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Tuesday, 21 February 2012

The Real Gold Bug?

These objects, made of plaster and fresh cement, conceal my
brand-new "fossils", as I will start to reveal next weekend.

Yes, I know I promised some stuff on fossil simulations, but I am still doing the photos for that series, because I decided the ones I had weren't good enough.

The first batch of my new  "fossils" are made, and you can see them in this shot on the left, but please be patient while the cement cures.  I have to wait for a fortnight or so, before I start cleaning away the plaster matrix.

Now here's some geochemistry I prepared earlier.

I'm doing quite a lot of heavy science at the moment, on the topic of gold, and theories about the origin of gold deposits. The usual dogma has ferociously hot (hundreds of degrees C hot) water at huge pressure, vipering up out of the earth, carrying gold in solution to higher levels, where it goes out of solution and forms veins. Later, under erosion and weathering, the gold may end up in rivers or gulleys.  There have always been those who wondered if the gold deposits may not have a biological origin.

I doubted it, but anything is possible, so I trawled the literature and came across a case where people found evidence in 2.65 billion-year-old Canadian gold that there had been a kind of bacterium (called an Archaean) around when the gold was laid down.  All they had was some lipids (oily stuff) that are only found in Archaeans, but it looked as though the little beasts were there at the same time, but the Archaea, or some of them, delight in swimming in scalding hot water.

So close, but NO seegar!  I trawled on.  And hit pay dirt.

I now think it quite possible that some bacteria may well play a role in forming some gold deposits. Dr Frank Reith from Australia's own CSIRO argued in 2006 that they are involved in the formation of secondary gold grains.  In brief, he found a living biofilm, a complex bacterial ecosystem, on the surface of gold grains. DNA profiling of this biofilm identified 30 bacterial species with populations unique to the gold grains when compared with the populations in the surrounding soils.

Working with samples from two gold mines, one (Tomakin Park near Ulladulla) in southern New South Wales, the other (the Hit or Miss gold mine near Cooktown) about 2000 km away in northern Queensland, Reith found one common bacterium and DNA sequence analysis of this species identified it as the bacterium Ralstonia metallidurans. He then put a culture of this bacterium in contact with dissolved gold, which as he explained,  is highly toxic to microorganisms. But instead of finding dead bacteria, he observed active gold precipitation going on.

I dug out a CSIRO press release on his work.  "A unique attribute of R. metallidurans is that it is able to survive in concentrations of gold that would kill most other micro-organisms." This research has significance for the mineral exploration industry – as current models of gold formation do not include a biological mechanism. "There may be new opportunities for the bio-processing of gold ores now that we have discovered bacteria that precipitants gold out of solution," he said.

Clearly then, at least one bacterium is capable of dealing with gold compounds and producing metallic gold. In the future, this could direct those seeking deposits in a different direction, or as he says, it might lead the way to more gentle ways of extracting gold from poor quality deposits. One interesting aspect that probably won't come to anything: we all have a biofilm in our mouths, though we call those swarming bacterial coatings "dental plaque" (there's some evidence that clogged arteries are also due to biofilms, and there's one in our bathroom basin that keeps defying me).

If we could incorporate Ralstonia metallidurans into the mix, could we get gold teeth more easily?  I think the cost of the gold mouthwash might be against it—not to mention the problems if you swallowed it.  I don't think I'll start pouring gold solutions down the drain in the hope of getting a gold-plated plughole, either.

Though, considering what the second half of his name means, calling St John Chrysostom, have you anything you'd like to tell us?

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