While it originated thousands of years earlier, copper mining in Michigan became an important industry in the 19th and early 20th centuries. Its rise marked the start of copper mining as a major industry in the United States.
Within the state of Michigan, copper is found almost exclusively in the western portion of the Upper Peninsula, in an area known as the Copper Country. The Copper Country is highly unusual among copper-mining districts, because copper is predominantly found in the form of pure copper metal (native copper) rather than the copper oxides or copper sulfides that form the copper ore at almost every other copper-mining district. The copper deposits occur in rocks of Precambrian age, in a thick sequence of northwest-dipping sandstones, conglomerates, ash beds, and flood basalts associated with the Keweenawan Rift.
Although native copper was the dominant ore mineral, some chalcocite (copper sulfide) was sometimes present, and, especially in the Mohawk mine, copper arsenide minerals such as mohawkite and domeykite. Gangue minerals included calcite, quartz, epidote, chlorite, and various zeolites. A number of copper mines also contained a notable amount of silver, both in native form and naturally alloyed with the copper. Halfbreed is the term for an ore sample that contains the pure copper and pure silver in the same piece of rock; it is only found in the native copper deposits of the Upper Peninsula of Michigan. [1]
By the time the first European explorers arrived, the area was the home of the Chippewa people, who did not mine copper. According to Chippewa traditions, they had much earlier supplanted the original miners. The first written account of copper in Michigan was given by French missionary Claude Allouez in 1667. He noted that Indians of the Lake Superior region prized copper nuggets that they found there.[4] Indians guided missionary Claude Dablon to the Ontonagon Boulder, a 1.5-ton piece of native copper along the Ontonagon River. When American prospectors arrived in the 1840s, pieces of copper were found in streams or on the ground. The copper pits abandoned by Native Americans led early miners to most of the first successful mines.
Copper being loaded onto a steamer in Houghton, Michigan, c1905The Michigan State Geologist Douglass Houghton (later to become mayor of Detroit) reported on the copper deposits in 1841, which quickly began a rush of prospectors. Mining took place along a belt that stretched about 100 miles southwest to northeast through Ontonagon, Houghton, and Keweenaw counties.[5] Isle Royale, on the north side of Lake Superior, was extensively explored, and a smelter built, but no mining of any importance took place there.[6] Some copper mineralization was found in Keweenawan rocks farther southwest in Douglas County, Wisconsin, but no successful mines were developed there.
Copper mining in the Upper Peninsula boomed, and from 1845 until 1887 (when it was exceeded by Butte, Montana) the Michigan Copper Country was the nation's leading producer of copper. In most years from 1850 through 1881, Michigan produced more than three-quarters of the nation's copper, and in 1869 produced more than 95% of the country's copper.[7]
Although the copper-mining region stretched about 100 miles from northeast to southwest, the most productive early mines, working fissure veins, were those at the north end in Keweenaw County (such as the Central, Cliff, and Phoenix mines), or at the south end in Ontonagon County (such as the Minesota Mine).
In Keweenaw County, the fissure lodes were nearly vertical mineralized zones with strike nearly perpendicular to that of the enclosing basalts and conglomerates. In Ontanogan county, by contrast, the fissures had strikes nearly parallel to, and dips slightly steeper than, the surrounding beds.
The miners sometimes found masses of native copper up to hundreds of tons. To extract a single mass of copper, miners could spend months chiseling it into pieces small enough to hoist out of the mine. Although they were pure copper, removing the masses took a great deal of effort, and was sometimes not even profitable. The majority of the copper recovered was "barrel copper" (pieces broken from the rock and hand sorted in the "rock house," and shipped to the smelter in barrels), and finer copper broken loose from the rock in stamp mills and separated by gravity in "buddles" or "jigs."
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[edit] Geology
Although native copper was the dominant ore mineral, some chalcocite (copper sulfide) was sometimes present, and, especially in the Mohawk mine, copper arsenide minerals such as mohawkite and domeykite. Gangue minerals included calcite, quartz, epidote, chlorite, and various zeolites. A number of copper mines also contained a notable amount of silver, both in native form and naturally alloyed with the copper. Halfbreed is the term for an ore sample that contains the pure copper and pure silver in the same piece of rock; it is only found in the native copper deposits of the Upper Peninsula of Michigan. [1]
[edit] Native American mining
Prehistoric Native Americans were the first to mine and work the copper of Lake Superior and the Keweenaw Peninsula of northern Michigan between 5000 BCE and 1200 BCE. The natives used this copper to produce tools. Archaeological expeditions in the Keweenaw Peninsula and Isle Royale revealed the existence of copper producing pits and hammering stones which were used to work the copper.[2] Fringe writers have suggested that as much as 1.5 billion pounds of copper was extracted during this period, but archaeologists consider such high figures as "ill-constructed estimates" and that the actual figure is unknown.[3]By the time the first European explorers arrived, the area was the home of the Chippewa people, who did not mine copper. According to Chippewa traditions, they had much earlier supplanted the original miners. The first written account of copper in Michigan was given by French missionary Claude Allouez in 1667. He noted that Indians of the Lake Superior region prized copper nuggets that they found there.[4] Indians guided missionary Claude Dablon to the Ontonagon Boulder, a 1.5-ton piece of native copper along the Ontonagon River. When American prospectors arrived in the 1840s, pieces of copper were found in streams or on the ground. The copper pits abandoned by Native Americans led early miners to most of the first successful mines.
[edit] Modern mining industry
Copper mining in the Upper Peninsula boomed, and from 1845 until 1887 (when it was exceeded by Butte, Montana) the Michigan Copper Country was the nation's leading producer of copper. In most years from 1850 through 1881, Michigan produced more than three-quarters of the nation's copper, and in 1869 produced more than 95% of the country's copper.[7]
[edit] Fissure veins
Commercial production began in 1844 at the Phoenix mine. Most early miners began with little knowledge or planning, and few mines ever saw production, much less profit. The first successful copper mine, the Cliff mine, began operations in 1845, and many others quickly followed. These first mines worked copper-filled fissure veins that cut across stratigraphic layers.Although the copper-mining region stretched about 100 miles from northeast to southwest, the most productive early mines, working fissure veins, were those at the north end in Keweenaw County (such as the Central, Cliff, and Phoenix mines), or at the south end in Ontonagon County (such as the Minesota Mine).
In Keweenaw County, the fissure lodes were nearly vertical mineralized zones with strike nearly perpendicular to that of the enclosing basalts and conglomerates. In Ontanogan county, by contrast, the fissures had strikes nearly parallel to, and dips slightly steeper than, the surrounding beds.
The miners sometimes found masses of native copper up to hundreds of tons. To extract a single mass of copper, miners could spend months chiseling it into pieces small enough to hoist out of the mine. Although they were pure copper, removing the masses took a great deal of effort, and was sometimes not even profitable. The majority of the copper recovered was "barrel copper" (pieces broken from the rock and hand sorted in the "rock house," and shipped to the smelter in barrels), and finer copper broken loose from the rock in stamp mills and separated by gravity in "buddles" or "jigs."
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