Metamorphic investigation of mid-P aluminous gneisses from the central Grenville Province

This is a metamorphic study of mid-P anatectic aluminous gneisses from the Manicouagan and lac du Milieu areas of the central Grenville Province. The rocks are derived from hydrothermally altered felsic protoliths and were metamorphosed at granulite facies conditions during the Grenvillian orogeny. The samples come from three locations separated by several tens of kilometers and exhibit a wide range of textures and bulk compositions. However, they all have the same peak mineral assemblage: garnet + biotite + quartz + K-feldspar +/- plagioclase +/- sillimanite with retrograde cordierite in some, and show evidence of partial melting and melt loss. In terms of mineralogy and bulk composition, the samples were divided into two groups, sillimanite-rich and sillimanite-poor, with a high and low Alumina index in the AFM space, respectively. Phase equilibria modeling in the Na₂O–CaO–K₂O–FeO–MgO–Al₂O₃–SiO₂–H₂O– TiO₂–O (NCKFMASTHO) system using Thermocalc constrained the P–T field of the peak mineral assemblage at 800–900ºC and 6–11kbar, with melt solidification in the range of 800–865ºC and 6–8kbar. The presence of sillimanite inclusions in garnet, and of only scarce, retrograde cordierite, is consistent with moderate dP/dT gradient ‘hairpin’ P– T paths, which were similar between the three locations. This study also investigated the role of Fe3+ on phase stability in mid-P aluminous systems. Fe³⁺ is problematic because although it is incorporated in the NaCKFMASTHO system, it is rarely measured in modeled minerals and rocks and its value is generally assumed. Biotite may contain significant amounts of Fe³⁺, and these were analysed by Mössbauer spectroscopy in selected samples, where they were found to be low (0-4%). In addition, the effect of increasing the bulk Fe³⁺ in the mid-P portion of phase diagrams was modeled. This increase added new minor phases and changed the phase proportions, as well as shifted phase boundaries to a small degree, but P–T paths remained largely unaffected. Finally, the two methods commonly used in phase equilibria modeling to account for melt loss were compared. In some cases there were major differences in the topologies between the ‘melt reintegration’ and ‘adding water’ methods, but the former method is the most consistent with the rock data, and should be the method of choice.

A study of methods used to analyze total oil and polycyclic aromatic hydrocarbons in produced water: steps towards the validation of molecularly imprinted polymers for use in marine environmetns

Produced water is a by-product of offshore oil and gas production, and is released in large volumes when platforms are actively processing crude oil. Some pollutants are not typically removed by conventional oil/water separation methods and are discharged with produced water. Oil and grease can be found dispersed in produced water in the form of tiny droplets, and polycyclic aromatic hydrocarbons (PAHs) are commonly found dissolved in produced water. Both can have acute and chronic toxic effects in marine environments even at low exposure levels. The analysis of the dissolved and dispersed phases are a priority, but effort is required to meet the necessary detection limits. There are several methods for the analysis of produced water for dispersed oil and dissolved PAHs, all of which have advantages and disadvantages. In this work, EPA Method 1664 and APHA Method 5520 C for the determination of oil and grease will be examined and compared. For the detection of PAHs, EPA Method 525 and PAH MIPs will be compared, and results evaluated. APHA Method 5520 C Partition-Infrared Method is a liquid-liquid extraction procedure with IR determination of oil and grease. For analysis on spiked samples of artificial seawater, extraction efficiency ranged from 85 – 97%. Linearity was achieved in the range of 5 – 500 mg/L. This is a single-wavelength method and is unsuitable for quantification of aromatics and other compounds that lack sp³-hybridized carbon atoms. EPA Method 1664 is the liquid-liquid extraction of oil and grease from water samples followed by gravimetric determination. When distilled water spiked with reference oil was extracted by this procedure, extraction efficiency ranged from 28.4 – 86.2%, and %RSD ranged from 7.68 – 38.0%. EPA Method 525 uses solid phase extraction with analysis by GC-MS, and was performed on distilled water and water from St. John’s Harbour, all spiked with naphthalene, fluorene, phenanthrene, and pyrene. The limits of detection in harbour water were 0.144, 3.82, 0.119, and 0.153 g/L respectively. Linearity was obtained in the range of 0.5-10 g/L, and %RSD ranged from 0.36% (fluorene) to 46% (pyrene). Molecularly imprinted polymers (MIPs) are sorbent materials made selective by polymerizing functional monomers and crosslinkers in the presence of a template molecule, usually the analytes of interest or related compounds. They can adsorb and concentrate PAHs from aqueous environments and are combined with methods of analysis including GC-MS, LC-UV-Vis, and desorption electrospray ionization (DESI)- MS. This work examines MIP-based methods as well as those methods previously mentioned which are currently used by the oil and gas industry and government environmental agencies. MIPs are shown to give results consistent with other methods, and are a low-cost alternative improving ease, throughput, and sensitivity. PAH MIPs were used to determine naphthalene spiked into ASTM artificial seawater, as well as produced water from an offshore oil and gas operation. Linearity was achieved in the range studied (0.5 – 5 mg/L) for both matrices, with R² = 0.936 for seawater and R² = 0.819 for produced water. The %RSD for seawater ranged from 6.58 – 50.5% and for produced water, from 8.19 – 79.6%.