mineral evolution and element mobility during episyenitization dequartzification and albitization in the postkinematic bohus granite southwest sweden abstract the petrography and geochemistry of two subsurface occurrences of pervasively albitized and episyenitized i e dequartzified granite in the central part of the postkinematic sveconorwegian bohus granite in southwestern sweden were studied the altered granite is whitened and consists of an albite microcline framework with a very fine grained interstitial assemblage of illite hematite ankerite anatase textural relations indicate that the initial dissolution of magmatic quartz accompanied by albitization of plagioclase left a vuggy reservoir rock which facilitated fluid penetration and thereby further alteration the subsequent stage is characterized by infilling of vugs by the very fine grained authigenic assemblage and by concomitant alteration of igneous minerals such as magnetite ilmenite and biotite deuteric alteration products of magmatic minerals are affected by these two alteration stages implying that episyenitization occurred widely after emplacement and cooling of the host granite mass balance calculations with reference to adjacent unaffected granite evince mainly si loss and na gain reflecting the observed mineralogical changes the volume decrease is estimated to be 9 owing to compaction accompanying the dequartzification and a slight porosity increase the calculations revealed a slight enrichment in hrees y essentially hosted by xenotime and a thorite xenotime solid solution both exsolved during recrystallization of monazite oxidation of ferrous iron and partial loss of chalcophile elements reflect oxidizing conditions the alteration episode is permo carboniferous and is possibly associated with circulation of oxidizing fluids through the bohus granite

apatite feldspar u pb thermochronometer a reliable mid range 450 c diffusion controlled system the u pb systematics of apatite are commonly dominated by simple volume diffusion without secondary growth and recrystallization that can affect u pb systematics of sphene monazite and zircon although apatite is a relatively low u mineral both u and pb are lattice bound and thus the u pb systematics are not controlled by micro inclusions as appears to be the case for other low u minerals such as garnet and staurolite closure temperature estimates from both experimental and empirical studies range from 425 c to as high as 500 c for typical diffusion radii 25 m and cooling rates 2 100 c ma respectively this range can be exploited to constrain cooling and exhumation histories of both igneous and metamorphic rocks in addition the closure temperature for pb diffusion in apatite fills a gap between that for pb diffusion in sphene 650 c and diffusion of ar in hornblende 500 c muscovite 350 c and biotite 300 325 c apatite is a common accessory phase in many rock types and u pb apatite dating can be a reliable and powerful thermochronometer as it combines mid range cooling ages with the strength of the u pb system in testing for isotopic closure precisions of u pb apatite dates can range from 1 2 to as low as 0 3 for proterozoic or archean dates the main limitation to accuracy of u pb apatite dates is a moderate to low ratio of u to pb and corresponding dependence of concordia coordinates on the choice of initial pb isotopic composition for proterozoic aged samples with measured 206pb 204pb of 100 the range of geologically reasonable initial pb isotopic compositions can shift the calculated u pb age by 60 ma fortunately even though the diffusion rate of pb in alkali feldspar is less than in apatite it appears that the isotopic composition of pb in coexisting feldspar is a good approximation of the initial isotopic composition in apatite for many geologic settings examples are given from an archean terrane in se wyoming that was unroofed and cooled during proterozoic uplift and from proterozoic terranes in sw us that have contrasting thermal histories

slab weakening by the exothermic olivine spinel phase change numerical modelling of mantle convection with lateral variations of viscosity and both the 670 km depth endothermic and the 400 km exothermic phase changes reveals that downwellings are weakened upon crossing the exothermic phase change a high temperature low viscosity section is developed within the downgoing current owing to both the olivine to spinel phase transition and the slowing down of the flow due to the 670 km endothermic transition this mechanism may cause the creation of a weak zone at 400 km that results in a preferential location for horizontal or vertical slab tearing as revealed by seismic gaps in many slabs

geochemistry and geodynamic origin of the mesoarchean ujarassuit and ivisaartoq greenstone belts sw greenland abstract the ivisaartoq ca 3075 ma and ujarassuit ca 3070 ma greenstone belts are the largest mesoarchean supracrustal lithotectonic assemblages in the nuuk region sw greenland both greenstone belts underwent polyphase deformation and amphibolite facies metamorphism and were in due course variously dismembered pillow lavas pillow breccia magmatic layering and relic sedimentary structures are well preserved in the ivisaartoq belt volcanic rocks include basalts and minor andesites and picrites boninite like rocks occur in the ujarassuit belt metasedimentary rocks in the ujarassuit belt occur as thin layers 0 5 1 0 m of biotite schists and in the ivisaartoq belt as 500 m thick biotite schists intercalated with minor quartzitic gneisses there is no field evidence indicating that the ivisaartoq and ujarassuit supracrustal rocks were deposited on older continental basement and their volcanic rocks do not exhibit any geochemical trends indicating contamination by archean upper continental crust four groups of amphibolites metavolcanic rocks were recognized in the ujarassuit greenstone belt on the basis of their ree and hfse characteristics 1 group 1 is characterized by near flat ree patterns la smcn 0 77 1 14 la ybcn 0 84 1 24 and moderate negative nb anomalies nb nb 0 60 0 79 2 group 2 displays lree depleted patterns la smcn 0 53 1 02 la ybcn 0 32 0 61 and pronounced negative nb anomalies nb nb 0 32 0 67 3 group 3 consists of lree depleted patterns la smcn 0 69 0 84 la ybcn 0 55 0 91 and absence of significant nb anomalies nb nb 0 92 1 15 and 4 group 4 has concave upward ree patterns la smcn 1 64 2 42 gd ybcn 0 57 1 01 and large negative nb anomalies nb nb 0 28 0 42 the depletion of lree in group 2 amphibolites appears to have resulted from mobility of these elements during metamorphism group 1 3 and 4 amphibolites retain their near primary geochemical signatures and their trace element patterns are comparable to those of phanerozoic oceanic island arc tholeiites iat normal mid ocean ridge basalts n morb and boninites respectively the trace element patterns of the least altered meta ultramafic rocks la ybcn 2 48 1 35 nb nb 0 31 0 60 are comparable to those of modern subduction related picrites amphibolites with an andesitic composition show large negative nb anomalies nb nb 0 21 0 55 enriched lree patterns la ybcn 6 29 15 64 and fractionated hree gd ybcn 2 61 3 12 implying deep melting in equilibrium with residual garnet in the source biotite schists and quartzitic gneisses have low chemical indexes of alteration values cia 46 to 62 and trace element characteristics indicating volcaniclastic sedimentary protoliths derived from poorly weathered felsic to mafic source rocks collectively the geochemical features of metavolcanic and metasedimentary rocks suggest that the ivisaartoq and ujarassuit greenstone belts represent dismembered fragments of mesoarchean supra subduction zone oceanic crust formed in an arc forearc backarc tectonic setting

chemical and physical responses to deformation in micaceous quartzites from the tauern window eastern alps micaceous quartzites from a subvertical shear zone in the tauern window contain abundant quartz clasts derived from dismembered quartz tourmaline veins bulk plane strain deformation affected these rocks at amphibolite facies conditions shape changes suggest net shortening of the clasts by 11 64 with a mean value of 35 quartz within the clasts accommodated this strain largely via dislocation creep processes on the high stress flanks of the clasts however quartz was removed via solution mass transfer pressure solution processes the resulting change in bulk composition allowed growth of porphyro blastic staurolite chlorite kyanite on the clast flanks matrix sio2 contents decrease from c 83 wt away from the clasts to 49 58 in the selvages on the clast flanks the chemical changes are consistent with c 70 volume loss in the high stress zones calculated shortening values within the clast flanks are similar to the volume loss estimates and are greatly in excess of the shortening values calculated from the clasts themselves flow laws for dislocation creep versus pressure solution imply large strain rate gradients and or differential stress gradients between the matrix and the clast selvages in a rock containing a large proportion of semirigid clasts weakening within the clast flanks could dominate rock rheology in our samples however weakening within the selvages was self limiting 1 growth of strong staurolite porphyroblasts in the selvages protected remaining quartz from dissolution and 2 overall flattening of the quartz clasts probably decreased the resolved shear stress on the flanks to values near those of the matrix which would have reduced the driving force for solution transfer creep extreme chemical changes nonetheless occurred over short distances the necessity of maintaining strain compatibility may lead to significant localized dissolution in rocks containing rheologic heterogeneities and overall weakening of the rocks may result solution transfer creep may be a major process whereby weakening and strain localization occur during deep crustal metamorphism of polymineralic rocks

enrichment of trace elements in garnet amphibolites from a paleo subduction zone catalina schist southern california the abundance p t stability solubility and element partitioning behavior of minerals such as rutile garnet sphene apatite zircon zoisite and allanite are critical variables in models for mass transfer from the slab to the mantle wedge in deep regions of subduction zones the influence of these minerals on the composition of subduction related magmas has been inferred and disputed from inverse modelling of the geochemistry of island arc basalt or by experiment although direct samples of the dehydration partial melting region of a mature subduction zone have not been reported from subduction complexes garnet amphibolites from melanges of circumpacific and caribbean blueschist terranes reflect high t 600 c conditions in shallower regions such rocks record geochemical processes that affected deep seated high t portions of paleo subduction zones in the catalina schist a subduction zone metamorphic terrane of southern california metasomatized and migmatitic garnet amphibolites occur as blocks in a matrix of meta ultramafic rocks this mafic and ultramafic complex may represent either slab derived material accreted to the mantle wedge of a nascent subduction zone or a portion of a shear zone closely related to the slab mantle wedge contact or both the trace element geochemistry of the complex and the distribution of trace elements among the minerals of garnet amphibolites were studied by inaa xrf electron microprobe and sem in order of increasing alteration from a probable metabasalt protolith three common types of garnet amphibolite blocks in the catalina schist are 1 non migmatitic clinopyroxene bearing blocks which are compositionally similar to morb that has lost an albite component 2 garnet amphibolite blocks which have rinds that reflect local interaction between metabasite metaperidotite and fluid and 3 migmatites that are extremely enriched in th hfse lree and other trace elements these trace element enrichments are mineralogically controlled by rutile garnet sphene apatite zircon zoisite and allanite alkali and alkaline earth elements are much less enriched in the solid assemblage and thus appear to be decoupled from the other elements in the inferred metasomatic process es the compositions of migmatitic garnet amphibolite blocks seem to complement that of average island arc tholeiite trace element metasomatism reflects fluid solid rather than melt solid interaction the metasomatic effects indicate that h2o rich fluid perhaps with a significant component of na al silicate and alkalis carried th u sr ree and hfse fractionations of lree in migmatites resemble those of migmatitic metasedimentary rocks underlying the mafic and ultramafic complex exotic lree deposited in allanite in migmatites could have been derived from fluids in equilibrium with subducted sediment if the paleo subduction zone represented by the mafic and ultramafic complex of the catalina schist had continued its thermal and fluid evolution a selvage of similarly enriched rocks might have been generated along the slab mantle wedge contact between 30 and 85 km depth rocks affected by subduction zone metasomatism although rarely recognized at the surface could be volumetrically significant products of the initiation of subduction and may prove to be geochemical probes of convergent margins that approach the significance of xenoliths in the study of other magmatic environments

petrology of amphibolite facies mafic and ultramafic rocks from the catalina schist southern california metasomatism and migmatization in a subduction zone metamorphic setting the catalina schist of southern california is a subduction zone metamorphic terrane it consists of three tectonic units of amphibolite high p greenschist and blueschist facies rocks that are structurally juxtaposed across faults forming an apparent inverted metamorphic gradient migmatitic and non migmatitic metabasite blocks surrounded by a meta ultramafic matrix comprise the upper part of the catalina amphibolite unit fluid rock interaction at high p high t conditions caused partial melting of migmatitic blocks metasomatic exchange between metabasite blocks and ultramafic rocks infiltration of silica into ultramafic rocks and loss of an albitic component from nonmigmatitic clinopyroxene bearing metabasite blocks partial melting took place at an estimated p 8 11 kbar and t 640 750 c at high h2o activity the melting reaction probably involved plagioclase quartz trondhjemitic melts were produced and are preserved as leucocratic regions in migmatitic blocks and as pegmatitic dikes that cut ultramafic rocks the metasomatic and melting processes reflected in these rocks could be analogous to those proposed for fluid and melt transfer of components from a subducting slab to the mantle wedge aqueous fluids rather than melts seem to have accomplished the bulk of mass transfer within the mafic and ultramafic complex

active or passive continental margin geochemical and nd isotope constraints of metasediments in the backstop of a pre andean accretionary wedge in southernmost chile 46 30 48 30 s provenance analysis of siliciclastic sedimentary rocks gives indications of the tectonic evolution and setting of source regions and the rocks contained in them the composition of sedimentary rocks ideally reflects the nature of these regions and only indirectly the tectonic setting of the basin where the erosional debris is deposited this makes it possible to interpret late devonian to early carboniferous metasedimentary basement rocks of the andes in southernmost chile as having been deposited at a passive margin despite geochemical indications of an active margin setting for the source rocks and the position of the metasediments in the backstop of an accretionary wedge major and trace elements point to felsic source rocks from an active margin environment the nd model ages of 1170 1490 ma indicate that the source rocks were part of an old continental crust in the late palaeozoic the end t values range between 7 and 2 these characteristics in combination with the regional geology suggest that the geochemical signal is dominated by rocks formed at an active margin which later acted as feeders for the sediments deposited in a passive margin environment if corroborated by research in progress this emphasizes the problem of deducing the tectonic setting of a depositional basin from provenance data

magnetite compositions from the baba ali iron deposit in the sanandaj sirjan zone western iran implications for ore genesis abstract the economically significant baba ali iron ore deposit is located in the sanandaj sirjan zone western iran is associated with diorite the mineralization trends in a ene wsw direction with thickness that varies from 30 m up to 50 m and a length of about 250 m the main mineral assemblages are massive magnetite epidote actinolite tourmaline quartz calcite and pyrite using different magnetite compositional discrimination diagrams the low concentrations of ti 0 11 wt al 0 06 wt cr 19 62 ppm and co 20 26 and high ni cr ratios 6 34 are consistent with a hydrothermal origin similar to typical skarn mineralization the different elemental compositions of various magnetite generations might be due to an ore forming fluid that initially a high t magmatic hydrothermal character then evolved to a lower temperture meteoric water dominated system it seems that fe bearing saline fluids infiltrated the carbonate host rocks causing high temperature acid metalliferous fluids to become neutralized during reaction with carbonates causing a decrease in iron solubility and saturating as a magnetite with increasing ph and decreasing the temperature the close spatial and temporal association of the mineralization with the fracture systems suggests that a pressure decrease also had a significant impact on the iron solubility triggering ore precipitation and replacement at relatively low temperatures 300 c under reducing conditions

u pb dating of serpentinization hydrothermal zircon from a metasomatic rodingite shell sudetic ophiolite sw poland abundant zircon grains were found within a metasomatic chlorite corrensite trioctahedral regularly interstratified chlorite smectite shell that surrounds rodingite from the jordanow gogolow jg serpentinite massif sudetic ophiolite bohemian massif the zircon grains bear two types of primary fluid inclusions containing either liquid co2 or aqueous solutions the inclusions were used to assign the p t conditions of the zircon formation 270 300 c ca 1 kbar using the crossed isochore method abraded single zircon grains give a u pb age of 400 4 3 ma which is interpreted as the age of zircon crystallization this zircon formed during rodingitization i e a metasomatic process directly connected with the serpentinization and thus provides the opportunity of direct dating of the early serpentinization process the zircon age from the jordanow gogolow massif is consistent with the crystallization age of metagabbro protoliths from the sudetic ophiolite as determined by oliver et al j geol soc lond 150 1993 355 a ce anomaly combined with the mineralogical record of greenschist facies metamorphism of the mafic rocks from sudetic ophiolite suggests that the sm nd whole rock isotopic data of pin et al lithos 21 1988 195 353 21 ma possibly characterize the age of later metamorphic event

synthetic heavy mineral stratigraphy applications and limitations abstract a multi disciplinary study of the dominantly fluvial lower triassic otter sandstone formation east devon uk is presented the approach integrates a variety of methods including sedimentology conventional heavy mineral analysis single grain microprobe analysis and elemental whole rock geochemistry icp aes and icp ms a species level conventional heavy mineral study is compared to a whole rock geochemical analysis for the corresponding samples to investigate whether or not heavy mineral compositions can be discriminated from elemental whole rock data the comparison provides sufficient evidence that the absolute and relative abundance of some of the heavy minerals apatite iron titanium oxides monazite and zircon can be discriminated geochemically the established element mineral relationships are used to construct both synthetic heavy mineral assemblages and synthetic heavy mineral index values from the geochemical data which show considerable similarity to those of the conventional heavy mineral analysis the presented synthetic heavy mineral logs display intraformational packages that enable subdivision of this barren continental succession furthermore the observed subdivision is correlatable over a considerable distance when extended into the offshore wessex basin the chemical approach unquestionably lacks the sensitivity of conventional heavy mineral analysis however by comparison it is rapid this novel approach demonstrates that synthetic heavy mineral stratigraphy based as here on a well constrained stratotype has considerable potential for creating high resolution correlations in both outcrops and the subsurface and may be of significant value to people working with reservoir characterisation

mineralogy fluid inclusions and isotopes of the cihai iron deposit eastern tianshan nw china implication for hydrothermal evolution and genesis of subvolcanic rocks hosted skarn type deposits abstract most skarn deposits are closely related to granitoids that intruded into carbonate rocks the cihai 100 mt at 45 fe is a deposit with mineral assemblages and hydrothermal features similar to many other typical skarn deposits of the world however the iron orebodies of cihai are mainly hosted within the diabase and not in contact with carbonate rocks in addition some magnetite grains exhibit unusual relatively high tio 2 content these features are not consistent with the typical skarn iron deposit different hydrothermal and or magmatic processes are being actively investigated for its origin because of a lack of systematic studies of geology mineral compositions fluid inclusions and isotopes the genetic type ore genesis and hydrothermal evolution of this deposit are still poorly understood and remain controversial the skarn mineral assemblages are the alteration products of diabase three main paragenetic stages of skarn formation and ore deposition have been recognized based on petrographic observations which show a prograde skarn stage garnet clinopyroxene disseminated magnetite a retrograde skarn stage main iron ore stage massive magnetite amphibole epidote ilvaite and a quartz sulfide stage quartz calcite pyrite pyrrhotite cobaltite overall the compositions of garnet clinpyroxene and amphibole are consistent with those of typical skarn fe deposits worldwide in the disseminated ores some magnetite grains exhibit relatively high tio 2 content 1 wt which may be inherited from the diabase protoliths some distinct chemical zoning in magnetite grains were observed in this study wherein cores are enriched in ti and magnetite rims show a pronounced depletion in ti the textural and compositional data of magnetite confirm that the cihai fe deposit is of hydrothermal origin rather than associated with iron rich melts as previously suggested fluid inclusions study reveal that the prograde skarn garnet and pyroxene formed from high temperature 520 600 c moderate to high salinity 8 1 23 1 wt nacl equiv and 46 wt nacl equiv fluids massive iron ore and retrograde skarn assemblages amphibole epidote ilvaite formed under hydrostatic condition after the fracturing of early skarn fluids in this stage had lower temperature 220 456 c and salinity 8 4 16 3 wt nacl equiv fluid inclusions in quartz sulfide stage quartz and calcite also record similar conditions with temperature range from 128 to 367 c and salinity range from 0 2 to 22 9 wt nacl equiv oxygen and hydrogen isotopic data of garnet and quartz suggest that mixing and dilution of early magmatic fluids with external fluids e g meteoric waters caused a decrease in fluid temperature and salinity in the later stages of the skarn formation and massive iron precipitation the 18 o values of magnetite from iron ores vary between 4 1 and 8 5 which are similar to values reported in other skarn fe deposits such values are distinct from those of other iron ore deposits such as kiruna type and magmatic fe ti v deposits worldwide taken together these geologic geochemical and isotopic data confirm that cihai is a diabase hosted skarn deposit related to the granitoids at depth

field and geochemical characteristics of mesoarchean to neoarchean volcanic rocks in the storo greenstone belt sw greenland evidence for accretion of intra oceanic volcanic arcs abstract the storo greenstone belt southern west greenland consists of thrust imbricated slices of mesoarchean 3060 ma and neoarchean ca 2800 ma mafic to ultramafic volcanic rocks volcaniclastic sediments and gabbro anorthosite associations the belt underwent polyphase metamorphism at upper amphibolite facies conditions between 2650 and 2600 ma the contacts between the mesoarchean and neoarchean volcanic rocks and surrounding eoarchean to neoarchean tonalite trondhjemite granodiorite ttg gneisses are tectonic and typically bounded by high grade mylonites regardless of age the volcanic rocks are dominated by mafic amphibolites with a tholeiitic basalt composition near flat to slightly enriched light rare earth element lree patterns la smcn 0 91 1 48 relatively flat to slightly depleted heavy ree hree gd ybcn 1 0 1 28 and pronounced negative nb ta anomalies nb nb 0 34 0 73 on chondrite and primitive mantle normalized diagrams these geochemical characteristics are consistent with subduction zone geochemical signatures and partial melting of a shallow

trace elements in magnetite as petrogenetic indicators we have characterized the distribution of 25 trace elements in magnetite mg al si p ca sc ti v cr mn co ni cu zn ga ge y zr nb mo sn hf ta w and pb using laser ablation icp ms and electron microprobe from a variety of magmatic and hydrothermal ore forming environments and compared them with data from the literature we propose a new multielement diagram normalized to bulk continental crust designed to emphasize the partitioning behavior of trace elements between magnetite the melt fluid and co crystallizing phases the normalized pattern of magnetite reflects the composition of the melt fluid which in both magmatic and hydrothermal systems varies with temperature thus it is possible to distinguish magnetite formed at different degrees of crystal fractionation in both silicate and sulfide melts the crystallization of ilmenite or sulfide before magnetite is recorded as a marked depletion in ti or cu respectively the chemical signature of hydrothermal magnetite is distinct being depleted in elements that are relatively immobile during alteration and commonly enriched in elements that are highly incompatible into magnetite e g si and ca magnetite formed from low temperature fluids has the lowest overall abundance of trace elements due to their lower solubility chemical zonation of magnetite is rare but occurs in some hydrothermal deposits where laser mapping reveals oscillatory zoning which records the changing conditions and composition of the fluid during magnetite growth this new way of plotting all 25 trace elements on 1 diagram normalized to bulk continental crust and elements in order of compatibility into magnetite provides a tool to help understand the processes that control partitioning of a full suit of trace elements in magnetite and aid discrimination of magnetite formed in different environments it has applications in both petrogenetic and provenance studies such as in the exploration of ore deposits and in sedimentology

trace element rich brines in eclogitic veins implications for fluid composition and transport during subduction primary and pseudosecondary fluid inclusions occur in oscillatory and sector zoned omphacite in eclogitic veins from the monviso ophiolitic complex in the western alps the inclusions contain aqueous brines and daughter crystals of halite sylvite calcite dolomite albite anhydrite and or gypsum barite baddeleyite rutile sphene fe oxides pyrite and monazite this daughter mineral suite indicates high solubilites of na k ca mg fe zr ti p ba ce la th and s species and provides direct evidence for transport of high fieldstrenght large ion lithophile and light rare earth elements as dissolved species during subduction fluid inclusion heterogeneities preserved within and between adjacent grains in the veins however suggest that the scale of fluid equilibration was small a crack seal geometry in some of the veins implies that fluid release in pulses rather than steady flow controlled mineral deposition and growth in the veins from these observations we develop a model of fluid release and entrapment in which pulses of fluid are associated in time with increments of shear and tensile failure the rate of fluid release and the reduction in porosity both depend on the rate of plastic flow vein fluids may initially be derived from decreptitation of early fluid inclusions in the host eclogites small scale fluid heterogeneities implied by the fluid inclusions in the veins are best interpreted in terms of limited fluid flow and hence limited metasomatism we conclude that element recycling into the mantle wedge during subduction will depend at least as strongly on fluid transport mechanisms as on element solubilities in the fluid phase at monviso despite evidence for high trace element solubilities in saline brines the elements were not removed from the downgoing slab prior to teaching depths of 40 km

zircon and titanite u pb dating of the zhangjiawa iron skarn deposit luxi district north china craton implications for a craton wide iron skarn mineralization abstract the north china craton hosts numerous iron skarn deposits containing more than 2600 mt of iron ores mostly with an average grade of 45 wt fe which have been among the most important source of high grade iron ores for the last three decades in china these deposits typically form clusters and can be roughly divided into the western and eastern belts which are located in the middle of trans north china orogen and to the west of the tan lu fault zone in the eastern part of north china craton respectively the western belt mainly consists of the southern taihang district as well as the linfen and taiyuan ore fields whereas the eastern belt comprises the luxi and xu huai districts the zhangjiawa deposit in the luxi district has proven reserves of 290 mt at an average of 46 fe up to 65 the iron mineralization occurs mainly along contact zones between the kuangshan dioritic intrusion and middle ordovician marine carbonate rocks that host numerous evaporite intercalations titanite grains from the mineralized skarn are closely intergrown with magnetite and retrograde skarn minerals including chlorite phlogopite and minor epidote indicating a hydrothermal origin the titanite grains have extremely low ree contents and low th u ratios consistent with their precipitation directly from hydrothermal fluids responsible for the iron mineralization ten hydrothermal titanite grains yield a weighted mean 206 pb 238 u age of 131 0 3 9 ma mswd 0 1 1 which is in excellent agreement with a zircon u pb age 130 1 ma of the ore related diorite this age consistency confirms that the iron skarn mineralization is temporally and likely genetically related to the kuangshan intrusion results from this study when combined with existing isotopic age data suggest that iron skarn mineralization and associated magmatism throughout both the eastern and western belts took place coevally between 135 and 125 ma with a peak at ca 130 ma as such those deposits may represent the world s only major phanerozoic iron skarn concentration hosted in precambrian cratons the magmatism and associated iron skarn mineralization coincide temporally with the culmination of lithospheric thinning and destruction of the north china craton implying a causal link between the two

red staining of the wall rock and its influence on the reducing capacity around water conducting fractures abstract red staining and alteration of wall rock is common around water conducting fractures in the laxemar simpevarp area se sweden which is currently being investigated by the swedish nuclear fuel and waste management co skb in common with many other places red staining is often interpreted as a clear sign of oxidation but relevant analyses are seldom performed the area is dominated by palaeoproterozoic crystalline rocks ranging in composition from quartz monzodiorite to granite in this study wall rock samples have been compared with reference samples from within 0 1 to 1 m of the red stained rock in order to describe mineralogical and geochemical changes but also changes in redox conditions a methodology for tracing changes in mineralogy mineral and whole rock chemistry and fe3 fetot ratio in silicates and oxides in the red stained wall rock and the reference rock is reported the results show that the red stained rock adjacent to the fractures displays major changes in mineralogy biotite plagioclase and magnetite have been altered and chlorite k feldspar albite sericite prehnite epidote and hematite have been formed the changes in chemistry are however moderate k enrichment ca depletion and constant fetot are documented the fe3 fetot ratio in the oxide phase is higher in the red stained samples whereas the fe3 fetot ratio in the silicate phase is largely similar in the wall rock and the reference samples because most of the fe is hosted in the silicate phase the decrease in reducing capacity fe2 if any in the red stained wall rock is very small and not as high as macroscopic observations might suggest instead the mineralogical changes in combination with the modest oxidation and formation of minute hematite grains in porous secondary minerals in pseudomorphs after plagioclase have produced the red staining increased porosity is also characteristic for the red stained rock moderate alteration in the macroscopically fresh reference rock shows that the hydrothermal alteration reaches further from the fracture than the red staining the extent of the red staining can therefore not be used in the same way as the extent of the alteration adjacent to a fracture the increase in porosity in the red stained rock may result in enhanced retention of radio nuclides due to an increased sorptivity and diffusion close to the fracture the hydrothermal alteration causing the red staining is thought to have occurred at temperatures of about 250 400 c based on the secondary mineralogy the major part of this alteration in the area is assumed to be related to fluid circulation associated with the intrusion of the mesoproterozoic gotemar and uthammar granites nearby

insights into the formation of the dasuji porphyry mo deposit north china craton gained from mineral chemistry data abstract the dasuji mo deposit is located within the northern margin of the north china craton based on vein cross cutting relationships mineral assemblages and alteration characteristics the formation of the deposit can be divided into four stages stage 1 consisting of two vein types developed in deep is characterized by k feldspathization with minor molybdenum mineralization stage 2 containing four distinct vein types is the main stage of molybdenum mineralization accompanied by sericitization and silicification stage 3 is involved in lead zinc mineralization associating with carbonatization and fluorination and stage 4 is characterized by no mineralization this paper presents new mineral magnetite rutile molybdenite and pyrite chemistry data that provide new insights into the formation of this deposit the magnetites within veins in the deposit have chemical compositions that are indicative of a magmatic origin suggesting that these magnetites hosted in quartz were captured from syn mineralization granites in the area molybdenite w pb zn and cu concentrations increase with the decreasing temperature of formation suggesting the initiation of w pb zn and cu precipitation at the end of the second stage of mineralization the stage 3 pyrite within the deposit contains the highest concentrations of pb zn and cu consistent with the pb zn cu mineralization that formed during this stage the majority of the f ion deposition occurred at the end of stage 3 and the fluids associated with stage 4 were meteoric water dominated

mineralogy of the sulphide deposits at sulitjelma northern norway abstract the pyritic vms deposits at sulitjelma northern norway have been regionally metamorphosed at amphibolite facies during the caledonide orogen the deposits contain a wide diversity of sulphide sulphosalt and related minerals which are systematically discussed with reference to their occurrence paragenesis and mineral chemistry most of these minerals are however rare to absent within the massive deposits which are dominantly composed of pyrite with subordinate chalcopyrite sphalerite and pyrrhotite galena arsenopyrite cubanite molybdenite stannite and tetrahedrite occur in minor amounts syn metamorphic mobilisation has however resulted in the redistribution of a range of elements including cu pb sb as ni and au these elements have been reconcentrated into mobilised segregations where they have crystallised under retrograde conditions into a range of discrete phases ore mobilisation which took place along tectonically controlled pathways is however of a highly localised nature with a considerable range in mineral textures and parageneses observed in different samples typical associations within these mobilisates include a range of cu pb sb and cu pb as sulphosalts including bournonite meneghinite seligmannite and jordanite breithauptite nisbite costibite arsenopyrite and gudmundite co existing galena is characterised by elevated concentrations of ag bi and se argentian tetrahedrite 9 17 wt ag the chief ag carrier in the deposits as well as other ag bearing phases including pyrargyrite hessite and empressite are strongly enriched in the mobilisates gold as electrum 50 75 wt au and more rarely as aurostibite is also relatively enriched in the mobilisate samples over those from more massive parts of the deposits a further range of minerals including native antimony native arsenic allargentum dyscrasite argentite mckinstryite jalpaite and native silver occur as low temperature breakdown products of earlier formed minerals preserved textures do not contradict a model involving more than a one phase of mobilisation during the metamorphic evolution

mineralogy of an ancient lacustrine mudstone succession from the murray formation gale crater mars the mars science laboratory curiosity rover has been traversing strata at the base of aeolis mons informally known as mount sharp since september 2014 the murray formation makes up the lowest exposed strata of the mount sharp group and is composed primarily of finely laminated lacustrine mudstone intercalated with rare crossbedded sandstone that is prodeltaic or fluvial in origin we report on the first three drilled samples from the murray formation measured in the pahrump hills section rietveld refinements and fullpat full pattern fitting analyses of x ray diffraction patterns measured by the msl chemin instrument provide mineral abundances refined unit cell parameters for major phases giving crystal chemistry and abundances of x ray amorphous materials our results from the samples measured at the pahrump hills and previously published results on the buckskin sample measured from the marias pass section stratigraphically above pahrump hills show stratigraphic variations in the mineralogy phyllosilicates hematite jarosite and pyroxene are most abundant at the base of the pahrump hills and crystalline and amorphous silica and magnetite become prevalent higher in the succession some trace element abundances measured by apxs also show stratigraphic trends zn and ni are highly enriched with respect to average mars crust at the base of the pahrump hills by 7 7 and 3 7 times respectively and gradually decrease in abundance in stratigraphically higher regions near marias pass where they are depleted with respect to average mars crust by more than an order of magnitude in some targets the mn stratigraphic trend is analogous to zn and ni however mn abundances are close to those of average mars crust at the base of pahrump hills rather than being enriched and mn becomes increasingly depleted moving upsection minerals at the base of the pahrump hills in particular jarosite and hematite as well as enrichments in zn ni and mn are products of acid sulfate alteration on earth we hypothesize that multiple influxes of mildly to moderately acidic pore fluids resulted in diagenesis of the murray formation and the observed mineralogical and geochemical variations the preservation of some minerals that are highly susceptible to dissolution at low ph e g mafic minerals and fluorapatite suggests that acidic events were not long lived and that fluids may not have been extremely acidic ph 2ph 2 alternatively the observed mineralogical variations within the succession may be explained by deposition in lake waters with variable eh and or ph where the lowermost sediments were deposited in an oxidizing perhaps acidic lake setting and sediments deposited in the upper pahrump hills and marias pass were deposited lake waters with lower eh and higher ph

mineralogy and geochemical behavior of trace elements of hydrothermal alteration types in the volcanogenic massive sulfide deposits ne turkey abstract volcanogenic massive sulfide vms deposits of the eastern pontides turkey are hosted by the maastrichtian eocene dacite and rhyodacite series accompanied by lesser andesite and basalts as well as their pyroclastic equivalents with tholeiitic to calc alkaline affinity the ore mineral assemblages are chalcopyrite sphalerite galena chalcocite covellite bornite and tetrahedrite potassic phyllitic sericitic argillic kaolinitic and smectitic silicic propylitic and hematitic alteration is commonly associated with these deposits hfse lile trte and ree contents show strong variability in different alteration types resulting from interaction with acid or alkaline fluids sample groups showed chondrite normalized enrichment of lree relative to hree and sub parallel trends except for the hematitic and phyllitic alteration types mree are strongly depleted in the zones of most intense silicification and kaolinization most sample groups have strongly to slightly negative eu anomalies ranging from 0 35 to 0 88 mean hematitic 1 45 and propylitic altered rocks 1 11 have slightly to moderately positive anomalies the negative eu anomalies indicate the low temperatures of fluids 200 c no ce anomaly was observed except for phyllitic alteration where a slight positive anomaly was noted the chondrite normalized trace and ree patterns of the altered rocks are similar to each other suggesting that they were derived from a common felsic source the alteration groups formed from acid intermediate and alkaline hydrothermal solutions some transition base and precious metals and volatile elements were clearly enriched especially in the hematitic silicic kaolinitic and phyllitic altered samples the other elements exhibit different behaviors in different sample groups ree behavior is relatively immobile in the silicic hematitic kaolinitic and partially in moderately and propylitic altered rocks based on mass balance calculations lile and hfse appear mobile in the altered sample groups except in the propylitic altered rocks trte behave as relatively immobile in most of samples except in some of the silicic and phyllitic altered rocks and especially in the hematitic altered samples hfse most of the transition w mo cu and sb and some other trace elements pb as hg bi se and tl are enriched in the hematitic altered samples and in the some silicic altered samples the highest as bi mo se and hg concentrations in the hematite altered samples can be used to distinguish other alteration types and may be a useful indicator in a prospect scale base metal exploration

sphysicochemical conditions of fluid wall rock interaction at amphibolite facies conditions in two archean hydrothermal gold deposits in the mt york district pilbara craton western australia synamphibolite facies archean gold mineralization in the mt york district pilbara craton western australia is hosted in metamorphosed banded iron formation main hill breccia hill prospect amphibolites and ultramafic schists zakanaka prospect mineralization at main hill occurs in quartz breccias with sulfide matrices and in altered wall rock adjacent to quartz biotite amphibole clinopyroxene veins alteration associated with quartz veins is zoned with biotite pyrrhotite vein selvedges and a distal calcic amphibole arsenopyrite lollingite zone hydrothermal biotite and actinolite have highest mg mg fe ratios where associated with abundant sulfarsenides in the distal alteratin zone whole rock geochemical analyses and calculated metasomatic reactions indicate the addition of k al s as au ag and ni during hydrothermal alteration mineralization at zakanaka is characterized by a broad wall rock alteration halo of biotite amphibole and zoned quartz calc silicate veins proximal to ore

partial least squares discriminant analysis of trace element compositions of magnetite from various vms deposit subtypes application to mineral exploration abstract the petrography and mineral chemistry of magnetite from fifteen volcanogenic massive sulfide vms deposits in canada and the lasail vms deposit in oman as well as from two vms associated banded iron formations bif austin brook new brunswick canada and izok lake nunavut canada were investigated using optical microscopy electron probe micro analyzer epma and laser ablation inductively coupled plasma mass spectrometry la icp ms the method of robust estimation for compositional data robcompositions was applied to investigate geochemical censored data among thirty seven elements analyzed by epma and or la icp ms in magnetite from the studied deposits bedrock lithologies only the results for si ca zr al mg ti zn co and ni contain pls da shows that variable compositions of magnetite slightly discriminate different studied deposits bedrock lithologies the geochemical observations suggest that the variation in magnetite chemistry from different vms settings might be sourced from differences in 1 the composition and temperature of parental magmas or hydrothermal fluids 2 the composition of host bedrocks 3 the composition of co forming minerals and 4 oxygen fugacity pls da distinguishes magnetite compositions from the studied vms deposits and bifs from that of the other ore deposit types including ni cu porphyry cu mo au iron oxide copper gold iron oxide apatite and the bayan obo ree fe nb deposit magnetite from the vms settings on average contains lower concentrations of si zr al mg ti zn co and ni relative to that from the other mineral deposit types pls da of magnetite data from vms deposits and bifs of the bathurst mining camp as well as pls da of magnetite compositions from various mineral deposit types yield discrimination models for application to mineral exploration for vms deposits using indicator minerals in quaternary lithified sedimentary rocks

the role of decarbonization and structure in the callie gold deposit tanami region of northern australia the callie deposit is the largest 6 0 moz au of several gold deposits in the dead bullock soak goldfield of the northern territory s tanami region 550 km northwest of alice springs the callie ore lies within corridors up to 180 m wide of sheeted en echelon quartz veins where they intersect the 500 m wide hinge of an ese plunging f1 anticlinorium the host rocks are the blake beds of the paleoproterozoic dead bullock formation which consist of a 350 m thick sequence of lower greenschist facies graphitic turbidites and mudstones overlying in excess of 100 m of thickly bedded siltstones and fine sandstones the rocks are fe rich and dominated by assemblages of chlorite and biotite both of which are of hydrothermal and metamorphic origin a fundamental characteristic of the hydrothermal alteration is the removal of graphite a process which is associated with bleaching and the development of bedding parallel bands of coarse biotite augen gold is found only in quartz veins and only where they cut decarbonized chloritic rock with abundant biotite augen and no sulfide minerals auriferous quartz veins differ from barren quartz veins by the presence of ilmenite apatite xenotime and gold and the absence of sulfide minerals the assemblage of gold ilmenite apatite xenotime indicates a linked genesis and mobility of ti p and y in the mineralizing fluids geochemical analysis of samples throughout the deposit shows that gold only occurs in sedimentary rocks with high feo feo fe2o3 and low c c co2 ratios 0 8 and 0 2 respectively this association can be explained by reactions that convert c from reduced graphitic host rocks into co2 and reduce ferric iron in the host rocks to ferrous iron in biotite and chlorite these reactions would increase the co2 content of the fluid facilitating the transport of ti p and y from the host rocks into the veins both co2 and ch4 produced by reaction of h2o with graphite effervesced under the lower confining pressures in the veins this would have partitioned h2s into the vapor phase destabilizing au bisulfide complexes the loss of co2 and h2s from the aqueous phase caused precipitation of gold ilmenite apatite and xenotime it is proposed that this process was the main control on gold precipitation oxidization of iron in the very reduced wall rocks resulting in reduction of the fluid provided a second mechanism of gold precipitation in previously decarbonized rocks contributing to the high grades in some samples although sulfide minerals especially arsenopyrite did form during the hydrothermal event host rock sulfidation reactions did not play a role in gold precipitation because gold is absent near rocks or veins containing sulfide minerals sulfide minerals likely formed by different mechanisms from those associated with gold deposition both the fold architecture and subsequent spatially coincident sinistral semibrittle shearing ensured that the ore fluids were strongly focused into the hinges of the anticlines within the anticlines a reactive cap of fine grained graphitic reduced fe rich turbidites above more permeable siltstones and fine sandstones impeded fluid flow ensuring efficient removal of graphite and the associated effervescence of co2 from the fluid caused the precipitation of gold exploration for similar deposits should focus on the intersection of east west shear zones with folds and fe rich graphitic host rocks

the hydrous component in andradite garnet twenty two andradite samples from a variety of geological environments and two synthetic hydroandradite samples were studied by fourier transform ir spectroscopy their spectra show that h enters andradite in the form of oh amounts up to 6 wt h 2o occur in these samples those from low temperature formations contain the most oh some features in the absorption spectra indicate the hydrogarnet substitution sio 4 4 o 4h 4 4 whereas others indicate additional types of oh incorporation the complexity of the spectra due to multi site distribution of oh increases with increasing complexity of the garnet composition

geochemical processes and petrogenetic evolution of rodingite dykes in the ophiolite complex of othrys central greece rodingite dykes occur in serpentinised harzburgites in the othrys ophiolite hydrogrossular and diopside along with chlorite appeared first and mark the initiation of rodingitisation of the dolerite protolith subsequently calcite formed after diopside and consequently reacted with chlorite to enrich the rodingites in diopside and garnet apatite also forms at the late stages of alteration several geochemical exchanges were triggered by variably alkaline and continuously evolving fluids passing through the serpentinising peridotites a possible t xco2 path along with a reaction series are proposed for the development of the rodingitic assemblages that entail a fluid phase leaching of the peridotite was triggered by fluids very rich in co2 and carbonate complexes are thought to be responsible for mobilization of cr and ni under such conditions ree also were mobile and the presence of co32 and po43 ions that complexed them further assisted their transportation zr mobilised at increased ph conditions with the aid of the oh and po43 during the late stage of alteration and due to the incorporation of more saline fluids after formation of calcite and apatite in the two metasomatic stages respectively the ree complexes were destabilised due to reduced activity of co32 and po43 and free rees were able to precipitate onto garnet cr and ni hydroxides were precipitated after formation of calcite in the rodingite the saline fluids were also reducing hence eu remained in its divalent state and was highly absorbed on garnet surfaces the rodingitisation at othrys ophiolite occurred in a subduction regime as it is implicated by the very rich in co2 fluid phase which is readily explained by involvement of subducted carbonate sediments and is favoured by the development of structural zones that acted as conduits to the metasomatising fluid phase

very low solubility of rutile in h2o at high pressure and temperature and its implications for ti mobility in subduction zones the solubility of rutile in h2o has been measured at 1000 1100 c 1 2 gpa the data indicate that solubility is very low over the investigated range with a maximum of 4 7 millimol kg h2o at 1100 c 2 gpa the data were fit with the equation log m ti 4 892 10470 t 0 1923 p where m ti is ti molality t is in kelvins and p in gpa when compared to previous results the new data indicate substantially lower solubility opposite pressure dependence and thermodynamic properties of the reaction rutile tio2 aq that are now consistent with other oxide hydrolysis reactions calculations of ti transport during mantle metasomatism by h2o in subduction zone environments predict much lower ti mobility at all conditions these results offer strong support for models of ti retention in eclogites during slab devolatilization and require that examples of significant ti mass transfer be explained by complexing agents in solution most likely aluminosilicate complexes

polymetallic mineralization at the browns deposit rum jungle mineral field northern territory australia the rum jungle mineral field northern territory australia forms part of the paleoproterozoic pine creek orogen the geology of the area comprises two archean granitic basement domes overlain by a paleoproterozoic sequence of metasedimentary and subordinate metavolcanic rocks the rocks have been deformed and metamorphosed to greenschist facies during the 1880 ma barramundi orogeny but the original stratigraphic succession has been preserved the browns deposit browns and its extension browns east hosted within black carbonaceous pelites of the paleoproterozoic whites formation is the largest base metal deposit found to date in the pine creek orogen present resource estimates are 39 million metric tons mt at 0 44 percent cu 3 61 percent pb 0 11 percent co and 0 09 percent ni browns and 31 mt at 1 29 percent cu 1 28 percent pb 0 13 percent co and 0 13 percent ni browns east major sulfide minerals in the ore zone are galena sphalerite chalcopyrite pyrite and the main carrier of ni and co siegenite ni co 3 s 4 digenite group minerals and bornite ca bearing plumbogummite pbal 3 po 4 2 oh 5 h 2 o arsenopyrite and gersdorffite are present in minor quantities ore minerals occur as fine grained wisps parallel to the main bedding parallel foliation and as coarse grained mono and polyminerallic aggregates that crosscut the foliation total noncarbonate carbon contents of unaltered rocks range from 1 07 to 7 51 wt percent total sulfur contents range from 2 13 to 6 14 wt percent petrographic studies and raman spectroscopy identify three varieties of carbonaceous matter primary syngenetic premetamorphic epigenetic grain coating and postmetamorphic epigenetic uraniferous migrated altered rocks are rarely encountered values of 34 s for sulfides range from 5 to 15 per mil and are interpreted to reflect a combination of inorganic thermochemical reduction of seawater and bacterial activity no specific sulfur isotope patterns for individual minerals can be established indicating nonequilibrium conditions homogeneous lead isotope signatures of galena 206 pb 204 pb 16 20 16 22 207 pb 206 pb 15 48 15 51 208 pb 207 pb 35 86 35 92 suggest that all pb was derived from a single crustal source and paragenetically late crosscutting galena appears to have been remobilized from bedding parallel galena despite the occurrence of uranium in similar rocks nearby uranium is quantitatively insignificant in the browns deposit and is not genetically related to base metal mineralization instead it is linked to brittle deformation in the waning stages of orogenesis the browns deposit differs from other well known sediment hosted stratiform ore deposits both the zambian copperbelt and the polish kupferschiefer deposits are copper dominant and hosted in sedimentary sequences with significant psammitic components the pb zn ag deposits of the proterozoic australian zinc province also have significant carbonate in their host rocks e g carbonaceous dolomitic and siltstone at mcarthur river and lack economically interesting cu co and ni the nearby woodcutters pb zn ag deposit in rocks of similar age also differs in structural setting veins dominant metals and pb isotopes from the browns deposit

redistribution of hfse elements during rutile replacement by titanite titanite growth at the expense of rutile during retrograde hydration of eclogite into amphibolite is a common phenomenon we investigated an amphibolite sample from the tromso eclogite facies terrain in northern norway to gain insight into the trace element distribution between rutile and titanite during incomplete resorption of the rutile by titanite patchy compositional zoning of al ti and f in titanite relates to the presence of a fluid with variable ti al and or f during its growth laser ablation icp ms and electron microprobe data for high field strength elements hfse nb zr ta and hf of rutile resorbed by titanite indicate a pronounced enrichment of these elements in the rim of a large single rutile crystal 8 mm and a systematic decrease towards uniform hfse contents in the large core hfse contents of smaller rutile grains 0 5 mm and rutile inclusions 100 m in the titanite overgrowth are similar or higher than in the rims of large rutile crystals element profiles from the rim inward demonstrate that hfse enrichment in rutile is controlled by diffusion hfse ratios in diffusion altered rutile show systematic variations compared with the uniform core composition of the large rutile modelling of zr and nb diffusion in rutile indicates that diffusion coefficients in rutile in fluid dominated natural systems must be considerably higher than those determined experimentally at 1 bar in dry systems variations of hfse contents in the newly formed titanite show no systematic spatial distribution hfse ratios in titanite and the rims of rutile are different indicating different solid fluid distribution coefficients in these minerals element fractionation by diffusion into the relict rutile and during fluid mediated growth of new titanite could substantially change the hfse budget of these minerals and could affect their use for geochemical tracing and other applications such as zr based geothermobarometry

trace elemental modification in magnetite from high grade metamorphosed bifs in the southern north china craton abstract magnetite as a common oxide mineral in banded iron formations bifs and ore deposits is an ideal provenance indicator for mineral exploration and its composition has long been used for genetic studies of ore deposits however many ore deposits particularly the bifs worldwide have undergone various grades of secondary metamorphism or hydrothermal alteration it is still unclear whether the original magnetite composition was modified during the secondary processes and if so to what extent the compositions were modified in this study we conduct mineralogical and la icp ms trace elemental investigations on magnetite from the amphibolite to granulite facies metamorphosed bifs in the southern north china craton the new results were compared with those of unmetamorphosed and greenschist facies metamorphosed bifs worldwide to understand how the original composition of magnetite was modified during different grades of metamorphism magnetite grains from the amphibolite to granulite facies bifs have low cr co ni and ga less than 10 ppm and slightly variable v and zn these elements do not show remarkable changes during high grade metamorphism when compared with the unmetamorphosed and greenschist facies metamorphosed magnetite indicating that these elements in magnetite are immobile during metamorphism a very narrow range of fe2 fe3 mole ratios of the high grade metamorphosed magnetite roughly suggest limited changes of oxygen fugacity during metamorphism which is also supported by the limited change of cr and v contents high mn contents in these magnetite grains are associated with low mg contents possibly due to the fact that these elements occupy the same site in magnetite structure compared with unmetamorphosed magnetite the high grade metamorphic magnetite in the bifs of the southern north china craton has elevated al ti and mn such a change of magnetite compositions is mainly controlled by coexisting fe mg silicates that formed during high grade metamorphism for example our new results of trace elemental mapping on magnetite show that the edge of magnetite grains that are in contact with fe mg silicates e g hornblende grunerite and pyroxene are remarkably enriched in mg mn al si and na compared to the cores some elements up to 10 times more all these features indicate that elemental diffusion and exchange between magnetite and coexisting silicate minerals during high grade metamorphism have extensively modified original compositions of magnetite from bifs

epeirogenic uplift above a detached slab in northern central america p wave tomographic images reveal that the northern central america highlands east of the modern volcanic arc overlie a detached slab hypsometric analysis of the highlands in honduras demonstrates that the region is a dissected plateau that is disrupted by normal faults near the north american caribbean plate margin the dissected central american plateau contains a network of superimposed rivers with meanders cut into bedrock such a geomorphic character indicates that the regional uplift occurred in the absence of tilting we propose that the epeirogenic uplift of northern central america is the buoyant upper plate response to the influx of mantle asthenosphere following the break off and sinking of the slab

numerical modelling of earthquake flow in the southeastern carpathians vrancea effect of a sinking slab abstract the earthquake prone vrancea region is modelled as a system of perfectly rigid blocks separated by infinitely thin plane faults the interaction of the blocks along the fault planes and with the surrounding medium is assumed to be a viscous elastic the displacements of the block system are caused by motions of boundary blocks the velocities of the motions are found from a model of mantle flows induced by a sinking slab beneath the vrancea region when a ratio of stress to pressure for some portion of a fault plane exceeds a certain strength level a stress drop earthquake occurs as a result of the numerical simulation a catalog of synthetic earthquakes is produced several numerical experiments for various model parameters show that the spatial distribution of synthetic events is significantly sensitive to the directions of the block movements small variations in a slab rotation control the pattern of the synthetic seismicity the results of the analysis show that the catalogs obtained by the simulation of the block structure dynamics have certain features similar to those of the real earthquake catalog of the vrancea region

thermomechanical modelling of slab detachment abstract slab detachment or breakoff is appreciated as an important geological process as shown by recent tomographic imaging using a 2 d upper mantle model 660 km deep and 2000 km wide we have investigated with a 2 d finite difference and marker in cell numerical technique the multi resolutional character of the thermomechanical phenomena related to this complex geological process our experiments show that this process can be initiated in form of slab necking by a prolonged 8 30 my period of slab weakening due to thermal diffusion 60 c my due to strong positive thermal feedback from shear heating detached slab fragments sink rapidly with a tendency for coherent rotation the influence of temperature and pressure dependent thermal conductivity on the process of thermal weakening of the slab is quite significant this supports the idea that the breakoff process is triggered by thermal diffusion on a time scale linearly dependent on heat conductivity rapid topographic changes and increasing volcanic activities due to the melting of subducted oceanic crust are possible scenarios of this vigorously driven geodynamic process

in situ trace element and sulfur isotope analysis of pyrite in a paleoproterozoic gold placer deposit pardo and clement townships ontario canada extensive pyrite bearing auriferous cobble and boulder conglomerates are present in the basal 30 in of the mississagi formation in pardo and clement townships ontario canada the sedimentology of the conglomerates combined with regional geology indicates limited fluvial transport in a gravel bed braided river with local hyperconcentrated flows with material derived from a highly restricted catchment area postdepositional overprinting of the conglomerates is related to the penokean orogeny at 1 85 to 1 5 ga and alkali metasomatism at similar to 1 7 ga several pyrite varieties including detrital and postdepositional recrystallized and altered grains are present in the conglomerates detailed in situ laser ablation inductively coupled plasma mass spectrometry la icpms analysis of pyrite revealed that the gold in the deposit is intimately associated to large detrital pyrite grains as invisible au with lesser amounts of free gold postdepositional pyrite and pyrite overgrowths have very low au content elements such as pb bi sb te ag and hg together with au were mobilized during hydrothermal alteration and dissolution of detrital pyrite grains small scale transport and reprecipitation formed part of the postdepositional pyrite and free gold in immediate contact with postdepositional grains in contrast ni co and as were not mobilized external fluid infiltration is negligible and is indicated only by minor compositionally distinct late sulfide veinlets crosscutting the conglomerates sulfur isotope analysis of detrital pyrite yields generally positive delta 34 s values 0 97 9 26 0 the delta 34 s sulfur isotope composition of pyrite overgrowths and postdepositional grains overlaps the isotopic range of the detrital grains suggesting a near closed s system during postd epositional processes however the detrital pyrite tends to have slightly negative delta 33 s while the postdepositional and overgrowth pyrite are either neutral or slightly positive the s isotope composition of the detrital pyrite is compatible with an origin of s as dissolved sulfate in an ocean under a low oxygen atmosphere the potential source of the au bearing detrital pyrite appears to have been an as yet undiscovered archean deposit located within 1 to 8 kin of the placer deposit

mineralogical characterization of acid weathered phyllosilicates with implications for secondary martian deposits abstract the detection of phyllosilicates and sulfates on mars has revealed a complex aqueous history which suggests distinct geochemical environments separated temporally and spatially recent observations by mro crism in mawrth vallis have shown that phyllosilicate deposits exhibit a specific stratigraphy which remains incompletely understood moreover mer spirit has evidenced association between phyllosilicates amorphous silica and sulfates we investigated the hypothesis that these parageneses resulted from the acidic weathering of older phyllosilicate deposits we exposed nontronite fe rich smectite montmorillonite al rich smectite and kaolinite to h 2 so 4 solutions at ph 0 2 and 4 and at a temperature of 60 c after the acid treatment a combination of mineralogical techniques was used to assess the degree of alteration of the three phyllosilicate minerals xrf xrd and esem measurements show that nontronite was the most unstable when acid leached followed by montmorillonite and then kaolinite progressive acidic leaching of nontronite leads to alteration of the phyllosilicate to amorphous silica along with fe sulfate and anatase and the formation of an acidic al fe rich solution alteration of montmorillonite resulted in the formation of fe al ca and mg sulfates and a al rich leaching solution comparatively leaching of kaolinite resulted in the formation of al sulfates and a al rich solution as well with only slight alteration of the primary mineralogical features the effects of acid leaching of the phyllosilicates were also observed in nir reflectance spectra allowing a comparison with crism spectra from mawrth vallis based on our results we propose a new model where acid leaching of mixed phyllosilicate deposits leads to kaolinite overlaying montmorillonite which in turn caps fe mg smectites leaching of cations and subsequent evaporation leads to sulfate deposits as supported by geochemical modeling while amorphous silica remains as a residue depending on the intensity ph and length of exposure of acidic leaching our model can explain the stratigraphic distribution of phyllosilicates and the association of sulfates silica and smectites

titanium mobility in metamorphic systems a review abstract titanium is a dispersed lithophile element commonly regarded as chemically immobile at sub magmatic temperatures however a growing number of field studies demonstrate that ti is somewhat mobile in certain environments this review examines the current state of knowledge concerning the mobility of ti during alteration and metamorphism of crustal rocks also considered are relevant ti oxide solubility data from experiments and determinations of ti concentrations in natural waters where ti mobility is well documented its length scale is 10 m however ti may move greater distances in deep crustal shear zones the solubility of ti oxides in geologic fluids is strongly temperature dependent under low to medium grade metamorphic conditions ti mobility is limited by the low solubility of ti oxides in the associated fluids under eclogite conditions ti mobility is probably limited not by ti oxide solubility which reaches 1 ti but by restricted fluid flow in low permeability rocks

fluid channelling during ductile shearing transformation of granodiorite into aluminous schist in the tauern window eastern alps ductile shearing in the core of the tauern window austria transformed metagranodiorite into si undersaturated garnet chlorite staurolite schist at a depth of c 35 40 km during the alpine orogeny four distinct zones have been recognized extending from the wallrock into the centre of the shear zone zone i unaltered metagranodiorite with subordinate amphibolite zone ii biotite white mica garnet schist zone iii biotite phengite schist zone iv quartz absent garnet chlorite staurolite schist with garnets up to 10 cm across whole rock analyses show a dramatic decrease in sio2 from 65 wt in zone i to 35 wt in zone iv ca na and sr also decrease across the shear zone whereas al ti fe mg p cr ni zn and rb all increase towards zone iv mass balance calculations indicate that shearing was accompanied by up to 60 volume loss near the centre of the shear zone comparison of the tauern window samples with other shear zones in granitic hosts indicates that silica loss accompanied by gains in mg fe and ti is typical for volume loss shear zones but is distinctly different from the element behaviour exhibited in shear zones that are thought to represent approximately isovolumetric behaviour in the samples studied here volume loss appears to have resulted from channellized fluid flow during shearing producing time integrated fluid fluxes of 108 cm3 cm 2 in zone iv this large volume of fluid may have originated in part from dehydration of flysch carried beneath the metagranodiorites during eocene movement on the north penninic subduction zone development of an inverted thermal gradient during subduction would have allowed the fluid to scavenge large amounts of silica from the shear zone during ascent and heating

evolution of rodingites along stratigraphic depth in the iti and kallidromon ophiolites central greece abstract rodingitised rocks were collected from the neighbouring iti and kallidromon ophiolites they comprise metasomatic assemblages after serpentinised lherzolite and harzburgite gabbro and dolerite dykes the main mineral phases in the metasomatised mantle and gabbroic rocks include grossularitic garnet chlorite and diopside whereas epidote group minerals were mainly developed at the expense of the dolerite dykes the fluid phase involved in the metasomatic reactions was highly alkaline in the metasomatising peridotites and less alkaline in the altered gabbro and dolerite under such conditions ti is assumed to have remained immobile in the whole process while zr remained constant in the stratigraphically upper rodingitised gabbro and dolerite transportation of rare earth elements zr cr and ni from the altered mantle segment to the upper gabbro level was assisted by the presence of carbonate and hydroxyl ligands after consequent breakdown of the carbonate complexes these elements were deposited in the rodingitised gabbro and dolerite rare earths were mainly integrated in the neoblastic diopside whereas cr and ni likely formed insoluble hydroxides in that less reducing environment the metasomatic event happened in the mantle wedge close to the subduction of the pelagonian carbonates that strongly enriched the fluid phase in co 2 the entrance of an externally derived hydrothermal fluid was responsible for the reduction of ph at the higher levels and the calculated influx of si in the system

evidence for hfse and ree mobility during calc silicate metasomatism mesoarchean 3075ma ivisaartoq greenstone belt southern west greenland abstract the mesoarchean ca 3075 ma ivisaartoq greenstone belt consists dominantly of variably deformed and metamorphosed mafic to ultramafic flows basalts to picrites in addition there are minor serpentinites gabbros clinopyroxene rich cumulates and volcaniclastic and siliciclastic sedimentary rocks primary volcanic structures such as pillows and volcanic breccia are well preserved in low strained zones the belt underwent intense metasomatic hydrothermal alteration between 3075 and 2961 ma an early stage of calc silicate metasomatism stage i resulted in the formation of epidosites in pillow cores pillow interstitials and intrusive margins of gabbroic dykes this alteration appears to have resulted from sea floor hydrothermal alteration a second stage of calc silicate metasomatism stage ii formed centimeter to meter scale layers concordant to discordant relative to the regional foliation these layers consist of diopside garnet epidote plagioclase quartz titanite vesuvianite calcite actinolite scheelite the second stage calc silicate rocks are associated with shear zones and their origin is attributed to interaction of reactive fluids with mafic and ultramafic rocks during regional metamorphism both stages of calc silicate metasomatism caused significant mobilization of major elements si mg ca fe na k and mn lile rb cs sr ba pb and lree heavy rare earth elements hree and hfse th nb ta zr ti remained relatively immobile during stage i metasomatic alteration but were variably disturbed during the stage ii metasomatism accordingly the stage ii calc silicate rocks exhibit evidence for significant mobility of th nb and ta on a local scale 1 4 m whereas zr and ti were not significantly mobilized this resulted in calc silicates with complementary trace element patterns displaying extreme negative to positive nb anomalies nb nb 0 19 7 28 transition metals ni v co cr and sc were relatively immobile during both metasomatic events amphibolites spatially related to the second stage calc silicate rocks preserve mineralogical and major element characteristics consistent with a mafic to ultramafic composition however their near primary magmatic trace element compositions were variably modified due to strong ree mobility during the stage ii metasomatic event this gave rise to various ree characteristics including lree enriched lree depleted and u shape ree patterns some of these element patterns resemble those shown by modern boninites and mid ocean ridge basalts n morb in contrast the least altered amphibolites exhibit similar trace element patterns to those displayed by the least deformed non metasomatized mafic and ultramafic pillow flows they possess relatively flat trace element patterns with negative nb ta anomalies indicating a subduction zone geochemical signature

principal component analysis of magnetite composition from volcanogenic massive sulfide deposits case studies from the izok lake nunavut canada and halfmile lake new brunswick canada deposits abstract magnetite grains from the izok lake nunavut canada and the halfmile lake new brunswick canada volcanogenic massive sulfide deposits and from till covering the nearby areas were investigated using the scanning electron microscopy sem electron probe micro analyzer epma laser ablation inductively coupled plasma mass spectrometry la icp ms and optical microscopy the method of robust estimation for compositional data rob composition was applied to censored geochemical data and the results were analyzed by principal component analysis pca textural relationships and mineral association of magnetite reveal the history of formation and contribute to the explanation of characteristic compositional differences of magnetite from different geological settings the integration of petrography and mineral chemistry allows discriminating magmatic metamorphic and hydrothermal magnetite grains in the vms deposits bedrock samples magmatic magnetite is found in izok lake gabbro and halfmile lake syenite felsic ash tuff and gossan samples whereas magnetite in izok lake massive sulfides gahnite rich dacite and iron formations formed during the amphibolite facies metamorphism in halfmile lake andesite magnetite recrystallized during greenschist facies metamorphism in the magnetite alteration zone associated to the halfmile lake deposit hydrothermal magnetite has been overprinted by metamorphic magnetite halfmile lake massive sulfides in chloritic argillite contain hydrothermal magnetite pca identifies discriminator elements and their contributions to magnetite composition from different izok lake lake and halfmile lake bedrock samples the results suggest that si ca zr al ga mn mg ti zn co ni and cr are discriminator elements for vms deposits and their host bedrocks the distinct chemical signatures for magnetite from various bedrock lithologies demonstrate that magnetite grains of the same origin share more similarities in chemistry as high ti indicates magmatic sources for magnetite whereas high si ca and mg are indicative of hydrothermal settings variable compositions of metamorphic magnetite suggest that the chemistry of this type of magnetite is controlled by the composition of host rocks the grade of metamorphism and oxygen fugacity pca of epma and la icp ms data of magnetite from the izok lake and halfmile lake bedrock samples yield discrimination models for classification of magnetite grains from till decreases in the proportion of magnetite grains with the chemical signature of the izok lake massive sulfides and gahnite rich dacite down ice from the izok lake deposit show the use of magnetite chemistry in geochemical exploration in the halfmile lake area till magnetite grains with the signature of vms mineralization make a glacial dispersal train more than 2 km down ice from the deposit

effects of water on dynamically recrystallized grain size of olivine abstract recrystallized grain size versus stress relationship for olivine has been determined under water poor and water rich conditions we found that when the water content in olivine exceeds 800 ppm h si the size of recrystallized grains is about two to three times larger than under water poor conditions compared at the same stress level microstructural observations of deformed samples show that the ratio of recrystallized grain size to that of subgrains increases significantly with water content and that the volume fraction of grains containing subgrain boundaries is smaller under water rich conditions than under water poor conditions these observations suggest that the enhancement of grain boundary mobility by water is more significant than that of dislocation recovery leading to a larger size of recrystallized grains under water rich conditions

experimentally based water budgets for dehydrating slabs and consequences for arc magma generation phase diagrams of hydrous mid ocean ridge mor basalts to 330 km depth and of hydrous peridotites to 250 km depth are compiled for conditions characteristic for subduction zones a synthesis of our experimentally determined phase relations of chlorite lawsonite epidote zoisite amphibole paragonite chloritoid talc and phengite in basalts and of phase relations from the literature of serpentine talc chlorite amphibole and phase a in ultramafics permits calculation of h2o contents in hydrous phase assemblages that occur in natural compositions this yields the information necessary to calculate water budgets for descending slabs starting from low grade blueschist conditions 10 20 km depth with h2o contents between 5 and 6 wt for hydrated oceanic crust complete dehydration is achieved between 70 and 300 km depth as a function of individual slab geotherms hydrous phases which decompose at depth below volcanic arcs are lawsonite zoisite chloritoid and talc phengite in mafic compositions and chlorite and serpentine in peridotite approximately 15 35 of the initially subducted h2o are released below volcanic arcs the contribution of amphibole dehydration to the water budget is small 5 20 and occurs at relatively shallow depth 65 90 km in any predicted thermal structure dehydration is a combination of a stepwise and a continuous process through many different reactions which occur simultaneously in the different portions of the descending slab such a dehydration characteristic is incompatible with single phase dehydration models which focus fluid flow through a unique major dehydration event in order to explain volcanic fronts as a consequence of continuously progressing dehydration water ascending from the slab will be generally available to depth of ca 150 200 km the fluid rising from the subducting lithosphere will cause partial melting in the hot portion of the mantle wedge we propose that the volcanic front simply forms above the mantle wedge isotherm where the extent of melting is sufficient to allow for the mechanical extraction of parental arc magmas thermal models show that such an isotherm ca 1300oc locates below volcanic fronts slab surface depths below such an isotherm are compatible with the observed depths of the slab surface below volcanic fronts 1998 elsevier science b v all rights reserved

mineralogical and geochemical characteristics of hydrothermal alteration and episyenitization in the konigshain granites northern bohemian massif germany the late hercynian granites of konigshain underwent multistage hydrothermal processes extensive high temperature late magmatic alteration is for example indicated by low zr hf and an ree pattern displaying the tetrad effect intensive post magmatic alteration of the granite occurred along brittle structures at least two main stages of post magmatic hydrothermal alteration are involved the first high temperature stage which is characterized by albitization and or quartz leaching episyenitization resulted from fluid rock interaction with late magmatic fluids that very probably mixed with external low salinity fluids quartz dissolution was triggered by vapour condensation and or the cooling of these fluids below 450 c along brittle structures the high porosity resulting from quartz leaching during stage 1 assisted subsequent circulation of low temperature fluids at stage 2 the latter is characterized by the chloritization and illitization of episyenites almost all major and trace elements were enriched or depleted during one of the main alteration stages however zr hf th and ti were immobile during post magmatic alteration the significant depletion of lree and the enrichment of hree in albitized samples is controlled by the dissolution of monazite and the new formation of hree rich polycrase y or aeschynite y during post magmatic stage 1 negative ce anomalies of episyenites are associated with illitization and suggest oxidizing conditions during stage 2

geochemical discrimination of clastic sedimentary rock sources abstract factors controlling the geochemistry of a clastic sedimentary rock can include 1 composition of source terrain 2 chemical weathering 3 hydraulic sorting 4 diagenesis 5 metamorphism and 6 hydrothermal alteration a linear solution inferring source terrain composition from geochemistry of the sediment is impossible in this multivariate system as several unknowns will commonly be present the use of graphical analysis of element pairs circumvents the problem chemically immobile elements will maintain invariant ratios during rock mass change caused by either addition or depletion of mobile elements this results in chemically immobile element scattergrams exhibiting linear trends along radians extending from the origin if the major mineral phases of the immobile elements have behaved in a hydrodynamically similar manner as chemically mobile element plots will produce a scatter of points this relationship can be used to test chemical immobility and similarity in hydrodynamic sorting history the constraint on analysis is that the source area must be compositionally uniform or the sediment well mixed prior to delivery to the basin a second technique using sio2 plots has also been developed to investigate element mobility and hydrodynamic behaviour of the mineral phases containing the elements sio2 immobile element plots result in a linear arrangement of points extending towards either 0 or 100 sio2 the 0 intercept position occurs for elements with major mineral phases concentrated in sand the 100 intercept for those concentrated in clays plotting chemically mobile elements produces different patterns and this can be used to gain information on alteration and sorting history elemental ratios for chemically immobile elements with similar hydrodynamic behaviour will be the same as those for the weighted average composition of the source material this provides a powerful tool for deducing source terrain from sediment geochemistry techniques outlined above were tested on archaean metasandstones from superior province canada immobile element ratio diagrams for nb al ti and zr al ti indicate that a calc alkaline extrusive intrusive suite lying to the north of the study area was the source and not five other volcanic suites in the region this conclusion agrees with previous clast lithology studies and accentuates the applicability of the geochemical techniques

cenozoic climate change as a possible cause for the rise of the andes causal links between the rise of a large mountain range and climate have often been considered to work in one direction with significant uplift provoking climate change here we propose a mechanism by which cenozoic climate change could have caused the rise of the andes based on considerations of the force balance in the south american lithosphere we suggest that the height of and tectonics in the andes are strongly controlled both by shear stresses along the plate interface in the subduction zone and by buoyancy stress contrasts between the trench and highlands and shear stresses in the subduction zone depend on the amount of subducted sediments we propose that the dynamics of subduction and mountain building in this region are controlled by the processes of erosion and sediment deposition and ultimately climate in central south america climate controlled sediment starvation would then cause high shear stress focusing the plate boundary stresses that support the high andes

hydrothermal mobility of ti zr and ree examples from the bergell and adamello contact aureoles italy contact metamorphic marbles affected by metasomatic fluids at the contact to the bergell and adamello intrusives contain various accessory minerals zirconolite allanite titanite rutile geikielite hoegbomite which provide new evidence for the hydrothermal mobility of ti and zr in both examples ti and zr migrated along with u th y and ree in a metasomatic fluid rich in potassium the composition of the main minerals fluorine rich phlogopite pargasite and titanian clinohumite and the abundance of fluor apatite demonstrate that fluorine and phosphorus were important components of the fluid the textural relationships indicate that the formation of the accessory phases is linked to the crystallization of the hydrous minerals

formation of silica by low temperature acid alteration of martian rocks physical chemical constraints 1 theoretical geochemical modeling has been used to evaluate the formation conditions of amorphous silica during aqueous alteration of typical martian igneous rocks at 0 c the models show that some silica can form during low temperature alteration of mafic to ultramafic rocks over a large range of ph and water rock ratios silica dominated deposits like those found at the columbia hills in gusev crater on mars could form at solution ph below 2 and water rock ratios of 102 104 high water rock conditions could represent acid flow through rocks solution discharge from an acid spring and or surface flow of released solutions low ph favors dissolution of silicates and saturation of solution with respect to relatively insoluble silica which then precipitates partial evaporation or freezing of released solutions would also cause precipitation of amorphous silica modeling shows that ti oxides are also present in silica rich deposits more soluble minerals e g ferric oxides phyllosilicates could precipitate downstream from partially neutralized evaporated or frozen solutions temperatures above 0 c are not required to form abundant silica through acid alteration of martian rocks

element and sr isotope signatures of titanite as indicator of variable fluid composition in hydrated eclogite abstract the trace element signature sr common pb u th ree and hfse of titanite gives important information about the formation process of metamorphic titanite we investigated titanite from different textural positions of a strongly retrogressed eclogite from the tromso norway high p area it shows characteristic titanite rims around partially absorbed rutile interpreted as grown during retrogression and hydration of the high p assemblage the titanite rims around rutile are polycrystalline and in contact with the plagioclase amphibole matrix large idioblastic single crystal titanite grew in veins without relics of precursor rutile compositional zoning of al ti f in titanite of both textural positions is irregular and not related to core or rim position in the crystals there is no evidence for systematic growth sequences or diffusion reflecting changing p t conditions or systematic changes of fluid composition trace element patterns of titanite la icp ms data however show systematic variations in the coupling and decoupling behaviour of strongly fluid mobile sr u moderately fluid mobile ree and little fluid mobile nb ta zr hf elements the trace element signatures of titanite from the two different fabric positions reflect contrasting characteristic fluid compositions single crystal titanite equilibrated with fluid that was channelled in the vein polycrystalline titanite on rutile records the composition of a fluid that had migrated along grain boundaries in the amphibole plagioclase matrix fluid from the matrix also contributed to the geochemical signature of vein titanite whereas influence of fluid from the vein on the composition of polycrystalline titanite in the matrix is not evident 87sr 86sr isotope ratios of the different titanite types support the inference from trace elements of spatially and temporally variable fluid sources

ore formation at the washan iron oxide apatite deposit in the ningwu ore district eastern china insights from in situ la icp ms magnetite trace element geochemistry abstract iron oxide apatite ioa deposits are an important type of iron deposit that may host large reserves of iron and other elements the washan deposit in the ningwu ore district is a classic giant ioa deposit hosted by porphyritic diorite at washan four fe mineralization stages have been identified with clear crosscutting relationships forming four types of ores disseminated ores breccia ores and magnetite actinolite and magnetite apatite actinolite veins trace element concentrations and single grain geochemical profiles of magnetite from the four fe mineralization stages were obtained via laser ablation inductively coupled plasma mass spectrometry la icp ms the geochemical profiles show consistent ti v mg and al contents from cores to rims indicating that magnetite might have crystallized quickly under relatively stable conditions in each stage compatible element e g co v ni and cr contents of the washan magnetite are similar to those of magmatic fe ti v deposits with high v and ti contents indicating a close magmatic link increasing mg al mn ni and ga contents and decreasing cr content from early to late stages imply increasingly intense reactions between fe bearing fluids and country rocks e g diorite and evaporites which also suggests a magmatic hydrothermal origin we propose a new genetic model for ore formation at the washan ioa deposit first an fe rich liquid which may have formed via liquid immiscibility ascended through the magma system resulting in the disseminated ores and albite alteration in the porphyritic diorite with cooling and crystallization of the magma the intrusive rocks developed fractures and brecciation which may have provided pathways for fe bearing fluids after the breccia or massive ores formed the pathways would have been quickly sealed by mineral precipitation continuous liquid immiscibility and magma crystallization may have produced similar fluids with more sedimentary material involved and its markers displayed when the fluid pressure overcame the lithostatic pressure the fractures that developed may have provided the necessary conduits for emplacement of the magnetite actinolite and magnetite actinolite apatite veins subsequently the magmatic hydrothermal system might have remained active during cooling and differentiation while pyrite quartz and calcite veins formed

breakdown mechanisms of titanclinohumite in antigorite serpentinite cerro del almirez massif s spain a petrological and tem study abstract veins with titanclinohumite ti chu and olivine occur close to clinopyroxenite layers scattered through the antigorite serpentinites from the cerro del almirez ultramafic massif sierra nevada betic cordillera s spain they formed at estimated maximum p t conditions of 1 3 gpa and 475 c due to simultaneous breakdown of former ti rich clinopyroxene and brucite in the presence of 6 vol of free water breakdown of ti chu single crystals to an olivine ilmenite framework was gradual small relict patches of ti chu appear even at some distance from the reaction front and ilmenite grains coarsen and become less frequent away from the front detailed tem data support this interpretation olivine in equilibrium with ti chu is structurally and chemically homogeneous whereas ti chu shows ubiquitous intermixed 001 olivine lamellae product olivine close to the front shows pervasive and continuous 001 ti chu lamellar faults these become less frequent away from the reaction front due to the completion of the ti chu breakdown this textural sequence suggests both progressive transfer of ti to ilmenite and progressive release of h 2 o during the breakdown of ti chu a second hydration breakdown reaction can be observed very locally in the contact between ti chu and diopside producing a symplectitic intergrowth of tremolite and ilmenite textural features of both reactions point to a very limited availability of water during ti chu breakdown this suggests that veins operated as closed systems complete obliteration of ti chu owing to the antigorite dehydration breakdown can be observed in the almirez massif rocks this precludes oh ti chu from atg serpentinite as an efficient water or titanium carrier into deep mantle in hot subduction zones

the significance of titanite and apatite u pb ages constraints for the post magmatic thermal hydrothermal evolution of a batholithic complex berens river area northwestern superior province canada abstract titanite apatite and in one case rutile from a suite of twenty seven samples representing the major phases of an extensive and well dated archean plutonic domain of the northwestern superior province have been dated by u pb to determine the temporal progress of thermal and hydrothermal events accompanying and following major plutonism and to assess the isotopic behaviour of these geochronometers most samples contain 1 dark brown titanite with 350 20 ppm u showing shapes and textural relationships indicative of a primary magmatic origin and yielding ages corresponding either to the time of magmatic crystallization or to that of secondary metamorphic or magmatic events known in the area 2 pale titanite with 30 2 ppm u showing textural evidence for a secondary origin by breakdown of biotite hornblende oxide or older titanite and yielding ages that in general post date the major plutonic and metamorphic events in the area 3 apatite containing 30 5 ppm u occasionally up to 150 ppm u showing igneous shapes and textural relationships but yielding post magmatic ages similar to those of coexisting pale titanite 4 rutile in one sample postdating the ages of coexisting titanite and apatite the common coexistence of two noncoeval titanite generations demonstrates that the often invoked mechanism of pb diffusion during slow cooling in this case has no general validity the distribution of primary dark titanite ages however could be explained by late closure to diffusion or alternatively as the result of resetting by the thermal or hydrothermal effects caused by younger plutonic activity the ages of the secondary pale titanites probably reflect crystallization during discrete retrogressive events promoted by moderate heating or enhanced fluid activity the correspondence between pale titanite and apatite ages suggests that the same processes also caused the isotopic resetting of apatite on a regional scale the data pattern permits the identification of domains characterized by differences in the length and intensity of the thermal and hydrothermal processes the most protracted activity is recorded in northern domains of the berens river area whereas the gold mineralized red lake area in the south underwent a very rapid decline of the thermal hydrothermal activity these data also highlight important differences between the red lake and other gold camps of the superior province such as hemlo and val d or where hydrothermal activity locally associated with mineralization occurred as much as 30 80 m y after the major orogenic developments

intra basaltic soil formation sedimentary reworking and eodiagenetic k enrichment in the middle to upper ordovician dunn point formation of eastern canada a rare window into early palaeozoic surface and near surface conditions mafic flows of the middle to upper ordovician dunn point formation of eastern canada were deeply weathered under warm and relatively humid conditions before being buried by subsequent flows in the absence of superior plants and in the context of relatively low atmospheric carbon levels the soils developed alkaline groundwater conditions through mineral water interactions which resulted in an enhanced mobility of al relative to si in most palaeosols of that formation although the vegetation cover was volumetrically insignificant compared with that of subsequent geological times it was apparently producing very efficient chelates which for most palaeosols of the succession generated a well defined cheluviation pattern for not only al and fe but also and mainly ti which is typically immobile in modern soils the resulting soils developed an al fe ti depleted upper horizon that was enriched in si probably through periodic ground saturation long term climatic variations related to orbital cycles are inferred to have accounted for a second type of soil in the succession which contrasts with the former by showing a si depleted and less al fe ti depleted upper horizon some soil material was substantially reworked by surface runoff but such occurrences can be easily differentiated from in situ soil material in terms of texture structure and composition a thick overlying rhyolite flow is thought to be responsible for providing abundant k in solution which was incorporated in the underlying basalt palaeosols as exchangeable cations within a probably montmorillonitic clay precursor to the fe mg rich phengite that later developed during deep burial and orogenic compression

fluid rock interaction in autoliths of agpaitic nepheline syenites in the ilimaussaq intrusion south greenland abstract within the 1 16 ga old ilimaussaq intrusion up to 700 m large autoliths occur in one stratigraphic unit of the layered floor series of agpaitic nepheline syenites kakortokites these autoliths consist of two different rock types augite syenite and naujaite agpaitic nepheline syenite all three rock types show a number of alteration features related to the entrapment of the autoliths in the kakortokite magma caused by the interaction with a fluid phase in the kakortokites the oxidation of primary arfvedsonite to aegirine and fluorite is restricted to the close proximity to the autoliths close to the surrounding kakortokite the primary mafic phases of the augite syenites augite fayalite fe ti oxides are completely replaced by arfvedsonite aenigmatite biotite aegirine and fluorite the decomposition of primary hastingsite to spectacular aegirine augite nepheline aenigmatite symplectites can be observed up to several meters inside the autoliths additionally fluorite formed at grain boundaries of primary nepheline in the naujaite autoliths primary arfvedsonite is replaced by aegirine biotite intergrowths and abundant aenigmatite is occasionally replaced by ti rich aegirine and fe ti oxides the mineral reactions in the autoliths are used to decipher details of the late to post magmatic processes in a peralkaline syenitic intrusion mineral equilibria record an evolution governed by falling temperature 620 to ca 500 c and increasing relative oxygen fugacity from fmq 1 to above fmq 4 quantification of the observed mineral reactions reveals the infiltration of the autoliths with an oxidizing fluid phase rich in na and f and minor addition of k volatiles h and f and in some cases also fe ti and ca mg released from primary autolith phases were mainly just relocated within the autoliths

paleoproterozoic tectonic history of the cerbat mountains northwestern arizona implications for crustal assembly in the southwestern united states structural mapping metamorphic analysis and u pb geochronology from the cerbat mountains of northwestern arizona place new constraints on the tectonic significance and timing of the boundary between the mojave and yavapai proterozoic crustal provinces in the southwestern united states the cerbat mountains are the easternmost range that exhibits wholly mojave pb isotopic signatures yet their paleoproterozoic structural history is strikingly similar to that of the yavapai province two pervasive deformational events are recognized in the cerbat mountains d1 fabrics are well preserved in the northern cerbat mountains and are characterized by a north northwest striking moderately northeast dipping foliation s1 that is axial planar to macroscopic recumbent folds that we interpret to be west to southwest vergent similar structures have been documented locally in the yavapai province d1 is bracketed between 1740 and 1721 ma in the cerbat mountains on the basis of u pb zircon ages of the big wash granite 1737 4 3 ma and the diana and chloride granites 1719 1 2 and 1721 2 4 ma respectively d2 fabrics dominate the central and southern cerbat mountains and include a subvertical northeast striking foliation that truncates and transposes s1 d2 is bracketed between 1721 and 1682 ma on the basis of u pb ages of the diana and chloride granites and post d2 granite dikes in the eastern cerbat mountains 1682 5 2 4 ma the structural style orientation and timing of d1 and d2 fabrics in the cerbat mountains are identical to those of the yavapai province supracrustal rocks within the cerbat mountains were subjected to two periods of metamorphism that correspond temporally to the two periods of deformation the early phase occurred at 675 725 c and 5 6 kilobars the later phase occurred at 650 700 c and 3 5 4 5 kilobars we propose that the mojave and yavapai provinces were sutured together between ca 1740 and 1720 ma during regional d1 deformation collisional orogenesis in the eastern mojave province may have resulted in the tectonic burial of rocks in the cerbat mountains to depths of 20 km d2 between 1720 and 1682 ma corresponds to the widespread yavapai orogeny and is interpreted to record accretion of the amalgamated mojave yavapai terrane to proterozoic terranes that are now located in colorado

reequilibration processes in magnetite from iron skarn deposits textural and compositional data for magnetite from nine iron skarn deposits in canada romania and china show that most samples have reequilibrated by dissolution and reprecipitation oxy exsolution and or recrystallization the dissolution and reprecipitation processes are most extensive and are present in most magnetite samples examined whereas the oxy exsolution occurs only in high ti magnetite forming exsolution lamellae of fe ti al oxides electron microprobe analysis indicates that the reequilibration processes have significantly modified the minor and trace element compositions of magnetite notably si mg ca al mn and ti whereas oxy exsolution is effective in decreasing the ti content of high ti magnetite many analyses of magnetite grains from the skarn deposits plot variably in the banded iron formations bif iron oxide copper gold iocg or porphyry cu fields using the ti v versus ca al mn discrimination diagram this pattern suggests that trace element data for magnetite that has unusual composition and or reequilibrated cannot be reliably used as a petrogenetic indicator mixing of externally derived saline fluids with fe rich magmatic hydrothermal solutions an increase in temperature and local decreasing pressure and f o 2 are considered the most important causes for the dissolution and reprecipitation or recrystallization of the magnetite increasing f o 2 and decreasing temperature may facilitate oxy exsolution of fe ti al oxides in high ti magnetite results presented here highlight the importance of detailed textural characterization prior to in situ chemical analysis of magnetite grains so that mineral compositions can be properly evaluated in terms of the genesis and evolution of iron skarn deposits

multi stage formation of ree minerals in the palabora carbonatite complex south africa the 2060 ma old palabora carbonatite complex pcc south africa comprises diverse ree mineral assemblages formed during different stages and reflects an outstanding instance to understand the evolution of a carbonatite related ree mineralization from orthomagmatic to late magmatic stages and their secondary post magmatic overprint the 10 rare earth element minerals monazite ree f carbonates bastnasite parisite synchysite ancylite britholite cordylite fergusonite ree ti betafite and anzaite are texturally described and related to the evolutionary stages of the pcc the identification of the latter five ree minerals during this study represents their first described occurrences in the pcc as well as in a carbonatite complex in south africa the variable ree mineral assemblages reflect a multi stage origin 1 fergusonite and ree ti betafite occur as inclusions in primary magnetite bastnasite is enclosed in primary calcite and dolomite these three ree minerals are interpreted as orthomagmatic crystallization products 2 the most common ree minerals are monazite replacing primary apatite and britholite texturally related to the serpentinization of forsterite or the replacement of forsterite by chondrodite textural relationships suggest that these two ree minerals precipitated from internally derived late magmatic to hydrothermal fluids their presence seems to be locally controlled by favorable chemical conditions e g presence of precursor minerals that contributed the necessary anions and or cations for their formation 3 late stage post magmatic ree minerals include ancylite and cordylite replacing primary magmatic ree sr carbonates anzaite associated with the dissolution of ilmenite and secondary ree f carbonates the formation of these post magmatic ree minerals depends on the local availability of a fluid whose composition is at least partly controlled by the dissolution of primary minerals e g ree fluorocarbonates this multi stage ree mineralization reflects the interplay of magmatic differentiation destabilization of early magmatic minerals during subsequent evolutionary stages of the carbonatitic system and late stage fluid induced remobilization and re precipitation of precursor ree minerals based on our findings the palabora carbonatite complex experienced at least two successive stages of intense fluid rock interaction

the replacement of plagioclase feldspars by albite observations from hydrothermal experiments oligoclase and labradorite crystals have been experimentally replaced by albite in an aqueous sodium silicate solution at 600 c and 2 kbars the replacement is pseudomorphic and is characterised by a sharp chemical interface which progresses through the feldspar while preserving the crystallographic orientation reaction rims of albite up to 50 m thick can be readily achieved within 14 days re equilibration of plagioclase in an 18o enriched sodium and silica bearing solution results in oxygen isotope redistribution within the feldspar framework structure the observed characteristics of the reaction products are similar to naturally albitised plagioclase and are indicative of an interface coupled dissolution reprecipitation mechanism chemical analyses demonstrate that the albitisation is accompanied by the mobilisation of major minor and trace elements also including elements such as al and ti which are commonly regarded as immobile during hydrothermal alteration the results contribute to developing our understanding of the close association between large scale albitisation and secondary ore mineralisation which is common in nature

geology and geochemistry of early arc volcanic rocks from guam the island of guam is located at the southern end of the mariana fore arc and was the site of early arc volcanism between 43 and 32 m y ago two volcanic units were erupted during the early evolution of guam the late middle eocene facpi formation and the late eocene to early oligocene alutom formation the facpi formation is composed largely of interbedded boninite series pillow lavas pillow breccias and dikes although arc tholeiite series rocks cap the formation in some areas the alutom formation is composed of interbedded volcanic breccias tuffaceous sandstones lava flows and sills calc alkaline arc tholeiite and boninite series compositions are all found in the alutom formation primitive boninite series rocks are relatively high in sio 2 mgo and ni and low in a1 2 o 3 and tio 2 contents compared to basaltic rocks from the arc tholeiite series additionally they have low ti zr ratios and high k zr rb zr and ba zr ratios although no calc alkaline basalts are found in the early arc formations of guam basalts with chemical characteristics transitional between boninite and tholeiite series rocks may be genetically linked to the calc alkaline series among the analyzed samples here are a few with anomalously high y and rare earth element ree contents chemical variation in the boninite series can be explained by early fractionation of olivine and clinopyroxene followed by plagioclase clinopyroxene and orthopyroxene the arc tholeiite series chemical trends can be explained by early olivine fractionation followed by plagioclase clinopyroxene orthopyroxene and magnetite the composition of the least silicic calc alkaline series andesite can be modeled by fractional crystallization of olivine clinopyroxene plagioclase and magnetite from a transitional basalt derivation of more silicic calc alkaline series rocks requires magma mixing or crustal assimilation in addition to crystal fractionation involving hornblende all basalts from the early volcanic series of guam were erupted in an arc setting the boninite series magmas were produced by hydrous partial melting of depleted mantle at relatively shallow levels whereas the arc tholeiite and calc alkaline series magmas were generated by partial melting of less depleted mantle at deeper levels we suggest that because the calc alkaline series parent basalts most likely were richer in incompatible high field strength hfs elements and sio 2 than were the tholeiitic parents they were generated by lower degrees of melting

ti al zoning of experimentally grown titanite in the system cao al2o3 tio2 sio2 nacl h2o f evidence for small scale fluid heterogeneity chemical zoning according to the substitution al oh f ti o is a common phenomenon in natural titanite and can be used to reconstruct its growth conditions we synthesized titanite which has a zoning pattern similar to that found in natural titanite that grew at the expense of rutile visible in element distribution maps as a patchy irregular pattern run conditions in the system cao al 2 o 3 tio 2 sio 2 nacl h 2 o caf 2 were 600 c 0 4 gpa 1 to 107 days duration natural rutile crystals were placed in a perforated pt tube within an outer au capsule containing wollastonite al 2 o 3 optionally powdered caf 2 and a nacl brine to simulate conditions where rutile is transformed into titanite by a hydrous ca si al f fluid driven by a chemical potential gradient between inner and outer capsule spontaneous nucleation of titanite is restricted to a small number of crystals on the rutile surface in the inner capsule growth proceeds from sparse isolated titanite crystals after 1 day to assemblages of several 100 m large crystals in a reaction rim in the long time runs titanite is strongly zoned in al ti and shows up to 0 5 al per formula unit pfu in experiments containing f without f substitution is limited to 0 25 al pfu the range of the ti al exchange is already large in short run times and the same heterogeneity is observed in long time runs the al ti distribution with and without f in compositional domains up to several tens of micrometers is patchy and irregular no relation of the zoning with time core rim or preferred growth directions was observed in the case of fluid mediated growth mineral growth zoning represents a disequilibrium at supersaturated conditions the concentration of ti in the fluid is likely the limiting factor for titanite growth considering the low solubility compared to that of al ca and si titanium is not transported in significant amounts into the outer capsule indicating low mobility in contrast to al ca and si which are transported into the inner capsule assuming buffered al concentration from dissolution of the al source we speculate that the ti al of the fluid at the precipitation site was controlled by the local ti concentration which varies over the distance from the rutile surface to the growing titanite crystal and produces the irregular patchy zoning

anatase nanoparticles on supergene platinum palladium aggregates from brazil titanium mobility in natural waters abstract supergene aggregates of platinum palladium pt pd intermetallic compounds from the corrego bom sucesso alluvial deposit minas gerais brazil are coated with abundant poorly crystalline nanoparticles of anatase tio 2 the anatase coating is widespread suggesting that the surface of the pt pd grains catalytically destabilised ti which was likely dissolved by organic ligands in the ground waters association of tio 2 nanocrystallites with organic matter further suggests that biogenic processes could have mediated their formation these anatase coated pt pd grains demonstrate an unexpected ti mobility in supergene environments

redistribution and mobilization of titanium zirconium and thorium in an intensely weathered lateritic profile in western australia abstract the mobility of titanium zirconium and thorium elements commonly considered insoluble during supergene weathering is still not well understood especially in intensely weathered regolith thus an intensely weathered lateritic profile jg developed on meta granitoids in jarrahdale western australia was investigated the mobility of ti zr and th has been assessed at both mineral assemblage and profile scales and the mode of occurrence has been investigated through the combined use of geochemical data from bulk regolith particle size fractions and sequential extractions with in situ data determined by electron probe micro analyzer and synchrotron x ray powder diffraction neoformed poorly crystalline phases containing trace to minor amounts of zr ce and th unassociated with silicates or phosphates were identified on the walls of al fe rich pores in the ferruginous duricrust this implies that some mobilization and redistribution of zr and th occurs within a sample scale breakdown of primary thorite and rare earth element rich fluorocarbonates is thought to be the source for zr and th in the neoformed phases rather than zircon thus the mineral hosts of zr ti and th in the parent rock and their relative susceptibility to weathering are the fundamental controls on subsequent mobility during initial weathering trace amounts of th in secondary phases such as rhabdophane and florencite show translocation of th at the mineral scale while strong partitioning of th into gravel rather than matrix reflects redistribution of th at the profile scale the absence of primary sphene from the regolith and the presence of partially dissolved ilmenite and rutile grains in the ferruginous mottled zone suggest mobilization and translocation of ti at a mineral assemblage scale furthermore the fluctuation of ti zr in the ferruginous zone is in contrast to the consistency of zr hf throughout the profile in general within the range of parent meta granitoid this suggests that ti and zr fractionate from each other and partition between gravel and matrix during extreme weathering and advanced lateritization this study demonstrates that ti zr and th are mobile at a variety of scales an important consideration that is often overlooked when calculating element mass flux in intensely weathered regolith