INVESTIGATING THE ORIGIN OF PEGMATITE DIKES IN UNIONVILLE, PENNSYLVANIA AND THE GEOCHEMICAL INTERACTIONS WITH SURROUNDING SERPENTINITES
Due to historical mining in the area, outcrop is rare; therefore, general field relationships were determined by presence of localized pits and tailings piles. Existing maps largely disagree with location of pegmatite mine pits, suggesting existing maps may require revision. Pegmatite samples varied in texture by location but maintained a consistent mineralogy (Ab>Qtz>Ms>Tur). Most pegmatite thin sections exhibit some foliation, representing strain imposed on the rocks. Intermediary ‘reaction rocks’ are generally microcrystalline with extensive veining and brecciation, although they exhibit a gradient of textures depending on proximity to the pegmatite or serpentinite.
Mineralogical and geochemical data indicates that the Unionville Pegmatites are within the Muscovite-Rare Element pegmatite class. Concentrations of Si, Ce, Sr, Ni, and Cr reveal a consistent compositional gradient from pegmatite to serpentinite in strong agreement with textures observed in thin section. Examination of this geochemical gradient allows for an understanding of component exchange between pegmatites and serpentinites. Plotting trace element concentrations on petrographic discrimination diagrams suggests that the Unionville Pegmatites originated in a volcanic arc setting rather than an anatectic/metamorphic setting.