The only book on the subject of the Chachapoya mummies (with just a few pages devoted to them at that) is Keith Muscutt's Warriors of the Clouds, which was used as the main source of the Discovery Channel's documentary on the Chachapoya Mummies. 

Amazon.com says: "Muscutt's heavily illustrated, inviting text helps place the Chachapoya empire in the larger context of Andean prehistory."