fluid inclusion and stable isotope studies at the chicote tungsten deposit bolivia the chicote tungsten deposit is situated along a major north northwest to south southeast structural trend in lower paleozoic sediments of the eastern cordillera of bolivia kami and amutara are ore deposits similar to chicote they occur along the same structural trend over a distance of 35 km no igneous rocks are exposed in the vicinity of these mines the tungsten bearing veins at chicote are restricted to a zone of pervasive hydrothermal alteration extending over an area of 3 250 by 1 000 m with a vertical range of over 1 600 m whole rock k ar dating of the sericite rich wall rock indicates a maximum age of 26 1 m y for the mineralization the mineral paragenesis follows an oxide sulfide carbonate sequence peripheral to the tungsten mineralization is a zone of tin bearing veins fluid inclusion studies demonstrate that the ore fluids are complex brines with salinities of 5 to 48 equiv wt percent nacl and trapping temperatures of 195 degrees to 530 degrees c the salinities and temperatures of the fluids display a progressive decrease with time stable isotope analyses for delta 18 o and delta d on vein quartz and siderite suggest that the mineralizing fluids were magmatic in origin despite strong similarities in mineralogy between chicote and other tungsten deposits such as panasqueira in portugal and pasto bueno and san cristobal in peru there are important differences the ore fluids were far more saline than the typical worldwide trend and were dominantly magmatic the distal setting of the chicote mineralization from the parent felsic intrusion is explained by migration of ore fluids along the major amutara chicote kami structural feature the hypersaline chicote ore fluids provided a suitable medium for the transport of tungsten and precipitation was probably caused by a decrease in temperature and pressure

fluid inclusion study of xihuashan tungsten deposit in the southern jiangxi province china the xihuashan tungsten deposit is closely related to a small highly evolved granitic intrusion the fluid phases associated with the wolframite bearing quartz veins have been investigated using microthermometry and the raman microprobe they are highly variable in density and composition the earlier fluids are low density and low salinity co2 bearing aqueous solutions circulating at temperatures up to 420 c and low salinity 2 3 equiv wt nacl aqueous solutions without traces of co2 circulating at high temperatures 280 400 c involved in a specific hydrothermal fracturing event limited unmixing occurs at 380 c and 200 100 bar in response to a sudden pressure drop the second types of fluids related to deposition of idiomorphic drusy quartz are typical co2 bearing aqueous solutions with low salinity 2 5 equiv wt nacl homogenizing at low to moderate temperatures 180 340 c the late fluids characterize the sulfide deposition stage they are aqueous fluids with variable salinities homogenizing in the liquid phase between 100 and 275 c the xihuashan hydrothermal evolution resulted from a discontinuous sequence of specific events occurring between 420 and 150 c and during a continuous hydrothermal evolution of the system during cooling the role played by the co2 rich fluids in the transport and deposition of tungsten in the hydrothermal environment is discussed

neoproterozoic adakitic plutons in the northern margin of the yangtze block china partial melting of a thickened lower crust and implications for secular crustal evolution abstract numerous neoproterozoic felsic and mafic ultramafic intrusions occur in the hannan region at the northern margin of the yangtze block among these the wudumen and erliba plutons consist of granodiorites and have shrimp zircon u pb ages of 735 ma the rocks have high k 2 o 0 8 3 6 wt and na 2 o 4 4 6 4 wt and low mgo 0 4 1 7 wt they also have high sr y 32 209 and la yb n ratios 4 4 38 6 their e nd values range from 0 41 to 0 92 and zircon initial 176 hf 177 hf ratios from 0 282353 to 0 282581 these geochemical features are similar to those of adakitic rocks produced by partial melting of a thickened lower crust our new analytical results combined with the occurrence of voluminous arc related mafic ultramafic intrusions emplaced before 740 ma lead us to propose that the crustal evolution in the northern margin of the yangtze block during neoproterozoic involved 1 rapid crustal growth and thickening by underplating of mafic magmas from the mantle which was modified by materials coming from the subducting oceanic slab from 1 0 to 0 74 ga and 2 partial melting of the thickened lower crust due to a thermal anomaly induced by upwelling of asthenosphere through an oceanic slab window producing the 735 ma adakitic wudumen and erliba plutons our model suggests that the crustal thickness was more than 50 km at the northern margin of the yangtze block at 735 ma and rule out the possibility of a mantle plume impact causing the 735 ma magmatism in the region

3 μm spectrophotometric survey of m and e class asteroids many asteroids show absorption features diagnostic of hydrated minerals in the 3 m region of the spectrum reflectance studies in this region can determine the hydration state of surface minerals and by inference the thermal histories of bodies we have made spectrophotometric observations of eight e class m class x class and p class asteroids in december 1991 and eight e class and m class asteroids in august 1993 using the infrared telescope facility on mauna kea hawaii in 1991 we discovered a 3 m absorption band on the e class asteroid 44 nysa and the p class asteroid 50 virginia and found a possible absorption on the e class asteroid 64 angelina we confirmed the presence of a 3 m absorption band on 44 nysa and on the m class asteroid 92 undina t d jones et al 1990 icarus 88 172 192 and detected this feature on the m class asteroid 201 penelope in 1993 these data demonstrate that high albedo and medium albedo objects such as e and m class asteroids can be hydrated and need not be interpreted as primarily of igneous origin we revise the interpreted mineralogy of some e and m class asteroids as a result

850 790 ma bimodal volcanic and intrusive rocks in northern zhejiang south china a major episode of continental rift magmatism during the breakup of rodinia abstract shrimp u pb zircon ages and geochemical and nd isotopic data are reported for mid neoproterozoic igneous rocks in northern zhejiang province south china the shenwu dolerite dykes the daolinshan granite diabase complex and the shangshu bimodal basalt rhyolite volcanic rocks were dated at 849 7 ma 794 9 ma and 792 5 ma respectively all the studied mafic rocks are tholeiitic in compositions and exhibit overall moderate enrichments in most incompatible trace elements resembling intraplate basaltic rocks in continental rifts the 850 ma shenwu dolerites are the earliest anorogenic basaltic rocks identified so far after the ca 1 1 0 9 ga sibao orogeny but seem to predate the neoproterozoic rifting our results are clearly at variance with the alternative tectonic model that an active continental margin existed along the southern margin of the yangtze block until ca 800 ma the intensive 790 ma bimodal volcanic and plutonic rocks part of a major phase of mid neoproterozoic rifting are concurrent with the widespread mid neoproterozoic intraplate magmatism throughout south china they are most likely related to the proposed mantle superplume that led to the breakup of the supercontinent rodinia

radar observations of asteroid 216 kleopatra radar observations of the main belt m class asteroid 216 kleopatra reveal a dumbbell shaped object with overall dimensions of 217 kilometers by 94 kilometers by 81 kilometers 25 the asteroid9s surface properties are consistent with a regolith having a metallic composition and a porosity comparable to that of lunar soil kleopatra9s shape is probably the outcome of an exotic sequence of collisional events and much of its interior may have an unconsolidated rubble pile structure

metal silicate mixtures spectral properties and applications to asteroid taxonomy the reflectance spectra of combinations of olivine orthopyroxene and iron meteorite metal show systematic variations in spectral properties which can be used to constrain many of the physical and chemical properties of the assemblages the presence of metal most noticeably affects band area ratios peak peak and peak minimum reflectance ratios and band widths these parameters are also affected to varying degrees by the abundance and grain size of the metal and silicates and the composition of the silicates band width and band areas are useful for determining metal abundance in olivine metal and orthopyroxene metal assemblages respectively mafic silicate grain size variations are best determined using band depth criteria band centers are most useful for determining mafic silicate composition analysis of the reflectance spectrum of the s class asteroid 8 flora on the basis of these spectral parameters indicates a surface composed of approximately 50 wt metal 40 wt olivine fa 35 10 10 wt orthopyroxene fs 30 25 35 and perhaps a few weight percent of clinopyroxene a substantial amount of the surface seems to consist of a fine grained 45 m size component analysis of the reflectance spectrum of the a class asteroid 446 aeternitas suggests a surface assemblage of approximately 35 wt metal 55 wt olivine fa 20 10 7 wt clinopyroxene fs 17 and 3 wt orthopyroxene fs 45 a substantial fine grained 45 m size surface component is also indicated for this asteroid

garnet geochemistry of tungsten mineralized xihuashan granites in south china abstract the xihuashan complex intrusion in south china which is emplaced at ca 154 ma mainly comprises medium grained porphyritic biotite granite medium grained biotite granite and fine grained two mica granite medium grained biotite and fine grained two mica granites are important tungsten bearing granites and contain an unusual amount of garnet garnets from this intrusion are dominated by almandine and spessartine which constitute 94 to 99 of the total molecular composition of the garnet these garnets display unusual compositional zoning the cores of these garnets are rich in heavy rare earth element hree y ca and contain abundant hree and y rich mineral inclusions their rims are free of mineral inclusions and have low of these elements two types of fluorite inclusions exist in garnet y fluorite and y poor fluorite garnet exhibits specific mn zoning with a relatively mn poor core but a relatively mn rich rim thus constituting a specific spessartine inverse bell shaped profile that belongs to typical magmatic garnets all analyzed garnets have high ree content and exhibit hree enriched and lree depleted patterns with strong negative eu anomalies the incorporation of ree into garnet is in part controlled by its crystal chemistry with ree3 following a coupled substitution of the type fe2 mn2 1viii ree3 1viii si4 1iv z3 1iv the texture and compositional zoning of garnet suggest that garnet growth is largely controlled by the pressure temperature composition condition of magmatic evolution internal crystal chemical parameters and kinetics during mineral growth the garnet core grows in near equilibrium with magmatic melt under a relatively high pressure temperature p t condition by contrast the garnet rim grows rapidly by the coexisting melt fluid phase and co2 rich volatile environment under a relatively low p t condition which is virtually unfavorable for the incorporation of ree into the magmatic garnet structure garnet fingerprints the magmatic hydrothermal transition during crystallization of these granites

the m x asteroid menagerie results of an nir spectral survey of 45 main belt asteroids abstract diagnostic mineral absorption features for pyroxene s olivine phyllosilicates and hydroxides have been detected in the near infrared nir approximately 0 75 2 50 m spectra for 60 of the tholen classified tholen 1984 1989 m x asteroids observed in this study nineteen asteroids 42 exhibit weak band i approximately 0 9 m band ii approximately 1 9 m absorptions three asteroids 7 exhibit a weak band i approximately 1 05 1 08 m olivine absorption four asteroids 9 display multiple absorptions suggesting phyllosilicate oxide hydroxide minerals one 1 asteroid exhibits an s asteroid type nir spectrum and 18 asteroids 40 are spectrally featureless in the nir but have widely varying slopes tholen m asteroids are defined as asteroids exhibiting featureless visible wavelength spectra with moderate albedos tholen 1989 tholen x asteroids are also defined using the same spectral criterion but without albedo information previous work has suggested spectral and mineralogical diversity in the m asteroid population rivkin et al 1995 2000 busarev 2002 clark et al 2004 hardersen et al 2005 birlan et al 2007 ockert bell et al 2008 2010 shepard et al 2008 2010 fornasier et al 2010 the pyroxene bearing asteroids are dominated by orthopyroxene with several likely to include higher ca clinopyroxene components potential meteorite analogs include mesosiderites cb ch chondrites and silicate bearing nife meteorites the eos family olivine bearing asteroids are most consistent with a co chondrite analog the aqueously altered asteroids display multiple weak absorptions 0 85 0 92 0 97 1 10 1 40 and 2 30 2 50 m indicative of phyllosilicate hydroxide minerals the spectrally featureless asteroids range from metal rich to metal poor with meteorite analogs including nife meteorites enstatite chondrites and stony iron meteorites

e type asteroid spectroscopy and compositional modeling 1 we present near infrared spectroscopic observations 0 8 2 5 m of e type asteroids we combine these observations with visible wavelength spectra obtained by other researchers and perform hapke theory mixing model simulations of e type asteroid spectra in order to constrain possible compositions aubrites were originally suggested as the meteorite analog for the e type asteroids because of their similar visible wavelength colors and high albedos the designation e was originally linked with the mineral enstatite common in aubrite meteorites more recently the sulfides troilite and oldhamite have been suggested as possible components of e type asteroids we tested the suggested compositional interpretations of aubrite meteorites and or aubrites enhanced with sulfides we also tested compositions of aubrites mixed with low iron silicate minerals we find that e types can be separated into three groups on the basis of inferred composition nysa like e types are consistent with silicate mineralogy higher in iron than the mineral enstatite angelina like asteroids are consistent with silicate mineralogy including a sulfide such as oldhamite and hungaria like e types are not inconsistent with aubrites our results indicate that some e type asteroids may be composed of materials that are not sampled by meteorites

fluid fractionation of tungsten during granite pegmatite differentiation and the metal source of peribatholitic w quartz veins evidence from the karagwe ankole belt rwanda abstract the identification of a magmatic source for granite associated rare metal w nb ta and sn mineralisation in metasediment hosted quartz veins is often obscured by intense fluid rock interactions which metamorphically overprinted most source signatures in the vein system in order to address this recurrent metal sourcing problem we have studied the metasediment hosted tungsten bearing quartz veins of the nyakabingo deposit of the karagwe ankole belt in central rwanda the vein system 992 2 ma is spatiotemporal related to the well characterised b rich f poor g4 leucogranite pegmatite suite 986 10 ma to 975 8 ma of the gatumba gitarama area which culminated in nb ta sn mineralisation muscovite in the nyakabingo veins is significantly enriched in granitophile elements rb cs w and sn and show alkali metal signatures equivalent to muscovite of less differentiated pegmatite zones of the gatumba gitarama area pegmatitic muscovite records a decrease in w content with increasing differentiation proxies rb and cs in contrast to the continuous enrichment of other high field strength elements nb and ta and sn this is an indication of a selective redistribution for w by fluid exsolution and fluid fractionation primary fluid inclusions in tourmaline of these less differentiated pegmatites demonstrate the presence of medium to low saline h 2 o nacl kcl mgcl 2 complex salt e g rb cs fluids which started to exsolve at the g4 granite pegmatite transition stage laser ablation inductively coupled plasma mass spectrometry shows significant tungsten enrichment in these fluid phases 5 500 ppm fractional crystallisation has been identified previously as the driving mechanism for the transition from g4 granites less differentiated biotite biotite muscovite towards muscovite pegmatites and eventually columbite tantalite mineralised pegmatites the general absence of tungsten mineralisation in this magmatic suite including the most differentiated columbite tantalite mineralised pegmatites of the gatumba gitarama area emphasises the efficiency of fluid saturation to extract crystal melt incompatible tungsten from the differentiating melt phase fluid melt crystal partitioning calculations support the concept of a magmatic hydrothermal fluid source for tungsten and constrain the range of permissible crystal melt and fluid melt partition coefficients together with realistic values for water solubility in the parental g4 granitic melt consequently we propose that for highly differentiated b rich f poor granite systems fluid saturation started prior to or at the granite pegmatite transition stage resulting in apical to peribatholitic tungsten veins systems that are paragenetically older than the final pegmatite stage

genesis of a magmatic metamorphic hydrothermal system the sn w polymetallic deposits at pilok thailand cassiterite wolframite and base metal mineralization in the pilok area are hosted by veins and stockworks in the apical portion of leucocratic granite stocks close to their contacts with pelitic metasedimentary rocks a minimum pressure of emplacement of approximately 1 500 bars is indicated by the presence of two coexisting feldspars in the granites and a moderate depth is supported by a lack of coeval volcanism and absence of porphyritic textures that characterize hypabyssal intrusions a contact metamorphic metasomatic aureole in the surrounding pelitic metasediments consists of tourmaline biotite and muscovite zones that are superimposed on muscovite chlorite zone regional metamorphism whole rock carbon analyses demonstrate a volatilization of graphite in the metasediments as a function of distance from the intrusion and the presence of andalusite in the aureole constrains the maximum pressure to approximately 3 800 bars the earliest mineralization is late magmatic to early postmagmatic wolframite cassiterite intergrown with li and f rich muscovite in pegmatite pods the bulk of the wolframite mineralization was subsequently deposited in veins with potassic alteration which could have originated either by orthomagmatic or remobilization processes finally cassiterite and sulfides chalcopyrite sphalerite were deposited in association with greisen alteration and formed as a result of the remobilization of tin from the host granite fluid inclusion and stable isotope data indicate the involvement of at least four fluid types a moderately saline fluid of presumed magmatic origin aqueous carbonic metamorphic fluids low temperature and low salinity meteoric fluids and high salinity formational or metamorphic fluids the isotopic compositions of waters calculated from delta o 18 analyses of quartz muscovite and cassiterite and delta d analyses of muscovite range from 1 4 to 9 4 and 63 to 118 per mil respectively these are consistent with the mixing of magmatic and organic rich metamorphic fluids oxygen isotope thermometry indicates temperatures of 350 degrees to 500 degrees c for cassiterite mineralization the oldest preserved fluid inclusions are primary aqueous carbonic inclusions from wolframite and cassiterite mineralization both the homogenization of the carbonic phase and the bulk

shrimp zircon u pb geochronological and whole rock geochemical evidence for an early neoproterozoic sibaoan magmatic arc along the southeastern margin of the yangtze block abstract it has been generally accepted that the south china block was formed through amalgamation of the yangtze and cathaysia blocks during the proterozoic sibaoan orogenesis but the timing and kinematics of the sibao orogeny are still not well constrained we report here shrimp u pb zircon geochronological and geochemical data for the taohong and xiqiu tonalite granodiorite stocks from northeastern zhejiang southeastern margin of the yangtze block our data demonstrate that these rocks dated at 913 15 ma and 905 14 ma are typical amphibole rich calc alkaline granitoids formed in an active continental margin combined with previously reported isotopic dates for the 1 0 ga ophiolites and 0 97 ga adakitic rocks from northeastern jiangxi the timing of the sibao orogenesis is thus believed to be between 1 0 and 0 9 ga in its eastern segment it is noted that the sibao orogeny in south china is in general contemporaneous with some other early neoproterozoic 1 0 0 9 ga orogenic belts such as the eastern ghats belt of india and the rayner province in east antarctica indicating that the assembly of rodinia was not finally completed until 0 9 ga

fluid rock interaction is decisive for the formation of tungsten deposits tungsten mineralization is typically associated with reduced granitic magmas of crustal origin while this type of magmatism is widespread economic tungsten deposits are highly localized with 90 produced from only three countries worldwide therefore the occurrence of reduced magmatism while necessary for tungsten enrichment seems to be insufficient to form such rare deposits here we explore the mechanisms that lead to wolframite precipitation and evaluate whether they may exert a decisive control on tungsten global distribution tungsten differs from other rare metals enriched in magmatic hydrothermal ore deposits because it is transported as an anionic species precipitation of the main tungstate minerals scheelite cawo 4 and wolframite fe mn wo 4 thus depends on the availability of calcium iron or manganese we demonstrate quantitatively that magmatic fluids at panasqueira portugal provide tungsten in solution whereas the host rock contributes the iron required to precipitate wolframite the combination of special source conditions with specific reactive host rocks explains why major wolframite deposits are rare and confined to a few ore provinces globally

molybdenite re os and muscovite 40ar 39ar dating of the xihuashan tungsten deposit central nanling district south china abstract the xihuashan tungsten deposit in the central nanling region south china is an important vein type ore deposit hosted in cambrian strata and mesozoic granitic intrusions wolframite and molybdenite are the principal ore minerals the gangue minerals are mainly quartz and muscovite wolframite and molybdenite are products of the first stage hydrothermal activity whereas muscovite formed dominantly at the second stage molybdenite re os and muscovite 40ar 39ar dating have been carried out to investigate the age of mineralization re os isotopic dating for molybdenite associated with wolframite yield a precise well constrained isochron age of 157 8 0 9 ma mswd 1 5 ar ar isotopic analyses of muscovite yield a plateau age of 152 8 1 6 ma in agreement with an inverse isochron age of 152 8 1 6 ma which is 5 mys younger than the re os age the molybdenite re os age is interpreted as the age of tungsten mineralization this age coincides well with the zircon u pb age of the host granitic intrusion reported previously the 5 mys difference between molybdenite re os and muscovite 40ar 39ar ages probably represents the duration of hydrothermal activity the results show that the xihuashan tungsten deposit is one of many important tungsten tin deposits formed during 150 to 160 ma associated with large scale lithospheric extension in south china

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

mesozoic large scale magmatism and mineralization in south china preface abstract south china is famous for its polymetallic deposits with more than 50 of the world s w and sb reserves and 20 of the sn reserves as well as abundant cu mo pb zn au ag ta nb hree and u this special issue reports recent progress on the tectonic evolution magmatism and ore deposits of south china which leads to a more comprehensive understanding of the mesozoic large scale magmatism and mineralization events 1 south china has been located in backarc settings during multiple subductions since the paleozoic which may have contributed to pre enrichments of the ore forming materials 2 the pacific plate subduction was a principle factor that controlled the late mesozoic large scale magmatism and mineralization in south china through flat subduction ridge subduction slab tearing and slab rollbacks

refining the asteroid taxonomy by polarimetric observations abstract we present new results of polarimetric observations of 15 main belt asteroids of different composition by merging new and published data we determined polarimetric parameters characterizing individual asteroids and mean values of the same parameters characterizing different taxonomic classes the majority of asteroids show polarimetric phase curves close to the average curve of the corresponding class we show that using polarimetric data it is possible to refine asteroid taxonomy and derive a polarimetric classification for 283 main belt asteroids polarimetric observations of asteroid 21 lutetia are found to exhibit possible variations of the position angle of the polarization plane over the surface

the origin of kibaran late mid proterozoic tin tungsten and gold quartz vein deposits in central africa a fluid inclusions study composition and evolution of fluids depositing tin and tungsten ores in kibaran quartz vein deposits allow the modelling of devolatizing evolved granites as their source at depth fluids forming gold quartz veins and breccias are different from the first especially by showing characteristics of a high pressure environment all deposits are controlled by compressional deformation whose fading phases affect earlier formed veins these findings lead to the conclusion that both anatectic melting resulting in intrusion of fertile granites and the generation of fluids forming gold deposits are the final consequence of deep crustal metamorphism the latter was caused by crustal thickening immediately preceding the metallogenetic climax

a precise u pb age on cassiterite from the xianghualing tin polymetallic deposit hunan south china we report the first precise u pb isotope data on cassiterite from the large xianghualing tin polymetallic deposit in the central nanling district south china the results show that four separates from sample xf 51 have a relatively narrow range of 206pb 238u apparent ages varying from 152 to 157 ma and the three 206pb 238u apparent ages yield a weighted average value of 156 4 ma mswd 0 32 separates from two other cassiterite samples do not have sufficient radiogenic pb to generate a reliable 206pb 238u age seven separates from the above three cassiterite samples define a well constrained 238u 206pb isochron corresponding to an age of 157 6 ma mswd 34 a comparison of the u pb cassiterite ages with published ar ar dates on muscovite from this deposit and k ar age data on biotite from the pluton genetically related to the tin mineralization in this area demonstrates that the u pb isotope system of cassiterite is a potential geochronometer combined with the ar ar dates of muscovite from this deposit we can constrain the absolute age of tin polymetallic mineralization in xianghualing at 154 157 ma the dates obtained in this study consistent with the published geochronological results from other important deposits in this region reveal that the large scale tungsten tin mineralization in the central nanling region was predominantly emplaced during 150 161 ma

wolframite solubility and precipitation in hydrothermal fluids insight from thermodynamic modeling abstract wolframite a solid solution series between hubnerite mnwo4 and ferberite fewo4 is the main tungsten bearing ore mineral in vein type tungsten deposits much progress has been made on characterizing the mineralizing fluids precipitating wolframite but it remains poorly understood what are the mechanisms depositing wolframite effectively and the variables controlling mn fe ratios in wolframite this study examines chemical controls on wolframite solubility in hydrothermal fluids and mn fe ratios in wolframite using thermodynamic models for fluids in the systems of w mn cl na o h and w fe cl na o h the fluid buffered models are established based on the characteristics of vein type tungsten deposits the modeling results indicate that solubilities of hubnerite and ferberite in hydrothermal fluids at typical w mineralizing conditions 300 400 c 500 1500 bars 5 15 wt nacl equivalent ph 4 6 reach up to hundreds of ppm the predominant tungsten manganese and iron species in fluids are h w o 4 m n c l 2 0 and f e c l 4 2 respectively an increase in ph and a decrease in fluid temperature and salinity are efficient mechanisms precipitating hubnerite and ferberite from acidic hydrothermal fluids hubnerite and ferberite are also significantly dissolved in alkaline hydrothermal fluids but their solubilities in alkaline fluids are insensitive to fluid temperature and salinity this may affect w mineralization at stages with different ph levels e g the greisen stage and the alkaline stage the mn fe ratio of mineralizing fluids is the principal variable controlling mn fe ratios in wolframite more supply of fe than mn from the fertile magma tends to produce fe rich mineralizing fluids this may be one of reasons why ferberite is more common than hubnerite in tungsten deposits and why hubnerite is more likely to precipitate at an early stage

a radar survey of m and x class asteroids abstract we observed ten m and x class main belt asteroids with the arecibo observatory s s band 12 6 cm radar the x class asteroids were targeted based on their albedos or other properties which suggested they might be m class this work brings the total number of main belt m class asteroids observed with radar to 14 we find that three of these asteroids have rotation rates significantly different from what was previously reported based on their high radar albedo we find that only four of the fourteen 16 psyche 216 kleopatra 758 mancunia and 785 zwetana are almost certainly metallic 129 antigone has a moderately high radar albedo and we suggest it may be a ch cb bencubbinite parent body three other asteroids 97 klotho 224 oceana and 796 sarita have radar albedos significantly higher than the average main belt asteroid and we cannot rule out a significant metal content for them five of our target asteroids 16 psyche 129 antigone 135 hertha 758 mancunia and 785 zwetana show variations in their radar albedo with rotation we can rule out shape and composition in most cases leaving variations in thickness porosity or surface roughness of the regolith to be the most likely causes with the exception of 129 antigone we find no hydrated m class asteroids w class rivkin a s howell e s lebofsky l a clark b e britt d t 2000 icarus 145 351 368 to have high radar albedos

sm nd and rb sr isotopic chronology and cooling history of ultrahigh pressure metamorphic rocks and their country rocks at shuanghe in the dabie mountains central china abstract ultrahigh pressure metamorphic uhpm rocks at shuanghe area in the dabie mountains occur as a uhpm block within the regional granitic gneiss a sm nd isochron defined by garnet omphacite rutile from coesite bearing eclogite yield an age of 226 3 3 2 ma another sm nd isochron defined by garnet two phengites form uhp gneiss yield a similar age of 226 5 2 3 ma the two consistent sm nd ages defined by three uhpm minerals suggest that nd isotopic equilibrium between uhpm minerals in these rocks during uhp metamorphism has been achieved this may correspond to the age of peak metamorphism with an average metamorphic temperature of 800 c it is demonstrated that the retrograde metamorphism of uhpm rocks occurred in an open chemical system whereas the nd and sr isotopic systematics of uhpm minerals may have remained closed nd and sr isotopic disequilibrium between uhpm minerals and retrograde metamorphic minerals has been observed therefore the tie line of garnet or phengite and whole rock containing retrograde metamorphic minerals gives an old sm nd age and a young rb sr age respectively with no geologic significance however a rb sr ages of 219 0 6 6 ma defined by phengite garnet from a uhpm gneiss indicates that the uhpm rocks at shuanghe cooled down to 500 c at that time it suggests that the uhpm rocks at shuanghe experienced the first rapid cooling during 226 219 ma on the other hand the rb sr ages of 174 7 8 to 169 2 3 3 ma defined by retrograde minerals amphibole or biotite with closure temperature ranging from 450 to 300 c and intensely retrograded metamorphic rocks reflect a second rapid cooling during this time interval this is consistent with the rapid cooling time of 190 170 ma of the orthogneiss in the dabie su lu uhpm belt obtained by ar ar dating method in contrast to uhpm rocks the nd isotopic composition of the garnet in granitic gneiss has been reset during retrograde metamorphism and is in equilibrium with those of retrograde epidote and biotite which yields a sm nd isochron age of 213 5 ma indicating the retrometamorphic time corresponding to amphibolite facies in addition the biotites from the granitic gneiss yield rb sr ages of 171 173 ma similar to those of the uhpm rocks these data suggest that the country rocks granitic gneiss may have a similar cooling history to the uhpm rocks at shuanghe two stages of rapid cooling of uhpm rocks at shuanghe may correspond two stages of fast uplift the initial rapid uplifting and cooling of uhpm rocks during 226 219 ma may be caused by compression tectonics during subducting time of the continental crust whereas the later rapid cooling may reflect the exhumation of the entire subducted continental crust by extension during the early middle jurassic

greisenization and albitization at the tikus tin tungsten deposit belitung indonesia tikus is the most important granite hosted primary tin tungsten deposit on the tin island belitung the bulk of the ore is located in greisen zones which enclose very irregularly shaped bodies composed almost exclusively of quartz or cassiterite or wolframite a small volume of ore is also located in albitized granite which grades into albitite detailed geochemical studies indicate that the greisen and albitite were formed by alteration of a k feldspar megacrystic medium grained biotite granite greisenization produced an enrichment in sn avg 3 000 ppm w 1 110 ppm fe 2 o 3 mno bi cs cu f li pb rb and zn as well as a depletion of na 2 o cao and sr albitization is characterized by an enrichment in na 2 o cao al 2 o 3 cu f pb sr and zn as well as by a depletion of k 2 o mgo sio 2 and ba however sn 2 100 ppm and w 914 ppm were concentrated only with moderate albitization albitized granite whereas extreme albitization albitite is characterized by low concentrations of these metals co 2 h 2 o ch 4 salt fluid inclusions with highly variable co 2 h 2 o ratios are the most abundant type in the quartz of the greisen as well as in the coarse grained quartz or cassiterite or wolframite bodies enclosed in it they homogenize in the 200 degrees to 340 degrees c range and indicate minimum trapping pressures of 0 7 to 2 kbars co 2 ch 4 inclusions with densities of 0 53 to 0 99 g cm 3 without a visible h 2 o phase are less common aqueous inclusions without a visible co 2 phase are subordinate in greisen and enclosed quartz bodies 0 5 8 equiv wt nacl but are the only type observed in albitized granite 1 18 equiv wt nacl the cacl 2 nacl ratios are high in the albitized granite up to 1 1 the homogenization temperatures are in the 150 degrees to 355 degrees c range it is assumed that an evolutionary relationship exists between greisenization and albitization na and ca were released through fluid silicate reactions during greisenization and the fluids lost co 2 ch 4 with falling temperature the resulting na ca enriched aqueous fluids deposited albite and fluorite by replacement reactions in the granite surrounding the greisen the major deposition mechanism for cassiterite and wolframite was ph increase and concurrent temperature decrease in both greisen and moderately albitized granite with secondary muscovite and topaz strong albitization albitite did not increase the fluid ph and therefore did not precipitate cassiterite or wolframite

manganese chromium isotope systematics of enstatite meteorites abstract we present results of a study of the 53 mn 53 cr isotope systematics in the enstatite chondrites and achondrites aubrites the goal of this study was to explore the capabilities of this isotope system to obtain chronological information on these important classes of meteorites and to investigate the original distribution in the inner solar system of the short lived radionuclide 53 mn our earlier work lugmair and shukolyukov 1998 shukolyukov and lugmair 2000a has shown that the asteroid belt bodies are characterized by essentially the same initial 53 mn abundance however we have found the presence of a gradient in the abundance of the radiogenic 53 cr between the earth moon system mars and the asteroid vesta if this gradient is considered as a function of the heliocentric distance a linear radial dependence is indicated this can be explained either by an early volatility controlled mn cr fractionation in the nebula or by an original radially heterogeneous distribution of 53 mn the enstatite chondrites are suggested to form in the inner zones of the solar nebula much closer to the sun than the ordinary chondrites therefore their investigation may be an important test on the hypothesis on a radial heterogeneity in the initial 53 mn we have studied the bulk samples of the eh4 chondrites indarch and abee and the el6 chondrite khairpur although these meteorites have essentially the same mn cr ratio as the ordinary chondrites the relative abundance of the radiogenic 53 cr is three times smaller than in the ordinary chondrites because these meteorites are primitive undifferentiated and no mn cr fractionation had occurred within their parent bodies this difference is a strong argument in favor of an initially heterogeneous distribution of 53 mn in the early inner solar system this finding is also consistent with formation of the enstatite chondrites in the inner zones of the solar nebula using the characteristic 53 cr excess of the enstatite chondrites and the observed gradient their place of origin falls at about 1 4 au or somewhat closer to the sun i e 1 0 1 4 au we also present chronological results for the enstatite chondrites and achondrites the absolute 53 mn 53 cr ages of the eh4 chondrites are old 4565 ma the el6 chondrite khairpur is 4 5 ma younger which is in good agreement with the 129 i 129 xe data from the literature the age of the aubrite pena blanca spring appears to be similar to those of the enstatite chondrites while that of the aubrite bishopville is at least 10 ma younger which is also in agreement with the 129 i 129 xe data the results from bulk samples of aubrites indicate that the last mn cr fractionation in their parent body occurred 4563 ma ago and imply an evolution of the mn cr isotope system in an environment with an higher than chondritic mn cr ratio for several millions of years

asteroid 21 lutetia at 3 μm observations with irtf spex abstract we present observations of asteroid 21 lutetia collected 2003 2008 using the spex instrument on the nasa infrared telescope facility irtf covering 2 4 m we also reevaluate nsfcam observations obtained in 1996 rivkin a s lebofsky l a clark b e howell e s britt d t 2000 icarus 145 351 368 taken together these show deeper 3 m band depths of order 3 5 in the southern hemisphere of lutetia and shallower band depths of order 2 or less in the north such variation is consistent with observations at shorter wavelength by previous workers nedelcu d a et al 2007 astron astrophys 470 1157 1164 lazzarin m et al 2010 mon not r astron soc 408 1433 1437 who observed hemispheric level variations from c like spectra to x like spectra while the shallowness of absorption bands on lutetia hinders identification of its surface composition goethite appears plausible as a constituent in its southern hemisphere beck p quirico e sevestre d montes hernandez g pommerol a schmitt b 2011 astron astrophys 526 a85 a89 mathematical models of space weathered goethite are most consistent with lutetia s southern hemisphere spectrum but more work and further observations are necessary to confirm this suggestion

origin and tectonic significance of a mesozoic multi layer over thrust system within the yangtze block south china abstract in the yangtze block south china a well developed mesozoic thrust system extends through the xuefeng and wuling mountains in the southeast to the sichuan basin in the northwest the system comprises both thin and thick skinned thrust units separated by a boundary detachment fault the dayin fault to the northwest the thin skinned belt is characterized by either chevron anticlines and box synclines to the northwest or chevron synclines to the southeast the former structural style displays narrow exposures for the cores of anticlines and wider exposures for the cores of synclines thrust detachments occur along silurian fs and lower cambrian fc strata and are dominantly associated with the anticlines to the southeast this style of deformation passes gradually into one characterized by chevron synclines with associated principal detachment faults along silurian fs cambrian fc and lower sinian fz strata there are however numerous secondary back thrusts therefore the thin skinned belt is like the valley and ridge province of the north american applachian mountains the thick skinned belt structurally overlies the thin skinned belt and is characterized by a number of klippen including the xuefeng and wuling nappes it is thus comparable to the blue ridge province of appalachia the structural pattern of this thrust system in south china can be explained by a model involving detachment faulting along various stratigraphic layers at different stages of its evolution the system was developed through a northwest stepwise progression of deformation with the earliest delamination along lower sinian strata fz analyses of balanced geological cross sections yield about 18 1 21 total 88 km shortening for the thin skinned unit and at least this amount of shortening for the thick skinned unit the compressional deformation from southeast to northwest during late jurassic to cretaceous time occurred after the westward progressive collision of the yangtze block with the north china block and suggests that the orogenic event was intracontinental in nature

a new investigation of hydration in the m type asteroids abstract we obtained 2 4 m spectra of six m type asteroids using the spex spectrograph at nasa s infrared telescope facility we find evidence for hydrated minerals on all six asteroids including two that were previously thought to be dry one of our targets 216 kleopatra shows rotational variability in the depth of its 3 m feature we also studied three of these asteroids in the 0 8 2 4 m range using the nics instrument at the telescopio nazionale galileo tng in la palma spain the discovery of spectral signatures of hydrated minerals on so many m types is difficult to reconcile with a highly thermally evolved composition it has been suggested that the hydrated minerals could have been delivered to m types via impacts with primitive objects or that the m types may actually have primitive compositions that are not represented in meteorite collections understanding the origin and type of hydration on these asteroids will help determine which of these interpretations is correct

rock acoustics and rock mechanics their link in petroleum engineering seismic data represent the most important source of information about underground formations that have not been accessed by excavations or drilling when target formations can be reached by drilling more accurate velocity data are available via logging the primary use of the seismic information is still to map structure however there is a growing interest in using seismic data to derive intrinsic information about rock properties such as porosity clay content etc porosity estimation has traditionally also been the main application of sonic logs in fact an established school of thought holds that velocities in sedimentary rocks are primarily a measure of porosity the lower the velocity the higher the porosity

monazite and xenotime u th pb geochronology by ion microprobe dating highly fractionated granites at xihuashan tungsten mine se china zircon monazite and xenotime have proven to be valuable chronometers for various geological processes due to their commonly high u th and low common pb contents however zircons that have crystallized in highly fractionated granites often have such high u contents that radiation damage can lead to scattered u pb ages when measured with secondary ion mass spectrometry sims in this study monazite and xenotime were separated from a number of highly fractionated granites at the xihuashan tungsten mine southeast china for alternative dating methods by sims for monazite analysis obvious excess 204 pb signal mainly from interference of 232 th 144 nd 16 o 2 was observed in high th 2 wt monazite which hinders 204 pb based common pb correc tions a 207 pb based common pb correction method was used instead by employing power law relationships between pb u versus uo2 u p b th versus tho2 th and suitable exponentials monazites with tho2 contents in the range of 3 19 do not exhibit this matrix effect inde pendent sims u pb ages and th pb ages of three phases of xihuashan granite samples were consistent with each other and yielded dates of 158 7 0 7 158 0 0 7 and 156 9 0 7 ma respectively xenotime does show marked matrix effects due to variations of u th and y or total rare earth element ree referred as rree hereafter contents suitable correction factors require end member standards with extremely high or low u th and y or rree con tents no excess 204 pb was observed indicating that the 204 pb based common pb correction method is feasible independent 207 pb 206 pb ages can be obtained although multi collector mode is necessary to improve precision the main difficulties with dating xenotime are when high th u mineral inclusions are ablated we can identify when this occurs however by comparing the measured uo2 u and tho2 th with those in xenotime standards three xeno time samples from the first phase of xihuashan granite yielded a weighted mean 207 pb 206 pb date of 159 5 4 4 ma mswd 1 0 and a 206 pb 238 u date of 159 4 0 9 ma mswd 1 6 which are consistent with mona zite u pb and th pb ages from the same granites this study demonstrates that monazite and xenotime are better sims chronometers for highly fractionated granites than zircon which can yield doubtful ages due to high u contents

oxygen isotopic compositions of enstatite chondrites and aubrites oxygen isotopic compositions have been measured for ten eh chondrites eight el chondrites and nine aubrites the mean 18o and 17o values are 5 31 and 2 74 5 57 and 2 96 5 24 and 2 70 respectively within the eh group more equilibrated meteorites are fractionated toward higher heavy isotope abundances than the less equilibrated meteorites small departures of individual meteorites from a common mass fractionation occur for some of the eh samples the aubrites may be genetically related to either the eh or el group or to both almost all of the measured isotopic compositions are indistinguishable from the terrestrial oxygen isotope fractionation line suggesting a genetic relationship among the earth the moon and the enstatite the meteorites

stress dependent wave velocities in sedimentary rock cores why and why not abstract rocks exhibit stress dependent wave velocities when their constitutive behaviour shows nonlinear elasticity the main physical mechanism responsible for stress dependency is opening or closure of cracks which is particularly important in brittle rocks crack formation is also associated with breaking of grain contacts we observe by using synthetic sandstones formed under stress a strong stress dependence during unloading simulated coring the reloaded material also shows a strong stress dependency in particular at stress levels below the virgin stress state but also above thus stress dependency as seen in cores taken from great depth is mainly a result of core damage stress independency is associated with linear elasticity such as in well cemented rocks or near the virgin stress conditions as observed here with synthetic sandstones but also occurs in ductile materials where there is a strong component of plasticity we demonstrate stress independence in synthetic sandstone at stress close to the virgin stress state in the elastic regime but also well above in the non elastic deformation regime high porosity high clay content shale was found to rather stress insensitive this is thought to be a result of the ductility of the rock caused mainly by the strong affinity of water to clay mineral surfaces

infrared microthermometric and stable isotopic study of fluid inclusions in wolframite at the xihuashan tungsten deposit jiangxi province china the xihuashan tungsten deposit jiangxi province china is a world class vein type ore deposit hosted in cambrian strata and mesozoic granitic intrusions there are two major sets of subparallel ore bearing quartz veins the ore mineral assemblage includes wolframite and molybdenite with minor amounts of arsenopyrite chalcopyrite and pyrite there are only two phase aqueous rich inclusions in wolframite but at least three major types of inclusions in quartz two or three phase co2 rich inclusions two phase pure co2 inclusions and two phase aqueous inclusions indicating boiling fluid inclusions in wolframite have relatively higher homogenization temperatures and salinities 239 380 c 3 8 13 7 wt nacl equiv compared with those in quartz 177 329 c 0 9 8 1 wt nacl equiv these distinct differences suggest that those conventional microthermometric data from quartz are not adequate to explain the ore formation process enthalpy salinity plot shows a linear relationship implying mixing of different sources of fluids although boiling occurred during vein type mineralization it seems negligible for wolframite deposition mixing is the dominant mechanism of wolframite precipitation in xihuashan 34s values of the sulfides range from 1 6 to 0 1 indicative of a magmatic source of sulfur 18o values of wolframite are relatively homogeneous ranging from 4 8 to 6 3 oxygen isotope modeling of boiling and mixing processes also indicates that mixing of two different fluids was an important mechanism in the precipitation of wolframite

ca 825 ma komatiitic basalts in south china first evidence for 1500 c mantle melts by a rodinian mantle plume mantle plume or superplume activities have repeatedly been invoked as a cause for the breakup of the neoproterozoic supercontinent rodinia with supportive evidence including radiating dike swarms globally synchronous anorogenic igneous activity large scale lithospheric doming and unroofing and geochemical signatures similar to recent plume related magmatism however high temperature magmas such as picrite or komatiite a requisite product of mantle plume activities have not previously been identified for those events we present here geochronological and geochemical data from a suite of pillow lavas in central south china sensitive high resolution ion microprobe shrimp u pb dating of zircons from an evolved member of andesitic composition within the suite indicates that the lavas were erupted at 823 6 ma all but a few highly evolved crust contaminated basaltic rocks are characteristically high in mgo 10 2 17 5 ni 183 661 ppm and cr 677 1672 ppm but low in tio2 0 5 0 7 al2o3 10 6 12 7 and feot total fe as feo 7 4 10 5 typical of komatiitic basalts our geochemical modeling which removes the effect of olivine crystallization suggests that their primary magma has typical komatiitic compositions with mgo 20 feot 11 sio2 47 tio2 0 48 al2o3 10 ni 860 ppm and cr 1780 ppm such a high mgo content in the primary melts implies a melt temperature of 1500 c suggesting that the yiyang komatiitic basalts were generated by melting of an anomalously hot mantle source with potential temperature t p 260 50 c higher than the ambient mid oceanic ridge basalt morb source mantle similar to that of modern mantle plumes the yiyang komatiitic basalts are thus the first solid petrological evidence for the proposed ca 825 ma mantle plume that played a key role in the breakup of the supercontinent rodinia

tracing metal sources in peribatholitic hydrothermal w deposits based on the chemical composition of wolframite the example of the variscan french massif central abstract we present a complete dataset for major minor and trace elements in wolframite fe mn wo4 based on the example of several peribatholitic hydrothermal w deposits located in the variscan french massif central fmc the wolframite samples were characterized down to the micrometer scale by combining scanning electron microscopy observations and in situ chemical analysis by electron probe microanalyzer and laser ablation inductively coupled plasma mass spectrometry most samples are fe dominated wolframites and are characterized by variable fe fe mn values for the studied deposits from 0 36 to 0 86 without significant alteration features wolframites present intracrystalline variations for concentrations of several minor and trace elements principally for nb ta and sn which reflect growth zoning the minor and trace element compositions of the different wolframite samples show at first order similar enrichments in ta nb sn zn and in as well as depletions in lree li th ti zr hf pb v co and mg compared to the upper continental crust second order compositional variations are observed between the studied deposits which can be separated in four main regional geochemical groups this work highlights that the chemical composition of wolframite is controlled by both the crystallochemical parameters and the composition of the primary hydrothermal fluid the regional variations observed in the geochemical signatures of wolframite reflect local variations in the composition of the hydrothermal fluid i e variable metal sources therefore this suggests that the minor and trace element contents in wolframite likely represent direct markers of the source of the hydrothermal fluid and ultimately of the metals the comparison between the trace element compositions of wolframite with the compositions of regional granitic rocks and worldwide shales suggests that evolved peraluminous granites represent the main source of metals in peribatholitic hydrothermal w deposits from the fmc whereas metasedimentary rocks have a limited to no influence on the metal budget

contrasting fluid behavior during two styles of greisen alteration leading to distinct wolframite mineralizations the echassieres district massif central france abstract the echassieres district of central france hosts diverse magmatic and magmatic hydrothermal deposits of rare metals mostly related to the well known beauvoir granite tungsten mineralization crops out at three distinct wolframite occurrences the two most important of which are related to two distinct magmatic bodies emplaced ca 335 and 310 ma monnier et al 2019 the mineralization occurred at 335 ma formed during a hydrothermal episode marked by precipitation of topaz replacing quartz in a stockwork system and as veinlets in the surrounding schist fluid inclusions in topaz and quartz display similar features i e all have low salinity contain significant amount of licl display constant liquid vapor ratios and homogenized within a narrow temperature range th 380 c no evidence for fluid pressure variations was observed and temperature decrease is considered to be the main cause for wolframite deposition the younger w mineralization is related to greisenizing fluids that altered the beauvoir granite and generated several quartz topaz and apatite veins all greisen related fluid inclusions display low salinity however th are spread from ca 190 to 400 c and several populations exhibit heterogeneous liquid vapor ratios while others consist of only vapor rich fluid inclusions respectively these populations are interpreted to have been trapped during boiling or flashing vaporization of the fluid in contrast with the other regional veins flashing was particularly intense in the mazet veins which host the bulk of the last wolframite generation consequently it is proposed that flashing is the key factor that triggered w precipitation this work highlights the role of two physical parameters pressure and temperature whose variations played a preponderant role on wolframite mineralization it documents in depth an example of greisen fluid evolution providing critical information on w behavior in orthomagmatic fluids and on greisen related rare metal deposits

an extension of the bus asteroid taxonomy into the near infrared the availability of asteroid spectral measurements extending to the near infrared resulting from the development of new telescopic instruments such as spex rayner 2003 provides a new basis for classifying asteroid reflectance spectra we present an asteroid taxonomy classification system based on reflectance spectrum characteristics for 371 asteroids measured over the wavelength range 0 45 to 2 45 microns this system of 24 classes is constructed using principal component analysis following most closely the visible wavelength taxonomy of bus 1999 which itself builds upon the system of tholen 1984 nearly all of the bus taxonomy classes are preserved with one new class sv defined for each class we present boundary definitions spectral descriptions and prototype examples a flow chart method is presented for classifying newly acquired data spanning this wavelength range when data are available only in the near infrared range 0 85 to 2 45 microns classification is also possible in many cases through an alternate flow chart process within our sample several classes remain relatively rare only 6 objects fall into the a class 349 dembowska and 3628 boznemcova reside as the only objects in their respective r and o classes eight q class objects are all near earth asteroids we note 1904 massevitch as an outer main belt v type while 15 other v type objects have inner main belt orbits consistent with an association with vesta

mixing of magmatic hydrothermal and metamorphic fluids and the origin of peribatholitic sn vein type deposits in rwanda abstract the fluid sources of granite related sn quartz vein deposits are commonly obscured by fluid mixing or fluid rock interactions as a result fluid inclusions minerals and isotopes in these veins indicate an intermediate composition between magmatic and metamorphic but the degree of mixing between these endmembers is currently unquantified this study presents a novel quantitative approach to assess the degree of mixing between magmatic hydrothermal and external metamorphic fluids in the formation of peribatholitic sn quartz veins in particular fluid mixing in the sn mineralized rwamagana musha ntunga pegmatite quartz vein field in east rwanda has been evaluated by the following four methods quartz stable isotopes muscovite geochemistry fluid inclusion microthermometry and la icp ms and geochemical modelling the quartz stable isotope data 18o 13 1 to 15 8 v smow d 27 6 to 59 7 v smow cannot uniquely differentiate between a metamorphic fluid origin or an initial magmatic hydrothermal fluid origin with subsequent metamorphic fluid mixing or host rock interaction however granitophile element concentrations in magmatic muscovite from pegmatites and hydrothermal muscovite from associated sn quartz veins are equally high indicating a close genetic link rb 530 8740 ppm li 110 1990 ppm sn 87 810 ppm cs 62 420 ppm primary h2o co2 n2 nacl medium saline magmatic fluid inclusions in quartz of pegmatites 12 7 wt nacleq and h2o co2 n2 nacl low saline fluid inclusions in barren metamorphic quartz veins 4 9 wt nacleq were analyzed by la icp ms these results show an enrichment in li rb sn and cs for the magmatic fluid while the metamorphic fluid is characterized by low granitophile element concentrations and high sr and ba contents the expected rb cs and rb sn signature of the sn quartz vein muscovite was modelled using the measured fluid endmember compositions confirming mixing between magmatic and metamorphic fluids in the formation of the veins the quantification suggests that the hydrothermal sn quartz vein fluid contains 5 80 of an external metamorphic fluid component

petrophysical laboratory measurements for basin and reservoir evaluation the quality of computer modelling in basin and reservoir studies critically depends on the quality of input data core measurements may directly provide such data cores also help establish correlations between log measured parameters and parameters required in basin or reservoir evaluation correlations may also permit simple index measurements to be used for data assessment instead of more tedious laboratory procedures this paper summarizes different petrophysical laboratory techniques that can be utilized for these purposes the importance of performing laboratory measurements under representative conditions and to account for core damage effects is underlined

microfracturing and fluid mixing in granites w sn ore deposition at vaulry nw french massif central abstract the vaulry w sn mineralisation located at the eastern boundary of the blond rare metal leucogranite is contained in a set of subvertical quartz veins locally with muscovite and minor quartz selvages the sequence of deposition was 1 milky quartz predominantly as fracture filling generally affected by subsequent ductile deformation 2 hyaline quartz wolframite cassiterite 3 minor sulphides other sets of quartz veinlets although generally barren are observed in the blond massif fluid migration at the microscopic scale within the granite and in the vicinity of quartz fractures was constrained by studying the geometry of fluid inclusion planes and fluid inclusion chemistry in and outside the mineralised area three major sets of subvertical fluid inclusion planes are recognised a n050 060 e set mostly developed in the veins and in the immediate vicinity a n110 130 e set regionally developed in the granite and a n140 160 e set of local extent as a whole the density of fip decreases from the mineralised zones toward the barren part of the pluton except for the n140 160 e set these are locally abundant around quartz veinlets with similar orientations that form a broad n s band near the blond locality mineralising fluids observed as primary inclusions in cassiterite and in undeformed hyaline quartz are mostly aqueous with moderate salinity and a minor volatile component at variance with many other w sn deposits in the variscan belt ore deposition occurred around 315 c at an estimated depth of 5 5 km under hydrostatic to slightly suprahydrostatic pressures it resulted from fluid mixing in the central part of a large hydrothermal system between two end members i a hot 425 430 c moderately saline fluid that contained a diluted volatile component and although na dominated minor amounts of li and ca the estimated 18o indicates that this fluid was completely equilibrated with the tectono magmatic pile pseudo metamorphic fluid ii a cold 230 c low salinity fluid evolved meteoric water that mixed with and eventually overprinted the early moderately saline fluid responsible for granite muscovitization at 425 430 c later a second hydrothermal system was initiated by the percolation of heated meteoric water with very low salinity the system was by then at least 3 5 km deep and the fluid was heated to 300 c these characteristics are reminiscent of the ca 305 ma episyenitic hydrothermal system known elsewhere in the n limousin

precise molybdenite re os and mica ar ar dating of the mesozoic yaogangxian tungsten deposit central nanling district south china the yaogangxian deposit in the central nanling region south china consists of vein type ore bodies hosted in cambrian to jurassic strata and mesozoic granitic intrusions wolframite and molybdenite are the dominant ore minerals intergrown with gangue minerals of quartz feldspar phlogopite and muscovite we have carried out molybdenite re os and phlogopite and muscovite 40ar 39ar dating to better understand the timing and genesis of mineralization re os dating of eight molybdenite samples yielded model ages ranging from 152 0 3 5 to 161 1 4 5 ma with an average of 156 0 ma the re os analyses give a well defined 187re 187os isochron with an age of 154 9 2 6 ma mswd 2 4 hydrothermal phlogopite and muscovite display extremely flat 40ar 39ar age spectra phlogopite yields a 40ar 39ar plateau age of 153 0 1 1 ma whereas muscovite yields a plateau age of 155 1 1 1 ma both 40ar 39ar ages are in good agreement with the re os ages placing the timing of tungsten mineralization at about 154 ma this age is consistent with the field relationships our new data when combined with published geochronological results from other major deposits in this region suggest that large scale w sn mineralization occurred throughout the central nanling region in the late jurassic

physical properties of shale at temperature and pressure deformational properties p wave and s wave velocities and electrical resistivity were measured for three north sea malm shales in the laboratory under pressures to 800 bars and temperatures to 100 c these data were used to evaluate how factors such as mineralogy microstructure compaction and pore fluid conductivity affect a shale s seismic and electrical responses deformation in the shales is dominated by inelastic processes which cause time dependent changes in velocity resistivity and pore pressure overall shales are less sensitive to pressure changes as compared to sandstones of similar porosity however changes in temperature result in large changes in physical properties as compared to sandstones or shaly sands p wave and s wave velocities may decrease by as much as 10 percent over the temperature range studied and calculated activation energies for surface conduction are nearly twice those observed in shaly sands these comparisons emphasize fundamental differences in fabric among the

spectral variability on primitive asteroids of the themis and beagle families space weathering effects or parent body heterogeneity themis is an old and statistically robust asteroid family populating the outer main belt and resulting from a catastrophic collision that took place 2 5 1 0 gyr ago within the old themis family a young sub family beagle formed less than 10 myr ago has been identified we present the results of a spectroscopic survey in the visible and near infrared range of 22 themis and 8 beagle families members the themis members investigated exhibit a wide range of spectral behaviors including asteroids with blue neutral and moderately red spectra while the younger beagle family members look spectrally bluer than the themis ones and they have a much smaller spectral slope variability four themis members including 24 themis have absorption bands centered at 0 68 0 73 m indicating the presence of aqueously altered minerals the best meteorite spectral analogues found for both themis and beagle families members are carbonaceous chondrites having experienced different degrees of aqueous alteration prevalently cm2 but also cv3 and ci and some of them are chondrite samples being unusual or heated the presence of aqueous altered materials on the asteroids surfaces and the meteorite matches indicate that the parent body of the themis family experienced mild thermal metamorphism in the past we extended the spectral analysis including the data available in the literature on themis and beagle families members and we looked for correlations between spectral behavior and physical parameters using the albedo and size values derived from the wise data the analysis of this larger sample confirms the spectral diversity within the themis family and that beagle members tend to be bluer and to have an higher albedo the differences between the two families may be partially explained by space weathering processes which act on these primitive surfaces in a similar way than on s type asteroids i e producing reddening and darkening however we see several themis members having albedos and spectral slopes similar to the young beagle members alternative scenarios are proposed including heterogeneity in the parent body having a compositional gradient with depth and or the survival of projectile fragments having a different composition than the parent body

metal source and wolframite precipitation process at the xihuashan tungsten deposit south china insights from mineralogy fluid inclusion and stable isotope abstract the xihuashan tungsten deposit hosted in the late jurassic granitic pluton in the nanling range of south china has a total resource of about 81 300 tonnes of wo 3 with an average ore grade of 1 08 wo 3 wolframite is the dominant ore mineral and intergrown with quartz in the main mineralization stage ore forming fluids trapped in wolframite have d and 18 o values from 82 to 64 and 7 4 to 8 8 respectively those in quartz have similar d 72 to 58 and 18 o 6 8 to 8 0 values indicative of a magmatic fluids simultaneously trapped by quartz and wolframite la icp ms analyses for individual fluid inclusion show that this mineralizing fluid contains measurable li rb cs k na ti cu zn as and w 1 to 125 ppm with average of 19 ppm while depleted in fe and mn the wolframite from the xihuashan tungsten deposit contains high feo 10 9 to 17 7 wt and mno 5 9 to 12 7 wt contents with fe fe mn atomic ratio of 0 46 to 0 75 thus requires the availability of external fe and mn we detect that the fe and mn contents in mica from the greisen are remarkably lower than primary mica from granite some magmatic micas were observed in greisen and were subjected to hydrothermal alteration compared to the core the rim of these micas depleted in fe mn f and na the siderite and pyrophanite are formed along cleavage planes of altered magmatic mica that are evidence to be due to fe and mn release during granite alteration thus we demonstrate quantitatively that magmatic fluids at xihuashan provide w in solution whereas the hosted granite alteration contributes fe and mn to precipitate wolframite it is also supported by wolframites have trace and rare earth elements characteristics similar to those of granite and some characteristics similar to the greisen therefore the ore forming fluids has components derived from the last highly evolved residual granitic melt and components acquired by releasing through the hosted granite alteration fluid rock interaction exert a principle control on wolframite precipitation based on mineralogy fluid inclusion and stable isotope we proposed three stage process to illustrate the genetical link between tungsten mineralization and granite

spectroscopic survey of m type asteroids abstract m type asteroids as defined in the tholen taxonomy tholen d j 1984 asteroid taxonomy from cluster analysis of photometry ph d dissertation university of arizona tucson are medium albedo bodies supposed to have a metallic composition and to be the progenitors both of differentiated iron nickel meteorites and enstatite chondrites we carried out a spectroscopic survey in the visible and near infrared wavelength range 0 4 2 5 m of 30 asteroids chosen from the population of asteroids initially classified as tholen m types aiming to investigate their surface composition the data were obtained during several observing runs during the years 2004 2007 at the tng ntt and irtf telescopes we computed the spectral slopes in several wavelength ranges for each observed asteroid and we searched for diagnostic spectral features we confirm a large variety of spectral behaviors for these objects as their spectra are extended into the near infrared including the identification of weak absorption bands mainly of the 0 9 m band tentatively attributed to orthopyroxene and of the 0 43 m band that may be associated to chlorites and mg rich serpentines or pyroxene minerals such us pigeonite or augite a comparison with previously published data indicates that the surfaces of several asteroids belonging to the m class may vary significantly we attempt to constrain the asteroid surface compositions of our sample by looking for meteorite spectral analogs in the relab database and by modeling with geographical mixtures of selected meteorites minerals we confirm that iron meteorites pallasites and enstatite chondrites are the best matches to most objects in our sample as suggested for m type asteroids for 22 kalliope we demonstrate that a synthetic mixture obtained enriching a pallasite meteorite with small amounts 1 2 of silicates well reproduce the spectral behavior including the observed 0 9 m feature the presence of subtle absorption features on several asteroids confirms that not all objects defined by the tholen m class have a pure metallic composition a statistical analysis of spectral slope distribution vs orbital parameters shows that our sample originally defined as tholen m types tend to be dark in albedo and red in slope for increasing value of the semi major axis however we note that our sample is statistically limited by our number of objects 30 and slightly varying results are found for different subsets if confirmed the albedo and slope trends could be due to a difference in composition of objects belonging to the outer main belt or alternatively to a combination of surface composition grain size and space weathering effects

maximum and minimum water contents of granitic melts generated in the crust a reevaluation and implications abstract recent results of studies aimed to determine the water solubilities and the liquidus temperatures in synthetic and natural granitic systems are used to constrain the minimum water contents of granitic melts generated in the crust as a function of pressure temperature melt composition and water activity it is concluded that melts generated in the crust at high temperature and low water activities such as a type granites contain higher water contents than previously assumed up to 20 at 800 900 c and 3 7 kbar as a consequence the melt fraction produced at a given amount of available water can be up to 20 lower the minimum water content of melts generated by partial melting of crustal protoliths especially quartzofeldspathic rocks can be predicted adequately from the liquidus curves in granitic systems this water content can be higher if the melt composition departs from a minimum or eutectic quartzofeldspathic composition melts generated from quartzofeldspathic rocks at low temperature 750 c and below are necessarily water rich 5 wt h 2 o and have approximately the same viscosity or even slightly lower viscosities than melts generated at higher temperatures viscosities in the range 10 4 3 10 5 4 pa s recent experimental data also show that the value of the positive d p d t slope of the liquidus curves for fixed water contents above 800 c is lower than predicted by previous models thus adiabatic decompression produces a higher amount of melt than previously assumed at high temperature the formation of melt by adiabatic decompression can be up to 50 higher than assumed

high calcium pyroxene as an indicator of igneous differentiation in asteroids and meteorites our analyses of high quality spectra of several s type asteroids 17 thetis 847 agnia 808 merxia and members of the agnia and merxia families reveal that they include both low and highcalcium pyroxene with minor amounts of olivine 0 4 high calcium pyroxene is a spectrally detectable and petrologically important indicator of igneous history and may prove critical in future studies aimed at understanding the history of asteroidal bodies the silicate mineralogy inferred for thetis and the merxia and agnia family members requires that these asteroids experienced igneous differentiation producing broadly basaltic surface lithologies together with 4 vesta and its smaller vestoid family members and the main belt asteroid 1489 magnya these new asteroids provide strong evidence for igneous differentiation of at least five asteroid parent bodies based on this analysis of a small subset of the near infrared asteroid spectra taken to date with spex at the nasa irtf we expect that the number of known differentiated asteroids will increase consistent with the large number of parent bodies inferred from studies of iron meteorites

reappraisal of the ages of neoproterozoic strata in south china no connection with the grenvillian orogeny the jiangnan fold belt separates the yangtze and cathaysia blocks in south china and has long been considered grenvillian in age in order to place south china in central rodinia it consists of deformed early neoproterozoic strata that are unconformably overlain by undeformed late neoproterozoic strata and intruded by undeformed and unmetamorphosed granitic plutons zircons from the early neoproterozoic strata yield u pb ages as young as 830 ma and one granitic pluton has a zircon u pb age of ca 827 ma the 830 ma mafic rocks along the southeastern margin of the yangtze block have arc affinity geochemical characters whereas mafic rocks younger than 830 ma have typical ocean island basalt oib like compositions thus we suggest that the early neoproterozoic strata were deposited on an active continental margin prior to amalgamation of the yangtze and cathaysia blocks at ca 830 ma the overlying late neoproterozoic strata were deposited in the intracontinental rifted nanhua basin at 820 730 ma and probably reflect backarc spreading above the long lived 950 735 ma oceanic subduction zone along the northern and western margin of the yangtze block this model is consistent with the secular tectonic evolution of south china during the neoproterozoic the jiangnan fold belt is therefore not a grenvillian feature as previously suggested and there is no evidence to place south china in central rodinia instead we believe that south china was located in a marginal position relative to this supercontinent

almahata sitta asteroid 2008 tc3 and the search for the ureilite parent body abstract this article explores what the recovery of 2008 tc3 in the form of the almahata sitta meteorites may tell us about the source region of ureilites in the main asteroid belt an investigation is made into what is known about asteroids with roughly the same spectroscopic signature as 2008 tc3 a population of low inclination near earth asteroids is identified with spectra similar to 2008 tc3 five asteroid families in the main belt as well as a population of ungrouped asteroids scattered in the inner and central belts are identified as possible source regions for this near earth population and 2008 tc3 three of the families are ruled out on dynamical and spectroscopic grounds new near infrared spectra of 142 polana and 1726 hoffmeister lead objects in the two other families also show a poor match to almahata sitta thus there are no main belt spectral analogs to almahata sitta currently known space weathering effects on ureilitic materials have not been investigated so that it is unclear how the spectrum of the main belt progenitor may look different from the spectra of 2008 tc3 and the almahata sitta meteorites dynamical arguments are discussed as well as ureilite petrogenesis and parent body evolution models but these considerations do not conclusively point to a source region either other than that 2008 tc3 probably originated in the inner asteroid belt

can slab melting be caused by flat subduction slab melting has been suggested as a likely source of adakitic arc magmas i e andesitic and dacitic magmas strongly depleted in y and heavy rare earth elements existing numerical and petrologic models however restrict partial melting to very young 5 ma oceanic crust typically at 60 80 km depth paradoxically most of the known pliocene quaternary adakite occurrences are related to subduction of 10 45 ma lithosphere which should not be able to melt under normal subduction zone thermal gradients we propose an unusual mode of subduction known as flat subduction occurring in 10 of the world s convergent margins that can produce the temperature and pressure conditions necessary for fusion of moderately old oceanic crust of the 10 known flat subduction regions worldwide eight are linked to present or recent 6 ma occurrences of adakitic magmas observations from chile ecuador and costa rica suggest a three stage evolution 1 steep subduction produces a narrow calc alkaline arc typically 300 km from the trench above the asthenospheric wedge 2 once flat subduction begins the lower plate travels several hundred kilometers at nearly the same depth thus remaining in a pressure temperature window allowing slab melting over this broad distance and 3 once flat subduction continues for several million years the asthenospheric wedge disappears and a volcanic gap results as in modern day central chile or peru the proposed hypothesis which reconciles thermal models with geochemical observations has broad implications for the study of arc magmatism and for the thermal evolution of convergent margins

spectra of extremely reduced assemblages implications for mercury we investigate the possibility that mercury s crust is very reduced with feo concentrations of less than 0 1 wt we believe that such a surface could have a composition of enstatite plagioclase diopside and sulfide similar to the mineral assemblages found in aubritic meteorites to test this hypothesis we investigated the spectra of aubrites and their constituent minerals as analogs for the surface of mercury we found that some sulfides have distinctive absorption features in their spectra shortwards of 0 6 m that may be apparent in the spectrum of such an object determination of the surface composition of mercury using orbital x ray spectroscopy should easily distinguish between a lunar highlands and enstatite basalt composition since these materials have significant differences in concentrations of al mg s and fe the strongest argument against mercury having an enstatite basalt composition is its extreme spectral redness significant reddening of the surface of an object such as mercury is believed to require reduction of feo to nanophase iron thus requiring a few percent feo in the material prior to alteration

a new age constraint on the onset of the neoproterozoic glaciations in the yangtze platform south china abstract a sample from the top of the banxi group early neoproterozoic in hunan province south china was dated by the shrimp zircon u pb method the resulting age of 725 10 ma probably solves the debate between the synglacial and the preglacial correlation of the liantuo formation and indicates that the liantuo formation most likely correlates with the preglacial banxi group since the banxi danzhou group is upwardly transitional to the glacial jiangkou group the age becomes a new maximum age constraint on the onset of the jiangkou glaciation which therefore most likely correlates with the sturtian glaciation

near ir spectral evidence for the presence of iron poor orthopyroxenes on the surfaces of six m type asteroids abstract the first verifiable near infrared absorption features in the 0 9 m spectral region are reported for asteroids 16 psyche 69 hesperia 110 lydia 125 liberatrix 201 penelope and 216 kleopatra these weak features 1 3 are attributed to orthopyroxenes present on the surfaces of these asteroids 16 psyche and 125 liberatrix have full rotational coverage while 69 hesperia 110 lydia 201 penelope and 216 kleopatra have 75 rotational coverage qualitative 2 m absorption features are present but are very weak 1 absorption band positions suggest relatively low abundances of calcium and iron in the pyroxenes this indicates relatively reducing redox conditions for these asteroids their parent bodies and the nebular regions in which they formed four potential interpretations for these asteroids include 1 they are exposed metallic cores or core fragments of differentiated parent bodies with residual orthopyroxene mantle material 2 they are the result of a smelting like reaction that converts olivine to pyroxene and metallic iron in the presence of carbon at high temperatures 3 they are analogs to the primitive metal rich bencubbinite meteorites or 4 they represent metallic surfaces which have accumulated silicate debris from external sources of the two original interpretations for the m asteroids the enstatite chondrite interpretation chapman and salisbury 1973 icarus 19 507 522 gaffey and mccord 1979 mineralogical and petrological characterizations of asteroids in gehrels t ed asteroids univ of arizona press tucson pp 688 723 can be eliminated for these asteroids because the pyroxene in enstatite chondrites is iron free and does not exhibit such absorption features the iron meteorite interpretation remains valid but with modification for m asteroids 16 psyche and 216 kleopatra these spectral results combined with previous determinations of high radar albedos indicate that these bodies are most probably exposed core fragments of differentiated bodies m asteroids 69 hesperia 110 lydia 125 liberatrix and 201 penelope exhibit similar spectral features consistent with exposed core fragments but radar observations would be needed to confirm a high metal abundance observations of m asteroids 136 austria and 325 heidelberga suggest the absence of absorption features in the 0 4 to 2 5 m region within the scatter of the data verification of the presence or absence of features across the surfaces of these two asteroids requires full rotational coverage the interpretations for these featureless m asteroids are not well constrained but remain consistent with the iron meteorite and enstatite chondrite interpretations

in situ elemental and isotopic compositions of apatite and zircon from the shuikoushan and xihuashan granitic plutons implication for jurassic granitoid related cu pb zn and w mineralization in the nanling range south china abstract the nanling range south china was world famous for hosting abundant granitoid related copper lead zinc cu pb zn polymetallic ore deposits and quartz vein type wolframite w ore deposits both of which have roughly similar formation ages predominately between 150 and 160 ma with a peak of ca 156 ma in this study accessory minerals from typical cu pb zn bearing and w bearing granitic rocks are compared in terms of elemental and isotopic compositions apatite from w bearing granites in the xihuashan pluton has lower end t value 11 9 to 8 6 than that from cu pb zn bearing granitic rocks in shuikoushan with end t value of 8 7 to 4 2 and initial 87sr 86sr ratio of 0 7097 0 7109 zircon grains in xihuashan yielded ehf t value from 14 9 to 11 4 18o value from 8 6 to 10 4 and highly variable and negative 7li value 45 8 to 3 8 whereas those in shuikoushan have relatively higher ehf t value 10 6 to 8 1 lower 18o value 8 4 9 7 and highly variable 7li values from 12 7 to 17 6 in situ hf o li isotopic compositions of zircon and sr nd isotopes of apatite suggesting that the shuikoushan granitic pluton was likely generated from dehydration melting of amphibolite from a metal fertile mafic source in the middle to lower crust whereas the xihuashan granitic pluton could be derived from partial melting of metapelite with minor amphibolite in the middle to upper crust the geochemical records in accessory minerals fingerprint that the shuikoushan granitic magma was characterized by high cl content 0 11 1 44 wt and logfo2 value fmq 1 whereas the xihuashan granitic magma have elevated f 3 51 4 80 wt and li 3 49 42 4 ppm contents with low logfo2 value