Let me pour liquid mineral (9)
I believe the answer is:
petroleum
'mineral' is the definition.
'let me pour liquid' is the wordplay.
'liquid' is an anagram indicator.
'let'+'me'+'pour'='letmepour'
'letmepour' is an anagram of 'PETROLEUM'.
(Other definitions for petroleum that I've seen before include "Source of fuel" , "Crude oil" , "Hydrocarbon oil" , "Oil well product" , "Fuel oil" .)