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Peerless Mine (Monitor; Monarch; Protector), Keystone, Keystone District, Pennington Co., South Dakota, USA

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Latitude & Longitude (WGS84): 43° 53' 25'' North , 103° 25' 10'' West
Latitude & Longitude (decimal): 43.89028,-103.41944
Köppen climate type:BSk : Cold semi-arid (steppe) climate

A pegmatite mine located in sec. 8, T.2S., R.6E., near Keystone.

Mineralization is comprised of several irregular, zoned pegmatite dikes in quartz-mica schist.

Workings include open cuts, pits and underground development plus 7 drill holes.

Mineral List

51 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 Macrostrat.org

1600 - 2500 Ma

ID: 2472506
Metagraywacke unit 2

Age: Proterozoic (1600 - 2500 Ma)

Description: Middle part of metagraywacke unit Xgw. Lithologically similar to unit Xgw3. Pelitic parts may contain sillimanite near Harney Peak Granite. Unit underlies mica schist unit (unit Xts) in Pactola Lake area but is shown as Xgw where Xts pinches out to the north. Overlies unit Xqc to the southeast in the Rockerville-Keystone area, where unit may be as much as 2,000 m thick and is largely proximal turbidites. North of Hill City, unit apparently pinches out.

Reference: Redden, J.A., E. DeWitt. Maps Showing Geology, Structure, and Geophysics of the Central Black Hills, South Dakota. U.S. Geological Survey Scientific Investigations Map 2777. [73]

1600 - 2500 Ma

ID: 2797792

Age: Proterozoic (1600 - 2500 Ma)

Description: Light- to dark-gray, silceous mica schist and impure quartzite. Differentiated where possible into three primary tongues or lenses. (Xgw1, Xgw2, and Xgw3) Thickness from 1,000 ft to over 5,000 ft (305-1,524 m).

Lithology: Major:{mica schist,quartzite}

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 Macrostrat.org, used under Creative Commons Attribution 4.0 License

This page contains all mineral locality references listed on mindat.org. 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 mindat.org 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.


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Meeves, H., et al (1966), Reconnaissance of beryllium-bearing pegmatite deposits in six western states, US Bur. Mines Info. Circ. 8298: 33 (Table A-1).
American Mineralogist (1985): 70(9-10): 1044-1049.
Rocks & Minerals: 57: 55.
Rocks & Minerals: 75(3): 156-169.
USGS Bull 380D
Sheridan, D. M.; Stephens, H. G.; Staatz, M. H.; Norton, J. J. (1957) Geology and beryl deposits of the Peerless pegmatite, Pennington County, South Dakota. USGS Prof Paper 297A

Mineral and/or Locality  
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