Several theories of origin have been proposed for the emery deposits associated with the Cortlandt series of basic plutonics which lie south and east of Peekskill, New York. These are: (1) magmatic segregation; (2) absorption (assimilation) of aluminous sedimentary material (Manhattan schist); and (3) contact-metamorphism, under which two different stages of development have been considered—(a) hydrothermal contact-metamorphism; and (b) deposition in marginally solidified endomorphosed norite and exomorphosed schist by emanations released from the still-liquid portions of the magma.
Detailed field and petrologic studies of the emery have been made at Emery Hill, where the principal deposits are located. New evidence disclosed objections to the earlier theories and led to the formulation of a revised theory of genesis. The emery deposits are believed to be contact-metamorphic (pyrometasomatic) in origin, but were formed at a much earlier stage than previously thought. They are believed to have been formed by emanations that were released by the magma during intrusion and these emanations passed through the country rock (Manhattan schist) only a short distance in advance of the magma. Thus, the formation of emery took place during the early liquid-magmatic stage of the basic Cortlandt intrusives.
Detailed descriptions of the emery, the rock types, and their relations are given. Reference is made to usage of the terms “hornfels” and “endomorphism” because of their significance to a study of the emery deposits.