Composition of Li-F granite melt and its evolution during the formation of the ore-bearing Orlovka massif in Eastern Transbaikalia |
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| Authors: | E V Badanina L F Syritso E V Volkova R Thomas R B Trumbull |
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| Institution: | (1) Helmholtz Centre Potsdam, GFZ - German Research Centre for Geosciences, Potsdam, Germany;(2) ARC Centre of Excellence in Ore Deposits, University of Tasmania, Hobart, Australia;(3) Geological Department, St.-Petersburg State University, St. Petersburg, Russia |
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| Abstract: | By the example of the Orlovka massif of Li-F granites in Eastern Transbaikalia, the major- and trace-element (Li, Be, B, Ta,
Nb, W, REE, Y, Zr, and Hf) compositions of the parental melt and the character of its variations during the formation of the
differentiated rock series were quantitatively estimated for the first time on the basis of electron and ion microprobe analysis
and Raman spectroscopy of rehomogenized glasses of melt inclusions in quartz. It was shown that the composition of the Orlovka
melt corresponded to a strongly evolved alumina-saturated granitoid magma (A/CNK = 1.12–1.55) rich in normative albite, poor
in normative quartz, and similar to ongonite melts. This magma was strongly enriched in water (up to 9.9 ± 1.1 wt %) and fluorine
(up to 2.8 wt %). Most importantly, this massif provided the first evidence for high B2O3 contents in melts (up to 2.09 wt %). The highest contents of trace elements were observed in the melt from pegmatoid bodies
in the amazonite granites of the border zone: up to 5077 ppm Li, 6397 ppm Rb, 313 ppm Cs, 62 ppm Ta, 116 ppm Nb, and 62 ppm
W. Compared with the daughter rock, the Orlovka melt was depleted at all stages of formation in SiO2 (by up to 6 wt %), Na2O (by up to 2.5 wt %), and, to a smaller extent, in Ti, Fe, Mg, Sr, and Ba, but was enriched in Mn, Rb, F, B, and H2O. |
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