Much emphasis recently has been placed on the relative importance of replacement and injection in ore deposition. As a phase of this discussion much attention has been paid to included fragments in veins. Microscopic examination of ores reveals much information on these processes. Until the publication of the “Ore Magmas”1 many of the mineral relationships observed microscopically were attributed, and rightly so, it is believed, to replacement. There has been a growing tendency since then to interpret a later mineral as injected in the earlier, or as having consolidated from a more or less stationary ore magma.2 It seems worth while, therefore, to present some of the microscopic evidences of replacement or of possible injection. This does not necessarily mean that the process observed microscopically was the dominant one on a large scale, but it is at least strongly indicated.

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