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UBC Theses and Dissertations

Mineralogy, geochemistry, and geochronology of the KIN property pegmatites in eastern British Columbia Caudle, Dana

Abstract

Rare earth element- and Nb-bearing NYF-type pegmatites are located on the KIN property, approximately 95 km northeast of Revelstoke, British Columbia. They intrude amphibolite grade rocks of the Neoproterozoic Horsethief Creek Group in the Omineca Belt of the Canadian Cordillera. The Cordillera has traditionally been associated with LCT-type pegmatites, making the presence of NYF-type pegmatites on the KIN property particularly unusual. These pegmatites are found in-situ in four localities and contain significant amounts of allanite-(Ce), monazite-(Ce), chevkinite-(Ce), aeschynite-(Ce), euxenite-(Y), Nb-rich rutile, ilmenite, amphibole, and fluorapatite within plagioclase and Ba-rich feldspar and quartz. Additionally, the pegmatites contain textures and minerals, such as epidote-rimmed allanite and the breakdown of monazite into apatite and allanite in a corona texture, which can be attributed to Ca, F, and Si-rich fluids having been introduced during metamorphism. These pegmatites were dated by U-Pb zircon methods at approximately 79 Ma, and likely formed from an A-type source. Along with the NYF-type pegmatites, A-type REE-bearing syenites, coarse grained I-/S-type granites, and tourmaline bearing granitic pegmatite float samples are located on the property. The granite and syenite were identified as potential parental rocks for the mineralized pegmatites and this hypothesis was tested using geochemistry and geochronology. The granite is undeformed and has been dated by U-Pb zircon methods at approximately 76 Ma; this evidence, along with its geochemical signature suggests that the granite cannot be the parent for the pegmatites. Geochemical and elemental characteristics within the syenites suggest possible linkage to the pegmatites; however, syenite in the immediate area has been dated to 378 Ma, nearly 300 million years older than the pegmatites. In view of this the geochemical match and age discrepancy, it is possible that the pegmatites formed from partial melting of these older syenites at approximately 79 Ma.

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