EXOTIC JACOBSITE FIND IN GRANITOIDS OF THE SUSHCHANY-PERZHANSKAYA ZONE ON THE UKRAINIAN SHIELD

Abstract

While studying rocks and minerals in the central part of the Sushchany-Perzhanskaya tectonic zone at the northwest periphery of the Ukrainian shield, we found jacobsite in a geologically unusual situation, i.e., in the Perzhanskiy host granite of Late Proterozoic age and in the genetically related feldspar metasomatite. Data indicate that jacobsite was formed in the early pneumatolytic stage. It crystallized under pressure (stress) in a reducing environment when the rocks reacted with high-temperature emanations containing iron, manganese and magnesium. Rapid cooling probably helped to produce the spherical forms of this mineral. This paper discusses the mineralogy of this exotic jacobsite.