Conditions of formation of lizardite, chrysotile and antigorite, Cassiar, British Columbia

A continuous series of serpentine textures, between pseudomorphic and non-pseudomorphic, are reported in the Cassiar chrysotile asbestos deposit, these minerals and textures being distributed with respect to shear zones in the interior of the serpentinite such that the degree of recrystallization and replacement increases nearer the shear zones. Patterns of spatial distribution suggest that recrystallization and replacement were caused by infiltration-driven metamorphism as the serpentinite equilibrated with an externally derived fluid. Chemical changes accompanying the recrystallization at 250 + or - 25 degrees C and <<<$I> 1 kbar indicate that local equilibrium is attained, and that equilibrium was approached at the thin-section scale near the shear zones. The assemblages and mineral compositions are consistent with P-T estimates from the MgO-SiO (sub 2) -H (sub 2) O model for the serpentine phase diagram; however, Fe (super 3+) may have had an important role in promoting isothermal changes among lizardite, chrysotile and antigorite.