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Minesota Mine (Minnesota Mine), Rockland, Ontonagon Co., Michigan, USA

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Latitude & Longitude (WGS84): 46° 44' North , 89° 11' West
Latitude & Longitude (decimal): 46.73333,-89.18333
Köppen climate type:Dfb : Warm-summer humid continental climate
Other regions containing this locality:Keweenaw Peninsula, Michigan, USA

An underground copper mine consisting of eleven shafts and several adits located near Rockland, MI. The Minesota Mine was organized in 1848 and worked two fissure veins that were very rich in copper. The mine operated until 1885, when it was closed. The mine was consolidated into the Michigan Mining Co. holdings in 1899. The Minesota Mine produced approx. 34.7 million lbs. of refined copper.

The Minesota Mine got its name from an error in the recording of the original deed, when the second "n" was accidently left out. It was never changed, and the Minesota name hung around [the mine is nonetheless referred to as "Minnesota Mine" in numerous contemporanean reports; see e.g. Henwood (1871) and the references quoted therein]. The Minesota Mine was more famous for its exceptionally large masses of native copper discovered underground. It was not uncommon for masses up to 50 tons being discovered in the shafts and levels, but on March 7, 1857, a mass was discovered that would become the largest single mass of native copper ever found to this day. When processed, it was estimated to weigh around 527 tons (there were 27 tons of chisel chips produced from cutting up the mass!). Today, the collector can still find some of those chisel chips in the mine piles, as well as copper, silver, and micro minerals.

Mineral List

16 valid minerals.

Regional Geology

This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.

Click on geological units on the map for more information. Click here to view full-screen map on

1000 - 1200 Ma

ID: 2928167
Portage Lake Volcanics

Age: Stenian (1000 - 1200 Ma)

Stratigraphic Name: Portage Lake Volcanics

Description: Lava flows, mostly basalt, andesite and felsite flows and subordinate interflow sedimentary rocks.

Comments: This unit is the same as unit Yp on paper map of Sims (1992). Description is taken from that unit description.

Lithology: Major:{basalt}, Minor:{basaltic andesite}, Incidental:{rhyolite, sandstone mudstone}

Reference: Horton, J.D., C.A. San Juan, and D.B. Stoeser. The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States. doi: 10.3133/ds1052. U.S. Geological Survey Data Series 1052. [133]

Data and map coding provided by, used under Creative Commons Attribution 4.0 License

This page contains all mineral locality references listed on This does not claim to be a complete list. If you know of more minerals from this site, please register so you can add to our database. This locality information is for reference purposes only. You should never attempt to visit any sites listed in without first ensuring that you have the permission of the land and/or mineral rights holders for access and that you are aware of all safety precautions necessary.


Henwood, W.J. (1871): Observations on Metalliferous Deposits: On the Native Copper of Lake Superior. Transactions of the Royal Geological Society of Cornwall 8(1), 385-489. [as Minnesota Mine]

Dana 6:22, 505 & 1086

Dana 7:I:101

Rocks & Minerals: 58:112

Butler, B.S., and Burbank, W.S. (1929): The Copper Deposits of Michigan. USGS Prof. Paper 144, 238 pp.

Clarke, D.H. (1978): Copper Mines of Keweenaw: Minesota Mining Company, No. 11, 28 pp.

The Copper Country Rock & Mineral Club (2001): Red Gold and Tarnished Silver, 2nd Ed., 44 pp.

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