One in the pits wears this halo? (9)
I believe the answer is:
headlight
'one in the pits wears this' is the definition.
(miners wear headlights)
'halo?' is the wordplay.
I cannot quite see how this works, but
'halo?' could be 'light' (halo is a kind of light) and 'light' is present in the answer.
The remaining letters 'head' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for headlight that I've seen before include "clarifies the way forward" , "Car beam" , "Given shiner" , "What motorist may use" , "Bright lamp on front of car etc" .)