Geochemical Constraints on the Origin of the Sterling Hill and Franklin Zinc Deposits, and the Furnace Magnetite Bed, Northwestern New Jersey
Published:January 01, 2001
Craig A. Johnson, 2001. "Geochemical Constraints on the Origin of the Sterling Hill and Franklin Zinc Deposits, and the Furnace Magnetite Bed, Northwestern New Jersey", Part I. Proterozoic Iron and Zinc Deposits of the Adirondack Mountains of New York and the New Jersey Highlands Part II. Environmental Geochemistry and Mining History of Massive Sulfide Deposits in the Vermont Copper Belt, John F. Slack, Jane M. Hammarstrom, Robert R. Seal
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The Purpose of this chapter is to review two aspects of the geochemistry of the Sterling Hill and Franklin zinc-ironmanganese deposits and the Furnace magnetite bed that underlies the Franklin deposit. These are (1) oxidation and sulfidation states determined from heterogeneous phase equilibria, and (2) stable isotopic compositions determined from analyses of carbonate, silicate, oxide, and sulfide minerals. The data place constraints on the genesis of the ores, which is the topic of the final section of the chapter. This review draws heavily from the results of my own dissertation research on Sterling Hill (Johnson, 1990; Johnson et al., 1990a) and from recent and continuing projects (Johnson et al., 1990b, Johnson, 1994, 1996, 1997; Volkert et al., 2000); it also includes the sulfur isotope results obtained by Ault (1957). For a complete review of the geology of the deposits, the reader is referred to the chapter by Metsger (2001), and to Metsger et al. (1958) and Frondel and Baum (1974). A complete catalog of the extensive literature on the deposits is given by Dunn (1995).
The Sterling Hill and Franklin deposits are located in northwestern New Jersey within the Reading Prong-Hudson Highlands terrane, which is a belt of Mesoproterozoic sedimentary and igneous rocks that was regionally metamorphosed during the Grenvillian orogeny at about 1.0 Ga. Although the question has arisen as to whether the zinc and associated metals in these deposits were emplaced before or after the metamorphic event, it is now clear from structural, geochronologic, and phase equilibrium studies
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Part I. Proterozoic Iron and Zinc Deposits of the Adirondack Mountains of New York and the New Jersey Highlands Part II. Environmental Geochemistry and Mining History of Massive Sulfide Deposits in the Vermont Copper Belt
This First day of the field trip visits Proterozoic iron deposits at the Podunk and Skiff Mountain iron mines, in the eastern Adirondack Mountains of New York state. Included are roadcuts to see representative lithologies and structures in the region surrounding the iron deposits. The origin of these iron deposits has been controversial, but studies by Foose and McLelland (1995) and more recently by McLelland et al. (2001b, 2001c) provide strong evidence for a high-temperture, intramagmatic origin related to late stages the Lyon Mountain Granite and correlative intrusions during the latter part of the 1090 to 1030 Ma Ottawan orogeny. The great majority of the deposits consist of low Ti magnetite ore accompanied by apatite and aegerine-augite. The apatite has high concentrations of rare-earth elements (REE) indicating to Foose and McLelland (1995) that the deposits are of Kiruna (REE-Au-U-Cu) type. This is further supported by persistent sodic (i.e., albitic) alteration associated with the ores. Most of the iron ores appear to be undeformed although they may occur in strained host rocks. Deposits are intimately associated with late tectonic to post-tectonic Lyon Mountain Granitic Gneiss that was emplaced at ca. 1055 Ma, during the waning stages of the ca. 1090 to 1030 Ma Ottawan Orogeny.