Eric: You would expect that they would use heap leaching, however I responded to the question asked, and that person spoke as if they were to use vat leaching. I have just joined the thread and have to get up to speed. If there were huge environmental costs placed on a heap leach operation, it could become economic to use a vat, as long as the material can be fine enought to get a high rate of extraction in the shorter vat leach time. I saw one large vat operation in Kirkland Lake(ERG Resources, now bankrupt) with a vat 50 feet circular and 15 feet deep, made of welded steel on a concrete base, to extract old mine tailings that were around 150 mesh. Their grade was 0.07 Ox/ton. they went broke. Kirkland Lake is a harsh winter environment, and the strong mine union in the area was also partly to blame by placing excessive costs on the unit, in addition they had trouble with the metallurgy as the gold was shielded by pyrite, which formed over central gold granules. The cyanide could not penetrate the tight crystal structure of the pyrite to get the gold out. I saw assay around 4 gms/ton for IMPCF, or 0.08 Oz per ton, plus a similar amount of platinum(which may not leach at the same rate with the same chemicals as gold, and could present difficulties) The group seems to be making a valiant effort, and if they succeed they will have an immense mine. If the gold is the only thing they canextract for now at 4 gms/ton itis worth $28 per ton, and as long as they do not have a sulfide shielding problem they will be ok. If there is sulfide shielding the gold grains they will have to expose the material in a heap with aeration and some moisture to allow bacterial action to oxidize the sulfide to sulhite/sulphate. After this the iron will no longer shield the gold. It must be an aerobic oxidation process. but I may be wrong. But there has to be a reason why the desert sirts have been there for so long unexploited for the most part.
Bill Jackson |
