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Geology of the Coquhalla Serpentine Belt between Spuzzum and Boston Bar, British Columbia Osborne, Willis Williams

Abstract

The Coquihalla Serpentine Belt extends north-northwest forty miles from a point southeast of Hope, British Columbia to just south of Boston Bar. Sections of the northern part of this belt and the surrounding rocks from Spuzzum to Boston Bar were mapped. The serpentine belt here consists of partially serpentinized harzburgite with generally more intense serpentinization toward the margins. North of a point east of Spuzzum the belt is found entirely within the probable Permian Hozameen Group of spilitic lava and tuff, chert, and argillite. South of the point where mapped, the serpentine is found between the Hozameen and Jurassic to Lower Cretaceous Ladner Group of predominantly slate with some graywacke. Several sills and a small stock of granitic rock were found in the mapped areas. Field evidence and laboratory data favor intrusion of the material in the serpentine belt into a pre-existing fault either by plastic deformation of solid harzburgite or by squeezing up in the fault. Serpentinization occurred probably during intrusion and most likely involved a volume for volume reaction whereby water from outside was added to the harzburgite and silica and magnesia were carried away. The volcanic and sedimentary rocks of the area show the effects of low grade regional metamorphism. Minerals formed include albite, epidote, calcite, stilpnomelane and tremolite-actinolite. Much of the albite in the spilitic rocks is believed to have formed from a more calcium-rich feldspar whereby the sodium was derived from water and/or included sediments during or after extrusion.

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