Native copper was mined and used by Native Americans in the Upper Peninsula (UP) a few thousand years before French explorers arrived there. During the 19th century, upon receiving reports about the copper occurrences in the UP, the U.S. Government quickly mobilized people to map and survey the area. The news of copper occurrences in the UP spread quickly to the general populace and speculators and the UP became the site of the first significant mining boom in the U.S. Veins rich in native copper were the first deposits to be exploited, but by 1865 the native copper occurrences hosted by the conglomerates and basalts of the 1.1 billion year-old Portage Lake Volcanic sequence became the focus of prospectors and miners. The landscape was dotted with headframes throughout the northern part of the western UP and the area was the leading U.S. copper producer from 1844 until 1887 when the Butte, Montana copper deposit, a.k.a., “The Richest Hill on Earth”, overcame it.
During the 20th century, the Calumet & Hecla Mining Company and Copper Range Company produced the majority of copper from this 100-mile long belt. Production abruptly terminated in 1968 due to the higher operating costs related to deeper mining and persistent labor issues. Total production from these mines is estimated at over 5 million tonnes of copper, of which 85% came from four mines, at an average grade of 2% copper. 58.5% of this production came from brecciated and amygdaloidal volcanic flow tops, 39.5% from interbedded conglomerates, and 2% from veins. During the 1970s, vain attempts were made to rejuvenate copper mining in this belt, most notably by Homestake Mining.
Near the end of the 19th century, almost coincident with the discovery of minable iron deposits in other parts of the UP, copper was discovered in the shales and siltstones of the Nonesuch Formation south of Ontonagon. Early efforts at mining this sequence were not successful until the U.S. Government, which was determined to secure a domestic supply of copper, financed the construction of the White Pine Mine and related mill, smelter, refinery, and power plant in 1953.
Lake Superior Region Metallogeny
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Forward Looking Statements