diamond stories and kimberlite discovery in wisconsin

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.

USGS Circular 843

• http://pubs.er.usgs.gov/pubs/cir/cir842

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.