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

Ferritungstite occurs at the Flo property on Kalzas Mountain, near May o, Yukon. It is hosted by ferberite-bearing quartz veins, which form a stockwork in tourmalinized metasediments of the Grit Unit of the Wind ermere Supergroup. The ferritungstite replaces ferberite, and lines so lution cavities, cleavages and crystal margins of the ferberite. Cryst als are yellow to orange to brown octahedra up to 0.1 mm across. There are two generations of ferritungstite: an early Cs-bearing generation , and a later Cs-free one. The crystal structure of Cs-free ferritungs tite, Fd3m, with an a cell edge of 10.352(1) Angstrom, has been refine d to R = 1.95%, wR = 2.30% for 84 observed reflections (MoK alpha radi ation). Ferritungstite is isostructural with pyrochlore, with structur al properties closest to those of the variety having the defect pyroch lore structure. The sample studied is similar to kalipyrochlore: it ha s H2O dominant at the pyrochlore A and phi sites, tungsten dominant at the B site, and O and OH at the O site. On the basis of electron-micr oprobe and X-ray-diffraction data, the formula is ([H2O]0.59Ca0.06Na0. 02)(Sigma 0.67) (W1.46Fe0.543+)(Sigma 2)(O4.70OH1.30)(Sigma 6)([H2O]K- 0.80(0.20))(Sigma 1). Ferritungstite is part of a potential subgroup o f tungsten pyrochlores; nomenclature problems prevent formal inclusion of the tungsten pyrochlores into the pyrochlore group at present.