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The Mariscal Quicksilver Mining District is located in Big
Bend National Park, Texas, approximately five miles from the Rio Grande River.
The Park, which receives over 300,000 visitors per year, lists the Mariscal Mine
in its visitor brochures and guides, resulting in frequent visitation. The
Mariscal cinnabar mines operated primarily between 1900 and 1943. An on-site
retort facility produced approximately 1,400 flasks of quicksilver from ore
extracted from the mines. The facilities were dismantled in the 1950s, leaving
numerous shafts and adits unsecured. The adits and shafts accessed several mine
levels with some as deep at 437 feet.
The Park Service had constructed closures over many of the
openings using cyclone fence and discarded motor grader blades. The closures
provided for the casual visitor’s safety, but had been
compromised by some of the park’s more inquisitive
visitors.
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Pre-existing Closure
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Closure of the Mariscal Mine opening was determined to be a
priority and the Railroad Commission’s Abandoned Mine Land Reclamation Program
and the National Park Service began developing closure plans. Since 1993, the
Railroad Commission has had a cooperative agreement to reclaim abandoned mines
on Park Service lands in Texas.
Investigators identified four species of bats using the mine
complex and found a large maternity colony of Townsends Big-eared bats (Corynorhinus
Townsendii). The investigators also felt strongly that the mine complex was
acting as a cold air trap and could be functioning as a winter hibernaculum.
Protection of the sensitive natural resources were factored into the
construction plans. The bat colony was protected from construction disturbances
by limiting the construction window to December to April. The Park Service was
responsible for removing sensitive plants from the construction disturbance
areas, storing them and replanting after project completion.
Project construction began in January 1995 and was completed
three months later in April. The completed project included:
- Bat gate closures were installed over seven adits that were determined to
be bat access points to the old mine workings.
- Shaft grate closures were placed over eight shafts that provided essential
ventilation to the mine workings.
- Bat gate cupolas (essential angle iron bat gates in a box configuration)
were installed. A hole was cut into the steel grated shaft closure and the
cupola was fitted over the hole. these were placed over shafts that were
thought to be used by the bats.
- Corrugated metal pipe with a bat gate insert was constructed at the base
of a large unstable slope. Closure consisted of inserting a metal pipe five
feet into the opening and extending outside the opening twenty feet. An
angle iron metal gate was then welded over the pipe opening. The slope was
graded over the exposed pipe and a rock wall was constructed over the end of
the pipe to blend with the surrounding landscape.
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Bat Cuppola Closure
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Corrugated Metal Pipe Closure
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A survey by a bat biologist from the University of New Mexico
determined that the post-gating hibernating population is at least comparable to
the pre-gating hibernating population and highly significant. The survey also
concluded that the maternity population is still intact numbering from several
hundred to over one thousand, making it the largest Townsend’s Bat maternity
colony in Texas and perhaps the United States.
In April of 1996, the National Park Foundation awarded its
1996 National Park Partnership Leadership Award for Protection and Visitor
Services to the National Park Services Southwest System Support Office, Big Bend
National Park, National Park Service’s Geologic Resources Division, and the
Railroad Commission of Texas for its abandoned mine land reclamation efforts in
Big Bend National Park. The award recognized the Mariscal Mine closures as
protecting the public from the hazards associated with the abandoned mine
workings, while preserving significant biological and cultural resources.
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