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Environmental Change in Middle Ordovician carbonates near Little Cataraqui Creek Conservation Area, Kingston ON

Tue, 14 May 2013 04:00:00 GMT

Title: Environmental Change in Middle Ordovician carbonates near Little Cataraqui Creek Conservation Area, Kingston ON Authors: Shuster, Sonya Abstract: The Black River Group is a carbonate succession in southern Ontario and northern New York State that was deposited in the Middle Ordovician. The rocks of this Group accumulated in a tropical shallow marine environment. The focus of this study is a 16m succession, exposed in a road cut north of Kingston, Ontario. The section is divided into three main zones. The bottom 10m consists primarily of carbonate mudstones with some calcite nodules and a sparse and highly restricted fossil assemblage of mainly salinity tolerant invertebrates such as ostracods. These rocks are interpreted as being a series of primarily peritidal deposits that were generally stressed and hypersaline. The next 2m is primarily an ooid grainstone, with and without fossils. It is interpreted as having been deposited in a sand shoal. The upper 4m consists primarily of floatstones with a lime-mud or fossil-wackestone matrix as well as some oolites and contains an abundant and diverse fossil assemblage that includes stenohaline organisms such as echinoderms and articulate brachiopods. The upper part is interpreted as being deeper water within the photic zone and contains an ooid sand shoal and a bryozoan biostrome, among other facies. This upper part is generally less stressed and had normal marine salinity. The deepening-upwards trend observed in this outcrop is consistent with the Black River Group as a whole, and is generally regarded as reflecting the regional sea level rise that was occurring at this time due to the passing of the peripheral bulge.

Stable Thallium Isotope Fractionation in Uraninites

Wed, 08 May 2013 04:00:00 GMT

Title: Stable Thallium Isotope Fractionation in Uraninites Authors: Tupper, Wynn Abstract: Thallium isotopic ratios, (ε205Tl = 205Tl/203Tl deviation from a reference ratio) are measured in uraninite samples representative of diverse geochemical systems responsible for high grade UO2 precipitation. Notably those deposit styles involve from the reduction of uranium complexes in aqueous solutions, and uraninite precipitation from saline fluids. Measureable isotopic fractionation, ε205Tl, must produce a result that exceeds analytical reference error. Thallium isotopic ratios are obtained by multiple collector-inductively coupled plasma mass spectrometry (MC-ICP-MS). For reliable MC-ICP-MS results require that thallium is extracted entirely from the mineral sample. Digestion of uraninite samples is a series of acid digestions, and consequent thallium separation from ion exchange chromatography conducted by acids with minor (~2%) concentrations of oxidizing agents, such as Br2, to disable ion reduction. Separation of Thallium is done in correspondence with molybdenum separation for a separate study on Mo isotopic ratios. Thallium is sensitive to oxidation changes in fluids. Further, the sampled deposit styles display a spectrum of oxidation conditions, solution compositions, temperatures and pressures, theoretically yielding various detectable ε205Tl values. Data for eight samples are produced, where all ε205Tl are negative relative to NIST, the most negative being -5.5 and the least being -0.7. Correlations with various multi-element data, 234U/238U, 235U/238U, and deposit chemistry are graphed to assess the ability to predict ε205Tl. It appears that ε205Tl data is negatively correlated which uranium and thallium concentration, as well as Fe+Mn concentration in. The explanation of this is the ability of thallium to be present as a trivalent ion within basinal high temperature alkaline solutions, those fluids associated with unconformity related deposit types. However, an alternate explanation is that the depletion of thallium correlated to alteration and subsequent interaction of uraninites by fluids after genesis that result in ε205Tl values near 0 at such low concentrations of thallium. Description: Thallium isotope geochemistry

Characterization of Uranium and Rare Earth Element Mobility and Attenuation Downstream of Decommissioned Tailings Impoundments at the Bicroft Mine near Bancroft, Ontario

Mon, 06 May 2013 04:00:00 GMT

Title: Characterization of Uranium and Rare Earth Element Mobility and Attenuation Downstream of Decommissioned Tailings Impoundments at the Bicroft Mine near Bancroft, Ontario Authors: Laidlow, Allison Abstract: Attenuation of uranium (U) and rare earth elements (REEs) has been observed in stream and wetland sediments, but the geochemical and mineralogical processes involved in sequestering these elements in natural systems are not well understood. The decommissioned Bicroft Uranium Mine near Bancroft, ON uses a modified stream and wetland system to reduce the concentrations of U and other metals in tailings pond effluent to levels below the Provincial Water Quality Objectives. The Bicroft Mine was operated from 1957 to 1963, and processed low-grade (~0.17 wt% U3O8), disseminated U hosted by pegmatite dykes in amphibolite gneiss, forming 2,284,421 tonnes of tailings, deposited into two tailings impoundments. The Bicroft site has since operated as a passively attenuating stream and wetland remediation system for 55 years, demonstrating the potential longevity and viability for long-term sequestration of U and REEs through natural attenuation. To identify U and REE hosts and their stability in the natural environment, colloids, tailings, stream and wetland sediments were analyzed using various methods, including tangential flow filtration (TFF), ICP-ES/MS, scanning electron microscopy, and synchrotron techniques (bulk and µXANES, µXRF, and µXRD). The results show that Fe- and Mn-oxyhydroxides, goethite, and birnessite are the main mineral hosts for U and REEs in both the colloids and sediments. In addition, detrital grains of U- and REE-bearing minerals were found >200 m downstream in colloids and wetland sediments, showing the potential for long range transport of colloids and particulates in the stream system. Seasonal influences on the stability of trace metals in sediments were observed, and may demonstrate the limitations of passively attenuating remediation systems as a viable method for attenuation. Changes in the redox state of the stream system were observed to influence the attenuation of U and REEs, however, changes in the redox state with depth in the wetland sediments were not observed, and showed no direct influence on the attenuation of U and REEs. The results of this study will help to develop better monitoring strategies for U tailings sites and should reduce the impacts of future U mining operations. Description: Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2013-05-06 07:44:03.327

Characterization and 40Ar/39Ar Dating of Hornblende from the Nelson Plutonic Suite, Southern Kootenay Arc, SE, B.C.

Thu, 02 May 2013 04:00:00 GMT

Title: Characterization and 40Ar/39Ar Dating of Hornblende from the Nelson Plutonic Suite, Southern Kootenay Arc, SE, B.C. Authors: Pickett, Jessica Abstract: From Mid-Jurassic to Eocene time the Kootenay Arc in southeastern B.C. experienced several episodes of tectonism, metamorphism and plutonism. The focus of this study is the tectonothermal history of the Mine and Wall stocks (biotite-hornblende-epidote granodiorite; U-Pb dates; 171 and 168 Ma) which are the most easterly plutons of the Nelson Suite in the area. Previous K-Ar and 40Ar/39Ar studies of micas from these plutons revealed cooling and overprinting dates between 166 Ma in the west and 67 Ma in the east. For this study, 11 hornblende separates were prepared from the same rocks, checked for purity by SEM and chemically analyzed by electron microprobe. 40Ar/39Ar age spectra for most of these hornblendes show well defined plateaux with plateau dates of ~170 Ma. Inverse isochron reveal the presence of excess 40Ar and yield better estimates of the time of cooling through the closure temperature of hornblende indicating that most of these plutons had cooled to < 500 oC by ~168 Ma. Only hornblende from the Mine stock east of the Next Creek fault shows evidence of a later thermal disturbance in Cretaceous or later time. New Al-in-Hornblende pressure estimates increase to the north and east, and are in general agreement with previous estimates from pelitic assemblages (4 to 6 Kbar) in the contact aureole. Highest pressures are east of the Next Creek fault near the eastern margin of the Mine stock. This zone marks a sharp decrease in mica dates. West of the fault, mid-Jurassic to Early-Cretaceous dates with no evidence of Eocene overprinting are typical. The higher pressures and Late Cretaceous-to-Eocene dates east of the fault are consistent with east-side-up differential uplift and unroofing related to regional Eocene extension.