Abandoned mercury mines dot Lake, Sonoma, Napa counties

The Sulphur Bank mine was part of the “quicksilver,” or mercury mining boom that took hold in the 1870s in Lake County, as well as Sonoma and Napa counties.

Hundreds of mines dotted the coast mountain ranges during the rush to extract mercury from the area’s reddish deposits of cinnabar ore. Mercury was used to refine gold and silver, but also was employed as an ingredient for wood processing, early photography and medical uses.

The mining claims in the Mayacmas Mountains had fanciful names like Fandango, Mohawk, Socrates, Rattlesnake and Silverado, the hideaway for Robert Louis Stevenson on the flanks of Mount St. Helena.

The workers at Sulphur Bank were mostly Chinese, but there were also immigrants from Sweden, Norway, Ireland and Mexico, according to 1880 census records.

Partially an open pit and partially a tunneling operation, the mine yielded the cinnabar ore, or mercury sulfide, which was treated in furnaces and retorts, turning it into gas and recondensed as elemental mercury.

Flasks of the silvery fluid were hauled by horse wagon on a long hilly ride, to be shipped out by train in Calistoga.

There were incidents of mercury miners being poisoned by toxic gas with their eyes swelling shut for a week or more. Mercury exposure also caused a condition known as “salivation,” where workers lost their teeth from receding gums.

Today, abandoned mercury mines in Sonoma County and their potential for contamination occasionally get renewed scrutiny from officials.

Claudia Villacorte, a supervising engineer with the North Coast Regional Water Quality Board, said her agency needs more staff members to assess abandoned mines in the region and determine which need attention.

But, she said, “the majority of them are pretty stable, from what I grasp, in terms of active leeching into waterways.”

An exception appears to be the area surrounding Jackson Mercury Mine, 4 miles north of Guerneville, that was tested in 2015 for mercury in the soil. The mine operated from 1946 to 1971.

Water-quality regulators said the dilapidated mine buildings off Sweetwater Springs Road drew attention because of their high visibility. Heavy winter rains raised questions about the possibility of contaminants from the large mining waste piles making their way into nearby Wilson Creek, which flows to the Russian River.

Mining wastes were evident in the creek bed, and sampling of creek bank soils indicated mercury concentrations above hazardous thresholds.

A staff report concluded further investigation may be warranted along with creek clean-up and erosion control, to keep more waste from going into the creek.