CIMRM Supplement - "Temple of Mithra", Verjuy, nr. Maragheh, Iran.
And on the article goes, with nothing Mithraic that I could see (although the preview was cut-off before the end).
A little earlier, on p.217-8, there is discussion of another cave complex in the area, the Rasadkhana caves at Maragha.
The list of diverse possible parallels at the front of the quote makes it abundantly clear that we are in speculation land.
I also discuss this material in a post elsewhere2.
2. Gallery of Images
These were kindly taken and sent in in April 2014 by Jona Lendering of Livius.org.
Translation of the sign at the entrance to the caves: