Presentation on theme: "Summitville Gold Mine Disaster San Luis Valley, SW Colorado."— Presentation transcript:
Summitville Gold Mine Disaster San Luis Valley, SW Colorado
Summitville Gold Mine Located at 3800 meters elevation in the San Juan Mountains of south-western Colorado, USA. Southwest Colorado 7-11m of snowfall per year surrounded by the Rio Grande National Forest sparked national debates about effects of modern mining activities and the amendment of 1872 Mining Law
Map of Site
Mining History Gold, discovered in Significant gold production from underground works occurred until Population grew to stamping/crushing machines, before mining abandoned in early 1900's due to: - most of the gold harvested - fall in price of gold - too much snow: avalanches, landslides, and cave-ins
The Cyanide Leaching Process By the 1980 ’ s mining technology had advanced and techniques had been developed such as cyanide leaching, this made the mining of low grade ores economical. Summitville, like many other mines received renewed interest.
The Cyanide Leaching Process The Process: - Waste piles (tailings) or other finely crushed gold ore, are mixed with/sprayed with cyanide solution. - The gold-cyanide solution is drained off and processed with zinc to extract a solid mixture of gold/zinc - Sulphuric acid is the used to dissolve the zinc leaving just gold.
SCMCI Mining Activities 1985 Summitville Consolidated Mining Company, Inc (SCMCI) were issued a permit to mine (after initial rejection) Construction of large scale open-pit gold mine commenced. $3,000,000 bond laid down 1986 HDPE liner for leach pad laid down by subcontractor The liner was damaged in construction, it remained and leaked cyanide
The leach pads were 73 acres in area, and about 55m high Snowfall (ET) underestimated. Spring runoff forced the discharge of excess water contaminated with acid, heavy metals, and cyanide. (non- permitted) Permission was granted for limited discharge SCMCI could not reach the limits
1991 Cyanide and toxic heavy metals such as Fe, Al, Zi, Cu, Mn, Ni were released into the Alamosa River. Killed all fish and most other aquatic life over a 17 mile stretch.
1992 SCMCI ceased active mining and began environmental remediation Installed water treatment plant although progress was slow. Large snow fall likely, another probable toxic release. State mining legislature issue a report in November estimating $20,000,000 clean up cost 3 days later SCMCI declare bankruptcy abandon the site 16 th December EPA take control of cleanup: 200 million gallons of cyanide laced water, 3 x this after spring runoff Cleanup est. $150,000,000 to date.
Site Risk Effects on Watercourses All fish killed along a 17 mile stretch of Alamosa river Stocked trout killed in reservoir and holding ponds. Effects on Soils Farmland irrigated by contaminated Alamosa river. Increased pH levels. Increased concentrations of heavy metals.
Site Remediation Designed to slow the acid mine drainage of the site since 1992: Detoxifying Capping and re-vegetating the heap leach pads Removing waste rock piles Backfilling mine pits Plugging adits and other entrances Expansion of runoff holding ponds Operation of water treatment
Site Remediation Since 2001: Site wide reclamation and re-vegetation New water treatment plant Continuing collection of clean water and treatment of contaminated water