Geologic Setting and History of Mining in the Animas River Watershed, southern Colorado

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1 Geologic Setting and History of Mining in the Animas River Watershed, southern Colorado Virginia T. McLemore New Mexico Bureau of Geology and Mineral Resources, New Mexico Tech, Socorro, NM

2 On August 5, 2015, EPA personnel caused the release of wastewater at the Gold King mine, Colo. into the Animas River Gold King adit Animas River

4 Gold King mine Church et al. (2007)

5 Gobla et al., 2015

6 Purpose To provide geologic and historical background of the Gold King-Animas River spill and mining in the Animas River watershed To address the path forward in preventing similar spills or where do we go from here? (from Church et al., 2007; Church, 2014; Gobla et al., 2015 among other references)

7 Location and topography Northernmost headwaters of the Animas River watershed in San Juan County, Colo Drainage basins of the Animas River at and upstream from Silverton, Colo Two main tributaries, Cement and Mineral Creeks Silverton is 9,305 ft and some of the mountain peaks in the headwaters rise to more than 13,800 ft 150 sq miles

8 Church et al., 2007, Professional Paper 1651

9 Geological Setting Late Oligocene volcanic centers that erupted many cubic miles of lava and volcanic tuff and formed the Silverton caldera (27.6 Ma), which is nested within the San Juan caldera (28.2 Ma) Followed by multiple episodes of hydrothermal activity that produced widespread areas of pyrite alteration and quartz-pyrite-metals veins Most of the host rock is very fractured and permeable=complex groundwater flow paths

10 Gold King mine Yager and Bove, 2007, Professional Paper 1651

11 Geologic setting Subsequent weathering of hydrothermally altered rock, particularly the acid sulfate and the quartz-pyrite-sericite alteration that was extensive in the watershed, is a natural source of source of metals and acidity (Church et al. 2007, among other studies) Not all elevated concentrations of metals and low-ph conditions found in streams are the result of historical mining

12 Gold King mine Yager and Bove, 2007, Professional Paper 1651

13 In 1874, it was noted that water in both Cement and Mineral Creeks contained iron sulfate, making the water undrinkable (Rhonda, 1876)

14 WHAT IS WEATHERING? Physical, chemical, and/or biological processes at or near the earth s surface that result in reductions of grain size, changes in cohesion or cementation, and change in mineralogical composition that convert rocks to soils and can produce acid drainage Occurs in the country rocks before mining Occurs in the mine waste materials after mining

15 WHAT IS WEATHERING? Weathering is simply the consequence of exposing rocks to the conditions at the Earth s surface fairly low temperatures low pressures organic activity Requires chemically active substances such as water and the gases of the atmosphere

16 Factors affecting pyrite oxidation =generation of acid drainage (AD) Oxygen concentration Temperature ph Pyrite surface area Concentration of ferric iron (Fe+3) The presence of bacteria Water

17 Time Scales of Weathering and Generation of AD Unaltered (fresh) rocks (age Ma) Vein deposits (age Ma) Other land forms and surfaces (such as debris flows, ages unknown) Ferricretes and other stream terrace deposits (thousands to million years) Mine features (0-140 years)

18 Mining History

19 History of mining in the Animas River Watershed Early mining by the Spanish (presence of arrastra used to recover gold and silver) Rediscovered about 1860 Development begin in 1871 with the Little Giant mine Extensive mineral exploration did not begin until after the signing of the Bernot Treaty with the Ute Tribe in 1873 Production increased with construction of the railroad to Silverton in July 1882 Smelter in Durango

20 Legacy Mines 1872 mining law was a product of gold rushes and other mining booms in the west during the 1800s Allows US citizens and firms to explore for minerals and establish rights to federal lands Contains no environmental provisions Required that every mining claim have a discovery hole or shaft and annual assessment work = many mine features that we see today Assessment work requirement abolished in 1990s

21 US Environmental Regulations 1935 Executive Order Stopped discharge of mine waste and tailings in waterways did not always apply to arroyos Federal Lands Regulation 1960s-70s 1970s Federal Regulations Clean Water Act (CWA) Federal Surface Mining Control and Reclamation Act (SMCRA) Federal Land Policy and Management Act (FLPMA) Among other legislation

22 Note Miners were not required to reclaim their sites until the 1990s and most followed acceptable mining practices of the time. It is important to recognize that these early miners were not breaking any laws, because there were no laws to break.

23 Another Caution Only a limited amount of Federal land has any mineral resource potential Mineral deposits form by natural geologic processes in specific places in the world Mineral deposits are not always found in the most convenient places in the world Most mining claims do/did not result in active producing mines For every ~1000 promising prospect areas, only 1 may make it to production =results many mine features

24 Sunnyside mine Reuben J. McNutt staked on August 18, 1873 In 1896, the Silverton Northern Railroad was extended to Eureka, Colorado, to serve the Sunnyside mine American Tunnel in 1959 gave new life to the Sunnyside mine, which operated from blowout in 1978 that drained Lake Emma and required two years to repair 7 million short tons of ore over its life span of 118 years

25 Gold King mine Production started in 1886 In 1899, the Silverton, Gladstone, and Northerly Railroad was built to Gladstone 665,000 tons of ore averaging g/t gold, , production amounted to g/ton Ag, 0.71% Pb, and 0.52% Cu Mining operations ended around 1923 Exploration in the 1970s 7 levels Level 1 at 12,160 ft Lower Gold King portal 10,617 ft = American Tunnel and drained higher workings

26 Sunnyside mine Gold King mine Gobla et al., 2015; map prepared by Kirstin Brown

27 Eureka mining district Red Mountain mining district South Silverton mining district Yager and Bove, 2007, Professional Paper 1651

28 5,397 mine shafts, adits, tunnels, and prospects Church et al., 2007, Professional Paper 1651

29 Mills, tailings, smelters Church et al., 2007, Professional Paper 1651

30 By 2007, more than $20,000,000 had been spent on remediation in the watershed (Church et al., 2007; Church, 2014). Both private and public (EPA, USFS, State of Colorado, BLM) funds have been used for these remediation efforts.

31 Church et al., 2007, Professional Paper 1651

32 Challenges for reclamation efforts Complex land ownership (USFS, BLM, orphaned properties held by San Juan County for delinquent taxes, private) Issues of financial liability Technical approaches needed to mitigate acid mine drainage without resorting to costly treatment facilities The need for adequate space to build new repositories to move those mine wastes that cannot be mitigated in place Effect of reclamation on tourism in a historical mining district such as Silverton Understanding the groundwater system, which affects all the mines in the area and the potential for work on one mine affecting conditions at another What are the pre-mining conditions What should a long-term monitoring plan consist of? What should we test for? What media should be tested (water, crops, fish, plants)? What are the pathways? What is safe and what is not safe? (Church et al., 2007; Church, 2014; Gobla et al., 2015)

MINERALOGY AND CHEMISTRY OF MINE WASTE ROCK PILES IN MINING DISTRICTS IN SOUTHERN COLORADO AND NEW MEXICO

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