Old coins — tons in Argos circulating (6)
I believe the answer is:
groats
'old coins' is the definition.
'groats' can be an answer for 'coins' (groat is a kind of coin). I am not certain of the 'old' bit.
'tons in argos circulating' is the wordplay.
'tons' becomes 't'.
'in' indicates putting letters inside.
'circulating' indicates anagramming the letters.
'argos' anagrammed gives 'groas'.
't' put into 'groas' is 'GROATS'.
Can you help me to learn more?
(Other definitions for groats that I've seen before include "old pieces?" , "Crushed grain of various cereals" , "Old English coins" , "John's" .)