Gas in mine one detected (4)
I believe the answer is:
neon
'gas' is the definition.
(neon is a gas)
'in mine one detected' is the wordplay.
'in' indicates the answer is hidden within the clue.
'NEON' is hidden in the letters of 'mine one detected'.
(Other definitions for neon that I've seen before include "illuminating agent" , "Colourless noble gas" , "Atomic number 10" , "Gaseous element, in advertising signs, say" , "Small plant; colour" .)