Title: Conditions of formation of lizardite, chrysotile and antigorite, Cassiar, British Columbia
Abstract: Observations at the Cassiar (British Columbia) cbrysotile asbestos deposit have defined a continuous series of serpentine textures, between pseudomorphic and nonpseudomorphic. These minerals and textures are distributed with respect to shear zones in the interior of the serpentinite such that the degree of recrystallization and replacement increases as the shear zones are approached. Pafierns of spatial distribution suggest that recrystallization and replacement were caused by infiltration-driven metamorphism as the serpentinite equilibrated with an externally derived fluid. The shear zones served as conduits forthe fluid. The recrystallization and replacenent of lizardite formed after olivine and of that formed after enstatite proceed independently early in ihe process, such tiat composition of tle variols serpentine minerals was controlled by the bulk composition of the precursor. fitrt io the process, Fet*/[rlg, CrlAl and Fe3+(Mg + Si) values, and the distribution of boron, between serpentine after olivine and that formed after enstatite indicate that equilibrium was closely approached. The formation of a chrysotile + antigorite assemblage marks this transition. The recrystallization of lizardite and its replacement by.chrysotile + antigorite ocqined a1250 t 25'C and a P(H2O) of less than 1 kbar, The temperatures and pressures of serpentinization cal b9 modeled in the system MgO-SiO2-H2O 6MSII because: l) clinochlore is stabilized by the breakdown of cbromite, rather than a serpentine mineral, and 2) nagnetite is both a product and a reactaat in the conversion oflizaxdite to antigorite, indicating that it is not an essential compound in the conversion of lizardite to antigorite. The mineralogy, textures and compositions of lizardite and cbrysotile indicate that they are polymorphs in the MSH system.
Publication Year: 1995
Publication Date: 1995-08-01
Language: en
Type: article
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Cited By Count: 69
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