In the novel A Pocket Full of Rye, the Blackbird Mine is a mine in East Africa owned by Mr MacKenzie. Rex Fortescue went to Africa to survey the mine and found it to be worthless. While Rex was in Africa Mr MacKenzie died. Upon his return to England Rex had papers to prove that he owned the mine. Mrs MacKenzie was sure that Rex lied and was responsible for her husband's death.
While sorting their father's affairs Lance Fortescue offered to take over the businesses in Africa including the failed mine, and thus not forcing his brother to sell parts of the successful businesses to give him his part of the inheritance. What Percival didn’t know was that the mine had become very valuable after deposits of uranium was found there.