Petrogenesis of Perthite Pegmatites in the Black Hills, South Dakota

The study of some pegmatites of the Black Hills, South Dakota, has led to the conclusion that metasomatic replacement played a significant role in their formation. Microcline microperthites of these pegmatites were not products of magmatic crystallization but were formed by complex processes of perthitization. The hypothesis of the metasomatic origin of the perthites is supported by chemical analyses and microscopic features of the perthites and country rocks and by field observations.