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

archean lamprophyre dikes of the superior province canada distribution petrology and geochemical characteristics shoshonitic lamprophyre dikes of late archean age are a volumetrically minor yet widespread component of magmatism in the superior province and preferentially occur along major structures that delineate subprovince boundaries lamprophyre swarms are most prominently developed in fault graben where they are associated with alkali gabbro and trachytes and molasse sediments mineralogically the dikes are characterized by zoned phlogopite or hornblende phenocrysts restriction of feldspar to the groundmass globular segregations of k feldspar and calcite panidiomorphic texture and the sporadic presence of crustal xenoliths compositionally fresh dikes have contents of sio2 47 51 wt tio2 0 55 0 60 and p2o5 0 36 1 58 and k2o na2o ratios 1 5 2 3 and mg numbers 78 80 comparable to phanerozoic shoshonitic lamprophyres unaltered dikes are characterized by extreme enrichments of the lithophile elements k rb ba cs th u and light rare earth elements lree and enhanced abundances of cr 650 920 ppm co 37 42 ni 264 355 and sc 22 28 mid ocean ridge basalt normalized plots display 1 consistent enrichments of k rb and ba relative to sr and lree 2 variable enrichments of rb and ba relative to k and 3 troughs at ta nb and ti compared with fresh rocks altered samples have systematically lower k rb ba and sr contents but similar ree distributions and profiles from th yb and sc ni on normalized diagrams suites of post archean ultramafic lamprophyres in the superior province are enriched in large ion lithophile elements lile lree and compatible elements relative to their archean counterparts and lack troughs at ta nb and ti emplacement of the lamprophyres was diachronous from north 2705 ma to south 2674 ma probably being related to localized extension during the successive accretion of individual subprovinces archean lamprophyre magmas were derived from a depleted mantle source variably enriched in lile and lree by sediments and altered oceanic crust with small variable degrees of crustal contamination whereas the post archean lamprophyres lacked a plate margin setting

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

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

paleomagnetism of the 1 1 ga coldwell complex ontario canada implications for proterozoic geomagnetic field morphology and plate velocities we report new paleomagnetic data from the 1108 ma intrusive coldwell complex ontario canada to investigate the apparent reversal asymmetry observed in some midcontinent rift mcr rocks the rocks of eastern and central part of the complex are reversely magnetized with a group mean direction of d 114 8 i 63 7 95 3 6 n 30 the corresponding paleomagnetic pole at plat 47 2 n plong 206 5 e a95 4 8 is located close to the paleomagnetic poles from nearly coeval reversely magnetized rocks of the mcr system including the lower lava flows at mamainse point the rocks of western part of the complex are normally magnetized with a group mean direction d 298 0 i 56 9 95 5 8 n 10 that passes the reversal test with respect to the reversed group mean direction our results do not support the previous model in which the complex was emplaced during two periods of reversed geomagnetic field polarity separated by a period of normal polarity and hence encompasses two geomagnetic reversals instead our new data indicate that the coldwell complex records only two polarity intervals separated by a symmetrical reversal at 1102 1105 ma this reversal is likely equivalent to the lowermost reversal recorded at mamainse point and provides further evidence that the apparent reversal asymmetry reflects a plate motion rather than a persistent nondipole field geometry together with a high quality data from the 1098 ma north shore volcanics our data indicate a rapid velocity of laurentia at 25 4 cm yr the fast plate motion may reflect a decreased mantle drag due to vigorous mantle indicated by widespread intraplate magmatism at 1 1 ga

petrology of alkaline lamprophyres from the coldwell alkaline complex northwestern ontario a suite of alkaline lamprophyre dikes emplaced in centers i and ii rocks of the coldwell alkaline complex is composed of camptonites with calcite ocelli camptonites with quartz macrocrysts amphibole camptonites monchiquites and sannaites the camptonites are characterized by phenocrysts of olivine aluminian pyroxene kaersutite and titanian ferropargasite set in a matrix of magnesian hastingsite augite plagioclase biotite magnetite sphene and minor nepheline quartz macrocrysts occur as corroded euhedral single crystals monchiquites are petrographically similar to the camptonites but are characterized by the presence of an isotropic groundmass sannaites contain aluminian and chromian diopside phenocrysts set in a matrix of ferroan pargasite aluminian diopside biotite albitized plagioclase and epidotized alkali feldspar major element compositions indicate the ocellar camptonites amphibole camptonites and monchiquites have affinities with alkali olivine basalt and that monchiquites and c

the petrology of the layered gabbro intrusion eastern gabbro coldwell alkaline complex northwestern ontario canada evidence for multiple phases of intrusion in a ring dyke abstract the coldwell alkaline complex is a large 350 km2 gabbro and syenite intrusion on the north shore of lake superior it was emplaced at 1108 ma during early magmatic activity associated with the formation of the mid continent rift of north america the eastern gabbro forms a partial ring dyke on the outer margin of the complex and consists of at least three discrete intrusions the largest of these is the layered gabbro that comprises a 300 m thick fine to medium grained basal unit overlain by up to 1100 m of variably massive to layered gabbroic cumulates which vary from olivine gabbro to anorthosite several xenoliths of archaean metamorphic rocks that range in size from 10 s to 100 s of meters are present in the central part of the intrusion within discrete horizons in the layered gabbro are many centimeter to meter scale gabbroic xenoliths the main cumulus minerals in order of crystallization are plagioclase olivine and clinopyroxene fe ti oxides biotite and fe ti oxide are the dominant intercumulus phases orthopyroxene occurs not as a cumulus phase but as peritectic overgrowths on cumulus olivine a detailed petrographic and mineral chemical study of samples from two stratigraphically controlled traverses through the layered gabbro indicates that the stratigraphy cannot be correlated along the 33 km strike of the ring dyke mineral compositions show both normal and reversed fractionation trends these patterns are interpreted to record at least three separate intrusions of magma into restricted dilatant zones within the ring dyke possibly associated with ongoing caldera collapse calculations of parental melt composition using mineral melt equilibria show that even the most primitive gabbros crystallized from an evolved magma with mg of 0 42 0 49 the presence of orthopyroxene overgrowths on cumulus olivine suggests rising silica activity in the melt during crystallization and implies a subalkaline parentage for the layered gabbro

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

formation of high δ18o fayalite bearing a type granite by high temperature melting of granulitic metasedimentary rocks southern china comment huang et al 2011 1 describe a granite that they interpret as crystallized from an a type magma derived from a metasedimentary protolith sun et al 2011 2 had already described a similar example with high initial 87sr 86sr and low nd the important question is whether these a types

mesozoic overthrust tectonics in south china whether south china was a platform or a para platform after the mid paleozoic deformation or whether the mountains of huanan south china form a mesozoic collision type orogen depends upon whether the ophiolite melange in the yangtze region is precambrian basement or was overthrust onto a foreland thrust belt during the mesozoic this paper presents evidence of tectonic windows under the melange and basement klippes above the melange in the yangtze region

isotopic geochemistry zircon u pb ages and hf isotopes of a type granites from the xitian w sn deposit se china constraints on petrogenesis and tectonic significance abstract zircon u pb geochronological geochemical and petrological analyses have been carried out on the xitian granite emplaced in the middle part of shi hang zone which is closely related to the economically important xitian tungsten tin deposit in hunan province southeast china la icp ms zircon u pb dating of two representative samples yielded weighted means 206 pb 238 u age of 151 7 1 2 ma and 151 8 1 4 ma these granites are comprised mainly of k feldspar quartz plagioclase fe rich biotite and minor fluorite and are characterized by enrichments in rb th rees total ree 159 351 ppm and hfses e g zr and y but depletions in ba sr p eu and ti they are metaluminous to weakly peraluminous and show a clear a type granite geochemical signature with high sio 2 73 44 78 45 wt total alkalis na 2 o k 2 o 2 89 8 98 wt fe 2 o 3 mgo ratios and low p 2 o 5 cao mgo and tio 2 contents in situ zircon hf isotope analysis suggests their e hf t values ranging from 7 43 to 14 69 sr nd isotope data show their e nd t values in the range of 9 2 to 7 3 with corresponding t dm2 ages of 1 72 1 56 ga these characteristics indicate that the xitian granite originated from partial melting of metamorphic basement rocks with a certain amount of mantle derived materials combined with previous geochemical and isotopic data it is derived that mantle crust interaction was gradually enhanced from the early to late stages of magmatism the ore forming materials and fluids of the xitian w sn deposit are mainly produced by the early yanshanian granitic magmatism which is also responsible for the late jurassic ca 152 ma a type granitic rocks that host the w sn polymetallic deposits distributed along the shi hang zone implying a significant mesozoic extensional event in southeast china likely caused by the subduction of the paleo pacific plate

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

petrology and geochemistry of late stage intrusions of the a type mid proterozoic pikes peak batholith central colorado usa implications for petrogenetic models abstract the 1 08 ga anorogenic a type pikes peak batholith front range central colorado is dominated by coarse grained biotite amphibole syenogranites and minor monzogranites collectively referred to as pikes peak granite ppg the batholith is also host to numerous small late stage plutons that have been subdivided into two groups e g wobus 1976 studies in colorado field geology colorado school of mines professional contributions colorado 1 a sodic series sio 2 44 78 wt k na 0 32 1 36 composed of gabbro diabase syenite quartz syenite and fayalite and sodic amphibole granite and 2 a potassic series sio 2 70 77 wt k na 0 95 2 05 composed of biotite granite and minor quartz monzonite differences in major and trace element and nd isotopic characteristics for the two series indicate different petrogenetic histories potassic granites of the late stage intrusions appear to represent crustal anatectic melts derived from tonalite sources based on comparison of their major element compositions with experimental melt products in addition nd isotopic characteristics of the potassic granites e nd 1 08 ga 0 2 to 2 7 overlap with those for tonalites granodiorites ca 1 7 ga boulder creek intrusions e nd 1 08 ga 2 4 to 3 6 exposed in the region some of the partial melts evolved by fractionation dominated by feldspar the late stage potassic granites share geochemical characteristics with most of the ppg which is also interpreted to have an anatectic origin involving tonalitic crust the origin of monzogranites associated with the ppg remains unclear but mixing between granitic and mafic or intermediate magmas is a possibility syenites and granites of the sodic series cannot be explained as crustal melts but are interpreted as fractionation products of mantle derived mafic magmas with minor crustal input high temperature and low oxygen fugacity estimates e g frost et al 1988 american mineralogist 73 727 740 support a basalt fractionation origin as do e nd values for sodic granitoids e nd 1 08 ga 2 2 to 0 7 which are higher than e nd values for colorado crust at 1 08 ga ca 1 0 to 4 0 enrichments in incompatible elements e g rare earth elements rb y and depletions in compatible elements e g cr sr ba in the sodic granitoids compared to coeval mafic rocks are also consistent with fractionation accessory mineral fractionation release of fluorine rich volatiles and or removal of pegmatitic fluids could have modified abundances of ce nb zr and y in some sodic granitoid magmas gabbros and mafic dikes associated with the sodic granitoids have e nd 1 08 ga of 3 0 to 3 5 which are lower than depleted mantle at 1 08 ga and their trace element characteristics suggest derivation from mantle sources that were previously affected by subduction related processes however it is difficult to characterize the mantle component in these magmas because assimilation of crust during magma ascent could also result in their observed geochemical features the pikes peak batholith is composed of at least two petrogenetically different granite types both of which exhibit geochemical characteristics typical of a type granites models proposed for the petrogenesis of the granitoids imply the existence of mafic rocks at depth and addition of juvenile material to the crust in central colorado at 1 1 ga

an experimental study of trace element partitioning between zircon and melt as a function of oxygen fugacity abstract the partitioning of p sc ti sr y nb the rare earth elements ree hf ta th and u between zircon and a synthetic andesitic melt was determined as a function of oxygen fugacity f o 2 over a range of fourteen log units from qfm 8 to qfm 6 where qfm is the quartz fayalite magnetite oxygen buffer at 1300 c and 1 atm using sims and la icp ms the partition coefficients of ce and eu were found to vary systematically with f o 2 relative to those of the other ree producing ce and eu anomalies similar to those that are characteristic of natural igneous zircon these anomalies coexist at terrestrial f o 2 s and were used to quantify eu 3 eu 2 eu 3 and ce 4 ce 3 ce 4 in the melt the partition coefficients of the redox invariant trivalent cations are in excellent agreement with lattice strain theory the values of d ree are related to those determined for natural samples by the expected dependence on temperature the incorporation of ree 3 in zircon was independent of the presence of p d u d th was found to vary systematically with f o 2 indicating the presence of u 4 u 5 and u 6 in the melt at terrestrial conditions d ti was independent of f o 2 despite an expectation of significant ti 3 in the most reduced experiments

s type granitic magmas petrogenetic issues models and evidence abstract despite a perception that it represents a perverse divergence it is perfectly possible to believe in the existence of s and i type granites and the implications for the nature of their protoliths and to disbelieve in the applicability of the restite unmixing model for chemical variation in granitic magmas white and chappell erected the s i classification with impeccable validity the isotopic evidence demands contrasting source reservoirs for s and i type granitic magmas however the major advance was not the classification but the recognition that highly contrasting parental materials must be involved in the genesis of granitic magmas the restite unmixing model is commonly seen as a companion to the s i classification but it is really a separate issue this model implies that the compositions of granites image those of their source rocks in a simple way however there are other equally valid models that can explain the data and none of them represents a unique solution the most cogent explanation for the high grade metasedimentary enclaves in most s type granites is that they represent mid crustal xenoliths restitic enclaves are either rare or absent inherited zircons in s type rocks are certainly restitic however the occurrence of a substantial restitic zircon population does not imply an equally substantial restitic component in the rest of the rock zircon and zirconium behaviours are controlled by disequilibrium and kinetics and zr contents of granitic rocks can rarely be used to infer magma temperatures since the dominant ages among inherited zircons in lachlan fold belt lfb s type granites are ordovician and proterozoic it seems likely that crust of this age but geochemically different from the exposed rocks not only underlies much of the lfb but also forms a component in the granite magma sources the evidence is overwhelming that the dark microgranular enclaves that occur in both s and i type granites are igneous in origin they represent globules of quenched more mafic magma mingled and modified by exchange with the host granitic magma however magma mixing does not appear to be a significant process affecting the chemical evolution of the host magmas likewise the multicomponent mixing models erected for some granitic rock suites are mathematically nonunique and in some cases violate constraints from isotopic studies s and i type magmas commonly retain their distinct identities this suggests limited source mixing limited magma mixing and limited wall rock assimilation though intermediate types certainly exist they are probably relatively minor in volume crystal fractionation probably plays the major role in the differentiation of very many granitic magmas including most s types especially those emplaced at high crustal levels or in the volcanic environment minor mechanisms include magma mixing wall rock assimilation and restite unmixing isotopic variations within plutons and in granite suites could be caused by source heterogeneities magma mixing assimilation and even by isotopic disequilibrium however source heterogeneity coupled with the inefficiency of magma mixing is probably the major cause of observed heterogeneity normal geothermal gradients are seldom sufficient to provide the necessary heat for partial melting of the crust and crustal thickening likewise fails to provide sufficient heat generally the mantle must be the major heat source this might be provided through mantle upwelling and crustal thinning and possibly through the intra and underplating of mafic magmas upper crustal extension seems to have been common in regions undergoing granitic magmatism migmatites probably provide poor analogues of granite source regions because they are mostly formed by fluid present reactions granitic magmas are mostly formed by fluid absent processes where we do see rare evidence for arrested fluid absent partial melting the melt fraction is invariably concentrated into small shear zones veinlets and small dykes thus it seems likely that dyking is important in transporting granitic magma on a variety of scales and at many crustal levels however one major missing link in the chain is the mechanism by which melt fractions in small scale segregations occurring over a wide area can be gathered and focused to efficiently feed much wider spaced major magma conduits answers may lie in the geometry of the melting zones and in the tendency of younger propagating fractures to curve toward and merge with older ones self organization almost certainly plays a role

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

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

oxygen fugacity of yanshanian granites in south china and implications for metallogeny abstract oxygen fugacity fo 2 of magmas exerts an important control on the speciation of multivalent elements in magmatic hydrothermal processes which has a great significance for mineralization this paper examines the relationships between oxygen fugacity and mineralization associated with yanshanian jurassic to cretaceous granites in south china which hosts many world class w sn cu mo au pb and zn deposits the oxygen fugacities of yanshanian granites were evaluated using published chemical compositions of biotite and the redox states were further constrained with whole rock fe 3 fe 2 as well as zircon ce 4 ce 3 ratios from the literature systematic differences in oxygen fugacity between granites related to cu au mo cu pb zn w sn and w sn mineralization and between ore bearing and barren granites were found log fo 2 values relative to nno buffer are 1 08 to 13 07 average 4 22 for cu au mo related granites 1 01 to 5 36 average 3 51 for cu pb zn related granites 1 51 to 5 68 average 3 78 for w related granites 1 70 to 3 22 average 1 71 for w sn related granites and 5 32 to 2 43 average 0 83 for sn related granites in the biotite fe 3 fe 2 mg 2 ternary and log fo 2 t diagrams the cu au mo related granites are located between the mh and nno buffers and above the mh buffer and sn and w sn related granites are centered around the nno buffer and spread toward the fmq and mh buffers whereas the cu pb zn and w related granites are plotted between the nno and mh buffers similar trends were also observed for whole rock fe 2 o 3 feo ratios and zircon ce 4 ce 3 ratios in areas of cu au mo mineralization ore bearing granites have higher oxygen fugacities than barren granites regional scale variations of oxygen fugacities coupled with changes in la sm and ba th ratios which are considered as proxies of subducted sediments and slab dehydration fluids support the distinction of two metallogenic systems in the yanshanian period in south china a jurassic system related to ne to sw subduction and a cretaceous one related to se to nw subduction of the paleo pacific plate each with a trend of decreasing oxygen fugacities in the direction of subduction

tectonics and metallogeny of mainland southeast asia a review and contribution abstract the southeast asia region is endowed with a diversity of mineral resources notably porphyry related skarn epithermal and sediment hosted orogenic gold deposits formation of these deposits was associated with a long and complex tectonic history of gondwana supercontinent break up arc magmatism backarc basin development together with arc continent and continent continent collisions that created the present day mainland se asia this paper summarizes historical and current se asian geological research and ore deposit studies here we present a new tectonic and metallogenic model for phanerozoic mainland se asia from this model we conclude that incipient arc backarc basin magmatism is the key to the formation of many important ore deposits in the truong son and loei fold belts the two major metallogenic belts in mainland se asia in addition triassic to cenozoic arc continent and continent continent collisions have led to the formation of many sediment hosted orogenic gold deposits in the sukhothai and the sibumasu terranes oblique cretaceous to recent subduction along the andaman sunda trench was responsible for gold and copper gold molybdenum porphyry and epithermal mineralization along the kawlin wutho mt popa arc in myanmar in the north and the sumatran volcanic arc in the south we anticipate that the present emphasis on exploring for shallower level epithermal deposits will increasingly lead to exploration for deeper level porphyry and porphyry related skarn systems in the coming decades

paleomagnetism of the late precambrian coldwell complex ontario canada abstract the coldwell complex is a large multiphase alkaline intrusion on the north shore of lake superior it was emplaced into archean metavolcanics of the superior province in at least three distinct magmatic episodes during the late precambrian giving isotopic ages ranging from 1010 to 1188 ma detailed af and thermal demagnetization was done on 416 specimens from 33 sites representing all petrologic phases additional data are included from an unpublished 1972 study by w a robertson the oldest magnetic component pca was found in 19 episode i sites with a reversed mean direction of d 121 0 i 70 9 104 95 3 3 its pole position falls on the keweenawan apwp at an age of 1109 5 ma the second component pcb was found in 11 sites with a normal mean of d 301 8 i 60 1 49 95 5 8 that indicates an age of 1103 5 ma the youngest component pcc was found in nine episode iii sites and gives a reversed mean of d 119 1 i 54 3 101 95 5 1 that indicates an age of 1095 5 ma the assigned ages agree closely with recent u pb zircon ages but are distinctly older than the k ar and rb sr ages these paleomagnetic results require some changes in existing models for the petrologic evolution of the complex and indicate a much more rapid three stage cooling history than previously postulated they also provide strong evidence against the proposed concept of an asymmetrical geomagnetic field in middle keweenawan time

jurassic intraplate magmatism in southern hunan eastern guangxi 40ar 39ar dating geochemistry sr nd isotopes and implications for the tectonic evolution of se china the mesozoic geology of se china is characterized by intensive and widespread magmatism however the tectonic regime that accounted for the mesozoic magmatism has been an issue with little consensus a comprehensive study of ar 40 ar 39 dating geochemistry and sr nd isotopes has been conducted on basalts from southern hunan and syenite intrusions from eastern guangxi three episodes of jurassic magmatism i e alkaline basalts of c 175 ma in age syenitic intrusions of c 160 ma and high mg basalts of c 150 ma are identified the older c 175 ma alkaline basalts are characterized by low sr i sr 0 7035 0 7040 and high nd epsilon nd t 5 to 6 isotopic compositions and oib like trace element patterns e g nb la 1 in contrast the younger c 150 ma high mg basalts have high sr i sr c 0 7054 and low nd epsilon nd t c 2 isotopic compositions and incompatible trace element patterns of arc affinity the c 160 ma syenitic intrusions display a relatively large range of sr and nd isotopic compositions i sr 0 7032 0 7082 epsilon nd t 5 5 to 4 1 with the qinghu syenites having the lowest i sr highest epsilon nd t and oib type incompatible trace element patterns analogous to the c 175 ma alkaline basalts such a secular variation in rock types and geochemical and isotopic characteristics reveals changes in melt segregation depth and mantle sources which are inferred to have resulted from the post indosinian orogenic lithosphere extension and thinning the c 175 ma alkaline basalts are suggested to have formed by small degrees of decompression melting of the astheno sphere or an enriched lithospheric mantle source accreted by asthenosphere derived melts during the initial extension the c 160 ma syenitic and c 150 ma high mg basaltic rocks mainly originated from the enriched lithospheric mantle that melted owing to a raised geotherm caused by lithosphere thinning this interpretation is at odds with the active continental margin related to the subduction of palaeo pacific plate but consistent with continental rifting and extension for the mesozoic of se china

a hybrid origin for the qianshan a type granite northeast china geochemical and sr nd hf isotopic evidence abstract major and trace element whole rock sr and nd isotope and zircon hf isotope data are reported for a suite of a type granites and mafic microgranular enclaves from the early cretaceous 126 2 ma qianshan pluton liaodong peninsula northeast china with the aim of investigating the sources and petrogenesis of a type granites the qianshan pluton includes hornblende alkali feldspar granite graphic biotite granite and mafic microgranular enclaves the hornblende alkali feldspar granites have high sio 2 fe 2 o 3t mgo k 2 o na 2 o rb zr and lree contents and low ba and sr concentrations with strongly negative eu anomalies their high rb sr 87 rb 86 sr 16 76 24 15 and initial 87 sr 86 sr ratios 0 7215 to 0 7283 negative e nd t values 14 1 to 16 5 and zircon e hf t values 18 9 to 11 5 indicate they were mainly derived from a crustal source but with involvement of high e nd t and e hf t materials graphic biotite granites have similar geochemical features and sr nd hf isotopic compositions to enclaves indicating they were the result of crystal fractionation of evolved mafic magmas but with involvement of low e nd t and e hf t materials the mafic enclaves have an igneous texture and contain acicular apatite suggesting quenching of mafic magmas that have co mingled with the host granites they have low initial 87 sr 86 sr ratios 0 7097 0 7148 negative e nd t 14 5 to 11 9 and zircon e hf t 17 1 to 6 9 values and are enriched in liles and lrees and depleted in hfses when coupled with the high mgo mg up to 54 this indicates derivation from an enriched lithospheric mantle source but contaminated by crustal materials geochemical and sr nd and zircon hf isotopic compositions rule out simple crystal liquid fractionation or restite unmixing as the major genetic link between enclaves and host rocks instead magma mixing of mantle derived mafic and crustal derived magmas coupled with crystal fractionation is compatible with the data this example shows that at least some a type granites formed through a complex process involving mantle and crustal derived magma mixing crystal fractionation and infracrustal melting

implications for timing of andean uplift from thermal resetting of radiation damaged zircon in the cordillera huayhuash northern peru abstract the cordillera huayhuash is a north south oriented range along the drainage divide of the northern peruvian andes the range has high topography with peaks in excess of 5500 m and the second highest peak in peru nevados yerupaja 6617 m bedrock is dominated by folded mesozoic miogeoclinal rocks unconformably overlain by mid tertiary volcanics intruded by late tertiary granitic rocks and silicic dikes zircon fission track zft and u th he zhe dating of zircons along a west east transect elucidates the thermal evolution of exhumed and uplifted rocks the stability of fission tracks in zircons is a function of single grain radiation damage in samples with grain to grain variability in radiation damage resetting results in variable resetting and multiple age populations low retentive zircons lrzs which have a partly disordered crystalline structure have significant radiation damage and a low temperature of annealing ca 180 200 c high retentive zircons hrzs which are nearly cry

generation of metaluminous a type granites by low pressure melting of calc alkaline granitoids melting experiments on two calc alkaline rocks a tonalite and a granodiorite demonstrate that shallow dehydration melting of hornblende and biotite bearing granitoids generates metaluminous a type granitic melts profuse crystallization of calcic plagioclase orthopyroxene during low pressure p 4 kbar incongruent melting explains all of the major and trace element characteristics of a type granites e g their low al ca mg sr and eu contents and high ga al and k na ratios as well as their common association with anorthositic and mangeritic rocks the residual assemblage produced during melting of the same rocks in the deep crust p 8 kbar is dominated by clinopyroxene and as a consequence most of the chemical features diagnostic of a type granites are lost the high temperatures 900 c and low h 2 o contents 4 wt that are characteristic of a type magmas are adequately explained by the h 2 o poor nature of the granitoid source materials and require neither a granulitic nor a f rich source previous attempts to explain the origin of a type granites have focused on the nature of the source material these experiments show that pressure of melting is at least as important as source composition in engendering a type melts

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

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

marathon dikes rb sr and k ar geochronology of ultrabasic lamprophyres from the vicinity of mckellar harbour northwestern ontario canada the ultrabasic lamprophyre dikes from the vicinity of mckellar harbour northwestern ontario are composed essentially of a mixture of phlogopite olivine primary carbonate spinel and apatite with associated perovskite and melilite petrologically and chemically they have strong affinities with alnoites and magmas derived from upper mantle sources in stable continental regimes rb sr isotopic studies give an isochron age of 1 65 0 12 ga 2 with an initial 87sr 86sr ratio of 0 70167 0 00036 2 this age is considerably older than the neohelikian keweenawan magmatic event associated with the development of the lake superior basin e g 950 1170 ma k ar data indicate a mean whole rock age for the dikes of 1144 ma and a pseudoisochron age of 1120 34 ma 2 these ages are thought to reflect partial degassing of phlogopite and incomplete updating of the rocks under thermal influences induced by the intrusion of the coldwell alkaline complex at 1044 ma ages of carbonatitic and alkaline rock

a review of the relationships between granitoid types their origins and their geodynamic environments abstract granitoids are divided into several types according to their mineral assemblages their field and petrographical features and their chemical and isotopic characteristics this typology complements most of the recent classifications because it is not based solely on chemical and isotopic criteria but also on the field petrographical and mineralogical criteria it thus has the advantage of distinguishing the various granitoid types in the field in most cases the proposed classification shares many similarities with the twenty most used genetic classifications of granitoids both types of peraluminous granitoids are of crustal origin the tholeiitic alkaline and peralkaline granitoids are of mantle origin and both types of calc alkaline granitoids are of mixed origin and involve both crustal and mantle materials each granitoid type is generated and emplaced in a very specific tectonic setting each stage of the wilson cycle is characterised by typical associations of granitoids well typed and precisely dated granitoids can then complement structural approaches and indicate on the geodynamic environment with reference to some case studies the use of granitoids as tracers of the geodynamic evolution is also proposed and discussed

rutile saturation in hydrous siliceous melts and its bearing on ti thermometry of quartz and zircon the tio2 solubility of rutile saturated hydrous siliceous melts has been investigated at p 1 gpa and t 650 1000 c for several representative felsic compositions the dissolution of a rutile crystal into a tio2 undersaturated melt provides information on both tio2 solubility and ti diffusion results of this study confirm that tio2 solubility is strongly dependent on both temperature and melt composition but not on the amount of h2o present for a given t t io2 content decreases as the melts become more felsic the solubility of tio2 is given by log ti ppm 7 95 5305 t 0 124fm

on ferroan a type granitoids their compositional variability and modes of origin we recognize eight types of ferroan granitoid that can be distinguished on the basis of major element chemistry these include alkalic granitoids that may be metaluminous or peralkaline alkali calcic granitoids that may be metaluminous peraluminous or peralkaline calc alkalic granitoids that may be metaluminous or peraluminous and rare calcic ferroan granitoids these granitoids may form by two distinct end member processes extreme differentiation of basaltic melts results in ferroan granitoids that are either peralkaline alkalic and alkali calcic or metaluminous alkalic alkali calcic and calc alkalic with alkalinity increasing with increasing pressure of differentiation partial melting of tonalitic to granodioritic crust produces alkali calcic to calc alkalic granitoids that are metaluminous at low pressures and peraluminous at high pressures it is likely that a combination of these two processes plays some role in the formation of most ferroan granitoids most granitoids that are referred to as ferroan however the term has become more confusing than edifying because it has been applied to a broad spectrum of granitoid compositions with varying petrogenesis for this reason we recommend that the term be discontinued and ferroan used in its stead

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

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

zircon u pb ages and geochemistry of devonian a type granites in the iraqi zagros suture zone damamna area new evidence for magmatic activity related to the hercynian orogeny abstract the damamna granite dg is located in the shalair valley area in northeast iraq within the sanandaj sirjan zone ssz the zircon u pb ages for the dg rocks are 364 372 ma indicating crystallization of the granitic body the dg rocks are a type granites hypersolvus and peraluminous they are enriched in sio2 alkalis ga al ga zr and rb sr and depleted in cao mgo sr p and ti these rocks show steep ree patterns with lree enrichment relative to hree la yb n 5 7 42 5 and pronounced negative eu anomalies reflecting feldspar fractionation the geochemical characteristics and relationships suggest that the dg rocks are anorogenic and were emplaced in an extensional tectonic regime having an oib like magma affinity the dg rocks are characterized by low y nb ratios 0 2 1 5 and positive end 371 ma values 1 6 to 4 2 which indicate a mantle origin in the y nb yb ta diagram the dg rocks plot in the a1 type granite field with slightly higher y nb values and a tendency of transitioning from a1 to the nearby a2 field which possibly indicates a slight crustal contamination effect the isotopic and geochemical data suggest that a combination of enriched mantle source magma with crustal contamination and fractional crystallization contributed to the generation of the magma for the dg the geochemical and geochronological results for the dg rocks in the ssz suggest an extensional zone that probably represents an early stage of neo tethys opening during the late devonian or earlier and this was associated with the hercynian orogeny and tectono magmatic activity in northern arabia and northwestern iran

rb sr geochronology of the coldwell complex northwestern ontario canada the coldwell complex of northwestern ontario is north america s largest structurally and petrologically complex alkaline intrusion situated on the north shore of lake superior it consists of at l

active detachment faulting above the peruvian flat slab the cordillera blanca detachment fault in the peruvian andes is to our knowledge the first active detachment to be documented above a modern flat slab crustal detachment has unroofed the ca 8 ma cordillera blanca batholith now the backbone of the highest mountain range in peru large magnitude slip along the fault was thermally enhanced by emplacement of the batholith the penultimate magmatic event prior to flattening of the nazca slab however extensional models based on arc magmatism and crustal thickening alone do not adequately explain the scale or structural asymmetry of a series of young deep seated west dipping normal faults across peru here we show that the onset of detachment faulting coincided with subduction of the aseismic nazca ridge and consequent flattening of the nazca slab we propose that slab buoyancy from ridge subduction triggered extensional collapse of the prethickened continental crust and that this buoyancy drove footwall uplift that exceeds basin subsidence the west dipping asymmetry of late cenozoic extensional faults in peru may be controlled by a preexisting crustal anisotropy older thrusts and or formation of riedel like shears kinematically linked to the flat nazca slab

a gravity study of the coldwell complex northwestern ontario and its petrological significance gravity studies of the coldwell alkaline complex show that the complex is associated with a positive gravity anomaly the anomaly indicates that a significant volume of dense material occurs below the current levels of exposure of principally felsic rocks a new high resolution gravity profile used to model the infrastructure of the complex shows that the felsic rocks form a 3 5 km thick layer over a differentiated basic intrusion this intrusion is interpreted to consist of a layer of gabbro 3 5 km in thickness underlain by 3 km of peridotite and or pyroxenite intrusion of the basic magma was associated with keeweenawan continental rifting the presence of large volumes of basic magma supports the hypothesis that some of the coldwell felsic rocks were derived by differentiation of a basic parent

geochronology and magmatic oxygen fugacity of the tongcun molybdenum deposit northwest zhejiang se china the tongcun mo porphyry deposit in northwest zhejiang is hosted in three porphyry units huangbaikeng songjiazhuang and tongcun from southwest to northeast u pb zircon ages of 162 3 0 ma for the huangbaikeng porphyry 159 9 3 0 ma for the songjiazhuang porphyry and 167 6 155 6 ma for the tongcun porphyry indicate that these intrusions formed during the jurassic and are most likely associated with the northwestward subduction of the izanagi plate trace element compositions of zircons from the tongcun deposit constrain the oxygen fugacity fo2 of the magma using zircon ce anomalies and ti in zircon temperatures the average magmatic fo2 for the porphyries in the tongcun deposit is fayalite magnetite quartz fmq 2 7 which is similar to the shapinggou fmq 3 2 and dabaoshan fmq 3 5 mo porphyry deposits but much higher than that of the reduced cretaceous ore barren shangjieshou porphyry fmq 1 1 around 8 km away from the tongcun deposit the distinct difference in magmatic oxygen fugacity between the jurassic and cretaceous porphyries may help to explain the absence of mo porphyry mineralization in northwest zhejiang during the cretaceous

the relationship between a type granites and residual magmas from anorthosite evidence from the northern sherman batholith laramie mountains wyoming usa abstract anorthosite complexes commonly are spatially and temporally associated with a type granite batholiths but their genetic relationship if any has been difficult to determine this study focuses on the northern portion of the 1 43 1 44 ga sherman batholith which is located adjacent to the 1 44 ga laramie anorthosite complex laramie mountains wyoming usa the northern sherman batholith is an ideal place to resolve the relationship of a type granite with anorthosite because of the age of the crust into which it is emplaced most a type granites are intruded into crust only slightly older than the granites themselves and there is little isotopic contrast between potential mantle and crustal source rocks the northern sherman batholith intrudes archean crust that by 1 44 ga had developed nd sr and pb isotopic compositions that differed greatly from contemporaneous mantle the northern sherman batholith is an iron enriched metaluminous alkalic to alkali calcic batholith most of the batholith is composed of fayalite granite with minor volumes of monzodiorite and olivine gabbro hypabyssal dikes of these compositions crop out in the highest structural levels exposed in the area the northern sherman batholith is less differentiated and has assimilated less felsic crust than the southern portions which intrude more fertile proterozoic crust northern sherman batholith rocks are compositionally and isotopically very similar to monzonitic and dioritic rocks of the laramie anorthosite complex none of these rocks have isotopic compositions similar to their archean host rocks precluding derivation solely from such sources instead northern sherman batholith granites like laramie anorthosite complex rocks are related to mantle derived tholeiitic magmas emplaced at the base of the crust the tectonic environment and magmatic processes that lead to the formation of massif anorthosite are also conducive to the formation of voluminous a type granite of which the northern sherman granite is a prime example

petrogenesis of malaysian granitoids in the southeast asian tin belt part 2 u pb zircon geochronology and tectonic model in our complementary geochemical study part 1 the malaysian granitoids of the southeast asian tin belt were divided into a middle permian to late triassic i type dominated eastern province indochina terrane and a triassic to early jurassic transitional i s type main range province sibumasu terrane separated by the bentong raub suture zone which closed in the late triassic previous geochronology has relied on only a few u pb zircon ages together with k ar and whole rock rb sr ages that may not accurately record true magmatic ages we pre sent 39 new high precision u pb zircon ion microprobe ages from granitoids and vol canics across the malay peninsula our results show that ages from the eastern province granitoids span 289 220 ma with those from the main range province granitoids being entirely late triassic spanning 227 201 ma a general westerly younging magmatic trend across the malay peninsula is considered to refl ect steepening and roll back of the bentong raub subduction zone during progressive closure of paleo tethys the youngest ages of subduction related granites in the eastern province roughly coincide with the youngest ages of marine sedimentary rocks along the paleo tethyan suture zone our petrogenetic and u pb zircon age data support models that relate the eastern province granites to pre collisional andean type magmatism and the western main range province granites to syn and post collisional crustal melting of sibumasu crust during the late triassic tin mineralization was mainly associated with the latter phase of magmatism two alternative tectonic models are discussed to explain the triassic evolution of the malay peninsula the fi rst involves a second late triassic to jurassic or early cretaceous east dipping subduction zone west of sibumasu where subduction related hornblende and biotite bearing granites along sibumasu are paired with main range crustal melt tinbearing granites analogous to the bolivia cordilleran tin bearing granite belt the second model involves westward underthrusting of indochina beneath the west malaya main range province resulting in crustal thickening and formation of tin bearing granites of the main ranges cretaceous granitoids are also present locally in singapore ubin diorite on tioman island in the noring pluton of the stong complex eastern province and along the sibumasu terrane in southwest thailand and burma myanmar refl ecting localized crustal melting

isotopic and paleomagnetic constraints on the mesozoic tectonic evolution of south china in order to better constrain the paleogeographic evolution of south china we measured sm nd and rb sr isotopic compositions for 23 mesozoic granites that crop out throughout the area tightly grouped neodymium depleted mantle model ages 1 4 0 3 ga suggest the region is underlain by relatively homogeneous proterozoic crust and fail to define crustal provinces neither the isotopic nor geologic data suggest that a mesozoic suture exists however granites possessing anomalously high sm 8 ppm and nd 45 ppm concentrations relatively high initial epsilon neodymium 4 to 8 and high but variable initial 87sr 86sr 0 759 to 0 713 form a northeast trending zone that coincides with two prominent mesozoic basins southeast of the zone lie the majority of mesozoic intrusives and upper triassic to lower cretaceous extensional basins found in south china mesozoic paleomagnetic poles are well clustered northwest of the zone pre cretaceous poles southeast of it are discordant with respect to those from the northwest the only recognized tectonostratigraphic terrane in south china lies southeast of the zone the terrane is bordered by a northeast trending sinistral fault that was active in the mesozoic other faults in south china have similar attitudes ages and sense of shear together the observations suggest that the mesozoic tectonic regime in south china consisted of strike slip activity plus concomitant rifting as terranes or fragments of similar crust were transported north along sinistral faults the zone defined by the granites enriched in nd and sm demarcates displaced terranes to the southeast from relatively stable land to the northwest

highly fractionated jurassic i type granites and related tungsten mineralization in the shirenzhang deposit northern guangdong south china evidence from cassiterite and zircon u pb ages geochemistry and sr nd pb hf isotopes abstract the shirenzhang tungsten deposit is a classic wolframite quartz vein type deposit located in northern guangdong province eastern segment of the nanling w sn polymetallic belt the ore veins controlled by the nw striking fault system are mainly hosted in the ordovician metasedimentary rocks and can also be found with less amount in the cupola of the concealed granitic stock displaying a typical five floor vertical zonation proposed by the chinese geologists the concealed granitic stock mainly comprises two intrusive facies the porphyritic biotite granite g1 in the outer zone and the medium to fine grained monzogranite g2 in the inner zone in this paper we report new cassiterite u pb ages and pb isotopes of sulfides for the shirenzhang tungsten deposit combined with new zircon u pb ages and hf isotopes elemental geochemistry and sr nd pb isotopes of the concealed granitic rocks with aims to elucidate the origin of the ore related granites and the link between the tungsten mineralization and granitic magmatism la icp ms zircon u pb dating gives the weighted mean ages of 164 2 ma for g1 and 162 4 ma for g2 respectively cassiterite from the wolframite bearing quartz vein and the drusy quartz vein yield the weighted mean ages of 164 2 ma and 160 2 ma respectively these ages suggest that both the granitic intrusion and related w sn mineralization in the shirenzhang deposit were initiated during the late jurassic ca 160 ma the shirenzhang granitic rocks are weakly peraluminous highly fractionated i type granites detailed elemental and isotopic data demonstrate that the granitic rocks were derived from partial melting of the paleoproterozoic basement rocks at a relatively shallow depth of 30 km triggered by underplating of basaltic magma and underwent extensive fractional crystallization of hornblende biotite feldspar and monazite and or allanite a continental arc setting induced by northwesterly subduction of the paleo pacific plate is suggested for the genesis of the shirenzhang i type granites the comparable pb isotopic compositions of feldspar and sulfides imply that the lead in the ore veins was of magmatic origin integrating the spatial temporal relationship between the ore veins and the concealed granitic rocks with the pb isotopes from the sulfides and granites we suggest that the tungsten mineralization is genetically linked with the concealed granitic rocks in the shirenzhang deposit fractional crystallization and melt fluid interaction may play an important role on the formation of the granite related tungsten mineralization

u pb geochronology of the coldwell complex northwestern ontario canada reply the coldwell complex gives a u pb zircon age of 1188 56 ma a u pb tritomite age of 1126 6 ma and a pb pb potash feldspar age of 1139 55 ma these ages are all significantly older than the previously published rb sr and k ar ages we interpret these ages as follows 1 emplacement of the complex at 1188 ma as part of the initial stages of the keweenawan rifting event at depth 2 slow cooling leading to closure of the u and pb systems in tritomite and potash feldspar between 1139 and 1126 ma and 3 continued slow cooling leading to closure of the rb sr system in the complex at an average age of 1053 10 ma and of the k ar system at 1035 ma

petrology of syenites from center iii of the coldwell alkaline complex northwestern ontario canada center iii of the coldwell alkaline complex consists of metaluminous hypersolvus syenites which in order of intrusion are magnesiohornblende syenite contaminated ferro edenite syenite ferroedenite syenite and quartz syenite contaminated syenites were formed by the assimilation of coeval basaltic volcanic rocks the suite as a whole is characterized by the presence of a wide variety of amphiboles ranging in composition from magnesiohornblende through ferroedenite and ferrorichterite to arfvedsonite pyroxenes are rare and hedenbergite is present in significant amounts only in quartz syenite whole rock major element data indicate that the majority of the syenites do not represent liquid compositions the syenites have high contents of nb zr th u y and ga and have the geochemical character of a type granitoids rare earth and other trace element abundances suggest that the quartz syenites cannot be differentiates of the magma that formed the ferroedenite syenites all syenites are considered to ha

linking zircon u pb and garnet sm nd ages to date loading and metamorphism in the lower crust of a cretaceous magmatic arc swakane gneiss wa usa abstract synorogenic basin development and subsequent collapse and loading provide important constraints on the late cretaceous crustal structure of the north america cordillera high grade metasedimentary rocks of the swakane gneiss in the north cascades have been interpreted to include ca 73 ma detrital zircon that requires a protolith age considerably younger than metamorphic ages of adjacent terranes this detrital interpretation requires rapid loading rates of 7 8 mm yr heating to 750 c in garnet preserves compositional evidence for growth during high pressure amphibolite facies metamorphism and little subsequent modification new garnet rock sm nd isochrons of 73 5 1 2 71 3 2 8 and 65 8 0 7 ma tightly constrain the timing of garnet growth swakane gneiss zircons preserve complex magmatic detrital and metamorphic histories most zircons have distinct cores and homogeneous overgrowths detrital zircon cores include significant proterozoic and mesozoic components with low u th ratios homogeneous metamorphic zircon rims have high u th 5 and define an array of concordant u pb dates from 75 to 63 ma the new zircon u pb and garnet sm nd ages establish that the youngest regional metamorphism was diachronous and occurred between 75 and 63 ma our dataset precludes post 73 ma deposition and instead suggests that sedimentation occurred after ca 91 ma and ended before ca 75 ma using these age constraints for deposition and metamorphism we propose new loading rates of 1 3 mm yr and conclude that the swakane gneiss protolith was likely deposited in a small short lived intra arc basin that subsided filled in and collapsed quickly due to overthrusting of arc crust

petrogenesis and tectonic setting of the early mesozoic xitian granitic pluton in the middle qin hang belt south china constraints from zircon u pb ages and bulk rock trace element and sr nd pb isotopic compositions abstract the xitian pluton in southeast hunan province is one of the early mesozoic indosinian granitic plutons in the south china block it is composed of biotite adamellite with k feldspar megacrysts biotite adamellite and biotite granite that have u pb zircon ages of 229 9 1 4 ma 223 6 1 3 ma and 224 0 1 4 ma respectively the indosinian granitoids in the xitian pluton belong to s type granites with highly radiogenic initial 87sr 86sr ratios 0 71397 0 71910 negative end t values ranging from 10 1 to 9 4 and old nd model ages 1858 1764 ma they are enriched in radiogenic pb isotopes with 206pb 204pb t ranging from 18 130 to 18 903 207pb 204pb t from 15 652 to 15 722 and 208pb 204pb t from 38 436 to 39 037 respectively these features indicate that the granitoidswithin the xitian pluton were formed from magmas generated by remelting of metapelite and metapsammite of the paleoproterozoic metamorphic basement at temperatures of ca 800 c with low oxygen fugacity the sr nd isotopic compositions of the rocks from xitian pluton indicate that the granitic magmas were mixed with less than 10 mantle derived magmas we suggest that the xitian pluton was emplaced in an extensional tectonic setting related to release of compressional stresses within the thickened crust during the early mesozoic

in situ trace elements and sr isotopes in scheelite and s pb isotopes in sulfides from the shiweidong w cu deposit giant dahutang ore field implications to the fluid evolution and ore genesis abstract the shiweidong w cu polymetallic deposit with resources of 300 000 t wo3 and 200 000 t cu is one of the major tungsten polymetallic deposits in the giant dahutang ore field this study conducted a series of in situ analyses on scheelite and sulfides aiming to provide some new insights into the sources hydrothermal ore forming processes fluid evolution history and genesis of this deposit which is of importance to understand the formation of the super large dahutang ore field quartz vein and veinlet disseminated type tungsten ore bodies are mainly hosted in neoproterozoic granodiorite and or the yanshanian porphyritic two mica granites four stages of mineralization from early to late are identified in this deposit 1 pegmatite stage 2 silicate oxide stage 3 oxide sulfide stage and 4 sulfide stage the 34sv cdt values of stage 3 chalcopyrite and pyrite are from 1 73 to 1 46 and from 1 66 to 0 31 respectively indicating a magma related hydrothermal origin the 206pb 204pb 2067pb 204pb and 208pb 204pb ratios of pyrite range from 18 169 to 18 295 15 650 to 15 679 and 38 496 to 38 525 respectively revealing a crust origin for the pb trace element compositions of scheelite show that the both stage 2 scheelite scheelite ii and stage 3 scheelite scheelite iii have high contents of nb and rees the scheelite ii has a narrow range of the y ho ratios 16 2 31 0 obviously negative eu anomalies eu eu 0 04 0 46 and relatively low 87sr 86sr ratios of 0 72640 0 73336 whereas scheelite iii shows variable y ho ratios of 20 6 96 9 positive eu anomalies eu eu 1 31 7 11 and relatively high 87sr 86sr ratios of 0 73496 0 76098 these data indicated that the eu anomalies and sr isotopic compositions of scheelite ii were inherited from magmatic hydrothermal fluids whereas those of scheelite iii were sourced from modified fluids due to intense fluid rock interaction and input of meteoric fluids our data also reveal that the rees of scheelite ii and scheelite iii are mainly controlled by the substitution mechanism of 3ca2 ca 2ree3 the w rich reduced fluids and intense fluid rock interactions which could provide enough w and ca are likely the key factors for the formation of scheelite in the shiweidong tungsten deposit

petrogenesis of the late mesozoic guposhan composite plutons from the nanling range south china implications for w sn mineralization voluminous granite plutons were emplaced in the late mesozoic in the nanling range south china accompanied by large scale polymetallic deposits most plutons are composite composed of major phase granites and highly differentiated late stage granites previous studies have proposed fractionation of both granite types and polymetallic deposits from a common magma we choose to study the ages chemistry and nd hf isotopes of the guposhan complex from the range and propose a different model for the origin of the granite and relationship with associated polymetallic mineralization in the nanling range the major phase granites of the guposhan complex contain medium coarse grained biotite granite and hornblende bearing biotite granite with mafic microenclaves mmes emplaced at 161 1 ma on the contrary the late stage granite is fine grained with apparent zircon ages of 154 3 ma the major phase granites show large variation in chemical compositions and in whole rock nd and zircon hf isotope ratios with end t 6 0 to 1 9 and ehf t 4 5 to 1 5 respectively we suggest that their origin is attributable to a magma mixing process between felsic magma derived from melting of proterozoic basement rocks and mantle derived mafic magma the mafic magma could be represented by the parental magma of the mmes within the plutons which have low sio2 high mgo and high end t values up to 1 8 the late stage granite shows end t and ehf t values similar to the major phase granites but are chemically more evolved sio2 75 80 more reduced and water deficient and in particular are fluorine bearing numerical geochemical modeling and the petrological data indicate that the late stage granite was produced during a new thermal event rather than being produced due to fractional crystallization of the earlier major phase granite the polymetallic deposits are genetically linked with the late stage granite we suggest that a break off of the flat subducted pacific slab beneath the cathaysia block in the late mesozoic resulted in the upwelling of asthenosphere and formation of basaltic magma that underplated and triggered partial melting of the basement rocks forming felsic melts and followed by mixing of the mafic and felsic magmas in an extensional regime

solubility of cassiterite in evolved granitic melts effect of t fo2 and additional volatiles abstract the aim of this experimental study was to determine the solubility of cassiterite in natural topaz and cassiterite bearing granite melts at temperatures close to the solidus profiles of sn concentrations at glass crystal sno 2 interface were determined following the method of harrison t m watson e b 1983 kinetics of zircon dissolution and zirconium diffusion in granitic melts of variable water content contributions to mineralogy and petrology 84 66 72 the cassiterite concentration calculated at the sno 2 glass interface is the sno 2 solubility experiments were performed at 700 850 c and 2 kbar using a natural f bearing peraluminous granitic melt with 2 8 wt normative corundum slightly h 2 o undersaturated to h 2 o saturated melt compositions were chosen in order to minimize the loss of sn to the noble element capsule walls at the nickel nickel oxide assemblage ni nio oxygen fugacity buffer the solubility of cassiterite in melts containing 1 12 wt f increases from 0 32 to 1 20 wt sno 2 with an increasing temperature from 700 to 850 c at the ni nio buffer and a given corundum content sno 2 solubility increases by 10 to 20 relative to an increase of f from 0 to 1 12 wt sno 2 solubility increases by 20 relative to increasing cl content from 0 to 0 37 wt in synthetic granitic melts at 850 c we show that cl is at least as important as f in controlling sno 2 solubility in evolved peraluminous melts at oxygen fugacities close to the ni nio buffer in addition to the strong effects of temperature and f o 2 on sno 2 solubility an additional controlling parameter is the amount of excess al corundum content at ni nio and 850 c sno 2 solubility increases from 0 47 to 1 10 wt sno 2 as the normative corundum content increases from 0 1 to 2 8 wt at oxidizing conditions ni nio 2 to 3 sn is mainly incorporated as sn 4 and the effect of excess al seems to be significantly weaker than at reducing conditions

petrogenesis and tectonic significance of paleoproterozoic meta mafic rocks from central liaodong peninsula northeast china evidence from zircon u pb dating and in situ lu hf isotopes and whole rock geochemistry abstract the central liaodong peninsula is located in the northwestern part of the jiao liao ji belt in the eastern block of the north china craton surface rocks in this region are voluminous meta mafic rocks which mainly comprise amphibolite and metamorphic gabbro or diabase we present zircon cathodoluminescence images u pb dates and lu hf isotope data as well as whole rock geochemical data for these rocks in order to constrain the tectonic nature and evolution of the jiao liao ji belt zircons from these meta mafic rocks can be divided into two groups with one having a typical magmatic origin and the other a metamorphic origin zircon u pb dating and lu hf isotopic results show that the magmatic zircons have two peak ages at 2503 and 2154 ma with the former have hf 7 1 to 8 1 and single stage model ages t hf 2 50 2 55 ga indicating that these captured or inherited zircons formed at ca 2 50 ga by partial melting of coeval juvenile crust the younger magmatic zircons have hf 3 2 to 9 6 mainly varying from 7 4 to 9 6 average 8 7 and t hf 2 15 2 34 ga peak at 2 19 ga suggesting that the meta mafic rocks were emplaced at ca 2 15 ga and derived by partial melting of depleted mantle the metamorphic zircons yield a peak age of 1897 ma and have hf 4 5 to 6 8 these zircons can be further divided into three groups on the basis of hf isotope data i e hf 4 5 to 2 3 0 6 to 1 0 and 3 1 to 6 8 t hf 2 39 2 54 2 26 2 39 and 2 03 2 11 ga respectively indicating they were derived by reworking of neoarchean paleoproterozoic ancient crust and some paleoproterozoic juvenile crust thus there existed two crustal growth events at 2 50 and 2 15 ga and one reworking event at ca 1 90 ga in the eastern block geochemical data show that these meta mafic rocks are characterized by sio 2 47 3 49 8 wt tio 2 0 97 1 59 wt k 2 o 0 39 1 95 wt na 2 o k 2 o 1 03 4 85 mg 39 52 cr 29 247 ppm and ni 24 4 73 4 ppm these features combined with low total rare earth element concentrations ree relative enrichment in light ree significant positive rb ba k and p anomalies and depletions in high field strength elements e g nb ta and ti indicate derivation by partial melting of depleted lithospheric mantle that had been metasomatized by subduction derived fluids with little or no crustal contamination during magma ascent given our dating results and the regional geological framework we propose that the subduction in the eastern longgang block took place at least in age of 2 15 ga and that the meta mafic rocks in the central liaodong peninsula may have formed in a back arc basin however the tectonic location of this magmatic arc and its relationship with the nangrim block need to be further studied to confirm this hypothesis

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

proterozoic ferroan feldspathic magmatism abstract the proterozoic eon is characterized by an unusual abundance of ferroan feldspathic rocks that range in composition from granite to quartz syenites to feldspathoid bearing syenites three associations of ferroan rocks may be recognized on the basis of major element compositions 1 metaluminous alkalic to alkali calcic syenites and granites associated with anorthosites and iron rich basaltic rocks 2 alkaline intrusions in continental rifts and 3 calc alkalic metaluminous to peraluminous granitoid plutons that are less strongly ferroan than the other two groups the first two groups form by differentiation of tholeiitic to alkali basaltic parental magmas the third by partial melting of quartzo feldspathic crust although all three associations may form in intraplate settings only the alkaline intrusions which typically contain high incompatible trace element abundances plot entirely within the within plate granite fields on trace element discrimination diagrams processes of crustal melting and magma mixing have had a greater effect on the trace element compositions of ferroan granitoids from the other two associations causing some rocks to plot outside this field of these three associations the granitoids associated with anorthosites are the most voluminous and are essentially restricted to the proterozoic special conditions perhaps related to the presence of a long lived supercontinent under which widespread mantle upwelling took place appear required to explain the abundance of these rocks ferroan alkaline rocks although rarely preserved in archean crust are present in proterozoic and phanerozoic rifts the earliest alkaline intrusions thus may mark the establishment of rigid continents capable of rifting the formation of ferroan calc alkalic granites does not appear to be time dependent these granites have been generated throughout earth history in response to crustal melting

zircon u pb and sm nd geochronology and geochemistry of the sn w deposits in the northern guposhan ore field nanling range southern china abstract the guposhan ore field located in the central part of the nanling range and close to the giant central south peninsula tin ore belt is well known for its large scale sn w mineralization and hosts a series of middle to large scale sn w deposits in this study medium to fine grained biotite granite outcropped in the mining area have zircon u pb ages of 162 8 1 3 ma mswd 0 54 and 162 7 1 2 ma mswd 0 66 respectively these zircon ages are consistent to the sm nd isotopic age of minerals garnet hornblende clinopyroxene and orthopyroxene from the skarn type ores which is 160 4 4 8 ma mswd 1 3 these granites are characterized by high content of sio2 k2o na2o and rees and high ga al ratios indicating that they belong to highly fractionated a type granites with high k calc alkaline and aluminous peraluminous signatures the zircon lu hf isotopes of these granites have ehf t values and tdmc ages of 2 66 to 1 71 and 1 32 1 38 ga respectively combined with the previous studies it was proposed that the magma was formed by the mixing of crust mantle components ca 50 and ca 50 respectively in addition magmas are characterized by low temperatures of ca 710 c and oxygen fugacity log fo2 values of 18 5 to 16 4 formation of these granites were likely related to an intraplate extensional tectonic setting triggered by roll back of the subducted paleo pacific plate beneath the south china block scb these granites are in favor of the sn w mineralization making the guposhan ore district a large scale sn w mineralization ore field in the nanling range

geology and genesis of kafang cu sn deposit gejiu district sw china kafang is one of the main ore deposits in the world class gejiu polymetallic tin district sw china there are three main mineralization types in the kafang deposit i e skarn cu sn ores stratiform cu ores hosted by basalt and stratiform cu sn ores hosted by carbonate the skarn mainly consists of garnet and pyroxene and retrograde altered rocks these retrograde altered rocks are superimposed on the skarn and are composed of actinolite chlorite epidote and phlogopite major ore minerals are chalcopyrite pyrrhotite cassiterite pyrite and scheelite sulfur and pb isotopic components hint that the sources of different types of mineralization are distinctive and indicate that the skarn ore mainly originated from granitic magma whereas the basalt hosted cu ores mainly derived from basalt microthermometry results of fluid inclusions display a gradual change during the ore forming process the homogenization temperature of different types of inclusions continuously decreases from early to late mineralization stages the salinities and freezing temperatures exhibit similar evolutionary tendencies with the t homogenizaion while the densities of the different types keep constant the majority being less than 1 oxygen and hydrogen isotopic values o and d of the hydrothermal fluids fall within ranges of 3 1 to 7 7 with an average of 6 15 calculated at the corresponding homogenization temperature and 73 and 98 with an average of 86 5 respectively microthermometry data and h o isotopes indicate that the ore forming fluid of the kafang deposit is mainly derived from magma in the early stage and a mixture of meteoric and magmatic water in late stage molybdenite re os age of the skarn type mineralization is 83 4 2 1 ma and the stratiform ores hosted by basalt is 84 2 7 3 ma which are consistent with the la icp ms zircon age of the xinshan granite intrusion 83 1 0 4 ma the evidence listed above reflects the fact that different ore styles in the kafang deposit belong to the same mineralization system

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

noble metal abundances of late archean 2 7 ga accretion related shoshonitic lamprophyres superior province canada abstract shoshonitic magmatism occurred in transpressive geodynamic settings within the superior province during the diachronous accretion of allochthonous subprovinces over 2720 to 2680 ma which culminated in stabilization of this archean craton the dikes are interpreted to have formed from low degrees of partial melting of depleted mantle metasomatically enriched in lile and lree during a prior subduction accretion event selenium contents of the dikes range from 50 130 ppb and s from 150 1000 ppm with s se ratios of 1150 18 000 signifying open system behaviour of s during autometasomatic and late hydrothermal alteration based on the se contents and assuming magmatic s se ratios of 5 000 primary s contents of the alkaline magmas were undersaturated at 650 ppm mgo and ni are correlated and ir during evolution of the shoshonitic magmas olivine pyroxene controlled ir concentrations and probably rh platinum and palladium correlate with ti implying that these pge were controlled by timagnetite fractionation

control of magmatic oxidation state in intracontinental porphyry mineralization a case from cu mo au deposits in the jinshajiang red river metallogenic belt sw china abstract the jinshajiang red river porphyry cu mo au metallogenic belt jrmb is the most important intracontinental porphyry cu mo au mineralizing zone in the sanjiang region southwest china the belt contains a number of giant deposits including yulong 6 50 mt cu and beiya 315 t au in the northern and center parts and several small deposits in the southern part e g tongchang 0 03 mt cu mo chang anchong 0 04 mt cu mo habo 0 57 mt cu mo and chang an 31 t au in order to investigate the mechanisms controlling the variation in size of these deposits the la icp ms zircon u pb dating bulk rock geochemistry and zircon trace element analyses have been performed on the mineralization related porphyries from the tongchang district zircon u pb dating yielded concordant ages of 34 2 0 6 ma tongchang 33 7 0 8 ma chang anchong 35 7 0 5 ma habo and 34 6 1 2 ma chang an these porphyries are peraluminous with relatively high potassium contents k 2 o 4 2 5 7 wt and show shoshonitic affinities bulk rock fe 2 o 3 feo ratios vary from 0 51 to 0 97 typical of moderately oxidized to strongly oxidized magmas zircon ce 4 ce 3 values vary between 25 9 and 371 8 with a mean of 129 3 the log o 2 values vary from 20 7 to 9 6 and plot within the range of fmq fayalite magnetite quartz oxygen buffer to mh magnetite hematite oxygen buffer indicating an oxidizing parental magma the mineralized porphyries from the yulong and beiya deposits which were previous considered to have formed under the same tectonic conditions as those in the tongchang district have higher mean zircon ce 4 ce 3 values of 249 4 and 399 5 suggesting that the oxygen fugacities of the porphyries in the tongchang district is relatively lower this might imply that oxygen fugacity is an important factor that led to the differentiation of deposit size in the jrmb and that larger porphyry deposits are associated with more oxidized magmas

early jurassic a type granites in southeast china shallow dehydration melting of early paleozoic granitoids by basaltic magma intraplating abstracta type granites are widespread in most orogenic belts and their petrogenesis has played an important role in reconstructing orogenic events however their sources even today are a subject of considerable controversy at least four models have been proposed for their formation namely melting of a previously melted source fractionation of basaltic magma anatexis of crustal igneous sources and magma mixing here we present early jurassic a type granites in southeast se china as an example of a shallow ca 15 20 km depth igneous crust derived a type granite we present detailed laser ablation icp ms zircon u pb dating and major and trace element and sr nd isotopic data for these granites and assess their origin and relationship to the geodynamics of the late mesozoic extensive magmatism in se china the associated granites include the zhaibei keshubei zhulanbu and guangze plutons which were emplaced during the interval 191 188 ma and occur in a northeast trending belt parallel to