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UBC Theses and Dissertations

Petrology, structure and origin of the Copper Mountain intrusions near Princeton, British Columbia Montgomery, Joseph Hilton


The Copper Mountain intrusions, which include the Voigt and Smelter Lake dioritic stocks, Armstrong Bluffs monzonite-syenite complex, and the differentiated Copper Mountain stock are part of a continuous alkali-calcic rock series ranging in composition from pyroxenite to perthosite pegmatite. The series is believed to be derived from a single parent magma of basic diorite composition and to have formed through crystallization differentiation. The age of the series, determined by potassium-argon methods, is about 195 m.y. Parent magma was intruded into Nicola group (Upper Triassic) rocks by forceful injection with structural readjustment of the country rock. The Voigt and Smelter Lake stocks (diorite) crystallized without apparent differentiation. Armstrong Bluffs monzonite-syenite complex is believed to have formed, by repeated tapping of a differentiating magma which was emplaced at intervals after crystallization of diorite in Voigt and Smelter Lake stocks. In Copper Mountain stock, after crystallization of a dioritic roof and outer zone, magma differentiated to form a continuous series from pyroxenite to perthosite pegmatite Differentiation resulted through a combination of thermal convection, chemical diffusion, crystal armoring and crystal settling. Differentiation began with the formation of gabbro and was initiated by convection currents which were formed as a result of temperature gradients in a mobile, volatile-charged magma. When the composition of the magma approached the Ab-Or side of the Ab-Or-An ternary system, subsolvus crystalliza- tion was succeeded by hypersolvus crystallization and the development of perthosite pegmatite. Feldspars from the Copper Mountain intrusions, studied by X-ray powder technique, exhibit a range of thermal state from intermediate to low temperature types. Feldspar geothermometry suggests a range of crystallization from above 8.20°C to about 500°C.

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