PRELIMINARY RESULTS OF NEW BEDROCK MAPPING OF THE SOUTHEASTERN PART OF THE PARADOX LAKE QUADRANGLE, NEW YORK

The eastern Adirondack Highlands of New York are an important location for understanding the geologic setting of low-Ti Kiruna-type magnetite-apatite mineral deposits with high concentrations of rare earth elements (REEs). Recent 1:12,000-scale mapping in a portion of the Paradox Lake quadrangle was undertaken to understand the relationship between the tectonic history of the Adirondacks and the emplacement of ore deposits and REEs. The quadrangle contains ca. >1203 Ma Grenville Supergroup paragneisses, a large exposure of the ca. 1154 Ma Marcy Anorthosite, and a variety of felsic intrusive rocks. The mapped area is the southeastern corner of the quadrangle, near the abandoned Harris and Paradox Lake mines. The map area is divided into northern and southern domains by the E-W-trending Paradox Lake. The northern domain exposes Whiteface-type anorthosite along the margin of the Marcy massif and mangeritic to charnockitic gneisses (ca. 1160-1140 Ma), all of which contain a NE-striking SE-dipping mylonitic fabric. Grenville Supergroup paragneisses consist of NW-SE-striking calc-silicate rocks, marble, and amphibolite, along with a biotite-rich granite gneiss of unknown age. Post-dating most rocks and penetrative fabric development is the Lyon Mountain Granite Gneiss (LMG); the host to the two iron mines. Northeast of the lake, N-S striking layering in the LMG is sub-parallel to foliation within the paragneisses, but locally it is at a high-angle to foliation in rocks along the margin of the massif possibly due to post-emplacement faulting. Two types of LMG occur: a pinkish-white microperthite granite, believed to be the primary composition, and a white to gray quartz-albite rock, associated with magnetite ore. South of Paradox Lake, rocks were strongly deformed into a dominant E-W orientation. A phase of large, isoclinal folding pre-dates the LMG and a younger phase of open folding post-dates all rocks. The southern area contains less LMG and a more diverse suite of supracrustal rocks, including khondalite. Controls on the N-S transition are under investigation, but might involve large-scale strain partitioning around the Marcy massif. Work is also underway to determine the timing and intensity of thermo-tectonic events and implications for ore deposition within the orogenic history of the eastern Adirondacks.