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