IDENTIFICATION OF TWO METAL CONTAMINANTS IN SOLUTION WITH CU ISOTOPES IN FIRST, SECOND AND THIRD ORDER STREAMS NEAR DEXING MINE, CHINA

Stable isotope values of copper contaminants found in solutions, particulates, soils and minerals collected within the local region downstream of the Dexing Mine were used to delineate the reach of metallic waste from the longstanding mining operation. The Dexing Mine is the largest open pit porphyry copper deposit mining operation in Asia and has been in operation continuously for 30+ years, allowing for long-term and thorough spoliation of the area. Concentrations of copper ions in solution vary throughout the watershed, with the highest, 440 ppm closest to the mine and 0.05ppm further from the main source site. Two distinct mineral isotope values are seen within the sample suite, being chalcopyrite and pyrite. Chalcopyrite, the main ore mined at Dexing, has a smaller range of reasonable isotope values than the latter, staying within values closer to zero. Pyrite has a much broader range of values, extending extremely in both lighter and heavier directions.

In the streams surrounding the Dexing mine, two different isotope values from the dissolved minerals chalcopyrite and pyrite can be differentiated. Values interpreted as being consistent with a chalcopyrite origin have values that fractionate predictably by +1.5 (per greater). Values seen as being pyrite, or from weathered tailing piles, have unique values greater than +6 ‰, and high isotope values were seen throughout the watershed. Particulate copper isotope values in the waters are complicated and vary greatly, so no clear pattern could easily be made with our understanding of it thus far. The highest copper isotope values are tied to waters closer to the tailings’ source. The tailings themselves were found in two soil samples taken near the largest tailings site, and visible sulfides were present. The sulfides from the soil produced copper isotope values that relate directly with the dissolved copper isotope values found in the waters collected downstream of the tailing sites. With thorough sampling, unique isotope values from the dissolved pyrite tailings and the primary-source chalcopyrite allow for the tracing of the metallic pollutants throughout the complicated watershed. These techniques may be applied to other contamination zones elsewhere and prove its usefulness in tracking transition metal pollutants in other industry impacted sites.