the scheelite skarn deposit of salau ariege french pyrenees between 1971 and 1986 the scheelite deposit of salau located in the french hercynian pyrenees produced 930 000 metric tons of ore with 1 50 percent wo 3 13 950 metric tons of wo 3 the skarn deposit is hosted in a devonian carbonate and partly detrital series intruded by a late carboniferous stock in the devonian series the lithostratigraphy and geochemistry of which is described in some detail a unit of so called barregiennes i e rythmic alternations of limestones and silts appears to be very favorable for extensive development of skarns and overprinted ores the hercynian orogeny involved polyphase deformation regional metamorphism of greenschist facies and late intrusions of granite granodiorite deformation included two coaxial stages of tight isoclinal folding and one important later stage which partly controlled the intrusion of the granodiorite stock followed by three stages of brittle deformation ore deposition is related to faulting stages 0 and 1 and orebodies are cut into slices by stage 2 reverse faults the salau intrusion includes various rock types belonging to two slightly different calcalkaline trends one of these trends characterized by its low k contents is unusual in the pyrenees the local shapes of the intrusion apophyses and embayments are important controls of the orebodies after isochemical contact metamorphism the skarns and ores developed in two main stages related to the infiltration of two quite different types of fluids during the first stage 540 degrees 450 degrees c anhydrous skarn formation was followed by an intergranular development of pyrrhotite scheelite quartz calcite in equilibrium with the earlier hedenbergite the resulting tungsten grade is uneconomic the associated fluids probably of magmatic origin had a high salinity in the second stage 450 degrees 350 degrees c no new skarn formed transformations of the silicate rocks are observed a first substage of epidotization was followed by the development of intermediate grossularite almandine spessartite garnet and finally by the main ore stage with scheelite pyrrhotite arsenopyrite and other sulfides with some gold two types of fluid inclusions are found in this stage one is similar in composition to the first stage the other is characterized by low salinity and high co 2 and ch 4 contents

felsic magmatic phases and the role of late stage aplitic dykes in the formation of the world class cantung tungsten skarn deposit northwest territories canada abstract a field and petro chemical classification of felsic magmatic phases fmps at the world class cantung w skarn deposit was undertaken to document the evolution of magmatism and the relationships between different fmps metasomatism and mineralization early fmps include moderately differentiated zr hf 18 26 ti zr 14 15 biotite monzogranitic plutons and early biotite rich granitic dykes and compositionally similar quartz feldspar porphyry dykes late highly fractionated zr hf 8 17 ti zr 3 13 fmps sourced from a deeper monzogranitic intrusion include 1 leucocratic biotite or tourmaline bearing dykes derived from localized entrapments of residual magma and 2 sub vertical ne trending aplitic dykes derived from a larger segregation of residual fluid and incompatible element enriched magma the aplitic dykes have textures morphologies spatial associations and a pervasive calcic metasomatic mineral assemblage ca plagioclase quartz or clinozoisite indicative of syn mineralization emplacement very late stage overpressuring and initiation of sub vertical fractures into the overlying plutonic carapace and country rocks by supercritical magmatic fluid led to an interaction with calcareous country rocks that resulted in an increased aca2 in the fluid and the concurrent precipitation of w skarn residual magma also ascended with and quenched in equilibrium with the magmatic fluid to from the aplitic dykes then was metasomatized by the fluid as it interacted with calcareous country rocks overall highly fractionated and moderately to very highly undercooled fmps at cantung provide evidence for a large and evolving felsic magmatic system at depth that segregated and maintained a stable fluid and incompatible element enriched residual magma until the latest stages of crystallization the detailed study of fmps associated with magmatic hydrothermal mineral deposits allow us to refine our understanding of these mineralizing systems and better define metallogenic and exploration models for intrusion related mineralization

synthetic fluid inclusions xvii pvtx properties of high salinity h2o nacl solutions 30 wt nacl application to fluid inclusions that homogenize by halite disappearance from porphyry copper and other hydrothermal ore deposits fluid inclusions that homogenize by disappearance of the halite crystal after the vapor bubble has disappeared have been reported from a wide range of ore forming systems while this inclusion type is most commonly observed in porphyry copper and similar magmatichydrothermal ore deposits they have also been reported from iron oxide copper gold iocg mississippi valley type orogenic lode greenstone gold massive sulfide unconformity u and mantotype deposits as well as from non ore associated granitoids and oceanic crust the lack of experimental data to interpret microthermometric data from these inclusions combined with poor petrographic characterization of inclusion origin has led to a wide range of inferred pt trapping conditions for the inclusions the relationship between liquid vapor homogenization temperature thl v halite dissolution temperature tmhalite and pressure has been determined using synthetic h2o nacl fluid inclusions that homogenize by halite disappearance the experimental data cover the range thl v 150 to 500 c and tmhalite 275 to 550 c an empirical equation describing the relationship between pressure thl v and tmhalite has been developed to estimate formation pressures from microthermometric data and is valid from pressures along the liquid vapor halite curve to 300 mpa a detailed literature review reveals that the results of this study cannot be applied retroactively to estimate pressures of previously reported inclusions that homogenize by halite dissolution for several reasons first most workers have not collected and reported the data in a manner that allows one to determine if the inclusions have trapped a single homogeneous phase and have not leaked or changed volume following trapping thus it is not possible to determine if the inclusions show consistent microthermometric behavior within a group of coeval inclusions additionally many published studies provide only summaries of results from numerous samples or present the data graphically precluding application of our results to individual inclusions however based on our review it appears that much of the published data for inclusions that homogenize by halite dissolution represent inclusions that have either trapped a halite crystal along with the liquid or have reequilibrated by necking and or stretching results from this study have been used to estimate minimum formation pressures for inclusions from the ditrau alkaline massif transylvania romania the musoshi stratiform copper deposit zaire the bismark skarn deposit northern mexico the naica chimneymanto deposit mexico the questa porphyry molybdenum deposit new mexico and the bingham canyon porphyry cu mo deposit utah in each case pressures estimated using results from the present study are in good agreement with previous pressure estimates however in some cases estimated pressures both our estimates as well as those of other authors appear to be unreasonably high based on the geologic setting at the time of formation these results highlight the currently limited understanding concerning pressures depths of ore formation

fluid chemistry structural setting and emplacement history of the rosario cu mo porphyry and cu ag au epithermal veins collahuasi district northern chile the rosario cu mo ag deposit is located in the collahuasi district of northern chile it comprises high grade cu ag au epithermal veins superimposed on the core of a porphyry cu mo orebody rosario has mining reserves of 1 094 million metric tons mt at 1 03 percent copper an additional 1 022 mt at 0 93 percent copper occurs in the district at the nearby ujina and quebrada blanca porphyry deposits the rosario reserve contains over 95 percent hypogene ore whereas supergene sulfide ores dominate at ujina and quebrada blanca mineralized veins are hosted within lower permian volcanic and sedimentary rocks lower triassic granodiorite and late eocene porphyritic quartz monzonite the rosario fault system a series of moderate southwest dipping faults has localized high grade cu ag au veins at cerro la grande similar high grade cu ag au veins are hosted in north northeast trending sinistral wrench faults normal movement in the rosario fault system is interpreted to have been synchronous with sinistral strike slip deformation at la grande hydrothermal alteration at rosario is characterized by a k feldspar core focused in the rosario porphyry that grades out to a secondary biotite albite magnetite assemblage paragenetic relationships indicate that magnetite was the earliest formed alteration product but has been replaced by biotite albite vein crosscutting relationships indicate that k feldspar formed during and after biotite albite alteration chalcopyrite and bornite were deposited in quartz veins associated with both k feldspar and biotite albite assemblages the early hydrothermal fluid was a hypersaline brine 40 45 wt nacl that coexisted with vapor between 400 degrees and 600 degrees c weakly mineralized illite chlorite intermediate argillic alteration of the early k and na silicate assemblages was caused by moderate temperature 250 degrees 350 degrees c moderate salinity brines 10 15 wt nacl molybdenite was precipitated in quartz veins that formed between the potassic and intermediate argillic alteration events these fluids were 350 degrees to 400 degrees c with salinities between 10 and 15 wt percent nacl porphyry style ore and alteration minerals were overprinted by structurally controlled quartz alunite pyrite pyrophyllite dickite and muscovite quartz phyllic alteration assemblages the quartz alunite pyrite alteration formed at 300 degrees to 400 degrees c from fluids with a salinity of 10 wt percent nacl the pyrophyllite dickite assemblage formed between 250 degrees and 320 degrees c from dilute 5 wt nacl fluids an upward flared zone of muscovite quartz pyrite altered rocks surrounds the fault controlled domain of advanced argillic alteration thick veins 0 5 2 m wide of fault hosted massive pyrite chalcopyrite and bornite precipitated brines with a salinity of 30 wt percent nacl at temperatures of 250 degrees to 300 degrees c pressure depth estimates indicate that at least 1 km of rock was eroded at rosario between formation of the k na silicate and advanced argillic assemblages this erosion was rapid occurring over a period of 1 8 m y the rosario porphyry intruded immediately after the incaic tectonic phase implying that it was emplaced as the domeyko cordillera underwent gravitational collapse expressed as normal faults in the upper crust gravitational sliding potentially accelerated exhumation and helped to promote telescoping of the high sulfidation environment onto the rosario porphyry the hydrothermal system responsible for porphyry cu mineralization at rosario was partially exhumed prior to the formation of high sulfidation ore and alteration assemblages this implies that emplacement of a second blind intrusion occurred somewhere beneath the rosario and cerro la grande high sulfidation vein systems and is supported by the fault geometry and zoning of precious metals and sulfosalts at the district scale

the cantung e zone scheelite skarn orebody tungsten northwest territories a revised genetic model the unusually large and high grade orebody developed as a result of infiltration metasomatism shortly following the epizonal intrusion of an upper cretaceous peraluminous biotite monzogranite pluton thermal metamorphism attained the pyroxene hornfels facies and was accompanied by the formation of minor folds and a foliation parallel to contact in the inner aureole subsequently following a temperature drop of 50 degrees to 100 degrees c initial hydrothermal activity at 450 degrees to 500 degrees c generated a zoned array of anhydrous and hydrous reduced skarn facies skarn formation occurred under a confining pressure of ca 1 or 0 3 kb from sphalerite geobarometry and was associated with extensive brittle and ductile deformation of the exoskarn contact zone scheelite abundant in all skarn facies except the garnet pyroxene is everywhere strongly correlated with pyrrhotite and shows little textural evidence of dissolution in the course of skarn development the hydrothermal fluid was a predominantly or entirely nonboiling moderately saline 4 14 equiv wt nacl brine which is inferred to have contained cacl 2 fecl 2 mgcl 2 and kcl in addition to nacl the skarn generating fluids apparently remained essentially constant in composition during the protracted mineralizing event modified journal abstract

reassessment of continental growth during the accretionary history of the central asian orogenic belt we argue that the production of mantle derived or juvenile continental crust during the accretionary history of the central asian orogenic belt caob has been grossly overestimated this is because previous assessments only considered the palaeozoic evolution of the belt whereas its accretionary history already began in the latest mesoproterozoic furthermore much of the juvenile growth in central asia occurred in late permian and mesozoic times after completion of caob evolution and perhaps related to major plume activity we demonstrate from zircon ages and nd hf isotopic systematics from selected terranes within the caob that many neoproterozoic to palaeozoic granitoids in the accreted terranes of the belt are derived from melting of heterogeneous precambrian crust or through mixing of old continental crust with juvenile or short lived material most likely in continental arc settings at the same time juvenile growth in the caob occurred during the latest neoproterozoic to palaeozoic in oceanic island arc settings and during accretion of oceanic island arc and precambrian terranes however taking together our data do not support unusually high crust production rates during evolution of the caob significant variations in zircon ehf values at a given magmatic age suggest that granitoid magmas were assembled from small batches of melt that seem to mirror the isotopic characteristics of compositionally and chronologically heterogeneous crustal sources we reiterate that the chemical characteristics of crustally derived granitoids are inherited from their source s and cannot be used to reconstruct tectonic settings and thus many tectonic models solely based on chemical data may need re evaluation crustal evolution in the caob involved both juvenile material and abundant reworking of older crust with varying proportions throughout its accretionary history and we see many similarities with the evolution of the sw pacific and the tasmanides of eastern australia

synthetic fluid inclusions in natural quartz iii determination of phase equilibrium properties in the system h2o nacl to 1000 c and 1500 bars phase equilibria in the system h2o nacl have been determined to 1000 c and 1500 bars using synthetic fluid inclusions formed by healing fractures in inclusion free brazilian quartz in the presence of the two coexisting immiscible h2o nacl fluids at various temperatures and pressures petrographic and microthermometric analyses indicate that the inclusions trapped one or the other of the two fluids present or mixtures of the two salinities of the two coexisting phases were obtained from heating and freezing studies on those inclusions which trapped only a single homogeneous fluid phase results of the present study are consistent with previously published data on the h2o nacl system at lower temperatures and pressures and indicate that the two phase field extends well into the p t range of most shallow magmatic hydrothermal activity as a consequence chloride brines exsolved from many epizonal plutons during the process of second boiling should immediately separate into a high salinity liquid phase and a lower salinity vapor phase and produce coexisting halite bearing and vapor rich fluid inclusions this observation is consistent with results of numerous fluid inclusion studies of ore deposits associated with shallow intrusions particularly the porphyry copper deposits in which halite bearing and coexisting vapor rich inclusions are commonly associated with the earliest stages of magmatic hydrothermal activity

spatial and temporal distribution of the orogenic gold deposits in the late palaeozoic variscides and southern tianshan how orogenic are they abstract a principal uncertainty in models of orogenic ore deposits concerns their ages relative to orogenic processes the yardstick of the relation has resided loosely in the peak of metamorphism age estimates in the variscides and tianshan indicate that most orogenic ore deposits were formed in the course of the late carboniferous to middle triassic with a peak between 305 and 280 ma their locations settings and ages suggest an association with coeval lithosphere scale strike slip deformation which played a role in the destruction of the orogenic system following crustal shortening this destruction tends to invalidate the orogenic association of the orogenic ore deposits observation of a mantle signature in some of these ore deposits and in coeval magmatic rocks suggests that the strike slip belts tapped into sub crustal levels here lithological composition had been modified by subduction during the stage of construction consequently any orogenic element in the ore deposit models is apart from location only an element of inheritance of subduction modified lithosphere features acquired during construction of the orogen these features may however well have been crucial for the formation of the ore deposits in view of the translithospheric extent of the strike slip belts fluids which contributed to the ore deposits may have come from at least the entire in part metasomatized lithosphere column the ore deposits could probably not have been formed without these deep reaching strike slip systems a model is proposed for the geological setting of the orogenic gold deposits in the variscides and the southern tianshan it consists of plutono metamorphic elements in the mantle in the lower and in the middle crust within a transpressional to transtensional tectonic framework of translithospheric faults and associated domes and pull apart basins with shallow marine to terrestrial sediments and interlayered felsic and mafic volcanics the thermal engines of these systems were probably in localized upwellings of the asthenosphere prompted and controlled by the lithosphere scale deformation at the time at an even larger scale oroclinal bending of the old orogenic backbone may have played yet another role in the localization of the ore deposits the thesis of specific localized tectono thermal engines is at odds with the original proposals of a relation between orogenic ore deposits and regional metamorphism it suggests that the late palaeozoic gold antimony mercury ore deposits in the variscides and the southern tianshan are more akin to the intrusion related ore systems

peraluminous i type granites abstract s type granites always contain more al than the amounts of na ca and k in the rock required to form feldspars primarily owing to their derivation from source components that had previously been weathered those rocks are therefore always saturated in al or peraluminous many i type granites are also peraluminous despite i type source rocks typically not being saturated in al it has previously been suggested that this may result from the fractional crystallisation of amphibole however data from compositionally zoned high temperature plutons in the lachlan fold belt show that it is difficult to generate large quantities of peraluminous melt by removal of amphibole most of the i type granites 95 in the lachlan fold belt formed at lower temperatures and almost half of those rocks for which bulk chemical compositions are available are peraluminous among these granites there are 98 separate suites for which there are chemical data for two or more samples with 47 suites that include both metaluminous more mafic and peraluminous more felsic compositions the origin of those peraluminous compositions is fundamental to any understanding of i type granite petrogenesis in this region compositional variations caused by the assimilation or by partial melting of supracrustal rocks are very small as the isotopic variations within these rocks are dominantly between different suites not within suites the partial melting of more mafic source rocks rather than the fractional crystallisation of more mafic magmas is favoured for the origin of these rocks partial melting is the most likely process involved in the petrogenesis of felsic granites where broadly granodioritic monzogranitic batholiths are associated with lesser amounts of tonalite and very minor amounts of mafic rock experimental studies have shown that the melts generated by the partial melting of basaltic to andesitic rocks under crustal conditions are mostly peraluminous during the dehydrational melting of i type granite source rocks at pressures below the garnet stability field biotite and amphibole melt incongruently to yield pyroxenes the excess al is incorporated into the felsic liquid resulting in the generation of peraluminous melts in this instance the excess al in felsic i type granites is a function of the melting process and unrelated to the bulk composition of the source the observed gradation from peraluminous felsic granites to metaluminous compositions in less felsic rocks in largely isotopically closed systems could happen in two ways at higher temperatures of partial melting ca and other components of clinopyroxene could dissolve in the melt with the melt eventually becoming metaluminous alternatively minerals residual from partial melting dominantly pyroxenes and plagioclase could be incorporated in suspension in the melt so that the resulting bulk magma is metaluminous examples of these two extremes and of intermediate cases are well developed among the granites of southeastern australia

geology mineralization and fluid inclusion characteristics of the meliksu reduced tungsten skarn deposit alai tien shan kyrgyzstan insights into conditions of formation and regional links to gold mineralization abstract the meliksu w skarn deposit 10kt wo3 with average grade of 6 6 wo3 in the alai segment of the southern tien shan is related to an early permian granitoid pluton that comprises ilmenite series to ilmenite titanite bearing medium k metaluminous to peraluminous i type granitoid monzonite diorite tonalite granodiorite to granite rocks there is a regional scale continuum from these intrusions to transitional weakly reduced to weakly oxidized metaluminous i type granitoid suites accompanied by reduced intrusion related au deposits magmatic evolution also included coeval high k to shoshonitic suites and younger early permian post collisional to within plate alkaline from monzogabbro to nepheline syenite and carbonatite intrusions indicative of an extensional tectonic regime consistent with this evolution toward an extensional environment reduced w skarns and associated reduced intrusion related au mineralization in the region may evolve toward sb hg as au w mineralization exhibiting the carlin type affinity the deposit bears signatures of reduced w skarn deposits with dominant pyroxene hedenbergite rich prograde and retrograde skarns scheelite was mostly deposited during the propylitic amphibole chlorite calcite quartz with abundant pyrrhotite and minor chalcopyrite and phyllic quartz sericite albite fe carbonate with sulfides bi ag and au minerals alteration stages silver mineralization is particularly abundant that together with very high w grades low au grades intense calcic sodic and sodic alteration and coarse grained sericite muscovite quartz aggregate possibly reveal a root level of reduced w skarn deposits fluid inclusions data indicate formation of retrograde mainly pyroxene quartz amphibole skarn from aqueous dominantly magnesian sodic chloride moderately saline 16 18 wt nacl eq high pressure 1 9 0 7 kbar moderately hot 400 500 c fluid propylitic alteration assemblages were formed from slightly less saline 11 13 wt nacl eq high pressure 1 8 0 5 kbars lower temperature 370 450 c ca enriched fluid phyllic alteration assemblages were formed from high pressure 2 2 0 1 kbars boiling methane rich carbonic aqueous cooling from 350 to 335 c to 275 265 c fluid high fluid pressures at different hydrothermal stages are consistent with a deep level of mineralization at a lithostatic depth of 9 0 km a strong enrichment in heavy sulfur isotope 34sfluid varies from 6 5 0 4 to 8 0 0 3 can reflect sulfur sourcing from sedimentary rocks enriched in seawater sulfate with sulfur isotope homogenization in a magmatic chamber

an experimental study of sulfidation reactions involving andradite and hedenbergite three sulfur buffering sulfide silicate reactions which limit the stabilities of the skarn silicates andradite garnet and hedenbergite pyroxene under sulfidizing conditions were studied hydrothermally at a pressure of 2 kb over the temperature range 700 degrees to 350 degrees c reaction 1 andradite s 2 wollastonite anhydrite quartz pyrite or pyrrhotite reaction 2 andradite magnetite s 2 anhydrite quartz pyrite or pyrrhotite andreaction 3 hedenbergite s 2 andradite quartz pyrrhotite the equilibrium value of the sulfur fugacity f sub s 2 for each reaction assemblage at any given temperature was calculated from the measured composition of a coexisting sulfur fugacity indicator pyrrhotite or sphalerite as appropriate the log f sub s 2 data were adequate for the determination of the log f sub s 2 1 t relations for each of the andradite sulfidation reactions owing to excessive scatter in the data for the hedenbergite sulfidation reaction however the log f sub s 2 1 t relation for this reaction derived from the log f sub o 2 data of burton et al 1982 is preferred to the one developed by gamble 1976 1978 the log f sub s 2 1 t relations for the three sulfidation reactions were combined with equilibrium data available in the literature for other reactions in the model system ca si fe o s and used to construct quantitative isothermal isobaric log f sub s 2 log f sub o 2 phase diagrams applicable to the formation of ca si fe skarns the quantitatively derived phase relations were found to be consistent in all major respects with the schematic phase relations deduced by burt 1972a and b the influence of diopside component on the stability of hedenbergitic pyroxene was also studied diopside was found to enlarge the stability field of hedenbergitic pyroxene increasing the temperature at which pyroxene becomes stable with pyrite from 288 degrees c for end member hedenbergite burton et al 1982 to 395 degrees c for 50 mole percent diopside diopside was found to be less effective than the johannsenite component in stabilizing hedenbergitic pyroxene

geology mineralization and fluid inclusion characteristics of the chorukh dairon w mo cu skarn deposit in the middle tien shan northern tajikistan abstract the chorukh dairon deposit is part of the metallogenic belt of w mo cu mo au w and au deposits along the late paleozoic active continental margin of the tien shan it is related to the late carboniferous multiphase pluton with successive intrusive phases of early monzogabbro through monzonite quartz monzonite to monzogranite and leucogranite and the latest lamprophyre dikes the deposit is an example of complex w mo cu magmatic hydrothermal system related to magnetite series shoshonitic igneous suite it contains zones of w cu mo oxidized prograde and retrograde skarns with abundant scapolite plagioclase k feldspar andradite garnet magnetite as well as molybdoscheelite and minor chalcopyrite and molybdenite skarns are overprinted by hydrosilicate alteration assemblages with amphibole chlorite epidote quartz calcite scapolite albite scheelite and chalcopyrite and are cut by quartz carbonate barite fluorite sulfide veins the fluid evolution included a release of high temperature 400 500 c high pressure 900 1100 to 700 800 bars high salinity magmatic hydrothermal aqueous chloride fluid with its direct separation from crystallizing magma and formation of prograde and retrograde skarns fluid enrichment in ca up to 15 22 wt cacl 2 at the retrograde skarn stage was possibly related to magmatic differentiation and provided intense molybdoscheelite deposition from a homogenous fluid in contrast hydrosilicate alteration assemblages were formed at lower temperatures 350 400 c initially from a homogenous and then from a boiling ca rich 20 22 wt cacl 2 magmatic hydrothermal fluid with the latter contributing to the most intense scheelite deposition the stable isotope data 13 c co 2 3 0 0 5 and 18 h 2 o 6 5 0 5 34 s 7 5 to 7 7 obtained for the hydrosilicate stage minerals suggest significant fluid sourcing from magmatic and meteoric waters as well as from sedimentary rocks enriched in seawater sulfate possibly evaporites although a strongly homogenous character of the isotopic composition reveals intense isotope homogenization in a magmatic chamber some light sulfur isotope enrichment of sulfides from the quartz carbonate barite fluorite sulfide veins 34 s 6 0 to 6 1 may be linked to the evolution of the magmatic source toward more mantle related sulfur species as these veins were formed after emplacement of the late mafic lamprophyre dikes

composition and evolution of ore fluids in a magmatic hydrothermal skarn deposit the chemistry of brine vapor and low salinity fluid inclusions measured by proton induced x ray emission from the bismark skarn deposit mexico is consistent with an evolving magmatic hydrothermal system with no evidence for external fluid inputs the results support a model that invokes early phase separation of magmatic fluids into brine and vapor two phase field at high temperature and lithostatic pressure followed by the entrapment of a low salinity magmatic fluid one phase field at lower temperature and hydrostatic pressure the early brine and vapor inclusions contain high pb and zn concentrations and low cu however the vapor contains significantly more cu than the brine and was likely transported as a sulfur complex the fluid phase changes observed and behavior of cu are comparable to those of porphyry cu systems the later low salinity fluid at bismark represents a distinct pulse of magmatic fluid with a high k ca ratio in which base metals including cu were transported by chloride complexes paragenetic relationships and variations in the relative concentrations of cu pb and zn suggest that this fluid was primarily responsible for ore deposition the relative cu pb and zn concentrations in fluid inclusions at bismark are consistent with those measured from base metal ores in high temperature carbonate replacement deposits throughout mexico and suggest that the bulk metal budget of these deposits is primarily controlled by magmatic hydrothermal fluids deficient in cu

architecture and mineral deposit settings of the altaid orogenic collage a revised model abstract the altaids are an orogenic collage of neoproterozoic paleozoic rocks located in the center of eurasia this collage consists of only three oroclinally bent neoproterozoic early paleozoic magmatic arcs kipchak tuva mongol and mugodzhar rudny altai separated by sutures of their former backarc basins which were stitched by new generations of overlapping magmatic arcs in addition the altaids host accreted fragments of the neoproterozoic to early paleozoic oceanic island chains and neoproterozoic to cenozoic plume related magmatic rocks superimposed on the accreted fragments all these assemblages host important many world class late proterozoic to early mesozoic gold copper molybdenum lead zinc nickel and other deposits of various types in the late proterozoic during breakup of the supercontinent rodinia the kipchak and tuva mongol magmatic arcs were rifted off eastern europe siberia and laurentia to produce oceanic backarc basins in the late ordovician the siberian craton began its clockwise rotation with respect to eastern europe and this coincides with the beginning of formation of the mugodzhar rudny altai arc behind the kipchak arc these earlier arcs produced mostly cu pb zn vms deposits although some important intrusion related orogenic au deposits formed during arc arc collision events in the middle cambrian and late ordovician the clockwise rotation of siberia continued through the paleozoic until the early permian producing several episodes of oroclinal bending strike slip duplication and reorganization of the magmatic arcs to produce the overlapping kazakh mongol and zharma saur valerianov beltau kurama arcs that welded the extinct kipchak and tuva mongol arcs this resulted in amalgamation of the western portion of the altaid orogenic collage in the late paleozoic its eastern portion amalgamated only in the early mesozoic and was overlapped by the transbaikal magmatic arc which developed in response to subduction of the oceanic crust of the paleo pacific ocean several world class cu mo porphyry cu pb zn vms and intrusion related au mineral camps which formed in the altaids at this stage coincided with the episodes of plate reorganization and oroclinal bending of magmatic arcs major pb zn and cu sedimentary rock hosted deposits of kazakhstan and central asia formed in backarc rifts which developed on the earlier amalgamated fragments major orogenic gold deposits are intrusion related deposits often occurring within black shale bearing sutured backarc basins with oceanic crust after amalgamation of the western altaids this part of the collage and adjacent cratons were affected by the siberian superplume which ascended at the permian triassic transition this plume related magmatism produced various deposits such as famous ni cu pge deposits of norilsk in the northwest of the siberian craton in the early mesozoic the eastern altaids were oroclinally bent together with the overlapping transbaikal magmatic arc in response to the northward migration and anti clockwise rotation of the north china craton the following collision of the eastern portion of the altaid collage with the siberian craton formed the mongol okhotsk suture zone which still links the accretionary wedges of central mongolia and circum pacific belts in the late mesozoic a system of continent scale conjugate northwest trending and northeast trending strike slip faults developed in response to the southward propagation of the siberian craton with subsequent post mineral offset of some metallogenic belts for as much as 70 400 km possibly in response to spreading in the canadian basin india asia collision rejuvenated some of these faults and generated a system of impact rifts

auriferous arsenopyrite pyrite and stibnite mineralization from the siflitz guginock area austria indications for hydrothermal activity during tertiary oblique terrane accretion in the eastern alps

hercynian post collisional magmatism in the context of paleozoic magmatic evolution of the tien shan orogenic belt abstract the hercynian tien shan tianshan orogen formed during late palaeozoic collision between the karakum tarim and the kazakhstan paleo continents in order to constrain timing of hercynian post collisional magmatism 27 intrusions were sampled for u pb zircon dating along a ca 2000 km long profile in uzbekistan and kyrgyzstan the samples were dated utilizing sensitive high resolution ion microprobe shrimp ii the obtained ages together with previously published age data allowed the timing of hercynian post collisional magmatism to be constrained and interpreted in the context of the paleozoic magmatic evolution of the region apart from hercynian post collisional magmatism two older magmatic episodes have been recognized and the following sequence of events has been established 1 approximately 10 ma after cessation of continuous caledonian magmatism a number of late silurian early devonian intrusions were emplaced in the middle and northern tien shan terranes between 420 and 390 ma the intrusions probably formed in an extensional back arc setting during coeval subduction under the margins of caledonian paleo kazakhstan continent 2 the next relatively short late carboniferous episode of subduction under paleo kazakhstan was registered in the kurama range of the middle tien shan calc alkaline volcanics and granitoids with ages 315 300 ma have distinct metallogenic affinities typical for subduction related rocks and are not found anywhere outside the middle tien shan terrane west of the talas farghona fault 3 the early permian hercynian post collisional magmatism culminated after the closure of the paleo turkestan ocean and affected the whole region across terrane boundaries the post collisional intrusions formed within a relatively short time span between 295 and 280 ma the model for hercynian post collisional evolution suggests that after collision the tien shan was affected by trans crustal strike slip motions which provided suitable conduits for ascending asthenospheric material and heat influx in the crust this produced both granitoid magmas and hydrothermal fluid flow as a result post collisional intrusions and orogenic au deposits known in the region formed coevally and were tectonically controlled 4 between 240 and 220 ma a triassic thermal event affected the region resulting in resetting and growth of new zircon grains which is detected on a regional scale probably the influx of heat into the crust during the triassic was tectonically focused and varied significantly in different terranes in the region under investigation the triassic thermal event was not accompanied by any significant magmatic activity thus after cessation of hercynian post collisional magmatism ca 280 ma ago there was a long magmatically quiet period in the tien shan

geological characteristics tectonic setting and preliminary interpretations of the jilau gold quartz vein deposit tajikistan the southern tien shan metallogenic province of central asia hosts a number of important gold resources including the jilau gold quartz vein system in western tajikistan these deposits were formed at the late stages of continent continent collision in association with subduction related magmatism metamorphism and continental margin deformation attributed to the central asian hercynian orogeny jilau is hosted by a hercynian syntectonic granitoid intrusive that was emplaced into bituminous dolomite country rocks economic mineralisation is associated with a dilational jog within a high angle oblique dextral reverse slip shear zone that was undergoing brittle ductile deformation the orebody takes the form of shear zone subparallel quartz veins and lenses that emanate from a steeply plunging ore shoot of veins and stringers within a silicified and sulphidised granodiorite core it is thought to have formed by a dynamic process in which fluid flow was governed by a fault valve mechanism numerous cycles of fluid pressure build up fault failure jog dilation fluid flow phase separation of low salinity h2o co2 ch4 n2 fluids and sealing took place gold appears together with scheelite and bismuth minerals predominantly as inclusions in arsenopyrite in quartz veins and altered wall rock and is mainly associated with quartz containing fluid inclusions enriched in ch4 the correlation between high gold grades and high ch4 concentrations suggests that components of the mineralising fluids were derived from or passed through the reducing carbonaceous rocks in the contact aureole of the intrusive the occurrence of au and w in an adjacent hercynian skarn deposit and in the jilau orebody infers that the ore metals in both these systems were ultimately derived from a magmatic source

the dog bay liberty line and its significance for silurian tectonics of the northern appalachian orogen1this article is one of a series of papers published in this cjes special issue in honour of ward neale on the theme of appalachian and grenvillian geology 2geological survey of canada contribution 20100257 the dog bay line a silurian suture key to deciphering appalachian accretionary history was first recognized in newfoundland it marks where the ordovician tetagouch exploits ensimatic back arc basin teb which had opened within the leading peri gondwanan gander terrane finally closed here we extrapolate this suture into new england placing it between the liberty orrington miramichi inliers lom and the merrimack fredericton trough mft southeastward marine strata of the mft overlie the teb passive margin exposed in the ganderian st croix block and display southeast vergent structures transected by acadian cleavage they structurally underlie southeast vergent thrusts at the base of the lom northwestward the lom central maine matapedia trough cmmt and lower silurian igneous rocks record elements of the upper plate trench arc system respectively a subduction complex forearc basin and arc the cmmt forearc received detritus both from the northwesterly arc region and also from the

geology and structural evolution of the muruntau gold deposit kyzylkum desert uzbekistan abstract the muruntau gold deposit in the kyzylkum desert of uzbekistan is the largest single deposit 1100 tonnes of gold of the class of low sulfide syndeformation synigenous gold deposits formed in the brittle ductile transition zone of the crust within transpressional shear zones hosted by the cambrian to ordovician besopan suite the ores were deposited in pre existing thrust fault and metamorphism related permeabilities and in synmineralization dilational zones created in a large fault related fold the besopan suite is a 5 000 m thick sequence of turbiditic siltstones shales and sandstones the ore is primarily localized at the base of the besopan 3 unit which is a 2 000 m thick series of carbonaceous shales siltstones sandstones and cherts initial gold deposition took place within the sangruntau tamdytau shear zone which was developed along the stratigraphic contact between the besopan 3 and besopan 4 units during the mineralization process folding of the besopan suite and a left step adjustment in the sangruntau tamdytau shear zone were caused by two concurrent events 1 the activation of the left lateral muruntau daugyztau shear zone that developed at nearly a 90 angle to the preceding shear zone and 2 the intrusion of granitoid plutons these structural events also resulted in the refocusing of hydrothermal fluid flow into new zones of permeability

the giant muruntau gold deposit geologic geochronologic and fluid inclusion constraints on ore genesis we reinterpret the regional geologic setting of the giant muruntau gold deposit and report new 40 ar 39 ar isotope age determinations and a laser raman microprobe analysis of fluid inclusions new 40 ar 39 ar isotope age determinations of hydrothermal sericite selvages to gold stage quartz veins are in excellent agreement with older rb sr dates on auriferous quartz veins they suggest triassic sericite formation at 245 and 220 ma some 30 m y later than subjacent felsic intrusions as defined by rb sr data these dates call into question the role of magmatic fluid metal and heat input indeed the rb sr pluton ages may be a reflection of hydrothermal activity rather than cooling from magmatic conditions the muruntau deposit is situated adjacent to a major rift which has been periodically active from the devonian to the tertiary and has accumulated a substantial thickness of chemical volcaniclastic and clastic sediments including red beds and evaporites we infer that the muruntau deposit is so large because of the presence of a major source of reduced sulfur in these nearby evaporitic sediments via thermochemical sulfate reduction some support for the role of reduced sulfur is provided by the presence of detectable h2s in fluid inclusions from late stage auriferous quartz veins reduced sulfur rich fluids could have been focused into the depositional site along major northeast trending structures which have influenced rift basin architecture as recently as the jurassic oxidation could therefore be an important ore precipitating mechanism a change from early ch4 to later syngold co2dominant fluid inclusions may be an indication of this process

a review of shallow ore related granites textures volatiles and ore metals shallow texturally complex granites can be associated spatially introduction and temporally with hydrothermal alteration and mineralization granite related ore deposits include porphyry and skarn the formation of a granite related ore deposit represents the confluence type ores and other hydrothermal deposits that are of many chemical and physical geological factors including magma spatially and temporally associated with granitic sensu composition e g concentrations of ore metals chlorine and water lato rocks in this paper i emphasize characteristics magma oxidation state the relative timing of crystallization magma found in porphyry style cu mo au deposits and some ascent magmatic volatile phase exsolution and the depth of em related systems however my treatment here is not meant placement early magmatic crystallization of ore metal rich minerals to cover the full range of granitic rocks and mineralization coupled with late exsolution of the magmatic volatile phase is that make up the granite related ore systems the forpromoted by deeper emplacement levels and lower magmatic water mation of granite related ore deposits by orthomagmatic concentrations and leads to low eyciencies of removal of compatible hydrothermal processes is dependent upon many physical elements from melts into the magmatic volatile phase s water and chemical magmatic factors including but not limited concentrations in the melt and pressures of crystallization can be to the composition and evolution of the associated estimated from phase equilibria and textural relationships of horn magmas the rate of magma ascent the depth and blende in some felsic systems physical factors avect the dynamics geometry of magma emplacement and the local temof fluid magma melt and volatile phase movement which in turn perature and stress fields at the site of magma emavect the size of zones of alteration and mineralization granite placement detailed studies of the igneous rocks textures can record the partial history of some dynamic processes associated with ore deposits can therefore yield critical miarolitic cavities are good evidence for magmatic volatile phase information regarding the source of metals and ligands exsolution both miarolitic cavities and pegmatitic texture exhibit in the ore generative hydrothermal solutions that are evidence for external nucleation of crystals nucleation controlled operative in the formation of granite related ores in this phenomena expressed as variations in granite textures can result review i will present a series of narratives consistent in from a multiplicity of causes including undercooling of the melt my view with prevailing field and experimental data on textural elements such as pegmatite aplite skeletal crystals and the orthomagmatic hydrothermal theory for the genesis graphic textures can form as a result of undercooling interconnected of some granite related deposits volumes of the magmatic volatile phase allow for advection of some high level granites i e those that are emplaced hydrothermal ore fluids through the magma in shallow granitic at depths of 8 km or less represent the crystallized systems miarolitic cavities can be interconnected consistent with remains of magmas that were associated with subvolcanic this hypothesis ore generative hydrothermal systems therefore studies of shallow granites aimed at understanding magmatic evolution and volatile phase exsolution at shallow levels are necessary if we are to understand ore genesis and the deep inputs to present day geothermal systems as well as evaluate hazards associated with the volcanic

recrystallization fabrics of sheared quartz veins with a strong pre existing crystallographic preferred orientation from a seismogenic shear zone abstract microstructural investigations were carried out on quartz veins in schist protomylonite and mylonite samples from an ancient seismogenic strike slip shear zone sandhill corner shear zone norumbega fault system maine usa we interpret complexities in the microstructural record to show that 1 pre existing crystallographic preferred orientations cpo in the host rock may persist in the new cpo patterns of the shear zone and 2 the inner and outer parts of the shear zone followed diverging paths of fabric development the host rocks bounding the shear zone contain asymmetrically folded quartz veins with a strong cpo these veins are increasingly deformed and recrystallized with proximity to the shear zone core matrix accommodated rotation and recrystallization may position an inherited c axis maximum in an orientation coincident with rhomb or basal slip this inherited cpo likely persists in the shear zone fabric as a higher concentration of poles in one hemisphere of the c axis pole figure leading to asymmetric crossed girdle or paired maxima c axis patterns about the foliation plane three observed quartz grain types indicate a general trend of localization with decreasing temperature 1 large 100 m low aspect ratio

geochemical constraints on the genesis of the scheelite dome intrusion related gold deposit tombstone gold belt yukon canada the scheelite dome intrusion related gold deposit western selwyn basin yukon is hosted in hornfelsed metasedimentary strata that lie adjacent to the exposed apices of a monzogranite to quartz monzonite plutonic complex of the mid cretaceous tombstone tungsten magmatic belt tintina gold province alaska and yukon a variety of mineralization styles occur throughout a 10 3 km east trending corridor and include reduced au and w rich skarns au w and ag pb zn sb rich quartz tension vein arrays and multiphase fault veins and isolated zones of au rich sericite carbonate altered rock integrated u pb shrimp data for magmatic zircon and ar ar data for magmatic and hydrothermal biotite indicate that gold mineralization occurred within 1 to 2 m y of magma emplacement fluid inclusion oxygen isotope and arsenopyrite geothermometry data indicate that hydrothermal minerals formed at depths of 6 to 9 km over a temperature range from 550 c high temperature au rich skarns formed at 400 c whereas vein hosted mineralization formed at 280 to 380 c in skarns au is strongly associated with enrichments of bi te w and as whereas a variety of au rich veins occur with as rich type 1 and te and w rich type 2 end members silver pb zn sb veins are typically au poor and represent the latest and lowest temperature phase in the hydrothermal paragenesis the fluid inclusion data indicate that all mineralization styles were formed from low salinity 4 wt nacl equiv aqueous carbonic fluids consistent with the composition of fluid inclusions within infilled miarolitic cavities in the intrusive rocks however the nonaqueous fluid was predominantly ch 4 in skarn co 2 in au te and au w veins and a fluid with roughly equal amounts of co 2 ch 4 and n 2 in au as and ag pb zn sb veins oxygen isotope data are consistent with a mineralizing fluid of predominantly magmatic origin that was variably modified to more positive 18 o values during interaction with 18 o enriched metasedimentary strata sulfur isotope data suggest two possible sources of sulfur a magmatic source characterized by 34 s values of approximately 5 to 0 per mil and sulfur from the metasedimentary country rocks characterized by more negative 34 s values of approximately 15 to 10 per mil collectively the data indicate that gold at scheelite dome was deposited from a magmatic hydrothermal system interaction of magmatic fluids with graphitic hornfels rocks resulted in reduction of the ore fluids higher ch 4 co 2 ratios and modification of the oxygen and sulfur isotope values of the ore fluids toward those of the metasedimentary hornfels progressive reduction and cooling of hydrothermal fluids in addition to phase separation in vein hosted mineralization were the mechanisms for gold deposition compared to other intrusion related gold deposits associated with the tombstone tungsten magmatic belt magmatism exposed mineralization at scheelite dome is predominantly hosted by hornfelsed metasedimentary rocks this results in more diverse mineralization styles and a greater spread of isotope and fluid inclusion data

geodynamics and metallogeny of the central eurasian porphyry and related epithermal mineral systems a review abstract major porphyry cu au and cu mo deposits are distributed across almost 5000 km across central eurasia from the urals mountains in russia in the west to inner mongolia in north eastern china these deposits were formed during multiple magmatic episodes from the ordovician to the jurassic they are associated with magmatic arcs within the extensive subduction accretion complex of the altaid and transbaikal mongolian orogenic collages that developed from the late neoproterozoic through the palaeozoic to the jurassic intracratonic extension the arcs formed predominantly on the palaeo tethys ocean margin of the proto asian continent but also within two back arc basins the development of the collages commenced when slivers of an older proterozoic subduction complex were rifted from an existing cratonic mass and accreted to the palaeo tethys ocean margin of the combined eastern europe and siberian cratons subduction of the palaeo tethys ocean beneath the karakum and altai tarim microcontinents and the associated back arc basin produced the overlapping late neoproterozoic to early palaeozoic tuva mongol and kipchak magmatic arcs contemporaneous intra oceanic subduction within the back arc basin from the late ordovician produced the parallel urals zharma magmatic arc and separated the main khanty mansi back arc basin from the inboard sakmara marginal sea by the late devonian the tuva mongol and kipchak arcs had amalgamated to form the kazakh mongol arc by the mid palaeozoic the two principal cratonic elements the siberian and eastern european cratons had begun to rotate relative to each other drawing in the two sets of parallel arcs to form the kazakh orocline between the two cratons during the late devonian to early carboniferous the palaeo pacific ocean began subducting below the siberian craton to form the sayan transbaikal arc which expanded by the permian to become the selanga gobi khanka arc by the middle to late permian as the kazakh orocline continued to develop both the sakmara and khanty mansi back arc basins were closed and the collage of cratons and arcs were sutured by accretionary complexes during the permian and triassic the north china craton approached and docked with the continent closing the mongol okhotsk sea an embayment on the palaeo pacific margin to form the mongolian orocline subduction and arc building activity on the palaeo pacific ocean margin continued to the mid mesozoic as the indosinian and yanshanian orogens significant porphyry cu au mo and au cu deposits were formed during the ordovician in the kipchak arc e g bozshakol cu au in kazakhstan and taldy bulak porphyry cu au in kyrgyzstan silurian to devonian in the kazakh mongol arc e g nurkazgan cu au in kazakhstan and taldy bulak levoberezhny au in kyrgyzstan devonian in the urals zharma arc e g yubileinoe au cu in russia devonian in the kazakh mongol arc e g oyu tolgoi cu au and tsagaan suvarga cu au in mongolia carboniferous in the kazakh mongol arc e g kharmagtai au cu in mongolia tuwu yandong cu au in xinjiang china koksai cu au kounrad cu au and the aktogai group of cu au deposits in kazakhstan carboniferous in the valerianov beltau kurama arc e g kal makyr dalnee cu au in uzbekistan benqala cu au in kazakhstan late carboniferous to permian in the selanga gobi khanka arc e g duobaoshan cu au in inner mongolia china triassic in the selanga gobi khanka arc and jurassic in the selanga gobi khanka arc e g wunugetushan cu mo and jiguanshan mo in inner mongolia china in addition to the tectonic geologic and metallogenic setting and distribution of porphyry cu au mo mineralisation within central eurasia the setting geology alteration and mineralisation at each of the deposits listed above is described and summarised in table 1

geological development and phanerozoic crustal accretion in the western segment of the southern tien shan kyrgyzstan uzbekistan and tajikistan abstract the tien shan form a high intracontinental mountain belt lying north of the main india asia collision mountains and consist of re activated paleozoic orogens the western segment of the southern tien shan lies northwest of the pamir and west of the talas fergana fault the stratigraphy lithology igneous and metamorphic petrology and geochemistry of this segment indicate that it was formed by the assembly of lower paleozoic arcs which developed into microcontinents with upper paleozoic mature shelf and slope clastic and carbonate sediments precambrian continental crust is confined to two small blocks along its southern margin the bulk of the southern tien shan consists of vendian to silurian oceanic and slope clastic rocks resting on oceanic lithosphere and overlain by thick passive margin devonian to mid carboniferous mature shelf clastics and carbonates these are unconformably overlain by syn and post orogenic immature clastic sediments derived from mountains on the north formed by closure of a carboniferus southern tajik and a northern vendian to carboniferous turkestan ocean with the southern tien shan microcontinent sandwiched between associated with these collisions are late carboniferous to permian intrusives which form three south to north though overlapping suites a southern calc alkaline granodiorite granite suite an intermediate gabbro monzodiorite granite suite and a northern alkaline monzodiorite granite alaskite suite the gabbro monzodiorite granite suite forms the earliest subduction related magmatism of the southern tien shan rare earth element patterns are consistent with derivation from a primitive or slightly enriched mantle the other suites show more crustal contamination rb and sr vary with depth and degree of partial melting and are consistent with progressive involvement of crustal material in partial melts during collision the gradual change in composition within each complex lasting in some cases from 295 to 250 ma the entire permian may be explained by a consecutive shift in the melting sedimentary cover of the subducting plate from oceanic crust through transitional crust to marginal continental crust like the central asian orogenic belt the main focus of igcp 420 the tien shan represent a net addition of continental crust during the phanerozoic very little of the belt has any precambrian precursor

shoshonitic lamprophyre dykes and their relation to mesothermal ausb veins at hillgrove new south wales australia abstract the hillgrove mineral field in the southern part of the new england orogen of northeastern new south wales australia contains numerous mesothermal au sb vein systems calc alkaline shoshonitic lamprophyre cal dykes are also associated with mineralisation with dilational lode structures acting as conduits for dyke intrusion which has occurred before and after major quartz stibnite veining dykes include minette and vogesite compositions and were emplaced in the late permian 247 255 ma at the same time as regionally extensive i type magmatism in the new england orogen least altered dykes are enriched in mg k ba rb sr zr th cr and ni relative to i type intrusives although chemical affinities are evident between lamprophyres and the more mafic members of the high k moonbi plutonic suite hillgrove lamprophyres are commonly enriched in sb as hg au w and bi with respect to average cal compositions evidence indicates this is most likely due to contamination of magma during intrusion through mineralised structures rather than a primary magmatic feature partially resorbed xenocrystic stibnite occurs in dykes which have intruded lode structures probably facilitated by the low melting point of stibnite 550 c and its incorporation into the magma carbon and oxygen isotopic data from carbonates in least altered post lode lamprophyres are indistinguishable from carbonate in altered dykes and veins implying that hydrothermal interaction continued after dyke intrusion although it is unlikely that lamprophyre dykes have been a direct source for mineralisation at hillgrove the close temporal and spatial relation of dykes mesothermal au sb veins and i type intrusions are interpreted to be manifestations of the post collisional setting and influx of mantle derived heat and partial melts into the new england orogen during the late permian

implications of a newly dated ca 1000 ma rhyolitic tuff in the indravati basin bastar craton india abstracta rhyolitic tuff with a minimum thickness of about 2 5 m occurs at the top of the sedimentary succession of the indravati group in south central india the tuff is a high k low na rhyolite with dominantly k feldspar phenocrysts cathodoluminescence color of the quartz phenocrysts is blue u pb isotopic analyses la mc icpms of magmatic zircons separated from the tuff give a weighted mean average 207pb 206pb age of ma that we interpret as the age of crystallization we conclude that the closure age of the indravati succession is ca 1000 ma very similar to that of the chhattisgarh and vindhyan successions the age of this tuff is identical within analytical errors to those of the sukhda and dhamda tuffs in the chhattisgarh basin some 350 km away we suggest that these three tuffs represent a ca 1000 ma rhyolitic flare up possibly related to the assembly of rodinia and docking of india and east antarctica

multiple sources for mineralizing fluids in the charmitan gold tungsten mineralization uzbekistan mineral assemblages present within the charmitan gold tungsten quartz vein mineralization have been investigated for their cathodoluminescence behaviour chemical composition and noble gas isotope systematics this inventory of methods allows for the first time a systematic reconstruction of the paragenetic relationships of quartz scheelite sulphides and native gold within the gold mineralization at charmitan and provides the basis to utilise noble gas data in the discussion of sources and evolution of ore forming fluids the vein quartz is classified into four generations based on microscopic and cathodoluminescence investigations quartz i shows intense brittle deformation as associated scheelite i undeformed scheelite ii overgrows scheelite i and has lower light rare earth element and higher intermediate rare earth element contents as well as higher strontium concentrations scheelite ii is associated with the economic gold mineralization and formed during re crystallisation and re precipitation of material which was partly re mobilised from early scheelite i during infiltration of gold bearing fluids early stage native gold inclusions are often associated with stage 2 sulphides scheelite ii and bismuth tellurides and contain ag 3 6 24 4 wt hg 1 0 wt and bi 0 2 wt later stage electrum grains occur in association with stage 3 sulphides and sulphosalts and contain hg 0 8 wt and elevated sb concentrations up to 3 0 wt noble gas isotope data 3he 4he 0 2 0 4 ra for hydrothermal ore fluids trapped in the gold related sulphides and sulphosalts stage 2 pyrite and arsenopyrite stage 3 pyrite sphalerite galena and lead sulphosalts suggest that diverse fluid sources were involved in the formation of the charmitan gold deposit these data are indicative of a small but significant input of fluids from external deep seated mantle and possibly lower crust sources a decrease in the input of mantle helium and an increasing role of crustal helium from early to later stages of the mineralization is suggested by the measured 3he 4he and 40ar 4he ratios sulphides from ore veins in meta sedimentary rocks contain higher portions of meteoric fluids than those in intrusive rock types as indicated by their lower 3he 36ar ratios the 3he 36ar ratios in the meta sedimentary rocks agree well with ratios typical of gold mineralizations in the tien shan gold province completely hosted by meta sedimentary sequences indicating intense fluid wall rock interaction