- Nonesuch Shale
The Nonesuch is a lacustrine sequence of shale, siltstone, and sandstone, 150 to 210 m thick, that conformably overlies the alluvial Copper Harbor Conglomerate and is conformably overlain by the fluvial Freda Sandstone. Together, the Copper Harbor, Nonesuch, and Freda make up the Oronto Group. The Nonesuch is Middle Proterozoic, with an estimated age of approximately 1.1 billion years. It was deposited in the Midcontinent Rift. The Nonesuch beds contain common organic carbon and pyrite.
Copper was discovered in the Nonesuch in the 1800s, but early mining efforts, such as those at the Nonesuch Mine in Ontonagon County, Michigan, failed because of the difficulty of recovering the fine grains of native copper.
The Copper Range Company opened the White Pine mine in Ontonagon County, Michigan, in 1955. The principal ore minerals were chalcocite and native copper. The underground mine produced copper from the Nonesuch Shale until it closed in 1995.
The Nonesuch Shale has sufficient organic carbon content (greater than 0.5%) to be considered a potential sourcebed for petroleum. Oil identified as Precambrian has been found seeping into the White Pine copper mine in Michigan. Exploration wells have been drilled to Nonesuch-equivalent sediments in the rift basin in Michigan, Wisconsin, and Iowa, but no petroleum deposits have been discovered.
- ^ William C. Kelly and Gail K. Nishioka, "Precambrian oil inclusions in late veins and the role of hydrocarbons in copper mineralization at White Pine," Geology, May 1985, p.334-337.
- ^ Scott W. Imbus and others, "Organic geochemistry and sedimentology of middle Proterozoic Nonesuch Formation - hydrocarbon source rock assessment of a lacustrine rift deposit," in Lacustrine Basin Exploration, Tulsa, Okla.: American Association of Petroleum Geologists, p.197-208
- ^ Albert B Dickas, “Midcontinent rift system: Precambrian hydrocarbon target,” Oil and Gas Journal, 15 October 1984, p.151-159.
- ^ Walter S. White and James C. Wright, "Sulfide-mineral zoning in the basal Nonesuch Shale, northern Michigan," Economic Geology, November 1966, p.1171-1190.
- ^ J.A. Seglund, “Midcontinent Rift continues to show promise as petroleum prospect,” Oil and Gas Journal, 15 May 1989, p.55-58.
- Copper mining in Michigan
- Midcontinent Rift
Iowa Geological Survey: Exploring the Midcontinent Rift, PDF file, retrieved 27 December 2008.
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