Summary:
Kusmunda Opencast mine is located in the south-central part of Korba coalfield in Korba district of Chhattisgarh state of India.
The Korba Coalfield, constituting the south-central part of the vast stretch of Gondwana sediments of Son-Mahanadi Valley, is located between the North Latitudes 22°15' and 22°30' and East Longitudes 82°15' and 82°55'. It has a total aerial extent of about 520 sq.km. It is elongated in an east-west direction and 64 km long and 4.8 km to 16 km wide. The southerly flowing Hasdeo river divides the coalfield into two parts, the western part being larger than the eastern part. The Kusmunda coal Block lies in the western part of the coalfield.
The strata in general have a southerly dip varying from 4° to 10° except in the north-eastern part of the coalfield in Rajgamar-Kesla sector where the dip is easterly. Rolling dips in confirmation with the anticlinal nature of the basins have also been recorded in Korba Coalfield. A prominent East-West strike fault dipping towards south divides the coalfield in two parts influencing the stratigraphic disposition. In the north of this fault, i.e. in Dilwadih-Banki-Surakachhar areas, only Karharbari with superior grade thin seams are preserved. In the south of this fault, i.e. in Dipka-Gevra-Kusmunda-Manikpur sector, the entire succession is preserved. The sedimentary strata in the Korba Coalfield are not affected by igneous intrusive.
The general strike of the strata is NW-SE to E-W in major part of the block. Whereas in the northern part of the block, the strike takes swings NE-SW to NW-SE due to anticlinal structure. Generally, the dip direction is towards south and southwest in the major part of the block. There is a large variation in the amount of dip from 4°-10° in different parts of the block.
The entire block is capped with thick soil cover. The structural interpretation arrived mainly based on the sub-surface data obtained through boreholes. However, the general structural characters of the block are as a result of the regional tectonic behaviour of the coalfield and fall well within the regional frame work.
The northern part of the block is an extension of a doubly plunging anticline with its axis NWSE. The strata are almost flat at the anticlinal hinge around boreholes CMKL-44, 57, 67, 54 and 61. The plunge of the anticline is 10° in NW direction between borehole NCKK-11 and CMKL87, whereas it becomes flat in the north-western part outside the block. Altogether 32 faults have been deciphered in the block. However, presence of a few minor faults cannot be ruled out. The comparative study of the throw of various faults in different seams shows that the throw of the same fault sometimes changes from seam to seam. Such phenomenon here has been explained due to (i) Anticlinal nature of the basin, (ii) Resultant change in gradient (iii) change in thickness of intervening parting between coal seams. Almost all the faults traversing the block have evidenced by intersecting in the boreholes as well as observed in mine working. To avoid confusion, the nomenclature of the faults has not been changed from the adjoining block. However, the numbering of faults have been kept in continuity for those faults which originate within the block.
Description of coal seams
The existence of three well defined coal seams has been proved in the project area. These seams are named as Lower Kusmunda, Upper Kusmunda and E&F in ascending order.
The Lower Kusmunda seam is composite in the western part of the mining block and it splits into mainly two sections in the eastern part. There is a grey shale/sandy shale band at 30-40m from the roof of the seam that has a tendency of increasing in thickness from west to east. In the area where the thickness of the band becomes 3m and above, the Lower Kusmunda seam has been considered to split up in to 2 sections, Lower Kusmunda Top and Lower Kusmunda Bottom.
The Upper Kusmunda, a composite seam has tendency to increase in thickness from north to south. Three sections on the basis of seam composition can be clearly identified as top shaly coal section, middle interbanded section and bottom coaly section.
Seam E&F, which is the top most horizons in the block has also splitting tendency in the bottom part with the development of a carb shale band. However, the thickness of this band is less than 3m in the project area and hence E&F seam has been considered as a single horizon. Altogether 23 faults have been deciphered in the block. Out of these, two faults F2-F2 and F10-F10 having throw of 10-75m & 5-95m are the major faults. However, presence of a few minor faults cannot be ruled out.