Bacteria Precipitate Gold

Roman A. Amosov and a team of Russian scientists from the Central Institute for Geological Exploration of Non-ferrous and Noble Metals, Institute of Paleontology, Russian Academy of Sciences, and from the Institute of Microbiology, Russian Academy of Sciences, led by, have managed to simulate in the laboratory the process of precipitation of gold which in the natural geothermal wells is promoted by blue-green algae (cyanobacteriae).

For the purposes of the experiment Vladimir Orleanski of the Institute of Microbiology, grew cyanobacteriae in the medium containing high percentage of gold chloride (from 200-300 mg up to 500 mg per milliliter). Each day Vladimir Orleanski would alternate the above medium with a regular one, which did not contain gold chloride. This way the microbiologist simulated the environment of the pulsatory thermal wells located in the geological break-up areas. The matter is that such wells regularly discharge from the lower crust the hot solutions rich in chlorides of noble metals. The microbiologist has achieved a remarkable result – in the course of the experiment gold was precipitating on the surface and inside the cells of cyanobacteriae.

It is worth noting that precipitation of gold from chloride solutions takes place only in the daylight, the process ceasing in the dark. Precipitation of gold appears to be a previously unknown photochemical process. Evidently, biological molecules serve as catalysts in the process. For half a year the scientists continued to grow the blue-green algae in the medium containing gold chloride. The algae colonies obtained this way had an evidently expressed laminated structure, where regular sections alternated with auriferous ones. Spectroscopic analysis of dried up cyanobacteriae has proved that they contain gold in the form of oxide. The way the microorganisms oxidise gold is still unclear, since noble metals are extremely difficult to oxidise.

The microorganisms` remnants are rather frequently found in the ores of non-ferrous metals, bauxites, phosphorites and other raw materials. The scientists have repeatedly made the assumptions that bacteria play a certain role in the formation of raw materials, including non-ferrous metal deposits. When R. A. Amosov found the remnants of blue-green algae in the gold mined from the Vorontsovo deposit in the Urals, this finding prompted him the hypothesis that the cyanobacterae were able to precipitate gold from geothermal solutions. As a result, R. A. Amosov has come to the idea of simulating this process in the laboratory.

The environment of a natural geothermal well can be simulated via the replacement of regular medium by the medium with high content of ions of gold and via the reverse replacement. However, the concentration of gold in the course of the experiment significantly exceeded its concentration in a natural geothermal well. Nevertheless, it should be acknowledged that it takes thousands of years for the deposit to be formed in the natural environment, while in the experiment gold was precipitated within half a year only.

Now the scientists have got solid experimental proof of the hypothesis that some gold deposits are of biological origin (at least, the Vorontsovo deposit is). The researchers also believe that it may be possible to get gold from thermal wells with the help of microorganisms.

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