Petrographic, geochemical and geochronological study of albitization associated with vein type uranium mineralization in the Beaverlodge district, northern Saskatchewan
Autor: | Kennicott, Jacklynn Adell |
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Přispěvatelé: | Chi, Guoxiang, Ashton, Kenneth, Raharimahefa, Tsilavo |
Jazyk: | angličtina |
Rok vydání: | 2017 |
Popis: | A Thesis Submitted to the Faculty of Graduate Studies and Research In Partial Fulfillment of the Requirements for the Degree of Master of Science in Geology, University of Regina. xi, 263 p. Albitization has long been noted as having a spatial association with uranium mineralization in the Beaverlodge uranium district; however, a genetic relationship between the two has yet to be demonstrated. Previous studies mainly focused on albitization in 1.94-1.92 Ga granite, but new field and petrographic studies have shown that albitization is found to also occur in the ca. 2.33 Ga Murmac Bay Group amphibolite and the ca. 1.82 Ga Martin group sedimentary rocks. There are two types of albitization: pervasive, replacement-type (R) and vein-type (V), which are grouped into two generations: generation 1 (Ab1-R and Ab1-V) and generation 2 (Ab2-R and Ab2-V). The pervasive, replacement-type albitization occurs primarily as extensive alteration zones in granitic rocks (Ab1-R-G) and as irregular patches in amphibolite (Ab1-R-A) near albite-bearing veins (Ab1-V-A). The massive albitization zones in granites are composed dominantly of albite (Ab1-R-G), which mimics the original grain size in the unaltered granites and is characterized by an abundance of microscopic red iron oxide inclusions. The Ab1-R-G postdates the regional foliation in the granites, but shows varying degrees of deformation. Along some grain boundaries, and internally, Ab1-R has locally been deformed and polygonized. New growth of finer grained, subhedral albite (Ab2-R) characterized by fewer or no microscopic iron oxide inclusions, specular hematite, subhedral rutile and local subhedral-euhedral apatite, followed by carbonate (cab1) is spatially associated with these deformed grain boundaries. The vein-type albitization is divided into two generations (Ab1-V and Ab2-V) that are considered coeval with the replacement generations, based on petrographic similarities and timing relationships. Ab1-V veins are essentially monomineralic, composed of albite grains typically containing abundant microscopic iron oxide inclusions and exhibiting evidence of brittle-ductile deformation. Ab2-V veins are characterized by euhedral albite crystals that are relatively free of hematite inclusions and have grown perpendicular to, and lining, the straight-sided vein margins. The cores of Ab2-V veins are typically filled by carbonate (cab2). Ab1-V and Ab2-V veins are developed in Murmac Bay Group amphibolite, Martin group sedimentary rocks and granites of several ages. Ab1-V veins are crosscut by Ab2-V veins, some of which are anomalously radioactive in amphibolite-hosted uranium occurrences. Chlorite grown before, after and between Ab1-V and Ab2-V vein generations in the amphibolite has temperatures in the range of 202-329°C, which partially overlaps temperatures reported by previous workers (238 to 310°C) based on chlorite geothermometry for the vein-type uranium mineralization in the Beaverlodge uranium district. Uranium mineralization in the district occurs as veins, breccia ores in a variety of rock types and in Martin group conglomerate units. The main ore mineral is pitchblende. Mineralized veins include quartz, quartz-carbonate, carbonate and quartz-carbonate-albite types that locally cross cut pervasive type albitization (Ab1-R). Pitchblende in breccias is commonly patchy and irregular, cements breccia clasts, and is associated with chlorite and other gangue minerals, including carbonate and quartz. Dating of these breccia-type pitchblende occurrences from four thick sections by LA-ICP-MS (laser ablation – inductively coupled plasma – mass spectrometry) techniques during this study gave a wide array of ages (~200-1500 Ma). Alkaline mafic volcanic rocks emplaced during Martin group deposition provide a maximum age constraint for mineralization hosted by the Martin group at 1.82 Ga. When impurities from these breccia-type uraninites are plotted versus their calculated chemical ages, a reference line can be drawn to give an age just over 1800 Ma. This age is broadly consistent with the timing of D4 deformation and Martin volcanism. At least one generation of mineralization is broadly coeval with the second generation of albitization (Ab2-R and Ab2-V) and is syn- to post-Martin group. Student yes |
Databáze: | OpenAIRE |
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