9. BHP Slag Heap - 1886
The first BHP smelting furnaces, the north smelters, were erected in 1886 to extract precious metals from ore by heating and melting. Eventually, each of the mines had a sprawl of industrial buildings on the surface, and mills for concentrating ore. Each also developed large heaps of ‘gangue’ (mined rock that is not ore), tailings (waste from concentrating) and slag (molten waste from smelting). The process of producing silver-lead bullion uses limestone and ironstone as ‘flux’, added to the furnace during smelting to form slag. Slag is a black, silty substance created by the separation of metal from stone.
The first smelters belched noxious fumes over the ever-expanding city until 1898. For the next 131 years, the fortunes of the mines and the city rose and fell together with metal prices, strikes, world wars and technological breakthroughs.
BHP erected a second smelter in the south of Broken Hill in 1888. In 1889, a concentration mill with a capacity of 1,500 tons of ore per week was built on the east side of the line of lode. This was replaced in 1894-97, on the south smelters’ slag heap, with a mill capable of 10,000 tons per week. The stone foundations of the later mill survive today, close-by, near Delprat Shaft.
BHP ceased smelting at Broken Hill in 1898.
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