Ningyoite in uranium deposits of south-central British Columbia

Ningyoite has been found in the uranium deposits of southern British Columbia, where it constitutes the major uranous (U4+) phase present. It occurs as accretionary stars, crystal mats and aggregate masses of spindle- or lozenge-shaped crystals that rarely exceed 2 mm in length. Occasionally it is present as single crystals in cleavage cracks of saleeite. The mineral forms in pyritiferous organic-rich fluvial sediments (Tyee deposit) or carbonaceous sandy mudstones (Blizzard deposit). In transmitted light ningyoite is greenish brown and displays a slight pleochroism. Extinction of the spindle-shaped grains is parallel and the mean index of refraction is between 1.60 and 1.70. Ningyoite is orthorhombic a 6.75(1), b 12.00(1), c 6.38(1) A, V 516.78 A3, Z = 3, diffraction aspect C***. Electron-microprobe analysis failed to detect rare-earth elements in ningyoite from British Columbia. Rare-earth elements were detected in only some ningyoite aggregates from the type locality in Japan. It is proposed that the formula for ningyoite be written Casub(2-x)Usub(x)(POsub(4))sub(2).nHsub(2)O, where x is approximatly less than 1. Optimum conditions for the formation of ningyoite are attained when weakly alkaline groundwaters leaching granitic basement complexes and containing high concentrations of U and PO4 infiltrate pyritiferous, organic-matter-rich sediments