Mineral Leeching

Types of Engineering involved: Mining, Chemical, Environmental

Turtle Island is rich in minerals and metals including gold, silver, zinc, diamonds and coal; these all interest mining companies. Many of these minerals and metals lie deep within traditional lands. In many places where companies no longer operate, mines are abandoned.

After mining, rocks are no longer underground and give off chemicals.  Rock contains sulphides - sulfur and other minerals mixed together. When rock is exposed to air or water through natural weathering processes, the sulphides react to produce sulfuric acid. The acid can move (leech) into the nearby soil or watershed.

After mining, much more sulfuric acid is produced than in natural conditions. In addition, the acid can dissolve the traces of metal left in the waste rock, dragging poisonous heavy metals such as lead, zinc, copper, arsenic, selenium, mercury, and cadmium into the ground and surface water. If engineers don’t check, this mineral leeching can destroy local aquatic life and habitat.

We try and avoid leeching but damage is still being done, especially by abandoned mines. Mineral leeching is a possible long-term problem of mining. There are ways to minimize and even avoid leeching, but they work best when put in place before working the mine begins. Clean-up is always harder: some abandoned  coal mines in England still leech minerals today, almost 2000 years after being abandoned by the Roman empire.

For more information visit Mining Watch Canada and Natural Resources Canada.