J. Cent. South Univ. (2018) 25: 1162-1172

DOI: https://doi.org/10.1007/s11771-018-3815-7

Sustainable lignite resource planning at Thar coalfield, Pakistan

Fahad Irfan SIDDIQUI¹, Abdul Ghani PATHAN¹, Bahtiyar NVER², ²

1. Department of Mining Engineering, Mehran University of Engineering and Technology,Jamshoro 76062, Pakistan;

2. Department of Mining Engineering, Hacettepe University, Beyttepe Ankara 06800, Turkey

Central South University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2018

Abstract: Thar coalfield is a new coalfield in Pakistan with estimated lignite resource of more than 175 billion tons. Resource planning is an essential part of the strategic plan for optimal and economical exploitation of Thar lignite. Main objective of the present research is to assess Thar coalfield as a single deposit and identify the areas suitable for surface mining, underground mining and waste dump at Thar coalfield. The cumulative stripping ratio distribution map has been developed for Thar coalfield, covering an area of 1691.04 km² around 12 exploratory blocks. Lithological data of 693 drill holes have been used to calculate the cumulative stripping ratio in every borehole, which varies from 3.7 m:m to 88.1 m:m with an average value of 12.85 m:m. Cumulative stripping ratio is divided into six ranges, viz: 4–6, 6–8, 8–10, 10–15, 15–20 and >20 m:m. Contours are digitized around all boreholes showing various ranges of stripping ratios. From the cumulative stripping ratio distribution map, it is concluded that 665.72 km² area, which constitutes 39.37% of the total assessed area, is suitable for surface mining and 989.82 km² area, constituting 58.53%, is appropriate for underground mining and outside waste dumps. Whereas, 2.1% area is no coal zone, only suitable for outside waste dumping. The developed map of cumulative stripping ratio distribution may be used as a guide map for the preparation of mining master plan for Thar coalfield.

Key words: openpit; stripping ratio; Surpac; sustainable development; Thar coalfield

Cite this article as: Fahad Irfan SIDDIQUI, Abdul Ghani PATHAN, Bahtiyar NVER, . Sustainable lignite resource planning at Thar coalfield, Pakistan [J]. Journal of Central South University, 2018, 25(5): 1165–1172. DOI: https://doi.org/10.1007/s11771-018-3815-7.

1 Introduction

Pakistan is facing the worst electricity shortfall of its history, due to a persistent and widening gap between supply and demand. In June, 2014, the deficit reached up to 5000 MW while the generating capacity was 13250 MW of electricity and the demand varied around 18000 MW. There are number of reasons that contribute towards perennial electricity deficit, reduced production of electricity by independent power producers (IPPs) due to the shortage of oil and gas supply, excessive transmission and distribution losses, substantial circular debt, political & bureaucratic overlapping and last but not least, the non- development of indigenous energy resources. Currently, Pakistan is spending an upward of US$ 14 billion on imports of crude oil, petroleum products, coal, LPG etc, to meet energy requirements [1].

Coal is the predominant fuel used for electricity generation worldwide and account for 41% of overall worldwide electricity generation [2].Unfortunately, the share of coal in electricity generation in Pakistan is very negligible (less than 1%) as compared to world average. Pakistan has huge coal deposit at Thar coalfield, containing more than 175 billion tons of lignite resources. Thar coal resources have an estimated potential of generating 50000 MW of electricity for a period of 400 years; thus, providing an opportunity for large scale mining & power generation over a long period of time. The Thar lignite is still unexploited due to a number of reasons, e.g., political instability, law & order situation, unclear mineral/coal policy, lack of planning, non-technical executives, and bureaucratic obstacles.

Intelligent planning is required for sustainable development of Thar coalfield keeping in view of the principles of sustainable planning and development. Sustainability is regarded as the most critical factor for strategic mine planning and development.

For large-scale lignite exploitation, it would be appropriate to thoroughly review the likely impacts in terms of their implications for sustainable development and must be in accordance with the current legislation for environmental protection, energy efficiency, optimal lignite resource utilization, materials saving, recycling and reuse [3]. Many developed and developing countries have devised their long-term lignite production and utilization policies and plans based on the principles of sustainable and responsible mining [4–14]. LIAO et al [15] devised a master plan of Fuxin coal mine area in China by combining ecological vulnerability index and coal reserve estimates and designated five different exploitation zones, appropriate, optimized, moderate, restrictive and forbidden zones. It is suggested that the developed plan may be used to optimize existing mining operation at Fuxin mining area. DANICIC et al [6] thoroughly scrutinized the technical and economical issues resulted from improper initial planning at opencast lignite mines in Serbia. A identified number of challenges need to be addressed for sustainable development of Indian coal sector. SUTCU [16] carried out a GIS-based study to produce potential coalfield map at Milas-Yatagan Basin, Turkey. The potential coalfield map was classified into five categories as very high, high, medium, low and very low probability areas based on probability index values.

NVER et al [17] proposed an innovative and sustainable method of brownfield planning based on cumulative stripping ratio. The method has been successfully applied at Karapinar coal deposits located at inner Anatolia, Turkey. Seam thicknesses and levels were highly heterogeneous and variable, which were impossible to correlate seams to form 3D solids; therefore, cumulative stripping ratios were calculated for each seam and contours of cumulative stripping values were effectively utilized for openpit geometry and volume calculations.

Twelve exploration blocks are developed at Thar coalfield. All blocks are explored and assessed independently. Thus the true picture of resource distribution in coalfield area has not been evolved. It is crucial to assess Thar coalfield as a single deposit for the development of mining master plan. Keeping in view of the importance of the matter, this research project was conceived to assess Thar coalfield as a single deposit and identify the areas suitable for surface mining, underground mining and waste dump at Thar coalfield. The basic idea of this approach is to obtain cumulative stripping ratio in every borehole and digitize the contours of different stripping ratios around all boreholes in 12 exploration blocks at Thar coalfield. The research has led to the development of cumulative stripping ratio distribution map to establish the appropriate areas for surface mining, underground mining and waste dump.

2 Case study

2.1 Exploration history and current status of Thar field

Thar coalfield is situated at district of Tharparkar, Sindh Province, Pakistan between latitudes 24^o15'N–25^o45'N and longitudes 69^o45'E– 70^o45'E. Thar coalfield is connected with Karachi by 410 km metaled road. The location of the coalfield is shown in Figure 1. Bara formation of Paleocene/Eocene age is the coal bearing formation and contains various lignite seams. Sandy/silty claystone and sandstones are major coal-measure rocks of Bara formation. The average thickness is around 95 m, lying at a depth of 100 m to 220 m [18, 19]. The basement rock is slightly to moderately weathered granite comprising fine to coarse grains of quartz. The carbonaceous clay stone is medium light grey to brown in colour containing carboniferous petrified roots, carbonaceous materials and rare sandy resin globules. The olive grey to dark-grey claystone containing petrified coal roots and pyretic resin globules overlies this sediment [20]. A number of coal seams ranging from 0.5 to 21 m thickness occur at an average depth of 180 m. The sub-recent formation overlies the Bara formation. It comprises of siltstone, sandstone, claystone, with average thickness of 70 m and lies at the depth of 52–125 m. The recent formation overlying the sub-recent formation consists of sand dunes. This sand is fine to medium grained, yellowish grey in color containing sub-rounded and moderately sorted grains of ferromagnesian minerals. Figure 1 shows the general lithology of the Thar coalfield.

The earliest indication of coal at Thar was reported in 1980 during water well drilling at Khokharpar, drilled by UNICEF/PHED. Later in 1988, British Overseas Development Agency (ODA) and Sindh Arid Zone Development Authority (SAZDA) discovered coal while drilling water wells near village of Khario Ghulam Shah [21]. The core samples and drill cuttings were analyzed by Geological Survey of Pakistan (GSP) and United States Geological Survey (USGS) and confirmed the presence of lignite in the area. In 1989, GSP/USGS carried out geophysical logging of water wells and ascertained occurrence of thick coal bed in Thar area. Detailed exploration was carried out jointly by USGS and GSP under Coal Resources Exploration & Assessment Program (COALREAP) from 1989 to 1994. A total of 21 boreholes were drilled at large spacing of more than 18 km to ascertain the occurrence of coal in entire Thar region [22, 23]. Hypothetical lignite resources of Thar field are anticipated around 175.506 billion tons. To date, 12 exploration/administrative blocks have been explored separately by various agencies viz: GSP, Shenhua Group (China), Rheinbraun (Germany), Sindh-Engro Coal Mining Company (SECMC), Deep Rock Drilling (DRD), Sino-Sindh Resources, Oracle coalfields, from 1994 to 2012. Figure 2 shows the location of boreholes completed by various exploring agencies.

2.2 Borehole database

The lithological data from 693 boreholes drilled by different exploration agencies from 1994 to 2012 in all 12 blocks of Thar coalfield is used in this research. The obtained information includes, northing and easting coordinates, elevation, dip & azimuth, and geological intercepts. All the exploration data were maintained in excel sheets and exported to Geovia Surpac 6.2 geological database. Table 1 presents the structure of Surpac geological database used in this research.

2.3 Cumulative stripping ratio calculations and contours digitization

The stripping ratio is the governing economic parameter, on the basis of which it is decided to exploit the coal either by developing an open pit mine or an underground operation. It is commonly defined as the ratio of waste to coal and can be expressed in various terms such as t : t, m³: t, m³ : m³, and m : m. Cumulative stripping ratio is considered in multiple seam environment, which also includes the interburden waste between the seams. The aim of this research is to establish appropriate areas for different mining operations at Thar coalfield based on cumulative stripping ratio distribution. The basic idea of this approach is to obtain cumulative stripping ratio for each coal interval in every borehole and digitize the contours of different stripping ratios. The m:m stripping ratio is used in this study.

Figure 1 General lithology of Thar coalfield, Pakistan [23]

Figure 2 Location of drillholes in all exploration blocks completed by different companies

Table 1 Structure of Surpac geological database used in this research

A short sub-routine developed by NVER et al [17], is used to calculate stripping ratio for each coal interval in all the boreholes, using MATLAB platform. Figure 3 shows a flow chart of the program structure. The obtained cumulative stripping ratio values for all boreholes were imported to Surpac geological database. An example of cumulative stripping ratio calculated for each coal interval in different boreholes is shown in Figure 4.

The stripping ratio contour digitization process involves four steps, starting with snap point digitization of minimum stripping ratio value in every borehole column. In the 2nd step, raw polygons are made from individual points having similar stripping ratio values. The third and fourth steps involve smoothing of raw polygons and triangulation of string polygons to form colored contours showing different cumulative stripping ratio classes. Figure 5 shows schematic representation of contour digitization process.

Figure 3 MATLAB program structure for calculation of cumulative stripping ratio

Figure 4 Cumulative stripping ratio calculated for successive coal intervals

3 Results and discussion

Cumulative stripping ratio in every borehole has been calculated, which varies from 3.7 m:m to 88.1 m:m, with an average value of 12.85 m:m. Cumulative stripping ratio is divided into six ranges, viz: 4–6, 6–8, 8–10, 10–15, 15–20 and >20 m : m. Based on these ranges, cumulative stripping ratio distribution map has been developed, covering an area of 1691.04 km², as shown in Figure 6. Cut-off cumulative stripping ratio for surface mining operation is taken as 10. It should be kept in mind that cumulative stripping ratio values are calculated on borehole data basis and the results can be used to preliminarily determine the openpit and underground mining areas.

Figure 5 Schematic representation of contour digitization procedure

Figure 6 Cumulative stripping ratio distribution in all exploration blocks

From the cumulative stripping ratio distribution map, it is calculated that 665.72 km² area, which constitutes 39.37% of the total assessed area, is suitable for surface mining and 989.82 km² area, constituting 58.53%, is appropriate for underground mining and outside waste dumps. The waste material excavated from surface mines can be dumped on top of the underground mining areas. Whereas, 2.1% area is no coal zone, only suitable for outside waste dumping.

Figure 7 shows the block wise distribution of underground, surface and no-zone areas. It is clear from Figure 7, that blocks II, VI and VIII are highly suitable of surface mining operations. Whereas, blocks IIIB, VII, XI and XII are suitable for underground mining. Blocks I, III, IV, V, IX and X are partly suitable for both surface and underground mining operations.

Figure 7 Distribution of surface, underground and no- coal zone areas in different blocks

Details of area distribution in different stripping ratio classes are summarized in Table 2. The area of the minimum cumulative stripping ratio class (4–6) is 70.08 km² which mostly occurs in blocks II and VIII. Similarly, the areas of the maximum cumulative stripping ratio class (>20) occurs mostly in inter-block area, blocks IX and IIIb. The maximum no-coal area of 25.61 km² was found in block VIII, i.e 70% of the total no-coal zone in entire Thar field.

Table 2 Details of areas falls in different stripping ratio classes

4 Conclusions

The main objective of the present research is to establish specific areas/sections for particular mining operation. The cumulative stripping ratio distribution map has been developed for Thar coalfield, by obtaining cumulative stripping ratio for each coal interval in every borehole and digitizes the contours of different stripping ratios around the boreholes. The map provides a technical justification to allocate different exploration blocks for appropriate mining operation. On the basis of cut off stripping ratio of 10:1 m:m, it is concluded that 39.89% of total blocks area is suitable for surface mining and 57.97% is appropriate for underground mining and outside waste dumps, whereas 2.12% area is no coal zone, only suitable for outside waste dumping.

It is the first time, that Thar coalfield has been evaluated as a whole, which is necessary for the preparation of development plan. Otherwise, improper planning and locations of open pits would certainly lead to irreversible loss of resources. The developed cumulative stripping ratio distribution map may be used as guide map for future planning of Thar Coal resource.

Acknowledgment

Authors are grateful to British Council, Pakistan, Higher Education Commission, Pakistan and Mehran University of Engineering & Technology, Jamshoro, Pakistan for providing financial support under INSPIRE program (SP-247) for this study. Authors are also thankful to Thar Coal Energy Board (TCEB), Energy Department Government of Sindh Pakistan for providing the necessary exploration data. Authors also like to express their profound gratitude to Hacettepe University, Ankara, Turkey for providing necessary support for the conduct of this research.

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(Edited by YANG Hua)

中文导读

巴基斯坦Thar煤田的可持续褐煤资源规划

摘要：Thar煤田是巴基斯坦的一个新煤田，估计褐煤资源超过1750亿吨。资源规划是战略规划的重要组成部分，是优化和经济开发Thar褐煤的重要组成部分。本研究的主要目的是将Thar煤田作为单一矿床进行评价，并确定适合在Thar煤田进行地表开采、地下开采和排土场开采的区域。为Thar煤田编制了累积剥蚀比分布图，覆盖面积达1691.04 km²，有12个勘探区块。利用693个钻孔的岩性资料，计算了每个钻孔的累积剥蚀率(3.7–88.1 m ：m)，平均值为12.85 m ：m。累计剥蚀率分6个范围，分别为4–6，6–8，8–10，10–15，15–20和>20。所有钻孔周围的等高线都被数字化，显示出不同的剥离比范围。从累积剥蚀率分布图可以看出，665.72 km²的面积(占评估总面积的39.37%)适合地表开采，989.82 km²的面积(占58.53%)适合于地下开采和外部废物堆放。而2.1%的地区不属于煤区，只适合于外部倾倒废物。所开发的累积剥蚀率分布图可作为制定Thar煤田开采总体规划的指导图。

关键词：露天矿；剥蚀率；Surpac；可持续发展；Thar煤田

Received date: 2017-02-15; Accepted date: 2017-06-05

Corresponding author: Fahad Irfan SIDDIQUI, Master of Engineering, Assistant Professor; Tel: +92-333-3783844; E-mail: fahad_03mn@hotmail.com; ORCID: 0000-0002-2094-2236