scholarly journals Copper Isotope Constraints on the Genesis of the Keweenaw Peninsula Native Copper District, Michigan, USA: A Comment

Minerals ◽  
2018 ◽  
Vol 8 (11) ◽  
pp. 506 ◽  
Author(s):  
Alex Brown
Keyword(s):  
Copper Isotope ◽  
Native Copper ◽  
Keweenaw Peninsula

Well-grouped δ65Cu values (−0.3 to +0.8‰)  from120 samples of native copper fromthe Keweenaw native copper district have been attributed [...]

scholarly journals Copper Isotope Constraints on the Genesis of the Keweenaw Peninsula Native Copper District, Michigan, USA: Reply

Minerals ◽  
2018 ◽  
Vol 8 (11) ◽  
pp. 508
Author(s):  
Theodore Bornhorst ◽  
Ryan Mathur
Keyword(s):  
Copper Isotope ◽  
Native Copper ◽  
Opportunity To Respond ◽  
Keweenaw Peninsula

We appreciate the opportunity to respond to Brown’s [...]

Paleomagnetism of the native copper mineralization, Keweenaw Peninsula, Michigan

2019 ◽  
Vol 56 (9) ◽  
pp. 932-947 ◽  
Author(s):  
D.T.A. Symons ◽  
K. Kawasaki
Keyword(s):  
Remanent Magnetization ◽  
White Pine ◽  
Native Copper ◽  
Time Limits ◽  
Clastic Rocks ◽  
Copper Mineralization ◽  
Lake Formation ◽  
World Class ◽  
Keweenaw Peninsula ◽  
Basaltic Flow

The age and genesis of Michigan’s world-class native copper deposits are poorly constrained. The copper is hosted by basaltic flow tops and conglomeratic interbeds of the 1095 ± 2 Ma Keweenawan Portage Lake Formation. Progressive thermal demagnetization isolates stable hematite remanent magnetization components at 28 paleomagnetic sites. Paleomagnetic tilt tests show that magnetite in massive flow interiors is primary (1095 ± 2 Ma) and that hematite throughout the formation is syntectonic. The altered cupriferous deposits contain primary ∼1095 Ma and secondary ∼1053 Ma hematite in various proportions. The Caledonia Mine’s basaltic mineralization carries the ∼1053 Ma hematite dominantly whereas the Delaware Mine’s conglomeratic interbed mineralization carries the ∼1095 Ma hematite dominantly. The ∼1095 Ma hematite is attributed mostly to magnetite exsolution during flow extrusion and to weathering oxidation between extrusion events. An infusion of epigenetic hydrothermal fluids emplaced the native copper with additional hematite and polarity self-reversing titanohematite at 1053 ± 7 Ma. Importantly, paleomagnetic evidence supports a 1053 ± 7 Ma age also for the White Pine stratiform sedimentary copper mineralization, for the oxidation of the Oronto Group clastic rocks to red beds, and for the time limits of major tectonic uplift and deformation on the Keweenaw Peninsula.

Tracing the Source of Native Copper Mineral Specimens with Copper Isotope Values

2016 ◽  
Vol 91 (4) ◽  
pp. 352-356 ◽  
Author(s):  
Marc Wilson ◽  
Debra L. Wilson ◽  
Ryan Mathur
Keyword(s):  
Copper Isotope ◽  
Native Copper ◽  
Copper Mineral

Age of native copper mineralization, Keweenaw Peninsula, Michigan

1988 ◽  
Vol 83 (3) ◽  
pp. 619-625 ◽  
Author(s):  
Theodore J. Bornhorst ◽  
James B. Paces ◽  
Norman K. Grant ◽  
John D. Obradovich ◽  
N. King Huber
Keyword(s):  
Native Copper ◽  
Copper Mineralization ◽  
Keweenaw Peninsula

Remagnetization in Keweenawan rocks. Part I: conglomerates

1981 ◽  
Vol 18 (3) ◽  
pp. 599-618 ◽  
Author(s):  
H. C. Palmer ◽  
H. C. Halls ◽  
L. J. Pesonen
Keyword(s):  
Igneous Rocks ◽  
Secondary Mineral ◽  
Native Copper ◽  
Late Precambrian ◽  
Normal Polarity ◽  
Keweenaw Peninsula ◽  
Partial Chemical

Conglomerate tests are used to show that Late Precambrian Keweenawan conglomerates on the Keweenaw Peninsula, Michigan and at Mamainse Point, Ontario have suffered a partial chemical remagnetization that predated tectonic tilting. At Mamainse Point the overprint was acquired during the final normal polarity stage of Keweenawan volcanism, whereas on the Keweenaw Peninsula it occurred after cessation of volcanism and has a maximum Late Freda Sandstone age. The extent of overprinting on the Keweenaw Peninsula increases westwards along a 40 km strike length in the Copper Harbor Conglomerate, and may at least in part be related to secondary mineral zonation (including native copper) in the underlying Portage Lake volcanics. It is shown that neither of the two overprinting episodes can be responsible for the reversal asymmetry observed in Keweenawan igneous rocks.

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