How to Build a Gold Factory

Irene popped down to Christchurch to get the inside story on how to build your own gold factory, in five easy step no less.

STEP ONE: Learn to weld stuff

We’re sitting at Kevin Brown’s kitchen bench with a fresh cuppa’ tea in hand. Kevin is one of the scientists behind a recent paper about gold in geothermal fluid that I recently blogged about here because it prompted some amusing headlines.

He starts by describing himself as an inorganic geochemist. As the name suggests, this is a branch of chemistry probing the non-organic bits of the Earth. By the time my mug is empty, Kevin had also described himself as a frustrated engineer—I guess we’re all more than our qualification suggests. 

Like so many students, Kevin worked his way through university. Odd jobs inevitably became a part of who we are. Alongside working in a rope factory and cleaning his own lab in the wee hours, Kevin worked as a fitter and turner: “so I can weld and do stuff, and it’s kinda handy.”

The test rig pipe with (from left to right) 2 DSIR staff, Peter Roberts (red hat) and Kevin Brown (leaning on the truck)

STEP TWO: Grab a mate who’s as curious as you are

In 1983 Kevin published a paper called Gold Deposition from Geothermal Discharges in New Zealand. It caused a bit of kerfuffle. People were asking if the gold could be extracted. Struck with curiosity, Kevin teamed up with Peter Roberts from Spectrum Resources in the late 80’s. Together they’d build three pilot geothermal gold extraction plants.

STEP THREE: Have a great design, scrap it, redesign

Peter and Kevin knew that boiling was the key to getting the gold out of the geothermal water, so they made a pressure container to boil the fluid as it passed through the pipe. It was a little over a meter long with a series of mesh inserts inside. The gold would deposit on the mesh.

But during the first trial of the pressure container, the fluid smashed a hole through the mesh. They hadn’t accounted for the huge velocity the water would have. Back at the drawing board, they designed a bend in the entry pipe to reduce the force.

Kevin chuckled, “If something doesn’t work, you just suck and see… I’m a suck and see scientist”.

STEP FOUR: Prepare to be amazed

Peter and Kevin were on a steep learning curve. They were shocked that, once boiling, most of the gold dropped out of the geothermal water in something like 100 milliseconds. This was worked out by measuring the concentration of gold that had formed on a series of meshes inside the kit and by knowing how fast the water was travelling.

The kinetics involved were extreme.

STEP FIVE: Prepare to be disappointed

But the test plant project eventually had to wind up because of challenges that couldn’t be overcome at that time.

The economics didn’t work at the current gold price. “It was going to cost something like 5 million dollars to get ½ a million dollars of gold out, but that was when gold was 200 dollars an oz.” Today the gold price is a little over USD$1300 per oz, which is not far from solving the economics problem.

Another challenge was that the gold extraction process was hard to integrate with a geothermal power station. To make gold you need to boil the fluid. To make electricity you need to boil the fluid. Two bites of the same apple meant someone would go hungry. Perhaps in the future, this challenge can be met with an innovative design that allows many uses of the geothermal resource that people pipe to the surface.

The test rig in place next to the geothermal well and a plume of vented steam.

Mesh from the rig after it’s been blasted apart by high-velocity fluids in the first test rig design. This sent them back to the drawing board.



Posted on

April 18, 2017