A rather superficial blog article on removing mold from books suggests a light bleach/water wipe, but a book conservator in the comments threads wrote:
Some notes from a book conservator, just hoping to avert any disasters.
Bleach, while it kills mold, contains chlorine which forms an acid and will damage the paper. It will remain in the paper and continue to damage it over time. Conservators never use chlorine bleach on books. Sunlight is the best thing, even though it may cause some bleaching. If the paper turns dark in the sun, it’s probably because it contains acidic materials, stains, lignin … many times the paper or printing will fade. Test a relatively unimportant page to see before doing the whole book. Alcohol and water are very dangerous for leather and may cause it to blacken, so test in an inconspicuous place. And while some people have had success with microwaving books to kill mold, other have totally destroyed the books and even started fires. Depends on what the book is made of. I would only nuke a book if I was willing to throw it out otherwise.
Other hints you can glean across the interwebz include HEPA vacuuming, and wiping with alcohol or hydrogen peroxide. But the overall objective is first to isolate the moldy books from uncontaminated ones, then to dry them out and kill and remove the mold, or at least find some way to store the books hermetically so they don't contaminate the others. Staining seems to be the least of anyone's concerns when it comes to moldy books.
Given that the gold lettering looks to have some form of metallic ink in it, I wouldn't recommend microwaving.