Grinding for gold

In Randy Clarkson's garage, behind the Mini Cooper and a bunch of plastic Tupperware bins, sits a small metal machine. It's a portable cement mixer with the bowl ripped off. Welded in its place is a thick tube of eight-inch steel pipe.

by Genesee Keevil

In Randy Clarkson’s garage, behind the Mini Cooper and a bunch of plastic Tupperware bins, sits a small metal machine.

It’s a portable cement mixer with the bowl ripped off. Welded in its place is a thick tube of eight-inch steel pipe. The pipe has a metal lid, sealed with a soft rubber gasket, that screws down like the hatch of a ship.

Clarkson takes a handful of heavy steel rods – some thin, some fat – stuffs them in the pipe and screws on the lid, then flips the whole contraption on its side. It sounds like hail on a tin roof as the cylinder, powered by the cement-mixer motor, methodically spins the rods.

If Clarkson had thrown a bucket of gold mining muck into the machine alongside the rods, the alchemy would have been almost instantaneous.

The machine takes sludge from sluice boxes and miraculously recovers more gold – a lot more gold.

In one bucket of sluice box slime, Clarkson’s machine unearthed 10 ounces of gold. That’s $15,000 from a bucket of discarded dirt.

“There are few things more popular than gold recovery,” he says. “Except maybe the mousetrap.”

The freelance mining engineer has spent much of his life chasing gold – particularly, radioactive gold.

It started in the 1980s, when Clarkson was in South America with the Canadian International Development Agency, teaching small-scale miners how to recover gold without using much mercury. To track recovery rates, he radiated the gold then followed the radioactive materials through the sluice boxes and shaking tables, all the way to the trash heap.

That’s when Clarkson discovered placer miners were only recovering 30-to-60 percent of the precious metal. So he started tweaking sluice boxes, working with the Klondike Placer Miners’ Association and the University of Alaska, Fairbanks.

He played around with centrifugal force and gravity, the sluice box combo that pulls gold from pay dirt. By the time Clarkson was done, sluice boxes were 99 percent more effective, and his design became the Canadian standard.

Clarkson thought he was done with gold recovery. But in 2013, the Klondike Placer Miners’ Association got back in touch. There was still that bit of gold getting through the shaking tables and sluice boxes – gold caught up in high-density minerals, what miners refer to as “difficult concentrates.” This thick slurry tends to end up in buckets, jars, peanut butter tubs, waiting for some magic machine to recover the residual gold.

There are lots of gold recovery machines out there, says Clarkson. “But most have no foundation in science, they’re not tested, and they’re secretive.” They’re also astronomically expensive, usually upwards of $20,000.

The Klondike Placer Miners’ Association wanted Clarkson to figure out a foolproof way to get at the gold trapped in these difficult concentrates.

“It felt like they were asking me for another miracle,” says Clarkson. He took the bait, went back to the University of Alaska, Fairbanks and began playing around with rod mills, which also start at $20,000.

He figured if he could somehow pulverize the difficult minerals, which tend to be brittle, while flattening the gold, which is more malleable, it would be easy to separate. But the gold kept getting pulverized too. Clarkson tried shaking tables, magnetic separators, nothing worked. “Our only success was grinding up the gold,” he says. “But then it was still hard to separate.”

On a whim, Clarkson loaded the mill to a third of its capacity. Immediately, his recovery rate rose from 30 percent to over 80. With less material in the mill, the heavy concentrates were crushed to powder while the gold was flattened, sitting shiny and smooth on the screen, as the pulverized heavy minerals were washed away.

But the rod mill he was using to do it cost $20,000.

It wasn’t until he spotted a portable cement mixer at a Whitehorse industrial supply shop that the light bulb went on. The mixer was $800. He changed the drive pulleys to make it spin faster, pulled off the mixing bucket and replaced it with heavy pipe and a custom lid, created by local welders, threw in some rods, cut by a local steel supplier, and had a portable rod mill for under $2,000.

The first field test saw Clarkson running to the cookhouse with a screen full of flattened gold. “It surprised the hell out of me how well it worked,” he says. “I just had to show someone.”

In less than eight minutes, he’d found more than $15,000 worth of gold in one bucket of muck.

Clarkson doesn’t plan to get rich off his magic machine. In fact, he’s putting all the blueprints and plans online, so miners can make mock-ups. “I don’t want to grow old and grey holding onto ideas and not publishing them,” he says.

There are already three machines on order in Whitehorse, and Clarkson hasn’t even finished tweaking it yet. He wants to put a screen over the pipe canister, so it catches the gold without putting it through a separate washing process, and has plans for a bigger model, in case miners want to get more muck through faster. Theses plans will also be public.

“My objective is not to make a living selling equipment – I want people to build it,” he says. “I’m an engineer, I make my money being way ahead of everyone else, not from patenting things.”

This column is co-ordinated by

the Yukon Research Centre at

Yukon College with major financial support from Environment Yukon and Yukon College. The articles are archived at  http://www.yukoncollege.yk.ca/research/publications /newsletters_articles

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