Monday, April 25, 2011

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+ + SO42- + 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++ SO42- + 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.

Wednesday, April 13, 2011

feng shui on the trail AW 33

This month, John in the Taconic Mountains has asked about how we incorporate geology into our homes. I was thinking about some landscaping we had done in the backyard or about the fireplace in Ed Abby's old home in Moab UT where the rocks represent the stratigraphic column of the Canyonlands. BUT

I didn't have any pictures. I know that this isn't exactly what John had in mind, but it sure beats the shelf with my "prettiest" hand samples.

Last week I was visiting Zion National Park and hiked up the West Rim Trail past the infamous Angels Landing. While walking up "Wally's Wiggles" we saw this fantastic example of a Navajo sandstone iron concretion used in the retaining wall. Whoever was trail crew leader had a great eye for aesthetics and incorporated some fun geology in the trail.

Looking way down at Wally's Wiggles. Click the image for a larger version.

the concretion in the wall
up close

Monday, April 11, 2011

A history lesson

A few weeks ago I attended a ski/snow shoe tour of the Red Mountain Mining District courtesy of the Ouray Historical Society and the Uncompahgre River Project. The area I took the most pictures was the picturesque Yankee Girl mine.

The Yankee Girl was discovered in 1881 and by the time most mining had ceased in 1896 over 3 million dollars of gold, silver and lead had been brought to market (while leaving tons of debris on he ground near the mine). The Yankee Girl. like most mines in the district took advantage of several volcanic breccia chimneys, a result of the creation of the Silverton caldera. The most productive ore seems to be associated with the quartz porphyry found in the chimneys. Lead and zinc ore paid he bills, the silver provided the profit and the little gold that was found provided the headlines.

lunch at the Guston mine

The Yankee Girl headframe
The Yankee Girl up close. The main mine shaft dropped over 1000 feet from this point.