Effects of past and present mining on fine sediment geochemistry of floodplain soils, Horsefly River, BC, Canada
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Active and abandoned mine sites are known to be a dominant source of metal contamination in fluvial systems worldwide. Small-scale mining of minerals like gold, copper and zinc has been prevalent in interior British Columbia, Canada since the 19th century. The region is also characterized to provide an important habitat for wildlife of which the river gravel beds for several salmon species are a prime example. This thesis investigated the impact of past and present mining on floodplain soils of the Horsefly River, BC, Canada. The abandoned Black Creek placer mine was specifically studied. Floodplain cores were analysed for metal distributions of arsenic, cadmium, zinc, lead, selenium and copper, elements often associated with gold placer mining. The anthropogenic part (residual part) of these metal concentrations was determined by subtracting that part stemming from local geology from the total concentration measured. The concentrations representing local geology were determined using a normalization procedure combined with regression analysis. The cores were also analysed for 210Pb abundance from which age-depth profiles were established. Three floodplain cores were analysed this way: (1) upstream of the Black Creek inlet into the Horsefly River, (2) downstream of the Black Creek inlet, (3) at the Horsefly delta (55 kilometers downstream). It was concluded that there were no present effects of the Black Creek mine on the fine sediment geochemistry of the Horsefly floodplain. A past mining response of this mine was reflected in a peak in arsenic related to the early 1930s. Present day elevated concentrations of selenium in the catchment indicated a further upstream located source unrelated to the Black Creek mine and this signal was also present in the Horsefly delta. Furthermore, elevated concentrations of lead, cadmium and zinc were present in the Horsefly delta, which were absent in the upper Horsefly catchment. These concentrations were not related to mining activities.