Mining and Toxic Metals Redoil Case Study

Posted by Michael Hewitt on December 23rd, 2011 8:17am

REDOIL (Resisting Environmental Destruction On Indigenous Lands)  has released a case study of the proposed Donlin Creek Mine (Alaska) called "Mining and Toxic Metals".

The following are brief extracts from the report, which describes in detail the effects on health and the environment of toxic metals released by mining operations. Some of the metals referred to in the Redoil Study are present in the KGHM Ajax ore body (e.g. lead and arsenic). 

It is not known if the Ajax ore body has been assayed for mercury.

A link to the complete report is provided here.

Extracts from the Redoil Case Study, "Mining and Toxic Metals"

"Mining activities are known to release significant amounts of toxic metals into the surrounding environment. Some toxic metals frequently associated with mining include mercury, arsenic and lead. These substances are present at low concentrations in soil, rock and water, but the process of mining may release quantities harmful to the health of people and the environment.

How Mining Releases Toxic Metals

Large amounts of waste rock and tailings contaminated with toxic metals can be produced by mine sites. In the case of the Donlin Creek mine, there are only 0.072 ounces of gold for every ton of ore, a figure that does not take into account the waste rock. Toxic substances contained within the rock and tailings are more easily released once these substances are processed/milled and left in mine pits, underground workings, waste rock piles, and tailings impoundments where they are exposed to the environment.

Mercury can be released from waste rock and mine tailings directly into the atmosphere even at normal environmental temperatures because mercury evaporates at a much lower temperature than other metals. Once in the atmosphere, it can later be deposited in soils and waters miles from the mining site.

Dust emissions from the mine site during blasting and mining operations could contain any toxic metals that occur locally. For example, dust emissions at Alaska’s Red Dog mine are responsible for severely contaminating the surrounding environment with lead and cadmium.

Rain water leaches toxic substances from waste rock and mine tailings into soil and waterways. Additionally, rain can deposit toxic metals from the air, present as vapours or attached to dust particles, into waterways.

One of the major sources of toxic metals associated with mining is acid mine drainage. When waste rock excavated from the mine is exposed to air (oxygen) and water, it chemically reacts to form several acids, including sulphuric acid. This acid leaches toxic metals from the rock and surrounding environment. Acid mine drainage is known to have very high concentrations of metals including iron, mercury, arsenic and antimony. Acid mine drainage may contaminate both surface and ground water.  Once acid mine drainage begins to form it is usually impossible to stop and is difficult and costly to remedy. According the EPA, the variable size and mineral composition of waste rock makes accurate prediction of AMD difficult."


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