Native Copper Specimen - Keweenaw Peninsula Michigan - 3+ Pounds
- Country: United States - Michigan
- Type: Raw Specimen - Copper Mineral
- Composition: Copper
- Weight: 3+ Pounds
Extending from upper Michigan into southern Lake Superior (the world's largest freshwater lake), the Keweenaw peninsula contains one of the largest and most unique copper deposits in the world. It is the only district where native copper was the primary mineral mined throughout the life spans of its mines.
Extending approximately 150 miles long and 50 miles wide, the Keweenaw fault extends along the length of the peninsula and marks the boundary between the Mid-continent rift and continental rocks. The rift valley was filled with a combination of extrusive volcanic rocks with minor amounts of intrusive igneous rocks and sediments derived from the igneous rocks. The Greenstone flow is one of the largest lava flows in the world and can be mapped for 90km on the peninsula; it is also found on Isle Royale 90 km northwest on the other side of the rift valley. It has a thickness of up to 400m with an volume estimated to be between 800 to 1,500km3 of lava. Other flows on the peninsula can be mapped for even greater lengths of up to 160km.
The copper from the glacial float as well as shallow mines has been utilized for approximately 7000+ years. Native Americans may have mined between 100 and 500 million pounds of copper from deposits on the peninsula and Isle Royale and the fissure veins were the first type of deposit to be exploited by the early prospectors in the 1840's to 1880's. The entire peninsula from Keweenaw Point to the Ontonagon River area contain ancient mining pits. The mines produced large masses of native copper (up to 520 tons), but were of irregular distribution, difficult to find, and most did not pay back their investors. The greatest production of copper was from gas pockets in the lavas, interstitial spaces in the breccias developed on the top portions of the flows, and porosity between rock clasts in sedimentary rocks derived from the volcanics. More than 11 billion pounds of copper have been produced in the district over the 150 years of recorded mining activity.
At the time of this listing the only mining that is currently operating in the region is the Caledonia mine for copper and other mineral specimens. Several of the mines offer tours, giving visitors a taste of the conditions under which the miners worked and lived.
Many of the world's best specimens of native copper have been found in these mines. The district has also has seen the production of silver crystals, copper included calcite crystals, chalcocite, copper arsenides, and secondary copper minerals. Lapidary material found on the peninsula has included datolite, chlorastrolite (massive pumpellyite, the state gemstone of Michigan), and Lake Superior agates.
*Specimen condition is based on our professional opinion. Pictures are representative of the specimen that you will receive, actual specimen may differ slightly*