cgsecurity.org

I was using the official SD Card Format Utility from the SD Card Association and assumed it would only work on SD cards. Well, one of my HDDs apparently popped up on the list and when I was trying to quickly wipe a bunch of cards, i must have accidentally quick formatted my external HDD.

Since it was an SD Card Utility, it formatted the drive to ExFAT.

The original file system was native Intel-based Max OSX (which is GUID/EFI I think, or is it HFS?) I had a few months of unbacked up data that can't afford to lose. TestDisk does not seem to be puling up the complete filesystem. Currently running a deeper scan, has a long way to go.

Did you try to run TestDisk / Quick Search to have a try to find your previous HFS+-partition?
TestDisk should be executed as superuser.
Under disk selection I've often seen that user selected rdisk instead of disk.
I'm not as much an Apple tech savvy and know the basics only.
I'd need an Apple computer to make exhaustive tests.
When testdisk finds more HFS+-partitions, you should have a look which partition fits best.
The start of the partition would be important ( it shouldn't start somewhere in the middle) and at the bottom of the display, you can watch the size.
The size should match also.

Fiona