Pyrrhotite and associated sulphides and their relationship to acid rock drainage in the Halifax Formation, Meguma Group, Nova Scotia

The physical disruption of sulphide-bearing metasedimentary rocks of the Halifax Formation leads to oxidation of iron-sulphide minerals and the generation of acid rock drainage (ARD). Although pyrrhotite occurs in many places throughout the Halifax Formation, previous ARD studies have not considered in detail the mineral chemistry, texture, and distribution of this mineral nor how these factors may potentially influence the development of ARD. For this study, pyrrhotite-bearing samples of the Halifax Formation were collected in the field and from drill core at four locations in southwestern Nova Scotia. Samples were taken from different geological settings, such as proximal and distal to granitic intrusions and from different stratigraphic positions, to obtain a variety of mineral assemblages. Petrographic, microprobe and X-ray diffraction work indicate that the pyrrhotite in all samples is mainly monoclinic Fe7Sg, and its composition is relatively homogeneous regardless of geological environment. Inclusions of chalcopyrite and detectable quantities of As, Co and Ni are common. In regionally metamorphosed, grecnschist-facies areas, pyrrhotite is preferentially aligned along cleavage planes and thus is easily accessible to oxidizing air and fluids. Because pyrrhotite is regionally developed, contains potentially toxic trace elements, and occurs along cleavage planes, it is considered to play a significant role in ARD development in the Halifax Formation. Also, pyrrhotite oxidizes substantially faster than many other sulphide minerals and may be especially significant in the early stages of ARD. RÉSUMÉ La dislocation physique des roches métasédimentaires sulfuriféres de la Formation d'Halifax mène à une oxydation des minéraux renfermant du sulfure de fer ainsi qu'à la production d'exhaures de roches acide (ERA). Même si on relève la présence de pyrrhotine en de nombreux endroits partout à l'intérieur de la Formation d'Halifax, les études antérieures des ERA ne se sont pas attardées de fa÷on approfondie sur la nature chimique minérale, la texture et la répartition de ce minéral ni sur la manière dont ces facteurs peuvent éventuellemcnt influer sur l'apparition des ERA. Les chercheurs ont, aux fins de cette étude, prélevé sur le terrain ainsi que sur des carottes de sondage à quatre emplacements dans le sud-ouest de la Nouvelle-Écosse, des échantillons de la Formation d'Halifax renfermant de la pyrrhotine. On a prélevé les échantillons de différents cadres géologiques stratigraphiques, comme des intrusions proximales et distalcs à granitiques et différentes positions stratigraphiques, afin d'obtenir toute une variété d’associations minérialogiques. Des travaux à la microsonde, de diffraction aux rayons X et pétrographiques révèlent que la pyrrhotine de tous les échantillons est essentiellement du F7Sg monoclinique et qu'elle est d'une composition relativement homogene, peu importe I'environnement géologique. Les inclusions de chalcopyrite et de quantités détectablcs d'As, de Co et de Ni sont courantes. Dans les secteurs des faciès des schistes verts régionalement métamorphisés, la pyrrhotine est principalement alignée le long de plans de clivage et elle est ainsi facilement accessible aux fluides et à l'air oxydants. Vu la présence régionale de la pyrrhotine, vu qu'elle renferme des éléments traces pouvant être toxiques et vu qu'elle sc trouve le long de plans de clivage, on considère qu'elle joue un rôle prépondérant dans la production des ERA à l'intérieur de la Formation d'Halifax. La pyrrhotine s'oxyde par ailleurs bcaucoup plus rapidement que de nombreux autres minéraux sulfurls et ce facteur peut être particulièrement déterminant dans les premiers stades de la production des ERA. [Traduit par la rédaction

Structure, metamorphism and tectonic setting of metasedimentary rocks and mafic-ultramafic inclusions in the Dashwoods subzone of the Dunnage zone, southwestern Newfoundland

The Dashwoods subzone of the Dunnage zone in southwestern Newfoundland is characterized by high grade metasedimentary schists and gneisses and disrupted ophiolite complexes (Annieopsquotch Complex and Long Range Mafic-Ultramafic Complex) all intruded by hornblende-biotite granodiorite to tonalite. A previously reported age of the granitoid rocks is 456 ± 3Ma. This study focuses on an area east of the Long Range Fault, on the western side of the Dashwoods subzone and contains all the major lithostratigraphic units characteristic of the Dashwoods subzone. -- Metasedimentary rocks are separated into two main units: metapsammites to the west and metapelites to the east. Mafic-ultramatic inclusions lie within shear zones in the metapelites and are interpreted to represent parts of a disrupted ophiolite suite. All rocks within the shear zones (both metapelite and mafic-ultramatic) are extensively retrogressed to greenschist facies mineral assemblages but evidence of a higher grade, amphibolite facies metamorphism is evident in rocks that have not been completely retrogressed. The mafic-ultramafic rocks are interpreted to have undergone the full range of metamorphism and deformation that has affected the metasedimentary rocks. Geothermobarometry calculations suggest that the higher grade metamorphic event may have reached temperatures in the order of 800°C with pressures in the order of 5 to 7 kbars. -- The metasedimentary rocks are correlated with the Fleur de Lys metasediments found in northeastern Newfoundland on the basis of similar stratigraphic position along the eastern edge of the miogeocline of eastern North America. An upper age of deposition of the metasediments is approximately middle Ordovician as constrained by the age of the granitoid rocks. Silurian mafic bodies in the Dashwoods subzone have not been affected by high grade metamorphism or high degree of deformation and the Dashwoods subzone had probably stabilized by late Ordovician to Silurian time

Ruptured Anterior Communicating Artery Aneurysm Causing Bilateral Oculomotor Nerve Palsy : A Case Report

A rare case of bilateral third cranial nerve palsy due to a ruptured anterior communicating artery aneurysm is presented. A 68-yr-old woman was semicomatose with bilaterally fixed dilated pupil, abducted eyes, and ptosis. A computed tomography demonstrated extensive hemorrhage spreading around the both Sylvian and interhemisheric fissure without focal mass effect. Intracranial pressure via extraventricular drainage before surgery was 15-50 mmHg. Three months later, brain MRI showed infarction of left posterior cerebral artery territory and lacuna infarction of the pons. Eleven months after aneurysm repair, nerve palsy improved slowly and recovered partially. The patient communicated well with simple words. The author reviewed and discussed the possible mechanism of this rare neuro-ophthalmological manifestation in view of a false localizing sign

Evaluation of the French Haut Taux de Combustion (HTC) Critical Experiment Data

In the 1980s, a series of critical experiments referred to as the Haut Taux de Combustion (HTC) experiments was conducted by the Institut de Radioprotection et de Surete Nucleaire (IRSN) at the experimental criticality facility in Valduc, France. The plutonium-to- uranium ratio and the isotopic compositions of both the uranium and plutonium used in the simulated fuel rods were designed to be similar to what would be found in a typical pressurized-water reactor fuel assembly that initially had an enrichment of 4.5 wt% {sup 235}U and was burned to 37,500 MWd/MTU. The fuel material also includes {sup 241}Am, which is present due to the decay of {sup 241}Pu. The HTC experiments include configurations designed to simulate fuel handling activities, pool storage, and transport in casks constructed of thick lead or steel. Rights of use for the HTC experiment data were purchased under an agreement that limits release of the information. Consequently, a detailed and complete description of the experiments is not presented in this report. This report discusses evaluation of the four HTC data reports, modeling of the experiments, sensitivity and uncertainty analysis, and upper subcritical limit (USL) calculation. The report also presents some conclusions and recommendations concerning use of the HTC experiment data for burnup credit applications. The similarity of the HTC experiments with PWR spent nuclear fuel has been quantified using sensitivity/uncertainty analysis, confirming that the HTC experiments are significantly more applicable to the validation of burnup credit calculations than other available mixed-oxide (MOX) experiments. The HTC experiments were designed and executed with a high level of rigor, resulting in experimental uncertainties that are lower than many of the earlier MOX experiments. The HTC data reports, together with information provided in this report, provide sufficient data to allow for either detailed or simplified computational models to be developed. The HTC experiments substantially strengthen the technical basis for validation by adding to the previously small number of applicable experiments against which to compare burnup credit applications. Existing MOX experiments found to be applicable are also identified in this report