The evolution of metasomatic uranium ore systems in the Kitts-Post Hill belt of the Central Mineral Belt, Labrador, Canada
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Keywords:
Uraninite
Metasomatism
Rare-earth element
Trace element
Breccia
Uranium ore
The Central Mineral Belt (CMB) in Labrador, Canada, hosts multiple U (±base ± precious metal) showings, prospects and deposits in metamorphosed and variably hydrothermally altered Neoarchean to Mesoproterozoic, igneous and sedimentary rocks. Previous work has recognized U mineralization locally associated with Fe-Ca and alkali metasomatism typical of metasomatic iron oxide and alkali-calcic alteration systems (IOAA) that host iron oxide-copper-gold (IOCG) and affiliated critical metal deposits. However, the type, extent and temporal or genetic relationships between the diverse Fe, Ca and alkali metasomatism and the regionally distributed U mineralization remains poorly understood. Combined unsupervised machine-learning and classification of alteration from a large geochemical dataset distinguish the main alteration phases in the CMB, identify compositional changes related to U mineralization, and infer lithological/mineralogical information from samples with censored (i.e., missing), limited and/or inaccurate metadata. Weak to intense Na and Na + Ca-Fe (Mg) metasomatism in the southwest (Two-Time and Moran Lake areas) and eastern (Michelin area) portions of the CMB pre-dates U mineralization and Fe-oxide breccia development, similar to albitite-hosted U and IOCG deposits globally. Rare earth elements and spider diagrams highlight both preservation and disruption of normally immobile elements. Principal component and cluster analysis indicate significant variations in Fe-Mg ± Na contents in the rocks from combinations of Na, Ca, Fe, and Mg-rich alteration, while protolith REE signatures can be locally preserved even after pervasive albitization-hematization. Cluster analysis identifies mineralized felsic and mafic rocks in the Michelin deposit and Moran Lake area, facilitating inference of relevant lithological/mineralogical information from samples lacking or with limited meta-data. The methods outlined provide rapid and relatively inexpensive means to optimize identification of mineral systems within large geochemical datasets, verify drill core or field observations, highlight potentially overlooked alteration, and refine economic mineral potential assessments. Based on our results and previous work, we suggest the mineral potential of the southwestern and eastern CMB needs to be re-assessed with modern exploration models for IOAA ore systems and their iron oxide-poor variants.
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The Thelon basin, Nunavut, shares many similarities with the uranium-producing Athabasca basin, Saskatchewan; however, the uranium deposits associated with the Thelon basin are still poorly understood. The Kiggavik project area (AREVA Resources Canada) is located near the northeastern terminus of the Thelon basin and comprises multiple uranium deposits hosted exclusively in basement rocks. The Bong deposit is hosted dominantly by Neoarchean metagraywacke of the Woodburn Lake group. A five-phase metallogenetic model is proposed for the Bong deposit, with three stages of uraninite identified. The premineralization phase is characterized by host-rock silicification. Mineralization is separated into three main stages. Stage 1 uraninite (U1; ca. 1500 Ma) is preserved in highly fractured and altered disseminated grains that are overgrown by later stages of uraninite. Stage 2 uraninite (U2; ca. 1100 Ma) forms veinlets parallel to D 1 foliation and coats and fills fractures in organic matter nodules and blebs. Stage 2 uraninite is associated with pervasive illite that formed from ~190°C fluids ( δ 18 O: −6.4‰, δ 2 H: −97‰), which remobilized much of Stage 1 uraninite and completely overprinted Stage 1 alteration. At ~1000 Ma an oxidizing fluid deposited uraninite along redox fronts (U3) while altering and remobilizing Stage 1 and 2 uraninite. Post-uranium-oxide minerals include drusy quartz, calcite, and illite accompanied by uranyl phases (e.g., uranophane, Ca-U).
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Illite
Geochronology
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Uraninite
Uranium ore
Fluorite
Deposition
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Based on field observations,microscope,X-ray diffraction,QEMSCAN and electron microprobe techniques,this paper studies in detail the mineral composition,texture and structure of uranium ore of the alaskitetype uranium deposit in the Gaudeanmus area,Namibia.Uranium minerals of this area are mainly uranium oxides,U-Ti-oxides and uranium silicates,in which,uranium oxides include uraninite,pitchblende and thor-uraninite;UTi-oxides include brannerite,betafite,uranpyrochlore and euxenite;uranium silicates include uranophane,coffinite and uranothorite.Uraninite,thor-uraninite and U-Ti-oxides are mostly panidiomorphic or hypidiomorphic granular texture,disseminated structure,and most of pitchblende and uranium silicates are aphanocrystalline texture,metasomatic relict texture and veined structure.Thus,the alaskite-type uranium deposit of this area was formed together by the original magma crystallization differentiation,later hydrothermal reformation and supergenesis.
Uraninite
Uranium ore
Texture (cosmology)
Metasomatism
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The distribution of REE in a zoned ultramafic pod formed by incomplete re-equilibration of ultrabasic and quartzofeldspathic reactant compositions has been studied. Transport of the heavy REE (HREE) as well as the light REE (LREE) over several metres has occurred during the diffusion-controlled metasomatism of the protolith mineral assemblages. The largest resultant concentration range (Eu) exceeds two orders of magni- tude. In general, REE abundances increase towards the marginal zones, and differences between the behaviour of LREE, middle REE (MREE) and HREE subgroups are observed. LREE are least mobile in the aqueous transporting medium. Complexing by carbonate ligands is probably not an important factor in this system, and the final REE distribution is thought to be governed largely by the crystal structure of the major zonal minerals. THE conditions that can give rise to element mobility during processes of rock alteration, metamorphism or metasomatism are of current importance since certain trace elements, including the rare earths, are sometimes used as indicators of a rock's parentage. This use is based on the
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Ultramafic rock
Rare-earth element
Protolith
Trace element
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Uranium ore
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Uraninite
Uranium ore
Solubility equilibrium
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