Magnetite Mineralization of the Hammondville Pluton: Poly-Phase Kiruna Type IOCG Magnetite-Apatite Deposits in the Lyon Mountain Granite

• Main Author: Geer, Phillip
• Format: Thesis
• Language: unknown
• Published: University of Massachusetts Amherst 2020
• Subjects: Kiruna; Quadrangle
• Online Access: https://dx.doi.org/10.7275/19182236; https://scholarworks.umass.edu/masters_theses_2/965

Recent mapping of the Eagle Lake Quadrangle, NY, coupled with whole-rock geochemistry and microscopy has offered insight into the petrogenesis of the magnetite-apatite deposits of the Hammondville mining district in the eastern Adirondack Mountains. This study provides insight into the magmatic history of the ca. 1060-1050 Ma Lyon Mountain Granite (Hammondville Pluton) which is intimately related to, and hosts the deposits in this area. Magnetite seams are commonly surrounded by well layered magnetite gneiss, which typically parallel the seams, although in some outcrops appear to be slightly truncated by them. Mineralization is generally concordant with the weak layering found throughout the rest of the pluton, and similarly lacks a pervasive metamorphic fabric. Sub-solidus deformation is recorded in some localized shear zones that occur in both the seams and host-granite indicating post-crystallization and post-mineralization deformation events. These episodes could have provided conduits for fluids responsible for growing younger zircon that past workers dated and interpreted as a separate time of mineralization. We conclude that magnetite mineralization likely occurred as separate magma, or magnetite rich fluid, injected into the Lyon Mountain Granite either as a syn-magmatic process, or while it was still a crystalline mush.