Abstract

The pre-Caledonian NYF Skoddefjellet pegmatite in Wedel Jarlsberg Land, Svalbard, contains xenotime-(Y) that is partly replaced by fluorapatite-hingganite-(Y) reaction coronas. Hingganite-(Y) contains up to 2.0 wt.% of Gd2O3, 4.7 wt.% of Dy2O3, 3.3 wt.% of Er2O3 and 5.5 wt.% of Yb2O3. Such unusual, previously undescribed, xenotime-(Y) breakdown was caused by Ca- and F-bearing fluids interacting with the pegmatite. The occurrence of hinnganite-(Y) as a breakdown product of xenotime-(Y) implies that a Be-bearing phase (beryl in this case) was also involved in the reaction. There are few Ca-bearing primary phases in the pegmatite, indicating that the source of fluid was probably located in the generally Ca-richer host rocks (metasediments), though the fluid composition was modified during metasomatism of the pegmatite (i.e. beryl dissolution).

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