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Abandoned Mineral Lands
What are Abandoned Mineral Lands?
Abandoned mineral lands (known as AML) are one of many types of disturbed lands in the National Park System. AML sites are 1) underground and surface mines, 2) placer and dredge sites, and 3) oil, gas, and geothermal wells. Commodities mined at these sites ranged from soft rocks such as coal and sand/gravel to hard rock minerals such as gold, lead, and copper. Sites can contain waste rock (unprocessed rock), tailings (processed rock), abandoned roads, fuel storage tanks, drainage diversions, buildings such as mills and assay shops, deteriorating structures such as headframes and tramways, and abandoned heavy equipment.
Legacy of Mineral Development
Not surprisingly, the legacy of abandoned mineral lands spans North America. Mining for flint, obsidian, and native copper for tools and weapons, turquoise for jewelry, and clay for pipes began with the arrival of prehistoric peoples. During the 16th century, expectation of mineral wealth drove Coronado's conquistadors beyond the edge of civilization to the heart of an unknown continent. Later, the lure of gold and the prospect of great wealth were responsible for Europeans settling in the western United States. With the beginning of the industrial age, the young nation, hungry for energy, exploited its mineral resources of coal, oil, gas, and uranium, and this too left its mark on the land. Deserted, these sites stand in silent testimony to those who pioneered this country in search of mineral wealth.
Has mining occurred in national parks?
The answer is yes, and, in fact, mining still occurs in some parks. Most abandoned mines inside national park boundaries, however, are not from recent mining operations but from operations that existed before parks were established.
An estimated 3,100 abandoned mineral sites can be found in the National Park System, in all 7 regions of the system, and in 45 states. This number translates to 8,400 mined features, 700 oil and gas wells, 1,000 quarries, and 33,000 disturbed acres. Additionally, the National Park Service estimates that 5,000 miles of abandoned access roads exist. Abandoned mineral lands are lands that were disturbed by mineral extraction --underground mining, surface mining, dredging, and oil and gas exploration--and then abandoned. Abandoned mineral lands can be underground with numerous mine openings such as adits and shafts or on the surface in the form of strip mines, quarries, open wells, or pits. Abandoned mineral lands are not only the actual mine or well but include access roads and trails, historic buildings such as mills and company towns, tailings and waste rock piles, and abandoned machinery such as ore carts, steam engines, and pump jacks.
Hazards — Stay Out and Stay Alive!
Occasionally, adventurous people enter abandoned mines and wells. Some are injured or do not make it out because they fell victim to one or more of the many hazards associated with abandoned mineral sites:
Vertical Mine Openings
Falling down vertical openings is the most common cause of death and injury in abandoned mines. Darkness, loose debris, and false floors can hide vertical openings. Weathered rock at the edge of an opening can break away and slide into the hole under the weight of a person.
Deadly Gases and Oxygen Deficiency
Lethal concentrations of methane, carbon monoxide, carbon dioxide, and hydrogen sulfide can accumulate in underground passages. Pockets of still air with little or no oxygen can be encountered. By the time persons feel ill, they are no longer able to react.
Cave-Ins
Mines can cave in at any time! The effects of blasting and weathering destabilize once-competent bedrock through time.
Unsafe Structures
Support timbers, ladders, cabins, pump jacks, tanks, and other related structures may seem safe but can easily crumble under a person's weight. Do not be fooled by appearances!
Unstable Explosives
Unused or misfired explosives are deadly. Because old explosives become unstable, minimal vibrations from a touch or footfall can trigger an explosion.
Highwalls
Vertical cliffs--also called highwalls--from which material was extracted are common features of open pit mines and quarries. These highwalls can be unstable and prone to collapse. Do not climb near or on highwalls.
Water Hazards
Many abandoned mines become flooded. Shallow water can conceal sharp objects, drop-offs, and other hazards.
Pits
Mud pits once used for oil and gas operations can contain hazardous materials and may be the consistency of quicksand.
Radioactivity
Some of the materials that were mined, such as uranium and thorium, are radioactive. Because the effects of radiation exposure are cumulative through a lifetime, any can be harmful or fatal to humans, wildlife, and plants.
Designed for the Short-Term
Mines were constructed and maintained to be safe only while they were in operation. When the miners departed in search of more lucrative deposits, they often left vertical openings uncovered and removed the water pumping and ventilation systems. Support structures, timbers, and ore pillars were removed or left to rot.
Mines Are Not Caves
Caves are formed naturally over thousands or even millions of years. Mines, in contrast, are formed in comparatively short periods of time through blasting, a process that fractures and destabilizes the wall and roof rocks. Most underground mines do not have natural ventilation and consequently can have lethal air traps. Even experienced cavers can die exploring mines.
Rescues
Mine rescues are extremely hazardous. Mine rescue teams, despite their extensive training, are at significant risk every time they enter an abandoned mine. The tragic and unfortunate reality is that most mine rescues turn into body recoveries.
Environmental Consequences
Abandoned mineral lands can have detrimental effects on soils, water, plants, and animals. The extent of the effects in National Park System units is not known. Inventories are incomplete and parks are still evaluating sites. The following examples are common environmental consequences associated with abandoned mineral lands.
Water Resources
Water is one of the resources most frequently harmed by abandoned mines and wells. Water is also the main vehicle that carries abandoned mineral land impacts beyond the immediate site. Elevated concentrations of metals and increased amounts of suspended sediment, acidity, petroleum, and brine threaten surface and underground water quality and aquatic habitats.
Acid Mine Drainage
Acid is created as metals oxidize in sulfide ore and waste rock. Acid allows toxic metals to dissolve and wash into streams and lakes. Acid mine drainage occurs at only a few of the abandoned mines in the National Park System. At some of these sites, the water coming out of the mines is so acidic that it can actually burn a person's skin.
Metal Contamination
Mining metals requires extracting ore from the ground, crushing the ore to the size of sand grains, and removing the desired mineral. Often the excess material--tailings--is deposited on the surface. During storms and snow melts, water flows over and through the tailings. The tailings still contain relatively large amounts of metals such as lead, zinc, copper, and cadmium. The water interacts with the metals and transports them to nearby streams. Some metals, at concentrations as small as a few parts per million, can damage or kill aquatic plants and animals.
During oil and gas drilling, a circulating fluid called mud is used to remove the cuttings from the well bore. This fluid often contains additives that are laden with heavy metals such as chromium and barium. In the past, when a well was completed, these muds were often left at the site, allowing the metals to leach into streams, lakes, and aquifers.
Erosion and Sedimentation
Disturbed lands and unprotected slopes are susceptible to erosion. Uncontrolled surface drainage can remove soils and may make large areas unstable. Every year, sediments from mine sites cause significant damage to downstream resources.
Petroleum and Brine
Unplugged or improperly plugged oil and gas wells pose serious threats to park resources. Leaking well fluids can contaminate surface and subsurface waters that in turn jeopardize the safety of public water supplies. Contamination of this type can continue for years without being discovered. Water supplies for natural springs may also be affected, damaging resources miles away from the contaminated well.
Hazardous Materials
Mining and drilling, like other industrial processes, require a variety of chemicals. Discarded drums and tanks are often found on abandoned mineral lands inside underground passages, buried in waste rock piles, or just haphazardly scattered around the site.
Scenic Resources
Although some mine and wells are historically significant, most are eyesores. Piles of trash and debris, open pits, waste rock piles, and access roads blemish the otherwise pristine landscapes of the parks. Surface mines and quarries often have the greatest impacts on scenic vistas. In some cases, hundreds of thousands of cubic yards of material have been removed, making restoration extremely difficult.
Wildlife and Vegetation
Mining often stripped away not only the vegetation but also the topsoil that is needed to reclaim the site when mining operations cease. The area left behind is barren and incapable of supporting plant and animal life. Bare soil continues to erode and is carried away from the site to nearby streams and rivers. Here, the sediment clogs stream channels, reducing fish habitat and interfering with natural flow patterns. Even when these effects seem minor at first glance, they may impair larger ecological communities. Soils and water contaminated with heavy metals or chemicals from mineral processing may be harmful to wildlife. These contaminants can become increasingly concentrated in animals higher up the food chain in a process called biomagnification. Affected animals could die or become unable to reproduce.
Mines as Habitat
Abandoned mines do not always have negative consequences. They sometimes provide habitat for wildlife including some rare or endangered species. Some woodrats, bats, salamanders, and owls use mines as habitat. In many parks, special mine closures protect critical habitat and correct safety hazards. Some bat species, which are endangered because their native habitats were destroyed, have begun to inhabit abandoned mine openings. When conditions are suitable, bats can use mines for summer roosts, winter hibernation, nurseries for raising young, and a stopover during migration. Of the 43 bat species native to the United States, 29 rely on mines for a portion of their habitats. The continued survival of several bat species may depend on the few mines and remaining caves that meet the habitat needs of these animals.
Mitigating Hazards
The mitigation and reduction of hazards from abandoned mineral lands are often complicated and expensive procedures. The National Park Service establishes the priority for mitigation by considering the level of danger and potential for resource damage. Each site is unique. The chosen method for mitigating a hazardous site depends on several things: available materials at the site, the type of rock, the difficulty of reaching the site, and money. Parks use a variety of methods to close hazardous mine openings. Because of limited funding, parks can usually afford only to fence the hazard and post signs, temporary solutions. Other common mine closure techniques include backfilling, blasting, expandable foam, rock and mortar walls, and bat gates.
During mitigation of abandoned oil and gas sites, well bores are properly plugged and capped. Cementing the wellbore with concrete at the production zone and the groundwater zone prevents contamination of water supplies.
Reclamation and Restoration
Scars on the land may last thousands of years even if mined areas stabilize and the vegetation recovers. Carefully planned reclamation can restore natural processes and greatly speed site recovery. Reclamation in the National Park System focuses on reestablishing landscapes and environments that mimic the surrounding undisturbed lands. Mine structures such as mills, shops, headframes, and others of historic value are stabilized and preserved. Otherwise, the pre-mine condition is restored wherever possible. Reshaping the surface stabilizes slopes and drainages, waste rock piles, tailings ponds, highwalls, and access roads. This reshaping often requires the use of heavy equipment to contour the land to look and function like the surrounding undisturbed lands. The restoration of stream channels also provides for the reintroduction of plants and animals that were lost because of mining. The same type of earthmovers that created the mineral extraction scars are often the best suited to remove them.
Cleanup or treatment of toxic materials prevents further impairment of the environment.
The goals for revegetation of mine sites in the National Park System are the restoration of native plant populations and patterns. The first consideration is the suitability of the soil for revegetation. In harsh conditions, topsoils, compost, or specific nutrients can be added. Specialized nurseries may be needed to propagate suitable plant materials. Sometimes, revegetation work is focused on establishing pioneering species to allow for natural succession. Time and nature then restore the natural productivity in the site.
The National Park Service Abandoned Mineral Lands Program
The National Park Service closes between 10 and 100 mine openings and plugs 5 abandoned oil and gas wells each year. In 1993, the estimated cost of reclamation of all remaining abandoned mineral land sites in the National Park System was $200 million.
Volunteer and Cooperative Projects
Each year, national parks benefit from the hard work of thousands of volunteers. Volunteers assist with the inventory of abandoned mines and wells, construction of mine closures, and revegetation of mine sites. Without volunteers, the National Park Service could not afford the labor-intensive projects. Often, the National Park Service uses outside specialists to conduct scientific research for restoration projects. The service established cooperative agreements with several other federal agencies, state agencies, and universities for the study environmental impairments in abandoned mineral land sites in park units.
Cultural Preservation
Many parks boast rich mining histories and are active in preserving and even reconstructing mining-related historic structures and landscapes. Three park units were established with the specific purpose of preserving the American mining heritage: Klondike Gold Rush National Historical Park , Yukon-Charley Rivers National Preserve, and Keewanaw National Historical Park. The first two of these parks commemorate the Alaskan gold rush of 1898, and the latter, established in 1992, celebrates the internationally significant copper mines in the upper Michigan peninsula. Evidence of earlier mining can also be viewed in the National Park System. Alibates Flint Quarries National Monument in Texas and Wupatki National Monument in Arizona preserve the remains of prehistoric extraction sites, and Pipestone National Monument in Minnesota protects the pipestone (red mudstone) quarries of the Yankton Sioux.
Interpretation and Education
The National Park Service wants people to know that mining and abandoned mineral lands are often part of the park scene. Mining interpretive displays and presentations are part of the program at several parks. In other parks, special regional events such as discoveries and local gold rushes are commemorated. Visitor centers often have books on mining history and folklore. Educators have recognized that parks make excellent classrooms. Mining-related topics are used to enhance school curricula in history, geography, science, and even art. Some national parks and state agencies offer school outreach programs, including abandoned mineral lands safety information for children.
Last Updated: November 17, 2011
