Those are develop-edit cache entries.
Consider purging your Camera Raw cache, and/or reducing it's maximum size (see Lr preferences).
Thank you so much, Rob! I have all images already on the MacPro with LR - thinking I could just delete these cache files as I still have the images separately
You're welcome gunsue.
If ACR/Lr not running, you can delete the entire contents of the folder containing the .dat files, assuming that folder is indeed the ACR cache folder - you should also see an Index.dat file, and NO other files (besides the Cache00000001234.dat files I mean). That is exactly what happens when you click the Purge Cache button in Lightroom's preferences dialog - it deletes the contents of said folder. But note: it's contents will be regenerated as you use the software again, BUT today's entries are smaller than yesterday's (assuming you are using Lr4 or Lr5), so it won't take as much space as it would, or did (and maybe still is), from when you had Lr3, 2, or 1.
Anyway, consider putting a 5 or 10 GB (or less) cap on it (maximum size) to be sure it doesn't take too much room in the future.
Note: you can simply make the folder non-writable if you are really pressed for space and ACR/Lr will simply not create cache entries at all. That will adversely affect performance, but only a tiny bit (a surprisingly small amount, like a small fraction of a second when loading a photo for develop).