Effects of mining on fine sediment quality; a comparison with regional metal background concentrations
MetadataShow full item record
The impact of an abandoned hydraulic gold mine and an open cast copper-gold mine on the quality of fine-grained sediment (<63 µm) was investigated at several creeks in the Quesnel river catchment catchment in British Columbia, Canada. Bed sediment samples, suspended sediment samples, vertical profiles and/or corings were collected at five field sites. Bed sediment samples were collected at weekly intervals and the suspended sediment samples were collected at 3 weeks intervals using time-integrated isokinetic samplers. Vertical profiles were taken at four sites and corings were taken at two sites. Three field sites drain an open cast copper-gold mine, one site drains an abandoned hydraulic gold mine, and one site drains a natural area and was used as control site. Enrichment ratios were calculated for all the samples with aluminium or iron as reference metal. Background values for these calculations are taken from a data of a geochemical atlas of British Columbia (Jackaman and Balfour, 2008). Examining these background values shows that the three geological units in which the sample sites are located have significantly different background values: - Kamloops group has lower selenium (Se) values than the other two geological units. - Snowshoe group has higher manganese (Mn) values than the Kamloops group, has lower mercury (Hg) values than the other two geological units, has higher lead (Pb) and zinc (Zn) values than the other two geological units . - Nicolai group has higher arsenic (As), manganese (Mn), and copper (Cu) values than the other two geological units. All the field sites show enrichment of one or several metals. Selenium enrichment is occurring at sites that are draining the open cast copper-gold mine and the control site. Manganese enrichment is occurring at sites that drain the open cast copper-gold mine. Copper enrichment occurs at location two sites that are draining this mine. Arsenic enrichment is occurring at locations in one specific geological unit. And Lead enrichment is occurring only at the abandoned hydraulic gold mine. Selenium and copper enrichment is probably originating from the tailings from the mine. Arsenic enrichment could be originating from exposure of quartz-calcite veins, these veins are exposed due to logging (which increases erosion) and/or road construction, and lead enrichment at the abandoned hydraulic gold mine could be due to exposure of a vein of lead. Weathering and erosion of this vein may have caused the enrichment of lead at the sample site. At locations draining the open cast copper-gold mine, samples that hold younger sediment show more enrichment in selenium and manganese than samples with older sediment, whereas the control site does not show differences between younger and older sediment. At the location near the abandoned hydraulic gold mine only the vertical profile samples are enriched with lead, the bed and suspended sediment samples are not enriched. Results from this study were compared with results from Smith and Owens (2010) who conducted research on the impact of various land uses on the quality of fine-grained sediment (<63 µm). One of the same sites that has been used in this study (site H1) was used by Smith and Owens (2010) as well. Cadmium seems to be less (factor 0.4) in this study and manganese and selenium seems to be higher in this study with a factor of 2.1 and 2.3 respectively. Also copper seems to be lower in this study, although not much. The decreased metal production at the mine could explain the lower copper values. The increased tailings may be an explanation the higher selenium values.