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GEOREF RECORD

Copper deposits of the western Upper Peninsula of Michigan

Theodore J. Bornhorst and Robert J. Barron
Copper deposits of the western Upper Peninsula of Michigan (in Archean to Anthropocene; field guides to the geology of the Mid-Continent of North America, James D. Miller (editor), George J. Hudak (editor), Chad Wittkop (editor) and Patrick I. McLauglin (editor))
Field Guide (Geological Society of America) (September 2011) 24: 83-99

Abstract

The western Upper Peninsula of Michigan is well known for hosting significant concentrations of copper in copper-dominated deposits. Most of the copper is hosted by rocks of the Mesoproterozoic Midcontinent Rift. Copper deposits in the western Upper Peninsula can be subdivided into two overlapping world-class copper mining districts. The Keweenaw Peninsula native copper district produced 11 billion lbs of copper and a lesser unknown but significant quantity of silver. Native copper deposits in this district are stratiform and hosted by tops of rift-filling subaerial basaltic lava flows and interflow coarse clastic sedimentary rocks. These deposits are interpreted to be the result of mineralizing hydrothermal fluids derived from rift-filling basaltic volcanic rocks that migrated upwards, driven by late Grenvillian compression of the rift some 40-50 million years following cessation of active rifting. The Porcupine Mountains sediment-hosted copper district produced or potentially will produce 5.5 billion lbs of copper and 54 million ounces of silver. These stratiform/stratabound deposits are hosted in rift-related black to gray shale and siltstone and dominated by chalcocite rather than native copper. Chalcocite is interpreted to be the result of introduction of copper-bearing fluids during diagenesis and lithification of host sediments. At the now-closed White Pine Mine, the chalcocite mineralizing event was followed by a second stage of native copper deposition that demonstrates a spatial and temporal overlap of these two world-class mining districts. While these two districts have been dormant since 1996, favorable results from recent exploration at Copperwood suggest a revival of the mining of copper-dominated deposits in the western Upper Peninsula of Michigan.


ISSN: 2333-0937
EISSN: 2333-0945
Serial Title: Field Guide (Geological Society of America)
Serial Volume: 24
Title: Copper deposits of the western Upper Peninsula of Michigan
Title: Archean to Anthropocene; field guides to the geology of the Mid-Continent of North America
Author(s): Bornhorst, Theodore J.Barron, Robert J.
Author(s): Miller, James D.editor
Author(s): Hudak, George J.editor
Author(s): Wittkop, Chadeditor
Author(s): McLauglin, Patrick I.editor
Affiliation: Michigan Technological University, A. E. Seaman Mineral Museum, Houghton, MI, United States
Affiliation: University of Minnesota-Duluth, Department of Geological Sciences, Duluth, MN, United States
Pages: 83-99
Published: 201109
Text Language: English
Publisher: Geological Society of America, Boulder, CO, United States
References: 49
Accession Number: 2012-009895
Categories: Economic geology, geology of ore deposits
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. strat. col., 1 table, geol. sketch maps
N46°45'00" - N47°28'00", W89°00'00" - W87°42'00"
Secondary Affiliation: Natural Resources Research Institute, USA, United StatesMinnesota State University, USA, United StatesWisconsin Geological and Natural History Survey, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201205
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