Perhaps the earliest Greek coin type depicting a gorgon was a series of rare electrum staters. We don’t know when they were struck but the style of their reverse punches suggests they were probably created before Athens struck the silver Wappenmünzen series around 520 BC. Ingrid Krauskopf and Stefan-Christian Dahlinger date this coinage to 650-600 in their LIMC entry on gorgon iconography.
These early electrum gorgons are very rare. I have only been able to find mention of two staters and four or five of the 1/3 stater pieces. Liselotte Weidauer pointed out in 1975 that both the 1/3 staters (which depict a single gorgon) and the double gorgon staters come from the same obverse die. When striking the 1/3 staters, the blank was somehow held over one half of the die.
I wish I could inspect a cast of the stater. From the published photographs it is hard to understand the border design on the double gorgon. I also struggle to see how the the 1/3 staters could receive two punches of the reverse without slipping out of the much larger obverse die. I also can’t figure out what order the reverse punches were done on the stater. It looks like the long vertical punch was applied last, which is the opposite of what I had expected, but I just can’t tell from the pictures.
Weidauer and John Kroll believe the reverse punches resemble the “I am the badge of Phanes” electrum coins depicting a deer, and they suggest Ephesos as the most likely mint. The British Museum’s 1/3 stater was apparently found on Rhodes and George Hill suggested an origin in Southern Ionia. The double gorgoneion design is very unusual. I don’t know of any other Greek examples but a similar double depiction of the Egyptian god Bes can be seen on a Philistian drachm.