The ’adarkon /darkmon is a monetary unit of uncertain value.
According to some scholars, the ’adarkon and the darkmon are not the same coin, the former coin corresponding to the Persian daric and the latter one to the Greek drachma. In all of the passages listed above, however, it is possible that the reference is to a weight of gold and not to coins.
In 1CH 29:7 it does not seem necessary to retain the actual numbers nor to give the amounts with too much precision. GNT provides a good model with “190 tons of gold, 380 tons of silver, 675 tons of bronze, and 3,750 tons of iron.” The mention of coins in this verse is anachronistic, as coins did not make their first appearance until several hundred years after the time of David. It is possible that the writer of Chronicles has converted the amount of gold into a monetary unit contemporary with the time of writing.