Mercury used in western mining: Where did it all go?

Gould_&_Curry mine comstock lode

Advances in US mining in recent decades have helped reduce the industry’s impact on the environment. While there is still room for additional progress, the difference between today and 125 years ago is staggering.

Consider the amount of mercury that was used – and ultimately dumped – into western rivers in the second half of the 19th century in the quest for silver.

Mercury, or as it was better known then, quicksilver, was critical in the removal of silver and gold from ore in the western United States. As the Alta California newspaper noted in 1890, it was pretty easy to determine how much mercury ended up rivers, streams and land: however much was used.

“In the silver mines of a certain region, in order to ascertain the amount of quicksilver dissipated and lost, it is only necessary to know the amount bought, for not an ounce is ever sent out from the mines to be sold,” the publication wrote in January 1890.

The paper estimated that between 1860 and 1889, more than 20.5 million pounds of mercury was used just in the huge silver strikes in the Comstock Lode in western Nevada. While some was likely vaporized, making the surrounding atmosphere toxic, most of the element seeped into the environment, according to the Alta California.

In Nevada, mercury was used to extract silver and gold from ore through the Washoe Process, a concentrating process in which silver was mixed with mercury, either in a drum or on an amalgamation table, where the precious metal bond with mercury. The resulting product was called amalgam.

The silver was then recovered from the mercury by retorting, which involves distilling off the mercury from the amalgam.

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