Hi Paul. Another ongoing hypothesis on these pieces is that they are Oriental imitations of the Spanish doubloon, intended for circulation. Two of the three other pieces I have seen (including the nice one auctioned by Ponterio some time ago) were reportedly found in that area. However, all these pieces bear some resemblance to the attached proclamation medal, 1st reported by Betts ("Some undescribed Spanish-American Proclamation Pieces", 1898) and later listed in Medina's 1919 work.
The illustration and description ae from Betts.
Nice and rare piece :-)