Abstract title; Geology and geochemical characteristics of coal-bearing source rocks in Nariin sukhait deposit, southern Mongolia

The Nariin Sukhait mine is located in the southwest of Umnugobi province 50 kilometers from Mongolia's border with China at Shivee Khuren within the Nariin Sukhait deposit, which has relatively complex geological features. The most prominent feature relating to the Nariin Sukhait coal deposit is the arcuate, east-west trending Nariin Sukhait fault. The coal-bearing section, interpreted to be middle Jurassic in age, is exposed primarily in a window adjacent to this fault.

The chemical composition of whole indicates (variable composition, values of the ratio Th/U > 3.8-4.2, values Th/Sc 0.3-0.8, values LaN/YbN > 5 and values Eu/Eu* 0.6-0.9) indicates components derived from the active continental margin type. The low CIA values (50–60) indicate the absence or poor chemical weathering in the source area.

SEM-CL-imaging of sandstone quartz from Nariin sukhait show three types of quartz:  early Q1 cementation has gray to slightly grey luminescences, postdated compaction, and reduced intergranular porosity associated with illite formed during eogenesis. Q2 is characterized by dark luminescence overgrowths and is more voluminous in the thinly bedded sandstones than in the thickly bedded sandstones filling most of the remaining pore space during mesogenesis. Q3 was formed during the early telogenesis stage fully cementing the sandstones and the fractures were filled by hydrothermal chlorite and sulfides. Significant amounts of trace elements Al, Ti, Ca, K and Fe has been detected in quartz overgrowths. Al varies consistently between each cement with averages of 1324, 1523, and 1352 ppm for the Q1, Q2, and Q3 generations, respectively.

The geochemical, SEM-CL imaging and EPMA data results suggest a relatively igneous source, whit felsic composition. The sedimentary environment of the sandstone and argillite of these sedimentary rocks was the poor chemical weathering in the source area.