I think that the radius around the mining world portal that we don't have permission to is too big. I mean why do we need that big of a radius? You have to spent like 3 minutes just finding a place you can mine in! I mean I understand that you need a radius so that people don't destroy the portal and so that when you step out of the portal you don't fall right into a big hole. But do you really need that big of a radius?
You should make a suggestion in the suggestions forum about this. I think it is a good idea to see if we can make the area like, one chunk.
The area around the spawner would quickly become mined out and useless, and you would spend much more time figuring that out than you currently do travelling to a fresh spot. Instead, why not use "/wild land" to teleport to a random location? The random places are often (though not always) fresh, and you can simply teleport again if you want a different location or biome.
I would have done that a long time ago but I didn't know you could use /wild in the mining world. Thanks for telling me.