The CIMRM contains no photo, and the location is different, but the photo above sounds like the CIMRM 2253 item.
CIMRM entry
2253.
I am informed that in the museum at Ghighen there is a fragment of a relief
(Br. ± 0.08) with a representation of Mithras as a bullkiller, with dog and serpent.
The head of Mithras and of the bull are lost.