Home – Home – Jornals – Russian Geology and Geophysics 2003 number 5

A hierarchic systematics of granitic pegmatites is proposed, which is based on the factors of different ranks responsible for characteristics of pegmatite fields as a whole and of individual pegmatite bodies. Three main levels of classification are as follows: formations (subformations) - minerogenic (geochemical) evolution sequences - paragenetic types of pegmatites. The pressure under which pegmatites began to crystallize was taken as the main discriminating factor for pegmatitic formations (subformations). In general, five pegmatitic formations are recognized, combined into three groups. The low-pressure group (<2.5 kbar) includes crystal-bearing and rare-metal-rare-earth formations. The crystal-bearing formation is subdivided into fluorite-rock-crystal-bearing and subrare-metal subformations. The rare-metal formation of moderate pressure (2-5 kbar) is subdivided into petalite and spodumene subformations. The mica-bearing and feldspar formations are included into the group of high-pressure formations (>5 kbar). The mica-bearing formation is divided into rare-metal-muscovite and muscovite subformations. Several minerogenic (geochemical) evolution sequences in every formation (subformation) are recognized. And every evolution sequence combines several paragenetic types of pegmatites - from simple (barren) to most productive for a certain mineral.
Pegmatites with primary (residual) mineralized cavities (miaroles, pockets) are understood as miarolitic facies, peculiar to a varying degree to every pegmatitic formation. The intensity of miarolitic facies manifestation decreases from low-pressure crystal-bearing to high-pressure mica-bearing and feldspar formations. The presence of residual miaroles is not sufficient evidence for referring pegmatites to low-pressure (shallow) formations.