Late Paleozoic and Early Mesozoic rare-metal granites in Central Mongolia and Baikal region: review of geochemistry, possible magma sources and related mineralization

Abstract

The Central Asian Orogenic Belt (CAOB) was a scene of intense granitoid magmatism during the Phanerozoic with formation of vast batholiths: Angara-Vitim and Daurian-Khentei. In the Late Paleozoic and Early Mesozoic times, the peripheral zones of batholiths underwent granitic magmatism associated with rare-metal mineralization. Petrological and geochemical studies show that the rare-metal Li-F granites formed, with a gap about 100 My, large igneous provinces of the Mongol-Okhotsk Belt. Late Paleozoic rare-metal granites build a series of multiphase plutons in the Baikal region (e.g. Kharagul 318 ± 7 Ma, Bitu-Dzhida 311 ± 10 Ma and Urugudei 321 ± 5 Ma). The early medium-grained biotite granites and leucogranites were followed by topaz-bearing microcline-and amazonite-albite granites and a series of dikes. The Early Mesozoic epoch was marked by the formation of the Daurian-Khentei Batholith in the center of area and rifting zones with alkaline and rare-metal granite plutons on the peripheries. In contrast to the Late Paleozoic, small Early Mesozoic intrusions (e.g., Avdar Pluton ~10 km 2 , 212-209 Ma) of rare-metal Li-F granites within the Avdar-Khoshutul series of granitoids coexisted with sizable plutons (e.g., Janchivlan Pluton ~70 km 2 , 227-195.3 Ma). Rare-metal Li-F granites of the Janchivlan Pluton produced small domal intrusions composed of microcline-albite, amazonite-albite and albite-lepidolite granites. The Sn-Ta-Nb mineralization is associated with albite-lepidolite granites. The rare-metal granites of the Baikal region and Central Mongolia of contrasting ages show an identical geochemical signature of Li-F granites. It is expressed by increase in F, Li, Rb, Cs, Sn, Be, Ta and Pb and decrease in Sr, Ba, Zn, Zr, Th and U contents in course of multiphase intrusions formation. The geochemical data confirm the magmatic model for genesis of the studied rare-metal Li-F granites. However, this process of magma differentiation was terminated with formation of albitites, microclinites and muscovite greisens. The whole-rock geochemistry and isotopic composition of the granites points to the Precambrian crust of the Baikal region (T 2DМ = 1.0-1.3 Ga) as the most likely source. We propose the formation of the initial granitic melts due to anatexis of the higher levels of the continental crust, with fluids released during granulite-facies metamorphism in the lower crust. The rare-metal Li-F granites of the studied provinces are intraplate formations geochemically different from the Early Paleozoic collisional granitoids. This could be caused by the influence of deep-seated source on the occurrence of rare-metal magmatism.

Rare-Metal Granites of the Tigriny Massif (Sikhote-Alin): Geochemistry, Mineralogy and Specific Nature of Evolution

“…Проблема происхождения и закономерностей эволюции этих магм является объектом длительной и бурной дискуссии. В качестве наиболее реальных механизмов рассматривается плавление пород нижней и средней коры под воздействием высокофтористых флюидов, отделившихся либо от нижнекоровых толщ при их гранулитовом метаморфизме [25,29], либо от мантийных магм при их кристализации. Полученные нами данные пока не дают возможности корректно оценить источники и механизмы происхождения первичных магм редкометалльно-гранитной ассоциации, но позволяют реконструировать некоторые особенности их эволюции.…”

Early Jurassic Rare Metal Granitic Pluton of the Central Asian Orogenic Belt in North-Central Mongolia: Tungsten Mineralization, Geochronology, Petrogenesis and Tectonic Implications

“…The intrusions of the megadome show a concentrically zoned arrangement (Figure 2) where the Khentei batholith is in the center of the bulge and is surrounded by three rift zones: Western Transbaikalian, Kharkhorin (Karakorum), and North Gobi. The rift zones consist of horsts, grabens, and depressions containing Upper Permian to Upper Triassic clastic sedimentary rocks and bimodal volcanic suites (Yarmolyuk et al, 2002) and Mesozoic granitic plutons (e.g., Dostal et al, 2014Dostal et al, , 2015bAntipin et al, 2016). The age of the plutons of the rift zones range typically between 221 and 186 Ma (Yarmolyuk et al, 2002;Dostal et al, 2014).…”

“…One of such plutons in north-central Mongolia is the TP which hosts a tungsten deposit (Tsagaan Davaa). Unlike some weakly mineralized granitic bodies such as Janchivlan and Avdar (Antipin et al, 2016), which occur in the rift zones along the margins of the Khentei batholith, Early Jurassic TP is located within the batholith but along its margins (Figure 2). It is one of the shallow-seated granitic intrusions, which are discordant and are surrounded by contact-metamorphic aureoles.…”

From magmatic arc to a post-accretionary setting: Late Palaeozoic granitoid plutons in the northwestern Trans-Altai Zone, Mongolia

“…Late Palaeozoic calc-alkaline to alkaline and even peralkaline intrusive and extrusive igneous rocks in Mongolia and northern China evolved at the final stage of amalgamation in this part of the CAOB (Jahn 2004;Liu et al 2013;Mao et al 2014;Antipin et al 2016;Zhou et al 2021). The intra-plate magmatic activity at the margin of the Siberian Craton was related to Late Palaeozoic-Early Mesozoic Central Asian extension that was manifested in the formation of several rifts of different ages (e.g., Chen and Jahn 2004;Jahn 2004;Kovalenko and Chernov 2008;Buriánek et al 2012Buriánek et al , 2016Yarmolyuk et al 2013;Kozlovsky et al 2015).…”