Ann: Coburn Project Update, page-8

This is hard to watch

i remember mining at 3000tph 1% grade and it IS hard to get recoveries due to a lapping effect of the larger silica grains with the tail of the HM. The HM tail, silica lap maybe 50% of the 1% grade in the spirals, so if you cut too hard you loose too much 50% recoveries, and if you don't cut, you end up with too much silica. The answer sometimes is wet screens between spirals to remove large quartz

its still the same with 4% grade but you can afford to 50% of 1% because your still left with 3.5% which is 87.5% recoveries.

does this make sense ?

the plant design needs to be so much more on tune for 1% than it does 4% due to the spiral lapping of sand to HM