The Summitville story

The Summitville gold mine is situated high (3,800 metres) in the San Juan Mountains of southwestern Colorado. Gold was first discovered there in 1870, and significant production from underground workings occurred prior to 1900.

In 1903, the Reynolds adit was driven to drain the underground workings and serve as an ore haulage tunnel. Production occurred sporadically through the 1950s.

The district received some exploration attention in the 1970s as a copper prospect, but no mining for copper was pursued. Similar to many historic gold mining districts in the western U.S., Summitville received renewed interest in the early 1980s because of technological advances that allowed extraction of low-grade ores with cyanide heap-leach techniques. In 1984, Summitville Consolidated Mining Company, a unit of now-defunct Galactic Resources of Vancouver, initiated open-pit mining of gold ore from rocks surrounding the historic underground workings, and heap-leached the ore to produce gold and silver.

According to a U.S. Geological Survey report, environmental problems developed soon after the initiation of open-pit mining. Cyanide-bearing processing solutions began leaking into an underdrain system beneath the heap-leach pad, where they then mixed with acid ground waters from the Cropsy waste dump. Cyanide solutions also leaked from transfer pipes directly into the Wightman Fork several times over the course of mining.

Summitville Consolidated Mining had ceased active mining and had begun environmental remediation when it declared bankruptcy in December 1992 and abandoned the mine site. The mine had cost $200 million to build, but gold sales over its short life netted only $120 million.

At the request of the State of Colorado, the U.S. Environmental Protection Agency (EPA) took over the site and began a remediation program, with initial work focused on increased treatment of the heap-leach solution to avert a release of cyanide solution from the heap.

The EPA estimates that the cleanup cost will total US$152 million, but because water treatment is expected to be required in perpetuity, precise cost estimates have been difficult to make.