How We Mine
To understand how a mine site is reclaimed it is important to first
understand why and how we mine and the problems we create in the
process. Mining, the process of exploring for and removing valuable
minerals from the earth for human consumption, is one of the oldest
and most important undertakings of humankind. Mining, like agriculture,
is the lifeblood of our civilization. We use coal, oil, gas, metal
minerals (i.e. iron ore, gold), non-metallic minerals (salt, gypsum,
potash), sand, and gravel for heating, electricity, powering automobiles,
and building nearly everything we use. Mining affects our standard
of living and impacts almost everything we do.
There are three main categories of mining: coal, hardrock, and
non-metal. All three types of mining employ either underground or
surface mining techniques. Underground mining requires the boring
of adits (horizontal entrances and tunnels for accessing minerals)
and vertical shafts into the earth in order to obtain and recover
mined minerals. Surface mining requires the excavation of overburden
soil and rock in order to access the mineral of interest. Most of
mining today is done by surface mining because of technical advances
in the size and mechanical efficiency of huge earth moving equipment.
Although this is true today, there are thousands of miles of adits
and tunnels in the U.S. that still exist from the days when underground
mining was the norm.
Surface mining for coal is often called "strip" mining.
Coal generally deposits in relatively flat "seams" between
layers of rock. Once overburden material has been removed to uncover
the coal seam, the seam is blasted and coal is scooped up by huge
front-end loaders or electric shovels and transported to a coal
processing plant. At the plant, the coal goes through screening
and flotation using high gravity liquids to separate the raw coal
from all of the non-combustible "waste rock" and minerals.
The courser waste rock is transported and stockpiled adjacent to
the mined out area where the material is eventually used to fill
the pit after mining is completed. The finer waste material ("tailings")
that goes through the refining process but is not recovered as coal,
is discharged as a thick slurry into a man-made impoundment. The
waste rock and tailings contain sulfide minerals (i.e. pyrite) that,
when exposed to air and water, produce acidic, metal laden wastewater.
For more information on this subject, see the acid mine drainage
formation section.
Surface mining for metal and non-metal minerals is often called
"open-pit" mining. The process is similar to coal mining
where overburden material is removed to uncover the valuable ore
bodies. Metal and non-metal materials, in contrast to coal, usually
occur in nature as ores, i.e. combined with other materials, and
not in seams of pure material. The ore must be treated using chemicals
(i.e. cyanide heap leaching) or heat to separate the desired mineral
from the ore. For more information on cyanide heap leaching, see
the cyanide and other chemical releases section. In the process,
significant amounts of waste rock and tailings are formed; much
more than in coal mining. The waste material associated with metal
ores are more of a problem than non-metallic ores since the waste
associated with metal ores often contains sulfide minerals (i.e.
pyrite) which when exposed to air and water create acidic, metal
laden runoff that poses a huge problem for the mining industry.
For more information on this subject, see the acid mine drainage
formation section.
Surface mining, although the most efficient, is the most environmentally
destructive method for mining. Although this is true, underground
mines present a significant environmental problem as well since
most of the mining that has occurred in the U.S. thus far has been
underground. Before regulations required mine site reclamation,
many underground mines in the U.S. were abandoned without clean
up. Because the responsible parties abandoned the sites after mining
activities were completed, these sites are often left unreclaimed
today and can present serious environmental problems. Government
(either federal or state) becomes responsible for cleaning up these
sites and because there are so many of them, it will take many years
before all abandoned mine sites are reclaimed.
For more information on the mining process and related topics,
see the following web links:
Problem | Compliance
| Health & Safety | Sampling
| Analytical | Data
Quality
Site Assessment | Prediction
| Construction | GIS
| Monitoring & Assessment
|
