Continental hydrothermal sedimentary siliceous rock and genesis of superlarge germanium (Ge) deposit

Science in China ser D Earth Sciences 2004 Vol 47 No. 11973-984Continental hydrothermal sedimentary siliceous rock andgenesis of superlarge germanium(Ge) deposit hosted incoal: a study from the Lincang Ge deposit, Yunnan, ChinaQI Huawen", HU Ruizhong, SU Wenchao, QI Liang& FENG Jiay1. Key Laboratory of Ore Deposit Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China2 Department of Earth Sciences, Nanjing University, Nanjing 210093, ChinaCorrespondenceshouldbeaddressedtoQiHuawen(email:qihuawen@sina.com)Received December 23. 2003Abstract There are abundant hydrothermal sedimentary structures and plant fragment fossilsin the siliceous rocks from the Lincang Ge deposit. the major element compositions of thesesiliceous rocks are characterized by high content SiO2, low TiO2 and Al2O3 concentrations, andlow AV(Al+Fe+Mn)ratios (0.010 on average). The siliceous rocks are distinctly enriched in Ge,Sb, As, W, and secondly enriched in Cs, U, Mo and Tl. Their total REE content are generally lessthan 1ug/g, LREE relatively concentrated, and the values of Eu anomaly and Ce anomaly varyfrom 0.452 to 5.141 and 0.997 to 1. 174, respectively. Their NAS-normalized REE patterns areplain or left-inclined. The Oxygen isotope compositions of these siliceous rocks are similar tothose of the hydrothermal siliceous sinter. the above characteristics, as well as the geologicalsetting of the deposit, indicate these siliceous rocks formed in continental hydrothermal environment. As the interlayer or cliff of the Ge-rich coal seams, siliceous rocks tightly contacted withore-body, and the contents of Ge in siliceous rocks vary from 5.6 to 360 ug/g (78 ug/g on aver-age). The Ge content increased in coal which close to the siliceous rocks. With the increase ofGe content, the typical trace element ratios (i.e, Ge/Ga, Nb/Ta and U/Th) and REE patterns ofGe-rich coal are more close to those of the siliceous rocks the ge concentrated in coal seamsof the Lincang Ge deposit might be transported by the hydrothermal water, which demonstratedby the siliceous rocks, during the coal-forming processesKeywords: siliceous rock, continental hydrothermal sedimentation, superlarge Ge deposit, LincangDOI:10.1360/02yc0141The study on marine hydrothermal sedimentation tion and metal mineralization. The Lincang Ge deposittends to be perfect at present, and a suit of hydrother- hosted in coal with independent commercially worthmal sedimentary distinguishing criterions (including while value and a superlarge deposit scale, have beenstructure,conformation, geochemistry, etc. )has been discovered recently in China 3. As the typical depositfound-12. While it is unsubstantial on the study of of dispersed element Ge mineralization, this deposithydrothermal sedimentation in continental deposi- has中国煤化工 ers after been foundtional environment, and little was known about the Theed on the geologicalrelation between continental hydrothermal sedimenta- charaYHCNMHCopyright by Science in China Press 2004Science in China ser. D Earth Sciencesand the existent form or mode of Ge in coal 3-1812 kmThese results have shown that Ge mainly exist in theform of organic complex 6. I, the characteristics ofGe-bearing coal, the distribution and existing form ofBangGe in the lincang ge deposit are similar to those ofthe ge-bearing coal in other parts of the word.ItzhongzhuNIalso show that the sources of ge concentrated in coalare related to two-mica granites in the west region ofthe coal-bearing basin, but the pathway by which Geentered the coal-forming basin or coal seams is still in□controversy.The Ge mineralization was not a simple, indeFig. I. The sketch geological map of the Bangmai Basin(modifiedpendent geological event in coal, the ore-bodies after ref (13). 1, Neogene Strata; 2. Ge-rich sections of the coal seamsshould genetically connected with the surrounding 3, syndepositional faults:4, two-mica granite: 5, biotite granite: 6,geological materials. Therefor, it is difficult to explain unconformity interfacethe particularity of Ge mineralization in coal of the the Ge in the Lincang Ge deposit is unevenly distrib-Lincang Ge deposit, if only limited on the study of uted no matter in vertical or horizontal direction of theGe-rich coal itself. Hu et al. 3 and Su et al. 5 have coal seams, most industry-worthwhile valueGepreliminarily studied the siliceous rock and regarded mainly occurs in the lignite of the first coal-bearingthey are of hydrothermal origin. abundant hydrother- cycle(nib )close to the basement granites. This cyclemal sedimentary structures and plant fragment fossils is mainly composed of conglomeratic coarse sandin the layered siliceous rocks have been found for the stone, fine sandstone, siltstone, coal seams, layerefirst time in further detailed research of this report, siliceous rocks and carboniferous siliceous limestonewhich not only provide the direct evidences of hydro- There is no significantly Ge mineralization and a laclthermal sedimentation, but also definitely define the of siliceous rock in the coal seams of the upper twotime of hydrothermal activities. Based on the studies coal-bearing cycles(Nib and Nib ) In Nib, the geon the geological and geochemical characteristics of ore-bodies are bedded, accordant with the strata, thesiliceous rock, the spatial distribution of Ge and the coal seams generally are Ge ore-bodies. The spacialgeochemical characteristics of Ge-bearing coal sam- distribution of Ge-rich sections of the coal seams, theples, the relation between siliceous rock and Ge min- siliceous rocks and the syndepositional faults in theeralization was studied in this paper.basement coincided with each other(fig. I and fig. 3)1 Geological setting of the Lincang Ge depositThe Ge contents in these ore-bodies lie in a wide rangefrom 20 to 2500 ug/g, 852 ug/g on average(51 sam-The Lincang Ge deposit, which include Dazhai ples)Ge deposit and Zhongzhai Ge deposit, is located in thecoal-bearing clastic rock Bangmai Basin with Ge-rich 2 Sample and methodgranites(ate= 3.9 ug/g) as the basement in the Lin-The fresh siliceous rocks in the cliff and intercang county, Western Yunnan Province (fig. 1)31. layer of the coal seams(Ge ore-body) in the first coal-Strata in the basin consist of the Cenozoic Neogene bearing cycle(Nib) of Zhongzhai were collected asBangmai Group, and can be divided into three coal- the samples in this study. All samples were washedbearing cycles(N1b, NIb and NIb )(fig. 2). At present, with distilled water, and were ground and passedthe proven Ge reserve of the Lincang Ge deposit is up throuto superlarge deposit scale with 860t Ge in Dazhai and majat lest 200t Ge in Zhongzhai. prospecting data showL..中国煤化工 iter desiccation,,therCNMHGearth element(REEweretory of Ore DepositContinental hydrothermal sedimentation and the Lincang Ge deposit975Stati.Stratam graphIcLithological characterscolumnQuaternaryQ0-10Eluvium. sliderock and alluviaNb0-21Coarse sandstoneNb19-81Siltstone, argillaceous siltstone withbundant thin ferruginous zoneNb1-3463o with 3 to 8 interlayered coal seams withthickness up to l m, half dull-half|Nb0-179Fine sandstone siltstone coarse sandstone with 6 toNb144-26317 interlayered coal seams with thickness up to 3 m, Coalhalf bright coal. The second coal-bearing sectionNb795Conglomerae with interbedded coarse sandstoneCoarse sandstone, carboniferous siltstone, limestone,siliceousrocks with 8 to 14 interlayered coal seCoal andNb219364with thickness up to 14 m thick half bright-bright germaniumal. The first coal-bearing sectionGranitic clastic rock(giant grained conglomerate,Nb|20-686conglomeratic coarse sandstone, coarse sandstone)with few interlayered fine sand-stone and siltstoneto coarse grained biotite, muscovite and twoIndosinian graniteanites with silicified zone and quartz vein inFig. 2. The sketch strata table of the Bangmai Basin(simplified after the data of No. 209 geological team, Yunnan Province)Geochemistry, Chinese Academy of Sciences, and 3 Lithological characters of siliceous rockoxygen isotope analysis were made in the Institute ofThe siliceous rocks are gray-black with solidOre Deposit Geology, Chinese Academy of Geo- massive bedded or lentoid conformation. its thicknesssciences. The major element contents were determined varies from 20--60 centimeters. They mainlyby using the wet chemical method. The trace elements unevenly distribute as interlayer or the cliff of theand REEs were analyzed by a Finnigan MAT ELE- main ore-body of Zhongzhai Ge deposit MicroscopicMENT high resolution ICP-MS with detection limit up studies show siliceous rock are grain-setting structure,to 10. All analyses were calibrated with international and partial zonal or radial chalcedony filled structurerock reference materials(GBPG-1 and AMH-1)and distinctly distinguishing from the sedimentary clasticparallel samples. The analytical precisions for differ- quartz. The peripheral portions of the zonal structureent trace element are given in table 2, and for REEs consist of co-center laminated radial chalcedony withare better than 5%. The oxygen isotope compositions cruciforpolarized light, while thewere analyzed by using BrFs method, MAT 251 EM medium中国煤化工 shape or grainedMS and SMoW international standard with analytical quartz.CN Gry similar to thoseprecision of 0. 2%of the mammillary structure named by Chen XianpeiScience in China ser D Earth SciencesCK4-17equal angle in line. The carbonaceous annulusesCK4-26CK4.18CK4-30sometime were cut by the late vien. Abundant plantfragment fossils and a few pyrites have been found inthe layered siliceous rocks. Pyrites generally are cubicwith spherica4 Geochemical character4. 1 Major element geochemistryThe siliceous rocks in the Lincang Ge depositmainly consist of Sio2, the SiO2 contents vary fromN,b 84.31% to 97,60%,92.77% on average, the secondaryconstituents are loss in ignition(carbonide in dominance), and the content of the other element are verylow(table 1). Their major element compositions are上3similar to those of the typical marine hydrothermal6siliceous rocks in the other part of the world. TheFig 3. No. 302-21 explorative cross-section of the Lincang Ge de- Na2O/K2O ratios of most marine hydrothermal siliposit(simplified after the data of No. 209 geological team, Yunnan ceous rocks are less thanl. while the ratios of the sili-5. mudstone: 6. ranitic clastic rock.ceous rocks from the Lincang Ge deposit are higherthan 1in upper Devonian hydrotheraml sedimentary siliceousrocks, Guangxi, and these structure can be regardedThe Al/(Al+Fe+Mn)atomic ratios are an imporas the main lithological characteristics of hydrother- tant indicator to evaluate the content of hydrothermalmal sediments. Many carbonides and carbonaceous sedimentary components in various sediments, and theannuluses were found in the siliceous rocks from the ratios decrease with the increase of the content ofLincang Ge deposit. The carbonides were reciprocally hydrothermal components. Low TiO2 and Al2O3 con-filled with silicide. The radial and zebraic chalcedo- tent are the typical characters of the hydrothermal si-nies in the carbonaceous annuluses were intersectant at liceous rocks. The Al/ (Al+Fe +Mn) ratios of the sili-Table 1 mnt composition of the siliceous rocks from the Lincang Ge deposit(%)Feo Mno Mgo Cao Na 0 KO P2Os LO Sum AV(Al+Fe+Mn) Na/K84310.010.010.200.060.110.200.120.0200813.3199,430.008Z2796.750.020.020600.120.070.100.200.110.020.121.5099630.025550ZZ-3897600010.030.860.100070.100400.110.010.110.2699.660.02896.3900010.010.750.150.110.100.500.120030.111.509977001075789.830.0010.010.540.100070.100.200.110.040.158.7099850.01495.520.0020.021.320.320.100.110.100.120.030.081609932001140095.600.020.010.390.100060.100.100.110040.073.2099.800018Z7996090.010020.720.200080.110.200.120.0300321099710020400890600010.020.704.700.200.110.700.110020.154069983Zz-8786590.0030011.320.300080.104600.100020076.3599540.006average92770010.020820.630.090.100.720.110.030.1042699.65001095300.040.411.030.580.030.190.680.060080251.0699.710.15355098460.0060010460.140.0500010.2600iYH中国煤化工001l100Franciscan92.300091.310.272.360.530.280.110.10.29CNMHG 0.209 1.46wQL, YL, Franciscan and Shimanto: The average composition of marine hydrothermal cherts and associated rocks in the West Qinling,Yangla copper deposit in West Yunnan, the Franciscan and Shimanto terranes, respectively: LOl: loss on ignition; Na/K: Na: O/K_OContinental hydrothermal sedimentation and the lincang ge deposit977ceous rocks from the Lincang Ge deposit vary from0.004 to 0.028, 0.010 on average, TiO2 contents rangefrom 0.001%to 0.02%,0.01% on average, and Al2O3contents vary from.01% to 0.03%0, 0.02% on averageThey are less than the Al/(Al+Fe+Mn)ratios, TiO2 andAl2O3 contents of the typical marine hydrothermalsiliceous rocks in the other part of the world, respectively(table 1). In the Triangle diagram of Al-Fe-Mnin different rocks, the siliceous rock samples fall intothe hydrothermal field (fig. 4). So the major elementcompositional characters of the siliceous rocks from Fig. 4. Triangle diagram of Al-Fe-Mn in different rocks(based on refsthe lincang Ge deposit indicate that the siliceous [] and [ll D I, Biogenetic and non-hydrothermal sediments: Il, hydro-rocks in the area were hydrothermal sedimentsthermal sediments:, siliceous rock from the Lincang Ge deposit.4.2 Trace element geochemistryGe deposit are distinctively enriched in Ge, Sb, As andW, secondly enriched in Cs, U, Mo and Tl in variousin c hydrothermal sediments are relatively enriched degree. The Co/Ni ratios of the siliceous rocks are lessin Cu, Ni and depleted in Co". The high contents of than 1, while U/Th ratios are greater than 1. In theBa, As, Sb and B in sediments are the important evi- U-Th diagram of various sediments, the siliceousdence for hydrothermal sedimentation>. Results(ta- rocks fall into hydrothermal field (fig. 5). In the trian-ble 2)show that the siliceous rocks from the Lincang gle diagram of Fe-Mn-(Co+Ni+Cu)x10 in differentTable 2 Trace element compossiliceous rocks from the Lincang Ge deposit(ug/g)AP(%)Zz19z27z38Z45z6179z2811.210Cr144.519.69512.57.518.113.0185.81.62.21,52.5290.097.68.429732950580.770.571060.350420.390.390.610360291.64886GARs10355.014112.571.612.2320090.800.170.390.210.680.16140.2661.311561.50.311.681.021.551.561,401.291.821.252.7661.59007006040.040.090.080.050.090.100980.67101.8cBH170450I0.8L.571.791698.20.241.042.472300440.120.020040.050033020030.020.00.050010.010.010002769.595T0070.0510.361191.250.9908101.430.190.09中国煤化工12350123.251.211.35AP: Analytical precision; CV: the Clark values of the element after Taylor(19CNMHo its Clark value(concen-tration coefficients)Science in China ser. D Earth Sciencesediments, the siliceous rock fall into the hydrothermal(Cu+Co+N)×10field close to the Fe-end member (fig. 6). The traceelement composition and its characters also indicatethat the siliceous rocks from the lincang Ge depositre hydrothermal sedimentv、UTh=1.0Fig. 6. Triangle diagram of Fe-Mn-( Cu+ Co+ Ni)x10 in defferent101001000sediments(based on ref [41). HN, Hydrogenic sediments; ND, Hydro-Th(×106genic concretion: ED, Eastern Pacific Hydrothermal metalliferoussediments; CR, hydrothermal Fe and Mn-crust sediments: HD, hydro-Fig. 5. U-Th diagram of various sediments(based on refs. [5] and thermal sediments; RH, Red Sea hydrothermal sediments; F, Francisan[lID.I, TAG hydrothermal area; Il, Galapagos spreading center deposits; hydrothermal cherts; siliceous rock from the Lincang Ge deposit.V. East Pacific Rise crest deposits: VI. Langban hydrothermal sedi- normalized rEE pattens are the common charactersments: VIL, ordinary manganese nodules: VIl, ordinary pelagic sedi- of many hydrothermal cherts-12. Results(table 3ments: IX, laterites; X, fossil hydrothermal deposits(En Kafala ores);.and table 4) show that the total REE content of thesiliceous rock from the Lincang Ge deposit.siliceous rocks from the Lincang Ge deposit vary from4.3 REE geochemistry0.200 to 2.324 ug/g, usually less than 1 ug/g, LREE/REE composition and their characters are imporHREE>l, the values of Eu anomaly (Ew/Eu*)and Cetant indicators distinguishing hydrothermal sediments anomaly(Ce/Ce*)vary from 0.452 to 5.141 and 0.997from Non-hydrothermal sediments!. Low total ree to 1. 174, respectivelycontent and the left-inclined north american shaleThe North American Shale-normalized ree patTable 3 The REE contents of the siliceous rocks from the Lincang Ge deposit (ug/g)DyT0.3010.5890033nd006100060.0640013006800210067001400790014Z-190.2690.5740.0590.1620.076002000570.0090.0670.0190.0630008007500130.1440253ndnd0.0170.0040.0140.0050.0240.002002100020.01300030.1180.2590.026nd0.0330.01000210.0030.0200.004001500010.0130003zZ-381300050.01300040.0210.0050.0170.0030.0.00.0820.1490.011nd0.0170.00400180.0020.02200050.0150.0020.0320006Z2-450.2200.348nd0.0200.00300210.0040.0270.00500150.0040.0160.002ZZ-50.5661.2420096nd0.1080.0160.1040.0170.08900180.04800110.0610.0070.54413940.1410.4060.1140.02001500870.0210.04700090.059001100560.089nd00020.002000500020.0130.0020.0140.00300170.002Z-6003200730.006nd001500110.00900020.0120.0030.006000200190003ZZ-790.1670.275ndnd0.03200030013000300180.0040.01300030.01500021210.2710029nd0.025001300200.004002300040.0090.0010.0150002nd0.009nd0.0070.00100140.00500210.0040.0160.002zZ-810.0920.1440.0590.120nd001300160.015000300190.00500180.0020.0190.0040.2590413d0.0030.0130.025Z8700300.0630.005nYHS00040.0250.006中国煤化工?0040500CNMHG00010018003Chondrite0.340910.1210.640.19500730.260.0320.220.034nd: No detected; chondrite data after Wataki( 1971)in ref. [20]Continental hydrothermal sedimentation and the Lincang Ge deposiTable 4 The ree geochemical parameters of the siliceous rock from the Lincang Ge de∑ REE LREE HELREE/HREE Eu/Eu* Ce/ Ce. (La/Yb)NCLa/Sm)N(Gd/BiNZ乙1914821.1560.13239506650.6330.5510.0826.7221.0320.978307809101.093ZZ 450.8100.7160.097.6150.4521.0001.1lZZ-572.3242.0580.26677250.56709676.3283.1521,406zZ-610.1760.0573.0832.599zZ-790.6778.082.8980931ZZ-810.285007836774.4871.12905320.7620.6350.1275.0004.1068901Z乙880.1450.0552.6355.1411.1471.0781.912The content of the no detected element are calculated using chondrite normalization, then the REe geochemical parameters were calculatedEu/Eu'=[EuN(SmNXGdn)], where N stands for chondrite normalizationterms of the siliceous rocks from the Lincang Ge de- ing ridge and in an ocean-basin floor setting are 0. 29posit are plain or left-inclined (fig. 7), basically similar and 0.55, respectively, while the Ce anomaly is noto those of the typical marine hydrothermal siliceous distinctive or even positive( Ce/Ce*0.90 to 1.30)inrocks(chert). There is a lack of negative Ce anomaly, the chert deposited in continental margin regimes 7)which usually appears in marine hydrothermal 4.4 Oxygen isotope charactersbut a weak positive Ce anomaly in theNorth American Shale-normalized ree patterns of theThe analyzed results of oxygen isotope compossiliceous rocks from the Lincang Ge deposit, this maytion of 1l siliceous rock samples from the Lincang Gebe attributed to these siliceous rocks formed in the deposit(table 5)show that8OsMow values vary fromcontinental depositional environment. The available10.9%0 to 15.7%0, 13.5%0 on average, distinguishstudies have shown that the average values of Ce from those of the volcanic genetic siliceous rocksanomaly(Ce/Ce*)of chert deposited near the spread- (1.9%0-5.2%0, 3.3%0-12.4%)and biochemicalZ19Z乙57-+ZZ.88Z261Z-38-z727一Zz8720.010.0l敏含声0.00a)0.00010.0001La Ce Pr NdSmEuGdTbDyHoErTmYLa Ce Pr NdSmEuGdtbDy HoErTmYbLuFig. 7. The North American Shale-normalized REE pattems of the siliceous rocks from the Lincang Ge deposit.Table 5 The oxygen isotope composition of the siliceous rocks from the Lincang Ge depositRockcosmo%eZZ19139l5.7z-2713.8ZZ-74ZZ-3813.6siliceous rockSiliceous r中国煤化工Z7-4513.3Z7-5713.3YHCNMHG13.5Z-8913.613.5Science in China ser D Earth Sciencesgenetic siliceous rocks(21.6%0-26.7%0) 4, are close in waters with one or more of the following characterto those of hot-spring siliceous sinter (12.2 %oistics: 1)high temperature, 2)high dissolved solidscontent and high alkalinity. The absence of positive5 Siliceous rocks and Ge mineralizationcorrelations between Ge concentrations and those of5.1 The possibility of Ge being transported byimportant inorganic ligands like CI, HCO3, H2S, Nahydrothermal watersuggests Ge does not form complexes with theseligands. The redox potential of most hydrothermal andGe and silicon have identical outer electronic surficial environments is too high to cause significantstructure, very similar atomic and ionic radii, and exist formation of divalent Ge species such as Ge", GeOhin solution as similar hydroxyacids [Ge(OH)4 and or Ge(OH ). As a result tetravalent Ge(like Si)isSi(oH)4I, Ge behaves as a heavy stable isotope tracer present as hydroxide complexes in most natural fluidsfor Si in many low temperature geological processes. with the exception of seawater and organic-rich surfi-In most circumstances the continental crustal rockscial waters[ 23). The solubilities of the tetrahedral Geand minerals contain 1-2 ug/g Ge, display atomic oxide are positively correlated with the temperaturesGe/Si ratios near 1x10. Ge/Si ratios in clean rivers, of the solution, and the distribution of Ge hydroxidein seawater, and in biogenic opal are about 10,nearspecies as a function of pH and temperature is similarto crustal value". In hydrothermal fluids, the atomic to that of silicon hydroxide species. However, the sigGe/Si ratio is much higher than that of rivers, oceans, nificant differences between Ge(OH)4(ag) and Siand crustal rocks. both Ge concentration and Ge/Siratios increase with temperature in most hydrothermal (OH)4(aq) enthpaies of formation and heat capacitieswater23-26) For example, the Ge/Si ratios in hydrcan lead to large variations with temperature of Ge/sithermal fluids from black smoker vents on the eastatio in a solution in equilibrium with Ge-bearing silicates. For example caculations show that the Ge/siPacific Rise very from8×10°tol4×10, much moregreater than the ratio entering the ocean via riversratios in solutions in equilibrium with Ge-bearing(0.54x10 )and being recycled in seawater (0.7wollastonite(Ca(Si, Ge)O3)increases by an order of10). The ratio in Icelandic hydrothermal systems magnitude when temperature is raised from 25 to 500is up to 10, and even 104-103 in hot springs of the This can be responsible for the high values of Ge/SiMassif Central. france. Ge concentrations in searatios measured in high temperature crustal fluids 23)water and river waters are 0.05 and 0.03 to 0. 10 ng/The above facts indicate that hydrothermal waterrespectively. Ge is enriched in hydrothermal water and can transport abundant Ge with sufficient supply of Gesome ground waters relative to waters in rivers and from sources the Ge contents in siliceous rocks fromseawater. Ge concentrations in geothermal waters in the Lincang Ge deposit vary from 5.6 to 360 ug/g, 78Japan are most frequently in the range of 1-15 ng/g ug/g on average and 49 times than crustal clark valuebut value as high as 40 ng/g are reported, in geother- (1.6 Hg/g), implying that the hydrothermal watermal waters in Icelandic lie mostly in the range 2-30formed siliceous rocks indeed transported abundantng/g/2, in the lincang Ge deposit area vary from 3.5to 44.1 ng/g", there is an overall positve relation be-.Getween the Ge content of the water and its temperature 5.2 The spacial distribution of siliceous rocks andin hot spring waters in Iceland and the Lincang Ge Ge ore-bodydeposit areaAccording to the variation of the cliff and bottomKraynov(1965)found that highest Ge occurred of theTHs中国煤化工cross-sections wereCNMHG1)Zhang Lin, Han Yanrong, Yuan Qingbang, Ge source and geochemical cucpuon ca In Licang County, Yunnan Provce,1996Continental hydrothermal sedimentation and the Lincang Ge depositselected to study the variation of Ge content in coal respectively. Prospecting data show the spacial distriseams in Nib(fig 8). In the cross-section(a) in Daz- bution of Ge-rich sections in coal seams, syndeposihai, the coal seams mainly consist of half bright-bright tional faults and siliceous rocks are accordant withcoal with a thickness about 10 m and sandstone as the each other (fig. 1 and fig. 3). These facts indicatecliff rock, without any interlayer. The Ge contents vary that when the Ge(silicon) rich hydrothermal waterfrom 78 to 1800 ug/g, and Ge distinctly concentrated entered the coal-forming basin, for its strong tendencyin the lower portion of the coal seams. In(b) cross- toward accumulation in organic matters, Ge was ad-section in Zhongzhai, the coal seams contain 31 to 440 sorbed by the organic matter such as humic acids inug/g Ge with carboniferous siliceous limestone as the coal and was transferred from the hydrothermal waterliff rock and interlayered sandstone. Ge obviously into the coal seams. At the same time, for its low or-concentrated in the upper and lower portion of the coal ganic affinity, silicon was reserved and formed theseams. As the interlayer or the cliff of the Ge-rich coal indicator of hydrothermal sedimentation(the siliceousseams,the siliceous rocks tightly contacted with Ge rocksore-body in space. The Ge content increased in coalclose to the siliceous rocks. In(c)cross-section in5.3 Trace element and rare earth elementZhongzhai, the Ge content in coal seams with siliceousThe previous studies show that the materialrocks as the cliff rock and interlayered siliceous rocks sources of Ge in the coal seams of the Lincang Geand argillaceous rock vary from 1100 to 2500 ug/g. In deposit are related to the two-mica granites in the west(d)cross-section, the Ge contents of two coal samples region of the Bangmai Basin, but the pathway bylose to the siliceous rocks are 1600 and 2100 ug/g, which Ge entered the coal-forming basin is still in40400800120016002000Geμg·gl100200300400500Ge/μg·gl m100015002000250030006M凵中国煤化工圖彐7ig. 8. The Ge content vs. depth diagram of coal sample from the main ore-beCN Goal; 2, thin-bedded coal; 3.oblique bedded coal; 4, carboniferous siliceous limestone; 5, siliceous rock: 6, sandstone: 7, argilliteScience in China ser. D Earth Sciencescontroversies, and the opinions can be summarized in of hydrothermal sediments are characterized by thethree different genetic types: 1)the adsorption of concentration of HREE. If Ge in coal seams from thecoal-forming plants6), 2)transportation of weathering Lincang Ge deposit was transported by hydrothermal8and 3) transportation of water which formed siliceous rocks, the REE patternshydrothermal water"3. Available data also show that of Ge-rich coal should be more and more close totoo much Ge are poisonous to the growth of plant, and those of the hydrothermal sediments (the siliceoushigh grade plant could not adsorb abundant Ge. The rocks) with the increase of Ge content in coal or thecontributions of coal-forming plant to Ge mineraliza- degree of coal being influenced by hydrothermal watertion in the Lincang Ge deposit are less than 4%. Results(table 7) show that with the increase of GeUnder about the same continental materials inputting content in the coal from the Lincang germanim de-backgrounds, the opinion of weathering of granites posit, the LREE/HREE ratio gradually decreased,couldn,'t explain why Ge mineralization only existed (La/Yb)N and(Gd/Yb)N ratios were more and morein the first coal-forming cycle(Nib ) with hydrother. close to those of the siliceous rocks from Zhongzhaimal genetic siliceous rocks, and no Ge mineralization The Chondrite-normalized REE patterns of low Gein the two upper coal-forming cycles without hydro- (<100 ug/g)coal and Ge-free coal are similar to thosethermal sedimentof the two-mica granites in the basement, demonstrateThe trace element and REE compositions of dif- that their rEe mainly came from the basement twoferent samples in different strata have been analyzed in mica granites. However, especially when Ge content isthis study. Results(table 6)show that compared to more than 1000 ug/g, the Chondrite-normalized REEGe-free coal samples in N,b, with the increase of Ge patterns of Ge rich coal are more and more similar tocontent in coal, the characteristic trace element ratios those of the hydrothermal siliceous rocks in Zhongzhai(especially U/Th, Nb/Ta and Ga/Ge)of Ge-rich coal in (fig 9). These facts imply that except the similar ma-NIb are close to those of the siliceous rock, whileterial sources with Ge-free coal and low germaniumthose ratios of Ge-free coal in Nib are close to those coal, the Ge-rich coal was superimposed the otherof the granitic clastic rock. Compared to non-hydro- elements (including REE, Ge and other elements)thermal sediments, the NAS-normalized REE patterns transported by hydrothermal water.Table 6 The average trace elemental ratios of different rocks in the Lincang Ge depositStrata Sample number Ge content/ug.g" Rb/Cs Z/Hf Ba/Sr U/Th Nb/Ta Ge/Ga<1001.65100-2001012.19260695200-1000026032.74Dazhai Ge-rich coal61000-15001.185.382411868514314>15001525.702.21.1746624496537.62l1<100l.261.624318.212910.3l00-1000808.184045.18382754Ge-rich coa1000-15001.37143.12>150048.510.322.9Zhon14820.611.614.0459Ge-free coalSiliceous rock中国煤化工2498107Granitic clastic rock NibCNMHG59289013Two-mica granite Basement1.70Continental hydrothermal sedimentation and the Lincang Ge deposit983Table 7 The average REe geochemical parameters of different rocks in the Lincang Ge depositGe content(10)EREe LREE HREE LR/HR Eu/Eu* Ce/Ce* (La/Yb)n (La/Sm)N (Gd/Yb)N<10079886675941.27259700.5381.1115.5963681112210020013018.5215982.5396.2940.3941.0793.0471.612Ge rich coalin dazhai200-1000490287423.2754694.2540.4351.049503725151.2621000-150013004849365311963.0540.2851.1332.0650.87615001600300519.9610.0919781.8764529.1625.213.9556.3730.3891.15254652.4731.461Ge-rich coal200-1000340254521334.12051770.3791.0324.8362.261in zhongzhai1000-2000140019.1613.393.4623.7480.3471082.3852.0430.827>2000240018.2214.433.78538130.33510952.2430.777<10644061349456756.15704571.1046.1961777Siliceous rock770.8400.7020.15146370.5291.13646713.8890.834Granitic clastic rock252110963621.684450109090359923031006Two-mica granite160.2220.8886.42920681.741LRHR=LREE/HREE: Eu/Eu*=[EuN(SmN X GdN)], where N stands for chondrite normalization.triangle diagram of Al-Fe-Mn in different sediments(3) The siliceous rocks are distinctively enriched in GeSb, As, W, and secondly enriched in Cs, U, Mo and TCo/Ni ratios are less than 1. and U/Th rations are moresamples fall into the hydro-thermal field in the U-Th diagram and Fe-MCo+Ni+Cu)x10 triangle diagram (4) The total REE好d占dcontents of the siliceous rocks are very lowless than 1 ug/g, their North American Shale-normal-001La Ce Pr NdSmEuGdTbDyHoErTmYbLuized ree patterns are plain or left-in-clined. (5)TheOSMow values of the siliceous rocks vary fromFig 9. The Chondrite-normalized ree patterns of different rock inthe Zhongzhai Ge deposit. 1, Coal in Nib with Ge content less than1010.9%0 to 15.7%0, 13.5%o on average, close to those ofug/g: 2, coal in N, with(10-100) ug/g Ge: 3, coal in N, b with (1000 the hot-spring siliceous sinter. As the interlayer or the-2000)Hg/g Ge; 4, coal in Nib with Ge content more than 2000 ug/g: cliff of the Ge-rich coal seams, the siliceous rocks5, Ge-free coal in N b; 6, two-mica granite 7, siliceous rock.tightly contacted with ore-body in space. The siliceous6 Discussions and conclusionrocks contain 5.6 to 360 ug/g Ge, 78 ug/g on averageThe Ge content rapidly increased in the coal close toThe following evidences can well explain the sithe siliceous rocks. The characteristic trace elementliceous rocks from the Lincang Ge deposit werehydrothermal sediments: (1)Abundant hydrothermalratios and Chondrite-normalized REe patterns ofGe-rich coal are more and more similar to those of thesedimentary structures and plant frag fossil were foundsiliceous rocks with the increase of ge content in coalin the siliceous rocks, and the existing of plant fossilThe siliceous rocks can be regarded as the prospectingindicates the hydrothermal water activities and thecoal-forming process happened basically in the samecriteria of the Lincang Ge depositperiod. (2) The siliceous rock mainly consist of SiO2vad from the above discussions that(92.77% on average), its AV/(Al+Fe+Mn)ratios vary the中国煤化工 ang ge deposit werefrom 0.004 to 0.028, 0.010 on average. The siliceous hydroCNMHGGe in coal seams ofrock samples fall into the hydrothermal field in the the Lincang Ge deposit were mainly transported intoScience in China ser. D Earth Sciencesthe coal-forming basin by the hydrothermal waters 13. Hu Rui-zhong, Bi Xianwu, Ye Zaojun et al, The genesis of Lin-which formed the siliceous rocks during the coalcang ge deposit-A preliminary investigation, Acta Minerforming processesalogica Sinica(in Chinese), 1996, 16(2): 97-10214. Hu Ruizhong, Bi Xianwu, Su Wenchao et al., Ge-rich hydrothercknowledgements This work was jointly supported by the Statemal solution and abnormal enirchment of Ge in coal, ChineseKey Fundamental Research Developing and Planning Program of ChinaScience Bulletin, 1999, 44(suppL. ) 257--258(Grant No. G1999043210)and the National Natural Science Foundation 15. Su Wenchao, Hu Ruizhong. Qi Huawen et al, Geochemistry ofof China( Grant No. 40302018)siliceous rocks and Ge mineralization of Lincang superlarge GeReferencesposit in Yunnan province, Chinese Science Bulletin, 1999.44( suppl.):1561571. Yomamoto,K Geochemical characteristics and depositional en- 16. 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