Quartzite and biotite schist in fault contact; Middle Proterozoic metasedimentary rocks; southern Belt province (IDYm;0)

State	Idaho
Name	Quartzite and biotite schist in fault contact; Middle Proterozoic metasedimentary rocks; southern Belt province
Geologic age	Middle Proterozoic
Original map label	Y2nm
Comments	One large polygon, assigned to Y2nm on ID001 is here changed to Y3sm4. The "quartzite" here is argillized feldspathic metasandstone with argillite mud chips, as in the Mt. Shields Fm of the Missoula Gp (Y4n). This is in fault contact with underlying biotite schist and quartzite, that resemble metamorphosed Apple Creek Fm, intruded by gabbroic sills with associated copper skarns (Y3sm), (Michael O'Neill, oral communication, 2004). These rocks have been mapped as Helena and Empire (Y3), Spokane Fm (Y2) and Greyson Fm (Y1) on ID025, as Helena Fm and Lemhi Gp on ID184, and as Precambrian undivided on ID111).
Primary rock type	quartzite
Secondary rock type	mica schist
Other rock types	meta-argillite; calc-silicate rock; gabbro; skarn
Lithologic constituents	Major Metamorphic > Quartziteargillized feldspathic quartzite, Missoula Gp? Minor Metamorphic > Argillite (Greenschist)argillite, silty argillite, siltite, Spokane and Greyson Fms? Metamorphic > Schist (Amphibolite, epidote-amphibolite)biotite schist, Lemhi Gp, Apple Creek Fm? Incidental Metamorphic > Skarn (Greenschist)chalcopyrite in green skarn marginal to gabbro sills Igneous > Plutonic > Gabbroicgabbroic sills in Lemhi Gp, Apple Creek Fm? Metamorphic > Hornfels (Greenschist)tremolite-actinolite calc-silicate hornfels after Helena dolomite?
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. [http://pubs.er.usgs.gov/publication/i2765] Mitchell V.E.. and Bennett, E.H., 1979, Geologic map of the Elk City quadrangle, Idaho: Moscow, Idaho, Idaho Bureau of Mines and Geology, Geologic Map Series, Elk City 2o Quadrangle, scale 1:250,000. Ruppel, E.T., O'Neill, J.M., and Lopez, D.A., 1993, Geologic map of the Dillon 1o x 2o quadrangle, Idaho and Montana: U.S. Geological Survey Miscellaneous Investigations Series, Map I-1803-H, 1:250,000 scale. [http://pubs.er.usgs.gov/publication/i1803H]
Geographic coverage	Lemhi