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The Lake Ellen Kimberlite is a poorly exposed volcanic breccia located about northeast of Crystal Falls in the Upper Peninsula of Michigan. The first publication in 1981 〔Cannon, W., Murdrey, M. (1981) "The Potential for Diamond-Bearing Kimberlite in Northern Michigan and Wisconsin", U. S. Geological Survey Circular No. 842.〕 describing the feature led to speculation that this or similar kimberlites in the area might have been the source of the diamonds discovered a century before in Wisconsin as well as a period of exploration by several minerals firms. The kimberlite was discovered in 1971 when a logging road was bulldozed through the area exposing the unusual looking rock. The exposure consists of several small areas otherwise overlain by glacial till. Magnetic survey work done in 1956 〔Gair, J. E., and Wier, K. L., 1956, Geology of the Kiernan Quadrangle, Iron County, Michigan: U.S. Geological Survey Bulletin 1044, 88 p〕 depicts an elliptical positive anomaly long in an east–west direction and wide, which probably defines the limits of the pipe. The kimberlite is intruded into volcanic rocks of the Proterozoic Hemlock Formation. The exposed material is grayish green to reddish, iron stained highly weathered and consists of disaggregated rubbly fragments up to . It is generally accepted that the pipe was emplaced about 180 million years ago. The lake Ellen Kimberlite is popular with rock hounds as the classic indicator minerals (pyrope, magnesian ilmenite and chrome diopside) for kimberlite are easily found in the material, though few are of gem quality and size. While there was considerable interest in diamond exploration in Michigan’s Upper Peninsula and northern Wisconsin for several years, no diamonds of commercial interest have been found. ==See also== *Kimberlite *Lamproite *Elliott County Kimberlite 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Lake Ellen Kimberlite」の詳細全文を読む スポンサード リンク
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