Presentation on theme: "Summitville Gold Mine Disaster"— Presentation transcript:
1 Summitville Gold Mine Disaster San Luis Valley, SW Colorado
2 Summitville Gold MineLocated at 3800 meters elevation in the San Juan Mountains of south-western Colorado, USA.Southwest Colorado7-11m of snowfall per yearsurrounded by the Rio Grande National Forestsparked national debates about effects of modern mining activities and the amendment of 1872 Mining Law
4 Mining History Gold, discovered in 1870. Significant gold production from underground works occurred until 1900.Population grew to 700.112 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
5 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.
6 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.
7 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 down1986 HDPE liner for leach pad laid down by subcontractorThe liner was damaged in construction, it remained and leaked cyanide
8 1987-1990 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 dischargeSCMCI could not reach the limits
9 1991Cyanide 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.
10 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 cost3 days later SCMCI declare bankruptcy abandon the site16th December EPA take control of cleanup: 200 million gallons of cyanide laced water, 3 x this after spring runoffCleanup est. $150,000,000 to date.
11 Site Risk Effects on Watercourses All fish killed along a 17 mile stretch of Alamosa riverStocked trout killed in reservoir and holding ponds.Effects on SoilsFarmland irrigated by contaminated Alamosa river.Increased pH levels.Increased concentrations of heavy metals.
12 Site RemediationDesigned to slow the acid mine drainage of the site since 1992:DetoxifyingCapping and re-vegetating the heap leach padsRemoving waste rock pilesBackfilling mine pitsPlugging adits and other entrancesExpansion of runoff holding pondsOperation of water treatment
13 Site Remediation Since 2001: Site wide reclamation and re-vegetation New water treatment plantContinuing collection of clean water and treatment of contaminated water