Microscopic Particles Recovered : Tiny Gold ‘Nuggets’ Lead to Another Nevada Boom

If a Stanford University researcher’s hunch is correct, the Earth’s crust contains more gold than California’s Forty-Niners could have imagined in their wildest dreams.

The gold, however, is in the form of submicroscopic nuggets only a few hundred angstroms wide. In fact, geologist Mike Hochella said, a chunk of this type of gold a thousand angstroms across is considered “particularly big.”

Hochella’s “big” nugget is invisible without the use of a transmission electron microscope, since a thousand angstroms equal about four-millionths of an inch.

Hochella and an applied earth sciences professor, Marco Einaudi, are working to unlock the secrets contained within tiny slices of earth taken from gold deposits near Carlin, Nev., an area rich in the invisible gold specks.

Can Be Milled

“You can’t see gold in the rock,” Barbara Bakken, a doctoral candidate working with Einaudi, explained in a research project update last week, “yet they can pour it out of the mills without any problem.”

And they do.

Newmont Gold Mining Co. last year squeezed nearly 500,000 ounces of gold out of the Carlin deposits. The company estimated that the Carlin mining district still contains 12 million ounces of gold, worth about $5 billion at today’s prices.

While prospectors who flooded into California in 1849 and the Yukon at the turn of the century sought gold either by mining for veins or panning for nuggets and dust, a new kind of gold deposit requiring new extraction techniques was discovered near Carlin in 1961.

The Carlin deposits are unusual, Bakken said, because of the small size of the particles and the way in which they are evenly distributed through sedimentary rocks.

Not Just Everywhere

Also, she said, they are highly localized in Nevada and Utah.

Whether such deposits exist elsewhere on the Earth is what Bakken, Einaudi and Hochella hope to discover.

“We know that the gold was transported to the site by hydrothermal solutions,” Einaudi said. “The solutions were probably between 200 and 250 degrees Celsius when they arrived at the site.”

At some ancient time, probably between 15 million and 40 million years ago, conditions were just right for the gold-bearing hydrothermal solutions to interact with minerals as they passed through the limestones.

“Something happened,” he said, “to the fluid at a magical place in the rock, and the gold was deposited.

“My job is to find out what happened--and why there.”

Geological Puzzle

Bakken said determining why the Carlin deposit formed--and if the process was duplicated in other areas--was “kind of like putting a puzzle together backwards.”

Hochella said research on samples from the Nevada site could lead to techniques helping future prospectors stake their claims, knowing they will be striking it rich.

“If (Bakken) can help unlock the secrets behind how this particular deposit formed,” he said, “hopefully, that could be extended to the exploration for these deposits in this country and around the world.

“In fact, the gold deposits in the crust of the Earth might be a whole lot more numerous than we originally anticipated.”

Meanwhile, Nevada is the hot spot for gold companies.

“Nevada is called the Silver State,” Einaudi said, “but it should be called the Gold State.”

The Carlin area, he said, “right now is crawling with mining companies. The Canadians have come down, the Australians are starting to arrive, and they’re having success at finding these deposits.”