Brownie groups bagging pound coins, primarily obsolete currency (9)
I believe the answer is:
sixpences
'obsolete currency' is the definition.
(historical coins)
'brownie groups bagging pound coins primarily' is the wordplay.
'brownie groups' becomes 'sixes' (six can mean a group of Brownie Girl Guides).
'bagging' indicates putting letters inside (I've seen this in other clues).
'pound' becomes 'pen' (I've seen this before).
'primarily' indicates taking the first letters.
The first letter of 'coins' is 'c'.
'pen'+'c'='penc'
'sixes' enclosing 'penc' is 'SIXPENCES'.
(Other definitions for sixpences that I've seen before include "small change from earlier on" , "Former coins" .)