2 61 ga potassic granites and crustal reworking in the western dharwar craton southern india tectonic geochronologic and geochemical constraints abstract we present combined field structural data and spot image analysis petrographic data u pb zircon ages nd isotopes and whole rock geochemical data for the late archaean granite plutons from arsikere banavara ab suite and chitradurga jampalnaikankote hosdurga cjh suite in the western dharwar craton wdc ab plutons are syn kinematic with respect to the development of dome and basin patterns resulting from partial crustal diapiric overturn d1 whilst cjh suite plutons show deformation patterns resulting from the superimposition of large scale regional strike slip shearing d2 onto d1 syn emplacement fabrics sims u pb zircon ages of 2614 10 ma for the chitradurga pluton cjh and of 2617 3 ma for the arsikere pluton ab define the minimum age of the d1 strain pattern the cjh and ab suites are mainly high k granites whose origin is to be sought in partial melting of an old 3 0 ga depleted lower crust of intermediate composition the cjh and ab suites correspond mainly to the ca1 and ca2 types of archaean calc alkaline granites and some facies to the transitional ttg their heterogeneous chemical compositions indicate involvement of various sources and also significantly different depths of partial melting to produce these granites these results allow documenting regional partial reworking of the wdc 2615 ma ago requiring an ht event to have taken place before 2 61 ga and thus different from the 2 55 to 2 51 ga granulite facies metamorphic episode associated to regional scale strike slip shearing d2 that affected the entire craton partial reworking of the older lower crust at 2 61 ga and associated deformation would result from heat advection and or crustal thickening that may relate to voluminous mafic greenstone volcanism and moderate shortening at that time

fluid inclusions in the harney peak granite black hills south dakota usa implications for solubility and evolution of magmatic volatiles and crystallization of leucogranite magmas abstract experimental and theoretical studies have shown that magmatic fluids have strong influence on phase equilibria of granitic systems a microthermometric study of fluid inclusions in the proterozoic harney peak granite black hills south dakota usa was undertaken to obtain direct evidence for the composition and evolution of magmatic fluids in a leucogranitic system and to evaluate their effect on liquid lines of descent of leucogranite magmas a previous stable isotopic study has demonstrated that the granite has not interacted with nonmagmatic fluids since its crystallization therefore fluids found in the inclusions are of magmatic origin and present an opportunity to directly sample magmatic fluids trapped during crystallization of a granitic magma and during subsolidus conditions the harney peak granite was emplaced as multiple sills dikes and small intrusions many of which differentiated into coupled aplite pegmatite layers three types of fluid inclusions are found in the granite type 1 consist of variable saline h 2 o c0 2 mixtures with minor ch 4 or other gases inclusions of this type are found in tourmaline and quartz in aplite layers are generally isolated and have negative crystal shapes they are interpreted to be primary there is a general increase in salinity and decrease in isochore temperature with decreasing co 2 h 2 o ratio of the inclusions the trend is ascribed to progressive change in fluid composition with crystallization due to the differential solubility of co 2 and h 2 o in the high silica magma isochores coupled with independently determined crystallization temperatures suggest entrapment pressure 3 5 kbar consistent with geobarometry in the wallrocks type 2 inclusions are carbonic fluids dominated by co 2 whereas type 3 inclusions are saline aqueous fluids without a detected carbonic component both types are mostly found along healed fractures in quartz they are interpreted to be secondary inclusions that formed as a result of unmixing of type 1 inclusions at subsolidus conditions during uplift and cooling of the harney peak granite dome freezing point depressions birefringent daughter crystals phase equilibria considerations and track mapping of b and li distribution in thin sections all indicate that both type 1 and type 3 inclusions contain solutes such as k li and b in addition to nacl using published solubility models for h 2 o and co 2 in granitic melts and the composition of the most co 2 rich type 1 inclusions x co 2 0 55 the initial h 2 o and co 2 concentrations in the harney peak granite magma are deduced to have been 3 5 wt and 1500 ppm respectively the relatively low water concentration is consistent with temperatures of dehydration melting reactions that produced the magma it is suggested that the aplite pegmatite segregations found in parts of the harney peak granite are the result of initial rapid near liquidus crystallization of minerals with high na k ratios including plagioclase and tourmaline along a wide range of increasing h 2 o aplite crystallization was followed by crystallization of relatively potassic residual liquid enriched in fluxing elements under conditions of high h 2 o

magnetic fabric in the malanjkhand granite central india implications for regional tectonics and proterozoic suturing of the indian shield abstract in this paper field microstructural and anisotropy of magnetic susceptibility ams data are presented from the 2 48 ga malanjkhand granite and adjacent gneiss with an aim to evaluate the time relationship between fabric development in the granite and regional tectonics the central indian suture cis that demarcates the southern margin of the ne sw to ene wsw trending central indian tectonic zone citz and is a consequence of the accretion between the northern and southern indian shields lies to the north of the granite the northern margin of the granite that has proximity to the cis is mylonitized and shows a dextral top to the ne sense of shear field and magnetic foliation in the gneiss are parallel to each other as well as to the field foliation in the western and northwestern margin of the granite also the field fabrics in the granite and gneiss curve clockwise into the cis the magnetic foliation trajectories curve from a ns orientation in areas remote from the cis to a ne sw orientation in parts that are proximal to the cis in the north the granite shows synmagmatic deformation fabrics such as preferentially oriented zoned feldspar phenocrysts as well as evidence of high t solid state deformation fabric such as chessboard pattern in quartz magnetic anisotropy increases towards the cis which is inferred to support synmagmatic deformation it is concluded that the tectonic evolution of the citz and emplacement fabric development in the malanjkhand granite were synchronous phenomena wnw ese directed convergence led to transpression which is inferred to be responsible for the emplacement of the granite it is concluded that in the malanjkhand granite the development of syndeformational emplacement fabrics to syntectonic cooling was a continuum and the suturing of the northern and southern indian shields along the cis took place during the palaeoproterozoic period thus the study provides an insight into the amalgamation and stabilization of the indian shield during the late archaean palaeoproterozoic time

oxidized and reduced mineral assemblages in greenstone belt rocks of the st ives gold camp western australia vectors to high grade ore bodies in archaean gold deposits hydrothermal sulfide oxide gold mineral assemblages in gold deposits in the archaean st ives gold camp in western australia indicate extremely variable redox conditions during hydrothermal alteration and gold mineralization in space and time reduced alteration assemblages pyrrhotite pyrite occur in deposits in the southwest of the camp e g argo junction deposits and moderately to strongly oxidized assemblages magnetite pyrite hematite pyrite occur in deposits in the central corridor in the northeast e g north orchin revenge deposits reduced mineral assemblages flank the central corridor of oxidized deposits and locally cut across it along e w trending faults oxidized mineral assemblages in the central corridor are focused on gravity lows which are interpreted to reflect abundant felsic porphyritic intrusions at about 1 000 m below present surface hydrothermal magnetite predates and is synchronous with early phases of gold associated albite carbonate pyrite biotite chlorite hydrothermal alteration later stage gold associated pyrite is in equilibrium with hematite the spatial distribution and temporal sequence of iron sulfides and oxides with gold indicate the presence of at least two spatially restricted but broadly synchronous hydrothermal fluids with contrasting redox states sulfur isotope constraints support the argument that the different mineral assemblages reflect differences in redox conditions the 34s values for pyrite for the st ives gold camp range between 8 4 and 5 1 with the negative values occurring in oxidized magnetite rich domains and slightly negative or positive values occurring in reduced pyrrhotitic domains preliminary spatial and paragenetic analysis of the distribution of iron sulfides and oxides in the st ives camp suggests that gold grades are highest where the redox state of the hydrothermal alteration assemblages switches from relatively reduced pyrrhotite pyrite to relatively oxidized magnetite pyrite and hematite pyrite both in space and time gold deposition is inferred to have occurred where fluids of contrasting redox state mixed

evolution of archaean crust in the dharwar craton the nd isotope record abstract a synthesis of the available nd isotope data from the dharwar craton puts important constrains on antiquity of crust extent of basement terranes and events marking juvenile crustal addition and crustal recycling the craton is divided into two blocks namely eastern dharwar craton edc and western dharwar craton wdc nd model ages trace crust extraction as far as 3 5 ga back in both the blocks although rock record of such antiquity is yet to be found in the craton in wdc 3 35 3 0 ga is the most significant period of juvenile crustal addition as well as crustal recycling significantly depleted mantle 1 5 to 6 4 existed below the wdc as early as 3 35 ga which was probably refertilized in a later event from the resultant chondritic to slightly enriched mantle 0 3 to 0 4 juvenile mafic crust was added to the wdc during 2 9 2 6 ga a widespread crustal recycling event at 2 6 ga marks the last major event in this block in edc 3 3 3 0 ga granitoids occur as vestiges and show nd model ages higher than crystallizations ages suggesting recycling of palaeoarchaean crust during 2 7 2 5 ga extensive juvenile magmatism took place in edc from variably depleted mantle 1 4 to 5 6 which is later than the global 2 7 ga peak of crustal growth attendant crustal recycling destroyed most of the earlier crust distribution of nd model ages suggests in contrast to general believe that palaeoarchaean crust was not only abundant in the wdc but also widespread in an area extending from the wdc edc boundary to further 60 150 km east up to the hungund ramagiri kolar hrk belt this belt appears to be a major crustal boundary along which terranes of different nd isotope signatures were amalgamated during the late neoarchaean by horizontal accretion major neoarchaean crustal recycling events documented in the dharwar craton are missing from nd isotope record of the eastern block eb of the north china craton this fact does not support correlation between the two cratons as suggested by some authors

the origin of brown hornblende in the artfjallet gabbro and dolerites brown hornblende occurs in minor amounts in the artfjallet gabbro and dolerites except in quartz dolerites where a pale green hornblende occurs in the gabbro brown hornblende is mostly ti bearing pargasite or kaersutite it occurs along veins of orthopyroxene as rims around and blebs in pyroxenes with orthopyroxene in coronas between olivine and plagioclase and in coronas between ilmenite and plagioclase in the olivine dolerites and orthopyroxene dolerites brown hornblende is ferroan titanian pargasite or ferroan kaersutite the pale green hornblende in the quartz dolerites is a magnesio hornblende the hornblendes in the dolerites are interstitial or granular in some dolerites occurring as coarse oikocrysts it is proposed that under certain conditions the ti content of hornblende can be used as a thermometer derived from experimental data of helz 1973 microstructures compositions and formation temperatures 1 040 c show that the brown hornblende in the gabbro is not magmatic but of subsolidus origin probably it formed as a result of the introduction of water into the gabbro during a deformation event that occurred early in the cooling history of the gabbro least squares modelling of hornblende formation indicates that all magmatic minerals must have participated in the reaction and that the reaction probably was not isochemical microstructures compositions and formation temperatures 1 030 965 c of brown hornblende in the dolerites are consistent with late stage crystallization from the magma for the pale green hornblende in the quartz dolerites a magmatic origin is likely but cannot be proven

exsolution of magmatic volatile phases from cl enriched mineralizing granitic magmas and implications for ore metal transport abstract to understand cl dissolution in aluminosilicate liquids and the exsolution of cl rich magmatic volatile phases experiments were conducted to determine the solubility of nacl kcl and h2o in felsic liquids at 0 5 and 2 kbar the cl content of h2o poor nacl saturated and kcl saturated silicate liquids is low i e 1 3 wt to very low i e 0 2 wt and varies with changes in pressure and composition the cl concentration increases with the f concentration and the molar al na ca mg si ratio of the liquid and decreases with increasing activity of h2o in the system exsolution of a volatile phase depends on the partial pressures of all dissolved volatiles and low cl solubilities in nacl saturated and kcl saturated silicate liquids imply that exsolution of a cl bearing volatile phase will occur early in cl bearing granitic magmas i e prior to extensive melt crystallization and or at comparatively low water fugacities the solubility behavior of h2o and cl is very similar to that of co2 and h2o in felsic liquids small quantities of co2 are known to facilitate volatile phase exsolution holloway 1976 and in a similar manner volatile phases may exsolve early in cl enriched granite magmas whereas 5 to 6 wt dissolved h2o is necessary for volatile phase exsolution from a co2 free and cl free haplogranite liquid at 2 kbar and 800 c a cl rich brine will exsolve if the liquid contains only 1 wt h2o and 0 26 wt cl at the same conditions these new solubility data are interpreted in light of h2o f and cl concentrations in felsic liquids determined from silicate melt inclusions to constrain the exsolution of cl bearing magmatic volatile phases from mineralizing granitic magmas felsic magmas genetically associated with cu porphyry and mo porphyry mineralization contain sufficient h2o and cl to become saturated with respect to a hypersaline brine without strong pressure reduction boiling of the volatile phase i e exsolution of immiscible vapor and brine or strong volatile enrichment resulting from extensive crystal fractionation experiments were also conducted to investigate the solubility of mo in highly saline volatile phases coexisting with granitic liquids at 2 and 0 5 kbar the apparent partition coefficient for mo in the volatile phase s relative to silicate liquid d mo is defined as the computed concentration of mo in a volatile phase or phases the measured concentration of mo in granite glass d mo ranges from 8 to 80 as the nacl and kcl content of the volatile phase s increases from 15 to 90 wt because mo does not complex with cl in aqueous fluids it appears that mo solubility may be a strong function of the activity of na and k in alkali chloride rich volatile phases

lead isotopic compositions of the western dharwar craton southern india evidence for distinct middle archean terranes in a late archean craton abstract lead and sr isotopic compositions of whole rocks and feldspar separates from several fielddefined suites of rocks from the western dharwar craton of southern india elucidate a complex history of the area the evolution of the craton earlier than 3 0 ga is difficult to determine because of thermal and metasomatic overprinting at 3 0 ga many whole rocks were completely reset then but feldspar separates preserve some of the earlier history apparently a series of terranes evolved from the mantle over the period 3 4 to 3 0 ga to form the western dharwar craton in each case metamorphism and anatexis of older terranes accompanied extraction of juvenile material from the mantle the oldest gneisses 3 4 ga had radiogenic pb and sr isotopic compositions when they formed and were derived from older crustal protoliths that were plausibly accreted to the crust at or even before 3 8 ga the old gneisses were greatly depleted in rb probably at 3 4 ga when the protoliths of younger magmatic rocks may have separated from the mantle younger gneisses apparently formed from these mafic intermediate protoliths in the age range of 3 2 to 3 0ga the 3 0 ga event in the central part of the craton was accompanied by intrusion of small diapiric trondhjemites formed by melting of older crust and penecontemporaneous metasomatism of country rocks by hydrous fluids carrying u and other lithophilic elements the resultant deep crust was greatly depleted in heat producing elements and the craton has been inactive since 3 0 ga except for production of minor granites from depleted source regions at 2 5 2 6 ga the lack of activity at 2 5 ga contrasts strongly with extensive magmatism and metamorphism in surrounding areas that had not undergone depletion at 3 0 ga lower crustal depletion also has caused present day reduced heat flow to be very low

mineralogy and geochemistry of microgranular enclaves in palaeoproterozoic malanjkhand granitoids central india evidence of magma mixing mingling and chemical equilibration palaeoproterozoic ca 2 480 ma felsic magmatism of malanjkhand region of central indian precambrian shield referred to as malanjkhand granitoids mg contain xenoliths of country rocks and mesocratic to melanocratic fine grained porphyritic microgranular enclaves me the shape of me is spheroidal ellipsoidal discoidal elongated and lenticular varying in size from a few centimeters to about 2 m across the contact of me with the host mg is commonly sharp crenulate and occasionally diffuse which we attribute to the undercooling and disaggregation of me globules within the cooler host mg the me as well as mg show hypidiomorphic texture with common mineral hbl bt kfs pl qtz assemblage but differ in modal proportions the variation in minerals composition presence of apatite needles elongated biotites resorbed plagiclase ocellar quartz and other mafic felsic xenocrysts strongly oppose the restite and cognate origins of me compositions of plagioclases an3 an29 amphiboles mg mg fe2 0 55 0 69 and biotites mg mg fe2 0 46 0 60 of me are slightly distinct or similar to those of mg which suggest partial to complete equilibration during mafic felsic magma interactions al in amphibole estimates the mg pluton emplacement at ca 3 4 0 5 kbar and therefore magma mixing and mingling must have occurred at or below this level the hbox fe rightleftharpoons hbox mg substitution in biotites of me and mg largely suggests subduction related calc alkaline metaluminous i type nature of felsic melts most major and trace elements against sio2 produce near linear variation trends for me and mg probably generated by the mixing of mafic and felsic magmas in various proportions trace including rare earth elements patterns of me mg pairs however show partial to complete equilibration most likely governed by different degrees of elemental diffusion the available evidence supports the model of me origin that coeval mafic enclave and felsic mg magmas produced a hybrid me magma layer which injected into cooler partly crystalline mg and dispersed mingled and undercooled as me globules in a convectively dynamic magma chamber

isotope c and o composition of auriferous quartz carbonate veins central lode system gadag gold field dharwar craton india implications to source of ore fluids abstract carbon 13 c pdb and oxygen 18 o smow isotopic compositions of auriferous quartz carbonate veins qcvs of gold deposits from sangli kabuliyatkatti nagavi nabapur and mysore mining areas developed on the central lode system of the gadag gold field ggf in the neoarchaean gadag schist belt of the dharwar craton southern india have been examined for the first time to understand the origin of the mineralising fluids in majority of the samples 46 out of 49 13 c pdb of carbonates of the qcvs fall in the range from 2 2 to 9 7 and the 18 o values range from 12 0 to 30 5 smow the calculated fluid 13 c c compositions for these deposits range from 2 1 to 9 6 and 18 o h 2 o from 6 8 to 25 9 respectively carbonate 13 c and fluid 13 c c compositions of the carbonates of the qcvs of the ggf are not only distinct from the carbon isotope range of marine carbonates or meta sedimentary carbonates of the chitradurga schist belt but are consistent with c isotope values of magmatic 5 3 burrows et al 1986 and or mantle 6 2 ohmoto 1986 carbonates as dissolution decarbonation reactions during metamorphism of pre existing carbonate carbonated rocks produce co 2 with 13 c values similar to or more enriched than parent rock the carbonate or fluid 13 c ratios of the qcvs which fall in the compositional range of mantle magmatic derived co 2 or carbonates obtained in this work cannot be the result of metamorphism the present study corroborates our previous reports from ajjanahalli and g r halli gold deposits sarangi et al 2012 occurring in the vicinity of the southern extension of the same crustal scale shear zone on which all the ggf deposits are located the age of gold mineralisation in this area has been reported to be 2522 6 ma by sarma et al 2011 chardon et al 2011 have proposed large scale remobilization of the older gneissic basement as well as emplacement of juvenile granites between 2559 ma and 2507 ma close to the crustal scale shear zone along the eastern margin of the chitradurga schist belt based on these observations and our isotope studies it is proposed that gold mineralising fluids were derived from mantle juvenile magmatic melts and were channelled through crustal scale shear zones to give rise to the gold deposits in the ggf

formation of al rich titanite catisio4o caalsio4oh reaction rims on ilmenite in metamorphic rocks as a function of fh2o and fo2 abstract reaction rims of titanite on ilmenite are described in samples from four terranes of amphibolite facies metapelites and amphibolites namely the tamil nadu area southern india the val strona area of the ivrea verbano zone northern italy the bamble sector southern norway and the northwestern austroalpine otztal complex the titanite rims and hence the stability of titanite catisio4o and al oh titanite i e vuaganatite hypothetical end member caalsio4oh are discussed in the light of fh2o and fo2 buffered equilibria involving clinopyroxene amphibole biotite ilmenite magnetite and quartz in the systems cao feo fe2o3 tio2 sio2 h2o o2 cftsh and cao feo fe2o3 al2o3 sio2 h2o o2 cfash present in each of the examples textural evidence suggests that titanite reaction rims on ilmenite in rocks from tamil nadu val strona and the bamble sector originated most likely due to hydration reactions such as clinopyroxene ilmenite quartz h2o amphibole titanite and oxidation reactions such as amphibole ilmenite o2 titanite magnetite quartz h2o during amphibolite facies metamorphism or as in the case of the otztal complex during a subsequent greenschist facies overprint overstepping of these reactions requires fh2o and fo2 to be high for titanite formation which is also in accordance with equilibria involving al oh titanite this study shows that in addition to p t bulk rock composition and composition of the coexisting fluid fo2 and fh2o also play an important role in the formation of al bearing titanite during amphibolite and greenschist facies metamorphism

an overview of the relationship between granitoid intrusions and gold mineralisation in the archaean murchison province western australia in the archaean murchison province of western australia granitoid batholiths and plutons that intruded into the ca 2 7 2 8 ga and ca 3 0 ga greenstone belts can be divided into three major suites suite i is a ca 2 69 ga monzogranite granodiorite suite which was derived from anatexis of old continental crust and occurs as syn tectonic composite batholiths over the entire province suite ii is a trondhjemite tonalite suite termed i type derived from partial melting of subducted basaltic crust which intruded as syn to late tectonic plutons into the greenstone belts in the northeastern part of the province where most of the major gold deposits are situated one of the suite ii trondhjemite plutons has a pb pb isochron age of 2641 36 ma and one of the structurally youngest tonalite plutons has a minimum pb pb isochron age of 2630 1 4 3 ma suite iii is a ca 2 65 2 62 ga a type monzogranite syenogranite suite which is most abundant in the largely unmineralised southwestern part of the province gold deposits in the province are mostly hosted in brittle ductile shear zones and were formed at a late stage in the history of metamorphism deformation and granitoid emplacement at one locality mineralisation has been dated at 2636 8 4 2 ma through a pyritetitanite pb pb isochron lead and sr isotope studies of granitoids and gold deposits indicate that although most gold deposits have initial pb isotope compositions most closely similar to those of suite ii intrusions both suite i and suite ii intrusions or their source regions could have contributed solutes to the ore fluids these preliminary data suggest that gold mineralisation in the murchison province was temporally and spatially associated with suite ii i type granitoids in the northeastern part of the province this association is consistent with the concept that archaean gold mineralisation was related to convergent style tectonic settings as generation of both suite ii i type granitoids and hydrothermal ore fluids could have been linked to the dehydration and partial fusion of subducted oceanic crust and old sialic crust or its anatectic products may also contribute solutes to the ore fluids integration of data from this study with other geological and radiogenic isotope constraints in the yilgarn block argue against direct derivation of gold ore fluids from specific i type granitoid plutons but favour a broad association with convergent tectonics and granitoid magmatism in the late archaean

mineralization and deformation of the malanjkhand terrane 2 490 2 440 ma along the southern margin of the central indian tectonic zone the malanjkhand cu mo au deposit located near the northwest margin of the malanjkhand batholith terrane is a strategic and significant porphyry style deposit that experienced a protracted 50 m y deformational history shortly after its formation at 2 490 8 ma stein et al 2004 in a recent study panigrahi et al 2004 averaged u pb shrimp zircon data from a pooled set of samples from the malanjkhand batholith to advocate a meaningless intermediate age of 2 476 ma for the malanjkhand granitoid and its cu mo au deposit in the northwest part of the malanjkhand batholith re os dating of occurrence specific molybdenite captures not only the age of porphyry style mineralization and associated magmatism but also elucidates a complex deformational history that extends to 2 450 ma in the central part of the malanjkhand batholith re os dating of delicate spindles of accessory molybdenite occurring with pristine muscovite in miarolitic cavities within the undeformed microgranitoid at the devgaon mo prospect unequivocally shows that deformation ceased at this location no later than 2 470 2 465 ma the deformational history recorded at the malanjkhand deposit in the northwest most likely reflects prolonged transpressive convergence and docking of the malanjkhand terrane with units in the poorly understood proto central indian tectonic zone citz along its southern margin the central indian shear zone the timing for this convergence is late archean early paleoproterozoic

diffusion in magmas at depth in the earth the effects of pressure and dissolved h2o abstract experimental data on cation diffusion in silicate melts and glasses at atmospheric pressure cannot be quantitatively applied to diffusion in magmas at depth because pressure and dissolved h2o have significant effects diffusivities of ca and cs in soda lime aluminosilicate melt are reduced by roughly an order of magnitude as pressure increases from 1 to 30 kbar at 1100 c in the case of calcium the pressure effect is smaller at higher temperatures the influence of dissolved h2o is opposite to and for some ions far more important than that of pressure at 700 c cs diffusion in granitic obsidian is enhanced by four orders of magnitude by the addition of 6 wt h2o and ca diffusivity increases by 2 5 orders of magnitude sodium diffusion on the other hand is relatively immune to changes in h2o content the retarding effect of pressure on diffusion in deep seated magmas is largely compensated by higher magmatic temperatures such that overall depth effects on diffusion are of secondary importance diffusion rates in mantle melts are probably well approximated by 1 atm near liquidus values diffusion rates in crustal magmas however are extremely sensitive to h2o content so that models of rate controlled processes in hydrous magmas may be grossly in error if 1 atm diffusivity values are used

phosphorus and the rare earth elements in felsic magmas an assessment of the role of apatite abstract the solubility of fluorapatite in 17 silica rich melts in the system na 2 o k 2 o al 2 o 3 sio 2 with and without cao or caf 2 was determined at 1 kbar water pressure and 750 900 c apatite saturation occurs at levels of dissolved p 2 o 5 ranging between 0 04 0 02 and 0 28 0 13 wt with only 4 values outside the 0 09 0 20 wt range the results demonstrate not only that apatite is a common liquidus phase in felsic melts but also that under most circumstances it remains in the residue during episodes of partial fusion of the crust given a solubility limit of 0 14 wt dissolved p 2 o 5 the mean of the experimental values a source containing as little as 0 05 p 2 o 5 must be 35 melted before apatite is lost from the residue and no longer buffers the melt p 2 o 5 concentration at the saturation value higher abundances of p 2 o 5 in the source postpone the loss of residual apatite to still higher degrees of melting and if the source p 2 o 5 content exceeds 0 14 wt apatite must be residual for all degrees of melting increasing in abundance as melting proceeds the generally secondary influence of apatite on the rare earth element ree patterns of melt and residue is most apparent when garnet and or amphibole is minor or lacking in the residue fractional crystallization of intermediate e g andesitic magmas toward felsic compositions invariably results in saturation in apatite and some consequent depletion of ree in the melt

evolution of hf and hcl activity in magmatic volatiles of the gold mineralized emerald lake pluton yukon territory canada we examine the halogen contents of biotite amphibole and apatite from four magmatic phases of the emerald lake pluton to document the evolution in composition of magmatic volatiles in this system and to determine if this evolution is consistent with the nature and distribution of weak gold mineralization in the pluton in general the variations in halogen compositions of hydrous minerals are greater between magmatic phases than within single magma batches and the abundance of chlorine decreases and fluorine increases in hydrous minerals during the evolution of the emerald lake pluton by applying the internally consistent thermodynamic database and mineral activity composition relationships that account for coupled site substitution we further employ biotite and apatite compositions as independent monitors of fluid composition most analyzed biotite exhibits textural and or compositional features characteristic of late subsolidus halogen exchange with fluid however we have identified biotite that appears to retain halogen contents indicative of magmatic conditions fluorine contents of these biotites range from around 1 5 syenite and monzonite to greater than 2 2 wt in a late stage pegmatite dike chlorine by contrast shows a more restricted range of values and typically falls between 1 0 syenite and monzonite and 0 6 wt pegmatite apatite inclusions within anhydrous phenocrysts have fluorine contents of around 3 3 syenite to greater than 3 7 wt granite while chlorine contents fall from 0 5 to 0 1 wt with evolution from syenite to granite phases of the pluton the fluid a hcl a hf conditions recorded by biotite and apatite are in close agreement these two independent measures of hcl and hf both show a modest decrease in hcl hf as the system evolves the highest log a hcl a hf values 0 6 to 0 3 are associated with magmatic volatiles of syenite the first phase to intrude at emerald lake activity ratios recorded from the second phase monzonite show a slight fall to 0 4 to 0 1 a similar drop is recorded in the transition to hydrothermal activity recorded in biotite from a late pegmatite dike 0 1 to 0 1 a decrease in log a hcl a hf is consistent with a loss of chlorine and residual enrichment of fluorine in the magma due to progressive release of a chlorine bearing metalliferous fluid the relatively small variation in inferred fluid hcl and hf activity suggests that the magmatic volatiles present during crystallization were relatively homogeneous and argues against both the incursion of external fluids and of substantial temporal variation in fluid composition from the magma source furthermore if magmatic volatiles are the source of the gold mineralization found across all phases of the emerald lake pluton as advocated by other workers our data would suggest that the mineralizing fluids were remarkably homogeneous and distributed throughout the pluton the disseminated and low grade nature of mineralization may be at least in part a consequence

uniformity in sulfur isotope composition in the orogenic gold deposits from the dharwar craton southern india the sulfur isotope composition of sulfides mainly pyrite and arsenopyrite from gold deposits prospects of the dharwar craton such as hutti hira buddini uti kolar chigargunta ajjanahalli and jonnagiri has a narrow range 34s 1 1 to 7 1 such craton scale uniformity of the above gold camps is noteworthy in spite of the wide diversity in host rock compositions and their metamorphic conditions and suggests a magmatic or average crustal source of sulfur for all deposits studied in addition our study points towards gold precipitation from reduced ore fluids with near homogeneous sulfur isotope compositions

fluorine as a tool in the petrogenesis of quartz bearing magmatic associations applications of an improved f oh biotite apatite thermometer grid abstract fluorine contents of whole rock and biotites allow to discriminate quartz bearing magmatic associations through the nature of protoliths and petrogenetic processes f and rb are used to discriminate crustal and mantle derived melts with the exception of calcalkaline association in which mantle contribution may be significant the other quartz bearing associations are essentially derived from crustal melting by biotite and or amphibole vapor absent reactions based on experimental data and on an improved biotite apatite thermometer grid closure temperatures from near liquidus to near solidus conditions as well as fh2o fhf evolution during cooling are determined for the different magmatic associations it appears that the liquidus temperature and fh2o fhf decreases in the order high silica alkaline high k calcalkaline and calcalkaline associations while the solidus temperature follows an inverse order the fh2o fhf values for the peraluminous associations vary over a wide range and overlap the fh2o fhf values of the high k calcalkaline and calcalkaline associations

gold and metal enrichment in natural granitic melts during fractional crystallization metal evolution in a composite granitic pluton was tracked by analyzing melt inclusions in 11 quartz samples from 7 zones at the timbarra gold deposit australia we present the first quantitative microanalyses of gold au in granitic silicate melt inclusions using laser ablation inductively coupled plasma mass spectrometry and show how au and other metals become enriched during fractional crystallization in a granite intrusion au was enriched during fractionation from a monzogranite to a highly fractionated alkali feldspar granite similar enrichment behavior for other metals implies that no gold enriched precursor melt is required and fractional crystallization can enrich the au concentration to economic levels the low content of accessory oxides and sulfides the absence of early cl bearing fluids the volatile content in the melt and a prolonged crystallization constitute important factors for extensive metal enrichment during crystal fractionation these characteristics play a crucial role in felsic highly fractionated plutons and their associated deposits such as intrusion related au deposits the gold enrichment during fractionation also implies that au is directly sourced from the granites

influence of co2 on melting of model granulite facies assemblages a model for the genesis of charnockites it is shown that partial melting studies at crustal pressures in sio2 rich portions of the system kalsio4 mg2sio2 h2o co2 can be used in modeling the anatectic origin of charnockites the univariant reaction phlogopite sanidine quartz vapor enstatite liquid yields an sio2 rich melt granite analog at 3 kbar the vapor composition at the solidus is buffered to high h2o contents by virtue of the coexistence of phlogopite with its breakdown products with higher pressures 8 and 15 kbar the fluid phase is buffered to higher co2 contents and the melt composition becomes enriched in k2o and mgo charnockite analog melting relations are controlled through the expansion of the quartz liquidus field relative to the enstatite and sanidine fields with increasing pressure it is noted that partial melts generated at the base of the crust in the presence of co2 rich fluid will be of an alkaline nature and will crystallize enstatite at lower pressures co2 saturated melting of similar sio2 rich bulk compositions phlogopite absent through the reaction enstatite sanidine quartz co2 liquid occurs at temperatures above 1000 c to about 15 kbar

late archaean 2550 2520 ma juvenile magmatism in the eastern dharwar craton southern india constraints from geochronology nd sr isotopes and whole rock geochemistry the results of field geochronologic geochemical and isotopic studies are presented for the granitoids that occur east of the closepet batholith up to the kolar schist belt ksb field data such as common foliation strong shear deformation occasionally leading to mylonitization together with petrographic data including reduction in grain size with corroded borders show characteristics of the syn kinematic emplacement of the granitoids single zircon evaporation ages define a minimum age of 3127 ma for the tonalitic trondhjemitic granodioritic ttg basement and 2552 2534 ma plateau ages for the emplacement of the granitoids which slightly predate 20 30 ma the emplacement of the 2518 ma closepet batholith major and trace element data together with isotopic data suggest at least four magmatic suites from closepet batholith to the east which have independent magmatic evolution histories the observed data are compatible with magma mixing for the closepet batholith melting of ttg and assimilation fractional crystallization processes for bangalore granites either melting of heterogeneous source or different degree of melting of the same source for the granitoids of hoskote kolar and fractional crystallization for the western margin of the ksb isotopic nd sr and geochemical data lree and lil elements suggest highly enriched mantle and ancient ttg crust for the closepet batholith enriched mantle and ttg crust for the bangalore granites c a chondritic mantle source for the granitoids of hoskote kolar and the quartz monzonites of the western margin of the ksb and slightly depleted mantle for granodiorites of the eastern margin of the ksb we interpret all these geochronologic geochemical and isotopic characteristics of granitoids from the closepet batholith to the east up to the ksb in terms of a plume model the centre of the plume would be an enriched hot spot in the mantle that lies below the present exposure level of the closepet batholith melting of such an enriched mantle hot spot produces high temperature magmas closepet that penetrate overlying ancient crust where they strongly interact and induce partial melting of the surrounding crust these magmas cool very slowly as the hot spot maintains high temperatures for a long time thus they appear younger 2518 ma on the contrary to the east the plume induces melting of c a chondritic or slightly depleted mantle that produces relatively colder and less enriched magmas which show less or no interactions with the surrounding crust and cool rapidly and appear slightly older 2552 2534 ma this plume model can also account for late archaean geodynamic evolution including juvenile magmatism heat source for reworking inverse diapirism and granulite metamorphism in the dharwar craton

a 2 5 ga porphyry cu mo au deposit at malanjkhand central india implications for late archean continental assembly abstract eight re os ages from six molybdenite samples representative of the cu mo au mineralization at the giant malanjkhand deposit in madhya pradesh were obtained using id ntims these data provide a clear late archean early paleoproterozoic age for this deposit and by implication for its calc alkaline granitoid host among other diverse models the origin of malanjkhand has been debated as orogenic lode style associated with development of a quartz reef in a shear zone or as porphyry style associated with a pink granitoid intrusion that is conspicuously present in the vicinity of the brittle ductile deformed quartz reef previous models included middle proterozoic ages for the cu mo au mineralization based on poorly constrained rb sr and k ar data direct dating of molybdenite shows that stringer mineralization in the quartz reef and disseminated and vein mineralization in the granite were contemporaneous at 2490 8 ma 2489 5 1 4 ma based on regression without uncertainty in the 187re decay constant mswd 0 5 n 5 additional molybdenite from the quartz reef dated at 2475 and 2450 ma represents at least two pulses of reworking that we suggest configured the elongate and arcuate quartz reef into its present position we suggest that the quartz reef is a high silica stockwork cap embedded in its primary potassic alteration halo and subsequently tilted so that it lies convex to the east with deeper levels exposed to the north petrographic evidence coupled with high re concentrations for molybdenites 400 650 ppm support this scenario and suggest that malanjkhand is a subduction related stockwork porphyry style cu mo au deposit involving mantle malanjkhand geology shares little affinity with three surrounding and tectonically juxtaposed terranes we suggest that the malanjkhand cu mo au deposit and the surrounding batholith containing multiple cu mo au prospects may be the vestiges of a microplate captured along the north margin of the nearly amalgamated southern indian craton at 2 5 ga as the southern craton began to converge with the northern indian craton or other protocontinents now embedded or consumed within the central indian tectonic zone citz this scenario could imply an early paleoproterozoic age for the earliest development of the citz at least in the region of the central indian shear suture cis whose marked ene trend imprints the northwestern part of the malanjkhand batholith and the cu mo au deposit based on a compilation of 2 5 ga events in both the southern and northern indian cratons we suggest that some units in the citz linked an extensive and continuous late archean early paleoproterozoic orogenic belt that may extend to the moyar bavali bhavani attur palghat and cauvery shear zones in southern india and include inboard units of the eastern ghats and the aravalli delhi orogenic belts robust geochronology that can be tied to the early history within these orogenic belts is scarce and extensive reworking during grenvillian and pan african time creates a pervasive overprint at some localities this late archean early paleoproterozoic belt preserves sutures within a coalesced late archean continent that included east antarctica napier and vestfold hills complexes at 2 5 ga

partitioning of cl and f between fluid and hydrous phonolitic melt of mt vesuvius at 850 1000 c and 200 mpa abstract the solubilities of cl and or f bearing fluids in phonolitic melts of vesuvius volcano have been determined experimentally at temperatures of 845 865 c and 1000 c and pressure of 200 mpa at 845 865 c the maximum cl concentration in the melt m cl coexisting with cl rich 35 5 wt fl cl and f free fluid is about 0 5 wt an addition of f to the system increases the cl content of the melt up to 0 7 wt at 39 wt cl and 13 wt f in the fluid s the relationship between m cl and fl cl indicates that low density vapor and dense brine phases might have coexisted in some experiments the relationship between m cl and fl cl at 1000 c is similar to that determined at 845 865 c implying that variations of temperature in the range 850 1000 c have no significant effect on the partitioning of cl between fluid and phonolitic melt the concentration of f in phonolitic melt coexisting with f rich fluid s reaches at least 0 9 wt at 845 865 c and 1 3 wt at 1000 c the comparison of data from experiments conducted in au and pt capsules indicates that f may react with au which influences the quality of the experimental results the partition coefficients of f between bulk fluid and melt fl m d f are higher than 1 in all experiments indicating that fluorine is preferentially incorporated into the fluid phase in phonolitic systems in contrast to fl m d f values determined in rhyolitic systems the influence of cl on fl m d f is not detectable at the conditions of our experiments the experimental data imply that mt somma vesuvius phonolitic magmas from the eruptions between a d 79 and a d 1944 may have coexisted with cl rich and f rich fluid phase s prior to eruption

reply to discussion on age of granitic activity associated with copper molybdenum mineralization at malanjkhand central india by holly stein judith hannah aaron zimmerman and richard markey

gold mineralisation and alteration of penakacherla schist belt india constraints on archaean subduction and fluid processes abstract in the dharwar craton southern india gold deposits are found mostly along the six arcuate shear zones passing through late archaean greenstone belts 2 7 ga one such shear zone complex extends for about 400 km within and along the ramagiri hungund schist belt the penakacherla sector of this shear zone is excellently exposed enabling a detailed investigation of synorogenic gold mineralisation and its relationship to associated hydrothermal alteration metamorphism and deformation under ne sw compression associated with archaean subduction processes converted mafic volcanic rocks into amphibolites and intermediate to felsic volcanic rocks into quartz mica schists continued compression generated a 50 100 m wide shear zone complex consisting of mafic phyllonites advection of hydrothermal fluids through this shear zone and reaction between fluids and the mafic phyllonites resulted in a silicified k metasomatic assemblage mainly consisting of chlorite amphibole k mica plagioclase ankerite quartz fe oxides pyrite chalcopyrite and arsenopyrite networks of quartz and carbonate veinlets a few millimeters to a few centimeters thick formed along the foliation planes giving rise to microscopic alteration envelope in which individual veinlet systems are merged into one another to form a composite alteration system gold is found within these quartz veinlets mafic phyllonites and at their mutual contacts hydrothermal fluids have modified the primary major minor trace and lree compositions of host rocks such that their mutual behaviour became non systematic some hfse and hree also show minor mobility but the overall ree pattern generally resembles that of the precursor mafic volcanic rocks mass and volume loss gain by si and ca has made significant impact on al ti and zr abundances which are generally immobile during hydrothermal alteration however element pairs such as zr hf v sc and nb ta maintain primary inter element ratios although their absolute abundances are drastically diluted similarly ree in highly silicified and carbonatised samples are reduced but patterns remain similar to those of relatively least altered mafic phyllonites with la n yb n between 1 and 3 in some samples lree enrichment is observed elevating in la n yb n from 3 to 11 pathfinder elements and base metals such as as cd cu pb zn and sb have been added along with the au and ag 13 c of carbon varies from 16 to 21 suggesting a biogenic origin whereas coexisting pyrite 34 s ranges from 1 to 3 pointing towards the involvement of magmatic or average crustal sulphur overall concentrations of k rb sr ba nb ta ti cs cr co v y and sc and many of the ratios such as k rb la sc la yb indicate that metamorphism devolatilisation and dehydration of an oceanic subducting slab might have partially contributed the mineralising fluids and generated the alteration assemblage observed in the host rocks fluid sources were mantle and greenstone belt dehydration and devolatilisation generating observed compositional and alteration diversity

magmatic co 2 and saline melts from the sybille monzosyenite laramie anorthosite complex wyoming there are three populations of fluid inclusions in quartz from the sybille monzosyenite early co2 secondary co2 and rare secondary brines the oldest consist of low density co2 0 70 inclusions that appear to be co magmatic the densities of these inclusions are consistent with the inferred crystallization conditions of the sybille monzosyenite namely 3 kilobars and 950 1000 c the other types of inclusions are secondary they contain co2 0 50 and secondary brine inclusions that form trains radiating out from a decrepitated inclusion the sites of these decrepitated inclusions are now marked by irregularly shaped fluid inclusions and solid inclusions of salt and carbonate rather than fluid inclusions feldspar contain abundant solid inclusions these consist of magmatic minerals hedenbergite hornblende ilmenite apatite and graphite intimately associated with k na chlorides we interpret these relations as follows the sybille monzosyenite formed from a magma that contained immiscible droplets of a halide rich melt along with a co2 vapor phase the salt was trapped along with the other obvious magmatic minerals during growth of the feldspars co2 may have also been included in the feldspars but it probably leaked later during exsolution of the feldspars and was not preserved both the saline melt and the co2 vapor were trapped in the quartz the melt inclusions in the quartz later decrepitated perhaps due to progressive exsolution of fluids to produce the secondary h2o and co2 inclusions these observations indicate that the sybille monzosyenite which is a markedly anhydrous rock was actually vapor saturated rather than being h2o however the vapor was co2 rich and possibly related to an immiscible chloride rich melt

late archaean granites a typology based on the dharwar craton india abstract extensive field work in the eastern dharwar craton associated with petrographic and geochemical major and trace elements investigations allows four main types of late archaean granitoids to be distinguished 1 na rich granitoids of trondhjemitic tonalitic and granodioritic composition ttg that are characterised by strongly fractionated ree patterns and low hree contents and generally interpreted as slab melts generated by partial melting of metamorphosed hydrated basalt most likely in a subduction environment 2 sanukitoids which are k and mg rich monzonites and granodiorites with ttg like ree patterns associated with marked lile enrichment and considered to result from the reaction of slab melts generated in a subduction environment with and assimilation of mantle wedge peridotite 3 uncommon high hfse mg and k granites with strongly ree and lile enrichment that probably formed by partial melting of an enriched mantle source unlike in the genesis of sanukitoids in this case the slab melt is considered to be wholly consumed by reaction with mantle minerals resulting in mantle enrichment subsequent melting of this enriched mantle probably in a post subduction setting gives rise to high hfse mg and k magmas as demonstrated for the closepet granite dharwar craton the hot mantle derived magma can induce melting of continental crust and then mix with the anatectic products 4 k rich mg poor anatectic biotite granites with ree patterns that are less fractionated and show negative eu anomalies these granites result from the remelting of old basement or recently accreted plutons both with ttg compositions such anatexis can occur either in a subduction or in a post subduction environment this typology based on the well exposed dharwar craton can be extended to late archaean granitoids from all over the world about such 500 analysis were compiled and a number of discriminant diagrams based on both major and trace elements are proposed the most likely tectonic setting for the observed rock types is an accretionary orogen with accretion of continental blocks above a subduction system followed by thermal reworking of the newly accreted continental material however it has been found that archaean subduction related granitoids are significantly different from their modern counterparts implying progressive changes in the modes of magma generation at convergent margins from the archaean to the present

chlorine partitioning between a basaltic melt and h2o co2 fluids at mount etna abstract partitioning experiments between a basaltic melt from mt etna and a low density hydrous fluid or vapor containing h 2 o or h 2 o co 2 were performed at 1200 1260 c at pressures between 1 and 200 mpa either near the nickel nickel oxide nno buffer or at two log units above it nno 2 and with different chloride concentrations most of the experiments were done at chloride brine undersaturated conditions although at the highest cl concentrations explored brine saturation might have been reached the average partition coefficients d cl fluid melt over the range of cl concentrations were derived on a weight basis by plotting the calculated concentrations of cl in the fluid phase versus the measured ones in the melt for h 2 o cl experiments in which the cl concentration in the melt was 0 4 wt a negative dependence between d cl f m and pressure is observed d cl fluid melt in h 2 o cl bearing experiments ranges between 11 14 at 1 and 25 mpa to 6 at 200 mpa at nno and between 4 at 50 mpa and 13 at 100 mpa at nno 2 addition of co 2 at nno yields lower partition coefficients than in co 2 free conditions over the pressure range investigated the negative pressure dependence observed for h 2 o cl experiments disappears when co 2 is present in the system overall once co 2 is introduced in the system cl fugacity in the silicate melt tends to increase thus resulting in a decrease of d cl f m application to mt etna shows that the composition of the volcanic plume in terms of cl records very shallow pressures of magma equilibration with its exsolved fluid

oxygen isotope ratio of quartz veins from the auriferous ramagiri penakacherla schist belt and surrounding granitoids in the eastern dharwar craton a case for a possible link between gold mineralization and granite magmatism abstract in the eastern dharwar craton among the many shear zone hosted lode gold deposits those at ramagiri and penakacherla are located near the western margin of the craton mineralized quartz sulfide carbonate veins are hosted by the schistose metavolcanic and carbonaceous metasedimentary rocks in close spatial association with granitoids having quartz and quartzofeldspathic veins representing hydrothermal activities associated with them mineralized quartz veins from the ore zones in ramagiri and penakacherla regions and quartz or pegmatitic veins from the surrounding granitic terrane were chosen for 18 o analysis samples from the schistose and granitic domains show 18 o quartz values in the range of 10 4 14 9 and 9 3 10 9 respectively the ore zone fluids from the ramagiri and penakacherla regions give 18 o values of 7 9 1 5 and 5 1 0 8 calculated at pressure corrected temperatures obtained from fluid inclusion microthermometry the late magmatic fluid is relatively 18 o poor with 18 o values estimated at 4 5 0 7 and the value is closer to what is obtained for the ore zones based on the 18 o values reported and a possible magmatic contribution to ore fluid deciphered from fluid inclusion characteristics a genetic relationship between granitic magmatism and gold mineralization is surmised the observed increase in the 18 o 16 o ratio from the magmatic fluid to ore fluid in the shear zone is attributed to interaction of the magmatic fluid with host metasediments that agrees well with the variation in the co 2 ch 4 ratio of carbonic component in such fluids

mid late holocene climate variability in the indian monsoon evidence from continental shelf sediments adjacent to rushikulya river eastern india we present elemental and grain size distributions obtained from the sediment core of the continental shelf adjacent to the rushikulya river mouth eastern india to quantify the paleoclimatic changes the retrieved 1 60 m long well dated core spans the past ca 6800 cal bp the modern spatial distribution of grain size and geochemistry of the inner mid shelf sediments has been carried out to understand the seafloor morphology and sedimentary processes based on the modern investigations the proportion of particle size clay vs sand and variation in elemental values tio2 vs al2o3 has been used to interpret the changes in terrigenous supply the grain size and elemental distribution data from the core sediments indicates a period of enhanced surface water runoff from 6800 to 3100 cal bp followed by a drier condition 3100 cal bp to present suggesting weakening of monsoon the weakening of the monsoonal strength is coeval with other records from the indian sub continent and suggests response of indian monsoon to changing solar insolation during late holocene

chemical composition of rock forming minerals in gold related granitoid intrusions southwestern new brunswick canada implications for crystallization conditions volatile exsolution and fluorine chlorine activity chemical composition of rock forming miner als in appalachian siluro devonian granitoid intru sions southwestern new brunswick was systematically determined by electron microprobe the mineral chem ical data together with petrographic examination was used to test magmatic equilibration and to constrain crystallization conditions volatile exsolution and fluo rine chlorine activity of fluids associated with these intrusions mineralogical distinction between late silu rian to early devonian granodioritic to monzogranitic series gms and late devonian granitic series gs rocks is evident although both are subsolvus i type to evolved i type granitoids oxidized to reduced gms rocks consist of quartz plagioclase an 10 k feld spar biotite apatite titanite zircon monazite hornblende pyroxene magnetite ilmenite and sulfide gs rocks comprise quartz k feldspar pla gioclase an 10 mica group minerals zircon mon azite apatite sulfide ilmente magnetite topaz columbite and xenotime inter intrusion and intra intrusion variations in mineral chemistry are in terpreted to reflect petrogenetic processes e g assim ilation and fractional crystallization during granitoid evolution although magmatic equilibration among rock forming minerals are disturbed by subsolidus hy drothermal processes gms rocks appear to have higher magmatic temperatures variable levels of emplacement a range of fo2 i e reduced intrusions 10 16 7 10 13 4 and oxidized intrusions 10 14 0 10 10 5 bars and rela tively low fhf fhcl ratios 10 3 0 10 1 0 in exsolved fluids compared to gs rocks reduced gms intrusions bear higher gold potential and thus may be prospective targets for intrusion related gold systems

hydrothermal gold mineralization at the hira buddini gold mine india constraints on fluid evolution and fluid sources from boron isotopic compositions of tourmaline we determined the boron isotope and chemical compositions of tourmaline from the hira buddini gold deposit within the archean hutti maski greenstone belt in southern india to investigate the evolution of the hydrothermal system and to constrain its fluid sources tourmaline is a minor but widespread constituent in the inner and distal alteration zones of metabasaltic and metadacite host rocks associated with the hydrothermal gold mineralization the hira buddini tourmaline belongs to the dravite schorl series with variations in al fe fe mg ca ti and cr contents that can be related to their host lithology the total range of 11b values determined is extreme from 13 3 to 9 0 but 95 of the values are between 4 and 9 the boron isotope compositions of metabasalt hosted tourmaline show a bimodal distribution with peak 11b values at about 2 and 6 the wide range and bimodal distribution of boron isotope ratios in tourmaline require an origin from at least two isotopically distinct fluid sources which entered the hydrothermal system separately and were subsequently mixed the estimated 11b values of the hydrothermal fluids based on the peak tourmaline compositions and a mineralization temperature of 550 c are around 1 and 10 the isotopically lighter of the two fluids is consistent with boron released by metamorphic devolatilization reactions from the greenstone lithologies whereas the 11b rich fluid is attributed to degassing of i type granitic magmas that intruded the greenstone sequence providing heat and fluids to the hydrothermal system

jurassic rifting at the eurasian tethys margin geochemical and geochronological constraints from granitoids of north makran southeastern iran this study focuses on an east west trending belt of granitic to intermediate intrusions and their volcanic cover in the northern dur kan complex a continental slice outcropping to the north of the exposed makran accretionary wedge in southeastern iran field observations petrographic descriptions trace element and isotope analyses combined with u pb zircon geochronology are presented to determine the time frame of magmatism and tectonic setting during the formation of these rocks results document three magmatic episodes with different melt sources for 1 granites 2 a diorite trondhjemite plagiogranite sequence and 3 diabases and lavas granites dated at 170 175 ma represent crystallized melt with a strong continental isotopic contribution the diorite trondhjemite plagiogranite sequence is 165 153 ma old and derives from a mantle magma source with minor continental contribution east west trending diabase dikes and bodies intruded the granitoids which were eroded and then covered by valanginian 140 133 ma alkaline lavas and sediments alkaline dikes and lavas have a mantle isotopic composition temporal correlation with plutonites of the sanandaj sirjan zone to the northwest defines a narrow nw se striking and nearly 2000 km long belt of jurassic intrusions the increasing mantle influence in the magma sources is explained by thinning of continental lithosphere and related mantle upwelling decompression melting accordingly the formation of the studied igneous rocks is related to the extension of the iranian continental margin which ultimately led to the formation of the tethys related north makran ophiolites

flooding of sinking creek garretts spring karst drainage basin jessamine and woodford counties kentucky usa tashamingo subdivision in sinking creek karst valley a tributary of the garretts spring drainage basin in jessamine and woodford counties kentucky was flooded in february 1989 to determine the cause of flooding the groundwater basin boundary was mapped discharge data were measured to determine intake capacity of swallets and hydrologic modeling of the basin was conducted swallet capacity was determined to be limited by the hydraulic parameters of the conduit rather than by obstruction by trash flooding from a precipitation event is more likely and will be higher when antecedent soil moisture conditions in the watershed are near saturation hydrologic modeling shows that suburban development of 20 percent of the southeast basin will cause a small increase in flood stage at tashamingo subdivision

age of granitic activity associated with copper molybdenum mineralization at malanjkhand central india the malanjkhand copper molybdenum deposit in the bhandara craton central india is hosted by a granite complex which consists of regionally dominant grey granitoid and pink granitoid confined to the mineralized zone new shrimp rg data on zircons from both granite types are inferred to have crystallized during the same magmatic pulse at ca 2 48 ga the discrepancy between zircon age and earlier obtained rb sr whole rock age is attributed to modification of the rb sr system by hydrothermal overprint similarity in petrographic features and chemical affinity in combination with identical age strongly indicate that the pink granite is the hydrothermally altered variety microclinization and silicification of the grey granite the spatially associated main cu mo mineralization event at malankhand appears to be broadly contemporaneous with and genetically related to the emplacement of the host granitoids at about 2 48 ga

evidence of magmatic co 2 rich fluids in peraluminous graphite bearing leucogranites from deep freeze range northern victoria land antarctica fine grained peraluminous synkinematic leuco monzogranites skg of cambro ordovician age occur as veins and sills up to 20 30 m thick in the deep freeze range within the medium to high grade metamorphics of the wilson terrane secondary fibrolite graphite intergrowths occur in feldspars and subordinately in quartz four main solid and fluid inclusion populations are observed primary mixed co2 h2o inclusions al2sio5 brines in garnet type 1 early co2 rich inclusions brines in quartz type 2 early co2 ch4 up to 4 mol h2o inclusions graphite fibrolite in quartz type 3 late ch4 co2 n2 inclusions and h2o inclusions in quartz type 4 densities of type 1 inclusions are consistent with the crystallization conditions of skg 750 c and 3 kbar the other types are post magmatic densities of type 2 and 3 inclusions suggest isobaric cooling at high temperature 700 550 c type 4 inclusions were trapped below 500 c the skg crystallized from a magma that was at some stage vapour saturated fluids were co2 rich possibly with immiscible brines co2 rich fluids brines characterize the transition from magmatic to post magmatic stages progressive isobaric cooling t 670 c led to a continuous decrease off o 2 can entering in the graphite stability field at the same time the feldspars reacted with co2 rich fluids to give secondary fibrolite graphite decrease oft andf o 2 can explain the progressive variation in the fluid composition from co2 rich to ch4 and water dominated in a closed system in situ evolution the presence of n2 the late stages indicates interaction with external metamorphic fluids

partitioning of fluorine and chlorine between biotite and granitic melt experimental calibration at 200 mpa h 2 o experiments from 640 to 680 c 200 mpa h2o at fo2 nno employing a natural f rich vitrophyric rhyolite from spor mountain utah assessed the effect of variable mg 100mg mg mn fe on the partitioning of fluorine and chlorine between biotite bt and melt over this temperature interval bt fluorite quartz is the sole liquidus phase partition coefficients for fluorine between biotite and glass dfbt melt show a strong dependence on the mg of bt dfbt melt varies from 1 5 to 7 2 over the range of mg from 21 to 76 a strong linear correlation between dfbt melt and mg has a slope of 9 4 and extrapolates through the origin i e dfbt melt 0 at mg 0 an annite siderophyllite solid solution in these experiments dclbt melt values 1 to 6 in the same experiments vary inversely with mg the al content of biotite does not vary with the aluminum saturation index asi molar al2o3 alkali and alkaline earth oxides of melt but two exchange mechanisms involving al appear to operate in these micas 1 alvi aliv siiv mgiv and mgiv 2aliv 2siiv iv the effects of other components such as li or other intensive parameters including fo2 have yet to be evaluated systematically at comparable mg of bt however the spor mountain rhyolite yields higher dfbt melt values than an li rich strongly peraluminous melt previously investigated the results indicate that the mg of bt exerts the principal control on halogen partitioning with asi and t as second order variables the experimental partition coefficients compare well with other experimental results but not with most volcanic rocks magmatic bt from most rhyolites records higher dfbt melt due to reequilibration with degassed h2o depleted magma and perhaps with f2o 1 exchange that may accompany oxidation fe3 o fe2 oh 1 this behavior is evident in magmatic biotite from a zoned peraluminous rhyolite complex near morococala bolivia bt is sharply zoned with f rich rims but bt core melt inclusion pairs fall on our experimental curve for dfbt melt these experimental data can be used in part to assess the preservation of magmatic volatile contents in plutonic or volcanic silicic rocks for plutonic rocks the actual f content of melt not a relative activity ratio involving hf species can be reasonably estimated if the mica has not undergone subsolidus reequilibration this information is potentially useful for some shallow level ca poor magmas that are thought to be rich in f e g a and s type granites but do not conserve f well as rocks

beginning of melting and composition of first melts in the system qz ab or h 2 o co 2 solidus temperatures have been determined for minimum melt compositions in the system qz sio2 ab naalsi3o8 or kalsi3o8 at p fluid 2 5 and 10 kbar and at various water activities the dry solidus was investigated in a dry argon environment water activities ah2o between 0 0 and 1 0 were obtained by using h2o co2 mixtures the or ab or ratio of first melts increases considerably with decreasing water activity at 10 kbar it is 0 28 in the water saturated system and 0 56 at water activity 0 1 the qz content does not change with changing water activities the ab content of minimum melts formed at high pressures and low ah2o may remain almost constant in ascending magmas that are cooling and crystallizing qz content increases at the expense of the or component solidus temperatures decrease considerably when ah2o increases slightly from zero at 10 kbar the temperature difference between dry melting and the solidus for ah2o 0 1 is 120 c the influence of pure co2 on the solidus is very limited in the investigated p t range the solidus is approximatively 760 c at ah2o 0 5 between 2 and 10 kbar and approximatively 830 c at ah2o 0 3 this means that melting of quartz feldspar assemblages may induce dehydration reactions at p t conditions of the granulite facies

drainage and flooding in karst terranes flooding in karst terranes is a commonly occurring geo hazard it causes damage to property businesses and roadways it can lead to the formation of cover collapse sinkholes and groundwater contamination generally three types of flooding or their combinations are related to karst recharge related sinkhole flooding flow related flooding and discharge related flooding understanding of the type of flooding is essential for solving the flooding problem areas prone to karst flooding should be recognized and restrictions and laws on land use should be implemented runoff and erosion control plans should address the unique characteristics of karst features digging out clogged sinkholes creating retention basins or installing class v injection wells are possible solutions to improve drainage of storm water solutions to flooding problems in karst areas should also be coordinated with the water quality control to prevent groundwater contamination

geochemistry and petrogenesis of granitoids around the kolar schist belt south india constraints for the evolution of the crust in the kolar area the peninsular gneiss surrounding the n s trending kolar schist belt in the dharwar craton includes several components of granitic rocks that range in composition from tonalite to granite on the west the different phases are referred to as the dod the dosa and the banded gneiss and the patna granite the gneisses on the east are dominantly of one type and are referred to as the kambha gneiss the champion gneiss occurring within the eastern part of the belt is compositionally similar to the plutonic dod gneiss and probably represents a near surface intrusion late aplites are present on both sides of the belt the banded gneiss was formed by partial melting of tonalitic rocks and the aplites were formed by the action of aqueous fluids during amphibolite grade metamorphism excepting these two rocks all other granitoids seem to have been formed from silica oversaturated parent magmas derived from lile enriched mantle sources by fractionation processes including liquid immiscibility and fractional cry

water resource management in karstic catchments the case of the asso torrent basin southern italy in karstic endorheic basins the hydraulic works for runoff regulation marshland reclaiming and defense from inundations usually consist of channels tributary to sinkholes vertically connected to aquifers through karstic conduits and fractures the drainage capacity of such basins reduces as conduits and fractures are progressively clogged by sediments thus floodings may occur during heavy rains the sinks may also be utilized to inject treated wastewater underground this note concerns the management issues of the asso torrent basin italy where the recharge through water sinks preserves the deep aquifer from saltwater intrusion the basin represents a controversial case for which the sequence of infrastructures produced a critical system and nowadays it is difficult to find a compromise among mitigation of flood hazard safeguard of groundwater resources and preservation of human health the hydrogeological framework and the hydraulic works executed in the basin are described followed by considerations on the environmental effects of the decision making process finally statements concerning alternative measures for the management of the water resources are given management actions conforming to the integrated water resources management recommendations fail in the studied case because there is an intrinsic difficulty to transform the related concepts to practical and robust solutions

partitioning of f between h2o and co2 fluids and topaz rhyolite melt implications for mineralizing magmatic hydrothermal fluids in f rich granitic systems fluid melt distribution coefficients for f have been determined in experiments conducted with peraluminous topaz rhyolite melts and fluids consisting of h2o and h2o co2 at pressures of 0 5 to 5 kbar temperatures of 775 1000 c and concentrations of f in the melt ranging from 0 5 to 6 9 wt the major element f and cl concentrations of the starting material and run product glasses were determined by electron microprobe and the concentration of f in the fluid was calculated by mass balance the h2o concentrations of some run product glasses were determined by ion microprobe sims the solubility of melt in the fluid phase increases with increasing f in the system the solubility of h2o in the melt is independent of the f concentration of the system with up to 6 3 wt f in the melt no evidence of immiscible silica and fluoriderich liquids was detected in the hydrous but water undersaturated starting material glasses 8 5 wt f in melt or in the water saturated run product glasses f concentrates in topaz rhyolite melts relative to coexisting fluids at most conditions studied however df wt f in fluid wt f in melt increases strongly with increasing f in the system maximum values of df in this study are significantly larger than those previously reported in the literature linear extrapolation of the data suggests that df is greater than one for water saturated peraluminous granitic melts containing 8 wt f at 800 c and 2 kbar df increases as temperature and as h2o h2o co2 of the fluid increase for topaz rhyolite melts containing 1 wt f and with h2o rich fluids df is independent of changes in pressure from 2 to 5 kbar at 800 c for melts containing 1 wt f and in equilibrium with co2 bearing fluids the concentrations of f in fluid increases with increasing pressure f and lithophile element enriched granites may evolve to compositions containing extreme concentrations of f during the final stages of crystallization if f in the melt exceeds 8 wt df is greater than one and the associated magmatic hydrothermal fluid contains 4 molal f such f enriched fluids may be important in the mass transport of ore constituents i e f mo w sn li be rb cs u th nb ta and b from the magma

interpretation of post entrapment fluid inclusion re equilibration at the three mile hill marvel loch and griffins find high temperature lode gold deposits yilgarn craton western australia abstract fluid inclusions that are interpreted to be related to vein filling of quartz veins at the three mile hill and marvel loch gold deposits in amphibolite facies rocks and the griffins find deposits in granulite facies rocks in the yilgarn craton of western australia are dominantly low salinity h 2 o co 2 ch 4 mixtures or co 2 ch 4 fluids at each deposit inclusions have a wide range of compositions with respect to both the aqueous carbonic ratio and the co 2 ch 4 ratio of the carbonic phase and most fluids could not have been in equilibrium with the mineral assemblage in the vein and adjacent rock inclusion densities suggest a range of p t conditions of entrapment and are in general not consistent with the conditions of vein formation indicated by vein assemblages diffusional addition of h 2 into inclusions diffusional loss of h 2 o and reduction of inclusion volume are possible during cooling and uplift along the inferred p t path the inclusion populations could have been derived from an originally uniform population of low salinity aqueous dominated h 2 o co 2 inclusions by a combination of these processes inclusion modification as the cause of the complex inclusion populations is supported by relations of molar volume to composition and to an extent by variations in fluid salinity if inclusion re equilibration is the cause of inclusion variability it was of variable intensity within a single vein system and within individual clusters of inclusions in some samples and is suggested to have been a function of the local petrological and textural environment

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

mineral thermobarometry and fluid inclusion studies on the closepet granite eastern dharwar craton south india implications to emplacement and evolution of late stage fluid the closepet granite cpg a spectacularly exposed magmatic body along with other intrusive bodies to the east of it typifies the late archean granitic activity in the eastern dharwar craton edc south india in the present study the p t fo2 conditions of emplacement and physico chemical environment of the associated magmatic hydrothermal regime of cpg have been retrieved on the basis of mineral chemical and fluid inclusion studies amphibole plagioclase ti in amphibole and ti in biotite geothermometers along with al in amphibole geobarometer have been used to reconstruct the emplacement temperature and pressure conditions in the majority of the pluton estimated temperatures of emplacement of cpg vary from to 740 to 540 c a variation of pressure from 4 8 to 4 1 kilo bars corresponding to this temperature range was obtained while there is a faint south to north negative gradient in temperature the variation of pressure does not seem to follow this trend and indicates more or less same crustal level of emplacement for the body between ramanagaram kalyandurga segment extending for about 230 km mineral chemistry of biotite indicates crystallization of cpg under high oxygen fugacity conditions mostly above qfm buffer with no clear spatial variation in the fugacity of halogen species in the late stage magmatic fluid it may be surmised that barring the southernmost part of cpg there is no perceptible variation in the physicochemical environment of emplacement fluid inclusion studies in the granitic matrix quartz and pegmatite vein quartz show dominance of h2o and h2o co2 fluids respectively in them the difference in the fluid characteristics is interpreted in terms of the initial loss of co2 rich fluid from granitic magma and aqueous rich nature during the later stages of crystallization of quartz the exsolved co2 rich fluid was responsible in formation of the later quartz and pegmatitic veins at different crustal levels and also possibly was responsible in co2 induced metamorphism charnockitization preserved in the kabbaldurga area in the southernmost part the fluid characteristics in the vast tract of cpg revealed from mineral chemical and fluid inclusion studies make a case for its involvement in gold mineralization in the schist belts in edc

the malanjkhand copper molybdenum deposit india mineralization from a low temperature ore fluid of granitoid affiliation copper and subordinate molybdenum mineralization at malanjkhand occurs within a fracture controlled quartz reef enclosed in a pink granitoid body surrounded by grey granitoids constituting the regional matrix sulfide bearing stringers pegmatites with only quartz microcline and sulfide disseminations all within the pink granitoid represent other minor modes of occurrences despite this diversity in mode of occurrence the mineralogy of ores is quite consistent and conform to a common paragenetic sequence comprising an early ferrous stage of precipitation of magnetite i and pyrite i and the main stage chalcopyrite mineralization with minor sphalerite pyrite ii magnetite ii molybdenite and hematite both stages witnessed continuous precipitation of quartz microcline chlorite biotite and epidote the enclosing pink granitoid and the regional grey granitoids display alteration features such as saussuritization of plagioclase breakdown of hornblende and chloritization of biotite on a regional scale indicating interaction with a pervasive fluid quartz and microcline precipitation mostly restricted within the pink granitoid postdates this alteration four types of primary inclusions were encountered in quartz from ore samples 1 type i aqueous biphase l v inclusions the commonest variety in all ore types 2 type ii aqueous carbonic laq lcarb vcarb 3 type iii pure carbonic lcarb vcarb type ii and iii being restricted to stringer and pegmatitic ores and 4 rare polyphase laq vaq calcite gypsum inclusions quartz in granitoids contain primary type i inclusions only type i inclusions from ore samples furnish a temperature range after a rough pressure correction to the th maxima of 140 180 c of 150 275 c and a moderately low salinity of 4 12 wt nacl equivalent this is inferred to represent the signature of the major component f2 of the ore fluid a few type i inclusions of higher tm up to 380 c and low salinity and density represent the other f1 identifiable component of the ore fluid present in low proportion the th maxima and the total range in salinity of type i inclusions in quartz from granitoids are strikingly similar to those from the ore samples composition of syn ore chlorites furnished a temperature range of 185 327 c which conforms to the fluid inclusion microthermometric data pressure estimates using standard fluid inclusion geobarometric methods vary from 550 to 1790 bar in the stringer ores observed temperature salinity density relationships are best explained by a two stage evolution model of the ore fluid the first stage witnessed mixing of the two components f1 and f2 in unequal proportion bringing about mineralization the second stage of evolution was marked by the separation of a carbonic component on continued sulfide precipitation and attendant increase in salinity of the fluid the f1 component emerged as a distinct heated and co2 s charged entity due to steam heating and contamination of the early ingressed f2 fluid at the fracture zone the pervasive fluid phase in the surrounding granitoids contributed the f2 component

comparative petrogenesis and tectonics of paleoproterozoic malanjkhand and dongargarh granitoids central india abstract the malanjkhand granitoid mg and two units of dongargarh granitoids dgs represent contemporaneous episodes of paleoproterozoic felsic magmatism in the bastar craton central india a comparative geochemical study is carried out between the mineralized malanjkhand granitoid mg and barren dongargarh granitoids dgs that occur adjacent to each other separated by the dongargarh group of rocks major element oxides geochemistry reveals that mg is granite granodiorite whereas dg is strictly granite in composition and both plutons show calc alkaline affinity geochemical discrimination indicates that mg is an i type whereas an a type affinity can only be suspected in case of dg and both can be labeled as peraluminous trace element data from these paleoproterozoic granitoids indicate that they evolved in a tectonic environment similar to continental rift setting hfse ratios suggest variable degree of fractionation of highly differentiated granitic magma was a very complex crystallization process results in the formation of these two granitoids by common mechanism possibly fluid separation might be involved highly fractionated ree and depleted mree patterns with eu anomaly absent in mg and negative in dg inferred that the parental magma derived by low degree partial melting of heterogeneous mafic source probably amphibolitic in nature followed by progressive differentiation zircon saturation temperature and zr content reveals that mg crystallized from wet melt whereas dg crystallized from relatively dry melt but both are classify as hot granites thermobarometric calculations indicates that mg has emplaced at upper level whereas dg at relatively deeper or middle upper level in the continental crust the origin of palaeoproterozoic granitoids in central india has attributed to the magma mixing process between crustal derived felsic and mafic magma contributed by basaltic underplating in a continental rift environment

temporal relationship between granite cooling and hydrothermal uranium mineralization at dalongshan in china a combined radiometric and oxygen isotopic study abstract a combined study using multi radiometric dating and oxygen isotopic geothermometry was carried out for mesozoic quartz syenite alkali feldspar granite and associated hydrothermal uranium mineralization at dalongshan in the middle lower yangtze valley of east central china radiometric dating of the quartz syenite yields a whole rock rb sr isochron age of 135 6 4 3 ma a zircon u pb isochron age of 132 9 2 2 ma and k ar ages of 126 2 118 3 and 94 4 ma for hornblende biotite and orthoclase respectively the alkali feldspar granite yields a whole rock rb sr isochron age of 117 3 3 3 ma a zircon u pb isochron age of 114 7 2 1 ma and k ar ages of 112 2 109 3 and 88 4 ma for hornblende biotite and orthoclase respectively oxygen isotope thermometry for both granites gives temperatures of 685 to 720 555 to 580 435 to 460 and 320 to 330 c for hornblende magnetite biotite and orthoclase respectively when paired with quartz the systematic differences among the ages by the different techniques on the different minerals are used to reconstruct the cooling history of the granite the results yield rapid cooling rates of 27 4 to 58 6 c ma from 800 to 300 c in the early stage but slow cooling rates of 6 3 to 7 2 c ma from 300 to 150 c in the late stage the regular sequence of oxygen isotope temperatures for the different quartz mineral pairs demonstrates that diffusion is a dominant factor controlling the closure of both radiometric and o isotopic systems during granite cooling pitchblende u pb isochron dating yields an uranium mineralization age of 106 4 2 9 ma which is younger than the age of the granite emplacement and thus considerably postdates the time of magma crystallization but is close to the closure time of the k ar system in the biotite this points to a close relationship between granite cooling and ore forming process it appears that hydrothermal mineralization took place in the stage of slow cooling of the granite whereas the rapid cooling of the granite was concurrent with the migration of hydrothermal fluids along fault structures therefore the activity of the ore forming hydrothermal system is temporally dictated by the cooling rates of the granite and may lag about 25 to 30 ma behind the crystallization timing of associated granite

dissecting through the metallogenic potentials of precambrian granitoids case studies from the bastar and eastern dharwar cratons india

orogenic gold common or evolving fluid and metal sources through time abstract orogenic gold deposits of all ages from paleoarchean to tertiary show consistency in chemical composition they are the products of aqueous carbonic fluids with typically 5 20 mol co 2 although unmixing during extreme pressure fluctuation can lead to entrapment of much more co 2 rich fluid inclusions in some cases ore fluids are typically characterized by significant concentrations of ch 4 and or n 2 common estimates of 0 01 0 36 mol h 2 s a near neutral ph of 5 5 and salinities of 3 7 wt nacl equiv with na k ca mg this fluid composition consistency favors an ore fluid produced from a single source area and rules out mixing of fluids from multiple sources as significant in orogenic gold formation nevertheless there are broad ranges in more robust fluid inclusion trapping temperatures and pressures between deposits that support a model where this specific fluid may deposit ore over a broad window of upper to middle crustal depths much of the reported isotopic and noble gas data is inconsistent between deposits leading to the common equivocal interpretations from studies that have attempted to define fluid and metal source areas for various orogenic gold provinces fluid stable isotope values are commonly characterized by the following ranges 1 18 o for precambrian ores of 6 to 11 and for phanerozoic ores of 7 to 13 2 d and 34 s values that are extremely variable 3 13 c values that range from 11 to 2 and 4 15 n of 10 to 24 for the neoarchean 6 5 to 12 for the paleoproterozoic and 1 5 to 10 for the phanerozoic secular variations in large scale earth processes appear to best explain some of the broad ranges in the o s and n data fluid rock interaction particularly in ore trap areas may cause important local shifts in the o s and c ratios the extreme variations in d mainly reflect measurements of hydrogen isotopes by bulk extraction of waters from numerous fluid inclusion generations many which are not related to ore formation radiogenic isotopes such as those of pb sr nd sm and os measured on hydrothermal minerals are even more difficult to interpret for defining metal source particularly as the low salinity ore fluids transport limited amounts of these elements and significant amounts of these may be locally added to the minerals during alteration reactions at the sites of gold deposition noble gas and halogen data are equally equivocal fluid exsolution from granitoids emplaced into the upper and middle crust metamorphism of the crust or fluids entering trans crustal fault zones from below the crust all remain as permissive scenarios associated with orogenic gold formation as the abundant geochemical data are equivocal however geological and geochronological data weigh heavily against a magmatic hydrothermal model in the upper to middle crust there is no universal temporal association between orogenic gold and magmatism and where there is an overlap in age there is no specific type of magmatism consistently associated with gold formation nor element zonation around any specific pluton a crustal metamorphic model for fluid and metal sources is very consistent with geological geochronological and geochemical data although metamorphism on a regional scale that releases these components into major fault zones can be associated with many processes along active continental margins these can include crustal thickening and radiogenic heating slab rollback and heating during crustal extension or subduction of a spreading ridge heating the base of an accretionary prism in rare examples where phanerozoic orogenic gold deposits are hosted in precambrian high grade metamorphic terranes fluids and metals must however enter a transcrustal fault system from a sub crustal source this could either be a devolatilized subducted relatively flat perhaps stalled slab and its overlying sediment or the corner of the fertilized mantle wedge that releases a fluid during a thermal event

geochronological constraints on meso and neoarchean regional metamorphism and magmatism in the dharwar craton southern india this contribution addresses the time framework of the regional metamorphism in the three crustal provinces making the archean dharwar craton we present results of texturally controlled in situ epma chemical dating of monazites chemical dating of monazite separates as well as sm nd garnet whole rock isochrons and shrimp u pb zircon ages for pelites amphibolites and granitoids over target areas typical of the various crustal levels of the provinces the western dharwar craton has undergone a major thermal pulse at 2 52 ga followed by slow cooling to ca 2 4 ga and recorded earlier thermal events around 3 0 ga and 3 1 ga the central dharwar craton records a major high grade thermal imprint at ca 2 55 2 51 ga followed by cooling up to 2 45 ga and earlier thermal events at ca 2 62 and 3 20 ga in the eastern dharwar craton the widespread thermal pulse between 2 55 and 2 52 ga is best recorded from 2 52 ga on the entire craton ultimately and contemporaneously undergoes the main event of regional ht lp metamorphism the contrasted thermal records of the three provinces reflect their accretion age s and their degree of involvement in a wide latest archean hot orogen which sets the capacity of these lithospheric segments to be impact by deformation and mantle fluxes the tectonic setting of latest archean hot orogeny is compatible with active plate margin processes having interacted with mantle instabilities i e plumes the tectonic setting of pre 2 5 ga thermal pulses is difficult to assess but considering their systematic links with documented magmatic pulses they may have been generated in contexts comparable that of latest archean hot orogeny where lateral constrictional flow of hot orogenic crust achieves gravity driven flow 3d mass redistribution of viscous lower crust submitted to convergence

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

u pb ages for zircon and titanite from the ramagiri area southern india evidence for accretionary origin of the eastern dharwar craton during the late archean abstract the north south trending ramagiri schist belt is trident shaped with three prongs separating three granitic terranes whereas the western and eastern prongs contain metatholeiites and banded ferruginous quartzite the central prong includes felsic metavolcanics and volcanogenic metasediments the u pb zircon age for the pyroclastics in the central prong of the ramagiri schist belt is documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape 2707 pm 18 end document ma considered as the time of emplacement of the felsic volcan

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