A REFINEMENT OF THE STRUCTURE OF FERRITUNGSTITE FROM KAEAS MOUNTAIN. YUKON, AND OBSERVATIONS ON THE TUNGSTEN PYROCHLORES

Ferritungstite occurs at the Flo property on Kalzas Mountain, near Mayo, Yukon. It is hosted by ferberite-bearing quartz veins, which form a stockwork in tourmalinized metasediments of the Grit Unit of the Windermere Supergroup. The ferritungstite replaces ferberite, and lines solution cavities, cleavages and crystal margins of the ferberite. Crystals are yellow to orange to brown octahedra up to 0.1 mm across. There are two generations of ferritungstite: an early Cs-bearing^generation, andalaterCs-freeone.Thecrystalstructureof Cs-freeferritungstite, Fd3m,withanacelledgeof 10.352(1)A,hasbeen refined to R = 1.957o, wR = 2.307o for 84 observed reflections (Mo(o radiation). Ferritungstite is isostructural with pyrochlore, with stnrctural properties closest to those of the variety having the defect pyrochlore structure. The sample studied is similar to kalipyrochlore: it has HrO dominant at the pyrochloreA and Q sites, tungsten dominant at the B site, and O and OH at the O site. On the basis of electron-microprobe and X-ray-diffraction data the formula is ([H2O]6.reCan.s6Nao.oz)x.or 1Wr.n6Fe3i6.5a):z(O4.70OH130)>6([H2O]0.80K0.20)>r. Ferritungstite is part of a potential subgroup of tungsten pyrochlores; nomenclature problems prevent formal inclusion of the tungsten pyrochlores into the pyrochlore group at present