Quicksilver: Trapping gold with mercury

How did goldseekers wash out the gravel from their pans without losing any specks of gold? The answer is liquid mercury, known in the 1800s as quicksilver.

quicksilver

ad for Quicksilver July 28, 1860

Imagine a gold miner at the water’s edge filling a gold pan with water and then shaking it around in a circular motion. It takes several dips of the pan to get the gravel out. Then the smaller pebbles have to be picked out by hand until all that’s left is black sand (iron ore).  With some more water added to the pan there might be some yellow ‘colour’ in the pan. How to quickly retrieve most of the gold? To solve that problem miners would pour a few ounces of quicksilver (liquid mercury) into the pan before they started. In a few minutes the ‘quicksilver’ would engulf all the fine gold fragments and form a solid mixture (amalgam).

How much quicksilver was used?

How much quicksilver was used during the Fraser River gold rush or the Cariboo gold rush? No one knows for sure. It was easy to use but extremely dangerous to handle.

Quicksilver was poured along the riffles in rocker boxes and sluice boxes. The high density of mercury allowed gold and gold-mercury amalgam to sink while sand and gravel passed over the mercury and through the sluice. Large volumes of turbulent water flowing through the sluice caused many of the finer gold and mercury particles to wash through and out of the sluice before they could settle.

Gravel and rocks that entered the sluice at high speed caused the mercury to break into tiny particles. These tiny mercury particles became airborne. In the meantime, more mercury would be added to the sluice boxes. The bottoms of some sluice boxes eventually became coated with mercury.

Working a claim at Emory Bar

Some mercury was lost from the sluice, either by leaking into underlying soils and bedrock or being transported downstream with the placer tailings. If it was too cold, the mercury was ineffective.

The Daily Colonist published a letter February 12, 1859 from a miner working a claim on Emory Bar who wrote “…the coldness of the water thickens the quicksilver so much as to prevent a full half of the fine gold from being taken up or amalgamated as it would when the weather is warm.”

Dissolving the mercury

Some miners would take their amalgam down to Victoria where an assayer would dissolve the mercury under intense heat.


Did you know? Mercury is made by  roasting crushed cinnabar ore (HgS) in a furnace. Cinnabar  is mined in only a few places in the world. The New Idria Quicksilver Mining Company in central California started operation in 1854 and closed in 1972; the town of Idria was abandoned as a result.