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.