Mineral discovered by wicked sort, we hear, by pub (8)
I believe the answer is:
Here is my best explanation:
'mineral' is the definition.
(I've seen this before)
'wicked sort we hear by pub' is the wordplay.
'wicked sort' becomes 'sinner'.
'we hear' indicates a 'sounds like' (homophone) clue.
'by' means one lot of letters go next to another.
'pub' becomes 'bar' (I've seen this before).
'sinner' sounds like 'cinna'.
'discovered by' is the link.
(Other definitions for cinnabar that I've seen before include "Red mineral", "Mineral", "Bright red mineral containing mercury", "Red mercury sulphide", "Heavy red mineral containing mercury" and "Brian can make vermilion pigment".)