I am sure Hoov would have a more technical answer here but from my layman perspective, the head calc is the gold that was recovered thru gravity only that would of made it into a dore bar. The gravity tail assay is the gold that could not be separated by gravity and ends up in the tailings. This remainder can then be further processed with cyanide.
However, to put some numbers to this, if we start with a 2g sample, we would recover 1.74 grams thru gravity. That leaves us with a solution with 0.26g. Are we going to go thru all the EA issues and risk that cyanide brings to the table to go after the last 12%-1% was non recoverable according to this early metallurgy report?
Seems to me that we could be quite successful with gravity only.
G.