Field examinations within the region of Rabinal and Salamå in Central Guatemala have shown that large areas of the crystalline core of the Antillean Cordillera consist of albite gneisses. Within these rocks there exist isolated areas of micro-cline-plagioclase granites. Microscopic examination of the different rocks give evidence that the granite arose through a potash metasomatose of plagioclase-dominated gneissic rocks. It is concluded that the albite gneisses arose through a sodium metasomatose of phyllites and mica schists, and that the granite arose through a potash metasomatose of parts of the albite gneisses. The modes of transformation are discussed, as is also the relationship between feldspatizations within the deeper parts of geosynclines and zonal distribution of ore deposits.