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California Aspects

Mercury was a key element in the California Gold Rush due to its role in separating precious metals such as gold and silver from contaminants. This method of processing gold and silver has been an important component of human civilization for thousands of years and was used by Romans to purify gold using procedures that are still in use in some parts of the world to this day. In California individual prospectors could start out with a small leather bag of mercury, pan the streams for small nuggets or flecks of gold, separate the gold from the gravel by amalgamating it with mercury, then vaporizing the mercury and pocketing the gold. This provided a very quick and dirty method for an individual prospector to harvest his treasure.

The extensive panning activity along California's streams soon exhausted the readily available gold and led to the development of hydraulic mining about 1862. Hard rock mining and dredging was also initiated during this period. A very significant step in all of these procedures involved the use of large quantities of mercury to dissolve the precious metal and then harvest the gold by retorting the amalgam.

Beginning in 1850 the Coast Range on the west side of the Sacramento Valley provided most of the mercury used in the Gold Rush. Around 300 mines produced approximately 140,000 tons of mercury that supported the California Gold Rush and gold mining activities in Alaska and the whole Pacific Rim. Most of it was transported eastward in 76 pound flasks to the Sierra Nevada and surrounding areas. Due to the inefficient extraction and condensation procedures used in procuring the mercury, and its later use in the amalgamation and separation of the gold and silver, mercury vapor was released into the atmosphere. This resulted in a buildup in the whole Sacramento watershed area. It has remained a major pollution problem for more than a hundred years and will likely continue long into the future. A modified geobiochemical mercury cycle as it applies to the Sacramento Watershed Area is shown below.

Mercury is a heavy metal that is unique in that it slowly vaporizes when exposed to the atmosphere and its gaseous elemental form is not water soluble. It becomes water soluble and incorporated into rain drops after being oxidized into ionic mercury (Hg++) in the atmosphere in the presence of ozone and oxygen. The polluted water droplets return the mercury back to earth where it is deposited on soil, some of which is carried by erosion into the waterways. A great deal of the ionic mercury becomes complexed with organic and inorganic particles present in the water. It can also be acted upon by microorganisms to form a variety of organic and inorganic compounds that are eroded into nearby streams and transported into the estuaries of the San Francisco Bay-Delta region. Long after the mercury mining has ceased and gold and silver processing has diminished, mercury and its compounds persist. A permanent legacy of these mercury releases remains not only locally but in snow capped glaciers, peat bogs and sediments located hundreds and even thousands of miles away.

Cache Creek is a tributary of the Sacramento River whose watershed area includes a number of large abandoned mercury mines and a gold mining and processing facility. One of these abandoned mercury mines (the Sulfur Bank Mercury Mine), currently an EPA Superfund site, is still releasing mercury-containing leachate into nearby Clear Lake. This and other mines sites contribute to the contamination of Cache Creek which has been estimated to account for about 50% of the mercury carried into the Bay Delta region each year. During the 1995 high water period it was estimated that approximately 1,000 Kg of mercury, mostly in particulate form was carried downstream into the Delta and Bay areas. (Foe, et al 1997)

Additional References:

Winged Mercury and the Golden Calf
Two elements, one economic theory, and a cascading torrent of collateral damage
By Rebecca Solnit
Orion Magazine, Sept./Oct. 2006

Mercury Contamination in the Yuba and Bear River Watersheds
A Report of the South Yuba River Citizens League

By Fraser Shilling, Ph.D.

Mercury Contamination from Historic Gold Mining in California
By Charles N. Alpers and Michael P. Hunerlach

Mercury and Methylmercury in Water and Sediment of the Sacramento River Basin, California (a thorough and detailed study)
Joseph Domagalski, USGS
Applied Geochemistry (2001)16:1677-1691
Download PDF

Mercury Effects, Sources, and Control Measures
Alan B Jones & Darrel Slotton
with contributions from
Chris Foe & Joe Domagalski
Download PDF

Interagency Team Studying Mercury Contamination in California Watersheds
edited by Erin Klaesius May 2000

Mercury From Gold Rush Days Found In California Fish
USGS Press Release
September 28, 2000

Environmental Mercury in California
By Walter C. Swain, May, 2000

Mercury Bioaccumulation in Fish in a Region Affected by Historic Gold Mining: The South Yuba River, Deer Creek, and Bear River Watersheds, California, 1999
By Jason T. May, Roger L. Hothem, Charles N. Alpers, and Matthew A. Law

Minings tarnished legacy - an abandoned mercury mine (Winter 2000)
UC Davis Magazine

Inoperative Mercury Mines fingered as a major source of mercury contamination in California water (11/6/2000)
UC Santa Cruz Currents