Adopt a Mine

IMPORTANCE OF PROTECTING MINES

J. Scott Altenbach 1 and Richard E. Sherwin 2
Department of Biology University of New Mexico Albuquerque, New Mexico

Abstract

The archaeological and historical resources that historic mines provide in parts of North America are locally highly significant and often totally ignored in the consideration given to their non-destructive safeguarding. Mines may provide time capsules from the late nineteenth and early twentieth centuries that have no equal. Those time capsules have seen wholesale obliteration along with bat habitat by destructive closure. Another resource in the eyes of geologists, mineralogists, and the mining community is the idea that historic mines provide human-accessible “windows into the world” that cannot be equaled by core drilling techniques and are not likely ever to be created again. The complicated balancing act pits public safety (more accurately fears of liability) and accelerated destructive safeguarding (where time is money) against protection with non-destructive closure that may require more time-consuming evaluation and may be more costly or less convenient. Critical in this balancingact is the role of the scientific community in providing  accurate assessment of the biological needs of wildlife, the actual patterns of mine use, and a reasonable assessment of the impacts associated with alternative closure options. The desperation decision-making on the part of biologists, a necessity in the face of the aggressive, often uniformed, often-arrogant closure programs in the last decade must give way to an unbiased scientific approach to the impacts of alternative closure methods if non-destructive closure efforts are to continue with success.

Key Words: abandoned mine, mine reclamation, mine remediation, bat roost, wildlife management, bat gate, roost protection.

Introduction

Abandoned mines and caves are analogous in that both represent subterranean habitat. As such, internal conditions may be similar as both provide some sort of buffer from ambient conditions and usually provide habitats not locally available on the surface (Humphrey, 1975; Kirbo –this volume; Sherwin, et al., 2000a; Sherwin, et al., 2000b, Sherwin, et al., 2002; Tuttle and Stevenson, 1978). Both caves and abandoned mines are available in all shapes and sizes, include a wide range of climatic conditions, and are widely distributed. Both resources are located in a broad range of geographic conditions across a wide-range of habitats (vegetative, elevation, etc). However, there are some subtle, yet fundamental differences between caves and abandoned mines that make a profound difference in how both resources are managed. The differences between both resources are mostly attributable to the greater instability observed in abandoned mines relative to caves.

The geological and hydrological processes that cause the formation of caves generally occur over geological time scales, allowing sufficient time for weathering to stabilize cave features and form.
Abandoned mines are created over short temporal periods using violent processes (drilling, blasting, etc.). Many hard rock mines were excavated in brecciated or faulted ground where mineralization subsequently occurred, further compounding the ephemeral nature of internal workings. Mine workings were created to access and remove ore-bearing rock. Internal workings were designed to last only for the period of ore extraction and were not intended to last for prolonged periods of time.

To help support fractured overburden, mine engineers often called for internal support in the form of timbers or pillars (load-bearing rock left in place). However, ground supports were often minimal since timber was expensive and required additional time to place (“men were cheaper than timber” – Crampton 1956). When pillars were used, they were often robbed during the final stages of ore extraction and timbers were often pirated by later mining activities. Even when supports were left in place, subsequent stabilization often causes overburden to settle (causing pillar failure) and high humidity causes timbers and other wooden supports to rot over time. This combination of faulty ground, violent ore extraction processes, and lack or failure of internal supports, leaves abandoned mines exhibiting varying degrees of internal instability. In many cases, insufficient time has passed for internal workings to settle into stable form. A single mine may include portions that range from extremely stable (haulage tunnels through country rock that undercut ore zones) to dangerously unstable, further complicating the diagnosis of underground conditions. In addition, different types of mines are often viewed as more or less stable than others. For example, coal mines and uranium mines typically undercut sedimentary material (i.e., sandstone) leaving a flat roof (back) that is likely to fail into a more stable arch configuration. In addition to varying structural integrity, abandoned mines include a host of dangerous conditions such as toxic or oxygen displacing gasses, old explosives, vertical hazards (often hidden), abandoned equipment and even dangerously high levels of radiation. While those with appropriate training and experience can avoid these hazards, abandoned mines present a serious threat to the general public and even to those skilled in cave exploration.

Those interested in abandoned mine exploration, artifact hunting, and similar recreational activities often ignore the dangers associated with abandoned mines and many are drawn to these sites. Even those not actively seeking abandoned mines are not insulated from their dangers. Abandoned shafts or open stopes are often relatively inconspicuous and were often covered with timbers, sometimes in-turn covered with dirt and debris. As timbers begin to rot, structural integrity is lost, and additional weight (vehicle driving over, human walking across, heavy snow, etc) may cause failure. As a result of the risks associated with abandoned mines, they cannot be regarded as having recreation potential. Most abandoned mines are viewed as an attractive nuisance by land managers (Sherwin et al. 2000a).

Abandoned mines have been identified as a threat to the public and most States have initiated abandoned mine reclamation programs. These programs are intended to locate and secure abandoned mines (through portal closure) and eliminate associated hazards. While the level of organization and effectiveness of these programs varies, the net result is the annual loss of hundreds of abandoned mines each year. At least 32,738 openings have been closed since the initiation of formal reclamation programs (Meier and Garcia, 2001). In addition, unknown numbers of abandoned mines are also closed by private landowners to ameliorate issues of liability, or are lost to renewed mining activities in historically mined areas. In addition, mine workings often initially penetrated weathered, unconsolidated ground, and the lack of portal maintenance following abandonment has often allowed slope creep and
portal failure. An unknown number of mines are closed annually as the result of natural weathering processes. Regardless of the cause of closure, the net result is annual loss of open abandoned mines in
the landscape (mines are being lost without replacement since modern, underground mining is relatively uncommon).

The unstable nature of mines (relative to caves) represents a fundamental distinction that pervades every aspect of their management and represents a single point of divergence from which mines need to be distinguished as a separately managed resource. Those determining the appropriateness of protecting caves with bat gates must weigh the costs and benefits of restricting or eliminating access. The burden of proof is on them to demonstrate that the presence of sensitive resources (geological, hydrological, historical or biological) warrant the exclusion of the public from a given cave. Conversely, those who attempt to protect abandoned mines must provide supporting evidence that sensitive resources warrant the protection of individual mines from permanent closure. They must have sufficient evidence to offset the potential costs of allowing the persistence of potentially dangerous resources in the environment.

In addition, caves are generally closed on a site-by-site basis, and are not usually part of large-scale closure programs observed in abandoned mine reclamation. Caves often have a tradition of use, with varying amounts of information available regarding the types and sensitivity of resources maintained within. Those visiting caves are more than just “spelunkers.” Visitors often include cavers for whom subterranean exploration and cave conservation is a passion. These cavers often maintain excellent field notes documenting the condition and extent of passages, relevant observations, and documentation of negative impacts to cave resources (both biotic and abiotic). Cavers often stand as a voice for the resource and many caves have been protected as a result of efforts from local individuals and caving grottos. When pre-closure data are not available, there is an added luxury of time (supposing that resources are not in imminent danger) to collect suitable data to determine the appropriateness of cave protection. Projects that threaten abandoned mines are generally conceived and conducted over much shorter time periods. In most cases, the actual timeline of closure projects (location of workings through closure) is less than one year with most of these projects including dozens to hundreds of discrete mine workings. There is generally no information available regarding the extent and condition of subterranean workings, let alone the resources in those mines. In short, those managing abandoned mines often face the daunting task of locating, surveying and collecting data at dozens to hundreds of mine workings and then making sound management decisions for individual closures, often within a single season, with no available baseline data.

Resources Provided by Abandoned Mines

Cultural Resources. Much of the early history of the western United States was built upon the availability of natural resources. The location of mineral deposits and the resultant financial booms associated with extracting these resources were pivotal for the establishment of infrastructures upon which settlement was predicated (Hardesty 1987). Many mining techniques were developed or refined in the western United States, and miners were drawn from all over the world (particularly Europe and Mexico). Evidence of these booms, diverse settlements, and technological advances remain at mining camps (Hardesty 1987; Sagstetter and Sagstetter 1998).

Historical and archaeological resources from historical mining have been discussed most frequently in terms of those located on the surface (Hardesty 1987; E. Twitty 2002). In fact, surfaces associated with abandoned mines are routinely evaluated by archaeologists during mine closure and mine expansion projects following State Historic Preservation Office (SHPO) guidelines. However, artifact hunters, campers and explorers have permanently altered the historical integrity of many mining camps. As a result, the quality and quantity of surface feature documentation and protection during safeguarding projects varies dramatically depending on the remoteness of the site and the degree of climatic variability (surface features are subject to weathering). While pre-closure cultural surveys are conducted on all State and Federal lands, there has been little call for appropriately trained archaeologists and few have any training or familiarity with the history of mining. Archaeological reports identifying a steam dome from an uncommon and very old steam boiler as a “piston cylinder” and another which states flatly that gasoline hoisting replaced steam hoisting within a narrow time span (because of supposed greater efficiency of gasoline hoists), illustrate the lack of expertise of those conducting surveys (Altenbach, personal observation.).

Even though archaeological evaluations of surface features often leave much to be desired, underground evaluation is typically nonexistent. This is unfortunate because underground archaeological resources can be perfectly preserved in dry workings and surprisingly well preserved even in damp or wet conditions.

Some mines are virtual time capsules with artifacts maintained in such pristine condition that one can imagine hearing the sounds of voices and machinery, and even smelling the sweat and powder smoke in the air. They can provide a detailed view of the chronology of the mining operation, as well as many details of the techniques and technology of historical mining. Many of these details including subtleties of hand drilling, blasting, timbering, haulage, development and hoisting, have been lost. These details have only been rediscovered through the exploration and study of internal conditions and artifacts (Altenbach,1997). A wide variety of large and small machinery remaining in underground workings is otherwise known only from illustrations in old suppliers catalogs.

The lack of concern over historically significant resources available in abandoned mines is perplexing.

Perhaps the mines are not old enough to warrant concern from most archaeologists, however, most mines are old enough for protections mandated under the National Historic Preservation Act (1966, amended 1976 and 1980).

The lack of concern regarding historical artifacts in underground workings is evinced by the fact that the authors have surveyed in excess of 10,000 abandoned mine workings, yet only a single reclamation manager in one State program (H. Milford, New Mexico Abandoned Mine Lands Bureau) has ever queried regarding the historical resources in the surveyed mines. Even cursory documentation of underground resources
by surveying biologists would be more appropriate than the current program of disinterest.

It has been suggested that permanent closure of mines affords the best protection for cultural resources. However, solid closures (backfill, wall installation) often increase internal humidity, accelerating the weathering process, causng the permanent loss of cultural resources.

In addition, without even cursory documentation of sites that contain significant cultural resources, it is hard to imagine that they will be rediscovered. We propose that the discovery of significant historical resources in abandoned mine workings should be sufficient to warrant protection, or at least, documentation.

Unique Geological Resources. Another resource that is typically ignored during both pre-closure surveys and subsequent determination of closure or protection is the geologic and mineralogical information that is lost in destructive closure. Mine geologists view abandoned mines as “windows into the world” that offer detailed looks at the geological history of that particular area. The view afforded through abandoned mines is not possible by any other means (R. Eveleth, personal communication).
Surface evaluation of geologic conditions is often limited by alteration due to weathering. Although core drilling can provide information about subsurface geological features, it necessarily takes a narrow and nearly linear sample of the underground, easily missing major localized features. In addition, some types of drilling destroy much of the macro-morphology of investigated formations and often causes dramatic surface disturbance. In areas where abandoned mines are present, they are often the first resource investigated during prospecting and evaluation phases of mining operations. In addition, allowing access to underground workings allows claim holders (or landowners) to advertise their property to larger mining interests. Many universities (particularly those with mining programs) use abandoned mines as laboratories for training and educational purposes. In some cases, abandoned mine workings follow fault caves or intersect cave features, in which case protection might be warranted under the Cave Resource Protection Act (1988 –vugs are exempted).

In the current climate of severe and costly regulation, coupled with the high costs associated with creating underground workings, these windows are unlikely to be opened again. Therefore, we propose that abandoned mines that contain unique geological features may warrant protection from destructive closure.

Unique Biological Resources. The fact that bats use abandoned mines and that abandoned mines represent important roosting habitat for bats has been well documented (Altenbach and Pierson 1995; Altenbach et al. 2001; Ducummon 2001; McAney 1999; Sherwin et al. 2000a; 2000b; 2001; 2002; Tuttle and Taylor 1998; Twente 1960). Abandoned mines are known to be critical to many species of bats in at least portions of their range (see Sherwin and Altenbach, this issue). While the importance of abandoned mines to bats is becoming more widely accepted, closures still occur with little regard for the biological importance of these resources. Some mining companies and even mine reclamation projects interpret regulations to consider only endangered species. At least one Federally funded reclamation program on Navajo Nation Lands has closed all of its coal mines and virtually all of its hard rock mines without biological evaluations of any kind (D. Martinez personal communication).

Published accounts of the proportion of abandoned mines used by bats and the degree of their dependence on them varies regionally, but run as high as 70 percent (Sherwin et al. 2000a; 2000b; 2002). In addition, determining biological significance is somewhat subjective and also varies regionally.

For example, colony sizes considered to be significant for some species in the West might be considered insignificant for Eastern species with colony sizes that often number in the thousands (Tuttle and Taylor 1998; Altenbach and Pierson 1995; Sherwin et al. 2001). In some regions in New Mexico approximately 15 percent of surveyed abandoned mines have documented bat use significant enough to warrant protection from closures through the installation of bat-compatible closures (Altenbach in lit.). In regions of Nevada and Utah, proportions of mines identified as significant bat habitat vary from as low as 6% to over 50% (Sherwin et al. 2002). If these figures are applied to the tens of thousands of mines that have been closed over the last 15 years in which no biological surveys (or inadequate surveys) were conducted, it is clear that there has been substantial loss of roosting habitat. It is also possible that these same closures caused direct mortality through the entombment of roosting colonies (see Tuttle and Taylor 1998; Ducummon 2001).

What are the Responsibilities of Persons Conducting Mine Surveys and Making Recommendations for Non-Destructive Closures?

The fact that abandoned mines represent important roosting habitat for many species of bats, and that they are disappearing at a rapid rate makes it important that critical roosts be located and identified prior to closure. The time constraints imposed by mine closure projects make the management of abandoned mines particularly challenging. This is further compounded by the more complex patterns of use described for colonies roosting in abandoned mines relative to those roosting in caves (Sherwin et al, 2000a; 200b; 2002). In populations of C. townsendii studied throughout the Southwest and Great Basin, colonies roosting in abandoned mines were less spatially and temporally stable than those roosting in caves. In addition, a greater amount of survey intensity was required at abandoned mines (relative to caves) before patterns of use could be discerned (Sherwin et al., 2000a, 2000b). This further compounds the problems facing those who manage time-sensitive abandoned mine closure projects. Altenbach et al. (2001) suggest that observed complexity in the use of abandoned mines by bats makes a cookbook approach inappropriate. Specific techniques for conducting roost surveys are discussed by Brown (this volume).

The requirements for pre-closure bat evaluation have grown along with the costs of bat-compatible closure methods. Agencies and private entities have quite reasonably started to demand more accountability on the part of those asking that a particular mine be protected. If a mining company or State mine reclamation program is going to invest in a bat-compatible closure on a mine or several mines, it is reasonable that they see justification for the significance of the bat use at the mine and the probability that the closure will have the desired effect in bat conservation. The responsibilities of the biologists surveying the mine for bat use and making recommendations about the gate design fall into several categories.

The first responsibility of those overseeing mine closure projects is to locate all openings that will be affected. Following the location of openings biological surveys must be initiated that maximize the
probability of detecting bat use or, equally important, reliably determining that the mine is not used. The costs and benefits of external versus internal surveys are discussed at length by Altenbach and Milford (1995) and Altenbach, et al. (2001). Altenbach, et al. (2001) discusses the experience, equipment and training requirements for underground surveyors.

Reasonable recommendations about appropriate closure methods should not be made without at least cursory internal evaluation, as external surveys provide no power to resolve negative data. Sherwin et al. (2000a, 2000b, 2002) discuss the level of intensity that may be required to adequately resolve negative data. Managers must ensure that qualified persons, with adequate training in both mine survey and bat survey techniques conduct evaluations. Bad examples of survey techniques abound. For example, a biologist working for an environmental consulting firm in Arizona was observed evaluating shafts for bat use by dropping rocks down the shaft and then equating the lack of exiting bats as indicative of no actual use by bats. This type of disturbance to bats in lateral workings off of a shaft or even on the shaft rib would more likely drive bats deeper into the workings making any out-flight highly unlikely (see Altenbach, et. al. –2001- for an overview of shaft evaluation). This same consultant routinely misidentified roosting A. pallidus as C. townsendii during roost surveys in Nevada. Diagnostic features of both species make misidentification difficult, suggesting that this person did not even have a basic familiarity with bats. Yet this individual was making decisions regarding the permanent elimination of hundreds of potential abandoned mine roosts (Brown, personal communication). Many inexperienced surveyors have watched a mine entry at night, observed no activity and pronounced the mine “free of bats” while tens or even thousands of bats exited from a less conspicuous opening a short distance away. Subsequent surveys by competent surveyors in mine reclamation projects have repeatedly found significant bat use in mines declared bat-free by various biological consulting companies.

It is critical that surveying biologists understand the natural history of the species involved to determine the significance of observed use. Sherwin et al. (2000a, 2000b, 2001), illustrate that colonies of C. townsendii routinely move between roosts over the course of a single maternity season with colonies often moving long distances between roosts.

Following adequate biological surveys, managers must determine which mines will be protected with bat gates. In cases where mines cannot be maintained (in the case of mine expansion, or inadequate portal integrity), suitable mitigation roosts need to be located and protected. This may involve expanding surveys beyond the immediate area of impact and often involves contact with additional mining companies of or private landowners.

Managers must ensure that bats have vacated roosts prior to site destruction. Techniques for excluding bats from roosts are discussed by Brown et al. (2001) and by Sherwin and Haymond (2002). Typically, exclusion activities should be conducted at all openings at which closures are intended.

Conclusion

While abandoned mines are superficially very similar to caves, they are very different resources requiring different management strategies. The fundamental difference between caves and abandoned mines stems from the inherent dangers associated with abandoned mines. These dangers have resulted in the creation of State and Federal abandoned mine reclamation programs and privately funded closures, both aimed at ameliorating issues of liability. In addition, abandoned mines are disappearing as a result of renewed mining in historically mined areas. As a result, abandoned mines are a threatened resource and it is important that sites that represent critical bat roosts be located and protected from closure.

We propose that no qualitative statement can be given regarding the impacts of the creation of abandoned mines on various species of bats. We have no baseline data regarding historical population densities; we do not truly know the historical distribution of caves (although this might be obtainable). Without the application of appropriate research, designed studies and the testing of actual hypotheses, we will continue to manage this system based on hunches and best guesses. We suggest that sufficient data is not currently available to determine an “endpoint,” but as long as we continue to manipulate the landscape at such vast scales, we have an obligation to mitigate these impacts.

Literature Cited

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Brown, P. E., J. S. Altenbach, and R. E. Sherwin. 2001. Evicting bats when gates won’t work: unstable mines and renewed mining. Pp. 187-192, in K. Vories and D. Throgmorton, eds. Bat Conservation and Mining, a Technical Interactive Forum. Office of Surface Mining, USDI, Alton,
IL and Coal Research Center, SIU, Carbondale, Illinois.

Crampton, F. 1956. Deep enough: a working stiff in the western mining camps. University of Oklahoma Press.

Ducummon, S. L. 2001. Ecological and economic importance of bats. Pp. 7-16, in K. Vories and D. Throgmorton, eds. Bat Conservation and Mining, a Technical Interactive Forum. Office of Surface Mining, USDI, Alton, IL and Coal Research Center, SIU, Carbondale, Illinois.

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Meier, L., and J. Garcia. 2001. Importance of mines for bat conservation. Pp. 17-28, in K. Vories and D. Throgmorton, eds. Bat Conservation and Mining, a Technical Interactive Forum. Office of Surface Mining, USDI, Alton, IL and Coal Research Center, SIU, Carbondale, Illinois.

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Townsend’s big-eared bat in Utah and Nevada. Transactions of the Western Section of the Wildlife Society, 36:15-20.

Sherwin, R. E., J. S. Altenbach, and P. E. Brown. 2001. Methods for determining local mine characteristics of importance to bats. Pp. 109-114, in K. Vories and D. Throgmorton, eds. Bat Conservation and Mining, a Technical Interactive Forum. Office of Surface Mining, USDI, Alton,
IL and Coal Research Center, SIU, Carbondale, Illinois.

Sherwin, R. E., J. S. Altenbach, and W. L. Gannon. 2002. Inherent spatial and temporal variability in the use of roosts by Townsend’s big-eared bat. Wildlife Society Bulletin, xx:xxx-xxx. (In Press).

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1 Dr. J. Scott Altenbach is Professor and Associate Chair Department of Biology, University of New Mexico and for the last twelve years has been involved with evaluation of abandoned mines and research on their use by bats. He has worked with bats for 43 years and is also experienced in contract blasting as a hardrock miner in Colorado. He is a student of historical mining technology and has over 10,000 hours experience in abandoned mines in New Mexico, Arizona, California, Nevada, Utah, Colorado, Texas, Minnesota and Wisconsin. His specialty is shaft evaluation, recently surveying his thousandth shaft. He holds a Ph.D. in Zoology from Colorado State University where his dissertation was on Bat Locomotor Morphology.
2 Richard E. Sherwin is a doctoral candidate in the Department of Biology at the University of New Mexico. His current research focuses on habitat and roosting requirements of Western species of cavern dwelling bats, with particular emphasis on the relationship of Corynorhinus townsendii to abandoned mines. He has been involved with a large-scale assessment of the success of management practices (the use of bat gates) for maintaining colonies of bats in the Western U.S. He has surveyed over 5,000 mines and caves in the U.S. and Central America.

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