Your intuition along with common wisdom will have you believe the Effect of Grind Size on Gold Recovery is always uni-directional or proportional.  Truth is it really depends on what your mineralogy tells you and what the effective gold grain liberation size is. If you are already finer than needed, going finer yet will not help.

Here I present an examples with gold recovery goes unaffected by a finer grind size.

The flowsheet tested in the gold extraction process is: Gravity Concentration followed by Froth Flotation.

A series of gravity concentration tests, followed by hand panning techniques were conducted on the composite at various primary grind sizes. The tailings from these tests were subject to rougher testing to evaluate the effect of primary grind size on gold recovery. At selected primary grind size, cleaner tests were conducted to evaluate the effect of regrind size. A combined pan and cleaner concentrate was then subjected to cyanidation to evaluate the effect of pre-aeration on gold extraction and sodium cyanide consumption.

A series of rougher flotation tests was conducted on the composite; following gravity concentration of the sample at four various primary grind sizes. Potassium Amyl Xanthate (PAX) was used as the collecting agent.

Overall gold recovery was unaffected by primary grind size over the range of 73 to 197µm P80. Gold from the feed was 95 to 97 percent recovered into the pan and rougher concentrates, containing between 20 to 33 percent of the feed mass. Higher mass recoveries were observed at the finer primary grind sizes.

Gold recovery was about 41 to 47 percent from the feed to the pan concentrate. Rougher flotation recovered between 50 and 54 percent of the feed gold to the rougher concentrates.