The primary acid-generating process at these sites is the dissolution of pyrite:

2FeS2 + 7O2 + 2H2O > 2FeSO4 + 2H2SO4

Iron and/or sulfur oxidizing bacteria (e.g. Thiobacilli), which are commonly ubiquitous in these sites, significantly increase the kinetics of this reaction.

In the absence of bacteria elemental sulfur (S), not sulfuric acid, is produced and the further oxidation of S to sulfate (SO4

2-) is so slow that it is considered to be insignificant. Thus, purely chemical acid generation is very slow.

ACID MINE DRAINAGEIntroduction

IRON MOUNTAIN, CALIFORNIAIntroduction

From the 1860s through 1963, the Iron Mountain Mine site was periodically mined for Fe, Ag, Au, Cu, Zn, and S.

Though mining operations were discontinued in 1963, underground mine workings, waste rock dumps, piles of mine tailings, and an open mine pit still remain at the site.

Historic mining activity at IMM has fractured the mountain, exposing minerals in the mountain to surface water, rain water, and oxygen.

This sulfuric acid runs through the mountain and leaches out Cu, Cd, Zn, and other heavy metals. This acid flows out of the seeps and portals of the mine.

Much of the acidic mine drainage ultimately is channeled into the Spring Creek Reservoir by creeks surrounding IMM.

The Bureau of Reclamation periodically releases the stored acid mine drainage into Keswick Reservoir. Planned releases are timed to coincide with the presence of diluting releases of water from Shasta Dam. On occasion, uncontrolled spills and excessive waste releases have occurred when Spring Creek Reservoir reached capacity. Without sufficient dilution, this results in the release of harmful quantities of heavy metals into the Sacramento River.

IRON MOUNTAIN, CALIFORNIAIntroduction

Stalactite and stalagmites of melanterite, an iron

sulfate mineral, containing zinc and copper. pH of drip water was -0.7.

Beaker is 2 l.

Stalagmite of acid-iron-sulfate salts, Richmond mine, Iron Mountain, CA.Minerals: black-voltaite, purple-coquimbite, white-rhomboclase

H2SO4 + CaCO3 > H2O + CO2 + CaSO4

IRON MOUNTAIN, CALIFORNIAMore Information

http://toxics.usgs.gov/topics/rem_act/iron_mountain.html http://www.genomenewsnetwork.org/articles/2004/02/06/

iron_mtn.php