Geochemistry of coals from the Elk Valley coalfield, British Columbia, Canada

The Elk Valley coalfield of British Columbia is one of the major coal producing areas in Canada. The coals are of Cretaceous and Jurassic–Cretaceous age and range in rank from high-volatile to low-volatile bituminous (%Ro_max: 0.8–1.6). Coal seams from outcrops and active mines in this coalfield were analysed for rank and maceral composition using reflected light microscopy, for geochemistry using AAS, INAA, and ICPES, and also by proximate and ultimate analyses. The Elk Valley coal seams contain low average concentrations of hazardous elements such as As, Mo, Pb, and Se. However, there are seams that contain relatively high concentrations of some of these elements, such as 8 mg/kg and 108 mg/kg of arsenic. When the geochemistry of coal seams is compared within the different parts of the coalfield, the elemental composition amongst the seams from various sections located in the central area of the coalfield is similar. Coal seams in the northern area of the coalfield have different geochemistry than coal seams in other areas of the coalfield; seams in the northern area have much higher As, Br, Cr, Cu, Fe, K, and Na content, but contain less Ca.     

Stability analysis of a horizontal coalbed methane well in the Rocky Mountain Front Ranges of southeast British Columbia, Canada

This study describes a wellbore stability analysis undertaken for a horizontal coalbed methane well in the Mist Mountain Formation, SE British Columbia, Canada. Three triaxial compression tests, with ultrasonic velocities, were conducted on 38-mm-diameter core plugs taken from a large, fresh block of Seam 7. Due to the small size of the tested samples, the laboratory-derived strength values were reduced to reflect the in-situ stress conditions considered relevant for a 156-mm-diameter horizontal well. The vertical stress gradient was calculated by integrating a bulk density log from an offset well. Horizontal maximum and minimum stresses were estimated from regional stress data, whereas formation pressure was estimated on the basis of a local hydrological study. The 2D elastoplastic STABView™ numerical modeling code was used to forecast horizontal wellbore stability. The sensitivity of the predicted yielded zone size was examined for varying linear and non-linear rock strength criteria, horizontal in-situ stresses, bottom-hole pressures, formation pressure, drilling depth, and wall-coating efficiency. Stability analysis was performed at bottom-hole pressures ranging from overbalanced to underbalanced in order to simulate the conditions expected during drilling and production. The effects of weak bedding planes and varying well trajectories were also investigated. When drilling at 650 m depth under underbalanced to slightly overbalanced conditions, a high probability of getting the drill pipe stuck was predicted. STABView™ showed that, if the 38-mm-diameter core plug strengths were used directly for forecasting purposes, the predicted yielded zone would be almost 20% overgauge when drilling at balanced conditions. When peak cohesion of coal was reduced by 50% to reflect the conditions expected along weak intervals of a horizontal wellbore, the predicted enlarged borehole was almost 85% overgauge under the same drilling conditions. The most unstable trajectory has N–S azimuth, which is perpendicular to the maximum horizontal stress in the study area. STABView™ indicates that a production liner should be inserted immediately following the drilling of the horizontal well in this structurally complex geologic setting since pressure drawdown and reservoir pressure depletion would undoubtedly lead to enlarged yielded zones and collapse of the wellbore over time.     

The Khyex River landslide of November 28, 2003, Prince Rupert British Columbia Canada

On November 28, 2003, at about 00:30 PST, 35 km east of Prince Rupert in northwestern British Columbia, an extremely rapid, retrogressive liquefaction earth flow, or a clay flow-slide, severed the natural gas pipeline. As a result, Prince Rupert residents were without natural gas heat for 10 days. The landslide has a steep main scarp that is 45 m high by 345 m wide. It consists of glaciomarine sediments mantled by rubbly colluvium lying on, and against smooth bedrock of the valley wall. It covers an area of 32 ha, and displaced about 4.7 M m³ of material. This displaced material flowed up and down river over a distance of 1.7 km, blocked the river, and caused flooding upstream for a distance of 10 km. This landslide is the most recent of four large landslides that have occurred over the last four decades in glaciomarine sediments in northwestern British Columbia.     

Early growth of the last Cordilleran ice sheet deduced from glacio-isostatic depression in southwest British Columbia, Canada

Relative sea level at Vancouver, British Columbia rose from below the present datum about 30,000 cal yr B.P. to at least 18 m above sea level 28,000 cal yr B.P. In contrast, eustatic sea level in this interval was at least 85 m lower than at present. The difference in the local and eustatic sea-level positions is attributed to glacio-isostatic depression of the crust in the expanding forefield of the Cordilleran ice sheet during the initial phase of the Fraser Glaciation. Our findings suggest that about 1 km of ice was present in the northern Strait of Georgia 28,000 cal yr B.P., early during the Fraser Glaciation.     

Example of a debris-flow risk analysis from Vancouver Island,British Columbia,Canada

In July 2005, a debris flow and a water flood occurred on two adjacent gullies in the White River area, on northern Vancouver Island in British Columbia, Canada. The 16,000 m³ debris flow buried approximately 7.5 ha of second-growth trees, buried approximately 500 m of a forestry road, and reached two fish-bearing streams. The water flood eroded approximately 240 m of the same forestry road and plugged four culverts before overtopping and inundating the road. To better plan for future events, risk analyses of debris flows, debris floods, and water floods were carried out for the two gullies involved, plus a third adjacent gully. The elements at risk that were analyzed included, in order of priority: users of the forestry road, the fish-bearing streams, the forestry road itself, and a timber bridge. Using a series of qualitative, but defined, relative-risk matrices, the following components of specific risk were estimated for each of the three types of events on each of the three gullies for each of the four elements at risk: probability of occurrence, probability that the event will reach or otherwise affect the site of the element at risk, the probability that the element at risk will be at the site when the event occurs, and the probability of loss or damage resulting from the element being at the site when the event occurs.     

Advance of alpine glaciers during final retreat of the Cordilleran ice sheet in the Finlay River area, northern British Columbia, Canada

Sharp-crested moraines, up to 120 m high and 9 km beyond Little Ice Age glacier limits, record a late Pleistocene advance of alpine glaciers in the Finlay River area in northern British Columbia. The moraines are regional in extent and record climatic deterioration near the end of the last glaciation. Several lateral moraines are crosscut by meltwater channels that record downwasting of trunk valley ice of the northern Cordilleran ice sheet. Other lateral moraines merge with ice-stagnation deposits in trunk valleys. These relationships confirm the interaction of advancing alpine glaciers with the regionally decaying Cordilleran ice sheet and verify a late-glacial age for the moraines. Sediment cores were collected from eight lakes dammed by the moraines. Two tephras occur in basal sediments of five lakes, demonstrating that the moraines are the same age. Plant macrofossils from sediment cores provide a minimum limiting age of 10,550-10,250 cal yr BP (9230 ± 50 ¹⁴C yr BP) for abandonment of the moraines. The advance that left the moraines may date to the Younger Dryas period. The Finlay moraines demonstrate that the timing and style of regional deglaciation was important in determining the magnitude of late-glacial glacier advances.     

Extensive deformations of rock slopes in southern Coast Mountains, southwest British Columbia, Canada

Extensive deformations of mountain slopes occur in crystalline intrusive rocks in the southern Coast Mountains of British Columbia. Typical morphological evidence of slope movement includes extensive systems of tension cracks, grabens, and antislope scarps (collectively referred to here as linears). These landforms involve displacements along penetrative joints observed in surface exposures. Kinematic tests on rock-structural data indicate that the observed patterns of linears are generally consistent with the feasible gravitational movements along the dominant discontinuities. Most sites indicate sliding as the most likely initial mode of movement, followed by or accompanied by toppling and toppling-induced sliding movements, and do not support the view that linears are the traces of active faults.     

DRASTIC-Fm: a modified vulnerability mapping method for structurally controlled aquifers in the southern Gulf Islands,British Columbia,Canada

DRASTIC, the methodology for mapping the intrinsic vulnerability of aquifers, is modified to incorporate the structural characteristics of fractured bedrock aquifers. In these aquifers, groundwater flow is predominantly through fractures, with large-scale fracture zones and faults acting as primary conduits for flow at the regional scale. The methodology is applied to the southern Gulf Islands region of southwestern British Columbia, Canada. Bedrock geology maps, soil maps, structural measurements, mapped lineaments, water-well information and topographic data, assembled within a comprehensive GIS database, form the basis for assigning traditional DRASTIC indices, while adding the structural indices necessary for capturing the importance of regional structural elements in recharge and well capture zone determinations.     

Navigating the tensions in collaborative watershed governance: Water governance and Indigenous communities in British Columbia,Canada

First Nations in British Columbia (BC), Canada, have historically been—and largely continue to be—excluded from colonial governments’ decision-making and management frameworks for fresh water. However, in light of recent legal and legislative changes, and also changes in water governance and policy, there is growing emphasis in scholarship and among legal, policy and advocacy communities on shifting water governance away from a centralized single authority towards an approach that is watershed-based, collaborative, and involves First Nations as central to decision-making processes. Drawing on community-based research, interviews with First Nations natural resource staff and community members, and document review, the paper analyzes the tensions in collaborative water governance, by identifying First Nations’ concerns within the current water governance system and exploring how a move towards collaborative watershed governance may serve to either address, or further entrench, these concerns. This paper concludes with recommendations for collaborative water governance frameworks which are specifically focused on British Columbia, but which have relevance to broader debates over Indigenous water governance.     

The geochemistry of selenium associated with coal waste in the Elk River Valley,Canada

Selenium (Se) concentrations more than 12 times greater than the provincial freshwater quality guideline (2 µg/L) were detected in the Elk River downstream from the five open-pit coal mines in southeastern British Columbia's Elk River Valley. To identify possible sources of Se to the Elk River, samples from the coal-bearing Mist Mountain Formation were studied using X-ray diffraction, elemental and oxide analyses, sequential extractions and heavy liquid separation. Between 2.5 and 21.3% of the total Se in the five types of materials studied is water-soluble and 1.0 to 10.6% is associated with hydrous ferric and manganese oxides. Se associated with sulphides and organic material varies between 60 and 84% of the total Se and Se in the silicate structure varies from 5.9 to 24.7%. The ratio of sulphides to the total of organic carbon is well-correlated with the amount of Se in materials closely associated with coal seams containing less than 6 mg/kg of Se (r=0.916). This may suggest that the amount of organic matter present during deposition affects the amount of Se incorporated into sulphides.     

Tracking recorded fires using charcoal morphology from the sedimentary sequence of Prosser Lake, British Columbia (Canada)

Quantitative analyses of variations in morphological features of charcoal were undertaken in a ²¹⁰Pb-dated sediment core from Prosser Lake (British Columbia, Canada). Seven morphological types of charcoal were defined by particle shape, major-minor axis ratio, apparent porosity and progradation to unburned material. The distribution of morphotypes and total charcoal abundances were assessed as a proxy for fire events recorded between 1919 and 2000 and to subsequent mechanisms of transportation-sedimentation to lake sediments. Charcoal morphotypes showed distinct relationships to recorded area burned by fires. Fragile charcoal fragments with highly irregular porosity (termed Type M) displayed the strongest correlation to burned area (r² = 0.51; P = 0.0001) and did not produce any false-positive signal for fires recorded within a radius of 20 km around the lake. We infer that high porosity and low density Type M fragments are aerially transported and directly deposited on the lake, and that the fragility of Type M charcoal prevents significant quantities from being secondarily transported and incorporated into the sedimentary record. We propose that charcoal morphology is an important but underutilized technique that can yield important insights into fire type, proximity and transportation-sedimentation processes.     

Determining the circulation depth of thermal springs in the southern Rocky Mountain Trench, south-eastern British Columbia, Canada using geothermometry and borehole temperature logs

Geochemical data for thermal spring waters along the southern Rocky Mountain Trench in British Columbia, Canada were examined. The range of equilibration temperatures for the thermal springs is between 24 and 59°C, assuming that there is minimal mixing with colder shallow waters that might lead to a lowering of the calculated equilibration temperature. The chalcedony geothermometer is found to be the most appropriate given the carbonate host rocks. Temperature logs from 11 boreholes in the vicinity were used to calculate representative geothermal gradients, which range from 23.8 to 55.7°C/km with an average of 24.8±8.0°C/km. Using the average gradient and the range of equilibration temperatures calculated for each spring, the minimum range for the depth of origin of the thermal waters is 0.9–2.2 km. Heat flow values range from 90.3 to 155 mW/m², with an average of 109.1±21.0 mW/m². The moderate to high heat flow and heat generation result in generally higher temperatures at shallow depths, thus offering an explanation for the occurrence of thermal springs. The alignment of the thermal springs likely relates to the preferred northwest–southeast orientation for major thrust faults along the Rocky Mountain Trench, and with waters routed from depth along deep faults.

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Resumen Se examinan datos geoquímicos de aguas de fuentes termales a lo largo de la Trinchera sur de las Montañas Rocosas en Columbia Británica, Canadá. El rango de temperaturas de equilibrio para las fuentes termales se encuentra entre 24 y 59°C, asumiendo que existe mezcla mínima con aguas someras más frías que podrían conducir a un descenso de la temperatura de equilibrio calculada. El geotermómetro de calcedonia se ha encontrado que es el más apropiado debido a las rocas encajonantes carbonatadas. Se utilizaron los registros de temperatura de 11 pozos de la zona para calcular gradientes geotermales representativos, los cuales varían de 23.8 a 55.7°C/km con un promedio de 24.8±8.0°C/km. Utilizando el gradiente promedio y el rango de temperaturas de equilibrio calculadas para cada manantial, se estimó que el rango mínimo para la profundidad de origen de las aguas termales varía de 0.9 a 2.2 km. Los valores de flujo de calor varían de 90.3 a 155 mW/m², con un promedio de 109.1±21.0 mW/m². El flujo de calor moderado a alto y la generación de calor resultan en temperaturas generalmente más altas a profundidades someras ofreciendo de este modo una explicación para la ocurrencia de fuentes termales. El alineamiento de fuentes termales posiblemente se relaciona con la orientación preferida noroeste-sureste de fallas inversas principales a lo largo de la Trinchera de las Montañas Rocosas, y con aguas ascendentes profundas que se mueven a lo largo de fallas profundas.

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Résumé Les données géothermiques de sources thermales le long de la partie sud du fossé des Montagnes Rocheuses en Colombie Britannique, Canada, sont étudiées. Léchelle des températures déquilibre des sources thermales se situe entre 24 et 59°C, en assumant quil y a un mélange minimum avec les eaux froides de surface, ce qui conduit à une sous-évaluation de la température déquilibre. La calcédoine apparaît être le géothermomètre le plus approprié vu les roches hôtes carbonatées. Les diagraphies de température provenant de 11 forages proches ont été utilisées pour calculer le gradient géothermique représentatif, gradient compris entre 23.8 et 55.7°/km avec une moyenne de 24.8°/km. En utilisant le gradient moyen et les valeurs de température déquilibre calculées pour chaque source, la profondeur minimum des eaux thermales se situerait entre 0.9 et 2.2 km. Les flux de chaleur sont évalués entre 90.3 et 155 mW/m, avec une moyenne de 109.1±21.0 mW/m. Le transfert moyen de chaleur et la génération de chaleur résulte en températures ordinairement plus élevées aux faibles profondeurs, qui ainsi offre une explication à loccurrence de sources thermales. Les alignements de sources thermales sont vraisemblablement en relation avec lorientation Nord-Sud des principales failles-vraies le long du fossé des Montagnes Rocheuses, et avec lécoulement des eaux des profondeurs le long des failles.

     

Accumulation models for coalbed methane in medium- to high-rank coals: examples from the southern Qinshui Basin and southeastern Ordos Basin

The majority of known coalbed methane (CBM) production worldwide comes primarily from high-abundance CBM-enrichment areas or ‘fairways.’ The high-abundance CBM-enrichment areas are primarily characterised by large CBM resources with high single-well productions. CBM accumulation areas from the medium- to high-rank coals in the southern Qinshui Basin and the Hancheng CBM fields in the Ordos Basin were investigated based on regional geological analyses and physical analogue experiments. The results show that gas contents in the study areas increase with depths over the range from approximately 300 to 800 m, while permeabilities generally decrease with depths. Intervals with optimal gas content and permeability exist at a moderate depth along an inclined coal seam under the coupled control of temperature and stress. Brittle–ductile transition deformation increases the permeability and the pore-specific surface areas of coals. The gas content and permeability of the CBM reservoirs are shown to be two key factors determining the formation of high-abundance CBM areas. The coupling of gas enrichment and high permeability provides a favourable combination for CBM accumulation and high production. Combining CBM exploration and development practices in the study areas with physical analogue experiments, two CBM-enrichment models for medium- to high-rank coal have been recognised for different geological conditions, including (1) the model controlled by the depth in the slope zone and (2) the model controlled by the coal brittle and ductile in the deformation zones.     

Physical partitioning of mercury in till: an example from central British Columbia, Canada

The physical partitioning of Hg into different grain size fractions of till is predominantly controlled by the primary bedrock mineralogy, the distance of glacial transport, and the relative stability of cinnabar (HgS) in the soil weathering environment. At sites located short distances down-ice from bedrock cinnabar mineralization, the highest Hg concentrations in unoxidized till were measured in the sand- and granule-sized fractions reflecting the abundance of cinnabar in those size ranges. Similar partitioning was measured in oxidized till as cinnabar was found to be relatively resistant to postglacial weathering. Discrete clay-sized cinnabar grains obtained from the unoxidized till were viewed under the scanning electron microscope and suggest that the terminal grade of cinnabar is in the clay-sized range. In till collected from areas barren of cinnabar mineralization, the highest Hg levels were found in the clay-sized fraction which is attributed to the high adsorption of Hg by clay minerals.     

Siliceous microfossil record of late Holocene oceanography and climate along the west coast of Vancouver Island, British Columbia (Canada)

Diatoms, silicoflagellates, and biogenic silica (BSi) were analyzed from two piston cores recovered from Effingham Inlet, British Columbia. Relatively productive marine conditions from 4850 to 4000 cal yr BP were followed by a transition to the modern ocean-climate regime marked by a decreased siliceous microfossil production since 2800 cal yr BP. This change in the northeast Pacific climate was characterized by an apparent cooling associated with higher rainfall and lower light levels. The reduced abundance of most spring-summer bloom diatom taxa (Skeletonema-Thalassiosira-Chaetoceros) was coupled with a decreased abundance of diatoms normally associated with incursions of offshore water into coastal inlets. This pattern reflected a weaker summer upwelling along Vancouver Island associated with the insolation-related increase in the strength of the Aleutian Low and a weakened North Pacific High. After ca. 2800 cal yr BP, diatom assemblages also indicated more frequent periods of relatively low spring-summer surface water salinity and a disruption of the typical bloom sequence, indicative of increased climatic variability. A period of warmer and drier climate conditions and possibly increased coastal upwelling offshore occurred ca. 1450-1050 cal yr BP. The most recent 500 yr are marked by reduced diatom production and the appearance of three distinct diatom biomarkers in the stratigraphic record (Rhizosolenia setigera ca. AD 1940; Minidiscus chilensis ca. AD 1860; Thalassionema nitzschioides morphotype A, ca. AD 1550). The oceanographic changes recorded in Effingham Inlet are correlative with other marine and terrestrial paleoenvironmental records in the northeast Pacific Ocean.     

The abnormal pressure regime of the Pennsylvanian No. 8 coalbed methane reservoir in Liulin–Wupu District, Eastern Ordos Basin, China

Coalbed methane reservoir pressure is an important parameter used to assess the producibility of coalbed methane wells. Practices indicate that high production of coalbed methane well is partly related closely to abnormally high pressure. Permo-Carboniferous coalbed methane resources are very abundant in the Liulin–Wupu District, Eastern Ordos Basin, which has been the highlight of coalbed methane exploration in China in recent years. In this district, the abnormally high pressure is present locally in the Pennsylvanian No. 8 coalbed methane reservoir (the Taiyuan Formation). Based on the distribution of the abnormally high pressure, burial history, hydrocarbon generation, hydrodynamics, and sealing regimes, the authors suggest that the abnormal coalbed methane reservoir pressure is related closely to local hydrodynamic trapping. The gas generated during the qualification is preserved, owing to the confinement of lower permeable roof and floor rock layers, and water trapping in the updip direction (like the “fairway” in San Juan Basin). As a result of pressure reconstruction event, the abnormally high pressure is formed during the uplifting stage. The current coalbed methane wells with high production are always located in abnormally high pressure areas. Therefore, the areas with abnormally high pressure in Liulin–Wupu District can be the preferred areas for commercial coalbed methane development.     

An investigation into the effects of diffusion on salinity distribution beneath the Fraser River Delta, Canada

Electrical conductivity (EC) and geochemical data were interpreted to determine the nature, origin and distribution of salinity in pore waters of sediments in a deltaic environment. The role of diffusion as a mechanism for transporting saline water within lower permeability prodelta and delta slope sediments is specifically investigated. Characteristic vertical salinity profiles at several different regions of the Fraser River Delta, British Columbia (Canada) are identified, including relatively shallow salinity zones in areas currently and historically near main river channels, and deeper salinity zones reaching up to 300 m depth in delta-front and inland areas. Comparison of salinity profiles with the results of a simple salt transport model suggests that diffusion may be a significant mechanism controlling the observed distribution of salinity in current or former estuarine areas of the delta.Density-effects were found not to be significant given the low permeability of the silt through which the salt is diffusing; however, in similar environments with higher permeability sediments, density effects may be significant. In inland and delta front areas, salinity extends to a considerable depth in the silts, beyond what would appear to be possible by diffusion alone, and points to a connate origin.     

Numerical modeling of hydrothermal fluid flow coupled with mass transport: An example from the Devonian Wabamun Group, northeast British Columbia, Canada

Several researchers have suggested that upward and lateral hydrothermal fluid flow was responsible for dolomitization of various Devonian and Mississippian reservoirs in the Western Canada Sedimentary Basin (WCSB) based on sedimentological, geochemical and diagenetic evidence. In this study, a numerical model was applied to investigate hydrothermal fluid flow in the Wabamun Group, Parkland field, northeastern British Columbia, Canada. Our numerical results indicate that faults play the most critical role in controlling hydrothermal fluid flow. They provide a pathway connecting the basement of the basin and overlying sedimentary layers. Upwelling fluid flow via faults may bring reactants and heat from underlying strata to shallow formations for diagenetic reactions (e.g. dolomitization and/or chertification) or forming ore deposits. Salinity distribution of formation water, permeability configuration of host rock and regional fluid flow are also important factors affecting hot and brine fluid flow and accompanying heat and mass distribution.     

3D seismic analysis of the Coast Shear Zone in SE Alaska and Western British Columbia: Broadside analysis of ACCRETE wide-angle data

The multidisciplinary ACCRETE project addresses the question of continental assemblage in southeast Alaska and western British Columbia by terrane accretion and magmatic addition. The previous studies of this project yielded important information for understanding the structures across the Coast Shear Zone (CSZ) and the formation of the CSZ and the Coast Mountains Batholith (CMB). The present study extends these interpretations into pseudo-3-D by using two additional wide-angle ACCRETE seismic lines. By analyzing the broadside wide-angle data using a series of laterally homogeneous 2-D models, we derive a lower-resolution 3-D velocity model of the outboard terranes and constrain variations in crustal thickness across and along the CSZ. Models of the broadside data confirms major structural and compositional trends extend along strike to the northwest. The key features are: a) a steep Moho ramp only  15-km wide is coincident with the CSZ and divides thin (25 ± 1 km) crust to the west below the west-vergent thrust belt (WTB) from thicker ( 31 ± 1 km) crust to the east below the CMB, (b) low-velocity mantle (7.7--7.9 km/s) extends beneath the entire study region indicating high crustal and upper-mantle temperatures below the WTB and CMB, and (c) the Alexander terrane is characterized by strong mid-crustal reflectivity and high lower crustal velocities that are consistent with gabbroic composition. This study extends the earlier interpretation and implies that the ramp is indeed likely associated with transpressional tectonics and magmatic crustal addition east of the CSZ.