With an area of 55 000 hectares, the Pilanesberg National Park surrounds one of only three alkali volcanic craters in the world - the other two being in Greenland and in what was formerly the Soviet Union.
The crater is a fascinating alkaline complex produced by intrusive volcanic activity some 1300 million years ago. Pilanesberg is one of the largest volcanic complexes of its kind in the world. Its rare rock types and structure make it a unique geological feature.
Ancient, even by geological time scales, this extinct volcano is the most perfect example of an alkaline ring complex. A number of rare (but not necessarily economically important) minerals occur in the park. Pilanesberg National Park Alkaline Ring Complex rates high amongst the world's outstanding geological phenomena.
Some 1200 million years ago the otherwise featureless plains of the surrounding bushveld were overshadowed by an enormous volcano towering some 7000 meters - significantly higher than today's peaks of Africa's highest point, Mount Kilimanjaro in Kenya.
Through time, this huge volcano weathered into four concentric rings which, today, rise up to 700 meters above the plains - a mere tenth of the original volcano height. The rocks that now form the hills are the remains of the magma pipes which once fed the volcano from deep below its summit.
Geologically, the area is world famous. Its structure, termed the "PNP Alkaline Ring Complex" was formed by volcanic eruptions some 1 200 million years ago. Ancient, even by geological time scales this extinct volcano is the most perfect example of an alkaline ring complex. There are only two other alkaline volcanoes in the world, in Russia and in Greenland. Neither are as clearly defined as PNP. A number of rare (but not necessarily economically important) minerals occur in PNP. PNP clearly rates high amongst the world's outstanding geological phenomena.
Pilanesberg National Park has the following geological features / rock types:
Volcanic Tuff
Uranium-bearing Tuff
White Foyite
Green Foyaite
Red Foyaite
Green Foyaite
Ledig Foyaite
Kimberlite
Kimberlite occurs in the Earth's crust in vertical structures known as kimberlite pipes; the result of explosive diatreme volcanism from very deep mantle derived sources -- often with considerable CO2 and volatile components and at between 150 and 450 kilometres depth. These volcanic explosions produce vertical columns of rock that rise from deep magma reservoirs. The surface expression is rarely preserved but is usually similar to a maar volcano.
The diameter of a kimberlite pipe at the surface is typically a few hundred meters to a kilometer. Many kimberlite pipes are believed to have formed about 70 to 150 million years ago. It is this depth of melting and generation which makes kimberlites prone to hosting diamond xenocrysts. Kimberlite sometimes contains diamonds and kimberlite pipes are the most important source of mined diamonds today. The deposits occurring at Kimberley, South Africa were the first recognized and the source of the name. Nepheline syenite is a related rock type.
Nepheline Syenite
Red Syenite
Syenites are a coarse-grained intrusive igneous rock of the same general composition as granite but with the quartz either absent or present in relatively small amounts. Syenites are formed from alkaline igneous activity.
 North West Province Travel Guide
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