Acid Mine Drainage (hard rock mines)/Acid Rock Drainage Working Group
The Snake River in Colorado. The water is at a pH between 4 and 5. The reddish coloring is due to iron oxide precipitates and the whitish coloring is due to aluminum oxide precipitates. Photo by: Garrett Rue.
CWEST Participants: Kate Campbell, Blaine McCleskey, Diane McKnight, Kirk Nordstrom, Rob Runkel, Joe Ryan, Andrew Todd
Metals
Metals are vital for modern civilization. They are in our cars and airplanes, our computers and cell phones, our houses and office buildings, our electrical wiring, cooking pots, and more. They also form an essential part of the history of the western U.S. and Alaska. The California gold rush, Colorado’s Pike’s Peak gold rush, and Alaska’s Klondike gold rush led to the migration of hundreds of thousands of miners to the region in the last half of the 19th century. The General Mining Act of 1872 likewise contributed to the exploration and settlement of the west by giving individuals exclusive rights for the mining of hardrock minerals such as gold, silver, lead, copper, and zinc on federal lands (USGAO 2011).
Map of Known Abandoned Mine Lands (AML) on Bureau of Land Management (BLM) lands only. From BLM AML Inventory website. Downloaded on March 21, 2014.
What are acid mine and acid rock drainage?
Pyrite (also known as fool's gold). Photo: Wikimedia Commons, Jon Zander.
Acid drainage with a pH of -0.7. Although water with negative pH may occur, it is rare to find it accumulating in amounts that you would be able to collect in a cup as shown above.
The production of drainage with low pH and high dissolved metal concentrations can also occur naturally (acid rock drainage or ARD) through the weathering of pyrite and other mineral ores. However, the often large-scale land disturbances introduced by mining and mineral processing activities leads to the greater exposure of minerals to both air and water, intensifying acid drainage generation.
Acid drainage pathways in the water system
Tailings piles near Keystone, Colorado. Adit, Richmond Mine, Iron Mountain, California. Tailings piles are the waste soils that remain once mineral ores have been processed. Photo by: Sabre Duren.
Adit, Richmond Mine, Iron Mountain, California. Adits are horizontal or nearly horizontal shafts built into hill or mountain sides enabling mining operations to drain mines and access underground mineral ores.
Impacts of acid mine and acid rock drainage
Low pH values and high metal concentrations is harmful to fish and other aquatic life, and affects the ability of water to be used for drinking and for recreational purposes such as fishing. It also causes corrosion on infrastructure like bridges. When AMD or ARD water is used for snow-making, sometimes issues arise if the acid drainage is exported to a non-AMD/ARD stream. Alternatively if non-AMD/ARD water is diverted for snowmaking, this could potentially exacerbate metals levels in an AMD/ARD stream if the snowmaking water would have acted to dilute the instream metals concentrations.There is some life though that not only survives but thrives in the extreme environments of AMD/ARD streams including organisms such as bacteria, yeast, archea, fungi, and algae.
Collaborative research
USGS and INSTAAR scientists are collaborating on a variety of research topics including studying the implications of climate change for AMD/ARD streams and remediation efforts, characterizing AMD sources and working with stakeholders to develop remediation strategies for a Colorado river basin, and studying AMD geochemistry and microbiology that could help us understand processes on the planet Mars. For more information on some of this research, please check out the links below.
- Climate Change and Natural Acid Rock Drainage in the Upper Snake River, Colorado
- Iron Mountain Mine, California, Superfund Site
References
Nordstrom, D. K. (2011). Mine Waters: Acidic to Circumneutral. Elements, 7(6), 393-398.
U.S. Government Accountability Office [USGAO] (2011) Abandoned Mines: Information on the Number of Hardrock Mines, Cost of Cleanup, and Value of Financial Assurances, Testimony Before the Subcommittee on Energy and Mineral Resources, Committee on Natural Resources, House of Representatives.
Conducting a Tracer Experiment in Peru Creek, Colorado
Learn what a tracer experiment is and how such experiments can provide us with information about metal transport in acid mine drainage streams.