Abandoned mine lands (AML) are those lands, waters, and surrounding watersheds contaminated or scarred by the extraction, beneficiation or processing of coal, ores, and minerals. Abandoned mine lands include areas where mining or processing activity is determined to have ceased.
Colorado’s abundant mineral wealth helped drive the economic development of the state and contributed to the development of the United States as a whole. Unfortunately, the mines that hosted these minerals have left a legacy of hazards ranging from environmental issues like water quality degradation and increased sedimentation, to physical hazards associated with the mines excavations themselves. Across the state, there are an estimated 23,000 abandoned mine sites on both public and private land.
The CGS has been involved in characterizing and understanding various aspects of abandoned mine lands in Colorado. An inventory of environmental degradation and physical hazards associated with abandoned mines on United States Forest Service property was conducted by CGS from 1991 to 1998. In all, 18,382 mine-related features were identified during this program and helped to identify sites that warranted further investigation and characterization. The CGS published a number of these mine site characterization reports.
Acid mine drainage (AMD) is water that is discharged from mining or mine-related operations, which contains high levels of dissolved metals and sulfates in conjunction with pH values less than 4.5 (acidic). AMD is formed from the reaction of various minerals (principally pyrite) with oxygen and water. AMD can degrade the water quality of streams and water supplies, often to the point of causing harmful effects to the aquatic life of the stream.
Sedimentation and Sediment Contamination
Surface runoff can carry AMD-originated silt and debris down-stream, eventually leading to stream clogging. Sedimentation results in the blockage of the stream and can cause flooding of roads and/or residences and pose a danger to the public. Sedimentation may also cause adverse impacts on fish.
Air pollution can occur from piles of earth materials left at an abandoned mine. Windblown dust can have significant impacts on nearby residents and wildlife. The toxicity of the dust depends on the proximity of environmental receptors and the composition of the material. In particular, arsenic and lead are contaminants of concern.
Various physical hazards may exist at abandoned mine sites. Mine openings such as tunnels and shafts are imminent hazards because they present an opportunity for falls as well as the potential for collapse onto adjacent areas. Dangerous gases may exist in mine workings and can quickly overcome an unsuspecting visitor. Historic structures and equipment can present a hazard as these features are often unstable and prone to collapse. The rule of thumb is
Stay Out and Stay Alive!
During the fall of 1993, the CGS inventoried mines in the Cinnamon Gulch area of the Dillon Ranger District, White River National Forest, near the town of Montezuma. This project was part of an eight-year, statewide inventory of abandoned mines on USFS-administered lands in Colorado. In September 2000, the Forest Service requested a watershed characterization study for Cinnamon Gulch, and more detailed studies on five mines in the area.
Field work for this study included a visit to each site to see if major changes had occurred since the inventory work in 1993. Although water samples were collected at some of the sites in 1993, additional samples and water tests were collected in 2001. In-stream samples were collected from some of the receiving streams in efforts to bracket selected mines or groups of mines and better quantify impacts to the watersheds. In addition, waste-rock piles on some of the mines were sampled on a grid pattern to assess their potential environmental effects. Waste-rock samples were analyzed for gold, silver, mercury, paste pH, acid neutralization potential, and potential acidity. Samples are also analyzed using x-ray fluorescence (XRF) to determine a suite of major, minor, and trace elements. A total of 39 water samples were collected from the Cinnamon Gulch watershed over two sampling events in 2001. During the high-flow sampling event in July, 19 water samples were collected, and during the low-flow event in October, 20 water samples were collected.
Additional mine or mining district reports:
Colorado Abandoned Mine Land (AML) Information map — May also be accessed through the CDPHE at the Mine Impacted Streams Task Force. The user interface is a GIS platform and includes AML information layers which can be projected on road maps, satellite imagery, property ownership maps, watershed maps, and so on. This platform is developed and maintained by Colorado State University’s One Water Solutions Institute.
O’Keeffe, Michael K., Peter E. Barkmann, F. Scot Fitzgerald, and Jonathan R. Lovekin. “OF‐19‐12 Colorado Abandoned Mine Land Inventory and Information Hub: Report on the Development and Data Sources.” Abandoned Mine. Open File Report. Golden, CO: Colorado Geological Survey, October 2019. — This comprehensive report examines the processes involved in the CGS’s involvement in the wider AML project.
Sares, Matthew A., Randal C. Phillips, John T. Neubert, Robert H Wood II, Jonathan R. Lovekin, Robert M. Kirkham, Robert G. Benson, et al. “ON-008-04 U.S. Forest Service Abandoned Mine Land Inventory Project – Colorado.” AML. Golden, Colorado: Colorado Geological Survey, June 3, 2020. — This dataset includes a compilation of USFS Ranger District reports on areas of particular interest; project field guidelines, a data dictionary, along with the GIS geodatabase files.
The driving force behind the project was the Federal Facilities Compliance Program, which is designed to bring federal facilities and lands into compliance with federal environmental laws including the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) (aka Superfund); the Resource Conservation and Recovery Act (RCRA); and the Clean Water Act (CWA) among other laws. The USFS Abandoned Mine Land Inventory Project was essentially a “discovery” process under CERCLA.
Colorado Abandoned Mine Land (AML) Information Sources
To request more information, record the specific information about a point on the map and call the AML manager, with the information from the information hub, at the agency listed on their website listed below.
Abandoned Mines dot gov — General information about abandoned mines on Federal lands, hosted by the Bureau of Land Management (BLM).
Bureau of Land Management (BLM) Colorado — Main BLM AML site, about the AML program.
Colorado Division of Reclamation Mining and Safety (CDRMS) — Inactive Mine Reclamation Program information.
Department of Energy (DOE) — DOE defense-related uranium mines program with contact information.
Environmental Protection Agency (EPA) Region 8 AML — EPA abandoned mine lands webpage.
Environmental Protection Agency (EPA) Region 8 — Main EPA Region 8 site with general contact information for Colorado.
National Park Service (NPS) AML — NPS abandoned mineral lands site.
United States Forest Service AML — USFS abandoned mine land site.
United States Department of Agriculture – Rocky Mountain Region — USFS Region 2 webpage, including Colorado, with contact information.
United States Geological Survey — USGS abandoned mine lands initiative.