Abstract

The Zealand Station beryl (aquamarine) and molybdenite deposit is located 25 km northwest of Fredericton, New Brunswick, along the northeastern cusp of the Hawkshaw Granite, previously dated at 411 ± 1 Ma (U–Pb titanite), of the multiphase Devonian Pokiok Batholith. A late-stage, southeast-trending, pegmatite–aplite dyke has abundant aquamarine associated with pegmatitic sections. An exposure of a pegmatitic dyke is predominantly quartz and K-feldspar that exhibits a border, intermediate, and core zone. The main pegmatite–aplite dyke has been dated at 400.5 ± 1.2 Ma using U–Pb thermal ionization mass spectrometry on magmatic zircon. This is consistent with the 404 ± 8 Ma age using the chemical U–Th – total Pb isochron method from the pegmatitic beryl-rich section. These ages link these pegmatitic to aplitic dykes to the Allandale Granite, which is the youngest (402 ± 1 Ma by U–Pb on monazite) and most evolved phase of the Pokiok Batholith. The granitic aplite and pegmatite dyke samples are predominantly magnesian with one pegmatite sample being ferroan (FeOt/(FeOt +MgO) = 0.64–0.94); the samples are slightly potassic and calc-alkaline with strong peraluminosity (A/CNK = 1.23–4.76). The various phases of dykes were derived from magma with crustal A-type source characteristics similar to the Allandale Granite. The Sm–Nd isotope values for the aplite dyke (εNd(400) = –2.15) and the Allandale Granite (εNd(400) = –1.6) reflect some assimilation of metasediments relative to other phases of the Pokiok Batholith. The pegmatite and aplite dykes are high-level, rare-earth element pegmatite phases (Nb–Y–F-type) with some Li–Cs–Ta-type characteristics.

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