He used a custom made Ashdown head and Hartke cabs IIRC
Edit:
Geezer Butler & Ashdown built for ‘The End’ and beyond...
I only have a small sample set, but them Geezer amps ain’t getting the best reviews based on what I’ve seen
He's been a longtime Hartke user but I saw a clip on yoot oob that said he was using Ashdown in the last few years. He's been at it so long that he could use a Gorilla practice amp and it'll sound like him.
Of all the big shows I have been to in the last year or so, I have noted that everyone has a very clean stage with few if any amps on stage. A couple of notables - Roger Glover has TC Electronics cabinets on stage and John Petrucci has Mesa Boogie cabinets on stage for endorsement reasons, and in both cases they aren't miked. So, they are not playing through those rigs - everything is going through the PA. Then you take a look how long the artist pages are for Kemper, Fractal and Tech 21. It leads one to the conclusion that anything on stage is a prop. The players are on IEMs and all the sound is coming through the PA.
Having said that - I know that going direct to PA is an expensive solution available to the big touring acts and perhaps not as accessible to smaller acts/smaller venues. So, in all, I take those endorsements with a very big grain of salt. In many cases, the endorsement is a revenue stream to the artists that was set up by management.