17 year old Chinkapin Oak with a disease?

[jkolko]

I have a wonderful 17 year old Chinkapin Oak, that is starting to shed leaves. It's not Oak Wilt (at least I don't think it is - the leaf pattern doesn't match wilt descriptions); it has this growing on its base: https://imgur.com/a/7ymqqz2

 

There are tons of ants on the base, and when I dig out around the stump, I was overrun with ants.

Anyone help me with a diagnosis? Is it dying? Is there anything I can do?

 

Some more photos (attached)

https://imgur.com/n6MyM6v https://imgur.com/vkkq9ar https://imgur.com/0RTg7HD https://imgur.com/f4i9tGx https://imgur.com/0zdCrzI https://imgur.com/Qi8vaUe https://imgur.com/KS3LHu5 https://imgur.com/RgheqBo

 

I'm in Austin, Texas. It gets plenty of sun and water. No other trees in the yard have any issues.

:(

[kram]

Looks like Pseudoinonotus dryadeus growing at the base which means it has root crown rot, likely from the stones keeping it wet.