As i have just discovered yet more spawn mining this point obviously needs reiterated.

DO - Mine under your own plot (WITHIN your boundaries)

DONT - mine outside your boundaries (Even if you find a cave. if it goes outside your boundary. Tough, you'll have to leave it.)

You can however explore the caves. just do not mine anything.

Here's a little insight for you.
Imagine digging down in your properties boundaries to suddenly find someone has mined out all the ores. Would you be happy about that?

This goes for !everyone! unless given permission due to needing to do a CFUK build project.

Let me just say it one more time.

DON'T mine outside of your spawn builds boundaries.