Sedimentary Exhalative Origin for Magnetite Deposits of the New Jersey Highlands

The New Jersey Highlands and contiguous Hudson (New York) Highlands host hundreds of small, worked-out magnetite mines, and the major zinc-oxide deposits of Franklin and Sterling Hill. The origin of the magnetite ore remains controversial. Two temporally distinct genetic models have been proposed for magnetite: 1) a pre-Ottawan, sedimentary exhalative model in which ores were deposited on or near the sea floor as precipitates from iron-enriched hydrothermal fluids; 2) a late Ottawan, fluid alteration model in which the current mineral composition of ores was derived from Fe-rich, alkaline fluids, associated with late episodes of granitic plutonism (Low-Ti Kiruna-type deposits), or in which deposits derived from metamorphogenic fluids circulating in a regional shear zone leached metals from host rocks and precipitated them in veins and faults. Detailed mapping of ore deposits and host rocks near Wanaque, NJ, Ringwood, NJ and Warwick, NY reveal that ore bodies are hosted by supracrustal rocks deposited in a back-arc basin. At Wanaque and Warwick, ores are stratiform and stratabound. Discordant ore bodies at Ringwood are associated with a feeder zone, presumed to have intersected the paleosurface at a steep angle. Sharply-layered quartz-diopside gneiss is spatially associated with ore at Wanaque and Warwick, and massive diopsidite is spatially associated with ore at all three locations. Diopsidite in these rocks is non-aluminous, iron-enriched and shares these characteristics with modern metalliferous sediments. Massive diopsidite and quartz-diopside gneiss are interpreted to be metamorphosed carbonate facies iron formation, and associated magnetite to be metamorphosed oxide-facies iron formation.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author