Login or register (free and only takes a few minutes) to participate in this question.
You will also have access to many other tools and opportunities designed for those who have language-related jobs (or are passionate about them). Participation is free and the site has a strict confidentiality policy.
as you mention, billons are minted from debased metal, so the coin is, in effect, a debased coin (or debased-metal coin). In this case धातुत्तहासित सिक्का should be regarded as an apt translation, in my opinion.
Billon Coin isa
small-denomination devalued metallic coin whose face value exceeds the value of its metal content and its minting expense. It is a replacement for gold and is, in the final analysis, a sign of value. Used mainly in the retail trade, the billion coin fulfills only the function of a means of exchange and, to a limited extent, of a means of payment. Since 1933 only billon coins have been put into circulation by all countries.
Billon coins are minted from low-grade silver and from copper, nickel, aluminum, and other metals. The minting of billon coins, in contrast to minting coins of full value, brings the state a monetary profit and is a closed minting—that is, it is produced from metal belonging to the state. The release of billon coins is limited by the exigencies of monetary circulation, and their distribution among coins of various denominations and their maximum wear limits are decided on the basis of practical experience.
Automatic update in 00:
35 mins confidence: peer agreement (net): +3
Explanation: धातुत्तहासित सिक्का means "debased coin", which I think is pretty close to what you have in mind.
In this reference 'billon coins' have been called 'highly debased coins'