Copper mining in Michigan
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.
This series of lava "is at least 15,000 feet thick in the Michigan copper district" and consists of "several hundred flood basalt flows."
Archaeologist Susan Martin wrote that "The competent excavation of many prehistoric archaeological sites in the Lake Superior basin reveals the continuous use of copper throughout the prehistoric time range, in association with all of the other items of material culture (projectile points, pottery and the like) that are without a doubt the products of native technologies.
Many of these sites have been dated reliably by radiocarbon means.... Clearly, copper-working continues up until the years of aboriginal contact with seventeenth-century Europeans.
"[1]: 306 The 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.
[1][6]: 16–17 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.
[7] Some copper mineralization was found in Keweenawan rocks farther southwest in Douglas County, Wisconsin, but no successful mines were developed there.
In Keweenaw County, the fissure lodes were nearly vertical mineralized zones with strike nearly perpendicular to that of the enclosing basalts and conglomerates.
In Ontonagon County, by contrast, the fissures had strikes nearly parallel to, and dips slightly steeper than, the surrounding beds.
To extract a single mass of copper, miners could spend months chiseling it into pieces small enough to hoist out of the mine.
In the 1850s, mining began on stratiform native copper deposits in felsite-pebble conglomerates and in the upper zones of basalt lava flows (locally called amygdaloids).
Many mines reopened during World War II, when wartime demand pushed copper prices higher.
Some towns which existed primarily due to copper mining include Calumet, Houghton, Hancock, and Ontonagon.
Mine rock processing operations left many fields of stamp sand, some of which grew so large as to become hazards to navigation in the Keweenaw Waterway.
Virtually every part of the Copper Country was cleared of timber, to the extent that only a few small areas of old-growth forest like (the Estivant Pines) are left.
[12] The company applied to government agencies to continue mining by in-situ leaching, using sulfuric acid to recover an additional 900 million pounds (410,000 metric tons) of copper by SX-EW.
The Michigan Department of Environmental Quality approved the permit in May 1996, and White Pine installed a pilot in-situ leaching project.
White Pine, which had already started to recover copper from the pilot project, suspended solution mining in October 1996, and applied for to the EPA for the permit.
The University of Montana undertook extensive efforts to restore and revegetate the barren landscape from 1997 to 1999, but it is unclear whether this has been successful.
[16] The July 7th 2021 edition of the local news outlet Keweenaw Report has the headline: Mining set to return to White Pine.
Eagle Mine is located on the Yellow Dog Plains, about 25 miles northwest of Marquette, in Michigan's Upper Peninsula.
On March 13, 2013, the Michigan Department of Environmental Quality (DEQ) issued Orvana Corporation, of Toronto, Ont.
[19] Orvana estimates that approximately one billion pounds of copper are present at their site, along with smaller quantities of silver.
