MERCURY CONTAMINATION AND FLOODPLAIN SEDIMENTATION FROM FORMER GOLD MINES IN NORTH GEORGIA¹

Abstract

Gold was discovered in Georgia in 1829 and mined until about 1940 in the Dahionega Gold Belt of the north Goorgia Piedmont. Streams there are characterized by gravel beds and fine sandy to silty banks. Historical mining‐related alluvium is clearly distinguished from prehistoric alluvium because it is contaminated with mercury (Hg), which was used by miners to amalgamate gold. Mercury concentrations in historical floodplain sediments range from 0.04 to 4.0 mg kg−1, exceeding background (0.04 mg kg1) by as much as two orders of magnitude near the core of the mining district and decreasing in the downstream direction. Low levels (≤ 0.1 mg kg1) of Hg are established within about 10–15 km from the source mines. The mercury‐contaminated sediment exceeds sediment quality guidelines set by many agencies, and is a significant nonpoint source for mercury pollution. Hydraulic mining of saprolite, which began in 1868, and cutting of forests associated with mining and settlement caused unusually rapid sedimentation (1–3 cm yr−l) and floodplain aggradation in the region. After mining ceased, streams adjusted by downcutting and forming an historical‐age terrace. A new floodplain is currently being formed as streams migrate lateraily and erode the mining‐related sediment of the historical terrace. High magnitude floods are contained within the confines of the historical terrace, thus limiting quantities of over‐bank sedimentation, causing channel bank erosion, and transmitting high sediment yields to reservoirs in the region.

Linkages between forest soils and water quality and quantity

“…Trimble (1974) estimated that 10-30 cm of native topsoil were lost as a consequence across the region. This type of agricultural erosion was not limited to the southeastern Piedmont (Knox, 2006), and mining activities in parts of the Appalachian Mountains also contributed large quantities of sediment to streams (Leigh, 1994). The cotton-farming era ended abruptly in the 1930s, and since then, much of the southeastern Piedmont reverted to or was planted to forest.…”

Trace metal storage in recent floodplain sediments along the Dill River, central Germany

“…Frequently, metal concentrations decrease with distance from the former mines, a trend usually attributed to deposition of a majority of metals in close proximity to the mined areas and the addition of cleaner sediments from downstream tributaries. Highly contaminated channel banks and near-channel floodplain sediments have been shown to serve as a source for metal contamination during floods (Leigh, 1994;Schwartz et al, 2006;Ciszewski and Turner, 2009;Wyżga and Ciszewski, 2010;Foulds et al, 2014). Industrial activity can also serve as a source of trace metals, as has been documented in western Europe along rivers such as the Rhine (Dehner, 1994;Middelkoop, 2002;Wijnhoven et al, 2006) and Elbe (Förstner, 2003, Krüger andGröngröft, 2003;Schulz-Zunkel et al, 2013;Zachmann et al, 2013).…”

Mercury Hazards from Gold Mining to Humans, Plants, and Animals

“…Mercury was the only significant trace metal contaminant resulting from former gold mining activities in Georgia, exceeding the USEPA "heavily polluted" guideline for sediments of >1.0 mg Hg/kg. Other metals examined did not exceed the "heavily polluted" sediment guidelines, which are >50 mg/kg for copper, >200 mg/kg for lead, and >200 mg/kg for zinc (Leigh 1994(Leigh , 1997.…”

“…In northern Georgia, gold was discovered in 1829 and mined until about 1940 (Leigh 1994(Leigh , 1997. Extensive use of mercury probably began in 1838 when stamp mills (ore crushers) were introduced to help recover gold from vein ore, with about 38% of all mercury used in gold mining escaping into nearby streams.…”