"50m of 1.5% Cu, with no indication of the true width, although the diagram indicates it could be about 14m,".
simple Ol' merekat janti the old 3:4:5 is best approxxwwimate for that drill section - so that would be 30m in width at that drill point exit. Push that out across the lense and say the base of the fork is 60-70M by eye.