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Portage Lake Volcanics, Keweenaw County, Michigan, USA i
Regional Level Types
Portage Lake Volcanics - not defined -
Keweenaw County County
Michigan State
USA Country

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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

Mindat Locality ID:

127388

Long-form identifier:

mindat:1:2:127388:8

GUID (UUID V4):

a85aa36b-b6a2-46cf-8f20-9169752d3079

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

ⓘ 'Chlorite Group'

5 valid minerals.

Detailed Mineral List:

Formula: CaCO₃

References:

Heinrich, E. W., Robinson, George Willard (2004) Mineralogy of Michigan (2nd ed.) A.E. Seaman Mineral Museum and Michigan Technological University, Houghton, MI. 252pp.

ⓘ 'Chlorite Group'

References:

Heinrich, E. W., Robinson, George Willard (2004) Mineralogy of Michigan (2nd ed.) A.E. Seaman Mineral Museum and Michigan Technological University, Houghton, MI. 252pp.

Formula: (Mg,Fe)₉((Si,Al)₈O₂₀)(OH)₁₀ · nH₂O

References:

Heinrich, E. W., Robinson, George Willard (2004) Mineralogy of Michigan (2nd ed.) A.E. Seaman Mineral Museum and Michigan Technological University, Houghton, MI. 252pp.

Formula: CaAl₂Si₄O₁₂ · 4H₂O

References:

Heinrich, E. W., Robinson, George Willard (2004) Mineralogy of Michigan (2nd ed.) A.E. Seaman Mineral Museum and Michigan Technological University, Houghton, MI. 252pp.

Formula: SiO₂

References:

Heinrich, E. W., Robinson, George Willard (2004) Mineralogy of Michigan (2nd ed.) A.E. Seaman Mineral Museum and Michigan Technological University, Houghton, MI. 252pp.

Formula: Ca(Al₂Si₄O₁₂) · 2H₂O

References:

Heinrich, E. W., Robinson, George Willard (2004) Mineralogy of Michigan (2nd ed.) A.E. Seaman Mineral Museum and Michigan Technological University, Houghton, MI. 252pp.

Gallery:

List of minerals arranged by Strunz 10th Edition classification

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

List of minerals for each chemical element

H	Hydrogen
H	ⓘ Corrensite	(Mg,Fe)₉((Si,Al)₈O₂₀)(OH)₁₀ · nH₂O
H	ⓘ Laumontite	CaAl₂Si₄O₁₂ · 4H₂O
H	ⓘ Wairakite	Ca(Al₂Si₄O₁₂) · 2H₂O
C	Carbon
C	ⓘ Calcite	CaCO₃
O	Oxygen
O	ⓘ Calcite	CaCO₃
O	ⓘ Corrensite	(Mg,Fe)₉((Si,Al)₈O₂₀)(OH)₁₀ · nH₂O
O	ⓘ Laumontite	CaAl₂Si₄O₁₂ · 4H₂O
O	ⓘ Quartz	SiO₂
O	ⓘ Wairakite	Ca(Al₂Si₄O₁₂) · 2H₂O
Mg	Magnesium
Mg	ⓘ Corrensite	(Mg,Fe)₉((Si,Al)₈O₂₀)(OH)₁₀ · nH₂O
Al	Aluminium
Al	ⓘ Corrensite	(Mg,Fe)₉((Si,Al)₈O₂₀)(OH)₁₀ · nH₂O
Al	ⓘ Laumontite	CaAl₂Si₄O₁₂ · 4H₂O
Al	ⓘ Wairakite	Ca(Al₂Si₄O₁₂) · 2H₂O
Si	Silicon
Si	ⓘ Corrensite	(Mg,Fe)₉((Si,Al)₈O₂₀)(OH)₁₀ · nH₂O
Si	ⓘ Laumontite	CaAl₂Si₄O₁₂ · 4H₂O
Si	ⓘ Quartz	SiO₂
Si	ⓘ Wairakite	Ca(Al₂Si₄O₁₂) · 2H₂O
Ca	Calcium
Ca	ⓘ Calcite	CaCO₃
Ca	ⓘ Laumontite	CaAl₂Si₄O₁₂ · 4H₂O
Ca	ⓘ Wairakite	Ca(Al₂Si₄O₁₂) · 2H₂O
Fe	Iron
Fe	ⓘ Corrensite	(Mg,Fe)₉((Si,Al)₈O₂₀)(OH)₁₀ · nH₂O

Other Regions, Features and Areas containing this locality

North America

Lake SuperiorLake

North America PlateTectonic Plate

Mid-continent DomainDomain

USA

Midcontinent RiftGeologic Province

This page contains all mineral locality references listed on mindat.org. This does not claim to be a complete list. If you know of more minerals from this site, please register so you can add to our database. This locality information is for reference purposes only. You should never attempt to visit any sites listed in mindat.org without first ensuring that you have the permission of the land and/or mineral rights holders for access and that you are aware of all safety precautions necessary.

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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