The article is devoted to the problem of the vertical amplitude of the Belomorian vein fields’ pegmatite genesis which has not been characterized so far. This problem became especially important at the initial stage of geological studies and commercial development of pegmatite areas. The theoretically best developed methodological approaches to in-depth prediction of vein pegmatite series are petrogenetic methods which tie the commercial values of granite pegmatite to the thermodynamic conditions of regional metamorphism of host magmatic gneiss complexes. This article is based on the principles of this approach. To address this task the author has determined the vertical residual thickness of pegmatite-bearing layers in all commercial deposits of the Belomorie muscovite pegmatite. On top the thickness is limited by the level of the regional Mz peneplain and from the bottom – mainly by the depth reached by drilling studies. The thickness varies within Nx10 to Nx100 m depending on the kinematics of the vertical displacement of pegmatite-bearing tectonic blocks. Besides, a reconstruction of the pre-erosional Rikolatva structure – the biggest commercial pegmatite deposit in the region, has been carried out to demonstrate that the vertical extent of vein series could be 6–7 km or slightly less (estimating from the altitudinal pressure level of 6 kb).