Abstract

A list is given of 137 species of minerals which are found in the region near Franklin, New Jersey. It is shown that these may be classified genetically into five groups of varying importance. Of the whole number of species, 111 are found in the zinc ore-bodies and 98 in these only; 13 are found in granite pegmatities; 18 in iron ores of pegmatic origin; 26 in the Pre-cambrian limestone and 5 in the Paleozoic limestone. These five paragenetic groups are described, those of less importance first and then the main group of the zinc-ore minerals. A paragenetic table for this group shows four main subdivisions viz:

1.Primary Ores: 2. Pegmatite Contact Minerals, (a) Skams and Recrystallization Products; (b) Pneumatolytic Products: 3. Hydrothermal Vein Minerals: 4. Surface Oxidation Products.

Each of these groups is described with examples of characteristic mineral associations.

The origin of the zinc ores is discussed. The author’s theory is that metasomatic deposits of hydrated oxides and silicates of iron, manganese and zinc were formed by replacement in the white limestone and that these ore-bodies were changed to their present mineral composition during the Pre-cambrian regional metamorphism simultaneously with the recrystallization of the enclosing limestone. Subsequent intrusions of pegmatites produced recrystallization of the primary minerals near contacts, and formed skarns by interaction of ores and magmatic materials. Pneumatolytic products of the pegmatite magma also reacted with the primary ores to produce numerous vein minerals and as the temperature fell hydrothermal veins of great variety were formed in the ore-body. These products of pegmatite intrusion are extremely diverse mineralogically but of minor importance compared to the great mass of the primary franklinite-willemite-calcite-ores.

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