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Doctor of Philosophy




Dr. Norman Duke


The Kurupung batholith is situated in a west dipping mylonite zone within theTransamazonian-aged Mazaruni granite greenstone terrane. Mylonitic shearing is a result of regional sinistral strike-slip faulting during the post-collisional stage of the Transamazonian orogenic cycle. Deformation was active between 2103 +/- 3 Ma, the age of the batholith, and 1995 +/- 15 Ma, the age of hydrothermal uranium and zircon mineralization. Mineral chemical and geochemical characterization of the batholith identifies a uranium-enriched low-Ti sanukitoid generated by partial melting of slab metasomatized mantle which retained unresorbed Cr-bearing mantle inclusions. Rapid unroofing to greenschist facies conditions at approximately 2094 +/- 5 Ma, juxtaposed the Kurupung batholith against Transamazonian volcaniclastics. Textural evidence supports a continuum from Cr-bearing clinopyroxene and hornblende to actinolite-biotite-magnetite-chlorite(1) and minor sausseritization of Ca-plagioclase to albite(1)-muscovite-epidote. Decompression resulted in Ba-Kfeldspar pegmatite dikes at 2085 +/- 9 Ma and voluminous Ba-Kfeldspar metasomatism at 2071 +/- 13 Ma. Pervasive replacement of early primary Ca-plagioclase by secondary Ba-Kfeldspar partitioned Na into the fluid phase resulting in pervasive albite(3) replacement. Lamprophyre dike injection at 2011 +/- 11 Ma marks the transition from ductile to brittle deformation within the mylonitic shear zone which allowed devolatilization of mantle-derived fluorine and CO2-rich fluids.

Meteoric ingress resulted in development of zones of mixing where chlorite(2) cemented albitite(3) breccia. Devolatilization along deeply penetrating shears resulted in a long-lived shear zone with Na metasomatism, diagnostic of an albitite-type uranium system. Fluorine and CO2-rich fluid interacted with zircon granules in the batholith and sequestered uranium and zircon from their marginal domains. The result was an F-rich fluid carrying uranium and zircon in solution re-precipitating uranium in hydrothermal zircon veins. The basement-hosted uranium mineralization of the Kurupung batholith pre-dates the Roraima sedimentation and hence, the mineralization is not unconformity related.

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