The skyrim source is a all outdoor location. Theres nothing to enter.
Question for those having problems: Are you fast-traveling to the source?
The reason I ask is how ore veins respawn within mines.
Since indoor ore veins will take 30 days to respawn, we avoid the mine for 31.
Then...
- Enter the mine
-
EXIT the mine- Enter the mine again and harvest the ore.
I know it sounds silly, but this has worked since the game's release. Waiting 30 days is required for the cell to be able to reset. Waiting 31 is just insurance so you don't have to start over. Entering the mine will show color in the veins, though mining is not available. Simply exit the mine and re-enter and you'll be able to mine.
Goofy as it sounds, it most definitely works.
However, since the Stahlrim source is
outdoors and outdoor environments take 10 days to re-seed, the waiting period should be 10 days (11 to be safe).
But to help ensure the source resets please avoid fast-traveling directly to the source. This would mechanically be akin to entering a mine, seeing ore color, yet not being able to mine. And since we know to exit the mine, re-enter,
then mine away...consider traveling to a nearby area and not directly to the Stahlrim source.
I've traveled to White Ridge Barrow on numerous occasions, made the short trek to the source, and was able to mine all 10 deposits every time.
A possible fix for your issue and something to consider.
Hope that helps