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

a late cretaceous tin metallogenic event in nanling w sn metallogenic province constraints from u pb ar ar geochronology at the jiepailing sn be f deposit hunan china abstract the jiepailing deposit located in southern hunan province china is a giant sn be f deposit in the nanling w sn province the sn be f mineralization is spatially associated with the jiepailing granite porphyry la mc icp ms zircon u pb dating of the jiepailing granite porphyry yielded a weighted mean 206 pb 238 u age of 90 5 0 9 ma mswd 0 32 which is interpreted as the emplacement age of the granite porphyry hydrothermal muscovite yields a plateau 40 ar 39 ar age of 92 1 0 7 ma mswd 0 9 which is well consistent with the zircon u pb age of the jiepailing granite porphyry responsible for the sn be f mineralization indicating a temporal link between the emplacement of the jiepailing granite porphyry and the sn be f mineralization our new high precise geochronological data suggest that the jiepailing giant sn be f deposit and related granite formed during the early late cretaceous 92 90 ma which provided convincing evidence for a previously unrecognized metallogenic event related to late cretaceous granitic magmatism in nanling region the occurrence of the late cretaceous sn metallogenic event identified in southern hunan province further highlights the importance of systematic metallogenic studies of the nanling w sn province integrated with high precise geochronological data obtained previously it is suggested that the nanling region mainly experienced three tectonomagmatic activities and lithospheric thinning events during mesozoic which are responsible for three sn w metallogenic events to form the world class nanling w sn metallogenic province

absolute timing of sulfide and gold mineralization a comparison of re os molybdenite and ar ar mica methods from the tintina gold belt alaska new re os molybdenite dates from two lode gold deposits of the tintina gold belt alaska provide direct timing constraints for sulfide and gold mineralization at fort knox the re os molybdenite date is identical to the u pb zircon age for the host intrusion supporting an intrusive related origin for the deposit however 40ar 39ar dates from hydrothermal and igneous mica are considerably younger at the pogo deposit re os molybdenite dates are also much older than 40ar 39ar dates from hydrothermal mica but dissimilar to the age of local granites these age relationships indicate that the re os molybdenite method records the timing of sulfide and gold mineralization whereas much younger 40ar 39ar dates are affected by post ore thermal events slow cooling and or systemic analytical effects the results of this study complement a growing body of evidence to indicate that the re os chronometer in molybdenite can be an accurate and robust tool for establishing timing relations in ore systems

geological and geochronological constraints on the formation of the jurassic maozaishan sn deposit dayishan orefield south china abstract the dayishan orefield in the central nanling belt is one of the most important sn districts in south china within this district there are more than seven medium to large sn sn cu and pb zn sn deposits the mineralization is associated with altered granites and greisen quartz veins both of which occur in the inner part of the dayishan granite batholith cassiterite is the principal ore mineral accompanied by subordinate molybdenite cassiterite separates from altered and mineralized granite and greisen quartz veins have concordia ages of 156 5 2 8 ma mswd 3 1 and 158 0 1 8 ma mswd 1 4 respectively molybdenite separates from molybdenite quartz veins that crosscut the greisen alteration have a re os isochron age of 157 9 7 7 ma mswd 26 whereas zircon separates from the porphyry monzogranite have a u pb age of 156 3 1 2 ma these ages are identical within the analytical error and together with the field relationships provide tight constraints on the sn mineralization at around 156 ma rhenium contents of the molybdenite suggests that the ore forming materials were derived from a crustal source whereas s and pb isotopic data point to mixed sources we suggest that the maozaishan deposit was formed by intrusion of the related pluton and occurred in the late jurassic during a period of lithospheric thinning and crustal extension of the south china block

highly fractionated early cretaceous i type granites and related sn polymetallic mineralization in the jinkeng deposit eastern guangdong se china constraints from geochronology geochemistry and hf isotopes abstract the recently discovered jinkeng deposit located in eastern guangdong province se china is a granite related cassiterite sulfide type sn cu pb zn deposit in the cathaysia block zircon u pb dating of the biotite granite and fine grained granite associated with the deposit yielded concordant ages of 144 7 0 8 ma and 141 1 1 3 ma respectively these ages are consistent within error with the molybdenite re os isochron age of 139 3 2 5 ma for the deposit indicating a temporal link between the emplacement of granitic plutons and polymetallic sn mineralization combined with the regional mineralization ages we propose that the 145 135 ma interval represents another significant period of sn w mineralization in southern china in addition to those already recognized the biotite granite and fine grained granite have similar geochemical characteristics both are weakly peraluminous high k and calc alkaline containing abundant si na and k and low concentrations of fe mg ca and p compared to primitive mantle and unfractionated granitoids they are enriched in rb th u k and pb have relatively high rb sr and low k rb values are depleted in ba sr and ti and have prominent negative eu anomalies eu 0 05 0 19 characteristic of highly fractionated i type granites zircons from these granites have ehf t values ranging from 9 2 to 3 3 and hf model ages tdm2 of 1776 1406 ma suggesting that the granites formed by the partial melting of proterozoic basement material and contain a minor mantle derived component highly fractionated and reduced fo2 below nno magma facilitated the enrichment of sn existing knowledge on the tectonic evolution of this region and new data from this study indicate that the granites and associated sn mineralization in the jinkeng deposit formed in an extensional environment at 140 ma likely related to the rollback of the paleo pacific plate

origin of nodules in mixed siliciclastic carbonate sandstones the lower eocene roda sandstone member southern pyrenees spain abstract calcite cement is heterogeneously distributed in the eocene roda sandstone member strongly cemented nodules and layers intercalated within less well lithified sandstones are common the nodules yield valuable information about the factors that controlled the onset and the degree of cementation all nodules are associated with abandonment surfaces formed when sedimentation ceased for a variable length of time the nodules represent a first stage in the development of continuous hardgrounds the initiation of early cementation was dependent on a combination of several parameters such as grain sorting and the presence and amount of carbonate nucleation centers early cementation began at distinct points now manifested by nodules aggrading into layers in cases where sedimentation had ceased for a sufficient length of time the resulting variability in the amount of cement determines the present day difference in weathering behaviour between nodules and the adjacent less well cemented sandstones

mantle derived noble gases in ore forming fluids of the granite related yaogangxian tungsten deposit southeastern china more than 90 of the tungsten resources of china are in the nanling region of south china and the yaogangxian vein deposit is the largest tungsten deposit in this region the tungsten deposits have ages of 150 160 ma and are spatially temporally and genetically related to granites which were previously believed to be produced by crustal anatexis this paper provides he and ar isotope data of fluid inclusions in pyrite and arsenopyrite from the yaogangxian w veins 3he 4he ratios range from 0 41 to 3 03 ra where ra is the 3he 4he ratio of air 1 39 10 6 and 40ar 36ar ratios from 328 to 1 191 moreover there are excellent correlations between he and ar isotopic compositions the results suggest that the ore forming fluids are a mixture between a crustal fluid containing atmospheric ar and crustal 4he and a fluid containing mantle components it is likely that the former is a low temperature meteoric fluid and the later is a fluid exsolved from the w associated granitic magma which formed by crustal melting induced by intrusion of a mantle derived magma

paleomagnetism of the cambrian moore hollow group texas evidence for a primary magnetization carried by detrital magnetite petrographic and paleomagnetic studies of the cambrian moore hollow group texas establish the presence of three magnetic minerals and several components of magnetization hematite is the dominant carrier of the magnetic remanence in most samples and is primarily a diagenetic replacement of preexisting fe bearing phases hematite dominant samples have characteristic directions which range from shallow easterly to shallow southerly this distribution suggests multiple components of magnetization acquired at various times in the paleozoic the paleopole obtained for an unmineralized breccia 135 7 e 15 4 n represents either a chemical remanent magnetization of middle ordovician to early silurian age or a vector addition of two or more cambrian through silurian components mineralized breccias at the silver creek mississippi valley type deposit yield a permian direction 117 0 e 51 6 n because hematite in this deposit predates mineralization the permian age represents a maximum age for the mineralization at silver creek many samples contain goethite as a replacement of fe dolomite glauconite and pyrite the direction of magnetization carried by goethite is near the present geomagnetic field or in a minority of samples antipodal to it rounded ti magnetite was identified by sem in magnetic extracts from siliciclastic poor facies irm acquisition and thermal demagnetization confirms the presence of magnetite in these samples some samples contain an apparent modern viscous remanent magnetization the dominant component 72 samples 10 sites has a site mean declination of 93 8 and inclination of 14 5 with an 95 8 5 corresponding to a pole position at 163 0 e 0 6 s the presence of detrital magnetite polarity changes lack of evidence for prolonged burial and the proximity of this pole position to other late precambrian cambrian poles suggest that this component of magnetization indeed reflects the late cambrian paleopole for cratonic north america

shear bands in plane strain compression of loose sand experimental results are presented which characterize the behaviour of a loose fine grained water saturated sand tested under globally undrained and drained conditions in a plane strain apparatus the objective of this investigation is to provide insight into the phenomenon of shear banding in loose sand together with local measurements of boundary forces and deformations stereophotogrammetry is used to investigate the progression of strain localization in plane strain compression typical results and findings concerning the evolution of non homogeneous deformation are presented in detail shear banding occurred in both undrained and drained experiments on loose masonry sand in general temporary modes of strain localization observed during macroscopically uniform deformations of a specimen gave way to a single persistent shear band a clear pattern of onset of the formation of the persistent shear band mobilization of the maximum effective friction and complete formation of the band was observ

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

do stable isotopes in carbonate cement of mio pleistocene himalayan sediments record paleoecological and paleoclimatic changes non pedogenic carbonates such as carbonate cement and nodules in the sandstones are quite common in the terrestrial geological record unlike pedogenic carbonates their stable isotope ratios lack investigations for paleo climatic reconstructions the present investigation therefore explores the possibility of use of stable isotope studies of non pedogenic carbonates from the mb pleistocene siwalik group of sediments exposed in the ramnagar sub basin of the nw himalaya petrographic studies reveal the dominance of micrite fabric in carbonate nodules both of pedogenic and non pedogenic samples irrespective of specific stratigraphic unit however calcite as cement in the sandstones shows the dominance of micrite fabric in the younger in age sediments seventy two non pedogenic carbonate samples from the carbonate nodules and cement in the siwalik sandstones ranging in age between similar to 1 ma and 12 2 ma were analyzed for delta c 13 and delta o 18 values the delta c 13 values vary from 24 77 parts per thousand to 1 1 parts per thousand and delta o 18 values vary from 15 34 parts per thousand to 7 81 parts per thousand pedogenic and non pedogenic carbonates ranging in age between similar to 1 ma and 6 ma have largely similar delta c 13 values and the range of delta c 13 values indicate the dominance of c 4 type of vegetation however unlike pedogenic carbonates which showed the dominance of c 3 type of vegetation pre 7 ma on the basis of delta c 13 depleted isotopic values singh et al 2011 delta c 13 values are largely enriched in the corresponding aged non pedogenic carbonates revealing no information on specific type of vegetation likewise paleoprecipitational reconstructions from delta o 18 values in pedogenic carbonates showed a progressive increase in aridity from similar to 12 ma to recent excluding short term increases in rainfall monsoon intensity at around 10 ma 5 ma and 1 8 ma singh et al 2012 on the contrary such reconstructions are not possible from the delta o 18 values of non pedogenic carbonates and indeed the delta o 18 values of non pedogenic carbonates are largely depleted to as much as 6 parts per thousand from the corresponding pedogenic carbonates such differences in delta c 13 and delta o 18 values of non pedogenic carbonates from pedogenic carbonates are primarily due to the dependence of the former on groundwater conditions responsible for precipitating carbonate further a comparison of isotopic values between non pedogenic and pedogenic carbonates can be interpreted that post 6 ma and pre 6 ma non pedogenic carbonates were largely formed by shallow and deep groundwater conditions respectively the result of these investigative studies therefore suggests that the stable delta c 13 and delta o 18 values of non pedogenic carbonates unlike the pedogenic carbonates and irrespective of nature of calcite fabric showed their little importance in paleoclimatic and paleoecological reconstructions c 2014 elsevier b v all rights reserved

calcite cemented concretions in shallow marine and fluvial sandstones of the birket qarun formation late eocene el faiyum depression egypt field petrographic and geochemical studies implications for formation conditions abstract this work deals with field petrographic stable oxygen and carbon isotopic and elemental composition studies of pervasively calcite cemented concretions within shallow marine and fluvial host sandstones of the upper eocene birket qarun formation of el faiyum depression egypt in order to decipher their conditions of formation the studied concretions have been classified into two types type 1 and type 2 type 1 concretions occur in the fluvial sandstones deposited at the northern scarp of birket qarun some of these concretions are confined within the host sandstones while others appear as erosional remnants of the host sandstones they show oblate spheroidal to flattened ellipsoidal shapes and have variable diameters ranging from 0 5 to 3 m geometrically they are bedding parallel concretions with spacing ranges from 0 3 to 1 m petrographically the rocks of type 1 concretions are attributed to quartzarenite cemented by sparry calcite that exhibits poikilitopic texture these calcite cements are characterized by small ranges of 18o 8 36 to 9 73 pdb and 13c 11 01 to 15 04 pdb values they were originated from light root respired carbon and media of meteoric pore water geometry of these concretions is interpreted to correspond to fluid flow during early diagenetic processes type 2 concretions are recorded in the shallow marine sandstones deposited at gabal el lahun they are confined within the host rocks these concretions exhibit spheroidal to ellipsoidal shapes and range from 0 3 to 1 m in diameter geometrically the individuals of these concretions occur as scattered strata bound and continuously cemented layers microscopically the rocks of type 2 concretions are mainly belonged to quartzarenites cemented by micritic and microsparitic calcites these calcites have small ranges of 18o 3 4 to 4 60 pdb and 13c 0 78 to 1 67 pdb values the calcite cements of type 2 concretions are interpreted to be a result of dissolution of marine carbonate shells at shallow burial depth in slightly modified marine pore water geometry of these concretions was controlled by the spatial distribution of carbonate shells in their host sandstones this study imports an idea that variation of depositional environments of the host clastic rocks of concretions plays an important role in the difference of modes of formation of their concretions also caution should be made to simplify and generalize the conditions of formation of concretions in host clastic rocks deposited in one sedimentary basin of similar age

the internal structure of carbonate concretions in mudrocks a critical evaluation of the conventional concentric model of concretion growth abstract carbonate concretions have traditionally been viewed as forming concentrically through the progressive addition of carbonate to the outer edge of the growing concretion this conventional model of concretion growth is based mainly upon center to edge textural and geochemical trends that are consistent with concentric growth however a number of recent studies of concretions in mudrocks have documented complex zonation that is not compatible with the conventional concentric model in some cases complexly zoned concretions contain late stage cements that precipitated throughout the concretion body none of the center to edge relationships used to support the conventional concentric model exclude more complex modes of origin as concretions that fit the conventional model may be the exception rather than the rule high resolution petrographic analysis of concretions should always be used to characterize internal structure and mode of growth prior to interpretation of geochemical and textural data

a tentative discussion on differences between large scale tungsten and tin mineralizations in south china both tungsten and tin are the most prevailing mineral resources in china large scale tungsten and tin mineralizations took place mostly in south china especially in the nanling mountains and the neighboring areas the two elements are very closely related to and accompanied with each other and always occur together in most ore deposits however differences do exist between tungsten and tin mineralizations in many aspects spatial distribution shows that the eastern sector of the nanling mountains is characterized by strong and dense w mineralization while sn mineralization becomes stronger westwards china s two largest sn ore deposits are distributed in the western margin of the south china fold system although both tungsten and tin mineralizations have the same highest ore forming epoch of 160 150 ma the tin mineralization is spanned from the late xuefeng period 800 ma to late yanshanian movement 80 ma the late yanshanian movement is in fact another highlight of tin mineralization the tin bearing granite and tin mineralization show much closer relationship with the participation of mantle derived materials than tungsten mineralization therefore the large scale tin mineralization took place either near the so called shi hang zone where long term deep faulting was activated and a type granites were emplaced or during the late yanshanian period when the south china continent was in a strong tensional geodynamic environment the principal factors responsible for these differences may include the diversity of geochemical properties between the two elements and the differences in tectonic backgrounds stratigraphic characteristics and magmatic activities between the eastern part and the western part of south china

spatial variability drained and undrained deviatoric load response geotechnical properties vary in space geostatistical parameters such as the mean the standard deviation and the correlation length are characteristic for each sediment and formation history the effects of spatial variability on the drained and undrained shear response of soils are investigated using numerical parametric studies where multiple realisations are tested for selected geostatistical parameters results show that the mean undrained shear strength decreases as spatial variability and correlation length increase spatial variability prompts strain localisation along neighbouring weak zones under both drained and undrained loading heterogeneous contractive media show internal homogenisation during drained deviatoric loading and the drained shear resistance evolves towards the critical state media with higher variability and longer correlation length require higher strain to attain internal homogenisation anisotropy in spatial correlation causes anisotropy in shear strength an intermediate d

molybdenite re os and muscovite 40ar 39ar dating of the xihuashan tungsten deposit central nanling district south china abstract the xihuashan tungsten deposit in the central nanling region south china is an important vein type ore deposit hosted in cambrian strata and mesozoic granitic intrusions wolframite and molybdenite are the principal ore minerals the gangue minerals are mainly quartz and muscovite wolframite and molybdenite are products of the first stage hydrothermal activity whereas muscovite formed dominantly at the second stage molybdenite re os and muscovite 40ar 39ar dating have been carried out to investigate the age of mineralization re os isotopic dating for molybdenite associated with wolframite yield a precise well constrained isochron age of 157 8 0 9 ma mswd 1 5 ar ar isotopic analyses of muscovite yield a plateau age of 152 8 1 6 ma in agreement with an inverse isochron age of 152 8 1 6 ma which is 5 mys younger than the re os age the molybdenite re os age is interpreted as the age of tungsten mineralization this age coincides well with the zircon u pb age of the host granitic intrusion reported previously the 5 mys difference between molybdenite re os and muscovite 40ar 39ar ages probably represents the duration of hydrothermal activity the results show that the xihuashan tungsten deposit is one of many important tungsten tin deposits formed during 150 to 160 ma associated with large scale lithospheric extension in south china

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 magmatism and granitic dome in the wugongshan massif jiangxi province and their genetical relationship to the tectonic events in southeast china abstract in se china a mesozoic granitic dome coeval to extensional tectonics is exposed in the wugongshan massif its center is occupied by mesozoic granitoids and granitic gneisses and the e w trending late paleozoic mesozoic pingxiang and anfu basins are located along its northern and southern sides respectively in this paper the petrological geochemical major incompatible and rare earth elements and isotopic characteristics of the granitoids and granitic gneisses of this dome allow us to constrain their geodynamic evolution the wugongshan mesozoic k feldspar enriched granitoids consist of six granitic bodies and lie within a paleozoic metamorphic basement the caledonian shanzhuang granodiorite containing some dioritic enclaves occurs in the study area and is a calc alkaline type granodiorite characterised by lower sio2 and composed of andesine biotite quartz hornblende magnetite and sphene the mesozoic granitoids either indosinian plutons or yanshanian bodies show a geochemical affinity of peraluminous s type granite having higher sio2 k2o contents al k na 2ca enriched in rb th and depleted in eu they also exhibit lree enriched patterns and marked negative eu anomalies the yanshanian plutons also contain characteristic minerals such as sillimanite garnet and monazite the wugongshan mesozoic granitoids have higher isr values 0 70981 0 72885 and lower end t 10 6 to 14 7 an average of 12 6 than those of the early paleozoic shanzhuang granodiorite the mesozoic granitoids were likely derived from ancient sedimentary rocks by partial melting the wugongshan mesozoic granitoids contain three petrological zones that is an early cretaceous massive granitic zone in the core zone i a foliated granitic zone zone ii and a triassic granitic gneissic zone in the outer rim zone iii the petrological and geochemical features of massive granitoids zone i are similar to those of foliated granites zone ii and of granitic gneisses zone iii in this mesozoic dome moreover geometric and kinematic features within the ductile parts units 2 and 3 are also similar to those within the brittle part unit 1 of the dome all these features show that the geologic evolution of the wugongshan doming is a continuous process lasting from triassic to early cretaceous time published 40ar 39ar and k ar ages in the wugongshan mesozoic granitic rocks fall into two major age fields corresponding to two geodynamic events of intracontinental deformation and magmatic activity the first tectonothermal event dated at 226 259 ma on the granitic gneisses in the outer rim of dome can be linked to indosinian collision between the south china plate and the north china plate during triassic time the second event took place during the early yanshanian dated at 180 120 ma on the granites of the core of dome and are responsible for final doming of the wugongshan plutons this event may be related to a westward subduction of the paleo pacific oceanic plate under the se china continent during late jurassic early cretaceous time

syndepositional shallow water precipitation of glauconitic minerals abstract numerous studies have demonstrated that glauconitic minerals predominantly form in water depths of mid shelf to upper slope in modern oceans these areas tend to have slow sedimentation rates another commonly cited requisite for glauconitic mineral precipitation cambro ordovician strata from the southwestern us are rich in glauconitic minerals stratigraphic sedimentological and petrographic constraints indicate that the glauconitic minerals are autochthonous in marked contrast to the modern environments of deposition these cambro ordovician strata formed under very shallow water to tidal flat conditions the trough cross stratified deposits of the most glauconitic mineral rich accumulations glaucarenites indicate a high energy environment and probably a normal to high rate of sedimentation the presence of fibroradiated rims of glauconitic minerals on glauconitic mineral pellets echinoderm fragments and quartz grains demonstrates that the cambro ordovician glauconitic minerals precipitated on or in close proximity to the sea floor and prior to calcite precipitation consequently glauconitic minerals must have formed under markedly different conditions in the lower paleozoic than they do today thus the occurrence of glauconitic minerals in the rock record cannot be used a priori as an environmental indicator of either mid shelf and deeper water and or a slow rate of sedimentation

deposit density of tungsten polymetallic deposits in the eastern nanling metallogenic belt china abstract estimation of the number of undiscovered mineral deposits is critical for quantitatively assessing mineral resources traditional statistic methods are limited to analyzing the spatial distribution of mineral deposits which can be considered spatial point processes because of complexity self organized criticality and singularity properties in this study spatial statistic methods including average nearest neighbor distance fry analysis k function and fractal analysis are used to quantify the agglomeration and fractal characteristics of tungsten polymetallic deposits in the eastern nanling metallogenic belt enmb local singularity analysis for w sn mo bi be association is used to delineate the permissive areas for tungsten deposits the results show that tungsten polymetallic deposits are distributed with fractal clustering in region while at random in permissive areas the summary function comparison shows that the k function analysis based on a heterogeneous process may be more robust than on a homogeneous k function when quantifying the distribution of mineral deposits especially for endogenic deposits furthermore the concept of mineral equivalent is introduced in this study and the combination of mineral equivalent and radial density model for mineral deposits mitigates the problem of ignoring the proportion of large medium and small sized deposits in the uniform deposit density model the estimation results indicate that there are still good future prospects in this region this research not only extends the application of spatial statistics in quantifying the spatial distribution of mineral deposits but also provides a new approach to estimate the number of undiscovered mineral deposits

epithermal deposits in south china geology geochemistry geochronology and tectonic setting abstract south china block scb is the broad area including the yangtze craton in the northwest and huanan orogen in the southeast it is an important epithermal metallogenic province in china containing at least 1 high sulfidation hs and 42 low sulfidation ls au ag cu pb zn sb epithermal deposits porphyry type mineralization was recognized in four of the ls deposits and thus they were regarded as ls p type these 43 deposits are mainly located in 1 the lower yangtze river belt and 2 the northeastern jiangnan orogenic belt in the yangtze craton 3 the wuyi yunkai orogenic belt and 4 the southeast coastal volcanic belt in the huanan orogen they are mostly located in mesozoic volcanic basins especially where the regional faults and their subsidiaries occurred the host rocks include jurassic cretaceous volcanic sedimentary rocks coeval or slightly older subvolcanic granitoids and breccias and metamorphic basement rocks the alteration of the hs epithermal deposit zijinshan cu au zoned from silicic vuggy quartz through alunite to dickite and phyllic alteration zones from the ore veins outwards the alteration of the ls deposits is zoned from adularia chalcedony bladed calcite or quartz pseudomorphs after bladed calcite in ore veins to distal illite sericite chlorite kaolinite assemblages for those ls p systems besides the dominated ls alteration assemblages phyllic and potassium silicate alteration related to porphyry mineralization were identified acid leaching textures and vein stockwork and breccia structures are common in hs deposit while the ls epithermal deposits are characterized by open space filling crustifications colloform banding and comb structures the ore forming fluids are low temperature low salinity meteoric water dominated in most epithermal deposits in scb with variable input of magmatic water the ore components were derived from both the deep magma and host rocks and transported upwards or laterally and precipitated in the fracture systems by fluid boiling mixing and cooling most of the epithermal deposits are formed at depth of

k ca ages of authigenic sediments examples from paleozoic glauconite and applications to low temperature thermochronometry k ca ages of cambrian glauconites from the llano uplift central texas were determined in order to re evaluate the ability of the k ca system to constrain the timing of deposition of sedimentary packages all of the k ca ages presented here were found to be younger than their stratigraphic ages in addition to being too young the k ca ages are also highly variable ranging in age from silurian to permian the oldest subset of glauconite ages are in agreement with previously published rb sr ages from the same outcrop and provide further evidence for there having been a post depositional thermal or recrystallization event that reset both the rb sr and k ca systems the range of younger glauconite k ca ages is similar to the distribution of available apatite fission track ages for the llano basement k ca ages are interpreted as thermochronologic data reflecting partial retention of ca in thermally fluctuating basin conditions estimates of the closure temperature of ca in glauconite are found to be 60 90 c for cooling rates of 0 5 1 c my the k ca system is potentially useful as a low temperature thermochronometer with closure temperatures 100 c for glauconite

late jurassic sn metallogeny in eastern guangdong se china coast evidence from geochronology geochemistry and sr nd hf s isotopes of the dadaoshan sn deposit abstract the newly discovered dadaoshan sn deposit is located in the eastern guangdong sn w province coastal se china the sn mineralization hosted in jurassic porphyritic granite and the lower jurassic jinji formation sedimentary wall rocks is considered to be granite related in this study the porphyritic granite was la icp ms zircon u pb dated to be 153 2 1 2 ma consistent with the syn mineralization molybdenite re os age of 152 6 1 8 ma the porphyritic granite samples are weakly peraluminous a cnk 1 0 1 1 and high k calc alkaline the rocks contain high sio2 72 9 75 6 wt moderate rb sr 5 9 and low ree 136 223 ppm they are enriched in f li rb and sn depleted in ba sr p zr th nb and y and have distinct negative eu anomalies eu 0 09 0 18 suggesting that the porphyritic granite is highly fractionated i type granite the calculated initial 87sr 86sr 0 711582 0 715173 relatively low nd t 9 48 to 8 54 tdm2 1638 1814 ma and the zircon ehf t 14 2 to 5 1 two stage model ages 1528 2103 ma all suggest that the granite was mainly crustal derived with little mantle input sulfur isotopic compositions for the sulfides arsenopyrite and chalcopyrite 34s 1 1 to 1 4 average 0 1 imply a dominantly magmatic sulfur source the calculated zircon ce4 ce3 and eun eun ratios of the dadaoshan granite range from 1 0 to 112 mean 31 7 and from 0 04 to 0 37 mean 0 14 respectively indicating a low oxygen fugacity for the magma the reducing and highly fractionated nature of the dadaoshan granitic magma may have played a key role in the sn mineralization it was previously argued that the jurassic sn w mineralization and its causative magmatism were largely confined in the south china interior e g the nanling range our new data suggest that the late jurassic sn w mineralization and its causative magmatism actually extended to the se china coastal area the dadaoshan granite may have been generated from partial crustal melting led by underplating of mantle derived magmas in an extensional environment regional extension may have been related to the west directed flat slab subduction and delamination of the paleo pacific izanagi plate beneath the south china block another suite of early cretaceous sn w bearing granitic rocks in eastern guangdong may have mainly been crustal derived with minor mantle input and likely occurred under back arc extensional setting led by the paleo pacific subduction rollback

deep burial alteration of early diagenetic carbonate concretions formed in palaeozoic deep marine greywackes and mudstones bardo unit sudetes mountains poland carbonate concretions formed in bathyal and deeper settings have been studied less frequently than those formed in shallow marine deposits similarly concretions affected by catagenetic conditions have rarely been reported calcite concretions in deep marine mudstones and greywackes of the bardo unit sudetes mountains poland formed during early diagenesis and were buried to significant depths petrographic and geochemical elemental and stable c and o isotopic analyses document their formation close to the sediment water interface prior to mechanical compaction within the sulphate reduction zone and their later burial below the oil window although the concretions were fully formed during early diagenesis the effects of increased temperature and interaction with late diagenetic interstitial fluids can be discerned during maximum burial the concretions underwent thorough recrystallization that caused alteration of fabric and elemental and o isotope composition the initial finely crystalline cement was replaced by more coarsely crystalline sheaf like poikilotopic calcite in the concretions these large calcite crystals engulf and partially replace unstable detrital constituents the extremely low 18o values down to 21 2 vienna pee dee belemnite in the concretions are the result of the increased temperature in combination with alteration of volcanic glass both causing a significant 18o depletion of bicarbonate dissolved in the interstitial fluids recrystallization led to uniform o isotope ratios in the concretions but did not affect the c isotope signature the 13c values of the late diagenetic cements precipitated in the greywacke and in cracks cutting through concretions imply crystallization in the catagenetic zone and decarboxylation as a source of the bicarbonate these late diagenetic processes took place in a supposedly overpressured setting as suggested by clastic dykes and hydrofractures that cut through both concretions and host rock all of these features show how the effects of early and late diagenesis can be distinguished in such rocks

oxygen and carbon isotopic composition of marine carbonate concretions an overview abstract compilation of stable isotope data 18o and 13c for marine calcite siderite and dolomite concretions from a large number of studies reveals consistent and unanticipated isotopic trends although many of the dolomites have 18o values that are compatible with precipitation from unaltered seawater at low temperatures most of the calcites and siderites are far too depleted in 12o for such an origin this is surprising as most of the concretions appear to have formed very early in the diagenetic history of the sediments often within several meters of the sediment water interface the most likely cause of the anomalously depleted oxygen values is a decrease in pore water 18o values during early diagenesis a result perhaps of a significant influx of meteoric water into the marine shelf environment or water mineral interaction e g precipitation of 18o enriched minerals the carbon isotopic field for dolomite is quite different from that for calcite and siderite highly positive 13c values are fairly common only for dolomites this indicates that while dolomite concretions often form in sediments where methanogenesis is rapid precipitation of calcite and siderite concretions is restricted to sediments where either n methanogenesis takes place or where methanogenesis is not extensive enough to generate highly positive pore fluid 13c values this variation in carbon isotopic composition among the different minerals suggests that the rates of organic carbon oxidation and sedimentation may control the mineralogy of carbonate concretions high organic carbon oxidation rates favor dolomite and lower oxidation rates favor calcite or siderite

ore formation mechanism of the weilasituo tin polymetallic deposit ne china constraints from bulk rock and mica chemistry he ar isotopes and re os dating abstract china s w sn resources are dominant on a global scale a series of sn polymetallic deposits has been found in recent years at depth on the flanks of known volcanic subvolcanic cu pb zn ag deposits in the southern great xing an range ne china the large scale weilasituo tin polymetallic deposit formed at the depth of the weilasituo cu zn deposit is most typical of these types of deposit tin polymetallic orebodies are hosted in the early paleozoic xilingol complex and their mineralization is closely related to early cretaceous quartz porphyry in this contribution bulk rock and mica chemical compositions re os geochronology and he ar isotopic analyses are described in addressing the ore formation mechanism of the deposit geochemical characteristics indicate that the ore bearing quartz porphyry corresponds to the i type granite serie five types of mica have been identified in the study area based on detailed petrography and epma and la icp ms analyses i early magmatic fe li mica in albitized quartz porphyry ii late magmatic fe li mica in mineralized quartz porphyry iii hydrothermal fe li mica in a cryptoexplosive breccia pipe distributed around breccia fragments iv fe li mica in quartz veins and v fe li mica in plagioclase gneiss wall rock magmatic zinnwaldite from the upper mineralized part of the quartz porphyry is enriched in nb 100 160 ppm and ta 100 150 ppm hydrothermal zinnwaldite from the explosive breccia quartz veins and surrounding gneiss is unusually rich in mg up to 3 4 wt mgo and sn up to 200 ppm 3he 4he ratios of the weilasituo tin polymetallic and cu zn deposits are in the ranges 3 38 4 91 ra and 4 8 4 9 ra respectively indicating ore forming fluids sourced from mixed crustal and mantle materials molybdenite re os dating of w mineralization yielded an isochron age of 129 0 4 6 ma similar to the porphyry crystallization and mineralization ages of the weilasituo tin polymetallic deposit and also consistent with the mineralization age of the cu zn deposit we propose a new metallogenic model with all subtypes of w sn cu pb zn ag mineralization in the weilasituo area belonging to a single complex metallogenic system compared with other ore districts ore related granitoids in the southern great xing an range display relatively uniform emplacement ages and were derived from partial melting of juvenile lower crust rather than old basement their ore forming fluid source was greater influenced by mantle fluids than which found in south china

measuring unsaturated soil deformations during triaxial testing using a photogrammetry based method when characterizing an unsaturated soil using the triaxial test apparatus it is required to measure the soil deformation during loading recently a photogrammetry based method has been developed for total and localized volume change measurements on unsaturated soils during triaxial testing in this study more in depth discussions on the photogrammetry based method are addressed such as system setup the measurement procedure accuracy self check data post processing and differences from conventional image based methods also an application of the photogrammetry based method on unsaturated soil deformation measurements is presented through a series of undrained triaxial tests with different loading paths after testing three dimensional 3d models of the tested soils at different loading steps were constructed based on the 3d coordinates of measurement targets on the soil surface clear barreling processes for soils during deviatoric loading were observed through the constructed 3d models at diffe

the permian sn metallogenic event and its geodynamic setting in east kunlun nw china evidence from zircon and cassiterite geochronology geochemistry and sr nd hf isotopes of the xiaowolong skarn sn deposit abstract abundant granitoids are exposed along the east kunlun orogenic belt ekob and many skarn deposits occur at the contacts between intrusions and strata one such is the xiaowolong deposit a skarn type tin polymetallic deposit that is temporally and spatially associated with porphyry monzogranite tin mineralization is mainly hosted by the skarn in this study we reported zircon and cassiterite u pb ages whole rock geochemistry and sr nd hf isotopic data and used these to constrain the timing of intrusion and mineralization in the xiaowolong deposit and identify the origin of the ore related granites and the link between sn mineralization and granitic magmatism age determinations by la icp ms u pb zircon dating indicated that the porphyry monzogranite formed at 260 0 0 7 ma cassiterite from the ore bearing skarn yielded a tera wasserburg u pb lower intercept age of 258 0 3 7 ma these ages suggested that both granitic intrusion and related sn mineralization in the xiaowolong deposit were initiated during the permian ca 260 ma the porphyry monzogranites had high sio2 71 26 73 13 wt and al2o3 13 84 14 46 wt contents were alkali enriched k2o na2o 7 08 7 69 wt had a cnk values that ranged from 1 01 to 1 05 were enriched in light rees and large ion lithophile elements such as rb th u and k were depleted in high field strength elements and had relatively low zr nb y and ce contents they thus exhibited the geochemical characteristics of i type granite the porphyry monzogranite had consistent negative whole rock nd t 6 8 to 7 1 and magmatic zircon hf t values ranging from 7 4 to 1 6 and two stage hf model ages ranging from 1393 ma to 1758 ma detailed elemental and isotopic data demonstrated that the porphyry monzogranite were derived from partial melting of ancient crustal source and emplacement in a subduction tectonic setting the xiaowolong tin mineralization event indicated that the ekob has great potential for exploration focusing on permian triassic sn skarn deposits

sulfides associated with podiform bodies of chromite at tsangli eretria greece small bodies of pyrrhotite chalcopyrite minor pentlandite and magnetite occur at the peripheries of podiform bodies of chromite in ultramafic ophiolitic rocks at tsangli eretria central greece banding of magnetite and sulfide within the bodies is reminiscent of magmatic banding a magmatic origin has been proposed for similar sulfide masses in the troodos ophiolite panayiotou 1980 the compositions of the host rocks chromite and of the sulfides have been investigated on average the sulfide mineralization recalculated to metal content in 100 sulfide contains 0 55 ni 5 15 cu 0 29 co 9 ppb pd 179 ppb pt 16 ppb rh 112 ppb ru 31 ppb ir 58 ppb os and 212 ppb au these metal contents particularly the high cu cu ni ratio of 0 78 and the pt pd pt ratio of 0 95 are inconsistent with the sulfides having reached equilibrium with their ni rich host rocks at magmatic temperatures and accordingly it is concluded that they are not of magmatic origin the average 34s value of the sulfide bodies is 2 while that of a sample of pyrite from country rock schist is 15 6 these values are inconclusive as to the origin of the sulfur it is suggested that the sulfides have been precipitated by hydrothermal fluids possibly those responsible for the serpentinization of the host rocks the source of the metals may have been the host rocks themselves

zircon geochemistry of edong granitoids in the middle lower yangtze metallogenic belt eastern china constraints on w cu fe skarn mineralization abstract it has long been established that skarn deposits of different metals are associated with intrusions of different compositions intermediate felsic granitoids in the edong district of the middle lower yangtze metallogenic belt host skarn deposits with varying w cu fe proportions yet previous whole rock geochemical studies could not distinguish between the magmatic suites that formed the different skarn deposits in this study la icp ms zircon geochemical data are presented for the ruanjiawan w skarn 60300 t wo3 tongshankou cu skarn 0 6 mt cu tonglushan cu fe skarn 1 1 mt cu and 56 8 mt fe and jinshandian fe skarn 200 mt fe deposits in the edong district zircons from the ore forming intrusions of these skarn deposits are all characterized by heavy rare earth element hree enrichments and light rare earth element lree depletions with positive ce anomalies and slightly negative eu anomalies tungsten contents in zircons from the w ore forming intrusion 0 02 3 16 ppm w avg 1 14 ppm are generally higher than in zircons from the cu ore forming intrusion 0 00 0 24 ppm w avg 0 03 ppm copper content in zircons from the cu ore forming intrusion is higher than in those from the w ore forming intrusion fertile intrusive rocks from the four skarn deposits contain zircons with high calculated ce4 ce3 ratios ruanjiawan 71 7 tongshankou 207 5 tonglushan 263 6 jinshandian 189 0 fluorine content of the ruanjiawan intrusion is higher than the tonglushan and jinshandian intrusions followed by the tongshankou intrusion chlorine contents show the opposite trend we propose that the different source regions for the ore fertile intrusions is the critical factor that controls the metal content oxygen fugacity and volatile components our studies suggest that zircon geochemistry is a good indicator to distinguish tungsten causative intrusions from copper and iron ore related intrusions i e w content 1 14 ppm and ce4 ce3 ratios 207 5

genesis of the oxidized sn ores in the gejiu district yunnan province sw china abstract the gejiu sn ore district one of the largest sn producing area 300mt 1 wt sn in the world is located in the western margin of the cathaysia block sw china there are five types of sn ores in the gejiu district including greisen skarn veined tourmaline massive sulfide and oxidized among these types of sn ores the genesis of the oxidized sn ores is most controversial such as magmatic hydrothermal origin and sedimentary exhalative sedex or hot water deposition red sea type this paper reports u pb ages fluid inclusions trace elements and h o isotopes of cassiterite from the oxidized sn ores aiming to solve this issue la mc icpms cassiterite u pb dating yielded an age of 86 7 2 8 ma which is accordant with the formation ages 86 ma of granitic intrusions in the gejiu district two types of fluid inclusions in cassiterite from the oxidized sn ores were observed one type is co2 rich inclusions type 1 and the other type is aqueous inclusions type 2 the homogenization temperatures range from 220 to 366 c and the salinities range from 10 9 to 21 wt nacl equiv for the two types of fluid inclusions furthermore fluid inclusions in cassiterite from the oxidized sn ores located at 300 m far away from granitic intrusions have higher temperatures 357 366 c than those located at 500 m 273 330 c hence the ore forming temperatures tend to decrease with the distance far away from the magmatic hydrothermal center the vapor components for the two types of fluid inclusions are co2 and h2o respectively and the liquid phase compositions of them are all h2o the co2 in the ore forming fluids may source from marble by decarbonization this indicates that the precipitation of cassiterite is resulted from fluid immiscible the 18o values of fluid inclusions in cassiterite range from 6 1 to 7 7 and the d values range from 135 to 153 indicating a mixture of magmatic and meteoric waters trace elements show that cassiterite is rich in in rb and u but ba nb and ti are depleted in addition the lower sr 0 4 2 1 ppm and higher sc 35 9 53 7 ppm contents reflect that the formation of cassiterite is related to f rich intermediate acid magma cassiterite has a relatively low total ree contents 2 7 9 2 ppm with negative eu eu 0 14 0 76 and ce ce 0 1 0 6 anomalies indicating that the ore forming environment is oxidized this is consistent with the cassiterite precipitation conditions hence all the evidence supports that the oxidized sn ores are genetically associated with the gejiu granitic magmatism

mineral chemistry trace elements and sr nd hf isotope geochemistry and petrogenesis of cailing and furong granites and mafic enclaves from the qitianling batholith in the shi hang zone south china abstract the shi hang zone is an important ne trending mesozoic magmatic belt composed of granites with relative high end t values and young tdm model ages in south china however the petrogenesis and the tectonic environment for the shi hang zone magmatic rocks remain controversial we report here mineral chemistry geochemical and sr nd hf isotopic data for the cailing and furong granites and mafic microgranular enclaves mmes from the qitianling granite batholith in southern hunan province south china the qitianling granite batholith is a multi staged composite pluton with three phases cailing furong and huangtangling according to their ages and petrography the cailing 163 160 ma and furong 157 153 ma phases are mainly composed of porphyritic amphibole biotite monzogranite and they share similar geochemical and isotopic characteristics both of them show similar sio2 contents from 66 50 to 70 28 and metaluminous a cnk values of 0 80 to 0 98 the granites are characterized by high contents of large ion lithosphile elements lile such as rb th u pb high field strength elements hfse such as nb ta zr hf and zr nb ce y contents 350 ppm and high 10 000 ga al ratios 2 6 chondrite normalized ree patterns show relative enrichment of light rare earth elements lrees and significant negative eu anomalies mineralogical and geochemical features suggest that the cailing and furong granites are a type which can be further classified as a2 subtype they have relatively lower 87sr 86sr i ratios 0 7091 0 7132 higher end t values 5 5 to 7 6 and younger nd isotopic model ages 1 48 1 56 ga than those common s type granites in south china zircon ehf t values vary from 8 1 to 3 7 the mmes in the cailing phase show similar trace element and sr nd isotopic characteristics with the host granites but zircons from the mmes show different ehf t values 6 4 2 6 with those from the host granites 8 1 to 3 7 this indicates that the mmes and host granites were crystallized from different sources of magmas providing direct evidence for mafic felsic magma mixing processes the isotope data indicate that the cailing and furong granites from the qitianling batholith were derived from a hybrid magma consisting of about 80 felsic magma derived from old crust and about 20 mantle derived mafic magma the strong magma mixing at about 160 155 ma caused by intra arc rifting or back arc extension related to subduction of the paleo pacific plate is favored to explain the petrogenesis of the cailing and furong granites as well as the shi hang zone

constraints on the timing and genetic link of the large scale accumulation of proximal w sn mo bi and distal pb zn ag mineralization of the world class dongpo orefield nanling range south china abstract the world class dongpo orefield located in the nanling range south china is famous for its large scale accumulation of w sn mo bi pb zn ag deposits which includes the giant shizhuyuan w sn mo bi jinchuantang sn bi yejiwei sn cu and congshuban pb zn ag deposits the polymetallic mineralization around the qianlishan pluton exhibits systematic zoning and comprises proximal w sn mo bi skarn greisen and distal pb zn ag veins however the timing and genetic link of its proximal skarn greisen w sn mo bi and distal vein type pb zn ag mineralization are not well constrained here we present systematic geochronological data to constrain the geochronological framework and genetic model of the giant dongpo orefield the muscovite 40ar 39ar age of the greisen type ore in the shizhuyuan w sn mo bi deposit is 151 1 ma which is consistent with the formation of the skarn type ore and the qianlishan pluton thus indicating that they are genetically related and both formed contemporaneously at 151 ma the large scale accumulation of w sn mo bi in the shizhuyuan deposit may have occurred in a short duration of 1 ma the muscovite 40ar 39 ar ages 155 5 1 1 and 156 8 1 1 ma and molybdenite re os age 153 8 4 2 ma of the ma naoshan w sn fe mn pb zn deposit as well as the zircon u pb age 152 7 0 9 ma of the yejiwei sn cu deposit in the dongpo orefield are consistent with the age of the qianlishan pluton thus indicating that the proximal skarn greisen w sn mo bi mineralization in the dongpo orefield is genetically related to the qianlishan pluton in addition the rb sr dating of sphalerite indicates that the vein type pb zn ag mineralization in the congshuban area formed at 152 2 ma which is consistent with the la mc icp ms zircon u pb age 156 155 ma of the equigranular biotite granite indicating that the distal vein type pb zn ag mineralization is genetically associated with the qianlishan equigranular biotite granite by integrating the high precision geochronological data of this study with those of previous studies the new genetic model of the large scale accumulation of w sn mo bi pb zn ag in the dongpo orefield suggests that the proximal skarn greisen w sn mo bi and distal vein pb zn ag mineralization in the dongpo orefield are genetically related to the qianlishan pluton and that the mineralization type is mainly controlled by the characteristics of the wall rock

distribution of upper cenozoic carbonate cemented sandstones kuche depression northwest china insights from high resolution borehole micro resistivity imaging abstract high resolution micro resistivity images are used to study the distribution of neoformed carbonate concretions in upper cenozoic shallowly buried fluvial sandstones in the kuche depression northwest china the carbonate concretions are high resistivity white facies on borehole images most of them occur as patches 1 40 cm thick and in shapes ranging from equant oblate to elongate these concretions contrast markedly with the poorly cemented or uncemented host sandstones which appear as dark to immediate grayscale facies on the images three patterns of occurrence of carbonate concretions are identified isolated concretions discontinuously cemented layers and continuously cemented layers most concretions occur in fine grained low permeability laminae suggesting that their growth was controlled more probably by diffusion transport rather than advective transport grain size lamination and distribution of intergranular clay all potentially influenced the selective distribution of carbonate cement in the sandstones shale interbeds and terrigenous carbonate rock fragments in the sandstones are potential sources of carbonate cement

genetic relationship between silver lead zinc mineralization in the wutong deposit guangxi province and mesozoic granitic magmatism in the nanling belt southeast china more than 50 of the world s total reserves of tungsten are in china and most tungsten deposits are located in the nanling range in southeast china this study explores the potential genetic relationship between tungsten tin w sn mineralization and shallower ag pb zn deposits in the nanling range based on data from the wutong deposit guangxi province the lead oxygen carbon sulfur and strontium isotopic compositions of minerals at wutong indicate that a single crustal derived fluid was responsible for mineralization wutong likely formed at relatively low temperatures 200 300 c and low pressures as indicated by the similarity between homogenization temperatures of fluid inclusions and those estimated from s isotopic compositions of minerals the hubnerite age 92 3 104 4 ma indicates that the wutong mineralization is likely related to nearby late yanshanian cretaceous s type granites derived from proterozoic crust this mineralization event coincides with the last w sn mineralization event and the cretaceous peak of mineralization in the nanling range

origin of giant calcite cemented concretions temple member qasr el sagha formation eocene faiyum depression egypt abstract the temple member of the qasr el sagha formation contains spheroidal calcite cemented concretions in sandstone ranging from 70 cm to 9 m in diameter although most are 1 to 4 m in diameter most concretions are solitary oblate spheroids but some are prolate coalesced joined laterally or are compound enclose smaller concretions half the concretions have domains with a fairly uniform center to center spacing of 4 6 m but half have domains of random spacing both clusters and segregated concretions or occur in parallel rows of coalesced concretions miocene marine carbonate shells now preserved only inside concretions were the source of calcite cement as further supported by carbon and strontium isotopic signatures of cement 13c 2 to 1o oo pdb 87sr 86sr 0 70765 to 0 70770 concretions formed at shallow burial depths in meteoric pore water most 18o values of calcite are from 4o oo to 2o oo pdb at temperatures probably between 10 and 20 c spheroidal uniformly spaced concretions formed where carbonate shells were uniformly distributed and where nucleation sites were influenced by low carbonate saturation levels and widely spaced sites or at sites established by some self organization process concretions in orthogonal rows in the plane of bedding probably formed where shells were concentrated during deposition randomly spaced concretions formed where shells were unevenly spaced or where nucleation of concretions was rapid some temple concretions reached exceptional size in less than 20 my owing to a combination of conditions large initial aragonite and mg calcite shell concentration widely spaced concretion growth sites locally presence of a stable hydrologic regime over a long period of time and possibly bacterially mediated precipitation of calcite

extensional tectonics within a subduction type orogen the case study of the wugongshan dome jiangxi province southeastern china abstract in southeastern china the wugongshan massif consists of metamorphic rocks and granites generally considered as basement rocks formed during an early paleozoic orogeny our structural and radiometric reappraisal of this massif shows that it results from a mesozoic doming in the metamorphic rocks the foliation defines an e w elliptical shape and bears a n s stretching lineation the axial zone of the dome is occupied by oriented plutons the outer part of the dome consists of devonian quartzite carboniferous permian limestone and triassic jurassic sandstone ductile deformation observed in the permian carbonates and older units develops contrasting kinematics the northern and southern flanks present top to the north and top to the south motions respectively the same divergent pattern of motion is recorded from brittle structures up to the jurassic sandstone the late cretaceous red beds are undeformed in the axial zone coaxial flow indicated by symmetric pressure shadows and quartz fabrics predominates along the n and s flanks of the dome post folial recumbent folds are symmetrically overturned to the n and s respectively but at the two extremities of the dome the fold axes are parallel to the stretching lineation 40 ar 39 ar ages of biotite and muscovite from mylonite and granite suggest a late triassic age for the ductile deformation and an early cretaceous age for the final doming the wugongshan dome is similar to a metamorphic core complex formed in an extensional tectonic regime a model which emphasizes plutonism is discussed from permian to early cretaceous southeastern china was a subduction type orogen the crust of which was thickened by accretion of mantle derived magmas the emplacement of a large amount of mesozoic granitoids in southeastern china promoted thermal softening and gravitational instability that allowed the crust to extend the formation of the wugongshan dome and other metamorphic core complexes appears to be a the direct consequence of plutonic activity and crust rheology

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

geochronology geochemistry and hf isotopic composition of late cretaceous laojunshan granites in the western cathaysia block of south china and their metallogenic and tectonic implications abstract sn in and w rich granites are identified in laojunshan area in the western cathaysia block south china including coarse grained two mica monzogranite cmg and fine grained two mica monzogranite fmg laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb dating of cmg and fmg are from 85 6 0 8 ma to 90 37 0 7 ma and 89 9 1 4 ma respectively all samples have relatively high total alkalis contents 5 74 wt to 9 73 wt and al saturation indices 0 95 to 1 79 indicating that most of granites belong to the strongly peraluminous granites the granites are enriched in p rb cs sn li be and u and are depleted in ti mg co ni sr ba zr and hf the fractional crystallization of plagioclase and k feldspar was the principal process of magmatic differentiation that controlled rb sr ba and eu concentrations while rare earth elements were fractionated by accessory minerals such as apatite monazite or ilmenite these geochemical features suggest that most of rocks are highly fractionated s type granites the ehf t values of the zircon samples from cmg and fmg range from 12 88 to 1 19 with the two stage hf model ages ranging from 1 2 ga to 1 9 ga the geochemical and isotopic data show that the laojunshan granites are derived from a crystalline basement that has metamorphosed pelitic rocks from the mes paleoproterozoic continental crust the upwelling of the asthenosphere caused by a strong lithospheric extension led to the partial melting of the metamorphosed pelitic rocks to form widespread late cretaceous s type granites in the laojunshan area lithospheric extension and cretaceous magma in se yunnan are probably related to the palaeo tethys ocean crustal delamination which subducted beneath the indochina block

precise molybdenite re os and mica ar ar dating of the mesozoic yaogangxian tungsten deposit central nanling district south china the yaogangxian deposit in the central nanling region south china consists of vein type ore bodies hosted in cambrian to jurassic strata and mesozoic granitic intrusions wolframite and molybdenite are the dominant ore minerals intergrown with gangue minerals of quartz feldspar phlogopite and muscovite we have carried out molybdenite re os and phlogopite and muscovite 40ar 39ar dating to better understand the timing and genesis of mineralization re os dating of eight molybdenite samples yielded model ages ranging from 152 0 3 5 to 161 1 4 5 ma with an average of 156 0 ma the re os analyses give a well defined 187re 187os isochron with an age of 154 9 2 6 ma mswd 2 4 hydrothermal phlogopite and muscovite display extremely flat 40ar 39ar age spectra phlogopite yields a 40ar 39ar plateau age of 153 0 1 1 ma whereas muscovite yields a plateau age of 155 1 1 1 ma both 40ar 39ar ages are in good agreement with the re os ages placing the timing of tungsten mineralization at about 154 ma this age is consistent with the field relationships our new data when combined with published geochronological results from other major deposits in this region suggest that large scale w sn mineralization occurred throughout the central nanling region in the late jurassic

data for s isotopic geochemistry zircon and cassiterite u pb geochronology of the haobugao sn polymetallic deposit southern great xing an range ne china abstract the southern great xing an range sgxr is the most important tin polymetallic metallogenic belt in north china the lack of previous research on the genesis of the tin mineralization especially its exact age prevents development of a deep understanding of tin deposits in this area haobugao sn polymetallic deposit is a large skarn type deposit in the huangang ganzhuermiao sn fe cu pb zn ag metallogenic belt in the sgxr the ore body occurs in the contact zone between a yanshanian intrusion and permian dashizhai formation marble 34 s v cdt values of sulfides from the haobugao sn polymetallic deposit range from 4 7 to 3 5 with an average of 0 65 and these values strongly indicate a deep magmatic source for the sulfur in the ore minerals of the deposit in this paper we also report the results of la icp ms u pb dating of tin mineralization in no i ore body and of the underlying granite cassiterite from no 1 ore body deposited at 139 0 6 ma and the closely associated granite has an age of 142 9 1 6 ma the similar ages indicate that the tin mineralization was produced by early cretaceous magmatic hydrothermal activity these results together with the ages of other tin deposits and related granites indicate extensive granitic magmatism and tin mineralization during the early cretaceous in the southern segment of the great xing an range

submicroscopic accessory minerals overprinting clay mineral ree patterns celadonite glauconite group examples abstract samples of glauconite representing different stages of glauconitisation as well as different formation environments were analysed for rare earth elements ree and other trace elements using a combination of bulk sample and spatially resolved in situ techniques the results indicate that the high sensitivity spatially resolved technique of laser ablation inductively coupled plasma mass spectrometry la icp ms produces values up to two orders of magnitude lower than the bulk sample analyses this suggests that submicroscopic rare earth element bearing phases are distributed within the glauconite aggregates comprising the bulk samples analytical scanning electron microscopy asem revealed the presence of micrometre sized grains of apatite and pore filling precipitates of an unidentified ree ca phosphate approximate composition ca 0 3 0 4 ce 0 4 la 0 1 0 2 nd 0 1 po 4 in some glauconite grains the inherent ree concentrations of the glauconite aggregates i e glauconite crystallites without accidental mechanical inclusions or authigenic not layer silicate mineral precipitates was found to be relatively low e g typically less than 100 ppm and this value decreased with increasing glauconitisation smectite mica transformation through a series of recrystallisation processes these results suggest that the rees substitute for ca in the interlayer space of the layer silicate structure and therefore the ree content decreases as ca is progressively removed from the interlayer smectite mica transition la icp ms when combined with electron probe microanalysis epma or asem offers an opportunity to exclude submicroscopic accessory minerals from glauconite trace element analyses and so produces reliable trace element data for the respective minerals which host those elements these results illustrate that accessory minerals are difficult to eliminate from clay samples and that care needs to be taken in the interpretation of clay mineral ree distributions irrespective of the aggregation state of the studied clay i e whether finely dispersed within the sedimentary rock or forming millimetre sized aggregates model calculations showed that authigenic apatite associated with the studied green marine clays tends to have higher ree content than bioapatites the total ree content being above 10 000 ppm

contrasting diagenetic histories of concretions and host rock lion mountain sandstone cambrian texas white elliptical calcite cemented concretion nuclei up to 2 m long contrast markedly in color composition and diagenetic history from more glauconite rich concretion rinds and from dark green glaucarenite host rocks concretion nuclei are placers of loosely packed trilobite carapaces and minor quartz and glauconite tightly cemented with an average of 58 calcite cement the nuclei are shell lag deposits that were cemented by calcite at the sea floor or after burial of a few meters concretion rinds composed of sub equal amounts of quartz and compactionally deformed glauconite have an average of only 32 cement which consists of minor quartz overgrowths and later pore occluding calcite cement the rinds underwent burial for several million years to tens of million years to depths of several hundred meters before they were cemented the host rock is predominantly glauconite with very minor quartz and calcite cement 87 sr 86 sr ratios of host rock calcite cement are variable 0 7084 to 0 7093 but the lowest value suggests precipitation during the middle ordovician in the absence of significant amounts of carbonate cement the host rock underwent complete dissolution of trilobite carapaces and maximum compaction with total loss of porosity through squashing of glauconite grains maximum burial during this stage was completed by the end of ordovician time carbon and oxygen isotopic values of calcite from 16 samples show no differences between concretion nuclei rinds and host rocks 13 c ranges from 2 2 to 2 9 pdb and probably reflects derivation of carbon from trilobite carapaces and other skeletal grains 18 o ranges from 4 6 to 6 2 pdb and reflects either the original composition of the cement and trilobites or the modification of original grains by meteoric dominated ground water

temporal and spatial relationships of granitic magmatism and w mineralization insights from the xingguo orefield south china abstract in south china extensive multi phase magmatism was accompanied by w dominated polymetallic mineralization the xingguo orefield of southern jiangxi province in the eastern part of the nanling region is one of the most important w dominated mineralized regions in south china there are more than ten w deposits within or surrounding the jiangbei complex including the huamei ao quartz vein type w deposit wo3 67 400 tons at a grade of 1 344 the yanqian skarn type w deposit wo3 16 000 tons at a grade of 0 365 and the zhangjiadi quartz vein and greisen type mo w deposit mo 31 806 tons at a grade of 0 1 and wo3 1746 tons at a grade of 0 353 the orebodies all occur at the contact between the jiangbei complex and the sinian metasandstone or carboniferous permian limestone the jiangbei complex consists of three lithologies medium to coarse grained biotite granite j 1 medium to fine grained biotite monzonitic granite j 2 and fine grained biotite monzonitic granite j 3 which have zircon u pb ages of 160 7 1 1 ma 156 3 0 9 ma and 153 3 0 8 ma respectively the associated yanqian huamei ao wangnipai and liujiazhuang deposits have molybdenite re os ages of 159 2 2 3 ma 157 1 1 3 ma 157 7 1 4 ma and 157 9 1 6 ma respectively a summary of available age dates of intrusions in the xingguo orefield indicates that the granitic magmatism lasted for 8 m y ca 160 153 ma whereas the w mineralization occurred in a relatively short period 159 155 ma corresponding in age to the episode of large scale mesozoic 165 150 ma mineralization in south china low end t values 10 2 13 0 of the jiangbei granitic rocks and low re contents of the molybdenite suggest that the w dominated ores and associated granites in the xingguo orefield were derived mainly from crustal magmas all three lithologies of the jiangbei complex have similar geochemical characteristics and are classified as high k calc alkaline and peraluminous s type granites the zr hf nb ta eu rb sr and lree hree ratios all correlate positively with the w contents of the rocks and reach their highest level in the phase ii granites we propose a magmatic metallogenic model in which w was concentrated by fractionation of crustally derived magmas of phase i and then deposited in skarn greisen and quartz vein type ores by both magmatic and hydrothermal processes

giant calcite cemented concretions dakota formation central kansas usa giant spheroidal concretions cannonball concretions some nearly 6 m in diameter in fluvial channel fill sandstones at two localities of the dakota sandstone formed by import of cement constituents at a burial depth of 1 km during cannonball concretion growth a self organizational process restricted concretions to a relatively few but widely spaced and locally evenly spaced sites other forms of calcite cements at these localities are cement patches in the form of intergrown grape size concretions grapestone and locally pervasive cement an early episode of invasion by thermogenically generated h2s which reacted with iron oxides on detrital grains generated scattered pyrite crystals and decimetre scale spheroidal pyrite concretions intergranular volumes igv in the concretions range from 36 to 27 the absence of a trend in igv and of carbon and oxygen isotope ratios from cannonball centres to margins indicates that these concretions did not cement progressively outwards from the centre rather the modern spheres represent the spatial extent of nucleation sites that were not otherwise organized within that volume carbon and oxygen isotope values for concretion calcites plot along a swath between depleted values of 18c of 36 and 18o of 13 and enriched values of 4 and 6 respectively four groups of calcites are evident on the basis of trace element content and suggest that the calcite precipitated across a range of oxidation conditions that do not correlate strongly with the isotopic compositions although fluvial overbank sandstones have some pedogenic calcite the channel sandstones have at most a trace of pedogenic calcite and carbonate rock fragments so that the bulk of cement components were imported to the sandstones carbon and calcium sources for calcite cement include marine limestone carbonate shells and anhydrite in addition to hco derived from oxidized methane most likely derived from beds underlying or laterally in communication with dakota sandstones hco in ascending formation waters released during compaction mixed with meteoric water whose temperature and composition varied with time to generate the 7 range in 18ocalcite values measured

calibration of soil constitutive models with spatially varying parameters soil constitutive models are frequently calibrated from laboratory tests that utilize global boundary measurements which necessarily relegate soil response to that of a homogenized equivalent medium this paper demonstrates the applicability of advanced experimental technologies to enhance the state of model based predictions in soil mechanics by taking into account the possibility of material heterogeneity during model calibration by utilizing the full field displacement measurement technique of three dimensional digital image correlation displacements of the surfaces of deforming triaxial sand specimens are measured throughout deformation these displacements are assimilated into finite element fe models of the test specimen through solution of an inverse problem during optimization in which the difference between measured and predicted displacements across the specimen surface form the basis for the objective function model parameters are allowed to vary spatially throughout the specimen volume fe models allowing three different levels of spatial variability are tested results indicate that accommodating consideration of material heterogeneity during calibration leads to more accurate predictions of global stress strain behavior that are more faithful to observed full field response

geochronological and petrogeochemical constraints on the skarn deposits in tongshanling ore district southern hunan province implications for jurassic cu and w metallogenic events in south china abstract southern hunan province south china is located in the central part of the qin hang metallogenic belt and is characterized by abundant cu pb zn and w sn polymetallic ore deposits the cu pb zn deposits are associated with jurassic granodiorite porphyries whereas the w sn deposits occur within jurassic granite porphyries here we present geochronologic and geochemical data for the tongshanling cu mo pb zn deposit and the weijia w deposit in the district of tongshanling southern hunan zircon u pb dating and molybdenite re os geochronology indicate that the emplacement of the tongshanling granodiorite porphyry and the associated cu mineralization occurred at 162 160 ma slightly earlier than the formation of the xianglinpu granite porphyry and associated w mineralization at 159 158 ma the tongshanling granodiorite is high k calc alkaline weakly peraluminous and weakly fractionated with zircon e hf t values of 15 1 to 5 6 in contrast the xianglinpu granite is alkaline peraluminous and highly fractionated with e hf t values of 9 5 to 0 9 our data indicate that the tongshanling granodiorite is relatively oxidized and was formed by the partial melting of paleoproterozoic crustal material with inputs of mafic magma which was derived from a subduction modified lithospheric mantle in contrast the xianglinpu granite porphyry is relatively reduced and was formed by direct interaction between the crust and asthenospheric mantle the difference in magma generation and tectonics is considered to have resulted in the different types of mineralization associated with these two intrusive bodies

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

hydrothermal zircon geochronology age constraint on nanling range tungsten mineralization southeast china abstract the nanling range southeast china is well known for its wolframite bearing quartz vein wqv tungsten deposit this study focuses on the geochemistry and geochronology of zircons from the wqv and challenges the current view of the tungsten mineralization in the nanling range the features of the wqv zircons include 1 pale brown murky brown or orange red color and translucence under microscope 2 110 101 type crystal form 3 weak cathodoluminescence 4 enrichment of hf ranging from 1 97 to 7 83 wt hfo2 u ranging from 0 02 to 3 97 wt uo2 th ranging from 0 to 0 65 wt tho2 and p ranging from 0 to 1 82 wt p2o5 and 5 presence of solid hydrothermal and ore minerals and fluid inclusions these features indicate that the wqv zircons crystallized from hydrothermal fluids during tungsten mineralization the in situ la icpms u pb results of the wqv zircons from five different tungsten deposits in the nanling range yield similar ages ranging from 134 4 1 9 ma to 132 9 1 5 ma approximately 20 million years younger than proposed tungsten ore ages 155 5 ma several mineralization characteristics and field observations also cast doubt on the current model nanling range tungsten ore is the result of orthomagmatic processes the zircon characterization method provided in this study could be applied to tungsten metallogenic research in other parts of the world

the concretions of the bearreraig sandstone formation geometry and geochemistry the sandbodies of the bearreraig sandstone formation inner hebrides uk are cemented by two generations of calcite the first generation an inhomogeneous ferroan calcite 0 05 3 28 mol feco3 formed during sulphate reduction 13c 24 to 32 o pdb in marine porewaters 18o of cement from 1 to 4 o pdb at very shallow burial depths a few centimetres these cements are rare but form millimetre scale clusters of crystals which acted as nuclei to the later concretionary cements the second generation of cements are more homogeneous ferroan calcites mean 1 58 mol feco3 which evolve to progressively higher fe mg ratios they are sourced by shell dissolution 13c of cement from 1 to 3 o pdb into meteoric 18o of cement from 6 to 10 o pdb or mixed marine meteoric waters 18o of cement from 4 to 6 o smow these were introduced into the formation either during bathonian times as a freshwater lens or subsequent to partial inversion by confined aquifer flow corroded feldspars within the concretions suggest that an interval of at least 8 ma separated the deposition of the sediments from the onset of concretion growth abundant concretions are preferentially developed at certain horizons within the sandbodies where the early generation of ferroan calcite cements provided nuclei the latter formed close to the sediment water interface the concentration of cement within the sediment being related to sedimentation rate the relatively high concentrations of the first generation of cement upon which the concretionary horizons are nucleated formed during periods of minimal sedimentation

multiple mesozoic mineralization events in south china an introduction to the thematic issue mesozoic mineral deposits in south china include world class deposits of w sn and sb and those that provide the major sources of ta cu hg as tl pb zn au and ag for the entire country these deposits can be classified into polymetallic hydrothermal systems closely related to felsic intrusive rocks sn w mo granites cu porphyries polymetallic and fe skarns and polymetallic vein deposits and low temperature hydrothermal systems with no direct connection to igneous activities mvt deposits epithermal au and sb deposits recent studies have shown that they formed in the triassic indosinian jurassic cretaceous early yanshanian and cretaceous late yanshanian stages indosinian deposits include major mvt pb zn ag deposits and granite related w sn deposits early yanshanian deposits are low temperature sb au and high temperature w sn and cu porphyry types many late yanshanian deposits are low temperature au as sb hg and u deposits and also include high temperature w sn polymetallic deposits the formation of these deposits is linked with a specific tectonothermal evolution and igneous activities this special issue brings together some of the latest information in eight papers that deal with the origins and tectonic environments of mineral deposits formed in these stages we anticipate that this issue will stimulate more interests in these ore deposits in south china

a novel method for estimating sandbody compaction in fluvial successions clastic sedimentary successions are subject to variable amounts of compaction which causes a decrease in both the thickness and porosity of sand rich depositional units methods for estimating the degree of sediment compaction are needed for characterizing changes in the geometry and petrophysical properties of depositional elements in relation to their burial history conventional methods for estimating compaction of rock successions through the application of several empirical equations return estimations whose uncertainties can be significant and integrative approaches that can produce reliable estimations are therefore desirable to this end a new method is proposed here for the estimation of the degree of compaction of sandbodies in ancient channelized fluvial successions for outcropping fluvial successions the compacted geometry of channel fill margins cut into non cohesive deposits can be measured whereas the decompacted angle of repose of the material originally forming the channel banks can be estimated experimentally sediment compaction can therefore be estimated by comparing the observed geometry of the uppermost part of a channel fill margin with the angle of repose of the non cohesive bank material the proposed method has been applied to three different sand prone fluvial successions seen in outcrop for the purposes of i illustrating the approach and ii testing it through a comparison of its estimations against results produced by a conventional method based on thin section observations the comparison demonstrates that the two methods yield similar results highlighting how the proposed approach can be readily applied to the assessment of compaction in clastic successions for scopes of both pure and applied geological research

zircon u pb ages and hf o isotopes and whole rock sr nd isotopes of the bozhushan granite yunnan province sw china constraints on petrogenesis and tectonic setting abstract the bainiuchang silver polymetallic ore deposit is a super large deposit in the western part of the south china tungsten tin province or the nanling tungsten tin province the deposit is spatially and temporally associated with the bozhushan granite pluton our new data indicate that the bozhushan granitoids formed at 86 87 ma the granitoids are geochemically consistent with a type granite the bozhushan pluton consists predominantly of biotite granite that is characterized by weakly peraluminous to metaluminous compositions and high alkali contents na2o k2o 7 51 9 06 wt the granitic rocks are enriched in large ion lithophile elements lile rb th u and k but relatively depleted in ba and sr in addition they have high zr nb ce y contents 310 478 ppm and high 10 000 ga al ratios 2 7 3 1 the temperatures of the parental magmas for the bozhushan granites are estimated to be 790 842 c based on the zircon saturation thermometer isotopically the bozhushan granites are characterized by elevated initial 87sr 86sr ratios 0 7126 0 7257 and low end values 11 2 to 12 4 and high 18o values 7 91 9 58 and low ehf values 9 5 to 6 1 for zircon crystals which indicate a dominant continental crustal source the two stage hf model ages vary from 1 53 to 1 86 ga the isotopic compositions support the interpretation that the granitic rocks formed by melting of the meso and neoproterozoic metasedimentary basements of the cathaysia block these results together with geological records in the other parts of the western cathaysia block suggest that the formation of the bozhushan a type granites is related to lithospheric extension and asthenospheric upwelling that are associated with the change of plate motion in late cretaceous