Kiruna-type deposits; their origin and relationship to intermediate subvolcanic plutons in the Great Bear magmatic zone, Northwest Canada

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doi: 10.2113/gsecongeo.81.3.640
Authors:Hildebrand, Robert S.
Author Affiliations:Primary:
Geol. Surv. Can., Ottawa, ON, Canada
Volume Title:Economic Geology and the Bulletin of the Society of Economic Geologists
Source:Economic Geology and the Bulletin of the Society of Economic Geologists, 81(3), p.640-659. Publisher: Economic Geology Publishing Company, Lancaster, PA, United States. ISSN: 0361-0128
Publication Date:1986
Note:In English. Geol. Surv. Can.; Contrib. No. 10486. 69 refs.; illus. incl. 5 tables, geol. sketch maps
Summary:Magnetite-apatite-actinolite rocks, similar to those at Kiruna, Sweden, and the St. Francois Mountains, Missouri, are associated with seven epizonal plutons that intrude andesitic stratovolcanoes of a broadly folded, early Proterozoic continental magmatic arc located in the northwestern Canadian Shield. The plutons, mainly medium-grained quartz monzonite-monzodiorite-diorite (IUGS) sheets and laccoliths 5 to 25 km in diameter, are spatially, temporally, and compositionally related to host andesitic stratovolcanoes. They were emplaced at 2 to 3 km depth, are compositionally heterogeneous, metasomatically altered, and had plagioclase as the liquidus phase. In addition they have kilometer-wide alteration halos comprising an inner zone of nearly complete wall-rock albitization, an intermediate zone of magnetite-apatite-actinolite veins, pods, breccias and wall-rock replacement, and an outer zone of disseminated sulfides. One pluton (Balachey) has a halo that is more or less completely outside the body, but another (Rainy Lake) has a halo that is partly superimposed over it. Separation of iron phosphate and silicate melts by liquid immiscibility is not supported by: (1) the gradual replacement of plagioclase by chessboard albite toward the roof of the Rainy Lake pluton, (2) the chemical trends in the Rainy Lake intrusion, (3) the mineralogical zoning, low temperature mineralogy, and replacement textures of the magnetite-apatite-actinolite, and (4) the relationship of the magnetite-apatite-actinolite veins and bodies to the plutons. However, all available data are compatible with a deuteric origin. It is concluded that high temperature, low initial water content, and shallow-level emplacement by intermediate plutons are necessary for the development of Kiruna-type deposits. [G.J.N.]
Subjects:Actinolite; Amphibole group; Apatite; Chain silicates; Clinoamphibole; Diorites; Economic geology; Emplacement; Geochemistry; Hypabyssal rocks; Igneous rocks; Intrusions; Iron ores; Magnetite; Major elements; Metaigneous rocks; Metal ores; Metamorphic rocks; Metaplutonic rocks; Mineral deposits, genesis; Oxides; Paleoproterozoic; Phosphates; Plutonic rocks; Plutons; Precambrian; Proterozoic; Quartz monzonite; Silicates; Trace elements; Upper Precambrian; Canada; Canadian Shield; Great Bear Lake; North America; Northwest Territories; Western Canada; Igneous processes; Kiruna-type; Mackenzie District Northwest Territories
Abstract Numbers:87M/0404
Record ID:1986059540
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Abstract, Copyright, Society of Economic Geologists
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