Zirconium-bearing accessory minerals in UK Paleogene granites: textural, compositional, and paragenetic relationships

Abstract

Abstract. The mineral occurrences, parageneses, textures, and compositions of Zr-bearing accessory minerals in a suite of UK Paleogene granites from Scotland and Northern Ireland are described. Baddeleyite, zirconolite, and zircon, in that sequence, formed in hornblende + biotite granites (type 1) and hedenbergite–fayalite granites (type 2). The peralkaline microgranite (type 3) of Ailsa Craig contains zircon, dalyite, a eudialyte-group mineral, a fibrous phase which is possibly lemoynite, and Zr-bearing aegirine. Hydrothermal zircon is also present in all three granite types and documents the transition from a silicate-melt environment to an incompatible element-rich aqueous-dominated fluid. No textures indicative of inherited zircon were observed. The minerals crystallized in stages from magmatic through late-magmatic to hydrothermal. The zirconolite and eudialyte-group mineral are notably Y+REE-rich (REE signifies rare earth element). The crystallization sequence of the minerals may have been related to the activities of Si and Ca, to melt peralkalinity, and to local disequilibrium.

A Recently Discovered Trachyte-Hosted Rare Earth Element-Niobium-Zirconium Occurrence in Northern Maine, Usa

“…Importantly, numerous EDS spectra obtained on the Zr-silicate phase indicate that this mineral contains small amounts of P and HREE, consistent with the results of detailed microbeam studies of zircon from other settings that show these elements can occur as crystallographic substitutions (e.g., Hoskin and Schaltegger, 2003). Noteworthy in this context is the HREE-rich hydrothermal zircon occurring in some peralkaline granites of Scotland that contains up to 0.99 wt % Dy2O3 and 1.27 wt % Yb2O3 (Belkin and Macdonald, 2021).…”