Main features of inclusions in granitoids of the apical part of the Syrostan intrusion (Southern Urals)

The structure of the apical part of the Syrostan intrusion was studied while mapping the quarry for the development of the marble of the Dark Kingdom deposit. Among the granitoids uncovered by the quarry, along with xenoliths of marble and shales of the Uringinskaya stratigraphy assise of the Riphean, bodies-inclusions were found of diorites and migmatized amphibolites. Petrographic and morphological features of such inclusions made it possible to clarify the history of the formation of the Syrostan intrusive, to which the mineralization of tantalum-niobates and gold is confined. The performed studies have shown that the formation of magmatogenic rocks of the apical part of the intrusive occurred according to a different scenario than the central and bottom parts of it. The differences are related to the nature of the stages of formation of magmatic phases and with the powerful development of metasomatic granitization processes. Signs of active metasomatosis are recorded by microscopy methods and the results of the study of REE. At the first stage, diorite magma was introduced, which resulted in the formation of dike bodies. The second stage is associated with the processes of metasomatic granitization of the embedded substance and the emergence of plagiogranites. The nature of the Eu and Ce anomalies makes it possible to explain the appearance of newly formed plagioclase and quartz phases by the impact of weakly reduced magmatogenic fluid on rocks. The activity of the latter noticeably increased during periods of tectonic activity of the region, which was reflected in the development of discontinuous and plastic microdeformations in minerals. Finally, the third stage was caused by the final impact on the rocks of the filtered high-temperature fluid through tectonically weakened zones with the formation of K-spar mineralization and the partial transition of the substance to the molten state. The crystallization of the latter under eutectic conditions led to the formation of double-feldspar granite. © 2023 Author(s).