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

polymetallic epithermal fissure vein mineralization topia durango mexico part ii silver mineral chemistry and high resolution patterns of chemical zoning in veins

u th ages obtained by mass spectrometry in corals from barbados sea level during the past 130 000 years the study of the sea level record during the last glacial cycle has primarily proceeded indirectly by means of oxygen isotope measurements on foraminifera from deep sea sediments1 2 the direct approach of dating sea level indicators stagnated during the past decade mainly because the samples required to complete our knowledge of the past glaciations are below the present day sea level3 7 using the 14c ages of acropora palmata samples collected by drilling offshore the island of barbados fairbanks8 presented the first detailed chronology for the last deglaciation this radiocarbon chronology is limited to the past 30 kyr because of the short half life of 14c 5 730 yr we must therefore rely on other dating methods to obtain information for the whole last glacial cycle during the past four years 230th 234u dating of corals by thermal ionization mass spectrometry has been shown to be significantly more precise and accurate than the classical counting method9 14 we have used this technique to measure u th ages in coral samples from the barbados collection and from subaerially exposed outcrops see also ref 15 here we present results bearing on the sea level record for the past 130 000 years we conclude that the last deglaciation started 3 000 years earlier than previously thought and confirm that there were two surges in melt water8 at about 11 kyr and 14 kyr bp before present

neogene quaternary slow coastal uplift of western europe through the perspective of sequences of strandlines from the cotentin peninsula normandy france abstract the cotentin peninsula normandy france displays sequences of marine terraces and rasas the latter being wide late cenozoic coastal erosion surfaces that are typical of western european coasts in portugal spain france and southern england remote sensing imagery and field mapping enabled reappraisal of the cotentin coastal sequences from bottom to top the n cotentin sequence includes four previously recognized pleistocene marine terraces t1 to t4 at elevations

the geochemistry of carbonate replacement pb zn ag mineralization in the lavrion district attica greece fluid inclusion stable isotope and rare earth element studies strata bound carbonate replacement pb zn ag deposits in the lavrion district greece are spatially related to a late miocene granodiorite intrusion 7 10 ma and various sills and dikes of mafic to felsic composition the plaka granodiorite contains porphyry molybdenum mineralization and is locally associated with a ca fe skarn carbonate replacement deposits occur predominantly in marbles upper and lower marble of the basal unit kaesariani schists and along a major detachment fault that separates the basal unit from the upper unit orebodies are mainly strata bound carbonate replacement although sulfides also occur in veins the mineralogy of carbonate replacement deposits is dominated by base metal sulfides and sulfosalts of ag bi sn sb as and pb particularly at plaka and kamariza carbonates are intergrown with earlier formed sulfides and sulfosalts but are more abundant late in the paragenetic sequence with fluorite and barite fluid inclusion studies of sphalerite fluorite calcite and quartz in carbonate replacement deposits suggest that they were deposited from 132 to 365 c from co2 poor low to high salinity fluids 1 20 wt nacl equiv carbon and oxygen isotope compositions of calcite 13c 15 6 to 1 5 and 18o 9 2 to 17 3 intergrown with sulfides reflect variable exchange of the ore bearing fluid with the upper and lower marbles and proximity to the plaka granodiorite post archean australian shale paas normalized rare earth and yttrium patterns of the upper and lower marbles and calcite intergrown with sulfides show positive eu and negative ce anomalies as well as y ho ratios between 40 and 80 normalized rare earth and yttrium patterns of fluorite also have positive eu and negative ce anomalies such anomalies for both the carbonates and fluorite reflect the high ph or high f o2 conditions of the late stage hydrothermal fluids and the likely derivation of calcium from marine carbonates precursors of the upper and lower marbles the range of sulfur isotope compositions for sulfides 34s 4 9 to 5 3 with one outlier of 9 4 in carbonate replacement and vein deposits is due likely to a magmatic sulfur source with a contribution of reduced seawater sulfate sulfur isotope compositions of barite from carbonate replacement range from 34s 17 2 to 23 7 per mil and reflect miocene seawater sulfate values if a magmatic source of sulfur is assumed along with an average temperature of 250 c for the ore forming fluids as based on fluid inclusion studies sulfides in carbonate replacement deposits were deposited at values of log f o2 41 to 36 and a ph 5 8 to 9 1 however the range of sulfur isotope values does not rule out the possibility that sulfur in sulfides could have been produced by the reduction of seawater sulfate with no contribution from a magmatic source the carbonate replacement deposits resemble manto type sulfide deposits in mexico central colorado south korea nevada and northern greece

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

the upper mantle degree two pattern constraints from geoscope fundamental spheroidal mode eigenfrequency and attenuation measurements we have analyzed fundamental spheroidal mode spectra obtained from very long period geoscope records in terms of global distribution of eigenfrequencies and attenuation with a new data set and a different data processing approach involving time variable filtering and the removal of higher order effects in the spectra we confirm the strong upper mantle degree two signature in the eigenfrequency data the higher frequency content of the geoscope spectra allows us to put better constraints on the depth range at which this pattern originates which appears to be somewhat shallower than was proposed before while some effect may persist down to the bottom of the transition zone the frequency signature of the strongest degree two pattern requires an s velocity heterogeneity concentrated in the depth range 300 500 km and this signature is also apparent in the distribution of q which is indicative of a probable thermal origin the data also resolve a shallow degree 2 pattern well explained by heterogeneity spanning from the surface to depths of about 300 km and associated with the distribution of tectonic provinces it is shifted by about 45 with respect to the deep degree 2 pattern and its expression in the q data is not clear

genesis of the xianghualing sn pb zn deposit south china a multi method zircon study abstract the xianghualing sn pb zn deposit is situated near the center of the world class nanling w sn ore belt associated with the highly evolved laiziling granite of jurassic age previous studies focused mainly on geochemical and geochronological features of the mineralization related granite whereas research on the source evolution and geochronology of the ore forming fluids has been limited we carried out precise u pb dating trace element and hf isotopic analyses on magmatic and hydrothermally altered zircons from the skarn stage and sulfide stage ores in the xianghualing deposit zircon u pb dating results from the two ore forming stages show distinct geochronological populations the skarn stage ores contain mainly magmatic and hydrothermally altered zircons in three age clusters 150 ma 220 ma and 420 ma whereas the sulfide stage ores are characterized by abundant old detrital zircons ranging from 497 to 3409 ma with a peak at 800 1000 ma this pattern may indicate that magmatic hydrothermal events in the silurian and triassic were precursors to the main sn mineralization event in the jurassic when circulation of evolved fluids through older sedimentary rocks led to pb zn mineralization the jurassic zircons exhibit high trace element contents e g hf p y nb ta th u and low ti contents eu anomalies nb ta and th u ratios which imply that the laiziling magma experienced significant plagioclase biotite and muscovite fractional crystallization and that it interacted extensively with post emplacement f rich hydrothermal fluids the positive ce anomalies of these zircons ce ce 1 0 226 indicate that the magmatic hydrothermal fluids that led to the jurassic sn mineralization event were reducing the less negative ehf t values of triassic zircons 18 7 to 2 6 compared to the silurian zircons 14 6 to 2 3 suggest more limited interaction between the mantle and the magma source region the jurassic magmatic zircons in the skarns exhibit even more negative ehf t values 30 7 to 6 7 along with tdmc model ages ranging from 1627 to 3134 ma indicating that the jurassic magma was derived from partial melting of old continental crustal basement based on the combined study of zircons in the skarns and sulfide ores we propose a three stage ore genetic model for the xianghualing sn pb zn deposit

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

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

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

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

zircon records multiple magmatic hydrothermal processes at the giant shizhuyuan w sn mo bi polymetallic deposit south china abstract the supergiant shizhuyuan w sn mo bi polymetallic deposit is located in the nanling range and is intimately related to the qianlishan granite complex intruded during the late jurassic period the complex consists of three intrusive phases porphyritic biotite granite pbg equigranular biotite granite ebg and porphyritic granite dyke in this work the distinct geochemical features of magmatic and hydrothermally altered zircons from the qianlishan complex are used to reveal the magmatic hydrothermal evolution of the deposit whole rock geochemistry and mineralogy show that ebg samples have experienced stronger fractional crystallization than pbg samples zircon u pb dating constrains the intrusive episodes at 155 153 ma and 152 ma for the pbg and ebg respectively and subsequent hydrothermal events revealed by hydrothermal zircon ages at 154 153 ma and 152 150 ma hydrothermally altered zircon and paragenetic mineral inclusions from ebg samples show textures and compositional properties suggesting they were intensely altered by a zirconium saturated aqueous fluid type 1 enriched in most trace and metallogenic elements e g zr rees hf p u th nb ta ti pb al fe mg ca mn w and sn and volatiles f cl li co2 and h2o this fluid was relatively lower in temperature pressure and oxygen fugacity average ce4 ce3 11 2 type 2 fluid represented by hydrothermally altered zircons found in pbg was depleted in trace elements and had a relatively higher temperature and pressure and low fo2 ce4 ce3 2 12 29 16 type 3 fluid as evidenced by fluid altered zircons from the greisenized granite was likely a further evolved product of the type 2 fluid given its moderate cargo of most trace elements but also with exceedingly low ce4 ce3 values 2 9 33 45 the type 3 fluids might be precursors of w sn mineralizing fluids whereas the type 1 fluids were likely to represent mature ore forming fluids which were activated during the late skarn stage but before the retrograde mineralization stage compared with the fo2 of pbg and ebg magmas calculated by non altered magmatic zircons average ce4 ce3 31 47 and 49 21 it seems that the hydrothermal fluids generated by them became more reduced during the further evolution a progressive process can thus be divided pbg type 2 type 3 ebg type 1 with the gradual accumulation of ore forming materials the enrichment of most elements in hydrothermal zircons further indicates a substitution of y rees p hf u th ti nb ta ca k fe and mn for zr4 and si4 in the zircon lattice most fluid altered zircons exhibit a similar 176hf 177hf distribution range 11 to 6 but evidently elevated 176lu 177hf and 176yb 177hf ratios with magmatic ones this indicates that three types of hydrothermal fluids were magmatic derived whereas lu and yb were highly mobile during the hydrothermal event based on the results a magmatic hydrothermal evolution model is presented for shizhuyuan zircons this research highlights the use of zircon as a powerful tool in revealing the complex magmatic hydrothermal processes and perhaps mineralization potential in highly evolved granite associated mineralization systems

the origin of the tongkeng changpo tin deposit dachang metal district guangxi china clues from fluid inclusions and he isotope systematics tongkeng changpo is the largest tin deposit within the giant dachang polymetallic tin ore field in guangxi southern china which is part of a large skarn system associated with cretaceous granitoids the tongkeng changpo mineralization consists of veins and stockworks in the upper levels and replacement stratiform orebodies mantos at lower levels based on textural relationships three major mineralizing stages can be recognized stage i with cassiterite sulphides stannite tourmaline and quartz stage ii with cassiterite sulphides sulphosalts quartz and calcite and stage iii with calcite as the main phase the study of fluid inclusions has shown that there are two main fluid types co2 and nacl h2o homogenization temperatures are 270 to 365 c 210 to 240 c and 140 to 190 c for stages i ii and iii respectively salinities range from 1 to 7 wt nacl equiv in the early ore stage and 3 to 10 wt nacl equiv in the late stages laser raman spectroscopy indicates that the inclusion fluids in stages i and ii were of carbono aqueous composition with minor amounts of ch4 and h2s whereas those in stage iii were aqueous helium isotopic analyses of inclusion fluids indicate that the 3he 4he ratios in the ore veins are in between 1 2 to 2 9 ra ra 1 4 10 6 modern atmospheric ratio and range from 1 6 to 2 5 ra in the stratiform orebodies this range of 3he 4he ratios is significantly higher than that of crustal fluids 0 01 0 05 ra the similar characteristics of fluid inclusions and their he isotopic composition as well as age constraints indicate that the ore veins and stratiform orebodies of the tongkeng changpo deposit formed from the same hydrothermal system likely related to granite intrusions of the mesozoic yanshanian tectono thermal event in addition the high r ra ratios indicate a mantle contribution in the ore fluids

geochronology and isotopic character of ultrahigh pressure metamorphism with implications for collision of the sino korean and yangtze cratons central china the collision zone between the sino korean and yangtze cratons in central china is marked by subduction related metamorphic rocks composed of crustal protoliths these range in metamorphic grade from ultrahigh pressure eclogite to low greenschist facies the paragenesis of the ultrahigh pressure rocks coesite and diamond bearing indicates subduction to depths greater than 120 km as a result of continental collision despite extreme metamorphic conditions zircons have not undergone pb loss but rather illustrate two periods of growth crystallization between 700 and 800 ma and ultrahigh pressure metamorphism at 218 2 5 ma previous studies have predicted a time transgressive collision but age data presented in this study indicate that the collision was approximately coeval along the length of the suture u pb zircon ages of these ultrahigh pressure metamorphic rocks are 218 4 2 5 ma and 217 1 8 7 ma for the dabie mountains and shandong peninsula respectively the similar ages imply that the tan lu fault which offsets the ultrahigh pressure metamorphic rocks is a secondary feature not related to collision or subduction whole rock isotopic data show that both rb sr and u pb were open systems during metamorphism but that sm nd probably remained closed nd initial isotopes display crustal signatures indicating that the crust subducted as a coherent slab rather than becoming intercalated with mantle material at depth sm nd data in conjunction with u pb zircon dating indicate that the ultrahigh pressure rocks are not typical yangtze craton basement 2 9 ga but that they originally crystallized in a rift environment between 700 and 800 ma discrepancies between 40ar 39ar plateaus sm nd isochrons and u pb zircon ages render calculation of a p t t path unrealistic

composition and evolution of ore fluids in a magmatic hydrothermal skarn deposit the chemistry of brine vapor and low salinity fluid inclusions measured by proton induced x ray emission from the bismark skarn deposit mexico is consistent with an evolving magmatic hydrothermal system with no evidence for external fluid inputs the results support a model that invokes early phase separation of magmatic fluids into brine and vapor two phase field at high temperature and lithostatic pressure followed by the entrapment of a low salinity magmatic fluid one phase field at lower temperature and hydrostatic pressure the early brine and vapor inclusions contain high pb and zn concentrations and low cu however the vapor contains significantly more cu than the brine and was likely transported as a sulfur complex the fluid phase changes observed and behavior of cu are comparable to those of porphyry cu systems the later low salinity fluid at bismark represents a distinct pulse of magmatic fluid with a high k ca ratio in which base metals including cu were transported by chloride complexes paragenetic relationships and variations in the relative concentrations of cu pb and zn suggest that this fluid was primarily responsible for ore deposition the relative cu pb and zn concentrations in fluid inclusions at bismark are consistent with those measured from base metal ores in high temperature carbonate replacement deposits throughout mexico and suggest that the bulk metal budget of these deposits is primarily controlled by magmatic hydrothermal fluids deficient in cu

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

metallogenic model of the trepca pb zn ag skarn deposit kosovo evidence from fluid inclusions rare earth elements and stable isotope data the trepca pb zn ag skarn deposit 29 mt of ore at 3 45 pb 2 30 zn and 80 g t ag is located in the kopaonik block of the western vardar zone kosovo the mineralization hosted by recrystallized limestone of upper triassic age was structurally and lithologically controlled ore deposition is spatially and temporally related with the postcollisional magmatism of oligocene age 23 26 ma the deposit was formed during two distinct mineralization stages an early prograde closed system and a later retrograde open system stage the prograde mineralization consisting mainly of pyroxenes hd54 100jo0 45di0 45 resulted from the interac tion of magmatic fluids associated with oligocene 23 26 ma postcollisional magmatism whereas there is no direct contact between magmatic rocks and the mineralization the deposit is classified as a distal pb zn ag skarn abundant pyroxene reflects low oxygen fugacity 10 31 bar and anhydrous environment fluid inclu sion data and mineral assemblage limit the prograde stage within a temperature range between 390 and 475 c formation pressure is estimated below 900 bars isotopic composition of aqueous fluid inclusions hosted by hedenbergite d 108 to 130 18o 7 5 8 0 mn enriched mineralogy and high ree content of the host carbonates at the contact with the skarn mineralization suggest that a magmatic fluid was modified during its infiltration through the country rocks the retrograde mineral assemblage comprises ilvaite magnetite arsenopyrite pyrrhotite marcasite pyrite quartz and various carbonates increases in oxygen and sulfur fugacities as well as a hydrous character of min eralization require an open system model the opening of the system is related to phreatomagmatic explosion and formation of the breccia arsenopyrite geothermometer limits the retrograde stage within the temperature range between 350 and 380 c and sulfur fugacity between 10 8 8 and 10 7 2 bars the principal ore minerals galena sphalerite pyrite and minor chalcopyrite were deposited from a mod erately saline ca na chloride fluid at around 350 c according to the isotopic composition of fluid inclusions hosted by sphalerite d 55 to 74 18o 9 6 to 13 6 the fluid responsible for ore deposition was dominantly meteoric in origin the 34s values of the sulfides spanning between 5 5 and 10 point to a magmatic origin of sulfur ore deposition appears to have been largely contemporaneous with the retrograde stage of the skarn development postore stage accompanied the precipitation of significant amount of carbonates including the travertine deposits at the deposit surface mineralogical composition of travertine varies from calcite to siderite and all carbonates contain significant amounts of mn decreased formation temperature and depletion in the ree content point to an influence of ph neutralized cold ground water and dying magmatic system

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

a proposed new type of arsenian pyrite composition nanostructure and geological significance this report describes a new form of arsenian pyrite called as3 pyrite in which as substitutes for fe fe as s2 in contrast to the more common form of arsenian pyrite as1 pyrite in which as1 substitutes for s fe as s 2 as3 pyrite has been observed as colloformic overgrowths on as free pyrite in a hydrothermal gold deposit at yanacocha peru xps analyses of the as3 pyrite confirm that as is present largely as as3 empa analyses show that as3 pyrite incorporates up to 3 05 at of as and 0 53 at 0 1 at 0 27 at 0 22 at 0 08 at and 0 04 at of pb au cu zn ni and co respectively incorporation of as3 in the pyrite could be written like as3 y au 1 y 2 fe2 where au and vacancy help to maintain the excess charge hrtem observations reveal a sharp boundary between as free pyrite and the first overgrowth of as3 pyrite 20 40 nm thick and co linear lattice fringes indicating epitaxial growth of as3 pyrite on as free pyrite overgrowths of as3 pyrite onto as free pyrite can be divided into three groups on the basis of crystal size 8 20 nm 100 300 nm and 400 900 nm and the smaller the crystal size the higher the concentration of toxic arsenic and trace metals the yanacocha deposit in which as3 pyrite was found formed under relatively oxidizing conditions in which the dominant form of dissolved as in the stability field of pyrite is as3 in contrast reducing conditions are typical of most environments that host as1 pyrite as3 pyrite will likely be found in other oxidizing hydrothermal and diagenetic environments including high sulfidation epithermal deposits and shallow groundwater systems where probably kinetically controlled formation of nanoscale crystals such as observed here would be a major control on incorporation and release of as3 and toxic heavy metals in oxidizing natural systems

the hellenic subduction zone a tomographic image and its geodynamic implications new tomographic images of the hellenic subduction zone demonstrate slab penetration in the aegean upper mantle to depths of at least 600 km beneath greece the lower part of the slab appears to be detached at a depth of about 200 km whereas it still seems to be unruptured beneath the southern aegean schematically we derive minimum time estimates for the duration of the hellenic subduction zone that range from 26 to 40 ma this is considerably longer than earlier estimates which vary between 5 and about 13 ma

molybdenite re os and albite 40ar 39ar dating of cu au mo and magnetite porphyry systems in the yangtze river valley and metallogenic implications abstract the area of the middle lower yangtze river valley eastern china extending from wuhan hubei province to western zhenjiang jiangsu province hosts an important belt of cu au mo and fe deposits there are two styles of mineralization i e skarn porphyry stratabound cu au mo fe deposits and magnetite porphyry deposits in several nne trending cretaceous fault bound volcanic basins the origin of both deposit systems is much debated we dated 11 molybdenite samples from five skarn porphyry cu au mo deposits and 5 molybdenite samples from the datuanshan stratabound cu au mo deposit by icp ms re os isotope analysis nine samples from the same set were additionally analyzed by ntims on re os results from the two methods are almost identical the re os model ages of 16 molybdenite samples range from 134 7 2 3 to 143 7 1 6 ma 2 the model ages of the five samples from the datuanshan stratabound deposit vary from 138 0 3 2 to 140 8 2 0 ma with a mean of 139 3 2 6 ma their isochron age is 139 1 2 7 ma with an initial os ratio of 0 7 8 1 mswd 0 29 these data indicate that the porphyry skarn systems and the stratabound deposits have the same age and suggest an origin within the same metallogenic system albite 40 ar 39 ar dating of the magnetite porphyry deposits indicates that they formed at 123 to 125 ma i e 10 20 ma later both mineralization styles characterize transitional geodynamic regimes i e the period around 140 ma when the main ns trending compressional regime changed to an ew trending lithospheric extensional regime and the period of 125 115 ma of dramatic ew trending lithospheric extension

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

the last interglacial shoreline in northern brittany western france abstract shorelines of the last interglacial highstand in western france are mainly represented by rocky abrasion platforms on which fossil gravel barriers are located these coastal accumulations are scattered around islands ouessant belle ile and on the mainland they are buried by periglacial deposits consisting of successions of sandy gravelly units then heads loess and sands osl dating has allowed the first sandy gravelly layers to be dated to 90 ka and the loess and sands to 6 4 ka and 0 47 ka the comparison of the precise stratigraphy of several cross sections enables the reconstruction of the evolution of the landscape and the description of the configuration of the coastline at the end of the last interglacial

mapping the upper mantle three dimensional modeling of earth structure by inversion of seismic waveforms a method is presented for the inversion of waveform data for the three dimensional distribution of seismic wave velocities the method is applied to data from the global digital networks international deployment of accelerometers global digital seismograph network the selected data set consists of some 2000 seismograms corresponding to 53 events and 870 paths the moment tensors of the earthquakes are determined through an iterative procedure which minimizes the corrupting influence of lateral heterogeneity a global model is constructed for shear wave velocity expanded up to degree and order 8 in spherical harmonics and described by a cubic polynomial in depth for the upper 670 km of the earth s mantle although no a priori information is incorporated the model predictions reproduce much of what is known about the dispersion of mantle waves for example high phase velocities for shields low velocities at ridges and a strong degree 2 pattern for rayleigh waves since the method makes use of complete waveforms overtone data are also included it is shown that the model is reproducible in that substantially the same model can be constructed from each half of the total data set considered independently the model shows that shields and ridges are major features in the depth interval 25 250 km the ridges of the southern pacific and the larger shields persist to 350 km but the southeast indian rise is underlain by a high velocity anomaly at this depth as is much of the mid atlantic ridge at 450 650 km the major features are a broad region of high velocities incorporating south america much of the south atlantic and parts of west africa a broad region of low velocities in the central and eastern pacific high velocities in the western pacific and a low velocity anomaly beneath the red sea and the gulf of aden in the absence of a crustal correction degrees 2 and 3 show a high positive correlation with the geoid paradoxically this is largely destroyed when the distribution in crustal thickness is taken into account spherical harmonic degrees 4 7 show a significant negative correlation

reconciling fluid inclusion types fluid processes and fluid sources in skarns an example from the bismark deposit mexico the bismark deposit 8 5 mt at 8 zn 0 5 pb 0 2 cu and 50 g t ag located in northern mexico is an example of a stock contact skarn end member of a continuum of deposit types collectively called high temperature carbonate replacement deposits the deposit is hosted by massive sulfide within altered limestone adjacent to the bismark quartz monzonite stock 42 ma and the bismark fault alteration concurrently developed in both the intrusion and limestone the former contains early potassic alteration comprising k feldspar and biotite which was overprinted by kaolinite rich veins and alteration and later quartz sericite and pyrite with minor sphalerite and chalcopyrite prograde exoskarn alteration in the limestone consists of green andradite and diopside and transitional skarn comprising red brown andradite green hedenbergite and minor vesuvinite calcite fluorite and quartz the main ore stage post dates calc silicate minerals and comprises sphalerite and galena with gangue pyrite pyrrhotite calcite fluorite and quartz the entire hydrothermal system developed synchronously with faulting fluid inclusion studies reveal several distinct temporal compositional and thermal populations in pre syn and post ore quartz fluorite and calcite the earliest primary fluid inclusions are coexisting vapor rich type 2a and halite bearing type 3a type 3b contain sylvite brine inclusions 32 to 60 total wt salts that occur in pre ore fluorite trapping temperatures are estimated to have been in excess of 400 c under lithostatic pressures of 450 bar 1 5 km depth primary fluid inclusions trapped in syn ore quartz display critical to near critical behavior type 1c have moderate salinity 8 4 to 10 9 wt nacl equiv and homogenization temperatures th ranging from 351 to 438 c liquid rich type 1a and 1b calcite bearing inclusions occur as primary to secondary inclusions predominantly in fluorite and show a range in th 104 336 c and salinity 2 7 11 8 wt nacl equiv which at the higher th and salinity ranges overlap with type 1c inclusions oxygen isotope analysis was carried out on garnet quartz and calcite plus carbon isotopes in pre syn post ore and peripheral veins pre ore skarn related garnets have a 18omineral range between 3 9 and 8 4 quartz from the main ore stage range between 13 6 and 16 0 calcite from the main ore stage has 13c values of 2 9 to 5 1 and 18o values of 12 3 to 14 1 which are clearly distinct from post ore veins and peripheral prospects that have much higher 18o 16 6 27 3 and 13c 1 3 3 1 values despite the numerous fluid inclusion types only two fluid sources can be inferred namely a magmatic fluid and an external fluid that equilibrated with limestone furthermore isotopic data does not indicate any significant mixing between the two fluids although fluid inclusion data may be interpreted otherwise thus the various fluid types were likely to have formed from varying pressure temperature conditions through faulting during exsolution of magmatic fluids late stage hydrothermal fluid activity was dominated by the non magmatic fluids and was post ore

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

the 3 d shear wave structure in the mantle by overtone waveform inversion ii inversion of x waves r waves and g waves summary the 3 d upper mantle structure from the surface of the earth to a depth of about 1000 km is obtained by inverting waveforms of fundamental and higher mode surface waves minor and major arc waves of r waves g waves and x waves higher mode wave packets are used as basic data two features of the solution seem fairly robust one is the shallow structure in the upper few hundred kilometres which is strongly correlated with the age of the crust the second feature is the deep fast velocity anomaly near the western pacific indonesia philippines and mariana region and its antipodal region of south america both of which are subduction zones which forms a strong l 2 pattern simple slab models with 100 km thicknesses of 10 per cent faster velocity material do not explain such large scale fast velocity anomalies this may indicate large scale deformation of the 670 km discontinuity piling up of slabs in the upper mantle or thickening lithosphere in the lower mantle or large horizontal motions of subducted material these results are stable whether an earth model 1066a or prem is used as a starting model

geology geochemistry and age of the hukeng tungsten deposit southern china abstract the hukeng tungsten deposit located in the wugongshan area in central part of jiangxi province south china is a large scale quartz vein wolframite deposit it is hosted in the hukeng granitic intrusion based on the mineral assemblage and crosscutting relationship of the veins three mineralization stages are identified including 1 quartz wolframite stage 2 quartz fluorite wolframite stage and 3 quartz pyrite sphalerite wolframite stage the homogenization temperatures of fluid inclusions in vein quartz vary from 220 to 320 c and the salinities are from 0 to 10 wt nacl equiv corresponding densities range from 0 7 to 1 g cm 3 these features indicated that the ore forming fluids in the hukeng tungsten deposit have medium temperature low density and low salinity the 18 osmow values of quartz range from 10 8 to 14 4 with corresponding 18 o fluid values of 3 7 to 7 7 and d values of fluid inclusions of between 70 and 55 the combined isotopic data indicate that the ore forming fluids of the hukeng tungsten deposit were mainly derived from magmatic water with some minor input from meteoric water we have carried out molybdenite re os and muscovite 40 ar 39 ar dating to constrain the timing of mineralization re os dating of six molybdenite samples yielded model ages ranging from 149 1 2 0 to 150 7 3 7 ma with an average of 150 0 ma the re os analyses give a well defined 187 re 187 os isochron with an age of 150 2 2 2 ma mswd 0 60 hydrothermal muscovite yields a plateau 40 ar 39 ar age of 147 2 1 4 ma 40 ar 39 ar age is in good agreement with the re os age these ages show that the timing of tungsten mineralization occurred at about 150 ma our new data when combined with published geochronological results from the other major deposits in this region suggest that widespread w mineralization occurred in the late jurassic throughout south china

origin of high ag fahlores from the galena mine wallace idaho u s a tetrahedrite fahlores from the galena mine of the coeur d alene mining district wallace idaho have been found to be enriched in ag by the ag cu exchange reaction 1 10 cu 10 zn fe 2 sb 4 s 13 cu fahlore agsbs 2 in galena pbs galena cupbsbs 3 bournonite 1 10 ag 10 zn fe 2 sb 4 s 13 ag fahlore which occurred during cooling following fahlore mineralization this solid state reaction produced a distinct population of high ag fahlores found in galena rich samples quantitatively removed ag in an agsbs 2 component from galena and accounts for all of the bournonite mineralization this reaction has produced the most argentian fahlore yet found molar ag ag cu 0 443 in the district and forms a secondary overprint on any primary fahlore zoning that may have existed the results obtained here indicate that the galena and fahlore siderite stages of mineralization were virtually synchronous as this reaction has produced the same result despite the opposite relative age relationships of these mineralization stages exhibited in two of the mines studied multiple lines of evidence suggest a temperature between 320 and 350 c for this stage based on the ag ag cu of fahlores and fe zn partitioning between fahlore and sphalerite we estimate that fahlore compositions were frozen in by about 235 c roughly 40 c above corresponding temperatures obtained for the gold hunter vein of the lucky friday mine this result and the absence of readily detectable diaphorite pb 2 ag 3 sb 3 s 8 in the galena mine sample containing the highest ag fahlore indicate a faster cooling rate for the terrane in the vicinity of the galena mine

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

genesis of the hardat tolgoi ag pb zn deposit inner mongolia northeast china constraints from geology fluid inclusions and c o s pb isotope systematics abstract the hardat tolgoi ag pb zn deposit 4 3 mt at 3 15 pb zn and 26 4 g t ag is located in the erenhot east ujimqin polymetallic metallogenic belt on the western part of the great xing an range inner mongolia northeast china the ag pb zn mineralization mainly occurs as vein type ores hosted in argillaceous siltstone feldspar quartz sandstone with silty slate interlayers of the aobaotinghundi formation of lower devonian the hydrothermal ore forming process can be divided into three stages i e quartz pyrite arsenopyrite stage i quartz polymetallic sulfides stage ii and quartz calcite fluorite stage iii four types of fluid inclusions have been identified in the quartz bearing veins of each stage i e liquid rich two phase l type single liquid phase pw type vapor rich two phase v type and pure vapor phase pv type inclusions the fluid inclusions of stage i to iii yield homogenization temperatures of 285 407 c 202 317 c and 144 239 c with salinities of 1 2 9 2 wt nacl equiv 0 9 5 0 wt nacl equiv and 0 2 2 6 wt nacl equiv respectively the ore forming fluids at hardat tolgoi are characterized by moderate temperatures low salinities and low densities and dominated by the h2o nacl system carbon and oxygen isotope compositions of calcite demonstrate that the ore forming fluids come from a primary magmatic hydrothermal system with subsequent involvement of meteoric water at a later stage sulfur isotope analyses of sulfides yield 34sv cdt values of 1 8 to 8 7 with calculated 34sh2s values of 1 4 to 9 4 the 206pb 204pb 207pb 204pb and 208pb 204pb ratios of sulfides range from 18 141 to 18 468 15 521 to 15 617 and 38 040 to 38 377 respectively similar to those of granites from the hardat tolgoi deposit both sulfur and lead isotope data indicate that the ore forming metals were most likely derived from the magmatic reservoirs and sedimentary country rocks the available fluid inclusion results and isotope studies indicate that the pahse separation temperature decrease and fluid mixing resulted in large scale ag pb zn ore formation at hardat tolgoi

plume formation in the d double prime layer and the roughness of the core mantle boundary numerical simulations of the formation of thermal plumes in the d layer at the base of the earth s mantle show that plumes are initiated by coalescence of small scale convective instabilities within the low viscosity region immediately above the core mantle boundary cmb these instabilities support topographic roughness on the cmb having horizontal scales of 20 50 km and provide a source for scattered p waves seen as precursors to the phases pkikp and pkkp the calculated structure of fully developed plumes emerging from d consists of 5 50 cm yr 1 flow confined to 50 100 km thick vertical conduits with strongly temperature dependent viscosity plumes exhibit time dependent behaviour including upward propagating solitary conduit waves which may contribute to episodicity in hotspot volcanism

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

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

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

comparative geochemical study of scheelite from the shizhuyuan and xianglushan tungsten skarn deposits south china implications for scheelite mineralization abstract scheelite has been analyzed from the shizhuyuan and the xianglushan world class w deposits from the nanling w sn region and jiangnan w belt respectively the shizhuyuan deposit consists of proximal skarn and greisen w sn mo bi and distal pb zn ag veins the xianglushan deposit contains layer like sulfide scheelite and skarn w orebodies on granite cupolas overprinted by w greisen veins scheelite in skarn ores from the shizhuyuan contains higher concentrations of mo than those in the sulfide scheelite and skarn ores from the xianglushan deposit reflecting differences between oxidizing and reducing magmatic hydrothermal fluids under oxidizing conditions w is accompanied by mo partitions into exsolved fluids to form w mo garnet skarns whereas under reducing conditions little mo is carried by exsolved fluids to form w pyroxene skarns trace element patterns of scheelite from both deposits show negative ba sr zr and ti and positive ta anomalies rare earth element ree patterns of scheelite within skarns from the shizhuyuan deposit have negatively inclined and flat m type tetrad patterns and scheelite from the greisens displays flat and positively inclined m type tetrad patterns we infer that the fluids formed scheelite within the w skarns and greisens inherited parental magma trace element and ree characteristics depleted ba sr zr and ti enriched ta negative eu anomalies and tetrad effects whereas scheelite from sulfide scheelite veins and skarns of the xianglushan deposit also has w and mw type tetrad ree patterns the w type tetrad ree patterns are complementary to ree patterns from the renjiashan granite and the mw type tetrad ree patterns occur during a single evolutionary stage within a complex hydrothermal environment sulfide mineralization can form after or before w skarns the former like shizhuyuan deposit and the latter like xianglushan deposit the formation conditions of the latter included reducing conditions and sulfide firstly supersaturated in the melt resulting in sulfide drops which carried w aggregated on the cupolas w skarns and greisens in both deposits underwent generally successive processes related to water supersaturation in the melt following a temperature decrease and crystallization bubbles carried material changing from si and metal to si oxide complexes

orogeny and relative plate motions example of the japanese islands abstract the paleogeography of the eastern margin of asia near japan for the past 250 ma has been reconstructed on the basis of the relative motions between the oceanic plates and the eurasian plate engebretson et al 1982 and on land geology the relationships between the plate kinematics and orogeny are as follows calc alkaline magmatism is related to the presence of subduction when a plate boundary is a transform fault there is no volcanism very slow convergence rates do not give rise to magmatism migration of rft type triple junctions or ridge subduction produces forearc volcanism near the trench and also a wider volcanic zone uplift of low p t type regional metamorphic belts is related to collision episodes the uplift of the high p t blueschist belts on the contrary is not contemporaneous with them they appear to be related to the start of the subduction of a young plate after the migration of an rft type triple junction because the formation of a voluminous accretionary complex is contemporaneous with this and thrusting of this young accretionary complex beneath the uplifted metamorphic belt is often observed the underplating of the young accretionary complex beneath the older accretionary complex would be the cause of the uplift of the high p t type metamorphic belt the subduction of a young plate would thus be an important factor causing these orogenic events highly oblique convergence also results in formation of a serpentinite melange zone with fragments of blueschists presumably along a mechanical plate boundary in the forearc

alteration oxygen isotope and fluid inclusion study of the meishan iron oxide apatite deposit se china the meishan deposit 338 mt at 39 fe comprises massive ores in the main orebody and stockwork and disseminated ores along the main orebody four stages of mineralization and related alteration have been identified the second stage of mineralization which was the main stage of iron mineralization formed stringer disseminated iron ores as well as the main meishan orebody the fourth stage formed small pyrite and or gold orebodies above or alongside the main magnetite orebody stage 2 apatites have homogenization temperatures of 257 485 c and salinities of 7 3 11 wt nacleq calculated 18ofluid values of magnetite and apatite from the disseminated ores vary between 7 7 and 14 9 which is similar to values observed in the massive ores 8 1 12 9 the high 18o fluids at meishan have been interpreted as being of magmatic hydrothermal origin these fluids are indicative of the boiling of ore forming fluids quartz occurring as cavity fillings gives homogenization temperatures from 202 to 344 c with most values lying between 250 and 330 c corresponding salinities are 5 wt nacleq calculated 18ofluid values are 6 4 to 6 8 these values indicate that the lower temperature 250 330 c quartz was deposited from a cooling magmatic hydrothermal fluid stage 3 siderites contain fluid inclusions that homogenized between 190 and 310 c mainly between 210 and 290 c corresponding salinities are 4 8 wt nacleq stage 4 quartz carbonate veinlets contain fluid inclusions that homogenized at moderate to low temperatures 150 230 c and exhibit low salinities 2 10 wt nacl eq 18ofluid values of the mineralizing fluids for the quartz and calcite can be calculated to vary from 0 7 to 5 6 and 6 3 to 10 2 respectively while there is some overlap the 18o values of the fluids are generally lower than those observed in the massive and disseminated magnetite ores d values for the quartz and calcite vary between 154 and 123 and 123 and 111 respectively these values suggest late stage input of a shallow sourced isotopically light meteoric fluid at the temperature of pyrite and gold deposition the fluid inclusion and stable isotope data indicate a cooling magmatic hydrothermal system that progressed from isotopically heavy to isotopically depleted fluids as it cooled such fluid evolution is comparable with those of other kiruna type deposits worldwide

formation of anhydrous and hydrous skarn in cu au ore deposits by magmatic fluids most skarn ore deposits are characterized by two distinctly different alteration styles an early prograde stage with anhydrous minerals such as garnet and pyroxene forms from relatively high temperature hypersaline liquid a later retrograde stage with hydrous minerals such as epidote amphibole and chlorite plus sulfide ore minerals forms from lower temperature lower salinity fluids these two alteration stages commonly have been thought to reflect a dominance of magmatic and meteoric water respectively with relevance to the source of ore metals we report data from two different skarn systems one being part of the world s largest cu au resource stable isotope compositions of anhydrous and hydrous alteration minerals from both deposits indicate a magmatic source for both the prograde and retrograde stages 18o averages 5 0 per mil for garnet range 3 4 7 2 6 5 per mil for pyroxene 4 3 8 2 and 7 1 per mil for amphibole 4 3 8 7 the d values of late amphibole are more complex with magmatic values 77 to 78 for one deposit and both magmatic and lighter values for another deposit that could be explained either by magmatic degassing or by limited mixing with meteoric water we conclude that the differences in fluid composition prograde versus retrograde stages resulted from a magmatic fluid that intersected its solvus during the early stage creating vapor and hypersaline liquid whereas in the later stage this magmatic fluid did not intersect its solvus because it followed a different cooling path this late low salinity liquid only boiled once its vapor pressure curve was reached causing sulfide ore to precipitate during the retrograde stage

revisiting early middle jurassic igneous activity in the nanling mountains south china geochemistry and implications for regional geodynamics abstract early middle jurassic igneous rocks 190 170 ma are distributed in an e w trending band within the nanling tectonic belt and have a wide range of compositions but are only present in limited volumes this scenario contrasts with the uniform but voluminous middle late jurassic igneous rocks 165 150 ma in this area the early middle jurassic rocks include oceanic island basalt oib type alkali basalts tholeiitic basalts and gabbros bimodal volcanic rocks syenites a type granites and high k calc alkaline granodiorites geochemical and isotopic data indicate that alkaline and tholeiitic basalts and syenites were derived from melting of the asthenospheric mantle with asthenosphere derived magmas mixing with variable amounts of magmas derived from melting of metasomatized lithospheric mantle in comparison a type granites in the study area were probably generated by shallow dehydration related melting of hornblende bearing continental crustal rocks that were heated by contemporaneous intrusion of mantle derived basaltic magmas and high k calc alkaline granodiorites resulted from the interaction between melts from upwelling asthenospheric mantle and the lower crust the early middle jurassic magmatic event is spatially variable in terms of lithology geochemistry and isotopic systematics this indicates that the deep mantle sources of the magmas that formed these igneous rocks were significantly heterogeneous and magmatism had a gradual decrease in the involvement of the asthenospheric mantle from west to east these variations in composition and sourcing of magmas in addition to the spatial distribution and the thermal structure of the crust mantle boundary during this magmatic event indicates that these igneous rocks formed during a period of rifting after the indosinian orogeny rather than during subduction of the paleo pacific oceanic crust

large scale waveform inversions of surface waves for lateral heterogeneity 2 application to surface waves in europe and the mediterranean linear surface wave scattering theory is used to reconstruct the lateral heterogeneity under europe and the mediterranean using surface wave data recorded with the network of autonomously recording seismographs nars the waveform inversion of the phase and the amplitude of the direct surface wave leads to a variance reduction of approximately 40 and results in phase velocity maps in the period ranges 30 40 s 40 60 s and 60 100 s a resolution analysis is performed in order to establish the lateral resolution of these inversions using the phase velocity perturbations of the three period bands a two layer model for the s velocity under europe and the mediterranean is constructed the s velocity perturbations in the deepest layer 100 200 km are much more pronounced than in the top layer 0 100 km which confirms that the low velocity zone exhibits pronounced lateral variations in both layers the s velocity is low under the western mediterranean while the s velocity is high under the scandinavian shield in the deepest layer a high s velocity region extends from greece under the adriatic to northern italy several interesting smaller features such as the massif central are reconstructed one of the spectacular features of the reconstructed models is a sharp transition in the layer between 100 and 200 km near the tornquist tesseyre zone this would indicate that there is a sharp transition at depth between central europe and the east european platform the waveform inversion of the surface wave coda leads to good waveform fits but the reconstructed models are chaotic this is due both to a lack of sufficient data for a good imaging of the surface wave energy on the heterogeneities and to an appreciable noise component in the surface wave coda

the polymetallic magmatic hydrothermal xiangdong and dalong systems in the w sn cu pb zn ag dengfuxian orefield se china constraints from geology fluid inclusions h o s pb isotopes and sphalerite rb sr geochronology vein type deposits including the xiangdong w sn and dalong pb zn deposits occur in or near the dengfuxian composite granite pluton comprising predominantly triassic and minor jurassic intrusions liquid rich nacl aqueous inclusions vapor rich nacl aqueous inclusions liquid rich cacl2 nacl aqueous inclusions two phase ch4 rich inclusions three phase co2 h2o inclusions and three phase calcite bearing inclusions occur in the quartz veins at xiangdong whereas only liquid rich nacl aqueous inclusions occur at dalong the xiangdong veins formed at temperatures near 241 c from nacl cacl2 h2o ch4 co2 fluids averaging 11 4 wt nacl eq the dalong deposit formed at temperatures near 186 c from nacl h2o ch4 fluids averaging 6 2 wt nacl eq the ore forming mechanisms at xiangdong include fluid immiscibility during stage i fluid mixing during stage ii and mixing with meteoric water accompanied by cooling during stage iii the ore forming mechanisms at dalong include cooling and mixing with meteoric water oxygen and hydrogen isotopes suggest that the ore forming fluids from both deposits originated as mixtures of magmatic water with various amounts of meteoric water sulfur and strontium isotopes suggest an igneous origin for both deposits and possibly mixing with s and sr from sedimentary rock for dalong lead isotopes indicate that ore metals originated mainly from the upper crust with minor mantle contributions sphalerite from dalong gives a rb sr isochron age of 151 6 7 1 ma consistent with the mineralization age of xiangdong both the w sn and pb zn ore forming events are closely related to late jurassic magmatism which occurred in an environment of lithospheric extension and thinning

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

geometric effects of global lateral heterogeneity on long period surface wave propagation long period rayleigh waves from iranian earthquakes have large amplitude asymmetries between minor arc and major arc arrivals e g r 2 and r 3 at digital stations in the azimuth range n20 w to n60 e these asymmetries are as large as a factor of 2 at a period of 256 s and persist to periods greater than 300 s in some cases the entire rayleigh wave group arrival spanning periods from 100 to 300 s is either uniformly enhanced in amplitude or diminished to such a degree that the group arrival appears to be missing the amplitude anomalies are generally not accompanied by significant phase anomalies the irregular azimuthal distribution of the amplitude asymmetries and their occurrence for events with different focal mechanisms and epicentral separations of several hundred kilometers preclude an explanation of these observations by source complexity events in the mediterranean and nepal do not produce similar amplitude asymmetries at the same stations the anomalies are thus most likely due to focusing and defocusing propagation effects as a preliminary investigation of the effects of lateral heterogeneity of upper mantle velocity structure on long period surface wave amplitudes surface wave ray tracing calculations are performed using recently proposed global phase velocity distributions dramatic deviations from great circle paths are predicted for long propagation paths e g r 3 the particular spatial distribution of lateral velocity gradients around a given source location determines whether substantial amplitude asymmetries will be observed between minor arc and major arc arrivals and whether these will persist for sequential great circle orbits the 200 s period amplitude asymmetry observed at kip for the iranian source region r 2 4 r 3 is well predicted by the ray tracing results the absence of this anomaly for the other source regions is also predicted other observed anomalies are not all well predicted but it is clear that geometric effects can contribute significantly to the observed variations of rayleigh and love wave amplitudes this is the probable explanation for the instability of q estimates made from surface waves other source regions producing large surface wave amplitude anomalies include japan and southeastern alaska

fluid origin and structural enhancement during mineralization of the jinshan orogenic gold deposit south china the jinshan orogenic gold deposit is a world class deposit hosted by a ductile shear zone caused by a transpressional terrane collision during neoproterozoic time ore bodies at the deposit include laminated quartz veins and disseminated pyrite bearing mylonite most quartz veins in the shear zone with and without gold mineralization were boudinaged during progressive shear deformation with three generations of boudinage structures produced at different stages of progressive deformation observations of ore controlling structures at various scales indicate syn deformational mineralization fluid inclusions from pyrite intergrown with auriferous quartz have 3he 4he ratios of 0 15 0 24 ra and 40ar 36ar ratios 575 3 060 18ofluid values calculated from quartz are 5 5 8 4 and d values of fluid inclusions contained in quartz range between 61 and 75 the 13c values of ankerite range from 5 0 to 4 2 and ankerite 18o values from 4 4 to 8 0 the noble gas and stable isotope data suggest a predominant crustal source of ore fluids with less than 5 mantle component data also show that in situ fluids were generated locally by pervasive pressure solution and that widespread dissolution seams acted as pathways of fluid flow migration and precipitation the in situ fluids and fluids derived from deeper levels of the crust were focused by deformation and deformation structures at various scales through solution dissolution creep crack seal slip and cyclic fault valve mechanisms during progressively localized deformation and gold mineralization

trace elements u pb ages and hf isotopes of zircons from mesozoic granites in the western nanling range south china implications for petrogenesis and w sn mineralization abstract the e w trending nanling range located in the southern part of the south china block scb is characterized by widespread intra continental mesozoic granitoids and accompanying w sn polymetallic ore deposits detailed studies are presented on trace elements u pb ages and lu hf isotopes in zircons from the mesozoic a2 type like granitoids including the qianlishan qitianling xianghualing huashan guposhan niumiao tong an jinziling and jinjiling plutons from the western nanling range la icp ms u pb analyses of zircon indicate that these granites intruded mainly from ca 160 150 ma two types of zircon magmatic and late magmatic hydrothermal with similar ages can be distinguished based on their zircon trace element compositions the late magmatic hydrothermal zircons have high contents of metallogenic elements e g w and sn and may be closely related with the ore deposits the ehf t values of zircons from the mesozoic granitoids are mildly negative to positive indicating the reworking of both old and young crustal components the significant involvement of mesozoic juvenile mantle derived materials in the source can be excluded because of the rare occurrences of mafic rocks with radiogenic isotopic signatures in the area the average crustal residence age patterns of the mesozoic granites in the western nanling range are similar to those of the neoproterozoic magmatic rocks in the eastern part of the jiangnan orogen which may represent the neoproterozoic collisional belt between the yangtze and cathaysia blocks considering the specific isotopic and metallogenic features of the mesozoic granitoids in the study area we propose that the western nanling range may represent a western extension of neoproterozoic arc continent collisional belt in south china the mesozoic granitoids of this area may have been generated mainly by reworking of deeply buried neoproterozoic arc related volcanic sedimentary materials due to thermal perturbations triggered by the subduction of the paleo pacific plate in mesozoic time

genesis of the giant shizhuyuan w sn mo bi pb zn polymetallic deposit south china constraints from zircon geochronology and geochemistry in skarns abstract the giant shizhuyuan w sn mo bi pb zn polymetallic skarn type deposit which lies in the world famous nanling w sn metallogenic belt has a close affinity with the qianlishan granite complex previous studies focused on the qianlishan granitoids rather than relevant skarns where the evolutionary processes of skarn forming fluids mineralized fluids and sources of metals are debated this study carried out systematic epma and la icpms zircon u pb dating major and trace element and lu hf isotopic analyses for three types of skarns ore free greisen stockwork and sulfide bearing skarns at shizhuyuan the whole skarn zircons were classified into six age clusters 125 187 ma 235 ma 345 509 ma 677 772 ma 811 921 ma and 1000 ma and three genetic types detrital magmatic and hydrothermally altered among them the majority of the skarn zircons are of detrital origin 345 to 2225 ma peaking at 410 ma 710 ma and 905 ma and showing a wide range of th u ratios 0 05 7 09 they share similar characteristics of zircons hosted by devonian strata in south china suggesting the inheritance from wall rock the magmatic zircons in skarns can be further subdivided into two clusters triassic 235 ma and jurassic 150 ma which are derived from the corresponding granite ore free skarn contains only detrital zircons that have experienced the weakest alteration indicating the minor participation of granitic fluid the greisen stockwork skarn consists of both detrital zircons and jurassic magmatic hydrothermal zircons implying that granitic and stratigraphic materials may both contribute greatly to the w sn polymetallic mineralization sulfide bearing skarn includes abundant detrital zircon a few of triassic zircons but no jurassic zircons indicating that the latest sulfide mineralization was dominated by sediments rather than granitic rocks the two mineralized skarn zircons display elevated concentrations of most trace elements e g u ree ti y p nb and ta coupled with decreased si and zr which reflects strong fluid rock reaction the lowest ratios of ce ce 1 22 89 78 mean 24 13 in greisen stockwork skarn zircons reveal the most reducing environment for the main w sn mineralizing event jurassic zircons are homogeneous in 176hf 177hf 0 282352 0 282454 and ehf t 11 58 to 7 27 in well accord with local granitic rocks triassic zircons have variable ehf t 9 5 to 1 6 values suggesting more mantle input of precursor pluton before the jurassic main mineralization event based on the zircon geochronology in skarns we speculate that concealed triassic magmatism exists in the deep shizhuyuan area consequently a three stage ore forming model was established for the giant shizhuyuan deposit this study further illustrates that zircon can be used as an important indicator for ore genesis in complex metallogenic systems

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

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

effect of a global plume distribution on earth normal modes we show that a global distribution of small scale heterogeneities in the lower mantle induces both frequency splitting and amplitude scatter of low angular order modes these effects can be used in order to map the global distribution of small scale structures in the mantle such as plumes two independent datasets consisting respectively of lower mantle modes interaction coefficients and of observed amplitudes of core modes can then be used to constrain the low angular degrees of the spatial distribution and the mean size of heterogeneities allowing us to constrain the mantle structure at different scales if these heterogeneities are assumed to be plumes associated with hotspot activity the mean size of plumes obtained using the two datasets is then in good agreement with that obtained from geodetical or numerical convection studies

the effect of small scale structure on normal mode frequencies and global inversions presently very little is known about the characteristic length scales of the structures in the upper mantle in generating synthetic seismograms and in large scale inversions one usually assumes that the upper mantle is smooth so that ray theory can be used however it is known that structures in the mantle exist on a scale of a few hundred kilometers notably near subduction zones and other tectonic features in this paper a model of all the subduction zones and spreading ridges is used to investigate the effect of small scale structures on normal mode frequency shifts and on global inversions the normal mode frequency shifts for this model have the same characteristics as observed normal mode frequency shifts furthermore the global models obtained from inversions of synthetic data for the model of subduction zones and spreading ridges are similar in character to the models obtained from global inversions of real data for a realistic set of wave paths the model obtained from the synthetic inversions differs appreciably from a smoothed version of the true model this is due to an uneven path coverage and to a lesser extent due to neglecting scattering effects this means that the models obtained from global inversions of seismological data may contain appreciable artifacts

tectonics of south china key to understanding west pacific geology abstract south china is not a post caledonian platform but a composite of orogenic belts this late proterozoic mesozoic orogen is a collage of three continental fragments the three blocks are yangzi huanan and dongnanya and they are separated by the banxi nanpanjiang formerly xianggangzhe and gunanhai suture zones yangzi was separated from gondwanaland during late precambrian when an open ocean called banxi was present between the two continents tectonic processes at an active margin during sinian and early paleozoic time led to the genesis of an accretionary wedge complex the banxi melange and the huanan flysch nappes on the northern margin of huanan which was then the northern margin of the gondwana continent reorganization of plates during the devonian suspended subduction at the huanan active margin huanan was uplifted and unconformably overlain by transgressive deposits of devonian and or carboniferous age a remnant ocean the nanpanjiang sea still existed between yangzi and huanan and deep water sedimentation continued both at the southern margin of yangzi and at the northwestern margin of huanan the latter again became an active margin during late paleozoic when permian and triassic flysch sediments were deposited in foredeeps ahead of advancing nappes huanan and yangzi collided during the triassic and resulted in the deformation of the passive margin of the latter to form the yangzi deformed belt huanan was separated from a more southerly continent dongnanya in the devonian by seafloor spreading which created a late paleozoic and early mesozoic ocean gunanhai ocean a continuously deposited sequence ranging in age from devonian to triassic was laid down on the southern passive margin of huanan on the other side of the ocean the dongnanya permian strata include glacial marine deposits of gondwanaland affinity dongnanya became separated from gondwanaland during the late permian when it marched northward to be reunited with huanan the huanan passive margin sequence was deformed by folding and overthrusting after the late mesozoic collision of huanan and dongnanya scattered outcrops of the suture melange resulting from this collision occur at a few localities in coastal fujian dongnanya in our model was the mesozoic continent of southeast asia peripheral to mainland asia this may or may not have been the eastern continuation of the microcontinent sibumasu siam thailand burma malaysia sumatra the collision of dongnanya and asia gave rise not only to the gunanhai melange of coastal fujian but also to the ophiolite melanges parts of which are present in taiwan tailuko the philippines and western malaysia

mesozoic molybdenum deposits in the east qinling dabie orogenic belt characteristics and tectonic settings abstract the east qinling dabie orogenic belt accommodates the largest mo ore district in the world it contains 8 43 mt of proven mo metal reserves which accounts for 66 of the total proven chinese mo reserves the mo ore district includes 24 deposits and 12 occurrences with four major types of mo mineral systems i e porphyry porphyry skarn skarn and hydrothermal veins the latter can be further subdivided into quartz vein and carbonatite vein types although mo mineralization in the belt began in the paleoproterozoic 1680 24 to 2044 14 ma all economically significant deposits were formed during the mesozoic re os dating of molybdenite has shown that there are three episodes of mo mineralization i e late triassic 233 221 ma late jurassic to early cretaceous 148 138 ma and early to middle cretaceous 131 112 ma late triassic mo deposits developed as molybdenite quartz veins and carbonatite vein types stable isotope systematics c o s and high contents of re and sr indicate that the carbonatite mo veins are mantle derived porphyry and porphyry skarn mo mineral deposits were formed in the late jurassic to early cretaceous and early to middle cretaceous the late jurassic to early cretaceous granite porphyries that are associated with the mo deposits usually occupy less than 1 5 km2 at the surface and are situated in the east qinling area far west of china s continental margin on the other hand the early to middle cretaceous batholiths and granite porphyries with associated mo deposits are located in the dabieshan area and eastern part of the east qinling area the late jurassic to early creataceous granitoids and related mo deposits possibly formed in a back arc extensional setting of the eurasian continental margin which was probably triggered by the oblique subduction of the izanagi plate the early to middle cretaceous batholiths and granite porphyries are linked to the tectonic regime of lithospheric thinning asthenospheric upwelling and partial melting of the crust induced by a change in izanagi plate motion parallel to the continent margin in the east qinling dabie belt there are vein type pb zn ag deposits surrounding porphyry and or porphyry skarn mo w deposits forming well defined ore clusters the same spatial arrangement i e porphyry mo stockworks and outlying pb zn ag ore veins is also observed at the deposit scale thus mo porphyry stockworks and distal polymetallic veins belong to the same ore system and may reflect an outward temperature decrease from the highly fractionated granite plutons both porphyry stockworks and polymetallic veins can be used as vectors for further prospecting

mapping the lower mantle determination of lateral heterogeneity in p velocity up to degree and order 6 the data from the international seismological centre bulletins for the years 1964 1979 are used to derive a three dimensional model of lateral variations of the p velocity in the lower mantle unlike previous studies in which such perturbations were represented by a blocklike parameterization we seek the solution in the form r k 0k l 0l m 0l k r kalm cos m kblm sin m plm cos some 500 000 travel time residuals for teleseismic distances from 5000 earthquakes are used in an iterative procedure to derive the coefficients a and b the maximum k and l used are 4 and 6 respectively in each iteration in addition to solving for the three dimensional structure we also relocate all the earthquakes perturb the average travel time curve and determine station corrections for over 1000 stations particular attention is given to the problem of weighting the individual observations in order to avoid as much as possible the bias due to the uneven distribution of sources and receivers the resulting model shows a high level of perturbations just below the 670 km discontinuity and just above the core mantle boundary where the maximum perturbations reach 1 1 5 of the average velocity even for this highly smoothed model at a depth of 2000 km the rms perturbations are some 3 to 4 times lower than at either of the two boundaries the model predicts well the large scale pattern of observed travel time residuals for various source regions except for the distinct effects of the subduction zones the most striking large scale three dimensional feature of the model is a ring of high velocities circumscribing the pacific basin within a depth range from 1000 km to the core mantle boundary if the proportionality between perturbations in the velocity and temperature is assumed the derived pattern of anomalies could be consistent with a two boundary layer model of convection in the lower mantle some caution however should be exercised in interpreting the results near the 670 km discontinuity where the resolving power of our data set is limited by the lack of adequate control of the upper mantle structure at the same time a significant global increase in the level of perturbations in the lowermost mantle is established beyond question the results of dziewonski et al 1977 on the correlation between the equivalent geoid and the observed geoid for the angular order numbers 2 and 3 is confirmed but there is no significant correlation for degrees from 4 to 6 these calculations are made for the rigid earth richards and hager this issue show that introduction of finite viscosity can change the sign of a geoid anomaly in addition recent studies of lateral variations in the shear velocity reveal the presence of large scale anomalies in the upper mantle thus while the inferences made here with respect to the origin of the gravest orders of the geopotential field are not conclusive they point the way in which results from seismology can be used to address some of the basic questions of geodynamics

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

post magmatic hydrothermal circulation and the origin of base metal mineralization cornwall uk a detailed fluid inclusion study of post variscan quartz carbonate sulphide anhydrite fluorite veins hosted by palaeozoic basement porthleven menheniot cornwall and permo triassic sediments western approaches basin has identified two broad fluid types a high salinity 20 27 wt nacl low temperature 80 150 c brine is present in base metal mineralized veins hosted by palaeozoic rocks onshore and in sulphate bearing veins within the permo triassic offshore succession microthermometric data indicate that saline fluids found in the permo triassic basinal sequences have similar compositions to the base metal mineralizing fluids and confirms that such basins are likely sources for the mineralizing fluids a second hotter 200 c more dilute 0 5 wt fluid has been identified in fault hosted east west trending veins in the porthleven area it is likely that the temperatures of both the dilute and saline fluids have been affected by the local high heat producing cornubian granite batholith there is also limited evidence for fluid mixing of these two fluids which may have been responsible for base metal precipitation

holocene sea level variations and geomorphological response an example from northern brittany france in northern brittany an important geomorphological response to holocene sea level rise has been the development of coastal dunes with associated lagoons and marshes at anse du verger a marsh has formed behind a dune system which has been developing in situ for the last 4000 years the lithostratigraphy of the marsh comprises extensive peat formation with sands silts and occasional sand lenses the latter probably associated with storm surges the sequence dates from 10 320 120 bp after 3000 bp flood episodes on the marsh are more common while the upper marsh deposits can be correlated with the recent period of dune building prehistoric artifacts remains of cooking implements have been found on a cliff to the east of the marsh and are buried by washover deposits which indicates a sudden abandonment of a settlement possibly due to a storm surge soon after 2460 80 bp surge levels are proposed as a controlling factor on dune crest elevation

subduction zone thermal structure and mineralogy and their relationship to seismic wave reflections and conversions at the slab mantle interface seismological studies of the interface between downgoing slabs of subducted lithosphere and the overriding mantle provide constraints against which models of mantle and slab temperature and bulk composition can be tested these studies employing waves reflected and converted at the slab mantle interface suggest that a velocity contrast of 5 10 occurs over a distance of 10 20 km to depths of at least 350 km the authors have investigated whether such sharp contrasts can result form thermal structure compositional differences phase changes or other effects such as preferred mineral orientation using a mantle and slab temperature model a petrologic model of mantle and slab mineralogy and a data base of elastic properties of mantle and slab phrases theoretical seismic velocities were calculated and compared with the observed velocity contrast and boundary thickness constraints at 9 6 gpa and 1000c conditions modeled at the slab mantle interface at approximately 280 km depth cooler temperatures in the slab interior produce at constant composition only approximately a 1 75 v sub p increase into the slab in any of the peridotitic and eclogitic mineralogies investigated variation in v sub p among the different bulk compositions is only approximately 0 5 these contrasts are substantially lower than those obtained from the seismological studies andmore indicate that temperature and bulk compositional differences between mantle and slab are inadequate to cause the observed velocity contrasts they propose that phase transformations in mantle and slab mineralogies notably elevation of the olivine spinel phase change normally occurring at 400 km depth are important factors in these sharp contrasts other contributing effects may include preferential mineral orientation near the slab surface and at shallower depths the presence of partial melt or hydrous fluid evolved from dehydration reactions along the interface less

a review of the geodynamic setting of large scale late mesozoic gold mineralization in the north china craton an association with lithospheric thinning abstract abundant gold deposits are distributed along the margins of the north china craton ncc occurring throughout the precambrian basement and located in or proximal to mesozoic granitoids these deposits show a consistent spatial temporal association with late jurassic early cretaceous magmatism and are characterized by quartz lode or disseminated styles of mineralization with extensive alteration of wall rock their ages are mainly early cretaceous 130 110 ma and constrain a very short period of metallogenesis sr nd pb isotopic tracers of ores minerals and associated rocks indicate that gold and associated metals mainly were derived from multi sources i e the wall rocks precambrian basement and mesozoic granites and associated mafic rocks previous studies including high surface heat flow uplift and later basin development slow seismic wave speeds in the upper mantle and a change in the character of mantle xenoliths sampled by paleozoic to cenozoic magmas have been used to suggest that ancient cratonic mantle lithosphere was removed from the base of the ncc some time after the ordovician and replaced by younger less refractory lithospheric mantle the geochemistry and isotopic compositions of the mafic rocks associated with gold mineralization 130 110 ma indicate that they were derived from an ancient enriched lithospheric mantle source whereas the mafic dikes and volcanic rocks younger than 110 ma were derived from a relatively depleted mantle source i e asthenospheric mantle according to their age and sources relation to magmatism and geodynamic framework the gold deposits were formed during lithospheric thinning the removal of lithospheric mantle and the upwelling of new asthenospheric mantle induced partial melting and dehydration of the lithospheric mantle and lower crust due to an increase of temperature the fluids derived from the lower crust were mixed with magmatic and meteoric waters and resulted in the deposition of gold and associated metals

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

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

geology mineralogy geochemistry and zonation of the bajiazi dolostone hosted zn pb ag skarn deposit liaoning province china abstract the bajiazi zn pb ag skarn deposit is located in northwest liaoning province china the orebodies occur in a contact zone between yanshanian 170 177 4 ma quartz monzodiorite and middle proterozoic dolomitic marble of the gaoyuzhuang formation as well as along the nw and ns trending fault systems in carbonate wall rocks metasomatic mineralization zoning in the deposit is very pronounced from the intrusive contact zone to dolomitic marble along the nw trending fault system three ore bearing skarn zones may be distinguished magnesian skarn zone fe mo manganoan magnesian skarn zone cu s fe pb zn ag manganoan skarn zone zn pb ag magnesian skarn is composed of diopside forsterite tremolite spinel phlogopite chondrodite and serpentine accompanied by magnetite pyrite and molybdenite manganoan magnesian skarn consists mainly of manganoan diopside manganoan tremolite mangano anthophyllite and manganocummingtonite with minor spessartine and pyroxmangite the associated ore minerals are pyrite pyrrhotite and chalcopyrite with subordinate magnetite sphalerite galena and ag bearing minerals manganoan skarn is composed chiefly of spessartine pyroxmangite magnesian rhodonite manganocummingtonite and manganopyrosmalite with the associated ore minerals sphalerite galena alabandite and ag bearing minerals studies of fluid inclusions and s pb o and h isotopic compositions suggest that ore bearing fluids flowed from the deep contact zone of the intrusion in the southeast to the shallow depth in the northwest with decreasing temperatures oxidation state and increasing ph when the ore bearing fluids migrated their frontal part constantly reacted with the dolomitic carbonate wall rocks to form different types of skarn and mineralization sulfur and lead zinc were mainly derived from the deep lower crust while the middle proterozoic wall rocks may have provided most al si mg ca and mn for the formation of skarns the zonal model reflecting the variations in metallization assemblage skarn mineralogy composition 34 s isotope values and fluid inclusion characteristics can be used as a guide to exploration for zn pb ag skarn deposits

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

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

effect of sharp lateral heterogeneity on the earth s normal modes when inverting normal mode data for global large scale heterogeneity possible biases due to small scale structure are commonly ignored the authors conducted two experiments in the first one they calculated with a recently developed first order scattering formalism the effect of a simplified subduction zone model on the eigenfrequencies of the fundamental spheroidal mode branch the frequency shifts induced by this single subduction zone appear to be smaller by only a factor of 3 to 4 than shifts observed on long period seismograms or than shifts induced by existing models of global upper mantle inhomogeneity the second experiment involved a model of a hot spot plume on the core mantle boundary solving the variational problem with many coupling terms included the authors calculated the effect of such a plume on the amplitude of some low angular order modes the results suggest an effect at least as large as that due to available large scale mantle modes it thus appears that relatively small scale sharp lateral structure in different depth ranges of the earth may have an important effect on normal mode observations and that these effects may not be ignored in inversions of normal mode data

trace element and sr nd isotope geochemistry of fluorite from the xiangshan uranium deposit southeast china the trace element and sr nd isotope geochemistry of fluorite have been investigated in the xiangshan volcanic rock hosted uranium deposit in southeast china detailed sr nd isotope data of the hydrothermal fluorite closely associated with the uranium mineralization suggest that ore forming fluids were a combination of mantle derived fluid and fluids equilibrated with basement metamorphic rocks this model is consistent with previously published h o isotope data and is incompatible with meteoric water as the only ore forming fluid trace element geochemical profiles across the uranium orebody can be interpreted to reflect reaction between the host rocks and a mantle derived fluid containing high u and th with low th u ratios the mantle derived fluid is considered to have been u f and carbonate rich mixing with shallowly circulated meteoric water within the fractures of the host volcanic rocks caused dilution and cooling of the ore forming fluid and subsequent precipitation of fluorite and uranium ore