Evolution and mineralization of the Moose II Lithium-Tantalum Pegmatite Deposit, Northwest Territories, Canada
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Date
2013
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University of New Brunswick
Abstract
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.