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

comparison of granite related uranium deposits in the beaverlodge district canada and south china a common control of mineralization by coupled shallow and deep seated geologic processes in an extensional setting abstract many uranium deposits are related to granitic rocks but the mineralization ages are much younger thus excluding a direct magmatic hydrothermal link between the mineralization and the granites two such examples are the proterozoic vein type uranium deposits in the beaverlodge district in canada and the mesozoic granite related uranium deposits in south china both areas have been extensively studied but the critical factors that control the mineralization remain unclear the uranium mineralization in the beaverlodge district occurs in quartz carbonate albite veins and breccias developed within and near major deformation zones and are mainly hosted by ca 2 33 1 90 ga granitic rocks and ca 2 33 ga murmac bay group amphibolite these rocks are unconformably overlain by the martin lake basin which was formed during a period of regional extension in the later stage of the trans hudson orogeny and is filled with red beds a ca 1820 ma mafic magmatic event is manifested as volcanic rocks occurring within the martin lake basin and as dikes crosscutting the basement rocks and lower martin group strata uraninite u pb and pb pb ages range from ca 2290 ma to the granite related uranium mineralization in south china occurs mainly as quartz carbonate fluorite veins and as disseminations in the host rocks adjacent to fracture zones the deposits are hosted by or occur adjacent to granitic rocks and are spatially close to cretaceous tertiary red bed basins that were formed in a basin and range like tectonic setting related to roll back of the pacific plate these red bed basins contain intervals of bimodal volcanic rocks and are crosscut by coeval mafic dikes uraninite u pb ages dominantly range from 100 to 50 ma which is much younger than the host granites 145 ma and broadly contemporaneous with development of the red bed basins and mafic magmatism comparison of the two study areas reveals striking similarities in geologic attributes related to uranium mineralization specifically the development of large volumes of granitic rocks that are relatively enriched in uranium and the development of red bed basins with accompanying coeval mafic magmatism in extensional tectonic settings it is proposed that oxidizing basinal fluids from the red bed basins circulated into the underlying fertile granitic rocks along high permeability structural zones acquired uranium in the path through fluid rock interaction and precipitated the uranium where they encountered reducing agents elevated geothermal gradients associated with the mantle derived magmatism greatly enhanced the mineralization by facilitating the uranium extraction and transport processes thus it is the coupling of shallow red bed basin and oxidizing basinal fluid development and deep seated mantle derived magmatism and related thermal activity processes together with the pre enrichment of uranium in basement rocks particularly granitic rocks and pre existing deformation zones that controlled the formation of the granite related uranium deposits in both beaverlodge and south china and perhaps elsewhere in the world with similar geologic setting

alteration mineralogy and stable isotope geochemistry of paleoproterozoic basement hosted unconformity type uranium deposits in the athabasca basin canada unconformity type uranium deposits are characterized by mineralization developed along the contact between younger sandstone cover and underlying crystalline basement rocks mineralization may extend up to 400 m into the underlying basement rocks whereas sandstone hosted unconformity type deposits have been well studied deposits hosted primarily in the basement have not this study examines the deposits at rabbit lake dawn lake and mcarthur river in the athabasca basin of canada which are hosted by the metamorphic archean and early paleoproterozoic rocks forming the basement to younger late paleoproterozoic sandstones alteration is similar in the three deposits and is characterized by three distinct paragenetic stages 1 preore alteration involving illitization of plagioclase and amphibole followed by chloritization of biotite and illite which formed at ca 230 c 2 ore stage alteration characterized by uraninite and coarse grained illite which formed at ca 240 c 3 postore alteration comprising spherulitic dravite vein chlorite quartz calcite and fe cu co and pb sulfides which formed at ca 135 c fluid circulation associated with emplacement of later mackenzie dikes initiated partial recrystallization of uraninite a later stage of alteration includes kaolinite and iron hydroxide precipitation formed at much lower temperatures of ca 50 c stable isotope compositions of the alteration minerals in conjunction with their paragenesis indicate that oxidized basinal fluids d 43 to 21 18o 3 8 were derived primarily from evolved seawater and leached uranium from the overlying sandstones of the athabasca formation and transported it into the basement via infiltration along fracture zones associated with reverse faults graphitic units in the basement and preore alteration served as both physical fractured zones and chemical reductants traps for the uranium mineralization the basinal fluids were responsible for the preore illite chlorite synore uraninite illite and the early postore alteration events this differs from many other sandstone hosted deposits where both oxidized basinal and reduced basement derived fluids were responsible for uranium precipitation

u pb dating of single grain uraninite by isotope dilution thermal ionization mass spectrometry abstract uraninite can be used to measure u pb ages due to its high uranium and low common lead content accurate in situ u pb dating of uraninite by secondary ion mass spectrometry sims or laser ablation inductively coupled plasma mass spectrometry la icp ms requires a matrix matched external standard as a result of the different pb u fractionation behavior in varied matrices however being lack of the suitable uraninite standard in situ u pb dating technique of uraninite is hardly carried out in many laboratories in this paper a method with a detailed analytical procedure is proposed for u pb age determination of single grain uraninite by isotope dilution thermal ionization mass spectrometry id tims this method not only avoids the difficulty of looking for the ideal uranium mineral standards because of no need to make matrix effect calibration but also gives high precision ages with a small amount of sample used

organic geochemistry in a sequence stratigraphic framework the siliciclastic shelf environment of cretaceous series se france for a better understanding of siliciclastic shelf environments correlation between sequence stratigraphy and organic geochemistry is used our study is focused on the cretaceous deposits of marcoule gard france particularly on a close packed siltites layer 200 400 m thick which is well characterized as a marine flooding facies of a single trangressive regressive cycle during the uppermost albian and the lower cenomanian the stratigraphic data indicate a change in the depositional environment from offshore to shoreface organic geochemistry is used in order to characterize origin and variability of the organic matter in relation to the stratigraphic data the study is carried out on core samples from 2 drill holes mar 203 and mar 501 analyses of the aliphatic and aromatic hydrocarbons were performed using gc ms and focused on biomarker distributions the biomarkers indicate a contribution of mixed terrestrial and marine organic matter the changes in molecular signatures are related to variations in the source of organic matter marine versus terrestrial preservation conditions largely influenced by clay and early diagenesis environmental oxidation reduction and acidic conditions as well as bioturbation various environmental zones characterized by different molecular signatures can be distinguished resin derived biomarkers can be assigned to higher plant material input and may reflect the evolution and diversity of gymnospermae versus angiospermae during the transgressive regressive cycle the relative sea level variations are clearly correlated with the nature and the preservation of the organic matter for example the pr ph and pr n c 17 ratios as well as the regular steranes distributions underline the maximum flooding surface evidenced by other studies we observe a good correlation between the organic data and sequence stratigraphy changes in geochemical signatures reflect the 3rd order depositional cycles

a growing sandstone type uranium district in south yili basin nw china as a result of extension of tien shan orogen evidences from geochronology and hydrology abstract the mesozoic yili basin of nw china represents the largest known concentration of u deposits in china and contains five major deposits namely from west to east the 512 kujie ertai 513 511 510 mengqiguer and 509 deposits pre mining resources within the explored sandstone type uranium deposits in this area are reportedly as much as 20 000 t contained u the mineralization is hosted by the middle lower jurassic shuixigou group which from base to top is divided into the badaowan sangonghe and xishanyao formations the u pb isotopic analysis of ores from the kujie ertai and mengqiguer deposits indicate that they contain high and variable amounts of initial common pb meaning that the only possible way to date these deposits is by using u pb isochrons two major stages of uranium mineralization have been identified by the u pb isotope dating of uranium ores in this region the kujie ertai deposit apparently formed between 23 4 3 3 and 20 18 0 49 ma corresponding to a period of crustal thickening and uplift within the tien shan orogen this event 35 21 ma accommodated the majority of the strain generated by the northward collision of the indian plate with the asian plate however the dating of samples from the mengqiguer deposit yielded much younger ages between 0 61 0 24 and 0 347 0 0048 ma the western tien shan mountains expanded until the pliocene as a result of the far field influence of continuous penetration of the indian plate into the asian plate this activated reverse faults and folds in the piedmont of the tien shan mountains and caused the continuous uplift of the southern flank of the yili basin the uplift caused the erosion of anticline hinge zones introducing significant amounts of oxidizing water into the shuixigou group generating a second stage of uranium mineralization hydrological sampling also suggests that the mengqiguer deposit continues to grow indicating a possible third stage of uranium mineralization 0 ma this also indicates that the u within these deposits is derived not only from u bearing sediments but from the tien shan mountains as a result of groundwater cycling the evolution of the u contents of groundwater that was initially derived from cold springs that flow into the mineralized units indicates that these cold springs have an essential role in mobilizing u from the tien shan mountains with rivers flowing through areas of outcropping mineralized units acting as a source of mineralizing fluids during the formation of the mengqiguer deposit

an integrated sequence stratigraphic geochemical investigation of the jurassic source rocks in the north yellow sea basin eastern china the north yellow sea basin nysb is one of the petroliferous basins in the offshore region of eastern china an integrated sequence stratigraphic geochemical investigation was carried out to identify and assess the effective source rocks of recent oil discoveries in the nysb a total of four third order sequences the first j2sq1 and second j2sq2 third order sequence within the middle jurassic and the first j3sq1 and second j3sq2 third order sequence within the upper jurassic were identified in the jurassic succession in which four types of probable source rocks were distinguished namely lacustrine deep water mudstones lacustrine shallow water mudstones prodeltaic mudstones and deltaic plain mudstones the lacustrine deep water mudstones are widely distributed within the j2sq1 j2sq2 and j3sq2 sequences in the gentle tectonic slope and depression area they are characterized by moderate total organic carbon toc contents 0 79 3 72 wt with an average of 1 71 wt lower hydrocarbon potential indexes the amount of free hydrocarbons before analysis s1 and the amount of hydrocarbons that results from cracking of kerogen s2 i e s1 s2 in a sample during rock eval pyrolysis 0 97 mg hc g rock s1 s2 7 89 mg hc g rock with an average of 3 10 mg hc g rock and predominantly type ii to type iii kerogen in contrast the prodeltaic mudstones in j3sq2 have higher toc contents 1 5 4 0 wt with an average of 2 71 wt higher s1 s2 5 83 25 51 mg hc g rock with an average of 14 89 mg hc g rock and predominantly type i to type ii kerogen the oil source correlation results indicate that the oils discovered in the nysb mainly originated from the prodeltaic j3sq2 mudstones the effective source kitchen is mainly located in the northwestern part of the study area the factors controlling the occurrence of high quality prodeltaic source rocks are a sufficient supply of nutrients and terrigenous organic matter high depositional rates and a suboxic environment

low temperature oxygen isotopic fractionation in the uraninite uo3 co2 h2o system oxygen isotope fractionation factors for uraninite water and uo3 water were determined from a series of uraninite co2 and uo3 co2 exchange experiments between 100 and 300 c the measured fractionation factors are similar to the theoretical fractionation factors of hattori and halas 1982 at high temperatures and zheng 1991 at low temperatures and are nonlinear over the temperature range examined regression through these curve gives 1000 ln uo2 h2o 16 58 106 t2 77 52 103 t 77 48 1000 ln uo3 h2o 2 21 106 t2 25 06 103 t 45 90 with 2 errors of 2 5 diffusion coefficients of oxygen with temperature for uraninite and uo3 can be represented by d uraninite 3 1 10 10 exp 63981 rt and d uo3 1 3 10 15 exp 21 197 rt where the activation energies for uraninite and uo3 are 64 0 0 2 kcal mole and 21 2 0 2 kcal mol respectively exceptionally low 18o values of natural uraninites i e 32 to 19 5 from unconformity type uranium deposits in saskatchewan in conjunction with theoretical and experimental uraninite water and uo3 water fractionation factors suggest that primary uranium mineralization is not in oxygen isotopic equilibrium with coeval clay and silicate minerals the low 18o values have been interpreted as having resulted from the low temperature recrystallization of primary uranium mineralization in the presence of relatively modern meteoric fluids having 18o values of ca 18 despite petrographic and u pb isotope data that indicate limited alteration therefore it appears that uranium minerals can exchange oxygen isotopes with later fluids with only limited actinide remobilization and minor disturbances to their original chemical compositions and textures

ore deposits of the french massif central insight into the metallogenesis of the variscan collision belt the french massif central fmc represents the whole west european variscan wev belt in terms of both the geodynamic evolution and the metallic content thus a study of the metallogenic evolution of the fmc may elucidate the conditions that allow the mineralisation of a collision belt since recent collision belts e g the himalayas or the alps show that mineralisation does not necessarily result from the collision process the palaeozoic history of the fmc is divided into three geodynamic stages unevenly involved from the metallogenic view point the eo variscan stage cambrian to silurian was not important the meso variscan stage devonian early carboniferous was of limited importance and most of the mineralisations formed during the neo variscan stage late carboniferous early permian in addition some more mineralisation was produced during the mesozoic because of the thermal reactivation linked with the alpine orogenies

chemostratigraphy of the posidonia black shale sw germany i influence of sea level variation on organic facies evolution abstract during the toarcian widespread deposition of organic rich mudrocks black shales occurred across europe linked to a 3rd order sea level rise we provide a high resolution multi proxy chemostratigraphic study of the dotternhausen sections in sw germany embedded in a stratigraphic and palecological framework chemostratigraphy and paleoenvironmental reconstruction is based on rock eval and elemental analysis of bulk organic matter and biomarker analysis of aliphatic hydrocarbon fractions aliphatic biomarker ratios applied to reconstruct the facies development include pristane phytane and pristane phytane n c 17 n c 18 ratios carbon preference index c 27 c 29 sterane and hopane sterane distribution results show that sea level change exerted the major control on the composition of primary produced organic matter and on its redox controlled preservation changes in primary production and in the ratio of terrestrially versus marine derived organic matter take place drastically at the onset of black shale deposition the relative proportion of terrestrial versus marine biomass accumulation is independently assessed by highly correlative bulk organic matter properties hi values and biomarker ratios cpi the terrestrially derived end member yields hi values of 50 100 mg hc toc and cpi values of 1 4 2 0 whereas the marine end member has hi values of 600 700 mg hc toc and cpi values of 0 95 1 05 correspondingly the shift in plant versus bacteria derived biomass is discriminated by hi values and hopane sterane ratios data were grouped according to their position in the lowstand lst lower and upper transgressive tst highstand systems tract hst and maximum flooding surface mfz of the sequence stratigraphic framework occurrence of organic matter with a significant bacterial contribution is restricted to the lst and lowermost tst and shows hopane sterane ratios of 0 25 0 5 marine phytoplanktonic matter dominates the upper tst hst and mfz with organic matter giving hopane sterane ratios between 0 5 and 1 7 samples from the hst yield hi values between 450 and 500 mg hc toc which is consistently lower by 150 mg hc toc when compared to the tst the lower quality of the organic matter deposited in the hst is due to its longer settling times through a thicker oxygenated water column a strong correlation with relative sea level stand and the c 27 c 29 sterane ratio is observed lst exhibits c 27 c 29 sterane ratios of 0 7 during transgression values increase to 1 0 reaching a maximum at 1 4 during sea level highstand thus reflecting decreasing terrigenous input and shifts in near shore versus open marine algal communities episodic fluctuation of anoxia is discussed on the basis of a monsoonal climate model which infers significant surface run off during summer monsoon providing high nutrient supply and associated high primary productivity in combination with a density stratified water column excellent preservation conditions for organic matter were established dry winter conditions with inversion of the surface water flow regime led to seasonal export of bottom waters and episodic establishment of dysoxic conditions variations in the extent of annual flushing of sub basins on the toarcian shelf controlled long term organic matter accumulation rate paleoclimate variability and its connection with sea level stand is thus of paramount importance for different modes of organic matter accumulation and redox system stability

uranium deposits associated with na metasomatism from central ukraine a review of some of the major deposits and genetic constraints abstract the paper reviews geological structural mineralogical fluid inclusion geochemical and stable isotope characteristics of u deposits related to na metasomatism in the central ukrainian uranium province cuup the province contains numerous u deposits hosted in gneisses migmatites and granites of the ingul paleoproterozoic megablock and in iron formations along its margin with the fore mid dnieper mesoarchean megablock the richest u deposits are distributed along the nearly e w striking subotin mashorin tectonic zone but they are tightly controlled by n s and more rarely sw ne striking crustal scale shear zones na metasomatism and u mineralisation were controlled by protracted tectonic activity along these shears zones from ductile to brittle regimes of deformation a metasomatic zoning is developed from outermost unaltered lithologies inwards to dequartzified rocks episyenites aegirine albitites na metasomatites andradite epidote ca amphibole calcite rich rocks ca mg metasomatites and ultimately to biotite albitites k metasomatites main u ore deposition predominantly consisting of brannerite and uraninite with lesser amounts of u ferropseudobrookite is associated with the ca mg and k metasomatised zones superimposed on earlier aegirine albitites na metasomatites were formed at temperatures exceeding 500 c possibly triggered by the onset of a plume in the mantle associated with the intrusion of the highly potassic korsun novomyrgorod rapakivi granitic pluton at about 1750 1800 ma as constrained by u pb geochonologic data on the granites and uranium mineralisation these intrusions have been partly reworked tectonically with recrystallisation under lower p t conditions the mineral paragenesis of ca mg and k metasomatites crystallised during the cooling of the system down to 370 340 c ca mg and k metasomatisms resulted in further dequartzification of the rocks and their enrichment mainly in ca mg k u zr fe 2 and hf the hydrothermal fluids were oxidised moderately saline and highly alkaline the high alkalinity of the fluids explains the dissolution of quartz the deposition and stability of albite the high zr hf ratios up to 224 in the metasomatites and the high solubility of u and zr u deposition was controlled by mixing with a reduced fluid which explains the increase of whole rock fe 2 concentration during uranium deposition the last widespread hydrothermal event corresponds to a chlorite epidote paragenesis superimposed on all previous mineral associations at temperatures down to less than 100 c h o and c isotopic ratios in minerals and fluid inclusions extract from albitites suggest a surface formation water origin for the hydrothermal fluids producing na metasomatism and a mixed metamorphic surficial formation water origin for the fluids producing ca mg and k metasomatism and the main u mineralisation

some problems concerning relationship between mesozoic cenozoic lithospheric extension and uranium metallogenesis in south china previous studies have shown that there existed large scale lithospheric extension events during the cretaceous tertiary period in south china and that large scale uranium mineralization occurred at the same time in this area which resulted in the formation of many important uranium deposits such as granite hosted volcanics hosted and carbonaceous siliceous pelitic sedimentary rock hosted ones this paper reviews previous researches on lithospheric extension and uranium metallogenesis in south china since mesozoic and preliminarily discusses their temporal and spatial associations in order to precisely reveal the relationship between lithospheric extension and uranium metallogenesis it is suggested that at least two fundamental problems should be solved the first is the accurate episodes of extension and uranium mineralization and the second is the mechanism governing the control of the tectonic regime over the formation of the uranium deposits to probe into these problems it is necessary to accurately date the uranium deposits and the mafic dikes intruded during the mesozoic extension and to determine the role and origin of gaseous components such as co2 in ore forming fluids

in situ sims uraninite u pb dating and genesis of the xianshi granite hosted uranium deposit south china abstract the southeastern part of the nanling metallogenic province china is host to numerous granite hosted vein type hydrothermal uranium deposits the geology and geochemistry of these deposits have been extensively studied however accurate and precise ages for the uranium mineralization are scarce because the uranium minerals in these deposits are usually fine grained and may have formed in several stages therefore the ages previously obtained by the bulk dating techniques are possibly a mixed age the xianshi uranium deposit located in the southeastern part of the guidong granite complex is a major uranium deposit in south china the uranium mineralization from this deposit is mainly fine grained uraninite in quartz or calcite veins which are spatially associated with the cretaceous mantle derived mafic dykes micro raman spectroscopy and x ray diffraction analyses indicate that the dominant uranium mineral occurs as a rare form of uraninite u 3 o 7 three distinct generations of uranium minerals have been identified based on petrographic and field relations stage 1 uraninite has the lowest uo 2 and highest pbo contents whereas stage 3 uraninite has the highest uo 2 and lowest pbo contents uraninite from the xianshi deposit was dated using an in situ sims u pb dating technique the results show three distinct age groups 135 4 ma 113 2 ma and 104 2 ma which are in excellent agreement with the ages of three episodes of mantle derived mafic dykes therefore the xianshi uranium deposit has experienced at least three hydrothermal events that are responsible for the deposition of uranium ores which are genetically related to the emplacement of three sets of mafic dykes

detection of widespread fluids in the tibetan crust by magnetotelluric studies magnetotelluric exploration has shown that the middle and lower crust is anomalously conductive across most of the north to south width of the tibetan plateau the integrated conductivity conductance of the tibetan crust ranges from 3000 to greater than 20 000 siemens in contrast stable continental regions typically exhibit conductances from 20 to 1000 siemens averaging 100 siemens such pervasively high conductance suggests that partial melt and or aqueous fluids are widespread within the tibetan crust in southern tibet the high conductivity layer is at a depth of 15 to 20 kilometers and is probably due to partial melt and aqueous fluids in the crust in northern tibet the conductive layer is at 30 to 40 kilometers and is due to partial melting zones of fluid may represent weaker areas that could accommodate deformation and lower crustal flow

isotope geochronology geochemistry and mineral chemistry of the u bearing and barren granites from the zhuguangshan complex south china implications for petrogenesis and uranium mineralization abstract the zhuguangshan complex carries some of the most important granite hosted uranium deposits in south china here we investigate the changjiang and jiufeng granites which represent typical u bearing and barren granites in the complex using zircon u pb ages whole rock geochemistry sr nd isotopic and zircon hf isotopic data and mineral chemistry to constrain the petrogenesis and uranium mineralization la icp ms zircon u pb dating shows that both the changjiang and jiufeng granites were emplaced ca 160 ma these rocks show high silica weakly to strongly peraluminous compositions enrichment in rb th and u and depletion in ba nb sr p and ti these features coupled with the high initial 87 sr 86 sr ratios negative end t values and ehf t values and the paleoproterozoic two stage model ages of these two granites suggest that the two granites belong to s type granites and the parental magmas of the two granites were derived from the paleoproterozoic metasedimentary rocks however the granitoids show different mineralogical characteristics the biotite in the changjiang granite belongs to siderophyllite marking higher degree of chloritization whereas the biotite in the jiufeng granite is ferribiotite characterized by only slight chloritization compared with the jiufeng granite the biotite in the changjiang granite has lower crystallization temperature and oxygen fugacity but higher f content and the uraninite has higher uo 2 content but lower tho 2 content and stronger corrosion the chemical ages of uraninites from both granites are within error consistent with the zircon u pb ages and are considered to represent the emplacement ages of granites chemical ages of pitchblende in the changjiang granite yield 118 8 ma 87 4 ma and 68 6 ma representing multiple episodes of hydrothermal events that are responsible for the precipitation of u ores in the changjiang uranium ore field our study suggests that the degree of magma differentiation and physicochemical conditions of the magmatic hydrothermal system are the key factors that control the different u contents of these two granites the mineralogical characteristics of uraninite and biotite can be used to distinguish between u bearing and barren granites and serve as a potential tool for prospecting granite hosted uranium deposits

oil source rock correlations limitations and recommendations a rigorous defensible and causal oil source rock correlation definitively ties an individual source rock sample to an individual crude oil using genetically based internally consistent parameter matches such a correlation is a relationship established between the two components which is consistent with all known chemical geochemical and geological information and meets three criteria a the relationship must be causal the oil must arise at least in part from the specified source rock s b chemical data used in the correlation must be comparable the elemental molecular and isotopic data derived from the source rock must be of the same type as that derived from the oil and c all available geological data must be supportive clear geological evidence must exist which allows the proposed source rock to have sourced the oil the three points of this definition are satisfied and the correlation is successful if we solve one analytical and three geological problems natural extraction of crude oil from its source rock i e expulsion differs mechanically and temporally from laboratory extraction leading to a correlation problem referred to as extraction differences and representing the single greatest analytical uncertainty in correlation efforts geologically three aspects confound oil source correlations occurrence of multiple source units and or source units at differing maturity levels lateral and vertical depositional variations in source unit s organic matter and lateral and vertical variation in reservoir unit s organic matter these concerns are overcome by taking five actions for each oil source correlation effort 1 select representative samples using statistically defensible methods 2 establish the inherent compositional variability laterally and temporally due to depositional and maturation processes in each prospective source unit 3 assess the extent of migration induced changes in oil composition including post migration changes such as in reservoir alteration 4 support each correlation with migration histories derived from 4d models 5 iterate correlation results with new data gathered from ongoing exploration efforts these five actions will a allow correlation success to be measured more objectively b establish risking parameters for direct use in basin assessment and c provide baseline criteria for use in assessing the reliability of oil source rock correlations although these approaches will improve conventional oil source rock correlation efforts ultimately they may not be needed if inversion methods become more reliable the ability to invert compositional data for crude oil i e predict the age lithology maturity and other characteristics of a source rock solely through chemical analysis of its expelled oil could eventually result in successful oil source rock correlations in which source rock analysis for oil source rock correlation purposes is less critical

eastern asia and the western pacific timing and spatial distribution of rifting in china abstract a compilation of recognized rifts in china indicates that five distinct episodes of rifting have occurred these episodes occurred at approximately 2 3 ga 1 85 1 7 ga 1 0 0 7 ga 550 190 ma and 175 ma to present the timing and location of rifting has largely been a function of tectonic activity along the margins of the various chinese paleocontinents some of the oldest rocks in china are found in the sino korean and tarim cratons and most of the identified precambrian rifts are found within or on the margins of these cratons these cratons are viewed as the continental nucleus of china and fold belts and microcontinents have been accreted to this nucleus through time much of the locus of rifting has migrated away from this nucleus as has the location of the continental margin especially in the paleozoic beginning in the middle mesozoic rifting commenced along the entire eastern margin of china extension occurred concomitantly with subduction in a backarc setting this is the dominant cenozoic extensional regime in china and is still active today to date few cenozoic rifts have been found in western china where most tectonism is probably a consequence of the collision between india and china but it seems likely that more rifts will be discovered in this area as it becomes better studied

the source of uranium within hydrothermal uranium deposits of the motianling mining district guangxi south china abstract uranium deposits are diverse as a result of their formation in a wide variety of geological environments however the source of the uranium within these deposits is difficult to identify and as a result it is usually poorly understood this study focuses on the hydrothermal sanqiliu and sanqisi uranium deposits both of which formed within ne sw striking shear zones that cross cut the sanfang batholith and low grade metasedimentary rocks of the motianling district southern china the deposits contain vein hosted pitchblende quartz pyrite chlorite mica orebodies fluid inclusions within quartz in the orebodies in the district homogenize at temperatures between 205 c and 222 c indicating the deposit formed as a result of low to intermediate temperature hydrothermal activity pitchblende associated hydrothermal pyrite within the sanqiliu and sanqisi deposits has 34s values from 24 7 to 19 7 and from 6 0 to 13 6 respectively quartz separates from the sanqiliu deposit yield 18o values of 1 4 11 5 mean of 5 8 for syn ore hydrothermal fluids these stable isotope data indicate that the fluids that formed these deposits were derived from the sanfang granites sediments of the sibao group and meteoric sources in addition uraninite from the host sanfang granite yields u pb ages of ca 732 773 ma combining these data with the geology of the ore deposits in this region suggests that these deposits were generated from deeply circulating meteoric water and the uraninite within the highly fractionated sanfang granite is the source of the uranium within the sanqiliu and sanqisi uranium deposits

geologic evolution of petroliferous basins on continental shelf of china the coastline of southeastern china is about 18 000 km 11 200 mi in length and its aggregate continental shelf area within 200 m 660 ft water depth is well over 1 million km2 390 000 mi2 recent geophysical exploration and petroleum drilling records aid in understanding the geologic evolution of these petroliferous basins two types of tectonic basins are present on the continental shelf areas 1 bohai gulf south yellow sea and beibu gulf are intraplate polyphase rift depression basins and 2 east china sea mouth of the pearl river and the yingge sea are epicontinental rift depressions basins both types are believed to be of extensional origin the severe convergence of the indian plate with the eurasia plate produced east northeast s reading of the south china sea basin which resulted in two triple junctions on its northern margins the pacific plate was subducted by downthrust beneath the eurasia continental crust the extension mechanism could be the rising of an upper mantle plume to produce two weak north northeast trending fracture zones a series of intraplate and epicontinental rift depression basins was formed the depositional models and sea level variations of these basins have been interpreted from drilling records and seismic profiles they can be explained by the tectonoeustatic changes in sea level and cenozoic climatic changes in china

guidelines for evaluating petroleum source rock using programmed pyrolysis rock eval pyrolysis is used to rapidly evaluate the petroleum generative potential and thermal maturity of rocks accurate conclusions require programs every 30 60 ft 9 18 m understanding of interpretive pitfalls and supporting data such as visual kerogen vitrinite reflectance and elemental analyses the generative potential of coals is commonly overestimated by pyrolysis and is best determined by elemental analysis and organic petrography most coals show high s2 s3 5 and low hi values 300 mg hc g toc migrated oil and mud additives which alter rock eval data can sometimes be removed by special processing for immature rocks bimodal s2 peaks and pi values over 0 2 indicate contamination pyrolysis downgrades organic poor clay rich rocks which show lower hi and higher tmax values than isolated kerogen because of adsorption of pyrolyzate on the clays tmax values for small s2 peaks 0 2 mg hc g toc are unreliable tmax is affected by maturation organic matter type contamination and the mineral matrix s3 is sensitive to inorganic and adsorbed carbon dioxide and to instrumentation problems acidification of carbonate rich samples and proper maintenance improves s3 measurement constant sample weights 100 mg are recommended below a threshold weight tmax increases by up to 10 c and other parameters decrease organic rich samples which overload the detector can be diluted with carbonate detector linearity is determined by pyrolyzing various weights of an organic rich rock

mantle derived gaseous components in ore forming fluids of the xiangshan uranium deposit jiangxi province china evidence from he ar and c isotopes abstract the xiangshan u deposit the largest hydrothermal u deposit in china is hosted in late jurassic felsic volcanic rocks although the u mineralization post dates the volcanics by at least 20 ma the mineralization coincides with intrusion of local mantle derived mafic dykes formed during cretaceous crustal extension in south china ore forming fluids are rich in co 2 and u in the fluid is thought to have been dissolved in the form of uo 2 co 3 2 2 and uo 2 co 3 3 4 complexes this paper provides he and ar isotope data of fluid inclusions in pyrites and c isotope data of calcites associated with u mineralization pitchblende in the xiangshan u deposit he isotopic compositions range between 0 1 and 2 0ra where ra is the 3 he 4 he ratio of air 1 39 10 6 and correlates with 40 ar 36 ar although there is potential for significant 3 he production via 6 li n 3 h 3 he reactions in a u deposit due to abundant neutrons nucleogenic production cannot account for either the 3 he concentration in these fluids nor the correlations between he and ar isotopic compositions it is more likely that the high 3 he 4 he ratios represent trapped mantle derived gases a mantle origin for the volatiles of xiangshan is consistent with the 13 c values of calcites which vary from 3 5 to 7 7 overlapping the range of mantle co 2 the he ar and co 2 characteristics of the ore forming fluids responsible for the deposit are consistent with mixing between 3 he and co 2 rich mantle derived fluids and co 2 poor meteoric fluids these fluids were likely produced during cretaceous extension and dyke intrusion which permitted mantle derived co 2 to migrate upward and remobilize u from the acid volcanic source rocks resulting in the formation of the u deposit subsequent decay of u within the fluid inclusions has reduced the 3 he 4 he ratio and variations in u 3 he result in the range in 3 he 4 he observed with u 3 he ratios in the range 5 17 10 3 likely corresponding to u concentrations in the fluids

geophysical constraints on the link between cratonization and orogeny evidence from the tibetan plateau and the north china craton abstract understanding the geodynamic process of orogeny and cratonization and their transition is among the key topics of research in evaluating the link between plate tectonics and continental dynamics the tibetan plateau and the north china craton ncc two key areas in mainland china offer excellent laboratories to understand continental tectonics over a broad span of earth history particularly the deep structure of the lithosphere as imaged from geophysical data on the tibetan plateau and the ncc provide important clues in understanding orogeny and cratonization the tibetan plateau is the largest and highest plateau on earth in terms of mean altitude and is an important region for understanding the mechanisms of continent continent collision and cenozoic plateau uplift the ncc is an archean craton that underwent lithospheric disruption during the mesozoic here we reconstruct the main features of the structure of the crust and upper mantle from surface wave tomography and gravity modeling in tibet and its neighboring regions in order to understand the modality of the convergence and collision process between the indian and eurasian plates and the influence of this process on the uplift of the plateau in the ncc geological geochemical geophysical and tectonic investigations demonstrate that lithospheric destruction mainly occurred in the eastern block the crustal structure of the ncc is reconstructed from ambient noise surface wave tomography and the different possible disruption mechanisms are evaluated the vs shear wave velocity tomography results and the density structure of the crust and upper mantle to about 350 km depth demonstrate the lateral variation of the thickness of the metasomatic lid between the south and north of the bangong nujiang suture bns and the west and east of tibet which suggest that the leading edge of the subducting indian slab reaches the bns the subduction angle of indian plate indicates a transition from steep to shallow from the west to east tibet sections depicting the gravitational potential energy suggest that mantle flow contributes to the subduction of the indian plate as far as the bns and the transition from the asthenospheric layer to the metasomatic lid overlaps with the transition from north south shortening in south tibet to eastward tectonic escape in north tibet qiangtang and songpan ganzi blocks both vs and models suggest the following 1 north southward lower crust flow beneath the eastern ncc and interaction between the westward mantle flow and eastward escape flow beneath the central ncc in addition to the earlier proposed mechanisms of delamination and thermal erosion played important roles in the lithospheric disruption of the archean craton 2 mantle flow plays an important role in the continental tectonic transition between neighboring tectonic blocks and within the cycle between orogeny and cratonization

zircon u pb geochronology and geochemistry of granites in the zhuguangshan complex south china implications for uranium mineralization abstract the zhuguangshan complex composed of caledonian indosinian and yanshanian granites and cretaceous mafic dykes is one of the most important granite hosted uranium producers in south china here we present la icp ms zircon u pb and hornblende 40ar 39ar geochronology and whole rock and biotite geochemistry for the granites in this complex to evaluate the magmatism and its constraints on uranium mineralization samples collected from the fuxi youdong longhuashan chikeng qiling and sanjiangkou intrusions yield zircon weighted 206pb 238u ages of 426 7 5 4 ma 226 4 3 5 ma 225 0 2 7 ma 152 2 3 0 ma 153 9 2 1 ma and 155 2 2 1 ma respectively a new ar ar dating of the hornblende of the diabase from the changjiang uranium ore field yields a plateau age of 145 1 1 5 ma these results coupled with published geochronological data indicate that six major magmatic events occurred in the study area at 420 435 ma 225 240 ma 150 165 ma 140 ma 105 ma and 90 ma both u bearing and barren granites occur in this complex and they display differences in whole rock and biotite geochemistry the barren granites show higher al2o3 cao tfmm rb zr ba si mg la yb n and eu eu but lower sio2 alk rb di rb sr and tio2 mgo than those of the u bearing granites biotites in the u bearing granites are close to the fe rich siderophyllite annite end member with fe fe mg ratios higher than 0 66 whereas those in the barren granites are relatively close to the mg rich eastonite phlogopite end member with fe fe mg ratios

origin and tectonic significance of a mesozoic multi layer over thrust system within the yangtze block south china abstract in the yangtze block south china a well developed mesozoic thrust system extends through the xuefeng and wuling mountains in the southeast to the sichuan basin in the northwest the system comprises both thin and thick skinned thrust units separated by a boundary detachment fault the dayin fault to the northwest the thin skinned belt is characterized by either chevron anticlines and box synclines to the northwest or chevron synclines to the southeast the former structural style displays narrow exposures for the cores of anticlines and wider exposures for the cores of synclines thrust detachments occur along silurian fs and lower cambrian fc strata and are dominantly associated with the anticlines to the southeast this style of deformation passes gradually into one characterized by chevron synclines with associated principal detachment faults along silurian fs cambrian fc and lower sinian fz strata there are however numerous secondary back thrusts therefore the thin skinned belt is like the valley and ridge province of the north american applachian mountains the thick skinned belt structurally overlies the thin skinned belt and is characterized by a number of klippen including the xuefeng and wuling nappes it is thus comparable to the blue ridge province of appalachia the structural pattern of this thrust system in south china can be explained by a model involving detachment faulting along various stratigraphic layers at different stages of its evolution the system was developed through a northwest stepwise progression of deformation with the earliest delamination along lower sinian strata fz analyses of balanced geological cross sections yield about 18 1 21 total 88 km shortening for the thin skinned unit and at least this amount of shortening for the thick skinned unit the compressional deformation from southeast to northwest during late jurassic to cretaceous time occurred after the westward progressive collision of the yangtze block with the north china block and suggests that the orogenic event was intracontinental in nature

o and pb isotopic analyses of uranium minerals by ion microprobe and u pb ages from the cigar lake deposit we apply a rapid and accurate in situ technique to make u pb isotopic measurements of complexly intergrown uranium minerals and oxygen isotopic analyes of uraninite from the unconformity type cigar lake uranium deposit secondary uranium minerals intergrown with uraninite such as coffinite usio4 nh2o and calciouranoite cau2o7 5h2o were identified by highresolution transmission electron microscopy hrtem in situ u pb results from three stages of uraninite and coffinite define well correlated arrays on concordia with upper intercepts of 1461f47 1176f9 and 876f14 ma f1r these ages are interpreted as the minimum ages of mineralization correlate with the timing of clay mineral alteration f1477 ma associated with these unconformity type uranium deposits the ages of magnetization events at 1600 1450 and 900 ma from the athabasca basin and the grenvillian orogeny at f1100 ma in situ u pb isotopic analyses of uraninite and coffinite can document the pb u heterogeneities that occur on the scale of 15 30 am thus providing relatively accurate information regarding the timing of fluid interactions associated with the evolution of these deposits the high spatial resolution and precision of the ion microprobe allow us to measure d 18 o values of 20 100 am unaltered portions of uraninites from cigar lake the range of d 18 o values 33 9 to 20 4x are among the lowest reported for unconformity type deposits confirming that conventional fluorination analyses of material sampled at the mm scale are insufficient to avoid contamination from isotopically heavier coffinite and calciouranoite d 2002 elsevier science b v all rights reserved

element geochemistry mineralogy geochronology and zircon hf isotope of the luxi and xiazhuang granites in guangdong province china implications for u mineralization abstract the luxi and xiazhuang granitic plutons are parts of the guidong granite belt in northern guangdong province china they occur next to each other and have similar crystallization ages however the xiazhuang pluton hosts several important uranium u ore deposits whereas the luxi pluton does not this study compares the two plutons using whole rock geochemistry biotite compositions zircon u pb ages by la icpms and in situ zircon hf isotope data by la mc icpms to understand the fundamental controls results show that the two plutons have similar ages 237 ma for the luxi pluton and 234 ma for the xiazhuang pluton they also have similar geochemical features that are characteristic of s type granites zircons from both plutons have negative e hf t values 9 to 12 and a paleoproterozoic two stage hf model age t dm2 1838 ma to 2025 ma suggesting that their parental magmas were all derived from paleoproterozoic metasedimentary rocks the geochemical and petrological data suggest that these two plutons crystallized from magmas derived from the same parent at different stages the parental magma of the xiazhuang pluton is more evolved than that of the luxi pluton this factor plus different physical chemical conditions such as temperature volatile components and oxidation state resulted in higher u content and favorable u bearing species in the xiazhuang magmatic hydrothermal system u occurs mainly as uraninite in the xiazhuang pluton which facilitates u transfer from granite into co 2 rich hydrothermal fluid to form u ore deposits in contrast u occurs mainly as ree bearing minerals in the luxi magmatic system preventing u transfer to associated hydrothermal fluids as a result the xiazhuang pluton hosts several important uranium ore deposits whereas the luxi pluton is ore barren

mineralogical and geochemical constraints on the genesis of the granite hosted huangao uranium deposit se china abstract the huangao uranium deposit located in jiangxi province se china is hosted mainly by the indosinian medium to coarse grained porphyritic biotite granite as a batholith sanerer pluton and to a lesser extent by the yanshanian fine grained porphyritic biotite granite as stock the indosinian granite has a whole rock rb sr isochron age of 215 6 ma and the yanshanian granite has a whole rock rb sr isochron age of 155 7 6 4 ma both granites may be formed by anatexis of uranium rich precambrian and cambrian metasedimentary rocks deuteric alteration of primary accessory minerals zircon sphene apatite allanite monazite and xenotime in the granites and erosion of the granites under a hot dry palaeoclimate resulted in the partial liberation of uranium these processes were critical for the formation of the mesothermal to epithermal u deposit uranium in the deposit occurs as pitchblende along tectonic fractures interstitially in granular minerals and as cements of breccias the host rock alteration comprises pre ore alkali metasomatism and ore stage hydrothermal chloritization pyritization hematitization silicification damouritization and carbonatization other minerals present in the ore include pyrite galena sphalerite chalcopyrite hematite microcrystalline quartz chlorite calcite and fluorite fluid inclusion studies on quartz fluorite and calcite reveal that temperatures of the mineralizing fluids range from 110 to 260 c and give salinity values ranging from 11 7 to 21 6 wt nacl equivalent the 18 o and d values of the fluids range from 4 0 to 3 6 and from 81 3 to 56 6 respectively indicating meteoric water mineralogical fluid inclusion and isotopic data are consistent with a mesothermal to epithermal origin for the huangao deposit thermal activity at the huangao deposit was maintained from the emplacement of the indosinian granite at 215 ma until the intrusion of the lamprophyre dike at 105 ma magmatism in the district as well as radioactive decay of k u and th in the granite may have provided an essential or additional heat source for the formation of the hydrothermal solutions the u bearing hydrothermal solution was also heated and deep convective circulation was mainly driven by the regional tectonism this is supported by the u pb isochron age of four pitchblende samples at 48 ma which is in the time range of the late yanshanian regional tectonism that affected south china

uranium metallogenesis in south china and its relationship to crustal extension during the cretaceous to tertiary south china is rich in vein type hydrothermal uranium deposits hosted in granitic volcanic and carbonaceous and siliceous pelitic sedimentary rocks the uranium deposits are spatially associated with extensional structures and or mantle derived mafic dikes both the uranium deposits and mafic dikes are cretaceous to tertiary in age temporally coincident with the crustal extension carbon isotope analyses of calcite deposited in the main stage mineralization in the veins from 12 representative uranium deposits yield 13c values of ore forming fluids mainly from 4 to 8 per mil which are permissive of a mantle origin for the co2 in the ore forming fluids a mantle origin is consistent with the association of the deposits with mafic dikes and the 3he 4he ratios of ore forming fluids e g 0 10 2 02 ra for the volcanic hosted xiangshan uranium deposit isotopic compositions of h and o demonstrate that water in the ore forming fluids is predominantly meteoric in origin ore forming temperatures ranged approximately from 150 to 250 c uranium rich crustal rocks in south china may have been the sources for the uranium crustal extension and associated mafic magmatism are considered to have heated the rocks and allowed co2 possibly from mantle sources to migrate upward and to mix with co2 poor meteoric water the co2 rich hydrothermal fluids mobilized uranium from the source rocks and then the uranium was deposited in various host rocks to form the uranium deposits

production preservation and prediction of source rock facies in deltaic settings abstract this article hypothesizes that production and preservation of source rock type facies in deltaic systems both landward and seaward of a coastline is mutually exclusive time successive and related to the dynamics of relative sea level sedimentologic research in the holocene mississippi and rhone delta complexes suggests that rheotrophic peats and associated organic rich beds preferably accumulate in the accommodation space created behind landward stepping shorelines in a transgressive systems tract tst such a setting also allows for a sufficient supply of recharging fresh nutrient rich groundwater into the peat forming mires kosters e c suter j r 1993 facies relationships and systems tracts in the late holocene mississippi delta plain journal of sedimentary petrology 63 4 727 733 independently carried out quantitative paleoecological studies in the same delta systems and in addition in the orinoco and po deltas suggest that in a progradational setting highstand systems tract hst seasonally discharged nutrient and sediment laden river waters on the shelf may give rise to anoxia or dysoxia subsequent overfertilization of the shelf leads to accumulation of organic rich mud belts on the shelf vanderzwaan g j jorissen f j 1991 biofacial patterns in river induced anoxia in tyson r v pearson t h eds modern and ancient continental shelf anoxia geological society of london special publication no 58 pp 65 82 thus production and preservation of source rock type facies landward of a shoreline as peats and related sediments is preferred in a tst when accommodation space and nutrient supply are landward of the shoreline vice versa production and preservation of such facies seaward of a shoreline as organic rich shelf muds occurs preferentially in a highstand systems tract in that situation accommodation space is on the shelf where river fed nutrients are supplied as well this hypothesis suggests further potential for application of sequence stratigraphic concepts for improved understanding of the occurrence of source rock type facies

biomarker characterisation of an oil and its possible source rock from offshore korea bay basin abstract comparison of biomarker distributions in an oil and in sedimentary rock samples from an offshore well in korea bay basin indicates that an upper jurassic 500 m thick mudstone zone could form the source rock for the oil the organic material in this zone appears to be h rich and of sufficient abundance from pyrolysis measurements to generate oil it seems to derive primarily from bacterial lipids as reflected in high levels of bacterial hopanoids and predominance of amorphous kerogen macerals a higher plant wax contribution to the organic matter is indicated by an oep in n akanes c 20 and there may also be an autochtonous algal contribution sedimentological and biomarker evidence is consistent with input from a river delta prograding into a deep freshwater lake biomarker distributions suggest that pronounced bacterial reworking of allochthonous higher plant material had occurred in probably anoxic conditions high heat flows in a rapidly subsiding extensional basin probably account for the observed extensive aromatisation of monoaromatic steroidal hydrocarbons at a relatively early stage of sterane isomerisation

the geological evolution of the tibetan plateau the geological evolution of the tibetan plateau is best viewed in a context broader than the india eurasia collision zone after collision about 50 million years ago crust was shortened in western and central tibet while large fragments of lithosphere moved from the collision zone toward areas of trench rollback in the western pacific and indonesia cessation of rapid pacific trench migration 15 to 20 million years ago coincided with a slowing of fragment extrusion beyond the plateau and probably contributed to the onset of rapid surface uplift and crustal thickening in eastern tibet the latter appear to result from rapid eastward flow of the deep crust probably within crustal channels imaged seismically beneath eastern tibet these events mark a transition to the modern structural system that currently accommodates deformation within tibet

vorlanite cau6 o4 a new mineral from the upper chegem caldera kabardino balkaria northern caucasus russia the new mineral vorlanite cau 6 o 4 d calc 7 29 g cm 3 h 4 5 vhn 10 360 kg mm 2 was found near the top of mt vorlan in a calcareous skarn xenolith in ignimbrite of the upper chegem caldera in the northern caucasus kabardino balkaria russia vorlanite occurs as aggregates of black platy crystals up to 0 3 mm long with external symmetry 3 m the strongest powder diffraction lines are d a hkl 3 107 111 2 691 200 1 903 220 1 623 311 1 235 331 1 203 420 1 098 422 0 910 531 single crystal x ray study gives isometric symmetry space group fm 3 m a 5 3813 2 a v 155 834 10 a 3 and z 2 x ray photoelectron spectroscopy indicate that all u in vorlanite is hexavalent the mineral is isostructural with fluorite and uraninite u 4 o 2 in contrast to synthetic rhombohedral cauo 4 and most u 6 minerals the u 6 cations in vorlanite are present as disordered uranyl ions 8 ca 2 and 8 u 6 are disordered over a single site with average m o 2 33 a vorlanite is believed to be a pseudomorphic replacement of originally rhombohedral cauo 4 we assume that this rhombohedral phase transformed by radiation damage to cubic cauo 4 vorlanite the new mineral is associated with larnite chegemite reinhardbraunsite lakargiite rondorfite and wadalite which are indicative of high temperature formation 800 c at shallow depth

organic geochemical characteristics and depositional models of upper cretaceous marine source rocks in the termit basin niger abstract upper cretaceous marine mudstones are widely known as the most important source rocks in the western african rift basins however geochemical studies on their occurrence and formation mechanism are scarce in this study a detailed geochemical investigation within a sequence stratigraphic framework was carried out to reconstruct the palaeoenvironmental conditions and to establish models on the depositional history of upper cretaceous marine mudstones in the termit basin niger western african a total of six third order sequences dsq1 dsq2 ysq1 ysq2 ysq3 and msq1 from bottom to top were identified in the upper cretaceous the distribution of biomarkers from 33 mudstone samples in different sequences indicate that mudstones from ysq3 were mainly deposited in a suboxic to oxic environment with significant contributions from mixed terrigenous higher plants and lower aquatic organisms in fresh brackish water column in contrast the other sequences ysq2 ysq1 dsq2 and dsq1 mainly represent a suboxic to anoxic marine environment with a stratified water column 0 59

recurring patterns of total organic carbon and source rock quality within a sequence stratigraphic framework sequence stratigraphy has been combined with total organic carbon toc analysis from well logs core and cuttings to develop a model of toc accumulation in marine source rocks routine well profiling of toc in marine source rocks has revealed that recurrent patterns in the vertical distribution of toc occur that can be explained with sequence stratigraphic concepts the model assumes that the principle controls on organic carbon accumulation are 1 the presence of low oxygen conditions at the sediment water interface and 2 sedimentation rate under these circumstances toc will vary inversely with terrigenous clastic influx if accommodation is high clastic influx is low in distal locations and the resulting weight percent toc in basinal sediments is increased th maximum toc in a vertical profile through a single marine sequence probably correlates to the maximum flooding surface toc decreases above this surface due to increasing sediment dilution during highstand progradation and decreases below it with the higher sedimentation rate of the older transgressive systems tract commensurate with toc increase towards the maximum flooding surface the organic matter type becomes more marine and therefore increasingly oil prone several marine source rock examples are presented as well as a lacustrine example which also conforms to the marine model

sequence stratigraphic context and organic geochemistry of palaeogene oil shales jordan abstract the potential oil shales of the palaeogene muwaqqar chalk marl and umm rijam chert limestone formations are investigated from a subsurface location in the west of jordan detailed organic geochemistry data is placed in the context of a sequence stratigraphic framework derived from vertical foraminiferal biofacies and lithological changes and biostratigraphically calibrated using planktonic foraminiferal biozonation this shows that the transgressive systems tract of a selandian p4 probably p4a sequence has the best potential in the studied section to generate oil if subjected to induced pyrolysis a ypresian no older than e2 transgressive sequence has some potential whilst highstand systems tracts offer the least potential both the sequence model and oil shale potential compares well with equivalent age sediments in egypt and highlights that whilst the maastrichtian portion of the muwaqqar chalk marl formation is often regarded as the key interval for oil shale prospectivity parts of the paleocene succession also have some potential

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

direct evidence for the source of uranium in the baiyanghe deposit from accessory mineral alteration in the yangzhuang granite porphyry xinjiang province northwest china

evolution of uranium fractionation processes through time driving the secular variation of uranium deposit types uranium deposit types have evolved considerably from the archean to the present the major global drivers were 1 change of geotectonic conditions during the late archean 2 strong increase of atmospheric oxygen from 2 4 to 2 2 ga and 3 development of land plants during the silurian other significant variations of uranium deposit types are related to unique conjunctions of conditions such as those during phosphate sedimentation in the cretaceous earth s uranium fractionation mechanisms evolved through four major periods the first from 4 55 and 3 2 ga corresponds to formation of a thin essentially mafic crust in which the most fractionated trondheimite tonalite granodiorite ttg rocks attained uranium concentrations of at most a few parts per million moreover the uranium being essentially hosted in refractory accessory minerals and free oxygen being absent no uranium deposit could be expected to have formed during this period the second period from about 3 1 to 2 2 ga is characterized by several widespread pulses of highly fractionated potassic granite strongly enriched in u th and k late in this period peraluminous granite was selectively enriched in u and to a lesser extent k these were the first granite and pegmatite magmas able to crystallize high temperature uraninite the erosion of these granitic suites liberated thorium rich uraninite which would then be concentrated in placer deposits along with pyrite and other heavy minerals e g zircon monazite fe ti oxides within huge continental basins e g witwatersrand south africa and bind river canada the lack of free oxygen at that time prevented oxidation of the uraninite which formed the oldest economic uranium deposit types on earth but only during this period the third period from 2 2 to 0 45 ga records increased oxygen to nearly the present atmospheric level tetravalent uranium from uraninite was oxidized to hexavalent uranium forming highly soluble uranyl ions in water uranium was extensively trapped in reduced epicontinental sedimentary successions along with huge quantities of organic matter and phosphates accumulated as a consequence of biological proliferation especially during the late paleoproterozoic a series of uranium deposits formed through redox processes the first of these developed at a formational redox boundary at about 2 0 ga in the oklo area of gabon all known economically significant uranium deposits related to na metasomatism are about 1 8 ga in age the high grade large tonnage unconformity related deposits also formed essentially during the late paleoproterozoic to early mesoproterozoic the last period 0 45 ga present coincided with the colonization of continents by plants the detrital accumulation of plants within continental siliciclastic strata represented intraformational reduced traps for another family of uranium deposits that developed essentially only during this period basal roll front tabular and tectonolithologic types however the increased recognition of hydrocarbon and hydrogen sulfide migration from oil or gas reservoirs during diagenesis suggests potential for sandstone hosted uranium deposits to be found within permeable sandstone older than the silurian large uranium deposits related to high level hydrothermal fluid circulation and those related to evapotranspiration calcretes are only known during this last period of time probably because of their formation in near surface environments with low preservation potential

stratigraphical and lateral distribution of sedimentary organic matter in upper jurassic carbonates of se france abstract a detailed analysis of sedimentary organic matter som has been carried out in upper jurassic deep water marls and carbonates of the vocontian basin se france its main purpose is to analyse the vertical and lateral trends of som distribution in order to better understand processes and factors controlling the accumulation and preservation of organic constituents in basinal environments the vocontian basin is characterized by widespread oxic depositional environments in the upper jurassic as confirmed by the very low total organic carbon content less than 0 25 wt for such organic poor deposits palynofacies analysis represents the best tool to investigate som stratigraphic analysis of palynofacies trends has been performed within a pre established sequence stratigraphic framework defined by means of field sedimentology and subsequently complemented through lateral correlations biostratigraphical constraints and geochemistry this approach highlights the vertical signatures which are directly related to relative sea level changes furthermore lateral correlations of palynofacies trends at the scale of 3rd and 2nd order cyclicity permit the signatures observable at basin scale to be distinguished from those detectable only at local scale the former are controlled by factors affecting the whole basin such as eustasy regional tectonics and climate the palynofacies signatures at the scale of 3rd order cyclicity reflect relative sea level changes and the degradation state of som taking into account the preservation state of organic constituents leads to a better understanding of the relationship between som and sequence stratigraphy usually condensed sections about maximum flooding surfaces are characterized by a decrease in the relative proportion of the terrestrial organic constituents as far as sequence boundaries are concerned they are marked by an increase in the relative proportion of continental organic matter which results from a renewal of the erosion related to relative sea level fall an increase in fresh woody debris has not been systematically observed at sequence boundaries nevertheless the abundance of fresh woody debris tends to decrease stratigraphically towards maximum flooding intervals and laterally in a distal direction the vertical palynofacies signatures at the scale of 2nd order cyclicity appear to be controlled by tectonics in the upper oxfordian to lower kimmeridgian interval these signatures confirm the hypothesis of a regional uplift of the hinterland and or a differential basin subsidence related to the intense rifting activity in the proto atlantic or to the westward opening of the tethys

preface of special issue of applications of modern analytical techniques in the study of mineral deposits by rucheng wang and mei fu zhou guest editors

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

normal faulting in central tibet since at least 13 5 myr ago tectonic models for the evolution of the tibetan plateau interpret observed east west thinning of the upper crust to be the result of either increased potential energy of elevated crust1 or geodynamic processes that may be unrelated to plateau formation2 3 4 5 6 a key piece of information needed to evaluate these models is the timing of deformation within the plateau the onset of normal faulting has been estimated to have commenced in southern tibet between about 14 myr ago7 and about 8 myr ago8 and in central tibet about 4 myr ago9 here however we report a minimum age of approximately 13 5 myr for the onset of graben formation in central tibet based on mineralization ages determined with rb sr and 40ar 39ar data that post date a major graben bounding normal fault these data along with evidence for prolonged activity of normal faulting in this and other tibetan grabens support models that relate normal faulting to processes occurring beneath the plateau thinning of the upper crust is most plausibly the result of potential energy increases resulting from spatially and temporally heterogeneous changes in thermal structure and density distribution within the crust and upper mantle beneath tibet this is supported by recent geophysical and geological data10 11 12 13 14 15 16 17 which indicate that spatial heterogeneity exists in both the tibetan crust and lithospheric mantle

organic geochemistry characterization of the paleogene to neogene source rocks in the sayhut subbasin gulf of aden basin with emphasis on organic matter input and petroleum generation potential paleogene umm er radhuma and ghaydah and neogene sarar source rocks from sayhut subbasin in the gulf of aden basin were studied to provide information such as organic matter types paleoenvironmental conditions and petroleum generation potential this study is based on whole rock organic geochemical analyses and organic petrology the total organic carbon toc contents of the paleogene to neogene source rocks range from 0 43 to 6 11 with an average toc value of 1 00 indicating fair to very good source rock potential the paleogene ghaydah and umm er radhuma source rocks are relatively higher in genetic petroleum potential than neogene sarar source rocks mainly oil and gas are anticipated from the ghaydah and umm er radhuma source rocks with hydrogen index hi values ranging from 95 to 715 mg hydrocarbon hc g toc this is supported by the presence of significant amounts of liptinite macerals in the ghaydah and umm er radhuma source rocks the sarar source rocks are dominated by vitrinitic type iii kerogen hi 200 mg hc g toc and are thus considered to be gas source rocks the paleogene to neogene source rocks have vitrinite reflectance r o values in the range between 0 30 and 0 77 r o and pyrolysis maximum temperature values range from 412 c to 444 c 774 f to 831 f consistent with the immature to early mature oil window therefore the present day kerogen type in the paleogene to neogene source rocks is original and should not have been altered by thermal maturity the biomarker of organic matter suggests that the paleogene to neogene source rocks were deposited in a marine environment under suboxic to anoxic conditions the biomarkers also indicate that the paleogene to neogene source rocks contain a mixture of aquatic organic matter planktonic and bacterial and terrigenous organic matter with increasing terrigenous influence to sarar source rock samples highly hypersaline reducing conditions are also evidenced in ghaydah and umm er radhuma source rocks as indicated by the presence of the gammacerane biomarker low pristane to phytane ratios and homohopane distribution patterns

newly discovered uranium mineralization at 2 0 ma in the menggongjie granite hosted uranium deposit south china abstract the southeastern part of the nanling metallogenic province south china contains numerous economically important granite hosted hydrothermal vein type uranium deposits the miao ershan mes uranium ore field is one of the most important uranium sources in china hosts the largest chanziping carbonaceous siliceous pelitic rock type uranium deposit and several representative granite hosted uranium deposits the geology and geochemistry of these deposits have been extensively studied however accurate and precise ages for the uranium mineralization are scarce because uranium minerals in these deposits are usually fine grained and may have formed in several stages thus hindering the understanding of the uranium metallogenesis of this province the menggongjie mgj uranium deposit is one of the largest granite hosted uranium deposits in the mes ore field uranium mineralization in this deposit occurs at the central part of the mes granitic complex accompanied with silicification fluorination k metasomatism and hematitization the ore minerals are dominated by uraninite occurring in quartz or fluorite veinlets along fractures in altered granite in situ sims u pb dating on the uraninite yields the u pb isotopic age of 1 9 0 7 ma which is comparable to the chemical u th pbtol uraninite age of 2 3 0 1 ma such ages agree well with the eruption ages of the extension related quaternary volcanics 2 1 1 2 ma in south china suggesting that the uranium mineralization have formed at an extensional setting possibly related to the quaternary volcanic activities therefore our robust new dating results of the mgj uranium deposit make it the youngest granite hosted uranium deposit reported so far in south china and the mineralization event represents a newly identified mineralization epoch