A mining engineer was an engineer who specialized in the field of mining engineering; that is, the application of engineering science and technology for extracting and processing minerals from the environment.
Ches'sarro Seeto was a Bajoran mining engineer following the Occupation. (DS9: "Necessary Evil")
in 2375, during Miles O'Brien's rogue mission to New Sydney in the Sappora system, he met up with the Tigans, who ran a pergium mining operation on Sappora VII. Upon learning that O'Brien was an engineer, Yanas Tigan told him of a problem they were having with a trans-sonic drill that no one else was capable of fixing, and that she would be grateful if he could take a look at. Janel Tigan, Yanas' son, reminded his mother that "he's not a mining engineer," but she ignored him, and O'Brien nevertheless agreed to take a look at it, stating "it'll do me good to get my hands on a problem I can solve for a change." (DS9: "Prodigal Daughter")