Abstract

Economic chrysotile asbestos in the Great Serpentinite belt of New South Wales is restricted to a deposit in the bifurcated Woodsreef Serpentinite. Although the Woodsreef Serpentinite is dominated by schistose serpentinite, large bodies of partially serpentinized harzburgite and massive serpentinite, as well as tectonic inclusions of dolerite, gabbro, and rodingite, occur immediately south of the Slice (the minor arm of the bifurcation) in the central part of the ultramafic body.This central area has suffered a unique stress-strain history and the asbestos deposit is localized in heavily fractured massive serpentinite which is cut by narrow S 1 and S 2 zones of schistose serpentinite. Six types of asbestos veins are recognized: all are localized in stress-induced openings--either mineralized fractures, in extension cracks, in dilation sites in folds and kink bands, or along cleavage planes in bastite grains. Within these cracks, fiber formation took place by solution and recrystallization. As growth kept pace with the opening of cracks, the fibers became elongate parallel to the direction of maximum elongation in the XY plane of the strain ellipsoid. This fiber growth took place during S 1 and S 2 formation in the surrounding schistose serpentinite and is thus an integral part of the deformation in this part of the body.

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