"Becoming California, a series that brings the California Gold Rush alive with the people who lived it."

Crushed Rock & Chemicals Exposed the Gold


by Don Baumgart

Stamp mills were one of the unique inventions used in the California Gold Rush.

"Six tall, upright rods of iron, as large as a man's ankle, and heavily shod with a mass of iron and steel at their lower ends.." So begins Mark Twain's description of a Nevada stamp mill used to crush silver-bearing ore.

"...these rose and fell, one after the other, in a ponderous dance, in an iron box called a battery." Each of the stamps weighed 600 pounds. "One of us stood by the battery all day long, breaking up masses of silver-bearing rock with a sledge and shoveling it in.

"The ceaseless dance of the stamps pulverized the rock to powder, and a stream of water that trickled into the battery turned it to a creamy paste." Quicksilver, or mercury, in the battery box seized some of the liberated gold and silver particles and held on to them.

At the end of his brief stint shoveling ore into the Nevada stamp mill, Twain told his boss he thought the $10 a week was not quite enough. He asked for a new wage of $400,000 a month. He didn't get it and had to become a newspaperman.

A description of that same stamp mill process at a Nevada County gold mine, the North Star, also recounted the use of quicksilver. "Mercury is fed at regular intervals (into the battery box). A flask weighing 76 pounds would be used in nine days." Only 35 percent of it would be recovered, according to Emile Rector Abadie's account, Gold Milling at the North Star Mine. "There is a considerable loss of quicksilver," he concluded.

Placer mining started in Nevada County in 1848 as miners stooped over their pans, feet in the icy streams. A quartz ledge was found the summer of 1850. "Discoveries made on Gold Hill and Massachusetts Hill increased the excitement in quartz mining," Abadie writes. The first stamp mill in the state began operation that year in Nevada County.

By the close of 1864 quartz gold mining had taken $23 million from western Nevada County's Eureka-Idaho, North Star, and Empire mines.

At the North Star 40 stamps, each weighing 875 pounds, dropped on the quartz ore 86 times a minute. The life of one of the heavy steel shoes was 130 days.

While the giant stamps with their constant noisy banging were a very visible (and audible) part of hard rock gold mining, the use of mercury to gather up the bits of valuable ore was less noticeable. And its disappearance into the ground was even more invisible.

Today mercury in the environment has become a recognized health hazard. It has been found in plants and animals we use for food, such as eggs, fish, grain, and meat. In the mid-1950s more than 100 Japanese were poisoned by mercury-laden fish. The mercury came from industrial wastes dumped into the bay where the fish were caught. In the early 1970s tuna and swordfish sold in the U.S. were found to contain dangerous amounts of mercury. Soon both the U.S. and Canada had prohibited the dumping of industrial wastes containing mercury.

But what about all the mercury lost during stamp milling in Nevada County? Extremely dangerous, the silver-colored liquid metal affects the human brain and nervous system. It is cumulative; the body does not expel mercury it absorbs.

In 2003 a workshop was convened in Grass Valley to create plans to deal with the Gold Rush leftovers: hazardous mercury levels that now pose a possible danger in fish from five reservoirs and two streams in Nevada County.

Workshop participants learned from the California Office of Environmental Health that bacteria have converted the inorganic mercury used to extract gold into the more dangerous methylmercury. That substance can accumulate in fish in concentrations thousands of times greater than in the surrounding water.

Plans are being studied for a cleanup, but it will be expensive and long-coming. In the meantime the state urges people to eat local fish from certain waters only once a month. Just another side effect of a migration of disparate characters that, rivaling the Crusades, descended on California and changed it forever.

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Copyright Don Baumgart, 2006


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