Low temperature alteration of REE-rich chlorapatite from the Stillwater Complex, Montana

Chlorapatite is associated with coarse-grained olivine-rich rocks that host platinum-group element-bearing sulfide mineralization of the J-M Reef of the Stillwater Complex. The chlorapatite may contain in excess of 2 wt% of rare-earth elements (REE). The high-temperature magmatic-hydrothermal assemblage has undergone various degrees of serpentinization. A Cl-poor, very finely intergrown alteration assemblage occurs as pseudomorphs of, and along healed fractures in individual grains of primary chlorapatite. The early stage of alteration is marked by the leaching of REE and their precipitation as monazite prior to extensive loss of Cl from the host chlorapatite. The progressive destruction of chlorapatite led to increased chlorinity and acidity of the solution at the reaction front, which, in turn, enhanced the dissolution of monazite. The textural and compositional features demonstrate that the replacement of chlorapatite by hydroxyapatite occurs through recrystallization. -from Authors

Duke Scholars

Author Alan E. Boudreau Earth and Climate Sciences