Browsing by Author "Mcfarlane, Chris R.M."

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    Evolution and mineralization of the Moose II Lithium-Tantalum Pegmatite Deposit, Northwest Territories, Canada
    (University of New Brunswick, 2013) Anderson, Melissa O.; Lentz, David; Mcfarlane, Chris R.M.
    The Moose II rare-metal granitic pegmatite is located approximately 115 km east of Yellowknife, NWT, on the north shore of Great Slave Lake. The irregularly zoned dike is -430 m long by 61 m wide, and is discordantly hosted within polydeformed metaturbidites of the Neoarchean Yellowknife Supergroup. This deposit was mined for both lithium and tantalum (1946-1954). The pegmatite formed ca. 2652 Ma (U-Pb columbite ), which corresponds to a late magmatic period following a phase of extensive plutonism in the Slave Province. The size and orientation of the pegmatite suggest that it was emplaced into a dilatant zone along a north-trending shear zone. The dike displays extreme fractionation, manifested by the irregular spatial zonation of mineral assemblages, rare-metal enrichment, and the very high degree of chemical evolution. Mineralogical zones include: a narrow border zone, a fine-grained wall zone, several megacrystic intermediate zones, massive quartz and amblygonitemontebrasite core zones, saccharoidal ( aplitic) al bite zones, and muscovite-rich replacement zones. The degree of chemical evolution of the dike suggests that the pegmatite melt was injected a considerable distance from the progenitor pluton. Detailed internal fractionation trends show progressive evolution from the margins of the pegmatite inwards, and from the south section of the pegmatite towards the north. The economically important minerals present include: amblygonite-montebrasite (Li), spodumene (Li), and columbite-group minerals (Nb-Ta). Processes of niobiumtantalum mineralization are primarily magmatic, with enrichment during magmaticmetasomatism, and minor remobilization during hydrothermal metasomatism.
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    The geochemical, geochronologic, and isotopic constraints on U-ThREE pegmatites and related mineralization of south-central part of the the Wollaston Domain, Northern Saskatchewan, Canada
    (University of New Brunswick, 2013) McKeough, Michelle; Lentz, David; Mcfarlane, Chris R.M.
    In northern Saskatchewan, granitic pegmatites intrude Early Paleoproterozoic Wollaston Group metasedimentary rocks and interfolded granitoids that unconformably overlie Late Archean gneisses, all of which have been subjected to deformation during the protracted 1.86 to 1.77 Ga Trans-Hudson Orogeny. U-Th±REE-Y-Nb-pegmatite intrusions and fracture-controlled uranium mineralization characterizes the U-Th±REEY- Nb occurrences at Kulyk Lake, Eagle Lake, and Karin Lake mineral exploration properties in the south-central Wollaston Domain. The pegmatites are moderately to highly evolved, ranging from mineralogically simple- to complex-type pegmatites. The complex-type pegmatites are hybridized, due to bimetasomatic interaction with the host rocks. Saturation of U-Th±REE-Y-Nb occurs at the margins (predominantly border and wall zones) of the hybridized pegmatites, linking them genetically. These are rare-earth element class, NYF pegmatites (Nb-Y-F type), and are interpreted to have formed in a late syn- to post-collisional tectonic setting. The age constraints, textures and relatively high-T partial melting conditions (-750 to 800°C) confine the pegmatite's melt-forming conditions to an early deformational event dated between 1835 and 1805 Ma, followed by post-peak high-temperature retrograde metamorphism ca. 1770 Ma. Field relationships, textures, and geochemical variations between pegmatite groups provide strong evidence that U, Th, REE±Y- Nb phases in pegmatites from the Kulyk, Eagle, and Karin lakes continued to evolve in an open- to closed-system environment. Assimilation and/or fractional crystallization processes progressed during melt ascent, aiding in the exchange of U, Th, and REE accessory phases between continuous multiple pegmatite injections through various conduits during the Trans-Hudson Orogeny near peak metamorphic conditions. The mineralizing phases are progressively enhanced into the last stage of pegmatite evolution, when fluid fractionation would occur via infiltration of a volatile phase through partially crystallized portions of the pegmatite ( and eventually the host rocks) that will enhance metasomatic transfer, i.e., assist in the diffusion and advection of U, Th, and HFSEs (REEs and Zr) from the melt. Furthermore, mineralogical, textural, geochemical, geochronological, and isotopic data was used to expand on the fractionation model for these particular ascending NYF -type enriched melts, providing evidence for an immiscible phosphatic liquid during the evolution of the monazite showing at Kulyk Lake. These particular residual melts evolved via protracted fractionation that at a critical point will evolve into an immiscible phosphatic melt enriched in Fe, Ti, Th, Y and REE.