The mines with the highest concentration of gold in the world are rocks around submarine hydrothermal vents around Aogashima in the Izu Islands. The average concentration of gold at this site is as high as 17 grams per ton, which is very high compared to typical gold mines. ̇

A submarine hydrothermal vent is an outlet of a deep-sea hot spring. The metal dissolved in the hot spring goes out into the sea and is cooled and deposited.

It is Tokyo even though it is 400 km away from Tokyo.

A research group from the Japan Agency for Marine-Earth Science and Technology and IHI, a major machinery manufacturer, has developed a sheet made of a special alga that adsorbs gold to recover gold from the hot water.

The research group installed the sheet around a hydrothermal vent off Aogashima in August of the year before last (2021) and salvaged it in June of this year, nearly 2 years later.

According to the analysis, up to about 20ppm (20 grams per ton) of gold was adsorbed on the sheet, which is about 5 times the concentration of gold in the ore of the world’s major gold mines.

The researchers also found that not only gold but also silver was adsorbed at a maximum concentration of 7000ppm, more than 300 times that of gold.

The researchers say it is the first time in the world that gold in deep-sea hot water has been successfully recovered by adsorbing it onto a sheet of algae.