Gold had to be removed from the ore (rock) brought out of the mine. Milling processes crushed the ore to the size of sand. Mercury, cyanide or heat then isolated the gold particles. Deadwood Gulch mill men used several methods, including stamp/amalgamation, chlorination, cyanide leaching, and smelting.

The Slime Plant in front of you extracted gold from muddy, finely crushed ore. This slime was dried in large filter presses, then leached with cyanide solution, which dissolved the gold. Charles W. Merrill invented this variation of the cyanide process for the Homestake Mining Company. The company paid the inventor a percentage or the gold that his method saved – making Merrill a wealthy man. The plant operated from 1906 to 1973.

[Illustration captions, top right; bottom row, left to right:]

Workers exposed themselves to dangers in both industrial mining and milling. [Photo:] Black Hills Mining Museum.

The press floor in the Slime Plant. [Photo:] Homestake Mining Company

Filter presses in the Slime Plant. [Photo:] Homestake Mining Company.

A diagram of the layout of the Slime Plant. The sludge entering the mill at the top of the hill, on the left of the diagram.

Marker is at the intersection of Pine Street and Water Steet on Pine Street.

Courtesy hmdb.org

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