HR: 1340h
AN: H53A-1204    [Abstracts]
TI: A "Tail" Of Two Mines: Determining The Sources Of Lead In Mine Waters Using Pb Isotopes
AU: * Cousens, B L
EM: brian_cousens@carleton.ca
AF: Earth Sciences, Carleton University 1125 Colonel By Dr., Ottawa, ON K2E5S4 Canada
AU: Allen, D M
EM: dallen@sfu.ca
AF: Earth Sciences, Simon Fraser University, Burnaby, BC V5A1S6 Canada
AU: Lepitre, M E
AF: Earth Sciences, Simon Fraser University, Burnaby, BC V5A1S6 Canada
AU: Mortensen, J K
AF: Earth and Ocean Sciences, University of British Columbia, Vancouver, BC V6T1Z4 Canada
AU: Gabites, J E
AF: Earth and Ocean Sciences, University of British Columbia, Vancouver, BC V6T1Z4 Canada
AU: Nugent, M
AF: Earth Sciences, University of Ottawa, Ottawa, ON K1N6N5 Canada
AU: Fortin, D
EM: dfortin@science.uottawa.ca
AF: Earth Sciences, University of Ottawa, Ottawa, ON K1N6N5 Canada
AB: Acid mine drainage can be a significant environmental problem in regions where mine tailings are exposed to surface water and shallow groundwater flow. Whereas high metal concentrations in surface waters and groundwaters indicate that metals are being mobilized, these data do not uniquely identify the source of the contamination. The isotopic composition of Pb in mine waters is a superb tracer of Pb sources, because the isotopic composition of ore Pb is usually significantly different from that of host rocks, other surficial deposits, and aerosols. We have investigated metal mobility at two abandoned Pb-Zn mines in different geological settings: the sediment-hosted Sullivan Mine in southeastern British Columbia, and the New Calumet Mine of western Quebec that is hosted in metamorphic rocks of the Grenville Province. Ores from both mines have homogeneous Pb isotopic compositions that are much less radiogenic than surrounding host rocks. At Sullivan, the Pb isotopic compositions of water samples define a mixing line between Sullivan ore and at least one other more radiogenic end-member. Water samples with high Pb concentrations (0.002 to 0.3 mg/L) generally are acidic and have Pb isotope ratios equal to Sullivan ore, whereas waters with low Pb contents have near-neutral pH and have variably more radiogenic Pb isotope ratios. Thus not all the waters collected in the study area originate from Sullivan ore or mining operations, as previously thought. The dominant source of ore Pb in mine waters are the waste rock dumps. Based on their isotopic compositions, host shales or aerosols from the local Pb smelter are potential sources of non-Sullivan ore Pb; local glacial tills are an unlikely source due to their heterogeneous Pb isotopic composition. Similarly, at the New Calumet mine, water samples collected in direct contact with either ore at the surface or tailings have high Pb concentrations (up to 0.02 mg/L) and Pb isotope ratios equal to New Calumet Pb-Zn ore. However, all water samples collected downstream from the mine site have low Pb concentrations and variably more radiogenic Pb isotope ratios. Water samples from a well on the mine site and a pipe discharging water from below the tailings dam also have non-ore Pb isotope ratios. The isotopic compositions of low-Pb samples do not lie on a mixing line between ore and local host rocks, but rather lie on a mixing line between agricultural ditch and stream waters upstream of the mine and New Calumet ore. These waters may form a groundwater system flowing under the mine site that is virtually uncontaminated by the overlying ores and tailings. Compared to the Sullivan case, metals from the New Calumet ore and tailings are only weakly mobilized into local waters, probably due to buffering of waters by carbonate-bearing host rocks. We are impressed with the fingerprinting ability of Pb isotopes to track the sources of heavy metals in water systems, and suggest that other radiogenic isotopes (Sr, Nd) may also be useful in environmental studies.
DE: 1803 Anthropogenic effects
DE: 1831 Groundwater quality
DE: 1871 Surface water quality
DE: 1040 Isotopic composition/chemistry
DE: 1094 Instruments and techniques
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting