Most of the large magnetite ore bodies of the Highlands of northern New Jersey are lens or pod-shaped, and have sharply defined contacts which conform to the foliation of the country rock. Structural and microscopic evidence indicates that these deposits were emplaced by displacement as well as replacement of the enclosing rocks. The ore solutions were end-phase aqueo-igneous differentiates of the same magma from which the granitic gneisses of the area were derived. Deposition of the ore was preceded by the injection of pegmatites and followed by hydrothermal solutions. These processes were continuous and overlapping. The contact zone between a well foliated gneiss and a later intrusive is believed to have afforded a structural weakness which in most places controlled the loci of ore deposition.

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