the evolution of the earth s atmosphere and oceans a model describing the evolution of the present atmosphere and hydrosphere has been developed the model is based on the following experimental parameters a the abundance of mantle fluid occluded in arkansas diamonds b the 3 1 b y age of crystallization for an arkansas usa diamond c the depth range for diamond formation about 100 to 400 km and d the age for the earth of 4 67 b y the data for all occluded fluids except h2o and co2 are interpreted in terms of a first order mechanism for degassing of the earth a rate constant of 6 5 10 10yr 1 is obtained which gives good agreement for experimental values of atmospheric n2 and 36ar the constant is slightly higher than that for decay of 40k 5 5 10 10 yr 1 and suggests that the decay of 40k might be the main driving force for all processes occurring in this region of the mantle evidence indicates that c2 and h2o exist in two phases in the low seismic velocity region of the upper mantle if true this requires a transformation of the first order rate law to a zero order rate law for these fluids this was done and with h2o 3 4 108 tons yr 1 and co2 0 5 108 tons yr 1 the experimental and calculated values agree good agreement between the calculated and experimental abundance of all fluids in the atmosphere and hydrosphere gives strong support for the validity of the theoretical model to preclude possible fortuitous agreement four additional tests over different time spans were made one with n2 two with ar and one with h2o the experimental results and theoretical values agree to within 20 for these additional tests further supporting the model

plastic deformation of metamorphic pyrite new evidence from electron backscatter diffraction and forescatter orientation contrast imaging application of new scanning electron microscope techniques to the study of deformed metamorphic pyrite reveals evidence for plastic deformation not readily recognised by more traditional methods specifically use of forescatter solid state detectors in conjunction with tilted polished specimens of pyritic ore produces high quality crystallographic orientation contrast images which map the distribution of deformation domains within grains use of electron backscatter diffraction allows quantification of the crystallographic misorientations shown by the orientation contrast images combination of these techniques shows that the pyrite studied deforms by slip on 100 and more rarely 110 systems slip is often associated with distributed rotation of up to 20 about and more rarely axes pyrites may have simple histories involving rotation about a single axis or more complex histories involving rotation about different axes and more rarely in different domains of the same pyrite grain or sequential rotations about quite different systems typically distributed rotation about followed by discrete rotation about a non crystallographic axis

the isotopic composition of radiogenic helium and its use to study groundwater movement in confined aquifers abstract the 3 he 4 he ratio for radiogenic he is shown to be primarily determined by the abundance of li and neutron absorbing elements in the host formations and is almost independent of the radioelement abundance the 3 he 4 he ratios have been computed for various li contents in rock matrices with average abundances of other elements the 3 he 4 he ratio is specific for each formation and may therefore be used to study crustal diffusion of he it is shown however that both the 3he and 4he contents of continental basements are likely to exceed those of the mantle so that diffusion of mantle he through continental crust is not likely to occur changes in the 3 he 4 he ratio for dissolved he have potential for studying groundwater movement and mixing processes atmospheric he which was dissolved at recharge is progressively diluted by radiogenic he with an isotopic ratio characteristic of the aquifer as the groundwater migrates down dip mixing proportions for formation he and atmospheric he in aquifers for which there is admixture of fracture borne water and interstitially stored water can also be estimated from isotopic measurements these processes are discussed in relation to two aquifers in eastern england

fluid inclusions and hear isotopes in pyrite from the yinjiagou deposit in the southern margin of the north china craton a mantle connection for poly metallic mineralization abstract the yinjiagou poly metallic deposit is located at the southern margin of the north china craton smncc pyrite the most economically important mineral is associated with cu mo au pb zn and ag mineralization two main mineralization stages have been identified and studied a porphyry stage including the quartz molybdenite and quartz sericite pyrite qsp veins and a vein stage including the early and the late economically most important pyrite stages three types of fluid inclusions are distinguished in quartz and pyrite including liquid rich vapor rich biphase lv and halite bearing inclusions the transmitted and infrared microthermometry produced several results 1 each of the three types of fluid inclusions is trapped in the quartz of the porphyry stage with homogenization temperatures of 335 419 c and salinities of 4 7 49 6 wt nacl equiv the coexistence of halite bearing inclusions and low density vapor rich biphase lv inclusions indicates that the fluid was boiling the boiling elevated the fe and s levels in the hyper saline fluid as reflected by the development of pyrite chalcopyrite and s daughter minerals in the halite bearing inclusions 2 the fluid in the early pyrite also displays features characteristic of boiling with homogenization temperatures of 352 400 c and salinities of 3 7 42 4 wt nacl equiv whereas the late pyrite only contains liquid rich biphase lv inclusions with homogenization temperatures of 263 354 c and salinities of 6 0 21 3 wt nacl equiv the relationship between the decreasing salinity and the corresponding decreasing homogenization temperature clearly indicates extensive mixing and dilution 3 finally the infrared calibration indicates that the impact of infrared light intensity on the microthermometric results for the yinjiagou pyrite hosted fluid inclusions is limited the he ar isotopic analysis of the fluid inclusions in the pyrite indicates two different fluid sources that involve abundant mantle input the 3he 4he ratios in the porphyry stage are relatively uniform ranging from 1 39 to 1 78 ra ra 1 39 10 6 for air corresponding to 16 22 mantle 4he contribution this relatively constant range represents the actual helium isotopic composition of the fluids emanating from the cooling intrusions at depth the range of 3he 4he ratios in the vein stage is wide varying from 0 80 to 5 26 ra corresponding to 9 65 mantle 4he the significant variation in the 3he 4he ratios in the vein stage reflects mixing between two fluids these data indicate that there are two different fluid sources and separate evolutionary processes for the porphyry and vein stages and support a multi stage mineralization model the veinlet molybdenite mineralization was induced by the boiling and associated cooling of a magma sourced fluid that emanated from intrusions at depth the qsp veins are likely to be pressure release zones and late fluid flow channels the early pyrite mineralization may be attributed to the influx of a dominantly mantle derived fluid with high 3he 4he ratio 5 26 ra which is most likely related to a later more mafic magmatic event the precipitation of the most economically important pyrite resulted from the mixing and diluting of this mantle derived fluid with a surface derived fluid additionally the high 3he 4he ratios indicate a strongly extensional setting which is most likely related to the late jurassic to early cretaceous lithospheric modification and thinning of the smncc

timing of collision of the north and south china blocks controversy and reconciliation the qinling orogen was formed by the joining of the north and south china blocks but the timing of their integration has been debated for more than a decade the controversies obviously stem from different approaches to reconstruction of the integration history two contrasting lines of evidence yield two different ages for collision of the north and south china blocks middle paleozoic and late triassic the shangdan suture within the qinling was regarded in previous studies as the trace along which the north and south china blocks collided our studies however demonstrate that there are two sutures within the qinling the well documented shangdan suture and the newly discovered mianlue suture we show in this paper that the late proterozoic to early mesozoic evolution of the qinling involved interactions between the north china block the north and south qinling orogens and the south china block the middle paleozoic collision along the shangdan suture as constrained by some evidence accreted only the south qinling orogen to the southern part i e the north qinling of the north china block contemporaneous rifting of the south china block and subsequent drifting separated the south qinling from the south china block during the middle to late paleozoic the separation of the south from the north china blocks is supported by other evidence in particular geomagnetic data evidently it was the late triassic collision of the south china block with the south qinling orogen along the mianlue suture that led to final integration of the north and south china blocks

metal fractionation between magmatic brine and vapor determined by microanalysis of fluid inclusions the major and trace element compositions of individual fluid inclusions from a range of magmatic hydrothermal ore deposits were analyzed by laser ablation inductively coupled plasma mass spectrometry to explore the behavior of ore forming components during fluid phase separation boiling in high temperature saline fluid systems data from 13 samples showing unambiguous evidence for coeval trapping of a liquid brine and a coexisting vapor phase identify two groups of elements with drastically different geochemical behavior na k fe mn zn rb cs ag sn pb and tl preferentially partition into the brine probably as cl complexes whereas cu as au probably as hs complexes and b selectively partition into the vapor fluid phase separation is probably a major previously underestimated process in the chemical differentiation that contributes to the extreme range of selective element enrichments in magmatic hydrothermal systems from deep plutons through porphyry style and greisen deposits to epithermal mineralization and volcanic fumaroles

p t x conditions of hydrothermal fluids and precipitation mechanism of stibnite gold mineralization at the wiluna lode gold deposits western australia conventional and infrared microthermometric constraints the wiluna lode gold deposits are located in the archean wiluna greenstone belt in the northern sector of the norseman wiluna belt in the yilgarn craton of western australia they are hosted in subgreenschist facies meta basalts and controlled by the wiluna strike slip fault system and associated shear veins and breccias the 13 individual lode gold deposits have produced around 115 t au from 1901 to 1946 and 1986 to today historically they also produced 38 3 t as and 3 5 t sb gold formed in two stages stage 1 gold pyrite arsenopyrite is finely disseminated in the wallrock and breccia fragments whereas stage 2 gold stibnite is located in massive shear veins and breccia matrix as fracture fill and in banded colloform textured veins stibnite gold orebodies only occur in some of the deposits e g moonlight and northern part of the west lode and also display a restricted vertical extent being preserved only in the uppermost 200 m of stibnite bearing lodes petrographic conventional and infrared microthermometric and laser raman analysis on stibnite bearing quartz veins and breccias reveal that the antimony and gold rich hydrothermal fluid was of mixed h2o nacl co2 ch4 type microthermometric measurements reveal maximum homogenization temperatures of 340 c average 290 25 c and a wide range of salinities between 0 2 and 23 eq wt nacl aqueous carbonic fluid inclusions contain variable xco2 ch4 0 03 to 0 82 with the carbonic phase containing a maximum xch4 of 0 21 combined petrographic and microthermometric evidence suggests that the fluid inclusion properties reflect fluid immiscibility of a low salinity medium xco2 ch4 homogeneous parent fluid at about 290 c and pressures between 700 and 1 700 bar fluid immiscibility was triggered by cyclic pressure release during fault zone movement the decompression adiabatic cooling of the hydrothermal fluids shifted the ore fluid to lower temperatures significantly reduced the degree of stibnite undersaturation and caused stibnite to precipitate the deposition of stibnite reduced the ore fluid h2s concentration thereby destabilized gold bisulfide complexes in solution and caused gold precipitation locally this mechanism explains the intimate spatial association of stibnite and gold in quartz veins and breccias in the stibnite gold orebodies at wiluna

geochemistry isotope systematics and petrogenesis of the volcanic rocks in the zhongtiao mountain an alternative interpretation for the evolution of the southern margin of the north china craton abstract the xiong er volcanic rocks constitute a large paleo mesoproterozoic volcanic belt along the southern margin of the north china craton which are composed primarily of basaltic andesites and andesites with minor dacites and dacitic rhyolites the basaltic andesites and andesites from the xiong er volcanic rocks in the zhongtiao mountain show consistent nd t la nb and th nb values irrespectively of sio 2 which preclude significant crustal contamination during ascent both of these volcanic rocks share similar incompatible ratios e g la sm zr nb la nb indicating that the basaltic andesites and andesites originated from the same source the basaltic andesites are characterized by high mg number 45 55 precluding the possibility of their derivation from the melting of the lower crust variable ti eu zr sm and nb la ratios for the basaltic andesites with higher partial melting degree suggest that amphiboles remained as residues in the magma source indicating that the xiong er volcanic rocks were derived from hydrous magma non radiogenic nd isotopes for the xiong er volcanic rocks are inherited from a mantle source which had been enriched by the subduction related crustal recycling during archean to paleoproterozoic time basaltic andesites show hfse enrichments especially nb 4 7 ppm and high fe ti contents comparable with nb enriched basalts suggesting that the xiong er volcanic rocks were derived from a metasomatized mantle source similar to that of nb enriched basalts therefore the mantle source of the xiong er volcanic rocks in the zhongtiao mountain has been enriched in fe ti oxides and hfse by equilibrium reactions with the slab melts during late archean and paleoproterozoic subduction processes as evidenced by nd isotopes in the primitive mantle normalized trace element diagrams the xiong er volcanic rocks show enrichments in the lile and lree and negative anomalies on the nb ta ti similar to arc related volcanic rocks produced by the hydrous melting of the metasomatized mantle wedge in the paleo mesoproterozoic the xiong er volcanic rocks in the zhongtiao mountain were produced by the slab dehydration induced melting of an existing metasomatized mantle source and the fluids from the slab dehydration introduced significant lile and lree to the source masking its inherent hfse enriched characteristics the arc related characteristics of the xiong er volcanic rocks in the zhongtiao mountain suggest the xiong er volcanic belt constructs a subduction zone along the southern margin of the north china craton in the paleo mesoproterozoic implying that the craton may have recorded the outbuilding history of the columbia supercontinent during paleo mesoproterozoic time

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

global dynamics of the antarctic ice sheet the total mass budget of the antarctic ice sheet is studied with a simple axi symmetrical model the ice sheet has a parabolic profile resting on a bed that slopes linearly downwards from the centre of the ice sheet into the ocean the mean ice velocity at the grounding line is assumed to be proportional to the water depth the accumulation rate is a linear function of the distance to the centre setting the total mass budget to zero yields a quadratic equation for the steady state ice sheet radius r analysis of the equilibrium states sheds light on the sensitivity of the ice sheet radius to changes in sea level s and precipitation with respect to the present state prel for model parameters obtained by matching the analytical model to the present state of the antarctic ice sheet the sensitivity values are dr ds 2400 and dr dprel 4000 m the model can also be used to study transient behaviour of the ice sheet the characteristic relaxation time e folding time scale is about 3500 years forcing the model with a sea level and accumulation history over the past few hundred thousands of years yields antarctic ice volume curves that are similar to those obtained by comprehensive numerical modelling the current imbalance predicted by the model corresponds to a sea level rise of 0 25 mm yr 1

fluid inclusion noble gas and halogen evidence on the origin of cu porphyry mineralising fluids the naturally occurring noble gas isotopes 40ar 36ar 84kr and 129xe and halogens cl br i have been determined simultaneously in irradiated quartz vein samples by noble gas mass spectrometry quartz vein samples were collected from the potassic and propylitic alteration zones of six porphyry copper deposits pcd bingham canyon utah and silverbell ray mission pinto valley and globe miami in arizona in addition analyses of 3he 4he have been obtained from sulphide minerals hosted by the quartz veins at silverbell ray pinto valley and globe miami the majority of pcd fluids studied have br cl and i cl ratios that overlap those of fluids included in mantle diamond suggesting that the salinity had a juvenile origin the high i cl 121 10 6 mole m in samples from the propylitic zone of silverbell is attributed to the presence of sedimentary formation water 3he 4he ratios have r ra values in the range 0 3 to 1 72 and provide evidence for the involvement of a crustal component in addition to mantle volatiles 40ar 36ar ratios vary from meteoric values of 317 in the propylitic zone of bingham canyon and 323 in the skarn alteration of mission up to 3225 in the potassic zone of pinto valley fluids in both the potassic and propylitic alteration zones of every deposit are a mixture of a low salinity end member comprising meteoric water and air and a high salinity end member consisting of a mixed mantle and crustal fluid the 40ar cl ratio of fluid inclusions at pinto valley 10 4 m is similar to values obtained previously for mantle fluids the 40ar cl value is two orders of magnitude lower at bingham canyon where a depleted 36ar concentration 0 2 10 6 cm3 g below that of air saturated water asw and a range of highly fractionated noble gas compositions f84kr 13 and f129xe 160 indicate that boiling and pulsed fluid flow have occurred

morphology origin and infrared microthermometry of fluid inclusions in pyrite from the radka epithermal copper deposit srednogorie zone bulgaria pyrite samples from the radka epithermal replacement type volcanic rock hosted copper deposit bulgaria have been studied using near infrared ir microscopy two generations of pyrite based on their textures composition and behaviour in ir light can be distinguished electron microprobe analyses x ray elemental mapping and fourier transform infrared spectroscopy were used to study the relationship between crystal zoning trace element contents and ir transmittance of pyrite the observed crystal zoning is related to variable arsenic contents in massive fine grained and colloform pyrite from the early pyrite quartz assemblage and cobalt contents in pyrite crystals from the late quartz pyrite vein assemblage there is a negative correlation between trace element content and ir transmittance of pyrite the ir transparency of pyrite is thus a sensitive indicator of changes in trace element concentrations fluid inclusions have only been found in the second pyrite generation scanning electron microscopy observations on open fluid inclusion cavities permitted the crystallographic features of vacuoles to be determined a characteristic feature of primary fluid inclusions in pyrite is a negative crystal habit shaped mainly by 100 111 and 210 this complicated polyhedral morphology is the reason for the observed opacity of some isometric primary inclusions secondary fluid inclusion morphology depends on the nature of the surface of the healed fracture recognition of the primary or secondary origin of fluid inclusions is enhanced by using crystallographically oriented sections microthermometric measurements of primary inclusions indicate that the second pyrite generation was deposited at maximum p t conditions of 400 c and 430 bar and from a fluid of low bulk salinity 3 5 4 6 wt possibly kcl dominant there are large ranges for homogenisation temperatures in secondary inclusions because of necking down processes decrepitation features of some of pyrite hosted inclusions and of all inclusions in associated quartz indicate reheating of the veins to 500 550 c the late cobalt rich quartz pyrite vein assemblage in the radka deposit may be the shallow manifestation of deeper and genetically related porphyry copper mineralisation this is a common observation of many intermediate to high sulfidation epithermal replacement type ore bodies in this ore district and possibly the cretaceous banat srednogorie metallogenic belt in general

tectonics of the qinling central china tectonostratigraphy geochronology and deformation history abstract the qinling orogen preserves a record of late mid proterozoic to cenozoic tectonism in central china high pressure metamorphism and ophiolite emplacement songshugou ophiolite assembled the yangtze craton including the lower qinling unit into rodinia during the 1 0 ga grenvillian orogeny the lower qinling unit then rifted from the yangtze craton at 0 7 ga subsequent intra oceanic arc formation at 470 490 ma was followed by accretion of the lower qinling unit first to the intra oceanic arc and then to the sino korea craton subduction then imprinted a 400 ma andean type magmatic arc onto all units north of the northern liuling unit oblique subduction created silurian devonian wnw trending sinistral transpressive wrench zones e g lo nan shang dan and late permian early triassic subduction reactivated them in dextral transpression lo nan shang xiang shang dan and subducted the northern edge of the yangtze craton exhumation of the cratonal edge formed the wudang metamorphic core complex during dominantly pure shear crustal extension at 230 235 ma post collisional south directed shortening continued through the early jurassic cretaceous reactivation of the qinling orogen started with nw se sinistral transtension coeval with large scale early cretaceous crustal extension and sinistral transtension in the northern dabie shan it presumably resulted from the combined effects of the siberia mongolia sino korean and lhasa west burma qiangtang indochina collisions and pacific subduction regional dextral wrenching was active within a ne sw extensional regime between 60 and 100 ma an early cretaceous andean type continental magmatic arc with widespread early cretaceous magmatism and back arc extension was overprinted by shortening related to the collision of yangtze indochina block with the west philippines block strike slip and normal faults associated with eocene half graben basins record paleogene nne ssw contraction and wnw ese extension the neogene is characterized by normal faults and nne trending sub horizontal extension pleistocene quaternary nw se extension and ne sw contraction comprises sinistral strike slip faults and is part of the nw se extension imposed across eastern asia by the india asia collision

coupled variations in helium isotopes and fluid chemistry shoshone geyser basin yellowstone national park abstract early studies of 3he 4he variations in geothermal systems have generally attributed these fluctuations to either differences in the source of the magmatic 3he rich helium or to local differences in the deep flux of magmatic 3he rich helium kennedy et al 1987 however show that near surface processes such as boiling and dilution may also drastically affect 3 he 4 he ratios of geothermal vapors helium isotope ratios were determined for several hot springs at shoshone geyser basin of yellowstone national park for this study along with other noble gas data stable isotope data and water and gas chemistry data for each spring were also compiled the water chemistry indicates that there is one deep hot thermal water in the area which is mixing with dilute meteoric water that has entered the system at depth spring hco3 concentrations correlate with 3 he 4 he values as in nearby lower geyser basin this correlation is attributed to variable amounts of deep dilution of thermal waters with a relatively cool water that inhibits boiling at depth thus preventing the loss of co2 and therefore hco3 and magmatic he in the most diluted samples oxygen and hydrogen isotope data also support a boiling and dilution model but to produce the observed fractionations the boiling event would have to be extensive with steam loss at the surface whereas the boiling that affected the helium isotope ratios was probably a small scale event with steam loss at depth it is possible that deep boiling occurred in the basin and that small amounts of steam escaped along fractures at about 500 m below the surface while all subsequently produced steam was lost near or at the surface

isotope systematics and fluid inclusion studies of the qiyugou breccia pipe hosted gold deposit qinling orogen henan province china implications for ore genesis abstract the qiyugou gold deposits henan province are hosted in breccia pipes within the xiong er terrane qinling orogen on the southern margin of the north china craton in these deposits three paragenetic assemblages have been recognized an early k feldspar epidote quartz pyrite a middle quartz polymetallic sulfide and a late quartz carbonate adularia in this paper we review and interpret fluid inclusion and stable and radiogenic isotopic data of host rocks and ores fluid inclusions in quartz and calcite include water rich co 2 rich and daughter crystal bearing the co 2 rich and daughter mineral bearing fluid inclusions are common in the early stage quartz and absent in the late stage quartz and calcite which only contain water rich fluid inclusions accordingly the early stage ore fluids are magmatic in origin and characterized by high temperature 350 c high salinity 30 wt nacl equiv and are co 2 rich fluid boiling in the middle ore stage resulted in co 2 release decreasing oxygen fugacity and rapid precipitation of ore materials the late stage fluids have low temperature low salinity are co 2 poor and lack daughter minerals these fluids are probably sourced from meteoric water h o c isotope systematics confirm that the ore fluid system evolved from magmatic to meteoric the carbon and lead isotope ratios indicate that the meso neoproterozoic sequence south of the xiong er terrane was the likely source of the ore forming materials the qiyugou breccia pipes and their associated gold ores were emplaced during an extensional regime following a transition from collision to rifting tectonics linked to collision and subduction of the yangtze plate beneath the north china craton geochronological studies show that mesozoic magmatism in the region occurred between the triassic and cretaceous the triassic to jurassic magmas were mostly derived from partial melting of ancient crust whereas the cretaceous magmas show juvenile signatures indicating mantle derived components processes of fragmentation of lithospheric roots crustal and lithospheric thinning extension and rifting were probably associated with the subducting pacific izanagi plate these crust mantle geodynamic processes were responsible for the development of anorogenic granitic melts that interacted with the meso neoproterozoic volatile rich sedimentary successions producing a flow of gas rich hydrothermal fluids that resulted in the emplacement of the qiyugou auriferous breccia pipes we conclude that the qiyugou gold deposits are intrusion related explosive breccia pipe type that evolved from hypothermal through mesothermal to epithermal

the role of sulfur in the formation of magmatic hydrothermal copper gold deposits abstract essential resources of many rare metals including copper zinc molybdenum silver and gold occur in natural sulfide mineral deposits understanding the origin of these metal resources has been limited by a lack of data about the geochemistry of sulfur the most important and abundant element of ore deposits we report the first directly measured sulfur concentrations in high temperature fluids together with their ore metal contents using a new method for sulfur quantification in fluid inclusions by laser ablation inductively coupled plasma mass spectrometry la icp ms co genetic brine and vapor inclusions from magmatic hydrothermal ore deposits and granitic intrusions show an excess of sulfur over ore metals as required for efficient ore mineral precipitation the results demonstrate that s cu and au are highly enriched in vapor like magmatic fluids implying that such low salinity fluids are the key agent for the formation of porphyry copper and epithermal gold deposits

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

resolving mantle and crustal contributions to ancient hydrothermal fluids hear isotopes in fluid inclusions from dae hwa wmo mineralisation south korea abstract helium and argon isotopes from fluid inclusions in individual colour zones b c d and e of a large scheelite crystal from the 88 ma dae hwa w mo deposit south korea trace the source and history of the ore fluids a gradual decrease of the fluid 3 he 4 he 3 he 36 ar and 40 ar 36 ar from the core to the edge of the scheelite reflects the progressive dilution of a magmatic fluid by meteoric water and is consistent with the previously observed decrease of 18oh2o and fluid inclusion homogenisation temperatures th shelton et al 1987 the covariation of fluid inclusion he ar isotope systematics with 18o and th defines a magmatic component with 3 he 4 he 1 2 10 6 3 he 36 ar 0 01 and 40 ar 36 ar 1000 anomalously high helium and argon isotope ratios in zone d fluids represents undiluted magmatic noble gases this may reflect local variation in the magmatic gas flux or gas loss due to boiling of the hydrothermal fluids prior to mixing with magmatic gas helium and argon isotope systematics constrain mantle and crustal components in the hydrothermal fluids 40 ar 3 he 4 5 104 are close to the mid ocean ridge basalt value implying that 40ar is mantle in origin radiogenic isotope ratios of the mantle endmember 40 ar 4 he 0 69 0 06 are similar to contemporary geothermal fluids the coincidence of mantle derived he and ar in the fluids is strong evidence that mantle melting during late cretaceous subduction triggered the crystal melting responsible for granite formation 40 ar 4 he of the meteoric fluid 0 007 0 001 is far lower than the crystal production ratio 0 2 implying an origin in crust below 200 c

noble gas isotopes in corundum and peridotite xenoliths from the eastern north china craton implication for comprehensive refertilization of lithospheric mantle abstract noble gas isotopic ratios provide unique and important constraints for the evolution of the subcontinental mantle we present one step crushing noble gas isotope data from corundum and co existing mantle xenoliths and megacrystals from the changle volcanic fields in the middle part of the tan lu fault zone eastern north china craton the 3he 4he ratio is 7 6 8 3 times the atmospheric ratio ra in corundum indicating contributions of fluids from convective asthenosphere the 3he 4he ratio in titanomagnetite megacrystals ranges from 5 8 to 6 5 ra suggesting possible u th contamination in the crystal lattice with the 3he 4he ratio of host magma being higher than 6 5 ra the olivine and opx in lherzolite show high helium contents and homogeneous isotopic helium ratios 6 9 7 0 ra the cpx in wehrlite show significantly higher helium contents and slightly higher helium ratio 7 6 ra than co existing olivine 7 0 7 5 ra combined with isotope correlation diagrams the systematic difference in 4he abundance the 3he 4he and 4he 40ar ratios of cpx opx and olivine in pyroxenite lherzolite and wehrlite suggest comprehensive refertilization of lithospheric mantle in the eastern north china craton

timing and genesis of the adakitic and shoshonitic intrusions in the laoniushan complex southern margin of the north china craton implications for post collisional magmatism associated with the qinling orogen abstract the nww striking qinling orogen formed in the triassic by collision between the north china and yangtze cratons triassic granitoid intrusions mostly middle to high k calc alkaline are widespread in this orogen but contemporaneous intrusions are rare in the southern margin of the north china craton an area commonly considered as the hinterland belt of the orogen in this paper we report zircon u pb ages elemental geochemistry and sr nd hf isotope data for the laoniushan granitoid complex that was emplaced in the southern margin of the north china craton zircon u pb dating shows that the complex was emplaced in the late triassic 228 1 to 215 4 ma indicating that it is part of the post collisional magmatism in the qinling orogen the complex consists of from early to late biotite monzogranite quartz diorite quartz monzonite and hornblende monzonite which span a wide compositional range e g sio2 55 9 70 6 wt k2o na2o 6 6 10 2 wt and mg of 24 to 54 the biotite monzogranite has high al2o3 15 5 17 4 wt sr 396 1398 ppm and ba 1284 3993 ppm contents and relatively high la yb mostly 14 30 and sr y mostly 40 97 ratios but low yb mostly 1 3 1 6 ppm and y mostly14 19 ppm contents features typical of adakitic rocks the quartz monzonite hornblende monzonite and quartz diorite have a shoshonitic affinity with k2o up to 5 58 wt and k2o na2o ratios averaging 1 4 the rocks are characterized by strong lree hree fractionation in chondrite normalized ree pattern without obvious eu anomalies and show enrichment in large ion lithophile elements but depletion in high field strength elements nb ta ti the biotite monzogranite 228 ma has initial 87sr 86sr ratios of 0 7061 to 0 7067 end t values of 9 2 to 12 6 and ehf t values of 9 0 to 15 1 whereas the shoshonitic granitoids mainly 217 215 ma have similar initial 87sr 86sr ratios 0 7065 to 0 7075 but more radiogenic end t 12 4 to 17 0 and ehf t 14 1 to 17 0 the sr nd hf isotope data indicate that the rocks were likely generated by partial melting of an ancient lower continental crust with heterogeneous compositions as partly confirmed by the widespread presence of early paleoproterozoic inherited zircons mafic microgranular enclaves mmes characterized by fine grained igneous textures and an abundance of acicular apatites are common in the laoniushan complex compared with the host rocks they have lower sio2 48 6 53 7 wt and higher mg 51 56 cr 122 393 ppm and ni 24 79 ppm but equivalent sr nd isotope compositions indicating that the mmes likely originated from an ancient enriched lithospheric mantle the abundance of mmes in the granitoid intrusions suggest that magma mixing plays an important role in the generation of the laoniushan complex collectively it is suggested that the laoniushan complex was a product of post collisional magmatism related to lithospheric extension following slab break off formation of the adakitic and shoshonitic intrusions in the laoniushan complex indicates that the qinling orogen had evolved into a post collisional setting by about 230 210 ma