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Diamond Stories and
Kimberlite Discoveryin Wisconsin
The Wisconsin Diamond Storyor
It Ain’t Topaz
Mike MudreyUniversity of Wisconsin-Extension
Emeritus
Diamonds in Wisconsin
• Between 1876 and 1913, diamonds were found in at least seven localities in southern and central Wisconsin. All were found in Pleistocene gravel deposits or Holocene river gravel.
• The bedrock kimberlite source for these diamonds is unknown, but was presumed to be in northern Canada, the only area north of Wisconsin previously known to contain kimberlite.
Bedrock Geology
• From S. Dutch, Univ. Wisconsin-Green Bayhttp://www.uwgb.edu/dutchs/geolwisc/ssbr0.htm
Wisconsin Diamond
Occurrences and relations to glacial end
moraines
Vintage 1900 analysis of glaciogene origin of midwest
diamonds (Hobbs, 1901)
Wisconsin Diamond
Occurrences and relations to glacial end
moraines
Eagle Area
Photograph of lead castings of Eagle (top) and Oregon (bottom) diamond
Photograph of lead castings of Eagle (top) and Oregon (bottom) diamond (Hobbs, 1901)
Acquisition Card-American Museum of Natural History
Acquisition Card-American Museum of Natural History
!!!!! Stolen Oct 29 1964 !!!!!
Saukville
Burlington
Antigo micro-Diamond Discovery by Al Falster
Now in Weeks Hall Museum
Use of High-Resolution Aeromagnetic Data for Regional Geology Investigations, Southeastern Wisconsin (Where’s the
Kimberlite!)
M.G. Mudrey, Jr.
Wisconsin Geological and
Natural History Survey
Presented at the 1998 Institute on Lake Superior Geology, Minneapolis, Mn
Diamonds in Wisconsin• Between 1876 and 1913, diamonds were
found in at least seven localities in southern and central Wisconsin. All were found in Pleistocene gravel deposits or Holocene river gravel.
• The bedrock kimberlite source for these diamonds is unknown, but was presumed to be in northern Canada, the only area north of Wisconsin previously known to contain kimberlite.
Vintage 1900 analysis of glaciogene origin of midwest
diamonds (Hobbs, 1901)
Photograph of lead castings of Eagle (top) and Oregon (bottom)
diamond
Photograph of lead castings of Eagle (top) and Oregon (bottom) diamond (Hobbs, 1901)
Acquisition Card-American Museum of Natural History
Saukville (l) and Burlington (r) from USGS Circular 842
Wisconsin Diamond
Occurrences and relations to glacial end
moraines
Kimberlite Discoveries
• With the discovery of the Lake Ellen kimberlite in Iron County, Michigan, Cannon and Mudrey (1981) suggested the drift diamonds in Wisconsin may have come from a more local source.
• Carlson and Adams (1997) described a kimberlite in Kenosha , southeastern Wisconsin, which was defined by magnetics and drilling to be about 280 m across.
Map showing the location of diamond discovery sites, marginal moraines of major ice lobes and direction of ice movement, possible cryptovolcanic structures and the Lake Ellen kimberlite from USGS Circular 842
Map showing the location of diamond discovery sites, marginal moraines of major ice lobes and direction of ice movement, possible cryptovolcanic structures and the Lake Ellen kimberlite from USGS Circular 842
Bedrock Geology
• From S. Dutch, Univ. Wisconsin-Green Bayhttp://www.uwgb.edu/dutchs/geolwisc/ssbr0.htm
Diamonds and Kimberlite in Wisconsin
Diatreme Outline
Aeromagnetic Map, Pleasant Prairie
Details of Pleasant Prairie
Kimberlite Anomaly
Line profiles
Aerial photograph of kimberlite site
Photograph of kimberlite site, notice houses in background
Summary and Conclusions 1
• Flight-line spacing greater than 800 m will be ineffective in the identification of small, highly magnetic kimberlite.
• Because of weak intensity, aeromagnetic anomalies from kimberlite will only be evident where regional gradients are subdued and regional anomalies are weak.
Summary and Conclusions 2
• Other kimberlitic bodies may occur in Wisconsin and Illinois and may be the source for midwest diamond discoveries.
Summary and Conclusions 3
• Urbanization in the Milwaukee-Chicago corridor may discourage further geologic and geophysical analysis and competing land-use may make further exploration and ultimate development difficult.
