This process has been used for a long time and you see variations on it but the main theme remains.
Some do a vinegar bath before and some after. Many just use the salt roast.
The salt is added to washed ore (no vinegar left in it) and in most cases the technique says heat to red hot then drop into cold water.
At the heat levels and available oxygen the sulphides convert using the salt to chlorides. The sulfur will combine with the Sodium from the sodium chloride to make Sodium Sulphate so a lot of the sulphur will get trapped and not sent into the atmosphere.
Once the various metal sulphides have converted to chlorides they are water soluble.
So what you have done by heating with salt is break the sulphides down to varying degrees depending on how fancy you get with the process and taken the other sands to high heat.
When the mix hits the cold water you get thermal shock which fractures the mineral grains and the now soluble chlorides (former sulphides) are broken down.
If there is gold in either the sulphides or the other black sands it may be released.
For a panner only a small portion of the gold might be recoverable as a significant amount of the gold that is locked into sulphides and black sand is microscopic. You will be recovering the "nuggets".
I would stay away from salt and vinegar mixed though the vinegar can be used to clean free gold prior to amalgamation and some people think that it can be used to clean the gold liberated from the salt roast though I see little benefit to it at that point.
Also do not drive the heat too high as the chlorides will volitize at around 1500 degrees F. Lower in the presence of some exotics like tellurides. I would stay under 1000F.
For many panners just fracturing the sands will reduce the mineral grains and even if there is no new gold the fine gold that got away from your first pass at recovery will be easier to get out of the now much finer sands.
Kind of like fine grinding but with preservation of the gold sizes and lots of steam and fire - always fun.
The usual safety precautions apply.