ДУНД ПЕРМИЙН ТАВАНТОЛГОЙ ФОРМАЦЫН ЭЛСЭН ЧУЛУУНЫ ПЕТРОГРАФИ, ГЕОХИМИЙН СУДАЛГААНЫ ҮР ДҮН

Abstract

Middle Permian Tavantolgoi coal deposit lies in southern Mongolia and has more than 6 billion tons of coal including significant tonnage of coking coal. In 2017, exploration bore holes were drilled at Borteeg, the largest syncline of the deposit. Eighteen sandstone and two andesite samples for petrographical and geochemical analysis were collected from coal-bearing sequences that were intersected by 960 m deep bore hole. The sandstones are classified as litharenite suggesting that weathering intensity in source area was weak, probably due to short transport distance coupled with relatively arid to semiarid climate conditions. Provenance analysis (Q-F-L, Qm-F-Lt, and Qp-Lvm-Lsm diagrams) suggests that the sandstones are recycled sediments derived from transitional arc and undissected arc that were formed during the closure of Paleoasian ocean between southern Mongolia and North China block. The average value of CIA for the samples is 74.1, reflecting relatively weak intensity of weathering in source area, which is consistent with the results of petrography. The plotted data on A-CN-K diagram displays that sandstones were sourced mainly from Early Permian andesite and dacite, which are widely distributed around Tavantolgoi. It is also supported by Al2O3/TiO2 (avg. 19.6) and petrographical study. To infer tectonic setting, two multi-dimensional discrimination diagrams were used. The results suggest that the tectonic setting of Tavantolgoi syncline, in which the studied sandstone was deposited, was rift.