Summary:
The Coal Mine, situated in the Nariin Sukhait region, is one of the active coal mines in the area. It consists of two main pits: the Sunset Pit to the west and the Sunrise Pit to the east. The primary geological feature closely associated with the Ovoot Tolgoi Deposit is the Nariin Sukhait fault. This fault has a curved shape and runs in an east-west direction with a moderate dip. It extends latitudinally along the edge of the Ovoot region, with Middle Jurassic coal-bearing sedimentary rocks on its southern flank and Quaternary sediments on its northern flank.
Coal-bearing sedimentary rocks, such as conglomerates and sandstones, can be found within the southern portion of the fault. On the other hand, the northern part of the area has experienced the deposition of Quaternary sediments. The coal deposits are distributed along the southern side of the fault. Moving eastward from the southern side of Nariin Sukhait, there are several rifts that extend towards the north and northwest. These rifts act as divisions, creating multiple smaller blocks within the area of sedimentary rocks that contain coal. The sedimentary rocks in the area have a northward dip of approximately 45° to 60°. The presence of shallow folds suggests movement and deformation caused by tectonic forces. Furthermore, the Nariin Sukhait fault exposes Late Permian coal-bearing sequences.
The structural geology of the Ovoot Tolgoi deposit is considered to be highly complex. There are significant variations in the thickness of coal seam groups, individual plies, and interburden units. These thickness variations are attributed to structural deformations within the stratigraphic layers. The primary mechanisms responsible for these deformations are interpreted to be extensive shearing within the coal seams, leading to coal "stacking" and "wants", as well as thrust faulting, which results in the repetition of the stratigraphic sequence.
Sunrise Pit
The coal-bearing section in this area dips towards the southeast at an average angle of approximately 35°. Within this section, Seam No. 4 is positioned below Seam No. 5, while Minor Seams Nos. 6 and 7 are situated above Seam No. 5. Although a direct correlation has not been definitively established, it is probable that Seam Nos. 6 and 7 are equivalent to Seam Nos. 8, 9, and 10 in the Sunset Pit.
Sunset Pit
The Sunset Pit is divided into two distinct resource blocks: the southern block and the northern block. These blocks are separated by a thrust fault system that plays a crucial role in controlling the distribution of coal within the pit. In the southern block, the rocks have a steeper dip and have undergone movement over the northern block. The northern block contains a repetition of the upper seams, specifically Seam Nos. 8, 9, and 10.
The majority of the coal resources within the southeast-dipping coal-bearing sequence is found in Seam Nos. 5L and 5U. These coal seams likely contain significant coal deposits that can be economically extracted. Additionally, a significant portion of the coal resources in the Sunset Pit is located in the upper seams, specifically Seam Nos. 8, 9, and 10.
Coal Seams
The primary concentration of coal in the Sunset Pit is situated in an exposed area of upper Permian sediments, specifically within the hanging wall of the Nariin Sukhait Fault. Dashkhoral, et al. (1992) introduced the naming system for the seams in earlier studies, assigning ascending order labels to the upper seams. Seam No. 5, positioned in the middle of the sequence and known for its significant thickness, was designated as the thickest seam. Subsequent exploration activities led to the discovery of additional splits and seams within the previously identified coal packages.