November 8, 2021
6:00 - 7:30 pm
Note: ETGS members will receive an email with info for logging into the meeting.
Investigations at Abandoned Mine Sites in the Rocky Mountains
Gareth J. Davies, TDEC (Retired)
More than 23,000 abandoned mines are scattered all over the Colorado Rocky Mountains. Groundwater accumulates in these mine workings, and oxidized ore minerals produces a precipitate affectionately known as "yellowboy". Most of these mine sites are at high altitude, 2,400 - 3,700 m (8,000 - 12,000 ft) above sea level, and in alpine environments, with rapidly changeable weather (all four seasons in any day), very steep terrain, snow fields, loose rocks etc. Going inside the abandoned workings requires mine-safety training. Drilling rigs were helicoptered into high narrow valleys, and we spent time in wet, nasty, dark 130-year-old gold mines...an unforgettable "work" experience. As a miner's son from Wales, I felt quite at home, well...
The problem is that discharge from mine workings often impacts surface streams, kills aquatic species, and loads surface water with toxic heavy metals that eventually impact rivers. Many of the workings are abandoned and collapsed, so the water buildup behind blockages in drain tunnels freeze shut in winter, sometimes blowing out during the spring thaw. The ice plugs can fly cross valleys. One such event was the Gold King Mine above Silverton, CO which was not a blowout per se but a consequential collapse of an attempt to solve an inevitable potential blowout. The contamination from this event flowed all the way to the Grand Canyon.
The contamination problem is typically located in a deep source of "stoped" workings above the water table that discharge into drain tunnels. Typically, ~400 mg/L of Zn and other metals are discharged at the peak of snowmelt. The method we often began with was to trace (using injected dyes) from accessible mine workings, but this does not address the contaminated water from workings beyond the accessible areas. The stoped areas are huge voids (mined out) and often too dangerous to enter. In some cases, they have been excavated to the upper parts of mountains and fill with permanent snow and ice plugs. Some open in summer months and pose dangers to mountaineers and skiers. Later, I used natural uranium as a tracer which would yield data about water moving through the whole system. These data, combined with USGS tracing of surface streams and stable isotope data, support an attempt to describe the systems.
Gareth grew up in South Wales in a coal-mining community, next to a major karst area, and thus was interested in caves from the age of 15. He spent many years traveling in Asia, Europe, North America and Mexico exploring caves before marrying and moving to the US. He was awarded a BS degree from Millsaps College and an MS degree from the University of Southern Mississippi. His thesis dated speleothems from Tennessee cave using the uranium-thorium method. He moved to Oak Ridge and spent a couple of decades running his own company doing multiple tracer work from Puerto Rico to the US Rocky Mountains. After being a contractor, he later joined TDEC (now retired). He is a Fellow of the Geological Society of America.
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Page updated October 27, 2021