Tumbaga is an alloy comprised mostly out of gold and copper and was used very frequently in ancient American civilizations. The ratio of gold to copper varies wildly; some items have been known to contain as much as 97 percent gold or 97 percent copper. Some tumbaga has also been found to comprise up to 18 percent of other assorted metals.

In 1992, approximately 200 tumbaga bars were recovered in wreckage off of Grand Bahama Island. They were composed of gold, copper, and silver plundered by the Spaniards during the conquests of Cortez and Pizarro and hastily melted into bars of tumbaga for transport across the Atlantic. Because all the metals that reached Europe were melted back into their constituent metals in Spain, the bars found in the shipwreck are are the only known bars of tumbaga that remain.

Some scholars believe that the Golden Plates from which the Book of Mormon was allegedly translated were made from tumbaga instead of gold. Orichalcum, the legendary metal of the island of Atlantis, is commonly held to have been a gold/copper alloy, thus fitting the same description.

Tumbaga has a significantly lower melting point than gold or copper alone. It is harder than copper, but maintains malleability after being pounded.