​New discovery highlights link between ancient bacteria and gold deposits

A Curtin University research has uncovered a link between rocks containing an ancient bacteria and prehistoric gold deposits.

Siyu Hu made the discovery whilst working in the Macraes gold mine in Otago, New Zealand.

Combining traditional methods such as optical microscopy , scanning electron microscopy, and raman spectroscopy to map the way different ways organic material reflects laser light she found that in certain Jurassic rock bodies that gold often coexists with organic matter.

“These rocks were metamorphosed in the Jurassic, several hundred million years ago, and they’ve been uplifted by the Earth’s movement, so they lift up and explode onto the surface,” Hu said.

She explained that within this rock, two types of gold are typically present.

“The first is gold captured in quartz veins…this is very common, because gold is always transported by fluid and then deposits, mostly in quartz veins.

“The second kind is more interesting, because the gold is captured in graphitic rock in the host rock, which means there are no veins,” she said.

“The host rock contained a lot of organic matter, and probably, when the gold fluid passed through this area millions of years ago, this organic matter very slowly trapped the gold.”

According to ScienceNetwork WA, Hu identified four types of organic matter in the samples.

Of these, Type 1 and Typ4, co-existed with gold bearing sulphide material minerals, showing how they could have aided a part in the gold deposit.

Although she has yet to uncover the origins of Type 4, Hu said Type 1 is associated with ancient bacteria, highlight the potential sulphide reducing bacteria that helped to extract or adsorb gold, aiding its concentration.

She is currently investigating the link between Type 1 and 4 organic matter and gold.

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