Mounting thunderbolt drives on 2009MP VIA mac mini target disk mode

I recently purchased a refurbed 2009 mac pro, but then quickly realized it has no option for connecting thunderbolt peripherals. I also have a mac mini with TB, and several GRAIDs for work. I decided to try this:

Connect TB drives to mac mini, then boot Mini in Target Disk Mode and connect via Firewire to 2009 MacPro.

Once booted up on my Mac Pro, I open disk utility and see the 2 8tb GRAIDs listed as 4 4TB slices AAPL FireWire Target Media.

The slices have no information listed as to how much data is on them, though I know they are quite full. I have the option to mount each drive, but nothing happens when I click the mount button.

These are my work drives so I haven't experimented with re-formatting. But does anyone have any insight as to the potential to work with these drives in this way?