The unique pyrite-chalcopyrite deposit of the Eustis mine is described in detail. Attention is directed to its association with sodic rocks and to the localization of pyrrhotite and cubanite in the ore.The country rocks comprise schistose sodic porphyry, muscovite schist that has resulted from the metamorphism of the porphyry, and "green rock," a massive carbonate rock that is largely a hydrothermal alteration product of the schist. A study of the chemical analyses of these genetically related rock types is presented.The ore bodies consist of four large pyrite-chalcopyrite lenses arranged en echelon and extending down the dip of the enclosing schist for 6,500 feet to the present (1935) depth of mining. High temperature minerals, including anthophyllite and exsolved pyrrhotite and cubanite, have been localized where the chalcopyrite ore-body has been metamorphosed by the intrusion of a 40-foot camptonite dike.The source of the ore solutions is not definitely known, but it is thought that they came, not directly from the porphyry, but from a common magma, a magma characterized by the ability to yield sodic rocks and associated pyritic ore-bodies.

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