Presentation on theme: "Acid Mine Drainage. Terms Acid Mine Drainage (AMD) –Water that is polluted from contact with mining activity Acid Rock Drainage (ARD) –Natural rock drainage."— Presentation transcript:
Shift in Mining Techniques “Old school” –Abandoned mines –Tailings/waste rock piles –ARD “New School” –Cyanide heap leach mining
“New School” Cyanide Heap Leach –Extract gold from low grade ore –Ore crushed, placed in open air leach pads –Cyanide sprayed on top –Leaches gold as migrates through ore –Solution drained, gold recovered –Pretty huh?
Summitville Mine Rio Grande Headwaters Elevation 12,800’ Snowfall: 7-11 m/ year Population: 700 112 stamping machines Abandoned in early 1900s –Gold prices fell, diminishing returns, weather issues
Summitville 1984 –Application for mining permit 1985 –Large scale open pit gold mine –Cyanide leaching 1986 –Construction. Problems.
Summitville 1987-1991: Heap Leach Pad –73 acres –One pile >190’ –No outlet for water
Summitville 1987-1991 cont –Permit to discharge excess water. Limits in concentrations –Could not meet limits –Fish kills downstream for 17 miles in Alamosa River
Summitville 1992 –EPA assumes control, $20,000,000 to ‘fix’ –Heap leach pad near overflow, discharging 3,000 gallons/minute through leaks –200 million gallons of cyanide laced water –Not last till spring snowmelt
Costs To date: $185 million –Annually: $1.5 million Taxpayers foot bill Mine owner cost: $3 million bond
Conclusions AMD degradation can be acute because: 1) Mines act as collectors of groundwater 2) Water is in contact with high grade ore minerals 3) Mine dumps and tailings provide dramatically increased surface areas for the interaction of water, oxygen, and sulfide minerals. Acid rock drainage is generated at mines and naturally where sulfide minerals are present and the buffering capacity of the water is exceeded.