188.8.131.52 Reserves and Resources
Coal resources(or total coal resources) refer to the coal deposits which can be mined out and utilized or have potential value. They are composed of two parts: reserves and prognostic resources.
Coal reserves refer to coal resources which have been uerified through some geological work to be in line with the state standard for reserve calculation and have potential value for development and utilization. They also can be divided into two categories: the first one is usable reserves, namely, reserves that can be mined out under the present economic-technological conditions of coal mining and the second one is temporarily non-usable reserves, which can hardly be exploited now because of small thickness of coalbed, high ash content and low caloric value or complicated hydrogeological condition and technological problems. The Standard of Geological Exploration of Coal Resources promulgated by the National Commission of Mineral Reserves in 1986 has stipulated specific requirements in this regard.(Table 2.2.2).
The standard has also specified the depth for calculating reserves. For coal fields which are suitable for mining by medium-sized shafts with an annual production capacity of 450,000 tons or larger ones the coal reserves should be calculated down to a vertical depth not exceeding 1,000 m, but no more than 600 m for those fit for mining by small shafts (with an annual capacity of 300,000 tons or less)and 1,200 m for old mines.
Prognostic resources refer to the coal resources that are prognostically inferred by applying the geological theory of coal fields while taking into consideration coalfield characteristics and coal-forming conditions and regularities. According to the reliability of these factors prognostic resources can be divided into three categories: reliable, possible and speculated. Generally, prognostic resources are calculated down to a vertical depth of 2,000 m or less but actually it is mainly the part of them above the depth of 1,000 m that are currently of reference value.
The former Ministry of Coal Industry proclaimed that the prognostic coal resources of China(as of 1975)amounted to 4,492.7 billion tons, of which 2,104 billion tons lie above the depth of less than 1,000 m. Afterwards, the former Ministry of Geology and Mineral Resources predicted that they were estimated at 4,455 billion tons(as of 1988) and the China Bureau of Coal-field Geology estimated them to be 4,550.3 billion tons(as of 1992). Those figures are very much close to one another, showing that the calculating bases are basically similar.
With the geological exploration carried out year by year, the accumulative explored coal reserves have kept increasing. According to the statistics of the former Ministry of Geology and Mineral Resources, by the end of 1997, the accumulative explored coal reserves had accounted for 1,033.398 billion tons, in which 252.584 billion tons were reserves of detailed exploration and the retained reserves had totaled 1,007.625 billion tons, including 137.642 billion tons of detailed exploration reserves retained for operating and constructing shafts and 89,435 billion tons of unused reserves of detailed exploration. Since shaft construction is restricted by various factors, only a part of the unused reserves will be exploited. Now the illegal and irrationally distributed small coal mines run by townships and towns are being shut down by the government, so in order to make up this part of reduced production, more new shafts will have to be constructed and corresponding exploration of coal fields should also be carried out positively.
The global distribution of coal resources indicates that they are mostly abundant in the former Soviet Union, the United States and China. Owing to the different calculating methods and standards, they are not completely comparable. In terms of the total resources above a vertical depth of 1,800 m, the former Soviet Union had around 6,800 billion tons(1968), China around 4,500 billion tons(1992)and the United Sates around 3,600 billion tons(1974), holding the first three positions in the world.
(1) Major coal ages
There were many coal ages in China's geohistorical times, mainly the Carboniferous, Permian , Triassic, Jurassic, Cretaceous and Tertiary, with seven coal bearing rock series, that is, the Early Carboniferous , Carboniferous-Permian, Permian, Late Triassic, Early-Middle Jurassic, Early Cretaceous and Tertiary(see Fig. 2.2.1).
(2) Characteristics of geographical distribution
1) Extensive distribution. By the end of 1997 coal resources had been found to occur in almost all China's provinces , autonomous regions and municipalities except Shanghai Municipality and the Hong Kong Special Administrative Region, involving 63% of total number of counties. So far, 5392 coal occurrences and fields have been discovered and subjected to geological work of different levels ( excluding those in Taiwan). Coal is a variety of mineral resources and is the most extensive in distribution and most abundant in China.
2) Greater abundance in the West and the North than in the East and the South. We can see clearly this characteristic geographical distribution of coal resources in China if we divide China into eastern and western parts by the line linking the Da Hinggan Range, the Taihang Mountains and the Xuefeng Mountains and into northern and southern parts by the line connecting the Kunlun Mountains, the Qinling Mountains and the Dabie Mountains. The 12 provinces(municipalities and autonomous regions) in western China have 89% of the total coal resources but the 21 provinces(municipalities, autonomous regions and special administrative regions)in eastern China have only 11.% of the total. The 18 provinces(municipalities and autonomous regions) in northern China have 93.6 % of the total coal resources and the 15 provinces (municipalities and autonomous regions and special administrative regions)in southern China have only 6.4 %. The same is the case with the retained reserves: 87% in the west and 13% in the east; 90.5% in the north and 9.5% in the south. Such a framework has determined the long-term development situation of transporting coal from the north to the south and from the west to the east.
3) Relative concentration. In terms of total coal resources, 11 provinces (autonomous regions), namely Xinjiang and Inner Mongolia( each has over 1,000 billion tons )and Shanxi, Shaanxi, Ningxia, Gansu, Guizhou, Hebei, Henan, Anhui and Shandong(each has over 100 billion tons )have altogather 95.1%; and in terms of retained reserve, 13 provinces(autonomous regions)of Shanxi, Inner Mongolia and Shaanxi(each has over 100 billion tons )and Xinjiang, Guizhou, Ningxia, Anhui, Yunnan, Henan, Shandong, Heilongjiang, Hebei and Gansu(each has over 10 billion tons )have 96.1% of the national total. This is a favorable condition for the development of the coal industry.
(3) Coal-bearing strata
As a fossil fuel mineral formed of plant remains in geohistorical times, coal is closely linked with stratigraphy. There are seven major coal-bearing rock series in China.
1) Early Carboniferous coal-bearing strata. Represented by the Ceshui Formation, they are mainly distributed in South China and well developed in central and southern Hunan, northern and western Guangdong, with coal deposits of economic value formed in central Hunan. The Ceshui Formation has some synonymous units such as the Wanshoushan Formation in Yunnan, which lies in a lower horizon than the Ceshui Formation, the Furongshan Formation in northern Guangdong and the Simen Formation in northern Guangxi which are exactly in the same horizon of the Ceshui Formation and the similar sedimentary rocks to the east of Hunan, including the Zishan Formation in western Jiangxi, the Zhongxin Formation in eastern Guangdong, the Lindi Formation in western Fujian and the Yejiakuang Formation in western Zhejiang, which are obviously at a higher horizon.
2) Carboniferous-Permian coal-bearing strata. The Late Carboniferous Early Permian in the North China Platform are a suit of continuous and inseparable coal-bearing sediments, which are generally called the Carboniferous-Permian coal-bearing strata. In the northern and central parts of the North China Platform, the lithostratigraphic units of the coal-bearing strata are, in ascending order, the Benxi Formation(ferralite formation),Taiyuan Formation, Shanxi Formation, Lower Shihezi Formation, Upper Shihezi Formation and Shiqianfeng Formation, among which the Taiyuan Formation and Shanxi Formation are the major coal-bearing horizons. The coal-bearing strata in the southern part of the North China Platform is basically the same. The only difference is that the strata corresponding to the Upper Shihezi Formation are grayish green or grayish purple rather than purple, yellow and green in color and bear minable coal seams or even major coal seams, so they are named the Dafengkou Formation to make a distinction. In the southern part of the North China Platform, the Taiyuan Formation generally does not contain minable coal seams, but the Shanxi Formation contains a coal seam. The Dafengkou Formation contains 5~6 locally minable coal seams and in the Huainan area the No.13 coal seam of this formation is the main minable seam of prime importance.
3) Permian coal-bearing strata. When talking about the Permian alone, we mean the coal-bearing strata of South China. Coal fields in South China have low economic value, but the coal-bearing strata are diversified. The Permian coal-bearing strata in South China is collectively called the Longtan Formation, a lithostratigraphic unit of coal-bearing sediments located between the overlying Maokouan marine beds(limestone and siliceous rocks) and the underlying Changxingian marine beds(limestone and siliceous rocks ). Since the basement in the western part of South China is the relatively stable Yangtze Platform and that in the eastern part is the relatively active South China fold system, they show sharp differences both in the characteristics of coal-bearing strata and in coal seam stability. In the eastern part the Permian coal-bearing strata can be further divided into two types. The strata of the first type represented by these occurring at Longyan and Yongding in southwestern Fujian are called the Tongziyan Formation which is late Middle Permian, i.e. Maokouan, or Kazanian in age. Strata of the same age are also distributed in eastern and central Guangdong, western Zhejiang and eastern Jiangxi, forming a sedimentary province in southeast coastal areas. The strata of the second type are represented by those at Leping and Fengcheng of central Jiangxi, and in terms of lithostratigraphic characteristics they can be correlated in most of the area from northern Zhejiang to western Jiangxi. They are of the early Late Permian age and the Longtanian Formation is erected for them. The western part also has two types of Permian coal-bearing strata. The first one is represented by those at Liupanshui of Guizhou, which are separated into 3 members according to the lithstratigraphic characteristics with the central one being the major coal-bearing member containing dozens of coal seams, 1~2 of which are thick. The second one, represented by those at Xuanwei of Yunnan, consists of limnic coal-bearing strata of varying thickness , which are thick in the east and thin in the west, and contain one to dozens of coal seams. Between the east and west parts of South China , there is an active area, the relic of the Caledonian continental crust of South China, which is dominated by limestone deposits called the Wujiaping Formation. In central and western Guangxi these limestones are intercalated with coal beds and are otherwise called the Heshan Formation.
4) Late Triassic coal bearing strata. They are mainly distributed in southwestern and southeastern China. In southwestern China, they have the most extensive distribution in the Sichuan Basin with the Xujiahe Formation as the representative, which, 500~600 m in total thickness and middle Late Triassic , i.e., Norian in age, contains over 10 coal seams with 2~3 minable coalbeds. Besides, the area from Dukou in western Sichuan to Yongren in the northern Yunnan is an important Triassic coal bearing region, where the coal-bearing strata are called the Daqiaodi Formation, which, 2,200 m in thickness, constrains about 100 coal seams including 37 minable ones. This formation lies in a horizon possibly lower than the Xujiahe Formation and belongs to the Carnian-Norian. In southeastern China represented by those at Pingxiang of Jiangxi, the coal strata, belonging to the Norian -Rhaectian in age, are named the Anyuan Formation with three lithlogical members, of which the lower member, i.e. the Zijiachong Member, is coal-bearing. The Genkou Formation corresponds to the Anyuan Formation, while the Chutanlong and Yangmeilong Members of Hunan and the Dakeng and Wenbinshan Members of Fujian are also comparable to it.
5) Early-Middle Jurassic coal-bearing strata . With the Early-Middle Jurassic being the major coal-forming age in China, the coal-bearing strata of this age are concentratedly distributed in the northwestern part of China, including the Erdos Basin and some large basins in Xinjiang. In the Erdos Basin, they consist of the Fuxian Formation in the lower part and the Yan'an Formation in the upper part. The Fuxian Formation is limited in distribution, containing only some thin coal seams, while the Yan'an Formation can be divided into three parts based on lithology: the upper and lower parts are composed of coarse-grained rocks with thick but inconstant coal seams; the middle part is made up of fine-grained rocks with a number of thin coal seams .These rocks are mostly Middle Jurassic in age. It is considered that the Yan'an Formation is comparable to the Datong Formation in northern Shanxi and the Yima Formation in western Henan. The coal-bearing strata in the large basins in Xinjiang are represented by the Shuixigou Group, in which the Badaowan Formation in the lower part is a coal-bearing formation 800 m thick, bearing dozens of coal seams with a total thickness of dozens of meters; the Sangonghe Formation in the middle part is coal-free in it and the Xishanyao Formation in the upper part is another coal-bearing formation which has a thickness of 800 m and contains dozens of coal seams with a total thickness of scores of meters or even over 100 m.. The Badaowan Formation is Early Jurassic in age, the Xishanyao Formation belongs to the Middle Jurassic and the Sangonghe Formation is of the Early-Middle Jurassic age. This coal bearing stratohorizon is different from that in eastern Xinjiang.
6) Early Cretaceous coal-bearing strata. They are mainly distributed in three provinces of Northeast China and eastern Inner Mongolia and are well developed in a series of medium-sized and small basins. The coal-bearing strata in the Da Hinggan Range and the Hailar Basin are called the Jalainainur Group, which consists of the Damoguai Formation of coarse-grained rocks in the lower part, and the Yimin Formation of fine-grained rocks in the upper part, each containing several coal seam groups and very thick coal beds. Similar are the Bayanhua Group in the Eren area and the Holinhe Group in the Jirem League area. They are early to middle but mainly early Early Cretaceous in age. The Lower Cretaceous Series in western Liaoning consists of the Shahai Formation in the lower part and the Fuxin Formation in the upper part. Both of them are coal-bearing formations, but the Fuxin Formation is better for it has coal seams10~80 m in total thickness. Apart from the Fuxin basin, the Tiefa, Pingzhuang and Yuanbaoshan basins also contain good coal-bearing strata of early Early Cretaceous age. The coal-bearing strata in eastern Helongjiang are called the Jixi Group, which is composed of , from bottom to top, the Didao Formation, the Chengzihe Formation and the Muling Formation. The Didao Formation contains a volcanic rock series of Late Jurassic age; the Chengzihe Formation and the Muling Formation are composed of coal-bearing rock series, belonging to the Early Cretaceous. The Chengzihe Formation is 600~1,400 m thick, and contains over 20 minable coal seams, generally 1~2 m thick each. The Muling Formation is 300~1,000 m thick and contains 1~9 minable coal seams with a total thickness of 3~8 m. To the east of Sanjiang and Muling ,where a series of coal basins occur, strata of paralic facies called the Longzhuagou Group are well developed in the Hulin and Mishan area but they contain little coal. Studies done in recent years have indicated that the Jixi Group also contains , more or less, components of paralic facies.
7) Tertiary coal-bearing strata . Coal-bearing strata of the Tertiary period are distributed mainly in two areas and belong to different epochs. There are over 40 Tertiary coal basins in northeastern and northern China, where occur Early Tertiary coal-bearing strata represented by the Fushun Group in the Fushun Basin of Liaoning. The lower part of the Fushun Group belongs to the Paleocene epoch and the middle and upper parts are of the Eocene epoch. The similar formations are the Meihe Formation in the Meihe Basin and the Yangliantun Formation in the Shenbei Basin. Late Tertiary coal-bearing strata in Yunnan are distributed in over 100 small basins. Those of the Miocene epoch are named the Xiaolongtan Formation, in which the major coal member is 4.4~223 m thick, averaging 139 m, contains 37~163 stone bands and has a complicated structure. Besides, the coal-bearing strata of the Paleocene age are named the Zhaotong Formation which contains three minable coal seams with a total thickness of 40~100 m in general and 194 m in maximum.
(4) Coal accumulation provinces and charicteristics
1) South China Early Carboniferous coal accumulation provinces. After the Caledonian orogeny, a continental crust was formed in South China. However, the Qinzhou bay still remained in southern Guangxi and in the Early Carboniferous epoch sea water intruded along the west side of the Yunkai old land through the sea trough, giving rise to an epicontinental sea in the southern Yangtze area. Along the outer margin of the epicontinental sea, a littoral plain was formed in eastern Guizhou, northern Guangxi, northern Guangdong and central Hunan, and caused sedimentation of the Wanshoushan Formation, the Simen Formation and the Ceshui Formation. This was the macroenvironment of coal accumulation in the early Carboniferous epoch. The secondary condition for coal accumulation was that in the interior of the littoral plain, the NNE-trending Xuefeng uplift connected with the ENE-trending Jiangnan uplift and an elbow-like turning was formed. The inner side of the elbow was favorable to the development of swamps and the formation of coal seams. Therefore, good coal seams and some coal deposits of economic value have formed in the strata called the Ceshui Formation in the Xinhua, Lianyuan and Shaoyang areas of central Hunan.
2) North China Carboniferous-Permian coal accumulation province . The province covers the whole area of Beijing, Tianjin, Hebei, Shanxi, Shandong and Henan and a part or major part of Shaanxi, Gansu, Ningxia, liaoning, Jilin, Inner Mongolia, Jiangsu and Anhui, with a total land area of 1.2 million km2. It is the most important coal province at the present, as its coal resources, retained coal reserve and coal output from State-owned coal mines amount to 22% , 38 % and 60 % of the national totals respectively. Carboniferous-Permian coal-bearing deposits occur all over the whole coal basin, which , has "edges" on the north and south and is tilted and uplifted at the west end and opens to the east, and so is a large dustpan-shaped intraplate basin. Owing to the imbalanced movements of the plate-margin areas on the south and north, the basin uplifted in the south and down-warped in the north in the Carboniferous period and sea water flowed into the basin from the northeast. In the early stage of the Permian period, marine invasion turned to come from the southeast and then from the SSE direction. The transformation of tectonic mechanism controlled the development of coal-bearing sediments and the formation of coal seams. Thick coal seams of the Taiyuan Formation are distributed in the northern zone of the basin, whereas those in the central zone has less economic value because there are complicated hydrogeological conditions and the coal seams are mostly alternated with limestone beds. When sedimentation of the Shanxi Formation happened, the basin came into a mature stage of development, the terrain turned to be homogenied and the deposits of thick coal seams occurred all over the whole area. The southern zone of the basin was a sea area and remained in a littoral environment for a long time, so the coal seams kept forming till the Dafengkouan(late Shihezian) in the area south of 35°N.
3) South China Permian coal accumulation province . The continental crust of South China formed after the Caledonian orogeny was still under the control of two tectonic factors in the Permian period. One was the difference in basement. The basement of the Yangtze paraplateform area in the west was stable, so the coal basin was flat with wide facies zones, while the South China fold system in the east was active, so with rows of paleouplifts, the Basub was a zonal depression with narrow facies zones. The other one was the controling effect of the Caledonian residual Qinzhou trough and its northward extension on the disposition of the environment for coal formation. An epicontinental sea named the Wujiaping Sea was formed in this area and littoral plains with occasional sea water acitivities were formed in its eastern and western wings. The western wing was consisted littoral plains, large depressions and basalt platforms, so good coal fields were formed there, with those in western Guizhou, eastern Yunnan and southern Sichuan as the representatives. The eastern wing was composed of littoral plains and zonal depressions, represented by those in central and southern Hunan and the Pingle depression of Jiangxi . The Kangdian old land at the west end and the Cathysian old land at the east end constituted the boundaries of the coal basin, and continental deposits increased in the direction towards the old lands.
4) South China Late Triassic coal accumulation province. In the Mesozoic era, the difference between the eastern and western parts of South China became more distinct and it was impossible to form a unified coal basin. The Sichuan basin in the west remained wide and open, and influenced by the Longmenshan Indosinian folds on the northwestern side, the coal seams were thick in the west but thin in the east, coal accumulation shifted from west to east and marine facies beds reduced from west to east. The minable coal seams in the Xiaokuangzi Formation and in the lower member of the Xujiahe Formation are distributed in the northwestern part of the basin, while the minable coal seams in the upper member of the Xujiahe Formation are mainly distributed in eastern Sichuan. Besides, in the southwestern part of the basin controlled by N-S faulting, a rift basin, called the Chuxiong Basin, developed on a down-warping background. In the north of the basin the Dukou-Baoding area is an important coal province, where many thick coalbeds occur. In the eastern part strong Indosinian movement controlled the coal-bearing sedimentation of the late Triassic epoch. Sedimentation of this period happened within the range of two caecum-shaped bays where the sea water came from the area between Guangzhou and Shantou and then was divided into two branches by the highland in southern Jiangxi and eastern Guangdong. The east branch stretched to the Zhangping-Jian'ou area and coal bearing strata, equivalent to the Zijiachong Member, developed in Dakeng of Zhangping and than were overlapped by the Jiaokeng Formation in northern Fujian. The west branch flowed to northern Guangdong and southern and eastern Hunan and then turned ENE into the Wuyuan area along the Pingle depression. The marine faces beds reduced gradually from south to north and from west to east. All deposits equivalent to the Zijiachong Member contain good coalbeds, but those overlapped by the Sanqiutian Member or the Menkoushan Formation have only poor coal seams or even no coal at all.
5) Northwest China Early Middle Jurassic coal accumulation province. Sedimentary deposits of the Early-Middle Jurassic period are distributed in northern China: mainly in Northwest China and subordinately in North China. The Early Middle Jurassic period was the most important period for coal accumulation. In this province the total coal resources and retained coal reserves account for 65% and 40% of the national totals respectively. It has a great potential of coal resources because of the low level of its coal resources development. The Erdos, Jungar, Tuha Turpan Hami, Yiming and Tarim Basins are the five large and important coal basins , occupying 80% of the total coal resources of this period. The Erdos Basin used to be a part of the North China basin in the late Paleozoic period, after the Indosinian movement the North China basin underwent a change in tectonic framework: the eastern part uplifted and the western part subsided, and the sedimentary deposits of the Yanchang Formation, the Fuxian Formation, the Yan'an Formation and the Zhiluo Formation developed in succession in the Erdos area, of which the deposits of the coal-bearing Yan'an Formation were laid down throughout the whole basin, covering an area of 200,000 km2. The deposition of coalbeds was controlled by lithofaces and paleogeography.The Yan'an-Fuxian areas in the eastern part of the basin used to be the center of the lake basin with a deep water boby and so was unfavorable for coal formation, while the northern, western and southern parts of the basin used to be shore lakes and river swamps, where a great many minable coalbeds were developed, giving rise to a series of coal fields such as the Shenmu, Dongsheng, Lingwu, dingbian, Huanglin, Binxian and Huating coal mines. The four large coal basins in Xinjiang may be represented by the Junggar Basin, where the direct basement is Hercynides. In this basin the deposition of inland basin sediments started in the middle Permian, coal-bearing sediments developed in the early and middle Jurassic epoch, and a land area of 130,000 km2 is covered by the Shuixigou Group. As an asymmetric own warped basin, the Jungar basin was influenced by the folded mountain system on the southern side and so was deep in the south and shallow in the north. The basin underwent three development stages of being shallow-deep-shallow during the coal accumulation period, so the Badaowan Formation and the Xishanyao Formation in the lower and upper parts contain coalbeds while the Sangonghe Formation in the middle has no coal. The best position for coal forming was the southern margin of the basin, extending for 500 km from Usu in the west up to Jimsar in the east. In this zone there occur 50~60 minable coalbeds with a total thickness of 70~240 m and so the coal reserves are very considerable.
6) Northeast China Early Cretaceous coal accumulation province. This coal province consists of isolated basins concentrated in the northeastern three provinces and eastern Inner Mongolia. A series of basins, with similar characteristics in tectonics, sedimentation and coal accumulation, comprise basin swarms, most of which are of downfaulted type, and others are of down-warped basins with the S-N trending Da Hinggan Range and the Yilan-Yitong fault as the boundaries, the downfaulted basin swarms are divided into three belts, each having its own unique characteristics. The west belt, the largest basin swarm, is located mainly in Inner Mongolia and can be subdivided into two sectors: northern and southern. The northern sector, the Hailar basin swarm, is composed of 30 basins of various sizes. Here the coal-bearing strata are the Jalainur Group, which has two coal formations: upper and lower, developed in the southeastern part and only the upper coal formation in the northwestern part. The Jalainur, Yimin and Dayan coal basins are the representative ones in this sector. The southern sector, the Erlian Basin swarm is composed of 118 basins of different sizes.The coal-bearing strata in this sector are the Bayahua Group, in which the lower coal member is well developed in the east and the upper coal member is distributed extensively. The representative coal basins include the Holinhe, Bayanhua, Shenli and Bayanblulag basins. The central belt is located between the Da Hingan Range and the Yilan-Yitong fault zone. Its northern sector, the Songliao Basin swarm, is composed of 31 coal basins and the coal-bearing strata are the Shahai Formation and the Fuxin Formation. Both the two coal formations are well developed in the eastern part of the belt, with the lower formation being a good coal formation, while in the western part there occurs only the upper poor coal formation. The southern sector, the Chifeng-Tiefa basin swarm , is located in the conjunction area of the North China platform and the Hinggan-Mongolia folded belt. Different basements, however, have not caused distinct difference in the characteristics of the basins. The basin swarm consists of over 10 coal basins, where the Shahai Formation and the Fuxin Formation are coal-bearing strata.The famous coal basins in this stector include the Fuxin, Tiefa, Yuanbaoshan and Pingzhuang basins. The east belt is the Jidong Liaodong basin swarm composed of nearly 10 small and poor coal basins. To the east of the above mentioned faulted basins, there is a down-warped basin, i.e. the Sanjiang-Muling basin, which was developed and formed on the basement of the Wandashan Hercynides and Nadanhada Early Yenshanian folds. The basin suffered marine invasion from Sichote in the Late Jurassic, leading to the formation of coal bearing deposits during the subsequent marine regression. The coal strata are the Chenzihe Formation and the Muling Formation. The tectonic activities after the coal forming process resulted in the separation of the coal basin into the independent Jixi, Shuangyashan and Qitaihe coal fields, which are the important coking coal base in the Northeast.
7) Tertiary coal accumulation province. It actually involves two coal-forming epoches and consists of four coal accumulation subprovinces. There are two Paleogene coal accumulation subprovinces. The northern subprovince consists of two graben systems formed by two branches of the Tanlu fault. The eastern graben system, the Fushun-Mishan fault, is composed of the Fushun, Meihe, Dunhua and Hulin fault basins; the western one, the Yilan-Yitong fault, embodies the Yitong, Shulan, Wuchang fault basins. Besides, the Huangxian basin in Jiaodong Penlinsular may also have some relationship with the Tanlu fault. The southern subprovince is represented by the coal basins in Guangxi, of which the Baise basin, located on the southwest side of the Youjiang fault, is an important semigraben basin controlled by the fault and is better coaliferous in its south wing. The Tertiary coal province has two Neogene subprovinces: western and eastern. The western one, the Sichuan and Yunnan subprovince, has over 150 coal basins including the famous Xiaolongtan down warped basin and the Zhaotong erosional basin. The eastern one, the Taiwan subprovince, is situated at the western foot of the Central Range and is made up of miogeosynelinal sediments with a total thickness of 5,500 m. However, the coalbeds in them are not thick.
(5) Characteristics of coal resources disposition
From the geographical distribution and geological conditions of coal resources mentioned above, we can see the characteristics of coal resources disposition as follows:
1) Coal resources show a revered correlation with the development level of regional economies. Coal resources are mainly distributed in the economically underdeveloped provinces (autonomous regions)of Shanxi, Inner Mongolia, Shaanxi, Xinjiang, Guizhou and Ningxia, which have 82.8 % of the national total coal resources and 82.1% of the country's retained coal reserves, while the most developed 14 coastal provinces(municipalities and regions)of Beijing, Tianjin, Hebei, Liaoning, Shandong, Jiangsu, Shanghai, Zhejiang, Fujian, Taiwan, Guangdong, Hainan, Hong Kong and Guangxi, where much more energy is needed, are far from self-sufficient in coal resources since they only have 5.3 % of the national total coal resources and 5.5 % of the national total retained coal reserves. The coal production bases are far from the consuming markets and the distance will increase along with the westward shift of the construction focus of the coal industry. So, the coal transportation has become an unneglectable factor for it constrains the development of the coal industry and thus the rapid growth of the national economy .
2) The distribution of coal resources is reversed to that of water resources. China is relatively poor in water resources and its per-capita occupancy of water resources is 1/ 4 of the world's average. The distribution of water resources is imbalanced geographically. The 17 provinces(municipalities and autonomous regions )in northern China have only 21.4 % of the national total water resources and the region to the west of the Taihang Mountain has less water resources than that to the east. This shows a reserved correlation of the distribution of water resources to the distribution of coal resources. Water sources for industry and civil use have become a prominent problem in the process of coal production, washing and dressing. Meanwhile, the lagre-scale mining activities have increased water consumption. Consequently, the already fragile ecological environment has further deteriorated and the process of desertification has accelerated . How to achieve a coordinated and sound development has indeed become an important topic.
3) High-grade power -generating coal resources are abundant but high-grade anthracitic and coking coal resources are insufficient. The proportions of the retained reserves of various coals ( by the end of 1997 ) are shown in Table 2.2.3.From Table 2.2.3 we can see that noncoking coals occupy a large proportion in terms of China's retained coal reserves. The low-grade metamorphic bituminous coals(flame coal, noncaking coal, weak caking coal and unclassified coal)in particular, account for 42.5 % of the national total. They have common characteristics of low ash content, low sulfur content and good washability. In the major coal mines, for noncaking coal, ash content is 10.85 % and sulfur content 0.75 %; the average ash content in weak caking coal is 10.11 % and sulfur content 0.87 %. For instance, the famous weak caking coal from Datong and the noncaking coal from Shenfu and Dongsheng are praised as natural clean coal with ash contents of 5％~10 % and sulfur content < 0.7 %. They are not only high-quality power-generating coals, but part of them can be used as raw material for gasification. Anthracitic coal amounts to 11.5 % of the national total retained coal reserves and is concentrated mainly in Shanxi and Guizhou provinces. In Shanxi province the coal from the Shanxi Formation has low ash and sulfur contents and that from the Taiyuan Formation is high in sulfur content. Most coal in Guizhou has high sulfur content. Coals used for coking are estimated at 25.4 % of the total retained coal reserves. They are dominated by gas coal, which makes up 40.6 % of the total reserves of coking coals and the three basic coal types of fat coal, coke coal and lean coal account for 18.0%, 23.5 % and 15.8 % respectively. Most of the coking coals have a medium ash content and over 20 % of the coking coals contain over 2 % of sulfur and show poor washablity. All these show that quantilty of high-quality coking coals is small.Table 2.2.3Retained reserves of diffferent coals(×109 t)
4) Coalbeds are relatively deep buried with few of the reserves suitable for exploitation by opencut mining. There are 13 opencut mining districts(or coal fields)in China and the reserves for opencut mining amount to 41.243 billion tons, 4.1 % of the national total retained reserves. In the Carboniferous-Permian coal provinces in North China, only several coal fields can be mined in open pits, like the Pingsuo coal district of Shanxi, Hedong coal field and Jungar coal district of Inner Mongolia. In the Early-middle Jurassic , Early Cretaceous and Tertiary coal fields, where bituminous coal of low metamorphism and lignitic coal are predominant, more resources are suitable for opencut mining. Such coal fields include Shenfu of northern Shaanxi; Dongsheng of western Inner Mongolia, Shengli of central Inner Mongolia and Yimin, Holinhe, Baorixile and Yuanbaoshan of eastern Inner Mongolia; Xiaolongtan and Zhaotong of Yunnan as well as some mining areas of Xinjiang.In the reserves for opencut mining, the coalification is commonly at a low degree with the domination of lignite. The retained coal reserve for opencut mining amount to 34.252 billion tons, of which gas coal makes up 12.9 %, flame coal 11.7 %, noncaking coal 0.5 % and lignitic coal 74.9 %.
5) There is a great variety and abundance of paragenetic and associated minerals. There are quite a few categories of paragenetic and associated minerals in the coal strata and coalbeds. Among them Kaolin is distributed in coal strata of all ages but mailnly in those of the Carboniferous-Permian period in North China. Its representative occurrence localities are Datong and Jiexiu of Shanxi; Xinwen of Shandong; Tangshan of Hebei; Pubai of Shaanxi; Jungar of Inner Mongolia; Yangquan of Shanxi; Jiaozuo of Henan, and the Huainan and Huaibei of Anhui. Besides, kaolin occurrences have been found in coal districts of Northeast China, Xinjiang and Guangdong. According to incomplete statistics, up to now the explored reserves of kaolin in coal strata amount to 1.673 billion tons, prospective reserve 5.529 billion tons and predicted resource 11.086 billion tons. Kaolin deposits are of different scales from medium to super large. In China almost all fireclay comes from coal strata and 254 occurrence localities have been found in Shanxi, Henan, Hebei, Shandong and Guizhou with a retained reserve of 2.013 billion tons, 86 % of which is in the coal fields of North China. Most of China's bentonite deposits are located in Jilin and Guangxi with large reserves of high-quality bentonite. Of the total 31 large deposits 25 occur in coal strata with explored reserves of 888 million tons. The diatomaceous earth is mainly of the late Tertiary age and mostly associated with lignite. Its prospective reserves are 2.2 billion tons and explored reserves 270 million tons, of which 70.5 % is from coal strata. Most of oil shale in China is associated with coal and clay, 62 localities of its occurrences have been found with explored reserves of 32 billion tons and predicted resources of 727.7 billion tons. In terms of sulfur for industry, 67.6 % is from pyrite. Incomplete statistics show that in the whole country there are 240 occurrences of associated pyrite with retained ore reserves of 3.46 billion tons and 33.9 % are from coal strata. In addition, high-sulfur coal strata contain much sulfur and the state-owned coal mines have verified high-sulfur coal reserves of 11.2 billion tons with an average sulfur content of 3.5 %. Suppose the pyritic sulfur makes up 55 % of the total of sulfur contained, then it is estimated that there are 215 million tons of effective sulfur , equal to over 600 million tons of standard sulfur minerals. The reserves of gypsum minerals of China rank the first in the world and over 500 occurrence localities have been found with retained reserves of 57.4 billion tons, of which 11.57 billion tons are in coal measures and their overlying and underlying strata. Many useful minerals mentioned above occur as gangues in the coalbeds, or as their roof and floor beds, and some minerals from separate layers near coalbeds, so they can be mined together with coal or separately by using coal mining technology and equipment with slight modifications in the production and transportation systems. In this way the resources will be fully utilized, investment will be greatly saved and the lifetime of coal mines will be extended.