Your article gives not much to go on. If these coins are 2nd and 3rd century BC and the Coralli history "starts" in 188 BC with the rout of a Roman army unit we basically know nothing about the economic and political background of the coins.
Lead is an easy metal to work, due to its softness and low melting point. It is also dangerous to human health. While the Celts probably did not know this, they may have suspected something, reflected in "bad luck" sort of stories. Bottom line: official lead money is likely in an unstable political environment and lead coins could have been an emergency issue. Something like a promise to pay when the bad times are over. A large find (treasure) may also point to uncertain times. Roman army units stirring things up would support this speculation. However, the Zaravetz hill finds looks like a relative wealthy trading community. Its wealth would have made it vulnerable to the neighbours, so it might not have been the Roman's fault anyway.
A more daring theory would be that they are not coins but "tax tokens". Looking at your map, Zaravetz was a stronghold, close to a river bank of a river running North-South and into the Danube. That would be a perfect place for a market, market rights (obligatory unloading and perhaps selling) and a river toll. The Zaravetz powers that be may have issued these tokens against payment of those taxes, to be shown when checked. This might explain the treasure: the hoard was simply the stock of the unit in charge of tax collection. I would expect such a unit to be stationed alongside the market or river. It makes sense to make them look like coins: it makes them self-explanatory to the illiterate and those speaking another language, while the natives would have no trouble distinguishing them from silver coins. It would be helpful if you can confirm that silver coins of the same period and place exist.
In (much) later centuries, there are plenty of examples of lead being used for tokens - tokens for the poor, leads and lights tokens, loading/unloading tokens... It may be too much asked to draw a line from them to much earlier times. However, I personally find the explanation more convincing than a tribe with an economy that is advanced enough to use token money, even in an emergency.
Peter
