Help with problem with serpentine belt on ZR6

[wakeskier]

The serpentine belt on my 2007 ZR6 was getting a bit worn and there was actually a small split in it, so I replaced it today with a new one.
After about 15 minutes I heard the belt go after giving it a little gas after idling thru a no wake section. I quickly threw the old belt on and made it back taking it easy.
Looking at it more closely it seems the belt is sliding slightly off the idler pully (about 1/4 off) this seems to happen because the alternator bracket it's attached to moves some ( but the bolt is tight...)
Alternator spins freely
Any ideas how to fix?

I'm on vacation, and hoping to get this resolved tomorrow
(I'm pretty sure I'll be able to aquire a new belt on Sunday)

Thanks

[wakeskier]

Update:
After further investigation I was able to tighten up the alternator bracket. This seems to have resolved the issue.

BIG shout out to Adirondack Marine for hooking me up with a new belt on a Sunday!