Black Dust on Alternator Housing?

My Old '73 Dart is now 1200 miles out of "Hibernation" and I noticed some black dust on the front part of the alternator housing aft of the pulley upon one of my many trips under the hood each day! I think this is the original alternator. No noise or charging problems, but I wonder could the bearings be getting ready to burn up? Thanks in advance for your advice!

Mike