Dysprosian xenotime-(Y) from the Annie Claim #3 granitic pegmatite, southeastern Manitoba, Canada: Evidence of the tetrad effect?

Dysprosian xenotime-(Y) was found in the Annie Claim #3 pod of lepidolite-s ubtype granitic pegmatite within the Greer Lake intrusion of pegmatitic gra nite, in the Archean Bird River Subprovince of the Superior Province, in so utheastern Manitoba. It occurs as microscopic inclusions in spessartine and as discrete crystals, both enclosed in ferroan muscovite, also associated with manganocolumbite - manganotantalite, microlite, zircon and apatite. Th e xenotime-(Y) contains up to 14.88 wt.% Dy2O3 (and 7.59 wt.% Gd2O3, 3.31 w t.% Tb2O3), the highest concentration of Dy so far observed in this mineral . In chondrite-normalized REE patterns, the positive Tb anomaly is even hig her than that of Dy. Along with xenotime-(Y) and xenotime-(Yb) from other g ranitic pegmatites, altered granites and alpine veins, the Annie Claim #3 x enotime-(Y) shows prominent double segmenting of the Gd to Lu sequence, asc ribed by some authors to the tetrad effect in geological materials generate d from, or affected, by aqueous media. Analytical problems could not produc e this effect in the xenotime samples.