High Quality Content by WIKIPEDIA articles! The Premier Mine is an underground diamond mine owned by Petra Diamonds. It is situated in the town of Cullinan, 40 kilometres east of Pretoria, Gauteng Province, South Africa. Established in 1902, it was renamed the Cullinan Diamond Mine in November 2003 in celebration of its centenary. The mine rose to prominence in 1905, when the Cullinan Diamond — at the time the largest gem diamond ever — was discovered here. It is also the only significant source of blue diamonds in the world.