SUDOITE FROM CIGAR LAKE, SASKATCHEWAN

Abstract

Chlorite in the alteration zone around the Cigar Lake uranium deposit in the Athabasca basin, northern Saskatclewry-, has the composition : (Al2.s6Mg1.e2Feo.rJ(Si:.:o Alo.7dO1o(OH,F)6. This is a di-trioctati6ltrai--varietv, sudoite, with a IIb polytype structlrre, and characterized Qy an intense @6 reflection at 4.74 A and a d(060) of 1.5t5 A. Abundant sudoite occurs in a well-defined halo around the ore and probably formed at the expense of illite and kaolinite, during hydrothermal alteration associated with uranium mineralization.