Geology and mineralogy of spodumene pegmatites from Mountain Shoriya

Rare-metal spodumene pegmatites with Li and Ta-Nb mineralization are a part of the Tashelginsk-Mayzas iron-ore field (Mountain Shoria). The Tashelginsk pegmatite field is represented by oligoclase-microcline pegmatites with biotite, microcline-albite pegmatites with muscovite, and microcline-albite pegmatites with spodumene. Spodumene-bearing pegmatites are related to the marbles of the Tashelginsk metamorphic complex. In the outcrop, five pegmatite veins were revealed; they have average parameters: the length is up to 200 m, the thickness is 0.8-1.2 m, which is significant for exploration. The age of spodumene pegmatites is 407 ± 13 Ma (U-Pb, SHRIMP II method by zircons), whereas the age of overlapped dynamic metamorphic processes is 310 ± 2,6 Ma (Ar-Ar method by muscovites). Despite the wide range of numbers obtained by U-Pb and Ar-Ar methods, pegmatites were formed at least 100 Ma before the formation of the granites in this region. The pegmatites can be referred to the objects, which are not genetically connected with granitoid magmatism. The mineral-concentrates of lithium in spodumene pegmatites of the Tashelginsk ore field are spodumene - 6.24 ± 0.46 wt% Li2O, muscovite - 0.25 ± 0.04 wt% Li2O, and potassium feldspar - 0.003 ± 0.001 wt% Li2O. The fabric characteristics of pegmatites can be obviously seen in the Yurievskaya vein, which is the most revealed vein within the pegmatite field. These characteristics include deformations of spodumene crystals (even S-type crystals can be seen), feldspar and muscovite grains; streamline shape of fine-grained quartz aggregate over the spodumene and feldspars grains indicates the influence of the dynamic metamorphic processes during formation of a pegmatite vein, and sinkinematic nature of pegmatites. Interaction with host marbles occurred at the last stage of pegmatite forming, which was reflected in appearance of zones of high-calcium garnet, and replacement of Ta, Nb, and Ti oxides by calcium-bearing minerals like Ca-rich microlite and titanite. The similarity between accessory mineralization of spodumene and non-spodumene pegmatites indicates their genetic relationship. Minor development of the hydrolysis products of pegmatite primary minerals shows how insignificant the role of hydrothermal fluids is during pegmatite formations. The macro- and micro-mineral composition of spodumene pegmatites from the Tashelginsk ore field lets us consider them as prospective source of lithium ores in case cement is made out of quartz-feldspar waste of the ore-mining processes. The calculation of cost efficiency of processing the lithium ores from the Tashelginsk deposit showed that complex processing of initial ore is only effective. The complex processing includes (besides obtaining lithium products) obtaining the sludge for producing cement clinker, which is used for producing cement.

Keywords

Authors

References