The mineral extraction process varies depending on the mineral. Extracting gold can be done through amalgamation, gravity concentration or leaching. Historically, mines would use amalgamation (with mercury), but technological advances have now replaced this process. These processes are more efficient and require less regulation for worker safety. Today, most gold mining mills use a combination of gravity circuits and concentration leaching to separate gold from the ore.
While the main steps for extracting gold are the same, but the equipment used can vary from mine to mine. Each mine customizes the mill equipment according to what will work best with the geology of their deposit. For example, some mills used a ball mill, while others used a pebble mill. Campbell Red Lake Mines used roasters to breakdown their arsenopyrite-rich ore, while other mines in the district lacking this geological feature used different technology. As technology improved and provincial and federal governments started monitoring the environmental impact of mining, many of the area's mills introduced autoclaves.
Gold is generally grouped into two types during the extraction process - free-milling and complex. For free-milling gold, the gold is not fused strongly with the host rock and can be separated using a gravity circuit. Free-milling gold is easier, faster and less expensive to process. Complex gold is locked together with the ore and is separated through a concentrated leaching process such as cyanidation.
When many of the Red Lake mines started producing, their mills were only capable of processing 100-200 tonnes/day. Today this is something unimaginable as Goldcorp's Red Lake mill is capable of processing upwards of 3,100 tonnes/day. The historic mills were expanded and upgraded at least once, if not more as their production increased. Similar to the shift away from manual underground equipment, modern mills are computerized, having control rooms where the process is operated and monitored.
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Historic Red Lake Mining
Red Lake Geology
The Red Lake Gold Rushes
From Hudson to Headframe
The Mill Process
Contemporary Red Lake Mining
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