There are basically two methods of melting gold flakes and dust to recover gold available to the average person, the mercury method called Gold-Mercury Amalgam with its obviously toxic by-products and the Borax Method.

I do not recommend the mercury method it works but it is extremely toxic for generations.

The Borax Method is a technique of artisanal gold mining, with its basis in the principle that borax reduces the melting point of all minerals, including precious metals like gold. The melting point of gold is 1063 ˚C, which is a higher temperature than can be obtained by cheap torches and burners. By adding borax to the heavy mineral concentrate, the melting point temperature decreases, allowing people to melt gold out of their concentrate and salvage. By using borax, no mercury flour is produced, and gold recovery increases.

In contrast to the use of mercury (which relies on amalgamation of the impurities) this method relies on borax's ability to lower all the minerals' melting points, including that of gold. Since the gold is usually the heaviest of these minerals, it allows for concentrating the gold on the bottom of the crucible. The process requires considerably less heat than conventional refining methods, which can be obtainable even in remote locations (using charcoal).

After the ore is crushed into a fine powder, it's lightly panned to leave only the heaviest minerals in the pan. It's then thoroughly mixed by three times (by volume) as much of borax and a few drops of water. This mixture is then heated until the whole mixture is molten, after which molten droplets of gold collect on the bottom of the crucible.

While out in the field, a gold prospector can grind and wash a piece of ore, then mix it with borax in a plastic bag. The bag is then placed in a bowl or crucible and heated. The heating action is what triggers the borax to go to work. Once the borax melts, it lowers the melting temperatures of everything in the ore. As all of the minerals melt down, they separate from one another. As the process continues, the borax causes the other minerals to oxidize and breakdown even further. Gold is unaffected by this reaction and sinks to the bottom of the mixture, intact.

The mixture of oxidized impurities and flux becomes slag, which is scraped away to reveal the pure gold at the bottom of the crucible. Because borax is so cheap and effective at extracting gold, borax-based refining techniques were very popular during the 19th century gold rushes. It still continues today among individual prospectors and small-scale mining operations.