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Gold/Mining/Energy : Pacific Rim Mining V.PFG -- Ignore unavailable to you. Want to Upgrade?

To: Quickdraw who wrote (9448)	4/8/1998 5:05:00 PM
From: Bill Jackson	Read Replies (2) \| Respond to of 14627

If these are the leach column tests for the DD holes way back??, what going on? If it is the recent set of drill holes, again whats up? They should be doing qualifying fire assays on the material, and then select your leach stuff from an inspection of the FA results? How do they know what stuff to do the leach tests on in the columns? They would not leach test it all, they would have no reference to show % recoverred versus what is there in toto(from FA). A leach test is to simulate a real world heap leach facility. They grind the material to a certain size(? what size) and then leach it with leach solution by pumping it in the top and letting it trickle through the column and out the bottom and then pump it back in again, over and over. they will test the leeach liquid(leachate) from time to time to see how the cyanide, or other leach chemical get used, and add more if needed and run the test for a fixed time and see how much gold/silver they got out compared to what was in there to start with. So if you start with 10 Grams per ton and leach for 2 weeks and get out 8 grams , that is 80% recovery. If you leach for another 2 weeks and your recovery goes up to 83%, another 2 weeks and you get 84%, and you draw a graph of time versus % recovery. If you leach for ten years you will get to 99%, but go broke on pumping and labor costs. If you stop at 80% you lose 20% of the gold. If you grind it finer it leaches faster, and to a higher %, but it costs more to grind. The leach tests will test the grindeability and recovery% versus size and time and come up with the best economic mine. With low grade stuff, 1 gram per ton, you grind minimally, because the gold totals around $10 per ton in values. The silver makes a difference here. With high grade stuff with 20 grams per ton you can afford to grind it like flour to get max leached out. Do not forget that 20% of 20 grams is 4 grams, which is ore grade. So you do not want to leave ore grade tailings. As they operate the pit they could find that some areas have high grade and grinbd them fine. Others are low grade and grind them less. The big advantage of heap leach it the minimal cost, after grinding, that it takes to leach the heap. In essence you make a long flat compost heap shape.(50 feet wide and 1000 feet long?(it varies). You build it on a flat pad made of rubberized polyester so it will not leak,with a 24" pad of clay/sand under it to stop stone punctures, and the pad is sloped to drain towards a central trough. You then spray the leach liquid on the pile evenly and continuously. It runs down through the pile and extracts the gold/silver and gathers in the drainage tank, and gets pumped over the pile again. This can go on for 6 months as you slowly remove the gold/silver. The leachate must be watched to make sure it does not lose it's activity(add more cyanide) and the gold/silver might be removed from time to time during the process the make completion more rapid. After you have finished with the pile you move it away to your permanent tailings area?. The key for low grade heap leach is low cost minimally attended operation. Optimally the pads can be set up one beside the other and you build one a month, leach for a year, and after the year replace number 1 and start over again. (assuming you leach for a year to steady state) With high grade you mill fine and extract fast with a CIP setup, as it will remove all the gold in a few hours when ground to dust.(Expensive to grind fine, but worth it for high value stuff) Bill