ON THE ENIGMATIC ORIGIN OF MAGNETITE IN THE BEDROCK OF NEW YORK CITY

High concentrations of magnetite have been found in mica schist in several locations in Manhattan, New York. The preliminary laboratory investigations have confirmed a range of 20% to 30% magnetite by weight, within the samples studied. Most of the magnetite occurrences are located at, or near, intrusive contacts and within muscovite-rich zones in biotite schist. Surprisingly, magnetite is not found in such high concentrations in hornblende schists or amphibolites. Unusual concentration of moderate to abundant magnetite in mica schist perhaps indicates release of iron oxide from the mafic components during thermal metamorphism or metasomatism. Geochemical investigations are underway to provide a viable mechanism for the observed magnetite concentrations in the mica schist of Manhattan.