You are correct: this is from
Antioch.
I think it is
Prieur #282, which is the most common of the
Gordian III tetradrachms listed.
The
obverse legends are the same on all of
Gordian's tetradrachms, however the reverses are different.
Prieur describes the
obverse as Laureate, draped,
cuirassed bust, right; seen from behind.
The
reverse legend on your coin is ΔHMAPX EΞOYCIAC with SC in
exergue. On your coin just the tops of these letters are visible.
Prieur describes the
reverse as
Eagle facing,
head and tail left.
Below is a photo of my
Prieur #282 where the
reverse legend is
complete.
I'm curious what you see on this coin that makes you think it might be an unpublished
type?
(I get a 504 Gateway Time-out Error message when I try posting this reply with an attachment. That will have to wait until the
software problem gets fixed.)