Vertical variation of trace elements and its relation to the water-bearing capacity of Ordovician st

leonlineatwww.sciencedirectcomMININGScienceDirectSCIENCE ANDTECHNOLOGYELSEVIERMining Science and Technology 19(2009)0166-0169www.elsevier.com/locate/jcumtVertical variation of trace elements and its relation tothe water-bearing capacity of Ordovician strata,n Datun coal fieldLIU Huai-zhong, HAN Bao-pingSchool of Resources and Geoscience, China Universiry of Mining& Technology, Xuzhou, Jiangsu 221008, ChinaSchool of Environmental Science and Spatial informatics, China University of Mining Technology, XuzhouJiangsu 221008, ChinaAbstract: We tested for fourteen trace elements in samples collected from the Ordovician strata in Datun coal field. The verticalconcentration variation of these trace elements is reported. The relationship of the variation to the water-bearing capacity of theOrdovician strata is discussed. The minimum concentration of eleven(of 14 total) trace elements appears in the lower Majiagouformation. The maximum concentrations mainly appear in the Badou and Jiawang formations: eight maxima are located in Badouand four more are in Jiawang. The study of karst development and the water-bearing capacity of Ordovician strata shows that karstis well developed in the Majiagou formation and there is a consequent high water-bearing capacity in this formation: Badou andJiawang formations are contrary to this situation. the results illustrate that the minimum concentrations of most trace elementswithin certain Ordovician formations can be taken as strong evidence for the existence of a well developed karst and a high wa-Keywords: Ordovician; trace element; water-bearing capacity; Datun coal field1 IntroductionPingitore maintains that some behaviors of Zn andMn can be seen as important signs in early and laterGeochemists usually refer to those elements in the, limestone diagenesis. Huang also believes there arelithosphere whose concentrations are only l, or less more Sr and Mn and less Fe in linmestonethan 0.1, percent as trace elements. these are also undergone freshwater cementation diagenesis as com-called micro-elements, impure elements, rare elepared to metasomatic dolomite. Studies by Li showments or the like. Their concentration units are often that there is less Sr, Na and Mn in limestone whenexpressed as parts per million or parts per billion. freshwater takes part in its diagenesis. On the otherUnlike O, Si, Al, Fe, Ca, Mg, Na, K or Ti, the conhand, there are more of these elements in limestonecentrations of which taken together account for about associated with seabed diagenesis. Furthermore,99 percent of all rocks or minerals, the trace elements, compared to limestone, dolomitisation maked the Naespecially the lanthanides, tend to be used as indica- content increase, and the content of Sr and Mn de-have the same function as isotopes do/l-a"ey almost crease. According to Lis research on the geochemicaltors or fingerprints incharacteristics of trace elements in two different or-The studies of the trace elements in sedimentary dovician sections of the northern Anhui province oftrata are done to determine the source and surround- China, karstification contributes to the scattering andings of the strata Indices used in these studies might moving of almost all trace elements. As a result, tracebe the relative content of Boron, the ratio of B/Ga, elements and lanthanides occur in higher concentra-the ratio of Sr/Ba, the amounts of B, Rb and Ga, and tions in the bare sections typical of karst areas whileso othey are less concentrated in buried sections in thoseThe study of trace elements in carbonate rocksareas with less karst 91olves many aspects. Many scholars have discussedDatun coal field is located in Pei county in north-the role trace elements play in diagenesis. Land et westal. point out that Na can be used as an indicator for elem中国煤化工 from the ordothe salinity of solutions involved in diagenesisclanCN Ge Cambrian(E3dCorrespondingauthorTel+86516-83883907:E-mailaddressliuhuaizhong@xinhuanet.comLIU Huai-zhong et alertical variation of trace elements and its relation to the water- bearingdescribed in this paper shows the vertical variation of tions in the various sections. The data are from thethe trace elements and their relation to the wa- results of sample testing and statistical analysis.ter-bearing capacity of the different formations.able 1 Statistics from test samples from bores 972 and 9762 Vertical variation in trace elementsNo. BoreStratumThickness(m) SamplenumbeBoreholes drilled through the Ordovician stratumin the Datun Coal Field revealed the presence of theUpper of O,m58.77Badou formation(Ozb)and the Gezhuang formation9272Dee) of the middle Ordovician series 70.25 m and976 Daquan sect of o892341.43 m thick, respectively (borehole No. 972)976 Zhaisan sect of lsBorehole No 976 revealed the presence of the Ma-jiagou formation(Olm)58.77 m thick in its upper sec-10304tion and 92.72 m thick in its lower section. Also seenwere the Xiaoxian formation(O), thickness of 89.23m in Daquan section and 149.01 m in Zhaishan setion, the Jiawang formation(On), thickness 7.68 m,By computing the average content of each tracethe Sanshanzi formation(01,), thickness 103.04 m, as element in the segments, we can find how the con-well as the Fengshan formation of the upper Camcentration varies in the vertical direction. These re-brian series(E3d with a thickness of 60.78 m. Allsults are shown in Table 2. Fig. I illustrates how thesegments of the Ordovician strata were seen in both concentrations of typical trace elements change.Inholes( Because of a lacuna, no strata of the upper Fig. I, of Y axis, I means Ozb, 2 O2e,3 Upper Olm,4Ordovician appear in this area). The test samplesLower Olm, 5 Daquan O1x, 6 Zhaisan Oix, 7O1j, 8Otaken in the different strata are listed in Table 1. This and 9 e3table shows the variation of trace element concentra-Table 2 Average trace element content in the Ordovician2019%67200147145569.7251458387.125Upper of Oim201.1314243840442.328Lower of Olm2306331.03533.329Daquan sect of Oix 161. 69469535281340.52235569976 Zhaisan sect of On 174.37313.96860.328l6.500oo∈3072751614753172683.4585230024320230773.2315145CuPbCoMo4991746.4611806115.619.14029753Upper of Olm574632321314022Lower of O,m0Daquan sect of o3996226.51727,26169592877976 Zhaisan sect of OI 29. 15926.78443.9801263209011901877I32940.45022.204913474303.441.7200.352The maximum and minimum concentrations of 14The vertical variation in trace element concentraace elements appear in a certain order. The mini-ve factors related tomum concentration appears in the lower Majiagou diagenesis of the surroBut the variation hasformation. There are 11 of the 14 elements that fol- evenlow this distribution pattern. Concentration maxima the凵中国煤化工mutBappear in the Badou and Jiawang formations. Eight of tion iCN MH Gelopment and thethe 14 elements have their maximum in Badou while water-bearing capacity or some ordovician strata, inanother four have maxima in Jiawang. The statistics the next part.from this ahalysis appear in Table 3.7062612.6374323Concentration(ug/g)(b)RbFig. 1 Trace element concentration versus vertical positionTable 3 Concentration extrema in various strataStratumUpper Oim Lower Olm Daquan of OixZhaisan of oNZrMinCount of maxCount of min3 Relation between the vertical variation Oab is weak.conclusion is that the water-bearing capacity of theof trace element concentration and thewater-bearing capacity of various strata 3.2 Majiagou formation(Olm)The thickness of the Om varies from 58.77 mEleven of the 14 trace elements have their mini- (bore No 976)to 101.9 m(bore No 979). The litholmum concentration in the Majiagou formation. Eight ogy of this segment is powder and sand crystal dolo-haymaximum concentration in the Badou for- mite, leopard-like dolomite limestone, bioclast micmation and four more have maxima in the Jiawang rite and partially karst breccia, which is a heavy layerformation. We now consider the relationship between The karst is developed, features such as dissolutionthe vertical variation in a trace element and the wa- caves and crannies at depths of 470 m, 495.7 m andter-bearing capacity of the strata it exists in. The dis- 540 m have been observed in Kongzhuang Minecussion is based on an analysis of the hydrologicnorth ventilation shaft; calcite cluster crystals can becharacteristics of the three strata[)seen here as well3.1 Badou formation(O2b)The thickness of the Olm ranges from 89.79 m(bore No979)to 92.72 m(bore No 976). The lithol-The thickness of the remnant Ozb ranges from ogy of this segment is bioclasts, powder and sand18.02 m(bore No 8701)to 70. 25 m(bore No 972) crystal micrite and micrite in the upper side Bioclastsdue to denudation in bores 976 and 979. The O2b con- aresists of micrite limestone and leopard-like dolomite cods中国煤化工ies, and so onlimestone of medium thickness. The unit influx of LeopCN MHGars in the middlethis formation is 0.0901 L/(s. m) seen in bore 972. The palc suuctuic uI this was formed bymineral content of the water is 2.011 g/L and the wa- dolomitization of wormholes. Then bioclasts, powderter quality is of the SOa-CaNa type. Accordingly, the and sand crystal limestone and leopard-like dolomiteLIU Huai-zhong et alertical variation of trace elements and its relation to the water-bearinglimestone exist in the lower part of the formation. the studied trace elements have their minimum con-Caves and crannies are well developed in this seg- centration in the Majiagou formation. Eight tracement. For example, the height of the biggest dissolu- elements have maxima in the Badou formation andtion cave is 90 cm, seen in bore 979.another four have maxima in the Jiawang formationKarst is well developed in the Olm. The total 2)Water-rock interaction during the course of karstthickness of dissolution caves seen in bore 979 is development can contribute to the eluviation of trace6.24 m in the Olm section. Mud flow leakage is se- elements, which causes the trace element concentra-vere in this formation in both bores 976 and 979. The tions to be lower where karstell developedakage rate was 10.12 m h in 976. The unit influx in Therefore, the rule is that most trace elements have976 was 0.658 L/(s m), with a permeability coeffi- low concentrations in certain Ordovician segmentscient of 0. 1098 m/d, a mineral content of 4.029 g/L Low trace element concentrations can be used asand water quality of the SO4-CaNa type. In bore 979 solid evidence for well developed karst and a highthe unit influx was 1.102 L/(s-m)(OIm and O2g) and water-bearing capacitythe permeability coefficient was 0.431 m/d. The unitnflux at the Ordovician stratum seen in bore 979 was Acknowledgements1.896L/(s-m)and the permeability coefficient was0.285 m/d. The Ordovician stratum in bore ShuHere we express our sincere appreciation to serhas a unit influx of 3.695-3.888 L/(s-m). These data engineer Wang Chuanlin and Wang Cunbao of Datunindicate that the water-bearing capacity of the Olm Coal-electricity Co. Ltd for their help during theformation is high.course of the sampling and data collection. As well3.3 Jiawang formation(Oy)we appreciate the engineers of the Geology Instituteof CAS for their hard work in providing the highThe Oy ranges in thickness from 5.23 m(boreNo979)to 7.68 m(bore No 976). The lithology of quality test results.the upper Oy is argilliferous micrite dolomite andpowered crystal limestone, while the middle Ovcon-sists of calcite dolomite containing earth. Micrite or [1] Zhao Z H. Theory of Trace Element Geochemistry Bei-powered crystal dolomite exists in the lower parts.jing: Geological Publishing House, 1998. (In ChineseThe water-bearing capacity of this formation is ex- [2] Cai Z F, Zhu H M. Conspectus of Trace Element Chemtremely weak because it is less thick and has a highistry. Beijing: Atomic Energy Press, 1994. (In Chinese)content of argillaceous and poorly developed karst[3] Wu S B. Sedimentary facies and depositional model ofIt can be inferred from this analysis that the mawulabo formation, upper permian series in bogedajiagou formation, especially in its lower segment, haspiedmont depression, junggar basin. Acta Sedimena high water-bearing capacity due to the highly de-tologica Sinica, 2001, 19(3): 333-338.(In Chinese)veloped karst manifest by dissolved pores and wa- (4 Land L s, Hoops K Sodium in carbonate sedimentster-eroded caves. This means that the intensity ofand rocks: a possible index to the salinity of diageneticolution. J Sed Petrol, 1973(43): 614-617.water-rock interaction in this formation has been very (5 Pingitore JN E The behavior of Zn+and Mn2+duringgreat and that during the course of this interactionmany trace elements were leached into the ground-rol,1978(48):799-814ory and application. J Sed Pet-carbonate diagenesis: thewater. Hence, the concentrations of the ll trace ele- [6] Huang Z C, Yang S Y, Chen Z N The mineralogy com-nents is relatively small and most of the minimumparative study of protodolomite andnatic dolo-concentration values appear within this formation. Tomite. Science in China, 1996, 26(6)the contrary, the Jiawang formation consists mainlyof lark marlite, argillaceous dolomite, mudstone and (7 Li Y, In@c* diagenesis.Experimental PetroleumWang D X Geochemical characteristicsshale, including some tectonic breccia. Eluviation ofGeology, 1995. 17(1): 55-62. (In Chinesetrace elements from the strata is comparatively slightbecause of the argillaceous content, fewer wa- [8] LiDL, Wu GM Ree geochemical characteristics and itspaleokarst environmental marks of Ordovician in north-ter-eroded caves and the weakness of the water-rockem Anhui. Coal Geology Exploration, 1999, 27(4)Thus, many trace elerhave the10-15.(In Chinese)maximum concentration here in this stratum. This [9] Li D L Comparison on the geochemical characteristicssituation also occurs in the badou formationof karstified rocks from two Ordovician profiles innorthem Anhui. Carsologica Sinica, 1999, 18(4): 3224 Conclusions323. (In Chinese)中国煤化工 Characteristics and1)An analysis of the variation in traceconcentrations in the Ordovician series allows a gen-C N MH Grsity of Mining anderalized rule to be developed. It is seen that eleven of