| Part two of a four-part series about the Black Mesa Mine, operated by Peabody Western
in Northern Arizona. A pdf version of the entire series, complete with photos and illustrations, is available here.
by Terry Ertter
Forget the stereotypes. Peabody Energy’s Black Mesa coal mine in Northern
Arizona is nothing like the coal mines most of us have seen in the movies. At the
Kayenta and Black Mesa mines, most of the miners spend their days operating wheel
loaders, track-type tractors, draglines or other
pieces of heavy equipment. The machinery
does the dirty work.
As you can see from the photos of current
mining operations, taking coal out of the
ground, Arizona-style, requires some serious
excavating. Before Peabody’s mining crews
move in to begin working a section, reclaiming
crews run a fleet of scrapers and track-type
tractors at the site to pick up the topsoil and
haul it away to be stockpiled for later. In most
areas of Black Mesa, the soil goes down about
four feet to rock. Once the soil is out of the
way, mining crews come in, drill holes in the
surface rock and blast it.
At this point, an incredibly large piece of
equipment comes to the scene. The machine
is called a dragline, and it’s sort of a cross
between a crane and an excavator. The
dragline house (the part with the engine and
operating compartment) is roughly the size of a high school gymnasium, and the
boom is about the length of a football field. Cables running up the boom from the
housing are attached to a bucket with a capacity of 110 cubic yards! For comparison, Caterpillar’s largest shovel, the 5230B, has a bucket capacity of 21 cubic yards. The
dragline, which retails for around $75 million, could easily snatch up a D11 or two
and toss them aside.
The dragline’s job is to pick up a bucketful of shot rock, pivot 180 degrees and
dump the load. When all the rubble has been moved from one side of the dragline
to the other, crews come back with more explosives and blast another layer of rock to
be moved.
Eventually, the rock is cleared away to expose a seam
of coal. If the seam is relatively
shallow, a D10 or D11 can
simply rip the coal and doze it
into piles to be loaded by Cat
992 wheel loaders. Thicker
seams call for more drilling
and blasting.
All the blasting and earthmoving
changes the terrain
dramatically. On one side of the dragline, there’s a wide trench and a cliff of exposed rock and coal. The cliff is
called the highwall. On the opposite side of the dragline are tall piles of waste rock
referred to as spoil.
In the pit Tim May and I visited, the dragline was working in a horseshoe- shaped
pattern around the coal deposit. After the dragline works its way around the horseshoe,
the routine changes slightly. The first layer or two of shot rock now is dozed off
the highwall into the trench. When the trench is filled to the
same level as the ground the dragline rests on, the fill-rock is
leveled and the dragline moves onto its new roadway. The
dragline then works its way back around the horseshoe, piling
new rock over its previous roadway.
When the dragline finally reaches the center of the horseshoe,
and the coal is all removed, the dragline moves away to
a new site. Peabody reclamation crews move back in with
D11s and other earthmoving equipment to push the piles of
spoil back to where the rock came from. They shape the spoil
to match the surrounding, unmined terrain. The broken up
rock is not packed as densely as when it was a solid slab, so
the elevation is the same as before mining began even though
the coal has been removed.
Once the contours are right, scrapers from either Skanska
or Peabody haul the topsoil back and spread it to cover the
rock. D9s massage the dirt into position and pack it down.
When the dirt is in place and ready, crews come in to plant brush and grass to create
hardy range land. A couple of years go by, and the site looks like it’s never been
touched by a blade or a bucket.
Return to the main copywriting page |