Kurt C. Friehauf - Dept. of Physical Sciences, Kutztown
Univ., Kutztown, PA 19530
Robert C. Smith, II - Pennsylvania Geol. Survey,
Harrisburg, PA 17105
Richard A. Volkert - New Jersey Geol. Survey, Trenton, NJ, 08625
Friehauf,
Kurt C., Smith, Robert C., II, and Volkert, Richard A., 2001, Comparison of the
Geology of Proterozoic Iron Oxide Deposits in the Adirondack and Mid-Atlantic
Belt of Pennsylvania, New Jersey, and New York: in Potter, Mike, ed., Hydrothermal Iron-Oxide Copper-Gold
& Related Deposits A Global
Perspective - Volume 2: Australian Mineral Foundation Monograph series, p.
xxx-xxx. (in press)
Proterozoic hydrothermal iron oxide deposits occur within two metallogenic belts in the northeastern U.S.: the Adirondack region, and the Mid-Atlantic (Reading Prong) belt. A 175 km wide belt of Paleozoic cover separates these two regions, although some iron deposits occur in Proterozoic rocks near the unconformity, suggesting a possible continuation beneath the cover. Although potentially part of the same continuous metallogenic province sharing similar mineralogy, host rock composition, hydrothermal alteration, deposits in the two regions differ in degree of deformation. Differences in the degree of metamorphic deformation fuel the debate of the relative timing of mineralization, igneous activity, and metamorphism. Generally less deformed textures in the Adirondack deposits led workers in the New York deposits to conclude iron ores in the Adirondacks are associated with anorogenic granites that post-date peak metamorphism. Folded iron ores in granitic gneiss of the Mid-Atlantic belt suggest some deposits in eastern Pennsylvania, northern New Jersey, and southern New York predate peak metamorphism. REE-enriched deposits in both belts are characterized by abundant apatite, tourmaline, and manganese concentrations, as well as the presence of hematite-chlorite alteration in addition to magnetite. Unlike deposits hosted exclusively within granite gneisses, deposits within supracrustal rocks commonly contain significant sulphides and so are potential hosts for copper mineralization.