Abstract

A comparison of the Cassiar asbestos serpentinite body with other ultramafic bodies in the McDame map-area of northern British Columbia suggests that the critical conditions leading to ore deposition at Cassiar were as follows: 1) pervasive serpentinization of an ultramafic body resulting in mesh-structure serpentine, serpophite and bastite; 2) development of abundant fractures in the serpentinite body; 3) recrystallization of the serpentinite during low-grade metamorphism, perhaps equivalent to the upper part of the green-schist facies. Rocks of the area were probably folded while the nearby Cassiar granitic rocks were emplaced. This deformation produced a complex system of fractures in the serpentinite body. In a low-grade, contact-metamorphic environment asbestos-forming material diffused into fractures of low rock pressure and crystallized to form chrysotile-asbestos veins.

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