10. BHP Mill Foundations - 1897
These fortress-like stone foundations are the remains of BHP’s concentration mills that operated from 1894 to 1897. The company’s first concentration mill was built on the east side of the lode in 1889. Concentration is the process of separating valuable metals or minerals from the raw material, in this case ore. The first mill was closed due to subsidence.
A gravity mill with a capacity of 10,000 tons of ore per week was erected here in 1897. The mill produced high-grade lead, but millions of tons of zinc-rich waste product, or tailings, were dumped.
In 1904, the flotation process was added to the plant. Flotation involves crushing the ore to separate valuable minerals and gangue (mined rock that is not ore) components, pulping the particles of ore with water, and then separating the specific mineral. It operated until 1927 and was demolished in 1940.
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