Resources of Kaolinite Rocks in China Coal Measures

Journal of Chinu I'niversity of Geosciences. Vol. 11. No. 2, P. 154-157. June 2000ISSA J002-0705China Coal measures*“Resources of Kaolinite rocks ilDepartment of Resources Engineering, China University of Mining and Technology, Beijing 100083Xu HongliangMaterial Department, Zhengzhou Universily of Technology, Henan 450002ABSTRACTThe proved reserve of kaolinite rocks in China coal measures is about 1.673 billion tons. Theypes of kaolinite rocks contain tonstein, flintclay and soft kaolin. Their origin modes include alteration of volcanic ash, terrigenous clay deposit and weathering of coal and adjacent rocks. Theorganic matter and organic acid play an important role in the formation of kaolinite rocks of coaasures.the difference in properties between kaolinite rock and traditional kaolin requires difKEYIt processingoal measures, kaolinite rocks, reserve originThe kaolinite rocks are very abundant in China coal mea- Region. Table I shows the reserve amount of differentuality for industrial use. The geological feature, occurrence, ing strata of China is about 1. 673 billion tons. The total re-origin and processing techniques are largely different from serve is estimated by about 18 23 billion tons, which occupieshose of the traditional kaolins. The kaolinite rocks in China about 59 of worldwide kaolin(Yang et al., 1996). The tocoal measures are marvelous. but a large scale kaolinite de. tal proved reserve of kaolin (including traditional soft kaolinsit is rare in the world. The origin of kaolinite rocks in the and kaolinite rocks in coal mcasures )of all occurrences in Chicoal measures is under debate for a long time (Liu and Zhang, na is about 3. 048 billion tons of which 34.9 is the kaolinite1997: Liang. 1995: Bohor, 1993: Feng, 1989: Wiliamson, rocks of coal measures.1970)and no concluding remark is obtained so far.DISTRIBUTION AND RESERVE OF KAOLINITE ROCKS80IN CHINA COAL MEASURESerous. Late Triassic. Jurassic. Early Cretaceous and Tertiary 4al measures of China, espercially in the Permo- Carbonifer20s(Fig. 1). The richer the coal, the more abundant theIsLiaoning. Jilin. Shanxi, Henan. Shandong. Hcbei. AnhuiFigure l. Distribution frequency of kaolinite rock at dif-and Inner Mongolia Autonomous Regions, The most abun-ferent agesdant beds are located in the Permo-Carboniferous coal-bear-ing strata in Shanxi Province and Inner Mongolia Autonomous TYPES AND FEATURE OF KAOLINITE ROCKSr This paper is supported by National Natural Science Foundation of sures of China. Their geological features are listed inTable 2.Manuseript received Fehruary 14. 2000.Mineral中国煤化工Manuscript accepted March 10, 2000.CNMHG often more thanResource of Kaolinite Rocks in China Coal Measures155and up to 90 %-95 n in many good quality kaolinite SiO: and Al2O), which have the great influence on its usefulrocks of coal mcasures. The accessory minerals include 1/S ness. The molar ratios of SiO2/Al2 O, in kaolinite rocks aremixed-layer mineral. NH.-lllite. boemite, diaspore, chlorite, very close to the ideal value of kaolinite composition (the idealquarIz, feldspar. zircon, tourmaline. rutile. The Hinkley In ratios of Si(/AL2 O, for kaolinite are 2)(Table 3). The condex (HI) of kaolinite varies in different kinds and origins of tent of harmful impure clements, such as Fe Oa and TiO, arekaolinite, with the highest for the soft kaolin clay which is be- very low in the rocks, indicating that the kaolinite rocks intween 1. 33 and 1. 65 and the lowest for the terrigenous kaoli coal measures have very pure quality and great industrial usee which is between 0.45 and 1. 13. The Hinkley Index oftallinc and cryptocrystalline kaolinite in tonstein is be- DIFFERENCE OF KAOLINITE ROCKS IN COAL MEA-78 and 1.12SURES FROM TRADITIONAL KAOLINThe kaolinite rocks and traditional kaolin are very differTABLE I RESERVE AMOUNT OF KAOLINITEent in some propcrties(Table 4), which causes the differentROCKS IN SOME REGIONS10 processing techniques in industrial usc.perspectIve prognostIcregionrEsErveORIGIN OF KAOLINITE ROCKS IN COAL MEASURESInner Mongolia 82 389.6132663Origin ModeLiaoningf693.68528.134422Based on the mineralogical, petrologic and geochemical231,69.8evidence and the occurrence of the various types of kaoliniteHel3245rocks, three origin models are suggested as follows.31036.19701064.14Origin of bed-B kaolinite rock (flint clay )in Huainan co1146.2l5000qinghanl1132,9713022.941577.8This bed of kaolinite rock of 2-6 m in thickness,widespread and stable, is located in the lower part of139.8Henan20380Xiashihezi Formation of Upper Permian which was depositedShandongin a lower delta plain environment(Liu and Zhang. 1997; LiuAnhui051.8et al., 1994). Bed-B kaolinite rock can be divided into four15728425types: cryptocrystalline, silty. ferriferous, pelletoid and26oolitic. Among them, the oolites and pellets, which are com-Guizhi1.536plex aggregates of microcrystalline kaolinite and organic maSuchuanters, are very distinctive in microstructure, whose kaolinite20001220content is as high as 95 %-10D % Studies of sedimentoloHainan2000gy, geochemistry and paleontology show that the kaolinit167263.195528891 391.9 was mainly derived from the weathered materals in sourcerocks which were transported and deposited in a lacustrine enveral texture compositions were identified in the kali- vironment of the delta plain ( Liu and Zhang, 1997).Thenite rocks using polarized light microscope: intraclast, piso- widespread red kaolinite-bearing mudrocks above or belowlite,oolite, pellet, vermicular crystals, pseudomorphic crys- this kaolinite rock bed indicate that rubefication was developedpisolite and oolite are mostly found in"flint clay type",arranged in radiation around the grains were crystallized a atal after feldspar and biotite, matrix and organic matter. The in parent rocks in the source area. Some crystals of kaolinwhereas coarse vermicular and pseudomorph crystals are in alumino silicon gel. The organo-clay complcxcs and thenstein type.organo Al (or Si)gel played an important role in the long-disance transportation of the kaolinite-forming materials. TheChemical Compositionorigin model of this kaolinite rock bed is shown in Fig. 2.The ma jor chemical compositions of kaolinite rocks areTABLE 2 TYPES AND) THEIR FEATURES OF KAOLINITE ROCKShicknessstability textureunstein n the roofs, partings and floors of coal sear0.1-0.5 m ior parring type; stable cryptocrystalline, crystalline0.5-2.0mforflint clay Independent beds; not ad acent to the coal beds: 2-6mu中国煤化工wie,plwft kaolin assocated with surficial weathered coals0.5-3.tmCNMHG with highcrystallinityIiu Qinfu andTABLE 3 MASS FRACTION OF MAJOR ELEMENTS OF KAOLINITE ROCKS IN SEVERAL ARE/Ai, O, Fe O, TiOxSiO2/Al2O344.300.50ShouzhouZhungar44.38.230.490.0.42.47.4lHuaibei42,9740.860.71280.341.79-1.9314.3944.79ShangdianI 44 68 38.80 0.7404Shangdian2 43 71 37.TABLE 4 DIFFERENCE BETWEEN KAOL INITE ROCKS AND TRADITIONAL KAOLIN IN SOME PROPERTIESpropertieskaolinite rocksblocksgrey white, soft claymineralogymainly kaolinite, a little clastic minerals(quartz, mainly kaolinite or halloysite, generally mure clastic mInerals (quartz, feldspar andcontent of kaolnite generally more than 85 %egenerally less than 85%cryptocrystalline to coarse crystalsalteration of volcanic ashes, or sedimentation of weathering of igneous rocks (generally grante ) alter-terrigenous kaolin in coal basination by thermal fluid, sedimentation elc.other propertieslow dispersion, stickiness and plasticityigh dispersion, stickiness and plasticityOrigin of tonsteinsbe transformed and crystallized into kaolinite with the leach-onsteins.commonandwidespreadinPermo-carbonif.ingoffofthealkalineoralkalineearthionsandsiliconundererous coal measures of North China, usually occur in the the influence of organic acids. Figure 3 is the genctic model ofoofs, partings and floors of coal seams. This kind of rock is tonsteinvery good quality and widely used by many kaolin factories in REE are useful to indicate the ancestor minerals of kaoli-China. For the past decades, more and more tonsteins have nite- forming. The REE analysis shows that kaolinite rocksbeen reported by many geologists all over the world. They are formed by the alteration of acid volcanic ash are clearly richgenerally considered to be of volcanic origin (Williamson. LREE and their LREE/HREE ratios are bet ween 8. 25 and1970). At present, there is a tendency among geologists 10 18. 25, whereas the terrigenous kaolinite are poor in LREEexplain all the kaolinite rocks in coal seams by volcanic origin. and their LREE/HREE are between 2. 24 and 5. 98. The negHowever,it is hard to imagine that some kaolinite rock beds ative anomaly of Eu is for the kaolinite rocks derived from acidup to 0.5-2 m thick can be formed in this way, The authors, parent rocks, whereas positive anomaly of Eu is for kaoliniteherefore, suggest that the process to form tonsteins is com- rocks derived from neutral parent rocks.plicated and associated with many factorsinterfacAI(S) complexof clay mineralsFigure 2. Origin model of bed-B kaolinite rock in Huainancoalfield of Anhui Province.4 biotite and feidsparThe formation of tonsteins depends on two important factors tone is the primary kaolinite- forming materials and theother the transformation and crystallization of kaolinite in aFigure 3. Origin model of tonsteins.swamp environment at the diagenetic stage. Two types oforiginal materials can be transformed into kaolinite in a swamp Origin of soft kaolin clay associated with weathered coalsenvironment and at a diagenetic stage one is the terrigenous中国煤化工 high content of carand aluminosilicate minerals such as feldspar and biotiand with high HI.and the other is the volcanic ashes fallen into swamps. These The kCNMHGlow concentration oforiginal materials, which entered into the swamp basin, could Si-Al sol which were formed by the dissolution of surroundedResource of Kaolinite Rocks in China Coal Measuresrocks adjacent to weathered coal under the influcnce of fulvic(4)Micro-organism activity that results in aacid during the coal weathering. It is the low concentration of environment. Some micro organism canSi-Al sol and low temperature and pressure in ground environ- acid that may greatly dissolve the surrounded mineralsment that result in the formation of well-ordered kaolinitethrough the slow and regular arrangement of Si and Al ions in CONCLUSIONcrystallization(Fig. 4)The kaolinite rocks in the coal measure of North Chinaare in a very pure quality, and diversified in nature and originThe parent materials for kaolinite-forming and basin enviroby organicfactors for the formation of kaolinite rocksof S n ikaolin in coal measures. The former can be terrigenous transporta-ion minerals(such as clay minerals, feldspar and biotitevolcanic ash, leaching products formed by dissolution of previFigure 4. Origin model of soft kaolinite claous rocks affected by the organic acid of weathered coal. Thelatter supplies a suitable acid environment for the alteration ofRoles of Organic Matter and Micro-organism in Formation ofimportant role in the formation and transformation of kaolin-The micro-organism and organic matter are very impor. ite.rant in the formation of kaolinite rocks or kaolin clay inREFERENCES CITEDbasins. The role of organic matter includes followsBohor B F, Triplehorn DM, 1993. Tonstein: Altered Volcanic Ash(1)Creating the acid environment by organic acids.Layers in Coal-Rearing Sequences. Geological Society of Ameri-Many researches on modern and ancient swamps show thathe ph value in swamp or peat water ranges from 3. 3 to 7. 5. Feng B, 1989. Kaolinite Rock Altered by Volcanic Ash of PermoThis condition is suitable for the formation and preservation ofCarboniferous. North China. Sedimentologica Sinica, 1(1): 101kaolinite. At the diagcnetic stages organic matter can alsoproduce thLiang S, 1995. Study on Claystone Partings Altered by Volcanic Ashgiving rise to a suitable acid microenvironment for the crystin Coal Accumulation Area of North China. China Coal Geolo.ization and transformation of kaolgy,7(1):59-63Liu Q, Zhang P, 1997. The composition and Mineralization Mecha(2)Accelerating the solution of aluminosilicate minerals.nism of Kaolinite Rocks in Late- Palaeozoic Coal MeasuresThe aluminosilicate minerals, such as feldspar, mica. depositNorth China. Beijing: Marine Press. 95-102ed in swamp environment. will be greatly decomposed in the Liu Q. Zhang P, Yang X, 1994. Microscopic Characteristics and Ori-fluence of organic acids, forming organo-Al and organo-Sietoid Kaolinite Icomplexes providing affluent and basic materials for the forHuainan Coalfield. Anhui Province, East China. Scientia gea-mation of kaolinite. Al preserves coordination number six un-logical Sinica, 3(1):51-58der the influence of organic compounds, which is indispens Williamson I A, 1970. Tonstein Their Nature, Origin and Usesable for the kaolinite to be crystallized at low temperature andMining magazine,22(2):120-125,22(3):203-211Yang X, Wang X, Shun W, 1996. China Coal Industry Encyclopaediapressure.(3)Prompting the transformation of layered minerals.(Geology Survey Volume ) Beijing: China Coal IndustryThe very abundant organic matter or organic acid makes itasy for non- kaolinite clay minerals (such as mont morilloniteillite and biotite)deposited in swamp basin to be transformedinto kaolinite under acid conditions. The formation of watersolubleKCa, Mg and Si ions to a great extent from non kaoliniteclay minerals, thus accelerating the transformation process中国煤化工CNMHG