Linux Mint MATE: Disable encrypted volume password dialog

I'm running the MATE edition of Linux Mint on my laptop. I have an external USB disk with a LUKS container on it. The USB disk is connected to the laptop's docking station. Whenever I connect the laptop to the docking station, MATE pops up a window which says, "Enter a password to unlock the volume" along with a text field and options to forget the password immediately, remember until logout, or remember forever. (Not "don't show me this popup again," which is what I would prefer.) Under normal use, I want to have this external USB disk unmounted and idle. I have a cron job which unlocks the disk via a key file, mounts the partition, and runs an automated backup. I don't want this partition to be mounted all the time, nor do I want it to be accessible to my ordinary (non-privileged) user account. Is there any way to tell gvfs (or whatever is doing this) to please stop showing me the "enter password" dialog every time I dock my laptop to the docking station?