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Argillite, quartzite, and calc-silicate rock; Middle Proterozoic Yellowjacket Formation; southern Belt province

Intermediate Precambrian sediments, dark-colored, feldspathic quartzite with minor limestone beds of southern Idaho.
State Idaho
Name Argillite, quartzite, and calc-silicate rock; Middle Proterozoic Yellowjacket Formation; southern Belt province
Geologic age Middle Proterozoic
Comments Y1s represents the Yellowjacket Fm, which consists of calcareous, shallow-water deposits of metasandstone and siltite, below the Hoodoo Quartzite (ID025, ID090). Mudchips and scapolite after evaporite indicate shallow water deposition. These rocks are metamorphosed to upper greenschist facies. On map ID001 use of the Yellowjacket name and Y1s symbol was extended to other gray quartzites and siltites that are widespread in the Salmon River Mountains and northern Lemhi Range. In accordance with ID025 and ID090, these rocks are now assigned to the Lemhi Group (Y3s), and where possible, polygons on map ID001 have been re-classified accordingly.
Primary rock type meta-argillite
Secondary rock type quartzite
Other rock types calc-silicate rock
Lithologic constituents
Major
Metamorphic > Argillite (Greenschist)calcareous argillite and siltite, with local mud chips
Minor
Metamorphic > Quartzite (Greenschist)quartzitic beds, 70% quartz, 15% feldspar, 15% biotite
Metamorphic > Skarn (Greenschist)scapolitic calc-silicate rock after calcareous evaporitic sediment
Map references
Bond, J.G., Kauffman, J.D., Miller, D.A., and Venkatakrishnan, Ramesh, 1978, Geologic map of Idaho: Moscow, Idaho, Idaho Bureau of Mines and Geology, with contributions from U.S. Geological Survey, scale 1:500,000.
Unit references
Bond, J.G., Kauffman, J.D., Miller, D.A., and Venkatakrishnan, Ramesh, 1978, Geologic map of Idaho: Moscow, Idaho, Idaho Bureau of Mines and Geology, with contributions from U.S. Geological Survey, scale 1:500,000.
Evans, K.V. and Green, G.N., 2003, Geologic map of the Salmon National Forest and vicinity, east-central Idaho: U.S. Geological Survey Geological Investigations Series I-2765, scale 1:100,000 with pamphlet, 19 p.
Lund, Karen, in press, Geology of the Payette National Forest, Valley, Idaho, Washington and Adams counties, Idaho: U.S. Geological Survey Professional Paper 1666, scale 1:100,000.
Tysdal, R.G., 2000, Revision of Middle Proterozoic Yellowjacket Formation, central Idaho: U.S. Geological Survey Professional Paper 1601-A, p. A1-A13.
Counties Custer - Idaho - Lemhi - Valley