REE and other minerals in the West Moose River Pluton and associated rocks, Cobequid Highlands, Nova Scotia, and their association with fracturing

1 online resource (viii, 261 p.) : ill. (some col.), col. mapIncludes abstract and appendices.Includes bibliographical references (p. 43-46).The West Moose River pluton consists principally of an A-type granite emplaced immediately north of the Cobequid fault into Avalon terrane rocks in the latest Devonian-Early Carboniferous. Continued strike-slip fault movement in the shear zone caused the formation of pervasive fractures within the pluton, which have been shown to host REE-bearing minerals. The purpose of this study was to gain a better understanding of the source, timing, and distribution of REE-bearing minerals and their relation to regional events. Samples were collected from late mafic dykes, surrounding country rock, and the granite itself. Primary and secondary mineralogy were investigated using petrographic microscope, scanning electron microscope, and whole rock analysis. In total, 7 REE-bearing hydrothermal minerals were identified, with both the LREE- and HREE- type found in each lithology. The A-type granite seems the most likely source of hydrothermal REEs, and magmatic zircon for HREEs in particular; HREE-bearing zircon was the only primary REE-mineral identified, and occurred exclusively in the granite. Due to paragenetic association with carbonates, Fe-oxyhydroxides, and chalcopyrite, LREE remobilization likely occurred during the 323 Ma iron -oxide-copper-gold mineralization event. Hydrothermal HREE-minerals are either coeval with, or predate this event, and often contain Nb and Ti. LREE-minerals are most concentrated in late minette dykes, which show a positive correlation between REE concentrations and the amount of fracturing. The halogen rich content of minettes may provide favourable conditions for the precipitation of LREEs, and should be considered as future exploration targets and areas of research

A portrait of wellbore leakage in northeastern British Columbia, Canada

Oil and gas well leakage is of public concern primarily due to the perceived risks of aquifer contamination and greenhouse gas (GHG) emissions. This study examined well leakage data from the British Columbia Oil and Gas Commission (BC OGC) to identify leakage pathways and initially quantify incident rates of leakage and GHG emissions from leaking wells. Three types of leakage are distinguished: “surface casing vent flow” (SCVF), “outside the surface casing leakage” (OSCL), and “cap leakage” (CL). In British Columbia (BC), the majority of reported incidents involve SCVF of gases, which does not pose a risk of aquifer contamination but does contribute to GHG emissions. Reported liquid leakage of brines and hydrocarbons is rarer. OSCL and CL of gas are more serious problems due to the risk of long-term leakage from abandoned wells; some were reported to be leaking gas several decades after they were permanently abandoned. According to the requirements of provincial regulation, 21,525 have been tested for leakage. In total, 2,329 wells in BC have had reported leakage during the lifetime of the well. This represents 10.8% of all wells in the assumed test population. However, it seems likely that wells drilled and/or abandoned before 2010 have unreported leakage. In BC, the total GHG emission from gas SCVF is estimated to reach about 75,000 t/y based on the existing inventory calculation; however, this number is likely higher due to underreporting

Water footprint of hydraulic fracturing in Northeastern British Columbia, Canada

The method of hydraulic fracturing used to exploit unconventional shale gas has raised public concerns over the volumes of freshwater that are extracted for injection operations as well as the volumes of wastewater generated as a by-product of gas production. Using data from the British Columbia Oil and Gas Commission, this paper examines the volumes of produced and injected water from hydraulically fractured gas wells in Northeastern British Columbia. The two major producing shale gas basins in the province are the Montney and the Horn River. In this study, these are divided into several sub-basins based on existing geological and reservoir engineering applications. For each sub-basin the average volumes of wastewater- and injected water per well are calculated and then normalized to cumulative gas production. Ratios of injected water: gas production and wastewater: gas production are then applied to estimated volumes of remaining gas reserves in each sub-basin in order to calculate a total water footprint of future exploitation. These extrapolated water footprints were further elaborated into three scenarios of wastewater recycling rates: 0, 40, and 100% re-use. This study also compares the quality and quantity of wastewater produced from hydraulically fractured wells to their conventional counterparts in the province. Based on these calculations, the total future freshwater withdrawal and wastewater production volumes for all basins range from 1.65 to 3 billion, and 0 to 1.35 billion cubic metres, respectively. Volumes of freshwater withdrawal are relatively modest compared to other industries when considering the size of Northeastern British Columbia and the time-scale of extraction. In general, hydraulically fractured wells in Northeastern British Columbia produce volumes of wastewater that are equal to or lower than those required for injection. Unconventional gas wells often produce far less wastewater than their conventional counterparts

Fractured latest Devonian granites of the West Moose River pluton along the Cobequid Shear Zone, Nova Scotia: implications for regional mineralization

Latest Devonian (∼365–358 Ma) A-type granites in the Cobequid Highlands host complex sequences of rare-earth element (REE) and other hydrothermal minerals. The West Moose River pluton is the only pluton truncated and brittly deformed by the mid-Carboniferous (∼327 Ma) strike-slip Minas Fault Zone during the Alleghanian orogeny. Fractures in the granite provide a record of several deformational and hydrothermal events with distinct mineral assemblages. Early sodic alteration produced albitization of feldspar, and riebeckite and tourmaline veins. The δ18O of albite and albitized granite (5‰–6‰) is similar to other regional granites, suggesting a mantle source of albitizing fluids. Nearby halite deposits are younger and thus not a source of Na. Early chlorite veins were followed by potassic alteration and hydrothermal biotite, and by diabase and lamprophyre dyke emplacement. Euhedral magnetite occupies new cross-cutting fractures and vugs, correlated with regional iron oxide – carbonate – sulphide mineralization following initiation of the Minas Fault Zone. This change in stress field resulted in widespread fracturing of the granite, greatly increasing its permeability. Magnetite is postdated by titania minerals with hydrothermal REE minerals in dissolution voids. The spatial variation in REE mineral types indicates variable availability of F, Cl, and CO2 in mineralizing fluids derived from groundwater. REE mineralization is rare in veins in country rock, demonstrating local plutonic sources of REEs. The emplacement of REE minerals was complex in time and space and was a consequence of pervasive microfracturing of the granite.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Assessing the potential of cross-contamination from oil and gas hydraulic fracturing: A case study in northeastern British Columbia, Canada

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