The Premier (now Cullinan) kimberlite is situated on the farm Elandsfontein 480JR at the town of Cullinan, 25 kilometres northeast of Pretoria. It is the most important pipe in a cluster of twelve Group I kimberlite pipes that includes the:
	National Schuller Montrose Franspoort Small alluvial deposits occur downstream of the kimberlites. The mine was opened in 1902 and apart from brief closures between 1914 - 1916, and 1932 - 1945, it has consistently been a major diamond producer with a high frequency of finding diamonds larger than ten carats.  The most famous stone found at the mine was the famous 3,106 carat Cullinan Diamond, the largest gem diamond ever found. It was cut to form the 530 carat Great Star of Africa and 317 carat Lesser Star of Africa set in the Crown Jewels of Britain. The kimberlite pipe is dated at 1,180 Ma and the sill at 1,115 Ma.  It originally measured 32 hectares at surface, making it the largest diamondiferous kimberlite in South Africa.  The pipe has an elongate oval shape which comprises diatreme facies kimberlite to a depth of 550 metres, below which, it grades into the root zone. The pipe intrudes fenitised quartzites of the Transvaal Sequence and is cut by a gabbro sill of 75 metres thick at a depth of 350 metres below surface. Plans are well advanced through the C-Cut Project feasibility study to take underground mining to a depth exceeding 1,000 metres, and extend the life of the mine by a quarter century. Cullinan (Premier) is a complex body with three distinct kimberlite phases corresponding to three main phases of activity: The first phase produced a diatreme of "brown" tuffisitic kimberlite breccia (TKB) in the southeast, characterised by abundant shale and norite wall-rock inclusions. The second phase forms the main part of the pipe and comprises "grey" TKB characterised by an abundance of Waterberg quartzite, basement granite and gneiss inclusions. The third phase is a circular plug-like body comprised of "black" hypabyssal facies kimberlite, characterised by dark green pseudomorphs after olivine, intrusive into the western part of the pipe. Several later carbonatite dykes intrude, in a radial pattern, the black hypabyssal kimberlite and large blocks of quartzite "floating reef" are present in the grey kimberlite in the middle of the pipe.