Field Trip Day Two

Abstract

Abstract This Day of the field trip visits the large Chateaugay open pit of the Lyon Mountain group of iron mines, in the northern Adirondack Mountains, following by visits to roadcuts in the Adirondack Lowlands to the west, in the vicinity of the Balmat zinc mine. The Chateaugay open pit has superb exposures of iron ore remaining on walls and in the entrances to stopes, which clearly establish the geologic and paragenetic relations of the magnetite ores and yield compelling evidence for their high-temperature, intramagmatic origin via hydrothermal fluids (McLelland et al., 2001b, 2001c). A wide variety of rock types ranging from leucogranite to mineralized skarns are present. In the afternoon this day features stops at five roadcuts between the town of Gouverneur, New York, and the Balmat zinc mine to the east. These roadcuts provide a good overview of the regional geologic setting of the Balmat deposit, including stratigraphy, structure, deformation, and metamorphism. Whereas the geochronology in the Adirondack Highlands to the east is well established (e.g., McLelland et al., 2001c), the Lowlands is underlain mostly by metasedimentary rocks hence its precise age range is difficult to determine. One constraint is provided by U-Pb zircon ages of 1284 ±7 Ma, 1236 ± 6 Ma, and 1230 ± 33 Ma for the Gouverneur, Fish Creek, and Hyde School alaskite bodies, respectively, that occur in the Lowlands (Grant et. al., 1986; McLelland and Chiarenzelli, 1990; McLelland et al., 1992). Although these alaskite bodies were interpreted by Carl and Van Diver (1975) to