Sequence of REE-Th-U minerals in the Litsa uranium ore area (the Kola Region)

Mineralogical and petrographic study of REE-Th-U mineralization in rocks of the Litsa uranium ore area has been carried out to detail the sequence of formation of rare-earth, uranium and thorium minerals in rocks. The study has been aimed to Dikoe ore occurrence with the earliest in the area REE-Th-U mineralization described by previous workers. Rocks and minerals have been studied by means of optical and electron microscopy, as well as microprobe methods, this has made it possible to identify the relationship of minerals and the sequence of their crystallization. In monzodiorite veins and host biotite gneisses are found accessory minerals represented by monazite-(Ce), uraninite, zircon, apatite, and thorite, which are in close association with each other, but are formed at different stages of formation and transformation of the host rocks. Monazite-(Ce) with high thorium content (9–10 %) in association with apatite grows at the magmatic stage of monzodiorite crystallization both in the veins themselves and after the fine-grained mass of minerals in the biotite plates of the host gneisses. Magmatic zircon with elevated content of thorium and uranium crystallizes in veins together with monazite and apatite. The formation of uraninite, containing impurities of sulfur, yttrium and calcium, and associated with areas of granulation of plagioclase, occurs as a result of hydrothermal-metasomatic processes in veins simultaneously with the formation of textureless zircon rims with high calcium, iron, and hafnium content in the host gneisses. The development of galgenbergite and anglesite rims around uraninite grains reflects the next superimposed hydrothermal processes