If you are interested in the trend of this formula SH has an interesting dialogue going on. This 20% figure is a realistic historical mill concentrate figure. We have done a couple of shipments this week (Northboy). So you can get a feeling for where some of the numbers are coming from.
Quazzy mentions
"Northboy.. there are a few reasons to concentrate the ore to 20%. With our mill/concentrator it makes for less shipments. We remove the high magnesium/talc (easier to smelt for our buyers) and we can actually make profits at very low grades due to reduced shipping costs. Gary has mentioned on a couple occasions that we may be able to mine grades as low as 0.4% at McWAtters and still make a profit. This will increase the life of the mine and provide sufficient mill feed while Hart is developed."
Our technical report is due out by the end of the month so we should see more on this.