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

the 1 85 ga mo mineralization in the xiong er terrane china implications for metallogeny associated with assembly of the columbia supercontinent abstract the east qinling region in china hosting several tens of mesozoic magmatic hydrothermal mo deposits is one of the largest molybdenum belts in the world the recently discovered longmendian mo deposit luoning county henan province occurs within the xiong er terrane of the east qinling mo belt here the mo mineralization is confined to altered amphibolite which is replaced by microcline actinolite tremolite epidote and carbonate molybdenite is also observed in microcline dominated felsic differentiates but occurs within the altered amphibolite enclaves here we report re os isotope analyses of five molybdenite and four pyrite samples from longmendian which yield re os isochron ages of 1853 36 ma and 1855 29 ma respectively these ages are in good agreement with the metamorphic age of the taihua supergroup 1 87 1 84 ga the re os data presented in this study indicate that the period of 1 85 ga was a time of widespread melting generating leucocratic microcline dominated granitic melts the timing also coincides with the collision of the eastern and western blocks of the north china craton and its final cratonization at 1 85 ga coinciding with the incorporation of the north china craton within the paleoproterozoic supercontinent columbia

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

re os molybdenite age of the cu mo skarn ore deposit at suoerkuduke in east junggar nw china and its geological significance the suoerkuduke cu mo ore is a medium sized skarn deposit in the east junggar orogen of the southern altaids xinjiang northwest china we measured re os isotopes of a molybdenite veinlet from the

spatial variations in geochemical characteristics of the modern mackenzie delta sedimentary system the mackenzie river in canada is by far the largest riverine source of sediment and organic carbon oc to the arctic ocean therefore the transport degradation and burial of oc along the land to ocean continuum for this riverine system is important to study both regionally and as a dominant representative of arctic rivers here we apply sedimentological grain size mineral surface area and organic and inorganic geochemical techniques oc 13c oc and 14c oc 143nd 144nd 2h and 18o major and trace elements on particulate bank channel and lake surface sediments from the mackenzie delta as well as on surface sediments from the mackenzie shelf in the beaufort sea our data show a hydrodynamic sorting effect resulting in the accumulation of finer grained sediments in lake and shelf deposits a general decrease in organic carbon oc to mineral surface area ratios from river to sea furthermore suggests a loss of mineral bound terrestrial oc during transport through the delta and deposition on the shelf the net isotopic value of the terrestrial oc that is lost en route derived from relationships between 13c oc and surface area is 28 5 for 13c and 417 for 14c we calculated that oc burial efficiencies are around 55 which are higher 20 than other large river systems such as the amazon old sedimentary oc ages up to 12 14c ky suggest the delivery of both a petrogenic oc source with an estimated contribution of 19 9 as well as a pre aged terrestrial oc source we calculated the 14c age of this pre aged biogenic component to be about 6100 yrs or 501 which illustrates that terrestrial oc in the watershed can reside for millennia in soils before being released into the river surface sediments in lakes across the delta n 20 showed large variability in oc 0 92 5 7 and 13c 30 7 to 23 5 high closure lakes flooding only at exceptionally high water levels hold high sedimentary oc contents 2 5 and young biogenic oc with a terrestrial or an autochthonous source whereas no closure lakes permanently connected to a river channel hold sediments with pre aged terrestrial oc the intermediate low closure lakes flooding every year during peak discharge display the largest variability in oc content age and source likely reflecting variability in for example the length of river lake connections the distance to sediment source and the number of intermediate settling basins bank channel and suspended sediment show variable 143nd 144nd values yet there is a gradual but distinct spatial transition in 143nd 144nd nearly three e units from 11 4 to 13 9 in the detrital fraction of lake surface sediments from the western to the eastern delta this reflects the input of younger peel river catchment material in the west and input of older geological source material in the east and suggests that lake sediments can be used to assess variability in source watershed patterns across the delta

geochronology and isotope geochemistry of the baogutu porphyry copper deposit in the west junggar region xinjiang china abstract the baogutu copper deposit a newly discovered middle sized porphyry copper deposit is located in the west junggar region of xinjiang nw china baogutu is associated with a late carboniferous intrusive complex that was emplaced into lower carboniferous volcano sedimentary strata the intrusive complex comprises main stage diorites and minor late stage diorite porphyries their intrusive activity occurred in 313 0 2 2 ma to 312 3 2 2 ma based on u pb zircon sims analyses molybdenite separated from ore bearing quartz veins yields re os model ages from 309 4 4 4 ma to 314 1 4 5 ma with a weighted mean age of 312 4 1 8 ma biotites separated from fresh diorite and hydrothermal breccias in main stage diorites yield 40ar 39ar plateau ages of 308 26 1 88 and 305 69 1 76 ma respectively these dates obtained from three independent dating techniques constrain the ore forming age of the baogutu deposit stable isotopes h o s and radiogenic isotope pb have been used to discriminate the sources of the ore forming fluid at baogutu the 18o 1 14 1 74 and d 74 to 98 data indicate that the water of the ore forming fluids was derived from magmatic water the 34s values 0 24 to 0 4 show that the sulfur isotope composition of the ore fluids is characterized by magma sulfur lead isotope compositions 206pb 204pb 17 92 18 89 207pb 204pb 15 45 15 62 208pb 204pb 37 68 38 36 indicate that the lead of the ore fluids is derived from the mantle these data confirm the occurrence of a cu au mo mineralizing event at late carboniferous in the baogutu region and the ore forming fluids are mainly derived from the mantle the event is inferred to be associated with late carboniferous junggar oceanic crust subduction

a numerical simulation of the evolution of temperature and co2 stratification in lake nyos since the 1986 disaster a one dimensional numerical model has been applied to simulate the evolution of the temperature and co2 stratification in lake nyos since the 1986 disaster it incorporates a second moment turbulence closure scheme for mixing and heating and cooling in the upper layers of the lake the effects of inflowing stream water and input of the co2 heat and dissolved solids at the bottom of the lake are taken into account the model is initialized by conditions observed immediately after the disastrous outgassing event in 1986 and integrated forward for 10 years forced by seasonally modulated diurnal heating and nocturnal cooling and heavy summer time precipitation at the surface four possible conditions are investigated the first simulation considers the normal seasonal heating cooling cycle and steady input of heat dissolved solids and co2 at the bottom it shows that the upper layers of the lake are quite stable under normal seasonal forcing but the bottom layers reach high co2 concentrations in less than a decade the second simulation considers a brief introduction at the bottom of the lake of cooler waters that contain less co2 and temporarily destabilize the bottom layers the third and fourth simulations consider anomalous surface forcing conditions that can produce anomalous mixed layer deepening during the cooling seasons capable of releasing the co2 stored immediately below the normal mixed layer these results suggest that a destabilization of the bottom layers is more likely to lead to massive and catastrophic degassing the results also demonstrate the utility of a numerical model in investigations of caldera crater lakes such as lake nyos

prograde evolution and geothermal affinities of a major porphyry copper deposit the cerro colorado hypogene protore i region northern chile the middle eocene 51 8 0 6 ma hypogene protore underlying the supergene orebody of the cerro colorado porphyry cu mo deposit i region chile exhibits features not commonly documented in such hydrothermal systems early stage alteration of upper cretaceous plagioclase phyric andesite generated a sub horizontal blanket of pervasive extremely fine grained but texture preserving biotite 35 modal albite 40 magnetite 3 alteration 8 km 2 in area but lacking sulfide minerals at least seventy percent of the chalcopyrite pyrite stockwork mineralization was emplaced during the subsequent main stage alteration which comprises with decreasing depth quartz albite sericite chlorite clay smectite quartz sericite clay and andalusite diaspore pyrophyllite assemblages the deposit is apparently unique among documented central andean porphyry systems in the association of the highest grade copper mineralization with intermediate argillic alteration the subsequent transitional stage phyllic i e quartz sericite pyrite tourmaline alteration was associated with the emplacement of molybdenite rich breccia bodies the occurrence of undumortieri tized tourmaline veinlets cutting andalusite diaspore assemblages confirms that much of the advanced argillic alteration took place during the main stage early stage alteration was the product of nonboiling cool trapping temperature ca 380 c low salinity 8 wt nacl equiv fluids which added substantial k na mg fe 2 cl f and water to the host andesite the initial main stage fluids boiling at a paleodepth of ca 2 5 to 3 0 km were up to 160 c hotter 544 c and highly saline 52 wt nacl equiv as these fluids rose they cooled to 320 c were diluted to 37 wt nacl equiv deposited sulfides and leached k na ca mg fe 2 and cl from the host rocks yielding diverse broadly contemporaneous intermediate and advanced argillic alteration facies pressure estimates require that low density 0 3 g cm 3 and thus more acidic fluids were primarily responsible for the formation of the quartz sericite clay and shallow advanced argillic alteration subsequent phyllic alteration was similarly caused by boiling fluids which were hot 486 c and saline 47 wt at depth but cooler 334 c dilute 8 wt and vapor dominated at shallower levels even terminal stage pyrite veins formed at temperatures as high as 450 c albeit from low salinity 8 wt fluids following a major prograde thermal transition from the early to the main stage each sulfide depositing alteration episode at cerro colorado was generated by a pulse of high temperature fluid which cooled and diluted as it rose such changes in fluid characteristics temperature and alteration relationships are well documented in numerous geothermal fields where potassic alteration generally develops at ca 270 to 350 c and are likely to occur at an early stage in any hydrothermal system in which magmatic fluids exsolving at relatively high pressures ascend into the near surface environment the initial alteration at cerro colorado plausibly developed under conditions similar to those in nonexplosive geothermal systems in which hydrothermal fluids cool and disperse laterally at shallow depths extensive zones of biotite rich alteration generally barren and with a hornfelsic appearance occur in many andesite hosted porphyry copper deposits but few data are available elsewhere for mineralogical pressure temperature or metasomatic exchange relationships in such systems cerro colorado may however be representative of a subclass of porphyry copper deposits exhibiting unusually close analogies with geothermal systems

gas emission from diffuse degassing structures dds of the cameroon volcanic line cvl implications for the prevention of co2 related hazards abstract in the mid 1980s lakes nyos and monoun violently released massive gas mainly magmatic co 2 killing about 1800 people subsequent geochemical surveys and social studies indicate that lakes nyos and monoun event is cyclic in nature and may occur anywhere in the about 37 other volcanic lakes located in the corridor of the cameroon volcanic line cvl this potential threat motivated us to check if alike nyos and monoun the internal dynamic of the other lakes is also controlled by inputs of deep seated derived co 2 and attempt to measure and provide comprehensive insights on the passive gas emission along the cvl this knowledge shall contribute to the prevention of volcanic lake related hazards in cameroon and the refinement of the global carbon cycle we used in situ fixation and dry gas phase sampling methods to determine co 2 origin and the concentration and the accumulation chamber technique to measure diffuse co 2 emission from nine lakes and on soil at nyos valley and mount manenguba caldera the results suggest that although in minor concentrations compared to nyos and monoun ranging from 0 56 mmol kg 1 to 8 75 mmol kg 1 the bottom waters of some lakes also contain measurable magmatic co 2 with 13 c varies from 4 42 to 9 16 vs pdb that finding implies that under certain circumstances e g increase to volcanic and or tectonic activities along the cvl the concerned lakes could develop a nyos type behavioural scheme the diffuse gas emission results indicate that the nine surveyed lakes release approximately 3 69 0 37 kt km 2 yr 1 of co 2 to the atmosphere extrapolation to the approximately 39 volcanic lakes located on the cvl yields an approximate co 2 output of 27 37 0 5 kt km 2 yr 1 representing 0 023 of the global co 2 output from volcanic lakes in addition to the precedent value the gas removal operation in lakes nyos and monoun released approximately 2 52 0 46 10 8 mol km 2 yr 1 co 2 to the atmosphere from january 2001 to march 2013 more than double the per area co 2 released by the yellowstone volcanic system the co 2 emission from soil was estimated to be 4 57 1 30 kt km 2 yr 1 the soil gas geochemistry of the mount manenguba caldera also indicates a dominant magma derived co 2 mean 13 c 8 6 vs vpdb

geology geochronology fluid inclusion and h o isotope geochemistry of the luoboling porphyry cu mo deposit zijinshan orefield fujian province china abstract the luoboling cu mo deposit in the zijinshan orefield fujian province southeastern china is a large porphyry deposit hosted by the sifang granodiorite and the luoboling granodiorite porphyry the largest cu mo orebody is saddle shaped with various types of hydrothermal veinlets intensive hydrothermal alteration in the deposit is characterized by outward zoning from potassic overprinted by phyllic alteration to phyllic and alunite dickite alteration based on the mineral assemblages and crosscutting relationships of veins the ore forming process can be divided into three stages namely an early stage k feldspar quartz magnetite molybdenite veins associated with potassic alteration a middle stage quartz molybdenite chalcopyrite pyrite veins in phyllic zone and a late stage quartz gypsum veins in the phyllic and alunite dickite alteration zones six molybdenite separates yield a re os isochron age 104 6 1 0 ma which is identical to the age of emplacement of the sifang and luoboling granodiorite porphyries three types of fluid inclusions fis were observed at the luoboling deposit 1 nacl h 2 o aqueous 2 daughter mineral bearing and 3 co 2 h 2 o fluid inclusions fis of the early and middle stages are predominantly vapor rich aqueous and daughter mineral bearing inclusions together with minor co 2 rich and liquid rich aqueous inclusions whereas the late stage minerals only contain liquid rich aqueous inclusions homogenization temperatures and salinities of fis trapped in the early stage minerals range from 420 to 540 c and 0 4 to 62 9 wt nacl equiv respectively fis of the middle stage yield homogenization temperatures of 340 to 480 c and salinities of 0 5 to 56 0 wt nacl equiv co 2 content and the oxygen fugacity indicated by daughter minerals of fis trapped in middle stage minerals are lower than those in the early stage the liquid rich aqueous inclusions of the late stage homogenize at temperatures of 140 to 280 c yielding salinities of 0 4 to 8 4 wt nacl equiv the minimum estimated pressures of the three stages are 30 70 mpa 10 40 mpa and 1 10 mpa respectively corresponding to minimum ore forming depths of 1 2 8 km fluids trapped in early middle and late stages yield d values of 67 to 54 54 to 70 and 62 and 18 o values of 5 4 to 6 7 2 8 to 4 2 and 2 1 respectively fluid boiling which resulted in the formation of stockworks and the precipitation of sulfides occurred in the early and middle stages the fluids subsequently evolved into a low temperature low salinity system in the late stage along with an input of meteoric water the luoboling porphyry cu mo system was developed in a transition from continental arc to back arc extension region which was related to the westward subduction of the paleo pacific plate beneath the huanan orogen

fluid density control on vapor liquid partitioning of metals in hydrothermal systems hot aqueous fluids both vapor and saline liquid are primary transporting media for metals in hydrothermal magmatic systems despite the growing geological evidence that the vapor phase formed through boiling of magmatic ore bearing fluids can selectively concentrate and transport metals the physical chemical mechanisms that control the metal vapor liquid fractionation remain poorly understood we performed systematic experiments to investigate the metal vapor liquid partitioning in model water salt gas systems h2o nacl kcl hcl at hydrothermal conditions measurements show that equilibrium vapor liquid fractionation patterns of many metals are directly related to the densities of the coexisting vapor and liquid phases despite differences in the vapor phase chemistry of various metals that form hydroxide chloride or sulfide gaseous molecules of contrasting volatile properties water solute interaction is a key factor that controls the metal transfer by vapor like fluids in earth s crust these findings allow quantitative prediction of the vapor liquid distribution patterns and vapor phase metal transport in a wide range of conditions our density model accounts well for the vapor brine distribution patterns of na si fe zn as sb and ag observed in fluid inclusions from magmatic hydrothermal deposits for au and cu the partitioning in favor of the liquid phase predicted in a sulfur free system contrasts with the copper and gold enrichment observed in natural vapor like inclusions the formation of stable complexes of cu and au with reduced sulfur may allow for their enhanced transport by sulfur enriched magmatic hydrothermal vapors

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

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

a review of the cu ni sulphide deposits in the chinese tianshan and altay orogens xinjiang autonomous region nw china principal characteristics and ore forming processes abstract several cu ni sulphide deposits and occurrences have recently been discovered along parallel deep faults in the chinese tianshan and altay orogenic belts xinjiang province nw china the kalatongke and several other cu ni mineralized intrusions are located along the irtysh fault which separates the altay orogenic belt from the junggar basin the huangshan huangshandong xiangshan tudun erhongwa tula ergen and hongling deposits occur along the kanggurtag suture which separates the jueluotage orogenic belt from the turpan hami tuha basin the baishiquan tianyu and tianxiang deposits are located along the arqikekuduke fault which separates the jueluotage orogenic belt from the central tianshan precambrian terrane the poyi poshi and luodong deposits are located along the baidiwa fault which separates the central tianshan precambrian terrane from the beishan paleozoic rift re os dating of cu ni sulphide ores reveals that these cu ni ore belts formed in a narrow age range of 298 282 ma this age range is about the same as those of associated intrusions and dykes dated by the shrimp zircon u pb method tectonic and geochronological constraints suggest that the amalgamation of continental blocks mainly occurred during the late carboniferous in the central asian orogenic belt large scale hydrothermal and magmatic metallogenesis in the region occurred during post collisional stages of latest carboniferous to early permian age the cu ni sulphide deposits are part of this metallogenic event the cu ni orthomagmatic sulphide deposits in northern xinjiang are represented by 1 net textured type deposits by segregation of a cu ni metal sulphide melt and 2 magma conduit type some mafic ultramafic suites exhibit lithological zoning caused by strong differentiation stratiform orebodies are hosted by ultramafic rocks at the base of the magma chamber good examples are the kalatongke huangshandong and poshi deposits others such as the xiangshan baishiquan tianyu and tula ergen deposits are hosted by magma conduits consisting of peridotite troctolite and pyroxenite these ultramafic rocks either occur within faults or are surrounded by gabbroic and dioritic intrusions these two types of orthomagmatic cu ni sulphide deposits are also distributed along the same ore belts for instance the differentiated sill related huangshandong deposit co exists with the magma conduit type tula ergen deposit in the jueluotage orogenic belt orthomagmatic cu ni sulphide deposits in northern xinjiang formed during post collisional extension and are possibly related to a late carboniferous early permian mantle plume event the mafic ultramafic suites and associated cu ni deposits are commonly accompanied by dyke swarms and are characterized by elongated outcrops occurring along parallel e w trending regional faults these mafic ultramafic suites and accompanying dyke swarms are generally fractionated implying that they were feeders of presently eroded flood basalts

cu and mo re enrichment during ductile deformation a case study of the yuleken porphyry cu deposit eastern junggar nw china abstract porphyry cu deposits can be strongly deformed during subsequent tectonic evolution to date research pertaining to the deformation and the enrichment of mineralization in porphyry deposits has suffered from a paucity of proof here we describe the diagnostic petrologic and geochemical signatures of the yuleken porphyry cu deposit from stages of metallogenic overprinting the rocks studied in this work are from deformation metallogenic structures that have 1 a distinguished metallogenic and tectonic evolution 2 a three layer spatial deformation metallogenic structure 3 distinguishably different fluid components within protomylonite mylonite and ultramylonite zones and 4 variational geochemical characteristics of coexisting chalcopyrite and magnetite integrated sulfide and oxide mineral investigations pertaining to the mineral deformation and the trace element variation of the minerals chalcopyrite and magnetite in the yuleken porphyry cu deposit indicated that cu and mo can be enriched during ductile deformation through physical analogous geochemical characteristics of chalcopyrite from different stages and chemical migrations the elemental variation of magnetite magnetites from deformed stages have higher contents of ti v co mn and ga than those from other stages and the variation of the fluid components within the protomylonite mylonite and ultramylonite zones reveal that the migration and precipitation of cu mo and fe were influenced by oxygen fugacity fluid components and temperature variation in conclusion the arc related porphyry deposits were able to become involved in the ductile deformation zone inducing areas of cu and mo enrichment in theory units subjected to ductile deformation may have great potential for porphyry cu mo deposit formation under the influence of magmatism

palaeozoic collisional tectonics and magmatism of the chinese tien shan central asia abstract the chinese tien shan range is a palaeozoic orogenic belt which contains two collision zones the older southern collision accreted a north facing passive continental margin on the north side of the tarim block to an active continental margin on the south side of an elongate continental tract the central tien shan collision occurred along the qinbulak qawabulak fault southern tien shan suture the time of the collision is poorly constrained but was probably in in the late devonian early carboniferous we propose this age because of a major disconformity at this time along the north side of the tarim block and because the youshugou ophiolite is imbricated with middle devonian sediments a younger probably late carboniferous early permian collision along the north tien shan fault northern tien shan suture accreted the northern side of the central tien shan to an island arc which lay to its north the north tien shan arc this collision is bracketed by the middle carboniferous termination of arc magmatism and the appearance of late carboniferous or early permian elastics in a foreland basin developed over the extinct arc thrust sheets generated by the collision are proposed as the tectonic load responsible for the subsidence of this basin post collisional but palaeozoic dextral shear occurred along the northern suture zone this was accompanied by the intrusion of basic and acidic magmas in the central tien shan late palaeozoic basic igneous rocks from all three lithospheric blocks represented in the tien shan possess chemical characteristics associated with generation in supra subduction zone environments even though many post date one or both collisions rocks from each block also possess distinctive trace element chemistries which supports the three fold structural division of the orogenic belt it is unclear whether the chemical differences represent different source characteristics or are due to different episodes of magmatism being juxtaposed by later dextral strike slip fault motions because the southern collision zone in the tien shan is the older of the two the tarim block sensu stricto collided not with the eurasian landmass but with a continental block which was itself separated from eurasia by at least one ocean the destruction of this ocean in late carboniferous early permian times represented the final elimination of all oceanic basins from this part of central asia

in situ u pb hf and re os isotopic analyses of the xiangshan ni cu co deposit in eastern tianshan xinjiang central asia orogenic belt constraints on the timing and genesis of the mineralization abstract the timing and genesis of the major ni cu co sulfide deposit in the xiangshan intrusion have been studied based on newly obtained in situ u pb hf and re os isotopic analyses the sims u pb zircon ages of the gabbro hosting the ni cu co sulfide deposit indicate that the xiangshan intrusion was emplaced at 279 6 1 1 ma 95 confidence level mswd 1 30 n 15 on the basis of combined geological and geochronological evidence we suggest that the xiangshan and other adjacent ni cu deposits were formed in the same period sulphides have low common os concentrations and high re os ratios similar to sulphide ores from the duluth sally malay and voisey bay complexes the re os isotopic data from the disseminated and massive ores from the xiangshan intrusion do not form a single isochron as they have different initial os ratios the hf and os isotopic data suggest that the xiangshan intrusion and associated ni cu co mineralization were derived from crustally contaminated mantle melts the geochemical data show a tholeiitic affinity and a strong suprasubduction zone signature with negative nb sr and ti anomalies similar to n morb and e morb we suggest that the mafic ultramafic rocks and associated ni cu mineralization of the eastern tianshan orogen formed in an alaska type subduction zone arc setting some diagnostic features of ridge trench interaction are present in the chinese east tianshan orogen e g granites adakites high mg andesites near trench magmatism alaskan type mafic ultramafic complexes high temperature metamorphic belts that prograde rapidly from low grade belts and orogenic gold deposits the above distinctive rock groups are probably related to the same thermal event ridge subduction as in the cenozoic orogen of alaska we suggest that ridge subduction is the most plausible mechanism to provide the necessary heat ridge subduction provides an important promising model for understanding many aspects of the evolution of the chinese eastern tianshan orogen and by inference throughout much of central asia

energetics of gas driven limnic and volcanic eruptions abstract this paper lays the foundation for the rigorous treatment of the energetics of gas exsolution from a gas containing liquid which powers gas driven volcanic and limnic eruptions various exsolution processes reversible or irreversible slow or rapid are discussed and the maximum amount of kinetic energy derivable from a reversible gas exsolution process is obtained the concept of dynamic irreversibility is proposed for discussing the kinetic energy available from irreversible gas exsolution processes the changes of thermodynamic properties during gas exsolution processes are derived density pressure relations for gas liquid mixtures are presented including empirical relations for irreversible gas exsolution the energetics of gas driven eruptions through both fluid and rigid media including the role of buoyancy and the role of magma chamber expansion work are investigated for reversible processes the energetics can be used to discuss the dynamics of gas driven eruptions leading to maximum erupting velocities and maximum eruptible fractions for irreversible processes empirical relations and parameters must be employed the exit velocities of the lake nyos eruption and the 18 may 1980 eruption of mount st helens are modeled by incorporating possible irreversibility

fumaroles in ice caves on the summit of mount rainier preliminary stable isotope gas and geochemical studies abstract the edifice of mount rainier an active stratovolcano has episodically collapsed leading to major debris flows the largest debris flows are related to argillically altered rock which leave areas of the edifice prone to failure the argillic alteration results from the neutralization of acidic magmatic gases that condense in a meteoric water hydrothermal system fed by the melting of a thick mantle of glacial ice two craters atop a 2000 year old cone on the summit of the volcano contain the world s largest volcanic ice cave system in the spring of 1997 two active fumaroles t 62 c in the caves were sampled for stable isotopic gas and geochemical studies stable isotope data on fumarole condensates show significant excess deuterium with calculated d and 18o values 234 and 33 2 respectively for the vapor that are consistent with an origin as secondary steam from a shallow water table which has been heated by underlying magmatic hydrothermal steam between 1982 and 1997 d of the fumarole vapor may have decreased by 30 the compositions of fumarole gases vary in time and space but typically consist of air components slightly modified by their solubilities in water and additions of co2 and ch4 the elevated co2 contents 13 c co 2 11 8 0 7 with spikes of over 10 000 ppm require the episodic addition of magmatic components into the underlying hydrothermal system although only traces of h2s were detected in the fumaroles most notably in a sample which had an air 13cco2 signature 8 8 incrustations around a dormant vent containing small amounts of acid sulfate minerals natroalunite minamiite and woodhouseite indicate higher h2s or possibly so2 concentrations in past fumarolic gases condensate samples from fumaroles are very dilute slightly acidic and enriched in elements observed in the much higher temperature fumaroles at mount st helens k and na up to the ppm level metals such as al pb zn fe and mn up to the ppb level and volatiles such as cl s and f up to the ppb level the data indicate that the hydrothermal system in the edifice at mount rainier consists of meteoric water reservoirs which receive gas and steam from an underlying magmatic system at present the magmatic system is largely flooded by the meteoric water system however magmatic components have episodically vented at the surface as witnessed by the mineralogy of incrustations around inactive vents and gas compositions in the active fumaroles the composition of fumarole gases during magmatic degassing is distinct and if sustained could be lethal the extent to which hydrothermal alteration is currently occurring at depth and its possible influence on future edifice collapse may be determined with the aid of on site analyses of fumarole gases and seismic monitoring in the ice caves

fluid fluid interactions in magmatic hydrothermal ore formation hydrothermal ore deposits have provided some of the first geological evidence for the interaction of multiple fluids in the earth s interior including fluid mixing as well as fluid phase separation physical evidence comes from veins and breccias documenting the impact of fluids in breaking rocks and creating fracture permeability for ore formation as a result of the fluid expansion that is commonly associated with phase separation between melts and multiple fluids chemical evidence of fluid fluid interaction includes the precipitation of minerals in veins as a result of fluid boiling or mixing between chemically contrasting fluids fluid inclusions record interactions of multiple fluids especially in magmatic hydrothermal ore deposits and associated igneous rocks fig 1 in recent years fluid inclusions have contributed to a more quantitative understanding of the role of fluid fluid interactions since new microanalytical techniques allow determination of element concentrations in all types of fluids from low density vapor through aqueous and hypersaline liquids to hydrous salt melts roedder 1984 samson et al 2003 figure 1 geological evidence for fluid phase separation in ore forming magmatic hydrothermal systems a bonanza grade gold 1 wt that was precipitated together with fine grained pyrite in a fluidized breccia resulting from instantaneous boiling and expansion of magmatic fluids ascending from an underlying andesite porphyry intrusion the breccia consists of adularia sericite altered clasts of sedimentary wall rock s and nodules of originally colloidal pyrite with bright specks of gold p g both cemented by roscoelite r vanadium rich muscovite and late calcite c zone vii ore body porgera papua new guinea ronacher et al 2004 b bladed manganocalcite the characteristic habit of calcite precipitated from aqueous epithermal fluids as a result of the ph change following loss of co2 to a separating vapor phase madan bulgaria kostova et al 2004 c growth band in a euhedral quartz

large scale porphyry type mineralization in the central asian metallogenic domain a review abstract a series of porphyry type cu mo au deposits including some giant world class deposits such as kounrad aktogai kal makyr oyu tolgoi and chalukou occur in the central asian metallogenic domain camd the outline of the camd almost overlaps with that of the central asian orogenic belt caob which is located between the east europe siberia tarim and north china cratons the camd comprises sparsely exposed tectonic slices of precambrian high grade metamorphic basement rocks that are sandwiched between phanerozoic accretionary complexes and arc rocks according to geological metallogenic geochronological and tectonic setting characteristics the camd comprises three metallogenic provinces 1 the kazakhstan cu au mo 2 the mongolia cu au and 3 the northeast china mo cu metallogenic provinces early paleozoic 490 to 440 ma and late paleozoic 330 to 295 ma large scale porphyry type mineralization in the kazakhstan metallogenic province is intimately associated with the evolution of the central tianshan yili northern tianshan kokchetav chingiz paleozoic arc system which was terminated by the late permian closure of the western segment of the paleo asian ocean in contrast the 370 ma and 240 ma porphyry type mineralization of the mongolia metallogenic province is related to the tuva mongolia arc collage system that was formed during the evolution of the paleo asian ocean in the paleozoic and the mongol okhotsk ocean in the early mesozoic furthermore the northeast china metallogenic province was affected by three distinct geodynamic processes that were associated with the paleo asian mongol okhotsk and paleo pacific oceans during the paleozoic 250 ma the early mesozoic 200 ma and the late mesozoic 200 90 ma respectively except for the early paleozoic cu mineralization at duobaoshan 480 ma and bainaimiao 440 ma the porphyry type mineralization of this metallogenic province is predominantly characterized by widespread mesozoic mo mineralization in general porphyry type deposits of the camd have geological structural metallogenic alteration and fluid characteristics which are consistent either with those related to the oceanic subductional arc settings of the circum pacific metallogenic domain or with those of the continental collisional environment in the tethyan metallogenic domain the involvement of highly oxidized intermediate to felsic magmas is fundamental for the formation of porphyry deposits even though the prevalent mash and slab melting models can be employed to interpret the genesis of some porphyry cu deposits in the camd a here newly suggested model which is based on pre enriched mafic lower crust and the subduction of a relictic mid oceanic ridge is thought to explain the large scale copper mineralization in the balkhash west junggar metallogenic belt of the kazakhstan metallogenic province nevertheless most of the porphyritic suites associated with the mo deposits in the northeast china metallogenic province have relatively depleted mantle like neodymium and hafnium isotopic compositions suggesting that the ore forming granitic magma may have predominantly been derived from juvenile lower crust upwelling of asthenosphere may have triggered the melting of the lower crust during post collisional extension subsequent to the closure of the paleo asian ocean in the triassic the subduction of the paleo pacific ocean in the jurassic and the thinning of the lithosphere caused by rollback of the paleo pacific plate in the cretaceous ancient crustal components were only locally found to have been involved in the magma source of several medium large mo deposits

types geological features and geodynamic significances of gold copper deposits in the kanggurtag metallogenic belt eastern tianshan nw china occupying the middle of the central asia paleozoic accretionary and collisional orogenic belt the eastern tianshan area has a great economic potential due to au cu mineralization during syn and post orogenic events in the kanggurtag au cu metallogenic belt three major types of gold deposits have been recognized ductile shear zone hosted gold deposits magmatic hydrothermal gold deposits and epithermal gold deposits four kinds of copper deposits have also been identified recently the porphyry type the skarn type the magmatic type and volcanic sedimentary type tectonically the development of these late paleozoic gold and copper deposits was closely associated with the subduction and collision of the ancient tianshan ocean that intervened between the tarim craton and the siberian block in the early to mid carboniferous n dipping subduction beneath the dananhu arc generated magmatic intrusions leading to formation of the porphyry cu deposits the magmatic front migrated southward to form the yamansu arc upon the kanggurtag accretionary wedge in the latest carboniferous to early permian during the closure of the ancient tianshan ocean large mafic ultramafic complexes were emplaced resulting in several magmatic copper nickel deposits gold deposits of the shear zone type are controlled by the kanggurtag ductile shear zone which is related to collisional orogenesis the epithermal gold deposits are associated with extensional tectonics and post tectonic volcanic activity the tectonic settings geological features and temporal and spatial distributions of these different types of gold and copper deposits reflect to a great extent the accretionary and collisional tectonics that occurred between the northern margin of the tarim block and the southern margin of the siberian block

re os dating of chalcopyrite from selected mineral deposits in the kalatag district in the eastern tianshan orogen china the kalatag cu zn au district contains a number of economically important cu deposits in eastern tianshan in xinjiang nw china due to the lack of precise mineralization ages the metallogenesis of this area has long been a matter of debate in this study chalcopyrite re os isotope methods are used to date the south meiling cu zn and hongshi cu deposits in the eastern part of kalatag area the south meiling cu zn deposit is hosted in volcanic sedimentary rocks of the late ordovician to early silurian daliugou formation the deposit consists of two parts a concordant massive sulfide ores and discordant vein type ores located in the footwall strata the principal ore minerals are pyrite chalcopyrite sphalerite minor tetrahedrite galena and pyrrhotite gangue minerals include quartz sericite and barite and minor chlorite plagioclase and carbonate minerals the hongshi cu deposit represents a hydrothermal vein system hosted in the mafic volcanic rocks of daliugou formation the orebodies are associated with quartz veins and controlled by subsidiary faults of the kalatag fault the ore forming process can be divided into the early middle and late stages and is characterized by quartz pyrite quartz chalcopyrite pyrite and quartz carbonate gypsum veins respectively re os analyses of chalcopyrite from the south meiling cu zn deposit yield an isochron age of 434 2 3 9 ma and initial 187os 188os ratio of 0 647 0 098 mswd 0 59 re os analyses of chalcopyrite from the hongshi cu deposit yield an isochron age of 431 8 2 7 ma and initial 187os 188os ratio of 0 165 0 075 mswd 0 77 since chalcopyrite is the primary copper mineral we interpret these isochron ages as the timing of cu mineralization based on field geology and petrographic evidence these results suggest that the re os ages presented here provide for the first time a direct constraint on an early paleozoic cu mineralization event of the eastern tianshan orogen the high initial 187os 188os ratios 0 647 0 098 ratio of 434 ma chalcopyrite from the south meiling deposit suggest that the metal was sourced from a two end member mixing of crust and mantle materials moreover we propose that the vms mineral system and hydrothermal vein system of the kalatag district were related to the south dipping subduction of the kalamaili oceanic plate during the late ordovician silurian

stability and abundance of the trisulfur radical ion s 3 in hydrothermal fluids the interpretation of sulfur behavior in geological fluids and melts is based on a long standing paradigm that sulfate sulfide and sulfur dioxide are the major sulfur compounds this paradigm was recently challenged by the discovery of the trisulfur ion s 3 in aqueous s bearing fluids from laboratory experiments at elevated temperatures however the stability and abundance of this potentially important sulfur species remain insufficiently quantified at hydrothermal conditions here we used in situ raman spectroscopy on model thiosulfate sulfide and sulfate aqueous solutions across a wide range of sulfur concentration 0 5 10 0 wt acidity ph 3 8 temperature 200 500 degrees c and pressure 15 1500 bar to identify the different sulfur species and determine their concentrations results show that in the low density 0 2 g cm 3 vapor phase h2s is the only detectable sulfur form by contrast in the denser liquid and supercritical fluid phase together with sulfide and sulfate the trisulfur radical ion s 3 is a ubiquitous and thermodynamically stable species from 200 degrees c to at least 500 degrees c in addition the disulfur radical ion s is detected at 450 500 degrees c in most solutions and polymeric molecular sulfur with a maximum abundance around 300 degrees c in s rich solutions these results combined with revised literature data allow the thermodynamic properties of s 3 to be constrained enabling quantitative predictions of its abundance over a wide temperature and pressure range of crustal fluids these predictions suggest that s 3 may account for up to 10 of total dissolved sulfur s tot at 300 500 degrees c in fluids from arc related magmatic hydrothermal systems and more than 50 s tot at 600 700 degrees c in s rich fluids produced via prograde metamorphism of pyrite bearing rocks the trisulfur ion may favor the mobility of sulfur itself and associated metals au cu pt mo in geological fluids over a large range of depth and provide the source of these elements for orogenic au and porphyry epithermal cu au mo deposits furthermore the ubiquity of s 3 in aqueous sulfate sulfide systems offers new interpretations of the kinetics and mechanisms of sulfur redox reactions at elevated temperatures and associated mass dependent and mass independent fractionation of sulfur isotopes

multiple mineralization events of the paleozoic tuwu porphyry copper deposit eastern tianshan evidence from geology fluid inclusions sulfur isotopes and geochronology the tuwu porphyry cu deposit located in eastern tianshan nw china is hosted by a plagiogranite porphyry and carboniferous qi eshan group volcanic rocks based on crosscutting relationships and mineral assemblages hydrothermal alteration and mineralization processes at tuwu can be divided into four stages early propylitic alteration stage i porphyry mineralization stage ii overprinting mineralization stage iii and post mineralization stage iv the porphyry mineralization stage stage ii contributed to the majority of the cu mo resource with cu mineralization occurring mainly as quartz chalcopyrite veins stage iii also produced minor cu mineralization characterized by chalcopyrite anhydrite chlorite calcite assemblages fluid inclusion fi study reveals that stage ii is characterized by a high temperature high salinity highly oxidized and k rich h2o nacl cacl2 fluid fluid boiling and mixing likely occurred during the porphyry mineralization stage leading to the precipitation of chalcopyrite and pyrite alteration and mineralization in stage iii were derived from a s rich h2o nacl cacl fluid with fluid boiling leading to the precipitation of chalcopyrite the 34s values of chalcopyrite from stages ii and iii are 0 8 0 6 and 1 1 1 3 respectively suggesting magmatic sources for the ore forming components of both stages 40ar 39ar dating indicates that stage ii likely occurred at 328 1 1 4 ma around the age emplacement of the causative plagiogranite porphyry ca 337 7 330 3 ma we suggest the overprinting mineralization event occurred at ca 323 ma spatially and genetically related to the emplacement of the quartz albite porphyry at 323 6 2 5 ma

evidence of multi phase cretaceous to quaternary alkaline magmatism on tore madeira rise and neighbouring seamounts from 40ar 39ar ages abstract the tore madeira rise is a seamount chain located 300 km off the portugal and morocco coasts attributed to hotspot activity u pb ages of lavas from the northern and central tore madeira rise range between 103 and 80 5 ma whereas 40 ar 39 ar ages from the central and southern tore madeira rise yield ages ranging from 94 5 to 0 5 ma we performed new 40 ar 39 ar measurements to better understand the geodynamic history of the tore madeira rise plagioclase ages from the bikini bottom and torillon seamounts suggest ages of 90 ma and 60 ma respectively amphiboles from the seine seamount yield an age of 24 0 0 8 ma biotites from lavas of the ashton seamount give ages of 97 4 1 1 ma and 97 8 1 1 ma the geochronological database available on the tore madeira rise has been filtered on statistical criteria to eliminate unreliable ages the resulting database reveals three pulses of alkaline magmatism on the tore madeira rise at 103 80 5 ma at c 68 ma and between 30 ma and the present the magmatism was continuous from 103 ma until c 68 ma and from c 30 ma until the present on the tore madeira rise the surrounding seamounts and the portugal coast we suggest that the space time distribution of this magmatism results from the interaction between a wide thermal anomaly emitting magmatic pulses and the complex motion of the iberian plate supplementary material a detailed ar measurements dataset is available at http www geolsoc org uk sup18359

overprinting mineralization in the paleozoic yandong porphyry copper deposit eastern tianshan nw china evidence from geology fluid inclusions and geochronology abstract the yandong porphyry copper deposit is located in the southern part of the dananhu tousuquan island arc belt in eastern tianshan xinjiang nw china the dananhu tousuquan belt contains a number of large and medium cu deposits among which the yandong deposit 2 0 mt cu 0 67 is the largest the yandong cu deposit is hosted by plagiogranite porphyry and the carboniferous qi eshan group mafic to intermediate calc alkaline volcanic and pyroclastic rocks according to the crosscutting relationships and mineral assemblages the alteration and mineralization processes at yandong comprise three episodes the porphyry mineralization episode including potassic propylitic early phyllic and late phyllic stages the overprinting mineralization episode including main and post mineralization stages and lastly supergene alteration episode fluid inclusions fis in quartz from the potassic early late phyllic and post mineralization stages and anhydrite from the main post mineralization stages include four types 1 vapor liquid two phases w type 2 daughter mineral bearing s type 3 pure liquid pw type and 4 pure vapor pv type the potassic stage contains w s and pv type fis which yielded homogenization temperatures of 304 445 c mainly 340 400 c and salinities of 3 1 16 4 mainly 4 0 10 0 wt nacl eqv at the early phyllic stage three types of fis are identified i e the w s and pv type the s type and w type fis homogenized at 213 441 c mainly 280 300 c and 241 352 c mainly 300 320 c respectively with corresponding salinities of 33 1 52 0 mainly 34 0 40 0 wt nacl eqv and 0 9 15 9 mainly 0 9 4 0 wt nacl eqv respectively the late phyllic stage contains w s and pw type fis which homogenized at 146 248 c mainly 160 180 c with salinities ranging from 3 9 to 18 2 mainly 4 0 8 0 wt nacl eqv mineralization depths calculated from fis are 0 8 1 2 km stage i 0 6 1 8 km stage iiia and 0 4 0 7 km stage iiib fluid boiling and mixing likely occurred during the porphyry mineralization period leading to the precipitation of pyrite and chalcopyrite during the overprinting mineralization the w and pv type fis occur in the main mineralization anhydrite with homogenization temperatures and salinities being 248 421 c mainly 300 340 c and 5 3 13 8 mainly 8 0 10 0 wt nacl eqv respectively the post mineralization quartz and anhydrite homogenized at 105 195 c mainly 120 140 c with salinities of 0 5 13 6 mainly 8 0 10 0 wt nacl eqv the ore forming fluids may have predominantly been entrapped at 0 8 1 6 km stage iv and 0 3 0 6 km stage v the decreasing temperature may have led to the sulfides and sulfate precipitation and enrichment sericite 40 ar 39 ar dating of the altered plagiogranite porphyry yielded a plateau age of 332 8 3 8 ma consistent with the age of the early ore forming plagiogranite porphyry 339 332 ma re os dating of molybdenite coexisting with chalcopyrite anhydrite chlorite calcite assemblage yielded an age of 324 3 2 7 ma weighted mean consistent with the late quartz albite porphyry age zircon u pb 323 6 2 5 ma consequently we propose that at least two mineralization episodes may have occurred at yandong with the second episode contributing to the majority of the cu mo resources such overprinting mineralization style at yandong may represent a good example of the paleozoic cu deposits in the central asian orogenic belt

formation and maintenance of single thread tie channels entering floodplain lakes observations from three diverse river systems 1 tie channels connect rivers to floodplain lakes on many lowland rivers and thereby play a central role in floodplain sedimentology and ecology yet they are generally unrecognized and little studied here we report the results of field studies focused on tie channel origin and morphodynamics in the following three contrasting systems the middle fly river papua new guinea the lower mississippi river and birch creek in alaska across these river systems tie channels vary by an order of magnitude in size but exhibit the same characteristic morphology and appear to develop and evolve by a similar set of processes in all three systems the channels are characterized by a narrow leveed single thread morphology with maximum width approximately one tenth the width of the mainstem river the channels typically have a v shaped cross section unlike most fluvial channels these channels develop as lakes become isolated from the river by sedimentation narrowing of the connection between river and lake causes a sediment laden jet to develop levees develop along the margins of the jet leading to channel emergence and eventual levee aggradation to the height of the mainstem levees bidirectional flow in these channels is common outflows from the lake scour sediment and prevent channel blockage we propose that channel geometry and size are then controlled by a dynamic balance between channel narrowing by suspended sediment deposition and incision and widening by mass failure of banks during outflows tie channels are laterally stable and may convey flow for hundreds to a few thousand of years

subduction induced mantle heterogeneity beneath eastern tianshan and beishan insights from nd sr hf o isotopic mapping of late paleozoic mafic ultramafic complexes abstract extensive late paleozoic mafic ultramafic complexes in the eastern tianshan and beishan regions in the southern central asian orogenic belt caob represent an ideal opportunity to assess the characteristics of the mantle in this area whole rock nd sr and zircon hf o isotopic data from the mafic ultramafic complexes of the jueluotage belt middle tianshan massif and beishan rift were compiled for isotopic mapping end t and 87sr 86sr i values range from 5 5 to 9 5 and 0 702 to 0 706 respectively in the jueluotage belt and from 2 to 11 and 0 703 to 0 710 respectively in the middle tianshan and beishan zircon ehf t and 18o values are in the range of 6 0 17 0 and 4 14 8 00 respectively in the jueluotage belt 1 8 and 5 17 6 30 respectively in the middle tianshan and show large variations of 1 17 and 4 12 respectively in the beishan spatially the 87sr 86sr i ratios of mafic ultramafic complexes increase from the jueluotage belt and beishan to the middle tianshan while the end t values show an opposite trend and reflect a mixing character between depleted mantle and em ii reservoirs zircon ehf t and 18o values exhibit an apparent southward decreasing and increasing trends respectively from the jueluotage belt through middle tianshan to beishan rift their corresponding hf model ages increase continuously from north to south these observations demonstrate that the mantle sources beneath the eastern tianshan and beishan are compositionally heterogeneous which presumably result from significant and variable degrees of subduction related modification we therefore suggest that the late paleozoic subcontinental lithospheric mantle beneath the jueluotage belt was modified by slab derived melts and fluids during the subduction of the junggar ocean whereas the mantle beneath the beishan rift was influenced mainly by slab derived fluids during the subduction of the south tianshan ocean the unique similarities of the middle tianshan mafic ultramafic complexes reflect a two stage modification of their mantle source namely the sequential subduction of the early south tianshan ocean followed by subduction of the junggar ocean thus the subduction induced mantle heterogeneity beneath the caob is probably regional in scope

experimental simulations of gas driven eruptions kinetics of bubble growth and effect of geometry simulated gas driven eruptions using co2 water polymer systems are reported eruptions are initiated by rapidly decompressing co2 saturated water containing up to 1 0 wt co2 both cylindrical test cells and a flask test cell were used to examine the effect of magma chamber conduit geometry on erup tion dynamics bubble growth kinetics are examined quantitatively in experiments using cylindrical test cells uninhibited bubble growth can be roughly expressed as dr dt ld b 1 gt 1 3 for a co2 water polymer system at 0 22 7c and with viscosities up to 5 pa7s where r is the radius of bubbles l and d are the ostwald solubil ity coefficient and diffusivity of the gas in the liquid b is the degree of saturation decompression ratio and g characterizes how the boundary layer thickness in creases with time and is roughly 1 0 10 5 m s 1 3 in this system unlike the radius of cylindrical test cells which does not affect the eruption threshold and dynamics the shape of the test cells flask vs cylindrical affects the dynamics but not the threshold of eruptions for cylindrical test cells the front motion is characterized by constant acceleration with both dh the height in crease and dv the volume increase being propor tional to t 2 for the flask test cell however neither dh nor dv is proportional to t 2 as the conduit radius var ies test cell geometry also affects foam stability in the flask test cell as it moves from the wider base chamber into the narrower conduit the bubbly flow becomes fragmented affecting the eruption dynamics the frag mentation may be caused by a sudden increase in accel eration induced by conduit shape change or by the presence of obstacles to the bubbly flow this result may help explain the range in vesicularities of pumice and reticulite

methane escape from gas hydrate systems in marine environment and methane driven oceanic eruptions 1 huge quantities of ch4 are stored in marine sediment in the form of methane hydrate bubbles and dissolved ch4 in pore water here i discuss the various pathways for methane to enter the ocean and atmosphere including i methane hydrate dissolution or dissociation as it rises through seawater the dissociation rate can be 2 to 3 orders of magnitude greater than the dissolution rate ii the dissolution and expansion of a bubble with or without a hydrate shell as it rises through seawater there is a critical radius which depends on depth above which a bubble would reach the surface or even become larger as it rises i also propose and model the dynamics of a new type of terrestrial gas driven eruptions methane driven oceanic eruptions such eruptions not only represent a yet unrecognized geohazard but also provide a pathway for ch4 to rapidly enter the atmosphere as a greenhouse gas

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

early paleozoic magmatic record from the northern margin of the tarim craton further insights on the evolution of the central asian orogenic belt abstract the southern tianshan orogenic belt stob is an important region to understand the prolonged evolution of the central asian orogenic belt caob a comprehensive study of zircon u pb ages and lu hf isotopes whole rock elements and sr nd isotopes was carried out for two intermediate mafic intrusions in the baicheng and heiyingshan areas of southwest tianshan la icp ms zircon u pb dating yielded crystallization ages of 431 3 ma mswd 0 073 n 31 and 430 3 ma mswd 0 104 n 30 for the baicheng diorites and 423 9 2 1 ma mswd 0 5 n 12 for the heiyingshan gabbros these data in combination with other late silurian ages previously reported for the intrusive suites from the stob indicate an early paleozoic magmatic event in the region in situ zircon hf isotope data on two samples from the baicheng diorites show ehf t values of 2 4 to 4 9 and 0 2 to 6 and the heiyingshan gabbros exhibit similar ehf t values from 1 to 1 8 the dioritic pluton exhibits na rich arc type geochemical and calc alkaline affinity and shows trace element patterns characterized by enrichment in large ion lithophile elements rb ba k and sr and depletion in high strength field elements nb ta ti zr and hf these features resemble those of arc type igneous rocks combined with initial 87sr 86sr ratios of 0 7047 to 0 7064 and end t of 1 6 to 5 06 we infer that the magma from which the baicheng dioritic pluton formed was sourced from a mantle wedge which was subjected to metasomatism by fluids and melts related to subducted oceanic slab and the overlying sediments the heiyingshan gabbro shows a na rich nature and tholeiitic affinity they not only display supra subduction zone affinity but also are geochemically similar to e morb possible implying a back arc basin setting the initial 87sr 86sr ratios of the heiyingshan samples range from 0 7046 to 0 7051 and end t values vary from 1 76 to 5 19 we speculate that the upwelling of the asthenospheric mantle to the supra subduction wedge facilitated by subduction roll back provided the source for the heiyingshan gabbroic rocks together with other geologic evidence we correlate the generation of the baicheng diorite with the southward subduction of the south tianshan ocean during the early paleozoic the heiyingshan gabbroic plutons were probably formed in a back arc basin in response to the southward subduction of the paleo tianshan ocean in combination with coeval arc type magmatic rocks widely exposed in the southern margin of the central tianshan block a double sided subduction model is proposed to explain the evolution of the south tianshan ocean in the silurian

a genetic linkage between subduction and collision related porphyry cu deposits in continental collision zones the genesis of continental collision related porphyry cu deposits pcds remains controversial the most common hypothesis links their genesis with magmas derived from subduction modified arc lithosphere however it is unclear whether a genetic linkage exists between collision and subduction related pcds here we studied jurassic subduction related cu au and miocene collision related cu mo porphyry deposits in south tibet the jurassic pcds occur only in the western segment of the jurassic arc which has depleted mantle like isotopic compositions e g 87 sr 86 sr i 0 7041 0 7048 e nd t as high as 7 5 and e hf t as high as 18 by contrast no jurassic pcds have been found in the eastern arc segment which is isotopically less juvenile e g 87 sr 86 sr i 0 7041 0 7063 e nd t 4 5 and e hf t 12 these results imply that incorporation of crustal components during underplating of jurassic magma induced copper accumulation as sulfides at the base of the eastern jurassic arc inhibiting pcd formation at this time miocene pcds are spatially confined to the jurassic arc and the giant miocene pcds cluster in its eastern segment where no jurassic pcds occur this suggests that the arc segment barren for subduction related pcds could be fertile for collision related pcds miocene ore forming porphyries have young hf model ages and sr nd hf isotopic compositions overlapping with those of the jurassic rocks in the eastern segment whereas contemporaneous barren porphyries outside the jurassic arc have abundant zircon inheritance and crustlike sr nd hf isotopic compositions these data suggest that remelting of the lower crustal sulfide bearing cu rich jurassic cumulates triggered by cenozoic crustal thickening and or subsequent slab break off led to the formation of giant miocene pcds the spatial overlap and complementary metal endowment between subduction and collision related magmas may be used to evaluate the mineral potential for such deposits in other orogenic belts

lengthening plus shortening of river to lake connection times in the mackenzie river delta respectively via two global change mechanisms along the arctic coast 1 river deltas along the circumpolar arctic coast are lake rich and poorly understood ecosystems set in a region expected to change rapidly over the past 30 years annual river to lake connection times in the mackenzie delta have lengthened 30 days in the lowest elevation lakes and may have shortened in the highest elevation lakes respectively via sea level rise and declining effects of river ice breakup lengthened connection times indicate summer low water levels in the delta have increased by an amount 0 3 m equivalent to three times local sea level rise 0 1 m over the same period such an amplification effect of recent sea level rise has been completely unexpected and may be a result of enhanced storm surges in response to receding arctic sea ice or coastal backwater effects on the river flow shortened connection times are consistent with other work showing a decline in river ice breakup effects an important control on annual peak water levels

from crucible to graben in 2 3 ma a high resolution geochronological study of porphyry life cycles boyongan bayugo copper gold deposits philippines the boyongan and bayugo porphyry copper gold deposits are part of a belt of gold rich copper deposits in the surigao district of northeast mindanao philippines the detailed age relationships described in this study provide insight into the geologically short life cycles that characterize porphyry formation in dynamic arc environments since their late pliocene emplacement 2 3 2 1 ma shrimp sensitive highresolution ion microprobe u pb zircon dating at depths of 1 2 2 0 km these deposits were exhumed deeply weathered and buried weathering of these deposits led to the development of the world s deepest known porphyry oxidation profile 600 m thick at boyongan and a modest 30 70 m oxidation profile at adjacent bayugo this earlymiddle pleistocene supergene event followed a period of rapid uplift and exhumation in northeast mindanao 2 5 km ma u th he apatite age elevation spectrum subsequent rapid subsidence 0 34 km ma radiocarbon age elevation spectrum and burial of these deposits are attributed to a mid pleistocene shift from transpressional tectonics to the present day transtensional setting in northeast mindanao during this period debris flows volcanic material and fluviolacustrine sediments accumulating in the actively extending mainit graben covered the weathered deposits preserving the supergene profiles beneath 50 500 m of cover this detailed geochronological study documents the geologically short 2 3 ma time scales over which these major intrusion centered mineral deposits evolved from emplacement exhumation deep oxidation and burial highlighting the dynamism of tectonic processes in environments such as the philippine mobile belt 2012 geological society of america

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

junggar turfan and alakol basins as late permian to early triassic extensional structures in a sinistral shear zone in the altaid orogenic collage central asia the junggar turfan and alakol basins in northwestern china and kazakhstan formed as late permian to early triassic extensional structures in a broad sinistral shear zone between large strike slip faults that separate two main domains of the altaid orogenic collage this extension was in response to an inferred large l000 km sinistral motion of the east european craton with respect to the angaran craton during this time deformation associated with the formation of the basins was taken up in part by counter clockwise rotations of crustal blocks with respect to the altaid orogenic collage and to the angaran craton this event is the only important phase of extension in a region otherwise dominated by compressional tectonics throughout the phanerozoic the basement rocks of these basins formed by altaid subduction accretion through the latter half of the palaeozoic and the region was subsequently thrown into compression again during the mesozoic cimmeride and cenozoic alpide evolution

lake sedimentation in the mackenzie delta nwt spatial variation in lake sedimentation within the mackenzie delta was documented and total lake sedimentation over the past 30 years was estimated by classifying via aerial photography the flooding characteristics of a complete transect of lakes about 2600 lakes across the upper subaerial delta plain then selecting representative samples of lakes 81 lakes from the transect and a random sample of lakes from a second transect 7 lakes across the lower subaerial plain for direct measurement of sedimentation rates the depth corresponding to the 1963 sediment layer was obtained from a sediment core from each of these lakes by sampling the core at frequent depth intervals to identify the peak in 137 cs caesium 137 content lake sediment bulk densities as obtained from the cores averaged 931 kg m 3 a value lower than reported in previous studies using mean bulk density above each 137 cs peak and the depth of the 137 cs peak mean lake sedimentation for different lake types varied between 1 19 kg m 2 yr and 5 34 kg m 2 yr with a decrease in sedimentation as lake sill elevation increased values for the lower delta transect averaged 1 36 kg m 2 yr by combining relationships between sedimentation and lake type with a classification of lake types total sedimentation across the upper delta transect is estimated as 8 2 mt yr and 0 8 mt yr for the lower delta these values are lower than previously reported primarily because they are derived from lower bulk density values of the total upper delta sedimentation 17 occurs in high closure lakes 53 in low closure lakes and 30 in no closure lakes lake sedimentation is higher in the middle channel segment of the upper delta transect 44 of total sedimentation across the transect than in the east channel 25 or peel channel 32 segments

epithermal deposits in north xinjiang nw china the north xinjiang region nw china is an important part of the central asia orogenic belt situated at the junction of siberia tarim and kazakhstan plates it is an area characterized by multiple stages of phanerozoic continental growth during which several porphyry and epithermal systems were formed the relationship of these mineral systems to the geodynamic evolution of the region has not yet been well understood in this paper we list the main geological characteristics of 21 significant epithermal precious and base metal deposits in north xinjiang and classify them into high sulfidation and low sulfidation styles with the latter being predominant we have selected seven epithermal deposits representing different styles formed under different tectonic regimes and discuss their geology and geochemistry in some detail the deposit scale geology and geochemistry of epithermal systems in north xinjiang are essentially similar to those in other parts of the world all epithermal deposits in north xinjiang are hosted in volcanic rocks with ages ranging from devonian to triassic with the early carboniferous volcanic sequences being the most important followed by the permian and triassic the devonian early carboniferous host rocks belong to the calc alkaline series that developed in pre collisional arc back arc basin systems whereas the permian triassic host volcanic rocks of shoshonite series formed in post subduction regimes available isotopic ages of these epithermal systems cluster in two periods early carboniferous 320 ma and late carboniferous triassic 320 220 ma reflecting two metallogenic episodes that occurred during subduction related accretion and post subduction collision regimes respectively accordingly three groups of epithermal deposits in north xinjiang can be recognized as 1 pre collisional deposits without or with negligible collisional related modification 2 deposits formed in collision regime and 3 ore systems strongly overprinted by fluid flow in post subduction collision regime

geochemical characteristics of late carboniferous mineralization in the east tianshan a case study of the meiling deposit in the kalatage area abstract the meiling deposit in the kalatage area of the east tianshan which is the most recently identified late carboniferous hydrothermal vein deposit is located in a series of basic intermediate acidic volcanic pyroclastic rocks and contains ore bodies composed of single quartz sulfide veins and quartz sulfide vein groups in a stockwork en echelon arrangement with cu as the primary ore forming element and zn au and ag as secondary ore forming elements this study examines the geochemical characteristics of sub volcanic rocks and analyses fluid inclusions and stable isotopes h o and s to determine the metallogenic characteristics of the meiling deposit and discusses the pattern and geological significance of the mineralization in the kalatage area the quartz porphyry dacite porphyry and granite porphyry from the meiling deposit which are closely related to the mineralization are calc alkaline magmatic rocks that formed in an island arc setting most of the primary quartz fluid inclusions are liquid rich two phase fis with homogenization temperatures mainly of 154 251 c and salinities of 3 1 5 6 nacl equivalent and the sphalerite fluid inclusions are liquid rich two phase fis characterized by omogenization temperatures mainly of 156 263 c and salinities of 2 4 5 3 nacl equivalent which are low temperature and low salinity h and o isotope analysis show that in the polymetallic sulfide quartz stage the d values ranged from 79 3 to 54 0 the 18oh2o values ranged from 8 99 to 2 57 and the primary ore forming fluids were mixtures of a dominant meteoric water phase with minor amounts of magmatic fluid s isotope analysis shows that in the polymetallic sulfide quartz stage the 34s values of the main sulfides were distributed between 1 6 and 5 2 similar to the range of a homogenous sulfur source these results together with the s isotopic characteristics of the wall rocks from the meiling deposit demonstrate that the ore forming metals might have originated from the volcanic subvolcanic wall rocks these results show that the metallogenic characteristics of the meiling deposit are consistent with those of low temperature epithermal deposits and clearly demonstrate that the meiling deposit is a low temperature epithermal deposit that formed in an island arc setting the kalatage area provides a natural laboratory for studying the characteristics of geological mineralization during the arc basin system transformation process

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

paleozoic accretionary and collisional tectonics of the eastern tianshan china implications for the continental growth of central asia this paper deals with the various tectonic units in the chinese eastern tianshan orogenic collage in the central asian orogenic belt and discusses the paleozoic geological history of the several periods of accretion and collision of archipelago systems lying between the tarim and southern angaran continental margins the late ordovician silurian to early devonian eastern tianshan archipelago was characterized by a the harlik dananhu subduction system with a s dipping polarity in the north b a southerly n dipping subduction system beneath the central tianshan arc in the middle and c the south tianshan ocean against tarim in the south during the devonian to early carboniferous n dipping subduction led to the harlik dananhu arc and the kanggurtag forearc basin accretionary complex in the early to mid carboniferous the magmatic front associated with the n dipping subduction beneath the dananhu harlik arc migrated southwards forming the yamansu arc constructed upon the kanggurtag accretionary forearc by the late carboniferous the dananhu harlik arc was attached northwards to the angaran margin resulting in lateral enlargement of the angaran continent in the latest carboniferous to early permian a multiple soft collision left wide suture zones in the south that include the ophiolite strewn aqikkuduk shaquanzi and kumishi accretion collision complexes which were stitched by early permian post collisional plutons by re defining and re interpreting the various tectonic terranes this paper presents a new improved model for the paleozoic evolution of this part of central asia

contrasting ore styles and their role in understanding the evolution of the altaids abstract the altaids is a paleozoic orogenic collage in central asia it occupies 10 of the eurasian continent and it is one of the richest concentrations of mineral deposits in the world comparable to those of the circum pacific and tethyan orogenic belts in particular it contains many types of hydrothermal ore deposits that are sensitive to the nature and origin of their host terranes including porphyry copper gold molybdenum volcanogenic massive sulfide copper lead zinc and orogenic gold deposits which are all diagnostic of convergent continental margins extensional arc related submarine basins and transpressional terrane boundaries within the altaids porphyry copper deposits are mostly concentrated within the kazakhstan and tuva mongolia micro continents where they formed almost continuously from the early ordovician to permian only a few are cambrian and triassic and most are late carboniferous most volcanogenic massive sulfide ore deposits are distributed along the south urals and rudny altai in the western altaids where they formed in a short time window from the early to middle devonian important orogenic gold deposits formed along regional strike slip faults between craton island arc or micro continent boundaries from the neoproterozoic to permian mostly in the early permian in limited key areas volcanogenic massive sulfide deposits formed upon much older 100 ma basement rocks than those of coeval porphyry deposits indicating that the altaids could not have developed from a single arc furthermore the porphyry deposits outline the distribution of several continental fragments the combined area of which is far less than that of the altaids which suggests that extensive new juvenile material has been added into island arc systems which may have been accreted to surrounding continental margins these metallogenic distributions in localized areas were a result of the mechanisms of crustal growth within the overall tectonic evolution of the altaids and they are consistent with the interpretation that the altaids is a multiple subduction accretion collage

the crustal accretion history and tectonic evolution of the ne china segment of the central asian orogenic belt abstract the basement rocks in parts of ne china constitute a khondalitic sequence of sillimanite and garnet bearing gneisses hornblende plagioclase gneiss and various felsic paragneisses zircon u pb dating of garnet sillimanite gneiss samples from the erguna xing an jiamusi and khanka blocks indicates that high grade metamorphism occurred at 500 ma evidence from detrital zircons in paleozoic sediments from the songliao block also indicates the former presence of a 500 ma component this uniformity of u pb ages across all crustal blocks in ne china establishes a 1300 km long late pan african khondalite belt which we have named the ne china khondalite belt this indicates the blocks of ne china were amalgamated prior to 500 ma contrary to current belief one scenario is that this amalgamated terrane had a tectonic affinity to the siberia craton once forming part of the late pan african 500 ma sayang baikal orogenic belt extensively developed around the southern margin of the siberia craton this belt was the result of collision between currently unidentified terranes with the southeastern angara anabar province at about 500 ma where the rocks were deformed and metamorphosed to granulite facies it appears likely that at sometime after 450 ma the combined ne china blocks rifted away from siberia and moved southward to form what is now ne china the combined block collided with the north china craton along the solonker xar moron changchun suture zone at 230 ma rather than in the end permian as previously thought local rifting at the eastern extremity of the developing central asian orogenic belt caob resulted in the splitting away of the jiamusi khanka bureya blocks however this was only transient and sometime between 210 and 180 ma these were re united with the caob by the onset of pacific plate subduction which has dominated the tectonic evolution of the region since that time

hydrothermal evolution of the el teniente deposit chile porphyry cu mo ore deposition from low salinity magmatic fluids the magmatic hydrothermal evolution of the el teniente porphyry cu mo deposit in the central andes in chile is reconstructed based on field relationships scanning electron microscopy cathodoluminescence petrography and fluid inclusion analysis by microthermometry and laser ablation inductively coupled plasma mass spectrometry la icpms three major stages of cu mo mineralization are observed following the barren hydrothermal stage 1 the stage 2 mineralization is characterized by quartz anhydrite stockwork veins and breccias with chalcopyrite bornite and molybdenite both stages 1 and 2 are associated with pervasive potassic alteration quartz anhydrite veins with chalcopyrite bornite and molybdenite associated with phyllic alteration represent stage 3 mineralization stage 4 mineralization linked to the formation of the large braden diatreme is characterized by breccias and rare veins containing a lower temperature assemblage with tourmaline sericite and lesser tennantite bornite and chalcopyrite with late gypsum in local vugs ten fluid types are distinguished in this study based on petrographic and microthermometric criteria such as phase proportions daughter minerals homogenization behavior and salinity the hydrothermal evolution across the stages of cu deposition is characterized by the contraction of a vapor phase originating by phase separation during stage 2 overall cooling of the system at pressures fluctuating around the two phase fluid surface led to a transition from a two phase fluid state dominated by vapor at 410 c and 300 bars in stage 2 to a single phase low salinity fluid derived from cooling and contraction of magmatic vapor to a liquid which dominates during stage 3 mineralization at 350 c and 200 bars copper mineralization mainly formed from the vapor phase and its low salinity liquid derivatives representing a large volume of fluid with an initially high cu content 1 2 0 4 wt cu copper sulfides precipitated upon cooling between 410 and 320 c indicated by a drop of cu na k mn fe ratios of over four orders of magnitude through the evolution of the deposit from stage 2 to stage 4 the highest mo concentrations occur in residual brines resulting from extreme boiling as indicated by concurrent halite saturation recent geochronology cannell 2005 maksaev et al 2004 suggests a relatively long lived magmatic hydrothermal system at el teniente our fluid chemical data show no evidence for major crystal fractionation in a large fluid generating upper crustal magma chamber because cs na k mn fe is constant from pre ore to all syn ore fluids however the initiation of copper mineralization was associated with a 4 to 10 fold increase in the concentration of cu mo li and fe in the inferred main ore forming input fluid compared with pre ore fluids of intermediate salinity and otherwise very similar major and trace element ratios these data indicate that injection from depth of an exceptionally cu mo li and probably also s rich volatile phase into an already actively evolving upper crustal magmatic hydrothermal system triggered the formation of this unusually large and rich copper deposit

riverine sediment balance of the mackenzie delta northwest territories canada data acquisition by environment canada and others over the last 20 years now allows the first comprehensive synthesis of the riverine sediment balance of the mackenzie delta the data presented here are sediment inputs from the mackenzie and peel rivers at the delta head and river sediment transfers from the upper delta to the outer delta 1974 1994 in channel and overbank sedimentation including lakes post 1963 and in channel erosion along delta channels 1950 1981 these data indicate that the mean annual sediment input to the delta is about 128 mt and the corresponding loss to offshore is about 85 mt the net sedimentation of 43 mt is divided almost equally between the upper delta mostly on levees and lake beds and the outer delta mostly on lake shores gross sedimentation within the delta about 50 of which is on point bars is much higher estimated at about 103 mt annually the difference is the large amount of sediment reentrainment within the delta through bank erosion primarily along middle channel how much of this pointbar deposition is from settling of sediment delivered by the mackenzie and peel rivers as distinct from local sediment derived from bank scour within the delta is not known such within delta sediment exchange which could be as high as 50 mt might be important in determining the quality of sediment nutrients contaminants etc that it is being delivered offshore it would be naive to assume that all of this sediment is from the present day input of the mackenzie and peel rivers

multiple mineralization events in the eastern tianshan district nw china isotopic geochronology and geological significance abstract the eastern tianshan district occupies the middle of the central asian orogenic belt and has great economic potential for polymetallic mineralization more than 20 medium to large ore deposits have been discovered in this region since the late 1980s the timing of mineralization was previously thought to be hercynian but mesozoic ages for intrusions and mineralization have been repeatedly reported in recent years based on geochronological data and regional geological evidence it is suggested that the mineralization in the eastern tianshan was formed during multiple events the mineralization processes are related to an subduction island arc stage 360 320 ma with porphyry type and volcano sedimentary copper deposits a collisional accretionary stage 300 280 ma with orogenic type gold deposits a post collisional extension stage 280 245 ma with mafic ultramafic copper nickel and epithermal gold deposits and an intracontinental extensional stage 240 220 ma that gave rise to the jinwuozi gold deposit xiaobaishitou skarn w mo deposit and baishan porphyry mo re deposit

paleozoic multiple accretionary and collisional tectonics of the chinese tianshan orogenic collage abstract subduction related accretion in the junggar balkash and south tianshan oceans paleo asian ocean mainly in the paleozoic gave rise to the present 2400 km long tianshan orogenic collage that extends from the aral sea eastwards through uzbekistan tajikistan kyrgyzstan to xinjiang in china this paper provides an up to date along strike synthesis of this orogenic collage and a new tectonic model to explain its accretionary evolution the northern part of the orogenic collage developed by consumption of the junggar balkash ocean together with paleozoic island arcs northern ili issyk kul and chatkal located in the west which may have amalgamated into a composite arc in the paleozoic in the west and by addition of another two roughly parallel arcs dananhu and central tianshan in the east the western composite arc and the eastern dananhu and central tianshan arcs formed a late paleozoic archipelago with multiple subduction zones the southern part of the orogenic collage developed by the consumption of the south tianshan ocean which gave rise to a continuous accretionary complex kokshaal kumishi which separated the central tianshan in the east and other paleozoic arcs in the west from cratons tarim and karakum to the south cross border correlations of this accretionary complex indicate a general southward and oceanward accretion by northward subduction in the early paleozoic to permian as recorded by successive southward juxtaposition of ophiolites slices of ophiolitic melanges cherts island arcs olistostromes blueschists and turbidites which are mainly paleozoic in age with the youngest main phase being late carboniferous permian the initial docking of the southerly tarim and karakum cratons to this complicated late paleozoic archipelago and accretionary complexes occurred in the late carboniferous early permian in the eastern part of the tianshan and in the late permian in the western part which might have terminated collisional deformation on this suture zone the final stages of closure of the junggar balkash ocean resembled the small ocean basin scenario of the mediterranean sea in the cenozoic in summary the history of the altaids is characterized by complicated multiple accretionary and collisional tectonics

rb sr geochronology of single gold bearing pyrite grains from the katbasu gold deposit in the south tianshan china and its geological significance abstract the newly discovered katbasu gold deposit in the south tianshan region has a gold reserve of 76 t at an average grade of 3 84 g t it is the first large gold deposit in the central segment of the south tianshan gold mineralization is hosted within granite and is associated with potassic phyllic and chloritic alteration gold bearing pyrite occurs as disseminations in the host rock and as quartz sulfide veins cross cutting the potassic and phyllic alteration assemblage rubidium rb strontium sr analyses on sericite within five individual pyrite grains from a phyllic alteration sample yield an isochron age of 322 5 6 8 ma mswd 3 2 the host granite has a sims u pb zircon age of 351 4 1 1 ma mswd 0 13 the rb sr isochron age represents the mineralizing age of the katbasu gold deposit which significantly postdates the ore hosting granite but is consistent with the age of regional porphyry type mineralization at 320 ma in the south tianshan discovery of the katbasu gold deposits indicates huge potential for gold exploration in the central segment of the south tianshan as it is geologically similar to the western and eastern segments of the south tianshan which both host many world class gold deposits

spatio temporal sedimentation patterns in beaver ponds along the chevral river ardennes belgium with the recovery of the european beaver castor fiber and their capacity to engineer fluvial landscapes questions arise as to how they influence sediment transport including the spatio temporal trends and patterns of sedimentation in beaver ponds the chevral river ardennes belgium contains two beaver dam sequences which appeared in 2004 volumes of sediment deposited behind the dams were measured and grain size distribution patterns were determined flow discharges and sediment fluxes were measured at the inflow and outflow of each dam sequence between 2004 and 2011 1710 1 m3 of sediment was deposited behind the beaver dams with an average sediment thickness of 25 1 cm the thickness of the sediment layer was significantly p 0 001 related to the area of the beaver ponds along the stream beaver pond sediment thickness displayed a sinusoidal deposition pattern in which ponds with thick sediment layers were preceded by a series of ponds with thinner sediment layers a downstream textural coarsening in the dam sequences was also observed probably because of dam failures subsequent to surges differences in sediment flux between the inflow and outflow at the beaver pond sequence were related to the river hydrograph with deposition taking place during the rising limbs and slight erosion during the falling limbs the 7 year old sequences have filtered 190 19 ton of sediment out of the chevral river which is of the same order of magnitude as the 374 4 ton measured in pond deposits with the difference between the values corresponding to beaver excavations 60 24 ton inflow from small tributaries and runoff from the valley flanks hydrogeomorphic effects of c fiber and castor canadensis activity are similar in magnitude the detailed analysis of sedimentation in beaver pond sequences confirms the potential of beavers to contribute to river and wetland restoration and catchment management copyright 2013 john wiley sons ltd

high cu concentrations in vapor type fluid inclusions an artifact abstract studies of natural fluid inclusions have shown that cu commonly occurs at higher concentrations in vapor type inclusions than in coexisting brine inclusions a phenomenon which has been interpreted to arise from copper partitioning into the vapor phase in the first part of this study we attempted to experimentally reproduce this behavior in hydrothermal experiments covering a range of p t conditions 600 800 c 70 130 mpa fluid compositions nacl kcl fecl 2 0 5 6 6 wt s fluid acidities quench fluid ph 0 3 10 and sulfur speciation h 2 s dominated to so 2 dominated however as in several other studies we did not succeed in reproducing conditions under which cu partitions into the vapor phase in view of recent observations that quartz hosted fluid inclusions can diffusively loose or gain cu after entrapment we set out to determine if the evidence from natural fluid inclusions could be compromised for this purpose we synthesized vapor and brine inclusions from cu h 2 o nacl s fluids at 800 c 130 mpa and re equilibrated them in slightly different fluids at 800 c 70 mpa measuring some inclusions by la icp ms after each step vapor inclusions indeed experienced a dramatic increase in cu from 0 3 0 03 to 5 7 3 3 wt while brine inclusions remained largely unmodified leading to a change in the partition coefficient d cu vap brine from a true value i e before re equilibration of 0 4 0 05 to an apparent value of 8 3 4 9 the requirements for substantial diffusional gain of cu in fluid inclusions are a change in the ph of the surrounding fluid from 1 to more neutral and the presence of s in the pre existing fluid inclusions these requirements are also fulfilled in nature cooling magmatic hydrothermal fluids experience a change from acidic to more neutral ph due to buffering along the feldspar mica join and natural vapor inclusions typically contain significant amounts of sulfur a reversal experiment performed on natural quartz hosted fluid inclusions from the erongo granite namibia showed that this process can be reversed with the measured d cu vap brine value of 11 9 3 being modified to 0 06 0 04 thus d cu vap brine values 1 measured on natural fluid inclusions in quartz are likely a secondary feature caused by post entrapment copper diffusion realistic d cu vap brine values in porphyry cu environments are between 0 11 and 0 15 and reconstructed vapor brine mass ratios are in the order of 4 9 this suggests that the main transporting agent of cu at the porphyry level are brines and that models based on copper into the vapor phase are incorrect

rollover in volcanic crater lakes a possible cause for lake nyos type disasters abstract seemingly stably stratified fluids that is a heavier layer of fluid underlying an upper layer of lighter fluid can overturn if there is a heat flux through the system such events are termed rollover in the engineering literature occurring for instance in liquid natural gas tanks they take place as well in lakes and ponds in all such cases the stratification starts off with the heavier more dense fluid underlying lighter convection driven mixing at the stratification interface due to the heat flux as well as other processes serves to minimize with time the stabilizing density differences which may eventually cause the stratification to invert if gas has been contained under pressure in the lower layer this gas may explosively vent from the fluid as it suddenly rises to the top such as occurs in liquid natural gas tanks where rollover is a hazard these processes are quantifiable and are applied here to various scenarios that might refer to volcanic crater lakes whose lower layers are charged with volatiles provided herein are some examples of calculated conditions and calculated time of evolution leading to rollover with attendant release of gases from supersaturated ascending fluids these calculations suggest rollover could occur in volcanic lakes the august 1986 gas release at lake nyos is employed as an example these estimates were made taking note that water is commonly supersaturated in co2

how much water swept over the lake nyos dam during the 1986 gas disaster the toxic aerosol of water and carbon dioxide which was released from lake nyos in august 1986 passed over the natural dam which confines the lake and devastated the valleys to the north the gas release generated a wave of water which swept across the lake surface and damaged vegetation on the eastern and southern shore however the vegetation to either side of the spillway was undamaged and therefore despite a recent suggestion to the contrary any wave of water which passed over the dam could have been no more than a few centimetres high

dynamics of lake eruptions and possible ocean eruptions dissolved gas in liquid is able to power violent eruptions two kinds of such gas driven eruptions are known in nature explosive volcanic eruptions driven by dissolved h2o in magma at high temperatures and lake eruptions driven by dissolved co2 in water at low temperatures there are two known occurrences of lake eruptions one in 1984 lake monoun and one in 1986 lake nyos both in cameroon africa the erupted co2 gas asphyxiated 1700 people in the lake nyos eruption and 37 people at lake monoun here we review experimental simulations of co2 driven water eruptions and dynamic models of such eruptions and a bubble plume theory is applied to the dynamics of lake eruptions field evidence experimental results and theoretical models show that lake eruptions can be violent and theoretical calculations are consistent with the high exit velocities and eruption columns inferred from observations furthermore the dynamics of lake degassing experiments are consistent with theoretical models other kinds of gas driven eruptions are possible and may have occurred in nature in the past a concentrated and large release of methane gas or hydrate from marine sediment may result in an ocean eruption furthermore injection of liquid co2 into oceans might also lead to ocean eruptions if care is not taken the various kinetic and dynamic processes involved are examined and quantified

fluid inclusion and stable isotope study of the shagou ag pb zn deposit luoning henan province china implications for the genesis of an orogenic lode ag pb zn system abstract the shagou deposit located in the eastern qinling orogenic belt central china and hosted by the taihua supergroup is a large sized ag pb zn deposit and has proven reserves of 1 54 million tons of ore with grades of 767 g t ag 13 24 pb and 4 31 zn the ore forming fluids have been previously interpreted as products of direct exsolution of a crystallizing magma or sudden decompression of the fluid exsolved from magma defining the shagou deposit as an intrusion related system in this study the shagou deposit has been identified as an orogenic type mineralization system the hydrothermal ore forming process can be divided into the early quartz pyrite middle quartz polymetallic sulfides and late quartz carbonate stages four types of fluid inclusions in quartz can be distinguished between pc c w and pw types the early and middle stage quartz contains the pc c and w type fluid inclusions while only w and pw type fluid inclusions can be observed in the late stage quartz in the early stage the w type fluid inclusions homogenized at 173 369 c concentrating at 200 240 c with salinities ranging from 5 4 to 8 3 wt nacl equiv but in the middle stage the c and w type fluid inclusions homogenized at 112 313 c concentrating at 180 220 c with salinities ranging from 0 7 to 13 6 wt nacl equiv in the late stage the w type fluid inclusions homogenized at 108 253 c concentrating at 160 200 c with salinities ranging from 2 1 to 8 1 wt nacl equiv the fluids may have experienced a boiling process or fluid mixing in the middle stage the estimated trapping pressures of fluid inclusions in the middle stage ranged from 33 to 211 mpa corresponding to a mineralization depth from 3 3 to 7 7 km for the early stage fluids the calculated 18 o h 2 o and d h 2 o values are 7 5 9 1 96 2 to 110 5 respectively for the middle stage fluids these two values are 1 5 5 3 75 6 to 110 7 but change to 1 0 and 87 for the late stage suggesting an evolution from metamorphic to meteoric in origin in general the shagou ag pb zn deposit is similar in many respects to typical orogenic type mineralization systems

experimental study of the behavior of copper and zinc in a boiling hydrothermal system vapor liquid partitioning coefficients for cu and zn in aqueous fluid were determined under boiling conditions at 500 650 c and 35 100 mpa in sulfur bearing and sulfur free systems a synthetic fluid inclusion technique was used to sample the experimental system of coexisting vapor rich and liquid rich fluid inclusions the cu and zn concentrations in individual fluid inclusions were then analyzed by synchrotron radiation x ray fluorescence the vapor liquid distribution constant of cu k d m cu vapor m cu liquid where m denotes the molality of metal is found to be strongly dependent on the sulfur content in the experimental solutions in sulfur bearing systems cu preferentially partitions into the vapor phase whereas zn preferentially fractionates into the hypersaline liquid the k d values for cu and zn obtained in this study correspond well with those obtained from natural fluid inclusions in hydrothermal ore deposits the results suggest that differential volatility of metals is an important factor affecting the enrichment of certain metals in different hydrothermal ore deposits

giant porphyry deposits characteristics distribution and tectonic controls more than half of the 25 largest known porphyry copper deposits defined in terms of contained copper metal formed during three time periods the paleocene to eocene eocene to oligocene and middle miocene to pliocene these giant deposits are clustered within three provinces central chile northern chile and southwest arizona northern mexico other giant deposits occur in montana utah panama peru argentina irian jaya mongolia and iran compressive tectonic environments thickened continental crust and active uplift and erosion were associated with the formation of many of these deposits calc alkalic magmas are most favorable for the formation of giant porphyry copper deposits although several of the largest systems are associated with high k calc alkalic intrusions the 25 largest gold rich porphyry deposits are concentrated in the southwest pacific and south america with other occurrences in eurasia british columbia alaska and new south wales many of the deposits formed in the last 13 m y the largest of the deposits are associated with high k calc alkalic intrusions many calc alkalic porphyritic intrusions have also produced giant gold rich porphyries in the last 20 m y the formation of giant porphyry copper molybdenum and copper gold deposits in the circum pacific region has been closely associated with subduction of aseismic ridges seamount chains and oceanic plateaus beneath oceanic island and continental arcs in several examples these tectonic perturbations have promoted flat slab subduction crustal thickening uplift and erosion and adakitic magmatism coeval with the formation of well endowed porphyry and or epithermal mineral provinces similar tectonic features are inferred to be associated with the giant porphyry copper molybdenum provinces of northern chile eocene oligocene and southwest united states cretaceous paleocene topographic and thermal anomalies on the downgoing slab appear to act as tectonic triggers for porphyry ore formation other factors such as sutures in the overriding plate permeability architecture of the upper crust efficient processes of ore transport and deposition and in some cases formation and preservation of supergene enrichment blankets are also vital for the development of high grade giant ore deposits a low grade geochemical anomaly may be the final product of mineralization if ore forming processes do not operate efficiently even in the most favorable geodynamic settings

petrography geochemistry and geochronology of the host porphyries and associated alteration at the tuwu cu deposit nw china a case for increased depositional efficiency by reaction with mafic hostrock tuwu is the largest porphyry copper deposit discovered in the eastern tianshan mountains xinjiang china a newly recognized volcanic complex in the early carboniferous qi eshan group at tuwu consists of basalt andesite and diorite porphyry the plagiogranite porphyry was emplaced into this complex at 332 8 2 5 ma u pb zircon sims determination whole rock element geochemistry shows that the volcanic complex and plagiogranite porphyry formed in the same island arc although the complex was derived by partial melting of the mantle wedge and the plagiogranite porphyry by partial melting of a subducting slab the diorite and the plagiogranite porphyries have both been subjected to intense hydrothermal alteration and associated mineralization but the productive porphyry is the plagiogranite porphyry three alteration and mineralization stages including pre syn and post ore stages have been recognized the pre ore stage formed a barren propylitic alteration which is widespread in the volcanic complex the syn ore stage is divided into three sub stages stage 1 is characterized by potassic alteration with chalcopyrite bornite chalcocite stage 2 is marked by chlorite sericite albite alteration with chalcopyrite pyrite bornite stage 3 is represented by phyllic alteration with chalcopyrite pyrite molybdenite the post ore stage produced a barren argillic alteration limited to the diorite porphyry a specific feature of the tuwu deposit is that the productive porphyry was emplaced into a very mafic package and reaction of the resulting fluids with the ferrous iron rich hostrocks was a likely reason that tuwu is the largest porphyry in the district

simulation of co2 concentrations temperature and stratification in lake nyos for different degassing scenarios 1 a large gas cloud erupted unexpectedly in 1986 from lake nyos the larger of the two cameroonian killer lakes with devastating consequences regular monitoring subsequently revealed that the deep water of the lake was gradually recharged with co2 to preclude a similar event in the future a degassing pipe was installed in the lake in 2001 in the present study a one dimensional model is used to predict the effects of this pipe and other degassing options on the co2 concentrations and the stratification within the lake for the next 50 years the results of the simulations show that without degassing total co2 content would reach the preeruption value within a few decades the presently installed pipe is sufficient to reduce co2 pressures in the entire water column above the pipe inlet to 5 bar within 10 years and a steady state is reached within 50 years depending on the assessment of the risk due to the gas currently remaining in the lake and the costs involved the installation of additional pipes could be considered 1 to remove the gas more quickly and 2 as a backup for long term failures and maintenance once the steady state is reached degassing with one pipe is a practicable long term solution which can also be used for monitoring the approximate deep water co2 concentrations by nonprofessionals assuming a doubled deep water input in the future as an upper limit of the expected source strength the pipe is still able to prevent a co2 accumulation as a side effect the degassing operation strongly changes the stratification in the lake it transforms the lake from a meromictic to an oligomictic system and gradually removes the dissolved salts from the lake

ore geology and fluid evolution of the giant caixiashan carbonate hosted zn pb deposit in the eastern tianshan nw china abstract the caixiashan giant carbonate hosted zn pb deposit 131 mt 3 95 zn pb formed by replacement of dolomitized marble with stratiform massive and breccia bodies is located near the base of the proterozoic kawabulake group limestone and marble it is one of the largest carbonated hosted massive sulfides zn pb ore deposits in northwest china to have been discovered in recent years abundant pyrite occurs in dolomitized marble along fractures in dolomitized clasts in the host rocks and filling cracks in the host rock locally colloform or framboidal pyrites are observed in the early period and sometimes replaced by the later sphalerite the sulfide assemblage of the main ore stage is characterized by massive or disseminated sphalerite and galena with less pyrite than the earlier stage and minor pyrrhotite galena occurs as small veins cutting the early formed sphalerite dolomite and calcite are the main gangue minerals that co precipitated with these sulfides tremolite and quartz alteration commonly overprints the orebodies according to the crosscutting relationships and the different mineral associations within the host rocks and ore bodies three stages are recognized at caixiashan i e syn sedimentary pyrite stage i pyrite alteration sphalerite carbonate and galena pyrite carbonate stage ii 1 stage ii 2 and stage ii 3 respectively and magmatic metamorphic reworking stage iii calcite and quartz crystals are important host minerals among the three hypogene stages stages i iii although quartz mainly occurred in stage iii stage i contains only aqueous inclusions w type which were homogenized from 110 to 236 c main range of 138 198 c and average at 168 c main range average and the salinities are from 0 5 to 16 5 main range of 5 1 15 1 with average of 10 1 wt nacl eqv in the pyrite alteration of stage ii 1 the w type fluid inclusions homogenized from 175 to 260 c main range of 210 260 with average of 235 and the salinities range from 8 5 to 22 4 main range of 16 7 20 1 with average of 18 4 wt nacl eqv in the main zn pb mineralization stage stage ii 2 3 four types of fluid inclusions were identified an aqueous phase w type a pure carbon phase pc type a carbon phase containing c type and mineral bearing inclusions s type the w type fluid inclusions of stage ii 2 3 homogenized at 210 to 370 c main range of 253 323 and average at 270 and the salinities range from 5 9 to 23 1 main range of 13 3 20 3 with average at 16 8 wt nacl eqv c type homogenized at 237 c to 371 c and the salinities range from 6 4 19 7 wt nacl eqv s type fluid inclusions homogenized at 211 to 350 c and daughter minerals melted between 340 and 374 c during heating indicating a salinity range of 42 to 44 wt nacl eqv pc type fluid inclusions with homogenization temperatures of co 2 phase show large variation from 7 4 c to 21 2 c laser raman analyses show that ch 4 co 2 and so 4 2 coexist in the main mineralization stage fluids the magmatic metamorphic reworking stage only contains w type fluid inclusions which yield homogenized between 220 and 360 c main range of 251 325 and average at 288 with salinities ranging from 1 7 to 23 0 main range of 14 3 20 0 and average at 18 8 wt nacl eqv the textural features mineral assemblages and fluid geochemistry suggest that the zn pb ores were formed through hydrothermal convection of hot marine waters along the faults and fractures resulting in metal zn pb and fe enriched stratiform orebodies subsequent rapid precipitation of sulfides was triggered by sulfate so 4 2 thermal reduction with the ch 4 preserved in sedimentary rocks and early stage i pyrite bodies this process occurred at moderate temperatures ca 270 c higher temperature magmatic hydrothermal alteration overprinted the orebodies but only provided a minor contribution to the mineralization

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

trace elements and cathodoluminescence of quartz in stockwork veins of mongolian porphyry style deposits the combination of scanning electron microscope cathodoluminescence cl fluid inclusion analysis and high resolution electron probe microanalysis of al ti k and fe in vein quartz has yielded results permitting a greater understanding of the complex mineralisation of the central oyu tolgoi and zesen uul porphyry style deposits southern mongolia these data demonstrate the relationship between quartz precipitation dissolution and ore deposition as the mineralising fluid chemistry changed through time four major quartz generations are identified in the a type veins from the stockworks of both the central oyu tolgoi oti to otiv and zesen uul deposits zui to zuiv despite differences in the associated alteration and mineralisation style the observed cl textures and trace element signatures of the quartz generations are comparable between deposits the oti and zui stage formed both the primary network of a type veins and pervasive silicification of the host rock using the ti in quartz geothermometer crystallisation temperatures for oti and zui of between 598 c and 880 c are indicated the main stage of sulphide mineralisation was accompanied by the dissolution of pre existing quartz oti and zui and precipitation of a weakly luminescent generation of quartz otii and zuii with a low ti content reflected in a calculated temperature drop from approximately 700 c to 340 c in central oyu tolgoi and 445 c in zesen uul otii and zuii stage quartzes show high and variable al concentrations the next stage of quartz in both deposits otiii and zuiii forms a fine network of veins in cracks formed in pre existing quartz otiii and zuiii quartz contain measurable fluid inclusions of moderate salinity 3 17 1 wt nacl eq entrapped in the temperature range 256 c to 385 c otiii and zuiii are not related to any sulphide mineralisation the final otiv and zuiv stages are characterised by quartz calcite micro breccias that penetrate the a type veins based on the calculated entrapment temperatures the otiv zuiv stage crystallised between 212 c and 335 c and the quartz is characterised by elevated but variable al and fe contents the cl and trace element signatures of the oti to otiii and zui to zuiii stages of the two mongolian porphyries show similar features to those observed in porphyry style deposits from other regions this suggests that a common sequence of quartz crystallisation occurs during the formation of early veins in many porphyry copper systems

a review of cu dominant mineral systems in the kalatag district east tianshan china abstract the chinese east tianshan is the easternmost sector of the tianshan mountain range in the central asian orogenic belt caob and accommodates several events of magmatism crustal growth and mineralization the kalatag arc is unique in the east tianshan due to its widespread early paleozoic volcanic rocks which offers a special opportunity to study the early paleozoic cu dominant mineral systems in island arc setting in this region nine deposits have been discovered in recent years these deposits occur in paleozoic volcanic rocks between the kalatag fault and kabei fault and can be divided into six mineral systems i e vms cu zn epithermal cu porphyry cu au skarn fe cu magmatic cu ni sulfide and hydrothermally overprinted deposits among them vms epithermal porphyry skarn and magmatic cu ni sulfide mineralization are distributed in the southeastern central northwestern and westernmost kalatag respectively the mineralization and associated intrusive rock ages can be clustered into four episodes in the kalatag arc i e late ordovician silurian ca 450 430 ma middle devonian ca 390 380 ma late carboniferous ca 320 300 ma and permian ca 280 ma here paleozoic granitoids show similar geochemistry and isotopic features all paleozoic granitoids plot in the subalkaline field and predominantly tholeiitic to calc alkaline series with enrichment of large ion lithophile elements and depletion of high field strength elements these granitoids plot in a volcanic arc fields in tectonic discrimination diagrams which are characteristic of an island arc setting the fluid inclusions in porphyry and skarn system are characterized by high temperature high salinity low content of co2 whereas epithermal system represented by low temperature low salinity low content of co2 and the vms system can be described as medium temperature medium low salinity co2 bearing fluid h o isotopic data suggest that ore fluids were sourced from a mixing fluid between magmatic and meteoric water s pb isotopic data show that the sulfur mainly came from magma or ore hosting igneous rocks the yudai porphyry cu au deposit the hongshi epithermal cu deposit and the honghai au rich vms cu zn deposit formed at the same time related to a subduction environment the early paleozoic vms mineralization is generally overprinted by late magmatic hydrothermal fluids which may be due to multiple accretionary orogeny in kalatag island arc we propose that the north dipping subduction of the paleo tianshan ocean or south dipping subduction of the junggar ocean during late ordovician silurian which may led to the development of yudai porphyry copper hongshi epithermal copper and honghai vms copper zinc deposits in the kalatag arc after that north dipping subduction of the paleo tianshan ocean resulted to the formation of the middle devonian ca 390 380 ma and late carboniferous ca 320 300 ma cu mineralization finally the permian ca 280 ma magmatic copper nickel sulfide deposits associated with ultramafic mafic complexes developed in post collisional extension setting part of a large igneous province lip event associated with mantle plume upwelling

fluid inclusion study of the wunugetu cu mo deposit inner mongolia china hydrothermal alteration and mineralization at the wunugetu porphyry cu mo deposit china include four stages i e the early stage characterized by quartz k feldspar and minor mineralization followed by a molybdenum mineralization stage associated with potassic alteration copper mineralization associated with sericitization and the last pb zn mineralization stage associated with carbonation hydrothermal quartz contains three types of fluid inclusions namely aqueous w type daughter mineral bearing s type and co2 rich c type inclusion with the latter two types absent in the late stage fluid inclusions in the early stage display homogenization temperatures above 510 c with salinities up to 75 8 wt nacl equivalent the presence of s type inclusions containing anhydrite and hematite daughter minerals and c type inclusions indicates an oxidizing co2 bearing environment fluid inclusions in the mo and cu mineralization stages yield homogenization temperatures of 342 508 c and 241 336 c and salinities of 8 6 49 4 and 6 3 35 7 wt nacl equivalent respectively the presence of chalcopyrite instead of hematite and anhydrite daughter minerals in s type inclusions indicates a decreasing of oxygen fugacity in the late stage fluid inclusions yield homogenization temperatures of 115 234 c and salinities lower than 12 4 wt nacl equivalent it is concluded that the early stage fluids were co2 bearing magmatic in origin and characterized by high temperature high salinity and high oxygen fugacity phase separation occurred during the mo and cu mineralization stages resulting in co2 release oxygen fugacity decrease and rapid precipitation of sulfides the late stage fluids were meteoric in origin and characterized by low temperature low salinity and co2 poor

gold ore forming fluids of the tanami region northern australia fluid inclusion studies have been carried out on major gold deposits and prospects in the tanami region to determine the compositions of the associated fluids and the processes responsible for gold mineralization pre ore milky quartz veins contain only two phase aqueous inclusions with salinities 19 wt nacl eq and homogenization temperatures that range from 110 to 410 c in contrast the ore bearing veins typically contain low to moderate salinity 14 wt nacl eq h2o co2 ch4 n2 bearing fluids the co2 bearing inclusions coexist with two phase aqueous inclusions that exhibit a wider range of salinities 21 wt nacl eq post ore quartz and carbonate veins contain mainly two phase aqueous inclusions with a last generation of aqueous inclusions being very cacl2 rich salinities range from 7 to 33 wt nacl eq and homogenization temperatures vary from 62 to 312 c gold deposits in the tanami region are hosted by carbonaceous or iron rich sedimentary rocks and or mafic rocks they formed over a range of depths at temperatures from 200 to 430 c the groundrush deposit formed at the greatest temperatures and depths 260 430 c and 11 km whereas deposits in the tanami goldfield formed at the lowest temperatures 200 c and at the shallowest depths 1 5 5 6 km there is also evidence in the tanami goldfield for late stage isothermal mixing with higher salinity 21 wt nacl eq fluids at temperatures between 100 and 200 c other deposits e g the granites callie and coyote formed at intermediate depths and at temperatures ranging from 240 to 360 c all ore fluids contained co2 n2 ch4 with the more deeply formed deposits being enriched in ch4 and higher level deposits being enriched in co2 fluids from deposits hosted mainly by sedimentary rocks generally contained appreciable quantities of n2 the one exception is the tanami goldfield where the quartz veins were dominated by aqueous inclusions with rare co2 bearing inclusions calculated 18o values for the ore fluids range from 3 8 to 8 5 and the corresponding d values range from 89 to 37 measured 13c values from co2 extracted from fluid inclusions ranged from 5 1 to 8 4 these data indicate a magmatic or mixed magmatic metamorphic source for the ore fluids in the tanami region interpretation of the fluid inclusion alteration and structural data suggests that mineralization may have occurred via a number of processes gold occurs in veins associated with brittle fracturing and other dilational structures but in the larger deposits there is also an association with iron rich rocks or carbonaceous sediments suggesting that both structural and chemical controls are important the major mineralization process appears to be boiling effervescence of a gas rich fluid which leads to partitioning of h2s into the vapor phase resulting in gold precipitation however some deposits also show evidence of desulfidation by fluid rock interaction and or reduction of the ore fluid by fluid mixing these latter processes are generally more prevalent in the higher crustal level deposits

what drove late mesozoic extension of the northern china mongolia tract the northern china mongolia tract exhibited a tectonic transition from contractional to extensional deformation in late mesozoic time late middle to early late jurassic crustal shortening is widely thought to have resulted from collision of an amalgamated north china mongolia block and the siberian plate but widespread late late jurassic early cretaceous extension has not been satisfactorily explained by existing models some prominent features of the extensional tectonics of the northern china mongolia tract are 1 late jurassic voluminous volcanism prior to early cretaceous large magnitude rapid extension 2 overlapping in time of contractional deformation in the yinshan yanshan belt with development of extensionrelated basins in the interior of the northern china mongolia tract and 3 widespread occurrence of alkali granitic plutonism extensional basins and metamorphic core complexes in the early cretaceous a new explanation is advanced in this study for this sequence of events the collision of amalgamated north china mongolia with siberia led to crustal overthickening of the northern china mongolia tract and formation of a high standing plateau subsequent breakoff at depth of the north dipping mongol okhotsk oceanic slab is suggested as the main trigger for late mesozoic lithospheric extension of that tract slab breakoff resulted in mantle lithospheric stretching of the adjacent northern china mongolia tract with subsequent ascent of hot asthenosphere and magmatic underplating at the base of the crust collectively these phenomena triggered gravitational collapse of the previously thickened crust leading to late late jurassic early cretaceous crustal extension and importantly coeval contraction along the southern margin of the plateau in the yinshan yanshan belt the proposed model provides a framework for interpreting the spatial and temporal relationships of distinct processes and reconciling some seemingly contradictory phenomena such as the synchronous extension of northerly terranes during major contraction in the neighboring yanshan yinshan belt d 2003 elsevier b v all rights reserved

the contribution of fluid geochemistry to the volcano monitoring of stromboli abstract the persistent open vent mild explosive activity of stromboli volcano is episodically interrupted by more violent and dangerous explosive events major explosions and paroxysms according to the nature of erupted products paroxysms can be related either to the explosion of overpressured gas pockets located in the proximity of the magma column or to the sudden uprise of hot gas rich magma from a deep part of the plumbing system in both cases these more energetic explosive events should be preceded by an escape or a preferential uprise of the highly mobile volatiles which in turn should produce gas leakage anomalies at the surface in sites of high vertical permeability such as deep reaching faults in order to identify such gas leaking sites a systematic co2 soil flux survey has been carried out on the island using an accumulation chamber four hundred sixty one points have been measured with a high density in the summit crater area where high flux values have been found 10 3 10 2 cm s anomalous points are concentrated along the main ne sw axial feeding system of the volcano co2 soil flux decreases from the crater zone to the base of the volcanic cone where however an interesting gas leakage anomaly occurs pizzillo mofette in the pizzillo area thermal water wells also occur whose chemistry indicates an origin by sea water heated by hot gas soil gases have been sampled in the sites with the highest co2 flux in the crater area and at the base of the cone chemical and isotopic analyses indicate the presence of a deep gas component especially in the crater zone samples high co2 appreciable contents of he and h2 3he 4he values up to 3 55 13c of co2 2 the sc5 low flux fumarole on the crater rim has shown during six years a remarkable persistence of temperature 93 95 c with only minor fluctuations of chemistry appearance of anomalous peaks of h2 in correspondence with strombolian explosions was observed during a 2 h 30 min experiment of continuous recording of hydrogen content of the fumarole together with previous data on h2o co2 and he this experiment confirms that strombolian blasts produce rapid fluctuations in the fumarolic gas composition in the light of this study sc5 fumarole and pizzillo mofette look promising sites for the testing of a continuous geochemical monitoring system of stromboli volcano

the role of crustal contamination in the formation of ni cu sulfide deposits in eastern tianshan xinjiang northwest china evidence from trace element geochemistry re os sr nd zircon hf o and sulfur isotopes tulaergen xiangshan huangshan tianyu and baishiquan magmatic ni cu sulfide deposits which are all located in the eastern part of the central asian orogenic belt and associated with small mafic ultramafic intrusions with high grade cu and ni orebodies have similar ages of formation their magma sources are morb like and oib like depleted mantle modeling calculations of sr nd and zircon hf isotopic data show that about 10 15 of oceanic slab components are added into the source of baishiquan and tianyu intrusions but only less than 5 are in the three other intrusions the higher degree of subduction metasomatism in the baishiquan and tianyu magma sources is likely the result of the paleozoic multiple stage subduction moreover the relative enrichment of lile depletion of hfse and lower ce pb ratios indicate that these intrusions experienced crustal contaminations the effects of crustal contamination are also identified in the magmatic sulfide deposits by the higher zircon d 18 o higher sulfide cos and d 34 s values observed we propose a two stage crustal contamination model of the tulaergen xiangshan tianyu and baishiquan intrusions however the huangshan intrusion which has the highest degree of crustal contamination likely experienced only single stage upper crustal contamination 14 2 the addition of crustal s appears to be directly related to triggering s saturation in these deposits according to a simple s isotopic modeling calculation 11 2 9 1 2 and 2 1 of the crustal sulfur addition into the parental magma would be required to form the tianyu baishiquan xiangshan and tulaergen deposits respectively

ore geology and fluid inclusion geochemistry of the tiemurt pb zn cu deposit altay xinjiang china a case study of orogenic type pb zn systems abstract the tiemurt pb zn cu deposit is hosted in a devonian volcanic sedimentary basin of the altay orogenic belt and is thus interpreted to have formed by sea floor hydrothermal exhalation in previous studies our investigation discovered that the deposit is not stratiform or stratabound but structure controlled instead the hydrothermal ore forming process can be divided into the early middle and late stage represented by pyrite quartz polymetallic sulfide quartz and carbonate quartz veinlets respectively the early stage veins and contained minerals are structurally deformed and brecciated suggesting a compressional or transpressional tectonic regime the middle stage veinlets intrude and infill the fissures of the early stage assemblages and show no deformation suggesting a tensional shear setting the late stage veinlets mostly infill open space fissures that crosscut veins and replacements formed in the earlier stages four types of fluid inclusions fis including aqueous type w carbonic aqueous type c pure carbonic type pc and solid bearing type s are identified at the tiemurt deposit the early stage minerals contain the c and w type primary fis that are totally homogenized at temperatures of 330 390 c with low salinities of 0 8 11 9 wt nacl eqv whilst the late stage quartz or calcite contains only the w type fis with homogenization temperatures of 118 205 c and salinities of 1 4 3 4 wt nacl eqv this indicates that the ore fluid system evolved from co2 rich probably metamorphic to co2 poor meteoric fluids and that a significant co2 escape must have occurred all the four types of fis can be only observed in the middle stage minerals and even in a microscopic domain of a crystal representing an association trapped from a boiling fluid system these fis homogenize at temperatures ranging from 270 to 330 c with two salinity clusters of 1 9 14 5 and 37 4 42 4 wt nacl eqv respectively this implies that metal precipitation resulted from fluid boiling co2 escape and transient oversaturation the estimated trapping pressures of fis range from 130 to 380 mpa suggesting an alternating lithostatic hydrostatic fluid system controlled by a fault valve at the depth of 13 km therefore the tiemurt pb zn cu deposit is likely an example of orogenic pb zn cu systems formed in collision orogeny rather than a pre collision vms or sedex system developed in devonian and a new metallogenic model is proposed to interpret the formation of the tiemurt pb zn cu deposit

element migration of pyrites during ductile deformation of the yuleken porphyry cu deposit nw china abstract the strongly deformed yuleken porphyry cu deposit ypcd occurs in the kalaxiangar porphyry cu belt kpcb which occupies the central area of the central asian orogenic belt caob between the sawu er island arc and the altay terrane in northern xinjiang the ypcd is one of several typical subduction related deposits in the kpcb which has undergone syn collisional and post collisional metallogenic overprinting the ypcd is characterized by three pyrite forming stages namely a hydrothermal stage a py i a syn ductile deformation stage b py ii characterized by cu au enrichment and a fracture filling stage c py iii in this study we conducted systematic petrographic and geochemical studies of pyrites and coexist biotite which formed during different stages in order to constrain the physicochemical conditions of the ore formation euhedral fragmented py i has low pb and high te and se concentration and ni contents are low with co ni ratios mostly between 1 and 10 average 9 00 py i is further characterized by enrichments of bi as ni cu te and se in the core relative to the rim domains anhedral round py ii has moderate co and ni contents with high co ni ratios 10 average 95 2 and average contents of 46 5 ppm pb and 5 80 ppm te py ii is further characterized by decreasing bi cu pb zn ag te mo sb and au contents from the rim to the core domains annealed py iii has the lowest co content of all pyrite types with co ni ratios mostly

late paleozoic tectonic amalgamation of northwestern china sedimentary record of the northern tarim northwestern turpan and southern junggar basins sedimentary rocks contained in basins adjacent to the tian shan provide a long and complex record of the late paleozoic continental amalgamation of northwestern china complementing that provided by rocks preserved within the range this record which comprises dramatic changes in sedimentary facies sediment dispersal patterns sandstone provenance and basin subsidence rates broadly supports previous interpretations of a two part evolution of the tian shan late devonian to early carboniferous collision of the tarim continental block with the central tian shan followed by collision of this combined block with island arcs in the north tian shan and bogda shan in late carboniferous early permian times the first collision resulted in widespread angular unconformities within the tarim basin continued convergence following the collision created a long lived flexural foredeep along the northern margin of the tarim block which received at least 2000 m of lower carboniferous through lower permian fluvial and marine sediment derived from the interior of tarim subsequent early permian continental extension of the northern tarim basin resulted in the deposition of interbedded nonmarine siliciclastic sedimentary rocks and mafic to felsicvolcanic rocks sandstone within this interval was derived from the paleo tian shan and is composed predominantly of lithic volcanic grains similar to the rhyolite in contrast to the tarim basin calc alkaline volcanic rocks and volcanogenic sedimentary rocks dominated carboniferous and permian sedimentation in the northern turpan and northwestern junggar basins volcanic arcs remained active in the north tian shan and bogda shan through the early late carboniferous depositing a kilometers thick interval of deep marine sediment gravity flows in the northwestern junggar basin major arc magmatism ceased in the late carboniferous in response to closure of the oceanic basin between the combined tarim central tian shan block and the north tian shan bogda shan arcs upper carboniferous through lower permian rocks in the northwestern junggar basin compose the sedimentary fill of a bathymetric basin of oceanic depth on the northern side of the volcanic arcs culminating in a 1000 m thick marine regressive sequence middle to upper permian sandstones were derived from the uplifted paleo tian shan and bear the distinctive provenance imprint of granitic rocks presently exposed within the range late permian subsidence of the junggar basin accommodated 5 km of nonmarine sediments however the cause of this subsidence and its relationship to regional tectonic events remain controversial

volcanic lakes of the azores archipelago portugal geological setting and geochemical characterization abstract a representative set of 30 lakes from the azores archipelago portugal has been studied to obtain data on their volcanic setting and water geochemistry the majority of the studied lakes are located inside volcanic craters and subsidence calderas while the remaining lakes are located in topographic depressions not associated with volcanic centres in depressions of tectonic origin and inside lava caves in general the azorean volcanic lakes are small with surface areas between 8 94 10 4 km 2 and 4 35 km 2 and volumes between 2 4 10 3 and 4 78 10 7 m 3 median 3 99 10 4 m 3 presenting maximum depths between 0 8 and 33 m mostly of the na cl to na hco 3 type the lake waters are generally low temperature 11 9 24 6 c very dilute tds range between 11 0 and 356 2 mg l median 36 8 mg l and a clear exception is furna do enxofre lake graciosa island that shows a mg trend two types of lake waters can be recognized 1 one is characterized by na cl ratio close to the seawater value and have evolved and evolve by marine contribution and 2 na hco 3 type waters that in addition to sea salt input have been influenced by other processes e g water rock interaction hydrothermal seepage into the lake bottom evident from higher total co 2 content 365 1 mg l and sio 2 content 74 9 mg l as well demonstrated by in the furna do enxofre lake nevertheless volcanic contribution cannot be excluded for some lakes as furna do enxofre vertical profiles made at the deepest lakes of sao miguel reveal that major ion content varies little with depth largely independent of the occurrence of thermally driven density stratification in summer for some lakes however dissolved co 2 increases with depth and is kept in the hypolimnion in summer whereas the hco 3 content is stable suggesting that co 2 release exceeds acidity neutralization by water rock interaction during winter without stratification the dissolved co 2 increase is less sharp for the majority of the lakes with the exception of furnas and furna do enxofre lakes the co 2 enrichment observed for certain lakes e g furna do enxofre and furnas implies a volcanic input moreover as these lakes themselves are located near hydrothermal surface manifestations they therefore offer good targets of volcano monitoring in the azores

the production of digital elevation models for experimental model landscapes automated digital photogrammetry was used to produce digital elevation models of experimental model landscapes under controlled laboratory conditions as part of a series of rainfall erosion experiments looking at the evolution of landforms in response to erosion the method allowed the elevations of the experimental landscapes to be studied in great detail on a regular grid digital terrain map with relatively very little effort digital photogrammetry produced elevation data at a resolution of 6 mm with a standard deviation of 2 0 mm over an experimental catchment relief of approximately 200 mm this resolution is considerably better than that achievable by conventional manual photogrammetry the density of grid points was sufficiently high that small scale details such as knickpoints developing in channels were represented the method can facilitate the study of both experimental and natural landscapes in great detail copyright 2001 john wiley sons ltd