What about doing real research instead of watching videos?
What ever you melt will be the same purity as it initially have, unless you use some aggressive fluxes, then it can remove many of the base metals, if present.
It will not remove Silver which quite often is the main "contaminant".
You will find links to books in the library about testing , assaying and smelting, if I'm not mistaken. https://goldrefiningforum.com/forums/the-library.101/