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

the origin and evolution of canadian shield brines evaporation or freezing of seawater new lithium isotope and geochemical evidence from the slave craton abstract new chemical and isotopic data for deep seated calcium chloride brine from the miramar con gold mine yellowknife n w t strongly suggest that the brine salinity is of marine origin diagnostic marine properties include uniformly elevated br cl ratios typical of seawater concentrated beyond halite saturation and li br ratios 0 0254 0 0325 and 6 li compositions 32 1 to 36 3 similar to seawater 32 3 the mean 6 li for all mine water samples of 35 1 may reflect minor uptake of li by secondary minerals this interpretation is supported by analyses of altered metabasalt from fault zones which is enriched in li but depleted in 6 li 14 7 to 15 6 relative to the unaltered metabasalt 5 4 the mechanism responsible for concentrating the hypersaline brine end member is not unequivocal as evidence exists to support both evaporative and cryogenic processes on the one hand the devonian sedimentary record in the great slave lake region in conjunction with yellowknife brine isotopic compositions 2 h and 34 s so 4 that are similar to various devonian fluids support an evaporative origin on the other hand the na cl br cl relationship in the brine strongly suggests a cryogenic mechanism regardless of the concentrative mechanism the chemical data indicate that the yellowknife parent brine was concentrated 28 to 30 fold relative to seawater the extreme depletion of mg and enrichment of ca in the brines accompanied by sr ca ratios similar to that of seawater are accounted for by dolomitization of an aragonite rich marine sediment by the brine before infiltration into the crystalline basement rocks subsequent alteration of silicate minerals in the shield added additional ca and sr to the brine as indicated by their radiogenic 87 sr 86 sr ratios up to 0 7147 based on mineral balance calculations the major mineral products of the cryogenic and evaporitic concentration and evolution paths are significantly different the cryogenic evolution results in some 15 mirabilite 60 hydrohalite and 18 dolomite whereas the major minerals formed from the evaporitic evolutionary sequence are 36 halite 8 gypsum 17 dolomite and 30 albite the great similarity between the calcium chloride brine from yellowknife and other such canadian shield brines indicates that they may share a common marine origin

magmatism geological setting alteration and metallogenic potential of donghua area dehua county fujian province southeast china insights from porphyry zircon u pb and pyrite rb sr geochronology geochemistry and remote sensing abstract located in the southern section of the wuyi mountain metallogenic belt the dehua youxi yongtai dyy ore district is one of the potential areas of gold deposits in the fujian province southeast china gold mineralization is widely distributed in this district including qiucun shuangqishan ancun and dongyang gold deposits however the dyy ore district is still at a low degree of exploration and research this paper focuses on the donghua area in the northwest of the dyy ore district as its typical and integrated volcano magma mechanism revealed in this study combined approaches including zircon shrimp u pb geochronology rb sr isochron dating and mineral chemistry of pyrite and hyperspectral remote sensing are employed aiming to identify the magmatism alteration geological setting and metallogenic potential of the donghua area the zircon shrimp u pb ages of the granite porphyritic dykes in donghua are 154 6 1 1 ma and 153 2 1 2 ma respectively indicating that the dykes were formed in the late jurassic the rb sr geochronological age of hydrothermal epithermal pyrite in donghua is 153 7 2 4 ma which is almost coeval with that of the granite porphyritic dykes within error and consistent with the regional volcanic magmatic activity and the metallogenic age of the regional metallogenic event the granitic dykes in donghua exhibit the characteristics of both a type and i type granitoids thus indicating the presence of transitional geochemical characteristics as a result of the subduction of the pacific plate towards the eurasia the ca 154 153 ma magmatic event in the donghua area occurred at the beginning of large scale delamination of the continental crust the zoning distribution of the mineral alteration of chlorite dickite kaolinite and gypsum the interpretation of volcanic activity from the annular structure of hyperspectral remote sensing and the inferred deep seated intrusion emplacing from northwest to southeast are in agreement thus displaying the volcano magma alteration mechanism developed in the donghua area the magmatism dykes faults and neoproterozoic metamorphic rock provide favorable advantages for the mineralization in donghua suggesting metallogenic potential

petrogenesis and tectonic significance of late jurassic early cretaceous volcanic intrusive complex in the tianhuashan basin south china abstract the late mesozoic geological framework of south china is characterized by voluminous volcanic rocks and their intrusive counterparts however the ages petrogenesis and tectonic implications of the late mesozoic magmatism in south china especially those in the qinhang zone are poorly constrained the tianhuashan basin is one of the important volcanic basins along the southern margin of the qinhang zone and is mainly composed of the daguding and ehuling formations and their intrusive counterparts laser ablation inductively coupled plasma mass spectrometry la icpms u pb zircon data presented here in conjunction with our previously published data suggest that there are two distinct pulses of magmatism within the tianhuashan basin the granite porphyry was emplaced at 158 157 ma whereas large scale volcanic intrusive rocks were formed at 144 137 ma rather than in the late jurassic as previously regarded the tianhuashan volcanic intrusive rocks have similar whole rock element geochemical and sr nd and zircon hf isotopic compositions suggesting that they were probably derived from similar source regions these rocks exhibit clearly negative and variable bulk rock end t values in a range of 12 07 to 8 69 and low zircon ehf t values from 12 25 to 2 31 with paleo and mesoproterozoic two stage model ages for both nd and hf isotopes 1639 1915 ma and 1051 1970 ma respectively suggesting their derivation dominantly through partial melting of ancient crustal materials with involvement of a mantle derived component in variable proportions and followed by differential assimilation of upper crust during magma ascent an extensional setting associated with the roll back of the paleo pacific slab is favored to explain the petrogenesis of the tianhuashan volcanic intrusive complex the ehf t of zircon increases from late jurassic granite porphyry to early cretaceous magmatic rocks suggesting progressive crust mantle interaction in generating the episodic intermediate felsic magma eruption during late mesozoic our results suggest that the continental extension along the qinhang zone was weak during late jurassic and large scale lithospheric extension did not take place until early cretaceous with ongoing development of slab roll back

petrogenesis and tectonic implications of early cretaceous s and a type granites in the northwest of the gan hang rift se china the gan hang rift trending at least 450 km in a ne sw direction is a part of a mesozoic basin and range province in southeastern china detailed shrimp zircon u pb chronology major and trace element and sr nd hf isotope data of three granitic plutons and a diabasic dike in the northwest of the gan hang rift are used to explore the origin of these granites and their relationship to the evolution of the gan hang rift shrimp zircon u pb dating shows that the granitic plutons and diabasic dike were emplaced in the early cretaceous 122 129 ma the tongshan and damaoshan plutons close to the gan hang rift consist mainly of weakly peraluminous granitic rocks which show a2 subtype affinity these granites have initial 87sr 86sr ratios of 0 7080 0 7103 end t values of 1 4 to 5 6 and ehf t in situ zircon values of 3 8 to 1 2 detailed elemental and isotopic data suggest that they were formed by partial melting of granulitized mesoproterozoic metamorphic basement including metasedimentary and metaigneous rocks in the shallow 30 km crust at a high temperature 823 c these pure crustal melts underwent crystal fractionation of biotite plagioclase and k feldspar forming the more felsic end member of granitic rocks the ehu pluton more distant from the gan hang rift is composed of two mica granites which are strongly peraluminous and are s type granites these granites have higher initial 87sr 86sr ratios 0 7162 0 7191 and lower end t 7 1 to 7 4 and ehf t 6 8 in situ zircon values than the tongshan and damaoshan granites detailed elemental and isotopic data suggest that the ehu granites were formed by partial melting of paleoproterozoic metasedimentary basement in the deep 40 50 km crust at a relatively low temperature 757 c with no fractional crystallization and mantle derived magma mixing in their evolution the coeval diabasic dike is calc alkaline and has initial 87sr 86sr ratio of 0 7085 end t value of 0 9 and ehf t in situ zircon value of 7 1 suggesting that it was derived from the asthenospheric mantle wedge that had been metasomatised via addition of subducted sediment derived melt with monazite in the residual phase the association of early cretaceous 122 129 ma s and a type granites in the northwest of the gan hang rift marks the onset of back arc extension or intra arc rift with ongoing extension the crust and lithospheric mantle became progressively thinned the upwelling of asthenosphere triggered partial melting of both metasedimentary and metaigneous rocks in the more thinned crust close to the gan hang rift forming the a type granitic magmas such as tongshan and damaoshan whereas partial melting of metasedimentary rocks in the less thinned crust farther from the gan hang rift formed the s type granitic magmas such as ehu the red sediments with the total thickness more than 10 000 m have been successively deposited in the gan hang rift valley since the late early cretaceous 105 ma suggesting that this region experienced the most back arc extension

geochronology and geochemistry of the granitoids and ore forming age in the xiaoyao tungsten polymetallic skarn deposit in the jiangnan massif tungsten belt china implications for their petrogenesis geodynamic setting and mineralization abstract the xiaoyao tungsten polymetallic skarn deposit in the eastern jiangnan massif of yangtze block is located at the contact between a granodiorite pluton and sinian cambrian limestone the intrusions in the tungsten rich district comprise the xiaoyao and other granodiorite plutons and granite porphyry dikes the age determinations by la icp ms u pb dating of zircons indicate that the granodiorite formed at 149 4 1 1 ma whereas the granite porphyry was emplaced at 133 2 0 7 ma re os dating of molybdenite from the skarn orebodies yielded a weighted average age of 148 7 2 3 ma n 5 these ages indicate that the tungsten mineralization is temporally related to the granodiorite the granodiorites are metaluminous a cnk 0 86 0 98 and in the high k calc alkaline series they contain hornblende and have a negative correlation between p2o5 and sio2 indicating that they are typical i type intrusions the granite porphyries exhibit high alkali contents na2o k2o 7 97 9 53 elevated feot feot mgo ratios 0 83 0 94 high concentrations of zr nb ce and y and high zr saturation temperatures average of 812 c thus they are geochemically similar to a type intrusions the initial 87sr 86sr and end t values range respectively from 0 7074 to 0 7083 and from 7 9 to 1 3 for the granodiorite and from 0 7008 to 0 7083 and from 6 3 to 4 7 for the granite porphyry in addition two stage nd model ages t2dm of 1 0 1 6 ga for the granodiorite and 1 3 1 4 ga for the granite porphyry indicate that the proterozoic crustal rocks of the shangxi group could have contributed to the xiaoyao magmas the rhenium contents of the molybdenite grains vary from 32 to 136 ppm suggesting that the molybdenum was derived mainly from a mixture of mantle and crustal sources based on the new geochemical data and regional geological investigations we propose that the late jurassic mineralization related i type granodiorite was derived from the neoproterozoic shangxi metamorphic rocks with some additional input of mantle material the magmatism was triggered by asthenospheric upwelling induced by slab tearing during oblique subduction of the paleo pacific plate beneath the south china block

precambrian coal or anthraxolite a source for graphite in high grade schists and gneisses argues that without considering data for igneous carbon carbonatites or for ultrahigh metamorphic calcareous gneisses such as are found in the grenville province of north america the conclusion that the source of carbon for vein graphite is magmatic or carbonate carbon is not justified points out that marbles and calc silicate gneisses occur with the graphite bearing granulite facies rocks in sri lanka calcite may also be seen in the veins with the graphite concludes that whether the graphite in epigenetic veins in high grade schists and gneisses has variable carbon isotope ratios depends on whether it was derived from organic material in carbonate or noncarbonate metasediments

subgrain scale decoupling of re and 187os and assessment of laser ablation icp ms spot dating in molybdenite abstract reproducibility of re os molybdenite ages depends on sample size and homogeneity suggesting that re and os are decoupled within individual molybdenite crystals and do not remain spatially linked over time in order to investigate the re os systematics of molybdenite at the subgrain micron scale we report la icp ms re os ages for an archean molybdenite crystal from aittojarvi finland analyzed in situ in a white aplite matrix a related aittojarvi molybdenite a996d in the form of a very fine grained mineral separate is used as one of our in house ntims standards and thus its age of 2760 9 ma is well established measurements of 187 re 187 os 185 re on micron scale spots along 200 m traverses across the crystal yield a wide range of ages demonstrating that in this case microsampling of molybdenite does not produce geologically meaningful ages experimentation with mineral separations and sample size over a 7 yr period predicted that this would be the outcome we suggest that 187 os is more likely to be the mobile species based on its charge and ionic radius and that 187 os becomes decoupled from parent 187 re with time on the micron and larger scale incompatible charge and ionic radius for os ions formed during reduction of molybdenite forming fluids may explain the widely observed absence of common initial os in molybdenite geologically accurate ages for molybdenite can only be obtained for fully homogenized crystals or crystal aggregates so that any post crystallization 187 re 187 os decoupling is overcome a growing number of geologically accurate id ntims 187 re 187 os ages for homogenized molybdenite suggest that postcrystallization mobility of radiogenic 187 os must be limited to within the molybdenite mineral phase we suggest that radiogenic 187 os may be stored in micron scale dislocations kink bands and delamination cracks produced by deformation and that the unusual structure and deformation response of molybdenite results in an increased chemical stability in this mineral migration of 187 os into adjacent silicate phases is highly unlikely but other contacting sulfides may take in os in an example from a proterozoic skarn deposit at pitkaranta western russia we demonstrate minor loss of radiogenic 187 os from molybdenite and a corresponding gain in adjacent chalcopyrite such that the molybdenite age is not perceptibly disturbed whereas the resulting chalcopyrite ages are impossibly old therefore it is unadvisable to perform re os analytical work on any sulfide in contact or intimate association with molybdenite in addition to large errors in the age if the isochron method is employed initial 187 os 188 os ratios could be erroneously high leading to seriously errant genetic interpretations

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

late triassic melting of a thickened crust in southeastern china evidence for flat slab subduction of the paleo pacific plate abstract the dashuang complex in zhejiang province of southeast china is composed of two distinct lithologies syenite in the west and quartz monzonite in the east they record similar zircon u pb ages of 224 3 ma syenite and 226 2 ma and 227 1 ma quartz monzonite respectively but are notably different in petrography magnetic susceptibility whole rock chemistry zircon hf isotope and zircon trace element characteristics the west dashuang syenitic pluton the west body has high modal alkali feldspar high zircon saturation temperatures high whole rock and zircon mree hree ratios low fe mg ti contents and is depleted in ba sr and eu it also has low magnetic susceptibilities belongs to the ilmenite series and is a peraluminous and ferroan granitoid the east dashuang quartz monzonitic pluton the east body has abundant k feldspar megacrysts with hornblende titanite and biotite being the major ferromagnesian minerals in contrast to the west body the east body has lower zircon saturation temperatures lower whole rock and zircon mree hree ratios higher fe mg ti contents and shows no depletion in ba sr or eu the east body has higher magnetite contents high magnetic susceptibilities and belongs to the magnetite series it is a metaluminous and magnesian granitoid of arc affinity zircon hf isotopic data reveal that both bodies were derived from partial melting of paleoproterozoic igneous protoliths in the lower crust but the east body possibly incorporated subducted terrigenous sediments both bodies have higher melting temperatures and pressures than adjacent cretaceous granitoids reflecting their origin in a thickened hotter lower crust the most feasible model to explain their differences is variations in water content during crustal melting resulting in different melting and crystallization behaviors such melting in a triassic thickened crust with variable water involvement followed by cretaceous magmatism in an extensional setting is consistent with the flat slab subduction model proposed for south china the model involves crustal thickening and partial melting with mantle and lower crustal metasomatism during flat slab propagation in the triassic early jurassic and crustal thinning and extension from the mid jurassic to the cretaceous

geology geochronology and hf isotope geochemistry of the longtougang skarn and hydrothermal vein cu zn deposit north wuyi area southeastern china abstract the recently discovered longtougang skarn and hydrothermal vein cu zn deposit is located in the north wuyi area southeastern china the intrusions in the ore district comprise several small porphyritic biotite monzonite porphyritic monzonite and porphyritic granite plutons and dikes the mineralization is zoned from a lower zone of cu rich veins and cu zn skarns to an upper zone of banded zn pb mineralization in massive epidote altered rocks the deposit is associated with skarn potassic epidote greisen siliceous and carbonate alteration molybdenite from the cu rich veins yielded a re os isochron age of 153 6 3 9 ma which is consistent with u pb zircon ages of 154 0 1 3 ma for porphyritic monzonite 154 0 0 8 ma for porphyritic biotite monzonite and 152 0 0 8 ma for porphyritic granite geological observations suggest that the cu mineralization is genetically related to the porphyritic biotite monzonite and porphyritic monzonite all the zircons from intrusive rocks in the ore district are characterized by ehf t values between 13 41 and 4 38 and hf model ages tdm2 between 2054 and 1482 ma reflecting magmas derived mainly from a proterozoic crustal source molybdenite grains from the deposit have re values of 14 6 27 7 ppm indicative of a mixed mantle crust source the porphyry skarn abundant cu and hydrothermal vein type pb zn ag deposits in the north wuyi area are related to the late jurassic porphyritic granites and early cretaceous volcanism respectively the late jurassic mineralization related granites were derived from the crustal anatexis with some mantle input which was triggered by asthenospheric upwelling induced by slab tearing during oblique subduction of the paleo pacific plate beneath the south china block and the early cretaceous mineralization related granitoids mainly from crust material formed within a series of nne trending basins during margin parallel movement of the plate

the remarkable re os chronometer in molybdenite how and why it works the re os rhenium osmium chronometer applied to molybdenite mos2 is now demonstrated to be remarkably robust surviving intense deformation and high grade thermal metamorphism successful dating of molybdenite is dependent on proper preparation of the mineral separate and analysis of a critical quantity of molybdenite unique to each sample such that recognized spatial decoupling of 187re parent and 187os daughter within individual molybdenite crystals is overcome highly precise accurate and reproducible age results are derived through isotope dilution and negative thermal ion mass spectrometry id ntims spatial decoupling of parent daughter precludes use of the laser ablation icp ms microanalytical technique for re os dating of molybdenite the use of a reference or control sample is necessary to establish laboratory credibility and for interlaboratory comparisons the rb sr k ar and 40ar 39ar chronometers are susceptible to chemical and thermal disturbance particularly in terranes that have experienced subsequent episodes of hydrothermal magmatic activity and therefore should not be used as a basis for establishing accuracy in re os dating of molybdenite as has been done in the past re os ages for molybdenite are almost always in agreement with observed geological relationships and when available with zircon and titanite u pb ages for terranes experiencing multiple episodes of metamorphism and deformation molybdenite is not complicated by overgrowths as is common for some minerals used in u pb dating e g zircon monazite xenotime nor are re and os mobilized beyond the margins of individual crystals during solid state recrystallization moreover inheritance of older molybdenite cores incorporation of common os and radiogenic os loss are exceedingly rare whereas inheritance common pb and pb loss are common complications in u pb dating techniques therefore molybdenite ages may serve as point in time markers for age comparisons

re os geochronology and systematics in molybdenite from the endako porphyry molybdenum deposit british columbia canada precise re os molybdenite ages for the endako porphyry molybdenum deposit and the nithi mountain occurrence british columbia canada yield new information on the timing of molybdenite deposition three episodes of mineralization are indicated 1 154 ma 2 148 to 146 ma and 3 145 ma re os dates agree well with new u pb and 40 ar 39 ar data from granitoids of the nithi phase 155 2 1 5 ma the endako phase 148 4 1 5 ma and a preore dike 147 4 0 6 ma and the casey phase 145 1 0 2 ma plus hydrothermal biotite 144 5 0 75 ma villeneuve et al 2001 the excellent correlation between the re os dates from molybdenite and the ages of granitoids from the area indicates a direct genetic relationship between these plutons and molybdenite mineralization these re os data also provide further insight into the systematics and robustness of re os in molybdenite the endako molybdenum deposit is the product of two episodes of mineralization both associated with moderate salinity 5 15 wt nacl equiv and high temperature 440 c fluids a third low temperature 190 300 c hydrothermal event is associated with eocene faulting selby et al 2000 the clear distinction between two of the re os molybdenite dates in the deposit and the close agreement of these dates to the ages of granitoid intrusions suggest that the re os system in molybdenite is not reset by high temperature 440 c moderate salinity hydrothermal fluids in contrast magmatic biotite in a 147 ma preore dike has a 40 ar 39 ar age of 145 ma identical to the age of the hydrothermal biotite indicating that 440 c fluids reset the ar ar system in biotite hence we interpret that the re os isotope system in molybdenite is resistant to resetting by high temperature fluids 440 c in contrast to the 40 ar 39 ar system in biotite the re os system in molybdenite is also unaffected by postore hydrothermal fluids these data show that molybdenite can provide critical information in understanding sulfide mineral deposition in ore systems which is not recorded by other isotopic systems in alteration minerals

multiple dating and tectonic setting of the early cretaceous xianglushan w deposit jiangxi province south china abstract the xianglushan w deposit in northwestern jiangxi province south china is one of numerous large size w deposits along the northern margin of the jiangnan massif the deposit comprises lenticular and stratiform like orebodies mainly along the contact between argillaceous limestone of the cambrian yangliugang formation and a biotite granite pluton the mineralization is zoned from proximal w greisen within the cupolas of the biotite granite through w skarn and sulfide scheelite bands near the pluton to distal quartz sulfide scheelite veins the granitic pluton and an aplitic dyke in the mining area contain zircon grains with u pb ages of 123 8 0 8 ma and 117 3 1 7 ma respectively six molybdenite samples collected from skarn ores yielded a re os weighted mean age of 125 5 0 7 ma and muscovite separates from greisen ores yielded a 40 ar 39 ar plateau age of 122 8 0 78 ma the molybdenite re os and muscovite ar ar ages are consistent with the zircon u pb age of the hosting granite the xianglushan deposit is formed by an early cretaceous w dominated polymetallic ore forming event in the jiangnan porphyry skarn w belt zircon from biotite granites in the xianglushan deposit has negative e hf t values generally from 5 7 to 3 1 with corresponding two stage hf model ages of 1363 1218 ma reflecting derivation of magmas from a crustal source molybdenite has re contents from 12 12 to 22 77 ppm indicative of a mixed crustal mantle source but with a dominantly crustal component a compilation of precise ages for magmatism and mineralization in the jiangnan porphyry skarn w belt shows that there are two stages of mineralization at 150 135 ma and 130 120 ma respectively integrated with published data our results suggest that the xianglushan w deposit formed in an extensional tectonic setting during the early cretaceous

gold and silver metallogeny of the south china fold belt a consequence of multiple mineralizing events abstract the south china fold belt is part of the south china block that is interpreted to be the result of multiple tectonic and magmatic events that formed a collage of accreted proterozoic and phanerozoic terranes the jurassic to early cretaceous yanshanian period 180 90 ma a time of major tectono thermal events that affected much of eastern and southeastern china is of great metallogenic importance in the fold belt this period is linked to subduction of the pacific plate beneath the eurasian continent and is manifested by voluminous volcano plutonic activity of predominantly calc alkaline affinity the distribution of gold and silver deposits in the south china fold belt indicates the presence of two distinct metallogenic provinces a region of basement uplifts which are controlled by shear zones and form neoproterozoic inliers of metamorphosed iron rich rock types defines the first province in this province orogenic lodes and volcanic related epithermal deposits represent the more significant precious metal mineralization the second province is essentially confined to a belt of yanshanian felsic intermediate volcanic and subvolcanic rocks that extends along most of the southeastern china coast in an area known as the coastal volcanic belt deposits in the coastal volcanic belt are silver and or copper rich volcanic hosted and epithermal in character the precious metal metallogeny of the south china fold belt is interpreted to have developed in at least three stages one as a result of collision events during the caledonian orogeny ca 400 ma the second during the indosinian orogeny ca 200 ma and the third during or soon after the formation of the yanshanian magmatic belt yanshanian orogeny 180 90 ma the latter was responsible for a hydrothermal event that affected large sections of the belt and its proterozoic substrate this may have resulted in the redistribution and enrichment of precious metals from preexisting orogenic gold lodes in neoproterozoic basement rocks which are now exposed as windows in zones of tectonic uplift the yanshanian hydrothermal activity was particularly widespread in the coastal volcanic belt and resulted in the formation of both low and high sulfidation epithermal gold and silver and locally copper and other base metal mineralization it is suggested that the coastal volcanic belt has greater potential for world class epithermal and porphyry deposits than previously realised

geochronology geochemistry and sr nd hf s pb isotopes of the early cretaceous taoxihu sn deposit and related granitoids se china abstract the taoxihu deposit eastern guangdong se china is a newly discovered sn polymetallic deposit zircon u pb dating yielded 141 8 1 0 ma for the sn bearing granite porphyry and 145 5 1 6 ma for the biotite granite batholith it intruded the age of the granite porphyry is consistent within error with the molybdenite re os isochron age 139 0 1 1 ma of the sn mineralization indicating a temporal link between the two geochemical data show that the granite porphyry is weakly peraluminous contain high si na and k low fe mg ca and p and relatively high rb sr and low k rb values the rocks are enriched in rb th u k and pb and depleted in ba sr ti and eu resembling highly fractionated i type granites they contain bulk rock initial 87 sr 87 sr of 0 707371 0 707730 and end t of 5 17 to 4 67 and zircon ehf t values from 6 67 to 2 32 with late mesoproterozoic t dm2 ages for both nd and hf isotopes this suggests that the granite porphyry was likely formed by the partial melting of the crustal basement of mesoproterozoic overall residence age with minor mantle input 34 s cdt values of the taoxihu chalcopyrite and pyrite range from 0 1 to 2 1 average 0 9 implying a dominantly magmatic sulfur source the 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios of the taoxihu sulfide ores are 18 497 18 669 15 642 15 673 and 38 764 38 934 respectively indicating a mainly upper continental crustal lead source with minor mantle contribution the highly fractionated and reduced low calculated zircon ce 4 ce 3 and eu n eu n values nature of the ore forming granitic magma may have facilitated the sn enrichment and played a key role in the sn mineralization we propose that the ore forming fluids at taoxihu were of magmatic hydrothermal origin derived from the granite porphyry and that both the granite porphyry and the sn mineralization were likely formed in an extensional setting possibly related to the subduction slab rollback of the paleo pacific plate

insights from stable isotopes and hydrochemistry to the quaternary groundwater system south of the ismailia canal egypt summary stable isotopic ratios of water 18 o and 2 h and major dissolved ions were analyzed from samples collected from the area south of the ismailia canal egypt this region has recently experienced rapid growth that has increased both surface and groundwater use the data from the samples were used to identify recharge sources and mixing and salinization processes in the groundwater system in this region on the basis of the isotopic data and geochemical data four end members were defined representing groundwater in a quaternary aquifer groundwater in a miocene aquifer water in the ismailia canal and wastewater from the 10th of ramadan city several different mixing trends were recognized in the study area as a consequence of mixing with groundwater in the miocene aquifer groundwater in the quaternary aquifer was found to have depleted isotopic signatures and increased total dissolved ions tdi toward the south of the study area near subsurface miocene structural highs another mixing trend consisting of enriched isotopic ratios and lower tdi values toward the north in the quaternary aquifer indicated mixing with surface water i e the ismailia canal and freshwater ponds a third trend of locally high tdi values together with depleted stable isotopic data i e the ramsis area and the vicinity of the well field were interpreted to be due to excessive pumping for irrigation and reclamation activities which in turn resulted in upconing of the deeper saline groundwater from the miocene aquifer lastly leakage from the wastewater ponds into the recharge process was suggested by considering chemical and isotopic signature of the quaternary groundwater sample no 31 these results strongly indicate the urgent need for monitoring protection and remediation of the quaternary aquifer in order to guarantee the sustainability of water resources in the study area this work also illustrates the efficiency of using stable isotopes and major ion chemistry to improve our understanding of a flow system

revisiting the paleogene climate pattern of east asia a synthetic review abstract east asian paleogene climates have long been regarded as controlled by the planetary wind system which might result in a climate pattern with three latitudinally distributed zones two humid zones located separately in the north and south were lithologically designated by coals and oil shales while an arid zone in the middle was represented by red beds and evaporites because the middle arid zone was located along 30 n paleolatitude its presence had been further linked with a then subtropical high however this long standing model has recently been challenged by growing evidence from petrology sedimentology paleontology paleobiogeography paleoclimatology and climate modeling here we review the primary data from these disciplines and reinterpret their climate significances to revisit the east asian climate pattern during the paleogene petrologically while the occurrence of coals and or oil shales is accepted as an indicator for overall humid climates that of red beds and or evaporites is highly equivocal to exclusively indicate perennial arid climates unless their origins are carefully investigated in reality generic red beds merely represent an oxidizing environment not essentially associated with a single specific climate type meanwhile evaporites although typically precipitated in arid environments may be deposited in either perennial dry or seasonal monsoonal climates there is no solid evidence so far to convincingly support that the landscape of the so called middle arid zone was dominated by desert and or steppe under a then subtropical high during most of the paleogene the plant function type study additionally suggests that the middle arid zone appears to be lack of xerophytic vegetation even though some xerophytic or sclerophyllous plant taxa did sporadically occur interestingly paleozoological data show that the paleogene mammalian faunas were somewhat equably distributed over east asia strongly suggesting the evident absence of a critical biogeographical or climatic barrier stretched across the middle arid zone as the planetary wind model implied in contrast to the planetary wind model monsoonal or monsoon like paleogene climates have been broadly reported from the northern middle and southern east asia as well as adjacent regions of russia and kazakhstan if only the indicators for humid climates are considered simply due to the uncertainty of those for perennial arid climates east asia must have had a relatively dry region in the continental interior during the late eocene to oligocene transition likely caused by the continentality and or the rain shadow effect along with the global cooling the monsoonal interpretation is highly in agreement with the evidence from floras faunas basin analyses and modeling experiments and well explicates the paleogene climate distribution and seasonal dynamics of east asia however further studies will be largely needed to verify whether uniformly according to the modern criteria the paleogene climates of the east asia interior can be accurately attributed to the arid category

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

fluid inclusion and carbon isotope studies of quartz graphite veins black hills south dakota and ruby range montana abstract fluid inclusions and graphite are intimately associated in quartz veins that cut high grade metamorphic rocks in the black hills south dakota and at the crystal graphite mine in the southwestern ruby range montana measured fluid inclusion compositions and volumetric properties were compared with calculated compositions of graphite saturated fluids and with estimates of metamorphic p t conditions and carbon isotope ratios of graphite were measured to evaluate possible sources of carbon in veinforming fluids fluid inclusions from the two areas contrast markedly in their reliability as recorders of metamorphic fluid compositions and metamorphic conditions the 13 c of graphite associated with the veins indicates that the source of carbon was also different in the two areas in the black hills veins fluid inclusions are dominantly h 2 o co 2 mixtures with 24 96 mol co 2 and a maximum of 5 mol n 2 and 13 mol ch 4 isochores for the highest density inclusions pass near estimated peak metamorphic conditions 550 600 c 4 5 6 5 kbar and fluid inclusion compositions are compatible with thermodynamic predictions for fluids in equilibrium with graphite in the stated p t range at geologically reasonable o 2 graphite in a 12 cm wall rock alteration zone adjacent to one of the veins has uniform 13 c of 20 8 0 2 indicating that carbon in the vein forming fluid was derived largely from reduced organic carbon in the ruby range peak metamorphic conditions were higher 750 850 c 5 8 kbar in contrast to the black hills veins fluid inclusions are almost all co 2 ch 4 mixtures with unknown n 2 content many contain 20 equivalent mol ch 4 and mixed h 2 o co 2 inclusions were observed in only one sample inclusions in one vein have 84 97 mol ch 4 virtually all inclusion compositions are incompatible with computed graphite equilibria and inclusion isochores likewise do not pass through estimated metamorphic conditions the density and composition of most if not all inclusions have been modified subsequent to original trapping possibly through h 2 o loss the range of 13 c values of vein graphites 5 8 to 8 6 is nearly indistinguishable from values for graphite in dolomitic marble near the veins 4 8 to 7 1 carbon was probably mobilized through devolatilization reactions in the marble and precipitated as 13 c rich graphite in the veins at fairly constant temperature and from fluid of fairly constant composition

mesozoic metallogeny in east china and corresponding geodynamic settings an introduction to the special issue abstract the giant east china mesozoic metallogenic province hosts some of the world s largest resources of tungsten tin molybdenum antimony and bismuth ores of gold silver mercury lead zinc copper uranium and iron are also of major importance the province and its constituent metallogenic belts or regions south china middle lower yangtze river valley east qinling dabie interior of north china craton yan liao and north east china are the products of several pulses of igneous activity and mineralisation between 240 and 80 ma each successive stage has produced a distinctive suite of deposits that can be readily related to the geodynamic evolution of the region during the mesozoic this geodynamic evolution is linked to a complex series of tectonic events involving far field subduction plate collisions crustal thickening post collision collapse and rifting

petrogenesis of cretaceous adakitic and shoshonitic igneous rocks in the luzong area anhui province eastern china implications for geodynamics and cu au mineralization both adakitic and shoshonitic igneous rocks in the luzong area anhui province eastern china are associated with cretaceous cu au mineralization the shaxi quartz diorite porphyrites exhibit adakite like geochemical features such as light rare earth element lree enrichment heavy ree hree depletion high al2o3 mgo sr sr y and la yb values and low y and yb contents they have low end t values 3 46 to 6 28 and high 87sr 86sr i ratios 0 7051 0 7057 sensitive high resolution ion microprobe shrimp zircon analyses indicate a crystallization age of 136 3 ma for the adakitic rocks most volcanic rocks and the majority of monzonites and syenites in the luzong area are k rich or shoshonitic and were also produced during the cretaceous 140 125 ma they are enriched in lree and large ion lithophile elements and depleted in ti and nb and ba and exhibit relatively lower end t values ranging from 4 65 to 7 03 and relatively higher 87sr 86sr i ratios varying between 0 7057 and 0 7062 the shoshonitic and adakitic rocks in the luzong area have similar pb isotopic compositions 206pb 204pb 17 90 18 83 207pb 204pb 15 45 15 62 and 208pb 204pb 38 07 38 80 geological data from the luzong area suggest that the cretaceous igneous rocks are distributed along ne fault zones e g tanlu and yangtze river fault zones in eastern china and were likely formed in an extensional setting within the yangtze block the shaxi adakitic rocks were probably derived by the partial melting of delaminated lower crust at pressures equivalent to crustal thickness of 50 km i e 1 5 gpa possibly leaving rutile bearing eclogitic residue the shoshonitic magmas in contrast originated mainly from an enriched mantle metasomatized by subducted oceanic sediments they underwent early high pressure 1 5 gpa fractional crystallization at the boundary between thickened 50 km lower crust and lithospheric mantle and late low pressure 1 5 gpa fractional crystallization in the shallow 50 km crust the adakitic and shoshonitic rocks appear to be linked to an intra continental extensional setting where partial melting of enriched mantle and delaminated lower crust was probably controlled by lithospheric thinning and upwelling of hot asthenosphere along ne fault zones e g tanlu and yangtze river fault zones in eastern china both the shoshonitic and adakitic magmas were fertile with respect to cu au mineralization

in situ u pb zircon dating using laser ablation multi ion counting icp ms high resolution in situ u pb zircon geochronology on zoned grains can obtain isotope signatures from multiple growth or thermal events we present a method using laser ablation multicollector inductively coupled plasma mass spectrometry la mc icp ms to overcome complications associated with intricately zoned zircon crystals through in situ sampling of zircon volumes as small as 12 m 25 m and 40 m in diameter by about 10 m in depth high precision u pb age of a series of zircon standard covering a wide age range of 30 to 1 065 ma was acquired using la mc icp ms the precision of measured pb u ratios in homogeneous zircon is about 2 2 resulting in routinely achieved precision of u pb ages obtained by external calibration of 1 2 or better all masses of interest can be simultaneously recorded with a multi ion counting system mic operating in static mode and the short ablation required to achieve such precision results in spatial resolution that is superior to comparable u pb zircon analyses by single collector icp ms the resulting present u pb age for five zircon reference samples and two geological samples show an excellent agreement with the previously reported id tims or shrimp data

distinctive features of late palaeozoic massive sulphide deposits in south china abstract more than 20 sediment hosted massive sulphide deposits occur in late palaeozoic basins in south china these deposits are accompanied by a certain amount of volcanic rocks in the host sequence and are economically important for their cu pb zn au and ag reserves the deposits and their host strata were commonly intruded by mesozoic granitoids remobilisation of sedimentary ores and magmatic hydrothermal overprinting processes resulted in the coexistence of massive sulphides with vein skarn and porphyry type orebodies in the same region or within a single deposit the ore containing basins occur in different tectonic settings the lower yangtze basin occurs on a passive continental margin where the deposits are high in cu and au with minor pb and zn and recoverable ag co and mo the ores have a lower concentration of radiogenic lead and 34s values close to zero fluid inclusions are highly saline and na rich fluids and metals of the lower yangtze region are interpreted to have been derived essentially from deep sources including the precambrian basement by contrast basins of the nanling region formed in an intracontinental setting developed on a folded caledonian basement these deposits are higher in pb zn sn and w as well as cu with recoverable ag sb hg u bi tl and mo the ores are characterised by a higher concentration of radiogenic lead and a wide variation of 34s composition fluid inclusions have lower salinities and higher k na ratios fluids are considered to have been sourced substantially from seawater by convection metals for the nanling deposits were essentially derived from the caledonian basement by leaching the contrast in ore composition between these two regions appears to have been controlled by differences in basement composition of the ore forming basins

structural controls on groundwater flow and groundwater salinity in the spicers creek catchment central west region new south wales saline seepage zone development and hence the onset of dryland salinity is a major environmental problem occurring within the spicers creek catchment the primary objective of this paper was to identify previously unmapped faults and show the correlation between these faults and groundwater salinization as identified from this study there is a close association between geological structural features and the formation of saline seepage zones the most saline groundwaters in the catchment were encountered where two geological structures join and form a fault intersection these saline groundwaters are found at various depths within the fractured aquifers and changes in groundwater chemistry in the aquifers are associated with the presence of fault zones 18o and 2h stable isotopes together with 87sr 86sr isotopic ratios indicate that groundwaters within the fault zones are enriched in 18o and have a strontium signature similar to seawater this study identifies several geological structures in the spicers creek catchment and demonstrates that groundwaters with the highest salinity arise where fault intersections occur the results of this study may be used to interpret further the mechanisms leading to seepage zone formation in dryland salinity affected catchments located throughout the central west region of new south wales australia copyright 2006 john wiley sons ltd

tectonic implications from re os dating of mesozoic molybdenum deposits in the east qinling dabie orogenic belt abstract the east qinling dabie molybdenum belt is part of a larger east west trending metallogenic belt in eastern china most of the molybdenum deposits occur as porphyry or porphyry skarn type but there are also some vein type deposits following systematic re os dating of molybdenite from 13 deposits and comparisons with two previously dated deposits we have recognized that the molybdenum mineralization in the east qinling dabie belt was developed during hydrothermal activity linked to magmatism and the emplacement of granitoid stocks three pulses of granitoid magmatism and mo mineralization are recognized corresponding to significant tectonic events in the east qinling dabie belt vein type deposits dated at 233 221 ma were formed in detachment fractures indicating localized extension within the collisional setting of the north china and yangtze cratons i type and transitional i and s type granites and related mineralization dated at 148 138 ma may have formed part of a continental magmatic arc with widespread magmatism and back arc extension caused by subduction of the izanagi or paleopacific plate beneath the eurasian continent in a wnw ese direction in the late jurassic early cretaceous both s type and transitional s and i type granite associated porphyry molybdenum deposits dated at 131 112 ma are part of an extensive mineralization event throughout east china that can be ascribed to regional large scale lithospheric thinning delamination and thermal erosion

using major ions and stable isotopes to characterize recharge regime of a fault influenced aquifer in beiyishui river watershed north china plain a thorough understanding of recharge is usually a prerequisite for effective groundwater management the recharge regime remains unrevealed in the piedmont plain of the north china plain where is considered as the main recharge zone of the quaternary aquifer to characterize the recharge regime a case study is presented in the piedmont plain of the beiyishui river watershed the piedmont plain consists of proluvial fan and alluvial fan plain and groundwater quality in the two parts is distinct total dissolved solids and isotopic compositions are higher in the groundwater of proluvial fan than the groundwater of the alluvial fan plain local precipitation only recharges the groundwater in the proluvial fan fracture water ascending along a buried normal fault and lateral inflow from the proluvial fan feed the unconfined aquifer in the alluvial fan plain the runoff of the beiyishui river seeps in the streambed of upper reaches and then overflows seasonally in middle reach the recharge from middle reach to the aquifer is negligible in addition the fracture water originates from precipitation in the mountainous area with an average elevation about 500 m and discharges to the overlaying aquifer the contribution of fracture water to the aquifer was estimated to be 77 9 in the alluvial fan plain area due to the mixture in the aquifer major ions leached from soil of the proluvial fan are diluted and the hydrochemical pattern is changed from ca mg hco3 so4 to ca mg hco3 it is considered that fracture water is the major recharge source of the unconfined aquifer and the variation of precipitation in mountainous area would primarily affect the recharge this paper also shows the hydrological efficiency of buried normal fault as preferential flow

shrimp u pb zircon ar ar muscovite and re os molybdenite isotopic dating of the taoxikeng tungsten deposit south china block abstract the taoxikeng tungsten deposit is located in the jiangxi province in the southern part of china and is one of the largest wolframite quartz vein type tungsten deposits in the country the deposit is situated in sinian neoproterozoic to permian strata at the contact with the buried taoxikeng granite sensitive high mass resolution ion microprobe shrimp zircon u pb analysis of the granite has yielded dates of 158 7 3 9 and 157 6 3 5 ma which are interpreted as the emplacement age of the granite molybdenite separated from ore bearing quartz veins yields a re os isochron age of 154 4 3 8 ma and muscovite separated from greisen between the granite and country rocks yields 40ar 39ar plateau ages of 153 4 1 3 and 152 7 1 5 ma these dates obtained from three independent geochronological techniques constrain the ore forming age of the taoxikeng deposit and link the ore genesis to that of the underlying granite the taoxikeng deposit is an example of a jurassic regional scale tungsten tin ore forming event between 160 and 150 ma in the nanling region of the south china block the deposit s strikingly low rhenium contents 4 9 to 13 0 10 3 g g in molybdenite suggests that the ore was derived from a crustal source this conclusion is consistent with previously published constraints from s d and o stable isotopes sr nd systematics and petrogenetic interpretations of spatially related granites

geology isotopes and geochronology of the caijiaping pb zn deposit in the north wuyi area south china implications for petrogenesis and metallogenesis abstract the caijiaping pb zn deposit is a recently discovered subvolcanic hydrothermal deposit in the north wuyi area its mineralization is generally distributed at the contact of rhyolite porphyry and sandstone and in the interlayer crushed zone of early jurassic sandstone sulfide minerals in this deposit mainly consist of abundant sphalerite galena pyrite and chalcopyrite silicification chloritization and sericitization are widely developed and closely related to the pb zn mineralization the 34s values of early dark brown sphalerite marmatite main stage sphalerite and galena 1 1 2 5 average 0 83 suggest that the sulfur was mainly sourced from a magmatic system lead isotope ratios in the sulfide minerals rhyolite porphyry and sandstone are relatively homogeneous 206pb 204pb 17 786 18 612 207pb 204pb 15 504 15 635 208pb 204pb 38 115 38 798 and are compatible with metamorphic rocks of mesoproterozoic zhoutan group wuyi metamorphosed basement early jurassic sandstone deposited in an active continental margin or continental arc setting exhibits low textural maturity and displays geochemical similarities to the zhoutan group the rhyolite porphyry with features of volcanic arc granite also shows an affinity with the zhoutan group sims zircon u pb dating shows that the rhyolite porphyry was emplaced at 156 0 1 2 ma indicating that caijiaping mineralization formed later than 156 ma hf isotope compositions of the rhyolite porphyry ehf t 14 3 to 8 5 average 10 6 imply that it was mainly derived from reworking of ancient crust potassium feldspar selected from felsic veins within the ore cutting f4 fault yields a 40ar 39ar age of 120 0 4 0 ma indicating that the pb zn mineralization formed before 120 ma therefore the age of mineralization is bracketed between 156 and 120 ma combined with regional geological information we propose that the caijiaping mineralization mainly formed from magmatic hydrothermal processes in a regionally extensional setting and the wuyi metamorphosed basement significantly contributed to diagenetic and metallogenic processes in this deposit

fracture detection and groundwater flow characterization using he and rn in soil gases manitoba canada abstract surveys of the distribution and migration of he and rn were carried out in the well characterized granitic terrane of the aecl underground research laboratory url manitoba as part of a joint aecl research united kingdom department of the environment and united states department of energy research initiative the investigations were designed to determine whether concentrations of he and rn in soil gases could be used to identify locations of groundwater recharge and discharge from bedrock fractures the results obtained indicate that subsurface transport of he and possibly rn in this setting appears to be controlled largely by the groundwater flow system in the bedrock release of dissolved gases near the ground surface causes soil gas anomalies which reflect discharge from the deeper flow system in the recharge area of the deep groundwater flow system at the url site he abundances are close to the atmospheric level but the discharge area of the deep flow system is characterized by significant he anomalies up to 0 5 ppm above atmosphere levels for rn the recharge area has broadly distributed high concentrations probably caused by local rn production in u rich overburden while the discharge area has only localized concentrations of rn which are not at the same location as the he anomalies the general nature of the groundwater flow regime in both areas is reflected in the presence and distribution of the soil gas anomalies in addition major fractures in bedrock which act as preferential groundwater flow paths have been located from soil gas anomalies even when obscured by overburden of variable thickness and character the distribution of he in soil gas appears to be most representative of groundwater recharge and discharge conditions in the granitic rock while rn may be useful for locating specific channels where more rapid groundwater discharge is occurring from deep fracture zones

syn collisional transform faulting of the tan lu fault zone east china origin of the continental scale tan lu fault zone tlfz east china remains controversial about 550 km sinistral offset of the dabie orogenic belt dob and sulu orogenic belt sob is shown along the ne nne striking tlfz syn collisional sinistral ductile shear belts in the tlfz have been identified thirteen phengite bulk separates from the mylonites were dated by the 40ar 39ar method they gave cooling ages of the 198 181 ma for the shear belts along the eastern margin of the dob and 221 210 ma from the western margin of the sob distribution of the foreland basin deposits suggests that sinistral offset of the dob and sob by the tlfz took place prior to deposition of the upper triassic strata the marginal structures around the dob and sob support syn collisional faulting and indicate anticlockwise rotation of the dob during the displacement the folding and thrust faulting related to crustal subduction coeval with the tan lu faulting is older than the foreland basin deposition related to the orogenic exhumation several lines of evidence demonstrate that the tlfz was developed as a syn collisional transform fault during latest middle to earliest late triassic time when the dob and sob experienced crustal subduction of the south china block scb eastward increase of the crustal subduction rates is believed to be responsible for the sinistral transform faulting

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

reos dating of molybdenites from ore deposits in japan implication for the closure temperature of the reos system for molybdenite and the cooling history of molybdenum ore deposits abstract rhenium and osmium abundances were determined on molybdenites from eighteen ore deposits in japan fifteen vein type a skarn type a greisen type and a pegmatite type deposit re os ages obtained for molybdenites from northeastern central and southwestern japan are 100 130 ma 50 75 ma and ca 10 ma respectively reflecting the ages of regional igneous activities in individual areas for vein type ore deposits re os ages for molybdenites agree with rb sr whole rock ages of host granitoids while they are 3 12 ma older than k ar mineral ages of the host rocks on the other hand re os ages of molybdenites from skarn pegmatite and greisen type ore deposits agree with k ar ages of the host rocks the comparison of re os ages for molybdenites with rb sr and k ar ages of host rocks in vein type deposits suggests that re os closure temperature for vein molybdenite is close to whole rock rb sr closure temperature for host granitic rocks i e roughly estimated to be around 500 c and higher than k ar closure temperature for host granodiorites i e 230 370 c if the thermal history of vein molybdenites is essentially equivalent to that of host rocks one possible explanation for age discrepancies of 3 12 ma between re os ages for molybdenites and k ar ages for the wall rocks observed in vein type molybdenum deposits is that later thermal events after formation of molybdenum ores may reset k ar ages hydrothermal alteration might have occurred in such a temperature condition as to disturb k ar mineral systems in wall rocks and made them younger but not the re os system in molybdenite the other explanation might be that the age discrepancies correspond to a cooling interval from ca 500 to 300 c of host granitoid on the other hand the agreement of re os ages of molybdenites and k ar ages of host rocks in skarn pegmatite and greisen type deposits in this study indicates no later disturbance for k ar system in the wall rock or the rapid cooling of the ore and wall rocks after the formation of molybdenite deposits

three major metallogenic events in mesozoic in south china in mesozoic large scale metallogeny took place in south china which was called mesozoic metallogenic explosion based on detailed investigation the authors have recognized three major large scale metallogenic events in mesozoic all these events occurred in yanshanian period which has been considered as the post orogenic period of the indosinian orogenesis the first large scale metallogeny took place from 180 ma to 170 ma represented by cu pb zn au mineralization in northeastern jiangxi and southeastern hunan the second one was mainly mineralization of rare metals such as w sn nb ta closely related to crust remelting type granitoids during 150 139 ma the following 125 98 ma was the time for the third and perhaps the strongest large scale metallogeny which included sn u mineralization in nanling range region and au cu pb zn ag mineralization in the southeast coastal zone the three major metallogenic events resulted from lithospheric evolution of south china and had close genetic relation with extensional geodynamic background crust mantle interaction and participation of deep source heat and fluids

geochronology of the xingshan molybdenum deposit jilin province ne china and its hf isotope significance abstract the xingshan porphyry mo deposit is located in the lesser xing an range zhangguangcai range metallogenic belt ne china mineralization occurred in granodioritic porphyry and monzogranite which have zircon u pb ages of 171 7 2 2 ma and 170 9 4 6 ma respectively molybdenite re os dating indicates that mo mineralization occurred at 167 3 2 5 ma these geochronological data suggest that the magmatic and hydrothermal activities of the xingshan mo deposit happened during the middle jurassic in mesozoic positive ehf values 6 2 11 6 and young tdm2 473 826 ma of the monzogranite xs 3 and granodioritic porphyry xs 5 indicate that the source materials of xingshan ore bearing rocks are the juvenile crust which mainly accreted on the songnen block during the meso neoproterozoic xingshan porphyry mo deposits resulted from the magmatism and tectonism induced by the subduction of paleo pacific ocean

re os ages for archean molybdenite and pyrite kuittila kivisuo finland and proterozoic molybdenite kabeliai lithuania testing the chronometer in a metamorphic and metasomatic setting seven 187re 187os ages were determined for molybdenite and pyrite samples from two well dated precambrian intrusions in fennoscandia to examine the sustainability of the re os chronometer in a metamorphic and metasomatic setting using a new 187re decay constant 1 666 10 11y 1 with a much improved uncertainty 0 31 we determined replicate re os ages for molybdenite and pyrite from the kuittila and kivisuo prospects in easternmost finland and for molybdenite from the kabeliai prospect in southernmost lithuania these two localities contain some of the oldest and youngest plutonic activity in fennoscandia and are associated with newly discovered economic au mineralization ilomantsi finland and a cu mo prospect kabeliai lithuania two re os ages for vein hosted kabeliai molybdenite average 1486 5 ma in excellent agreement with a 1505 11 ma u pb zircon age for the hosting kabeliai granite pluton the slightly younger age suggests the introduction of cu mo mineralization by a later phase of the kabeliai magmatic system mean re os ages of 2778 8 ma and 2781 8 ma for kuittila and kivisuo molybdenites respectively are in reasonable agreement with a 2753 5 ma weighted mean u pb zircon age for hosting kuittila tonalite these re os ages agree well with less precise ages of 2789 290 ma for a rb sr whole rock isochron and 2771 75 ma for the average of six sm nd tdm model ages for kuittila tonalite three re os analyses of a single pyrite mineral separate from the same sample of kuittila pluton that yielded a molybdenite separate provide individual model ages of 2710 27 2777 28 and 2830 28 ma re 17 4 12 1 and 8 4 ppb respectively with a mean value of 2770 120 ma in agreement with the kuittila molybdenite age the re and 187os abundances in these three pyrite splits are highly correlated r 0 9994 and provide a 187re 187os isochron age of 2607 47 ma with an intercept of 21 ppt 187os mswd 1 1 it appears that the re os isotopic system in pyrite has been reset on the millimeter scale and that the 21 ppt 187os intercept reflects the in situ decay of 187re during the 160 to 170 m y interval from 2778 ma time of molybdenite pyrite deposition to 2607 ma time of pyrite resetting when the re os data for molybdenites from the nearby kivisuo prospect are plotted together with the kuittila molybdenite and pyrite data a well constrained five point isochron with an age of 2780 8 ma and a 187os intercept 2 4 3 8 ppt of essentially zero results mswd 1 5 we suggest that the pyrite isochron age records a regional metamorphic and or hydrothermal event possibly the time of au mineralization a proposed re os age of 2607 ma for au mineralization is in good agreement with radiometric ages by other methods that address the timing of archean au mineralization in deposits worldwide so called late au model molybdenite in contrast provides a robust re os chronometer retaining its original formation age of 2780 ma despite subsequent metamorphic disturbances in archean and proterozoic time

thermal maturation pattern in the southern bowen northern gunnedah and surat basins northern new south wales australia abstract comprehensive maximum vitrinite telocollinite reflectance data have been obtained for more than 260 polished sections from 28 petroleum exploration wells in the southern bowen and northern gunnedah basins and the overlying surat basin in an area from north of boggabri to the new south wales queensland border the samples studied were coal and dispersed organic matter dom taken from ditch cuttings and drill cores of the permian triassic and jurassic sedimentary successions vitrinite reflectance profiles show that the coals and dom in the early permian back creek group of the southern bowen basin have anomalously low suppressed reflectance values and a higher reflectance gradient rate of increase in vitrinite reflectance with depth relative to the overlying late permian triassic and jurassic sequences suppression of vitrinite reflectance is recorded in the early permian maules creek and goonbri formations in the northernmost part of the gunnedah basin relative to the overlying triassic and jurassic sequences dispersed organic matter in the marine sediments of the watermark and porcupine formations of the gunnedah basin also shows suppression of vitrinite reflectance the vitrinite in several wells of the study area however displays anomalously high reflectance in parts of the sequence due to the influence of igneous intrusions after allowing for heat effects due to intrusions and anomalies due to marine influence the reflectance gradient over equivalent intervals in the southern bowen basin is higher towards the west where the permian sequence pinches out and the triassic sequence overlies the basement vitrinite reflectance also increases at a higher rate with depth close to the gil gil ridge in the east and close to the moree high in the south this may reflect additional heat flow associated with the basement high features the areas between the gil gil ridge and the goondiwindi thrust in the east and to the west of the gil gil ridge appear to have lower reflectance gradients and equivalent or lower reflectance values despite the greater burial depths

boron in graphite content speciation and significance abstract the mean boron content of syngenetic graphite in metasedimentary rocks is significantly higher than that of epigenetic vein graphite or igneous graphite the boron commonly found in chemical analyses of natural graphites does not occur in solid solution with the carbon but rather is contained in a mechanically included borosilicate phase

mineralogy fluid inclusion petrography and stable isotope geochemistry of pb zn ag veins at the shizhuyuan deposit hunan province southeastern china the shizhuyuan polymetallic deposit is located in the central part of the nanling region southeastern china and consists of proximal w sn mo bi skarns and greisens and distal pb zn ag veins the sulfides and sulfosalts in the distal veins formed in three distinct stages 1 an early stage of pyrite and arsenopyrite 2 a middle stage of sphalerite and chalcopyrite and 3 a late stage of galena ag sn and bi bearing sulfides and sulfosalts and pyrrhotite combined sulfide and sulfosalt geothermometry and fluid inclusion analyses indicate that the early stage of mineralization occurred at a temperature of 400 c and involved boiling under hydrostatic pressure 200 bar with the temperature of the system dropping during the late stage to 200 c laser raman analysis indicates that the fluid inclusions within the studied minerals are dominated by h2o although some contain carbonate solids and ch4 gas vein hosted sulfides have 34s values of 3 8 6 3 that are interpreted as indicative of a magmatic source of sulfur the mineralization process can be summarized as follows an aqueous fluid exsolved on final crystallization of the qianlishan pluton ascended along fracture zones cooled to 400 c and boiled under hydrostatic conditions and with decreasing temperature and sulfur fugacity sulfide and sulfosalt minerals precipitated successively from the ag cu zn fe pb sb as s bearing fluid system

hydrogeochemistry groundwater ages and sources of salts in a granitic batholith on the canadian shield southeastern manitoba abstract the hydrogeochemistry of the lac du bonnet granitic batholith has been determined for the region of the whiteshell research area wra in southeastern manitoba canada this work forms part of the geosciences studies performed for the canadian nuclear fuel waste management program over the period 1980 1995 by atomic energy of canada limited aecl knowledge of the variation of groundwater chemistry and its causes is useful in assessing the performance and safety of a nuclear fuel waste vault located at depths of up to 1000 m in a crystalline rock formation of the canadian shield groundwaters and matrix pore fluids have been obtained by standard sampling methods from shallow piezometers in clay rich overburden from packer isolated borehole zones intersecting fractures or fault zones in the bedrock and from boreholes in unfractured rock in aecl s underground research laboratory url eighty six individual fracture groundwaters have been sampled and analysed from permeable zones in 53 boreholes drilled to depths of up to 1000 m in the lac du bonnet batholith in addition 28 groundwaters from piezometers in a large wetland area near the url have been sampled and analysed to determine the influence of clay rich overburden on the bedrock hydrogeochemistry analyses have been made for major and minor ions ph eh trace metals and stable and radioactive isotopes to characterise these groundwaters and relate them to their hydrogeologic regimes shallow groundwaters in the fractured bedrock are generally dilute tds 500 m na ca cl so4 waters of increasing salinity up to 50 g l with depth are found and in some fractures the waters have evolved to a ca na cl composition isotopic data indicate that these waters are warm climate and pre glacial in origin with residence times of over 1 ma pore fluids observed to drain from the unfractured rock matrix in the url facility are almost pure ca cl in composition 90 g l salinity and have a 2h 18o composition displaced well to the left of the global meteoric water line about which all other wra groundwaters lie this information indicates that these pore fluids have undergone prolonged water rock interaction and have residence times of 101 103 ma most of the deeper fracture groundwaters and pore fluids have low br cl ratios and moderate to high 34s values of dissolved so4 which indicates that their salinity could be derived from a marine source such as the basinal sedimentary brines and evaporites to the west of the batholith these fluids may have entered the batholith during early paleozoic times when sedimentary rocks were deposited over the granite and were driven by a hydraulic gradient resulting from higher ground in western canada the hydrogeochemical data and interpretations show that below 500 m in the wra fracture hosted groundwaters are very saline reducing and old and are therefore indicative of stagnant conditions over the period of concern for nuclear waste disposal 1 ma the intact rock matrix at these depths is extremely impermeable as indicated by the presence of pore fluids with unusual geochemical and isotopic characteristics the pore fluids may represent basinal brines that have evolved geochemically and isotopically to their current composition over periods as long as 103 ma

saline groundwater seepage zones and their impact on soil and water resources in the spicers creek catchment central west new south wales australia saline seepage zone development and hence dryland salinity is a major environmental problem which many arid to semiarid landscapes in australia are experiencing due to the geological complexity of the regional aquifer system and the heterogeneous nature of the local groundwater system each groundwater seepage zone in the spicers creek catchment central west new south wales australia possesses different mechanisms which control its development saline seepage zones have formed adjacent to a fault zone and two experimental sites were established through these groundwater discharge zones to understand geochemical processes which have led to the development of soil sodicity gully erosion and the flushing of salts into the surface water systems seepage zone groundwaters contain a distinctive geochemical signature with elevated concentrations of na cl hco3 ca sr b as and li the mixing of deep saline groundwaters together with ion exchange processes lead to a distinctive seepage zone groundwater chemistry being developed altering the landscape features within this rural groundwater system has developed water toxicity for crops soil sodicity leading to land degradation and waterlogging problems

non biogenic graphite in 3 8 ga metamorphic rocks from the isua district greenland abstract a 3 8 ga old metamorphic rock that contains up to 5 5 wt reduced carbon as graphite was found in the isua district greenland this rock exhibits a strong schistosity comprises mostly talc contains high mgo 28 0 wt ni 553 ppm and cr 267 ppm and low al2o3 2 13 wt and bears a high fe 2 o 3 feo ratio 0 94 the original rock was probably a submarine ultramafic tuff the carbon content and the 13c value of the rock vary on a microscopic scale a few mm3 scale from 0 7 to 5 5 wt and from 15 to 12 respectively the second rock a quartzite contains 0 13 wt c as reduced carbon with a 13c value of 11 25 these 13c values fall within the range 27 to 10 reported by previous investigators for graphite from the isua district the 13c values of the isua graphite have been interpreted by previous investigators e g schidlowski and aharon 1992 as metamorphic modification of organic matter with initial 13c values of 30 an important implication of this model has been that the 3 8 ga ocean already supported some biological activity however an examination of the carbon content vs 13c relationship of the graphite bearing rocks from isua has revealed that the 13c value generally increases with increasing carbon contents the rocks with 13c values less than 20 contain extremely small amounts of carbon the mineralogical and elemental characteristics of the rocks of this study a thermodynamic consideration of the temperature and composition of metamorphic fluids and carbon isotope mass calculations suggest that the major component of graphite with 13c values around 12 was formed by an inorganic rather than by a biological process the graphite appeared to have formed at temperatures between 700 and 400 c by one or both of the following two processes 1 reactions between co2 and ch4 co2 ch4 2c 2h2o during cooling of fluids with a co 2 ch 4 molar ratio of 1 and or 2 reactions between the feo component in the ultramafic rock with co2 rich fluids 4 feo co2 2 fe2o3 c the 13c c values for the fluids for both i and 2 were probably between 12 and 5 suggesting that the carbon bearing fluids could have been derived from the mantle

geology mineralogy and geochemistry of fault controlled hydrothermal cu au mineralization in the shanmen volcanic basin se china abstract the yukeng banling deposit is a typical fault controlled hydrothermal cu au deposit in the shanmen volcanic basin svb se china ore bodies commonly occur as lodes lenses and disconnected pods dipping sw with vertical zonation of ore minerals ore related hydrothermal alteration is well developed on both sides of the veins dominated by silicification sericitization chloritization and argillation with a banded alteration zonation the mineralization can be divided into three stages stages i ii and iii native gold is present as veinlets in fractures of fine grained pyrite from stage ii zircon u pb and rb sr isochron ages indicate that the cu au mineralization is coeval with the caomen alkaline granite and xiaokeng quartz diorite both emplaced at ca 102 ma microthermometric measurements of fluid inclusions in quartz and sphalerite from stage ii veins indicate that the yukeng banling deposit is an epithermal deposit six ore related quartz grains have d h2o values of 69 to 43 and 18 o h2o values calculated using total homogenization temperatures that range from 2 0 to 0 7 all samples plot in an area between the magmatic field and the meteoric line suggesting that the ore forming fluids are derived from a mixed source of magmatic and meteoric waters 34 s values for eight pyrite separates range from 2 1 to 4 1 with an average of 1 7 and 34 s values for galena and sphalerite are 2 3 and 2 2 similar to magmatic sulfur four alkaline granite samples have pb isotopic ratios 206 pb 204 pb t 18 175 18 411 207 pb 204 pb t 15 652 15 672 and 208 pb 204 pb t 38 343 38 800 three quartz diorite samples have ratios 206 pb 204 pb t 207 pb 204 pb t and 208 pb 204 pb t of 18 277 18 451 15 654 15 693 and 38 673 38 846 respectively these age calculated lead isotopic data for alkaline granite are similar to those for the analyzed sulfides co ni ratios for stage ii pyrites range from 1 42 to 5 10 indicating that the yukeng banling deposit records the past involvement of magmatic hydrothermal fluids the isotope data together with geological mineralogical and geochronological evidence favor a primary magmatic source for sulfur and metals in the ore fluids mixing of the cu and au rich fluids with meteoric water led to precipitation of the cu au veins along nw trending faults the yukeng banling deposit the contemporaneous caomen alkaline granite and xiaokeng quartz diorite in the svb formed under an extensional setting due to high angle subduction of the paleo pacific plate the extensional setting facilitated the formation of cu and au rich magmas which was derived from enriched mantle and lower crust

re os isotopic dating of molybdenites in the xiaoliugou w mo deposit in the northern qilian mountains and its geological significance abstract the xiaoliugou is a large scale w mo deposit newly explored in the northern qilian mountains caledonian fold belt northwestern china it is a vein and skarn type deposit genetically associated with the xiaoliugou caledonian granodiorite stock re os isotopic dating for the molybdenite in the deposit yields an isochron age of 462 13 ma 2 and model ages of 436 to 496 ma these results suggest that w mo mineralization occurred before the collision of plates and mineralized substances mainly originated from the crust

geological and isotopic evidence for magmatic hydrothermal origin of the ag pb zn deposits in the lengshuikeng district east central china the lengshuikeng ore district in east central china has an ore reserve of 43 mt with an average grade of 204 53 g t ag and 4 63 pb zn based on contrasting geological characteristics the mineralization in the lengshuikeng ore district can be divided into porphyry hosted and stratabound types the porphyry hosted mineralization is distributed in and around the lengshuikeng granite porphyry and shows a distinct alteration zoning including minor chloritization and sericitization in the proximal zone sericitization silicification and carbonatization in the peripheral zone and sericitization and carbonatization in the distal zone the stratabound mineralization occurs in volcano sedimentary rocks at 100 400 m depth without obvious zoning of alterations and ore minerals porphyry hosted and stratabound mineralization are both characterized by early stage pyrite chalcopyrite sphalerite middle stage acanthite native silver galena sphalerite and late stage pyrite quartz calcite the 34s values of pyrite sphalerite and galena in the ores range from 3 8 to 6 9 with an average of 2 0 the c o isotope values of siderite calcite and dolomite range from 7 2 to 1 5 with an average of 4 4 v pdb and from 10 9 to 19 5 with an average of 14 8 v smow respectively hydrogen oxygen and carbon isotopes indicate that the hydrothermal fluids were derived mainly from meteoric water with addition of minor amounts of magmatic water geochronology employing la icp ms analyses of zircons from a quartz syenite porphyry yielded a weighted mean 206pb 238u age of 136 3 0 8 ma considered as the emplacement age of the porphyry rb sr dating of sphalerite from the main ore stage yielded an age of 126 9 7 1 ma marking the time of mineralization the lengshuikeng mineralization classifies as an epithermal ag pb zn deposit

regional controls on the geochemical evolution of saline groundwaters in the edwards aquifer central texas geochemical and isotopic parameters are used to evaluate models for the evolution of saline groundwaters in the edwards aquifer which lies on the northwestern margin of the gulf of mexico sedimentary basin saline groundwaters termed badwaters range in salinity from 1000 to 12 500 mg l 1 total dissolved solids models for badwater evolution must account for complexities owing to 1 the range in compositions of saline basinal fluids that may migrate into the edwards aquifer from its down dip section and from underlying hydrostratigraphic units 2 the range of depositional diagenetic and mineralogic variations in the hist aquifer rocks 3 volcanic and intrusive igneous rocks that locally crosscut the aquifer 4 extensive faulting which in places juxtaposes edwards aquifer units with adjacent hydrostratigraphic units calcium mg na so4 cl and hco3 variations define six badwater hydrochemical facies strontium isotope values of freshwaters 87sr86sr 0 7077 0 7086 badwaters 0 7076 0 7094 and brines from aquifer rocks down dip 0 7078 0 7097 are nearly all higher than the range of most edwards aquifer rocks 0 7074 0 7077 and volcanic and intrusive igneous rocks that crosscut the aquifer 0 7032 0 7055 argillaceous carbonate rocks that underlie the edwards aquifer are likely sources of sr with high 87sr86sr values transitions between the hydrochemical facies in some locations correspond to changes in depositional environments in aquifer rocks and to changes in the intensity of faulting through the aquifer major element mineral saturation state and srca 87sr86sr variations in badwaters of the westernmost aquifer region indicate that incongruent dissolution of gypsum and recrystallization of calcite control the geochemical evolution of these badwaters srca na cl 87sr86sr variations in badwaters of extensively faulted areas to the east of the westernmost aquifer region are consistent with fluid mixing processes involving at least five endmember fluids including 1 saline groundwaters from two underlying hydrostratigraphic units 2 two endmember brines from down dip edwadrs aquifer equivalent units and 3 freashwaters that have interacted extensively with aquifer rocks the compositions of badwaters from the northeasternmost region reflect fluid mixing between freshwaters and saline groundwaters from underlying hydrostratigraphic units

the origin and evolution of saline formation water lower cretaceous carbonates south central texas u s a abstract land l s and prezbindowski d r 1981 the origin and evolution of saline formation water lower cretaceous carbonates south central texas u s a in w back and r letolle guest editors symposium on geochemistry of groundwater 26th international geological congress j hydrol 54 51ndash 74 systematic chemical variation exists in formation water collected from a dip section through lower cretaceous rocks of south central texas chemical variation can be explained by an interactive water rock diagenetic model the cyclic lower cretaceous shelf carbonates of the edwards group dip into the gulf of mexico coast geosyncline and can be considered to a first approximation as part of a complex aquifer contained by paleozoic basement beneath and by relatively impermeable upper cretaceous clay and chalk above the hydrodynamic character of this carbonate system is strongly controlled by major fault systems major fault systems serve as pathways for vertical movement of basinal brines into the lower cretaceous section formation water movement in this sytem has strong upfault and updip components the parent na ca cl brine originates deep in the gulf of mexico basin at temperatures between 200 and 250 c by the reaction halite detrital plagioclase quartz water albite brine other dissolved components originate by reaction of the fluid with the sedimentary phases k feldspar calcite dolomite anhydrite celestite barite and fluorite significant quantities of pb zn and fe have been mobilized as well as the brine moves updip out of the overpressured deep gulf of mexico basin and encounters limestones of the stuart city reef trend the buried platform margin small amounts of galena precipitate in late fractures continuing to rise upfault and updip the brine becomes progressively diluted on encountering significant quantities of dolomite in the backreef facies the ca rich brine causes dedolomitization although thermochemical consideration suggests that small amounts of several authigenic phases should precipitate most have yet to be found minor amounts of several kinds of calcite spar are present however as the brine evolves by dilution and by cooling no systematic changes in any cation cl ratio occur except for regular updip gain in mg as a result of progressive dedolomitization the formation water highly diluted by meteoric water eventually discharges along faults as hot mineral water

timing of skarn deposit formation of the tonglushan ore district southeastern hubei province middle lower yangtze river valley metallogenic belt and its implications abstract the tonglushan ore district in the middle lower yangtze river valley metallogenic belt includes the tonglushan cu fe the jiguanzui au cu and the taohuazui au cu skarn deposits they are characterized by ne striking ore bodies and hosted at the contact of triassic carbonate rocks and late mesozoic granitoid deposits new sensitive high resolution ion microprobe shrimp and laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb molybdenite re os and phlogopite 40 ar 39 ar ages indicate that these skarn deposits formed between 140 3 1 1 and 137 3 2 4 ma these dates are identical to the zircon u pb ages for host quartz diorites ranging from 140 2 to 139 1 ma these results confirm that both skarn mineralization and related intrusions were initiated during the early cretaceous the high rhenium contents 261 4 1152 g g of molybdenites indicate that a metasomatic mantle fluid was involved in the ore forming process of these skarn ore systems this conclusion is consistent with previously published constraints from sulfur deuterium and oxygen isotope compositions and the geochemical signatures and sr nd isotopic data of the mineralization hosting intrusions geological and geochronological evidence demonstrates that there were two igneous events in the tonglushan ore district the first resulted in the emplacement of quartz diorite during the early cretaceous 140 2 to 139 1 ma and the second is characterized by the eruption of volcanic rocks during the mid early cretaceous 130 2 to 124 2 ma the former is spatially temporally and genetically associated with skarn gold bearing mineralization 140 3 1 1 to 137 3 2 4 ma the recognition of these two igneous events invalidates previous models that proposed continuous magmatism and associated mineral deposits in the middle lower yangtze river valley metallogenic belt

saline ground waters and brines in the canadian shield geochemical and isotopic evidence for a residual evaporite brine component abstract saline ca na cl type groundwaters and brines sampled in deep mines over an extensive area of the canadian precambrian shield have elevated br cl ratios which may indicate that the chlorinity of these waters was derived from the infiltration of residual evaporitic brines remnants of the great marine incursions of the paleozoic era boron concentrations in these waters are generally low i e 11 b 10 b ratios of these waters are significantly greater than the average value for continental crustal rocks with the highest values 4 19 approaching that of present day seawater 4 20 moreover the boron isotopic ratios generally trend to higher values with increasing chlorinity which supports the conclusion from the br cl relationship that most of the chloride in shield brines is of marine origin rather than a product of water rock interactions if this is correct crystalline rocks must then be sufficiently permeable on a regional scale to have allowed the brine to infiltrate to depths of several kilometers where it now resides

precambrian vein pyrobitumen evidence for petroleum generation and migration 2 ga ago abstract isotopic optical reflectance and chemical analyses of large pure samples of lower proterozoic vein pyrobitumens anthraxolite and thucholite of older reports collected from five widely separated localities in the great lakes region of the united states and canada suggest that in the lower proterozoic oil was generated from kerogen and migrated in much the same way as during the phanerozoic furthermore maturation and organic metamorphism followed the same successive stages that mark the generation and destruction of phanerozoic petroleum kerogens derived from algae and bacteria were deposited with subaqueous muds that ultimately became black shales or slates some of the kerogen however yielded petroleum which migrated into fractures and subsequently became pyrobitumen the 13c values average 32 6 pdb this value compares favorably with those from phanerozoic petroleum and asphaltites and is consistent with the proposition that the carbon isotopes were fractionated by biological activity reflectance values of the pyrobitumens range from 0 9 for elliot lake ontario to 9 5 for iron river michigan and h c ratios range from 0 6 for elliot lake to 0 1 for sudbury ontario when compared with the stages of petroleum maturation these values indicate maturation which ranges from the catagenesis stage through the metagenesis stage of petroleum generation and metamorphism

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

genesis of the late jurassic shizitou mo deposit south china evidences from fluid inclusion ho isotope and reos geochronology abstract the shizitou deposit is a middle sized mo deposit in the qin hang metallogenic belt south china three stages of mineralization are recognized at the shizitou including the early stage characterized by barren quartz veins with potassic alteration followed by the main ore stage represented by quartz molybdenite veins with strong phyllic alteration and the late stage featured by quartz pyrite veins with weak propylitization two phase liquid rich aqueous type i two phase gas rich aqueous type ii and halite bearing type iii inclusions are present in the main ore stage veins but only type i inclusions occur in the early and late stages of veins type i inclusions in the early stage veins show homogenization temperatures th of 291 376 c with salinities of 2 2 9 5 wt nacl equivalent type ii and iii inclusions in the main ore stage veins display th of 266 351 c and 245 336 c and salinities of 0 6 3 5 and 28 0 36 2 wt nacl equivalent respectively type i inclusions in the late stage quartz pyrite veins have th of 209 288 c and salinities of 0 5 5 0 wt nacl equivalent fluid boiling took place in the main ore stage and promoted the quick precipitation of molybdenite from ore forming solutions raman analysis of fluid inclusions implies that mineralizing fluids contain little co 2 and n2 hydrogen and oxygen isotopes indicate that initial ore forming fluids were magmatic in origin and shifted gradually to meteoric regime re os dating of molybdenite gives a 187re 187os isochron age of 162 3 2 4 ma in response to a localized extensional setting resulting from the far field stresses of the initial subduction of the paleo pacific plate beneath the margins of the south china block

u pb zircon geochemical and sr nd hf isotopic constraints on age and origin of jurassic i and a type granites from central guangdong se china a major igneous event in response to foundering of a subducted flat slab abstract the mesozoic geology of se china is characterized by widespread jurassic to cretaceous igneous rocks consisting predominantly of granites and rhyolites and subordinate mafic lithologies however the tectonic regime responsible for the inland jurassic granites remains controversial we report here u pb zircon ages geochemical and sr nd hf isotopic data for the nankunshan alkaline granite and the fogang granitic batholith in central guangdong mineralogical and geochemical features suggest that the fogang and nankunshan rocks are i and aluminous a type granites respectively shrimp u pb zircon analyses yield consistent ages ranging from 159 3 ma to 165 2 ma for four samples from the fogang batholith and an age of 158 5 ma for the nankunshan granite the fogang granites having i sr 0 7098 0 7136 e nd t 4 3 to 12 2 and e hf t 11 5 to 3 1 for the magmatic zircons were derived from paleoproterozoic mafic intermediate igneous protolith with minor addition of mantle derived magmas the nankunshan rocks have relatively lower i sr 0 706 0 708 higher e nd t 0 3 to 2 4 and e hf t 5 7 to 1 1 for the magmatic zircons and some oib like trace element ratios they were likely generated through extensive fractional crystallization of mantle derived alkaline parental magma associated with crustal assimilation these 160 ma i and a type granites in central guangdong were emplaced coeval with the widespread 165 155 ma i and a type granites and syenites following the initiation of intraplate basaltic and or bimodal igneous magmatism at 180 170 ma in the adjacent regions we interpret these jurassic igneous rocks as anorogenic magmatism formed during a major igneous event in response to foundering of an early mesozoic subducted flat slab beneath se china continent

porphyry cu au mo epithermal ag pb zn distal hydrothermal au deposits in the dexing area jiangxi province east china a linked ore system abstract based on previous studies and detailed field investigations of the dexing porphyry copper deposit the yinshan ag pb zn deposit and the jinshan shear zone hosted gold deposit in the dele jurassic volcanic basin in the northeastern jiangxi province east china we propose that the three deposits share spatial temporal and genetic relationships and belong to the same metallogenic system dexing is a typical porphyry cu au mo deposit in which both ore forming fluid and metals are derived from the granite porphyry the yinshan deposit consists of a porphyry copper ore located in the cupola of a quartz porphyry stock in the lower part and ag pb zn ore veins in the upper part the hydrothermal fluids were mainly derived from the magma in the early stages of the mineralizing event and became mixed with meteoric waters in the late stages its ore metals are magma derived both the jinshan base metal veins and the hamashi dongjie and naikeng quartz vein type gold deposit are hosted by brittle ductile structures which are distal in relation to the porphyry intrusions and were formed by mixed magmatic fluids and meteoric water whereas the gold was mainly leached from the country rocks mesoproterozoic shuangqiaoshan group phyllite and schist the deposits show a distinct spatial arrangement from porphyry cu to epithermal ag pb zn and distal au we suggest a porphyry epithermal distal vein ore system model for this group of genetically related mineral deposits they were formed in a back arc setting in a middle jurassic active continental margin with magmas derived from the subducted slab

molybdenite re os dating zircon u pb age and geochemistry of granitoids in the yangchuling porphyry w mo deposit jiangnan tungsten ore belt china implications for petrogenesis mineralization and geodynamic setting abstract the yangchuling w mo deposit located in the jiangnan porphyry skarn jnb tungsten ore belt is the first recognized typical porphyry w mo deposit in china in the 1980 s stockworks and disseminated w mo mineralization occur in the roof pendant of a 0 3 km 2 monzogranitic porphyry stock that intruded into a granodiorite stock hosted by neoproterozoic phyllite and slate la icpms zircon u pb analyses suggest that of the monzogranitic porphyry and granodiorite were formed at 143 8 0 5 ma and 149 8 0 6 ma respectively six molybdenite samples yielded a re os weighted mean age of 146 4 1 0 ma geochemical data show that both granodiorite and monzogranitic porphyry are characterized by enrichment of large ion lithophile elements lile relative to high field strength elements hfse indicating a peraluminous nature a cnk 1 01 1 08 two granitoids are characterized by a negative slope with significant light ree heavy ree fractionation la yb n 8 38 23 20 and negative eu anomalies eu eu 0 69 0 76 the p 2 o 5 contents of the yangchuling granitoids range from 0 12 to 0 17 and exhibit a negative correlation with sio 2 reflecting that they are highly fractionated i type they have high initial 87 sr 86 sr ratios 0 7104 0 7116 low negative e nd t 5 05 to 5 67 and homogeneous e hf t between 1 39 and 2 17 indicating similar sources additionally two stage nd model ages t dm2 of 1 3 1 4 ga and two stage hf model ages t dm2 of 1 2 1 3 ga are consistent indicating that neoproterozoic crustal rocks of the shuangqiaoshan group could have contributed to form the yangchuling magmas considering the two groups of parallel late mesozoic ore belts namely the jiangnan porphyry skarn tungsten belt jnb in the south and the middle lower yangtze river porphyry skarn cu au mo fe ore belt yrb in the north the nanling granite related w sn ore belt nlb in the south the neighboring qin hang porphyry skarn cu mo hydrothermal pb zn ag ore belt qhb in the north as well as the southeastern coast porphyry skarn cu mo au ore belt scb recognized in south china in this paper we propose that the latest jurassic to earliest cretaceous granitoids and associated ores were formed during a tearing of the subducting izanagi slab this tearing of the subduction slab caused the upwelling of asthenosphere and the resulting mantle crust interaction the granitoid related w ore systems in jnb resulted from the remelting of the proterozoic crust the mafic ultramafic volcanic rocks of the shuangqiaoshan group intercalated with phyllite and slate ophiolitic melange and magmatic arc rocks mainly comprising i type granite basalt andesite rhyolite pyroclastics together with subduction related metasomatized lithospheric mantle would have provided additional mantle material in this case the partial melting of rocks of the shuangqiaoshan group can produce s i and transitional type granitoids after strong differentiation it formed tungsten bearing granitoids characterized by enrichment of high alkali silicon and volatile components in the yangchuling mine area the small monzogranitic porphyry stock has stronger fractionation volatile content and ore forming components than the older granodiorite resulting in the development of the porphyry w mo ore system