major types and time space distribution of mesozoic ore deposits in south china and their geodynamic settings the ore deposits of the mesozoic age in south china can be divided into three groups each with different metal associations and spatial distributions and each related to major magmatic events the first event occurred in the late triassic 230 210 ma the second in the mid late jurassic 170 150 ma and the third in the early mid cretaceous 120 80 ma the late triassic magmatic event and associated mineralization is characterized by peraluminous granite related w sn nb ta mineral deposits the triassic ore deposits are considerably disturbed or overprinted by the later jurassic and cretaceous tectono thermal episodes the mid late jurassic magmatic and mineralization events consist of 170 160 ma porphyry skarn cu and pb zn ag vein deposits associated with i type granites and 160 150 ma metaluminous granite related polymetallic w sn deposits the late jurassic metaluminous granite related w sn deposits occur in a ne trending cluster in the interior of south china such as in the nanling area in the early mid cretaceous from about 120 to 80 ma but peaking at 100 90 ma subvolcanic related fe deposits developed and i type calc alkaline granitic intrusions formed porphyry cu mo and porphyry epithermal cu au ag mineral systems whereas s type peraluminous and or metaluminous granitic intrusions formed polymetallic sn deposits these cretaceous mineral deposits cluster in distinct areas and are controlled by pull apart basins along the south china continental margin based on mineral assemblage age and space time distribution of these mineral systems integrated with regional geological data and field observations we suggest that the three magmatic mineralization episodes are the result of distinct geodynamic regimes the triassic peraluminous granites and associated w sn nb ta mineralization formed during post collisional processes involving the south china block the north china craton and the indo china block mostly along the dabie sulu and songma sutures jurassic events were initially related to the shallow oblique subduction of the izanagi plate beneath the eurasian continent at about 175 ma but i type granitoids with porphyry cu and vein type pb zn ag deposits only began to form as a result of the breakup of the subducted plate at 170 160 ma along the nne trending qinzhou hangzhou belt also referred to as qin hang or shi hang belt which is the neoproterozoic suture that amalgamates the yangtze craton and cathaysia block a large subduction slab window is assumed to have formed in the nanling and adjacent areas in the interior of south china triggering the uprise of asthenospheric mantle into the upper crust and leading to the emplacement of metaluminous granitic magma and associated polymetallic w sn mineralization a relatively tectonically quiet period followed between 150 and 135 ma in south china from 135 ma onward the angle of convergence of the izanagi plate changed from oblique to parallel to the coastline resulting in continental extensional tectonics and reactivation of regional scale ne trending faults such as the tan lu fault this widespread extension also promoted the development of ne trending pull apart basins and metamorphic core complexes accompanied by volcanism and the formation of epithermal cu au deposits granite related polymetallic sn w deposits and hydrothermal u deposits between 120 and 80 ma with a peak activity at 100 90 ma

genetic types mineralization styles and geodynamic settings of mesozoic tungsten deposits in south china abstract south china hosts the most abundant and largest tungsten w deposits in the world being a famous w metallogenic region located at the eastern part of the south china block which was formed by amalgamation of the yangtze and cathaysia blocks during the neoproterozoic these w deposits were mainly formed during the mesozoic the w mineralization is dominanted by greisen quartz vein skarn and porphyry types all of which are genetically related to the evolution of highly fractionated granitoids four episodes of w mineralization are recognized 1 late triassic 230 210 ma in the central and western parts of south china 2 middle jurassic ca 170 ma to early cretaceous ca 140 ma in the interior of south china with the mineralization being concentrated in southern jiangxi province between 165 and 150 ma 3 early cretaceous 136 120 ma with deposits across south china and 4 late cretaceous 100 80 ma mainly in the southwestern parts of south china these four periods of mineralization are closely related to the closure of paleo tethys and subduction of the paleo pacific plate in the late triassic these two events caused local extensional environments facilitating emplacement of the peraluminous granitoids and formation of the w deposits in the middle jurassic break off of the subducting oceanic plate resulted in emplacement of highly fractionated granites in the nanling region later anticlockwise rotation of the paleo pacific plate created widespread s type granitoids and associated middle jurassic to early cretaceous w mineralization in the interior of south china since 136 ma rollback of the subducting pacific plate resulted in weak w mineralization across south china finally a change of direction in the retreating plate from se to ese resulted in intensive mineralization of the southwestern part of south china

geological geochemical and mineralogical characteristics of the mandan and deh now bauxite deposits zagros fold belt iran the mandan and deh now bauxite deposits are located 40 km northeast of the dehdasht city in the zagros simply fold belt these deposits occur in eroded major nw se trending anticlines and occupy karst cavities near or at the boundary between the sarvak and ilam formations local uplifts at the end of the cenomanian and the mid turonian caused erosion and karstification of the sarvak formation these unconformities in the upper cretaceous favoured the formation and enrichment of bauxite deposits in the zagros fold belt the bauxite sequence in the mandan deposit consists of white gray black pisolitic red and yellow bauxites this sequence was repeated in the deh now area but without gray and black bauxites the present mineralogical studies of the sarvak formation and the mandan and deh now bauxite deposits indicate oxidizing to reducing conditions during the upper cretaceous in the zagros fold belt which had a significant effect on the compositions of the bauxites at least two phases of bauxitization can be distinguished in the study area i an oxidizing phase represented by boehmite diaspore hematite and kaolinite and ii a reducing phase represented by pyrite and chlorite geochemical data show that trace elements like zr hf nb ta th and u were enriched during bauxitization the bauxite deposits and carbonate rocks show similar ree patterns namely they are enriched in rees although the lrees are more enriched than the hrees mass change calculations demonstrate that mg mn ca k and p2o5 were leached out of the weathered system whereas al fe and si become concentrated in the residual system this study indicates that the mandan and deh now deposits are karst type bauxites formed by karstification and weathering of the sarvak formation

petrogenesis of triassic granitoids in the fengxian taibai ore cluster western qinling orogen central china implications for tectonic evolution and polymetallic mineralization abstract the petrogenesis and tectonic setting of the triassic granitoids and their relationship with the coeval au and pb zn polymetallic mineralization in the western qinling orogen wqo in central china remain debated the fengxian taibai ore cluster ftoc in the eastern part of the wqo hosts large scale triassic granitoids and numerous polymetallic deposits providing an excellent opportunity to constrain the controversies mentioned above in this work we choose the huahongshuping granodiorite pluton guji biotite monzogranite pluton taoerling biotite monzogranite dike dongtangzi granite porphyry dike and dagou dioritic dikes in the ftoc for a combined study on the zircon u pb geochronology whole rock major trace elements and sr nd isotopes la icp ms zircon u pb dating yields ages of 225 ma 224 ma and 227 217 ma for the huahongshuping pluton guji pluton and granitoid dikes respectively all these granitoids have metaluminous and high k calc alkaline series affinities and are enriched in large ion lithophile elements lile light rare earth elements lree and depleted in high field strength elements hfse with a marked lree hree fractionation la yb n 10 66 32 42 fractionation of lree la sm n 2 72 6 60 and negative eu anomalies eu 0 45 0 99 they have initial sr isotopic ratios of 0 7062 to 0 7082 and negative end t values of 9 42 to 8 09 the above features indicate that the ftoc granitoids were mainly derived from the partial melting of the neoproterozoic meta volcanic rocks induced by the decrease in pressure and the addition of water dehydrated from biotite with direct contribution of mantle materials combined with previous data on sedimentation deformation and metamorphism and tectonics we suggest that the wqo underwent the early mesozoic tectonic evolution from the subduction at 248 235 ma through syn collision at 235 225 ma to post collision at 225 195 ma integrating with the ore geology geochronology mineralogy and quartz and carbonate h o and in situ s isotope data of sulfides from different mineralization stages at representative au and pb zn deposits in literatures we proposed a conceptive model that the post collision process and granitic magmatic activity played an important role in the polymetallic mineralization within the ftoc

provenance of late carboniferous bauxite deposits in the north china craton new constraints on marginal arc construction and accretion processes abstract the north china craton ncc is bounded by two paleozoic accretionary arc terranes the north qinling terrane to the south and the bainaimiao terrane to the north the timing of arc accretion to the ncc and the architecture of the bainaimiao arc remain unclear during the building and accretion of the arcs along its margins the ncc experienced a long sedimentary hiatus since the ordovician which ended with the deposition of bauxite bearing sediments in the late carboniferous in this paper we report the u pb and hf isotopes of detrital zircons from the late carboniferous bauxite layer and use these data to constrain the tectonic evolution of the margin of the ncc the detrital zircons yield a minimum u pb age of ca 310 ma and a prominent age peak at ca 450 ma zircon crystals with ages of ca 330 ma and ca 1900 ma are more common in the bauxite samples from the northern part of the ncc than in those from the central part the ehf t values of the ca 450 ma detrital zircon crystals of the bauxite samples from the ncc are similar to those of the contemporaneous detrital zircon crystals from the north qinling arc terrane to the south but different from those of the contemporaneous detrital zircon crystals from the bainaimiao arc terrane to the north the ca 450 ma detrital zircon crystals in the ca 310 ma bauxite deposits are therefore interpreted to have been derived from the north qinling arc terrane the source of the ca 330 ma detrital zircon crystals of the bauxite deposits is interpreted to be the northern margin of the ncc where intermediate felsic plutons formed at ca 330 ma are common the results from this study support the interpretation that the paleozoic continental arc terranes and their concomitant back arc basins were developed along the margins of the ncc before ca 450 ma and the arc complexes were subsequently accreted to the craton in the late carboniferous this was then followed by the formation of a walled continental basin within the ncc

pulsed magmatic fluid releasing in the formation of the taoxihu sn polymetallic deposit eastern guangdong se china evidence from fluid inclusions cassiterite u pb geochronology and stable isotopes abstract the taoxihu deposit is a newly discovered sn polymetallic deposit in eastern guangdong se china the mineralization is related to an early cretaceous highly fractionated i type granite porphyry the ore forming process is divided into six stages i e garnet stage i quartz fluorite biotite stage ii quartz biotite cassiterite sulfides stage iii main mineralization quartz vein with minor sulfides and cassiterite stage iv quartz k feldspar biotite cassiterite sulfides stage v and quartz k feldspar chlorite sulfides stage vi fluid inclusion study shows that the hydrothermal fluids from stage ii salinity 5 9 to 13 2 wt and th 302 to 382 c to stage iv salinity 0 2 to 5 9 wt and th 275 to 315 c are of h2o co2 ch4 salt composition and show a trend of systematically decreasing temperature and salinity from early to late stages in contrast the fluids in stage v salinity 6 5 to 13 9 wt and th 223 to 343 c and stage vi salinity 6 0 to 11 8 wt and th 140 to 300 c are of the h2o salt compositional system and demonstrate also a trend of decreasing temperature and salinity with time representing a distinct hydrothermal event h o isotope data indicate that these two different fluid systems are all initially of magmatic origin in view of the almost identical cassiterite u pb ages of stage iii 139 7 1 1 ma and stage v 139 8 1 6 the two hydrothermal events are interpreted to represent two pulses of magmatic fluid releasing from the same magma chamber the first pulse is characterized by an initially single phase co2 bearing magmatic fluid that was subsequently subject to unmixing or phase separation in relation to hydraulic fracturing and decompression which lead to the main phase mineralization whereas the second pulse is the release of residual co2 free magmatic fluid which mixed with meteoric water and resulted in the second phase of mineralization

precise sm nd and u pb isotopic dating of the supergiant shizhuyuan polymetallic deposit and its host granite se china the supergiant shizhuyuan w sn bi mo deposit is hosted by the qianlishan granite a small highly fractionated granitic pluton 10 km 2 with multiple phases of intrusions within the early yanshanian granitoid province of se china strong alteration of skarn and greisen that formed in the contact zone between the first and second phases of granite intrusions and devonian limestone is responsible for the polymetallic mineralizations shrimp u pb zircon analysis indicates that the two early phases of the qianlishan granite formed contemporaneously at 152 2 ma metasomatic minerals garnet fluorite and wolframite separated from the skarn and greisen yield a sm nd isochron age of 149 2 ma that is interpreted as the formation age of the shizhuyuan deposit therefore the mineralization of the supergiant shizhuyuan polymetallic deposit formed contemporaneously with or very shortly after the intrusion of the small highly fractionated qianlishan granite

mineralogical characteristics of the karstic bauxite deposits in the xiuwen ore belt central guizhou province southwest china abstract the karstic bauxite deposits in the xiuwen ore belt of central guizhou province are hosted by the lower carboniferous jiujialu formation and show parallel unconformity with the overlying and underlying strata the ore bearing rock series that exhibits a typical coal bauxite iron structure is divided into three segments from the bottom upward namely an iron layer a bauxite layer and a coal layer based on the textural features and iron abundances the bauxite ores occurring in the middle segments are divided into three types of ores clastic compact and high iron the bauxite ores primarily comprise diaspore boehmite kaolinite illite and hematite with minor zircon pyrite rutile and feldspar the existence of rutile within diaspore lumps which were inherited from laterization suggests that diaspore was transformed from gibbsite and that karstic bauxite was transformed from laterite bauxite the results of x ray diffraction xrd scanning electron microscopy sem and electron probe x ray microanalyses epma suggest that diaspore and boehmite differ with regard to appearance and element abundance diaspore 2 10 m displays short prismatic or platy shapes and contains low sio2 abundances ranges from 0 2 to 0 51 wt whereas boehmite 0 2 5 m exhibits granular or irregular shapes and contains high contents of sio2 that vary between 2 71 and 10 4 wt the fe cu pb zn ba sulfide and sulfate mineral assemblages associated with cryptocrystalline kaolinites are discovered in the xiaoshanba deposit from the xiuwen ore belt mineralogical and geochemical studies reveal that the genesis of these assemblages is controlled by the decomposition processes of organic matter and the activities of microorganisms within the ore bearing rock series geochemical data suggest that elements rich in high organic cryptocrystalline kaolinite are produced from the adsorption effect of organic matter whereas the low concentration of these elements in pure kaolinite can be attributed to the scavenging effect during kaolinite crystallization in addition coexisting organic matter cryptocrystalline kaolinite and sulfide and sulfate minerals see sample xsb 14 indicate that the forming environment of the bauxite was hot humid tropical or subtropical climates

in situ la mc icp ms and id tims u pb geochronology of cassiterite in the giant furong tin deposit hunan province south china new constraints on the timing of tin polymetallic mineralization abstract the furong deposit located in southern hunan province china is a newly discovered giant tin deposit spatially associated with the a type qitianling granite the petrogenetic link between the giant furong tin deposit and the qitianling granite batholith remains controversial because of the lack of precise dating for the tin polymetallic mineralization here we report for the first time in situ u pb data on cassiterite obtained by la mc icp ms and the results are compared to id tims data the in situ la mc icp ms analyses of the cassiterites provide a reliable age constraint for tin polymetallic mineralization in the furong deposit yielding an isochron age of 159 9 1 9 ma at 95 confidence level mswd 18 which is indistinguishable from the id tims 206 pb 238 u weighted mean age of 158 2 0 4 ma the in situ u pb ages corroborate the ar ar dates published for the furong tin deposit which indicate that the mineralization is coeval with the emplacement of the qitianling granite batholith these results provide further evidence of a close temporal link between the pluton s emplacement and tin mineralization in the furong area the data obtained clearly demonstrate that in situ la mc icp ms u pb dating of cassiterite is a robust geochronometer for direct dating of tin polymetallic mineralization

trace and rare earth element geochemistry in tourmaline and cassiterite from the yunlong tin deposit yunnan china implication for migmatitic hydrothermal fluid evolution and ore genesis abstract yunlong tin deposit is a medial sized hydrothermal deposit in western yunnan province of china this deposit is unusual because the tin mineralization occurs exclusively within the migmatite bodies the genesis of the ore deposit has been hotly debated and various models have been proposed including granite related magmatic hydrothermal and migmatitic hydrothermal origins this paper reports a systematic trace and rare earth elements ree geochemical study in tourmaline and cassiterite from the orebodies and associated migmatites from the yunlong tin deposit tourmaline and cassiterite from this deposit show light ree lree enriched patterns with variable eu and ce anomalies consistent with hydrothermal fluids being derived from local high grade metamorphism and migmatization the data suggest that tourmaline and cassiterite were likely precipitated from migmatitic hydrothermal fluids and indicate that the yunlong tin deposit was probably formed during migmatitic hydrothermal process the high concentrations of transition metals e g sc ti v cr mn and zn in tourmalines are also consistent with this model the high concentrations of sn sr and especially sc v and cr in tourmalines can be used to discriminate tourmaline from barren deposits relative to those associated with economic tin mineralization

karst bauxite deposits in the zagros mountain belt iran more than 190 occurrences of bauxitic lateritic deposits were investigated in seven areas within the zagros simply folded mountain belt in southwestern of iran the bauxitic horizons are situated in eroded major nw se trending anticlines and occur in karst cavities near or at the boundary between the sarvak and ilam formations uplift in the cenomanian turanian period had exposed the sarvak limestone to karst weathering and during a period of unconformity layers of ferruginous argillaceous limestone debris developed and accumulated on its surface the ferruginous argillaceous debris was partly converted to bauxite folding and faulting in oligocene miocene time with ensuing erosion exposed the bauxitic horizons on the limbs and cores of anticlines the karst bauxite deposits are probably of authigenic origin as evidenced by their lithologic associations textural and mineralogy

new precise zircon u pb and muscovite 40ar 39ar geochronology of the late cretaceous w sn mineralization in the shanhu orefield south china abstract the shanhu orefield located in the northeastern guangxi province is an important part of w sn polymetallic metallogeny in the nanling region the shanhu w sn deposit is spatially associated with the yantianling granite la icpms zircon u pb dating of the yantianling granite yields late cretaceous ages of 100 9 2 2 ma and 100 8 2 3 ma hydrothermal muscovite 40ar 39ar dating yields plateau ages of 102 7 1 7 ma and 100 8 0 7 ma this date coincides well with the la icpms zircon u pb age of the yantianling granite indicating a spatial temporal link between the w sn mineralization and the granitic magmatism in combination with regional geological data it is suggested that a late cretaceous mineralization event related to granitic magmatism occurred in the nanling region which might have resulted from regional lithospheric extension

effective discharge in rocky mountain headwater streams summary whereas effective discharge q eff in mountain streams is commonly associated with a moderate flow such as bankfull discharge q bf this study found that the maximum discharge q max and not bankfull discharge is the channel forming or effective flow for gravel transport in plane bed streams where partial bed mobility causes steep gravel transport rating curves q eff may approach bankfull flow in some step pool channels where gravel moves over a static cobble boulder bed our conclusions are based on magnitude frequency analyses conducted at 41 gauged rocky mountain headwater streams because these gauged streams lacked gravel transport data as is typical comparable streams with measured transport rates were used to develop scaling relations for rating curve exponents with stream and watershed characteristics those scaling relations were then used to estimate the steepness of gravel rating curves at the 41 gauged but unsampled sites the measured flow frequency distributions were characterized by two fitted power functions the steepness of the flow frequency distributions and the estimated steepness of gravel transport relations were combined in magnitude frequency analyses to compute q eff

late cretaceous granitic magmatism and mineralization in the yingwuling w sn deposit south china constraints from zircon and cassiterite u pb geochronology and whole rock geochemistry abstract numerous late cretaceous w sn deposits associated with granitic rocks were developed in the southern part of south china however the relationship among granitic magma mineralization and tectonic setting remains disputed the yingwuling w sn deposit is spatially associated with k feldspar granite and biotite granite in the southwestern part of guangdong province south china la icp ms zircon u pb dating of k feldspar granite biotite granite and weathered ore bearing granites yielded ages of 79 ma which agree well with la icp ms cassiterite u pb age of 79 6 0 9 ma indicating a close genetic link between the yingwuling pluton and w sn mineralization geochemically both k feldspar granite and biotite granite show high sio 2 na 2 o k 2 o and low cao p 2 o 5 contents and they belong to shoshonitic series and high k calc alkaline series respectively high rb sr ratios and low nb ta and zr hf ratios of the yingwuling pluton indicate strong magmatic differentiation compared with k feldspar granite biotite granite experienced a higher degree of fractional crystallization as indicated by lower fe 2 o 3 tio 2 lree sr eu ba and zr contents and higher sio 2 hree rb cs and y contents their sr and nd isotope compositions initial 87 sr 86 sr 0 7027 and 0 7097 e nd t 5 6 and 5 7 are less radiogenic than that of the south china basement thus it is likely that some juvenile materials were involved in the formation of these granitic intrusions this is also favored by the wide range of zircon hf isotope values e hf t 6 6 to 0 8 which indicates mixing processes a type granite affinity of the yingwuling pluton shows that it was possibly formed in an extensional setting late cretaceous w sn deposits constitute an ew trending belt from guangdong to yunnan provinces which was compatible with the northward subduction of the neo tethys plate rather than the northwestward subduction of the pacific plate during late cretaceous combined with previous studies on magmatic rocks and tectonic activities during late cretaceous in south china this study suggests that the subduction of the neo tethys plate was most possibly responsible for the late cretaceous yingwuling granitic intrusion and associated w sn mineralization

modelling of fine and coarse sediment interaction over alternate bars abstract flume experiments demonstrated an ability to model bed features such as pavement and the alternate bar structure that are commonly encountered in natural gravel bed streams the effect of pool and riffle topography on the infiltration of fines into and their removal from the channel bed was examined fines were deposited first and removed last from the downstream side of the bar and from the pool area when there is no bed motion the flow is capable of completely removing the fines from the pavement but not from the subpavement when the bed is active both pavement and subpavement can be cleaned

changes in hydrologic regime by dams dams have major impacts on river hydrology primarily through changes in the timing magnitude and frequency of low and high flows ultimately producing a hydrologic regime differing significantly from the pre impoundment natural flow regime this paper presents the analysis of pre and post dam hydrologic changes from dams that cover the spectrum of hydrologic and climatic regimes across the united states our overall goals are to document the type magnitude and direction of hydrologic shifts because of impoundment using the entire database for the national inventory of dams nid for dams possessing longstanding u s geological survey usgs gages downstream we identified 21 gage stations that met length of record criteria encompassing an array of types of dams and spanning four orders of magnitude in contributing watershed area to assess hydrologic changes associated with dams we applied a hydrologic model the indicators of hydrologic alteration iha supplemented with orientation statistics for certain hydrograph parameters dams had significant impacts on the entire range of hydrologic characteristics measured by iha for many characteristics the direction and significance of effects were highly consistent across the 21 sites the most significant changes across these sites occurred in minimum and maximum flows over different durations for low flows the 1 day through 90 day minimum flows increased significantly following impoundment the 1 day through 7 day maximum flows decreased significantly across the sites at monthly scales mean flows in april and may tend to decline while mean flows in august and september increase other significant adjustments included changes in annual hydrograph conditions primarily in the number of hydrograph reversals that has generally increased for almost all sites following impoundment the number of high pulses has increased following impoundment but the average length declines the mean rate of hydrograph rise and fall has declined significantly these results indicate that the major pulse of dam construction during the previous century has modified hydrologic regimes on a nationwide scale for large and small rivers

trace and rare earth elements constraints on the sources of the yunfeng paleo karstic bauxite deposit in the xiuwen qingzhen area guizhou china abstract a number of carboniferous paleo karstic bauxite deposits occur in the xiuwen qingzhen area central guizhou province which constitute an important part of the central guizhou southern chongqing bauxite belt in southwestern china these deposits consist of lenticular and stratiform orebodies hosted in the lower carboniferous jiujialu formation which lies unconformably above carbonate rocks mainly dolomite of the middle and upper cambrian loushanguan group shilengshui formation and lower cambrian qingxudong formation although it is generally agreed that the bauxite resulted from weathering of cambrian rocks below the unconformity it remains unclear whether the carbonates alone can provide sufficient material for the formation of the deposits in this study we examined the mineralogy and major trace and rare earth elements geochemistry of bauxite and bauxitic clays from the yunfeng deposit in the xiuwen qingzhen area and compared them to previously published data of a paleo weathering profile consisting of loushanguan dolomite underlying the sub carboniferous unconformity and the black rock sequence of the lower cambrian niutitang formation in order to evaluate the sources of the bauxite the bauxite ores are composed of diaspore as the main ore mineral along with small amounts of pyrite arsenopyrite galena stibnite xenotime and uranium bearing minerals and are characterized by high contents of uranium and phosphorus chondrite normalized ree patterns and various bivariant diagrams commonly used to study the provenance of bauxite including eu eu vs tio2 al2o3 eu eu vs sm nd tio2 vs al2o3 tio2 th th vs ta th vs nb and nb vs ta suggest that the loushanguan dolomite and the niutitang black rock sequence are both potential source rocks however a comparison in u and th contents between the paleo weathering profile of the loushanguan dolomite and the bauxite samples suggests that the dolomite alone cannot provide the materials for the bauxite ores instead the black rock sequence may have contributed most of the ore forming materials which are mainly transported from source regions where the niutitang formation was exposed weathered and eroded therefore the yunfeng bauxite deposit is of mixed autochthonous and allochthonous origin

marginal bed load transport in a gravel bed stream sagehen creek california marginal bed load transport describes the condition when relatively few bed particles are moving at any time bed particles resting in the shallowest bed pockets will move when the dimensionless shear stress exceeds a value of about 0 020 as increases the number of bed particles moving increases significant motion of bed particles i e when a substantial fraction of the bed particles are moving occurs when exceeds a value of about 0 060 thus marginal bed load transport occurs over the domain 0 020 0 060 marginal bed load transport rates and associated hydraulic characteristics of sagehen creek a small mountain gravel bed stream were measured on 55 days at discharges ranging from slightly less than one half of the bank full discharge to more than 4 times the bank full discharge dimensionless shear stress varied from 0 032 to 0 042 and bed particles as large as the 80th percentile of the bed surface were transported the relation between reference dimensionless shear stress and relative particle protrusion for sagehen creek was determined by varying ri to obtain the best fit of the parker bed load function to the measured transport rates during the period of record water years 1954 1991 the mean annual quantity of bed load transported past the sagehen creek gage was 24 7 tons forty seven percent of all bed load transported during the 38 years of record occurred in just 6 years during 10 of the 38 years of record essentially no bed load was transported the median diameter of bed load was 26 mm compared to 58 mm in the surface bed material

a type granite belts of two chemical subgroups in central eastern china indication of ridge subduction abstract early cretaceous a type granites in the lower yangtze river belt central eastern china with both a 1 and a 2 chemical subgroups formed at 125 2 ma after a cretaceous ridge subduction remarkably a 1 and a 2 group granites are distributed in three zones roughly parallel to each other and to a slightly older adakite belt in general a 1 granites form in intraplate settings whereas a 2 granites near paleo convergent margins the alternate distribution of these two subgroup a type granites is compatible with a proposed cretaceous ridge subduction in the region the subduction of a dry and hot spreading ridge may have only released small amount of fluids so that metasomatism on the overriding lithosphere was undetectable correspondingly resulted in a 1 granites later on in contrast wetter and colder oceanic crust away from the spreading ridge was responsible for mantle metasomatism and consequently the formation of a 2 granites further away from the ridge the subduction angle was much steeper and dehydration of the slab had occurred earlier during the subduction and thus dramatically reduced mantle metasomatism corresponding to a 1 granites again both a 1 and a 2 granites formed within a short period of time due to slab window rollback after the ridge subduction the distribution of the a 1 and a 2 granites together with the adakite belt may be taken as discrimination indice for ancient ridge subduction

genesis of karst bauxite bearing sequences in baofeng henan china and the distribution of critical metals abstract bauxite bearing sequences are not only the main economic sources of aluminum but also of many critical metals the distribution of critical metals was determined from six bauxite profiles in baofeng and an evolution model was proposed for the formation of bauxite bearing sequences following a terrestrial deposition of the lower pisolitic bauxite horizon and the underlying clayey layer transportation and redeposition of bauxitic materials during submergence led to the formation of the upper bauxite horizon presenting finely clastic and oolitic textures as well as the intercalated clayey layers both bauxite ores and clay samples contain highly elevated contents of li b sc v ga zr nb w and total rees li contents are extremely low in high grade bauxite ores 10 92 44 77 ppm compared to highly elevated values in low grade bauxite ores 35 81 1601 ppm and clay samples 38 54 1965 ppm enlightening a new potential resource for li the bauxite bearing sequences resting on karstified carbonate the distribution pattern of ga is similar to that of li and the correlation analysis indicates that ga is primarily associated with silicates i e clay minerals the vertical distribution of li b v cr and ga shares the same pattern similar to that of k2o and sio2 being highly enriched in clayey layers relative to bauxite horizons both sc and total rees are also highly enriched in baofeng bauxite profiles highlighting a potential sc and rees resource

mineralogical control and characteristics of rare earth elements occurrence in carboniferous bauxites from western henan province north china a xrd sem eds and la icp ms analysis abstract high concentrations of rare earth elements ree are found in the bauxite deposits in the songqi area of henan province north china however no studies have been carried out on the occurrences of ree in these bauxite ores in this study we explored the ree occurrence and their possible enrichment mechanism in the songqi bauxite deposits using petrographic observation x ray diffraction xrd scanning electron microscope with energy dispersive spectroscopy sem eds and la icp ms techniques the major aluminum rich ore mineral in the songqi bauxite deposits is diaspore and other coexisting minerals include clay mineral aggregates with minor amounts of hematite pyrite anatase and zircon the bauxite ores are rich in ree and also some other critical metals li zr nb and ga most of the ree are adsorbed in the form of ions on the surface of clay minerals and diaspore and some heavy rare earth elements hree exist in the form of xenotime the sem eds and la icp ms analyses show that ree is closely related to the content of p and therefore it is possible that other dispersed and minor p bearing rare earth minerals may occur in the bauxite deposits except for the possible co adsorption of p and ree in the clays and diaspore

characterization and origin of aluminous a type granites from the lachlan fold belt southeastern australia the metaluminous to weakly peraluminous a type granites of the lachlan fold belt are a distinctive group of igneous rocks on the basis of chemical and mineralogical criteria those granites that contain 65 72 sio2 can be distinguished from other types on the basis of higher abundances of fetotal fetotal mg high field strength elements trivalent rare earth elements ga and zn mineralogically they contain fe rich hydrous mafic minerals and primary ilmenite and hence are reduced relative to the ni nio buffer however the extremely felsic a type granites sio2 72 have the same chemical and mineralogical characteristics as felsic fractionated i type granites recent analyses indicate that the lachlan fold belt a type granites have sc f alkali element trace transition element and h2o contents similar to those of other unfractionated i type granites rb sr and nd sm isotopic compositions are highly variable probably reflecting source region heterogeneity the metaluminous to weakly peraluminous a type granites of the lachlan fold belt are distinct from peralkaline rocks in terms of chemical composition petrography and field associations although these rocks have been grouped together as a single type in current classification schemes we propose that the metaluminous to weakly peraluminous a type granites such as those of the lachlan fold belt should be defined as aluminous a type granites and should not be grouped with peralkaline granites the lachlan fold belt aluminous a type granites have relatively high calculated zircon saturation temperatures we suggest that these granites were produced by high temperature partial melting of a felsic infracrustal source

climatic and hydrologic controls on upper paleozoic bauxite deposits in south china abstract the late paleozoic era was an interval of major tectonic and climatic changes including formation of the supercontinent pangea and the 60 myr long late paleozoic ice age lpia although bauxite formation declined globally from the carboniferous to the permian in conjunction with global cooling it was an interval of widespread bauxite formation in china in south china 1 the jiujialu formation bauxite deposits in central and northern guizhou zunyi area are of early middle visean age 2 the dazhuyaun formation bauxite deposits in northern guizhou wuchuan zheng an daozheng area to southern chongqing nanchuan area and southeastern guizhou fuquan kaili area are of late pennsylvanian early permian age and 3 the heshan formation bauxite deposits in western guangxi to yunnan are of middle late permian age in north china the benxi formation bauxite deposits are of late mississippian middle pennsylvanian age the contrasting trends in bauxite metallogenesis between china and the rest of the world imply different climatic patterns in the eastern tethys high annual humidity with seasonal dryness and pangea aridification this hypothesis is further supported by differences in the chemical index of alteration or cia 80 in the eastern tethys vs 50 in western pangea and in paleotemperatures mean annual temperature or mat 20 c in the eastern tethys vs 4 c in western pangea determined from permo carboniferous siliciclastic deposits permo carboniferous bauxite deposits in south china formed in coastal plain and coastal karstic depression environments in which the position of the groundwater table was related to sea level changes during the late paleozoic high frequency eustatic fluctuations caused by waxing and waning of gondwana icesheets controlled sedimentation in these coastal depositional systems leading to cyclic accumulation of coal and bauxite deposits and cycles of vadose and phreatic type bauxite formation the results of the present study show that during interglacial stages lateritization resulted from high pco2 high sea level and groundwater table elevations low precipitation and limited vegetation cover whereas during glacial stages bauxitization of these ferralitic weathering products was promoted by low pco2 low sea level and groundwater table elevations high precipitation and more extensive vegetation cover thus a unique combination of geographic climatic and eustatic factors accounted for widespread formation of bauxite in south china during the lpia

petrography and detrital zircon study of late carboniferous sequences in the southwestern north china craton implications for the regional tectonic evolution and bauxite genesis abstract the north china craton ncc has been flanked by the north qilian and north qinling arc accretionary belts to the south and southwest since 400 ma the part of the ncc to the east of the alax terrane e ncc experienced a long sedimentary hiatus and tectonic quiescence between the middle ordovician and the late carboniferous the northern margin of the e ncc was reactivated and uplifted with contemporaneous volcanism during the late carboniferous an event that partly induced the transformation of the e ncc from an erosional platform to a continental sedimentary basin however the factors controlling this transformation are still not fully understood a series of sedimentary rocks overlying ordovician carbonates in the southwestern e ncc contains a lower iron oxide layer and an upper phyllosilicate layer detrital zircons from different parts of the profile from the base to the top of the two layers have similar u pb ages these zircons have a minimum age of ca 300 ma and a prominent peak at ca 450 ma with subordinate peaks at ca 1000 and 2500 ma the near identical minimum age for the two layers suggests they were semi simultaneously deposited in the late carboniferous after the long hiatus in sedimentation detrital zircons with ages of 450 ma have initial hf isotopic compositions that vary from large negative to elevated positive these data together with the trace element compositions of these zircons indicate that these minerals formed in a continental arc environment samples from the upper sedimentary layer contain mica group minerals that are weakly buckled and fractured and have weathered to form clay minerals including chlorite and illite this suggests that the protolith of this sedimentary layer was dominated by mica schist or mica bearing granitoid that most likely located near the adjoined part between the north qilian and north qinling arc accretionary belts detrital zircons with the youngest ages ca 300 ma were considered to derive from the northern marginal region of the e ncc an area characterized by contemporaneous volcanism the co existence of the 450 and 300 ma groups of detrital zircons also suggests that the northern and southern marginal regions of the e ncc underwent almost simultaneous late carboniferous tectonic uplift and denudation a tectonic change that led to the formation of the sedimentary basins within the e ncc late carboniferous phyllosilicate layers within the profile are likely to be the equivalent of economically important diaspore and clay dominated bauxites within the e ncc suggesting that the diaspore in these bauxites was derived from mica group minerals by resolution precipitation processes

generation of late mesozoic qianlishan a 2 type granite in nanling range south china implications for shizhuyuan w sn mineralization and tectonic evolution abstract the late mesozoic qianlishan granitic complex in the western nanling range south china is associated with the shizhuyuan giant w sn mo bi polymetallic deposit it mainly consists of three phases of intrusions p 1 porphyritic biotite granite p 2 equigranular biotite granite and p 3 granite porphyry all three phases of granite contain quartz plagioclase k feldspar and fe rich biotite they have geochemical affinities of a type granites e g high feot feot mgo ratios 0 84 0 99 total alkali na2o k2o 7 50 9 04 wt high ga al ratios 10 000 ga al 2 6 and high zr nb y ce concentrations 350 ppm high y nb ratios 1 2 suggest that the qianlishan complex belongs to a2 type granite zircon u pb ages indicate a short age interval decreasing from 158 157 ma to 158 155 ma and to 154 ma for the p 1 p 2 and p 3 granites respectively these ages are similar to the mineralization age of the shizhuyuan tungsten polymetallic deposit within error the qianlishan granites were generated at low oxygen fugacity conditions based on the low values of zircon ce4 ce3 ratios 1 53 198 and significantly negative eu anomalies eun eun 0 03 0 13 in apatite new zircon ehf t values for the p 3 granite range from 13 0 to 4 4 similar to those previously obtained for the p 1 and p 2 granites both the granite and apatite grains therein are characterized by high f but low cl concentrations suggesting the influx of a high f cl component the p 2 granites especially contain higher f contents 1840 8690 ppm and w 7 158 ppm and sn 6 51 ppm concentrations and with stronger evolution features positive trends between f and w and sn of qianlishan complex indicate that high f source is crucial for mineralization of w and sn we consider that the lithospheric mantle source may have been metasomatized by subduction fluids in the far end of subduction zones to produce the a2 feature of the qianlishan granite and the fluorine was introduced through breakdown of phengite in the oceanic slab partial melting of the lithospheric mantle was induced by upwelling of the asthenospheric mantle as a consequence of slab rollback tungsten and tin have been enriched in reduced granitic magmas through fractionation enhanced by high f contents forming the giant polymetallic deposits

cretaceous granitic magmatism and mineralization in the shanhu w sn ore deposit in the nanling range in south china abstract abundant jurassic cretaceous w sn ore deposits are distributed in the nanling range in south china however the exact mineralization ages relationships between mineralization and granitic rocks and tectonic settings of these deposits remain controversial as a giant quartz vein type w sn deposit hosted in devonian sedimentary strata the shanhu orebodies are featured by located about 4 km far away from the yantianling muscovite granite zircon u pb dating of the yantianling granite yielded ages of 101 0 1 5 ma and 100 4 1 1 ma consistent with cassiterite u pb ages of quartz vein ores 100 2 1 0 ma and 100 5 1 1 ma indicating a close genetic relationship between the granitic magmatism and quartz vein type w sn mineralization the yantianling muscovite granite is characterized by highly silicious 72 01 74 62 wt high alkali na2o k2o 5 32 7 89 wt and strongly peraluminous a cnk 1 11 1 81 the granite is enriched in rb ta nd and u and depleted in sr ti and p it displays right declining chondrite normalized ree patterns with strongly negative eu anomalies and has low nb ta and zr hf ratios indicating that the granite experienced strong magmatic differentiation the yantianling granite has low whole rock end t values 9 5 to 9 3 zircon ehf t values 12 7 to 7 8 and paleoproterozoic model ages the granite belongs to s type and was derived from partial melting of meta sedimentary crust the low ce4 ce3 ratios averaging 47 of zircon from the yantianling granite indicated low oxygen fugacity similar to other w bearing granites in south china this study indicated that cretaceous granitic magmatism in the nanling range also has strong w sn mineralization potential combined with previous studies on coeval magmatic rocks and tectonic activities we propose that the yantianling s type granite and associated w sn mineralization in the nanling range were formed during the regional lithospheric extensional environment

origin of a mesozoic granite with a type characteristics from the north china craton highly fractionated from i type magmas we report geochronological geochemical and isotopic data for the mesozoic shangshuiquan granite from the northern margin of the north china craton the granite is highly fractionated with sio2 74 occurrence of annitic biotite high contents of alkalis k2o na2o rb y nb and heavy rare earth elements high feot mgo low contents of cao al2o3 ba and sr and large negative eu anomalies makes it indistinguishable from typical a type granites a mantle derived origin for the rocks of the granite is not favored because their high initial 87sr 86sr 0 706 and low end t 15 are completely different from either those of the lithospheric or asthenospheric mantle in fact their sr nd isotopes fall within the range of sr nd isotopic compositions of the archean granulite terrains and are comparable to those of mesozoic crustal derived i type granitoids in the region therefore the shangshuiquan granite is considered to be dominantly derived from partial melting of the ancient lower crust its parental magmas prove to be similar to i type magmas and to have undergone extensive fractionation during its ascent this is supported by the fact that some of the nearby hannuoba feldspar rich granulite xenoliths can be indeed regarded as the early cumulates in terms of their mineralogy chemistry sr nd isotopes and zircon u pb ages and hf isotopes it is furthermore argued that some of highly fractionated granites worldwide especially those with a type characteristics and lacking close relationship with unfractionated rocks may in fact be fractionated i type granites this suggestion can explain their close temporal and spatial associations as well as similar sr nd isotopes with i type granites our study also sheds new light on the petrogenesis of deep crustal xenoliths

differentiation of tholeiitic basalt to a type granite in the sept iles layered intrusion canada the undeformed 564 ma sept iles layered intrusion quebec canada is a large igneous body of c 20 000km3 from the base to the top it consists of a layered series dominated by troctolite and gabbro an anorthositic upper border series and a dominantly granitic upper series the parent magma of the layered series is inferred to be an iron rich tholeiitic basalt 48 wt sio2 15wt feot whole rock compositions from the chilled margin dykes cross cutting the layered series and silicic rocks from the upper series display continuous major and trace element geochemical trends ranging from basalts to ferroan metaluminous a type granites 77 wt sio2 initial 143nd 144nd 0 51201 0 51207 and 87sr 86sr 0 70353 0 70548 indicate a juvenile mantle source and minimal contamination by old crust 1 2 during crystallization geochemical modeling using the melts thermodynamic calculator combined with equations predicting mineral melt equilibria from experiments on tholeiitic basalts indicate that basaltic to monzonitic melt compositions are in equilibrium with the troctolites and gabbros of the layered series fe ti oxides saturate early in the layered series after 14 fractionation of plagioclase olivine cumulates further fractionation of fe ti oxide bearing gabbros drives the residual liquids toward silica enrichment and iron depletion major and trace element modeling indicates that the a type granites from the upper series were produced by protracted fractional crystallization of an iron rich basaltic parent magma at a fraction of residual liquid of only 8 the observed relative volumes of mafic cumulates and silicic rocks in the intrusion are in agreement with the calculations most of the intermediate compositions correspond to magmatic mafic enclave bearing granitoids and display geochemical evidence of hybridization intermediate compositions produced by fractional crystallization are scarce and a daly gap occurs from 57 to 67 wt sio2 this gap could result either from the fractional crystallization process or from silicate liquid immiscibility during that compositional interval

petrogenesis of the red mountain pluton laramie anorthosite complex wyoming implications for the origin of a type granite abstract the red mountain pluton the youngest intrusion in the laramie anorthosite complex is one of five monzonitic to granitic a type plutons intruded at 1 43 ga in the laramie mountains of southeastern wyoming the red mountain pluton ranges in composition from fayalite monzonite clinopyroxene quartz monzonite and biotite hornblende quartz syenite to granite the red mountain pluton is petrologically and geochemically distinct from the northern and southern sherman batholith the sybille intrusion and the maloin ranch pluton it has higher feo t feo t mgo and higher k 2 o is more strongly enriched in rees and at any given silica content it has lower abundances of tio 2 feo mgo cao and p 2 o 5 the fayalite monzonite in the red mountain pluton crystallized at temperatures around 1000 c and oxygen fugacities 1 2 log units below that of the fmq buffer similar to the crystallization conditions of the sybille and maloin ranch plutons the biotite hornblende quartz syenite crystallized at oxygen fugacities near or slightly below those of fmq most of the units in the pluton carry mantle like nd sr and pb isotopic compositions similar to the least contaminated anorthositic and ferrodioritic rocks of the lac indicating that the pluton evolved mainly via differentiation substantial crustal assimilation occurred only in the late dikes and the granite we suggest that all of the 1 43 ga a type intrusions in southeastern wyoming are ultimately derived from tholeiites extreme differentiation or partial melting produced monzonitic magmas that have assimilated varying amounts of siliceous crust the differences between the red mountain pluton and other a type granitoids in southeastern wyoming are related to the extent of differentiation prior to crustal assimilation the compositional ranges of a type granitoids in southeastern wyoming suggest that the geochemical spectrum of a type granites worldwide similarly are produced from evolved mantle derived melt that has assimilated varying proportions of crustal material

relative oxidation states of magmas inferred from ce iv ce iii in zircon application to porphyry copper deposits of northern chile major and trace element compositions of zircons and whole rocks from 14 barren and seven ore bearing calc alkaline intrusions from the chuquicamata el abra porphyry copper belt of northern chile have been measured in situ by excimer laser ablation ela icp ms these data permit the ce iv ce iii ratio within zircon to be calculated using a lattice strain model for mineral melt partitioning of ce iv and ce iii zircon ce iv ce iii and eun eun ratios and by inference magmatic oxidation states generally increase from older mafic to younger felsic units within this sequence porphyry copper mineralization is directly associated only with intrusions with zircon ce iv ce iii 300 and eun eun 0 4 such trends can be understood in terms of interdependent relations between oxygen fugacity sulfur speciation and solubility and chalcophile element partitioning in silicate magmas because zircon occurs in most calc alkaline intrusions and is resistant to subsolidus alteration zircon ce iv ce iii ratios provide a useful tool for evaluating the economic potential of such rocks for magmatic hydrothermal cu au mineralization the approach is general and may provide a means to infer relative oxidation state in a wide range of intermediate to felsic igneous rocks

genesis of the permian karstic pingguo bauxite deposit western guangxi china more than 0 5 billion tons of late permian bauxite overlies the karstic topography of the maokou formation of western guangxi in china here we provide new mineralogical geochemical sr nd pb isotopic and pyrite s isotope and trace element compositional data for the pingguo bauxite deposit aiming to further our understanding of the genesis of permian bauxite the pingguo bauxite contains three distinct layers a lower layer dominated by ferric clay or weathered iron ore a middle layer of cryptocrystalline and oolitic bauxite ore and an upper layer dominated by argillaceous bauxite the bauxite ore is mainly diaspore pyrite chamosite and anatase whereas the argillaceous bauxite contains diaspore kaolinite pyrophyllite pyrite and anatase two types of pyrite have been identified within the bauxite fine grained and framboidal pyrite py1 occurring in aggregates and coarse grained and euhedral pyrite py2 py1 is enriched in trace elements and is thought to have a diagenetic origin whereas py2 is deficient in trace elements and is considered to have formed by later recrystallization the s isotopic composition of pyrite 34 11 to 18 91 and visible ovoid microorganisms within the bauxite provide evidences of microbial activity during bauxite formation the sr nd pb isotopic composition of the bauxite indicates that these ores were generated by the weathering of basalts belonging to the emeishan large igneous province lip and limestones of the maokou formation microorganisms were likely to have enhanced the dissolution and weathering of the parent rock and facilitated the precipitation of diaspore under near surface conditions

importance of hydrogeological conditions during formation of the karstic bauxite deposits central guizhou province southwest china a case study at lindai deposit abstract karstic bauxite deposits are widespread in central guizhou province sw china and high grade ores are frequently sandwiched with overlying coal and underlying iron rich layers and form a special coal bauxite iron structure the lindai deposit which is one of the most representative karstic bauxite deposits in central guizhou province was selected as a case study based on textural features and iron abundances bauxite ores in the lindai deposit are divided into three types of ores i e clastic compact and high iron the bauxite ores primarily comprise diaspore boehmite kaolinite illite and hematite with minor quartz smectite pyrite zircon rutile anatase and feldspar the al 2 o 3 53 76 8 wt is the main chemical contents of the bauxite ore samples in the lindai district followed by sio 2 fe 2 o 3 tio 2 cao mgo s and p etc our geological data on the lindai deposit indicated that the ore bearing rock series and its underlying stratum have similar rare earth elements distribution pattern and similar y ho zr hf and eu eu values additionally all ore bearing rock samples are rich in mgo range from 0 16 wt to 0 68 wt and the plots of the dolomites and laterites lie almost on or close to the weathering line fit by the al bearing rocks in zr vs hf and nb vs ta diagrams suggesting that the underlying middle cambrian shilengshui formation dolomite is the parent rock of bauxite resources in the lindai district simulated weathering experiments on the modern laterite from the shilengshui formation dolomite in the lindai bauxite deposit show that hydrogeological conditions are important for karstic bauxite formation si is most likely to migrate its migration rate is several magnitudes higher than those of al and fe under natural conditions the reducing inorganic acid condition is the most conducive to al enrichment and si removal fe does not migrate easily in groundwater al enrichment and fe removal can occur only in acidic and reducing conditions with the presence of organic matter the geological and experimental studies show that coal bauxite iron structure in lindai deposit is formed under certain hydrogeological conditions i e since lateritic bauxite or al rich laterite deposited upon the semi closed karst depressions si can be continuously removed out under neutral acidic groundwater conditions the coal carbonaceous rock overlying the bauxitic materials were easily oxidized to produce acidic h 2 s h 2 so 4 etc and reductant groundwater with organic materials that percolated downward resulting in enrichment of al in underlying bauxite it also reduced fe 3 to its easily migrating form fe 2 moving downward to near the basal carbonate culminated in precipitating of ferruginous fes 2 feco 3 etc strata of the coal bauxite iron structure thus the bauxitic materials experienced al enrichment and si and fe removal under above certain hydrogeological conditions forming the high quality bauxite

discovery of the ree minerals and its geological significance in the quyang bauxite deposit west guangxi china most of the karstic bauxite deposits in china are enriched in ree and the ree has commonly been considered to be adsorbed on the surface of clay or diaspore minerals as ion state however occurrence of ree minerals in the bauxite deposits has not been reported by far in the quyang bauxite deposit from guangxi province we find ree minerals the minerals are parisite and churchite parisite is widely distributed in the ooids and matrix inducing positive ce anomaly of the ores whereas churchite is rare and occurred in the core of ooid the compositions of the ree minerals show the eu anomaly can change gently during the weathering and the eu anomaly analyses suggest that the ree in the ores are mostly derived from the underlying carbonates the parisite is formed in an alkaline condition while churchite in an acidic situation the co existence of the two minerals in the ores suggests the permian environment for bauxite formation is complex with great change of ph value moreover parisite is inferred to be formed earlier than the churchite

cassiterite u pb and muscovite40ar 39ar age constraints on the timing of mineralization in the xuebaoding sn w be deposit western china abstract the xuebaoding deposit in the songpan garze orogenic belt western china spatially associated with the xuebaoding granitic complex is a unique pegmatite type sn w be deposit within the giant songpan garze polymetallic belt a lack of precise geochronological constraints on the timing of mineralization for this deposit has precluded definitive statements relating to a genetic link between ore formation and granitoid intrusion up to now to address the temporal relationship between the emplacement of granite and the spatially associated sn w be polymetallic mineralization in the xuebaoding deposit systematic cassiterite u pb and muscovite ar ar dating were undertaken u pb data of cassiterite analyzed by in situ la mc icp ms provided an isochron age of 193 6 6 ma at 95 confidence level mswd 4 the 40 ar 39 ar dating on the muscovite intergrown with the cassiterite sample yielded a plateau age of 194 50 1 02 ma mswd 1 26 and an inverse isochron age of 194 53 1 05 ma mswd 1 34 both the ar ar dates overlap the u pb date within uncertainties placing the timing of tin mineralization at 193 194 ma this is consistent with field geological relationships that show veins cutting marble and granite and with previous sm nd dating within experimental error for scheelite and indicates that sn w polymetallic mineralization at the xuebaoding deposit occurred during the early jurassic combined with previous published trace element and ree data from the xuebaoding granites and other ore minerals as well as the timing of granite emplacement the temporal and genetic associations between granite intrusion events and sn w mineralization of this deposit have been discussed in this paper the results suggest that the pankou granite is genetically related to the polymetallic mineralization in xuebaoding sn w be deposit and further demonstrate that the latest phase of granitic intrusion is commonly favorable for sn and or w mineralization although the pukou granite also exhibits close relationships with the ore formation in its spatial distribution and element characteristics the possibility as a parent for this deposit is excluded duo to the time span from its emplacement to mineralization event that exceed the estimated life of modern geothermal systems

mesozoic large scale magmatism and mineralization in south china preface abstract south china is famous for its polymetallic deposits with more than 50 of the world s w and sb reserves and 20 of the sn reserves as well as abundant cu mo pb zn au ag ta nb hree and u this special issue reports recent progress on the tectonic evolution magmatism and ore deposits of south china which leads to a more comprehensive understanding of the mesozoic large scale magmatism and mineralization events 1 south china has been located in backarc settings during multiple subductions since the paleozoic which may have contributed to pre enrichments of the ore forming materials 2 the pacific plate subduction was a principle factor that controlled the late mesozoic large scale magmatism and mineralization in south china through flat subduction ridge subduction slab tearing and slab rollbacks

formation of high δ18o fayalite bearing a type granite by high temperature melting of granulitic metasedimentary rocks southern china the genesis of a type granites has been controversial fayalite granite is a member of the most reduced a type granites commonly thought to have been primarily sourced from tholeiitic rocks in this paper we report petrography whole rock geochemistry sr nd isotope and in situ zircon hf o isotope results for a fayalite bearing a type granite suite at jiuyishan in southern china high zircon 18 o 8 0 9 8 negative zircon ehf t 6 2 to 2 3 and evolved whole rock sr nd isotopes i sr 0 7151 0 7181 end t 7 4 to 6 6 indicate the reworking of old supracrustal rocks isotopic and geochemical results particularly downward inflections of zr and ba at 70 wt sio 2 point to fractional crystallization rather than magma mixing as the controlling process for the evolution of the igneous suite integrated petrological geochemical and isotopic studies present the first convincing case that reduced a type granites can also be generated by high temperature 960 c melting of granulitic metasedimentary rocks likely related to the upwelling of the asthenosphere and or underplating and intrusion of basaltic melts we emphasize that key factors for the genesis of this unique rock type are low oxygen fugacity f o 2 low f h 2 o and high temperature

a precise u pb age on cassiterite from the xianghualing tin polymetallic deposit hunan south china we report the first precise u pb isotope data on cassiterite from the large xianghualing tin polymetallic deposit in the central nanling district south china the results show that four separates from sample xf 51 have a relatively narrow range of 206pb 238u apparent ages varying from 152 to 157 ma and the three 206pb 238u apparent ages yield a weighted average value of 156 4 ma mswd 0 32 separates from two other cassiterite samples do not have sufficient radiogenic pb to generate a reliable 206pb 238u age seven separates from the above three cassiterite samples define a well constrained 238u 206pb isochron corresponding to an age of 157 6 ma mswd 34 a comparison of the u pb cassiterite ages with published ar ar dates on muscovite from this deposit and k ar age data on biotite from the pluton genetically related to the tin mineralization in this area demonstrates that the u pb isotope system of cassiterite is a potential geochronometer combined with the ar ar dates of muscovite from this deposit we can constrain the absolute age of tin polymetallic mineralization in xianghualing at 154 157 ma the dates obtained in this study consistent with the published geochronological results from other important deposits in this region reveal that the large scale tungsten tin mineralization in the central nanling region was predominantly emplaced during 150 161 ma

genesis of the gaosong sn cu deposit gejiu district sw china constraints from in situ la icp ms cassiterite u pb dating and trace element fingerprinting abstract the gaosong sn cu deposit in the gejiu ore district sw china is a large cassiterite sulfide deposit hosting total ore reserves of 67 4 mt 1 3 sn and 19 0 mt 1 1 cu two types of mineralization developed in the deposit i e cassiterite sulfide ore within the proximal skarn in contact with the gaofengshan biotite granite and fault controlled stratiform like cassiterite iron oxide sulfide ore in the distal carbonate country rock cassiterite grains are disseminated in both ores in situ u pb dating of one cassiterite sample from the cassiterite sulfide ore and two from the cassiterite iron oxide sulfide ore yielded weighted mean 206pb 238u ages of 84 3 1 4 ma 85 1 1 0 ma and 83 5 2 1 ma respectively the three mineralization ages are consistent with the emplacement age of the gaofengshan granite 85 8 0 6 ma within error suggesting a close temporal link between tin mineralization and granitic magmatism cassiterite grains can be divided into two types based on cathodoluminescence cl illustrations namely euhedral cst i and veinlet like cst ii in the cassiterite sulfide ore cst i has clear oscillatory zonation and is dull luminescing in the cassiterite iron oxide sulfide ore cst i core is dull luminescing blue in om cl and surrounded by a bright luminescing cst i rim yellow in om cl cst i is replaced by cst ii veinlets with bright luminescing yellow in om cl the sem cl luminescing intensity of cassiterite is mainly controlled by ti content elevated w and fe but low nb ta zr and hf concentrations of cassiterites from the gaosong deposit are distinctly different from those of cassiterites in vms sedex tin deposits but similar to those from granite related tin deposits the late cretaceous crystallization ages and trace element characteristics demonstrate that cassiterites from both ores were formed in a magmatic hydrothermal system associated with the gaofengshan granite and preclude the sedex origin of the stratiform like cassiterite iron oxide sulfide ore

geochronology and geochemistry of the late cretaceous xinpeng granitic intrusion south china implication for sn w mineralization abstract large scale late cretaceous granitic intrusions are developed in the southernmost margin of south china block they constitute an ew trending magmatic rock and mineralization belt from guangdong to yunnan province some of these late cretaceous granitic intrusions are associated with sn w mineralization but the mineralization potential of other intrusions in this belt remains unclear due to intensive weathering and thick sediment covers the xinpeng intrusion is the largest late cretaceous granitic intrusion in the yangchun basin situated in guangdong province which mainly comprises of medium to coarse grained biotite granite previous geological surveys showed that the xinpeng intrusion has undergone extensive alteration stream sediments around the xinpeng intrusion displayed sn and w geochemical anomalies in addition greisen type and quartz vein type tin occurrences have been discovered in the xinpeng intrusion which preliminarily shows a certain mineralization potential of tin and tungsten however little information is known about the geochronological and geochemical characteristics of the xinpeng intrusion and this limits our further assessment of its sn w mineralization potential here we summarize the geochemical characteristics of late cretaceous ore forming granites in south china and report the geochronological and geochemical characteristics of the xinpeng granitic intrusion for the first time la icp ms zircon u pb dating yielded a weighted mean 206pb 238u age of 77 4 0 8 ma for the xinpeng granitic intrusion linking it with the late cretaceous magma activity the xinpeng intrusion is high k calc alkaline and slightly peraluminous chondrite normalized ree elements of the xinpeng intrusion show seagull like patterns with strong negative eu anomaly high rb sr ratios and low nb ta zr hf ratios indicate the xinpeng granitic intrusion experienced highly magmatic differentiation attributed to high volatile f contents that can dramatically reduce the viscosity and solidus of magma the intrusion shows whole rock initial sr isotope of 0 717703 0 718420 and nd isotope of 5 6 5 7 and zircon hf isotope of 3 28 0 62 indicating crust derived source with some input of mantle materials taking into account all the characteristics the xinpeng intrusion agrees well with the common geochemical characteristics of late cretaceous sn w bearing granites in the yangchun basin indicating that the xinpeng granitic intrusion has a great potential of sn w mineralization

mineralogical and geochemical features of karst bauxites from poci western henan china implications for parental affinity and bauxitization abstract the poci bauxite deposits in western henan china are hosted in the lower member of upper carboniferous benxi formation unconformably overlying upon the paleokarst surface of the ordovician majiagou formation the orebodies comprise a high grade bauxite horizon characterized by the association of diaspore illite anatase and a basal iron rich horizon diaspore goethite hematite illite anatase sandwiched between the overlying clayey layer illite diaspore goethite anatase and the underlying clayey layer illite diaspore microcline goethite geochemical investigations reveal that rb cs ba cu zn are depleted while b ga bi v sc zr hf nb ta w u and th are enriched in bauxite horizons b is highly enriched in bauxite ores and clays contents 176 1061 ppm and positively associated with sio2 indicating b is mainly hosted in clay components e g dominantly illite which are considered a mixture of authigenic minerals transformed from kaolinites during diagenesis and unaltered detrital minerals mass change calculations reveal that hf zr nb ta u th sc cr and ga are stable relative to tio2 during the bauxitization process indicating these elements are mainly associated with anatase and diaspore the bauxite horizons and the underlying clays are more enriched in total ree contents rees and display more intense lree hree fractionation than the overlying clays provenance analysis shows that parental materials of poci bauxites were mainly derived from felsic dominated igneous rocks along the southern margins of the north china craton with minor contribution from siliciclastic sedimentary rocks and argillaceous components of underlying carbonates a conceptual model is proposed for the formation and evolution of poci bauxites uplift caused by the north qinling orogenesis along the southwestern margin of ncc led to the formation of karstic topography allowing aluminum rich source materials to be transported to the low karst plain and transformed into incipient bauxites under hot and humid tropical conditions when the platform was submerged fe2 ions were released from fe al oxides hydroxides under the reducing conditions associated with bacteria activity in an organic rich environment and redeposited as pyrites and siderites generating a high grade bauxite horizon and an iron rich bauxite horizon this marine modification resulted in further aluminum enrichment of bauxite ores

trace element content of karst bauxites and their parent rocks in the mediterranean belt this work deals with a concise but comprehensive study of trace element distribution in the bauxite deposits of mediterranean belt although the alloctonous and mainly detritic characters of several karst bauxite deposits are well established their parent rock has remained largely enigmatic evidence is available that some chemical elements notably zr cr and ga are largely immobile during the weathering and diagenesis and study of such trace elements in karst bauxites permits to make an approach to the lithological nature of their parent rocks it is shown by reference to analyses of bauxites from mediterranean areas that all the deposits studied are aligned from a cr rich pole related to ultramafics to another pole rich in ga and zr contents and in genetical relation with acidic parent rocks the results obtained by this way have been controlled by application of trace element accumulation coefficient which permits to distinguish four principal zones of bauxite derived from the parent rock of different lithological characters fig 3

genesis of the guangou karstic bauxite deposit in western henan china abstract the guangou bauxite deposit in western henan china is located in the north china block and to the north of the north qinling orogenic belt the orebody is hosted within the lower member of the carboniferous benxi formation which overlies unconformably upon the ordovician majiagou formation in the lower member of the benxi formation the bauxite orebody with a diaspore illite anatase mineral assemblage is sandwiched between underlying ferric clay illite hematite goethite and overlying top clay kaolinite quartz goethite according to field observations and geochemical evidence including trace and rare earth element ree compositions especially zr hf ratios the ferric clays were weathered from the underlying argillaceous limestones in the majiagou formation during this weathering process trace elements s zn ni cr v sc f ba and be are depleted li rb and b are enriched and zr hf bi ta ga nb and th are relatively immobile rees exhibit evident differentiation with enrichment of la ce pr and nd and depletion of gd tb dy ho er tm yb and lu the bauxite formed in weak reducing slightly basic water conditions according to the geneses of coexisting diaspore and anatase and it was altered during the epigenetic and second exposure periods forming kaolinite and goethite respectively interelemental relationship analyses of the ores suggest that the elemental behaviors of trace elements and rees in the bauxitization process are mainly controlled by the mineral compositions in bauxite ore and chemical properties of the elements for instance zircon rutile and anatase contain zr hf nb ta w and u based on geochemical evidence together with age data and chemical compositions of the detrital minerals both distant igneous rocks in the plate margin and paleozoic carbonates and precambrian rocks inside north china block provide the miscellaneous material for the bauxite ore and the top clay

partition coefficients of hf zr and ree between zircon apatite and liquid concentration ratios of hf zr and ree between zircon apatite and liquid were determined for three igneous compositions two andesites and a diorite the concentration ratios of these elements between zircon and corresponding liquid can approximate the partition coefficient although the concentration ratios between apatite and andesite groundmass can be considered as partition coefficients those for the apatite in the diorite may deviate from the partition coefficients the hree partition coefficients between zircon and liquid are very large 100 for er to 500 for lu and the hf partition coefficient is even larger the ree partition coefficients between apatite and liquid are convex upward and large d 10 100 whereas the hf and zr partition coefficients are less than 1 the large differences between partition coefficients of lu and hf for zircon liquid and for apatite liquid are confirmed these partition coefficients are useful for petrogenetic models involving zircon and apatite

metallogeny of tin magmatic differentiation versus geochemical heritage tio 2 sn and rb sr sn variation diagrams for granitic fractionation series from various tin and non tin provinces do not support the concept of geochemical heredity of tin i e the assumption of a primary crustal sn anomaly in tin provinces the controlling factor for the generation of tin granites is a special bulk distribution coefficient of sn probably dependent on the oxygen fugacity of the melt

critical discharge for entrainment of poorly sorted gravel entrainment criteria for gravel sized particles on river beds are usually defined in terms of shear stress but some workers have proposed that critical discharge relationships are more reliable and more convenient the critical shear stress in poorly sorted gravels is known from recent work to depend much more on relative than absolute grain size it is shown that this effect can be included in a semi theoretical equation for the critical unit discharge to move individual grain sizes in a poorly sorted bed comparisons with published data on critical discharges in a variety of rivers show that both the sensitivity of critical discharge to grain size and the absolute levels of critical discharge are predicted quite well however any prediction of critical discharge is sensitive to the assumptions made first about flow resistance and secondly about the critical stress to move average sized particles

genesis of the graphite orbicules in the huangyangshan graphite deposit xinjiang china evidence from geochemical isotopic and fluid inclusion data abstract the huangyangshan graphite deposit in the east junggar orogen china contains intriguing graphite orbicules this contribution is designed to present reasonably comprehensive assessment of their origin in this deposit the intrusive orebodies are mechanically juxtaposed against contacts with granitic wall rocks the orbicules are typically concentrically zoned in texture with a notable binary configuration involving a central core and an outer shell the orbicule cores possess mineralogical and compositional variations that are more or less similar to those of the granitic wall rocks the orbicule shells are composed of various ferromagnesian minerals clinopyroxene hornblende in stark contrast to the matrix where hornblende sanidine and albite have higher mg ab and an values respectively the replacement of silicates by graphite and sulfides pyrrhotite chalcopyrite pyrite is common the graphite throughout the matrix and orbicules features a patchy distribution of major elements c and dispersed elements cr ni co s cu zn as pb etc the carbon isotopic compositions of the orbicular ore are 20 9 to 20 5 analogous to those of the surrounding strata i e 25 6 to 19 3 the sulfur isotopic compositions of sulfides in the orbicular ore are 4 8 to 2 6 which differ from those of the surrounding strata i e 16 0 23 0 fluid inclusions principally comprise the volatile component ch4 and solid daughter minerals graphite chalcopyrite with tm 450 c vapor liquid two phase fluid inclusions formed under conditions of th 143 6 367 5 c p 3 194 bar and fo2 52 76 to 31 15 the hydrogen and oxygen isotopic values of the orbicular ore are d 110 3 to 107 0 and 18owater 10 1 11 7 zircons from the orbicular ore have 206pb 238u ages of 304 359 ma with a weighted average of 319 0 6 4 ma overlapping the geochronological age of the granitic host rocks 305 1 321 4 ma the orbicular ore has sio2 concentrations ranging from 53 30 to 72 61 wt falling within the compositional fields of granite quartz monzonite granodiorite diorite and monzodiorite in the tas classification diagram the sr nd and hf isotopic data from the orbicular ore indicate mixing between materials derived from the depleted mantle and materials derived from the crust with a dominant mantle contribution the petrographic geochemical isotopic and fluid inclusion characteristics indicate that the processes of incorporation of h2o and wall rock fragments liquid immiscibility and exsolution of a late magmatic fluid were responsible for orbicule formation in the huangyangshan deposit the following genetic model is proposed 1 in the late carboniferous a new orbicular magma containing organic matter derived ch4 and deep mantle so2 emplaced within the huangyangshan pluton contemporaneously crystal fragments and h2o were incorporated into the orbicular magma from the granitic host rocks 2 h2o saturation was reached in the orbicular magma and fostered segregation of a hydrous ferromagnesian melt orbicules with a silicic residual melt matrix 3 at approximately 630 c 2000 bar and 18 lgfo2 graphite and sulfides formed en masse through deuteric alteration 3ch4 2so2 2 fe2 7 si4o11 2 oh 2 hornblende 3c graphite 2fes pyrrhotite 8sio2 quartz 2 fe3si4o10 oh 2 fe3 oh 6 chlorite following the expulsion of a late magmatic fluid from the ferromagnesian melt

cassiterite la mc icp ms u pb and muscovite 40 ar 39 ar dating of tin deposits in the tengchong lianghe tin district nw yunnan china the tengchong lianghe tin district in northwestern yunnan china is an important tin mineralization area in the sanjiang tethyan metallogenic domain there are three n s trending granite belts in the tengchong lianghe area with emplacement ages ranging from early cretaceous to late cretaceous and early cenozoic tin mineralization is spatially associated with these granitic rocks however the petrogenetic link between the tin deposits and the host granites is not clear because of the lack of age data for the tin mineralization we investigate the possibility of direct dating of cassiterite from three typical tin deposits in the tengchong lianghe tin district using laser ablation multicollector inductively coupled plasma mass spectrometry la mc icp ms in situ la mc icp ms dating of seven cassiterite samples from the lailishan lls 1 and lls 2 xiaolonghe xlh wds dsp and hjs and tieyaoshan tys tin deposits yielded well defined 206pb 207pb 238u 207pb isochron ages to assess the accuracy of the in situ u pb dating of cassiterite 40ar 39ar dating of coexisting muscovite in samples lls 1 dsp and tys was also performed the cassiterite in situ u pb ages 47 4 2 0 71 9 2 3 and 119 3 1 7 ma respectively are in excellent agreement with the coexisting muscovite 40ar 39ar ages 48 4 0 3 71 9 1 4 and 122 4 0 7 ma respectively the u pb ages of cassiterite combined with the 40ar 39ar ages of muscovite indicate that there are three tin mineralization events in this district the lailishan tin deposit at 47 4 2 0 to 52 2 7 ma the xiaolonghe tin deposit at 71 6 2 4 to 3 9 2 0 ma and the tieyaoshan tin deposit at 119 3 1 7 to 122 5 0 7 ma these ages are highly consistent with the zircon u pb ages of the host granites it is su ggested that the cretaceous tin mineralization might have taken place in a subduction environment while the early tertiary tin metallogenesis was in a postcollisional geodynamic setting

bed load transport of mixed size sediment fractional transport rates bed forms and the development of a coarse bed surface layer fractional transport rates bed surface texture and bed configuration were measured after a mixed size sediment had reached an equilibrium transport state for seven different flow strengths in a recirculating laboratory flume fractional transport rates were also measured at the beginning of each run when the bed was well mixed and planar the start up observations allow us to describe the variation of fractional transport rates with bed shear stress for a constant bed surface texture and bed configuration the start up and equilibrium observations together allow for the first time an unambiguous description of the mutual adjustment among the transport the bed configuration and the bed surface as the transport system moves toward equilibrium we find that a substantial interaction exists among the transport bed surface and bed configuration bed forms and a coarse surface layer coexist over a range of bed shear stress under some flow conditions the size and shape of the bed forms are controlled by the presence of the coarse surface layer at higher flows the coarse surface layer is eliminated by scour in the lee of the bed forms if the bed surface is defined as that over which the bed forms move a coherent relation between the bed surface texture and the transport grain size distribution may be defined at equilibrium the transport rates of all fractions were not equally mobile defined as identical transport and bed grain size distributions although equal mobility was approached for runs in which the bed shear stress was more than twice that for initial motion of the mixture under some flow conditions the transport was observed to adjust away from equal mobility as the bed adjusted from a well mixed start up condition to an equilibrium state development of a partial static armor wherein some individual grains become essentially immobile even though other grains in the same fraction remain in transport is suggested to explain these adjustments between the transport and bed surface grain size distributions constraints on equilibrium mixed size sediment transport are defined the special conditions for which equal mobility must hold and the relevance to natural conditions of flume results and the equal mobility concept are discussed

flow resistance under conditions of intense gravel transport a study of flow resistance was undertaken in a channelized reach of the north fork toutle river downstream of mount st helens washington hydraulic and sediment transport data were collected in flows with velocities up to 3 m s and shear stresses up to 7 times the critical value needed for bed load transport details of the flow structure as revealed in vertical velocity profiles indicate that weak bed load transport over a plane gravel bed has little effect on flow resistance the plane gravel bed persists up to stresses 3 times critical at which point irregular bed forms appear bed forms greatly increase flow resistance and cause velocity profiles to become distorted the latter arises as an effect of flows becoming depth limited as bed form amplitude increases at very high rates of bed load transport an upper stage plane bed appeared velocity profiles measured in these flows match the law of the wall closely with the equivalent roughness being well represented by ks 3d84 of the bed load the effects noted here will be important in very large floods or in rivers that are not free to widen such as those cut into bedrock

geomorphology and endangered fish habitats of the upper colorado river 2 linking sediment transport to habitat maintenance alluvial reaches of the colorado river near grand junction colorado provide important habitat for the endangered colorado squawfish this paper examines recent changes in the geomorphology of the colorado river and addresses the question of what can be done to improve existing fish habitats observations of channel change during periods of above average runoff from 1993 through 1995 indicate minor scour and fill of the main channel but more significant scour and enlargement of side channel and backwater habitats and flushing of fine sediment from the bed modeled relations between discharge and dimensionless shear stress indicate that the threshold of bed load transport 0 03 occurs at about half the bank full discharge these flows are exceeded about 26 days per year on average the bank full discharge produces an average of 0 047 and is exceeded about 8 days per year the width and depth of the channel thus appear to be set by a discharge that produces an average boundary shear stress of 1 5 times greater than the critical shear stress the effective discharge is slightly less than the bank full discharge and approximately 80 of the total sediment load is carried by the highest 10 of all discharges

a new model for porphyry w mineralization in a world class tungsten metallogenic belt abstract the dongyuan deposit in the recently identified world class porphyry skarn w metallogenic belt east jiangnan orogen china is characterized by a set of nearly parallel and horizontal multi cycle orebodies within cupolas of porphyritic granodiorite almost every orebody from the top to the bottom shows similar vertical changes in vein morphology and mineral assemblage from 1 cm quartz feldspar scheelite calcite veins to 1 2 cm quartz feldspar muscovite scheelite veins to 2 5 cm quartz feldspar muscovite scheelite veins to 5 cm quartz veins from the bottom to the top of each orebody in every cycle the mole number of aliv in k feldspar decreases the concentrations of mn2 in calcite increases and the mole number of oh in muscovite decreases these changes reflect repetitive fluctuations in the concentrations of major elements that were involved in the precipitation of minerals as well as the physicochemical conditions of fluids during vein formation in the multi cycle orebodies the concentrations of mo are obviously lower in pyrite from the middle orebodies than in the top and bottom orebodies our data indicate that the ore forming fluids were sourced from multi batch fluids that were exsolved from magma the lree hree ratios in the scheelite decrease from the upper to lower orebodies similar trends are found within a single orebody from the top to the bottom of veins these trends were due to feldspar fractionation in the magmas and ore forming fluids respectively because the crystallization of feldspar tends to capture lrees therefore the following model is proposed for the formation of the dongyuan porphyry w deposit the magma crystallized first at the roof of the intrusion causing the underlying magmas to become oversaturated in h2o the exsolved h2o then accumulated at the boundary between the crystallized upper part and the underlying magmas as fluid pressures increased cracks formed in the overlying crystallized granodiorite and as a consequence the first cycle of vein networks was formed this process was repeated as the interface between magma and crystallized rock moved downwards thus forming the multi cycle w orebodies that are embedded in the pluton

effective sediment transporting discharge from magnitude frequency analysis the long term effectiveness of a geomorphic event of a particular magnitude is the product of the effect of a single event of that magnitude times the frequency with which it recurs magnitude frequency analysis if discharge frequency of a stream is assumed to be log normally distributed and if sediment transport rate is assumed to be a power function of discharge then transport effectiveness attains a maximum value at some discharge termed here the effective discharge that moves the most sediment over the long term the effective discharge and its recurrence interval may be predicted if both assumptions are correct analysis of 55 u s streams demonstrates that the observed and the predicted recurrence intervals of the effective discharge are in poor agreement this lack of agreement results from the failure of the power function of discharge to predict adequately the sediment transport rate above some high discharge threshold or thresholds the observed recurrence interval of the effective discha

late cretaceous granitic magmatism and sn mineralization in the giant yinyan porphyry tin deposit south china constraints from zircon and cassiterite u pb and molybdenite re os geochronology the yinyan porphyry tin deposit in western guangdong is spatially associated with quartz porphyry and granite porphyry la icp ms zircon u pb dating defined an emplacement age of 78 5 0 4 ma for the quartz porphyry and 79 2 0 9 ma for the granite porphyry la icp ms cassiterite u pb dating yielded tera wasserburg lower intercept ages of 78 5 0 6 78 6 1 2 and 78 2 0 7 ma for cassiterite from a cassiterite sulfide vein cassiterite sulfide ore and a cassiterite topaz quartz stringer respectively re os dating of molybdenite from seven different veins yielded an isochron age of 77 0 0 5 ma all these new age data are indistinguishable within analytical uncertainty and therefore indicate a genetic relationship between the sn mineralization and the porphyry magmatism in the yinyan deposit the ree tetrad effect and very low nb ta and zr hf ratios indicate that the quartz porphyry and the granite porphyry are highly evolved the u pb dated cassiterite is enriched in fe w and u and in high field strength elements hfses such as zr hf nb and ta the high fe nb and ta contents may be responsible for the dark luminescence of cassiterite in cl images the zr hf ratio of cassiterite may potentially be used to distinguish the mineralization type cassiterite from pegmatites has lower zr hf ratios 5 6 in comparison with granite greisen related 9 30 cassiterite cassiterite from the early hydrothermal stage typically contains higher amounts of ti nb ta zr and hf than that from the late hydrothermal stage in combination with published geochronological data of other sn w deposits in the western guangdong province two sn w metallogenic events at ca 85 and 77 80 ma have been identified these two metallogenic events are part of a larger scale 75 100 ma sn w mineralization event in south china which we suggest was probably related to the subduction of the neo tethyan oceanic plate

mineralogical and geochemical evolution of the bidgol bauxite deposit zagros mountain belt iran implications for ore genesis rare earth elements fractionation and parental affinity the present study focuses on the late cretaceous bidgol bauxite deposit in the zagros simply fold belt sw iran the orebody is located in the eroded major nw se trending koh e hosseyn anticline and hosted as discontinuous stratified layers and lenses within the upper member of the cenomanian turonian sarvak formation detailed mineralogical analysis reveals that diaspore hematite goethite anatase clinochlore chamosite and calcite are the major mineral components accompanied by minor amounts of detrital and ree bearing minerals such as rutile zircon and parisite the ore texture suggest that the bauxite material has an authigenic origin but in some parts it has been transported short distances from a primary in situ environment and redeposited in karstic depressions the spheroidal pisolites of the bidgol bauxite formed under conditions of low water activity favouring the formation of large diaspore cores and a single dry to wet climatic fluctuation the mass change calculations relative to the immobile element ti show that elements such as si fe mg k na and sr are leached out of the weathered system al ni zr ga cr and ba are concentrated in the residual system and hf ta co rb cs be and u are relatively immobile during the bauxitisation processes the nb th y v sc sn and ree are relatively immobile in the initial stage of bauxitisation processes in the bauxite ores but were slightly mobile at the later stage of bauxitisation geochemical data reveal progressive enrichment of the ree and intense lree hree fractionation toward the lower parts of the bauxite profile cerium behaves differently from the other rees especially lree and show positive anomalies in the upper horizons that gradually become negative in the deeper parts of the profile the distribution and fractionation of trace elements and rees during the bauxitisation process in the bidgol deposit are mainly controlled by the presence of ree bearing minerals fluctuations in soil solution ph ree ionization potential and the presence of bicarbonates or organic matter geochemical analyses confirm a protolith contribution from the bedrock argillaceous limestone and suggest that the source material for the bidgol bauxite was provided from a siliciclastic material derived from a continental margin the mid turonian uplift led to the formation of karstic topography rubbly breccia and a layer of ferruginous argillaceous debris that was affected by lateritic weathering under humid tropical climate subsequently mobile elements are removed from the profiles while al fe and ti are enriched resulting in the formation of the pristine bauxite materials when the platform subsided into the water again the pristine bauxitic materials were partly converted to bauxite during the exposure of bauxite orebodies on the limbs and crests of anticlines and subsequent eroding and accumulation in the karstic depressions during folding and faulting in oligocene miocene important factors such as intensity of the weathering drainage and floating flow may have improved the qualities of the bauxite ores

genetic relationship between the emeishan plume and the bauxite deposits in western guangxi china constraints from u pb and lu hf isotopes of the detrital zircons in bauxite ores abstract the formation processes and alumina sources of the large and super large bauxite deposits that have developed in west guangxi in the yangtze block have been debated for a long time shrimp zircon u pb dates combined with in situ hf isotopic data of the detrital zircons from permian bauxite ores in the western guangxi province china provide new constraints on the genesis of the bauxites in west guangxi u pb dating ages of the detrital zircons cluster around 256 ma and 261 ma this is consistent with the emplacement age of the emeishan plume thus it has been determined that the detrital zircons come from magmatic rocks related to the emeishan plume and that the emeishan plume has significant control on the formation of bauxites in addition this work presents new evidence for the evolution of the emeishan plume most of the e hf t values of the zircons around 256 ma and 261 ma are negative varying widely from 1 3 to 16 1 this data indicates the melting of yangtze block basement rocks and the mixing of magmas generated both from the mantle and from the crust occurred at the periphery of the plume in the main phase of emeishan lip magmatism this study verified that the plume induced uplift exposed carbonates as well as the mafic and felsic rocks generated by the emeishan plume to long periods of intense weathering under humid tropical conditions the weathering remnants of the high alumina magmatic rocks and carbonates were deposited on or transported to the paleokarst surface and converted to bauxites

permo carboniferous paleogeography and coal accumulation and their tectonic control in the north and south china continental plates abstract permo carboniferous strata in north china and south china were essentially controlled by paleogeography paleoclimate and plate tectonics during that time north china and south china were separate microcontinents located on opposite sides of the equator thus the characteristics of their coal deposits differ substantially in north china the coal seams were initially deposited on a north sloping epicontinental basin during the middle carboniferous by the middle of the late permian the locus of coal formation had shifted from the north to the south as a result of the uplift of the northern margin due to continental collision with the siberian plate as the paleoplate was situated in the low northern latitudes moist tropical climate and favorable geographic setting allowed the extensive development of late carboniferous and earliest permian peat swamps on the northern alluvial fluvial plain and central paralic regimes more significantly two thick coal sequences were formed in the transition belt between the alluvial apron and fluvial plain and the shoreline area where high groundwatertable fed by both rainwater and groundwater favored the formation of thick peat in swamps with northward drift the paleoplate entered the subtropic semiarid and arid climatic belt between the late early permian and early late permian coal formation was restricted to the paralic delta plain where locally oceanic wet climate and high groundwatertable prevailed following this the subduction of the paleo tethys beneath the southern margin of north china led to the upwarp of the southern margin and kept the delta system growing vertically for a considerable period so that it kept pace with shoreline fluctuations on the southern area the result was that multicycle deltaic coals were well developed at this stage in south china coal was formed in the coastal zone of an epeiric and shelf sea which connected the marinal basins the basins were frequently influenced by plate marginal tectonic movements and continental rifting related to back arc extension as a result coal formation was often interrupted by sea level fluctuations early carboniferous coal was deposited during the short regressions during the widespread transgression mainly on the restricted marine paralic plain where clastic deposition was active in the middle and late carboniferous no coal was formed because the paleoplate had drifted into a subtropic arid belt early permian coal accumulated at first in the northeast and later in the southwest due to tectonic influences in the late permian relatively thick and extensive coal was formed even though it was during a transgressive period in both the western and eastern margins under the equatorial hot humid conditions in general the seam geometry and quality particularly ash and sulfur of the coal was directly controlled by the geography and the changes in the depositional environments however the fluctuation in coal formation and the migration of thicker coal zones was indirectly controlled by paleoclimate and the sea level fluctuations in response to plate tectonic influences

mineralogical characteristics of the superlarge quaternary bauxite deposits in jingxi and debao counties western guangxi china abstract in recent decades more than 0 5 billion tons of ores scattered in the quaternary laterite in western guangxi china have been explored the ores were derived from a bauxite horizon in permian via physical break up and re sediment process utilizing various test methods i e xrd dta tg dtg sem eds and epma the mineralogical characteristics of the quaternary bauxite ores in jingxi and debao counties were investigated xrd was used together with tg dtg to obtain relatively accurate ore mineral abundance diaspore is the major phase whereas hematite kaolinite anatase chamosite gibbsite goethite illite and rutile are minor diaspore is characterized by a small particle size low degrees of crystallinity and complex chemical composition both gibbsite and goethite have a varied particle size and goethite crystals contain high al substitution and si it is clarified that diaspore chamosite and anatase were formed in a mildly reduced and alkaline depositional environment in permian while gibbsite hematite goethite and part kaolinite were precipitated from al 3 si 4 and fe 3 enriched solutions within an quaternary oxidized environment the ions al 3 si 4 and fe 3 are mostly released from chamosite in its dissolution process the different physicochemical conditions between the permian depositional and the quaternary weathering periods resulted in a complex mineral assemblage in the quaternary bauxite

cassiterite potential for direct dating of mineral deposits and a precise age for the bushveld complex granites u pb and pb isotopic measurements of cassiterite from the 200 ma tin deposits of belitung indonesia and 2100 ma zaaiplaats deposit in south africa demonstrate that cassiterite can be used to directly date mineral deposits rather than associated minerals such as zircon and rutile a precise u pb age of 2099 3 ma has been determined for cassiterites hosted in granites from the bushveld complex on conventional 207 pb 204 pb 206 pb 204 pb plots the data for the indonesian deposits give an age apparently older than that obtained from u pb plots perhaps indicative of inheritance of pb from an older source

mineralization and fluid inclusion study of the shizhuyuan w sn bi mo f skarn deposit hunan province china the shizhuyuan deposit china is a world class w sn bi mo f skarn deposit hosted by devonian limestone in the thermal aureole of the qianlishan granite complex the qianlishan complex comprises five separate intrusions including fine grained porphyritic biotite granite 182 187 ma granite 1 medium grained biotite k feldspar granite 158 163 ma granite 2 fine grained biotite and k feldspar granite granite 3 granitic porphyry 144 146 ma granite 4 and diabase 142 ma the upper part of the granite complex is characterized by extensive greisen alteration skarn zones distributed around the intrusions are mainly calcic consisting of garnet garnet pyroxene vesuvianite garnet and wollastonite vesuvianite progressively outward from the intrusion following the primary skarn formation some of the skarn zones underwent retrograde alteration the high garnet pyroxene ratio and the diopside rich and andradite rich compositions of the pyroxene and garnet indicate that the skarn belongs to the oxidized type mineralization consists of sn be veinlet ore type i in marble and porphyry massive w bi mo sn skarn ore type ii stockwork w sn bi mo f ore type iii and w sn mo bi greisen ore type iv mainly associated with granite 2 emplacement of granite 2 was accompanied by late intense fracturing characterized by stockwork mineralization type iii which was superimposed on massive skarn and greisen zones the stockwork ore consists mainly of greisen and skarn veins and veinlets with scheelite wolframite molybdenite cassiterite bismuthinite and fluorite the sm nd method has been used to analyze the sm nd concentration and data for pyroxene and garnet in the massive skarn type ii ore associated with granite 2 yields an isochron age of 157 ma this age corresponds closely to the age of granite 2 fluid inclusion studies of four types of ore samples reveal four types of inclusions aqueous two phase inclusions h2o co2 inclusions gas rich inclusions and daughter mineral bearing inclusions containing halite or calcite homogenization temperatures of fluid inclusions in skarn minerals range from 350 to 535 c the homogenization temperatures of fluid inclusions in greisen and stockwork are lower than that in skarn and range from 200 to 360 c the fluid inclusion data indicate that there are two types of fluids associated with the massive skarn and greisen having salinities from 26 to 41 wt percent nacl equiv and from 1 to 21 wt percent nacl equiv respectively the high salinity inclusions are daughter mineral bearing whereas the low salinity inclusions are dominantly aqueous with a few gas rich inclusions the results suggest the evolution of the ore forming fluids either by immiscibility or by mixing between a high temperature high salinity magmatic water and a low temperature low salinity fluid such as meteoric water consistent with previously published isotopic studies the shizhuyuan deposit is a multi element skarn highly enriched in w sn bi mo and f this is interpreted to reflect multiple sources and stages of mineralization which in turn may account for the large size of the shizhuyuan deposit

cobalt enrichment in a paleo karstic bauxite deposit at yunfeng guizhou province sw china abstract cobalt can be enriched in a variety of different geologic settings while it is mainly produced as a by product of sediment hosted stratiform cu deposits and magmatic ni cu deposits associated with mafic and ultramafic rocks in this study we report elevated co concentrations in a paleo karstic bauxite deposit at yunfeng guizhou province whole rock chemical analyses indicate that co is concentrated in carbonaceous ferruginous clay layers 167 962 ppm average 383 ppm n 5 and siderite layers 47 439 ppm average 213 ppm n 7 within the bauxite deposit the positive correlation between co and s together with petrographic and epma analyses suggests that co occurs primarily as co rich bearing sulfides sulfoarsenides rather than cobaltiferous oxides hydroxides as in most lateritic ni co deposits many of the co concentrations measured in this study are higher than the minimum grade 300 ppm or cut off grade 200 ppm for economic exploitation of co from sulfides or arsenides basing on these results we put forward the scientific significance of co enrichment in paleo karstic environments and the potential importance of co resources as by products of aluminum production in bauxite deposits

metallogeny of the large scale carboniferous karstic bauxite in the sanmenxia area southern part of the north china craton china abstract above two billion tons of bauxite were formed during the exposure of the north china craton ncc in 445 300 ma mineralogical geochemical and isotopic analyses of karstic bauxite deposits in the sanmenxia area situated within southern ncc were conducted to explore the genetic processes of carboniferous bauxite the bauxite contains three layers a lower fe bearing claystone layer a middle bauxite ore layer and an upper claystone layer fe bearing claystone is dominated by illite and hematite in the uplift and illite siderite and pyrite in the depression bauxite ore is composed of diaspore illite pyrite and anatase and the upper claystone consists of illite diaspore and anatase distinct pyrite 34s values 11 7 15 2 and 11 5 to 1 0 illite 87sr 86sr i 0 711917 0 713588 and 0 708000 0 711057 and end t 12 2 to 11 4 and 11 8 to 9 7 values and the immobile elemental ratios were obtained between the lower fe bearing claystone and upper bauxite ore and claystone together with chemistry of detrital rutile it is denoted the fe bearing claystone was formed from the underlying limestone whereas the bauxite ore and claystone were derived from both igneous rocks along craton margin and regional precambrian metamorphic rocks the visible microorganisms and wide development of framboidal pyrite with negative 34s within the bauxite ore provide evidences of microbial activity during bauxite formation bio leaching process after the deposition of allochthonous source materials caused the downward migration of ions al3 fe2 ti4 ree3 etc these ions encountered an alkaline and reducing condition in the karstic depression forming diaspore pyrite and anatase and ree enrichment at the bottom of bauxite ore this large input of raw materials warm and humid climate and microorganisms led to large scale bauxite formation in the ncc during late carboniferous

on why gravel bed streams are paved bedload transport in poorly sorted gravel bed streams downstream of dams is considered bedload and typical bed material subpavement size distributions are observed to be similar it follows that the coarse half of the subpavement moves through a reach at a rate near that of the fine half since coarser grains are intrinsically less mobile than fine grains it follows that some mechanism must act to nearly equalize mobility it is hypothesized that the pavement seen in gravel bed streams at low flow is in fact in place during typical transport events capable of moving all available sizes this pavement can provide the equalizing mechanism by exposing proportionally more coarse grains to the flow field data are used to quantify this concept and to develop a predictive relation for river pavement the model indicates that pavement should be absent in most sand bed streams in agreement with observation

cassiterite u pb geochronology constrains magmatic hydrothermal evolution in complex evolved granite systems the classic erzgebirge tin province saxony and bohemia

constraints of in situ zircon and cassiterite u pb molybdenite re os and muscovite 40ar 39ar ages on multiple generations of granitic magmatism and related w sn mineralization in the wangxianling area nanling range south china abstract the nanling range in south china hosts numerous w sn rare metal deposits associated with several cycles of polygenetic granitic intrusions in the wangxianling area of the middle nanling range igneous intrusions include the wangxianling and hehuaping granite plutons and more than 20 granite porphyry dykes the wangxianling pluton has a central phase of medium grained tourmaline two mica granite and a marginal phase of medium grained tourmaline muscovite granite the pluton hosts several tungsten deposits including shuiyuanshan and yejiwo mineralization type is dominantly scheelite greisen with subordinate scheelite skarn and wolframite quartz veins the hehuaping pluton composed of coarse grained biotite granite and granite porphyry dykes to the east of the wangxianling pluton have an associated hehuaping tin deposit with tin skarn and subordinate porphyry and greisen mineralization in situ zircon and cassiterite u pb dating molybdenite re os and muscovite 40ar 39ar dating techniques are used to refine the age spectra of granitic rocks and w sn mineralization in the wangxianling area granites of the wangxianling pluton have zircon u pb ages of 224 ma tungsten bearing quartz veins from both the shuiyuanshan and yejiwo tungsten deposits have an average molybdenite re os isochron age of 224 ma and muscovite of scheelite greisen from the shuiyuanshan tungsten deposit yields a 40ar 39ar plateau age of 214 ma the two mineralization ages are consistent with the zircon u pb age of the wangxianling pluton indicating a close association between pluton emplacement and w mineralization in the late triassic both the hehuaping pluton and granite porphyry dykes have zircon u pb ages of 156 ma in situ la icp ms u pb dating of cassiterite in both the tin skarn and tin greisen yields an average age of 156 ma showing that the sn mineralization occurred at a similar time to the late jurassic granitic magmatism thus two mineralization events are identified in the wangxianling area and include an earlier w dominant mineralization event and a later sn dominant mineralization event the earlier event is related both spatially and temporally to intrusion of the late triassic s type wangxianling granite pluton whereas the later mineralization is associated both spatially and temporally with intrusion of the late jurassic hehuaping a2 type granite pluton and a2 type granite porphyry dykes

combined zircon and cassiterite u pb dating of the piaotang granite related tungsten tin deposit southern jiangxi tungsten district china abstract the large low grade piaotang w sn deposit in the southern jiangxi tungsten district of the eastern nanling range south china is related to a hidden granite pluton of jurassic age the magmatic hydrothermal system displays a zonation from an inner greisen zone to quartz veins and to peripheral veinlets stringers five floor zonation model most mineralization is in quartz veins with wolframite cassiterite the hidden granite pluton in underground exposures comprises three intrusive units i e biotite granite two mica granite and muscovite granite the latter unit is spatially associated with the w sn deposit combined la mc icp ms u pb dating of igneous zircon and la icp ms u pb dating of hydrothermal cassiterite are used to constrain the timing of granitic magmatism and hydrothermal mineralization zircon from the three granite units has a weighted average 206pb 238u age of 159 8 0 3 ma 2 mswd 0 3 the cathodoluminescence cl textures indicate that some of the cassiterite crystals from the wolframite cassiterite quartz vein system have growth zonations i e zone i in the core and zone ii in the rim dating on cassiterite zone ii yields a weighted average 206pb 238u age of 159 5 1 5 ma 2 mswd 0 4 i e the magmatic and hydrothermal systems are synchronous this confirms the classical model of granite related tin tungsten mineralization and is against the view of a broader time gap of 6 myr between granite magmatism and w sn mineralization which has been previously proposed for the southern jiangxi tungsten district the elevated trace element concentrations of zr u nb ta w and ti suggest that cassiterite zone ii formed in a high temperature quartz vein system related to the piaotang granite pluton

li b rich rhaetian metabauxite tuscany italy reworking of older bauxites and igneous rocks abstract li b rich metabauxite layers occur in two outcrops of talus metabreccias intercalated between norian and liassic marbles in the alpi apuane tuscany italy field evidence petrographical geochemical and paleogeographic paleoclimatologic considerations suggest that bauxitic material was derived from a multistage reworking of late carboniferous early autunian primary deposits now completely removed the identified lithotypes are cookeite rich metabauxite cookeite bearing metabreccia chloritoid schist and chloritoid phyllite the mg content of calcite and the si content of muscovite and mineral assemblages indicate temperatures of 350 380 c pressures of f o 2 values of 10 30 to 10 24 for the alpine metamorphism in comparison with the average mesozoic bauxite of bronevoy et al 1985 the metabauxite is strongly enriched in si k ca mg li b be ni and ce it shows comparable contents of co la eu tb ta and th it is depleted in ga cr v zn mn hf u and is strongly depleted in sr f cu a metabauxite layer shows decreasing abundance of fe and ga from bottom to top with a pattern opposite to that of primary bauxite deposits inverted profile the strong enrichment of li and b is not related to evaporitic conditions since the mgo na 2 o and sr contents are too low and indicator minerals such as dravitic tourmaline albite and scapolite are missing during the permian volcanic products similar to the coeval peralkaline peraluminous rocks of corsica sardinia were widespread in tuscany b li rich minerals were produced by circulation of hot hydrothermal fluids within the permian volcanic rocks during and soon after their emplacement the erosion of such hydrothermal products supplied detrital material to the talus metabreccia

dating of subduction and differential exhumation of uhp rocks from the central dabie complex e china constraints from microfabrics rb sr and u pb isotope systems abstract the correlation of deformation fabrics and metamorphic reactions with geochronologic data of uhp metamorphic rocks demonstrate that the multistage subduction and exhumation history of the central dabie complex requires rapid subduction and rapid initial exhumation moreover these data show that volume diffusion is not the major resetting mechanism of radiogenic isotope systems thus our age data do not simply reflect a thermal cooling history in the investigated section the maximum age for uhp is given by the 244 3 ma 2 u pb age of a pre uhp titanite phenocryst that survived uhp metamorphism and subsequent tectonometamorphic events a minimum age for uhp is set by the 238 1 ma 2 238 u 206 pb mineral isochron age of titanite and cogenetic epidote these minerals formed from local partial melts during ascent and their age suggests fast exhumation and emplacement in the middle crust in the period of ca 238 218 ma the uhp terrain records ht metamorphism local partial melting and extensive pervasive strain below the eclogite jd grt stability field exhumation was polyphase with a first phase of fast exhumation succeeded by episodes of ht metamorphism and concomitant deformation at deep mid crustal level between 238 and 218 ma slow exhumation related to the final emplacement of tectonic units along greenschist facies shear zones did not cease before ca 209 204 ma the resetting and homogenization of radiogenic isotope systems were aided by dissolution precipitation creep which was the dominant deformation mechanism in quartz feldspar rocks in combination with fluid influx

cretaceous tectonic evolution of south china a preliminary synthesis abstract the cretaceous tectonic evolution of south china is characterized by widespread extensional basin and dome generation voluminous magma intrusion eruption and associated polymetallic mineralization all of which are of world wide interests that have stimulated the attention of geologists for more than half a century due to the lack of a comprehensive understanding of regional tectonic evolution and geodynamics of south china many controversies regarding the nature and origin of these features remain this paper attempts to make a review by synthesizing existing structural petrological geochronological and geochemical data of the cretaceous structures and magmas which guides us to propose a three stage tectono thermal evolutionary history of south china during the cretaceous period the earliest cretaceous 145 137 ma tectonic stage was characterized by syn orogenic shortening deformation and metamorphism under a nw se compressional setting which generated voluminous porphyry cu au ore bearing adakitic rocks in the lower yangtze river belt and gneissic granites in the coastal area its geodynamic origin was interpreted as combined effects of the pacific izanagi ridge subduction beneath the lower yangtze river belt and the pacific subduction beneath the cathaysia block this syn orogenic shortening stage was followed by a post orogenic stage 136 86 ma comprising two episodes of alternate extensional and shortening events the extension 136 118 ma in the earlier episode was dominated by a nw se extensional regime it led to significant taphrogenesis manifested by large scale extensional basins and voluminous magma intrusion eruption this extensional event was associated with a combination of the slab window opening during the ridge subduction and the rollback of the subducted pacific slab the subsequent nw se transpressional event led to cessation of active marginal magmatism and resulted in tectonic inversion of previous rift basins this transpression lasted from 117 ma to 108 ma and its driving mechanism was attributed to the collision between the eastern asian margin and the west philippine block the extension 107 86 ma in the later episode was dominated by a wnw ese extensional regime which led to a second phase of basin subsidence and produced numerous a and i type granites and bimodal volcanoes the tectonic regime then changed at ca 85 ma to wnw ese oriented transpression causing inversion of the late cretaceous rift basins and cessation of extension related magmatism the change of stress field from wnw ese extension to wnw ese transpression was related to the variations of the subducted slab dynamics i e the transition from either the ese ward retreat to wnw ward subduction of the pacific slab or the alternate stress during slab break off during the latest cretaceous a drastic change of regional tectonic stress orientation from wnw ese to n s occurred in south china the third stage predominated by n s extension was developed which caused a new phase of regional crustal subsidence along the youngest e w trending extensional structures

orebody vertical structure and implications for ore forming processes in the xinxu bauxite deposit western guangxi china abstract the xinxu bauxite orebodies which are contained in quaternary depressions overlying strata of permian to devonian age were formed through the break up oxidation and re sedimentation of a pre existing permian bauxite horizon with progressive karsitification the underlying strata of the quaternary orebodies were eroded out downwards in sequence gradually transiting from permian to devonian thus an older underlying stratum generally infers a higher degree of weathering a total of 47 exploration wells sampled each meter were chosen from several orebodies to evaluate the vertical distribution of four major components al 2 o 3 fe 2 o 3 sio 2 and loss on ignition in the ores the vertical evenness is quantified via a box gliding multifractal model the small width of the multifractal spectrum suggests that the vertical ore quality is even overall indicating an intertwining break up and mixing up processes during evolution of the quaternary orebody although the four components show complex spatial distributions topographic elevation displays a positive relationship with the mean fe 2 o 3 content and a negative correlation with the vertical unevenness of al 2 o 3 and fe 2 o 3 in the wells this is taken to reflect the more uniform oxidizing environment in the higher depressions which facilitates a homogeneous and greater increase of fe 2 o 3 content throughout the orebody in contrast the redox conditions in lower depressions are less oxidizing and varied in space inducing great variation in degree of fe 2 o 3 increase in the ores this study also demonstrates that in the xinxu deposit the ore forming redox environment has more impact on the ore quality than the degree of weathering as the contents show irregular vertical changes in the lower depressions it follows that it is the ancient redox environment rather than the modern conditions which affect the orebody vertical structure this clarifies the fact that the vertical structure of the orebody is jointly constrained by the physical melange accumulation of ores and the differences between the ancient redox environments in the higher and lower locations these factors should be the primary factors affecting the vertical structure of karst bauxite deposits

mineralogical and geochemical studies of boron rich bauxite ore deposits in the songqi region sw henan china the songqi region sw henan is an important bauxite province in china the bauxite ore deposits occur unconformably on the top of middle ordovician argillaceous carbonates the bauxite ores from the songqi region are characterized by unusually high boron contents in this paper we report the mineralogical and chemical compositions of selected bauxite ores from the region these new data together with existing geochemical data of soils in the region are used to evaluate the origin of boron enrichment in the bauxite ores the compositional characteristics of tourmaline in the bauxite ores suggests that this mineral was likely derived from a meta sedimentary protolith mass balance calculation reveals that tourmaline only accounts for a small portion of boron in the bauxite ores the majority of boron in the ores must occur in other forms possibly by ion absorption on the surfaces of diaspore and clay minerals in the songqi region the precambrian meta sedimentary rocks are known to contain abundant tourmalines whereas the cambrian ordovician argillaceous carbonates and the upper proterozoic shales are all enriched in boron in free ion state we suggest that these rocks provided tourmaline and boron ion to the bauxite deposits in the region most known bauxite deposits in the songqi region occur at the margins of boron rich soil domains suggesting that boron in soils is a potential exploration indicator for unknown bauxite deposits in this region

ages of ultrahigh pressure metamorphism and protolith orthogneisses from the eastern dabie shan u pb zircon geochronology the dabie shan contains two rare geologic features one the occurrence of ultra high pressure metamorphic rocks peak p 2 7 gpa uhp in the east central part of this belt and two some of these uhp rocks are characterized by anomalously 18o depleted oxygen isotopic compositions geochronological data are presented that constrain the age of the uhp metamorphism the ages of protoliths and potentially the age of hydrothermal alteration believed to be responsible for the anomalous oxygen isotopic compositions the age of uhp metamorphism in the eastern dabie shan is dated at 218 5 1 7 ma using u pb in zircon separated from host gneisses this age is identical within uncertainty with a less precise age using u pb in zircon separated from uhp eclogite 225 5 3 6 ma and with previously published ages from uhp eclogites of the dabie shan map relationships strongly support an in situ as opposed to exotic orgin of the uhp eclogites in this region the identical ages of uhp metamorphism in the gneisses and eclogites provides additional support for this interpretation the age of the protolith gneisses is dated as 772 5 9 5 ma based on the upper intercept of the zircons which accords well with other dates of granitic gneisses in the qinling belt the association of mafic and felsic magmatism is interpreted to reflect rifting along the northern margin of the yangtze block at this time these upper intercept ages may date the hydrothermal circulation of 18o depleted meteoric water which gave rise to the anomalously 18o depleted uhp protoliths of the dabie shan and sulu region the coincidence of these protolith ages with the early sinian glaciation of south china is consonant with the suggestion that the highly anomalous oxygen isotopic compositions in this region date from this time the upper intercept age of the eclogite is imprecisely determined at 447 82 79 ma but is younger than the host gneisses and is not characterized by anomalous oxygen isotopic compositions

particle size variations between bed load and bed material in natural gravel bed channels particle sizes of bed load and bed material that represent materials transported and stored over a period of years are used to investigate selective transport in 13 previously sampled natural gravel bed channels the ratio d of median particle size of bed material to the transport and frequency weighted mean of median bed load size decreases to unity with increasing drainage area bank full discharge dimensionless stream power and bed material sorting in channels with high values of d significant volumes of fine bed load are transported during discharges that are less than bank full which is commonly associated with general entrainment of the coarse pavement in many gravel bed channels this indicates transport of fine bed load over a more stable substrate of coarser bed material the apparent breakdown in equal mobility of the bed as a whole may be caused by areal segregation of poorly sorted bed material into superiorly sorted patches of varying mean size likely sources of selectively transported fine bed load include fine patches that have low entrainment thresholds and high virtual particle velocities a simple sediment budget applied to measurements from three channels indicates that velocities of material from fine patches in pools relative to velocities of average bed material are high in low order channels and decrease distally as more bed material that represents the bed as a whole is accessed for bed load by deeper annual scour

genesis of the maikhura tungsten tin skarn deposit tajik tien shan insights from petrology mineralogy and fluid inclusion study abstract the maikhura w sn skarn deposit is situated in the gissar segment of the southern tien shan it associates with a late carboniferous early permian composite granitoid pluton which includes earlier ilmenite series transitional metaluminous to peraluminous i type granodiorite and later magnetite series biotite to biotite tourmaline granite leucogranite the oxidized granitic intrusions exhibit a type granite affinity and define a geochemically and genetically distinct group of w sn deposits the deposit incorporates both pyroxene and garnet dominant prograde and retrograde skarns with scheelite and locally magnetite overprinted by highly reduced pyrrhotite stable post skarn mineral assemblages of hydrosilicate and phyllic alteration stages containing scheelite cassiterite and sulfides the fluid inclusions data indicate the involvement of carbonic free aqueous moderately saline 9 9 16 wt nacl eq high pressure 2 1 0 5 kbar hot fluid which was sourced from crystallizing magma and formed prograde calcic skarn this fluid evolved into a sodic chloride slightly less saline 8 6 11 wt nacl eq lower pressure 1 7 0 5 kbar cooler fluids toward the retrograde skarn stage this stage was characterized by deposition of scheelite in association with magnetite the hydrosilicate propylitic alteration was formed from a low salinity ca enriched homogenous aqueous carbonic methane rich fluid at lower temperatures 350 400 c with precipitation of scheelite and cassiterite particularly in phlogopite chlorite oligoclase quartz assemblage corresponding ph decrease explains the trend toward overlapping fields of insoluble cassiterite and scheelite the phyllic alteration assemblages were formed from a boiling aqueous carbonic co2 dominated low salinity fluid at temperatures of 310 250 c and pressure of 1 85 0 1 kbar the alteration evolving from chlorite through muscovite to albite dominant paragenesis indicates a trend toward higher ph less acidic conditions and was accompanied by precipitation of scheelite and cassiterite with further deposition of sulfides a homogeneity of 34s values suggests sulfur isotope homogenization in a magmatic chamber whereas their proximity to the meteorite standard supports a magmatic source of sulfur the depletion in heavy sulfur isotope of sulfides from hydrosilicate propylitic alteration 34s 1 8 to 0 7 to sulfides from phyllic alteration 34s 0 1 to 0 8 is consistent with the evolution from ilmenite series to magnetite series magmatic source

hf isotopic compositions of the standard zircons and baddeleyites used in u pb geochronology abstract zircon and baddeleyite u pb geochronological dating is widely used in solid earth sciences and the advent of rapid in situ methods of analysis such sims and icp ms has re emphasized the importance of having uniform standards recently it has been shown that hf isotopic data can provide important information on these minerals since they contain high concentrations of hf but have low lu hf ratios which results in negligible age correction however the complex internal structures that result from multiple thermal events such as inherited cores and metamorphic overgrowths require that the hf isotopic data be measured with high spatial resolution however the isobaric interferences of 176 yb and 176 lu on 176 hf hamper the precise determination of the 176 hf 177 hf ratio during in situ laser ablation mc icpms analysis it is shown here that mass biases of yb yb and hf hf change with time during analyses and behave differently for solutions and solid material therefore it is suggested that the mean yb value of the individual spot be used to obtain the precise isotopic composition for in situ zircon and baddeleyite hf isotopic analyses for low yb hf 176 yb 177 hf yb value have little effect on the accuracy of the hf isotopic composition however the appropriate yb isotopic abundance is necessary for high yb hf 176 yb 177 hf 0 001 zircons and baddeleyites since the interference of 176 yb on 176 hf is significant using the mean yb value of the individual spot and newly published yb isotopic abundance data six standard zircons and two standard baddeleyites have been investigated using a neptune mc icpms with 193 nm laser for zircons the obtained 176 hf 177 hf ratios are 0 282307 31 2sd for 91500 0 282680 31 2sd for temora 0 281729 21 2sd for cz3 282177 17 2sd for cn92 1 0 282983 17 2sd for fm0411 and 281234 11 2sd for phalaborwa the baddeleyites from phalaborwa and sk10 2 have 176 hf 177 hf ratios of 0 281238 12 and 0 282738 13 2sd these results agree well with the values obtained by the solution method and indicate that these standards have different hf isotopic compositions in which the extremely low 176 lu 177 hf and 176 yb 177 hf values of cz3 zircon and phalaborwa baddeleyite make them excellent standards for machine calibration during in situ zircon hf isotopic measurement with the other standards being more suitable for the development of the correction method

the formation of the late cretaceous xishan sn w deposit south china geochronological and geochemical perspectives abstract the xishan sn w deposit is spatially related to k feldspar granites in the yangchun basin western guangdong province south china la icp ms zircon u pb dating for the xishan pluton defines an emplacement age of 79 ma 78 1 0 9 ma 79 0 1 2 ma 79 3 0 8 ma consistent with the mineralization age of the xishan sn w deposit constrained by molybdenite re os isochron age 79 4 4 5 ma and la icp ms cassiterite u pb ages 78 1 0 9 ma and 79 0 1 2 ma for the cassiterite quartz vein these indicate a close genetic relationship between the granite and sn w mineralization the xishan k feldspar granites have geochemical characteristics of a type granites e g high total alkali na 2 o k 2 o 7 88 10 07 wt high ga al ratios 10000 ga al 2 6 and high zr nb ce y concentrations 350 ppm they are further classified as a 2 type granites the whole rock isotopic compositions of k feldspar granites initial 87 sr 86 sr 0 705256 0 706181 e nd t 5 4 to 4 8 and zircon e hf t values 7 8 to 2 0 suggest a mixed magma source the low zircon ce 4 ce 3 ratios 12 88 of k feldspar granites suggest low oxygen fugacities which is key for enrichment of tin in primary magmas the k feldspar granites have experienced strong differentiation as indicated by their high rb sr and k rb ratios and low nb ta and zr hf ratios which play an important role in ore forming element transportation and concentration a type granite characteristics of the xishan pluton show that it formed in an extensional environment the high f and low cl characteristics of the k feldspar granite are most probably attributed to slab rollback in the late cretaceous the xishan sn w deposit was located near the interaction of the circum pacific and the tethys tectonic realms late cretaceous sn w deposits including the xishan deposit form an ew trending belt from guangdong to yunnan province in south china this belt is in accordance with the direction of the neo tethys slab rollback in the late cretaceous in addition the ns trending extension has been recognized in the late cretaceous in south china we propose that the xishan sn w deposit should be attributed to the neo tethys slab rollback in the late cretaceous

the effect of fluorine on viscosities in the system na2o al2o3 sio2 implications for phonolites trachytes and rhyolites the effect of fluorine on melt viscosities of five compositions in the system na2o al2o3 sio2h as been investigateda t one atmospherea nd 1000 1600 cb y concentric cylinder viscometry the compositions chosen were albite jadeite and nepheline on the join naalolsio2 and two others of the join at 75 mole percent sio2 one peralkaline and one peraluminous all melt viscosities were independent of shear rate over two orders of magnitude indicating newtonian behavior all viscosity temperature relationships were arrhenian within error fluorine reduces the viscosities and activation energies of all melts investigated the viscosity reducing power of fluorine increases with the sio2 content of melts on the join naalo2 sio2 and is a maximum at na al molar i for melts containing 75 mole percent sio2 fluorine and water have similar effects on aluminosilicate melt viscosities probably due to depolymerization of these melts by replacement of si o si al bridges with si oh and si f bonds respectively evidence from slag systems shows that fluorine also reduces the viscosity of depolymerized silicate melts the viscous flow of phonolites trachytes and rhyolites will be strongly afected by fluorine it appears that fluorine contents of igneous rocks may be combined with water in calculation schemes for determining the viscosity of natural melts