From The Fairplay Flume (Lynda James):

According to Tom Eisenman, Park County Development Services coordinator, the pond was full and water washed over the edge, creating a groove at the top of the pond’s edge. The water then flowed into a lower area filled with boulders and cobbles that is not part of the mining operations. It traveled underneath the boulders and then flowed into the Middle Fork of the South Platte River. Mary Burns, mine office manager, told The Flume on Monday that as soon as the mine management realized the settling pond was overflowing on Thursday, Aug. 27, they stopped the mine from washing gravel and began repairs. She said that no chemicals are used at the mine, so nothing but silt entered the river.

More South Platte Basin coverage here.