the origin and evolution of skarn forming fluids from the phu lon deposit northern loei fold belt thailand evidence from fluid inclusion and sulfur isotope studies abstract the phu lon skarn cu au deposit is located in the northern loei fold belt lfb thailand it is hosted by devonian volcano sedimentary sequences intercalated with limestone and marble units intruded by diorite and quartz monzonite porphyries phu lon is a calcic skarn with both endoskarn and exoskarn facies in both skarn facies andradite and diopside comprise the main prograde skarn minerals whereas epidote chlorite tremolite actinolite and calcite are the principal retrograde skarn minerals four types of fluid inclusions in garnet were distinguished 1 liquid rich inclusions 2 daughter mineral bearing inclusions 3 salt saturated inclusions and 4 vapor rich inclusions epidote contains only one type of fluid inclusion liquid rich inclusions fluid inclusions associated with garnet prograde skarn stage display high homogenization temperatures and moderate salinities 421 6 468 5 c 17 4 23 1 wt nacl equiv by contrast fluid inclusions associated with epidote retrograde skarn stage record lower homogenization temperatures and salinities 350 9 399 8 c 0 5 8 wt nacl equiv these data suggest a possible mixing of saline magmatic fluids with external dilute fluid sources e g meteoric fluids as the system cooled some fluid inclusions in garnet contain hematite daughters suggesting an oxidizing magmatic environment sulfur isotope determinations on sulfide minerals from both the prograde and retrograde stages show a uniform and narrow range of 34 s values 2 6 to 1 1 34 s suggesting that the ore forming fluid contained sulfur of orthomagmatic origin overall the phu lon deposit is interpreted as an oxidized cu au skarn based on the mineralogy and fluid inclusion characteristics

simulation and analysis of 1991 u s geological survey refraction data from the new madrid seismic zone two orthogonal wide aperture seismic refraction lines were acquired in the new madrid seismic zone by the u s geological survey in 1991 these n s and e w oriented lines cross the blytheville arch and adjacent portions of the reelfoot rift ten shots were fired along the e w line eight shots were fired along the n s line iterative numerical modeling including scattering and viscoelasticity has been performed for all shots on both lines using a new eighth order staggered grid two dimensional finite difference solution based on superposition of relaxation mechanisms the main features in the data can be explained by the existence of a strong 15 km wide low velocity cap lying beneath the center of the blytheville arch between 1 5 and 2 5 km depth the data do not allow estimation of its extent along the axis of the arch but it is at least 30 km long and appears to become less prominant toward the southwest the arch itself has a low velocity background that extends to at least 5 km depth an additional low velocity layer the elvins shale lies generally between 3 and 4 km depth is upwarped at the edges of the arch and thins toward the edges of the reelfoot rift there is no evidence for anomalously low intrinsic q but the data may be interpreted to indicate strong local scattering that occurs west of the low velocity cap of the blytheville arch at depths that are similar to and slightly shallower than the cap additional strong scattering occurs at the western edge of the reelfoot rift an alternative interpretation attributes the apparent scattering at the blytheville arch to instrument noise

mineral deposit model for porphyry skarn polymetallic copper deposits in tongling ore dense district of middle lower yangtze valley metallogenic belt according to field investigations of major ore deposits along the middle lower yangtze valley metallogenic belt and a detailed study of the data available the authors put forward a mineral deposit model based on the tongling ore district the largest ore cluster in the belt the porphyry skarn cu au mo ore bodies developed around the roof pendants of the high potash calc alkaline granitoids have experienced strong fractionation since there are extensively distributed carboniferous permian carbonates both calcic and magnisian skarn deposits have most important economic significance as components of the porphyry skarn system the skarn and vein like gold deposits and veinlike pb zn ag deposits are distributed outward gradually from the intrusion and the porphyry skarn cu au mo ore deposits because the middle lower yangtze valley belt was a foreland basin during the collision between the south china massif and the north china craton and subsequently a depression belt during the post collision with a lot of decollement and detachment faults especially along the discontinuity boundary which occupied a large space the large ore bodies must have been formed along the large space such as the major ore body in the xinqiao s cu au polymetallic mine the strong retrograde alteration consisting of actinolite tremolite chlorite epidote or serpentine mg chlorite talc tremolite with typical wrigglite and laminated structures along either fractures or discordant boundary replaced the skarn at the contact with the granitoid intrusion there are also a lot of manto or stratabound skarn ore bodies replacing some carbonate layers of different ages this paper also indicates the correct utilization of the model together with some types of geochemical and geophysical technologies for further prospecting in similar tectonic settings

a comparative study of wollastonite skarn genesis in the central metasedimentary belt southeastern ontario canada abstract potentially economic wollastonite rich skarns are widespread in the central metasedimentary belt of southeastern ontario canada their genesis is evaluated through a comparative study of the platinova skarn ca 4 mt grading 35 wollastonite hosted by greenschist facies marble in the elzevir terrane the olden skarn ca 2 8 mt 35 in amphibolite facies marble of the sharbot lake terrane and the st lawrence skarn ca 9 mt 41 in granulite facies strata of the frontenac terrane the protolith for all of the wollastonite skarns was calcitic marble locally containing impurities but dolomitic marble may have been present at the st lawrence skarn each skarn is contiguous with an intrusive complex ranging from gabbro to granite in composition and displaying megascopic fabrics indicative of magma commingling and mixing the plutons are however of different ages and exhibit different geochemical characteristics in each skarn wollastonite is associated with varying proportions of diopside hedenbergite and grossular andradite skarn development is ascribed to the incursion of magmatogene silica rich co2 poor xco2 between 0 1 and 0 3 fluids rather than to regional metamorphism and pressures varying between 200 mpa at platinova and 350 mpa at olden at temperatures ca of 500 to 650 c the mountain grove pluton has an u pb zircon age of 1153 2 ma hornblende and biotite from the same sample gave 40ar 39ar plateau dates of 1058 14 and 1047 4 ma respectively and the olden skarn has been dated at 1074 5 ma 40ar 39ar phlogopite these 40ar 39ar dates are interpreted to record resetting by the contiguous 1070 ma mclean pluton u pb on titanite and 40ar 39ar on amphibole separates from the st lawrence skarn yield 1147 ca 8 and 1159 6 ma dates respectively similar to the u pb badelleyite age of the adjacent 1167 2 ma leo lake pluton the age similarities between the skarns and the adjacent plutonic rocks are permissive evidence for a genetic link evidence of magma mixing and commingling in all the plutons contiguous with the wollastonite skarns may indicate that the concentration and egress of magmatogene brines at pressures locally attending 400 mpa was facilitated by thermal and compositional perturbation in the parental magma chambers

granite and gabbrodiorite associated skarn deposits of nw iran abstract field and laboratory studies show that there are two types of skarn deposits in nw iran granite associated type i and gabbrodiorite associated type ii granite associated deposits are accompanied by cu and fe mineralisation whereas mn and fe are the main ore metals in gabbrodiorite associated skarn deposits there are some differences in the mineralogy of these skarn deposits bixbyite piemontite and cr bearing garnet are found only in gabbrodiorite associated skarns whereas idocrase occurs only in granite associated deposits type ii skarns show exoskarn features whereas some type i skarns have developed endoskarn as well evidence of boiling of hydrothermal fluid can be seen in both types and seems to be a common mechanism of mineral deposition gabbrodiorite associated skarns show higher f o 2 than granite associated deposits based on mineralogical and textural evidence mineralisation in both groups has started from about 550 c early formed anhydrous minerals have begun to be replaced by hydrous minerals from about 400 c it seems that due to low fluid content in the gabbrodioritic magma heated meteoritic water in the surrounding volcanoclastic and tuffaceous rocks was the main source of hydrothermal solution in the gabbrodiorite associated skarn system

paragenetic zoning and genesis of cu zn fe pb as sulfide skarn ores in a proterozoic rift basin gruvaasen western bergslagen sweden silicate sulfide and oxide assemblages indicate three stages of alteration and mineralization during stage 1 potassic alteration and zonal precipitation of sulfides occurred basic sills and dikes close to the ores underwent strong potassic alteration and slight sulfide mineralization and were altered to skarn metatuffites underwent potassic alteration and sulfide mineralization and were altered to skarn and dolomitic limestones underwent dedolomitization and sulfide mineralization and were altered to skarn during stage 2 the potassically altered tuffites were replaced by infiltrational metasomatic amphibole skarns which were subsequently replaced by pyroxene forsterite skarns at temperatures of about 550 degrees c the late stage 2 pyroxene skarns are reaction skarns that are largely synkinematic with respect to boudinage of sulfide skarn layers and development of foliation in the marbles amphibole and pyroxene skarn relationships suggest a telescoping effect during the formation of the skarns silicate assemblages in metatuffites indicate metamorphic pressures of about 2 5 kb during stage 3 retrogressive alterations crystallization of pyrite and remobilization of sulfides occurred largely syn to postkinematically with respect to boudinage modified journal abstract

alteration and mineralization at the zhibula cu skarn deposit gangdese belt tibet abstract the zhibula cu skarn deposit contains 0 32 mt cu metal with an average grade of 1 64 and is located in the gangdese porphyry copper belt in southern tibet the deposit is a typical metasomatic skarn that is related to the interaction of magmatic hydrothermal fluids and calcareous host rock stratiform skarn orebodies occur at the contact between tuff and marble in the lower jurassic yeba formation alteration zones generally grade from a fresh tuff to a garnet bearing tuff a garnet pyroxene skarn and finally to a wollastonite marble minor endoskarn alteration zonations are also observed in the causative intrusion which grade from a fresh granodiorite to a weakly chlorite altered granodiorite a green diopside bearing granodiorite and to a dark red brown garnet bearing granodiorite prograde minerals which were identified by electron probe microanalysis include andradite grossularite of various colors e g red green and yellow and green diopside retrograde metamorphic minerals overprint the prograde skarn and are mainly composed of epidote quartz and chlorite the ore minerals consist of chalcopyrite and bornite followed by magnetite molybdenite pyrite pyrrhotite galena and sphalerite three types of fluid inclusions are recognized in the zhibula deposit including liquid rich two phase inclusions type l vapor rich two phase inclusions type v and daughter mineral bearing three phase inclusions type s as the skarn formation evolved from prograde stage i to early retrograde stage ii and later retrograde stage iii the ore forming fluids correspondingly evolved from high temperature 405 667 c high salinity up to 44 0 wt nacl equiv and high pressure 500 600 bar to low moderate temperature 194 420 c moderate high salinity 10 1 18 3 and 30 0 44 2 wt nacl equiv and low moderate pressure 250 350 bar isotopic data of 34 s 0 1 to 6 8 estimated 34 s fluids 0 7 d h2o 91 to 159 and 18 o h2o 1 5 to 9 2 suggest that the ore forming fluid and material came from magmatic hydrothermal fluids that were associated with miocene zhibula intrusions fluid immiscibility likely occurred at the stage i and stage ii during the formation of the skarn and mineralization fluid boiling occurred during the stage iii which is the most important cu deposition mechanism for the zhibula deposit

geochemistry and evolution of ore forming fluids of the yueshan cu au skarn and vein type deposits anhui province south china abstract the yueshan mineral belt is geotectonically located at the centre of the changjiang deep fracture zone or depression of the lower yangtze platform two main types of ore deposits occur in the yueshan orefield cu au fe skarn deposits and cu mo au pb zn hydrothermal vein type deposits almost all deposits of economic interest are concentrated within and around the eastern and northern branches of the yueshan dioritic intrusion in the vicinity of the zongpu and wuhen intrusions there are many cu pb zn au s vein type and a few cu fe au skarn type occurrences fluid inclusion studies show that the ore forming fluids are characterised by a cl s na k chemical association hydrothermal activity associated with the above two deposit types was related to the yueshan intrusion the fluid salinity was high during the mineralisation processes and the fluid also underwent boiling and mixed with meteoric water in comparison the hydrothermal activity related to the zongpu and wuhen intrusions was characterised by low salinity fluids chlorine and sulphur species played an important role in the transport of ore forming components hydrogen and oxygen isotope data also suggest that the ore forming fluids in the yueshan mineral belt consisted of magmatic water mixed in various proportions with meteoric water the enrichment of ore forming components in the magmatic waters resulted from fluid melt partitioning the ore fluids of magmatic origin formed large cu au deposits whereas ore fluids of mixed magmatic meteoric origin formed small to medium sized deposits the sulphur isotopic composition of the skarn and vein type deposits varies from 11 3 to 19 2 and from 4 2 to 10 0 respectively these variations do not appear to have been resulted from changes of physicochemical conditions rather due to compositional variation of sulphur at the source s and by water rock interaction complex water rock interaction between the ore bearing magmatic fluids and sedimentary wall rocks was responsible for sulphur mixing lead and silicon isotopic compositions of the two deposit types and host rocks provide similar indications for the sources and evolution of the ore forming fluids hydrodynamic calculations show that magmatic ore forming fluids were channelled upwards into faults fractures and porous media with velocities of 1 4 m s 9 8 10 1 to 9 8 10 7 m s and 3 6 10 7 to 4 6 10 7 m s respectively a decrease of fluid migration velocity in porous media or tiny fractures in the contact zones between the intrusive rocks and the triassic sedimentary rocks led to the deposition of the ore forming components the major species responsible for cu transport are deduced to have been cucl cucl2 cucl32 and cucloh whereas au was transported as au2 hs 2s2 au hs 2 auhs and auh3sio4 complexes cooling and a decrease in chloride ion concentration caused by fluid boiling and mixing were the principal causes of cu deposition gold deposition was related to decrease of ph total sulphur concentration and fo2 which resulted from fluid boiling and mixing geological and geochemical characteristics of the two deposit types in the yueshan mineral belt suggest that there is a close genetic relationship with the dioritic magmatism geochronological data show that the magmatic activity and the mineralisation took place between 130 and 136 ma and represent a continuous process during the yanshanian time the cooling of the intrusions and the mineralisation event might have lasted about 6 ma the cooling rate of the magmatic intrusions was 80 to 120 c my 1 which permitted sufficient heat supply by magma to the ore forming system

viscoelastic seismic responses of 2d reservoir models the use of relaxation mechanisms has recently made it possible to simulate viscoelastic q effects accurately in time domain numerical computations of seismic responses as a result seismograms may now be synthesized for models with arbitrary spatial variations in compressional and shear wave quality factors q sub p and q sub s as well as in density rho and compressional and shear wave velocities v sub p and v sub s reflections produced by q contrasts alone may have amplitudes as large as those produced by velocity contrasts q effects including their interaction with v sub p v sub s and rho contribute significantly to the seismic response of reservoirs for ban limited data at typical seismic frequencies the effects of q on reflectivity and attenuation are more visible than those on dispersion synthetic examples include practical applications to reservoir exploration evaluation and monitoring q effects are clearly visible in both surface and offset vertical seismic profile data thus avo analyses that neglect q may produce erroneous conclusions

efficient 3 d viscoelastic modeling with application to near surface land seismic data three dimensional viscoelastic modeling is implemented by reparameterizing the viscoelastic wave equation for a standard linear solid the formulation uses weighting factors corresponding to relaxation frequencies and composite memory variables this novel 3 d formulation requires less computer memory than the traditional relaxation time formulation because one set of relaxation frequencies can be used for all mechanisms for all parts of a model and only three sets of composite memory variables are needed rather than the seven used in the standard implementation giving a net reduction of 40 in the total required memory computational time is also reduced approximately 25 because of reduced input output i o the algorithm is applied to 3 d modeling of the viscoelastic response of the near surface structure beneath a 3 d reflection survey in the ouachita frontal thrust zone of southeast oklahoma comparison of the 3 d field data with both viscoelastic and elastic response clearly demonstrates the importance of inclusion of viscoelasticity when accurate amplitude fitting is desired observed amplitude and traveltime variations can be explained by shallow velocity and q distributions obtained independently by 3 d tomography

mineral chemistry and h o s pb isotopic compositions of skarn type copper deposits in the jiurui district of the middle lower yangtze river metallogenic belt eastern china abstract the skarn type copper deposits are widespread in the jiurui district in the middle lower yangtze river metallogenic belt this paper reports a detailed study on mineral chemistry and h o s and pb isotopic compositions on skarn silicate and sulfide minerals in the three major skarn dominant deposits wushan dongleiwan and dengjiashan the wushan skarn deposit is characterized with prograde garnet dominated and clinopyroxene limited skarns with average andradite content of 83 and hedenbergite content of 10 whereas the dongleiwan and dengjiashan deposits are featured with retrograde skarn alteration with abundant hydrous minerals such as epidote and chlorite the garnet and clinopyroxene compositions show 59 andradite and 15 hedenbergite for the dongleiwan skarns and 43 and 22 for the dengjiashan skarns respectively the pistacite components ps value defined as fe3 fe3 al and fe3 fe2 value of epidote are 0 12 and 1 63 for the wushan skarns 0 30 and 32 73 for the dongleiwan skarns and 0 17 and 42 85 for the dengjiashan skarns it is suggested that the prograde skarn mineralization in the three deposits was all formed in a relatively oxidizing environment with the wushan showing the highest oxidation potential and the dengjiashan having the least oxidation potential however in the retrograde skarns the dongleiwan and dengjiashan deposits show higher oxidation potential than that of wushan the three deposits show similar sulfur isotopic compositions of 2 9 to 1 4 and similar lead isotopic compositions with 206pb 204pb 207pb 204pb and 208pb 204pb ratios of 17 900 to 18 205 15 538 to 15 649 and 38 170 to 39 025 respectively all the three deposits should have similar magmatic origin for the ore forming materials based on their s and pb isotopes the oxygen isotopic compositions of the prograde and retrograde fluids in the three deposits show some differences with 18ofluid values of 8 13 and 7 81 for the wushan 6 47 and 2 33 for the dongleiwan and 8 27 and 4 43 for the dengjiashan but the hydrogen isotopic compositions are similar for the prograde 65 to 31 and retrograde 64 to 33 fluids therefore the fluid origins and evolution may be different in each deposit the hydrothermal fluids for the prograde skarns in all three deposits were likely derived from magmatic hydrothermal sources but the dongleiwan and dengjiashan show a higher proportion of meteoric water input in the retrograde stage considering the similar average prograde temperatures 574 to 560 c as calculated from coexisting garnet clinopyroxene pairs and similar retrograde temperatures 281 to 246 c as calculated from chlorite chemistry for the three deposits we suggest that the trigger for deposition of sulfide ores in the wushan garnet dominated skarn deposit was mainly caused by system cooling with temperature drop along with magmatic intrusion and crystallization process the dongleiwan and dengjiashan skarn deposits constitute a well developed retrograde skarn system with abundant epidote chlorite quartz and calcite which probably caused by fluid mixing of high temperature saline magmatic hydrothermal fluids with cooler oxidizing and dilute meteoric water

mesozoic metallogeny in east china and corresponding geodynamic settings an introduction to the special issue abstract the giant east china mesozoic metallogenic province hosts some of the world s largest resources of tungsten tin molybdenum antimony and bismuth ores of gold silver mercury lead zinc copper uranium and iron are also of major importance the province and its constituent metallogenic belts or regions south china middle lower yangtze river valley east qinling dabie interior of north china craton yan liao and north east china are the products of several pulses of igneous activity and mineralisation between 240 and 80 ma each successive stage has produced a distinctive suite of deposits that can be readily related to the geodynamic evolution of the region during the mesozoic this geodynamic evolution is linked to a complex series of tectonic events involving far field subduction plate collisions crustal thickening post collision collapse and rifting

evaluation of the uncertainty in estimation of metal resources of skarn tin in southern china abstract this study is concerned with the problem of how many undiscovered mineral deposits can be expected to occur in the vicinity of any known deposit especially if the deposit is nearly mined out skarn tin deposits in southern china were chosen to demonstrate that fractal modeling can be a useful tool to characterize the spatial temporal distribution of mineral deposits and to quantify their grades and tonnages the results show that the spatial temporal distribution of skarn tin deposits as well as their grades and tonnages satisfy fractal statistic and suggest that 14 skarn tin deposits could be found around a known skarn tin deposit within a radius of 80 km monte carlo simulation was used to combine the number of deposits and the frequency distributions of grade and tonnage and to capture the uncertainty in estimation of metal resources at the 90 50 and 10 confidence levels tin metal resources amount to 6 ton 200 ton and 1 0 10 4 ton around a known tin deposit within a radius of 80 respectively

a petrological and fluid inclusion study of magnetite scheelite skarn mineralization at kara northwestern tasmania implications for ore genesis abstract the kara magnetite scheelite deposit is located about 40 km south of burnie in northwestern tasmania the deposit consists of a number of orebodies and the total mineable reserves are 1 7 mt of magnetite at 30 fe and 0 3 mt of scheelite at 0 52 wo3 the major orebodies at kara are hosted by the ordovician gordon limestone at the southern end of the devonian housetop granite adjacent to the granite or separated from it by the ordovician moina sandstone at least four paragenetic stages of skarn formation and ore deposition have been recognized stage i clinopyroxene garnet vesuvianite wollastonite quartz scheelite stage ii garnet vesuvianite magnetite scheelite apatite quartz stage iii magnetite amphibole epidote fluorite quartz chlorite garnet vesuvianite scheelite carbonate pyrite clinopyroxene and stage iv hematite fluorite calcite quartz fluid inclusions in clinopyroxene from stage i homogenize at 460 620 c mode 520 c stage ii gave homogenization temperatures of 349 578 c mode 500 c from scheelite and 360 570 c mode 500 c from vesuvianite the stage i clinopyroxene gave a salinity range of 10 0 12 0 equiv wt nacl with only one low value of 2 0 equiv wt nacl the stage ii mineral assemblages also showed moderate salinities of 12 0 and 17 8 equiv wt nacl from scheelite and vesuvianite fluid inclusions in quartz scheelite calcite and fluorite from the main scheelite mineralization phase stage iii homogenize at 230 360 c with a mode at 300 c and salinity varies from 0 2 to 19 8 equiv wt nacl the mineral paragenetic and fluid inclusion studies indicate that magnetite scheelite mineralization at kara was formed as a proximal skarn assemblage in carbonate host the skarn formation and ore deposition occurred in stages starting with prograde anhydrous clinopyroxene garnet metasomatism at relatively high temperatures 500 c this early assemblage was replaced by the subsequent retrograde deposition of hydrous mineral phases e g amphibole epidote and chlorite as temperatures decreased to 300 c or less deposition of scheelite predominantly occurred in association with hydrous minerals e g amphibole in stage iii the high temperature and moderate to high salinity ore fluids in early anhydrous skarn formation stages i and ii are consistent with fluids of magmatic origin in comparison the lower temperature and variable salinity from high 19 8 equiv wt nacl to as low as 0 2 equiv wt nacl in stage iii suggests a possible involvement of low salinity meteoric waters mixing with high salinity fluids originating from the nearby granite in the later hydrous skarn and ore formation

geochemistry of sulfide minerals from skarn cu au deposits in the fenghuangshan ore field tongling eastern china insights into ore forming process abstract in situ elemental compositions of sulfide minerals have been widely applied to trace ore forming processes of magmatic hydrothermal ore systems yet the application of elemental compositions of the sulfide minerals in skarn ore deposits is still restricted by the lack of understanding of their behaviors during the skarn formation processes in this study in situ la icp ms and epma elemental compositions of medium to coarse grained euhedral pyrite and xenomorphic granular chalcopyrite are investigated for the fenghuangshan and baoshantao skarn cu au deposits in the tongling region eastern china the results show that the studied pyrite samples have relatively consistent trace element composition characteristics while the chalcopyrite studied displays high zn ag and pb contents and relatively high bi content au ag cu pb bi sb and tl are mainly of lattice bound appearance in the pyrite structure the au ag sb pb and bi are mainly incorporated into the chalcopyrite structure as coupled substitutions low au mainly 1 and se tl mainly 10 ratios of the pyrite studied and high sn 10 ppm and low tl

effects of viscoelasticity on seismic wave propagation in fault zones near surface sediments and inclusions by defining anelastic effects through the superposition of relaxation mechanisms and incorporating them into the wave equation in terms of memory variables the time domain computation of responses of viscoelastic media with arbitrary spatial variations is feasible this approach is applied to simulation of the effects of realistic distribution of compressional and shear wave quality factors qp and qs in a sequence of viscoelastic models of increasing complexity from a homogeneous medium to a fault zone a near surface attenuating zone and inclusions with anomalous qp and qs values comparisons of elastic and viscoelastic responses for both surface and borehole recordings show pronounced q dependent attenuation analysis of data from viscoelastic media using elastic rather than a viscoelastic model may result in misleading or erroneous interpretations

avo in transversely isotropic media an overview the amplitude variation with offset avo responses of elastic transversely isotropic media are sensitive to contrasts in both of thomsen s anisotropic parameters and e the equation describing p p reflections indicates that the smaller the contrasts in isotropic properties compressional velocity shear velocity and density and the larger the contrasts in and e across an interface of reflection the greater the effects of anisotropy on the avo signature contrasts in are most important under small to medium angles of incidence as previously described by banik 1987 while contrasts in e can have a strong influence on amplitudes for the larger angles of incidence commonly encountered in exploration 20 degrees and beyond consequently using rutherford and williams avo classification of isotropic gas sands type i gas sands overlain by a transversely isotropic ti shale exhibit a larger decrease in avo than if the shale had been isotropic and type iii gas sands overlain by a transversely isot

formation of anhydrous and hydrous skarn in cu au ore deposits by magmatic fluids most skarn ore deposits are characterized by two distinctly different alteration styles an early prograde stage with anhydrous minerals such as garnet and pyroxene forms from relatively high temperature hypersaline liquid a later retrograde stage with hydrous minerals such as epidote amphibole and chlorite plus sulfide ore minerals forms from lower temperature lower salinity fluids these two alteration stages commonly have been thought to reflect a dominance of magmatic and meteoric water respectively with relevance to the source of ore metals we report data from two different skarn systems one being part of the world s largest cu au resource stable isotope compositions of anhydrous and hydrous alteration minerals from both deposits indicate a magmatic source for both the prograde and retrograde stages 18o averages 5 0 per mil for garnet range 3 4 7 2 6 5 per mil for pyroxene 4 3 8 2 and 7 1 per mil for amphibole 4 3 8 7 the d values of late amphibole are more complex with magmatic values 77 to 78 for one deposit and both magmatic and lighter values for another deposit that could be explained either by magmatic degassing or by limited mixing with meteoric water we conclude that the differences in fluid composition prograde versus retrograde stages resulted from a magmatic fluid that intersected its solvus during the early stage creating vapor and hypersaline liquid whereas in the later stage this magmatic fluid did not intersect its solvus because it followed a different cooling path this late low salinity liquid only boiled once its vapor pressure curve was reached causing sulfide ore to precipitate during the retrograde stage

the mineralogy of copper bearing skarn to the east of the sungun chay river east azarbaidjan iran abstract a calcic copper bearing skarn zone in east azarbaidjan nw of iran is located to the east of the sungun chay river skarn type metasomatic alteration and mineralization occurs along the contact between upper cretaceous impure carbonates and an oligo miocene cu bearing granitoid stock both endoskarn and exoskarn are developed along the contact exoskarn is the principal skarn zone enclosed by a marmorized and skarnoid hornfelsic zone the skarnification process occurred two stages 1 prograde and 2 retrograde the prograde stage is temporally and spatially divided into two sub stages a metamorphic bimetasomatic sub stage i and b prograde metasomatic sub stage ii sub stage i began immediately after the intrusion of the pluton into the enclosing impure carbonates sub stage ii commenced with segregation and evolution of a fluid phase in the pluton and its invasion into fractures and micro fractures of the marmorized and skarnoid hornfelsic rocks developed during sub stage i the introduction of considerable amounts of fe si and mg led to the development of substantial amounts of medium to coarse grained anhydrous calc silicates from texture and mineralogy the retrograde metasomatic stage can be divided into two discrete sub stages a early sub stage iii and b late sub stage iv during sub stage iii the previously formed skarn zones were affected by intense multiple hydro fracturing phases in the cu bearing stock in addition to fe si and mg substantial amounts of cu pb zn along with volatile components such as h 2 s and co 2 were added to the skarn system consequently considerable amounts of hydrous calc silicates epidote tremolite actinolite sulfides pyrite chalcopyrite galena sphalerite bornite oxides magnetite hematite and carbonates calcite ankerite replaced the anhydrous calc silicates sub stage iv was concurrent with the incursion of relatively low temperature more highly oxidizing fluids into skarn system bringing about partial alteration of the early formed calc silicates and developing a series of very fine grained aggregates of chlorite clay hematite and calcite

alteration mineralization and genesis of the zoned tongshan skarn type copper deposit anhui china abstract the tongshan skarn type copper deposit is located in the anqing guichi ore cluster of the iron copper metallogenic belt which occurs along the middle lower yangtze river valley china in the study area skarnization and mineralization took place along the contact zone between carbonates and granodiorite porphyries the contact zone shows significant horizontal and vertical variations in alteration and mineralization in the horizontal direction the garnet content is high in the skarns near the intrusive body proximal skarns the diopside content is high farther from the intrusive body distal skarns and hedenbergite is concentrated in the skarns adjacent to the marble zone limestones located far from the marble zone experienced a strong silicification in the vertical direction from higher to lower levels the rocks change from hornfels to calcareous skarn to magnesian skarn mineralogical studies show that the skarns near the intrusion are relatively oxidized and the garnet in the skarns is relatively andradite rich high concentrations of cu are found in the porphyries with quartz veins as well as in the calcic skarns magnesian skarns hornfelses and marbles which are located at distances of 13 10 43 and 25 m from the porphyries respectively high concentrations of zn are found in silicified limestones and skarns located even farther from the porphyries the present findings suggest that the tongshan deposit was subjected to prograde alteration and mineralization followed by retrogression the alteration can be divided into a sequence of stages contact metamorphism prograde metasomatism early retrogression and late retrogression the copper mineralization occurred mainly during the early retrogression and the copper was further enriched in quartz veins within the porphyries during the late stages of magma evolution

seismic attenuation effects of pore fluids and frictional sliding seismic wave attenuation in rocks was studied experimentally with particular attention focused on frictional sliding and fluid flow mechanisms sandstone bars were resonated at frequencies from 500 to 9000 hz and the effects of confining pressure pore pressure degree of saturation strain amplitude and frequency were studied observed changes in attenuation and velocity with strain amplitude are interpreted as evidence for frictional sliding at grain contacts since this amplitude dependence disappears at strains and confining pressures typical of seismic wave propagation in the earth we infer that frictional sliding is not a significant source of seismic attenuation in situ partial water saturation significantly increases the attenuation of both compressional p and shear s waves relative to that in dry rock resulting in greater p wave than s wave attenuation complete saturation maximizes s wave attenuation but causes a reduction in p wave attenuation these effects can be interpreted in term

spatio temporal characterization of the pliocene aquifer conditions in wadi el natrun area egypt wadi el natrun area has recently undergone extensive urban and agricultural expansion due to the absence of natural surface irrigation supplies the only source of water in the area is the pliocene groundwater aquifer as a result secondary salinization from increased abstractions is the major threat to the groundwater aquifer there is a dire need for efficient strategies to ensure long term sustainability of the area s productive agriculture these strategies should be based on scientific spatio temporal monitoring and analysis of the groundwater conditions that is also lacking to capture the spatio temporal variability in groundwater conditions field measurements of total dissolved solids electrical conductivity ph temperature and water level as well as lab based ionic composition were performed on 47 groundwater samples collected during 2006 and 2007 determinations of the hydrochemical characteristics water types salt assemblages and the sodium adsorption ratio were carried out on the samples reference data sets recorded in 1973 and 1997 were available for the area and were used to monitor the changes occurred in these periods geographic information system gis was appraised for mapping and for integrated analysis of the different layers remotely sensed change detection techniques were applied to the landsat tm and the etm imageries and used to highlight the extensive reclamation and urbanization and to find key trends for the alterations in the groundwater conditions and their spatial association with land covers results revealed a topographic depression induced flow pattern predominance of leaching and dissolution processes the presence of saline lakes over pumping from the pliocene aquifer and temporal changes in land uses are the main factors combined to control the spatio temporal variability in the groundwater results also clarified the presence of two northwestern and southeastern zones that varied distinctively in their hydrodynamic and hydrochemical characteristics the northwestern zone showed an average water level decline of 15 m the water of which is brackish av 2 037 mg l with dominant na cl and so42 ions the groundwater of this zone is characterized by high to very high salinity hazard and high to very high alkali hazard and is not recommended for irrigation on soils with poor drainage and without proper management for salinity control the southeastern zone showed water level decline less than 2 m the water of which is fresh av 424 mg l with major na hco3 cl and so42 ions and quality suitable for irrigation with medium to high salinity and low to medium alkali hazards the article represents the first step towards an integrated management of wadi el natrun groundwater resources within a gis framework

a tectono genetic model for porphyry skarn stratabound cu au mo fe and magnetite apatite deposits along the middle lower yangtze river valley eastern china abstract the middle lower yangtze river valley metallogenic belt yrb situated along the northern margin of the yangtze craton is characterized by porphyry skarn stratabound cu au mo fe deposits in the areas of uplift and magnetite apatite deposits in cretaceous fault basins following detailed field investigations and a review of published data we recognize two episodes of magmatism and mineralization in the yrb 1 156 137 ma high k calc alkaline granitoids associated with 148 135 ma porphyry skarn stratabound cu au mo fe deposits and 2 135 123 ma shoshonitic series associated with 134 9 122 9 ma magnetite apatite deposits a type granitoids and associated alkaline volcanic have a small age range from 126 5 to 124 8 ma and are temporally spatially and genetically associated with the second episode the geodynamic history of the yrb did not experience the paleozoic to mesozoic lithospheric thickening that took place in the north china craton this process is inferred to be linked to partial melting of the delaminated lower crust at high pressures resulting in the development of c type adakitic rocks the petrochemical and sr nd isotopic data show that both the shoshonitic series and a type granitoids are quite different from adakites with only some of the k calc alkaline granitoids having adakitic signatures previous ore genesis models were established based on an assumed relationship with adakites and a continuous tectono thermal evolution from 150 to 100 ma all data obtained for the middle lower yangtze river region consistently show that the tan lu regional strike slip fault zone initiated at 233 6 to 225 6 ma from the collision between the north china and yangtze cratons and was reactivated at ca 160 ma the tan lu fault was caused by the oblique subduction of the izanagi plate which along the yrb the low angle subducted slab and the overlying crust was disrupted or broken due to the disharmonious movement of the two blocks the high k calc alkaline granitoids magmas were derived from melting of the subducted slab with some input of crustal material these magmas were emplaced at the intersections between ne and ew trending faults and formed porphyry skarn stratabound cu au mo fe deposits between 156 and 137 ma after 135 ma the subducted plate changed its direction of motion to northeast now running parallel to the eurasian continental margin and leading to large scale continental extension the shoshonitic series and subsequent a type granitoids magmatism and the development of magnetite apatite ores in the yrb took place in both fault basins and ne trending rifts between 135 and 124 ma

2 5d full wavefield viscoacoustic invercion1 full wavefield inversion for distributions of acoustic velocity density and q on a vertical slice through a25d model is implemented for common source gathers in a cross hole geometry the wavefield extrapolation used is 3d so all geometrical spreading scattering reflection and transmission effects are correctly and automatically compensated for in order to keep the number of unknowns tractable application was limited to 2 5d models of known geometry the latter assurnes a prior step such as tomography to fix the layer geometries with the model geometry fixed reliable solutions are obtained using synthetic data from only two independent source locations solutions from data with noisy and missing traces are comparable to those from noise free data but with higher residuals when the source locations are spatially widely separated conunon source gathers may be summed and treated as a single wavefield to yield the same model estimates as when the individual source wavefields are treated separately at substantially reduced cost inversions for full 3d parameter distributions can be handled with the same software requiring only solution for more unknowns

fluid inclusion studies in quartz veinlets in the porphyry copper deposit at sungun east azarbaidjan iran abstract the porphyry copper deposit pcd at sungun is located in east azarbaidjan in the nw of iran the sungun porphyries occur as stocks and dikes ranging in composition from quartz monzodiorite through quartz monzonite and granodiorite to granite the stocks are divided into two groups 1 porphyry stocks i and 2 porphyry stock ii porphyry stock ii hosting the copper ore experienced intense hydro fracturing leading to the formation of stockwork type and anastomozing veinlets and micro veinlets of quartz sulfides carbonates and sulfates three distinct types of hydrothermal alteration and sulfide mineralization are recognized at sungun 1 hypogene 2 contact metasomatic skarn and 3 supergene four types of hypogene alteration are developed at sungun potassic propylitic potassic phyllic and phyllic four types of inclusion are common at sungun based upon their phase content 1 mono phase vapor 2 vapor rich 2 phase 3 liquid rich 2 phase and 4 multi phase solid halite is the principal solid phase the distribution pattern shape and phase contents of fluid inclusions in quartz veinlets at sungun are analogous to those from bingham and globe miami in western usa the fluid inclusion data at sungun showed that the liquid vapor homogenization temperature t h l v values for liquid rich 2 phase vapor rich 2 phase and halite bearing inclusions vary from 160 to 580 c from 200 to 600 c and from 160 to 580 c respectively the ascending unboiled fluid at the onset of the phyllic alteration episode had temperatures 580 c and was moderately saline 15 wt with the gradual decrease in temperature the salinity of this fluid gradually decreased so that its salinity at temperatures of 370 and 350 c the residual fluid remained undersaturated with respect to nacl however at temperatures t s nacl t h l v showed that they were developed under the maximum hydrostatic pressure head of 1500 m during the boiling events

tau p seismic data for viscoelastic media part 2 linearized inversion1 an approach to extraction of viscoelastic parameters from seismic data is implemented and succesfully tested viscoelastic inversion is performed using adaptive damping factors to control the sensitivity of the viscoelastic parameters in relation to the p seismic data a priori information is incorporated through the damping factors as standard deviations of the data and of the viscoelastic model parameters the stability of the inversion process is controlled by the variation of the damping factors as a function of the residual errors and parameter updates at each iteration tests on synthetic and real data show that p and s wave quality factors qp and qs in addition to p and s wave velocities and density cp cs and p can be extracted from p seismic information singular value decomposition analysis demonstrates that estimated qp and qs values are more affected by the presence of data inaccuracies and noise than are those of cp and p cs and qs are not uniquely recovered due to the limited contribution of p s converted waves knowledge of the viscoelastic parameters is of particular importance in accurately describing petrophysical properties of rocks and pore fluids existing in the subsurface this is demonstrated with real data from the gulf of mexico

application of petrophysical measurements to the prediction of seismic responses of differing lithologyor pore fluids1 determination of petrography and pore fluid content is an ultimate goal of an integrated seismic petrophysical study for lack of a general inversion technique forward modelling is useful in studying the relations between lithology stratigraphy pore fluid content and the seismic response this report describes a study of two clastic sequences in utah from which 32 rock samples were analysed a detailed petrographic study was done laboratory measurements were made of ultrasonic compressional and shear wave velocity as a function of pressure we computed the velocities at seismic frequencies for the samples when dry over pressured brine saturated and oil saturated the velocities were sensitive to the porosity carbonate cementation and the depositional facies we generated velocity profiles for hypothetical reservoirs for a range of saturation states the velocity profiles were used to generate synthetic seismic shot gathers to study the seismic response of these clastic reservoirs the fluid saturation strongly affects the seismic respone as does the presence of a coal seam an amplitude change with offset is often observed however stratigraphy appears to have a stronger effect on the seismic response

new u pb and re os age data and the geodynamic setting of the xiaojiayingzi mo fe deposit western liaoning province northeastern china abstract the xiaojiayingzi deposit located in the western liaoning province in northeastern china is a skarn type mo fe deposit with an average mo grade of 0 23 wt the deposit is temporally and spatially associated with fine grained diorite mo fe mineralization is present mainly as veins lenses and layers that are hosted by skarn new shrimp u pb zircon and re os molybdenite age determinations yielded a crystallization age for the diorite of 169 9 1 4 ma and a molybdenite re os isochron age of 165 5 4 6 ma the u pb and re os ages are identical within error the mineralization is therefore considered to be genetically related to diorite emplacement in the middle jurassic a high re content of 21 75 to 163 0 ppm with an average of 64 31 ppm in the molybdenite together with 34 s values between 3 3 and 8 0 of sulfides in the ores indicates that the metal source was a mixed crust mantle system from these geochronological data and previously presented regional geological relationships we propose that diorite emplacement and mo fe mineralization in the xiaojiayingzi mine resulted from an early stage of the subduction of the paleo pacific plate beneath the eurasian block