GEOLOGY, RESERVE ESTIMATION AND QUALITY ASSESSMENT OF THE SINDHALI LIMESTONE DEPOSIT, NEPAL

shows that there are ample opportunities for cement industries in Nepal but more detailed geological studies are required for further prospecting and exploration.

GEOLOGICAL SETTIN G The Sindhali limestone deposit is situated 22 km north of Gaighat, within the Lesser Himalayan autochthonous zone in eastern Nepal (Fig. 1). Geologically, the Sindhali limestone deposit area is divided into four major group viz. the Bhimphedi

Group, Phulchoki Group, Midland Group and the Tosh Group of the Lesser Himalaya. The Bhimphedi Group consists of the Raduwa Formation, Bhainsedobhan Marble, Kalitar Formation and the Kulekhani Formation from north to south respectively. The Sindhali limestone deposit lies within the Bhainsedobhan Marble which is well separated from the Sub-Himalayan Zone in south by the Main Boundary Thrust (MBT) that runs NW-SE direction passing through the confluence of the Puware and Trijuga Rivers. The entire part of the Lesser Himalaya and Sub-Himalaya Zones are crossed by a Chuniya River Transverse Fault (CTF) running N-S direction which offsets the whole sequence of rocks. The Mid -land Group consist of two formations the Dhading Dolomite and the Dandagaon Phyllite which unconformably lies over rocks of the Tosh Group that consists of rhodocrosite bearing sandstone, dark gray shale, marl beds and pseudo -conglomerate. Furthermore, the Lesser Himalaya of the Sindhali area is divided into Northern, Central and Southern tectonic zones, where the Northern Tectonic Zone is thrusted over the Central Tectonic Zone along the Mahabharat Thrust (MT) that brings limestone deposit over the top of the sequence. In the southern part of the Sindhali limestone deposit the Siwalik rocks outcropped as footwall of the MBT and are divided into the Lower and Upper Siwalik units. The Lower Siwalik is represented by alternation of siltstone, fine -grained sandstone and mudstone whereas Upper Siwalik is dominated by conglomerate and coarse -grained massive sandstone. Various geological investigations have been carried out in the Sindhali limestone deposit area. A detai l account on geological framework of the Udayapur limestone was described by Khattri (1977); reserve investigation and geological studies by Jha (1978) and ESCAP (1993) and investigation of exploration opportunities by Shrestha (2001). General geology and mining technique of the cement grade limestone of the Udayapur area was also described by Sah et al. (2003). SGEM 200 6 - Section I 155

38'59" Puware Gaun Tiltele Kubhinde Murkuchi CKF MBT MBT Sw Siwalik Group Ts T osh Group Dhading dolomite Dandagaon Phyllite Kulekhani Formation Kalitar Formation Bhaisedobhan Marble Raduwa Formation Dip/Strike Foliation Geological Contact Thrust Fault Road River/Stream Sindali CKF LEGEND

m Siruwani MBT Main BoundaryThrust MahabharatThrust Chunia Khola Thrust SukauraThrust CKF Tindhare 1000 750 500 250 MTST MBT CKF A B Sukaura Bayangri Khola Ra Bh Ka Dada

42 2930 Quarry site Fig. 1: Geological map and cross -section of the Sindhali area, eastern Nepal

1 Sub-Himalayan Zone The Sub-Himalayan Zone mostly exposed alon g the southern margin of the study area is mainly composed of Siwalik rocks such as alternation of mudstone, siltstone and sandstone and are well exposed along the downstream of the Trijuga River. The general attitude of the bedding is N54 0W/28 0 NE (Fig.1) .

2 Lesser Himalayan Zone Three tectonic sub-zones Northern, Central and Southern are well recognized within the Lesser Himalaya of the study area which are are separated by two thrusts the MT in the north and Sukaura Thrust (ST) in the south respective ly. Lithologically, the Lesser Himalayan rocks are dominated by low to high grade metamorphic rocks like limestone, dolomite, quartzite, phyllite, garnetiferious schist and banded gneiss.

3 Northern Tectonic Sub-Zone The Northern Tectonic Sub-Zone exposed in the northern side of the MT and the ST in the south is mainly composed of medium to high grade metamorphic rocks of the Bhimphedi Group which is divided into four geological formations from bottom to top: the Raduwa Formation, Bhainsedobhan Marble Kalitar Formation and the Kulekhani Formation respectively in the study area (Fig. 2). The Raduwa Formation is composed of coarsely crystalline excess garnet bearing two -mica schist with intercalation of medium grained quartzite. Towards the base, near MT rocks are highly crushed and 6th International Multidisciplinary Scientific GeoConference SGEM2006 www.sgem.org Int er nat ional Confer ence SGEM 200 6 156 conformably overlain by a thick sequence of well crystalline limestone with rare intercalation of dolomite, which seems to be equivalent to the Bhainsedobhan Marble of the Bhimphedi Group (Stocklin, 1980). The Bhainsedobhan Marb le composed of thick sequence of well crystalline milky white limestone, where the Northern tectonic zone is thrusted over the Central tectonic zone along the MT that brings the Sindhali limestone deposit over the top of the sequence (Figs. 3 & 5). The Bhainsedobhan Marble overlain by the Kalitar Formation and is also called the Rasuwa Formation (Khattri, 1977 and ESCAP, 1993) and is composed of intercalation of augen gneiss, quartzite and marble. The Kalitar Formation especially comprised of crystalline marble intercalated with gneiss in lower part whereas two mica schist with frequent intercalation of quartzite in the upper part of the formation. Fig. 2: Contact between the garnetiferious schist and the Bhainsedobhan Marble observed at Sindhali limesto ne deposit.

4 Central Tectonic Sub-Zone The Central Tectonic Sub-Zone that consists of the Dandagaon Phyllite of the Midland Group (Sah, 1999) consists of greenish gray phyllite with intercalation of greenish -white quartzite and dark gray slate is well exposed along the Trijuga, Chunia, and Pawar Rivers. The thick crushed zone is developed along the entire southern boundary of this tectonic zone by the ST having NW-SE strike and passing through the Sukaura village and upstream of Byangry River. The rock succession of this tectonic unit is thrusted over the younger rocks of the Southern Tectonic Zone.

5 Southern Tectonic Sub-zone (STS) The Southern Tectonic Sub -Zone is mainly composed of thick succession of stromatolites bearing dolomite of the Midland Group (Sah, 1999). The dolomite sequence is highly fragmented, thick bedded, massive and weathered. The Tertiary sedimentary rocks are well exposed along the Puwara and Byangri Rivers and disconfirmably lie over the Dhading Dolomite. The basal conglomerate mainly composed of sandstone and dolomite rocks is also well exposed in this area. The sedimentary succession is composed of rhodocrosite bearing sandstone and shale with SGEM 200 6 - Section I 157 marl beds and lenses of coals. This succession is well comparable to the Lower Tertia ry succession of the Tosh Group in western Nepal (Sah et al., 2003).

RESERVE ESTIMATIO N Reserve estimation is a fundamental part for the mineral exploration and economical extraction of mineral deposits. The estimation of reserve is to find the total volume and converting it into total tonnage where the total volume (m3) multiplied by the specific gravity of the mineral gives tonnage of the reserve in the metric tones. The total reserve of an area is determined by dividing the volume by the tonnage factor (TF). While estimating the reserve the weight of the material may not exactly be equal to the theoretical formula because of the fractures, cavities exist in the ore-body and therefore the specific gravity is required for suitable modification of rock porosity. In the present study, for correct determination of reserve the deposit is subdivided into eight numbers of ore reserve blocks on a plan section with each sample point as unit (Fig. 4). Each area is measured by planimeter. In case of horizontal beds or gently dipping ore-bodies, for each of ore reserve block, the area of influence is determined and is multiplied by true width of the ore body to obtain the volume. However, in steeply dipping ore bodies a vertical longitudinal section is used. The area in this section is converted into the area in the plan of the ore body by multiplying with dip factor. The average cross -section area (A) of the limestone body is calculated from all the cross - sections and the total volume is calculated multiplying this area by the perpendicular distance between each cross -section. The calculated total volume (V) of cement -grade limestone is 172066406.3 sq. m. The tonnage (T) of the limestone is found to be 3.3 and the total reserve is obtained by multiplying the volume (V) and area (A) giving

82337 million tons (Table.1). Fig. 3: Quarry site of the Sindhali limestone deposit 6th International Multidisciplinary Scientific GeoConference SGEM2006 www.sgem.org Int er nat ional Confer ence SGEM 200 6 158

2 2' 4 4'1' 3 3' SW NE SW NE SW NESW NE SW NE SW NE SW NE SW NE

m 500 Fig. 4: Cross -sections used to calculate the limestone reserve of the Sindhali area Table 1: Reserve estimation of limestone deposit Block No. Cross sections Cross- section Area m2 Average Cross - section Area m2 Length of Block in Volume of Block m3

5 162.5 1066406.25

5 150.0 10690625.0

5 250.0 14784375.0

0 312.5 49804687.5

5 350.0 58515625.0

0 350.0 26687500.0

5 662.5 37058593.75 Total 1106875 595387.5 2237.5 198607812.5 Total volume = 198607812.5 Specific gravity = 3 kg/ m3 (for limestone) Total reserve = Total volume x Specific gravity = 198607812.5 m3 x 3 kg/m 3 = 595823437.5 tones = 595.82337 million tones SGEM 200 6 - Section I 159

CHEMICAL ANALYSIS OF LIMESTONE For the manufacture of good quality of portland cement chemical analysis of the limestone is quite essential. The quality of the cement is particularly based on the chemi cal component like CaO, MgO, SiO 2, Al2O3, Fe2O3, Cr2O3 and NiO in the limestone. According to Nepal national standard, the quality of cement grade limestone should contain CaO > 45% and MgO < 3%. Different content of compound have different effects on qual ity of cement. Specially, MgO plays imperative role to vary the quality of portland cement. When the content of MgO is less than 2.2-3.0 % it is beneficial to make clinker. On the other hand when MgO is more then 3.0%, it reduces the burnability of raw meal, and increases the content of free lime in clinker and decrease the strength of cement (Liu and Li, 2005). The higher content of MgO impairs the soundness of cement (Fomicheva, 1989). Moreover, presence of P2O5, chlorine, fluorine and Mn2O3 in more than desired level reduces the quality of the portland cement. More than 0.5% of P2O5 in limestone results slow cement setting rate whereas less than 0.5% of fluorine is beneficial as a flux but excess than that increases balling action in the kiln (Li, 1996). In addition, if Mn 2O3 is more than 0.5% it affects the color and strength of the cement. In the present study we obtained the chemical components of the Sindhali limestone by chemical analysis within desired level (Table 2). Fig. 5: Cement grade limestone in Sindhali limestone deposit (Bhainsedobhan Marble) Table 2: Chemical composition of limestone (wt %) Sample No. CaO % MgO % SiO2 % Al 2O3 % Fe 2O3 %

52.20 2.03 4.09 1.09 0.60

48.46 2.74 5.73 1.15 0.59

49.12 2.91 4.34 1.29 0.56

47.36 3.05 4.47 1.37 0.52

47.12 3.04 5.02 1.21 0.57

48.58 2.93 4.56 1.28 0.62

48.02 2.53 6.02 1.39 0.52 6th International Multidisciplinary Scientific GeoConference SGEM2006 www.sgem.org Int er nat ional Confer ence SGEM 200 6 160

50.50 1.79 5.32 1.28 0.49

49.17 2.01 4.41 1.36 0.50

48.79 1.64 4.26 1.38 0.58

51.26 2.12 3.87 1.24 0.60

49.43 2.54 4.37 1.32 0.63

48.69 2.14 4.32 1.41 0.56

47.81 2.86 4.58 1.43 0.52

51.09 1.73 3.52 1.23 0.58

49.51 2.45 4.51 1.35 0.49

50.32 1.91 5.38 1.26 0.52

49.14 2.64 4.42 1.31 0.54

51.17 1.89 3.97 1.26 0.59

48.83 2.19 4.27 1.37 0.61 Average % 49.33 2.35 4.57 1.3 0.56

RESULTS Eight transverse sections taken to estimate the reserve by cross -section method shows the total volume of the limestone deposit is 172066406.3 sq. m, the tonnage of which is about 3.3 and total estimated reserve is 595.82337 tons. Sindhali limestone deposit shows uniform, well crystalline, greenish gray and good quality pure limestone with dolomite intercalations. Thirty -five outcrops and five borehole rock samples were taken from the different part of the deposit for chemical analysis. The samples collected for the chemical analysis was crushed into small pieces and powder for the treatment in the laboratory. The result obtained from the chemical analysis of representative samples of limestone gives different percentages of comp onents (average) as, CaO-49.33%, MgO -2.35%, SiO2 -4.57%, Al2O3-1.3 and Fe2O3-0.56%.

CONCLUSION The Sindhali limestone deposit is situated within the Lesser Himalayan autochthonous zone in eastern Nepal. Geologically, the area is divided into four major groups viz. the Bhimphedi Group, Phulchoki Group, Midland Group and the Tosh Group of the Lesser Himalaya. Tectonically the area is divided into Northern, Central and Southern tectonic zones, where the Northern Tectonic Zone is thrusted over the Central Tectonic Zone along the Mahabharat Thrust (MT) that brings Sindhali limestone deposit over the top of the sequence. Open cast mining is used for the excavation of limestone deposit by preparing benches drilling holes and blasting. In the preset study, total reserve estimation by cross -section method of the cement grade limestone is estimated to be 595.823 million tones. Chemical analysis of limestone gives the average value of the components of limestone as, CaO-49.34%, MgO -2.35%, SiO 2-4.57%, Al2O3-1.3% and Fe2O3-0.56%, which shows good quality of the limestone deposit for commercial production of portland cement. SGEM 200 6 - Section I 161 REFERENCES ESCAP, (1993). Geology and mineral resources of Nepal explanatory brochure, atlas of mineral resources of the ESCAP region. UN publi cation, vol. 9, 107 p.

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Society, London, vol. 137, pp. 1-34. 6th International Multidisciplinary Scientific GeoConference SGEM2006 www.sgem.org