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Gold/Mining/Energy : Prosperity Goldfields Corp
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To: pirate_gold who wrote (823)9/30/2011 1:25:13 PM
From: E. Charters  Read Replies (1) of 906
 
If you read the link on Valdez Creek, they worked all winter and kept the ore pile unfrozen with steam pipes. They also had an 11 to one stripping ratio. They removed 200 feet of overburden to get at the ore. It was not permafrost however, which needs summer thawing I would warrant. Yes it was high grade. 3.1 grams per cubic yard.

I think it could be done today with good grade in permafrost with lesser overburden. They do this today by ripping in late February, March and sometimes all winter, and thawing the material in heaps the spring and summer. The old time dredgers used to thaw the material over a two year period by drilling holes and pumping cold water into them. They dredged it during the summer of course. People have used water ponds to thaw for summer mining. I believe it would be possible to keep the piles unfrozen in the winter once they were thawed for an extended processing season. Most won't find it practical, but the economics could be there. I would think thermal blankets would work, combined with hot water pipes. You have to pump from a tank or pond as groundwater does not exist. The amount of heat you have to generate is given by the heat loss rate versus the cost of generating that much heat. Rock piles stay unfrozen in Northern Ontario if you trickle water and bacteria through them as they generate heat by the bacteria reaction. So from this we know the heat needs are not extreme. The other way of examining it is to estimate the time it takes for the pile to thaw from the heat of solar radiation. Off the top of my head I think you could do it for about 5 dollars a cubic yard. (a 5,000 HP boiler) It might be less in non permafrost areas as you could use ground water and a heat pump which has remarkable efficiency.
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