History lesson turns to a chemistry lesson

A few weeks ago I described a snowshoe history field trip of the Red Mountain Mining District. This area took out millions of dollars of metals in the late 19th century and early 20th century. Unfortunately the profits are long gone and we are left with the clean up. There was lots of evidence of iron in most every mine in the area. Obviously, the RED in Red Mountain is due to iron mineralization in the rocks.

What hard rock mining did was increase the air and water exposure to the iron pyrite found naturally in the geology of Red Mountain Pass. Iron pyrite (FeS2) reacts with the water and oxygen to form sulfate (SO4). which combines readily with water to form sulfuric acid and ferrous iron.

FeS₂ + O₂ + H₂O = Fe²⁺ + SO₄^2- + H⁺

The ferrous iron reacts with the air and water to create ferric iron. The ferrous ions are soluble in water while the ferric ions are not. The ferric ions precipitate out of the water coating the entire substrate with an almost impervious layer of iron. No matter the water chemistry, this iron pavement alone signals the end for any biology in the water, there is no place for macroinvertebrates to live, no place for aquatic plants to take hold. The food chain dies at the lowest trophic levels.

Fe²⁺ + O₂ + H⁺ = Fe³⁺ + H₂O

However, the water chemistry is not normal. Most biology needs a near neutral pH to live. The sulfate ions reacting with water results in the formation of sulfuric acid, lowering the pH to extreme acidic conditions. I have measured the pH of alpine creeks down to 2.0.

FeS₂ + Fe³⁺ + H₂O = Fe²⁺+ SO₄^2- + H⁺

Part of trying to fix the Uncompaghre water shed is to determine how bad was the water prior to mining. At the time, the miners did not do any environmental impact studies before they started digging. The best we can do are some anecdotal comments about catching fish just outside the mining camps- an impossibility today. It is obvious that there was natural mineralization present before the advent of mining. So, how much can be cleaned up today?

Do we have the will to clean up seriously degraded waterways way up in the headwaters?

Red Mountain #1

Looking for red rocks next to the channelized and embedded Red Mountain Creek
Part of an old tailings slurry pipeline. The miners used wooden flumes because the metal corroded to quickly with the acidic water.
Red Mountain Creek in the winter. The yellow water stands out nicely against the white snow.