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Geology, geochemistry, and origins of the Mount Bisson alkaline rocks, Munroe Creek, British Columbia, Canada Halleran, Arthur Alvin Douglas

Abstract

Igneous and metasomatic rocks comprise a newly recognizedsuite of REE enriched alkalic and granitic rocks within theWolverine metamorphic complex at Mt. Bisson. The alkaline rocksinclude Tertiary alkalic dikes, allanite pegmatites, syenitepegmatites and fenites. The fenites are the products ofmetasomatism of Wolverine amphibolites by Na, Fe³⁺, Sr, Ba, REE, Y and F enriched solutions. The granitic rocks include Cretaceous plutons, quartz-allanite pegmatites, monazite pegmatites and Tertiary plutons and pegmatites. Many of the granites have S-type granite characteristics representative of upper crustal melts. The mineral chemistry within these rocks requires that both closed and open chemical processes have participated. LREE solid solution data on coexisting allanite, titanite and apatite facilitate the recognition of closed and open chemical system processes in rocks. Closed chemical systems are recognized by: i) decreasing core to rim LREE concentrations, ii) fine scale oscillatory zoning paralleling crystallographic orientations, iii) consistency between texturally inferred crystallization sequence and the measured LREE contents of coexisting minerals, and iv) diminished LREE contents in phases which are inferred to crystallize after allanite. Open chemical system processes are suggested: i) where all of the above criteria are absent or ii) where one of these criteria is reversed. Additionally, three new mineral compositions; two for titanite and one for apatite occur at Mt. Bisson.

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