By Jack Caldwell - Mining Engineer - Robertson GeoConsultants

Here's an interesting issue: how to design a heap leach pad in a cold climate? The problem is in a cold place, the lixiviant (water & chemicals) that is introduced to the top of the pad of rock may freeze before it seeps through the pile of ore. Recall that the lixiviant is supposed to seep through the ore and chemically pull-out the gold, uranium, or whatever you are leaching for. Then you collect the seepage from the bottom of the pile and treat it to get out the gold et al.

If this seeping fluid with its valuable collection of gold et al. freezes before you can collect it, you are screwed—you cannot get the valuable gold. So how do you design your pile to avoid freezing?

The answer seems to be to put the pile of orein a valley. The idea is that there is thus a lesser exposed outer area and thus a lesser probability of freezing of the lixiviant seeping through the inner part of the pile.

I have not done the calculations to prove this, but am told this, and think it reasonable.

Please, if you know more, have solved this problem, are working a heap leach pad in a cold climate, have written a paper I have not read on the topic, please let me know.

PS. As a result of this posting, I have been sent a 1992 document by Richard A. Hughes called “Cold Climate Leaching Considerations.” It is a fine document. I have an e-copy that I can send if you email me your request. I am told Mr. Hughes is still active in Alaska, so we trust he is OK with this offer.