Clean up and see if it appears again. Could be some sort of termite or insect, even a queen wasp...
How fine are the shavings? Look up the door frame for signs of scratching/scraping.
OR totally different, are the screws tight holding the hinges? if the hinge is working loose, this could give the same signs...
Here in the U.S., the immediate thought would be carpenter ants. One would look around to see if there were an overabundance of fairly large (1/2 inch long) black ants scurrying around. If so, they'd most likely be climbing and descending nearby trees as well.
Biggest problem is that may have anest inside of the dwelling...