Experiments could explain gold’s forms

Experiments at the University of Massachusetts in Amherst may help explain why gold is found in two forms: as a solid in deposits in the earth and in water solution, far from such deposits.

The tests would seem to confirm the origins of some of the world’s gold producing belts, such as those in South Africa’s Witwatersrand, and in North and South Carolina, where gold is found not in nugget form in veins but disseminated by ancient water flows within layers of sedimentary rock.

While researching pollution cleanup, university microbiologists used bacteria to break down heavy metals that were in solution. They discovered that heavy metals such as gold were being consumed by microbes called extremophiles. The gold, found inside the earth’s hydrothermal vents, hot springs and other hot places, was ingested and heavy metal excrement was left behind as gold deposits.

According to lead researcher Derek Lovley, this would explain how the metal came to be in two different forms in very different environments. If the theory is true, scientists should be able to duplicate the microbe’s activities in the laboratory and extract gold from water containing dissolved particles.

“A vast number of bacteria have the ability to transfer electrons to iron through a reduction process,” says Lovley. “In other words, they digest one form of a metal and excrete it as another form. This transfer leaves behind deposits of solid metal in unlikely places on Earth or maybe even on Mars. What’s left behind is often more useful or more accessible to humans than the original form of the same substance.”

To test their theory, the team placed iron-reducing microbes into a gold solution. As hoped, the microbes rapidly converted the gold from the useless, oxidized and dissolved form to a more valuable, insoluble metal form. The gold had eaten the solution and left the gold as byproduct.

“There’s a significant amount of gold found in solution in some thermal springs and hydrothermal vents on the ocean floor,” explains Lovley. “The problem is that the gold is extremely diluted, so only a teeny amount is dispersed in a very large volume of water.”

The microbe connection with metals is not unusual. Bacteria are already known to be involved in the formation of an iron ore called limonite, and Lovley says they are also involved in the creation of certain ores of uranium.

He noted that the microbe process may be useful for mining companies who could one day take waste water containing dissolved gold and extract useful gold pieces.

— The preceding is an excerpt from Gold News, published by the Washinton, D.C.-based Gold Institute.