Lee Groat

Rare-earth element (REE) and high field strength element (HFSE) bearing Eocene and Neoproterozoic intrusions occur throughout southeastern Yukon, Canada. Poorly exposed outcrops of a REE-HFSE bearing fenite of unknown origin are found adjacent to the Neoproterozoic Pool Creek nepheline syenite, which is superimposed by Eocene volcanism. Fenites hold critical information about the original composition of their source intrusions and have implications as a vector towards associated REE-HFSE mineralization; however, fenites associated with syenitic intrusions are understudied in the literature. Rock and mineral textures and compositions of the Pool Creek nepheline syenite, altered syenite suites, fenites, and host units (quartzite and argillite) were compared to determine the source and timing of the fenitization event and to contribute to the collective knowledge of fenites associated with syenitic intrusions. The altered syenite and fenite suites show geochemical and mineralogical compositions that are transitional between their respective host units and the Pool Creek nepheline syenite. Interestingly, the fenitized units hosted in argillite have REE-HFSE contents up to 15x greater than those hosted in quartzite. The style of mineralization observed in this study is consistent with that of a silicate roof zone type deposit, indicating the orientation of the intrusive system. Relationships between unaltered and altered zircon textures and dates show that the ages of crystallization of multiple intrusive units and associated fenitization occurred between 620 to 660 Ma. Overlapping ages of different syenitic units suggest that the Pool Creek nepheline syenite forms a composite alkaline-silicate complex, rather than a single intrusive event. These lines of evidence suggest that the source of the fenitization that produced the alteration observed in the altered syenite and fenite suites is the Neoproterozoic Pool Creek nepheline syenite, and therefore that fenitization was driven by contact metasomatism between the nepheline syenite and host units. These findings show that the characteristics of the host rocks strongly influence the composition and distribution of fenite aureoles and REE-HFSE mineralization associated with syenitic systems. These conclusions demonstrate that understanding the compositional relationship between the source intrusion, associated fenite, and host yields a plethora of information about the magmatic system and controls on associated mineralization.

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The unusual black shale hosted emerald deposits of Colombia are an important source of the finest quality emeralds. The majority of world emerald deposits are related to granite pegmatites and metamorphic environments, however Colombian-type emerald is amagmatic and is associated with sedimentary-hydrothermal brines of largely evaporitic origin where the key emerald-forming elements are remobilized from black shale during regional compressional tectonism. The valuable gem quality mineralization of Colombian emerald deposits is so far unique, however the basic geological conditions that led to mineralization may not be as unusual. Similar black shale basins hosting evaporites are found worldwide, and could be prospective for Colombian-type emerald mineralization. Canada’s Selwyn Basin and periphery is one similar setting with the distinction of hosting two interesting beryl showings: the Mountain River Beryl (a variation of the Colombian beryl model) and the Lened emerald showing (in which black shale provided vanadium as an emerald chromophore). This thesis presents the results of applying Colombian-type emerald exploration criteria to Selwyn Basin stream sediment geochemistry data, in addition to clarifying the origin of emerald at the Lened showing located within the Selwyn Basin.The unusual black shale hosted emerald deposits of Colombia are an important source of the finest quality emeralds. The majority of world emerald deposits are related to granite pegmatites and metamorphic environments, however Colombian-type emerald is amagmatic and is associated with sedimentary-hydrothermal brines of largely evaporitic origin where the key emerald-forming elements are remobilized from black shale during regional compressional tectonism. The valuable gem quality mineralization of Colombian emerald deposits is so far unique, however the basic geological conditions that led to mineralization may not be as unusual. Similar black shale basins hosting evaporites are found worldwide, and could be prospective for Colombian-type emerald mineralization. Canada’s Selwyn Basin and periphery is one similar setting with the distinction of hosting two interesting beryl showings: the Mountain River Beryl (a variation of the Colombian beryl model) and the Lened emerald showing (in which black shale provided vanadium as an emerald chromophore). This thesis presents the results of applying Colombian-type emerald exploration criteria to Selwyn Basin stream sediment geochemistry data, in addition to clarifying the origin of emerald at the Lened showing located within the Selwyn Basin.We identified several prospective areas in Selwyn basin for further Colombian-type emerald exploration based on Na, K, Be, Cr/V, and rare earth element values, however there are important caveats regarding analytical techniques and the regional nature of silt sampling. We found that Lened is a unique skarn-hosted hydrothermal emerald occurrence (~100 Ma) in which Be was provided by a nearby granite pluton of similar age. The chromophore V was provided by local black shale/mudstone.

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The Deer Horn property is located 150 km south of Smithers in west-central British Columbia and covers 51 km². The deposit is an intrusion-related polymetallic system enriched in Au-Ag-Te-W-Cu with lesser amounts of Bi-Pb-Zn-Mo; the Au and Ag are hosted in telluride minerals. The quartz-sulfide vein system containing the main zones of Au-Ag-Te mineralization and sericite alteration is found in the hanging wall of a local, spatially related thrust fault. The age of the sericite alteration is 56 ± 2 Ma. Biotite K-Ar ages of 57–48 Ma for the nearby Nanika granodiorite intrusive suite indicates that it is likely genetically responsible for the Au-Ag-Te mineralizing event. The telluride minerals are 0.1–525 μm and commonly form whole euhedral to subhedral grains or composite grains of Ag-, Bi-, Pb-, and Au-rich telluride minerals (e.g., hessite, tellurobismuthite, volynskite, altaite, and petzite). Panchromatic cathodoluminescence imaging revealed four generations of quartz. Locally, oscillatory zoning observed in quartz II suggests the participation of hydrothermal fluids. Fine-grained veinlets of quartz III and IV intersect quartz I and II, which is evidence of at least two shearing events; veinlets of calcite intersect all generations of quartz. Three types of fluid inclusions were observed: (1) aqueous liquid and vapour inclusions (L-V); (2) aqueous carbonic inclusions (L-L-V); and (3) carbonic inclusions (V-rich). Fluid inclusions that are thought to be primary or pseudosecondary and related to the telluride mineralization were tested with microthermometry. Homogenization temperatures are 130.0–240.5 °C for L-V inclusions and 268.0–336.4 °C for L-L-V inclusions. Four of eight aqueous carbonic inclusions had solid CO2 melting temperatures from –56.8 to –62.1 °C, indicating the presence of 0.5–13.2% dissolved methane in these inclusions. Sulfur isotope analysis of ³⁴S/³²S using 20 samples of pyrite was conducted. δ³⁴S readings are close to 0 (from –1.6 to 1.6 per mil) and confirm that the sulfur is very likely magmatic/igneous in origin.

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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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The pegmatite field on Mount Begbie, near Revelstoke, B.C., is a Li-rich pegmatite field in the southern Canadian Cordillera that is relatively well-known among prospectors, but until now, under-studied by academics. Mapping the pegmatite field on the northeastern slope of the mountain revealed a dense population of S-type granitic pegmatites belonging to the LCT family with diverse ranges of mineralogy corresponding to barren, beryl-columbite, beryl-columbite-phosphate, and lepidolite-subtype compositions. Typically, the pegmatites are not strongly metamorphosed and show only rare foliation, meaning they primarily postdate the exhumation of the Thor-Odin Culmination that occurred during the Late Paleocene to Early Eocene. They are likely related to other granitic bodies (i.e., the Ladybird granite suite) resulting from the exhumation event rather than any other known intrusions in the Monashee complex. The dikes in the study area are elongate, with most at least 10 m long and are usually not more than one meter wide; the largest is approximately 520 m long and 10 m wide. Orientations of the pegmatites are dictated in part by conjugate shear planes developed in the host rock prior to the emplacement of the dikes; nearly all strike between 295° and 330° and have a subvertical dip. Fractionation is variable within the most primitive of the pegmatites and it may be controlled by localized fluid accumulation or the composition of the original source rock. Despite variability, fractionation within the pegmatite field increases from the southeast to the northwest, suggesting the source pluton may be located to the southeast of the study area at depth. Detailed examination of the minerals tourmaline, sekaninaite, beryl, rare-element oxides, and zircon as well as the mostly qualitative study of phosphates and other minerals provides insight into the geochemistry and mineralogy of the individual dikes. The results suggest that some of the primitive dikes are more fractionated than they appear and highlight other pegmatites as having unusual compositions for typical beryl-columbite and beryl-columbite-phosphate-subtype pegmatites. Elevated contents of Be and Li in sekaninaite and the presence of qitianlingite in the Mount Begbie pegmatite field are somewhat unique compared to other cordierite and rare-element oxide localities worldwide.

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This thesis explores in detail the petrology and petrogenesis of the Ren carbonatite sill andassociated fenites, located in the Monashee mountain range of British Columbia. Thecarbonatite body and fenites have been significantly deformed and metamorphosed, whichhas provided a unique petrological research opportunity, since only a few other carbonatiteoccurrences worldwide have been described from highly metamorphosed orogenic settings.This work aims to address knowledge gaps pertaining to the petrology, petrogenesis andeconomic exploration of comparable carbonatites in similar geotectonic settings.The effects of amphibolite facies regional metamorphism and progressive deformationare apparent throughout the carbonatite body and adjacent fenites. Many of the rocks displayremobilized, passively mixed components, boudinaged structures, and rheomorphic bands, aswell as foliation and porphyroblastic textures. Recrystallization of minerals at peakmetamorphic conditions (580–730 °C) is indicated primarily in undifferentiated calcite forwhich metamorphic solvus temperatures (~690 °C) were derived. Other minerals related tometamorphic recrystallization include rims of monazite-(Ce) around earlier fluorapatite,interstitial REE-silicates, and Ca- and Mg-amphibole forming late in the parageneticsequence, after primary silicates.Despite the metamorphic overprint and alteration, many petrological featurespertaining to the igneous paragenetic record have been preserved, such as textures of primaryminerals, compositional trends in phlogopite, clinopyroxene and amphibole, and whole-rockgeochemistry of rock units. Solvus temperatures (~760 °C) of calcite, higher than peakmetamorphic conditions, highlight preservation of the igneous component. The carbonatite isinferred to be a product of primitive mantle melts(s) that did not undergo significantfractionation processes, and intruded the crustal environment relatively undifferentiated. Thewhole-rock compositional trend of the fenites and partially fenitized host rocks suggestssodic-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 foreconomic extraction. Nevertheless, rare and new mineral candidates, (Fe,OH)-analogue tovästmanlandite-(Ce) and (Mg)-analogue to biraite-(Ce), discovered in the deposit by theauthor, emphasize its petrological and mineralogical significance.

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Borosilicates are oxygen-bearing boron minerals in which SiO₄ tetrahedra form an important structural component. They represent widespread constituents of rocks originating in the Earth’s crust and commonly provide insight into the rock-forming processes. Important borosilicates include tourmaline, axinite, werdingite, boralsilite, dumortierite, holtite, howlite, and grandidierite. Tourmaline is the most widespread borosilicate mineral and it can be used to study a wide variety of geological processes based on its high compositional variability. Dumortierite [(Al,☐)Al₆(BO₃)Si₃O₁₃(O,OH)₂] is second only to tourmaline as the most abundant borosilicate mineral, but remains relatively understudied in comparison. Isostructural holtite [(Al,Ta,Nb,☐)Al₆(BO₃)(Si,Sb,As)₃O₁₂(O,OH,☐)₃] is poorly constrained chemically. The ability to incorporate elements such as As, Sb, Bi, Nb and Ta make dumortierite and holtite unusual for silicate minerals. Synthesis experiments designed to better determine the relationship between holtite and dumortierite by synthesizing dumortierite and gradually replacing Si with As and Sb were carried out at the GeoForschungZentrum (GFZ) in Potsdam, Germany. Synthesis conditions were designed based on the previous work by Werding and Schreyer (1990). Experiments ranged from 3-5 kbar at 550-650 °C and 15-20 kbar at 600-700 °C. The less common borosilicate boralsilite [Al₁₆B₆Si₂O₃O₃₇] was the dominant phase produced in the attempts at synthesizing dumortierite. The results showed an increased stability range for boralsilite than had been previously studied and gave insight to simpler methods of synthesis. A detailed case study of the mineralogy of the Uvil’dy Lake pegmatite revealed a potentially unique locality for dumortierite and tourmaline evolution. The tourmaline shows a high Mn/(Fe + Mg) ratio within primary phases and increased Li, Fe and Mn-enrichment in later phases. Apart from being unusually yellow, the dumortierite from Uvil’dy was also anomalously high in Bi (~0.03 apfu). Eight additional samples of dumortierite from different global localities were analysed and were compared to approximately 1100 dumortierite and holtite compositions assembled from both published and unpublished data from worldwide localities. Including the analysed Uvil’dy samples, this extensive dataset gives a detailed look at the chemical relationship between dumortierite and holtite and allows them to be better constrained in terms of their chemical constituents.

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Carbonatites are rare magmatic rocks composed of greater than 50% carbonate minerals. They are generally associated with continental rift-related tectonic settings and are commonly enriched in rare earth elements (REE), Nb, and P. The Wicheeda carbonatite complex, located 80 km northeast of Prince George in British Columbia, Canada, has been historically explored for its REE potential, but until recently there has been very little scientific study. The purpose of this study was to explore the geology, mineralogy, geochemistry, and geochronology of the Wicheeda Carbonatite Complex. The complex consists of a carbonatite plug with a number of carbonatite and potassic-syenite dykes and sills emplaced into the sedimentary rocks of the upper Cambrian and lower Ordovician Kechika Group. Sodic-fenitization is common around the carbonatites and the degree of alteration and abundance of syenite outcrops increases away from the carbonatite plug. The complex was mapped over an area of 1.45 km². The REE mineralogy of the Wicheeda carbonatite was defined through optical petrography (86 thin sections), scanning electron microscopy, electron probe microanalysis (371 points on 14 mineral species), and single-crystal X-ray diffraction (7 samples). The REE mineralogy is complex, with multiple stages of primary, late-stage, rapidly cooling crystallization. It consists of Ca-REE-fluorocarbonates, Ba-REE-fluorocarbonates, ancylite-(Ce), monazite-(Ce), euxenite-(Y), and allanite-(Ce); the majority of these minerals are LREE rich. Whole rock isotopic analysis was completed for the Rb-Sr and Sm-Nd systems. An isochron age of 316 ± 36 Ma was determined using the Sm-Nd system, giving values for εNdT and ⁸⁷Sr/⁸⁶SrT that range from -0.5 to 0.5 and 0.70526 to 0.70659, respectively. Evidence from the Wicheeda Carbonatite Complex along with comparisons with other worldwide carbonatites, suggests that the complex formed from a dominantly silicate, parental, mantle melt emplaced into the continental lithosphere. The lithosphere underwent metasomatism and, potentially, low degrees of partial melting and/or the incorporation of previously subducted sediments for carbonatite generation.

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