold observed in our study. We conclude that gold must be accumulating in the geothermal reservoir over time, before the heated seawater is withdrawn, resulting in the very high concentrations found in the wells.

Dr Dieter Garbe-Schönberg, head of Kiel University's ICP-MS Laboratory, added that the gold might occur in the form of finely dispersed gold nanoparticles in the fluids.

The study also pointed out a previously unrecognised mechanism for the accumulation of gold in hydrothermal systems that could explain the formation of the metal-rich ore deposits.

Link to study: www.nature.com/.../ngeo2661.html