Being able to recover gold using a gravity method or process does not mean that gold is free and fully/completely liberated. For example, using Automated Digital Imaging System (ADIS) for Gold Search (ADIS is an optical screening and imaging equipment package customized to locate gold occurrences in ground sample), a sub-sample of 8 samples representing 8 lithology for an orebody deposit was subjected to gravity separation via Knelson gold concentrator. The gravity concentrate was submitted for ADIS to determine gold occurrences and associations. A summary of the results can be seen in this Table.
Of the gold particles observed in the gravity concentrate, if they were not liberated, then they were mainly associated with arsenopyrite or were interlocked with more than one mineral.
The average projected diameter of the observed gold particles was about 28um. Caution needs to be taken with regards to the interpretation of the results from Ore 6, Ore 7 and Ore 8, as less than 30 gold particles were observed in the gravity concentrate, statistically more gold particles should have been observed. They may have been too fine for ADIS or refractory.
https://en.wikipedia.org/wiki/Breccia
https://en.wikipedia.org/wiki/Hornfels
http://www.merriam-webster.com/dictionary/intrusion
https://en.wikipedia.org/wiki/Limestone
https://en.wikipedia.org/wiki/Volcanogenic_massive_sulfide_ore_deposit