Heap leaching can make a mess

Heap-leaching can make a mess A number of statements about the Carmacks Copper project were made in a letter to the editor on June 12: Mining is Making a Durable Contribution to Yukon. The Yukon Conservation Society would like to respond to some of thes

A number of statements about the Carmacks Copper project were made in a letter to the editor on June 12: Mining is Making a Durable Contribution to Yukon.

The Yukon Conservation Society would like to respond to some of these statements.

First, it was stated that sulphuric acid heap-leaching of copper ore is a well-known technology. What was not mentioned is that no company has ever completely detoxified one of these heaps.

The environmental assessment screening report for the Carmacks Copper project acknowledges that no sulphuric acid heap-leach copper mine has ever been successfully detoxified anywhere in the world. Incredibly, the proponent of the Carmacks Copper project still says they are confident that they can detoxify this heap. They have no plan in the event that they fail to detoxify the heap.

Second, there has never been a field-scale trial for the Carmacks Copper project. A small crib test (five by seven metres) was performed in the winter of 1993-94.

Settlement of the ore was so severe that the acid distribution pipes pulled apart and broke inside the heap, just like what could happen in the full-size heaps, illustrating one reason why these heaps are so hard to detoxify.

The proponent was never able to fully detoxify even this small crib test. Water monitoring at this site now shows a plume of groundwater contamination, possibly from this test. Clarification on whether the small crib test is contaminating the groundwater is needed prior to any further use of sulfuric acid heap-leaching technology.

Third, the full-scale water treatment plant at the mine is not scheduled to be built until the end of the project. What happens if the proponent of the Carmacks Copper mine goes broke before then?

This is what happened at the Mount Nansen mine and taxpayers had to foot the bill. The $3-million security bond that the Carmacks Copper mine is required to post is much too small to pay for a water treatment plant and remediation.

Fourth, the ore is mixed with concentrated sulphuric acid solution, not one per cent sulphuric acid solution. The proponent intends to use two applications of sulphuric acid. More than 90 per cent of the sulphuric acid used will be in approximately 35 per cent solution.

Later in the process, a one per cent solution will be sprinkled over the heap. This isn’t tomato juice, this is a toxic brew of acid and once it goes through the ore pile it will include heavy metals and chemical reagents.

The proponent is pushing ahead with the Carmacks Copper project despite repeated demands for real proof that this mine can be detoxified.

Unfortunately, YESAB and the Yukon government have given the go-ahead to have the whole mine used as a gigantic experiment. The proponent was not able to detoxify a five-by-seven metre test heap – why would Yukoners have any confidence that they can detoxify 13 million tonnes of ore?

This is another example of a “modern” mining company using questionable technology and posing a potentially huge risk to the environment.

Once again taxpayers will likely receive a toxic legacy which we will have to pay to clean up.

Karen Baltgailis

Yukon Conservation Society

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