History of Copper Mining in the Upper Penninsula, Michigan
Native copper mining in the Lake Superior region dates back at least 5,000 years. This is evidenced by numerous ancient pits found along the length of the Keweenaw Peninsula and also on Isle Royale across Lake Superior to the northwest. These ancient pits contain masses of native copper in various stages of removal together with crude stone tools that were used in mining the copper. Copper tools, as well as decorative and ceremonial objects made from Lake Superior copper, have been found throughout the upper Midwest, in the Mississippi Valley, and as far south as Mexico. The Lake Superior area source of this material is established by the unique presence of silver alloyed with the copper.
The earliest documented visits to the area were by Jesuit priests in 1672 who reported the presence of copper along the shores of Lake Superior (Butler and Burbank, 1929). The first recorded mining operation started in 1771 with an attempt to recover copper from what turned out to be a large glacial erratic.
A sustained copper industry began in 1830 when Douglas Houghton, Michigan's first State Geologist visited the region. His report in 1841 led to combined State and Federal topographic and geologic surveys in 1844 and in 1845 the Cliff mine, the first underground mine on the native copper lodes, was opened. The Calumet and Hecla mine, the largest by far in the district, was opened in 1864.
Most of the native copper production came from a 20 kilometer long belt between the towns of Houghton and Calumet, and was mined both from amygdaloidal zones in the tops of basalt lava flows and from interbedded conglomerates. During its productive period, from 1845 to 1977, the district produced 11.5 billion pounds of copper from over 300 million tonnes of ore. All of this production was from underground mines.
Concurrent with the development of the native copper mines, exposures of high grade silver and copper as chalcocite in siltstone units of the Nonesuch Formation were discovered and mined west of the town of Ontonagon in the western Upper Peninsula. The discovery by the Copper Range Company in the 1930s that lower grade zones of chalcocite mineralization extended over a very large area, coupled withincreasingly sophisticated milling techniques for treating fine-grained chalcocite mineralization, led to development of the White Pine mine in 1954 and subsequent discovery of the Copperwood deposit farther west. The White Pine mine produced 4.5 billion pounds of copper from 1954 to 1994. More recently, promising discoveries of copper as chalcocite have been made in the tops of basalt lava flows east of Calumet including the 543S and G-2 deposits (Highland's Keweenaw project).
(Reference: Butler, B. S. and Burbank, W. S., 1929, The Copper Deposits of Michigan: U. S. Geological Survey Professional Paper 144, 238p.)