morphological thermoelectrical geochemical and isotopic anatomy of auriferous pyrite from the bagrote valley placer deposits north pakistan implications for ore genesis and gold exploration abstract the bagrote valley in north pakistan belonging to the kohistan island arc is well known for regional placer gold mining however no economically feasible in situ hydrothermal gold deposits have been discovered in this region due to rugged terrain and remote nature of its location in the western himalaya the streams draining the main karakoram thrust mkt shyoke suture zone carry placer gold in sediments as well as old river terraces although the primary source remains unknown in this paper we employ a multiparametric approach including x ray diffraction xrd analysis thermoelectricity major and trace element geochemistry and isotopic characteristics of pyrite associated with placer gold with a view to identify the nature of the unknown deposits and ore forming fluids on the catchment of the bagrote valley pyrite in the bagrote valley placers is euhedral to subhedral indicating the proximal gold sources the high rate of occurrence of n type thermoelectric coefficients 89 with low p type 11 and crystallization temperature 290 c 380 c combined with chemical features indicate that the pyrite was derived from porphyry or epithermal type of magmatic hydrothermal gold deposits from the hinterlands of the bagrote valley the x ray elemental maps show that fe as mo and ni are homogenously distributed from core to rim suggesting stable crystallization condition without any alteration by later fluids the calculated chemical formula of pyrite of our samples is au0 0006fe s2 004 plots of au as and au fe shows that gold occurs in pyrite as micro to nano inclusion as au 0 the 34 s v cdt values of pyrite range from 0 6 to 0 9 with an average of 0 02 indicating the derivation of sulfur from a homogeneous magmatic source the pb isotope data indicates that the pb was sourced from orogenic type source with minor contribution of lower crust the narrow variations in 206 pb 204 pb and 208 pb 204 pb values suggest a single lead source the low medium and high mo ni ratios reflect a mixed provenance for the auriferous pyrite the average value of 71 8 of pyrite computed from thermoelectric parameters xnp suggests that the dominant part of the primary source that contributes to the placers might have already been eroded however the proximal source and with high content of gold in the pyrite grains up to 1160 ppm suggest the possibility of significant economic mineralisation below the present erosion level of the deposits in the hinterlands of bagrote valley

submillimeter scale zonation of δ18o in quartz and feldspar isle of skye scotland abstract laser probe analysis of oxygen isotope ratios in submillimeter domains of quartz and feldspar in hydrothermally altered granite reveals complex intragranular zonation that can be contoured within individual grains two samples collected within 10 m of each other in the maol na gainmhich epigranite mge isle of skye scotland are similar petrographically yet display very different 18o zonation patterns sk1 has isotopically zoned quartz 18 o 1 8 8 2 with intragranular gradients of 18o as great as 5 mm and individually homogeneous grains of k feldspar 0 2 which also display a large range of values 18 o 1 7 to 7 3 oxygen isotope gradients of more than 11 mm were measured in this sample in contrast sk4 has homogeneous quartz 18o 5 7 0 3 n 14 and a zoned k feldspar phenocryst 18 o 3 3 to 6 9 isotopic heterogeneity in quartz correlates with the degree of chlorite alteration in adjacent hornblende grains the isotopic heterogeneity revealed by the laser probe in single grains of quartz and feldspar is greater than the entire range of values displayed by bulk mineral analysis of samples collected throughout the mge pluton although the average values of 18o obtained by laser probe are identical to the average bulk values values in k feldspar suggest exchange at 400 c with infiltrating meteoric water 18 o 10 the marked differences in zonation profiles between samples on the outcrop scale suggest that permeability and isotope exchange during hydrothermal alteration was highly heterogeneous these microanalytical data for quartz and feldspar provide the first oxygen isotope evidence from pervasively altered granites that paleopermeability is caused at least in part by intracrystalline microfractures

argon and halogen geochemistry of hydrothermal fluids in the loch ainort granite isle of skye scotland highly turbid alkali feldspars from the loch ainort granite 59 ma isle of skye have been analysed using the 40ar 39ar method to obtain chronological and chemical k cl br i information concerning their origin and hydrothermal alteration three methods of gas extraction have been applied to neutron irradiated samples laser probe spot fusion of feldspars in vacuo crushing of a feldspar quartz separate and laser stepped heating of the crushed residue apparent ages obtained by laser probe spot fusion are mostly similar to the 59 ma intrusion age analyses of relatively pristine regions give some high apparent ages 59 ma indicating the presence of small amounts of 40are excess 40ar crushing releases significant amounts of 40are but is dominated by an 40ara atmospheric 40ar component 84kr 36ar values obtained by crushing are higher than air and are consistent with air equilibration with fresh water at low temperature 20 c therefore 40ara was most probably introduced as palaeoatmospheric argon dissolved in the circulating hydrothermal fluids that interacted with the granite thus supporting a meteoric origin for the fluids stepped heating gives a flat age spectrum and an age of 56 4 ma crushing and stepped heating both released significant amounts of halogens with high br cl and i cl ratios excess xe is also present as indicated by the high 132xe 36ar values it seems likely that the halogen and possibly xe enrichments resulted from interaction of the meteoric fluids with jurassic sedimentary country rocks

isolation of diagenetic overgrowths on quartz sand grains for oxygen isotopic analysis abstract diagenetic overgrowths on detrital quartz sand grains in sandstones can be isolated for direct measurement of their oxygen isotope ratios interfacial materials between detrital cores and diagenetic overgrowths are dissolved by etching with dilute hf the weakened interface breaks when grains are agitated ultrasonically subsequent particle size separation is an effective means of concentrating the diagenetic component

the relative timing of serpentinisation and mantle exhumation at the ocean continent transition iberia constraints from oxygen isotopes legs 173 and 149 of the ocean drilling program profiled a zone of exhumed mantle peridotite at the ocean continent transition oct beneath the iberia abyssal plain the zone of exhumed peridotite appears to be tens of kilometers wide and is situated betw

ion microprobe analysis of oxygen isotopes in garnets of complex chemistry abstract accurate ion microprobe analysis of oxygen isotope ratios in garnet is possible if appropriate standards are employed to correct for instrumental bias a component of which depends on the cation chemistry of the analyzed mineral in this study 26 garnet standards including 14 new standards that span the compositional range of pyrope almandine grossular spessartine and andradite were analyzed repeatedly by ion microprobe to develop a new method of correcting for instrumental bias in garnets all analyses were normalized to a single master garnet standard uwg 2 before bias from cation composition was considered bias due to cation composition in garnet was found to correlate with grossular content in pyralspite garnets and with andradite in ugrandite garnets bias is correlated with molar volume in garnets of all compositions in this study although this correlation is suitable as a correction scheme for bias a more accurate correction scheme based on the grossular and andradite compositions of garnet is proposed this method reproduces the bias of all but one standard to within a range of 0 4 an accuracy that is on the same order as the reproducibility 0 3 2 s d of the master garnet standard uwg 2 but that remains an independent source of error the new correction scheme is used to successfully reproduce laser fluorination analyses along a traverse of a polymetamorphic zoned skarn garnet from the adirondack mountains while previous analyses were at the mm scale the new data resolve a gradient of 18 o of 2 1 over 16 m if experimentally derived diffusion coefficients are correct these new results show that granulite facies metamorphism was significantly faster than previously assumed and the thermal peak was less than 5 myr

ion microprobe evidence for the mechanisms of stable isotope retrogression in high grade metamorphic rocks retrograde interdiffusion is widely proposed as the dominant factor in producing the stable isotopic fractionation among minerals in slowly cooled igneous and metamorphic rocks mineral zonation consistent with interdiffusion of stable isotopes has never been directly observed however leaving doubt as to the mechanism responsible for the bulk mineral isotopic compositions commonly measured ion microprobe analyses of oxygen isotope ratios in magnetite were combined with conventional bulk mineral analyses and diffusion modeling to document the relationship between mineral zonation and the mechanism of retrogression inferred from bulk mineral data two samples of magnetitebearing quartzo feldspathic lyon mountain gneiss from the adirondack mountains n y were studied in detail conventional stable isotope analysis of both samples indicates that isotope thermometers are discordant and were reset by as much as 200 c from the estimated peak temperature of 750 c the relative order of apparent temperatures recorded by various thermometers differs between the two samples however with t qtz fsp t mt qtz and t mt fsp in one sample and t qtz fsp t mt qtz and t mt fsp in the other diffusion modeling using the fast grain boundary model shows that the former pattern of apparent temperatures is consistent with closed system interdiffusion during cooling whereas the latter is not the modeling predicts that 0 5 mm diameter magnetite grains common to this rock type will contain isotopic zonation of 1 rims lower in 18 o than cores and that the cores of smaller 0 1 mm grains will be similarly lower than to the cores of large 0 5 mm grains ion microprobe analysis reveals that the zoning patterns of magnetite grains from the first sample contain clear core to rim zonation in multiple grains core rim 1 1 0 4 and predicted grain size vs core composition variations consistent with diffusion controlled resetting of bulk mineral fractionations in contrast the second sample shows irregular inter and intra granular variations over an 8 range consistent with open system alteration these results provide direct documentation of the importance of interdiffusion in affecting stable isotope distributions in slowly cooled rocks the correlations of bulk mineral resetting with zonation show that bulk mineral data when interpreted with detailed modeling can be used to determinate what processes controlling retrogression

variations in os isotope ratios of pyrrhotite as a result of water rock and magma rock interaction constraints from virginia formation duluth complex contact zones abstract os isotope ratios in pyrrhotite bearing pelitic rocks of the 1 85 ga virginia formation are variable with perturbations linked to the emplacement of the 1 1 ga duluth complex pyrrhotite in footwall rocks of the contact aureole show evidence for a mixing event at 1 1 ga involving a low 187 os 188 os fluid however because rocks with perturbed pyrrhotite os isotope ratios occur 1 km or more from the duluth complex the fluid is unlikely to have been of magmatic origin fluid inclusions in layer parallel quartz veins provide evidence of the involvement of a boiling fluid at temperatures between 300 and 400 c analyses of fluid inclusions via la icp ms show that the fluids contain up to 1 7 wt na 1 1 wt k 4330 ppm fe 2275 ppm zn and 415 ppm mg the veins also contain pyrite or pyrrhotite plus minor amounts of chalcopyrite bornite pentlandite and sphalerite the re os isotopic ratios of pyrite from the veins indicate that they crystallized from low 187 os 188 os fluids 18 o values of vein quartz range from 7 7 to 9 5 consistent with an origin involving fluid with a relatively low 18 o value between 2 and 5 meteoric water with such a low 18 o value could have interacted with the igneous rocks of the complex and would have acquired os with a low 187 os 188 os ratio strongly serpentinized olivine rich rocks of the complex are commonly characterized by such low 18 o values and we propose that the fluid involved in serpentinization was also responsible for the perturbation of the os isotopic system recorded by pyrrhotite in the virginia formation two important observations are that only pyrrhotite bearing assemblages in the contact aureole show isotopic perturbation and that intervals showing os exchange are spatially restricted and not uniformly distributed os exchange and mixing has occurred only where temperatures were sufficient to convert pyrite to pyrrhotite and where time integrated water rock ratios in the aureole were high enough to provide a supply of os troctolitic and gabbroic rocks of the partridge river intrusion duluth complex are characterized by os isotope ratios that are indicative of variable degrees of crustal contamination os values of 0 543 xenoliths of carbonaceous and sulfidic pelitic rocks of the virginia formation found in the igneous rocks provide evidence that os was released by organic matter and pyrite in the sedimentary rocks and assimilated by mantle derived magma however residual pyrrhotite produced as a result of pyrite breakdown in the xenoliths is characterized by 187 os 188 os ratios that are much lower than anticipated and similar to those of pyrrhotite in the contact aureole the os exchange and addition shown by pyrrhotite in the xenoliths highlight an unusual cycle of re os liberation during devolatilization kerogen maturation and pyrite to pyrrhotite conversion processes that contribute to magma contamination followed by os uptake by pyrrhotite during back reaction involving magma and or fluid characterized by a relatively low 187 os 188 os ratio the extreme os uptake recorded by pyrrhotite in the xenoliths as well as the lesser degree of uptake recorded by pyrrhotite in the contact aureole is in line with the high os diffusivity in pyrrhotite experimentally determined by brenan et al 2000 our data confirm that os isotope ratios in pyrrhotite bearing rocks may be readily perturbed for this reason caution should be exercised in the interpretation of os isotope ratios in rocks where pyrrhotite may be the primary host of os

hydrothermal alteration of tertiary igneous rocks from the isle of skye northwest scotland hydrothermal alteration of tertiary granites from skye involed the reaction of igneous amphibole biotite ferroaugite fayalite alkali feldspar plagioclase feldspar magnetite and ilmenite with aqueous fluid primarily to combinations of secondary alkali feldspar chlorite and montmorillonite lesser amounts of muscovite calcite epidote prehnite zeolite and pyrite also developed during mineralogical alteration of the granites there was a net addition to rock of h and a net loss of ca fe and probably na there is no positive evidence for a significant change in their al si mg or k contents hydrothermal alteration of skye granite involved not only large scale migration of 18o 16o d and h but also of ca fe and probably na mineral thermometry combined with textural observations suggests that chemical isotopic and most mineralogical alteration were synchronous and occurred at 350 450 c textural observations further suggest that the mechanism of isotopic exchange between granite and hydrothermal fluid primarily was solution reprecipitation

magmatism geological setting alteration and metallogenic potential of donghua area dehua county fujian province southeast china insights from porphyry zircon u pb and pyrite rb sr geochronology geochemistry and remote sensing abstract located in the southern section of the wuyi mountain metallogenic belt the dehua youxi yongtai dyy ore district is one of the potential areas of gold deposits in the fujian province southeast china gold mineralization is widely distributed in this district including qiucun shuangqishan ancun and dongyang gold deposits however the dyy ore district is still at a low degree of exploration and research this paper focuses on the donghua area in the northwest of the dyy ore district as its typical and integrated volcano magma mechanism revealed in this study combined approaches including zircon shrimp u pb geochronology rb sr isochron dating and mineral chemistry of pyrite and hyperspectral remote sensing are employed aiming to identify the magmatism alteration geological setting and metallogenic potential of the donghua area the zircon shrimp u pb ages of the granite porphyritic dykes in donghua are 154 6 1 1 ma and 153 2 1 2 ma respectively indicating that the dykes were formed in the late jurassic the rb sr geochronological age of hydrothermal epithermal pyrite in donghua is 153 7 2 4 ma which is almost coeval with that of the granite porphyritic dykes within error and consistent with the regional volcanic magmatic activity and the metallogenic age of the regional metallogenic event the granitic dykes in donghua exhibit the characteristics of both a type and i type granitoids thus indicating the presence of transitional geochemical characteristics as a result of the subduction of the pacific plate towards the eurasia the ca 154 153 ma magmatic event in the donghua area occurred at the beginning of large scale delamination of the continental crust the zoning distribution of the mineral alteration of chlorite dickite kaolinite and gypsum the interpretation of volcanic activity from the annular structure of hyperspectral remote sensing and the inferred deep seated intrusion emplacing from northwest to southeast are in agreement thus displaying the volcano magma alteration mechanism developed in the donghua area the magmatism dykes faults and neoproterozoic metamorphic rock provide favorable advantages for the mineralization in donghua suggesting metallogenic potential

textural control on gold distribution in as free pyrite from the dongping huangtuliang and hougou gold deposits north china craton hebei province china article i nfo pyrite from the dongping huangtuliang and hougou gold deposits hebei province china was investigated using a combination of ore microscopy including back scattered imaging and in situ laser ablation inductively coupled plasma mass spectroscopy la icp ms a range of elements including au te ag pb bi cu co ni and as was analyzed with the aim to constrain the textural controls and influence of superimposed deformation on the distribution of invisible gold in as free pyrite thedatasetshowsexcellentcorrespondence betweenmeasuredhighgoldvaluesandthreekeytexturalcriteria i areasofclusteredtellurideinclusions especiallyindongping ii microshearingandfracturing brecciation dongping and huangtuliang and iii pyrite recrystallization huangtuliang invisible gold is only at trace levels in the hougou and gold bearing telluride minerals are not observed this is considered to result from larger scale remobilization of gold during advanced brecciation and recrystallization of pyrite pyrite grains containing clustered inclusions have by far the highest gold concentrations up to 1 wt with consistent values of thousands of ppm au interpretation of textures and la icp ms data infers that in these areas the distribution of telluride inclusions extends pervasively from micron to nanoscale i e as fields of nanoparticles local employment of coupled dissolution reprecipitation reaction between pyrite and fluids driving the k metasomatic alteration dated at 150 ma is invoked to explain such patterns syn deformational grain scale mobilization of gold and other elements took place leading to a portion of the gold being recrystallized within fractures and microshears the deformational event leads to gold enrichment in the huangtuliang pyrite where brittle fracturing brecciation has been followed by a resorption and recrystallization in the latter case foam textured pyrites again without as can contain up to hundreds of ppm gold theinterpreted sequenceof pyritepost depositional eventsis inaccordancewith the protracted magmaticevolution of the area starting with variscan alkaline intrusions 390 ma and reactivated during the yanshanian orogeny 150 ma thestudyshows i thatas freepyritecanreadilycontainsignificantamountsofinvisiblegold bothasnanoparticles

separation kar dating and 18o16o ratio measurements of diagenetic k feldspar overgrowths an example from the lower cretaceous arkoses of the angola margin abstract k feldspar overgrowths adularia on detrital k feldspar were removed from the lower cretaceous 130 115 ma arkoses of angola and concentrated for oxygen isotopic analysis and k ar dating the concentration technique consisted of etching with dilute h2sif6 followed by ultrasonic agitation and particle size separation the diagenetic k feldspar content of each of fourteen subfractions as estimated by cathodoluminescence was between 45 and 92 percent the rest being mostly detrital microcline and in some cases small amounts of quartz and or albite extrapolation of 40 ar 40 k and 18 o 16 o ratios indicated a k ar age of the adularia of 98 16 ma and a 18o of 20 2 0 8 per mil smow the age is consistent with petrographic observations which suggest that precipitation of adularia occurred relatively early in the diagenetic history the k ar age together with the 18o value burial history and fluid inclusion data indicate that adularia formed at relatively shallow depth

quasi geostrophic 3d circulation and mass transport in the western bransfield strait during austral summer 1995 96 in the framework of the fruela carbon flux study two oceanographic surveys december 1995 and january 1996 were conducted by b i o hesperides in the western basin of the bransfield strait and southern drake passage the horizontal geostrophic velocity field is characterized by two jet like features linked to frontal hydrographic structures a meandering current off the continental shelf edge of the southern drake passage corresponding to the southern front of the antarctic circumpolar current and the bransfield current related to the bransfield front the first jet shows some changes in the meandering pattern from december 1995 to january 1996 whereas the second has a very stationary location and structure the estimated horizontal circulation and mass transports are compared with available current meter data and with previous geostrophic estimates in the context of a sensitivity analysis that takes into account the choice of the reference level and the station distribution the vertical velocity field has been computed by integrating the quasi geostrophic omega equation maximum estimated values are of the order of 1 m day which suggests that a phytoplankton bloom observed in the northern part of the study area in december and vanished one month later should not be attributed to frontal dynamic instabilities inducing upward motion and nutricline related lifting but rather to other hydrographic factors

contamination of the marcy anorthosite massif adirondack mountains ny petrologic and isotopic evidence oxygen isotope analyses of 101 samples from the marcy anorthosite massif 61 from this study 40 from taylor 1969 indicate that two major and distinct processes of crustal contamination have affected the massif ninety percent of the 93 samples with over 65 plagioclase are enriched in 18o by 2 6 relative to normal anorthosites or gabbros the average 18o for 83 enriched samples is 9 5 depletions in 18o occur in 8 of the samples which have values ranging from 3 0 to 5 8 only 2 of the samples fall within the normal magmatic range for anorthosites low 18o values of 3 0 to 5 8 in the anorthosite occur only near contacts and a gradient in 18o occurs near the contact within the border zone of the massif low 18o values in both the anorthosite and adjacent wollastonite skarns with 18o down to 1 3 were probably caused by isotopic exchange with heated meteoric water when the anorthosite intruded at shallow levels prior to grenvilleage 1 1 by granulite facies metamorphism the 18o enrichment was ascribed to exchange between anorthosite and 18o rich marble by means of a pervasive h2o co2 fluid during the regional metamorphism by taylor 1969 however a number of lines of evidence argue against this hypothesis 1 the preservation of premetamorphic low 18o values in anorthosite from the border zone as well as preserved gradients in 18o from a number of localities 2 mass balance calculations of the amount of marble necessary to produce the 18o enrichment 3 metamorphic phase equilibria which buffer p text co text 2 and p text h text 2 text o to low values and 4 recent oxygen isotope analyses show homogeneity which indicates that magmatic oxygen isotope compositions have been preserved we evaluated the importance of magmatic assimilation of country rock at the present level of intrusion as an alternative cause of the 18oenrichment samples from 2 distinct lobes of the massif were analyzed the ne lobe where xenoliths of metasedimentary country rock are common and the nw lobe where xenoliths are scarce and the country rock is dominantly granitic the mean values of 18o for these two lobes are 9 6 in the ne and 9 3 in the nw thus magmatic assimilation at the present level of exposure probably had only localized and relatively minor effects on the oxygen isotope composition of the massif this conclusion is supported by rb sr data variations in rb content and 87sr 86sr i show that such crustal contamination is localized generally occurring only in samples near the border zone all of the available results suggest that the 18o enrichment is a magmatic feature acquired prior to intrusion at the present level of exposure

the nature and genesis of gold silver tellurium mineralization in the metaliferi mountains of western romania precious metal au ag and base metal pb zn deposits in the metaliferi mountains of western romania occur in steeply clipping quartz ca mn carbonate veins which are hosted by miocene andesitic stocks and lava flows and surrounding sedimentary rocks the deposits consist predominantly of sulfides pyrite chalcopyrite sphalerite galena sulfosalts of as and sb and a diverse range of au ag tellurides the igneous host rocks have undergone mild pervasive propylitic alteration whereas immediately adjacent to the veins the wall rock alteration assemblages consist of quartz sericite k feldspar calcite and pyrite fluid inclusion stable isotope and thermodynamic data suggest that the majority of the mineralization and hydrothermal alteration in these deposits was caused by loci salinity 0 5 wt nacl equiv medium temperature 200 degrees 300 degrees c near neutral ph 5 6 fluids which underwent occasional boiling the fluid inclusion and stable isotope data support a model in which a metal bearing magmatic fluid was exsolved from a crystallizing calc alkaline melt and ascended to higher levels in the crust undergoing some isotopic exchange with surrounding sedimentary rocks but limited mixing with ground waters although the deposits in this part of the romanian carpathians exhibit many of the geologic characteristics of classic low sulfidation volcanic hosted au ag epithermal deposits they seem to have formed from essentially magmatic waters and there is little evidence for the incorporation of meteoric fluids into the hydrothermal system

oxygen isotope zoning in garnet oxygen isotope zoning was examined within garnet with the use of the stable isotope laser probe four metamorphic garnets from the regional metamorphic terrane in vermont and the skarn deposit at carr fork utah were examined and were found to be concentrically zoned in 18o values the largest variations in 18o values were observed in the regional metamorphic garnets where 18o values change by 3 per mil from core to rim these oxygen isotope zoning profiles reflect the changes in the 18o values of the rocks during garnet growth which are caused by infiltration of fluids and by dehydration reactions during metamorphism

mineralogical and isotopic studies of base metal sulfides from the jiawula ag pb zn deposit inner mongolia ne china abstract the jiawula ag pb zn deposit is located in the northern part of the da hinggan mountains metallogenic belt in the eastern section of the central asian orogenic belt sphalerite galena pyrite chalcopyrite and arsenopyrite are the major sulfide minerals occurring in this deposit here we report results from electron probe micro analysis epma thermoelectricity and sulfur isotope studies of the constituent silver minerals and sulfide phases of the jiawula deposit petrographic observations and epma study reveal abundant silver mineralization in the ore especially within sphalerite and galena discrete grains of silver minerals including argentite pyrargyrite and canfieldite and isomorphism in silver bearing sulfides are identified silver and tellurium contents in galena are relatively high and show interrelationship significant substitution of s by te in the galena lattice facilitates silver entering the galena structure which might have been promoted by relatively low lg fs2 the thermoelectric coefficient of pyrite shows a marked gradient from n type to p type from pre to post metallogenic stages pyrites in jiawula are enriched in co and as and in the absence of ni displaying features typical of epithermal deposits the isotopic data present a close relationship between the sulfur source and magmatism

geochemical and isotopic composition of auriferous pyrite from the yongxin gold deposit central asian orogenic belt implication for ore genesis abstract the yongxin gold deposit is a large fracture controlled ore deposit in the duobaoshan gold copper metallogenic belt within the eastern domain of the central asian orogenic belt caob silicification sericitization and potassic alteration are the main hydrothermal alteration types which display successive zoning surrounding the ore bodies pyrite galena sphalerite and chalcopyrite are the major metallic minerals in the deposit and gold is mainly distributed in pyrite here we investigate the trace element composition and isotope pb and s characteristics of pyrite from this deposit the auriferous pyrite is mainly allotriomorphic and homogeneous in chemistry with a homogenous distribution of as ni mo and fe from the core to rim of grains these features are consistent with the 207pb 206pb 206pb 204pb and 208pb 204pb 206pb 204pb of the grains that suggest a single source with no evidence for involvement of late fluids the 34s values range from 3 5 to 5 4 with an average of 4 48 suggesting a mantle derived magmatic provenance for the sulfur the high co content and co ni ratios low ni and mo ni ratios suggest a mafic ultramafic source for the yongxin gold deposit the co ni as relation indicates a magmatic hydrothermal affinity with a classification as epithermal gold deposit high arsenic and gold contents on the rims of pyrite grains indicate that au and as were simultaneously precipitated in anoxic low temperature and near surface conditions

nature and ore formation of the erdaohezi pb zn deposit in the great xing an range ne china abstract the erguna metallogenic belt is a large erdaohezi epithermal polymetallic sulfide pb zn deposit in the northern great xing an range that is associated with andesitic porphyry mineralization mainly occurs at the edges of andesitic porphyry and adjacent jurassic quartz porphyry and volcanic strata hydrothermal alteration minerals mainly include quartz sericite adularia chlorite and calcite while ore minerals include pyrite galena and sphalerite with minor argentite chalcopyrite and tetrahedrite three hydrothermal mineralization stages are recognized three categories of fluid inclusions fis are distinguished in quartz fluorite and sphalerite veins liquid rich gas rich and a few h2o co2 inclusions the stage i fis include all three inclusion types and present high homogenization temperatures 197 233 and salinities 0 7 6 8 wt nacl eq the stage ii fis mainly comprise liquid rich inclusions with a few h2o co2 types and present higher homogenization temperatures 167 190 and slightly higher salinities 0 9 7 6 wt nacl eq than those of stage i stage iii only contains liquid rich inclusions and presents the lowest homogenization temperatures 120 157 and salinities 0 5 4 8 wt nacl eq the ore forming fluids have low temperatures and salinities in an h2o nacl co2 ch4 system the o h isotope data 2 2 to 5 0 and 160 0 to 152 5 respectively suggest that ore forming fluids gradually evolved from mantle primary water to meteoric water sulfur strontium and lead isotopes imply a mixed crustal and mantle source for the ore forming materials sulfide rb sr dating yields a well defined isochron age of 130 5 3 6 ma from the main mineralization stage which is similar to the zircon age of 134 9 0 9 ma for the andesitic porphyry related to mineralization we therefore proposed that erdaohezi is a low sulfidation epithermal pb zn polymetallic deposit and fluid immiscibility was the dominant mechanism of ore deposition mineralization occurred in an early cretaceous back arc extensional setting that was related to the subduction of the paleo pacific plate

distinguishing magmatic from subsolidus epidote laser probe oxygen isotope compositions epidote occurs in four textural varieties in the mount lowe intrusion of southern california euhedra anhedra intergrowths and cross cutting veins of these conspicuous elongate euhedra which range up to 3 cm in length meet most of the established textural criteria for magmatic epidote equant anhedral grains which are 5 mm in diameter are texturally ambiguous although rare allanite cores are suggestive of a magmatic origin epidote intergrowths with hornblende and biotite also meet certain textural criteria for crystallization from a magma notably euhedral faces against biotite finally late stage veins of epidote cross cut all phases in the rock and are likely subsolidus oxygen isotopic compositions of these four textural varieties of epidote determined using the laser probe indicate that the use of textural criteria alone in establishing epidote parageneses can be misleading intracrystalline 18o variations in the euhedra document both magmatic and subsolidus compositions oxygen isotope compositions are bimodal averaging 5 36 0 13 n 11 and 4 66 0 23 n 21 these data combined with plagioclase and zircon 18o values are interpreted to indicate that magmatic oxygen isotopic compositions have been preserved where epidote 18o is greater than 5 significant portions of each euhedral crystal have been affected by subsolidus exchange and are characterized by epidote 18o values less than 5 intracrystalline 18o values of epidote anhedra range from 4 50 to 6 08 and thus also document both magmatic and subsolidus compositions subsolidus exchange is volumetrically less significant in the anhedra than in the euhedra values of 18o for intergrowths and late stage cross cutting veins of epidote average 3 81 0 22 and document clearly subsolidus growth the data confirm that in the mount lowe intrusion large euhedra of epidote are magmatic in origin consistent with textural evidence the data also indicate that equant anhedra of epidote are also magmatic in origin and thus the absence of good crystal faces does not necessarily indicate subsolidus growth the subsolidus origin of intergrowths of epidote with euhedral faces against biotite indicates that well developed crystal faces do not require growth from a magma finally the subsolidus origin of the vein epidote is consistent with textural evidence the increased resolution available with laser based oxygen isotope measurements offers an important test for documenting whether epidote is of magmatic or subsolidus origin given the barometric significance of magmatic epidote oxygen isotope compositions can be used to aid in the interpretation of epidote bearing plutons

a complete oxygen isotope profile through the lower oceanic crust odp hole 735b abstract odp hole 735b located on the southwest indian ridge at 57 e is an in situ sampled long continuous section of lower oceanic crust oxygen isotope compositions of constituent minerals of leg 176 gabbros have been measured by uv laser oxygen isotope microprobe together with existing data from leg 118 a complete oxygen isotope profile through the lower oceanic crust has been obtained most clinopyroxenes and olivines have normal mantle values of 5 5 and 5 2 respectively while plagioclases show slight 18 o enrichment relative to its mantle value of 6 1 down hole variations of hole 735b gabbro indicate a downward decreasing 18 o profile with a kink at a depth of about 800 m below sea floor above this depth gabbros are depleted in 18 o relative to unaltered basalts while below 800 m they show nearly unmodified 18 o values abundant seawater penetration appears to be limited to the upper part of the lower crust at odp site 735 800 m into the gabbroic layer and 2 2 5 km into the oceanic crust from the top of pillow basalts mass balance calculations show that the lower crust formed under this ultra slow spreading ridge has an average 18 o value of 5 5 the whole crust at site 735 has an overall 18 o enrichment with 18 o values of 6 0 to 7 8 depending on the possible variation of the 18 o values of the upper pillow basalts and sheeted dykes the apparent difference in oxygen isotope compositions of ocean crusts formed with different spreading rates has important implications on the buffering of ocean water over geological time as well as on the oxygen recycling between crust and mantle through subduction the difference of seawater penetration between fast and slow spreading ridges could be related to their particular magmatic tectonic history during the formation and aging of the crust however more analyses on continuous sections through oceanic and ophiolitic crust in different tectonic settings are required to derive any predictive models

pore water evolution in oilfield sandstones constraints from oxygen isotope microanalyses of quartz cement abstract oxygen isotope microanalyses of authigenic quartz in combination with temperatures of quartz precipitation constrained by fluid inclusion microthermometry and burial history modelling are employed to trace the origin and evolution of pore waters in three distinct reservoirs of the brae formation in the miller and kingfisher fields north sea oxygen isotope ratios of quartz cements were measured in situ in nine sandstone thin sections with a cameca ims 4f ion microprobe in conjunction with quartz cement paragenesis in the reservoirs constrained from textural and cathodoluminescence cl microscopy studies pore water evolution was reconstructed from the time of deposition of the sandstones in the upper jurassic until the present cl photomicrographs of quartz overgrowths in the brae formation sandstones show three cement zones a b and c which can be related to different oxygen isotope compositions 1 the earliest and thinnest zone a homogeneous cl pattern with probable 18 o values between 23 and 26 direct measurements were not possible precipitated in the sandstones at temperatures 18 o values between 15 and 18 precipitated in the sandstones most likely between 70 and 90 c 3 the third zone c homogeneous cl pattern and directly measured 18 o values between 16 and 22 precipitated in the sandstones most likely at temperatures 90 c calculated oxygen isotope compositions of pore waters show that zone a quartz cements and enclosing concretionary calcite precipitated from a meteoric type fluid 7 during shallow burial 18 o 7 to a more 18 o enriched fluid 18 o 4 as burial continued to 3 0 km data from zone c quartz cements are consistent with further fluid evolution from 18 o 4 to basinal type fluids with 18 o similar to the present day formation water oxygen isotope composition 0 6 at 4 0 km burial a similar pore water evolution can be derived for all three reservoirs studied indicating that hydrogeologic evolution was similar across sandstones of the whole brae formation the quartz cement zones observed in the brae formation sandstones and the pore water history derived for the area studied is analogous to published petrographic and pore water evolution data from the nearby brent group reservoirs and from reservoirs located in the haltenbanken area on the atlantic margin offshore norway considering quartz cement is a major porosity occluding phase in many reservoir sandstones and because pore waters both dissolve quartz and carry the dissolved silica to cementation sites the data presented are valuable for improving the understanding and prediction of reservoir quality development in sandstones globally

the role of the grain boundary at chemical and isotopic fronts in marble during contact metamorphism carbon and oxygen isotopic profiles around a low pressure metasomatic wollastonite reaction front in a marble of the hida metamorphic terrain central japan display typical metamorphic fluid enhanced isotopic zonations isotopic profiles obtained from detailed microscale analyses perpendicular to the chemical reaction front in calcite marble show that diffusion enhanced isotopic exchange may control these profiles carbon and oxygen isotopic behaviour in grain boundaries is remarkably different oxygen isotopic troughs 18o depleted rims around the calcite grain boundaries are widely observed in this contact aureole demonstrating that diffusion of oxygen in calcite grain boundary dominates over lattice diffusion in calcite in contrast no difference is observed in carbon isotopic profiles obtained from grain cores and rims there is thus no specific role of the grain boundary for diffusion of carbonic species in the metamorphic fluid during transportation carbon chemical species such as co2 and co3 ions in metamorphic fluid migrate mainly through lattice diffusion the carbon and oxygen isotope profiles may be modelled by diffusion into a semi infinite medium empirically lattice diffusion of oxygen isotopes is almost six times faster than that of carbon isotopes and oxygen grain boundary diffusion is ten times faster than oxygen lattice diffusion oxygen isotopic results around the wollastonite vein indicate that migration of the metamorphic fluid into calcite marble was small and was parallel to the aquifer from the stability of wollastonite and the attainment of oxygen isotopic equilibrium we suggest that diffusion of oxygen occurred through an aqueous fluid phase the timescale of formation of the oxygen isotopic profile around the wollastonite vein is calculated to be about 0 76 106 years using the experimentally determined diffusion constant

mineralogy fluid inclusions and s pb h o isotopes of the erdaokan ag pb zn deposit duobaoshan metallogenic belt ne china implications for ore genesis abstract the recently discovered erdaokan ag pb zn deposit is located in the duobaoshan gold copper metallogenic belt in the eastern part of the central asian orogenic belt the ore bodies occur mainly as veins hosted in the breccia three stages of mineralization including early magnetite quartz pyrite middle silver sulfide bitumen quartz and late carbonate stages were recognized here we report results from electron microprobe analysis epma s pb h o isotopes and fluid inclusions studies to gain insights into the salient characteristics of the ore mineralization and mechanism of silver precipitation the silver occurs mainly as argentite pyrargyrite and invisible silver in the tetrahedrite grains in which ag fe and as isomorphically substituted cu zn and sb respectively the homogenization temperatures of fluid inclusions in the early middle and late stage mineralisation range from 96 to 179 c 78 to 178 c and 98 to 191 c respectively the fluid salinities vary from 0 35 to 5 54 wt nacl equiv the 34s values of the pyrite and galena show a range from 0 97 to 9 31 206pb 204pb vary from 18 0125 to 18 1864 207pb 204pb from 15 561 to 15 081 and 208pb 204pb from 38 0445 to 37 6979 with a mean of 18 0298 15 5125 and 37 7281 respectively the d and 18owater values of the quartz from the ore body range from 119 1 to 109 7 and 4 64 to 1 98 respectively based on these results we argue that the ore forming fluids were derived from a magmatic source with fluid mixing as the dominant mechanism for silver precipitation involving hydrocarbon fluid interaction as inferred from the presence of bitumen in the ore

mineral assemblage of sandaowanzi tellurium gold deposit in heilongjiang province and its genetic significance the sandaowanzi tellurium gold deposit is a typical telluride gold deposit in northern heilongjiang province the ore deposit located in the central section of the da hinggan mountains microscope observation and electron microprobe analyses of mineral assemblages of this deposit reveal that 6 different kinds of tellurides such as petzite sylvanite calaverite hessite and altaite are existent in ores of this ore deposit lots of native gold occurring in veins of quartz and petzite or coexistent with tellurides were also found in this ore deposit epma test shows that au possesses 85 64 93 41 and ag possesses 6 17 13 48 in native gold which can be classified as ag bearing native gold with gold fineness of 864 938 tellurium could easily replace sulfur in middle low temperature making tellurium dispersed in lattice of sulfides in the isomorphous form whereas under high tellurium fugacity conditions tellurium could easily coexist with au and ag to form a number of tellurides

reddish metagranites from the gennargentu igneous complex sardinia italy insight into metasomatism induced by magma mingling the recrystallization of quartz and plagioclase to higher calcium concentrations the progressive increase in the mgo mgo feo of chlorite closer to the contact indicates that this phase also recrystallized the iron released during chlorite recrystallization was buffered by hematite formation in the pores of metasomatic k feldspar the gennargentu metagranites provide evidence that metasomatic fluids can play a major role in driving metamorphic reactions in contact aureoles for instance the expected increase of ca in plagioclase owing to thermal equilibration was not achieved in the high t zone of the aureole because of fluid assisted removal of cations we conclude that caution should be taken when interpreting the processes that underpin contact metamorphism in terms of thermally driven ionic diffusion alone because the role of fluids may be significant if not overwhelming in the domains closest to the magmatic source

origin of the badaguan porphyry cumo deposit inner mongolia northeast china constraints from geology isotope geochemistry and geochronology abstract the badaguan porphyry cu mo deposit is located in the derbugan metallogenic belt of northeastern inner mongolia china the host granodioritic porphyry and the wall rock granitic porphyry were emplaced at 230 ma and 238 ma respectively the granodioritic porphyry has 87 sr 86 sr i values of 0 70535 0 70549 e nd t values of 0 41 1 17 e hf t values of 1 30 6 51 and two stage model ages t dm2 of 1131 848 ma in contrast the granitic porphyry is characterized by e hf t values from 0 75 to 7 28 that yield t dm2 model ages of 1355 816 ma the geochemical and sr nd hf isotopic data for the magmatic rocks associated with the badaguan porphyry cu mo deposit indicate that these intrusions were generated by the partial melting of juvenile lower crust the 18 o values of ore fluids from different mineralizing stages are between 6 0 and 1 5 and the fluid d water values vary from 119 3 to 140 0 indicating a mixed fluid of magmatic and meteoric water the s pb isotopes show that the metal was mostly derived from a deep seated magma that involved some crustal materials with a narrow 34 s range 2 4 to 3 5 we infer that the badaguan porphyry cu mo deposit formed during a period of southeast directed subduction of the mongol okhotsk oceanic plate beneath the erguna block

ion microprobe analysis of oxygen isotope ratios in quartz from skye granite healed micro cracks fluid flow and hydrothermal exchange quartz grains in hydrothermally altered granites from the isle of skye are highly heterogeneous and not equilibrated in oxygen isotope ratio at the 20 m scale ion microprobe analysis of one grain shows a gradient of 13 over 400 m and a greater range in 18o than all quartz previously analyzed on the isle of skye other crystals from the same outcrop are homogeneous digitized cathodoluminescence images reveal patterns of magmatic zoning and brittle fracturing not otherwise detectable the ion probe analysis correlates low 18o values on a micro scale to one set of healed cracks thus quartz exchanges oxygen isotopes primarily by solution and reprecipitation along fractures in contrast to more reactive feldspar that appears to exchange from the grain boundary inward macroscopic models of isotope exchange are not realistic for these rocks the flow of hydrothermal fluids was heterogeneous anisotropic and crack controlled

u pb and re os geochronology of the bainaimiao cu mo au deposit on the northern margin of the north china craton central asia orogenic belt implications for ore genesis and geodynamic setting abstract the bainaimiao cu mo au deposit located at the northern margin of the north china craton ncc in central inner mongolia is a large cu dominant deposit orebodies are hosted in strongly deformed and metamorphosed granodiorite porphyry intrusions or in ew trending shear zones in greenschist and sericite felsic schist of the bainaimiao group mineralization can be divided into early middle and late stages characterized by quartz pyrite polymetallic quartz sulfides and carbonate quartz respectively hydrothermal activity led to pervasive silicification k feldspar biotite and chlorite epidote carbonate alteration eight samples from cu mo bearing quartz veins and massive sulfide ores in greenschist were collected from the viii orebody in the north ore belt and molybdenite separates were selected for re os analyses the concentrations of re and 187 os range from 216 6 to 1051 ppm and 2302 to 4913 ppb respectively all samples give re os model ages between 441 2 and 445 9 ma and yielded an isochron age of 445 0 3 4 ma mswd 0 26 with an initial 187 os of 4 17 ppb a granodiorite porphyry sample for shrimp u pb dating was collected from the underground of the xiii orebody of the north ore belt spots from 14 zircon grains have 206 pb 238 u values between 426 2 and 462 9 ma and form a tight cluster on concordia yielding a weighted mean 206 pb 238 u age of 445 6 ma this is considered to be the best estimate of crystallization age of the granodiorite porphyry the re os isochron age of the molybdenite is consistent with the shrimp u pb age of the granodiorite porphyry which indicates that the deposit is a porphyry system of paleozoic age according to geodynamic setting and geological history of the northern margin of the ncc the deposit was probably related to magmatic activity of the middle paleozoic ondor sum subduction accretion complex bainaimiao arc during the devonian the bainaimiao arc was accreted to the northern margin of the ncc collision between the bainaimiao arc and ncc led to regional metamorphism of the ore hosting terrane and ore metals were remobilized in this process gold mineralization was probably overprinted onto the earlier cu mo mineralization

the correlation of reaction and isotope fronts and the mechanism of metamorphic fluid flow infiltration of a metabasite sill from islay scotland by an h2o co2 fluid caused 1 modification of delta 18 o and 2 carbonation at the sill margins maps of delta 18 o and reaction progress were constructed from a 20 x 47 7 metre sample grid across

water rock interactions in the basement beneath long valley caldera an oxygen isotope study of the long valley exploratory well drill cores abstract the long valley exploratory well at the center of the resurgent dome of long valley caldera penetrated pre caldera basement rocks at a depth of 2101 72 2313 0 m beneath the caldera forming bishop tuff and post caldera early rhyolite the basement rocks contain prominent quartzites with ubiquitous milky white quartz veins with minor calcite and pyrite and fractures of varied orientation and geometry the other members of the basement sequence are very fine grained quartz rich graphitic pelites with calcite veins spotted hornfels and shallow intrusive rocks previous studies established the presence of a post caldera paleohydrothermal system 500 100 ka to a depth of 2000 m that affected the bishop tuff and a recent 40 ka to present hydrothermal system at shallow depth

the cause of the glacial to interglacial atmospheric co2 change a polar alkalinity hypothesis in an attempt to create a scenario for the cause of the glacial to interglacial co2 change recorded in air trapped in polar ice we call on an increase in the alkalinity of polar surface waters in this way we circumvent a major deficiency of the polar nutrient scenarios of sarmiento and toggweiler 1984 siegenthaler and wenk 1984 and knox and mcelroy 1984 namely our scenario does not require a drop in the nutrient content of polar surface waters in conformity with the demonstration by boyle 1988a b that the cadmium content of planktonic foraminifera from polar regions did not decrease from late glacial to holocene time the rise in alkalinity required by our model is a natural consequence of the demise during glacial time of north atlantic deep water as a major force in ocean circulation and of the nutrient maximum deepening of boyle 1988b rather than being original our hypothesis builds on the concept basic to the polar nutrient hypotheses namely that the co2 partial pressure in polar waters controls that for both the atmosphere and warm surface ocean it also requires the alkalinity increase in surface waters produced by boyle s nutrient deepening

oxygen isotope constraints on metamorphic fluid flow townshend dam vermont u s a fluid rock interaction during amphibolite facies metamorphism has been investigated for rocks exposed in a single 400 m long lithologically heterogeneous outcrop near townshend vermont usa oxygen isotopic compositions have been measured in profiles across single garnet crystals from thirteen samples and from hornblende and garnet separates from thirty three fine grained samples this outcrop was previously studied who measured large oxygen isotope gradients 3 per thousand in garnets from one sample and inferred large amounts of pervasive fluid flow all of the garnets that we have analyzed show less isotopic zonation le 1 per thousand twelve of them have zonation 0 5 per thousand and the mineral separate data imply both a strong correlation of isotopic composition with rock type and large gradients in peak metamorphic fluid isotopic compositions although devolatilization reactions in these rocks must have produced metamorphic fluids the data preclude cross foliation time integrated fluid fluxes greater than 300 600 cm sup 3 cm sup 2 during prograde amphibolite facies metamorphism the isotopic trends can all be interpreted in terms of closed system behavior channeled fluid flow or diffusive exchange of oxygen in an interconnected grain boundary fluid and within uncertainty cross strike advective fluxes could have been zero any significant flow at this locality was dominantly either layer parallel or channeled out of the system in veins more if all fluid flow occurred in veins then their spacing must have been less than 300 600 m the data are inconsistent with massive and pervasive metamorphic fluid flow across strike but do not address layer parallel flow less

diffusion in zircon despite its low abundance in most rocks zircon is extraordinarily useful in interpreting crustal histories the importance of u th pb isotopic dating of zircon is well and long established davis et al this volume parrish et al this volume zircon also tends to incorporate trace elements useful as geochemical tracers such as the ree y and hf a number of characteristics of zircon encourage the preservation of internal isotopic and chemical variations often on extremely fine scale which provide valuable insight into thermal histories and past geochemical environments the relative insolubility of zircon in crustal melts and fluids as well as its general resistance to chemical and physical breakdown often result in the existence of several generations of geochemical information in a single zircon grain the fact that this information is so frequently retained as evidenced through backscattered electron or cathodoluminescence imaging that often reveal fine scale zoning down to the sub micron scale has long suggested that diffusion of most elements is quite sluggish in zircon in this chapter we present an overview of the findings to date from laboratory measurements of diffusion of cations and oxygen in zircon because of its importance as a geochronometer attempts have been made to measure diffusion especially of pb for over 30 years but only in the last decade or so have profiling techniques with adequate depth resolution been employed in these studies resulting in a plethora of new diffusion data these findings have important implications for isotopic dating interpretation of stable isotope ratios closure temperatures and formation and preservation of primary chemical composition and zoning in zircon efforts have been made for some time to quantify and characterize diffusion in zircon most notably of pb in deference to its significance in interpreting pb isotopic signatures and refining understanding of thermal histories as is evident from

metallogeny and craton destruction records from the north china craton abstract the link between metallogeny and craton destruction in the north china craton ncc remains poorly understood particularly the mechanisms within the interior of the craton in this overview we summarize the major stages in the history of formation and evolution of the ncc the spatio temporal distribution and types of major ore species as well as mantle contribution to the metallogeny in an attempt to evaluate the geodynamic settings of metallogeny and the mechanisms of formation of the ore deposits the early precambrian history of the ncc witnessed the amalgamation of micro blocks and construction of the fundamental tectonic architecture of the craton by 2 5 ga the boundaries of these micro blocks and the margins of the ncc remained as weak zones and were the principal locales along which inhomogeneous destruction of the craton occurred during later tectonothermal events these zones record the formation of orogeny related gold copper iron and titanium during the early to middle paleoproterozoic with ages ranging from 2 5 to 1 8 ma the early ordovician kimberlite and diamond mineralization at ca 480 ma the late carboniferous and early to middle permian calc alkaline i type granitoids and gold deposits of 324 300 ma and the triassic alkaline rocks and gold silver polymetallic deposits occurring along these zones and the margins of the blocks correlate with rising mantle plume southward subduction of the siberian plate and northward subduction of the yangtze plate respectively the voluminous jurassic granitoids and cretaceous intrusives carrying gold molybdenum copper lead and zinc deposits are also localized along the weak zones and block margins the concentration of most of these deposits in the eastern part of the ncc invokes correlation with lithosphere thinning associated with the westward subduction of the pacific plate although magmatism and mineralization have been recorded along the margins and few places within the interior of the ncc in the jurassic their peak occurred in the cretaceous in the eastern part of the ncc marking large scale destruction of the craton at this time the junctions of the boundaries between the micro continental blocks are characterized by extensive inhomogeneous thinning we propose that these junctions are probably for future mineral exploration targeting in the ncc

zircon u pb and molybdenite re os dating of the chalukou porphyry mo deposit in the northern great xing an range china and its geological significance abstract the newly discovered chalukou giant porphyry mo deposit located in the northern great xing an range is the biggest mo deposit in northeast china the chalukou mo deposit occurs in an intermediate acid complex and jurassic volcano sedimentary rocks of which granite porphyry quartz porphyry and fine grained granite are closely associated with mo mineralization however the ages of the igneous rocks and mo mineralization are poorly constrained in this paper we report precise in situ la icp ms zircon u pb dates for the monzogranite granite porphyry quartz porphyry fine grained granite rhyolite porphyry diorite porphyry and andesite porphyry in the chalukou deposit corresponding with ages of 162 2 ma 149 5 ma 148 2 ma 148 1 ma 137 3 ma 133 2 ma and 132 2 ma respectively analyses of six molybdenite samples yielded a re os isochron age of 148 1 ma these data indicate that the sequence of the magmatic activity in the chalukou deposit ranges from jurassic volcano sedimentary rocks and monzogranite through late jurassic granite porphyry quartz porphyry and fine grained granite to early cretaceous rhyolite porphyry diorite porphyry and andesite porphyry the chalukou porphyry mo deposit was formed in the late jurassic and occurred in a transitional tectonic setting from compression to extension caused by subduction of the paleo pacific oceanic plate

ion microprobe study of intragrain micropermeability in alkali feldspars alkali feldspar cleavage fragments from the klokken layered syenite south greenland were heated to 700 c at 0 1 gpa in 99 h218o for 75 h these samples were then polished and imaged by ion microprobe for 18o the feldspars were known to contain areas of pristine braid micro perthite which were not turbid and areas of deuteric patch perthite which were turbid turbidity is related to the presence of micropores in the feldspars on imaging the grain it was found that the 18o had penetrated into the parts of the grain which were microporous and not into the pristine areas micropores are therefore responsible for rendering the feldspars permeable as well as porous the implications of micropermeable feldspars in several areas of geology are discussed

obtaining equilibrium oxygen isotope fractionations from rocks theory and examples a generalized approach for retrieving equilibrium isotope fractionations from natural rocks is proposed in which models of prograde reaction histories and retrograde diffusional exchange are used to identify coexisting minerals with similar isotope closure temperatures examples using literature data and new analyses from 32 natural amphibolite facies schists demonstrate both the feasibility and limitations of obtaining equilibrium oxygen isotope fractionations from minerals in natural rocks by screening samples according to the theoretical models natural data are shown to have highly consistent mineral fractionations 2 reproducibilities of 0 16 to 0 54 that within uncertainty reproduce experimental determinations among the minerals quartz biotite muscovite and calcic amphibole this correspondence indicates that the proposed theoretically based selection criteria improve the likelihood of measuring equilibrium fractionations the new data further corroborate the expected progressive enrichment of 18o in the orthosilicates with increasing al si relative to fe mg ky grt 1 05 st grt 0 6 and st cld 0 3 at 525 575 c in contrast typical samples that fail to satisfy screening criteria exhibit fractionations involving quartz biotite and amphibole that are strongly disequilibrium because of exchange during cooling theoretical screening of samples prior to isotope analysis allows robust independent assessment of theoretical and experimental determinations of equilibrium isotope fractionations

trace and minor elements in sphalerite from base metal deposits in south china a la icpms study laser ablation icp mass spectroscopy has been used to investigate the geochemistry of sphalerite in a range of nine zn pb deposits in south china the deposits which are of different ages and belong to different metallogenic provinces have been assigned to the following genetic types skarn hetaoping luziyuan syngenetic massive sulphide dabaoshan laochang and bainiuchang and mississippi valley type huize mengxing niujiaotang based on the features of the ore even though their origin is heavily debated based on other criteria the giant jinding deposit is considered separately sphalerite from each genetic class of deposit shows a distinct chemical signature sphalerite from the skarn deposits is characterised by elevated lattice bound concentrations of co and mn the distal character of these skarn systems is reflected by the low in content of sphalerite the three syngenetic massive sulphide deposits feature sphalerite strongly enriched in in sn and ga whereas the deposits of mvt type are typically enriched in ge cd tl and as these divergent characters are reflected in absolute element abundances as well as in element ratios time resolved depth profiles for sphalerite from the chinese deposits confirm the presence of elements such as co in ge ga and cd in solid solution but the dataset expands the understanding of sphalerite mineral chemistry by also indicating that other elements whose ability to enter the crystal structure of sphalerite has been previously debated ag sn tl sb may also be in solid solution sphalerite is a refractory mineral and trace element analysis of sphalerite shows promise as a tracer of ore genesis even in overprinted ores systematic work on larger sample suites may help define the geochemical signature of different metallogenic epochs in regions as geologically complex as south china and help resolve the mechanism by which many of the debated ore deposits were formed

cathodoluminescence and trace element zoning in quartz phenocrysts and xenocrysts quartz phenocrysts and xenocrysts are a common component of volcanic rocks but rarely contribute to our understanding of magmatic or eruptive processes due to an apparent internal chemical and structural homogeneity scanning electron microscopy cathodoluminescence imaging sem cl and secondary ion mass spectroscopy ion microprobe analysis sims are used here to demonstrate that quartz crystals in volcanic rocks show hitherto unrecognised internal structural and chemical zoning two contrasting crystal morphologies have been studied porphyritic euhedral bipyramidal quartz crystals in dacite from bonne nuit bay jersey uk show fine scale growth zoning in sem cl zones are narrow 1 40 m wide planar parallel to crystal faces and overgrow more broadly zoned rounded cores these crystals are interpreted to have formed at small degrees of undercooling by diffusion controlled growth quiescent magma conditions are indicated by the preservation of an al rich diffusive boundary layer which has not been removed by melt shearing during convection in contrast rounded and embayed porphyritic quartz grains in a quartz dacite from the esperanza mine e1 salvador northern chile show broad internal sem cl zones with irregular boundaries some of which are truncated by grain margins indicating dissolution crystal rounding may occur by dissolution or melting due to thermal or thermal chemical disequilibrium with surrounding melt and embayments by gas bubble enhanced convective dissolution are consistent with the development of incipient ocelli textures strings of amphibole inclusions adjacent to quartz rims several episodes of rounding can be recognised in some xenocrysts ion microprobe sims analysis of quartz from both samples shows that a1 contents are higher in areas of bright cl emission previous studies of cl in quartz have suggested that several factors control luminescence although a1 substitution for si in sio4 tetrahedra may be partly responsible for sem cl zoning recorded in volcanic quartz additional mechanisms including the effect of growth rate on defect density probably also play a major role

the rapid heating defocused beam technique a co2 laser based method for highly precise and accurate determination of δ18o values of quartz abstract we describe a laser fluorination technique specifically for quartz that allows both high accuracy and high precision determination of oxygen isotope ratios regardless of grain size the rapid heating defocused beam technique rhd utilizes a defocused 32 w co 2 laser at full power which delivers 17 w 20 w mm 2 to the sample to quickly react quartz in contrast other recent laser fluorination studies use a tightly focused laser beam and slow heating i e sharp and kirschner 1995 fouillac and girard 1996 kirschner and sharp 1997 and find laser analysis of fine grained quartz to be inaccurate three quartz standards nbs 28 qz bra and qz cwru were analyzed using the rhd technique at the university of wisconsin to test for grain size effects rhd analyses show no correlation between grain size and 18 o values and are in excellent agreement with 18 o values obtained using conventional fluorination techniques additional analyses of the same quartz standards performed at university of wisconsin using slow heating and a focused beam yield 18 o values that are both less precise and significantly up to 0 8 lower than the accepted values attempts to use the rhd technique with a 20 w co 2 laser which delivers 8 w 10 w mm 2 to the sample at brgm were unsuccessful probably due to insufficient power density of the defocused beam we conclude that the rhd technique yields excellent accuracy and precision but that power densities of 15 20 w mm 2 may be necessary across a large part of the sample surface we recommend the use of lasers with at least 30 w of power

dyke swarms and their role in the genesis of world class gold deposits insights from the jiaodong peninsula china abstract jiaodong peninsula located at the southeastern margin of the north china craton is well known for its rich endowment of super large gold deposits this region is also characterized by hundreds of intermediate mafic dykes that cluster into several dyke swarms in this study we present zircon u pb ages which show that the timing of dyke emplacement as ca 120 ma which followed the crystallization of the quartz diorite porphyry at ca 130 ma these ages coincide with the peak ages reported for magmatism and metallogeny in the central north china craton the various ages 2450 2570 and 154 ma from the inherited zircon crystals in these rocks suggest that substantial lower to middle crustal basement rocks and jurassic granitoids were involved during dyke emplacement the dyke swarms varying between alkaline and subalkaline are compositionally low si low ti lamprophyre and low si high ti dolerite porphyry in the western of the jiaodong peninsula whereas those in the eastern part are composed of both high si low ti and low si high ti lamprophyres these features imply multiple sources for the dykes from convective asthenospheric mantle to ancient enriched lithospheric mantle with magma generation at different depths involving mixture of slab derived hydrous fluids the source magmas of the dykes were hydrous and enriched in volatiles as well as ore components and their evolution occurred under high oxygen fugacity conditions the relatively rapid emplacement and cooling of the dyke systems enabled the migration of fluids into ore controlling faults or fractures we envisage that the dyke swarms played an important role in generating the world class gold mineralization of jiaodong

an early cretaceous ag pb zn mineralization at halasheng in the south erguna block ne china constraints from u pb and rb sr geochronology geochemistry and sr nd hf isotopes abstract the halasheng deposit located in the southern erguna block is a vein type ag pb zn deposit in the derbugan metallogenic belt the orebodies hosted in middle late jurassic volcanic rocks show a close spatial and temporal relationship with early cretaceous granites zircon u pb dating suggests that the granites were emplaced at 134 128 ma rb sr dating of ore related sphalerite gives an imprecise age of 122 18 ma indicating that the halasheng deposit formed in the early cretaceous whole rock major and trace element analyses show that the cretaceous granites belong to the metaluminous to peraluminous shoshonite to high k calc alkaline series and can be classified as a type granites they are enriched in large ion lithophile elements lile and light rare earth elements lree but depleted in high field strength elements hfse and heavy rare earth elements hree the quartz monzonite which has a spatial relationship with mineralization has low initial 87sr 86sr 0 7058 0 7069 and positive end t 0 42 0 61 and ehf t 3 47 6 45 with nd and hf two stage model ages of 0 81 0 85 ga and 0 69 0 86 ga respectively these geochemical features are similar to those of major mesozoic granite intrusions in the erguna block we propose that these graintes originated from partial melting of juvenile crust in an intraplate extensional setting taken together the halasheng ag pb zn deposit formed in the early cretaceous after the orogeny related to closure of the mongol okhotsk ocean the relatively low temperature of ag pb zn ore and alteration mineralogy suggest that there is only a distal relationship if any to nearby potentially causative granite intrusions

oxygen isotope zoning profiles in hydrothermally altered feldspars estimating the duration of water rock interaction the characterization of intragrain mineralogical and isotopic zoning patterns provides the basis for estimating the duration of fluid rock interaction associated with mineral replacement reactions in the rico colorado hydrothermal system oxygen isotope ratios in reaction rims on partially reacted plagioclase feldspar exhibit some of the largest gradients yet reported for individual grains to 15 o the extent of rim formation and accompanying isotopic exchange vary across the system as a function of temperature fluid isotope composition and the local fluid rock ratio distal feldspars show narrow rims with 1 8 o enrichments relative to pristine feldspars feldspars intermediate or proximal to the system s center have wide reaction rims or are completely exchanged and show 180 depletions formation times of reaction rims and associated isotopic patterns have been estimated with a coupled reaction diffusion model that suggests that hotter 250 350 c hydrothermal circulation was active for 100 300 k y in the center part of the system perhaps only while the igneous heat engine was still magma cooler 150 200 c circulation was widespread lasting for 1000 k y

bioaccumulation record and paleoclimatic significance in the western bransfield strait the last 2000 years abstract two gravity cores a 3 and a 6 from the western basin of the bransfield strait antarctica were recovered during the bio hesperides expedition fruela 96 both cores consist mainly of hemipelagic and laminated muds with black layers rich in sand sized volcanic ash geochemical analyses toc and opal radiometric dating techniques ams 14 c and 210 pb and micropaleontological analyses diatoms were performed on both cores ams analyses on toc yielded 14 c ages older than expected 3960 50 yr bp for the core top of a 3 and 3410 50 yr bp for a 6 210 pb analyses revealed that core top age for both gravity cores could be estimated to be about 100 15 yr bp the results of diatom analyses were related to the sequence of neoglacial events that have occurred over the last two millennia the abundance patterns of chaetoceros rs the biogenic silica content and the abundance of diatom valves agree with the high productivity values previously reported for the bransfield strait waters the significant recent reduction in resting spores of the diatom chaetoceros suggests as a reduction in surface productivity trend differences between chaetoceros resting spore abundance and toc contents are explained in terms of organic matter preservation diatom communities from the bransfield strait did not play an important role in the global co 2 cycle during cold periods bio and geochemical changes have an overprinted high frequency cyclicity at about 200 300 yr which might be related to the 200 yr solar cycle

geology of the sandaowanzi telluride gold deposit of the northern great xing an range ne china geochronology and tectonic controls abstract the sandaowanzi gold telluride deposit is a new discovery with dominance in gold tellurides in northeastern china the deposit is hosted in quartz veins intruding sub alkaline volcanic rocks there are two types of gold telluride ores in the sandaowanzi ore deposit i e the vein ores and the disseminated ores calaverite krennerite sylvanite petzite empressite hessite and stuetzite are the dominant au ag bearing minerals either in vein ores or in disseminated ores minor amount of other tellurides e g coloradoite altaite and sulfides e g pyrite sphalerite galena chalcopyrite and chalcocite mostly occur in the disseminated ores the gold bearing quartz veins crosscut volcanic host rocks which are dated at 135 3 124 7 ma by la icp ms u pb zircon method the latter unconformably overly a monzogranite dated as 181 6 ma diabase dikes dated at 116 6 ma intrude the gold bearing quartz veins the age data thereby bracket the timing of gold mineralization between 125 3 and 116 6 ma these geochronologic data are consistent with field relations regional comparison reveals that the widespread volcanism in the great xing an range is a product of the subduction of the izanagi plate beneath the eurasian plate gold telluride mineralization was contemporaneous with regional extension and magmatism as the subducting izanagi plate rolled back

evidence of a high productivity area off the coast of malaga from studies of diatoms in surface sediments abstract the assemblages of diatoms contained in nineteen surface sediment samples recovered off the coast of malaga province spain between 5 w and 4 38 w have been analysed the variations observed in the diatom assemblage point to the presence of nutrient enriched waters transported laterally from the centre of an upwelling that occurs to the west of the study area the utility of species such as paralia sulcata thalassionema nitzschioides and the spores of chaetoceros spp in the reconstruction of physico chemical and biological characteristics and of the spatial structure of the upwelling is confirmed

oxygen diffusion in monazite abstract we report measurements of oxygen diffusion in natural monazites under both dry 1 atm conditions and hydrothermal conditions for dry experiments 18o enriched cepo4 powder and monazite crystals were sealed in ag pd capsules with a solid buffer to buffer at nno and annealed in 1 atm furnaces hydrothermal runs were conducted in cold seal pressure vessels where monazite grains were encapsulated with 18o enriched water following the diffusion anneals oxygen concentration profiles were measured with nuclear reaction analysis nra using the reaction 18o p 15n over the temperature range 850 1100 c the arrhenius relation determined for dry diffusion experiments on monazite is given by d dry 1 9 10 6 exp 356 26 kj mol 1 r t m 2 s 1 there is no evidence of diffusional anisotropy under wet conditions at 100 mpa water pressure over the temperature range 700 880 c oxygen diffusion can be described by the arrhenius relationship d wet 3 1 10 17 exp 100 20 kj mol 1 r t m 2 s 1 under hydrothermal conditions at 800 c oxygen diffusion shows little dependence upon ph2o over the range 10 160 mpa oxygen diffusion under hydrothermal conditions has a significantly lower activation energy for diffusion than under dry conditions as has been found the case for many other minerals both silicate and nonsilicate given these differences in activation energies the differences between dry and wet diffusion rates increase with lower temperatures for example at 600 c dry diffusion will be more than 4 orders of magnitude slower than diffusion under hydrothermal conditions these disparate diffusivities will result in pronounced differences in the degree of retentivity of oxygen isotope signatures for instance under dry conditions presumably rare in the crust and high lower crustal temperatures 800 c monazite cores of 70 m radii will preserve o isotope ratios for about 500 000 years by comparison they would be retained at this temperature under wet conditions for about 15 000 years

kinetically limited isotope exchange in a shallow level normal fault mineral mountains utah we have conducted a stable isotope and geochemical study of the corral canyon fault zone a shallow level low angle normal fault on the west flank of the mineral mountains in southwest utah our stable isotope and geochemical data document the infiltration of local meteoric water during brittle deformation and hydrothermal alteration of the shear zone during tertiary basin and range extensional faulting within the fault zone 18o depletion correlates with progressive hydrothermal alteration and cataclasis demonstrating that the processes of fluid infiltration hydrothermal alteration fracturing comminution of grains and 18o exchange took place concurrently interpretation of our data using a model of combined fluid flow and kinetically limited isotope exchange leads us to conclude that the exposed fault zone was infiltrated by isotopically unevolved fluids from the wall rock adjacent to the fault zone and that an important component of fluid flow in this fault was between the wall rock and the fault zone rather than strictly within the fault plane we propose that the rate of isotopic alteration in shallow level fault zones is enhanced by comminution and recrystallization of grains during deformation so that fluids in the wall rock because of the relatively coarser grain size remain relatively unevolved until they infiltrate the fault zone where they rapidly become isotopically evolved due to exchange with cataclasized grains we present a general model for calculating the duration of isotopic alteration in flow systems characterized by kinetically limited isotope exchange calculated exchange durations for the corral canyon fault zone are short on the order of thousands to a few hundreds of thousands of years compared to the likely duration of deformation of millions of years the geologically short duration of isotope exchange leads us to suggest that the fluid flow responsible for the isotopic alteration was episodic of short duration and possibly related to discrete seismic events this result corroborates diverse lines of evidence that support a model of alternating fluid flow and permeability sealing by hydrothermal precipitation within fault zones

geology mineralogy and stable isotope geochemistry of the dzuunmod area in northern mongolia constraints for gold ore genesis and sources abstract the dzuunmod area located in the north khentii gold belt nkgb of northern mongolia includes lode gold deposits such as gatsuurt sujigtei and boroo with several minor gold deposits and occurrences they show similar hydrothermal alteration assemblages sericitic siliceous and potassic and ore mineral assemblages pyrite and arsenopyrite with minor amount of galena sphalerite and chalcopyrite gold occurs as native form and invisible gold in pyrite and arsenopyrite the major sulfide minerals are separated into earlier non auriferous stage and later auriferous grains containing invisible gold native gold postdates the major sulfide mineralization gold and arsenic content of pyrite grains indicates that gold exists mainly as solid solution form au 1 in the gatsuurt and boroo deposit whereas gold nanoparticle au0 is present in the sujigtei deposit high co ni and mo ni ratios of pyrite grain suggest a post sedimentary or hydrothermal origin and the ore forming fluid was significantly affected by fluid host rock interactions during mineralization processes large variation of 34s values of pyrite and arsenopyrite from 2 6 to 17 2 indicates that sulfur seems to be mainly derived from a source with heterogeneous sulfur isotope composition even though the role of magmatic sulfur as one of possible sulfur sources cannot be ruled out consistent with geological evidence relatively positive 34s values suggest that sulfidation plays an important role for gold and sulfide precipitation the calculated 18o values of hydrothermal fluid from the measured 18o values of quartz samples from 14 7 to 17 7 indicate a metamorphic derivation of ore forming fluid gold mineralization processes in the dzuunmod area seem to occur several times by multiple input of hydrothermal fluid and fluid host rock interactions the gold deposits in the dzuunmod area are considered to be orogenic gold type influenced by fluid host rock interactions in the deposit area

fluid rock interaction in the miocene post caldera tejeda intrusive complex gran canaria canary islands insights from mineralogy and o and h isotope geochemistry the intra caldera volcaniclastic deposits of the miocene tejeda caldera on gran canaria host an similar to 12 km diameter intrusive complex comprising a peralkaline trachytic to phonolitic cone sheet swarm surrounding a central core of hypabyssal syenite stocks both intrusive rock types display textural and mineralogical features indicative of secondary fluid rock interaction including 1 deuteric mineral phases e g aegirine alkali amphibole analcime 2 turbid alkali feldspars and 3 hydrothermal mineral phases phyllosilicates fe ti oxides mn oxides and quartz altered cone sheets have whole rock delta o 18 values ranging from 0 center dot 1 to 10 center dot 0 parts per thousand n 22 and whole rock delta d values between 62 and 149 parts per thousand n 28 three altered syenite samples have whole rock delta o 18 values of 2 center dot 5 1 center dot 5 and 0 center dot 9 parts per thousand and corresponding delta d values of 91 99 and 121 parts per thousand the h2o concentrations of the altered cone sheets range from 0 center dot 4 to 0 center dot 8 wt n 28 and the altered syenites have h2o concentrations of 0 center dot 5 0 center dot 5 and 0 center dot 6 wt respectively the majority of altered samples are depleted in o 18 relative to the typical delta o 18 range for unaltered trachytes and syenites delta o 18 6 8 parts per thousand indicative of interaction with local meteoric water delta o 18 c 8 parts per thousand at temperatures epsilon 150 degrees c only one cone sheet sample appears petrographically unaltered and has a typical igneous isotopic composition delta o 18 7 center dot 1 parts per thousand delta d 48 parts per thousand and a relatively high h2o concentration 2 center dot 2 wt a weak correlation r 0 center dot 55 between delta d and h2o is observed in the cone sheets reflecting the combined effects of magmatic h2o exsolution and subsequent deuteric and hydrothermal alteration no systematic variation in delta o 18 or delta d was detected across the cone sheet swarm most likely reflecting overprinting of isotopic compositions during successive intrusive events however the highest delta o 18 values 8 center dot 2 10 center dot 0 parts per thousand occur in clay bearing cone sheets from the central part of the intrusive complex suggesting enhanced infiltration of relatively cool meteoric water in this area overall at least three phases of fluid rock interaction can be distinguished 1 deuteric alteration c 300 500 degrees c by late magmatic fluids expelled from a solidifying crystal mush 2 hydrothermal alteration epsilon 150 300 degrees c by meteoric water during the final stages of crystallization and or immediately following solidification of the intrusive complex 3 retrograde alteration related to the influx of relatively cool 150 degrees c meteoric waters

constraints on the petrologic structure of the subduction zone slab mantle interface from franciscan complex exotic ultramafic blocks ultramafic blocks within mud matrix melange of the franciscan complex california preserve a series of metasomatic mineral zones generated by infiltration of si rich hydrous fluids during subduction we describe the petrology and geochemistry of the metasomatic zones and compare them to current model predictions for the metasomatism of the mantle wedge by subduction zone fluids fluid flow affected a cr spinel lherzolite protolith to form first serpentinite then a talc dominated rock and finally an amphibole rich assemblage a diverse suite of accessory minerals in the amphibole rich zone titanite clinozoisite zircon apatite suggests that the trace element signature of subduction zone fluids may be fractionated in this zone oxygen isotopic evidence suggests that the ultramafic blocks equilibrated with metasomatic fluids during serpentinization and that subsequent reactions occurred in equilibrium with these fluids in a temperature range of 450 500 c whole rock geochemistry indicates mobility of many elements into and out of the blocks during metasomatism including elements such as ti which are currently considered to have low solubilities in such fluids taken as a whole the blocks appear to preserve the metasomatic structure of the slab mantle interface in subduction zones and imply that the chemistry of slab derived fluids is modified as they pass through these metasomatic zones in the mantle wedge our results suggest that the primary composition of subduction zone fluids is not likely reflected by arc magmas instead we propose that arc magmas are derived from regions of the mantle fluxed by fluids residual to the metasomatic processes we observe

micro analysis of sulfur isotope ratios and zonation by laser microprobe the university of wisconsin laser microprobe mass spectrometer system combines high spatial resolution with precise accurate and rapid analysis of sulfur isotope ratios spot sizes of 100 200 m are routine and much higher spatial resolution may be possible analytical precision ranges from 1 0 15 pyrite pyrrhotite sphalerite to 1 0 43 galena chalcopyrite comparison of laser microprobe and conventional combustion analyses indicates that laser 34s values are approximately equal to or lower than combustion values for these minerals and an empirical correction of 0 1 sphalerite to 1 4 pyrrhotite is required variations in 18o of so2 laser power density and burn duration affect the magnitude of this correction thus consistent technique is critical natural samples were analyzed by laser microprobe to evaluate the extent of sulfur isotope ratio zonation coexisting sulfide mineral pairs from the rua cove mine alaska show that isotopic equilibrium exists in the stockwork feeder zone while disequilibrium characterizes coexisting pairs from the overlying more rapidly cooled massive sulfide blanket conventional sulfur isotope extraction data on these samples are not valid due to the fine grained intergrown nature of the sulfide phases which precludes satisfactory mineral separation isotopically homogeneous sphalerite and pyrite crystals were found in samples from the amphibolite facies balmat mine while isotopically heterogeneous pyrite crystals were found in a sample from the upper greenschist facies sullivan mine sulfur isotope zonation up to 2 9 in 200 m was found in banded sphalerite blacksmoker chimney material from the bayda mine oman retrograde sulfides from the marcy anorthosite massif vary by 4 2 over 1 cm and finely disseminated sulfides from an amphibolite granulite facies transition zone sample southern india are in disequilibrium across the 25 cm facies transition these results show that sulfur isotope homogeneity may be attained in the cores of annealed high grade metamorphic minerals while lower temperature retrograde or hydrothermally deposited minerals are often isotopically zoned due to temporal variations in fluid chemistry and temperature

rates and mechanisms of isotopic exchange background the proliferation of stable isotope laboratories in recent years has led to a marked increase in the routine use of stable isotope analyses in geochemical studies this trend is likely to continue because of the development of micro analytical techniques e g laser ablation ion microprobe femtomole carrier gas methods etc for stable isotope analysis and the potential of these techniques to reveal the detailed sequence of thermal and fluid histories preserved in the rock record see mckibben et al 1998 equilibrium isotope fractionation factors and rates of isotopic exchange form the cornerstones for the interpretation of stable isotope data from natural systems indeed determination of the distribution of the stable isotopes of c o h s in gases fluids and minerals has become a standard and extremely powerful approach in elucidating the temperatures material fluxes rock and fluid origins and time scales associated with ancient and active fluid rock interaction processes in the earth s crust see valley et al 1986 although the thermodynamic principles underlying isotopic fractionation behavior were developed more than fifty years ago by urey 1947 the calibration of fractionation factors has proven to be difficult during the last four decades a great deal of progress has been made in determining the equilibrium fractionations of 18o 16o d h 13c 12c and 34s 32s among fluid and mineral components at high temperatures 400 c both from experimental exchange studies theoretical calculations using vibrational spectra semi empirical calculations using bond type considerations and empirical calibrations based on natural assemblages see references in o neil 1986 kyser 1987 criss 1991 1999 chacko et al this volume of these the experimental method is the most direct because it involves the least number of a priori assumptions despite the utility of the equilibrium approach in quantifying the isotopic behavior in select water rock

geochronology and geochemistry of the wunugetushan porphyry cu mo deposit in ne china and their geological significance abstract the wunugetushan porphyry cu mo deposit is located in the manzhouli district of ne china on the southern margin of the mesozoic mongol okhotsk orogenic belt concentric rings of hydrothermal alteration and cu mo mineralization surround an early middle jurassic monzogranitic porphyry the cu mo mineralization is clearly related to the quartz potassic and quartz sericite alteration molybdenite re os and groundmass 40 ar 39 ar of the host porphyry dates indicate that the ore formation and porphyry emplacement occurred at 177 6 4 5 ma and 179 0 1 9 ma respectively geochemically the host porphyry of the deposit is characterized by strong lree hree fractionation enrichment in lile ba rb u th and pb and depletion of hfse nb ta ti and hree the sr nd pb isotopic compositions of the porphyry display an varied initial 87 sr 86 sr i ratio a positive e nd t values and high 206 pb 204 pb t 207 pb 204 pb t and 208 pb 204 pb t ratios these data indicate that the magmatic source of the host porphyry comprised two end members lithospheric mantle metasomatized by fluids derived from the subducted slab and continental crust we infer that the primitive magma of the host porphyry was derived from crust mantle transition zone based on regional geology and geochemistry of the host porphyry the wunugetushan deposit is suggested to form in a continental collision environment after closure of the mongol okhotsk ocean

ion microprobe analysis of 18o 16o in authigenic and detrital quartz in the st peter sandstone michigan basin and wisconsin arch usa contrasting diagenetic histories abstract the oxygen isotopic compositions of authigenic quartz cements in sandstones provide a monitor of the temperatures compositions and origins of pore occluding fluids during diagenesis but quartz overgrowths are too fine grained to be amenable to conventional isotopic analysis we have used a cameca ims 4f ion microprobe to determine oxygen isotopic variations in authigenic and detrital quartz in four samples of the ordovician st peter sandstone from the michigan basin and wisconsin arch midwestern usa ion microprobe isotopic analyses have been successfully accomplished with an internal precision of 1 1 and a spatial resolution of 20 30 m at low mass resolution using a high voltage offset technique repeated analyses of the quartz standard demonstrate a reproducibility of close to 1 1 sd in good agreement with that expected from counting statistics the four ion probe samples were chosen as representative of thirteen samples that were mechanically and chemically disaggregated sieved and analysed as a function of sieve size by conventional bulk mineral techniques conventional and ion microprobe analyses are mutually consistent supporting the accuracy of the ion microprobe analyses within sample isotopic variations of up to 13 and micro scale isotopic variations of at least 4 over a distance of 100 m have been measured within quartz overgrowths in a sandstone from the wisconsin arch overgrowths are uniformly higher in 18o than detrital grains and gradients of up to 25 exist across a few microns 18o enriched quartz overgrowths in sandstones from the wisconsin arch show complex cl zonation and reflect one of two possible processes 1 low temperature quartz precipitation during mixing of meteoric waters with upwelling basinal fluids 2 higher temperature quartz precipitation during episodic gravity driven upwelling of warm basinal fluids of comparable isotopic composition to michigan basin fluids from the illinois basin related to evolution of mississippi valley type pb zn ore forming fluids quartz overgrowths in michigan basin sandstones which derived their silica locally by pressure solution are thought to have precipitated continuously over a range of temperatures from hot basinal fluids of restricted isotopic composition and circulation detrital quartz shows significant intea grain and intergrain isotopic variation 5 13 but no significant inter sample variation consistent with a uniform source of granitoid and metamorphic quartz in space and time

study on pyrite thermoelectricity ore forming fluids and h o rb sr isotopes of the yongxin gold deposit central asian orogenic belt implications for ore genesis and exploration abstract the yongxin gold deposit is one of the prominent gold deposits in the duobaoshan gold copper metallogenic belt within the eastern domain of the central asian orogenic belt the deposit has recently been discovered therefore its genesis and economic significance remain unknown here we present the results of pyrite thermoelectricity fluid inclusion and h o rb sr isotopic studies of different minerals with a view to decipher ore genesis and ore prospecting in the yongxin gold deposit the rb sr isotopic composition of pyrite quartz and calcite indicate that the deposit was formed at 114 6 1 2 ma fluid inclusions and h o isotopic studies show that the yongxin gold deposit was formed at shallow depth with relatively low ore forming temperatures 120 355 c low medium salinity 0 wt to 10 wt and low moderate density 0 6 1 0 g cm3 the ore forming fluids were mainly magmatic which mixed with meteoric water triggering the precipitation of ore forming materials we trace the evolution of the ore fluids from deeper levels in the northwest part of the deposit to shallower levels in the southeast the thermoelectricity parameter values xnp of pyrite range from 188 to 85 and the values of erosional or exhumation level range from 97 to 71 with an average of 79 4 suggesting that the existing ore body is the lower part of the deposit 79 4 of the ore body has already been eroded thermoelectricity of pyrite shows a vertical distribution in the axial direction without significant change in the xnp values indicating that the ore body extends further combined with the pyrite thermoelectric coefficients in different altitudes we predict gold potential for the ores at further depth depending on the continued presence of the n p type pyrite our mineralogical mappings also suggest a prospecting potential in the two zones at depth beneath the northwestern part of the deposit

patterns and processes of oxygen isotope exchange in a fossil meteoric hydrothermal system cuillins gabbro complex isle of skye scotland oxygen isotope compositions of whole rock specimens and mineral separates from the cuillins gabbro complex isle of skye scotland are employed to determine the patterns and processes of18o depletion in the outer unlayered gabbro oug and associated dikes whole rock 18o values range from 4 8 to 1 1 smow and dike 18o values range from 4 7 to 2 8 mineral separates from three oug samples yield 18o values from 5 3 to 4 8 for augite and 4 1 to 0 8 for plagioclase an early small scale hydrothermal circulation system was initiated by the oug prior to the large scale hydrothermal convection established by the later layered cuillins complex lcc dikes were emplaced in the oug after intrusion of the lcc and had only a minor effect on hydrothermal circulation in the oug there is evidence of enhanced fluid flow along dike gabbro contacts isotopic compositions of augite separates demonstrate a normal 18o value for the oug magma with all18o depletion in the oug due to subsolidus exchange processes including diffusion and surface reaction the mineral separates yield a pattern of18o depletion consistent with a diffusion mechanism the bulk of the exchange having occurred in the plagioclase secondary mineral formation played a subordinate role in the18o depletion of the oug the calculated water to rock mass ratio necessary to effect the observed18o depletion in the oug is on the order of 0 2 although a much greater amount of water circulation probably occurred the cooling duration required to explain the measured18o depletion in the oug by diffusion is very short 140 years at 750 c 2400 years at 550 c compared to the duration necessary for pure conductive cooling 105 to 106 years rapid local cooling rates in the oug due to meteoric water convection are consistent with the observed18o depletion in oug samples

distribution of porphyry deposits in the eurasian continent and their corresponding tectonic settings in the eurasian continent there are three huge metallogenic belts of cu and mo porphyry deposits comprising the paleozoic central asian ore belt in the north the tethyan eurasian ore belt of jurassic to cenozoic age in the southwest and the east margin ore belt of the eurasian continent of jurassic to cretaceous age in the east the latter is considered to be part of the vast circum pacific ore belt some of the main features of the spatial temporal distribution of cu and mo porphyry systems and related geodynamic processes of the three metallogenic belts are described in particular the key role of postsubduction related porphyry ore systems is emphasized comprising collisional and post collisional cu mo porphyry deposits during the geological history of the eurasian continent the recurrent feature of these ore systems and related felsic rocks is their derivation from partial melting of stagnant or residual oceanic slabs and mixing with a variable amount of crustal material during magma ascent to shallower levels 2013 published by elsevier ltd

dehydration melting and fluid recycling during metamorphism rangeley formation new hampshire usa reflect the dewatering of structurally lower levels after nappe emmuscovite and biotite dehydration melting reactions near the peak placement if so then nappe emplacement occurred at t 475 c of metamorphism played a significant role in the reaction and fluid history of the rangeley formation in southwestern new hampshire usa evidence for in situ melting includes 1 the consistency among theoretical phase equilibria observed reaction textures and the inferred p t conditions 2 disseminated centimeter scale

stable isotope thermometry at high temperatures determination of accurate temperatures for geological events has been the grail of stable isotope geochemistry since the seminal 1947 paper by urey in theory this should be simple calibrated mineral pairs are common analysis is rapid and there is no significant pressure correction however in spite of widespread application the promise of reliable thermometry has been elusive stable isotope temperatures in metamorphic and igneous rocks are often controversial is the fractionation between two phases a thermometer speedometer rate dependant hygrometer p h2o dependant or chimera a number of factors have contributed to this uncertainty including incomplete and sometimes conflicting calibration of isotope fractionation factors limited understanding of the kinetics of mineral exchange and the lack of microanalytical techniques this situation has improved dramatically over the past decade permitting reliable and detailed thermal histories to be inferred in a landmark paper bottinga and javoy 1975 empirically calibrated the oxygen isotope fractionation factors among ten rock forming minerals at t 500 c their compilation shows that 84 of analyzed samples contain at least three minerals meeting a concordance test for equilibrium they concluded the great majority of igneous and metamorphic rocks has conserved a state of oxygen isotope exchange equilibrium if correct this bodes well for thermometry however this conclusion was contested by deines 1977 who critically examined the existing data and concluded that less than half of the rocks analyzed to date would yield concordant 18o derived temperatures while seeming irreconcilable both conclusions are based on fact all rocks contain some degree of disequilibrium but many also preserve a thermometric record it is the purpose of this review to discuss the new strategies for reliable isotope thermometry and to explore disequilibrium processes so they may be recognized and properly interpreted the organization of this paper will be to discuss the assumptions

s pb isotopic geochemistry u pb and re os geochronology of the huanggangliang fe sn deposit inner mongolia ne china abstract the huanggangliang fe sn deposit is located in the eastern section of the central asian orogenic belt caob and in the southern segment of the great hinggan range polymetallic belt this deposit is the largest tin based polymetallic ore deposit in the northern part of the north china plate the fe sn mineralization principally occurs in skarn zones which formed in the contact areas between granite intrusions and marbles twenty one 34 s v pdb values for sulfides from the huanggangliang fe sn deposit range from 2 3 to 2 7 with an average of 0 38 and these values are interpreted to reflect a deep magmatic source of the sulfur contained within the ore minerals of the deposit the distribution of lead isotopic compositions from sulfides in the huanggangliang fe sn deposit exhibits a generally concentrated field indicating that those sulfides have homogeneous lead isotopes and may derive from the same metallic source the existence of such identical pb isotopic compositions of sulfides and host granites suggests that granitic magmatism was probably largely responsible for the huanggangliang mineralization zircon la icp ms u pb dating from the huanggangliang granite exhibits a tight cluster on the concordia plot and yields a weighted mean 206 pb 238 u age of 139 96 0 87 ma which is considered to be the best estimate of the crystallization age of the huanggangliang granite results obtained from the molybdenite re os isotopic analysis indicate re os model ages of 133 6 to 141 5 ma and a weighted mean age of 135 1 2 3 ma the molybdenite re os dating yields an isochron age of 134 9 5 2 ma and an initial 187 os 188 os ratio of 0 22 0 35 the molybdenite re os isochron age is largely consistent with the zircon u pb age indicating that both granite intrusion and fe sn mineralization were associated with the mesozoic magmatism in ne china based on ore deposit geology isotope geochemistry and geochronology of the huanggangliang fe sn deposit and regional geodynamic evolution the formation of this deposit is believed to be related to lithospheric thinning which was caused by delamination and subsequent upwelling of the asthenosphere under the intra continental extension in ne china the dynamic setting for the geological processes should be linked to the nnw subduction of the izanagi plate beneath the eurasian plate during the mesozoic this subduction triggered intensive magmatism and mineralization events in the great hinggan range of ne china making this district an important cu mo sn fe ag pb zn metallogenic province

the oxygen isotope anatomy of a slowly cooled metamorphic rock the distribution of o isotope ratios in a slowly cooled metamorphic rock is investigated by a combination of ion microprobe and laser probe techniques the sample has unusually simple geometry centimeter size domains of feldspar and garnet separated by a one millimeter to one centimeter thick layer of millimeter size magnetite grains isotopic zonation at two different scales is documented a sharp decrease in 18 o in the outer 10 100 m of individual magnetite grains is in agreement with modeling of isotopic reequilibration during cooling by interdiffusion between feldspar and magnetite the presence of this zonation in the outer portions of magnetite grains that are adjacent to garnet indicates extensive transport along grain boundaries during diffusive exchange millimeter scale zonation in the polygranular layer of magnetite is caused by the interaction of volume diffusion and grain boundary transport the effects of which depend upon local textures grain boundaries enhance bulk diffusion in polygranular aggregates and allow exchange between nontouching grains the results document a complex textural control to millimeter scale o isotope zonation and geothermometry in slowly cooled rocks and document the importance of fast grain boundary transport in controlling diffusive exchange