Placer gold, little bits of gold not bound by other rock, can be found in waterways in and around Colorado's old mining districts. These include North Clear Creek west of Denver, Breckenridge, Alma, Fairplay, and Leadville (Heylmun 2002). However, because of its unique formation and ores, Cripple Creek, Colorado's most important mining district, has very little placer gold. This is undoubtedly the cause of its delayed discovery in the 1890s. For by 1859 prospectors from Georgia were the first Americans to find placer deposits in Cherry Creek near Denver, and the Colorado Gold Rush was on! The prospectors' discovery led to a Colorado industry that would produce more than 45 million ounces of gold and counting (Cappa, CGS 2002). What exactly did the lucky prospectors from Georgia find? Where did it come from, and how did it get there?

The reigning hypotheses asserts that "Placer deposits represent concentrations of gold derived from lode deposits by erosion, disintegration or decomposition of the enclosing rock, and subsequent concentration by gravity (Kirkemo, et. al., USGS 1993)." Once released from its matrix by weathering, tiny gold dust, flakes, grains, and nuggets flow downstream and collect in depressions and bars- where they patiently await the skilled hands of placer miners. These placer miners are also known as prospectors, gold panners, and can be otherwise ordinary people who have incurable Gold Fever.

However, research from USGS chemist John Watterson suggests that what placer miners might actually have isn't Gold Fever, it's the Gold Bug- or more precisely, bug-sweat (Helfferich 1993). When Watterson looked at thousands of placer gold particles from nine Alaskan sites with scanning electron micrographs he didn't see flakes or chips of gold released and worn by erosion. He saw tiny networks composed of hollow golden cylinders and orbs- the remains of colonies of soil dwelling bacteria (Helfferich 1994).

Very simply put, specialized types of bacteria metabolize sulfur while precipitating the previously bound up gold. In even simpler terms, they munch up sulfur and sweat gold. The gold then attracts other gold particles growing larger with time. This ability to precipitate metals from solution is called biomineralization.

Jennice McCafferty Wright
Museum Volunteer