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

To: Quickdraw who wrote (8719)	2/20/1998 5:20:00 PM
From: Enigma	Read Replies (3) \| Respond to of 14627

MAD was 43cents bid at the close. I'll look at the CM Oliver stuff when I get a chance, but as a mere bean counter I won't be much help at all. I was involved with an underground mine, and we did not bring any open pit mines into production, during my time . Barrick have a great deal of experience in the field - it will be interesting to see if these represent old views - but one is twice as high as the other. I wonder if the company is prepared to comment, or whether all of this will have to wait until April/May when various evaluations are done? I'll see if I can get some opinion on this. As it stands, it is a big difference of opinion, but it could be old hat. I don't get the feeling that Pacific Rim is concerned - but I haven't asked.

To: Quickdraw who wrote (8719)	2/20/1998 10:14:00 PM
From: Bill Jackson	Read Replies (2) \| Respond to of 14627

Rick, A stripping ratio usually refers to the amount of waste rock you have to mine for each unit of ore grade rock. So a stripping ratio of 7:1 means 7 tons of waste rock to 1 ton of ore grade. The waste might have gold/silver in it but below the point at which you separate ore from waste. The nature of the operation also has a lot to do with it. 1 Open pits. If for example you have found a 500 foot perfect cube with the top level with the surface the first stuff you dug would be 100% ore, as you got down a bit the walls would have to opened up in a conical manner and you would get some waste rock. the deeper you go the more the cone enlarges and eventually you reach a limit for that kind of operation. With a 45 degree pit wall your final pit would be1500 feet square and you would have stripped out 250 million cubic feet to get 125 million cubic feet of ore, a 2:1 stripping ratio. 1A Open pits with overburden. If that cube is down 300 feet you will have to make a large conical pit 300 feet deep and with 45 degree walls the pit would be 2100 feet square before it reached the cube, and you would have removed 715 million cubic feet and obtained the same 125 million cubic feet of ore for a strip ratio of about 6:1 The actual will be bigger as you rarely find nice cubes. As you get deeper you reach a point where the removal of the waste rock uses up all the value in the gold and the whole operation just makes wages for all. Long before this you do an underground mining scenario as undergound mining avoids the pit costs and replaces them with tunnel costs and an evaluation needs to be done as to the feasibilty of an underground mine. They are usually more costly, but if the ore body is big enough and valuable enough it can be done. In underground mining you use the term waste rock ratio, analogous to the stripping ratio, but refers to the rock you carve making tunnels and other forms of overcutting the rock that has no gold as you get out the rock with economic gold. This whole thing is called "grade control", and can make or break a mine, sou you must drill and sample often to make sure you do not spend money blasting and hauling waste rock to the mill and then refining it. If the ore is worth $40 per ton and is costs $20 per ton to mine and mill it and it costs $4 per ton to strip waste rock you have $20 left over from each ton and can do a max of 5:1 stripping ratio before you reach break even. This is an example and you need the mining and milling costs to refine this as well as the grade of gold and silver. Bill