Browsing by Author "McFarlane, Chris R.M."
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Item Geochronologic, petrographic, geochemical, and isotopic constraints on the origin of the uraniferous Lac Turgeon Intrusive Complex, Quebec(University of New Brunswick, 2014) Beal, Kristy-Lee; Lentz, David; McFarlane, Chris R.M.The Lac Turgeon Intrusive Complex (LTIC), along the north shore of the St. Lawrence Seaway in the Grenville Province of Quebec, is host to pegmatite-related uranium mineralization. The main zone has an inferred resource of 81.5 million tons U₃O₈, averaging 0.013% U₃O₈; isolated occurrences, including the Grandroy Zone, have revealed 20 m of 0.174% U₃O₈ in channel sampling and up to 0.213 % U₃O₈ over 5.4 m and 0.089 % U₃O₈ over 10.5 m in drill holes completed in 2009. The intrusion’s main lithologies include granite, pink pegmatite, and white pegmatite that contain biotite, muscovite, zircon, ilmenite, hematite, and magnetite with minor apatite, uranothorite, uraninite, monazite, and xenotime as accessory minerals. Previous mineralogical studies have also noted the presence of pyrochlore, churchite (YPO₄*2H₂O), zoned samarskite, allanite, titanite, bastnaesite, and titanobetafite. The texturally diverse complex has irregular and sharp contacts, highly radioactive late-stage felsic intrusives, local magmatic layering, and breccias. Mineral geochemistry and textures provide evidence of crystallization depths > 4-5 km in a fluid-rich environment and mineral saturation temperatures (monazite, zircon, and apatite) average between 686-894°C. The samples at the LTIC came from the same source with the granite less fractionated than the pegmatite phases (white pegmatite commonly more fractionated than the pink pegmatite) based on the fractionation factors of the large ion lithophile and high field strength elements. The granite and white pegmatite phases towards the outer rim of the complex reveal ages (U-Pb Monazite) of 969 Ma (±7Ma and ±6 Ma, respectively); a Double S Zone granite phase towards the center of the intrusion revealed a concordant age of 941 ± 2.7 Ma (U-Pb Monazite, Xenotime) confirming there are several fractionated intrusive phases present at the LTIC. The dates indicate the LTIC is a post-orogenic complex that crystallized at the current level of emplacement towards the end of the Rigolet orogenic phase but outside the area of penetrative Rigolet metamorphism. Geochemical evidence identify that the LTIC is a peraluminous granite-pegmatite intrusion with a complex mixture of previously melted, lower crustal and more juvenile crustal sources giving a crustal A-type (higher Ga, Nb and lower Ba) to S-type (high Rb, Al) affinity. Similar to other uranium deposits including the Limousin pluton in the French Massif Central, the complex increases in peraluminosity with a slight decrease in fractionation indicative of an L-type granite. L-type granites are the result of low degrees of partial melting of a Proterozoic, metasediment source (high ¹⁸O signature) that contains elevated uranium content. Batch-type melting would have commenced by adiabatic melting during uplift related to the orogenic collapse and reworking of normal-sense shear zones following the completion of the Ottawan orogenic phase of the Grenville Orogen. The U and Th values are highly variable (<2-4485 ppm and 0.7-620 ppm, respectively) with U/Th ratios ranging between 0.28 and 25. The average U/Th for the LTIC is 2.3 (+4.0/-1.5; based on log transform data). In most samples, uraninite is accompanied by increased accessory mineral content explaining the close relationship of uranium with La, Ce, Zr, and Y. The main zones associated with highly uraniferous phases, including the Double S, MA, and MB-zones, have a close association with hybridization that would have occurred during magma ascent or in the magma reservoir prior to ascent, as measured by higher CaO + MgO + FeOt. Hybridization is believed to be the main control for concentrated uranium mineralization for other post-orogenic Grenvillian pegmatites. Fractional crystallization is still a factor related to mineralization elsewhere in the intrusive complex including the J- and Lac Turgeon zones. The Grandroy Zone reveals evidence that albitization or sodium metasomatism (higher Na₂O and lower SiO₂ and K₂O and textural evidence) could play a role in uranium mineralization at that location.Item Petrogenesis of the archean Prestige leucogranite and spatially associated LCT pegmatites: insights from whole-rock and muscovite trace element geochemistry and apatite U-Pb geochronology(University of New Brunswick, 2018) Palmer, Emily, M; Lentz, David; McFarlane, Chris R.M.The Yellowknife pegmatite field is host to LCT-family rare-element pegmatites that are associated with Late Archean granitic magmatism. The Prosperous suite, a large plutonic suite composed of 14 two-mica S-type leucogranites, lies in the southwest quadrant of the pegmatite field. The plutons are spatially associated with the rare element pegmatites. Although the geology in this domain is the most thoroughly documented in the Slave Province, the ages of the major plutonic suites are poorly constrained. The Sparrow Lake pluton of the Prosperous suite is the only pluton to have previously been reliably dated at 2596 ± 2 Ma. The Prestige pluton, the focus of this thesis, has been classified as a member of the Prosperous suite and has previously been studied because of its high Li contents. Apatite U-Pb geochronology of the Prestige pluton yielded a concordant age of 2608 ± 4 Ma, which is interpreted to represent the crystallization age of the pluton. Based on geochemical and geochronological similarities, the Prestige pluton is interpreted to be a part of the Prosperous suite. The difference in age between the Sparrow Lake and Prestige plutons is attributed to different crustal levels of emplacement and, therefore, different cooling histories. Upper intercept and concordia ages for apatite from the intra- and inter-pluton pegmatites associated with the Prestige pluton yielded overlapping ages of 2588 ± 6 Ma and 2593 ± 6 Ma, respectively. The whole-rock geochemistry of the intra- and interpluton pegmatites exhibit similar trace element compositions and enrichment of incompatible elements, with averages of 22 ppm Sn, 9.5 ppm Ta, 19.6 ppm Nb, 21.0 ppm Cs, and 453 ppm Rb. Trace element analyses of muscovite via LA-ICP-MS reveal elevated concentrations of Rb, Cs, and Sn within the granite and pegmatites. In general, the rims of muscovite grains are enriched in Li, Cs, Sn, Nb, and Ta, which is attributed to normal magmatic fractionation processes. The whole-rock and muscovite geochemistry reflect increasing fractionation trends from the intra-pluton to inter-pluton pegmatites, as indicated by decreases in K/Rb, K/Cs, and Sr/Rb ratios. The similarity in age, geochemistry, and geothermometry of the intra- and inter-pluton pegmatites suggests they are comagmatic. Distinct differences in fractionation trends, crystallization ages, and muscovite geochemistry, in addition to a lack of field evidence of gradation, suggests that the Prestige granite is not parental to the spatially associated pegmatites. This study emphasizes the importance of geochronological and geochemical work to determine the petrogenesis of pegmatites to spatially related plutons. The source of the pegmatites in this study is not known. However, it is suggested to be a deep-seated magma chamber that has yet to be identified.Item Petrogenesis of tin-tungsten-molybdenum mineralized intragranitic systems within the highly evolved Mount Douglas polyphase intrusive complex, southwestern New Brunswick, Canada(University of New Brunswick, 2018) Mohammadi, Nadia; Lentz, David; McFarlane, Chris R.M.The Late Devonian Mount Douglas Granite, located in southwestern New Brunswick, is host to endogranitic, granophile-element Sn-, W-, Mo-, Zn-, Bi-, and U-bearing greisen/sheeted veins. It forms the eastern part of the Late Silurian to Late Devonian Saint George Batholith that was emplaced during the Acadian-Neoacadian orogeny. Three units of the highly evolved post-orogenic peraluminous Mount Douglas Granite (Dmd1, Dmd2, and Dmd3) were formed by progressively higher degrees of fractional crystallization. Investigations of these three phases were carried out using a combination of geological field work (mapping), gamma-ray spectrometry, petrographic and geochemical investigations, EPMA, SEM-EDS imaging, Laser ablation ICP-MS measurements, including U-Pb geochronological and radiogenic and stable isotopic studies, supported by Raman spectroscopy on certain minerals. The granite exhibits a hybrid S-type and A-type signature. Whole-rock δ[superscript 18]O (+6.0 to +7.3‰), high initial [superscript 87]Sr/[superscript 86]Sr (mean = 0.70764), positive [subscript εNd(368 Ma)] (+0.3 to +1.1), and Pb isotopic data indicate its derivation by partial melting of a predominately juvenile subducted Avalonian crustal source that was contaminated by supracrustal rocks. Magmatic biotite geochemistry, combined with whole-rock zircon saturation temperature estimates, suggest oxygen fugacity near Quartz-Magnetite-Fayalite (QFM) conditions for unit Dmd1, whereas units Dmd2 and Dmd3 have lower ƒO[subscript 2] and are more reduced. Mineralized greisen/sheeted veins are associated with highly differentiated medium-grained to porphyritic units, Dmd2 and Dmd3, that are the most prospective units of the pluton in terms of metallic mineral deposits. The most fractionated character of Dmd3 is evident by its highest SiO[subscript 2] content (avg. 76.4 wt.%.), higher contents of LILE (e.g., Li, Rb, Cs), HFS (Ta, Th, U), Y (≤ 138 ppm) and REE, and the most pronounced negative Eu anomalies (avg. Eu/Eu* = 0.08). The degree of fractionation in Dmd3 is also manifested by its lowest K/Rb (70-127), Nb/Ta (average = 4.9), and Zr/Hf (average = 23.5), and highest Rb/Sr ratios (average = 42), and also by geochemical compositions of magmatic biotite, K-feldspar, and monazite. The most important indices of magmatic evolution, K/Rb, K/Cs, Rb/Cs, K/Li, and Nb/Ta ratios of co-existing biotite and K-feldspar, decline with increasing degree of fractionation. The estimated K[subscript Rb] suggests a lower equilibration temperature for Dmd3, consistent with whole-rock zircon and monazite saturation temperatures. LA ICP-MS U-Pb geochronology of 157 in situ monazite grains along with 100 mounted zircon grains yielded a Late-Devonian crystallization age of 368 ± 3 Ma. With respect to timing of associated mineralization, there are at least two stages recognized in this system: (I) magmatic-related mineralization, which is recorded by new mineralization ages obtained on uraninite (366.4 ± 4.3 Ma; 2σ; n = 5) and cassiterite (363 ± 9 Ma; 2σ; n = 38), and (II) post-magmatic mineralization defined by hydrothermal monazite, and yielding a younger mineralization age ranging from 344 to 368 with an average of 357 ±7 Ma. The post-magmatic hydrothermal activity can be associated with the High Heat Production (HHP) nature of this pluton, in which the pluton acts as a ‘heat engine’ producing heat by radioactive decay of U, Th, and K that prolonged the hydrothermal fluid circulation (activity).Item Using biotite and apatite compositions to differentiate barren and mineralized silurian-devonian granitoid plutons in New Brunswick, Canada(University of New Brunswick, 2019) Azadbakht, Zeinab; Lentz, David; McFarlane, Chris R.M.Silurian-Devonian granites of New Brunswick (428-433 Ma) cover the compositional spectrum from I- through S-, and A-types and are associated with several styles of granophile mineralization, including porphyry, greisen, and vein-related of Sn, W, Cu, Mo, Au, and U. However, some of the intrusions are not known to be associated with mineralization despite their highly fractionated nature. Principle component analysis classified these granitoids to three groups (NB-1 to NB-3) and two singular granites (Lost Lake and Juniper Barren granites), based on geochemical characteristics using Zr/Ce to TiO2. NB-1 and NB-2 were further divided into a few subgroups using chondrite-normalized REE and mantle-normalized patterns. A general trend of increasing assimilation fractional crystallization exists from singular granites to NB-3 granites reflecting the more evolved nature of these granites. Singular granites are believed to have formed by reworking of an older crustal protolith through several different partial melting events in an arc environment. NB-1 granites are formed by partial melting of the lower crust, whereas NB-2 granites formed by varying degrees of partial melting of a mixed mantle- older crustal protolith. The geochemical differences among the subgroups in NB-1 and NB-2 are attributed to different degrees of assimilation fractional crystallization and secondary hydrothermal alteration. NB-3 granites are mainly crust-sourced and are associated with crustal thinning processes related to crustal delamination following the juxtaposition of various crustal blocks. Twenty-two biotite grains of different shape, size, and compositions were mapped with laser ablation-inductivity coupled plasma mass spectrometer (LA-ICPMS) to evaluate the extent in which magmatic biotite could retain its magmatic trace-element zoning. The result indicated that grains larger than 500×500 μm with minimum mineral inclusion and alteration retained better zoning. Large ion lithophile (LILE) element zoning including Ba, Cs, and Rb are the most common zoning observed within the examined biotite grains. More importantly, a large lithian-siderophyllite (>1×1 mm) from the Pleasant Ridge Granite display Sn, W, Ta, V, Ti, Cs, and Rb, but no Ba zoning that might indicate rapid cooling in this intrusion. Two hundred and nineteen biotite grains from both barren and mineralized intrusions analyzed with both electron microprobe analyzer (EPMA) and LA-ICPMS at the University of New Brunswick in order to investigate the suitability of mica geochemistry as a mineral exploration tool. Biotite colour in plane polarized light varies from reddish-brown in intrusions related to Sn-W mineralization to brown and greenish-brown in intrusions associated with Cu-Mo and Mo and mineralization in barren intrusions. The variations in colour reflect different oxygen fugacity for the host magmas and correspond to a reduced environment for Sn-W hosting intrusions versus the more oxidized magmas associated with the other types of mineralization. The calculated oxygen fugacity for these intrusions fall between the quartz-fayalite-magnetite (QFM) and nickel-nickel oxide (NNO) buffers with values of 10-15.5 to 10-13.0 bar. The Fe2+/(Fe2++Mg2+) of biotite decreases from a high mean of 0.77 ± 0.16 in Sn-W related intrusions to Mo-related intrusions (mean of 0.69 ± 0.06), to barren intrusions (mean of 0.66 ± 0.06). Biotite from intrusions related to Cu-Mo occurrences has the lowest Fe2+/(Fe2++Mg2+) with a mean value of 0.56 ± 0.12. Biotite composition displays contrasting geochemical characteristics between barren intrusions and those associated with various types of mineralization. Specifically, the content of compatible elements of biotite (e.g., Mg, Ti, Co, Ni, Cr, V, Sr, and Ba) increases, whereas contents of incompatible elements (e.g., Sn, W, Mn Ta, Ga, Sc, Mo, Rb, and Cs) decreases from Sn-W-related intrusions to Mo, Cu-Mo, and barren intrusions. These trends may reflect a more evolved nature of the Sn-W related intrusions. Barren intrusions have biotite worth the lowest calculated water content of (1-3 wt.%), whereas biotite grains from Mo and Sn-W-related intrusions have a much higher water content that ranges from 3 to 6 wt.%. The water content of intrusions related to Mo-mineralization is restricted to 4.0 to 4.5 wt.%. Biotite grains from Cu-Mo, barren, and Mo-related intrusions suggest a similar halogen fugacity for the parent magmas, i.e., fH2O/fHCl and fH2O/fHF in biotite range from 1.46 to 1.51 and 4.26 to 4.54, respectively. Conversely, biotite from Sn-W related intrusions have the lowest fH2O/fHF (<3.56) and highest fH2O/fHCl (>1.59), indicating a higher degree of halogen enrichment resulting from higher degree of fractional crystallization in these intrusions. Three metallogenic classification diagrams based on biotite mineral chemistry, V-Na-Li, Li versus Si, and Sn+W versus Ga, are proposed for the discrimination of barren and mineralized granitic systems. Seventy-four apatite grains from Silurian-Devonian granitoids of New Brunswick were analyzed with both EPMA and LA-ICPMS to investigate the ability of apatite geochemistry to differentiate barren and mineralized systems. Despite homogenous major-element and halogen content, apatite grains have various trace-element compositions. Apatite from the barren intrusion has the highest water content (> 0.3 wt.%), U (117 ppm), Th (133 ppm), and the lowest Sn content of <0.5 ppm and Fe of 828 ppm. Uranium and Th decrease markedly from barren to Cu-Mo to Sn-W and reaches to its lowest value of about 13 and 28 ppm, respectively, in Mo-related intrusions due to the crystallization of monazite and zircon. Apatite grains from the Sn-W-related intrusions have the highest Sn value of 4 ppm, which differentiate them from the rest of the grains. Four new classifications were introduced using apatite Sr, Mn, (Eu/Eu*)N, and LREE/HREE ratios to differentiate barren and mineralized granitoids in New Brunswick.