Leadmine Pond Gneiss is a new informal unit, named for Leadmine Pond in Sturbridge, MA, where the largest section through the unit is exposed. It is also exposed in several thin, structurally isolated belts to the west. Unit is characterized by medium-gray to white plagioclase-quartz-biotite gneiss with interlayered biotite-rich gneiss and amphibolite. Contains subordinate thin units of schist, quartzite, granofels, sillimanite-bearing gneisses, and calc-silicate rocks. Rocks assigned to the Leadmine Pond were previously considered gneiss members interstratified with schists of the Hamilton Reservoir Formation. Interpretation here is that unit is Precambrian(?) to Ordovician(?) basement unconformably underlying Rangeley Formation.

Source: GNU records (USGS DDS-6; Reston GNULEX).