| Abstrakt: |
Recovery of gold from arsenopyrite-hosted ore in the Giant Mine camp, Yellowknife, NWT, Canada, has left a legacy of arsenic contamination that poses challenges for mine closure planning. Seepage from underground chambers storing some 237,000 tonnes of arsenic trioxide dust, has As concentrations exceeding 4000 ppm. Other potential sources and sinks of As also exist. Sources and movement of water and arsenic are traced using the isotopes of water and sulphate. Mine waters (16 ppm As; As V /As III ≈ 150) are a mixture of two principal water sources - locally recharged, low As groundwaters (0.5 ppm As) and Great Slave Lake (GSL; 0.004 ppm As) water, formerly used in ore processing and discharged to the northwest tailings impoundment (NWTP). Mass balance with δ 18 O shows that recirculation of NWTP water to the underground through faults and unsealed drillholes contributes about 60% of the mine water. ;[emsp]>Sulphate serves to trace direct infiltration to the As 2 O 3 chambers. Sulphate in local, low As groundwaters (0.3-0.6 ppm As; δ 34 S SO 4 ∼ 4 ‰ and δ 18 O SO 4 ∼ - 10 ‰) originates from low-temperature aqueous oxidation of sulphide-rich waste rock. The high As waters gain a component of 18 O-enriched sulphate derived from roaster gases (δ 18 O SO 4 = + 3.5 ‰), consistent with their arsenic source from the As 2 O 3 chambers. High arsenic in NWTP water (∼ 8 ppm As; δ 18 O SO 4 = - 2 ‰) derived from mine water, is attenuated to close to 1 ppm during infiltration back to the underground, probably by oxidation and sorption by ferrihydrite. [ABSTRACT FROM AUTHOR] |
