Water geochemistry of mining and milling retention ponds in the 'New Lead Belt' of Southeast Missouri
Abstract
The heavy metal content and other geochemical data of the mine and mill waters of two mining operations in the 'New Lead Belt' of southeastern Missouri were determined and the efficiency of retention ponds in reducing high metal concentrations was investigated. The mine waters from two mines of this mining district, which is the largest lead producer in the world, showed a heavy metal content of less than 6 ppb copper, 66 ppb lead and 37 ppb zinc. They do not constitute a major source of pollution to the unspoiled streams of the region. The heavy metal content from the mill effluents was reduced to values similar to mine water, when the pond sizes were large enough. This refers to effluent flows of up to 10,000 gallons per minute and pond sizes of about 20 acres and up to twenty feet of depths. When the pond size was reduced to about 6 acres, copper and lead concentrations were still reduced sharply, but high zinc concentrations were lowered only slightly. The concentrations of calcium, magnesium, sodium and potassium and the pH of the mine water are similar to their concentrations in the streams. However, their concentrations are several times higher in the mill water. These elements can therefore be used to trace mine water in the streams. High zinc concentrations in streams caused by mill water are sharply reduced within 4 miles of stream flow. The retention ponds are not entirely efficient in preventing transport of metal rich rockflower into the streams.