PETROLOGY OF A BRECCIATED METASYENITE, TUPPER LAKE, NEW YORK

A small breccia zone south of Tupper Lake, N.Y. was studied to determine the origin of calcite veins that fill the fractures. The study area is along the west side of Route 30, about 5 miles south of the village of Tupper Lake. The host rock is metasyenite, approximately 1.1 billion years old. Within the metasyenite are brecciated zones filled with calcite and, locally, pyrite. Petrographic and electron microprobe analyses show that the metasyenite consists predominantly of potassium feldspar, with lesser amounts of quartz, hornblende, plagioclase feldspar, magnetite and apatite. Several relatively large grains of zircon are also present. Alteration minerals include chlorite, biotite and calcite. The calcite veins are a late feature, formed during brittle deformation of the rocks after the Grenville orogenic event. Carbon and oxygen isotopes were analyzed in duplicate. Delta 13C values averaged -4.303 per mil; the delta 18O values averaged -14.927 per mil. Both the carbon and oxygen isotopic compositions are consistent with the calcite being deposited from fluids that were evolved meteoric water or connate brines, but not of magmatic or mantle origin. This implies that the source of the calcite was from overlying layers of marble, frequent in the Adirondacks, that were dissolved and transported by water that originated at the surface.