Petrogenesis and sources for rocks of the alkaline rare-metal Burpala intrusion (Northern Baikal Region)

The results of petrologic and geochemical study of rocks of the Burpala alkaline intrusion composed of quartz syenites, alkaline nepheline-free and nepheline syenites, including ore-bearing ones, which is part of the Late Paleozoic North Baikal alkaline province, are presented. The studied rocks by chemical composition belong to foid monzosyenites, foid syenites and syenites, ranging from agpaitic to miascitic varieties. Close Sr-Nd isotopic characteristics, configuration of geochemical spectra confirm the syngenetic nature of magmas from which nepheline, alkaline and quartz syenites crystallized. Negative Eu anomaly in REE spectra and rather low Mg# of rocks testify in favor of a long process of fractional crystallization of rocks from the melt of alkaline-basic composition. The isotopic and geochemical characteristics of rocks of the Burpala intrusion reflect the predominance of metasomatized lithospheric mantle in the source. The formation of the rocks of the intrusion, according to the features of the trace element and isotopic data, was complicated by assimilation of upper crustal material, which was the most possible factor that determined the genetic relationship between nepheline and quartz syenites within the intrusion.