Return from a mine containing very little gold. It’s a problem (6)
I believe the answer is:
enigma
'a problem' is the definition.
(enigma is a kind of problem)
'return from a mine containing very little gold' is the wordplay.
'return' says the letters should be written backwards.
'from' becomes 'a' (I can't justify this - if you can you should believe this answer much more).
'containing' indicates putting letters inside.
'very little' indicates taking the first letters.
The initial letter of 'gold' is 'g'.
'a'+'mine'='amine'
'amine' placed around 'g' is 'amgine'.
'amgine' in reverse letter order is 'ENIGMA'.
'it's' is the link.
Can you help me to learn more?
(Other definitions for enigma that I've seen before include "Gamine being a bit of a puzzle" , "Coding device" , "WW two Ger. code device; puzzle" , "Riddle - German coding machine" , "Puzzle of gamine (6)," .)