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2001 Vol. 12, No. 1

Display Method:
Fischer Plots of Wumishan Cyclothems, Precambrian Records of Third~Order Sea Level Changes
Mei Mingxiang, Ma Yongsheng, Zhou Hongrui, Du Benming, Luo Zhiqing, Guo Qingyin
2001, 3(1)
Abstract:
TheMesoproterozoicWumishanFormation((1310±20)Ma~(1207±10)Ma)inJixian,Tianjinrepresentsasuccessionof3300meterthickcarbonatestratawherearethebestdevelopedstromatolitebiostromesandthrombolitebioherms.Thesebiostromesandbioherms,togetherwithtidal~flatdolomitesandmuddydolostones,formWumishancyclothemswithapproximatelysymmetricalfacies~successionfabrics,whichbelongtocarbonatemeter~scalecyclicsequencesofperitidaltype.Thesecyclothemsareoverlainbylagoondolomiticmudstonesandshalesandbyfrequentlydevelopedpaleosollayers,indicatingthattheboundaryofWumishancyclothemsismarkedbyaninstantaneously~exposedpunctuatedsurface.ViewedformtheregularlyverticalstackingpatternsofWumishancyclothemsinlong~termsequences,26thirdordersequencesmaybediscernedinWumishanFormation.Thesethird~ordersequencesmayalsobeincorporatedintosixsecond~ordersequences.Inordertostudythevariationrangeofthird~ordersea~levelchangesandtheformationperiodofthird~ordersequence,626cyclothemsarediscernedinthemiddleandupperpartsofWumishanFormationwheretheoutcropsarewelldeveloped.Interms ofthetotalthicknessandtheformationperiodofMesoproterozoicWumishanFormation,thecrustsubsidencerateinthesedimentaryperiodofWumishanFormationissupposedtobe3metersateachintervalof100thousandsyears.Basedonthisassumption,Fischerplotmightbedesignedtosimulatethethird~ordersea~levelchangingpattern.
Study on Sequence Stratigraphy of Zhujiang and Zhuhai Formations, Zhu Ⅲ Subbasin, Pearl River Mouth Basin, South China Sea
Nie Fengjun, Li Sitian, Wang Hua, Xie Xinong, Wu Keqiang, Jiang Meizhu
2001, 3(1)
Abstract:
TheearlyMioceneintheZhuⅢsubbasin,thePearlRiverMouthbasin,includestwoformations—ZhujiangandZhuhai.Thereare8third~ordersequences,S1,S2,S3,S4,S5,S6,S7andS8fromthebottomofZhuhaitothetopofZhujianginthesetwoformations.Thereareonlyonetransgressivesystemstract(TST)andonehighstandsystemstract(HST)ineachsequencebecausethewholeZhuⅢsubbasinwaslocatedupdiptheshelfbreakduringsequencedeposition.Theboundariesandmaximumfloodingsurfaces(mfs)areingoodresponsetobothgammaandacousticlogcurvesinthestudyarea.Inseismicprofile1249,sedimentsobviouslyonlapovertheunconformity(SB0,thebottomofZhuhaiFm),SB1andSB2,butobviouslyoveronlySB2inseismicprofile1283sincethewell~developedfaultsinthesubbasin.Thesandbodieswithhighporosityandpermeabilityforpetroleummigrationandaccumulationhadbeenreworkedbytidalcurrentsbeforetheirburial.Hence,thetidalinfluencedparasequencesetsoccurbothinTSTandHST.Throughdetailedanalysis,thesandbodiesinTSTaremorefavorableforpetroleumtomigrateandaccumulatethanthoseinHST.
Griesbachian Cyclostratigraphy at Majiashan Section, Anhui Province, China
Peng Yuanqiao, Tong Jinnan, Gao Yongqun
2001, 3(1)
Abstract:
TheLowerTriassicatMajiashanSection,depositedinthedeeppartoftheLowerYangtzecarbonateramp,istheonlyoutcropofthedeepLowerTriassicpreservedinthepresentLowerYangtzeregion.Evenso,thealternationsofmudrockandmarl(orlimestone)arestillverydistinctandrecognizable,thoughusuallymoreorlesscondensed.ThelithologicalandgeochemicalcyclesatMajiashanSectionarediscussedintermsofthesedimentarycharactersandthecontentsofsomeelementsanalyzedata2~centimeter~intervalwithnohiatusoftheLowerTriassic.ThedivisionresolutionoftheGriesbachianstratigraphymayincreasetothescaleoftenthousandyearsbythemudrock~marl(orlimestone)bundlesandthegeochemicalcycles.Theanalysisoftherelationshipbetweenthesedimentarycycles/thegeochemicalcyclesandtheMilankovitchcyclesmaysuggestthetimelimitandthesedimentaryrates.
Phytolith Records in Vermicular Red Earth: Implications for Bioclimatic Variations during Pleistocene
Gu Yansheng, Zhuo Ying, Zhang Zejun
2001, 3(1)
Abstract:
Phytolithanalysisisemployedinbioclimaticresearchintovermicularredearth,especiallyintoitsform,assemblageandzonation.Thephytolithassemblageisdividedinto10zones.Thestatisticsandmainfactoranalysisofphytolithshowthattheobtainedmainfactorloadcurvescouldsuggestaclimatechange.Combinedwithphytolithassemblagefeature,thebioclimaticvariationofvermicularredearthduringitsformationstage,consistingof5arid~coldstages,4warm~humidstagesand2mildstages,isreconstructedindetail.Theresearchresultsindicatethatphytolithrecordsareidealpaleoclimaticsignalsinvermicularredearth,andthatabundantinformationonenvironmentalevolutioncanbelocated.
Some Suggested Future Directions of Quantitative Resource Assessments
Singer Donald A
2001, 3(1)
Abstract:
Futurequantitativeassessmentswillbeexpectedtoestimatequantities,values,andlocationsofundiscoveredmineralresourcesinaformthatconveysbotheconomicviabilityanduncertaintyassociatedwiththeresources.Historically,decliningmetalpricespointtotheneedforlargerdepositsovertime.Sensitivityanalysisdemonstratesthatthegreatestopportunityforreducinguncertaintyinassessmentsliesinloweringuncertaintyassociatedwithtonnageestimates.Ofallerrorspossibleinassessments,thoseaffectingtonnageestimatesarebyfarthemostimportant.Selectingthecorrectdepositmodelisthemostimportantwayofcontrollingerrorsbecauseofthedominanceoftonnage~depositmodelsarethebestknownpredictorsoftonnage.Muchofthesurfaceiscoveredwithapparentlybarrenrocksandsedimentsinmanylargeregions.Becausemanyexposedmineraldepositsarebelievedtohavebeenfound,aprimeconcernisthepresenceofpossiblemineralizedrockundercover.Assessmentsofareaswithresourcesundercovermustrelyonextrapolationfromsurroundingareas,newgeologicmapsofrocksundercover,oranalogywithotherwell~exploredareasthatcanbeconsideredtrainingtracts.Coverhasaprofoundeffectonuncertaintyandonmethodsandproceduresofassessmentsbecausegeologyisseldomknownandgeophysicalmethodstypicallyhaveattenuatedresponses.Manyearlierassessmentmethodswerebasedonrelationshipsofgeochemicalandgeophysicalvariablestodepositslearnedfromdepositsexposedonthesurface—thesewillneedtoberelearnedbasedoncovereddeposits.Mineral~depositmodelsareimportantinquantitativeresourceassessmentsfortworeasons:(1)gradesandtonnagesofmostdeposittypesaresignificantlydifferent,and(2)deposittypesarepresentindifferentgeologicsettingsthatcanbeidentifiedfromgeologicmaps.Mineral~depositmodelsarethekeystoneincombiningthediversegeoscienceinformationongeology,mineraloccurrences,geophysics,andgeochemistryusedinresourceassessmentsandmineralexploration.Gradeandtonnagemodelsanddevelopmentofquantitativedescriptive,economic,anddepositdensitymodelswillhelpreducetheuncertaintyofthesenewassessments.
Grade~Tonnage, Ore Value~Tonnage, and Enrichment Ratio~Tonnage Models for Resource Assessment
Shoji Tetsuya
2001, 3(1)
Abstract:
Accordingtograde~tonnagediagramsofnickelandzincdeposits,theircriticalgradesare0.4%and3.4%,respectively,andhencetheformerresourcescanbeconsideredoptimisticandthelatterpessimistic.Thegrade~tonnagediagramofgolddepositsisconvexdownwardssuggestingthatthecriticalgradeis1×10-6inthelowgradepart.Theorevalue(OV)~tonnagediagramofalldepositsintheworldconsistsofthreeparts:high,middleandlowvalueclasses.Theenrichmentratio(ER)~tonnagediagramofalldepositsintheworldalsoconsistsofthreeparts:high,middleandlowratioclasses.NinequalitycategoriesdefinedbyERandOVarecharacterizedbysomekeywordsindicatingdeposittypesasfollows:categoryHH(highER~highOV:0.7%)by“unconformity”and“MississippiValley”,categoryHM(highERmiddleOV:0.7%)by“vein”,categoryML(middleER~lowOV:0%)by“sandstone”,“stockwork”and“dissemination”,categoryLMby“orthomagmatic”,“laterite”,komatiite“and”chemical“,andcategoryLLby“porphyry”,“dissemination”and“placer”.CategoryMMisnotcharacterizedbyanykeyword.Ifthecommoditiesofadepositaredefinedbyboththeenrichmentratioandtheorevalue,thedefinedcommoditiesarerelativelycoincidentforgoldandnickel,butdifferentforcopper,silverandzinc,andgreatlydifferentformolybdenumandlead.Depositscontainingleadand/orzincarecomplimentary.IfthecommodityPb+Znisapplied,mostleadorzincdepositsareclassifiedasPb+Znbybothdefinitions.Accessorymetalsarecommonlyexpectedfordepositsofkuroko~typezinc,epithermalsilver,massivesulfide~typezincandvolcanogeniczinc,butuncommonfordepositsoforthomagmaticchromium,chemicallyprecipitatedcopperandsandstone~typeuranium.
Selection of Multifractal Scaling Breaks and Separation of Geochemical and Geophysical Anomaly
Cheng Qiuming
2001, 3(1)
Abstract:
Spatiallysuperimposedmultipleprocessessuchasmultiplicativecascadeprocessesoftengeneratemultifractalmeasurespossessingso~calledself~similarityorself~affinitythatcanbedescribedbypowerlawtypeoffunctionswithincertainscaleranges.Themultifractalitiescanbeestimatedbyapplyingmultifractalmodelingtothemeasuresreflectingthecharacteristicsofthephysicalprocessessuchastheelementconcentrationvaluesanalyzedinrockandsoilsamplesandcausedbytheunderlyingmineralizationprocessesandtheothergeologicalprocesses.Thelocalandregionalgeologicalprocessesmayresultingeochemicalpatternswithdistinctmultifractalitiesaswellasvariablescalingranges.Separationofthesemultifractalmeasuresonthebasisofboththedistinctmultifractalitiesandthescalingrangeswillbesignificantforboththeoreticalstudiesofmultifractalmodelinganditsapplications.Multifractalscalingbreakshavebeenobservedfromvariousmultifractalpatterns.Thispaperintroducesatechniqueforseparatingmultifractalmeasuresonthebasisofscalingbreaks.Ithasbeendemonstratedthatthemethodiseffectivefordecomposinggeochemicalandgeophysicalanomaliesrequiredformineralexploration.Adatasetcontainingtheelementconcentrationvaluesofpotassiumandphosphorusinsoilsampleswasemployedfordemonstratingtheapplicationofthemethodforstudyingthefertilizerandyieldoptimizationinagriculture.
Weathered Mantle Hosted Gold Deposit at Shewushan, Hubei, Central China
Hong Hanlie, Wang Qinyan, Bian Qiujuan
2001, 3(1)
Abstract:
AsupergenegolddepositislocatedatShewushan,southHubei,CentralChina.TheAumassfractionofthesupergenedepositsrangesfrom1.0×10-6to19.5×10-6,withanaverageofabout2.2×10-6.Primarygoldmineralizationiscloselyassociatedwiththewelldevelopedfaultsandfracturesmainlyonthecrestofthereverseanticlinewithgoldmassfractionrarelyexceeding1.0×10-6(average0.6×10-6),thegoldoccursassmallAg~bearingparticlesinassociationwithilliteandkaolinite,andpartlyincorporatedwithinthelatticeofpyrite.Fluidinclusionstudiesonthegoldmineralizationyieldtrappingtemperaturesandpressuresfrom110℃to290℃and410×105to460×105Pa,respectively.Thesalinitiesofmineralizationfluidsrangefrom2.6%to8.4%w(NaCl,equivalent).Calculatedδ(18O)valuesandmeasuredδ(D)dataofthehypogenefluidsindicateameteoricorigin.Thesefluidsunderwentextreme18Oenrichmentbyreactingwithcountrycarbonaterock.Supergenegoldmineralizationisconfinedlargelytothelowerportionattheweatheredmantle;thegoldoccursassmallnativegoldparticlesaccompaniedbyclayminerals,kaoliniteandilliteandMnandFeoxides.Geochemicalinvestig ationshowsthatAu,togetherwithAsandSb,decreasesprogressivelyfromthetopoforebodytosome2kilometersawayanddefinealateraldispersionhalo.Itisproposedthatthegoldismobilizedbysurficialleachingandconcentratedatthelowerportionoftheweatheringprofile,andthio~sulfatemayplayanactiveroleingolddissolutionandre~precipitation.
Tectonic Dynamic Metallization of Silver~Gold Hydrothermal Flds in Proterozoic Gneiss Terrene Shear Zones, Suichang, Zhejiang, China
Wang Siyuan, Xiao Qibing, Zeng Jianguo
2001, 3(1)
Abstract:
TheSuichangmineisthelargestsilicifiedvein~typesilver~goldmineralizationsysteminSoutheastChina,whoseorebodiesarecontrolledbyshearzonesdevelopinginLowerProterozoicgneissterrenewithinitialmigmatization,whichiscoveredbyUpperJurassicandLowerCretaceousvolcanicrocksystemandcutbyacidicigneousveinsofJurassicandCretaceous.Theconclusionsareasfollows:(1)Theore~formingfluidisdefinedassuperhightectonic~metamorphicfluidonthebaseof:①δ(D)~δ(18O)values;②fluidinclusions;③traceelementsofpyritefromores.(2)TheshearzonesilicifiedorebodiesoccurredinProterozoic,JurassicandCretaceous,whichhavebeentransformedinpartbyorebearingcombquartzveinofvolcanism.
Chemical Characteristics of Stream Draining from Dudu Glacier: An Alpine Meltwater Stream in Ganga Headwater, Garhwal Himalaya
Ahmad Sarfaraz, Hasnain Syed Iqbal
2001, 3(1)
Abstract:
TheEC(electricalconductivity),pHandconcentrationsofmajoranions,cationsanddissolvedsilicaweredeterminedinthestreammeltwaterdrainingfromtheglacier.StreammeltwatersamplesweresampledduringJuneandOctober1997fromDuduglacier,Bhagirathivalley,GarhwalHimalaya.ThisstudyisanattempttorevealthehydrochemicalprocessesoperatingintheglacializedregimeofGarhwalHimalaya.Theresultsshowthattheabundanceorderofcationsandanionsinthemeltwaterisc(Ca2+)>c(Na+)>c(Mg2+)>c(K+)andc(SO2-4)>c(HCO-3)>c(NO-3)>c(Cl-).Therockweatheringisthemostimportantmechanismcontrollingthewaterchemistryinthebasin.Pyriteoxidationandcarbonationarethemainhydrogenionsupplyreactionscontributingtothechemicalweatheringinthebasin.ThereisadistinctdifferencebetweenthesoluteconcentrationsinsamplescollectedduringJuneandOctober.
Fluid Dynamic Field in Bozhong Depression, Bohai Bay Basin
Ye Jiaren, Chen Honghan, Yang Xianghua
2001, 3(1)
Abstract:
Thedatafromregionalgeology,boreholes,geophysicsandtestsareintegratedtoanalyzethefluiddynamicfieldintheBozhongdepression,BohaiBaybasin.Thecurrentgeothermalgradientisdeterminedtobeabout2.95℃/100mbyintegrating266drill~stemtest(DST)measurementsandcomparingwiththeglobalaveragevalue.Thepaleogeothermalgradientsarecalculatedfromthehomogenizationtemperaturesofsalineinclusions,whichvarybothlaterallyandvertically.Thedatafromsoniclogs,welltestsandseismicvelocitiesareusedtoinvestigatethepressurevariationsinthestudyarea.Themudstonecompactionisclassifiedasthreemajortypes:normalcompactionandnormalpressure,under~compactionandoverpressure,andpast~compactionandunder~overpressure.Thecurrentpressureprofileischaracterizedbynormalpressure,slightpressureandintenseoverpressurefromtoptobottom.Thefaults,unconformitysurfacesandinterconnectingporesconstituteacomplexnetworkofverticalandhorizontalfluidflowswithinthedepression.Thefluidpotentialenergyprofilespresenta“double~deck”structure.Thedepocentersaretheareaoffluidssupply,whereastheslopesandupliftsarethemainareasoffluidscharge.
Seismic Response of Base~Isolated Structures under Multi~component Ground Motion Excitation
Jiang Yicheng, Tang Jiaxiang
2001, 3(1)
Abstract:
Ananalysisofabase~isolatedstructureformulti~componentrandomgroundmotionispresented.Themeansquareresponseofthesystemisobtainedunderdifferentparametricvariations.Theeffectivenessofmainparametersandthetorsionalcomponentduringanearthquakeisquantifiedwiththehelpoftheresponseratioandtherootmeansquareresponsewithandwithoutbaseisolation.Itisobservedthatthebaseisolationhasconsiderableinfluenceontheresponseandtheeffectofthetorsionalcomponentisnotignored.