She and Allan - Haggard H. Rider

Wanting to learn if he can communicate with deceased loved ones, adventurer and trader Allan Quartermain seeks a meeting with the feared Zulu witch-doctor Zikali, who tells Allan to seek out a great white sorceress who rules a hidden kingdom far to the north and he charges Allan to take a message to her. He also gives Allan a necklace with a strange amulet, carved in Zikali's own likeness. Zikali claims it has great magical powers that will protect Allan on his journey, but he must on no account take it off.