LEGACY HG-CU CONTAMINATION OF ACTIVE STREAM SEDIMENTS AND FLOODPLAIN DEPOSITS IN THE GOLD HILL MINING DISTRICT, NORTH CAROLINA (Invited Presentation)

The first documented discovery of gold in the U.S. occurred in 1799 in the Piedmont of North Carolina, leading to the nation’s first gold rush between about 1830 and 1860. North Carolina led the nation in gold production until 1848, and produced more gold than any other state in the southern Piedmont gold belt. This study reports on the magnitude and distribution of mercury and copper contamination in channel sediments and floodplain deposits more than 100 years after large-scale gold mining ceased in the Gold Hill mining district. The District produced gold (with Hg amalgamation) and Cu from 1844 to 1915 and released mill tailings to the Little Buffalo Creek-Dutch Buffalo Creek river system (254 km²). Mercury and Cu concentrations decrease exponentially in both active channel and floodplain sediments from below Gold Hill to the mouth of Dutch Buffalo Creek over 20 km downstream, never reaching regional background levels. In channel sediments, a two-parameter regression model combining the effects of both watershed-scale dispersal processes (Log distance) and reach-scale sediment transport (sand %) explain 85% of Hg and 90% of Cu variance. Floodplain core contamination trends vary vertically and laterally and reflect the varying influences of source dilution, mining history, historical land use, and floodplain topography. A quarter of the floodplain samples contain Hg concentrations in excess of 5 times the maximum background level of 0.1 ppm. The main source of metal contamination to these river systems today is probably through bank erosion and release of stored contaminated mining period sediment.