Alkali metasomatism, a common geological process, is sometimes associated with uranium ore forming processes. Metasomatite uranium deposits are usually confined to areas of tectono-magmatic activity affected by intense sodium, sodium carbonate and potassium metasomatism along deep rooted fault systems. Granite, gneiss, migmatite, metasediments or metavolcanics could be metasomatised this manner and host uranium mineralization. Several sub-types and classes of mineralization are found, such as (a) sodium metasomatite with granite and metasediment or metavolcanic derived deposits; (b) potash metomomatite deposits; and (c) skarn deposits. Uranium mineralization associated with metasomatites is seen mainly in the Proterozoic times (1900 - 1700 Ma). A second episode is seen during 1500 - 1400 Ma and smaller discrete events occurred during 600 - 500 Ma. The source of the fluids responsible for the metasomatism and quartz dissolution is presumed to be metamorphic, derived from anatectic zones and ascending upwards along deep and large fractures.
Possible uranium sources include protoliths with high initial uranium, such as ortho-gneiss for the deposits hosted in granite, or conglomerates which can be the equivalent of Archean to Proterozoic quartz pebble conglomerates with detrital uraninite. Some 50 deposits worldwide are attributed to this type of deposits from several countries. The largest know metasomatite deposits are seen in the Kirovograd District, Ukraine. Other regions with similar deposits are Beaverlodge, Canada, Itatiaia, Brazil and the Kokchetav Massif, Kazakhstan. Presently a small part of the global production is from this type of deposits, but many of the metasomatite deposits are potential candidates for future production of uranium. Metasomatite deposits remain one of the least understood types due to the complexities in geological, geochemical and structural control in the origin and nature. Exploration for this type of deposit may require
Original URL: https://www.iaea.org/OurWork/ST/NE/NEFW/Technical-Areas/NFC/uranium-production-cycle-tm-metasomatite-2013.html
Managed & Built by I2M Consulting, LLC | © 2010-
