sims zircon u pb geochronology and sr nd isotopes of ni cu bearing mafic ultramafic intrusions in eastern tianshan and beishan in correlation with flood basalts in tarim basin nw china constraints on a ca 280 ma mantle plume zircon sims u pb dating of the poshi hongshishan bijiashan and huangshan ni cu bearing and xiangshan ni cu ti fe bearing mafic ultramafic intrusions in the eastern tianshan and beishan rift yields a relatively restricted range of 278 6 ma to 284 0 ma the histogram of compiled age data of basalts in the tarim basin and mafic ultramafic intrusions in the eastern tianshan and beishan rift has a peak of 280 ma which probably represents the time of mantle plume activity the basalts have lower end t values in the range of 9 2 1 7 and mg of 2 wt indicating that they were generated directly from a peripheral zone of the mantle plume by low degree of melting the mafic ultramafic intrusions have higher end t of 1 3 11 2 and mg of 33 90 and lower tio2

absolute timing of sulfide and gold mineralization a comparison of re os molybdenite and ar ar mica methods from the tintina gold belt alaska new re os molybdenite dates from two lode gold deposits of the tintina gold belt alaska provide direct timing constraints for sulfide and gold mineralization at fort knox the re os molybdenite date is identical to the u pb zircon age for the host intrusion supporting an intrusive related origin for the deposit however 40ar 39ar dates from hydrothermal and igneous mica are considerably younger at the pogo deposit re os molybdenite dates are also much older than 40ar 39ar dates from hydrothermal mica but dissimilar to the age of local granites these age relationships indicate that the re os molybdenite method records the timing of sulfide and gold mineralization whereas much younger 40ar 39ar dates are affected by post ore thermal events slow cooling and or systemic analytical effects the results of this study complement a growing body of evidence to indicate that the re os chronometer in molybdenite can be an accurate and robust tool for establishing timing relations in ore systems

u pb zircon and geochemical constraints on the age origin and evolution of paleozoic arc magmas in the oyu tolgoi porphyry cu au district southern mongolia abstract uranium pb zircon ages are linked with geochemical data for porphyry intrusions associated with giant porphyry cu au systems at oyu tolgoi to place those rocks within the petrochemical framework of devonian and carboniferous rocks of southern mongolia in this part of the gurvansayhan terrane within the central asian orogenic belt the transition from devonian tholeiitic marine rocks to unconformably overlying carboniferous calc alkaline subaerial to shallow marine volcanic rocks reflects volcanic arc thickening and maturation radiogenic nd and pb isotopic compositions e nd t range from 3 1 to 7 5 and 206 pb 204 pb values for feldspars range from 17 97 to 18 72 as well as low high field strength element hfse contents of most rocks mafic rocks typically have 2 are consistent with magma derivation from depleted mantle in an intra oceanic volcanic arc the late devonian and carboniferous felsic rocks are dominantly medium to high k calc alkaline and characterized by a decrease in sr y ratios through time with the carboniferous rocks being more felsic than those of devonian age porphyry cu au related intrusions were emplaced in the late devonian during the transition from tholeiitic to calc alkaline arc magmatism uranium pb zircon geochronology indicates that the late devonian pre to syn mineral quartz monzodiorite intrusions associated with the porphyry cu au deposits are 372 ma whereas granodiorite intrusions that post date major shortening and are associated with less well developed porphyry cu au mineralization are 366 ma trace element geochemistry of zircons in the late devonian intrusions associated with the porphyry cu au systems contain distinct th u and yb gd ratios as well as hf and y concentrations that reflect mixing of magma of distinct compositions these characteristics are missing in the unmineralized carboniferous intrusions high sr y and evidence for magma mixing in syn to late mineral intrusions distinguish the late devonian rocks associated with giant cu au deposits from younger magmatic suites in the district

role of fluids in the earthquake occurrence around aswan reservoir egypt 1 continuing seismicity for about 30 years near a large western embayment of the lake nasser about 50 km from the aswan high dam in egypt has led to a debate about the possibility of its relation with the reservoir impoundment the largest event in the region occurred on 14 november 1981 m 5 3 20 km beneath the wadi kalabsha embayment a westward extension of the lake aswan since then continuous monitoring of seismic activity has given an excellent opportunity to study the spatiotemporal distribution of seismicity in the area most of the immediate aftershocks of the 1981 main shock were located in the gebel marawa area at depths between 15 and 30 km depths of almost all earthquakes away from this zone were shallower than 12 km to quantify the effect of the reservoir impoundment on the seismicity of the aswan area we calculated changes in stress and pore pressure due to the reservoir impoundment using green s function approach the change in coulomb stress s is calculated on the fault planes responsible for majority of the seismicity of the region we found that for all the seismogenic faults s is negative i e stabilizing when we consider the effect of the reservoir load only whereas it is positive i e destabilizing when we include pore pressure for example at the hypocenter of the main earthquake shear stress normal stress and pore pressure due to reservoir operation are estimated as 5 5 13 2 and 13 5 kpa respectively which suggest that s is 3 1 kpa when we do not consider the effect of pore pressure and 5 7 kpa when contribution from pore pressure is considered hence the seismicity in the aswan lake region is driven by the pore pressure due to reservoir impoundment

major types characteristics and geodynamic mechanism of upper paleozoic copper deposits in northern xinjiang northwestern china abstract syn and post orogenic cu mineralization in the northern xinjiang paleozoic accretionary and collisional orogenic belt in northwestern china is of great economic interest about 40 cu bearing deposits have been discovered in the area making it one of the most important metallogenic belts in china according to their host rocks these deposits can be classified into four principal types 1 volcanic hosted massive sulfide cu pb zn deposits 2 porphyry cu mo au deposits 3 magmatic cu ni sulfide deposits and 4 cu mo au ag skarn deposits tectonically the development of these upper paleozoic deposits was closely associated with subduction and collision of the ancient asian ocean between the siberian block and the tarim craton an important metallogenic epoch involving formation of cu pb zn polymetallic deposits formed during southwestern rollback and associated slab detachment during devonian time 400 370 ma in southern altay southwestern direct rollback and associated slab detachment occurred during the devonian 400 370 ma in response to later collision at the accreted continetal margin xiao w j windley b f badarch g sun s li j l qin k z wang z h 2004 palaeozoic accretionary and convergent tectonics of the southern altaids implications for the lateral growth of central asia journal of the geological society of london 161 339 342 during which the ashele cu pb zn and keketale pb zn deposits formed subduction led to the accretion of the junggar ocean arc system in the middle devonian in the lower to middle carboniferous north dipping subduction beneath the dananhu arc triggered the emplacement of granitic porphyries in the tousuquan and dananhu island arc belt in the east tianshan leading to the formation of the tuwu and yandong porphyry cu mo au ag deposits in the upper carboniferous to lower permian large mafic ultramafic complexes were emplaced during closure of the ancient tianshan ocean resulting in the formation of several magmatic cu ni sulfide deposits including the kalatongke cu ni deposits in north junggar and cu ni sulfide deposits in the huangshan jing erquan area of east tianshan mountains also associated with this extensional event were emplacement of voluminous anatectic granitoids and eruption of volcanic rocks which led to formation of skarn cu mo suoerkuduk cu mo deposit and cu ag deposits weiquan cu ag deposit the tectonic settings geological features and temporal and spatial distribution of these different types of cu deposits reflect to a great extent the accretionary and collisional tectonics that occurred between the siberian block and tarim block

recognition of late ordovician yudai porphyry cu au mo mineralization in the kalatag district eastern tianshan terrane nw china constraints from geology geochronology and petrology abstract although the eastern tianshan terrane in xinjiang nw china occupies a critical position in the central asian orogenic belt caob the early paleozoic tectonic evolution and mineralization history of this terrane remain ambiguous the yudai deposit is a newly discovered porphyry cu mo au deposit in the kalatag district of the dananhu island arc a key area containing early paleozoic rocks in the eastern tianshan this paper reports the geologic characteristics molybdenite re os ages zircon la icp ms u pb ages and geochemical and lu hf isotopic findings regarding the ore hosting porphyries in the yudai deposit the yudai ore hosting porphyries include an early diorite porphyry and a late quartz diorite porphyry alteration and mineralization have formed distinct zones around the quartz diorite porphyry with disseminated vein or veinlet cu mo au mineralization types mainly related to potassic alteration e g biotite magnetite and quartz typical of a porphyry cu deposit two molybdenite samples have an re os weighted mean age of 449 5 4 2 ma and exhibit high re contents 2624 to 4704 ppm indicating a mantle component the observed mineralization was probably related to the quartz diorite porphyry which yielded a mean zircon 206pb 238u age of 452 7 2 8 ma the rock samples from the two porphyries mainly plot in the diorite field show metaluminous to weak peraluminous features and belong to tholeiitic to calc alkaline series with k2o na2o ratios of 0 16 0 34 and mg values of 44 2 50 3 the samples also exhibit steep chondrite normalized rare earth element and relatively flat heavy rare earth element patterns indicating residual amphibole with positive eu anomalies eu eu 1 09 1 45 the samples are enriched in large ion lithophile elements relative to high field strength elements typical of arc magma in addition the rocks show adakitic features sr y 47 8 73 5 and present high ba th and low th nb ratios indicating slab fluids the zircons from the quartz diorite porphyry mainly yield high ehf t values 13 5 14 7 and very young two stage hf model ages tdm2 494 556 ma consistent with a depleted mantle origin combined with the arc tectonic setting we propose that the ore metals and ore hosting porphyries at yudai were predominately derived from the partial melting of the amphibole bearing and fluid rich kangguer ocean slab that was subducted northward beneath the dananhu island arc in the late ordovician therefore the evolutionary history of the dananhu island arc can be traced back to the late ordovician the yudai deposit is the first age constrained early paleozoic porphyry cu deposit in the eastern tianshan terrane and the early paleozoic was an important epoch of mineralization on this terrane

the adakite connection of the tuwu yandong copper porphyry belt eastern tianshan nw china trace element and sr nd pb isotope geochemistry the tuwu yandong porphyry copper belt lies in the eastern tianshan mountains eastern section of the central asian orogenic belt the copper mineralization is mainly hosted in plagiogranite porphyries intruded into early carboniferous volcanic rocks of the paleozoic dananhu island arc between the tarim and siberian plates the plagiogranite porphyries have contents of 65 73 wt sio2 14 17 wt al2o3 0 9 2 2 wt mgo 3 16 ppm y 0 4 1 40 ppm yb 347 920 ppm sr and positive eu anomalies the rocks also exhibit positive nd t values 5 0 to 9 4 and low initial 87sr 86sr values 0 70316 0 70378 such features are similar to those of adakites derived from partial melting of a subduction related oceanic slab the mineralization age is early carboniferous 350 320 ma which is close to that of the porphyries the close relationship between the cu mineralization and the porphyry is also indicated by their similar sr nd pb isotopic compositions we suggest that the copper porphyry magma system in the dananhu island arc was formed by direct melting of an obliquely subducting early carboniferous oceanic slab

constraints on the timing of fe cu metallogenesis in the eastern aqishan yamansu shaquanzi metallogenic belt eastern tianshan nw china abstract the aqishan yamansu shaquanzi belt is a well known fe cu au metallogenic belt located in the central asian orogenic belt nw china numerous fe rich ores as well as polymetallic mineralization including cu pb zn and co and related magmatic hydrothermal alteration are hosted in volcanic rocks especially those in the eastern part of this metallogenic belt the complex geology of the belt and the divergent geochronological data obtained by different investigators and analytical methods have led to contrasting opinions on the deposit types and metallogenesis of the belt the present study focuses on the shaquanzi yamansu and heifengshan fe cu polymetallic deposits in the eastern part of the belt these deposits display fe dominated metallogenesis related to volcanic sedimentary exhalative processes and polymetallic metallogenesis related to volcanic hydrothermal metasomatism and skarnization caused by subsequent intrusion processes the shaquanzi yamansu and heifengshan deposits have undergone multiple periods of metallogenesis and contain late fe cu pb mo fe cu zn co and fe cu mineralization respectively using zircon u pb dating by laser ablation multi collector inductively coupled plasma mass spectrometry two rhyolite samples at the base and lower middle part of the tugutubulak formation and a basaltic andesite and a diorite dyke in the shaquanzi ore district yield concordant ages of 327 9 2 6 ma mean square of weighted deviates or mswd 0 015 327 8 1 4 ma mswd 1 03 285 9 2 0 ma mswd 0 81 and 276 3 1 4 ma mswd 0 21 respectively basaltic andesite from the upper yamansu formation in the yamansu deposit area yields a concordant age of 327 6 6 4 ma mswd 0 54 whereas rhyolite diorite dyke and granite stock from the heifengshan deposit give concordant ages of 285 7 1 3 ma mswd 0 01 273 7 1 6 ma mswd 1 2 and 274 4 2 5 ma mswd 0 20 respectively hydrothermal molybdenite in the shaquanzi deposit yields a weighted mean re os age of 314 6 1 7 ma mswd 0 29 and an isochron age of 316 6 ma mswd 0 46 a collation of previously reported ages and our new age data show that extensive magmatism occurred during the carboniferous early permian ca 350 270 ma in the aqishan yamansu shaquanzi belt with a peak period between ca 335 and ca 305 ma the yamansu formation and tugutubulak formation volcanic rocks formed at ca 348 334 ma early carboniferous and between ca 328 and ca 303 ma late early carboniferous to late carboniferous respectively in the eastern part of the belt fe dominated mineralization resulting from volcanic sedimentary exhalative processes e g ca 334 ca 322 and ca 286 ma and polymetallic mineralization resulting from volcanic hydrothermal metasomatism e g ca 334 323 ma as well as skarnization and magmtic hydrothermal caused by intrusions occurred at different stages e g ca 322 316 ca 299 and ca 274 ma leading to the superimposition of polymetallic mineralization between ca 334 and ca 273 ma

nature and evolution of hydrothermal fluids in the formation of the tuwu porphyry copper deposit in the eastern tianshan mountains nw china abstract the tuwu porphyry copper deposit is located in the eastern tianshan mountains xinjiang china lentiform like ore bodies are hosted in the early carboniferous qi eshan group and cu mineralization shows a close association with tonalite porphyry porphyry and country rocks have undergone extensive potassic chlorite sericite phyllic and propylitic alteration the mineralized veins in the tuwu deposit can be divided into earlier quartz biotite magnetite chalcopyrite veins stage i quartz chalcopyrite bornite pyrite veins stage ii and quartz molybdenite chalcopyrite pyrite calcite veins stage iii and later calcite quartz veins stage iv the stage ii and iii are the main cu mineralization stages at the tuwu deposit three types of fluid inclusions have been distinguished liquid rich l type vapor rich v type and halite bearing s type respectively laser raman spectra identified magnetite hematite chalcopyrite and pyrite at s type inclusions the quartz veins in stage i and ii contain all inclusion types l type and v type inclusions are recognized in stage iii quartz minerals but only l type inclusions are present in stage iv quartz minerals fluid inclusions in quartz of stage i ii iii and iv are characterized by homogenization temperature vary of 275 492 c 232 477 c 199 287 c and 133 227 c with corresponding nacl equiv salinities of 2 2 58 7 wt nacl equiv 1 4 58 3 wt nacl equiv 1 1 6 0 wt nacl equiv and 1 1 4 2 wt nacl equiv respectively initial ore forming fluids of the tuwu deposit belong to relatively oxidized h2o nacl system with moderate high temperature and salinity sulfur isotope data from chalcopyrite and pyrite suggest a magmatic source two types of chlorite type 1 and type 2 are recognized based on the relationship with metal sulfides electron microprobe analysis shows that chlorites are plotted in ripidolite and pycnochlorite decreasing fe fe mg ratios of chlorites indicate that the meteoric water was involved in the magmatic water combined with the positive correlation with aliv implying that the chlorite formed in a relatively reduced and acidic environment the hydrothermal fluids in type 1 chlorite bring large quantities of reduced metallic minerals compared to the barren fluids in type 2 chlorite the formation temperatures of chlorite are roughly coincident with the results that obtained from fluid inclusion studies which show a decrease trend changes in temperature redox ph and fluid rock interaction likely play an important role in the transportation and precipitation of metal sulfides of the tuwu deposit

precise determination of phanerozoic zircon pb pb age by multicollector sims without external standardization 1 zircon has long been recognized as the best geochronometer and the most important timekeeper in geosciences modern microbeam techniques such as sims and la icpms have been successfully applied to in situ u pb zircon age determinations at spatial resolutions of 20 30 m or less matrix matched calibration by external standardization of well characterized natural zircon references is a principal requirement for precise microbeam u pb zircon age determination due to fractionation effects between pb and u which usually result in an external age error exceeding 1 alternatively zircons with a closed u pb system can be directly dated by measurement of 207pb 206pb isotopic ratio without external standardization which has been a common practice for zircons older than 1 0 ga but not for relatively young 1 0 ga and particularly phanerozoic ones because of limitations of analytical precision we describe in this paper a method of 207pb 206pb measurement on phanerozoic zircons using a new generation of large radius magnetic sector multicollector cameca ims 1280 sims in combination with multicollector mode a nuclear magnetic resonance nmr magnet controller and oxygen flooding techniques we achieve precisions of 207pb 206pb ratio of 0 1 and 0 1 0 2 propagating to pb pb age errors 0 4 and 1 3 excluding u decay constant uncertainties for zircons of latest neoproterozoic and late paleozoic to mesozoic age respectively therefore the multicollector sims is capable of direct determination of zircon pb pb ages as young as mesozoic age with uncertainties of geological significance this technique is useful for direct dating of zircons in thin sections moreover it has significance for dating of some other u rich minerals i e baddeleyite and zirconolite that are not suitable for sims u pb dating by external standardization

yandong porphyry cu deposit xinjiang china geology geochemistry and sims u pb zircon geochronology of host porphyries and associated alteration and mineralization abstract the yandong porphyry copper deposit located in the eastern tianshan mountains xinjiang china is part of the central asian orogenic belt the yandong deposit is hosted by a volcanic complex in the early carboniferous qi eshan group and a felsic intrusion the complex consists of andesite basalt diorite porphyry and porphyritic quartz diorite the felsic intrusion is a plagiogranite porphyry emplaced within the complex the diorite porphyry and plagiogranite porphyry yield sims zircon u pb ages of 340 0 3 and 332 2 2 3 ma respectively element geochemistry shows that both the complex and plagiogranite porphyry formed in the dananhu tousuquan island arc a carboniferous magmatic arc the diorite porphyry and plagiogranite porphyry are host porphyries but the plagiogranite porphyry is a productive porphyry it caused the porphyry style cu mineralization and associated alteration the alteration assemblages include early potassic and propylitic assemblages these were overprinted by a chlorite sericite assemblage which in turn was overprinted by a late phyllic assemblage the phyllic alteration is associated with the highest cu grades the mineralization is recognized to include three stages from early to late stage 1 a potassic alteration associated with a chalcopyrite pyrite assemblage stage 2 represented by chlorite sericite alteration with a chalcopyrite pyrite assemblage and stage 3 the main ore stage that is marked by phyllic alteration with chalcopyrite pyrite molybdenite and producing more than 70 of the total copper production at yandong yandong may represent a common scenario for paleozoic porphyry cu systems in the central asian orogenic belt

pb u and th diffusion in natural zircon zircon zrsio4 is one of the most widely used minerals for determining the age origin and thermal history of rocks by u th pb geochronology but the parameters describing the solid state volume diffusion rates of these elements in natural zircon which are themselves important for establishing the limits on the applicability of zircon for geochronological studies have remained poorly quantified1 this is because of the measurement difficulties associated with the low p p m concentrations and low diffusion rates of these elements in natural zircon and the chemical and physical heterogeneity present in most crystals here we present direct measurements of the uranium thorium and lead loss from a thermally treated gem quality natural zircon and show that lead diffuses much faster than uranium or thorium we find that the u th pb isotopic system in natural zircon will typically have a closure temperature greater than 900 c which explains why zircon is apparently such a robust geochrometer and is capable of remaining isotopically closed through extended periods of high grade metamorphism and partial melting of the host rock

northwestern junggar basin xiemisitai mountains china a geochemical and geochronological approach abstract we report sims u pb zircon elemental and nd sr pb isotopic data for the volcanic rocks and their subvolcanic units from the xiemisitai mountains in the west junggar region xinjiang china aiming to determine their ages source regions and tectonic setting zircon u pb dating results of the volcanic rocks 422 5 1 9 ma 411 2 2 9 ma indicate that the volcanic strata occurred in the xiemisitai mountains at late silurian early devonian time rather than middle devonian as suggested previously they are probably the eastern extension of the early paleozoic cambrian silurian boshchekul chingiz volcanic arc of east kazakhstan in china the xiemisitai volcanic rocks include andesite rhyolite and their pyroclastic equivalents the subvolcanic units are felsite and granite porphyry andesite is moderately lree enriched with a marked negative nb anomaly and th yb enrichment rhyolite felsite and granite porphyry are enriched in lree and th and depleted nb the initial sr isotope values of the xiemisitai volcanic rocks and their subvolcanic units range from 0 702294 to 0 704456 e nd 420 ma from 0 19 to 1 88 with nd model ages ranging from 600 to 803 ma initial pb isotope ratios 206 pb 204 pb are 17 77 17 96 207 pb 204 pb are 15 49 15 54 and 208 pb 204 pb are 37 56 37 80 these features suggest that the xiemisitai volcanic rocks and their subvolcanic units derived from a mantle wedge significant mixed by subducted material emi in a subduction zone they also indicate significant involvement of neoproterozoic primitive crust in the formation of the xiemisitai magmatic arc these rocks are associated with a late silurian early devonian southward subduction of the oceanic lithosphere in the northern west junggar region this gives rise to an ew trending boshchekul chingiz volcanic arc and associated metallogenic belt in the northern west junggar region and adjacent kazakhstan

late and mid cretaceous mineralization in the northern canadian cordillera constraints from re os molybdenite dates new re os molybdenite dates are presented from three deposits casino cash and mt nansen in the dawson range yukon northern canadian cordillera the re os molybdenite dates provide constraints on the timing of sulfide mineralzation and together with 40 ar 39 ar and k ar mineral dates yield estimates for the longevity of the porphyry hydrothermal system at the casino deposit re os molybdenite dates associated with the potassic 75 05 0 28 74 69 0 28 ma alteration are nominally older to overlapping with re os molybdenite dates 74 4 0 28 ma n 2 with phyllic alteration and suggest that it is likely that potassic and phyllic mineralization alteration was contemporaneous the re os molybdenite dates are significantly older than hydrothermal k feldspar 40 ar 39 ar and k ar biotite dates 72 ma which most likely reflect the cessation of the porphyry hydrothermal system the molybdenite age data combined with silicate hydrothermal mineral dates suggest a porphyry hydrothermal system longevity of 4 16 to 1 94 casino 8 66 to 6 44 cash and 2 47 to 1 48 ma mt nansen these longevity estimates for porphyry hydrothermal systems are greater than previously proposed 50 c km may control the disparate re os molybdenite and 40 ar 39 ar k feldspar dates of the porphyry systems of this study the contrasting re os and 40 ar 39 ar dates clearly show the re os isotope system in molybdenite is resistant to prolonged 1 ma interaction with a high temperature 400 500 c hydrothermal fluid and that the re os isotope systematics in molybdenite unambiguously record directly the timing of sulfide mineralization this ability to directly date sulfide mineralization has identified mid pattison idaho creek 102 104 ma and late cretaceous zappa koffee 74 5 ma mineralization which is hosted by the mid cretaceous 104 102 ma casino plutonic suite the late cretaceous date is very similar to that for molybdenite mineralization at casino and we suggest that the zappa koffee mineralization is an area of late cretaceous porphyry mineralization for which the host pluton has not yet been discovered

geological characteristics and genesis of the tuwu porphyry copper deposit hami xinjiang central asia abstract the tuwu copper deposit located in the dananhu tousuquan island arc between the kazakhstan junggar and tarim plates is one of the largest porphyry copper deposits in western china ore hosting rocks consist of early carboniferous 333 2 ma granodiorite and plagiogranite porphyries both the porphyries are elongate the orebodies consisting of veinlet disseminated mineralization within the porphyries grade range from 0 30 to 1 50 cu mineralization can be assigned to six stages wall rock alteration associated with the mineralization include silicification chloritization epidotization sericitization and carbonatization three alteration zones have been recognized phyllic zone chlorite biotite zone and propylitic zone re os dating indicates a 322 7 3 ma age for the deposit 34 s values of the ore sulfides range from 0 9 to 1 3 with a mean of 0 11 reflecting a deep sulfur source 18 o values of quartz in the ores range from 7 70 to 9 70 and the 18 o value of chlorite in the ores is 6 62 calculated 18 o water values of quartz and chlorite range from 5 37 to 6 62 and the d values range from 48 to 63 suggesting that the ore fluids were mainly magma derived in the early stage of mineralization however values for the late mineralization stage decrease suggesting the addition of meteoric waters during the mineralization fluid inclusions within quartz grains are generally 3 to 30 m in size with gas proportions ranging from 5 to 60 mostly from 10 to 15 homogenization temperatures of fluid inclusions are relatively low bracketed between 101 and 409 c mostly between 100 and 200 c salinities exhibit a wide range from 0 35 to 14 61 wt nacl equiv with a mean of 7 72 wt nacl equiv suggesting that ore fluids have low to moderate salinity the ore bearing plagiogranite porphyries show a strong depletion in heavy rare earth elements with average values of yb and y of 0 65 and 5 90 ppm respectively this being a characteristic geochemical signature for adakite the geochemical signature of the adakites within the granitoid rocks represents a characteristic guide for further exploration for copper porphyry type ore deposit in eastern tianshan

modified kinematic model application to bed forms the kinematic wave theory originally developed for flood routing purposes is generalized in such a way that kinematic dynamic couplings are accounted for due to various forces the equations of continuity for water and sediment are transformed into a typical mass transport equation including convection diffusion and source terms each of these terms is shown to represent dynamic contributions of certain forces on the kinematics of the motion the theory is used to explain various aspects of bed form phenomena a numerical modeling method based on the proposed dynamic wave equation is suggested

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

granites in the sawuer region of the west junggar xinjiang province china geochronological and geochemical characteristics and their geodynamic significance abstract the sawuer region is located in the west junggar jimunai county of altay district and hefeng county of tacheng district xinjiang autonomous region in northwest china in the study area granitic intrusions are widespread and can be subdivided into i type granites tasite pluton sentasi pluton wokensala pluton and kaerjia pluton and a type a 2 granites kuoyitasi pluton and qiaqihai pluton the i type granites consist of granite adamelite granodiorite and the a type granites are mainly represented by alkali granite shrimp u pb dating results indicate that the granites in sawuer region were formed between 337 ma and 290 7 ma late carboniferous and early permian with the i type granites being formed between 337 ma and 302 6 ma and the a type between 297 9 and 290 7 ma from the older to the youngest granites their composition changes from calc alkalic to high k calc alkalic to alkali series and from i type to a type based on the characteristics of whole rock trace element and rare earth elements geochemistry this compositional range is the result of a change in the geodynamic regime from compressional to tensional during the late paleozoic strontium nd pb o isotope systematics suggest that both the i type and a type granites in sawuer were sourced from the mantle dm but with some crustal contamination for the kuoyitasi pluton the i type granites were formed by equilibrium partial melting while the a type granites were formed mainly by fractional crystallization based on the rb y nb and nb y ce discrimination criteria by eby eby g n 1992 chemical subdivision of the a type granitoids petrogenetic and tectonic implications geology 20 641 644 and pearce pearce j a 1996 sources and settings of granitic rocks episodes 19 120 125 and comparisons with granites in other regions of northern xinjiang the i type granites were emplaced during a transition from compressional to extensional settings in a post collision regime whereas the a type granites were emplaced in an extensional setting we concluded that the sawuer as well as the whole junggar region in northern xinjiang were involved in tectonism that gradually changed from compressional to extensional between the late carboniferous and early permian this late paleozoic granitic magmatism contributed to vertical crustal growth in the region

element transport and enrichment during propylitic alteration in paleozoic porphyry cu mineralization systems insights from chlorite chemistry abstract chlorite is one of the most widely developed minerals in propylitic alteration around porphyry deposits and can be used to investigate element transport and enrichment processes during hydrothermal alteration the paleozoic tuwu porphyry cu deposit metal reserve 0 7 mt cu 0 67 located in the southern margin of the central asian orogenic belt is one of the most economical and largest porphyry cu deposits in nw china the tuwu porphyry cu deposit comprises an early porphyry cu mineralization including potassic propylitic and phyllic alteration stages and later overprinting cu mineralization periods with chlorite found in both chlorite from the propylitic zone at tuwu is geochemically similar to propylitic chlorite in younger cenozoic porphyry systems but enriched in mg and k and depleted in fe and al relative to the overprinting chlorite scandium v ti and ga are enriched and li sr mn and zn are depleted in the tuwu propylitic chlorite proximal to the orebody consistent with cenozoic deposits compared with metamorphic chlorite from proterozoic metamorphic terranes in australia tuwu propylitic chlorite has higher mg and k lower fe al and as our results suggest propylitic alteration in the tuwu district is probably the product of cooling of fluids derived from the magmatic hydrothermal system but not from peripheral waters and trace element variations in chlorite are mainly controlled by temperature although other factors such as fault development could affect variation trends the common elemental features of chlorite in both paleozoic and cenozoic porphyry cu deposits indicate it could act as a potential tool for mineral exploration

geodynamics and metallogeny of the central eurasian porphyry and related epithermal mineral systems a review abstract major porphyry cu au and cu mo deposits are distributed across almost 5000 km across central eurasia from the urals mountains in russia in the west to inner mongolia in north eastern china these deposits were formed during multiple magmatic episodes from the ordovician to the jurassic they are associated with magmatic arcs within the extensive subduction accretion complex of the altaid and transbaikal mongolian orogenic collages that developed from the late neoproterozoic through the palaeozoic to the jurassic intracratonic extension the arcs formed predominantly on the palaeo tethys ocean margin of the proto asian continent but also within two back arc basins the development of the collages commenced when slivers of an older proterozoic subduction complex were rifted from an existing cratonic mass and accreted to the palaeo tethys ocean margin of the combined eastern europe and siberian cratons subduction of the palaeo tethys ocean beneath the karakum and altai tarim microcontinents and the associated back arc basin produced the overlapping late neoproterozoic to early palaeozoic tuva mongol and kipchak magmatic arcs contemporaneous intra oceanic subduction within the back arc basin from the late ordovician produced the parallel urals zharma magmatic arc and separated the main khanty mansi back arc basin from the inboard sakmara marginal sea by the late devonian the tuva mongol and kipchak arcs had amalgamated to form the kazakh mongol arc by the mid palaeozoic the two principal cratonic elements the siberian and eastern european cratons had begun to rotate relative to each other drawing in the two sets of parallel arcs to form the kazakh orocline between the two cratons during the late devonian to early carboniferous the palaeo pacific ocean began subducting below the siberian craton to form the sayan transbaikal arc which expanded by the permian to become the selanga gobi khanka arc by the middle to late permian as the kazakh orocline continued to develop both the sakmara and khanty mansi back arc basins were closed and the collage of cratons and arcs were sutured by accretionary complexes during the permian and triassic the north china craton approached and docked with the continent closing the mongol okhotsk sea an embayment on the palaeo pacific margin to form the mongolian orocline subduction and arc building activity on the palaeo pacific ocean margin continued to the mid mesozoic as the indosinian and yanshanian orogens significant porphyry cu au mo and au cu deposits were formed during the ordovician in the kipchak arc e g bozshakol cu au in kazakhstan and taldy bulak porphyry cu au in kyrgyzstan silurian to devonian in the kazakh mongol arc e g nurkazgan cu au in kazakhstan and taldy bulak levoberezhny au in kyrgyzstan devonian in the urals zharma arc e g yubileinoe au cu in russia devonian in the kazakh mongol arc e g oyu tolgoi cu au and tsagaan suvarga cu au in mongolia carboniferous in the kazakh mongol arc e g kharmagtai au cu in mongolia tuwu yandong cu au in xinjiang china koksai cu au kounrad cu au and the aktogai group of cu au deposits in kazakhstan carboniferous in the valerianov beltau kurama arc e g kal makyr dalnee cu au in uzbekistan benqala cu au in kazakhstan late carboniferous to permian in the selanga gobi khanka arc e g duobaoshan cu au in inner mongolia china triassic in the selanga gobi khanka arc and jurassic in the selanga gobi khanka arc e g wunugetushan cu mo and jiguanshan mo in inner mongolia china in addition to the tectonic geologic and metallogenic setting and distribution of porphyry cu au mo mineralisation within central eurasia the setting geology alteration and mineralisation at each of the deposits listed above is described and summarised in table 1

mount st helens potential example of the partial melting of the subducted lithosphere in a volcanic arc mount st helens 50 km to the west of mount adams and the main cascade volcanic chain is only 80 km above the subducting oceanic lithosphere the elevated temperatures off the subducting slab because of the close proximity of the juan de fuca ridge to the trench may induce slab melting at a depth of 80 km dacites from mount st helens have geochemical compositions off magmas that are derived by direct partial melting of metamorphosed basalts at high pressure i e relatively high ai al2o3 15 at 70 sio2 low y and yb because of garnet and amphibole stability in the source low sc and high sr and eu trace element modeling of the partial melting of mid oceanic ridge basalt morb from the juan de fuca ridge that yields a hornblende eclogite residue can reproduce the mount st helens data results off the model are quite distinct from data derived from the mount adams volcanic rocks in contrast mount adams is 135 km above the subducting slab and is associated with normal arc magmatism believed to be derived from the mantle above the subducting plate the cascade are has been active in its present locality because of oblique subduction for the past 7 m y the major volcanoes along the arc have existed for at least 500 ka but mount st helens has existed for 40 ka we suggest that the subducting plate may have reached elevated temperatures because of the approach of north america to the juan de fuca ridge at 40 ka which initiated melting of the slab