AllMovie

The Black Diamonds of the title are diamonds, and diamonds are a boy's best friend in this Richard Arlen-Andy Devine actioner. Arlen plays newspaperman Walter Norton, who attempts to investigate a mine explosion in which his father was injured. Norton's "inside man" helper is jovial miner Barney Tolliver (Andy Devine), who is in love with Norton's sister Nina (Mary Treen). Utilizing spool upon spool of stock footage from earlier Universal films, Black Diamonds builds steadily to an exciting cave-in finale. Reviewers in 1940 were kindly disposed to the film but didn't like the title, suggesting that it wasn't condusive to good business (Silly boys: the Arlen-Devine vehicles always made money).