the giant dexing porphyry cu mo au deposit in east china product of melting of juvenile lower crust in an intracontinental setting the dexing porphyry cu mo au deposit in east china 1 168 mt at 0 45 cu is located in the interior of the south china craton scc made up of two lithospheric blocks the yangtze and cathaysia blocks the cu mo au mineralization is associated with mid jurassic granodioritic porphyries with three high level intrusive centers controlled by a series of lineaments at the southeastern edge of the yangtze block available age data define a short duration 172 170 ma of the felsic magmatism and the mineralization 171 1 ma the deposit shows broad similarities with deposits in volcanoplutonic arcs although it was formed in an intracontinental setting porphyries associated with mineralization are mainly granodiorites which contain abundant phenocrysts 40 60 and carry contemporaneous microgranular mafic enclaves mmes they are mainly high k calc alkaline and show geochemical affinities with adakite characterized by relatively high mgo cr ni th and th ce ratios the least altered porphyries yielded relatively uniform end t values from 0 9 to 0 6 and wide 87sr 86sr i range between 0 7046 and 0 7058 partially overlapping with the sr nd isotopic compositions of the mmes and mid jurassic mafic rocks in the scc zircons from the porphyries have positive ehf t values 3 4 to 6 9 and low 18o values 4 7 to 6 3 generally close to those of depleted mantle all data suggest an origin by partial melting of a thickened juvenile lower crust involving mantle components e g neoproterozoic mafic arc magmas triggered by invasion of contemporaneous mafic melts at dexing the mmes show textural mineralogical and chemical evidence for an origin as xenoliths formed by injection of mafic melts into the felsic magmas these mmes usually contain magmatic chalcopyrite and have original variable contents of cu up to 500 ppm their geochemical characteristics suggest that they were derived from an enriched mantle source metasomatized by proterozoic slab derived fluids and supplied a part of cu au and s for the dexing porphyry system during their injection into the felsic magmas the 171 1 ma magmatic hydrothermal event at dexing is contemporaneous with the mid jurassic extension in the scc followed by 160 90 ma arc like magmatism in southeastern china with respect to the tectono magmatic evolution of the scc the emplacement of cu bearing porphyries and the associated cu mineralization occurred in response to the transformation from a tensional regime related to mid jurassic extension to a transpressional regime related to the subduction of the paleo pacific oceanic lithosphere

geochemical characteristics of biotite from felsic intrusive rocks around the sisson brook w mo cu deposit west central new brunswick an indicator of halogen and oxygen fugacity of magmatic systems abstract the sisson brook w mo cu deposit was formed by hydrothermal fluids likely related to the nashwaak granites muscovite biotite granite group i and biotite granite group ii and related dykes biotite granitic dykes group iii and a feldspar biotite quartz porphyry dyke group iv chemical data obtained using epma and la icp ms data of primary magmatic biotites were used to investigate magmatic processes and associated hydrothermal fluids trace element features of biotite in the group i two mica granite suggest other magmatic processes along with a simple fractional crystallization the k rb ratios and compatible elements cr ti co v and ba in biotite from groups ii iii and iv decrease whereas incompatible elements including ta tl ga cs li and sn increase with magma fractionation no correlation of cu w and mo with k rb ratios is evident suggesting that partitioning of cu w and mo into biotite may not be entirely controlled by magma fractionation halogen fugacity of the parental magma of the nashwaak granites and related dykes calculated from zircon saturation temperature shows that group i has high f hf f cl ratios broadly higher than 0 similar to the plutons at the henderson porphyry mo deposit the f hf f cl ratios of the other groups are generally lower than 0 comparable to the santa rita porphyry cu deposit the f h 2 o f hcl and f h 2 o f hf ratios inferred from biotite in the nashwaak granites and related dykes range from 3 to 5 and from 4 to 5 respectively the inferred oxygen fugacity shows that the dyke phases groups iii and iv have the oxygen fugacity around the nickel nickel oxide buffer the plutonic phases groups i and ii have the oxygen fugacity around the quartz fayalite magnetite qfm buffer at high temperatures and oxidized to nickel nickel oxide buffer at lower temperatures this oxidation process in the plutonic phases groups i and ii could be caused by h 2 release at or near h 2 o vapor saturation at high h 2 o fe 2 the magma associated with the biotite dykes group iii is more likely the source of the hydrothermal fluids at the sisson brook deposit since it has the highest differentiation degree and seems to have formed in an oxidized setting necessary for mo to concentrate in the late stage fluids

magmatic anhydrite in plutonic rocks at the el teniente cu mo deposit chile and the role of sulfur and copper rich magmas in its formation anhydrite occurs along with biotite feldspars quartz fe oxides and sulfides in fine grained igneous rocks that form the small porphyry a stock at el teniente these minerals crystallized together in the space generated by the intrusion of this stock and they do not replace preexisting phases planar crystal boundaries between anhydrite and other phases as well as the fact that plagioclase and biotite are fresh and unaltered also suggest that anhydrite is an igneous phase and not the product of secondary hydrothermal alteration plagioclase is unusually na rich ranging from oligoclase in mafic varieties of these rocks with 20 percent biotite to albite in more felsic samples with 20 percent these unusual anhydrite bearing plutonic rocks which contain up to 3 wt percent s and 0 5 wt percent cu are isotopically similar to all other igneous rocks related to the deposit these rocks formed during a late miocene period of regional compressive deformation with no coeval volcanic activity in the area of the deposit which prevented devolitalization of the oxidized parent magma in the large productive magma chamber inferred to have underlain el teniente at 4 km below the paleosurface this allowed igneous fractionation involving the recharge of mantle derived mafic magmas into the base of the chamber as well as volatile transfer and concentration near its roof to produce the cu and s rich magmas that formed the anhydrite bearing intrusive rocks

the sarcheshmeh porphyry copper deposit kerman iran a mineralogical analysis of the igneous rocks and alteration zones including halogen element systematics related to cu mineralization processes abstract the giant sarcheshmeh porphyry copper deposit is located 65 km southwest of kerman city southeastern iran numerous miocene porphyry stocks and dykes intruded thick sequences of upper cretaceous sedimentary and eocene volcanic rocks hypogene and supergene porphyry cu mineralization occurs within the granodioritic porphyry and host rock sequence which was extensively altered to a dominantly potassic phyllic and argillic assemblage with interstitial to distal propylitic types biotite bearing assemblages occur as both primary phenocrysts and secondary replacements showing variable size colour and shape fluorine contents 0 22 to 1 33 wt and x mg 0 54 to 0 71 in biotites from the potassic and phyllic zones are higher than those of non mineralized granitoids f 0 09 to 0 56 wt x mg 0 43 to 0 54 whereas their cl contents cl 0 05 to 0 24 wt are lower than those of the non mineralized granitoids cl 0 11 to 0 45 the biotites from the phyllic zone have higher log f h 2 o f hf and log f h 2 o f hcl values than those of the potassic zone as well as the granitoid and andesitic dykes the log f hf f hcl values determined for the granitoid potassic and phyllic zones are similar though more negative than those of the andesitic dykes the log f hf f hcl values have a similar range for biotite from the granitoid and potassic and phyllic zones the halogen fugacity ratios established for fluids associated with the sarcheshmeh deposit from their f and cl contents in biotite show that the granitoid potassic zone and phyllic zone are increasingly affected by meteoric waters the fluids that circulated in the phyllic zone are predominantly of meteoric origin possibly overprinting original phyllic zone halogen contents the cl intercept values of biotite in the granitoid and phyllic and potassic are similar to other ore forming systems and tend to be more cl rich than cl intercept values of biotites in common igneous rocks calculated f cl intercept values for biotite in the granitoid and potassic zone are also consistent with many other porphyry copper forming systems

bottom simulating reflectors seismic velocities and avo effects we obtain the wave velocities of ice and gas hydrate bearing sediments as a function of concentration and temperature unlike previous theories based on simple slowness and or moduli averaging or two phase models we use a biot type three phase theory that considers the existence of two solids grain and ice or clathrate and a liquid water and a porous matrix containing gas and water for consolidated berea sandstone the theory underestimates the value of the compressional velocity below 0 c including grain ice interactions and grain cementation yields a good fit to the experimental data strictly speaking water proportion and temperature are closely related fitting the wave velocity at a given temperature allows the prediction of the velocity throughout the range of temperatures provided that the average pore radius and its standard deviation are known the reflection coefficients are computed with a viscoelastic single phase constitutive model the analysis is carried out for the top and botto

compositions of biotite amphibole apatite and silicate melt inclusions from the tongchang mine dexing porphyry deposit se china implications for the behavior of halogens in mineralized porphyry systems abstract the dexing deposit located in the circum pacific ore belt is the largest porphyry copper deposit in eastern china it is composed of 3 separate plutons which host three mines tongchang fujiawu and zhushahong mines the porphyritic granodiorite samples studied in this investigation were collected from the tongchang ore forming pluton of this giant deposit this paper presents electron microprobe analyses of biotite apatite amphibole plagioclase potassium feldspar and rehomogenized glassy melt inclusions from the tongchang porphyritic granodiorites petrographic observations of the samples are consistent with portions of the granodioritic magma represented by our samples being overprinted by potassic hydrothermal fluid which variably altered these minerals all of the studied micas are mg rich biotites the biotites are separated into altered magmatic and secondary types based on their petrographic and geochemical characteristics the phlogopite components of the secondary biotites are typically higher than those of the altered magmatic biotites and the x mg values of all biotites correlate negatively with cl contents consistent with the mg cl avoidance principle the x mg values also correlate negatively with k 2 o na 2 o bao feo and tio 2 for both generations of biotites the calculated log f h 2 o f hcl values for 690 k of the coexisting potassic fluids which are determined from the altered magmatic biotite compositions range from 4 43 to 4 67 and are very similar to those of other major porphyry deposits however the log f h 2 o f hf and log f hf f hcl values for the same batch of hydrothermal fluids are significant higher and lower than those of these other porphyry deposits respectively the cl concentrations of amphiboles and melt inclusions range from 0 18 to 0 32 wt and 0 15 to 0 44 wt respectively most apatites trapped in biotite and plagioclase phenocrysts display a bimodal cl distribution 0 19 to 1 35 wt and 1 48 to 3 73 wt similarly the s contents of the apatite also show a distinct bimodal distribution reflecting the effects of variable anhydrite saturation during evolution of the tongchang melt and variable dissolution of anhydrite by saline aqueous fluids the cl contents of the apatites from the tongchang system are typically higher than those of other studied porphyry deposits furthermore the cl contents of the melt inclusions are at or very near the cl saturation levels 0 36 to 0 46 wt at 850 c and 50 mpa and 0 42 to 0 54 wt at 850 c and 200 mpa for these melt compositions at shallow crustal pressures these findings suggest that the area of the granodioritic magma represented by our samples and perhaps the bulk of the tongchang granodioritic magma was rich in cl the melt inclusion compositions are consistent with a high salinity hydrosaline liquid being exsolved directly from the granodioritic melt directly this high salinity hydrosaline liquid was likely very efficient at dissolving transporting and precipitating ore metals in the mineralizing magmatic hydrothermal system

apatite in granitoids related to polymetallic mineral deposits in southeastern hunan province shi hang zone china implications for petrogenesis and metallogenesis abstract the area of southeastern hunan province china located within the southwestern part of the shi hang metallogenic zone is characterized by abundant cu pb zn w and sn polymetallic ore deposits that are closely associated with coeval late mesozoic granodiorite porphyries and biotite granites respectively here we present new major and trace element concentrations and 87 sr 86 sr ratios of apatites from six ore bearing granitic rocks as determined by electron microprobe laser ablation inductively coupled plasma mass spectrometry and thermal ionization mass spectrometer which allow us to determine the main controls on the formation of these different types of mineralization and to explore how these controls are reflected in variations in apatite chemical and isotopic compositions the apatite data indicate that granodiorite porphyry intrusions related to cu pb zn mineralization are oxidized and formed as a result of slab dehydration melting of the mantle wedge overlying a subducted slab and the partial melting of crustal material the release of abundant cl and h 2 o rich fluids from the slab triggered mantle melting and the extraction of metals that were precipitated within the deposits in comparison granites related to w and sn deposits are moderately oxidized to reduced and were generated by the partial melting of crustal material with only limited input from mantle derived magmas granites associated with the w and sn mineralization formed in an intra arc rifting related tectonic environment the fact that these numerous polymetallic ore deposits formed in the same area during two successive periods of mineralization the first from 180 to 160 ma and the second from 160 to 140 ma indicates that the tectonic environment of southeastern hunan province evolved from a continental arc associated with the subduction of the paleo pacific plate and the formation of cu pb zn deposits to a later intra arc rifting environment associated with the formation of w and sn deposits as a consequence of slab roll back and mantle upwelling during the late jurassic this study reveals that apatite compositions can be used as a proxy to reflect the differences between granitoids and their associated mineralization and identify regional metallogeny and tectonic evolution

porphyry epithermal au ag mo ore formation by vapor like fluids new insights from geochemical modeling shallow magmatic hydrothermal systems are characterized by steep gradients in temperature and pressure and because the fluid is of low density and highly compressible the solubility of ore minerals in these systems varies considerably as a function of both temperature and pressure we use novel pressure and temperature dependent experimentally derived thermodynamic data to geochemically model the transport and deposition of au ag and mo by vapor and low to intermediate density supercritical fluids in the context of au and mo porphyry and au ag epithermal ore formation the results show that there is a strong compositional control on the au mo ratio of the parental ore fluid which can explain au mo zoning in porphyry ore deposits and the formation of au rich and mo rich subtypes gold solubility reaches a maximum between 320 c and 500 c depending on the fluid density whereas mo and ag concentrations decrease with decreasing temperature and pressure these differences in mineral solubility help explain the fractionation of au from ag and mo and the preferential mobilization of au into sites of epithermal ore deposition application of this modeling of metal solubility in vapor like fluids offers an important opportunity for understanding individual ore forming hydrothermal systems and determining the limiting factors for metal enrichment

restriction of h o isotopes for alteration and mineralization system of tongchang cu mo au porphyric deposit jiangxi province tongchang is the biggest porphyry cu mo au deposit in the dexing metallogenic ore concentation area for tracing the origin of ore forming fluid during complicated mineralization and alteration process of the tongchang porphyry cu mo au deposit the work has been mostly devoted to oxygen isotopes of rocks or spatial anomaly delineation of oxygen isotopes of whole rock whereas researches on combined hydrogen and oxygen isotopes of single minerals including altered minerals and gauge minerals are very insufficient according to detailed classification of different alteration and mineralization assemblages the authors analyzed h and o isotopes of quartz biotite chlorite and sericite of different stages in tongchang porphyry cu mo au deposit to evaluate the source and evolution of the ore forming fluid 18o and d values of water balanced with quartz and biotite from regular barren quartz veins in phyllite a1 quartz biotite veins a2 quartz magnetite veins a4 and quartz pyrite chalcopyrite veins b show that all the ore forming fluids were derived from magma except for partial contamination of b veins by a little meteoric water 18o and d values of quartz from the last low temperature d veins and carbonate veins lying at the end of the meteoric water granodiorite porphyry line indicate that the ore forming fluid during the last low temperature stages 180 200 were totally derived from meteoric water considerable variations of 18o and d values of biotite phenocrysts from fresh and chloridie hydromicazation porphyry suggest that minor amounts of meteoric water and regional metamorphic water were partially involved in the magmatic water during biotite phenocryst crystallization or late weak chloritization hydromicazation had already altered granodiorite porphyry chloritization was caused by magmatic water besides minor meteoric water while the sericitization was triggered by the reaction of meteoric water with phyllite in general potassium silicate alteration chloritization a veins and b veins were formed by the action of magmatic fluid and meteoric water entered the alteration mineralization system during chloritization however sericitiztion late low temperature d veins and carbonate veins of the tongchang deposit were formed by meteoric water

anhydrite solubility in differentiated arc magmas abstract the solubility of anhydrite in differentiated arc magmas was experimentally studied at 200 mpa and 800 1000 c over a range of oxygen fugacities from 0 5 log units above the ni nio buffer to the hematite magnetite buffer anhydrite is stable only at oxidizing conditions fo2 re reo2 whereas sulfides only form under reducing conditions the solubility of anhydrite in the melt ultimately regulates the amount of sulfur available to partition between melt and fluid phase during the eruption at oxidizing conditions the solubility product of anhydrite increases with temperature nbo t and melt water content we provide a new calibration of the anhydrite solubility product ksp xcao xso3 which reproduces all available experimental data with greatly improved accuracy ln k sp anhydrite 8 95 146 5 nbo t 2 696 10 4 t k 19 72 nbo t 10 4 t k 0 409 h 2 o wt in this equation the molar fractions xcao and xso3 in the melt as well as the number of non bridging oxygen atoms per tetrahedron nbo t are calculated on an anhydrous basis h2o refers to the melt water content t is temperature in kelvin we apply our model to estimate the sulfur yield of some recent volcanic eruptions and we show that the sulfur yield of the 1991 mt pinatubo dacite eruption was unusually large because only a small fraction of the sulfur was locked up in anhydrite in general high sulfur yields are expected when anhydrite solubility in the melt is high i e for somewhat depolymerized melts for rhyolitic systems most of the available sulfur will be locked up in anhydrite so that even very large eruptions may only have a small effect on global surface temperatures our model therefore allows improved predictions of the environmental impact of explosive volcanic eruptions

rock physics template rpt analysis of well logs and seismic data for lithology and fluid classification in cambay basin the cambay basin is 450 km long north south trending graben with an average width of 50 km having maximum depth of about 7 km the origin of the cambay and other basins on the western margin of india are related to the break up of the gondwana super continent in the late triassic to early jurassic 215 ma the structural disposition of the pre cambrian basement a complex of igneous and metamorphic rocks exposed in the vicinity of the cambay basin controls its architecture the principal lineaments in the basin are aligned towards ne se ene wsw and nnw sse respectively rock physics templates rpts are charts and graphs generated by using rock physics models constrained by local geology that serve as tools for lithology and fluid differentiation rpt can act as a powerful tool in validating hydrocarbon anomalies in undrilled areas and assist in seismic interpretation and prospect evaluation however the success of rpt analysis depends on the availability of the local geological information and the use of the proper model rpt analysis has been performed on well logs and seismic data of a particular study area in mid cambay basin rock physics diagnostic approach is adopted in the study area placed at mid cambay basin to estimate the volume in the reservoir sands from 6 wells namely a b c d e and f where oil was already encountered in one well d in the study area hydrocarbon prospective zone has been marked through compressional p wave and shear wave s wave impedance only in the rpt analysis we have plotted different kinds of graphical responses of lame s parameters which are the function of p wave velocity s wave velocity and density the discrete thin sand reservoirs have been delineated through the rpt analysis the reservoir pay sand thickness map of the study area has also been derived from rpt analysis and fluid characterization through this fluid characterization oil bearing thin sand layers have been found in well e including well d the sand distribution results prove that this methodology has able to perform reservoir characterization and seismic data interpretation more quantitatively and efficiently

temporal and spatial evolution of a gas hydrate bearing accretionary ridge on the oregon continental margin a seismic reflection survey on the oregon continental margin conducted in 1989 indicates the widespread presence of gas hydrate beneath the middle and lower slope of this accretionary margin the seismic signature of gas hydrate a bottom simulating reflector bsr with negative polarity that locally cuts across stratigraphic horizons is especially well developed beneath hydrate ridge this anomalously shallow accretionary ridge was drilled during ocean drilling program leg 146 to study fluid venting in this paper we focus on the seismic data from the southern part of hydrate ridge where little evidence of active venting has previously been reported but where the seismic data indicate a complicated subsurface plumbing system apparent disruptions of the bsr beneath the western ridge flank suggest dissociation of gas hydrate in response to slumping a double bsr beneath the southern crest suggests hydrate destabilization in response to tectonic uplift and folding on the basis of these and other observations we propose a qualitative model for the evolution of a hydrate bearing ridge in an active accretionary complex in which gas hydrate initially stabilizes the sea floor permitting construction of large ridges that are then eaten away by slumps along their margins the north to south variation in sea floor venting and subsurface seismic structure along hydrate ridge may reflect different stages in the temporal evolution of one of these ridges

immiscibility and continuous felsic melt fluid evolution within the rio blanco porphyry system chile evidence from inclusions in magmatic quartz the 5 2 to 3 9 ma late porphyries at rio blanco are spatially associated with hydrothermal tourmaline cemented breccias and a significant cu mo deposit magmatic inclusions in quartz from these rocks are used to better understand late stage magmatic processes particularly those involving melt melt and melt fluid immiscibility inclusions are represented by glass of common rhyolitic composition hereafter type 1 crystallized volatile rich felsic melt type 2 h2o and salt rich fluids and microphenocrysts coexistence of types 1 and 2 material within the same growth plane and within a single inclusion suggests that crystallizing rhyolitic magma separated into two silicate melts volatile poor and volatile rich the volatile rich silicate melt had a prolonged evolution extending below the solidus of volatile poor silicate melt with a progressive reduction of the silicate volatile ratio and ultimately to highly saline fluids the latter may have been the source of hydrothermal fluids that had the potential to transport metals the occurrence of immiscibility in the rio blanco rhyolites may be in some ways comparable to that in volatile rich pegmatites and strongly suggests that this process may be common in other se normal felsic magmas and important in the origin of mineralized porphyries

one dimensional reactive transport models of alteration in the tongchang porphyry copper deposit dexing district jiangxi province china in the tongchang porphyry copper deposit the main hydrothermal alteration is most intense in and near the contact zone and gradually attenuates inward and outward showing a symmetrical zoning with respect to the contact zone detailed field investigations of wall rock alteration and ore controlling fractures combined with laboratory studies of lithology mineral composition and fluid inclusions have led to an assessment of initial and boundary conditions and physical parameters such as species concentration mineral volume fraction temperature porosity reactive surface area and flow velocity required for dynamic modeling of this system we have developed a new program to model the coupled process of fluid flow involving advection and diffusion and chemical reactions incorporating mineral dissolution precipitation and have numerically simulated the spatial and temporal evolution of the systems for a duration of 100 000 yr in the simulations transient temperature fields are calculated for the main temperature range of ore formation from 200 degrees to 350 degrees c simulated mineral assemblages are generally in agreement with those observed in the real system the important conclusions drawn from the combined researches of geology and geochemistry as well as dynamics of coupled fluid transport and reactions are as follows fluid flow and reactions were mainly controlled by the fractures striking around north south and dipping to the west in the exocontact zone schistosity cleavages were also important fluid pathways in addition to the fractures the formation of closely spaced fractures in the contact zone and especially in the exocontact zone by tectonic activity after potassium metasomatism and the reactive flow from the contact zone inward and outward were the principal reasons for the occurrence of the contact zone symmetrical alteration zone in the porphyry body both the dissolution and precipitation of minerals were important the rate of dissolution or precipitation of minerals gradually decreased in time the nearer it was to the contact zone spatially the earlier the dissolution or precipitation of minerals was finished in the exocontact metamorphic wall rock the main processes were the transport and precipitation of sio sub 2 sub aq the rate of silification gradually decreased in time and space in the alteration of porphyry body na super was evidently removed from the alteration zone and ca super 2 removed from the intense alteration zone to weak alteration zone and the fluid was weakly acidic ph asymp 4 in the metamorphic wall rock sio sub 2 sub aq was mainly brought in from fluid the evolution of sio sub 2 sub aq cl super ca super 2 and co 3 super 2 was intimately correlated with alteration mineralization intensity

triggers for the formation of porphyry ore deposits in magmatic arcs porphyry ore deposits supply much of the copper molybdenum gold and silver used by humans a review of the main processes that trigger porphyry ore formation suggests that sulphide saturation of the magmas that supply the metals could be the overriding mechanism that helps control the temporal and spatial distribution of the ore deposits

electromagnetic surveying of seafloor mounds in the northern gulf of mexico seafloor controlled source electromagnetic data probing the uppermost 30 m of seafloor sediments have been collected with a towed magnetic dipole dipole system across two seafloor mounds at approximately 1300 m water depth in the northern gulf of mexico one of these mounds was the focus of a recent gas hydrate research drilling program rather than the highly resistive response expected of massive gas hydrate within the confines of the mounds the em data are dominated by the effects of raised temperatures and pore fluid salinities that result in an electrically conductive seafloor this structure suggests that fluid advection towards the seafloor is taking place beneath both mounds similar responses are seen at discrete locations away from the mounds in areas that might be associated with faults further suggesting substantial shallow fluid circulation raised temperatures and salinities may inhibit gas hydrate formation at depth as has been suggested at other similar locations in the gulf of mexico

equilibrium partitioning and subsequent re distribution of halogens among apatite biotite amphibole assemblages from mantle derived plutonic rocks complexities revealed abstract the concentration of halogens in apatite biotite and amphibole is investigated for a large variety of mantle derived plutonic rocks gabbros diorites monzonites olivine and pyroxene bearing monzonitic to granitic rocks syenites carbonatites and a phoscorite in all rocks studied apatite occurs as an early magmatic phase whereas biotite and amphibole may occur either as a late magmatic phase or as late stage potentially hydrothermal product replacing precursor olivine pyroxene and fe ti oxides ilmenite and magnetite based on electron microprobe analyses for f and cl and detailed textural observations we test existing models of halogen partitioning between apatite and biotite bromine concentration data for apatite biotite and amphibole are used to further refine our understanding of the geochemical similarities and differences between cl and br during magmatic and hydrothermal processes our data suggests that f and cl contents in apatite biotite and amphibole can indeed be useful monitors of the halogen systematics in magmas but they may also be subject to post magmatic changes to variable extents the relatively small radius and compatible f cation seems to be less prone to post magmatic alteration and is likely to best reflect the original magmatic halogen abundances especially in apatite however the larger and probably more incompatible cl anion is more easily re mobilized as reflected by strong redistribution of cl in biotite and amphibole which have been clearly overprinted by hydrothermal fluids in certain cases the ability of halogens to re distribute themselves after magmatic equilibrium partitioning as emphasized by our data suggests that observed partitioning especially between apatite and biotite may also be used as a very sensitive indicator for post magmatic hydrothermal processes

primary aqueous fluids in rhyolitic magmas melt inclusion evidence for pre and post trapping exsolution abstract this study examines melt inclusions containing bubbles of aqueous fluid l v and l v occurring in rhyolites from the okataina volcanic centre new zealand and the rio blanco cu mo deposit chile we demonstrate that these aqueous fluids coexisted with silicate melts magmas and represent either post trapping exsolution in the case of okataina or co trapping of phases already coexisting in the magma in the case of rio blanco microthermometry proves that some of the bubbles are a single phase aqueous liquid and all are shown by pixe analysis to be metal rich saline solutions as such these aqueous fluids provide the closest approximation to direct testing of the proposition that cooling magmas exsolve metal rich aqueous fluid in the case of pre trapping exsolution at rio blanco we show that some inclusions record and preserve magmatic emulsions melt aqueous fluid that are the first stage in the evolution of hydrothermal fluids we demonstrate that heating experiments on volatile rich melt inclusions can produce in situ exsolution of hypersaline metal rich aqueous fluid bubbles potentially permitting magma chamber processes to be experimentally modelled

magmatic hydrothermal evolution of the yuanzhuding porphyry cu mo deposit south china insights from mica and quartz geochemistry abstract the yuanzhuding porphyry cu mo deposit located in the southern section of the qinzhou hangzhou belt is characterized by successive generations of quartz bearing veins with complicated crosscutting relationships multiple analytical methods have been applied to different mica types and quartz bearing veins to reveal the evolution history of the yuanzhuding porphyry system four types of micas have been identified in the yuanzhuding porphyry cu mo deposit including magmatic biotite bt i metamorphic biotite bt ii hydrothermal biotite bt iii and hydrothermal sericite ser based on detailed petrological observations all three types of biotite belong to the mg biotite group but can be compositionally distinguished whereas ser lies in the transition zone between li phengite and li muscovite generally decreasing crystallization temperatures with increasing distances from the center of the porphyry have been revealed in bt ii and bt iii based on their compositional variations documenting the outward cooling trends of the yuanzhuding porphyry system early quartz bearing veins with potassic alteration are characterized by granular quartz with homogeneous cl textures in combination with their wavy vein walls which indicate the host rock was ductile during vein formation we infer that they were formed under dominantly lithostatic pressure late quartz bearing veins with sericitic alteration are typically euhedral quartz with growth zones of oscillating cl intensity and they are inferred to be formed under dominantly hydrostatic pressure intersection of fluid inclusion isochores with ti in quartz isopleths revealed that early quartz veins with potassic alteration located close to the ore forming porphyry were formed at up to 575 c late quartz veins with sericitic alteration were formed at 310 c formation depth of the yuanzhuding porphyry deposit is inferred to be 5 3 km hydrogen and oxygen isotopes of bt iii and quartz indicate that the ore forming fluid was mainly magmatic fluid the fluid pressure was high enough to remain stable in single phase through the entire fluid evolution history all fluid inclusions are vapor liquid inclusions the fluid salinity and the cl fugacity remained constantly low which may have limited the efficiency of cu extraction and transportation the hornfels host significant amounts of bt ii and may have served as a reservoir of ferrous iron to reduce the oxidized ore forming fluid and generate reduced sulfur effective metal precipitation occurred in the yuanzhuding porphyry system owing to the coexistence of the generation of reduced s2 and the drop of metal solubility caused by the decrease of fluid temperature

compressional and shear wave velocities in uncemented sediment containing gas hydrate 1 the competing hypotheses for gas hydrate formation at the particle scale in sediments describe processes of pore filling frame building or cementation new measurements of compressional vp and shear wave vs velocities in fine grained sands subjected to low confinement and monitored during formation of tetrahydrofuran hydrate indicate that hydrate nucleates in the pore space presumably at grain boundaries and grows with limited impact on the sediment shear stiffness vp and vs until crystals begin to interact with the granular skeleton at 40 hydrate concentration vs increases significantly more than vp at higher hydrate concentrations reflecting larger changes in the specimen s shear stiffness than its bulk stiffness the results indicate that seismic velocities and or their ratio vp vs have limited capability for locating hydrate or constraining hydrate concentrations

anisotropic effective medium modeling of the elastic properties of shales shales are complex porous materials normally consisting of percolating and interpenetrating fluid and solid phases the solid phase is generally comprised of several mineral components and forms an intricate and anisotropic microstructure the shape orientation and connection of the two phases control the anisotropic elastic properties of the composite solid we develop a theoretical framework that allows us to predict the effective elastic properties of shales its usefulness is demonstrated with numerical modeling and by comparison with established ultrasonic laboratory experiments the theory is based on a combination of anisotropic formulations of the self consistent sca and differential effective medium dem approximations this combination guarantees that both the fluid and solid phases percolate at all porosities our modeling of the elastic properties of shales proceeds in four steps first we consider the case of an aligned biconnected clay fluid composite composed of ellipsoidal inclusion

chemical composition of biotite from the casino porphyry cu au mo mineralization yukon canada evaluation of magmatic and hydrothermal fluid chemistry abstract the chemical composition of biotite has been determined for the dawson range batholith and the casino porphyry style cu au mo occurrence yukon territory canada biotite from the propylitic phyllic and potassic alteration zones of the casino occurrence possesses higher x mg al 2 o 3 sio 2 f and cl and lower tio 2 bao and mno concentrations than biotite outside these alteration zones this phenomenon is similar to that recorded for biotite of other porphyry cu deposits however the absolute concentrations of the oxides and halogens vary significantly among deposits calculated log f h 2 o f hf f h 2 o f hcl f hcl f hf ratios determined from biotite microprobe data indicate that hydrothermal fluids associated with potassic alteration at casino were similar to those associated with phyllic alteration in contrast fluids responsible for propylitic alteration had higher log f h 2 o f hf and less negative log f hf f hcl values the log f h 2 o f hcl and f hf f hcl ratios established for casino are similar to those for other porphyry cu deposits however log f h 2 o f hf values vary greatly among porphyry deposits this variation in log f h 2 o f hf values may be related to the source of the magmas and or magmatic processes assimilation fractional crystallization associated with melt on its ascent through the crust prior to the exsolution of magmatic fluids that are responsible for porphyry mineralization the biotite compositions from the dawson range batholith are either not consistent with the fe f and mg cl avoidance principles or record changes in the f cl ratio of the fluid during crystallization of the granitic body

eastern asia and the western pacific timing and spatial distribution of rifting in china abstract a compilation of recognized rifts in china indicates that five distinct episodes of rifting have occurred these episodes occurred at approximately 2 3 ga 1 85 1 7 ga 1 0 0 7 ga 550 190 ma and 175 ma to present the timing and location of rifting has largely been a function of tectonic activity along the margins of the various chinese paleocontinents some of the oldest rocks in china are found in the sino korean and tarim cratons and most of the identified precambrian rifts are found within or on the margins of these cratons these cratons are viewed as the continental nucleus of china and fold belts and microcontinents have been accreted to this nucleus through time much of the locus of rifting has migrated away from this nucleus as has the location of the continental margin especially in the paleozoic beginning in the middle mesozoic rifting commenced along the entire eastern margin of china extension occurred concomitantly with subduction in a backarc setting this is the dominant cenozoic extensional regime in china and is still active today to date few cenozoic rifts have been found in western china where most tectonism is probably a consequence of the collision between india and china but it seems likely that more rifts will be discovered in this area as it becomes better studied

sulfur partition coefficient between apatite and rhyolite the role of bulk s content experimental studies have been performed to constrain sulfur behavior during apatite crystallization and to determine sulfur partition coefficient between apatite and melt kd s apatite melt at oxidizing conditions crystallization experiments have been conducted with a hydrous rhyolitic melt and different bulk sulfur contents 0 15 to 2 wt s at 900 and 1 000 c 200 mpa and log f rm o 2 nno 3 6 the sulfur content in the glass increases with increasing amount of added s anhydrite crystallizes for s added 0 75 wt 0 10 and 0 13 wt so3 in glass at 900 and 1 000 c respectively the amount of anhydrite increases and the amount of apatite decreases with increasing amount of added sulfur the sulfur exchange reaction in apatite is influenced by the bulk composition of the melt e g p content however changing melt composition has only little effect on kd s apatite melt for the investigated rhyolitic composition the kd s apatite melt does not depend directly on temperature decreases from 14 2 to 2 7 with increasing s content in glass from so3 0 03 to 0 19 wt respectively and can be predicted from the following equation ln kd 0 0025 s in melt in ppm 2 9178 the combination of experimental data obtained for rhyolitic and andesitic melts reveals that the sulfur partition coefficient tends toward a value of 2 for high sulfur content in the glass 0 2 wt so3 using s in apatite as proxy for determining s content in melt is promising but additional experimental data are needed to clarify the individual effects of t f rm s 2 and p and ca content in the melt on s partitioning

origin of bottom simulating reflectors geophysical evidence from the cascadia accretionary prism vertical seismic profile vsp data from two drill sites on the cascadia margin show low velocity zones indicative of free gas be neath a bottom simulating reflector bsr offshore oregon at ocean drilling program odp site 892 velocities drop from an average of 1750 m s above the bsr to less than 1250 m s below it sonic logs confirm that seismic velocity in the sediments adjacent to the borehole is less than that of water for at least 50 m beneath the depth of the bsr at this site similarly at odp site 889 offshore vancouver velocities range from 1700 to 1900 m s in the 100 m above the bsr and drop abruptly to 1520 m s in the 15 m just beneath it the low velocities observed beneath the bsr are strong evidence for the presence of 1 5 free gas by volume the bsr at these two sites results from the contact between gas free sediments containing a small quantity of hydrate above the bsr and a low velocity free gas zone beneath it although the bsr is associated with the base of the hydrate stability field hydrate appears to account for relatively little of the velocity contrast that produces the bsr velocity above the bsr at site 889 is only about 100 m s greater than that expected for sediments of similar porosity sediments above the bsr at site 892 appear to have normal velocity for their porosity and may contain little hydrate

halogens in volcanic systems the transport degassing and atmospheric release of halogens from active volcanism on earth have been the focus of increasing interest over the last few decades and have recently been the subject of the 1st workshop on halogens in volcanic systems and their environmental impacts that was held in december of 2007 at yosemite lodge in yosemite national park california as an introduction to this chemical geology special issue collecting contributions from many of the participants at the workshop we review here recent advances in this field including experimental and theoretical investigations of halogen behaviour in volcanic and related magmatic systems we discuss previous research on several aspects of halogen geochemistry including halogen abundances in the mantle and magmas on earth the effects of halogens on phase equilibria and melt viscosities their partitioning between melt and fluid phase s upon decompression cooling and crystallisation of magmas in the earth s crust and their final atmospheric release as volcanic gases the role of halogens in the genesis of hydrothermal systems and in the transport of ore forming metals is also reviewed and we discuss our current understanding of atmospheric processing of volcanic halogens in both the troposphere and stratosphere and their consequent impacts in spite of these recent advancements our current understanding of halogen geochemistry at active volcanoes is still far too fragmentary and the key questions that require answers from future research are summarised in our conclusions

the assessment of marine gas hydrates through electrical remote sounding hydrate without a bsr marine gas hydrates prevalent in offshore sediments in canada and japan are a possible hydrocarbon resource a hazard to drilling and a source of a major greenhouse gas quantitative estimates of hydrate concentrations in deep sea sediment are difficult to obtain by conventional methods we have sought novel techniques specifically designed for assessment such as transient electric dipole dipole electromagnetics the latter method is based on the assumption of a reduced electrical conductivity in hydrate rich zones field trails of new apparatus on the cascadia margin have proven successful excellent data were collected and analysed using a differential phase method to reduce systematic error apparent resistivities collected on three lines demonstrate that the resistivity of the seafloor is remarkably uniform over the whole survey area the average hydrate concentration deduced with the aid of a reference model based on the electrical logs of odp holes 888 and 889 is about 17 26 of pore space 9 13 of sediment volume in the 100 m interval above the bsr the values are consistent with those obtained by other analyses further the presence of hydrate is predicted in a region to the east of 889b where there is no visible bsr

periodicity in extinction and the problem of catastrophism in the history of life the hypothesis that extinction events have recurred periodically over the last quarter billion years is greatly strengthened by new data on the stratigraphic ranges of marine animal genera in the interval from the permian to recent these data encompass some 13 000 generic extinctions providing a more sensitive indicator of species level extinctions than previously used familial data extinction time series computed from the generic data display nine strong peaks that are nearly uniformly spaced at 26 ma intervals over the last 270 ma most of these peaks correspond to extinction events recognized in more detailed if limited biostratigraphic studies these new data weaken or negate most arguments against periodicity which have involved criticisms of the taxonomic data base sampling intervals chronometric time scales and statistical methods used in previous analyses the criticisms are reviewed in some detail and various new calculations and simulations including one assessing the effects of paraphyletic taxa are presented although the new data strengthen the case for periodicity they offer little new insight into the driving mechanism behind the pattern however they do suggest that many of the periodic events may not have been catastrophic occurring instead over several stratigraphic stages or substages

giant ore deposits formed by optimal alignments and combinations of geological processes giant ore deposits are priority targets for mining companies a review of the characteristics of several giant porphyry and epithermal deposits worldwide suggests that they formed from ordinary processes that were fortuitously operating at maximum efficiency

petrogenesis of adakitic porphyries in an extensional tectonic setting dexing south china implications for the genesis of porphyry copper mineralization the dexing adakitic porphyries quartz diorite granodiorite porphyries associated with giant porphyry cu deposits are located in the interior of a continent south china they exhibit relatively high mgo cr ni and sr contents high la yb and sr y ratios but low yb and y contents similar to adakites produced by slab melting associated with subduction however they are characterized by bulk earth like nd sr isotope compositions end t 1 14 to 1 80 and 87 sr 86 sr i 0 7044 0 7047 and high th 12 6 27 2ppm contents and th ce 0 19 0 94 ratios which are different from those of cenozoic slab derived adakites sensitive high resolution ion microprobe shrimp geochronology studies of zircons reveal that the dexing adakitic porphyries have a crystallization age of 171 3ma this age is contemporaneous with middle jurassic extension within the shi han rift zone and within plate magmatism elsewhere in south china indicating that the dexing adakitic porphyries were probably formed in an extensional tectonic regime in the interior of the continent rather than in an arc setting their high th contents and th ce ratios and middle jurassic age argue against an origin from a neoproterozoic 1000ma stalled slab in the mantle taking into account available data for the regional metamorphic magmatic rocks and the present day crustal thickness 31km in the area we suggest that the dexing adakitic porphyries were most probably generated by partial melting of delaminated lower crust which was possibly triggered by upwelling of the asthenospheric mantle due to the activity of the shi hang rift zone moreover the dexing adakitic magmas must have interacted with the surrounding mantle peridotite during their ascent which elevated not only their mgo cr and ni contents but also the oxygen fugacity fo2 of the mantle the high fo2 could have induced oxidation of metallic sulfides in the mantle and mobilization of chalcophile elements which are required to produce associated cu mineralization therefore the cu metallogenesis associated with the dexing adakitic porphyries is probably related to partial melting of delaminated lower crust similar to the metallogenesis accompanying slab melting

a laboratory investigation into the seismic velocities of methane gas hydrate bearing sand remote seismic methods which measure the compressional wave p wave velocity vp and shear wave s wave velocity vs can be used to assess the distribution and concentration of marine gas hydrates in situ however interpreting seismic data requires an understanding of the seismic properties of hydrate bearing sediments which has proved problematic because of difficulties in recovering intact hydrate bearing sediment samples and in performing valid laboratory tests therefore a dedicated gas hydrate resonant column ghrc was developed to allow pressure and temperature conditions suitable for hydrate formation to be applied to a specimen with subsequent measurement of both vp and vs made at frequencies and strains relevant to marine seismic investigations thirteen sand specimens containing differing amounts of evenly dispersed hydrate were tested the results show a bipartite relationship between velocities and hydrate pore saturation with a marked transition between 3 and 5 hydrate pore saturation for both vp and vs this suggests that methane hydrate initially cements sand grain contacts then infills the pore space these results show in detail for the first time using a resonant column how hydrate cementation affects elastic wave properties in quartz sand this information is valuable for validating theoretical models relating seismic wave propagation in marine sediments to hydrate pore saturation

mineral chemistry of hydrothermal biotite from the kahang porphyry copper deposit ne isfahan central province of iran abstract the kahang porphyry cu deposit located northeast of isfahan city in central of iran is associated with a composite miocene stock and ranges in composition from diorite through granodiorite to quartz monzonite field observations and petrographic studies show that the emplacement of the kahang stock occurred in several pulses each associated with its related hydrothermal activity early hydrothermal alteration started with a potassic style in the central part of the system and produced a secondary biotite k feldspar magnetite assemblage accompanied by chalcopyrite and pyrite mineralization propylitic alteration that took place at the same time as the potassic alteration occurred in the peripheral portions of the stock subsequent phyllic alteration overprinted earlier potassic and propylitic alterations biotite grains from the potassic and phyllic zones show distinct chemical compositions the feo tio2 mno k2o and na2o concentrations in biotite from the phyllic alteration zone are lower than those from the potassic alteration zone the f and cl contents of biotite from the potassic alteration zone display relatively high positive correlation with the xmg the fluorine intercept values iv f from the potassic and phyllic alteration zones are strongly correlated with the fluorine chlorine intercept values iv f cl biotite geothermometry for the potassic and phyllic alteration zones based on the biotite geothermometer of beane 1974 yields a temperature range of 422 to 437 c mean 430 c and 329 to 336 c mean 333 c respectively the position of data in log xf xoh ratio vs xmg and xfe diagram suggests that biotite formed under dissimilar composition and temperature conditions in the potassic and phyllic alteration zones calculated log fugacity ratios of fh2o fhf fh2o fhcl and fhf fhcl show that hydrothermal fluids associated with the potassic alteration were distinctively different from those fluids associated with the phyllic alteration zone at kahang porphyry cu deposit the results of this research indicate that the chemistry of biotite is related to the chemical composition of the magma and the prevailing physical conditions during crystallization

experimental investigation of f cl and oh partitioning between apatite and fe rich basaltic melt at 1 0 1 2 gpa and 950 1000 c apatite melt partitioning experiments were conducted in a piston cylinder press at 1 0 1 2 gpa and 950 1000 c using an fe rich basaltic starting composition and an oxygen fugacity within the range of iw 1 to iw 2 each experiment had a unique f cl oh ratio to assess the partitioning as a function of the volatile content of apatite and melt the quenched melt and apatite were analyzed by electron probe microanalysis and secondary ion mass spectrometry techniques the mineral melt partition coefficients d values determined in this study are as follows d fap melt 4 4 19 d clap melt 1 1 5 d ohap melt 0 07 0 24 this large range in values indicates that a linear relationship does not exist between the concentrations of f cl or oh in apatite and f cl or oh in melt respectively this non nernstian behavior is a direct consequence of f cl and oh being essential structural constituents in apatite and minor to trace components in the melt therefore mineral melt d values for f cl and oh in apatite should not be used to directly determine the volatile abundances of coexisting silicate melts however the apatite melt d values for f cl and oh are necessarily interdependent given that f cl and oh all mix on the same crystallographic site in apatite consequently we examined the ratio of d values exchange coefficients for each volatile pair oh f cl f and oh cl and observed that they display much less variability k dcl fap melt 0 21 0 03 k doh fap melt 0 014 0 002 and k doh clap melt 0 06 0 02 however variations with apatite composition specifically when mole fractions of f in the apatite x site were low x f 0 18 were observed and warrant additional study to implement the exchange coefficient to determine the h2o content of a silicate melt at the time of apatite crystallization apatite based melt hygrometry the h2o abundance of the apatite an apatite melt exchange k d that includes oh either oh f or oh cl and the abundance of f or cl in the apatite and f or cl in the melt at the time of apatite crystallization are needed f if using the oh f k d and cl if using the oh cl k d to determine the h2o content of the parental melt the f or cl abundance of the parental melt is needed in place of the f or cl abundance of the melt at the time of apatite crystallization importantly however exchange coefficients may vary as a function of temperature pressure melt composition apatite composition and or oxygen fugacity so the combined effects of these parameters must be investigated further before exchange coefficients are applied broadly to determine volatile abundances of coexisting melt from apatite volatile abundances

solubility of anhydrite caso4 in nacl h2o solutions at high pressures and temperatures applications to fluid rock interaction anhydrite solubility in h2o nacl solutions was measured at 6 14 kbar 600 800 c and nacl mole fractions xnacl of 0 0 3 in piston cylinder apparatus solubilities were determined by weight changes of natural anhydrite in perforated pt envelopes confined with fluid in larger pt capsules in initially pure h2o at 10 kbar and 800 c caso4 concentration is low 0 03molal though much larger than at the same temperature and 1 kbar hematite buffered experiments showed slightly lower solubilities than unbuffered runs caso4 solubility increases enormously with nacl activity at 800 c and 10 kbar and xnacl of 0 3 caso4 molality is 200 times higher than with pure h2o whereas caso4 solubility in pure h2o decreases with rising t at low t and p the high p results show that anhydrite solubility increases with t at constant p at all xnacl investigated the effects of salinity and temperature are so great at 10 kbar that critical mixing between sulfate rich hydrosaline melts and aqueous salt solutions is probable at 900 c at xnacl 0 3 recent experimental evidence that volatile laden magmas crystallizing in the deep crust may evolve concentrated salt solutions could in light of the present work have important implications regarding such diverse processes as mount pinatubo type s rich volcanism high fo2 regional metamorphism and emplacement of porphyry cu mo ore bodies where anhydrite hematite alteration and fluid inclusions reveal the action of very oxidized saline solutions rich in sulfur

new contributions to the understanding of kiruna type iron oxide apatite deposits revealed by magnetite ore and gangue mineral geochemistry at the el romeral deposit chile abstract iron oxide apatite ioa or kiruna type deposits are an important source of iron and other elements including ree u ag and co the genesis of these deposits remains controversial with models that range from a purely magmatic origin to others that involve variable degrees of hydrothermal fluid involvement to elucidate the formation processes of this deposit type we focused on the chilean iron belt of cretaceous age and performed geochemical analyses on samples from el romeral one of the largest ioa deposits in northern chile we present a comprehensive field emission electron microprobe analysis fe empa dataset of magnetite apatite actinolite pyroxene biotite pyrite and chalcopyrite obtained from representative drill core samples two different types of magnetite grains constitute the massive magnetite bodies an early inclusion rich magnetite type i and a pristine inclusion poor magnetite type ii that usually appears as an overgrowth around type i magnetite high v 2500 2800 ppm and ti concentrations 80 3000 ppm and the presence of high temperature silicate mineral inclusions e g pargasite 800 1020 c determined by micro raman analysis indicate a magmatic origin for type i magnetite on the other hand high v 2300 2700 ppm and lower ti 50 400 ppm concentrations of pristine inclusion poor type ii magnetite indicate a shift from magmatic to hydrothermal conditions for this mineralization event furthermore the composition of primary actinolite ca and mg rich cores within type ii magnetite and the presence at depth of fluorapatite and high co ni ratios 1 10 of pyrite mineralization are consistent with a high temperature up to 840 c genesis for the deposit at shallow depths of the deposit the presence of pyrite with low co ni ratios

elastic properties of hydrate bearing sediments using effective medium theory accurate and detailed models of the seismic velocity structure of gas hydrate bearing sediments may be determined by careful analysis of controlled source seismic data however interpretation of these velocities in terms of hydrate saturation of the pore space has hitherto relied on semiempirical formulas and or simple effective medium theory we develop a rigorous theoretical scheme to relate the seismic properties of a clay rich hydrate bearing sediment to its porosity mineralogy microstructural features and hydrate saturation we consider separately the two possible end members for the distribution of hydrate in the pore space 1 hydrates are unconnected and located in the pore voids without appreciable grain contact and 2 connected hydrates are forming cement binding around the grains the scheme is transversely isotropic to allow for anisotropy due to alignment of clay platelets and is based on a combination of a self consistent approximation a differential effective medium theory and a method of smoothing for crystalline aggregates we have applied the scheme to lithological and seismic velocity data from ocean drilling program site 995 on the blake ridge southeastern u s continental margin to make estimates of the hydrate saturation it was found that the hydrates are probably unconnected and their volume concentration varies between approx 0 at 100 m below the seabed and approx 9 at 400 m depth just above the bottom simulating reflector if the clay platelet orientation distribution resembles the function we have used

the distribution and timing of molybdenite mineralization at the el teniente cu mo porphyry deposit chile this journal is published under the terms of green open access authors may post a copy of the accepted i e post peer review version of their paper https doi org 10 2113 econgeo 110 2 387 in a repository of their choice or to their personal website after the relevant embargo period has passed the embargo period will be 12 months from formal online publication

tracing the evolution and distribution of f and cl in plutonic systems from volatile bearing minerals a case study from the liujiawa pluton dabie orogen china fluorine and chlorine play an important role in magmatic differentiation hydrothermal alteration and related mineralization processes but tracing their evolution in magmatic and especially plutonic systems is not an easy task the f and cl in melts can be estimated from f and cl concentrations in minerals provided that partitioning between minerals and melts are constrained based on available partitioning models between mineral melt mineral fluid and melt fluid a set of equations has been derived to determine f and cl concentrations in melts from the compositions of amphibole biotite and apatite the new calculation procedure has been applied to a plutonic system the liujiawa pluton eastern dabie orogen china cl and f concentrations in amphiboles biotites and apatites from different rock types gabbronorite two pyroxene diorite clinopyroxene diorite and hornblende gabbro have been determined by electron microprobe most amphiboles show a negative correlation between log cl oh and mg number and a positive correlation between log f oh and a site occupation biotites from the gabbronorite and two pyroxene diorite show a slight positive correlation between log cl oh and mg which is however not the case for the clinopyroxene diorite apatites from all the samples are rich in f and show negative correlations between cl and f concentrations in our case study we demonstrate that the cl concentration in melt remains approximately constant at 1 000 2 000 ppm over the major crystallization interval but decreases strongly at near solidus temperatures as a result of fluid exsolution the f concentration in melt remains nearly constant at ca 2 000 3 000 ppm at high temperatures as well as near solidus conditions indicating that it is not largely affected by fluid exsolution because of its strongly preferred incorporation into melt interestingly the evolution of cl and f concentrations in melt with magmatic differentiation is similar to that determined in volcanic systems suggesting that the evolution of cl and f in melts during crystallization and late magmatic stages at depth plutonic systems is similar to that observed in volcanic systems during decompression and degassing

volatile variations in magmas related to porphyry cu au deposits insights from amphibole geochemistry duolong district central tibet ore forming fluid exsolution in a shallow magma chamber is a critical step in the formation of porphyry cu mo au deposits but one for which direct evidence is rarely found here ci abundance major trace element content and h isotope analysis of amphibole in diorite and barren granodiorite porphyry samples from the duolong porphyry epithermal cu au district are presented in order to reveal processes associated with fluid exsolution and magma evolution low al mg hornblende formed in ore bearing diorite at 750 860 degrees c and similar to 80 200 mpa on primitive mantle normalized diagrams these low al amphibole grains have slightly convex upward ree patterns with distinctly negative eu anomalies and negative anomalies in pb sr eu zr hf and ti anomalies suggesting crystallization from the same arc magma after plagioclase and magnetite crystallization a large variation in estimated melt h2o similar to 6 to 3 wt and ci content 0 09 0 38 wt as well as low 8d values 103 to 113 o indicate that the magma underwent large scale fluid exsolution contributing to the formation of duolong cu au mineralization additionally amphibole from a barren granodiorite porphyry shows two distinct populations distinguished by their a1 content this intrusion has low al amphibole mghornblende which formed at similar conditions to low al amphiboles in the diorite 790 870 degrees c and similar to 100 230 mpa whereas high al amphibole tschermakite formed at similar to 880 970 degrees c and degrees 210 400 mpa some high al amphibole phenocrysts have slightly convex ree patterns with no negative eu anomalies a depletion in nb zr and hf and positive sr ba and pb anomalies likely consistent with amphibole crystallization from more mafic basaltic andesitic melts low al amphibole in the granodiorite porphyry shows different compositional trends compared to those in the diorite suggesting that they crystallized from different magmas considering the evidence for mafic magma replenishment suggested by the positive correlation between al iv and mg values in high al amphibole the low al amphibole in the barren granodiorite porphyry likely crystallized from a new hybrid magma with mafic to intermediate felsic magma compositions meanwhile smaller variations in ci content 0 08 0 24 wt in low al amphibole was dominantly controlled by magma evolution shown by variable mg rather than fluid exsolution thus the low 8d values 102 to 122 o were likely inherited from evolved dioritic magmas that underwent fluid exsolution importantly the ci compositional variation of amphibole has a potential application as a powerful tool to identify ore bearing and barren intrusions within porphyry cu mo au deposits

quantitative characterization of gas hydrate bearing sediment using elastic electrical rock physics models abstract successful evaluation of reservoir resources in gas hydrate bearing sediments depends on the accurate estimation of reservoir parameters such as hydrate saturation porosity and clay content elastic and electrical measurements are affected by several rock and fluid properties and their joint interpretation can provide complementary information and improve the accuracy of reservoir characterization results in this work we propose a new rock physics inversion workflow based on 3d rock physics template of elastic and electrical attributes for the direct estimation of reservoir parameters we first conduct a quantitative analysis of the available well log data and core data to understand the morphology of gas hydrate within the marine sediment and choose the appropriate elastic rock physics model then we construct the 3d rock physics template by discretizing the 3d space of reservoir parameters and implementing the suitable elastic and electrical models to calculate the poisson s ratio p wave impedance and electrical resistivity for each combination of values of rock and fluid properties finally we superimpose the measurements on the templates and use a grid searching method to find the nearest gridded node to the data point and minimize the objective function of the mismatch between data and model predictions to investigate the feasibility of our proposed inversion scheme we test a rock physics model based on effective medium theory and a modified archie s equation and invert for reservoir parameters of gas hydrate bearing sediments at well 1250f and 1247b in hydrate ridge the good match between inversion results and core data suggests that the proposed inversion scheme is applicable to real data and allows combining elastic and electrical data for reservoir parameter estimation of gas hydrate bearing sediments

sediments with gas hydrates internal structure from seismic avo we interpret amplitude variation with offset avo data from a bottom simulating reflector bsr offshore florida by using rock physics based synthetic seismic models a previously conducted velocity and avo analysis of the in situ seismic data showed that the bsr separates hydrate bearing sediments from sediments containing free methane the amplitudes at the bsr are increasingly negative with increasing offset this behavior was explained by p wave velocity above the bsr being larger than that below the bsr and s wave velocity above the bsr being smaller than that below the bsr we use these avo and velocity results to infer the internal structure of the hydrated sediment to do so we examine two micromechanical models that correspond to the two extreme cases of hydrate deposition in the pore space 1 the hydrate cements grain contacts and strongly reinforces the sediment and 2 the hydrate is located away from grain contacts and does not affect the stiffness of the sediment frame only the second model can qualitatively reproduce the observed avo response thus inferred internal structure of the hydrate bearing sediment means that 1 the sediment above the bsr is uncemented and thereby mechanically weak and 2 its permeability is very low because the hydrate clogs large pore space conduits the latter explains why free gas is trapped underneath the bsr the seismic data also indicate the absence of strong reflections at the top of the hydrate layer this fact suggests that the high concentration of hydrates in the sediment just above the bsr gradually decreases with decreasing depth this effect is consistent with the fact that the low permeability hydrated sediments above the bsr prevent free methane from migrating upwards

interactive interpretation of 4d prestack inversion data using rock physics templates dual classification and real time visualization obtaining quantitative information from 4d seismic data about changes in the saturation and pressure in a reservoir due to production is very important for improved hydrocarbon recovery and management of the field however in heterogeneous reservoirs where the dynamic behavior varies spatially below the seismic resolution conventional 4d interpretation methods fail to track quantitative changes in individual lithologies the lack of information about the particular lithology to which a given 4d effect is connected can be detrimental to a general understanding of the reservoir and the forecast

amphibole and apatite insights into the evolution and mass balance of cl and s in magmas associated with porphyry copper deposits chlorine and sulfur are of paramount importance for supporting the transport and deposition of ore metals at magmatic hydrothermal systems such as the coroccohuayco fe cu au porphyry skarn deposit peru here we used recent partitioning models to determine the cl and s concentration of the melts from the coroccohuayco magmatic suite using apatite and amphibole chemical analyses the pre mineralization gabbrodiorite complex hosts s poor apatite while the syn and post ore dacitic porphyries host s rich apatite our apatite data on the coroccohuayco magmatic suite are consistent with an increasing oxygen fugacity from the gabbrodiorite complex to the porphyries causing the dominant sulfur species to shift from s2 to s6 at upper crustal pressure where the magmas were emplaced we suggest that this change in sulfur speciation could have favored s degassing rather than its sequestration in magmatic sulfides using available partitioning models for apatite from the porphyries pre degassing s melt concentration was 20 200 ppm estimates of absolute magmatic cl concentrations using amphibole and apatite gave highly contrasting results cl melt concentrations obtained from apatite 0 60 wt for the gabbrodiorite complex 0 2 0 3 wt for the porphyries seems much more reasonable than those obtained from amphibole which are very low 0 37 wt for the gabbrodiorite complex 0 10 wt for the porphyries in turn relative variations of the cl melt concentrations obtained from amphibole during magma cooling are compatible with previous petrological constraints on the coroccohuayco magmatic suite this confirms that the gabbrodioritic magma was initially fluid undersaturated upon emplacement and that magmatic fluid exsolution of the gabbrodiorite and the pluton rooting the porphyry stocks and dikes were emplaced and degassed at 100 200 mpa finally mass balance constraints on s cu and cl were used to estimate the minimum volume of magma required to form the coroccohuayco deposit these three estimates are remarkably consistent among each other ca 100 km3 and suggest that the cl melt concentration is at least as critical as that of cu and s to form an economic mineralization

constraints on magma degassing beneath the far southeast porphyry cu au deposit philippines k silicate alteration in the far southeast fse porphyry cu au introduction deposit formed at 1 4 ma concentric to dikes of quartz diorite magmas become saturated with volatile components as porphyry at 2 km paleodepth the hydrothermal system consisted they ascend in the crust and either erupt or crystallize of magmatic hypersaline liquid and vapor at 550 c and 50 at depth saturated magmas that remain at depth exsolve mpa lithostatic pressure advanced argillic alteration formed at an aqueous fluid that forms a hydrothermal system on the same time over the deposit at 1 km paleodepth from acidic separation from the magma chamber burnham 1979 condensates of the vapor at 1 3 ma k silicate alteration was although part of the exsolved fluid a low density vapor overprinted by 350 c magmatic liquid 5 wt nacl equiv may discharge to the surface from passively degassing at hydrostatic pressure sericite alteration and much of the cu au volcanoes hedenquist 1995 part will remain at depth mineralization formed at this later stage evolution of the magmatic and this dense residual magmatic liquid may be asfluid composition was simulated with a magma chamber cryssociated with hydrothermal mineralization in the portallization model homogeneous crystallization during early stage phyry ore environment hedenquist lowenstern convection is assumed whereas at 50 vol crystals the chamber 1994 becomes stagnant and crystallizes from rim to core over a narrow in this paper we use evidence from a porphyry ore crystallization interval the model calculation based on a magma deposit in the philippines to determine the composition chamber with 2 km thickness at 6 km depth 150 mpa and of the fluid that exsolved from the deeper parent magma 800 c saturated melt composition at 30 vol crystals 5 the evolving composition of the magmatic fluid at the wt h2o 0 2 wt cl and dd of 40 can reproduce the depth of the ore body can then be used to place constraints chemical and isotopic compositions of the early and late magmatic on the nature of the evolved magma chamber far below fluids the most critical factor controlling the compositional evolution the porphyry ore body this approach differs from that of the model hydrothermal system is the transition from convective of other studies where a portion of the parent magma to stagnant magma chamber crystallization there is also a sharp chamber is available to study directly e g at yerington decrease in the rate of fluid exsolution associated with this transition nevada dilles 1987 which can account for the thermal collapse of the fse porphyry the far southeast fse porphyry cu au deposit system from k silicate to sericite alteration and overlying lepanto epithermal cu au ore body are

finite element modelling of marine controlled source electromagnetic responses in two dimensional dipping anisotropic conductivity structures summary we present an adaptive finite element fe solution for the marine controlled source electromagnetic csem forward problem in 2 d dipping anisotropic conductivity structures our code is implemented on an unstructured triangular mesh which allows for arbitrary model geometries including bathymetry and dipping layers we have verified the fe code using a layered 1 d model with anisotropy for this model the fe algorithm provides accurate results the relative amplitude error between the analytical solution and numerical results for all electromagnetic components except hz for large offsets is less than 1 per cent and the error in phase is less than 0 5 we simulate the marine csem responses of a 2 d anisotropic model and the numerical results show that the csem fields are affected considerably by anisotropy in both the reservoir target and the surrounding sediment but to different extent

seismic investigations of a vent field associated with gas hydrates offshore vancouver island 1 a three dimensional seismic reflection survey was carried out over a gas hydrate field offshore vancouver island in the area of ocean drilling program leg 146 site 889 890 the area of investigation is located on the accretionary prism of the cascadia margin in water depths of 1200 1500 m several seismic blank zones were observed in the seismic data over a frequency range from 30 hz to 3 5 khz where the degree of blanking increases with seismic frequency time slices and selected horizon slices were used to define the spatial distribution of the blank zones the zones range from 80 m to several hundred meters in width one blank zone almost circular with a diameter of 400 m has a distinct seafloor expression it shows the characteristics of a mud carbonate mound and is probably associated with free gas expulsion hydrate was found at four sites with a piston corer within this blank zone at depths of 3 8 m below the seafloor we present a tectonic model that explains the blank zones to be a result of differential uplift along thrust faults the blank zones represent conduits for fluids and gas migrating upward blanking of the seismic energy is believed to be mainly the result of increased hydrate formation in lenses within the faults the blanking effect is enhanced locally because of scattering at carbonates formed at the seafloor

direct evolution of brine from a crystallizing silicic melt at the questa new mexico molybdenum deposit molybdenum mineralization in the southwest orebody at the questa deposit is associated with crystallization of aplite porphyry explosive brecciation and exsolution of magmatic hydrothermal fluids quartz k feldspar fluorophlogopite and molybdenite precipitated from exsolving aqueous fluids and cemented aplite porphyry and andesite wall rock clasts forming a magmatic hydrothermal breccia ore fluid inclusions in quartz in the breccia matrix trapped aqueous fluids that transported and precipitated molybdenum two fluid inclusion populations associated with molybdenite mineralization were identified the largest population commonly contains liquid vapor halite sylvite and one or more opaque daughter crystals these inclusions homogenize between 200 degrees and 500 degrees c and have a prominent mode at 360 degrees to 400 degrees c salinities vary from 31 to 57 wt percent nacl equiv low first ice melting temperatures suggest that additional fluid components possibly calcium or magnesium chlorides may be present approximately 80 percent of these inclusions homogenize by halite dissolution phase equilibria constraints require that these inclusions trapped fluids in the vapor absent field the remaining saline inclusions homogenize to liquid at temperatures above halite dissolution temperatures significantly the saline fluid did not coexist with a low density aqueous fluid a second population of inclusions contains fluids with salinities of 2 7 to 25 0 wt percent nacl equiv and homogenizes by vapor bubble disappearance vapor bubble expansion or critical behavior textural relationships and phase behavior during microthermometry indicate that these inclusions constitute a single population which formed as pressure and temperature fluctuated at near critical conditions pressure changes related to brecciation followed by crystallization and system resealing produced the observed fluids saline fluids were trapped as the system sealed following a major brecciation event these high salinity fluids were produced as the melt under pressure that increased from hydrostatic to lithostatic partitioned increasing amounts of chlorine into the exsolving aqueous fluid renewed fracturing and abrupt pressure decrease to hydrostatic conditions reduced the mass of chlorine partitioning to the exsolving fluid lower salinity fluids exsolved at near critical conditions and were trapped by inclusions that homogenize to liquid to vapor or by critical behavior the lack of cogenetic liquid and vapor rich fluid inclusions and phase equilibria constraints indicate that high salinity fluids or 57 wt nacl equiv were generated directly by the crystallizing magma and were not a product of aqueous fluid immiscibility

sulfur partitioning between apatite and melt and effect of sulfur on apatite solubility at oxidizing conditions the effect of sulfur on phosphorus solubility in rhyolitic melt and the sulfur distribution between apatite anhydrite melt and fluid have been determined at 200 mpa and 800 1 100 c via apatite crystallization and dissolution experiments the presence of a small amount of sulfur in the system 0 5 wt s under oxidizing conditions increases the solubility of phosphorus in the melt probably due to changing calcium activity in the melt as a result of the formation of ca s complexing cations apatite solubility geothermometers tend to overestimate temperature in ca poor s bearing system at oxidizing conditions in crystallization experiments the sulfur content in apatite decreases with decreasing temperature and also with decreasing sulfur content of the melt the sulfur partition coefficient between apatite and rhyolitic melt increases with decreasing temperature kdsapatite melt 4 5 14 2 at t 1 100 900 c under sulfur undersaturated conditions no anhydrite the sulfur partition coefficient is lower in anhydrite saturated melt 8 at 800 c than in anhydrite undersaturated melt suggesting that kdsapatite melt depends not only on the temperature but also on the sulfur content of the melt these first results indicate that the sulfur content in apatite can be used to track the evolution of sulfur content in a magmatic system at oxidizing conditions

magmatic precursors of hydrothermal fluids at the rio blanco cu mo deposit chile links to silicate magmas and metal transport in most porphryr systems the obscuring effects of hydrothermal processes and subsequent alteration along with limited exposure of source rocks preclude a detailed understanding of how and where metals and volatiles were derived however in this study we examine melt inclusions which have escaped alteration and that sampled all of the phases coexisting in the magma in late and postmineral rhyolitic units from the rio blanco cu mo deposit chile these inclusions demonstrate the existence of a volatile rich melt the exsolution from it of an aqueous volatile rich phase initially as melt vapor bubble emulsions and the disruption of these emulsions into melt and primary magmatic fluids trapping of these emulsions may explain the occurrence of melt inclusions containing widely varying proportions of melt and aqueous fluid found at rio blanco we demonstrate the sequestering of metals into the exsolved volatile phases and the derivation from these of possible ore forming hydrothermal fluids with particular reference to the implications for metal transport melt inclusions show differences between adjacent comagmatic intrusions that may be directly related to the extent of mineralization of the respective bodies in one of the rio blanco postmineral rhyolite bodies melt inclusions show exsolution of the volatile rich phase but only minor evidence of trapping of a metal rich vapor in contrast inclusions from an adjacent late mineral rhyolite body show similar volatile phase exsolution but also provide evidence of ponding of metal rich hydrothermal fluids during the final stages of cooling

magmatic salt melt and vapor extreme fluids forming porphyry gold deposits in shallow subvolcanic settings the recently discovered biely vrch deposit in the western carpathian magmatic arc is the most extreme example of a porphyry gold deposit being practically free of copper molybdenum or any other sulfide minerals microanalytical data on fluid inclusions in quartz veinlets including a characteristic type of banded veinlets show that this deposit formed from nearly anhydrous fe k na cl salt melts containing 10 ppm au coexisting with hydrous vapor of very low density this exceptional fluid evolution required an fe rich dioritic source magma that was emplaced at shallow subvolcanic depth 3 5 km directly exsolving a hypersaline liquid and magmatic vapor at high temperature 850 c during ascent to the level of the porphyry intrusion 0 5 1 km fluid expansion at high temperature but low pressure led to halite precipitation and further water loss to the vapor generating an increasingly fe k rich salt melt that transported high concentrations of au but negligible cu into the fractured porphyry stock the low sulfur fugacity resulting from fluid expansion suppressed precipitation of sulfide explaining the gold only enrichment in this globally recurring but rare type of gold ore

primary magmatic biotite in granitoid intrusions associated with late mesozoic jinchanggouliang erdaogou lode gold deposits north china craton linkage to gold mineralization abstract the late mesozoic jinchanggouliang and erdaogou lode gold deposits in the central segment of the northern north china craton are mainly hosted in late archaean metamorphic rocks of the jianping formation and jurassic volcanic sedimentary rocks these deposits are spatially and temporally associated with a series of i type granitoid intrusions i e the 128 136 ma duimiangou granodiorite complex with a massive margin and a porphyritic center at jinchanggouliang the 161 4 1 1 ma loushang quartz diorite intrusion and numerous syenite porphyry dykes 160 9 1 0 ma at erdaogou and the 227 217 ma xitaizi monzogranite batholith compositions of primary magmatic biotite in these granitoid intrusions have been used to investigate the nature of granitoid magmas and the evolution of magmatic processes and to identify possible linkages between gold mineralization and granitoid magmatism all primary magmatic biotite grains are mg rich in composition xmg mg mg fe 0 41 0 69 the cl contents of biotite 0 09 0 42 wt in the loushang quartz diorite and the duimiangou massive granodiorite correlate negatively with xmg and are consistent with the mg cl avoidance rule the cl contents of biotite 0 01 0 14 wt in the duimiangou porphyritic granodiorite syenite porphyry and xitaizi monzogranite on the other hand remain relatively constant and may be affected by multiple variables such as cl rich fluids and subtle changes in temperature halogen fugacity of the parental magma calculated from biotite shows that the duimiangou granodiorite complex at jinchanggouliang and syenite porphyry dykes at erdaogou have the log fhf fhcl ranges of 0 71 to 0 27 and 2 16 to 1 08 respectively and have similar log fh2o fhcl values from 3 53 to 4 23 oxygen fugacities logfo2 calculated from biotite equilibria for the duimiangou granodiorite complex and syenite porphyry dykes are 13 7 to 7 2 straddling on the nickel nickel oxide and hematite magnetite buffers the xitaizi monzogranite and the loushang quartz diorite have lower log fo2 values from 14 9 to 12 4 between the nickel nickel oxide and hematite magnetite buffers the duimiangou granodiorite complex and syenite porphyry dykes with high oxygen fugacities are similar to oxidized magmas associated with porphyry cu mo au deposits these results suggest that multiple episodes of i type granitoid magmas in the study area were rich in cl and high in oxygen fugacity especially those associated with the duimiangou granodiorite complex and syenite porphyry dykes the i type melts represented by the duimiangou granodiorite complex and syenite porphyry dykes as well as their related cl rich oxidizing fluids were likely efficient in dissolving transporting and precipitating gold for the formation of the jinchanggouliang and erdaogou lode gold deposits

an introduction to marine controlled source electromagnetic methods for hydrocarbon exploration early development of marine electromagnetic methods dating back about 80 years was driven largely by defense military applications and use for these purposes continues to this day deepwater frequency domain electric dipole dipole controlled source electromagnetic csem methods arose from academic studies of the oceanic lithosphere in the 1980s and although the hydrocarbon exploration industry was aware of this work the shallow water environments being explored at that time were not ideally suited for its use low oil prices and increasingly successful results from 3d seismic methods further discouraged investment in costly alternative geophysical data streams these circumstances changed in the late 1990s when both statoil and exxonmobil began modeling studies and fieldtrials of csem surveying in deep water around 1000 m or deeper specifically for characterizing the resistivity of previously identified drilling targets trials offshore angola in 2000 2002 by both these companies showed that

partitioning behavior of chlorine and fluorine in the system apatite silicate melt fluid the partitioning behavior of cl among apatite mafic silicate melt and aqueous fluid and of f between apatite and melt have been determined in experiments conducted at 1066 to 1150 c and 199 205 mpa the value of dclapatite melt wt fraction of cl in apatite cl in melt 0 8 for silicate melt containing less than 3 8 wt cl at higher melt cl contents small increases in melt cl concentration are accompanied by large increases in apatite cl concentration forcing dclapatite melt to increase as well melt containing less than 3 8 cl coexists with water rich vapor that containing more cl coexists with saline fluid the salinity of which increases rapidly with small increases in melt cl content analogous to the dependency of apatite composition on melt cl content this behavior is due to the fact that the solubility of cl in silicate melt depends strongly on the composition of the melt particularly its mg ca fe and si contents once the melt becomes saturated in cl additional cl must be accommodated by coexisting fluid apatite or other phases rather than the melt itself because cl solubility depends on composition the cl concentration at which dclapatite melt and dclfluid melt begin to increase also depends on composition the experiments reveal that dfapatite melt 3 4 in contrast to cl the concentration of f in silicate melt is only weakly dependent on composition mainly on melt ca contents so dfapatite melt is constant for a wide range of composition the experimental data demonstrate that the fluids present in the waning stages of the solidification of the stillwater and bushveld complexes were highly saline the cl rich apatite in these bodies crystallized from interstitial melt with high cl f oh ratio the latter was generated by the combined processes of fractional crystallization and dehydration by its reaction with the relatively large mass of initially anhydrous pyroxene through which it percolated

mineral chemistry and isotopic composition of magmatic re equilibrated and hydrothermal biotites from darreh zar porphyry copper deposit kerman southeast of iran abstract the darreh zar porphyry copper in the southeastern part of the urumieh dokhtar magmatic belt developed as a consequence of hydrothermal alteration related to the darreh zar granodioritc porphyry stock intruded into mafic volcanic rocks hydrothermal alteration and cu mo mineralization are focused on the darreh zar porphyry pluton belonging to miocene time and the neighboring basaltic country rocks a core zone of potassic alteration is enclosed by a peripheral zone of chlorite sericite sericitic argillic and propylitic alteration judging by petrographic features as well as chemical composition the biotites studied display variable size color and shape and occur as magmatic m re equilibrated r and hydrothermal h types the m and r type biotites are found in the darreh zar porphyry and the h type formed during potassic alteration within the darreh zar porphyry and the volcanic host rocks as well the hydrothermal biotites are characterized by the highest amounts of al 2 o 3 and k 2 o whereas the magmatic types are hosted by high level of tio 2 up to 4 38 wt x mg values vary between 0 31 and 0 61 which is increased from m to r biotites then decreased toward low temperature potassic alteration zone fluorine and chlorine contents from biotite types also vary between 0 07 to 0 56 wt and 0 14 to 0 38 wt respectively these values change to 2 94 to 2 15 wt and 3 6 to 4 4 wt for iv f and iv cl respectively in all types of biotites positive correlation is observed between x mg al 2 o 3 na 2 o k 2 o bao and f but with feo and cl it is negative the tio 2 content clearly decreases from the m to r and h type average 3 98 2 9 and 2 4 wt respectively a direct relation may be noted between mg and oxygen fugacity log f h 2 o f hf and log f h 2 o f hcl values range from 6 24 to 5 46 and 4 49 to 4 12 wt respectively oxygen fugacity increases during formation of re equilibrated biotites but it decreases in the course of potassic alteration crystallization temperatures range from 600 to 650 c 550 to 600 c and 450 to 550 c for magmatic re equilibrated and hydrothermal biotites respectively the m biotites from darreh zar have the d values of 89 to 101 and the calculated d values of the aqueous fluids 66 to 78 in equilibrium with the biotites are consistent with a large component of magmatic fluid which shows similarities with the biotite originated from the primary mantle source the 18 o also varies between 7 4 to 8 2 for fluids in equilibrium with biotites the obtained m biotite data from darreh zar porphyry indicates that there is no clear correlation between d values fe and mg contents but for d values al and fe 3 fe 2 some affinities were observed the isotopic data indicate that m biotites are formed at high temperature 620 20 c from fluids with the highest 18 o h 2 o 7 8 0 4 in comparison with the biotites from some other copper porphyries

sulfur evolution of oxidized arc magmas as recorded in apatite from a porphyry copper batholith uniformly sulfur rich cores abruptly zoned to sulfur poor rims 1 to 0 2 wt so3 in apatite from the yerington batholith nevada indicate that early magma that is crystal poor oxidizing and sulfate rich evolved to sulfate poor magma via crystallization of anhydrite a mineral observed in magmas from pinatubo and el chichon we predict that the characteristic zonation to sulfur poor rims of apatite in the yerington batholith is common in other oxidized hydrous calc alkaline magmas and can be used to track cryptic anhydrite saturation as well as to monitor sulfur evolution sulfate rich arc magmas such as yerington magmas may crystallize to produce hydrothermal fluids rich in chlorine copper and sulfur and porphyry copper ores

integrated analysis of well logs and seismic data to estimate gas hydrate concentrations at keathley canyon gulf of mexico abstract accurately detecting and quantifying gas hydrate or free gas in sediments from seismic data require downhole well log data to calibrate the physical properties of the gas hydrate free gas bearing sediments as part of the gulf of mexico joint industry program a series of wells were either cored or drilled in the gulf of mexico to characterize the physical properties of gas hydrate bearing sediments to calibrate geophysical estimates and to evaluate source and transport mechanisms for gas within the gas hydrates downhole acoustic logs were used sparingly in this study because of degraded log quality due to adverse wellbore conditions however reliable logging while drilling lwd electrical resistivity and porosity logs were obtained to tie the well log information to the available 3 d seismic data in this area a velocity log was calculated from the available resistivity log at the keathley canyon 151 2 well because the acoustic log or vertical seismic data acquired at the nearby keathley canyon 151 3 well were either of poor quality or had limited depth coverage based on the gas hydrate saturations estimated from the lwd resistivity log the modified biot gassmann theory was used to generate synthetic acoustic log and a synthetic seismogram was generated with a fairly good agreement with a seismic profile crossing the well site based on the well log information a faintly defined bottom simulating reflection bsr in this area is interpreted as a reflection representing gas hydrate bearing sediments with about 15 saturation overlying partially gas saturated sediments with 3 saturation gas hydrate saturations over 30 40 are estimated from the resistivity log in two distinct intervals at 220 230 and 264 300 m below the sea floor but gas hydrate was not physically recovered in cores it is speculated that the poor recovery of cores and gas hydrate morphology are responsible for the lack of physical gas hydrate recovery

remelting of neoproterozoic relict volcanic arcs in the middle jurassic implication for the formation of the dexing porphyry copper deposit southeastern china article i nfo the dexing copper deposit in southeastern china is a typical non arc porphyry deposit the origin of which has been a topic of debate for several decades here we present new results from u pb geochronology whole rock chemistry and sr nd hf o isotopic investigations on the ore forming granodioritic porphyry la icpms zircon u pb data suggest that the granodioritic porphyry was formed in the middle jurassic ca 172 5 ma probably associated with lithospheric thinning driven by either sub continental lithospheric mantle delami nation or asthenospheric upwelling the porphyry displays both arc like and adakitic trace element signa tures the adakitic features suggest that hree heavy rare earth elements rich minerals such as garnet and hornblende in the absence of plagioclase resided in the source region the arc like signatures are broadly comparable with those of the proximal neoproterozoic island arc rocks including the keratophyre from shuangxiwu group and associated granitoids indicating a potential genetic relationship the porphyry has chondritic end t of 0 28 to 0 25 and radiogenic ehf t of 2 to 7 and correspondingly uniform two stage depleted mantle nd model ages of 940 980 ma and hf model ages of 800 1100 ma mean 920 ma on nd and hf isotopic evolution diagrams these values are markedly similar to those of the adjacent neoproterozoic arc rocks when calculated forward to the mid jurassic zircons of the porphyry show mantle like oxygen isotope characters with 18 o values clustering in the range of 4 7 5 9 similar to the values for the neoproterozoic arc rocks mentioned above the geochemical and isotopic features recorded in our study suggest mantle derived magmas with no significant supracrustal input for the source of the por phyry with regard to the source of the cu ore we consider a model involving the remelting of sulfide bearing arc related lower crustal source furthermore the occurrence of a neoproterozoic vms volcanic massive sulfide type copper deposit the pingshui cu deposit in the shuangxiwu group might suggest that the lower crustal rocks related to a neoproterozoic relict island arc provided the source for copper during a second stage melting event we propose a new geodynamic model for the dexing porphyry cu deposit which envis ages that the sulfide bearing arc lower crustal rocks were generated during oceanic slab subduction in the early neoproterozoic the remnants of which were preserved at the crust mantle boundary subsequently in the middle jurassic these rocks were heated by asthenospheric upwelling and remelted to produce fertile magmas the magmas ascended along the northeast jiangxi fault and intruded into the jiuling terrane where cu precipitation occurred upon subsequent magma cooling and fluid exsolution

seismic velocities for hydrate bearing sediments using weighted equation a weighted equation based on the three phase time average and wood equations is applied to derive a relationship between the compressional wave p wave velocity and the amount of hydrates filling the pore space the proposed theory predicts accurate p wave velocities of marine sediments in the porosity range of 40 80 and provides a practical means of estimating the amount of in situ hydrate using seismic velocity the shear s wave velocity is derived under the assumption that the p to s wave velocity ratio of the hydrated sediments is proportional to the weighted average of the p to s wave velocity ratios of the constituent components of the sediment in the case that all constituent components are known a weighted equation using multiphase time average and wood equations is possible however this study showed that a three phase equation with modified matrix velocity compensated for the clay content is sufficient to accurately predict the compressional wave velocities for the marine sediments this theory was applied to the laboratory measurements of the p and s wave velocities in permafrost samples to infer the amount of ice in the unconsolidated sediment the results are comparable to the results obtained by repeatedly applying the two phase wave scattering theory the theory predicts that the poisson s ratio of the hydrated sediments decreases as the hydrate concentration increases and the porosity decreases in consequence the amplitude versus offset avo data for the bottom simulating reflections may reveal positive negative or no avo anomalies depending on the concentration of hydrates in the sediments

estimating the amount of gas hydrate and free gas from marine seismic data marine seismic data and well log measurements at the blake ridge offshore south carolina show that prominent seismic bottom simulating reflectors bsrs are caused by sediment layers with gas hydrate overlying sediments with free gas we apply a theoretical rock physics model to 2 d blake ridge marine seismic data to determine gas hydrate and free gas saturation high porosity marine sediment is modeled as a granular system where the elastic wave velocities are linked to porosity effective pressure mineralogy elastic properties of the pore filling material and water gas and gas hydrate saturation of the pore space to apply this model to seismic data we first obtain interval velocity using stacking velocity analysis next all input parameters to the rock physics model except porosity and water gas and gas hydrate saturation are estimated from geologic information to estimate porosity and saturation from interval velocity we first assume that the entire sediment does not contain gas hydrate o

apatite in igneous systems apatite is a minor but ubiquitous mineral in most igneous rocks although the modal proportion of apatite in common rocks is generally low it can reach high concentrations in enclaves cumulates and other rocks of low abundance i e rocks that constitute a small volume of the crust and mantle e g nelsonites the presence of apatite in most rocks is due not only to its low solubility in naturally occurring melts and aqueous solutions but also to the limited ability of common rock forming minerals to accept the amount of phosphorus that occurs in most rocks into their structure in this paper we will discuss some aspects of the occurrence texture composition physical chemistry and petrogenetic significance of apatite in felsic rocks i e andesite to rhyolite and their plutonic analogs in mafic i e basalts and related rocks and plutonic analogs and ultramafic rocks of the earth s crust and mantle fluorapatite is by far the most common member of apatite family found in igneous rocks however most natural fluorapatite contains some chlorine and hydroxyl as well and these constituents can attain high concentrations in some cases the other halogens bromine and iodine also occur in apatite but their concentrations are much lower than chlorine and fluorine many cations commonly substitute for calcium and phosphorus in apatite however they rarely reach concentrations that warrant the definition of a separate mineral species apatite can be described by the general formula a5 xo4 3z following sommerauer and katz lehnert 1985 the a site accommodates large cations e g ca2 sr2 pb2 ba2 mg2 mn2 fe2 ree3 eu2 cd2 na pan and fleet ch 2 in this volume and comprises two sites that exhibit vii fold

petrography and mineral chemistry of the composite deboullie pluton northern maine u s a implications for the genesis of cumo mineralization abstract biotite and apatite mineral chemistry particularly halogen abundances and ratios are used to investigate the relation of the two contrasting parts of the deboullie composite pluton syenite granodiorite located in northern maine biotite mineral chemistry helps to classify the weakly developed porphyry style mineralization cu mo associated with syenitic rocks of the deboullie pluton unmineralized syenite consists of k feldspar plagioclase quartz biotite hornblende clinopyroxene and minor amounts of apatite titanite magnetite zircon and allanite biotite and apatite occur within the matrix of the rocks and within small multiphase inclusions hosted by clinopyroxene the inclusions are interpreted to be crystallized melt inclusions rather than solid inclusions that were trapped by clinopyroxene during growth the multiphase inclusions consist of k feldspar quartz biotite apatite magnetite the f contents of biotite display a strong positive correlation with the phlogopite component or xphl xphl mg sum octahedral cations biotites from the multiphase inclusions have higher f contents and higher values of f f cl oh and xphl than biotites in the matrix that presumably formed later during crystallization and or re equilibrated with late stage fluids contents of tio2 largely overlap for the inclusion and matrix biotite apatite compositions plot within the fluorapatite field f f cl oh 0 57 0 99 apatites in the multiphase inclusions have higher cl contents than apatites in the matrix or those enclosed in biotite biotite apatite geothermometry for the multiphase inclusions yields magmatic or near magmatic temperatures 725 850 c biotite apatite pairs outside the inclusions yield temperatures that range from near magmatic 600 775 c to much lower x f x cl and xphl was used to infer hf hcl fugacity ratios in associated hydrothermal fluids and indicates that biotite from the deboullie pluton is strikingly similar to biotite from the porphyry cu deposit at santa rita new mexico but distinctly different from biotite from the porphyry mo deposit at henderson colorado the assemblage quartz magnetite titanite implies an oxidation state for the deboullie pluton well above the quartz magnetite fayalite buffer which is also consistent with magmas associated with porphyry cu deposits on a regional scale biotite compositions from granitic plutons in maine do not vary in a systematic manner this implies that biotite compositions no longer directly reflect source compositions finally biotite and apatite compositions of the syenite and granodiorite are different compositional ranges in the granodiorite are more restricted than those in the syenite this provides evidence that the two parts of this composite pluton had different origins and are not related by crystal fractionation

seismic velocity increase and deep sea gas hydrate concentration above a bottom simulating reflector on the northern cascadia continental slope the amount of gas hydrates in the accretionary wedge sediments of the northern cascadia subduction zone off vancouver island has been estimated from multichannel seismic mcs and ocean drilling program odp data derailed semblance velocity analyses and full waveform inversion of mcs data combined with previously published odp sites 889 890 sonic log and vertical seismic profile vsp data show that sediment velocities increase downward more rapidly than the no hydrate no gas reference profile from about 1500 m s near the seafloor to a maximum of 1900 m s just above the bottom simulating reflector bsr at a subbottom depth of 224 m immediately below the bsr the mcs velocities drop to 1700 m s a low velocity of 1500 m s from the vsp data probably represents a thin layer 20 m containing free gas the difference between the reference and observed velocities is used to estimate hydrate concentration which reaches a maximum of 20 30 of the pore space above the bsr a simple interpretation of the drill core chlorinity dilution data at the odp site yields a similar hydrate concentration of 35 the estimated hydrate concentration with subbottom depth represents about 7 m 3 of hydrate per square meter of seafloor the total methane gas at stp including hydrate above the bsr and the small amount of free gas below is about 800 m 3 per square meter of seafloor or 200 tcf trillion cubic feet on the vancouver island continental slope application of the same method in the blake bahama region of the eastern u s margin indicates that the velocity enhancement and inferred hydrate concentration are very similar

gas hydrates saturation using geostatistical inversion in a fractured reservoir in the krishna godavari basin offshore eastern india a reservoir of gas hydrates filling fractures was discovered in the krishna godavari kg basin during the indian national gas hydrate program nghp expedition 01 at site nghp01 10 the existing methods for estimating gas hydrate saturation from seismic data rely on establishing an empirical relation between acoustic impedance and density porosity from well logs assuming isotropic pore filling gas hydrate this method however yields a misleading saturation for fractured clay dominated sediments here we present a methodology to estimate gas hydrate saturation from seismic data based on geostatistical inversion it integrates the verticals detail of well log data with the lateral details from seismic data to produce highly detailed estimates of gas hydrate saturation first gas hydrate saturation is calculated from p wave velocities assuming anisotropic distribution at the well site then probability density functions pdfs between acoustic impedance and the calculated gas hydrate saturation at the well site are analyzed a markov chain monte carlo method is employed to integrate well logs with the seismic data to produce acoustic impedance finally crossplots and histograms at the well site are used to estimate gas hydrate saturations along the seismic line from inverted acoustic impedance the spatial distribution of gas hydrate varies both laterally and vertically along the line with an average saturation of 22 5 the estimate matches reasonably with the value at the wells crown copyright c 2013 published by elsevier ltd all rights reserved

can economic porphyry copper mineralization be generated by a typical calc alkaline melt numerical simulation of chlorine and copper partitioning between a crystallizing melt and exsolving aqueous fluids indicates that typical calc alkaline magmas contain sufficient copper chlorine and water to produce economic porphyry copper mineralization neither an elevated copper content in the magma nor an additional large volume of magma are required to provide metals or volatiles the most important variables that determine the volume of melt necessary to produce sufficient copper are the degree of compatible behavior displayed by copper the ratio of initial water in the melt to the water saturation level and the initial chlorine water ratio of the melt the absolute values for initial water in the melt and water content at saturation are relatively unimportant in determining the required melt volume the bulk salinity of the exsolved fluid may vary from 2 0 wt nacl to saturation levels 84 wt nacl at 700 c indicating that boiling is not necessary to produce high salinity brines at appropriate p t xnacl conditions the magmatic aqueous fluid separates into a saline liquid which transports most of the copper and a low salinity vapor the salinities of the two immiscible phases are governed by the p t conditions while the bulk fluid salinity determines the mass fractions of liquid and vapor formed pressure quenching causes rapid crystallization of the aplitic groundmass in porphyritic rocks associated with copper mineralization and significantly reduces the amount of chlorine and copper partitioning to the aqueous fluid this results in abrupt and possibly large reductions in fluid salinity and causes copper to become concentrated in the melt as copper is transported from the melt by the earliest exsolving fluids in deep 2 0 kbar systems and by late exsolving fluids in shallow 0 5 kbar systems the relative timing of pressure quenching aplite formation and fluid transport of copper from the melt can vary significantly in systems produced under different confining pressures model results incorporating petrologic constraints determined for yerington nevada are in good agreement with observed mineralization