a mine of information (about/on something)someone or something that can give you a lot of information about a particular subject and that is therefore very useful or helpful
[TahlilGaran] Dictionary of Contemporary English ▲
mine of information n. phr. A person, a book, etc., that is a valuable source of information.
A dictionary can be a mine of information. He is a mine of information on the stock market. [TahlilGaran] English Idioms Dictionary ▲