cedar,

Thanks for the explanation. I had seen something similar before, but didn't remember the details. I have one question (nitpick)- You say that gpt and g*m are the same for a 1m wide vein. Does that assume that there is one ton of rock in a cubic meter? I think you would have to divide g*m by the density of the rock (~2.6?) to get gpt, since one is grams/volume and the other is grams/weight.

I know that g*m is becoming more common in specifying grades, and in some ways it is more useful, as you made clear. g*m is nice when plotting cross-sections since it eliminates the need for the 3rd dimension. However, it does seem a bit less useful in that poorer grades spread over large widths are given the same "grade" as rich narrow veins. Doesn't make much difference as long as the total width is smaller than the minimum hole width you have to mine, but very wide veins or widely separated narrow veins might require the removal of a lot more rock. It would also make a difference in the amount you have to put through the mill and the relative milling costs.

I guess both ways have their advantages. Again, thanks for taking the time to bring me up to speed!

spiny