Mount Mineral Formation

(Probably correlates with Poplar Mountain Gneiss but is more aluminous) - Aluminous schist, amphibolite, and quartzite, undifferentiated; locally rich in garnet and kyanite, and with relict sillimanite and orthoclase from pre-Middle Ordovician metamorphism.
State Massachusetts
Name Mount Mineral Formation
Geologic age Proterozoic Z
Lithologic constituents
Major
Metamorphic > AmphiboliteAluminous schist, amphibolite, and quartzite, undifferentiated; locally rich in garnet and kyanite, and with relict sillimanite and orthoclase from pre-Middle Ordovician metamorphism.
Metamorphic > Metasedimentary > Metaclastic > QuartziteAluminous schist, amphibolite, and quartzite, undifferentiated; locally rich in garnet and kyanite, and with relict sillimanite and orthoclase from pre-Middle Ordovician metamorphism.
Metamorphic > SchistAluminous schist, amphibolite, and quartzite, undifferentiated; locally rich in garnet and kyanite, and with relict sillimanite and orthoclase from pre-Middle Ordovician metamorphism.
Comments Part of Bronson Hill Zone (Ordovician and Older Rocks). Single detrital zircon analyses from the muscovite-garnet bearing upper quartzite member of the Mount Mineral Formation yield ages of 459-439 Ma, indicating that the quartzite is younger than earliest Silurian and may correspond to the Clough Quartzite. Older grains include 1000 Ma, 900 Ma, and 600 Ma groups. Authors state that "drastic rethinking" is required if the rocks of the upper quartzite member of the Mount Mineral, which lie beneath 200 m of Ordovician plutonic rock, are actually Silurian, rather than Proterozoic. The middle mica schist and amphibolite member is shown as Ordovician(?) and the basal quartzite member as Proterozoic(?). The Mount Mineral overlies the Proterozoic Poplar Mountain Gneiss (Robinson and others, 1992) per MA016.
References

Zen, E-An (ed.), Goldsmith, R. (comp.), Ratcliffe, N.M. (comp.), Robinson, P. (comp.), Stanley, R.S. (comp.), Hatch, N.L., Jr., Shride, A.F., Weed, E.G.A., and Wones, D.R., 1983, Bedrock Geologic Map of Massachusetts: U.S. Geological Survey, Reston, VA, scale 1: 250,000.

https://pubs.er.usgs.gov/publication/70046713

Robinson, Peter, Tucker, R.D., Gromet, L.P., Ashendon, D.D., Williams, M.L., Reed, R.C. and Peterson, V.L., 1992, The Pelham Dome, central Massachusetts; stratigraphy, geochronology, and Acadian and Pennsylvanian structure and metamorphism, IN Robinson, Peter, and Brady, J.B., eds., Guidebook for field trips in the Connecticut Valley region of Massachusetts and adjacent states; Volume 1: University of Massachusetts, Geology Department Contribution, no. 66, New England Intercollegiate Geological Conference, 84th Annual Meeting, Amherst, MA, October, 9-11, 1992, p. 132-169.

NGMDB product
Counties Franklin - Hampshire