| Summary: | This thesis explores in detail the petrology and petrogenesis of the Ren carbonatite sill and
associated fenites, located in the Monashee mountain range of British Columbia. The
carbonatite body and fenites have been significantly deformed and metamorphosed, which
has provided a unique petrological research opportunity, since only a few other carbonatite
occurrences worldwide have been described from highly metamorphosed orogenic settings.
This work aims to address knowledge gaps pertaining to the petrology, petrogenesis and
economic exploration of comparable carbonatites in similar geotectonic settings.
The effects of amphibolite facies regional metamorphism and progressive deformation
are apparent throughout the carbonatite body and adjacent fenites. Many of the rocks display
remobilized, passively mixed components, boudinaged structures, and rheomorphic bands, as
well as foliation and porphyroblastic textures. Recrystallization of minerals at peak
metamorphic conditions (580–730 °C) is indicated primarily in undifferentiated calcite for
which metamorphic solvus temperatures (~690 °C) were derived. Other minerals related to
metamorphic recrystallization include rims of monazite-(Ce) around earlier fluorapatite,
interstitial REE-silicates, and Ca- and Mg-amphibole forming late in the paragenetic
sequence, after primary silicates.
Despite the metamorphic overprint and alteration, many petrological features
pertaining to the igneous paragenetic record have been preserved, such as textures of primary
minerals, compositional trends in phlogopite, clinopyroxene and amphibole, and whole-rock
geochemistry of rock units. Solvus temperatures (~760 °C) of calcite, higher than peak
metamorphic conditions, highlight preservation of the igneous component. The carbonatite is
inferred to be a product of primitive mantle melts(s) that did not undergo significant
fractionation processes, and intruded the crustal environment relatively undifferentiated. The
whole-rock compositional trend of the fenites and partially fenitized host rocks suggests
sodic-potassic alteration of the country rock during emplacement of the carbonatite sill.
The Nb-Ta and REE mineralizations of the Ren occurrence are both insufficient for
economic extraction. Nevertheless, rare and new mineral candidates, (Fe,OH)-analogue to
västmanlandite-(Ce) and (Mg)-analogue to biraite-(Ce), discovered in the deposit by the
author, emphasize its petrological and mineralogical significance. === Science, Faculty of === Earth, Ocean and Atmospheric Sciences, Department of === Graduate
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