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Portage Lake Volcanics, Keweenaw County, Michigan, USAi
Regional Level Types
Portage Lake Volcanics- not defined -
Keweenaw CountyCounty
MichiganState
USACountry

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Latitude & Longitude (WGS84):
47° North , 88° West (est.)
Estimate based on other nearby localities or region boundaries.
Margin of Error:
~74km
GRN:
N32W44
Mindat Locality ID:
127388
Long-form identifier:
mindat:1:2:127388:8
GUID (UUID V4):
0


The Portage Lake Volcanics (PLV) are the host rock unit for both native and sulfide copper deposits. The total thickness of the PLV is about 10 kilometers, of which 5 kilometers are exposed on the Keweenaw Peninsula (Cannon, 1992). The Portage Lake Volcanics consist of over 200 subaerial flood basalt lava flows with occasional interflow sediment layers (Bornhorst, 1997). A typical lava flow is about 10 to 20 meters thick and consists of a massive interior and the uppermost 5 to 20% being a vesicular flow top. About one-fourth of the individual flow tops are brecciated (White, 1968). Interflow sandstones and conglomerates, with a thickness of up to 40 meters, make up less than 5 volume percent of the PLV (Merk and Jirsa, 1982). Both the tops of lava flows, especially brecciated zones, and the interflow conglomerates host native copper ore deposits. Massive interiors do not contain copper or secondary minerals except along fractures and faults (Bornhorst, 1997). On the Keweenaw Peninsula, the PLV is overlain by Oronto Group sediments, including the Copper Harbor Conglomerate, Nonesuch Shale, and Freda Sandstone. The base of the PLV is cut by the once normal, graben bounding Keweenaw Fault, now a major high angle reverse fault with several kilometers of displacement (Bornhorst, 1997).

Select Mineral List Type

Standard Detailed Gallery Strunz Chemical Elements

Mineral List


5 valid minerals.

Gallery:

List of minerals arranged by Strunz 10th Edition classification

Group 4 - Oxides and Hydroxides
ⓘQuartz4.DA.05SiO2
Group 5 - Nitrates and Carbonates
ⓘCalcite5.AB.05CaCO3
Group 9 - Silicates
ⓘCorrensite9.EC.60(Mg,Fe)9((Si,Al)8O20)(OH)10 · nH2O
ⓘWairakite9.GB.05Ca(Al2Si4O12) · 2H2O
ⓘLaumontite9.GB.10CaAl2Si4O12 · 4H2O
Unclassified
ⓘ'Chlorite Group'-

List of minerals for each chemical element

HHydrogen
Hⓘ Corrensite(Mg,Fe)9((Si,Al)8O20)(OH)10 · nH2O
Hⓘ LaumontiteCaAl2Si4O12 · 4H2O
Hⓘ WairakiteCa(Al2Si4O12) · 2H2O
CCarbon
Cⓘ CalciteCaCO3
OOxygen
Oⓘ CalciteCaCO3
Oⓘ Corrensite(Mg,Fe)9((Si,Al)8O20)(OH)10 · nH2O
Oⓘ LaumontiteCaAl2Si4O12 · 4H2O
Oⓘ QuartzSiO2
Oⓘ WairakiteCa(Al2Si4O12) · 2H2O
MgMagnesium
Mgⓘ Corrensite(Mg,Fe)9((Si,Al)8O20)(OH)10 · nH2O
AlAluminium
Alⓘ Corrensite(Mg,Fe)9((Si,Al)8O20)(OH)10 · nH2O
Alⓘ LaumontiteCaAl2Si4O12 · 4H2O
Alⓘ WairakiteCa(Al2Si4O12) · 2H2O
SiSilicon
Siⓘ Corrensite(Mg,Fe)9((Si,Al)8O20)(OH)10 · nH2O
Siⓘ LaumontiteCaAl2Si4O12 · 4H2O
Siⓘ QuartzSiO2
Siⓘ WairakiteCa(Al2Si4O12) · 2H2O
CaCalcium
Caⓘ CalciteCaCO3
Caⓘ LaumontiteCaAl2Si4O12 · 4H2O
Caⓘ WairakiteCa(Al2Si4O12) · 2H2O
FeIron
Feⓘ Corrensite(Mg,Fe)9((Si,Al)8O20)(OH)10 · nH2O

Other Regions, Features and Areas containing this locality

North AmericaContinent
North America PlateTectonic Plate
USA

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References

White, W.S. (1968) The Native Copper Deposits of Northern Michigan, in Ridge, J.D., eds., Ore Deposits of the United States, 1933-1967 (the Graton Sales volume): American Institute of Mining, Metallurgical and Petroleum Engineering, New York, p. 303-325.
Merk, G.P., and Jirsa, M.A. (1982) Provenance and tectonic significance of the Keweenawan interflow sedimentary rocks: Geological Society of America Memoir 156, p. 97-105.
Cannon, W.F. (1992) The Midcontinent rift in the Lake Superior region with emphasis on its geodynamic evolution: Tectonophysics, v. 213, p. 41-48.
Bornhorst, T.J. (1997) Tectonic context of native copper deposits of the North American Midcontinent Rift System, in Ojakangas, R.W., Dickas, A.B., and Green, J.C., eds., Middle Proterozoic to Cambrian Rifting, Central North America: Boulder, Colorado, Geological Society of America Special Paper 312.
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