Nipissing High Grade Mill

Nipissing High Grade Mill. . , Ore from the Nipissing mines was sorted at a central picking plant into three grades for processing. The lowest grade ore, assaying under 100 oz per ton, was stored on dumps or sent to a Low Grade Mill to be concentrated by separating the silver and other metals from the rock in which it was found. The silver concentrate from the Low Grade Mill along with the mine ore that graded over 1,000 oz per ton was sent to a High Grade Mill for further processing. The concentrated ore from the High Grade process and the highest grade, mostly pure silver ore from the mine was then sent to a refinery. The remaining impurities were removed and the final concentrate was poured into silver bars. Initially the ore was processed by custom mills but, by 1912, all of the company ore was processed in plants on Nipissing Hill. , The Nipissing High Grade Mill and Refinery which stood at this location opened in February, 1911. The high grade ore was concentrated by a series of cyanide treatments before being directed to the onsite refinery. Over a period of 7 years, 11,331 tons of concentrate, carrying an average of 2,615 ounces of silver per ton, were treated at this site and 29.6 million ounces of silver were recovered. , By 1918, concentration techniques had improved to the extent that a cheaper and more efficient process was installed in the Low Grade Mill and the High Grade Mill was closed.