Age of native copper mineralization, Keweenaw Peninsula, Michigan

Economic Geology
By: , and 



Amygdaloidal flood basalts and conglomerates are the host for substantial deposits of native copper within the Portage Lake Volcanics in the Keweenaw Peninsula of Michigan. A wide variety of gangue minerals are associated with the regional hydrothermal alteration-mineralization event. Application of the Rb-Sr method to amygdule-filling microcline, calcite, epidote, and chlorite suggests an age of mineralization between 1,060 and 1,047 m.y. (+ or - [asymp] 20 m.y.). These results are supported by a fission track age on epidote of 1,044 + or - 169 m.y. The age of native copper mineralization determined in this study is consistent with geologic evidence which suggests that mineralization postdated the deposition of most or all of the overlying Freda Sandstone. Variable initial 87 Sr/ 86 Sr ratios between the low Rb/Sr phases suggest mixing of isotopically distinct sources of Sr during the generation and equilibration of the hydrothermal solutions.

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Publication type Article
Publication Subtype Journal Article
Title Age of native copper mineralization, Keweenaw Peninsula, Michigan
Series title Economic Geology
DOI 10.2113/gsecongeo.83.3.619
Volume 83
Issue 3
Year Published 1988
Language English
Publisher Society if Economic Geologist
Description 7 p.
First page 619
Last page 625
Country United States
State Michigan
Other Geospatial Keweenaw Peninsula
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