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> Mineral Leeching
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| Mineral
Leeching |  |
Types of Engineering
involved: Mining, Chemical, Environmental
Turtle Island is rich in mineral and metal deposits including gold, silver,
zinc, diamonds and coal; all of great interest to mining companies. Many of these
deposits lie deep within traditional lands. In many places they have been mined
to the point where it is no longer economical for companies to continue operations,
and so mines are abandoned.
Rock contains sulphides - a combination of
sulfur and other minerals. When rock is exposed to air or water through natural
weathering processes, the sulphides chemically react to produce sulfuric acid.
The acid can move (leech) into the nearby soil or watershed but, generally, there
isn't enough sulfuric acid produced through weathering to significantly raise
their acidity. During and after mining, however, large quantities of rocks that
are normally underground become exposed. Much more sulfuric acid is produced than
through natural conditions. In addition, the acid can dissolve the traces of metal
left in waste rock, dragging poisonous heavy metals such as lead, zinc, copper,
arsenic, selenium, mercury, and cadmium into the ground and surface water. Left
unchecked, this mineral leeching can destroy local aquatic life and habitat.
While steps are being made to avoid the negative effects of mining, damage
is still being done, particularly by abandoned mines. For example, a salmon breeding
river in northern BC, the Taku, is threatened due to the mineral leeching from
the abandoned Tulsequah-Chief Mine. Mineral leeching is a potential long-term
problem of mining. There are ways to minimize and even avoid leeching, but they
work best when put in place before operations begin. Clean-up is always harder:
some abandoned Roman coal mines in Britain still leech minerals today, almost
2000 years after being abandoned.
Look into it: http://www.miningwatch.org/emcbc/primer,
and
http://www.nrcan.gc.ca/mms/school/e_mine.htm | | | Back
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