chloride bearing materials in the southern highlands of mars chlorides commonly precipitate during the evaporation of surface water or groundwater and during volcanic outgassing spectrally distinct surface deposits consistent with chloride bearing materials have been identified and mapped using data from the 2001 mars odyssey thermal emission imaging system these deposits are found throughout regions of low albedo in the southern highlands of mars geomorphologic evidence from orbiting imagery reveals these deposits to be light toned relative to their surroundings and to be polygonally fractured the deposits are small

trace elements ree and isotopes o c sr to characterize the metasomatic fluid sources evidence from the skarn deposit fe w cu of traversella ivrea italy the skarn complex of traversella was formed at the expense of various rock types calcic hornfels gneiss dolomitic marble occurring in the contact aureole of the dioritic intrusion of traversella 30 5 ma application of phase equilibria has fixed the temperature of the primary stage of skarn formation between 550 c to 625 c similar applications indicate a larger range of temperature 525 c to 300 c for the secondary stage the different types of skarn primary stage are enriched in ree relative to the corresponding precursor rock t r 126 ppm protolith to 228 ppm inner zone for the skarn on gneisses t r 14 ppm to 71 ppm for the skarn on calcic hornfelses t r 12 ppm to 200 ppm for the skarn on dolomitic marbles but all the inner zones of these different types of skarn show a similar ree distribution with a slight lree fractionation and no eu anomaly it is inferred that the primary metasomatic fluid has a parallel ree pattern the oxygen isotope composition of water in equilibrium with the early stage of skarn at t 600 c ranges from 8 3 per mil to 8 9 per mil at the beginning of the first hydroxylation stage secondary stage the fluid 18o remains in the range observed in the primary stage but within it there is a sharp decrease from 8 0 per mil to 5 0 per mil during the sulphidation stage the fluid 18o decreases more gradually from 5 0 per mil to 3 0 per mil the isr of the early skarn silicates ranges from the values observed in the dolomitic marbles 0 70874 to 0 70971 to the isr of the intrusion 0 70947 to 0 71064 during the secondary stage there is a progressive increase of the minerals isr up to 0 71372 the ree pattern of the primary metasomatic fluid does not put any precise constraint on the primary fluid source on the other hand both stable and radiogenic isotopes suggest that the early high temperature metasomatic fluid was isotopically equilibrated with the dioritic intrusion this implies that this early fluid is either exsolved from the crystallizing intrusion or a metamorphic water previously equilibrated with the intrusion during the secondary stage the replacement of the early anhydrous phases by hydrated parageneses is accompanied by the mixing with meteoric fluid as indicated by stable 18o and radiogenic 87sr 86sr isotopes

decoding the oxygen fugacity of ore forming fluids from garnet chemistry the longgen skarn pb zn deposit tibet abstract the relationship between the compositional zonation of garnet in skarn deposits and the evolution of physicochemical conditions of ore forming fluids is not clear and needs further investigation this study presents the characteristics of trace elements of garnet from the longgen skarn pb zn deposit tibet with an aim to reveal the evolution trend of the physical and chemical conditions fo2 and ph of ore forming fluids and to explore the fingerprint of garnet trace elements in different types of skarn deposits based on robust alteration halo mineral assemblages and petrographic observation the garnets of the longgen skarn pb zn deposit are divided into two types 1 distal exoskarn garnet near limestone with ore bearing and fine oscillatory zoning adr39 9 75 0 grt1 adr represents andradite and 2 proximal exoskarn garnet core adr32 9 70 7 rim adr83 3 99 5 with pb zn rich mineral and coarse oscillatory zoning grt2 according to the total rare earth element ree content in the garnet compositional zone grt1 is further divided into three component zones grt1 1 heavy rare earth element hree enriched chondrite normalized ree distribution patterns and positive eu anomaly eu 1 eu 2 eusample euchondrite smsample smchondrite gdsample gdchondrite grt1 2 hree enriched ree patterns with negative eu anomaly eu 1 similarly five component zones were identified in grt2 grt2 1 ree rich ree patterns with eu 1 and grt2 5 lree enriched ree patterns with eu the fractionation of lree with hree and the behavior of eu indicate that the physical chemical conditions during the formation of grt1 1 grt1 2 and grt2 1 grt2 3 were near neutral ph 6 7 and changed to mildly acidic in grt1 3 and grt2 4 grt2 5 ph

chemical composition genesis and exploration implication of garnet from the hongshan cu mo skarn deposit sw china abstract in this study we present new mineral chemical data on the garnet from the hongshan cu mo deposit one of the largest skarn deposits in the sanjiang tethyan tectonic domain in sw china the aims are to unravel the formation mechanism of the oscillatory zoned garnet at hongshan and to explore possible applications using garnet trace element to distinguish different types of skarn deposits two generations of garnets i e poorly zoned garnet i grt i and the well zoned garnet ii grt ii are identified from the endoskarn and exoskarn at hongshan based on field and petrographic observations epma and la icp ms analyses show that grt i contains a narrow compositional range adr40 07 61 25 grs36 65 57 08 and chondrite normalized hree enriched and lree depleted patterns with minor positive eu anomalies in contrast grt ii shows a wide compositional range adr27 78 67 53 grs30 67 70 92 to almost pure andradite adr94 41 99 99 grs0 00 4 21 with interlayered al rich and fe rich zones in grt ii its al rich zone is chemically similar to grt i whereas its fe rich zone exhibits chondrite normalized lree enriched and hree depleted patterns with distinct positive eu anomalies the positive ree3 vs mg correlations and the poor ree3 vs y and ca correlations altogether indicate that the ree3 incorporated into garnet was co influenced by the menzerite type substitution mechanism c a 2 1 v i i i r e e 3 1 v i i i a l 3 1 v i m g 2 1 v i fluid chemistry and the physicochemical conditions of precipitation the higher u contents and hree enriched patterns of grt i suggest that it was formed under a relatively reducing and near neutral ph condition varying u contents and ree patterns across different oscillatory zones indicate that grt ii was probably formed under alternating physicochemical fluctuations led by repeating crack seal cycles in the hydrothermal system besides chemical data compilation suggests that the garnet from different types of skarn deposits has different compositions and can be used as mineral prospecting tools we suggested that discrimination plots such as eu vs v and ce vs u can distinguish cu skarn deposit from other skarn deposit types whilst the u vs w plot can discriminate between cu w w sn and w mo skarn deposits

ages and petrogenesis of the late triassic andesitic rocks at the luerma porphyry cu deposit western gangdese and implications for regional metallogeny abstract the tibetan plateau is one of the most significant cu poly metallic mineralization regions in the world and preserves important information related to subductional and collisional porphyry cu mineralization this study investigates a new occurrence of cu mineralization related andesitic porphyries in the western domain of the gangdese magmatic belt and assesses its petrologic zircon u pb geochronology whole rock chemistry and sr nd hf pb isotope data zircon u pb dating of three ore related porphyries yields crystallization ages of 212 211 ma these ages are consistent with previous molybdenite re os dating indicating a late triassic magmatic and cu mineralization event in the western gangdese magmatic belt nb ta and ti depletion th and lree enrichment and high la yb and th yb ratios in addition to high u yb ratios from zircons suggest that the magma was generated in an active continental arc setting the porphyries have radiogenic isotopic compositions with 87sr 86sr i 0 70431 0 70473 end t 1 1 to 3 8 207pb 204pb i 15 601 15 622 and 208pb 204pb i 38 450 38 693 as well as high positive zircon ehf t values from 6 2 to 10 6 mean value 8 3 corresponding to model ages tdm ranging from 509 ma to 819 ma mean 646 ma this suggests that the andesitic magmatism was dominantly sourced from depleted mantle materials that were modified by subducted oceanic sediment derived melts during the subduction of the neo tethys ocean the mineralization related porphyries contain amphibole and epidote as well as high whole rock fe2o3 feo and zircon ce4 ce3 ratios suggesting hydrous and highly oxidized parent magmas considering the existing cu mineralization and highly oxidized magma of the well preserved triassic andesitic igneous rocks in the western gangdese belt the subduction related continental arc magma system is favorable for subduction related porphyry cu deposits the existence of luerma porphyry mineralization demonstrates that there are at least five generations of porphyry cu mo au mineralization in the gangdese magmatic belt which advances the timeframe of porphyry mineralization to the late triassic

trace metals in pyrite and marcasite from the agua rica porphyry high sulfidation epithermal deposit catamarca argentina textural features and metal zoning at the porphyry to epithermal transition abstract agua rica is a world class cu mo au deposit located in catamarca argentina in which the porphyry and high sulfidation epithermal stages are juxtaposed due to the telescoping of the mineralizing system pyrite is the most abundant sulfide in the analyzed section of the deposit and shows variations in textures and trace metal content determined by la icpms between the porphyry and epithermal stages pyrite from the porphyry stage is fine grained and depleted in most trace elements analyzed except for traces of co up to 276 ppm and ni up to 131 ppm pyrite from the epithermal stage is texturally complex compositionally heterogeneous and the trace metal content varies with depth and within sub stages of mineralization at an intermediate depth 2625 m epithermal pyrite from the cement of the jig saw and clast supported hydrothermal breccias are enriched in cu up to 2961 ppm that correlates with the highest cu grades in the section this pyrite contains micro inclusions of sulfosalt minerals as inferred by la icpms elemental mapping and individual spot ablation profiles they are zoned and show a co rich core an intermediate zone enriched in cu and an outer rim rich in zn at shallower levels 3000 m epithermal pyrite cements in the heterolithic hydrothermal breccia are unusually rich in trace metals that correlate with the highest pb zn au and ag grades the ore stage pyrite occurs as either successive colloform bands on earlier co bearing cores or as veinlets infill the colloform pyrite bands and veinlets are as poor

porphyry cu mo au deposits related to melting of thickened mafic lower crust examples from the eastern tethyan metallogenic domain abstract most porphyry cu deposits in the world occur in magmatic arc settings and are formed in association with calc alkaline arc magmas related to subduction of oceanic lithosphere this contribution reviews a number of significant porphyry cu deposits in the eastern tethyan metallogenic domain they widely occur in a variety of non arc settings varying from post late collisional transpressional and extensional environments to intracontinental extensional environments related to orogenic and anorogenic processes their spatial temporal localization is controlled by strike slip faults orogen transverse normal faults lineaments and their intersections in these non arc settings these deposits are dominated by porphyry cu mo deposits with minor porphyry cu au and epithermal au deposits and exhibit a broad similarity with those in magmatic arcs the associated magmas are generally hydrous relatively high fo2 high k calc alkaline and shoshonitic and show geochemical affinity with adakites they are distinguished from arc magmas and or oceanic slab derived adakites by their occurrence as isolated complexes high k2o contents 1 2 8 5 and much wider range of end t values 10 to 3 and positive ehf t values 4 6 to 6 9 these potassic magmas are most likely formed by partial melting of thickened juvenile mafic lower crust or delaminated lower crust but also involving various amounts of asthenospheric mantle components key factors that generate hydrous fertile magmas are most likely crust mantle interaction processes at the base of thickened lower crust in non arc settings rather than oceanic slab dehydration as in arc settings breakdown of amphibole in thickened lower crust e g amphibole eclogite and garnet amphibolite during melting is considered to release fluids into the fertile magmas leading to an elevated oxidation state and higher h2o content necessary for development of porphyry cu mo au systems copper and au in hydrous magmas are likely derived from mantle derived components and or melts which either previously underplated and infiltrated at the base of the thickened lower crust or were input into the primitive magmas by melt mantle interaction in contrast mo and part of the s in the fertile magmas are probably supplied by old crust during melting and subsequent ascent

metallogenesis and the minerogenetic series in the gangdese polymetallic copper belt abstract the gangdese is a newly explored porphyry cu ore belt in china in fact except for the porphyry cu deposits there are a lot of other deposits forming a polymetallic copper belt in the southern gangdese sg i e southern lhasa terrane and gangdese back arc fault uplift belt gbafub also called lungar nyainqentanglha arc the gangdese polymetallic copper belt contains porphyry cu mo au cu au and mo cu skarn cu mo au w pb zn ag fe cu and mo w breccia type and hydrothermal vein type pb zn ag deposits the porphyry cu au mineralization occurred at the xiongcun area of sg during the middle jurassic 175 160 ma and was associated with island arc magmatism related to the northward subduction of the neo tethyan oceanic slab the cretaceous ca 112 ma skarn fe cu mineralization appeared at the nixiong area of gbafub and was generated in a back arc extensional setting related to the neo tethyan oceanic subduction beneath the lhasa terrane the paleocene eocene 65 51 ma porphyry mo cu skarn mo w and skarn pb zn ag deposits are located in the eastern part of gbafub and related to granitoids originating from the partial melting of the old crust with contributions from the mantle in contrast the paleocene eocene 60 45 ma porphyry cu skarn breccia and hydrothermal vein type pb zn ag and skarn fe cu deposits at the namling area were associated with granitoids derived from the partial melting of the mantle with some input of the old crust the oligocene 30 23 ma porphyry skarn cu mo w au mineralization occurred at the zedong area adjacent to north of the indus yarlung zangbo suture zone in a post collisional setting the intensified miocene 21 13 ma porphyry skarn cu mo au and skarn hydrothermal vein type pb zn ag deposits formed in the sg whereas the porphyry mo cu and skarn hydrothermal vein type pb zn ag deposits formed in the gbafub the porphyry mo cu mineralization have more substantial contributions from the old crust in addition to the mantle than those with porphyry cu mo au mineralization the source region of the high sr y intrusions associated with post collisional porphyry cu mo au mineralization is probably the arc magmas that were generated at the subduction stage and have remained stalled at the boundary between the crust and mantle since the neo tethyan ocean closed the early subduction of the neo tethyan oceanic lithosphere played a crucial role in the generation of ore deposits formed in collisional and post collisional settings six minerogenic series or groups can be recognized in the gangdese polymetallic copper belt 1 jurassic porphyry cu au minerogenic series related to island arc magmatism 2 cretaceous skarn fe cu minerogenic series in back arc extensional setting 3 paleocene eocene granitoids related polymetallic minerogenic series in collisional setting 4 oligocene porphyry skarn cu w mo au minerogenic series in post collisional setting 5 miocene cu mo au pb zn ag minerogenic series related to granitoids with substantial contributions from the mantle in post collisional setting and 6 miocene mo cu pb zn minerogenic series related to granitoids with significant contributions from the old crust in post collisional setting during mineralization some deposits underwent superimposed mineralization such as the jiru porphyry cu deposit where the eocene and miocene porphyry type cu mineralization occurred the minerogenic series can be applied to ore prospecting for example when either pb zn ag veins or porphyry skarn mo w cu orebodies are known in an area one of them could provide a useful exploration vector for the other

zonation patterns of skarn garnets records of hydrothermal system evolution chemically zoned skarn garnets provide a continuous record of hydrothermal processes in lower paleozoic sedimentary rocks within the contact aureole around the drammen granite in the oslo rift southern norway major and trace element zonation profiles the latter obtained using a scanning high resolution proton microprobe reveal early infiltration controlled growth of relatively grossular rich garnets the major and trace elements compositions being buffered by local mineral dissolution subsequent rapid epitaxial growth of andradite rich garnet on grossular rich cores marks the onset of vigorous and focused fluid flow along high permeability zones during this later stage the hydrothermal fluid composition was to a large extent externally controlled and the andradite precipitating from these fluids was characterized by high as and w contents the zonation patterns of the andradite rich garnets record at least five intermittent growth periods with rapid andradite precipitation from fluid batches with high f o 2 and progressively decreasing as and w contents thin layers poor in fe as and w but relatively high in al and mn represent periods of slow growth rates between the major pulses of hydrothermal fluids the marked rimward decrease in the as and w contents of the garnets may reflect influx of meteoric waters or exhaustion of these elements in the hydrothermal fluid reservoir caused by boiling controlled distillation processes at depth

from magmatic generation to uhp metamorphic overprint and subsequent exhumation a rapid cycle of plate movement recorded by the supra subduction zone ophiolite from the north qaidam orogen abstract the rapid subduction and exhumation of high pressure hp and ultrahigh pressure uhp rocks exposed in collisional belts play a critical role in understanding the evolution of geodynamics and plate tectonics in subduction zone environments herein ophiolitic fragments eclogites and amphibolites from a subduction channel exposed in the dulan terrane north qaidam orogen were investigated garnet compositional zoning from the studied eclogites records only a single cycle of subduction and exhumation new uranium lead u pb zircon ages of the current study combined with previous rutile u pb ages from eclogites indicate a rapid cycle of events starting with the generation of the magmatic protolith at ca 446 ma its subsequent subduction reaching a depth of ca 100 110 km at ca 435 ma and its exhumation into shallow portions of the crust which occurred at ca 416 ma thus a rapid 30 million years myr protolith generation subduction exhumation cycle could be recorded according to an ophiolitic rock association with island arc basalt iab like and mid ocean ridge basalt morb to ocean island basalt oib like trace element compositions the slab derived components determined by sr nd hf isotopes and the short time span of only about 11 myr between photolith generation and uhp metamorphism in eclogites the protolith of eclogite is best explained as a supra subduction zone ophiolite this finding likely records the closure of the south qilian ocean and the initiation of a continent arc collision at ca 446 ma furthermore starting with subduction erosion during continent arc collision in the early palaeozoic ophiolitic and arc related materials become subducted in the north qaidam it was inferred that such a rapid succession of events from protolith formation to uhp overprint and final exhumation could be explained by movements of rock material in a subduction channel thus this study provides a new view in understanding the mechanics of different episodes of subduction systems in north qaidam uhp metamorphic belt

the rare earth elements and uranium in garnets from the beinn an dubhaich aureole skye scotland uk constraints on processes in a dynamic hydrothermal system garnets from skarns in the beinn an dubhaich granite aureole isle of skye scotland have a large range of concentrations of uranium 0 2 358 ppm and the rare earth elements ree 23 4724 ppm variations in these concentrations correlate with major element zonation within the garnets and with changes in the shape of ree patterns typical patterns in most garnets display light ree lree enrichment flat heavy ree hree distribution and a negative eu anomaly these patterns are interpreted to represent equilibrium trace element exchange between pre existing pyroxene hydrothermal fluid and calcic garnets iron rich zones are characterized by positive eu anomalies and an increase in the abundance of the lree relative to the hree these patterns are interpreted as resulting from changes in ree speciation related to the introduction of externally buffered fluid to the skarn system relatively fe poor zones show strongly hree enriched patterns with negative eu anomalies and in some instances depletions in y relative to ho and dy which are interpreted as resulting from surface sorption of the ree during rapid disequilibrium garnet growth strong correlations between u abundance and the ree patterns indicate that the same processes have affected u distribution both types of pattern can be modified by the effects of closed system crystallization on ree abundance in the fluid and changes in fluid major element chemistry

thermal inertia mapping of mars from 60 s to 60 n twenty micrometer brightness temperatures are used to derive the thermal inertia for 81 of the martian surface between latitudes 60 these data were acquired by the two viking infrared thermal mappers in 1977 and 1978 following the two global dust storms of 1977 the spatial resolution used is 2 in latitude by 2 in longitude and the total range in derived inertia is 1 to 15 10 3 cal cm 2 sec 12 k 1 the distribution of thermal inertia is strongly bimodal with all values of thermal inertia less than 4 10 3 cal cm 2 sec 12 k 1 being associated with three disjoint bright regions mostly in the northern hemisphere sufficient dust is raised in global storms to provide fine material adequate to produce these low inertia areas but the specific deposition mechanism has not been defined at the low resolution used no complete exposures of clean rock were found there is some tendency for darker material to be associated with higher thermal inertia although the trend is far from one to one the distribution of high and low inertia areas is sufficiently nonrandom to produce a variation in whole disk brightness temperature with central meridian longitude this variation and the change in surface kinetic temperature associated with dust storms are factors in establishing the whole disk brightness temperature at radio and infrared wavelengths and will be important for those who use mars as a calibration source

oscillatory zoning in skarn garnet implications for tungsten ore exploration abstract the sangdong and weondong deposits taebaeksan mineral district south korea are tungsten skarn ore deposits andradite fe rich garnet is a characteristic mineral in these skarn deposits and is characterized by notable trace element contents w mo sn and u compared to grossular al rich garnet we report characteristics of the trace elements including w in the garnet structure from the vein skarn system outermost exoskarn and identify a relationship of exploration significance between the trace element composition and w ore the chemical characteristics of the garnets were determined using back scattered electron bse imagery electron probe micro analyzer epma point analyses and x ray dot mapping and laser ablation inductively coupled plasma mass spectrometry la icpms point analyses and mapping garnets in the study area are mainly composed of grandite grossular andradite garnets and exhibit compositional variation as oscillatory zoning the chondrite normalized ree patterns of al rich garnets are hree enriched in contrast fe rich garnets are lree enriched tungsten is strongly fractionated into the fe rich garnets average concentration 618 ppm compared to the al rich rims average concentration 19 ppm in addition other trace elements mo sn and u are also closely correlated with w and ree signatures the fe rich garnets are attributed to rapid growth by infiltration metasomatism during disequilibrium which caused the incorporation of these trace elements into the garnet structure that reflect the composition of the ore forming fluid consequently these results indicate that andradite is a useful indicator mineral in the exploration of tungsten ore deposits

rare earth element systematics in hydrothermal fluids abstract rare earth element concentrations have been measured in hydrothermal solutions from geothermal fields in italy dominica valles caldera salton sea and the mid atlantic ridge the measured abundances show that hydrothermal activity is not expected to affect the ree balance of either continental or oceanic rocks the ree enrichment of the solutions increases when the ph decreases high temperature solutions 230 c percolating through different rock types may show similar ree patterns

geochronology and geochemical characteristics of ore bearing porphyry in longgen lead zinc deposit of middle gangdese metallogenic belt tibet located in the middle section of the middle gangdese metallogenic belt the longgen porphyry skarn deposit is a recently discovered deposit in tibet however the high precision chronologic data of porphyritic intrusion and deposit are absent the zircon u pb ages are reported in this study based on whole rock major elements trace elements and zircon sr nd hf isotopic data of the ore bearing rocks in the longgen deposit the authors obtained for the first time the ore forming age of the middle section of the middle gangdese metallogenic belt zircon u pb ages of the granitic porphyry are divided into two groups 70 5 ma and 61 4 ma with the former probably recording an earlier magmatic fluid activity related to the initial collision of indian asian continent and the latter representing magmatic crystallization related to the extensional environment in the back arc of the active continent the ore bearing porphyry of the longgen deposit has high sio2 k2o rb th and u content and low tio2 p2o5content as well as strong negative anomalies of zr nd and sm variable ehf t 3 34 1 12 and ancient tcdm 1 06 1 19 ga in comparison with gangdise continental crust the ore bearing porphyry of the longgen deposit has high end t 3 34 1 12 and low 87sr 86sr i 0 708 026 0 709 071 these geochemical features suggest that the samples from the longgen deposit belong to the peraluminous s type granite the authors hold that the late cretaceous paleocene magmatism and mineralization in the middle section of the middle gangdese metallogenic belt might have been produced by partial melting of ancient crust materials of the gangdese micro continent accompanied by fractional crystallization resulting probably from underplating of mantle derived magmas in the epicontinental back arc extensional environment and the main collision setting of the collision between indian and eurasia

garnets in porphyry skarn systems a la icp ms fluid inclusion and stable isotope study of garnets from the hongniu hongshan copper deposit zhongdian area nw yunnan province china abstract the late cretaceous hongniu hongshan porphyry skarn copper deposit is located in the zhongdian area of northwestern yunnan province china garnets from the deposit have compositions that range from adr14grs86 to almost pure andradite adr98grs2 and display two different styles of zoning the garnets are predominantly of magmatic hydrothermal origin as is evidenced by their 18ofluid 5 4 6 9 and low dfluid 142 to 100 values both of which likely result from late stage magmatic open system degassing three generations of garnet have been identified in this deposit 1 al rich garnets grt i adr22 57grs78 43 are anisotropic have sector dodecahedral twinning are slightly enriched in light rare earth elements lrees compared with the heavy rare earth elements hrees have negative or negligible eu anomalies and contain high concentrations of f fluid inclusions within these al rich garnets generally have salinities of 12 39 wt nacl eq and have liquid vapor homogenization temperatures th of 272 331 c the grt i are most likely associated with low to medium salinity fluids that were generated by the contraction of an ascending vapor phase and that formed during diffusive metasomatism caused by pore fluids equilibrating with the host rocks at low w r water rock ratios these garnets formed as a result of the high f activity of the system which increased the solubility of al within the magmato hydrothermal fluids in the system 2 fe rich garnets adr75 98grs25 2 have trapezohedral faces and are both anisotropic with oscillatory zoning and isotropic these second generation fe rich garnets grt ii have high ree concentrations are lree enriched and hree depleted and generally have positive but variable eu anomalies all of the fe rich garnets contain high salinity fluid inclusions with multiple daughter minerals with salinities of 33 80 wt nacl eq some of them show higher temperatures of halite dissolution 465 591 c than liquid vapor homogenization temperatures 319 473 c and several fe rich garnets contain inclusion groups indicative of boiling the grt ii are associated with high temperature hypersaline fluids that were segregated from magma at a depth of at least 5 6 km and reacted with carbonates at depths shallower than 2 0 km 3 al rich garnet veins adr14 60grs86 40 contain allotriomorphic crystals have lower hfse high field strength element and ree concentrations than the other garnets and have hree enriched and lree depleted patterns with small eu anomalies that are typical of the majority of garnets the grt iii most likely formed from residual metasomatic fluids

la icp ms trace element geochemistry of garnets constraints on hydrothermal fluid evolution and genesis of the xinqiao cu s fe au deposit eastern china abstract the xinqiao cu s fe au deposit in the tongling ore district an important part of the middle lower yangtze river valley metallogenic belt in eastern china is located along the northern margin of the yangtze block the deposit consists of two major mineralization types stratiform and skarn the genesis of the former is disputed the more important stratiform orebody 90 of the total cu s and fe reserves has abundant garnet as the main gangue mineral similar to the skarn orebody hosted in the intrusive contact garnets from the xinqiao stratiform orebody range from pure andradite and 100 to and 50 gro 46 and can be divided into the early grt1 and late grt2 generation both generations contain low mno 0 19 0 89 wide range of y ho 39 0 40 7 for grt1 29 8 67 9 for grt2 and do not contain melt or fluid melt inclusions indicative of a magmatic hydrothermal replacement origin grt1 and the grt2 cores are grandite whilst the grt2 rims are mainly andradite with some grandite zones grandite is enriched in heavy rare earth elements hrees and displays low lree hree la n yb n and u concentrations with negative eu anomalies whereas andradite is hree depleted and displays high lree hree la n yb n ratios and u concentrations with positive eu anomalies the distinct trace element features suggest that the hydrothermal fluids for grt1 and the grt2 cores were of nearly neutral ph relatively oxidized and hree enriched whereas those for the grt2 rims had experienced episodic inflections between a mildly acidic relatively reduced and hree depleted fluid and a nearly neutral relatively oxidized and hree enriched fluid meanwhile they also reveal that grt1 and the grt2 cores may have formed by diffusive metasomatism in a closed system whereas the grt2 rims may have formed by infiltration metasomatism in an open fracture system possibly related to the unconformity that hosts the xinqiao stratiform orebody we propose that the xinqiao stratiform orebody may have formed from early cretaceous magmatic hydrothermal fluids associated with the jitou stock similar to the skarn type orebodies in the district

fluvial landscape development in the southwestern kalahari during the holocene chronology and provenance of fluvial deposits in the molopo canyon the southern kalahari drainage network is in a key position to analyze spatiotemporal changes in the tropical easterly and the temperate westerly circulation over the southern african subcontinent however due to the prevailing aridity paleoenvironmental archives within the southwestern kalahari are sparse and often discontinuous hence little is known about holocene environmental change in this region this study focuses on reconstructing paleoenvironmental change from the timing and provenance of fluvial deposits located within the molopo canyon which connects the southern kalahari drainage to the perennial flow regime of the orange river to gain insight into temporal aspects of fluvial morphodynamics within the molopo canyon the entire variety of fluvial landforms consisting mainly of slope sediments alluvial fans and alluvial fills were dated using optically stimulated luminescence osl we additionally applied a provenance analysis on alluvial fill deposits to estimate potential sediment source areas source areas were identified by analyzing the elemental and mineralogical composition of tributaries and eolian deposits throughout the course of the lower molopo the results allow the first general classification of fluvial landscape development into three temporally distinct deposition phases in the southern kalahari 1 a phase of canyon aggradation associated with short lived and spatially restricted flash floods during the early to mid holocene 2 a phase of fan aggradation indicating a decrease in flood intensities during the mid to late holocene and 3 a phase of canyon aggradation caused by the occurrence of supra regional flood events during the little ice age we interpret the observed spatiotemporal deposition patterns to latitudinal shifts of the tropical easterly circulation in the early to mid holocene and the temperate westerly circulation in the late holocene however despite marked changes in the provenance and timing of fluvial deposits in the molopo canyon throughout the holocene our analysis did not detect a contribution of sediments originating from the kalahari interior to the deposition of alluvial fills these results suggest that the southern kalahari drainage remained endorheic and therefore disconnected from the orange river throughout the holocene

the lhasa terrane record of a microcontinent and its histories of drift and growth article i nfo the lhasa terrane in southern tibet has long been accepted as the last geological block accreted to eurasia before its collision with the northward drifting indian continent in the cenozoic but its lithospheric architecture drift and growth histories and the nature of its northern suture with eurasia via the qiangtang terrane remain enigmatic using zircon in situ u pb and lu hf isotopic and bulk rock geochemical data of mesozoic early tertiary magmatic rocks sampled along four north south traverses across the lhasa terrane we show that the lhasa terrane has ancient basement rocks of proterozoic and archean ages up to 2870 ma in its centre with younger and juvenile crust phanerozoic accreted towards its both northern and southern edges this finding proves that the central lhasa subterrane was once a microcontinent this continent has survived from its long journey across the paleo tethyan ocean basins and has grown at the edges through magmatism resulting from oceanic lithosphere subduction towards beneath it during its journey and subsequent collisions with the qiangtang terrane to the north and with the indian continent to the south zircon hf isotope data indicate significant mantle source contributions to the generation of these granitoid rocks e g 50 90 0 70 and 30 100 to the mesozoic magmatism in the southern central and northern lhasa subterranes respectively we suggest that much of the mesozoic magmatism in the lhasa terrane may be associated with the southward bangong nujiang tethyan seafloor subduction beneath the lhasa terrane which likely began in the middle permian or earlier and ceased in the late early cretaceous and that the significant changes of zircon ehf t at 113 and 52 ma record tectonomagmatic activities as a result of slab break off and related mantle melting events following the qiangtang lhasa amalgamation and india lhasa amalgamation respectively these results manifest the efficacy of zircons as a chronometer u pb dating and a geochemical tracer hf isotopes in understanding the origin and histories of lithospheric plates and in revealing the tectonic evolution of old orogenies in the context of plate tectonics

pulsed magmatic fluid release for the formation of porphyry deposits tracing fluid evolution in absolute time from the tibetan qulong cu mo deposit the magmatic hydrothermal evolution of porphyry style mineralization in the shallow crust that is linked to magmatic processes at depth has been extensively studied using bulk sample isotopic analysis combined with relative timing constraints however a lack of evaluation of the fluid evolution process against an absolute time frame limits further understanding of the ore forming process here we quantify the fluid evolution process within an absolute time frame for the first time by integrating new in situ oxygen isotope data from the qulong porphyry cu mo deposit tibet with existing fluid inclusion data and high precision re os dates of co precipitated hydrothermal quartz and molybdenite respectively we demonstrate that vein quartz records primary oxygen isotopic compositions and reached oxygen isotope equilibrium with ore forming fluids and therefore is an archive of the isotopic composition and source of the ore forming fluids the 18oquartz and 18ofluid values in absolute time show periodic fluctuations that indicate the presence of three intermittent pulses of magmatic fluid flux which have been balanced by meteoric water as such the flux of magmatic fluid during ore formation was pulsed rather than being continuous the overall highest 18ofluid in the first pulse of mineralization with a gradual decrease to the second and third pulses is suggestive of a progressive reduction in the magmatic component of the hydrothermal fluids and by inference the mineralizing potential of the hydrothermal fluids this view is supported by a decrease in sulfide bearing fluid inclusions and metal grade through time our findings favor multiple fluid release events from a single cooling magmatic reservoir although multiple fluid melt recharge events remain a competitive alternative an additional implication is that the magmatic reservoir may have a lifespan of hundreds of thousands of years with fluid release events occurring over tens of thousands of years

geology mineral chemistry and formation conditions of calc silicate minerals of astamal fe lree distal skarn deposit eastern azarbaijan province nw iran the astamal fe lree skarn deposit is the largest iron skarn in nw iran it is a unique case as a distal skarn deposit which crops out approximately 600 m from the associated oligo miocene granodioritic pluton this deposit formed in the south southwest of the pluton where fractures and faults within the upper cretaceous volcano sedimentary host rocks acted as conduits for the mineralizing fluids the deposit contains three iron ore bodies southern northern and eastern the main mineral assemblage within the ore zones is characterized by magnetite pyrrhotite and pyrite with lesser quantities of chalcopyrite hematite goethite and limonite the skarn minerals predominantly comprise garnet epidote actinolite calcite quartz clinopyroxene and chlorite in order of abundance retrograde alteration is strongly developed in the skarn zone where most of the garnet has been pervasively altered to secondary minerals e g epidote calcite and quartz both in the rims and the cores whereas the majority of the clinopyroxene has been replaced by a hydrous retrograde mineral assemblage e g tremolite actinolite and chlorite garnets with andradite grossular compositions are the dominant mineral in the skarn zone which are generally isotropic with a narrow compositional range along the growth lines adr94 3 64 5grs21 9 2 7alm11 1 0 2 these garnets are fe rich and have high fe fe al ratios between 0 96 and 0 78 cu and ni are enriched in the garnets this suggests that these elements were enriched in the hydrothermal fluids from which the garnet precipitated this is supported by the presence of chalcopyrite and ni bearing massive magnetite in the study area which also suggests that cu and ni were enriched in the late stage ore bearing hydrothermal fluids clinopyroxene with a hedenbergitic composition is generally homogenous and has particularly high fe fe mg ratios between 0 99 and 0 86 and is poor in tio2 mno and cr2o3 high zn concentrations were also detected in the clinopyroxenes up to 1044 ppm despite an absence of significant zn mineralization such as sphalerite in the district therefore it is believed that the proportion of zn in the hydrothermal fluids decreased significantly from the time of clinopyroxene formation to the period of the sulfide deposition phase allanite and lree bearing epidotes are the main lree bearing minerals in this deposit the epidote is also fe rich with high fe fe al ratios between 0 32 and 0 44 due to a lack of replacement texture between both garnet and clinopyroxene and garnet and actinolite which is formed by alteration of clinopyroxene it is believed that these two minerals have grown simultaneously and are coexisting minerals in the astamal skarn these minerals can be stable and coexisting at temperatures between 490 and 560 c and log o2 16 to 31

garnet and scheelite as indicators of multi stage tungsten mineralization in the huangshaping deposit southern hunan province china abstract the huangshaping w mo pb zn deposit in southern hunan province south china contains multiple generations of garnet and scheelite in skarn and sulfide carbonate altered rocks optical characteristics and chondrite normalized rare earth element reen patterns obtained by in situ laser ablation inductively coupled plasma mass spectrometry analysis were used to distinguish different generations of garnet and scheelite these data show a clear correspondence of garnet reen patterns to major element zonation with hrees e g gd lu being depleted overall coarse grained garnets in the huangshaping deposit have extreme hree depletions and significant lree e g la eu enrichment particularly for ce pr and nd this indicates that rees in these garnets are the result of coupled substitutions ca2 viii 1 ree3 viii 1 and fe2 iv 1 al3 iv 1 medium grained garnets have reen patterns showing significant lree enrichment and depleted hrees with high sn contents this suggests that substitution of rees in these garnets occurs as ca2 viii 1 ree3 viii 1 sn4 iv 1 al3 iv 1 the fact that medium grained garnets have high sn contents indicates mineralizing fluids were oxidizing which is consistent with significant positive eu anomalies however hump shaped reen patterns for garnet rims suggest substitution by ca2 viii 2 na viii 1 ree3 viii 1 where nd tb are preferentially incorporated into the garnet lattice over other rees group 1a scheelite has black cores in cathodoluminescence images and reen patterns showing extreme lree enrichment and hree depletion group 1b scheelite has cores with fine oscillatory zoning and enriched lrees with depleted hrees similar to the reen patterns of group 2a scheelite that occur as rims with bright cl surrounding both group 1a and 1b scheelite the substitution mechanism for rees in these three types of scheelite is ca2 viii 3 viii 1 ree3 viii 2 with being a ca site vacancy the influence of ree speciation in the hydrothermal fluid dominates the reen patterns of these types of scheelite however for group 2b bright rims of scheelite rees are incorporated as ca2 viii 2 na viii 1 ree3 viii 1 similar to the garnet rims finally scheelite mo contents and eu values that decrease from group 1a to 2b support a temporal decrease in oxygen fugacity of the mineralizing fluids ratios of y ho and mo contents that decrease from group 1a and 1b to group 2a and 2b scheelites are similar to those in porphyry related skarn w mo and quartz vein au w deposits respectively our studies also suggest that all these scheelites in this deposit formed from magmatic fluids at the huangshaping deposit medium grained garnets associated with group 1a scheelite precipitated from evolved magmatic fluids during prograde metamorphism as indicated by their complementary y ho ratios paragentically younger scheelite particularly group 2b may have formed from dilute magmatic fluids that underwent large scale hydrothermal circulation the characteristics of group 1b and 2a scheelite likely reflect a transitional environment and fluid mixing during tungsten mineralization in the polymetallic huangshaping deposit

a mechanism for na incorporation in garnet an example from garnet in orthogneiss from the su lu terrane eastern china sodian and yttrian na y garnet occurs in orthogneisses of the su lu terrane of eastern china with major quartz microcline and albite and subordinate biotite titanite hematite and zircon acmite rich pyroxene muscovite epidote allanite and hastingsitic amphibole occur in a few of the samples the na y garnet can be divided into almandine spessartinegrossular ai 1 6 per formula unit pfu for 0 12 hereafter denoted as ai garnet and andradite spessartine feh 1 3 pfu hereafter denoted as feh garnet groups average composition of the ai garnet in each sample ranges from alm3ssps13prp grs49adr2 to aim2lsps67prpogrssadr7 the feh garnet contains a calderite component cdr and its composition is alm4 7spslo 2 prp 2adrs9 8 cdr3 12 na y and yb contents of the ai rich garnet reach 0 37 1 46 and 0 42 oxide wt respectively and na y yb 0 99 t 0 16 the feh garnet contains up to 0 11 2 1 and 0 48 wt of na20 y203 and yb203 respectively and its na y yb value 0 17 t 0 1 is lower than that of the ai garnet we conclude that na y and yb are incorporated in the ai rich garnet by the 8jna 8j y yb ca mn 2substitution whereas in the feh garnet y and yb are dominantly incorporated by the 8j y yb l4j ai feh ca mn sl substitution with up to 3 mol y yb for ca mn comparison ofna y yb of garnets in the orthogneisses and in some pegmatites implies that increasing pressure favors incorporation of na with y and yb and that under the albite epidote amphibolite facies or higher pressure conditions y and yb probably substitute into the garnet structure by 8jna 8j y yb ca mn 2 instead of the 8j y yb 4j al feh ca mn sl type substitution effective under lower pressure conditions

geochemical investigation of early cretaceous igneous rocks along an east west traverse throughout the central lhasa terrane tibet article i nfo bulk rock major and trace element sr nd isotope zircon u pb and hf isotope data are reported for early cretaceous igneous rocks sampled along an east west traverse through the central lhasa subterrane e80 00 e89 in southern tibet these results offer new insights into the pre cenozoic geology and tectonomagmatic evolution of the lhasa terrane and provide boundary conditions for the origin and evolution of the tibetan plateau our new data together with data from the literature indicate that the early cretaceous magmatism in the central lhasa subterrane lasted for a long period 143 102 ma with a magmatic flare up at 110 ma the latter is accompanied by mafic magmatism in this terrane the silicic rocks are metaluminous to peraluminous and enrichedinrb th and u and depleted inba nb ta sr p and ti withvarying initial 87

syn collisional magmatism at the longgen pb zn deposit western nyainqentanglha belt tibet petrogenesis and implications for regional polymetallic metallogeny abstract syn collisional orogeny generally lacks adequate fluids and has a low potential to form magmatic hydrothermal ore deposits however some syn collisional pb zn deposits have been recognized in the nyainqentanglha polymetallic belt npb central lhasa subterrane and ore related magma petrogenesis and the metallogenic geodynamic setting is limited in this study detailed petrology geochemical and geochronological data of ore related syn collisional granite porphyries are evaluated to constrain the timing of mineralization and discuss the genesis and evolution of ore related magma using the longgen skarn pb zn deposit as a case study zircon u pb dating of ore related porphyries provides a weighted mean age of 61 2 0 8 ma which is slightly earlier than the sphalerite rb sr age of 59 1 3 0 ma indicating that a paleocene pb zn mineralization event occurred during syn collisional orogeny the porphyries have high sio2 k2o na2o and are enriched in rb th u pb lrees and a cnk 0 94 1 15 but have low p2o5 and are depleted in nb ta and ti this suggests that the longgen granite porphyries are metaluminous to weakly peraluminous high k calc alkaline arc like granites these porphyries have highly radiogenic isotopic compositions with 87sr 86sr i 0 709513 0 713587 207pb 204pb i 15 657 15 713 and 208pb 204pb i 38 964 39 163 but low end t values from 6 7 to 6 0 as well as negative zircon ehf t values from 5 1 to 3 2 corresponding to tdm2 nd ages of 1 37 to 1 42 ga and zircon hf tdmc ages of 1 30 to 1 42 ga this demonstrates that the longgen granite porphyries may have been generated by the partial melting of mesoproterozoic basement continental crust materials with significant amounts 30 50 of mantle derived melt input paleocene eocene 65 45 ma magmatic rocks associated with pb zn and fe cu deposits are compiled in the npb the pb zn ore related granitoids have relatively lower whole rock end t and zircon ehf t values higher 87sr 86sr i values and older tdmc ages than the coeval granitoids associated with fe cu mineralization this indicates that mantle material is more critical for the development of fe cu ore related granitoids than granitoids associated with pb zn mineralization the final results show that different sources of paleocene eocene syn collisional magma in the npb are beneficial for different mineralization events during the syn collisional orogeny of the indian and asian plates