Tarzan and the Valley of Gold - Leiber, Fritz

The burning wreck of a passenger jet with a missing cargo of gold and a desperate plea from a friend lead Tarzan of the Apes deep into intrigue in the jungles of Brazil. Soon the ape-man finds himself facing his most deadly nemesis yet: a criminal mastermind named Vinaro, whose enemies perish in mysterious explosions of gold and flame. But that may be only the beginning of Tarzan's challenges. For if he is to defeat Vinaro, Tarzan must confront him in the legendary golden city of Tucumai, from where no outsider has ever returned.