major types and time space distribution of mesozoic ore deposits in south china and their geodynamic settings the ore deposits of the mesozoic age in south china can be divided into three groups each with different metal associations and spatial distributions and each related to major magmatic events the first event occurred in the late triassic 230 210 ma the second in the mid late jurassic 170 150 ma and the third in the early mid cretaceous 120 80 ma the late triassic magmatic event and associated mineralization is characterized by peraluminous granite related w sn nb ta mineral deposits the triassic ore deposits are considerably disturbed or overprinted by the later jurassic and cretaceous tectono thermal episodes the mid late jurassic magmatic and mineralization events consist of 170 160 ma porphyry skarn cu and pb zn ag vein deposits associated with i type granites and 160 150 ma metaluminous granite related polymetallic w sn deposits the late jurassic metaluminous granite related w sn deposits occur in a ne trending cluster in the interior of south china such as in the nanling area in the early mid cretaceous from about 120 to 80 ma but peaking at 100 90 ma subvolcanic related fe deposits developed and i type calc alkaline granitic intrusions formed porphyry cu mo and porphyry epithermal cu au ag mineral systems whereas s type peraluminous and or metaluminous granitic intrusions formed polymetallic sn deposits these cretaceous mineral deposits cluster in distinct areas and are controlled by pull apart basins along the south china continental margin based on mineral assemblage age and space time distribution of these mineral systems integrated with regional geological data and field observations we suggest that the three magmatic mineralization episodes are the result of distinct geodynamic regimes the triassic peraluminous granites and associated w sn nb ta mineralization formed during post collisional processes involving the south china block the north china craton and the indo china block mostly along the dabie sulu and songma sutures jurassic events were initially related to the shallow oblique subduction of the izanagi plate beneath the eurasian continent at about 175 ma but i type granitoids with porphyry cu and vein type pb zn ag deposits only began to form as a result of the breakup of the subducted plate at 170 160 ma along the nne trending qinzhou hangzhou belt also referred to as qin hang or shi hang belt which is the neoproterozoic suture that amalgamates the yangtze craton and cathaysia block a large subduction slab window is assumed to have formed in the nanling and adjacent areas in the interior of south china triggering the uprise of asthenospheric mantle into the upper crust and leading to the emplacement of metaluminous granitic magma and associated polymetallic w sn mineralization a relatively tectonically quiet period followed between 150 and 135 ma in south china from 135 ma onward the angle of convergence of the izanagi plate changed from oblique to parallel to the coastline resulting in continental extensional tectonics and reactivation of regional scale ne trending faults such as the tan lu fault this widespread extension also promoted the development of ne trending pull apart basins and metamorphic core complexes accompanied by volcanism and the formation of epithermal cu au deposits granite related polymetallic sn w deposits and hydrothermal u deposits between 120 and 80 ma with a peak activity at 100 90 ma

relation between depositional environment and the elemental composition of early diagenetic siderite early diagenetic siderites from marine and fresh water depositional environments are characterized by distinctive compositional trends siderite from fresh water environments is often relatively pure i e greater than 90 mol feco sub 3 and commonly attains end member composition siderite from marine environments however is always extremely impure and has extensive substitution of mg up to 41 mol and to a lesser extent ca up to 15 mol for fe in the siderite lattice in addition marine siderite generally contains less mn and has a higher mg ca ratio than fresh water siderite this compositional variation appears to result from differences in the chemistry of early marine and meteoric pore waters inasmuch as early marine pore waters generally have a higher mg sup 2 ca sup 2 ratio and contain less mn sup 2 and fe sup 2 and more ca sup 2 and mg sup 2 than meteoric waters

in situ gas hydrate hydrate saturation estimated from various well logs at the mount elbert gas hydrate stratigraphic test well alaska north slope abstract in 2006 the u s geological survey usgs completed detailed analysis and interpretation of available 2 d and 3 d seismic data and proposed a viable method for identifying sub permafrost gas hydrate prospects within the gas hydrate stability zone in the milne point area of northern alaska to validate the predictions of the usgs and to acquire critical reservoir data needed to develop a long term production testing program a well was drilled at the mount elbert prospect in february 2007 numerous well log data and cores were acquired to estimate in situ gas hydrate saturations and reservoir properties gas hydrate saturations were estimated from various well logs such as nuclear magnetic resonance nmr p and s wave velocity and electrical resistivity logs along with pore water salinity gas hydrate saturations from the nmr log agree well with those estimated from p and s wave velocity data because of the low salinity of the connate water and the low formation temperature the resistivity of connate water is comparable to that of shale therefore the effect of clay should be accounted for to accurately estimate gas hydrate saturations from the resistivity data two highly gas hydrate saturated intervals are identified an upper 43 ft zone with an average gas hydrate saturation of 54 and a lower 53 ft zone with an average gas hydrate saturation of 50 both zones reach a maximum of about 75 saturation

experimental calibration of the aluminum in hornblende geobarometer with application to long valley caldera california volcanic rocks a new geobarometer based on the al content of igneous hornblendes in equilibrium with melt fluid biotite quartz sanidine plagioclase sphene and magnetite or ilmenite has been calibrated experimentally the calibration was performed by equilibrating the required phase assemblage over the pressure range 2 8 kbar at 740 780c and then analyzing euhedral hornblendes in equilibrium with glass melt experiments were performed on natural samples of both volcanic and plutonic rocks earlier empirical calibrations of this geobarometer relied on analyzing natural hornblendes from plutons with the required phase assemblage and inferring pressure from nearby metamorphic country rocks the experimental calibration differs from the empirical calibrations especially above 5 kbar and shows that the al content of hornblendes in equilibrium with the required phase assemblage is greater for a given total pressure than previously thought the geobarometers uncertainty is dramatically reduced the derived equation is p plus minus 0 5 kbar 3 minus 3 46 plus minus 0 24 4 23 plus minus 0 13 al sup t the geobarometer is applied to post bishop tuff volcanic rocks from long valley caldera california and reveals that most rhyodacites in this complex erupted from depths of about 6 km these eruptions occurred over 500 000 yr suggesting that the rhyodacitic magma reservoir beneath longmore valley had reached a steady p depth t state less

high resolution particle size analysis of naturally occurring very fine grained sediment through laser diffractometry abstract in this paper we present results from a large number of experiments aimed at quantifying method and instrument uncertainty associated with laser diffraction analysis we analyzed the size distribution of fine grained sediment 24 hours prior to analysis and using 60 seconds of ultrasonication during analysis 2 obscuration a measure of the concentration of the suspension during analysis produced the most reproducible results at about 20 3 variations in refractive index settings can significantly alter estimated grain size distributions 4 assumed values for absorption the degree to which sediment grains absorb the light can have a profound effect on grain size results absorption settings near 0 resulted in unexpected bimodal grain size distributions for sediments in the 10 m size fraction and significantly skewed the fine grained tail of coarser samples probably because of sub optimal diffraction by particles with a diameter similar in size to the laser wavelength absorption settings closer to 1 produced very reproducible results and unimodal grain size distributions over a wide range of refractive indexes our study has shown that laser diffraction can measure very fine grained sediments 10 m quickly with high precision 5 at 2 standard deviations and without the need for extensive mineralogical determinations these results make possible a new generation of studies in which high resolution time series data sets of sediment grain size can be used to infer subtle changes in paleohydrology

magmatic epidote and its petrologic significance epidote is a major magmatic mineral in tonalite and granodiorite in a belt coextensive with the mesozoic accreted terranes between northern california and southeastern alaska textural and chemical evidence indicates that epidote crystallized as a relatively late but magmatic mineral that formed through reaction with hornblende in the presence of a melt phase the observed relations concur with experimental data on crystallization of epidote from synthetic granodiorite at 8 kbar total pressure plutonic rocks bearing magmatic epidote must have formed under moderately high pressures corresponding to lower crustal depths under fairly oxidizing conditions

gas geochemistry of the mount elbert gas hydrate stratigraphic test well alaska north slope implications for gas hydrate exploration in the arctic abstract gases were analyzed from well cuttings core gas hydrate and formation tests at the bpxa doe usgs mount elbert gas hydrate stratigraphic test well drilled within the milne point unit alaska north slope the well penetrated a portion of the eileen gas hydrate deposit which overlies the more deeply buried prudhoe bay milne point west sak and kuparuk river oil fields gas sources in the upper 200 m are predominantly from microbial sources c1 isotopic compositions ranging from 86 4 to 80 6 the c1 isotopic composition becomes progressively enriched from 200 m to the top of the gas hydrate bearing sands at 600 m the tested gas hydrates occur in two primary intervals units d and c between 614 0 m and 664 7 m containing a total of 29 3 m of gas hydrate bearing sands the hydrocarbon gases in cuttings and core samples from 604 to 914 m are composed of methane with very little ethane the isotopic composition of the methane carbon ranges from 50 1 to 43 9 with several outliers generally decreasing with depth gas samples collected by the modular formation dynamics testing mdt tool in the hydrate bearing units were similarly composed mainly of methane with up to 284 ppm ethane the methane isotopic composition ranged from 48 2 to 48 0 in the c sand and from 48 4 to 46 6 in the d sand methane hydrogen isotopic composition ranged from 238 to 230 with slightly more depleted values in the deeper c sand these results are consistent with the concept that the eileen gas hydrates contain a mixture of deep sourced microbially biodegraded thermogenic gas with lesser amounts of thermogenic oil associated gas and coal gas thermal gases are likely sourced from existing oil and gas accumulations that have migrated up dip and or up fault and formed gas hydrate in response to climate cooling with permafrost formation

fluid inclusion characteristics and geological significance of the xi ao copper tin polymetallic deposit in gejiu yunnan province abstract the newly discovered xi ao cu sn polymetallic deposit is located in the inner alteration zone of the laochang kafang granite edge in gejiu yunnan province the mineralization process of this deposit can be divided into four stages cassiterite and chalcopyrite mainly formed at stages ii and iii respectively fluid inclusions at different stages were studied by petrography microthermometry and laser raman spectrometry five fluid inclusion types are observed microthermometry results revealed that the ore forming fluid evolved from high temperature with low to intermediate salinity to low temperature with low salinity at stage i the fluid was under near critical conditions and then separated into coexisting liquid and vapor phases at stage ii finally the fluid was boiling and immiscible at stage iii a meteoric fluid mixing process was also observed at this stage laser raman spectra identified ch4 at the skarn and mineralization stages combined with other geological features the deposit was concluded to have formed under a relatively reduced environment the co2 component abruptly increased at stage iii and probably originated from the exterior fluorine may play an important role in mineralization cassiterite and chalcopyrite were mainly deposited at 340 440 and 300 400 c under pressures of 18 50 and 12 36 mpa respectively boiling and immiscibility are probably the main reason for mineral deposition the deposit of cassiterite and chalcopyrite showed similar salinities but higher temperatures than other mineralization types of deposits in the gejiu area this finding indicated that the study deposit probably represents the high temperature part of the gejiu mineralization system thereby benefiting mineral explorations in the gejiu area

numerical simulations of sand migration during gas production in hydrate bearing sands interbedded with thin mud layers at site nghp 02 16 abstract the geomechanical behavior of gas hydrate bearing sands during gas production is complex involving changes in hydrate dependent mechanical characteristics and also redistribution of stresses carried by the hydrate when an interbedded mud layer is present the complex response of the hydrate bearing sediments is more pronounced because hydrate dissociation tends to occur preferentially in the sands adjacent to the hydrate free mud layer which can act as a heat source this leads to non uniform sediment deformation and potentially to shearing deformation along the sand mud layers in addition since the hydrate bearing sand permeability becomes far greater than the mud permeability with hydrate dissociation a greater hydraulic gradient may exist along the interface between the sand mud layers these two behaviors may contribute to sand migration and thus a thorough study on the effect of a thin interbedded mud layer on the extent of sand migration is necessary this paper presents numerical sand migration modeling of sand mud interbedded hydrate bearing sediments found at site nghp 02 16 one of 25 sites drilled as a part of national gas hydrate program expedition 02 nghp 02 in the offshore of india subjected to depressurization for a comparison and better understanding simulation of homogeneous hydrate bearing sediments is also conducted it is found that greater sand migration occurs when the interbedded mud layer is present because of greater shearing deformation and greater pressure gradients at sand mud interface

zn he ar and sr nd isotopic compositions of the tongkeng tin polymetallic ore deposit in south china implication for ore genesis abstract the tongkeng tin polymetallic ore deposit in nandan county guangxi zhuang autonomous region southern china is the representative deposit of the largest scale in the famous dachang tin polymetallic ore field it consists of the upper tin polymetallic ores and the lower newly found zinc copper ores with the sn metal reserve of 680 000 tons average grade 1 4 500 000 tons of zn average grade 4 and 80 000 tons of cu average grade 0 2 the orebodies occur as layers and veins within the middle to late devonian siliceous rocks and carbonate rocks in this paper the isotopic compositions of zn he ar and sr nd of the tongkeng deposit have been studied systematically the results show that the isotopic composition of zn is quite homogenous with 66zn 0 22 0 34 in sphalerite samples of various colors from brown to black collected from different orebodies upper tin polymetallic and lower zinc copper ores in the tongkeng deposit it indicates that zn source mainly came from magmatic fluid as the calculated 66zn 0 42 0 54 of ore forming fluid is almost same as that of the longxianggai granite 0 41 0 55 but quite different from that of the marine carbonate average 0 91 he ar isotope study of pyrite shows that the exhalative substances might have been involved in the mineralization with 3he 4he 1 2 ra 2 5 ra in the upper tin polymetallic ores and 3he 4he 0 8 ra 1 9 ra in the lower zinc copper ores in the tongkeng deposit which is different from that of the longxianggai granite 3he 4he 0 7 0 8 ra but close to that of the devonian liujiang formation exhalative sedimentary sequences with 3he 4he 1 5ra the longxianggai granite has isr 0 719 in average end t 7 9 9 6 and nd model age t2dm 1 54 1 68 ga based on the geochemical characteristics of granite and sr nd and o isotopes the source rocks of the longxianggai granite may be mainly derived from the continental crust which is a typical remelted s type granite based on the results of this study and the previous data in the literature it is concluded that the mineralization in the dachang ore field is closely related to the cretaceous longxianggai granite in time and space with the main metal substances of zn most likely derived from the magmatic fluid classified into the type of post magmatic hydrothermal filling metasomatism the admixing of the early devonian spouting sediments in the mineralization was evidenced in the study of source trace and has led to the longtime dispute over the ore genesis

age and genesis of the w bi cu f au nui phao deposit northeast vietnam constrains from u pb and ar ar geochronology fluid inclusions study s o isotope systematic and scheelite geochemistry abstract northeast vietnam comprises several tectonic units which host number of metallic deposits of different types from orogenic gold to intrusion hosted pge deposits the lo gam domain being part of the ne vietnam hosts the lang vai gold district a several pb zn deposits and the recently discovered super large w bi cu f au nui phao deposit the nui phao deposit is 87 9 mt at 0 19 wo3 7 95 caf2 0 18 cu 0 19 g t au and 0 09 bi while the measured resource is 25 1 mt at 0 25 wo3 8 4 caf2 0 23 cu 0 26 g t au and 0 108 bi the nui phao deposit is a very interesting object for research due to location of the orebodies between of two granite massifs of the cretaceous da lien and triassic nui phao age consequently the temporal and genetic relationships of mineralization with a certain magmatic events are unclear here we present mineralogical compositional and geochronological data of the nui phao deposit in conjunction with physical chemical researches to understand the ore genesis and its genetic link to a certain magmatic events according to our observations at least three different mineral associations are distinguished at the nui phao deposit which include greisens skarns and quartz sulfide ore skarn and sulfide ore mineral assemblages generally contain abundant scheelite associated with pyrrhotite chalcopyrite and native bismuth the greisens consist of fluorite muscovite and rare molybdenite the results of fluid inclusions study indicate that at the nui phao deposit the initial ore forming fluid was represented by the reduced co2 ch4 h2o nacl cacl2 system characterized by high temperatures and moderate salinities the fluid boiling is the dominant mechanism for ore deposition at the nui phao deposit relatively homogeneous isotopic compositions of oxygen 18oh2o 6 73 to 9 24 and sulfur 34s 1 6 to 3 5 that closely correspond to magmatic source suggest that the ore forming fluid was generated from cooling granite pluton without contribution meteoric water the systematic studies of scheelite composition show that ree contents decrease from early to late scheelite generations which suggest gradual ree depletion of the ore forming fluid without significant fractionation between lree mree and hree the rees of scheelite are mainly controlled by the substitution mechanisms ca2 w6 ree3 nb5 and 3ca2 2ree3 ca by combining ree features y ho ratios and other characteristics of the nui phao deposit we propose a single magmatic source for hydrothermal ore firming fluids without fluid mixing a significantly contribution of material during fluid rock interaction is also unlikely the combination of mineralogical and geochemical features as well as complex studies of the formation conditions allowed us to conclude that gold at the nui phao deposit occur as impurities in the native bismuth the ages of the da lien and nui phao granite massifs and the nui phao deposit have been estimated to be ca 84 ma ar ar 244 ma u pb and ca 85 ma ar ar respectively indicating a genetic relationship between the mineralization and the cretaceous magmatic event

geochemical indicators of metalliferous fertility in the carboniferous san blas pluton sierra de velasco argentina in the sierra de velasco northwestern argentina undeformed lower carboniferous granitoids 350 334 ma intrude deformed lower ordovician granites and have been emplaced by passive mechanisms typical of tensional environments the semi elliptic about 300 km shallow emplaced san blas pluton is 340 330 ma old with 1ndt between 21 3 and 21 8 which indicates that different from the nearby famatinian ordovician granitoids the san blas pluton had a relatively brief crustal residence with an interaction between asthenospheric material and greywackes the cupola of the pluton was almost totally eroded down during the upper

mid crustal deformation in a continental margin orogen structural evolution and timing of the famatinian orogeny nw argentina new structural data from a mid crustal segment in the eastern sierras pampeanas coupled with geochronological methods and p t estimates reveal polyphase contractional deformation and metamorphism during the famatinian orogeny over a long period of time peaks of metamorphic monazite and zircon ages are recorded at c 500 ma between 484 and 465 ma and at c 440 ma between 484 and 465 ma the region attained high temperature ht low pressure lp conditions that resulted in widespread partial melting peak at c 470 ma a contractional phase occurred during this event as suggested by syn anatectic structures as well as folding at subsolidus conditions renewed contraction under subsolidus conditions is evidenced by reverse ductile shearing and folding at c 440 ma thrusting along the la chilca shear zone caused metamorphic inversion the consistent orientation of folds in the quebrada del molle metamorphic complex el portezuelo metamorphic igneous complex and the la chilca shear zone as well as wsw directed thrusting at the later shear zone indicate uniform wsw ene directed shortening this late deformation records the ocloyic tectonic phase and brought the famatinian orogeny to an end in the late ordovician to early silurian supplementary material analytical methods methods and description of the calculated p t pseudosection diagrams bulk compositions and electron microprobe u pb and 40ar 39ar data are available at https doi org 10 6084 m9 figshare c 4697189

depositional relations of cretaceous and lower tertiary rocks northeastern alaska analysis of depositional environments new paleontologic data and analogy with depositional patterns observed in areas to the west all indicate the need for revision of cretaceous and lower tertiary stratigraphy in northeastern alaska in the sadlerochit mountains area of the arctic national wildlife refuge the northern derived ellesmerian late neocomian kemik sandstone member and organic rich pebble shale member of the kongakut formation unconformably overlie jurassic and triassic rocks the unconformity which is of mid neocomian age is present throughout northernmost alaska and passes southward into a conformable shelf sequence after pebble shale deposition the depositional pattern is simply one of progradational basin filling from a southern brookian provena ce this pattern is represented in vertical sequence initially by deep marine basinal deposits succeeded by prodelta slope shales and ultimately by deltaic deposits that prograded to the east or northeast in a predictable fashion over most of the area the better known thick shallow marine and nonmarine units in the central north slope grade to thin prodelta or basinal turbidites some units are entirely missing owing to nondeposition on the south dipping flank of the basin no evidence exists for subaerial erosion to explain these marked stratigraphic changes in the sadlerochit mountains area which may be an extension of the barrow arch the pebble shale neocomian is overlain by about 1 600 ft 500 m of deep water deposits of late cretaceous age aptian and albian rocks are either absent by nondeposition or are represented by a thin condensed section here the upper cretaceous to lower tertiary section consists of basinal shale bentonite and thin bedded prodelta turbidites two noteworthy features in this sequence are an interval of organic rich shale of probable turonian to coniacian age just above the pebble shale and the placement of the cretaceous tertiary boundary within deep marine deposits unlike the western part of the north slope where deltaic deposition occurred in the early cretaceous prograding deltaic deposition d d not reach the western part of the wildlife refuge until early in the tertiary the consistent pattern of easterly deltaic progradation is complicated at igilatvik sabbath creek in the north central wildlife refuge by the occurrence of thick regressive dominantly nonmarine deposits of early tertiary age which apparently prograded into the basin from the south or southeast

mount elbert gas hydrate stratigraphic test well alaska north slope coring operations core sedimentology and lithostratigraphy abstract in february 2007 bp exploration alaska the u s department of energy and the u s geological survey completed the bpxa doe usgs mount elbert gas hydrate stratigraphic test well mount elbert well in the milne point unit on the alaska north slope the program achieved its primary goals of validating the pre drill estimates of gas hydrate occurrence and thickness based on 3 d seismic interpretations and wireline log correlations and collecting a comprehensive suite of logging coring and pressure testing data the upper section of the mount elbert well was drilled through the base of ice bearing permafrost to a casing point of 594 m 1950 ft approximately 15 m 50 ft above the top of the targeted reservoir interval the lower portion of the well was continuously cored from 606 m 1987 ft to 760 m 2494 ft and drilled to a total depth of 914 m ice bearing permafrost extends to a depth of roughly 536 m and the base of gas hydrate stability is interpreted to extend to a depth of 870 m coring through the targeted gas hydrate bearing reservoirs was completed using a wireline retrievable system the coring program achieved 85 recovery of 7 6 cm 3 in diameter core through 154 m 504 ft of the hole an onsite team processed the cores collecting and preserving approximately 250 sub samples for analyses of pore water geochemistry microbiology gas chemistry petrophysical analysis and thermal and physical properties eleven samples were immediately transferred to either methane charged pressure vessels or liquid nitrogen for future study of the preserved gas hydrate additional offsite sampling analyses and detailed description of the cores were also conducted based on this work one lithostratigraphic unit with eight subunits was identified across the cored interval subunits ii and va comprise the majority of the reservoir facies and are dominantly very fine to fine moderately sorted quartz feldspar and lithic fragment bearing to rich sands lithostratigraphic and palynologic data indicate that this section is most likely early eocene to late paleocene in age the examined units contain evidence for both marine and non marine lithofacies and indications that the depositional environment for the reservoir facies may have been shallower marine than originally interpreted based on pre drill wireline log interpretations there is also evidence of reduced salinity marine conditions during deposition that may be related to the paleo climate and depositional conditions during the early eocene

microbial community distribution in sediments from the mount elbert gas hydrate stratigraphic test well alaska north slope we studied the microbial communities collected from hydrate bearing sediments on the north slope of alaska to determine how abiotic variables e g grain size hydrate presence formation fluid gases may correspond to the type and distribution of microbes in the sediments the cores were acquired from sub permafrost eocene 46 55 million year old sediments in the bpxa doe usgs mount elbert gas hydrate stratigraphic test well within which hydrates are believed to have formed 1 5 mya forty samples eight of which originally contained hydrates were acquired from depths of ca 606 666 m below land surface five drilling fluid samples acquired from the same depth range were included in the analysis as a control for possible contamination by drilling fluid microbes during the drilling and handling of cores dna was extracted from 15 samples typically 1 ng dna g sediment was recovered and then amplified using polymerase chain reaction with primers specific for bacterial and archaeal 16s rdna genes which indicates the likelihood that microbes were present in all analyzed samples only bacterial dna amplicons were detected terminal restriction fragment length polymorphism t rflp was used to measure bacterial diversity in the respective samples non metric multidimensional scaling nms was used to determine the abiotic variables that may have influenced bacterial diversity nms analysis revealed that the microbial taxa present in the sediment were distinct from the taxa present in the drilling fluids suggesting that the sediments were not contaminated by the drilling fluids multi response permutation procedures mrpp found no significant difference between three sample groups identified a priori as being from within a hydrate zone outside of hydrate zone or on the edge of a hydrate non hydrate zone according to downhole nuclear magnetic resonance spectroscopy logs however among the several other abiotic parameters that were evaluated mud gas methane concentration and variables related to hydrate presence e g chloride concentration salinity and resistivity appeared to define the arrangement of microbial community signatures in plots resulting from nms analysis communities from hydrate and non hydrate layers each contained unique taxa as determined by the t rflp assay

the effect of hydrate saturation on water retention curves in hydrate bearing sediments the experimental measurement of water retention curve in hydrate bearing sediments is critically important to understand the behavior of hydrate dissociation and gas production in this study tetrahydrofuran thf is selected as hydrate former the pore habit of thf hydrates is investigated by visual observation in a transparent micromodel it is confirmed that thf hydrates are not wetting phase on the quartz surface of the micromodel and occupy either an entire pore or part of pore space resulting in change in pore size distribution and the measurement of water retention curves in thf hydrate bearing sediments with hydrate saturation ranging from sh 0 to sh 0 7 is conducted for excess water condition the experimental results show that the gas entry pressure and the capillary pressure increase with increasing hydrate saturation based on the experimental results fitting parameters for van genuchten equation are suggested for different hydrate saturation conditions

sulfide mineralogy in the polymetallic cassiterite deposits of dachang p r china several important mineral deposits of sn zn cu pb and other metals associated with devonian sediments and yanshanian cretaceous granitic rocks are known in the dachang district guangxi early genetic hypotheses related the origin of the deposits entirely to the yanshanian granites recently it was suggested that in devonian times an earlier syngenetic metal concentration may have occurred later overprinted by the yanshanian metallogeny this contribution is aimed at placing constraints on the physicochemical conditions during the yanshanian ore formation remobilization by studying the sulfide chemistry arsenopyrite sphalerite stannite and fluid inclusion data on the two major deposits in the area i e the polymetallic cassiterite deposit of changpo and the zn cu skarn deposit of lamo sphalerite and arsenopyrite are quite abundant in both deposits stannite is minor but fairly widespread at changpo and quite rare at lamo they are accompanied by pyrite pyrrhotite galena chalcopyrite cassiterite fluorite and a large variety of other sulfides and sulfosalts the main compositional data for sphalerite and arsenopyrite are summarized as follows

downhole well log and core montages from the mount elbert gas hydrate stratigraphic test well alaska north slope abstract the bpxa doe usgs mount elbert gas hydrate stratigraphic test well was an integral part of an ongoing project to determine the future energy resource potential of gas hydrates on the alaska north slope as part of this effort the mount elbert well included an advanced downhole geophysical logging program because gas hydrate is unstable at ground surface pressure and temperature conditions a major emphasis was placed on the downhole logging program to determine the occurrence of gas hydrates and the in situ physical properties of the sediments in support of this effort well log and core data montages have been compiled which include downhole log and core data obtained from the gas hydrate bearing sedimentary section in the mount elbert well also shown are numerous reservoir parameters including gas hydrate saturation and sediment porosity log traces calculated from available downhole well log and core data

numerical study of gas production from marine hydrate formations considering soil compression and hydrate dissociation due to depressurization abstract depressurization is considered a key method for extracting natural gas from marine gas hydrates in the petroleum industry permeability is one of the significant factors impacting gas production low permeability formations tend to be related to low gas production the effective permeability of hydrate bearing sediments depends on both porosity and hydrate saturation because the sediments bear external loads during depressurization analyses of gas production from hydrate should consider the volume change in the formation in response to earth stress in this paper several parametric analyses were conducted using a fully coupled thermo hydro chemo mechanical thcm model to analyze gas production during depressurization when considering soil compression the simulation results show that boundary effects exist when small models are used for long term simulations compression may result in a lower effective permeability in the hydrate dissociated zone than that in the hydrate undissociated zone the gas flow rate is affected by the difference in the effective permeability between the hydrate dissociated zone and the hydrate undissociated zone meanwhile lower downhole pressure leads to more serious soil compression which may not benefit gas production

the famatina complex nw argentina back docking of an island arc or terrane accretion early palaeozoic geodynamics at the western gondwana margin

fault controlled carboniferous a type magmatism in the proto andean foreland sierras pampeanas argentina geochemical constraints and petrogenesis abstract the intrusion of granitoids into the eastern sierras pampeanas in the early carboniferous took place after a long period of mainly compressional deformation that included the famatinian ordovician and achalian devonian orogenies these granitoids occur as small scattered plutons emplaced in a dominant extensional setting within older metamorphic and igneous rocks and many of them are arranged along a reactivated large shear zone a set of 46 samples from different granitic rocks huaco granitic complex san blas pluton and the la chinchilla stock from the sierra de velasco zapata granitic complex from sierra de zapata and the los arboles pluton from sierra de fiambala display high and restricted sio 2 contents between 69 2 and 76 4 wt on both feo feo mgo vs sio 2 and na 2 o k 2 o cao vs sio 2 plots the samples plot in the ferroan and alkaline calcic to calco alkaline fields feo feo mgo 0 88 1 0 na 2 o k 2 o cao 6 3 8 3 thus showing an a type granitoid signature the high concentrations for the high field strength elements hsfe such as y nb ga ta u th etc and flat ree patterns showing significant negative eu anomalies are also typical features of a type granites our petrogenetic model supports progressive fractional crystallization with dominant fractionation of feldspar and a source mineral assemblage enriched in plagioclase biotites have distinctive compositions with high feo mgo ratios 7 8 61 5 f 360 5610 ppm and cl 120 1050 ppm the feo mgo ratios together with the f and cl content of igneous biotites seem to reflect the nature of their parental host magmas and may be useful in identifying a type granitoids the isotopic data rb sr and sm nd confirm that the a type granites represent variable mixtures of asthenospheric mantle and continental crust and different mixtures lead to different subtypes of a type granite illustrating the lack of consensus about a type magma origin we conclude that prominent shear zones play an important role in providing suitable conduits for ascending asthenospheric material and heat influx in the crust a hypothesis that is in accord with other recent work on a type granites

comparison of the physical and geotechnical properties of gas hydrate bearing sediments from offshore india and other gas hydrate reservoir systems abstract the sediment characteristics of hydrate bearing reservoirs profoundly affect the formation distribution and morphology of gas hydrate the presence and type of gas porewater chemistry fluid migration and subbottom temperature may govern the hydrate formation process but it is the host sediment that commonly dictates final hydrate habit and whether hydrate may be economically developed in this paper the physical properties of hydrate bearing regions offshore eastern india krishna godavari and mahanadi basins and the andaman islands determined from expedition nghp 01 cores are compared to each other well logs and published results of other hydrate reservoirs properties from the hydrate free kerala konkan basin off the west coast of india are also presented coarser grained reservoirs permafrost related and marine may contain high gas hydrate pore saturations while finer grained reservoirs may contain low saturation disseminated or more complex gas hydrates including nodules layers and high angle planar and rotational veins however even in these fine grained sediments gas hydrate preferentially forms in coarser sediment or fractures when present the presence of hydrate in conjunction with other geologic processes may be responsible for sediment porosity being nearly uniform for almost 500 m off the andaman islands properties of individual nghp 01 wells and regional trends are discussed in detail however comparison of marine and permafrost related arctic reservoirs provides insight into the inter relationships and common traits between physical properties and the morphology of gas hydrate reservoirs regardless of location extrapolation of properties from one location to another also enhances our understanding of gas hydrate reservoir systems grain size and porosity effects on permeability are critical both locally to trap gas and regionally to provide fluid flow to hydrate reservoirs index properties corroborate more advanced consolidation and triaxial strength test results and can be used for predicting behavior in other nghp 01 regions pseudo overconsolidation is present near the seafloor and is underlain by underconsolidation at depth at some nghp 01 locations

mississippian volcanism in the south central andes new u pb shrimp zircon geochronology and whole rock geochemistry abstract in the northern extension of the famatina and the southern puna nw argentina prominent rhyolitic volcanic rocks traditionally referred to as ordovician are exposed resting on metamorphic basement and covered by thick late paleozoic siliciclastic successions we report new u pb shrimp ages from these rhyolites that show them to be of mississippian 348 342 ma age thus identifying a previously unknown volcanic event in this portion of western gondwana whole rock geochemistry and sr nd isotopic analyses suggest a crustal source for these rocks but with a juvenile input end t between 2 91 and 0 3 and tdm values between 1 09 and 1 1 ga this is different from the early paleozoic magmatism of western argentina where crustal recycling took place without any involvement of mantle material the carboniferous magmatism is compatible with an extensional environment developed along the terra australis accretionary orogen as a result of tectonic switching processes these rhyolites may be related to the coeval mississippian a type granites exposed to the east in the sierras pampeanas confirming the regional character of this magmatism

mantle derived helium in two peruvian hydrothermal ore deposits strong differences exist between the helium isotopic compositions of mantle derived magmas1 8 axial vent hotspring fluids9 14 subduction related magmas15 20 and many associated hot springs21 24 and the atmospheric and crustal values fig 1 here we report helium isotope ratios for two late tertiary fossil hydrothermal systems responsible for precious metal base metal and tungsten mineralization and compare them to those of circum pacific hot spring emanations the 3he 4he ratios of inclusion fluids hosted by gangue and sulphide minerals from casapalca and pasto bueno peru all lie between two and three times the atmospheric value indicating the presence of a dilute component of mantle helium consistent with previously reported stable isotope evidence for the presence of magmatic fluids during mineralization25 27 although post trapping modification of the helium isotope composition is possible we suggest that these apparently low values represent the composition of helium inherited from contributing magmas as a tracer of magmatic fluids in hydrothermal systems helium isotopes are decoupled from the factors that govern other stable isotope signatures

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

paleozoic to early cenozoic cooling and exhumation of the basement underlying the eastern puna plateau margin prior to plateau growth 1 constraining the pre neogene history of the puna plateau is crucial for establishing the initial conditions that attended the early stage evolution of the southern extent of the andean plateau we apply high to low temperature thermochronology data from plutonic rocks in northwestern argentina to quantify the paleozoic mesozoic and early tertiary cooling history of the andean crust u pb crystallization ages of zircons indicate that pluton intrusion occurred during the early mid ordovician 490 470 ma and the late jurassic 160 150 ma lower temperature cooling histories from40ar 39ar analyses of k feldspar vary substantially basement rocks underlying the western puna resided at temperatures below 200 c 6 km depth since the devonian 400 ma in contrast basement rocks underlying the southeastern puna were hotter 200 300 c throughout the paleozoic and jurassic and cooled to temperatures of 200 c by 120 ma the southeastern puna basement records a rapid cooling phase coeval with active extension of the cretaceous salta rift at 160 100 ma that we associate with tectonic faulting and lithospheric thinning the northeastern puna experienced protracted cooling until the late cretaceous with temperatures 200 c during the paleocene higher cooling rates between 78 and 55 ma are associated with thermal subsidence during the postrift stage of the salta rift and or shortening related flexural subsidence accelerated cooling and deformation during the eocene was focused within a narrow zone along the eastern puna eastern cordillera transition that coincides with paleozoic mesozoic structural and thermal boundaries our results constrain regional erosion induced cooling throughout the cenozoic to have been less than 150 c which implies total cenozoic denudation of 6 4 km

an expanded view of jurassic orogenesis in the western united states cordillera middle jurassic pre nevadan regional metamorphism and thrust faulting within an active arc environment klamath mountains california basaltic to basaltic andesitic volcaniclastic rocks and their contemporaneous mafic ultramafic intrusive complexes delineate a middle jurassic arc terrane within the klamath mountain province of northern california exposures of the supracrustal volcaniclastic rocks are restricted to a single fault bounded terrane but the deeper level intrusive complexes were emplaced into most if not all the pre late jurassic terranes of the klamath mountain region the pre late jurassic terranes thus constitute the basement of the middle jurassic arc u pb zircon analyses of 39 zircon fractions from 12 intrusive complexes plus k ar dating of the volcaniclastic strata demonstrate magmatic activity over the interval of 177 159 ma the active arc and its basement were imbricated by a compressive deformational event the signature of which included thrust faulting isoclinal folding and regional metamorphism several diverse lines of evidence including k ar dating of metamorphic rocks crosscutting relations of dated intrusive complexes to thrust faults and u pb dating of synmetamorphic intrusive complexes establish a distinctly pre nevadan middle jurassic age ongoing at 169 ma and over by at least 161 ma for this compressive deformational episode outboard and structurally beneath the middle jurassic arc and its basement are several terranes that collectively comprise the western jurassic belt these terranes were deformed and regionally metamorphosed during the late jurassic nevadan orogeny which occurred within the time interval of 157 150 ma as upper jurassic plutons with 150 to 142 m y old zircon ages have contact aureoles that overprint the nevadan fabric and the 157 m y old rogue formation was deformed in the nevadan event the middle and late jurassic compressive deformational events were thus distinct and separated by as much as 15 20 m y the relation between middle and late jurassic magmatism and deformation suggests that the klamath mountain province records the evolution of a considerably long lived arc system that evolved above an east dipping subduction zone in addition we suggest that this are system may represent an oceanic continuation of the long recognized early mesozoic arc terrane of the western u s cordillera

pre and post drill comparison of the mount elbert gas hydrate prospect alaska north slope abstract in 2006 the united states geological survey usgs completed a detailed analysis and interpretation of available 2 d and 3 d seismic data along with seismic modeling and correlation with specially processed downhole well log data for identifying potential gas hydrate accumulations on the north slope of alaska a methodology was developed for identifying sub permafrost gas hydrate prospects within the gas hydrate stability zone in the milne point area the study revealed a total of 14 gas hydrate prospects in this area in order to validate the gas hydrate prospecting protocol of the usgs and to acquire critical reservoir data needed to develop a longer term production testing program a stratigraphic test well was drilled at the mount elbert prospect in the milne point area in early 2007 the drilling confirmed the presence of two prominent gas hydrate bearing units in the mount elbert prospect and high quality well logs and core data were acquired the post drill results indicate pre drill predictions of the reservoir thickness and the gas hydrate saturations based on seismic and existing well data were 90 accurate for the upper unit hydrate unit d and 70 accurate for the lower unit hydrate unit c confirming the validity of the usgs approach to gas hydrate prospecting the mount elbert prospect is the first gas hydrate accumulation on the north slope of alaska identified primarily on the basis of seismic attribute analysis and specially processed downhole log data post drill well log data enabled a better constraint of the elastic model and the development of an improved approach to the gas hydrate prospecting using seismic attributes

evaluation of the performance of the oceanic hydrate accumulation at site nghp 02 09 in the krishna godavari basin during a production test and during single and multi well production scenarios author s moridis gj reagan mt queiruga af boswell r abstract 2018 elsevier ltd the objective of this study is to quantify by means of numerical simulation the response of the complex system of gas hydrate accumulations at site nghp 02 09 krishna godavari basin indian ocean to different production conditions and to determine the technical feasibility of gas production through depressurization induced dissociation the study assesses the suitability of the site for a long term production test involving a single vertical well and the long term potential of the deposit under full field production using a system of multiple vertical wells we simulate gas and water flow estimate the production performance of the accumulation and separately investigate the corresponding geomechanical response of the system results indicate that production from site nghp 02 09 under the conditions of a long term field test involving a single vertical well is technically feasible and can yield high gas production rates however an inability to fully isolate the water bearing zones results in production that is largely from dissolved gas rather than hydrate dissociation and is thus burdened by excessive water production given the estimated physical properties of the reservoir system site nghp 02 09 does not appear to be a promising location for a single well field test of gas production but may be a promising production target for full field production operations using a multi well system in which exterior wells can mitigate water inflows to allow interior wells to more effectively depressurize the formation and capture methane from gas hydrate dissociation geomechanical issues need to be carefully considered as significant displacements are possible which can be challenging to well construction and stability

experimental data for a proposed empirical igneous geobarometer aluminum in hornblende at 10 kbar pressure knowledge of the depth of solidification of talc alkalic plutons is critical to understanding and unraveling the complex spatial temporal and chemical evolution of orogenic belts an empirical geobarometer has recently been proposed based on the total al content alt of near solidus calcic hornblendes in tonalite and granodiorite intrusive rocks in the pressure range 1 to 8 kbar pressures were estimated from mineral assemblages in associated metamorphic country rocks we report experimental data on newly crystallized near solidus amphiboles in partly melted vapor absent garnet tonalite at 10 kbar that provide some experimental support for the proposed geobarometer consistent with the extrapolated empirical result and confirm its limited applicability to specific multimineral assemblages

the puncoviscana trough a large basin of late precambrian to early cambrian age on the pacific edge of the brazilian shield during the late precambrian to early cambrian a large basin with a homogeneous psammitic pelitic sediment fill existed in the area of the nw argentine andes it is now exposed in different tectonic levels this basin of meridional elongation was situated on a stable continental margin at the western edge of the brazilian shield it was underlain by segmented older continental crust according to the modal and chemical composition of the greywackes and subgreywackes a predominant metasedimentary source may be supposed four clastic facies types indicate a transport by gravity currents within a submarine fan system while massive red pelites represent cut off periods and rare carbonates deposition on rises the gravity currents derived from easterly directions the sedimentation age is proved by a rich ichnofauna and some medusoid impressions

the cassiterite polymetallic sulfide deposits of dachang guangxi people s republic of china the dachang mining district is the second largest producer of sn in china and an important source of other metals the known mineralizations can be divided into four groups 1 cassiterite cu fe pb zn sulfides and sulfosalts 2 zn cu skarn 3 sb w veins and 4 residual and placer concentrations of sn and fe oxides most orebodies are hosted by upper devonian calcareous marly and quartzitic formations in spatial association with cretaceous yanshanian magmatites a characteristic feature is the occurrence of stratiform lens shaped orebodies which appear to represent the root zone of overlying stockwork mineralizations the metallogeny of the district may be interpreted in terms of an upper devonian sn and polymetallic concentration with subsequent remobilization and possibly the introduction of additional elements during the late stages of the yanshanian magmatism

seafloor subsidence induced by gas recovery from a hydrate bearing sediment using multiple well system abstract the response behavior of the methane exploitation from natural gas hydrate ngh using multiple well system is complex and needs to be investigated as gas production from a single vertical well generally cannot meet commercial demand this study numerically investigates the production performance and geomechanical response of an unconfined hydrate deposit in shenhu area south china sea under single and multiple vertical well conditions for a single vertical well with a mild constant bottom hole pressure gas production is relatively stable however seafloor subsidence exhibits an initial rapid drop and a subsequent mild drop stage the vertical displacement is highly developed at the top and bottom of the production zone the results from doublet and triplet vertical wells indicate that both the gas and water production and seafloor subsidence increase with the increase in number of production wells the superimposition of subsidence leads to a deterioration in subsidence and the change in location for the largest subsidence which may affect the risk location of well instability the interference of pore pressure and subsidence increases with the decrease in well spacing however gas production decreases and water production changes insignificantly furthermore a same subsidence at seafloor cannot indicate the same evolution of subsidence in the vertical and lateral direction the results presented in this study help in balancing the production and subsidence of the ngh exploitation in complex well configurations

thermochronology of economic mineral deposits dating the stages of mineralization at panasqueira portugal by high precision 40 39 ar age spectrum techniques on muscovite 40 ar 39 ar age spectrum dates for 13 muscovites have been used to reconstruct the thermal history thermochronology of the panasqueira portugal tin tungsten deposit a deposit spatially associated with a belt of hercynian plutons muscovite samples with an age difference as small as 2 2 m y 0 7 of the age are statistically distinct statistics are even better for comparison of multiple samples from separate events that is a difference of 0 9 m y 0 3 can be resolved in this approximately 300 m y old deposit the major tin and tungsten ore forming stages which are the oxide silicate stage the main sulfide stage and greisenization occurred between 296 3 or 0 8 1 sigma and 291 6 or 0 8 m y 1 sigma the first substage of the oxide silicate stage was a short lived thermal pulse at 296 3 or 0 6 m y the fluids responsible may have emanated from the known granite cupola the main sulfide stage was active at 294 5 or 0 9 m y as a slightly longer lived pulse with oldest evidence for this stage 295 8 or 0 6 m y coming from areas farthest away from the known cupola and youngest evidence 293 5 or 0 8 m y closest to the cupola a second substage of the oxide silicate stage occurred as a short lived thermal pulse at 292 9 or 0 7 m y synchronous with greisenization of the cupola and alteration of the silica cap at 292 1 or 0 4 m y the duration of activity of the oxide silicate stage the main sulfide stage greisenization and alteration of the silica cap based on the ages of all 13 muscovites was greater than 4 2 or 0 5 m y 1 sigma minor argon loss from all dated muscovites occurred during later reheating probably during the longer lived pyrrhotite alteration stage a single center the known cupola had a prolonged role and was the source for main sulfide stage oxide silicate stage ii greisenization and alteration of the silica cap and possibly oxide silicate stage i and the pyrrhotite alteration stage however a separate source for these latter two stages cannot be ruled out this study is an example of a new and powerful application of 40 ar 39 ar age spectrum dating of muscovite because of the high precision demonstrated in this study it is now possible to establish time constraints necessary for solving some of the long standing problems in economic geology beyond this the unique geologic situation of panasqueira has allowed us to quantify the thermal characteristics of muscovite published fluid inclusion data have been used to estimate a muscovite argon closure temperature of approximately 325 degrees c during rapid cooling or short reheating and a temperature of approximately 270 degrees c during slow cooling or extended reheating argon loss patterns displayed by all dated muscovites resulted from reheating after original closure the mechanism for this argon loss appears to have been argon transport by volume diffusion thus 40 ar 39 ar age spectrum dating of muscovite can be used to evaluate thermal conditions controlling argon diffusion as well as age duration and number of episodes of mineralization

numerical analysis of gas production potential from a gas hydrate reservoir at site nghp 02 16 the krishna godavari basin offshore india feasibility of depressurization method for ultra deepwater environment abstract sandy gas hydrate reservoirs are considered to be promising deposits for gas recovery but the feasibility of the depressurization method in ultra deepwater environments remains unclear because high pressure gradient induced by depressurization may increase the water production and reduce the gas water ratio of produced fluid in numerical simulations this study predicts the gas production behavior of a hydrate reservoir site nghp 02 16 in the krishna godavari basin offshore india located in ultra deepwater depth 2546 5 m the reservoir properties such as the hydrate saturation and initial effective in situ permeability were determined from log data and pressure core analysis by comparing the hydrate saturations calculated from resistivity log with the estimations from p wave velocities of pressure cores the model parameters a m and n of archie s equation were determined as 1 8 2 0 and 2 9 respectively the initial effective permeability of the hydrate bearing layers with up to 78 hydrate saturation was estimated to range from approximately 0 01 to 1 0 millidarcy md at day 180 after the start of depressurization in a single vertical well the gas production rates ranged from 320 to 9500 sm3 d depending on the bottom hole pressure lowering the bottom hole pressure increased the gas production rate and gas water ratio of the produced fluid the bottom hole pressure of 10 mpa or less is recommended for the production test condition in this site however aquifer below the gas hydrate bearing zone and poor hydraulic sealing of the over and under burden increased the water production hydraulic isolation of the gas hydrate bearing layers is essential when applying depressurization in an ultra deepwater environment

genesis of the jianzhupo sb pb zn ag deposit and formation of an ore shoot in the wuxu ore field guangxi south china abstract the jianzhupo sb pb zn ag deposit in the southeastern dachang sn polymetallic ore belt guangxi region south china is the largest deposit in the wuxu district and is hosted by devonian limestone and mudstone the deposit mainly comprises a stage i jamesonite sphalerite ore shoot and stage ii jamesonite sphalerite calcite quartz jscq veins we use homogenization temperatures salinities and the h o isotopic compositions of fluid inclusions from the jianzhupo deposit to constrain the genesis of the deposit and determine factors that controlled the formation of the ore shoot fluid inclusions from both stages of mineralization contain large volumes of co2 and minor bitumen c6h6 and ch4 fluid inclusions from the ore shoot yield homogenization temperatures of 120 c 290 c mainly 250 c 270 c and salinities of 3 4 13 6 wt nacl equiv fluid inclusions from the stage ii mineralization yield homogenization temperatures of 150 c 350 c mainly 240 c 310 c and salinities of 1 4 12 0 wt nacl equiv ore forming fluids of the jianzhupo deposit yield 18oh2o and dv smow values of 4 9 9 9 and 78 to 111 respectively and plot close to the composition of magmatic water on the dv smow vs 18oh2o diagram co2 in the ore forming fluids was likely generated through deep skarnization beneath the wuxu ore field rather than from metamorphism thermal degradation or the oxidization of organic matter h o isotopic compositions of ore forming fluids that contain large volumes of co2 with minor bitumen and c6h6 indicate that they were derived from magmatic water that was mixed with basin brines ore forming fluids of the stage i ore shoot yield lower 18oh2o values 4 9 6 7 than those associated with the stage ii mineralization 7 5 9 9 moreover ore forming fluids of the ore shoot and the jscq veins yield strongly and weakly positive correlations between homogenization temperature and salinity respectively this difference suggests that rapid and large scale mixing between magmatic water and basin brines was the key factor that controlled the formation of the ore shoot

abundance and isotopic composition of helium in hydrothermal sulfides from the east pacific rise at 13 n abstract the helium isotopes composition of fluids trapped in hydrothermal sulfides from the east pacific rise 13 n were measured two extraction techniques i e crushing and heating were tested and sulfldes of different mineralogical types were studied the comparison between the two extraction methods suggests that both should give similar results provided the crushing efficiency is sufficiently high sulfides 3 he 4 he ratio for crushed samples are in the range 6 85 8 10 times the atmospheric ratio r a 1 38 10 6 and the measured helium concentration is of the order of 5 5 10 5 cm 3 stp per gram of trapped fluid comparison with the helium isotope composition of the hydrothermal vent fluids themselves shows that the mineral phases formed at the highest temperature i e with less dilution by the ambient seawater retain the helium information most effectively with values almost indistinguishable from the endmember vent fluid

indium in cassiterite and ores of tin deposits abstract the results obtained with la icp ms by less abundant lighter 113 in isotope and epma show that in cassiterite of cassiterite quartz veins the indium contents do not exceed 160 ppm while cassiterite from sn sulfide veins is characterized by higher indium contents from 40 to 485 ppm sulfides of sn sulfide veins unlike sulfides of cassiterite quartz veins also have the highest indium contents fe sphalerite 100 25 000 ppm chalcopyrite up to 1000 ppm and stannite up to 60 000 ppm indium contents in the sn sulfide ore of the tigrinoe and pravourmiiskoe deposits obtained using sr xrf icp ms and atomic absorption methods range from 10 to 433 ppm with average values of 56 65 ppm indium rich sn sulfide mineralization in five large sn ag ore districts of the far east russia khingansky badzhalsky komsomolsky arminsky kavalerovsky provides the impetus for further exploration of deposits with sn sulfide mineralization as the most promising indium resources in russia empirical observations from geology and geochronology of cassiterite quartz and sn sulfide mineralization show that the combined contribution from granite and alkaline subalkaline mafic sources and multistage ore forming processes doubled indium resources of deposits being the main factors in the formation of high grade indium mineralization

mount elbert gas hydrate stratigraphic test well alaska north slope overview of scientific and technical program abstract the mount elbert gas hydrate stratigraphic test well was drilled within the alaska north slope ans milne point unit mpu from february 3 to 19 2007 the well was conducted as part of a cooperative research agreement cra project co sponsored since 2001 by bp exploration alaska inc bpxa and the u s department of energy doe in collaboration with the u s geological survey usgs to help determine whether ans gas hydrate can become a technically and commercially viable gas resource early in the effort regional reservoir characterization and reservoir simulation modeling studies indicated that up to 0 34 trillion cubic meters tcm 12 trillion cubic feet tcf gas may be technically recoverable from 0 92 tcm 33 tcf gas in place within the eileen gas hydrate accumulation near industry infrastructure within ans mpu prudhoe bay unit pbu and kuparuk river unit kru areas to further constrain these estimates and to enable the selection of a test site for further data acquisition the usgs reprocessed and interpreted mpu 3d seismic data provided by bpxa to delineate 14 prospects containing significant highly saturated gas hydrate bearing sand reservoirs the mount elbert site was selected to drill a stratigraphic test well to acquire a full suite of wireline log core and formation pressure test data drilling results and data interpretation confirmed pre drill predictions and thus increased confidence in both the prospect interpretation methods and in the wider ans gas hydrate resource estimates the interpreted data from the mount elbert well provide insight into and reduce uncertainty of key gas hydrate bearing reservoir properties enable further refinement and validation of the numerical simulation of the production potential of both mpu and broader ans gas hydrate resources and help determine viability of potential field sites for future extended term production testing drilling and data acquisition operations demonstrated that gas hydrate scientific research programs can be safely effectively and efficiently conducted within ans infrastructure the program success resulted in a technical team recommendation to project management to drill and complete a long term production test within the area of existing ans infrastructure if approved by stakeholders this long term test would build on prior arctic research efforts to better constrain the potential gas rates and volumes that could be produced from gas hydrate bearing sand reservoirs

geophysical characterization of a fine grained gas hydrate reservoir in the shenhu area northern south china sea integration of seismic data and downhole logs abstract high concentrated gas hydrate deposits in fine grained sediment are proved to be eligible for exploitation with the current technology nevertheless new insights and more understandings of the accumulation of gas hydrate and characterization of hydrate reservoir in fine grained sediment are required which can facilitate the commercial production of gas hydrate in the future combining seismic data and downhole logs here we investigate a fine grained gas hydrate reservoir in the shenhu area northern south china sea scs gas hydrate with saturations of 10 45 occurs in fine grained sediment besides the typical bottom simulating reflectors bsrs and high amplitude reflection below bsr a high amplitude positive reflector referred to as the top of gas hydrate reservoir reflector tghr exists at the top of high concentrated fine grained gas hydrate reservoir according to the result of acoustic impedance inversion the tghr is considered to represent a transitional zone from the overlying water saturated sediment to the underlying high concentrated gas hydrate occurrence zone ghoz discontinuous bsrs beneath the traditional bsrs are also discovered in the study area which are interpreted as the seismic evidence of the sii gas hydrate in the shenhu area fluid flow features such as chimney structures and faults are found on the ridges where gas hydrate occurs indicating that gas migration plays a critical role in the formation of gas hydrate in the fine grained sediment our results provide valuable geophysical indications for detecting the presence of gas hydrate in fine grained sediments

multiple fluids involved in granite related w sn deposits from the world class jiangxi province china abstract this paper aims at providing new insights into w sn ore forming processes within one of the largest granitic provinces in the world nanling range south china which was emplaced during the jurassic cretaceous period the origin composition and pressure temperature conditions of fluids involved in the w sn ore forming processes have been investigated by microthermometry raman spectroscopy la icpms hydrogen isotope analyses of fluid inclusions and oxygen isotope analyses of minerals from the maoping and piaotang w sn deposits for each deposit pre quartz syn wolframite and cassiterite and post ore quartz topaz and fluorite minerals were studied in both deposits the vast majority of fluid inclusions are aqueous with salinities between 0 0 and 12 6 wt equiv nacl and homogenization temperatures between 136 and 349 c a minor proportion 5 of inclusions observed in the ore stage quartz from maoping have aquo carbonic compositions for both deposits four compositional groups are defined early quartz fluid inclusions are characterized by salinities between 0 4 and 9 0 wt equiv nacl trapping temperatures between 150 and 350 c and pressures between 20 and 150 mpa la icpms analyses of these fluid inclusions reveal a wide range of na k and li concentrations as well as relatively low metal contents w at piaotang fluid inclusions in wolframite as well as in post ore quartz and fluorite have salinities of 5 6 to 12 6 wt eq nacl trapping temperatures between 150 and 400 c and pressures of 20 to 150 mpa la icpms analyses of these fluid inclusions reveal similar compositions to early quartz fluid inclusions values of 18o in wolframite and quartz crystals range from 0 8 to 5 2 vsmow while the d values of fluid inclusions range from 66 to 62 vsmow collectively the data suggest the involvement of four aqueous fluid end members mixed episodically in the mineralization process a a low salinity low temperature metal poor low 18o low d fluid derived from meteoric water b a high salinity high temperature metal poor high 18o low d fluid derived from a differentiated peraluminous granitic magma c a high salinity high temperature metal rich lower d magmatic fluid derived from a more differentiated peraluminous granitic magma and d a high salinity high temperature metal rich high 18o low d magmatic fluid this study shows that multiple fluids with distinct magmatic and meteoric origins were involved in the formation of these w sn deposits and that the dilution of metal bearing magmatic fluids by meteoric fluids was probably the main driver for ore deposition the common fluid history of the two deposits studied as well as similarities with other deposits in the jiangxi province points toward common ore forming processes at the regional scale

permafrost associated natural gas hydrate occurrences on the alaska north slope abstract in the 1960s russian scientists made what was then a bold assertion that gas hydrates should occur in abundance in nature since this early start the scientific foundation has been built for the realization that gas hydrates are a global phenomenon occurring in permafrost regions of the arctic and in deep water portions of most continental margins worldwide in 1995 the u s geological survey made the first systematic assessment of the in place natural gas hydrate resources of the united states that study suggested that the amount of gas in the gas hydrate accumulations of northern alaska probably exceeds the volume of known conventional gas resources on the north slope researchers have long speculated that gas hydrates could eventually become a producible energy resource yet technical and economic hurdles have historically made gas hydrate development a distant goal this view began to change in recent years with the realization that this unconventional resource could be developed with existing conventional oil and gas production technology one of the most significant developments was the completion of the bpxa doe usgs mount elbert gas hydrate stratigraphic test well on the alaska north slope which along with the mallik project in canada have for the first time allowed the rational assessment of gas hydrate production technology and concepts almost 40 years of gas hydrate research in northern alaska has confirmed the occurrence of at least two large gas hydrate accumulations on the north slope we have also seen in alaska the first ever assessment of how much gas could be technically recovered from gas hydrates however significant technical concerns need to be further resolved in order to assess the ultimate impact of gas hydrate energy resource development in northern alaska

late cretaceous granites from the giant dulong sn polymetallic ore district in yunnan province south china geochronology geochemistry mineral chemistry and nd hf isotopic compositions abstract as a world class tin tungsten province south china is well known for its extensive mesozoic granitic magmatism the dulong district located in the western cathaysia block of the south china tin tungsten province is characterized by widespread mesozoic granitoids and accompanying sn polymetallic ore deposit 30 mt of sn it is one of the most important polymetallic tin ore districts in china in this study three mineralization related granite types were identified in the dulong district including the dulong coarse grained granite dcg the dulong fine grained granite dfg and the dulong porphyritic granite dpg detailed studies are presented on zircon u pb ages major and trace elements mineral chemical and nd hf isotopic compositions of the tin bearing granites from the dulong district la icp ms u pb dating of zircon grains from these three granite bodies yields ages of 90 1 0 7 ma 89 7 0 8 ma and 86 0 0 5 ma respectively geochemically the granites are strongly peraluminous with high contents of alkalis enrichment in p li rb cs ta sn w and u depletion in ti mg co ni sr ba zr hf th and rare earth elements fractional crystallization of plagioclase and k feldspar was the principal process of magmatic differentiation that controlled rb sr ba and eu concentrations whereas rare earth elements were fractionated by accessory minerals such as apatite and monazite the geochemical data suggest that the rocks are highly fractionated s type granites the granites show bulk rock e nd t values in the range of 12 2 to 10 8 and zircon e hf t values from 15 5 to 2 5 with meso paleoproterozoic t dm c ages for both nd and hf isotopes geochemical and isotopic data suggest that these highly fractionated s type granites dcg dfg and dpg were originated from the same episode of partial melting of the protolith which have analogous components of metamorphosed pelitic rocks from the meso paleoproterozoic continental crust extreme fractional crystallization resulted in enrichment of tin in the evolved granitic magma and the reduced magmas fo 2 below nno would efficiently remove sn into a hydrothermal fluid and lead to deposition of sn rich mineral phases the association of dulong and gejiu magmatism in the western cathaysia block may be likely to mark the onset of back arc extension or intra arc rift in the region during late cretaceous the upwelling of asthenospheric mantle may have triggered partial melting of metasedimentary rocks in the overlying crust to generate the s type granitic magmas

physical properties of sediment from the mount elbert gas hydrate stratigraphic test well alaska north slope this study characterizes cored and logged sedimentary strata from the february 2007 bp exploration alaska department of energy u s geological survey bpxa doe usgs mount elbert gas hydrate stratigraphic test well on the alaska north slope ans the physical properties program analyzed core samples recovered from the well and in conjunction with downhole geophysical logs produced an extensive dataset including grain size water content porosity grain density bulk density permeability x ray diffraction xrd mineralogy nuclear magnetic resonance nmr and petrography this study documents the physical property interrelationships in the well and demonstrates their correlation with the occurrence of gas hydrate gas hydrate gh occurs in three unconsolidated coarse silt to fine sand intervals within the paleocene and eocene beds of the sagavanirktok formation unit d gh 614 4 m 627 9 m unit c gh1 649 8 m 660 8 m and unit c gh2 663 2 m 666 3 m these intervals are overlain by fine to coarse silt intervals with greater clay content a deeper interval unit b is similar lithologically to the gas hydrate bearing strata however it is water saturated and contains no hydrate in this system it appears that high sediment permeability k is critical to the formation of concentrated hydrate deposits intervals d gh and c gh1 have average plug intrinsic permeability to nitrogen values of 1700 md and 675 md respectively these values are in strong contrast with those of the overlying gas hydrate free sediments which have k values of 5 7 md and 49 md respectively and thus would have provided effective seals to trap free gas the relation between permeability and porosity critically influences the occurrence of gh for example an average increase of 4 in porosity increases permeability by an order of magnitude but the presence of a second fluid e g methane from dissociating gas hydrate in the reservoir reduces permeability by more than an order of magnitude published by elsevier ltd

genesis of tin dominant polymetallic deposits in the dachang district south china insights from cassiterite u pb ages and trace element compositions abstract the dachang tin dominant polymetallic district in western south china hosts a total reserve of 110 mt ore 1 sn 3 5 by products of zn pb sb in and cu and 100 to 300 g t ag economic tin orebodies in the district mainly developed in devonian limestone black shale and siliceous rocks as massive stratiform and vein stockwork mineralization la icp ms u pb dating on seven cassiterite samples from the tongkeng changpo and gaofeng sn zn pb deposits and the dafulou huile and kangma sn zn deposits yields weighted mean 206pb 238u ages ranging from 90 3 1 8 ma to 95 4 4 9 ma these dates are significantly younger than the devonian ore hosted strata but agree well with the previously published zircon u pb ages of 96 6 93 9 ma for the longxianggai biotite granite within analytical uncertainties showing a close temporal link between the granitic magmatism and tin mineralization cassiterite grains from various ore types in the dachang district show clear growth zonations as reflected from their cathodoluminescence images la icp ms trace element analyses of cassiterite grains indicate that they have relatively high ti fe and w but low nb and ta contents which corresponds to the clear luminescencing chemical variations of cassiterite from different ore types i e cassiterite sulfide ores and cassiterite bearing quartz veins are indistinguishable except for more enriched fe in cassiterite from cassiterite quartz veins combined with cretaceous u pb ages elevated fe and w contents of cassiterite suggest tin dominant polymetallic deposits in the dachang district were formed in a granite related magmatic hydrothermal system controlled by the longxianggai biotite granite precluding their syngenetic origin

tectonic and magmatic evolution of the andes of northern argentina and chile abstract two orogenic cycles both with different evolution are developed in the western margin of the south american continent in northern argentina and chile the paleozoic hercynic cycle and the meso cenozoic andean cycle the hercynic cycle a wide marine basin extending westward of the cordillera oriental which developed in cambrian ordovician times marks the beginning of this cycle in contrast to peru and bolivia where this basin developed between two precambrian blocks the western margin of this basin in northern argentina and chile is still unknown the ordovician sedimentation and accompanied volcanism ends with the ocloyic deformation phase and its synkinematic granitic plutonism two basins were developed in the silurian devonian separated by the puna arc uplifted during this ocloyic phase the shallow water marine terrigeneous sediments which were deposited in them were deformed by a new tectono magmatic associated phase chanic phase carboniferous to lower permian marine carbonates were deposited west of the puna arc and red beds east of it later on during the permian to triassic a magmatic belt was developed along the cordillera occidental the rhyolites ignimbrites and the granitic to granodioritic related intrusives are well represented in chile although the overall geologic history of this period is known many problems concerning its origin and relations to plate tectonics are still unsolved the andean cycle during this cycle a series of magmatic arc systems related to the subduction of the pacific crust was built up along the western margin of south america huge volumes of calc alkaline lavas and related plutons were emplaced since the jurassic along belts parallel to the present coastline showing a general eastward migration trend up to the lower cretaceous an ensialic back arc basin was formed east of this magmatic arc thousands of meters of marine and continental sediments were deposited in it this basin disappeared during the middle cretaceous probably as a result of the final opening of the atlantic and the active westward movement of the south american plate since middle cretaceous times the magmatic arc has been the fundamental paleogeographic element the arc progressively migrated stepwise eastward each step marked by a tectonic phase subduction related crustal erosion could explain the lack of fore arc petrotectonic assemblages the eastward magmatic polarity which characterizes this section of the andes could also be explained by such a mechanism

compressibility and particle crushing of krishna godavari basin sediments from offshore india implications for gas production from deep water gas hydrate deposits abstract depressurizing a gas hydrate reservoir to extract methane induces high effective stresses that act to compress the reservoir predicting whether a gas hydrate reservoir is viable as an energy resource requires enhanced understanding of the reservoir s compressibility and susceptibility to particle crushing in response to elevated effective stress because of their impact on the long term permeability and geomechanical stability of the reservoir this study investigates physical and geomechanical properties of natural sediments with and without tetrahydrofuran thf hydrate subjected to high effective stresses of up to 25 mpa experimental results show the stiffness of hydrate free sediments is mainly governed by the stress state and history while the stiffness of hydrate bearing sediments reflects both the grain supporting nature of the interconnected hydrate phase and stress effects the poisson s ratio of hydrate bearing sediments at low stresses is dominated by the poisson s ratio of the interconnected pore filling phases and dominated at high stresses by elastic properties of both the skeleton and pore filling phases the stress void ratio responses of hydrate bearing sediments above the pre consolidation stress yields a slightly convex downward trend suggesting compressibility is influenced by the stiffness of thf hydrate and sediment grains rather than only by void space reduction the shape of the compression index cc trend may be attributed to an increasing effective gas hydrate saturation as the total pore volume decreases under loading the results also show that the presence of thf hydrate in sediments can mitigate particle crushing by suppressing particle rearrangement and supporting a portion of the load that would otherwise have to be carried by the sediment therefore the loss of hydrate crystals during gas production may exacerbate sand crushing

the early palaeozoic high grade metamorphism at the active continental margin of west gondwana in the andes nw argentina n chile the evolution of the early palaeozoic orogen of west gondwana in the cambrian to ordovician basement of the andes between 18 and 32 s is investigated for pressure and temperature conditions and age of metamorphism it is characterized by mid crust temperatures commonly above the wet granite solidus 650 c widespread felsic migmatite and rare granulite formed at pressures of ca 0 5 0 7 gpa locally 1 0 gpa these rocks represent the deepest exhumed sections of the early palaeozoic crust high pressure low temperature rocks are absent the crystallization ages compiled from the literature in combination with new data for near peak metamorphic conditions of these high grade metamorphic rocks in nw argentina and n chile are 530 500 ma and 470 420 ma both age groups are spatially overlapping radiogenic isotope signatures sr nd pb are used to characterize the early palaeozoic basement the pb and sr isotope compositions of the early palaeozoic basement indicate mixing arrays between pre palaeozoic unradiogenic and radiogenic crust crustal residence ages sm nd tdm indicate a prominent event of crust formation around 2 ga which is known continent wide this material was recycled during midproterozoic and early palaeozoic orogenies without prominent additions of new crust present in the isotope record i e accretion of compositional exotic material is absent

formation pressure testing at the mount elbert gas hydrate stratigraphic test well alaska north slope operational summary history matching and interpretations abstract in february 2007 the u s department of energy bp exploration alaska and the u s geological survey collected open hole pressure response data as well as gas and water sample collection in a gas hydrate reservoir the bpxa doe usgs mount elbert gas hydrate stratigraphic test well using schlumberger s modular dynamics formation tester mdt wireline tool four such mdt tests ranging from six to twelve hours duration and including a series of flow sampling and shut in periods of various durations were conducted locations for the testing were selected based on nmr and other log data to assure sufficient isolation from reservoir boundaries and zones of excess free water test stages in which pressure was reduced sufficiently to mobilize free water in the formation yet not cause gas hydrate dissociation produced readily interpretable pressure build up profiles build ups following larger drawdowns consistently showed gas hydrate dissociation and gas release as confirmed by optical fluid analyzer data as well as progressive dampening of reservoir pressure build up during sequential tests at a given mdt test station history matches of one multi stage 12 h test the c2 test were accomplished using five different reservoir simulators cmg stars hydrateressim mh21 hydres stomp hyd and tough hydrate simulations utilized detailed information collected across the reservoir either obtained or determined from geophysical well logs including thickness 11 3 m 37 ft porosity 35 hydrate saturation 65 both mobile and immobile water saturations intrinsic permeability 1000 md pore water salinity 5 ppt and formation temperature 3 3 3 9 c this paper will present the approach and preliminary results of the history matching efforts including estimates of initial formation permeability and analyses of the various unique features exhibited by the mdt results

helium isotopes as tracers of trapped hydrothermal fluids in ocean floor sulfides helium isotopes have been measured in fluids trapped in minerals from three mid ocean ridge hydrothermal systems at bare rock sites and at the sediment covered site at middle valley northern juan de fuca ridge fluid inclusion 3 he 4 he ratios from the bare rock sites are indistinguishable from those of the vent fluids and are close to the local basalt values values for 34 s of the host sulfide are consistent with variable contributions of seawater sulfate s to the basalt derived s in the hydrothermal fluids this does not affect inclusion hosted 3 he 4 he because of the high he concentration of the hydrothermal fluids relative to seawater fluid inclusion 3 he 4 he ratios from middle valley are a mixture of basalt derived he and radiogenic he acquired from pore fluids in the overlying pleistocene turbidite sediments after seawater basalt interaction the radiogenic he accompanies isotopicalty heavy s demonstrating that he isotopes may be used to distinguish pore fluids from seawater in hydrothermal systems

lower carboniferous post orogenic granites in central eastern sierra de velasco sierras pampeanas argentina u pb monazite geochronology geochemistry and sr nd isotopes the central eastern part of the sierra de velasco sierras pampeanas nw argentina is formed by the large huaco 40 30 km and sanagasta 25 15 km granite massifs and the small la chinchilla stock 2 2 km the larger granites intrude into ordovician metagranitoids and crosscut devonian mylonitic shear zones whereas the small stock sharply intrudes into the huaco granite the two voluminous granites are biotitic muscovitic and biotitic porphyritic syeno to monzogranites they contain small and rounded tonalitic and quartz dioritic mafic microgranular enclaves the small stock is an equigranular zinnwaldite and fluorite bearing monzogranite the studied granites are silica rich sio2 70 potassium rich k2o 4 ferroan alkali calcic to slightly calk alkalic and moderately to weakly peraluminous a cnk 1 06 1 18 huaco granite 1 01 1 09 sanagasta granite 1 05 1 06 la chinchilla stock they have moderate to strong enrichments in several lil li rb cs and hfs nb ta y th u elements and low sr ba and eu contents u pb monazite age determinations indicate lower carboniferous crystallization ages 350 358 ma for the huaco granite 352 7 1 4 ma for the sanagasta granite and 344 5 1 4 ma for the la chinchilla stock the larger granites have similar nd values between 2 1 and 4 3 whereas the younger stock has higher nd of 0 6 to 1 4 roughly comparable to the values obtained for the carboniferous san blas granite 1 4 to 1 7 located in the north of the sierra the huaco and sanagasta granites have a mainly crustal source but with some participation of a more primitive possibly mantle derived component the main crustal component can be attributed to ordovician peraluminous metagranitoids the la chinchilla stock derives from a more primitive source suggesting an increase with time in the participation of the primitive component during magma genesis the studied granites were generated during a post orogenic period in a within plate setting possibly as a response to the collapse of the previous famatinian orogen extension of the crust and mantle upwelling they are part of the group of middle devonian lower carboniferous granites of the sierras pampeanas the distribution and u pb ages of these granites suggests a northward arc parallel migration of this mainly post orogenic magmatism with time

excess40ar in metamorphic rocks from broken hill new south wales implications for40ar 39ar age spectra and the thermal history of the region 40ar 39ar age spectrum analyses of samples from broken hill new south wales indicate that the region has experienced a complex thermal history following high grade metamorphism 1660 ma ago the terrain cooled slowly 3 c ma 1 until about 1570 ma ago when the temperature fell below about 500 c following granitoid emplacement 1500 ma ago the region remained relatively cold until affected by a thermal pulse 520 40ma ago causing temperatures to rise to 350 c in some places during this event accumulated40ar was released from minerals causing a significant ar partial pressure to develop laboratory ar solubility data combined with the40ar 39ar age spectra gives a local estimate of this partial pressure of 10 4atm the region finally cooled below 100 c about 280 ma ago 40ar 39ar age spectrum analyses of hornblende plagioclase and clinopyroxene containing excess40ar are characterized by saddle shaped age spectra detailed analysis of plagioclase samples reveals a complex diffusion behaviour which is controlled by exsolution structures this effect in conjunction with the presumed different lattice occupancy of excess40ar with respect to radiogenic40ar appears to be responsible for the saddle shaped age spectra

formation history and physical properties of sediments from the mount elbert gas hydrate stratigraphic test well alaska north slope abstract the synthesis of available geological information and surface temperature evolution in the alaska north slope region suggests that biogenic and deeper thermogenic gases migrated through fault networks and preferentially invaded coarse grained layers that have relatively high hydraulic conductivity and low gas entry pressures hydrate started forming before the beginning of the permafrost eventually the permafrost deepened and any remaining free water froze so that ice and hydrate may coexist at some elevations the single tested specimen depth 620 47 620 62 m from the d unit consists of uncemented quartzitic fine sand with a high fraction of fines 56 by mass finer than sieve 200 the as received specimen shows no evidence of gas present the surface texture of sediment grains is compatible with a fluvial deltaic sedimentation environment and shows no signs of glacial entrainment tests conducted on sediments with and without thf hydrates show that effective stress porosity and hydrate saturation are the major controls on the mechanical and geophysical properties previously derived relationships between these variables and mechanical geophysical parameters properly fit the measurements gathered with mount elbert specimens at different hydrate saturations and effective stress levels we show that these measurements can be combined with index properties and empirical geomechanical relationships to estimate engineering design parameters volumetric strains measured during hydrate dissociation vanish at 2 4 mpa therefore minimal volumetric strains are anticipated during gas production at the mount elbert well however volume changes could increase if extensive grain crushing takes place during depressurization driven production strategies if the sediment has unexpectedly high in situ porosity associated to the formation history or if fines migration and clogging cause a situation of sustained sand production

mantle crustal and atmospheric noble gases in ailaoshan gold deposits yunnan province china abstract helium and argon isotopic and elemental compositions of fluids released by crushing pyrite grains are reported from the ailaoshan gold province china the province is a series of gold deposits hosted on a 200 km segment of a major normal fault formed during eocene extension the deposits have been well characterised using conventional geochemical and microthermometric techniques the results of which are consistent with a predominantly high temperature magmatic fluid present in the ore minerals in contrast analyses of noble gases from three gold deposits demonstrate the palaeofluids were a mixture between a mantle derived magmatic fluid and two different low temperature fluids similar to modern groundwaters the specific isotopic and abundance characteristics of helium and argon allow unequivocal identification of both a mantle derived component and a surface derived component to these fluids the magmatic fluid dominates deposits from the northern end of the fault the second groundwater is present only in deposits in the south of the province by assuming fluid inclusion homogenisation temperatures in coexisting quartz are representative of fluid temperature 3he heat ratios can be estimated the 3he heat ratios vary systematically along the fault from 30 10 12 cm3 stp j 1 in the northern deposits to

assessing the geomechanical stability of interbedded hydrate bearing sediments under gas production by depressurization at nghp 02 site 16 abstract establishing the geomechanical stability of marine sediments in the vicinity of a production well is one of the key design considerations in planning offshore gas production from marine hydrate reservoirs this paper presents an assessment of the sediment stability at india s national gas hydrate program expedition 2 nghp 02 site 16 area b offshore eastern india for which gas production is to be carried out by depressurization one important feature of the study is that extensive calibration of constitutive model parameters has been conducted based on laboratory test data from pressured core samples from analysis perspective the site is challenging because the hydrate reservoir consists of thin layers of hydrate bearing sands interbedded with mud moreover depressurization at the depth of a reservoir more than 2750 m below sea surface will lead to a pore pressure drop and accordingly an effective confining stress increase as high as 25 mpa in dealing with thin interbedded hydrate bearing strata meshing requirements for flow and geomechanical analysis are quite different from those for reservoirs with thicker massive layers an axisymmetric model and one way coupling simulations were thus adopted for this study in which the geomechanical study utilizes pore pressure and hydrate saturation output from the flow study but the flow study does not takes the porosity changes from the geomechanical analysis instead the reduction of porosity due to sediment deformation in the flow study is based on a pressure dependent pore compressibility relationship derived from geomechanical modeling the rationality is validated through back computing the pore compressibility from the geomechanical deformation results the study shows that large compression in the reservoir will result in movement of the sediments from above and below as well as laterally in smaller magnitudes and the sediment is deemed stable during the gas production period

an oxygen hydrogen sulfur and carbon isotope study of carbonate replacement skarn tin deposits of the dachang tin field china the dachang tin field located in guangxi province of southern china is one of the largest in the world it comprises the changpo bali and longtaoshan carbonate replacement tin deposits and the lamo cu zn skarn deposit these deposits are hosted by devonian carbonate rich sedimentary rocks which have been metamorphosed to calc silicate skarn and marble near the contact of the longxianggei granite calculated delta 18 o sub h 2 o values of the hydrothermal fluids in equilibrium with quartz cassiterite and calcite are 10 6 and 11 6 9 1 to 10 2 and 7 5 to 9 8 per mil respectively measured delta d values of fluid inclusion waters in cassiterite and calcite are 115 and 120 and 73 to 93 per mil respectively the decrease in the calculated delta 18 o sub h 2 o values from 11 6 to 7 5 per mil is attributed to increase in the co 2 content of the hydrothermal fluids the low delta d values of fluid inclusion waters in cassiterite may be the result of decreasing ch 4 co 2 as the originally magmatic fluid migrated from reducing conditions in carbonaceous black shale to oxidizing conditions in pure limestone oxygen and hydrogen isotope data indicate that the hydrothermal fluid was derived from the longxianggei granite variations in delta 13 c and delta 18 o values of calcite in orebodies altered limestone and marble are due to continuous isotopic exchange reaction between magmatic fluid and carbonate rocks at variable water to rock ratios between 300 degrees to 600 degrees c sulfur isotope data indicate that host rocks controlled the variations in sulfur isotope compositions of sulfide minerals in different deposits of the tin field with significant contribution of sulfur from magmatic fluids

alaska north slope regional gas hydrate production modeling forecasts abstract a series of gas hydrate development scenarios were created to assess the range of outcomes predicted for the possible development of the eileen gas hydrate accumulation north slope alaska production forecasts for the reference case were built using the 2002 mallik production tests mechanistic simulation and geologic studies conducted by the us geological survey three additional scenarios were considered a downside scenario which fails to identify viable production an upside scenario describes results that are better than expected to capture the full range of possible outcomes and balance the downside case an extreme upside scenario assumes each well is exceptionally productive starting with a representative type well simulation forecasts field development timing is applied and the sum of individual well forecasts creating the field wide production forecast this technique is commonly used to schedule large scale resource plays where drilling schedules are complex and production forecasts must account for many changing parameters the complementary forecasts of rig count capital investment and cash flow can be used in a pre appraisal assessment of potential commercial viability since no significant gas sales are currently possible on the north slope of alaska typical parameters were used to create downside reference and upside case forecasts that predict from 0 to 71 bm3 2 5 tcf of gas may be produced in 20 years and nearly 283 bm3 10 tcf ultimate recovery after 100 years outlining a range of possible outcomes enables decision makers to visualize the pace and milestones that will be required to evaluate gas hydrate resource development in the eileen accumulation critical values of peak production rate time to meaningful production volumes and investments required to rule out a downside case are provided upside cases identify potential if both depressurization and thermal stimulation yield positive results an extreme upside case captures the full potential of unconstrained development with widely spaced wells the results of this study indicate that recoverable gas hydrate resources may exist in the eileen accumulation and that it represents a good opportunity for continued research

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

rb sr geochronology of granitoid rocks from the pampean ranges argentina a reconnaissance rb sr geochronological investigation of granitoid rocks from the pampean range provides a framework whereby four culminations of igneous activity are delineated granitoids emplaced prior to 500 ma pre and synkinematic bodies ca 475 ma late kinematic bodies and ca 440 and 340 ma post kinematic bodies a number of the post kinematic granitoids have disturbed sr isotope systematics which is related to the formation of microcline megacrysts the carboniferous granitoids are distinguished by their high initial sr ratios i e 0 710 a feature compatible with an origin involving reworking of upper crust or crustal contamination there appears to be no systematic e w migration of granitoid emplacement during the ca 300 ma evolution of the basement rocks in the pampean ranges

physical properties of hydrate bearing sediments 1 methane gas hydrates crystalline inclusion compounds formed from methane and water are found in marine continental margin and permafrost sediments worldwide this article reviews the current understanding of phenomena involved in gas hydrate formation and the physical properties of hydrate bearing sediments formation phenomena include pore scale habit solubility spatial variability and host sediment aggregate properties physical properties include thermal properties permeability electrical conductivity and permittivity small strain elastic p and s wave velocities shear strength and volume changes resulting from hydrate dissociation the magnitudes and interdependencies of these properties are critically important for predicting and quantifying macroscale responses of hydrate bearing sediments to changes in mechanical thermal or chemical boundary conditions these predictions are vital for mitigating borehole local and regional slope stability hazards optimizing recovery techniques for extracting methane from hydrate bearing sediments or sequestering carbon dioxide in gas hydrate and evaluating the role of gas hydrate in the global carbon cycle

petrogenesis of the fiambala gabbroic intrusion northwestern argentina a deep crustal syntectonic pluton in a continental magmatic arc

episodic fresh surface waters in the eocene arctic ocean it has been suggested on the basis of modern hydrology and fully coupled palaeoclimate simulations that the warm greenhouse conditions that characterized the early palaeogene period 55 45 myr ago probably induced an intensified hydrological cycle with precipitation exceeding evaporation at high latitudes little field evidence however has been available to constrain oceanic conditions in the arctic during this period here we analyse palaeogene sediments obtained during the arctic coring expedition showing that large quantities of the free floating fern azolla grew and reproduced in the arctic ocean by the onset of the middle eocene epoch approximately 50 myr ago the azolla and accompanying abundant freshwater organic and siliceous microfossils indicate an episodic freshening of arctic surface waters during an approximately 800 000 year interval the abundant remains of azolla that characterize basal middle eocene marine deposits of all nordic seas probably represent transported assemblages resulting from freshwater spills from the arctic ocean that reached as far south as the north sea the termination of the azolla phase in the arctic coincides with a local sea surface temperature rise from approximately 10 degrees c to 13 degrees c pointing to simultaneous increases in salt and heat supply owing to the influx of waters from adjacent oceans we suggest that onset and termination of the azolla phase depended on the degree of oceanic exchange between arctic ocean and adjacent seas

energy resource potential of natural gas hydrates the discovery of large gas hydrate accumulations in terrestrial per mafrost regions of the arctic and beneath the sea along the outer continental margins of the world s oceans has heightened interest in gas hydrates as a possible energy resource however significant to potentially insurmountable technical issues must be resolved be fore gas hydrates can be considered a viable option for affordable supplies of natural gas the combined information from arctic gas hydrate studies shows that in permafrost regions gas hydrates may exist at subsurface depths ranging from about 130 to 2000 m the presence of gas hydrates in offshore continental margins has been inferred mainly from anomalous seismic reflectors known as bottom simulating reflectors that have been mapped at depths below the sea floor ranging from about 100 to 1100 m current estimates of the amount of gas in the world s marine and permafrost gas hydrate accumulations are in rough accord at about 20 000 trillion m3 disagreements over fundamental issues such as the volume of gas stored within delineated gas hydrate accumulations and the concentration of gas hydrates within hydrate bearing strata have demonstrated that we know little about gas hydrates recently however several countries including japan india and the united states have launched ambitious national projects to further examine the resource potential of gas hydrates these projects may help answer key questions dealing with the properties of gas hydrate reservoirs the design of production systems and most important the costs and economics of gas hydrate production

examination of core samples from the mount elbert gas hydrate stratigraphic test well alaska north slope effects of retrieval and preservation abstract collecting and preserving undamaged core samples containing gas hydrates from depth is difficult because of the pressure and temperature changes encountered upon retrieval hydrate bearing core samples were collected at the bpxa doe usgs mount elbert gas hydrate stratigraphic test well in february 2007 coring was performed while using a custom oil based drilling mud and the cores were retrieved by a wireline the samples were characterized and subsampled at the surface under ambient winter arctic conditions samples thought to be hydrate bearing were preserved either by immersion in liquid nitrogen ln or by storage under methane pressure at ambient arctic conditions and later depressurized and immersed in ln eleven core samples from hydrate bearing zones were scanned using x ray computed tomography to examine core structure and homogeneity features observed include radial fractures spalling type fractures and reduced density near the periphery these features were induced during sample collection handling and preservation isotopic analysis of the methane from hydrate in an initially ln preserved core and a pressure preserved core indicate that secondary hydrate formation occurred throughout the pressurized core whereas none occurred in the ln preserved core however no hydrate was found near the periphery of the ln preserved core to replicate some aspects of the preservation methods natural and laboratory made saturated porous media samples were frozen in a variety of ways with radial fractures observed in some ln frozen sands and needle like ice crystals forming in slowly frozen clay rich sediments suggestions for hydrate bearing core preservation are presented

water permeability in hydrate bearing sediments a pore scale study permeability is a critical parameter governing methane flux and fluid flow in hydrate bearing sediments however limited valid data are available due to experimental challenges here we investigate the relationship between apparent water permeability k and hydrate saturation sh accounting for hydrate pore scale growth habit and meso scale heterogeneity results from capillary tube models rely on cross sectional tube shapes and hydrate pore habits thus are appropriate only for sediments with uniform hydrate distribution and known hydrate pore character given our pore network modeling results showing that accumulating hydrate in sediments decreases sediment porosity and increases hydraulic tortuosity we propose a modified kozeny carman model to characterize water permeability in hydrate bearing sediments this model agrees well with experimental results and can be easily implemented in reservoir simulators with no empirical variables other than sh results are also relevant to flow through other natural sediments that undergo diagenesis salt precipitation or bio clogging

geologic implications of gas hydrates in the offshore of india krishna godavari basin mahanadi basin andaman sea kerala konkan basin gas hydrate resource assessments that indicate enormous global volumes of gas present within hydrate accumulations have been one of the primary driving forces behind the growing interest in gas hydrates gas hydrate volumetric estimates in recent years have focused on documenting the geologic parameters in the gas hydrate petroleum system that control the occurrence of gas hydrates in nature the primary goals of this report are to review our present understanding of the geologic controls on the occurrence of gas hydrate in the offshore of india and to document the application of the petroleum system approach to the study of gas hydrates national gas hydrate program of india executed the national gas hydrate program expedition 01 nghp 01 in 2006 in four areas located on the eastern and western margins of the indian peninsula and in the andaman sea these areas have experienced very different tectonic and depositional histories the peninsular margins are passive continental margins resulting from a series of rifting episodes during the breakup and dispersion of gondwanaland to form the present indian ocean the andaman sea is bounded on its western side by a convergent margin where the indian plate lithosphere is being subducted beneath southeast asia nghp 01 drilled logged and or cored 15 sites 31 holes in the krishna godavari basin 4 sites 5 holes in the mahanadi basin 1 site 2 holes in the andaman sea and 1 site 1 hole in the kerala konkan basin holes were drilled using standard drilling methods for the purpose of logging while drilling and dedicated wireline logging as well as through the use of a variety of standard coring systems and specialized pressure coring systems nghp 01 yielded evidence of gas hydrate from downhole log and core data obtained from all the sites in the krishna godavari basin the mahanadi basin and in the andaman sea the site drilled in the kerala konkan basin during nghp 01 did not yield any evidence of gas hydrate most of the downhole log inferred gas hydrate and core recovered gas hydrate were characterized as either fracture filling in clay dominated sediments or as pore filling or grain displacement particles disseminated in both fine and coarse grained sediments geochemical analyses of gases obtained from sediment cores recovered during nghp 01 indicated that the gas in most all of the hydrates in the offshore of india is derived from microbial sources only one site in the andaman sea exhibited limited evidence of a thermogenic gas source the gas hydrate petroleum system concept has been used to effectively characterize the geologic controls on the occurrence of gas hydrates in the offshore of india

the proto andean margin of gondwana an introduction a basic background is presented for the discussion of the early palaeozoic geology of western argentina covered by this book this includes the definition and terminology of orogenic cycles on this part of the gondwana margin represented by the eastern sierras pampeanas the pampean orogeny early cambrian relates to an intense but short lived period of terrane collision predating the rifting of the precordillera terrane from laurentia the famatinian cycle is predominantly represented by intense subductionrelated magmatism of early middle ordovician age developed on the continental margin of gondwana during the rifting and drifting of the precordillera terrane the grenvillian basement of the latter is further exemplified by a new rb sr whole rock isochron age of 1021 12 ma for orthogneisses from the western sierras pampeanas a mid ordovician granite in this area dated at 481 6 ma by u pb ion microprobe data may be related to rifting while the precordillera terrane was still attached to laurentia a divergence of opinion is pointed out between some authors in this book who favour mid ordovician collision of the precordillera with gondwana and others who place it much latter in silurian or devonian times