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Sources Of Hydrothermal Fluids Inferred From Oxygen And Carbon Isotope Composition Of Calcite, Keweenaw Peninsula Native Copper District, Michigan, Usa, Thomas Bodden, Theodore J. Bornhorst, Florence Bégué, Chad Deering

Michigan Tech Publications

The Mesoproterozoic North American Midcontinent Rift hosts the world’s largest accu-mulation of native copper in Michigan’s Keweenaw Peninsula. During a regional metamorpho-genic‐hydrothermal event, native copper was deposited along with spatially zoned main‐stage minerals in a thermal high. This was followed by deposition of late‐stage minerals including minor copper sulfide. Inferences from the oxygen and carbon isotopic composition of main‐stage hydrothermal fluids, as calculated from 296 new and compiled isotopic measurements on calcite, are consistent with existing models that low‐sulfur saline native copper ore‐forming fluids were domi-nantly derived by burial metamorphic processes from the very low sulfur basalt‐dominated rift fill at …