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Gold/Mining/Energy : Desert Dirts, Gold & Platinum, the emperors new clothes -- Ignore unavailable to you. Want to Upgrade?

To: go4it who wrote (1568)	7/20/1998 9:47:00 PM
From: Tim Hall	Respond to of 1913

Charles, I will try to find some early info. about the carlin deposits. I recall not controversy about heap leaching. It was popular and accepted when I took my first mining classes in 1968. TIm Hall

To: go4it who wrote (1568)	7/21/1998 12:26:00 PM
From: Bill Jackson	Read Replies (1) \| Respond to of 1913

Charles, most gold is leached. When you have a high grade deposit it has enough gold to grind it to a powder and then it is leached as a stirred mush in a tank for some hours. Since it is a fine powder the leaching agent penetrates fast and gets the gold. If the gold is sulfide trapped you grind it fine and use flotation with sulfide sticky bubbles to take the sulfide out. After that is is roasted to burn the sulfide and can then be smelted directly into metal or leached again. When there is a very small amount of gold you cannot afford to crush it fine as the energy cost is high so you do a heap leach test and crush it to 3 different sizes and see what % leaches out in a few months. This will give you a graph of size versus extraction % and you can they decide how much money to spend crushing to get the max % extracted. In situations like this flotation cannot be done but you can use sulfur eating bacteria to leach the pile for a year prior to cyanide leach. The thing is heap leach costs to make the watertight pad and it costs to crush to size and pile it on the pad. The leaching can cost a few $ a day as it needs only alittle pump energy and extra cyanide to keep the pile leaching and you leave it leach for a year with the pump running. A 1 HP pump will cost about $2 in electricity a day and that can circulate a huge heap. Once a week you assay the liquid and add cyanide and from time to time you strip the gold. One man can probably look after 40 heaps as they will all be in different phases and it is all automated. In the 30' and 40's gold was too cheap for many Nevada heaps to be done. Once it went to $800 it sprang to life and has now been perfected, as you know. Bill