ce anomalies in the lew85300 eucrite evidence for ree mobilization during antarctic weathering abstract there is abundant evidence for widespread ree mobilization in antarctic eucrites resulting in ce and eu anomalies and lower whole rock ree abundances relative to typical eucrites using secondary ion mass spectrometry sims we investigated the microdistribution of ce anomalies in the antarctic polymict eucrite lew85300 ce anomalies positive and or negative are present in all three of the minerals plagioclase pyroxene and silica analysed the anomalies occur in grains from all four clasts as well as in mineral and lithic fragments from the surrounding matrix thus there appears to be no lithologic association silica which has been heavily shocked and altered exhibits a lree enriched pattern with negative ce and eu anomalies consistent with a derivation of the ree from ca phosphate dissolution trivalent ree are leached from the phosphates with preferential retention of tetravalent ce and redeposited on silica pyroxene is also widely affected by ree mobilization due to an extensive shock induced microcrack network along cleavage planes a tendency for the largest ce anomalies to occur at low lree concentrations suggests that pyroxene itself experienced ree leaching with concomitant ce retention ce anomalies are rare in plagioclase because this mineral lacks an extensive network along which ree can be mobilized the widespread ree mobilization and evidence for other forms of weathering requires that trace element data be used cautiously especially for antarctic eucrites

the origin and mode of emplacement of lujavrites in the ilimaussaq alkaline complex south greenland abstract lujavrites are rare meso to melanocratic agpaitic nepheline syenites that are characterized by elevated contents of elements such as li be zr ree nb th and u they are the most evolved members of the three large composite agpaitic complexes lovozero kola peninsula russia pilansberg south africa and ilimaussaq south greenland and are inferred to stem from the same deep fractionating magma sources that fed the earlier members of the complexes the composition of the melts that evolved into lujavrites is however not well known the agpaitic part of the ilimaussaq complex is divided into a roof series a floor series of cumulates and an intermediate series of lujavrites sandwiched between the two in the traditional view the lujavrites formed from residual melts left between the downward crystallizing roof series and the floor cumulates new field observations and geochemical data suggest that the floor cumulates and the main mass of lujavrites constituted a separate intrusive phase which was emplaced into the already consolidated roof series rocks largely by piecemeal stoping studies of the contact facies of the floor cumulates indicate that the initial magma of the floor cumulate lujavrite sequence was peralkaline nepheline syenitic with enhanced contents of zr hf hree y nb ta f ba and sr subsequent crystallization in a closed system resulted in the formation of the floor cumulates and lujavrites chemical analyses of dykes within and outside the complex represent stages in the magmatic evolution of the agpaitic rocks

influence of fluorine on the solubility of manganotantalite mnta2o6 and manganocolumbite mnnb2o6 in granitic melts an experimental study abstract solubility experiments of manganotantalite mnta 2 o 6 and manganocolumbite mnnb 2 o 6 were conducted under nearly fluid saturated conditions in synthetic haplogranitic hpg and natural granitic ng melts containing different amounts of fluorine at 800 to 1000 c and 200 mpa the experiments were carried out in cold seal pressure vessels at 800 c with water or ar as a pressure medium and in internally heated pressure vessels 1000 c with ar as a pressure medium the f contents vary from 0 to 11 43 wt in experiments using hpg melts and from 0 61 to 3 78 wt in experiments using ng melts additionally the ng melt contains minor amounts of p 2 o 5 0 44 to 0 64 wt in hpg melts alumina saturation index including mn asi mn 0 88 to 0 99 the solubility product values at 800 c yield log k sp ta and log k sp nb ranging from 3 36 0 10 to 2 92 0 10 mol kg and from 3 01 0 11 to 2 87 0 06 mol kg respectively in ng melts the log k sp ta and log k sp nb vary from 3 00 0 04 to 2 35 0 13 mol kg and from 2 83 0 06 to 2 67 0 18 mol kg at 800 c respectively the solubility products of both mnta 2 o 6 k sp ta and mnnb 2 o 6 k sp nb are not significantly affected by the f content for a given melt composition data are virtually identical within error the variation of the solubility products observed in this study is rather attributed to the changes in melt structure e g polymerization and in particular to the alumina saturation index by contrast there is no evidence for the formation of complexes associating f and nb and or ta our results also indicate that the structural changes caused by the incorporation of f in natural water rich silicate melts are not expected to significantly influence the maximum concentrations of nb and ta in granitic or pegmatitic melts coexisting with manganotantalite and manganocolumbite

chemical processes affecting the mobility of major minor and trace elements during weathering of granitic rocks abstract the behaviour of 38 major and trace elements as well as changes in the mineralogy have been examined in 10 weathering profiles developing on some portuguese granitic rocks element mobilities are calculated from geochemical data normalized with respect to ti in the fresh parent rock chemical elements are divided into two groups immobile and mobile on the basis of their geochemical distribution during weathering elements that are immobile during weathering are zr hf fe al th nb sc and the ree very mobile are ca na p k sr ba rb mg and si mobile elements are derived mainly from leachable minerals such as feldspars micas and apatites whereas immobile elements are either concentrated in resistate phases or strongly adsorbed by secondary minerals the geochemical behaviour of mn cr v fe and ce is very dependent on redox conditions redox transformations of these elements can be used to set limits on the oxidation state of a weathering suite the ree are mobilized or fractionated during late stages of weathering but not during moderate stages of weathering this fractionation is caused by selective leaching of rocks composed of both stable and unstable minerals containing ree

investigation of the excavation damaged zone around deep tbm tunnel using a voronoi element based explicit numerical manifold method abstract a voronoi element based explicit numerical manifold method is adopted to investigate the evolution process and failure characteristics of the excavation damaged zone around a deeply buried tbm tunnel an explicit time integration scheme of numerical manifold method is adopted as the numerical platform based on which a voronoi polygon assemblage is generated to approximate the blocky structure of the surrounding rock mass resulting from discrete fracture networks a new mathematical mesh generation method is developed to better adapt to the voronoi polygons and an excavation algorithm including both in situ stress equilibrium and tbm excavation modelling techniques is proposed to capture the mechanical response of the tbm tunnelling process with the newly developed ve enmm approach the progressive failure process of the surrounding rock mass in a headrace tunnel of yindajihuang project is simulated and the formation mechanism of the excavation damaged zone is explored simulation results show that a large extent of excavation damaged zone is easily formed in the highly fractured rock mass due to the high in situ stress in deep grounds besides relatively large convergence displacements are predicted around the tunnel surface leading to a high risk of tbm shield jamming as in the practical situation however the development of damaged zone is effectively restrained and the convergence displacements are well controlled by an early installation of the tunnel lining segments thus preventing the occurance of tbm shield jamming additional simulations are conducted to study the effects of the lateral in situ stress ratio on the excavation damaged zone it is inferred that the increase of lateral stress ratio facilitates the fracturing of the surrounding rock mass which results in a larger extent of the damaged zone and more severe squeezing deformation compared with those under lower lateral stresses

a comparative study of gabbro and granite weathering in the piedmont of the southeastern u s a gabbros and granites weather in quite different fashions granites develop extensive weathering rind systems 2 m thick in which plagioclase is altered to a gibbsite kaolinite assemblage in rindlets adjacent to the fresh rock contact in the outer rindlets the clay fraction is dominated by kaolinite and dioctahedral vermiculite not surprisingly granitic weathering rind systems display relative depletions of si na ca rb and sr and relative enrichments of sesquioxides in contrast gabbro weathering rind systems are characterized by many thin 1 cm rindlets whose alteration products are dominated by limonitization of ferromagnesian minerals apart from a decrease in feofe2o3 ratios in the outer rindlets there is little relative depletion or enrichment of major elements in gabbro weathering rinds as compared to their fresh rock cores this contradiction in goldich s stability series is explained if weathering rinds are produced faster on gabbros than in granite outcrops thus the low degree of mineral alteration in gabbro rindlets reflects a shorter time of residence for minerals in this system compared to rindlets on granitic outcrops biotite and perthitic microcline were separated from a fresh granite and its attendant weathering rind system during alteration the albitic blebs of the perthite are dissolved leaving no trace of residual clay the result is a porous microcline whose composition is equivalent to the microcline matrix in the unweathered perthite progressive alteration of biotite results in oxidation of octahedrally coordinated fe2 with concomitant loss of k this results in the formation of dioctahedral vermiculites in outer rindlet samples of granite

petrogenetic and mineralization processes in paleo to mesoproterozoic rapakivi granites examples from pitinga and goias brazil abstract the 1 8 ga pitinga granites agua boa and madeira massifs in amazonas northern brazil are within plate shallow level rapakivi granites associated with an extensional fracture system they comprise an early facies of pyterlitic to wiborgitic rapakivi granite a fine to medium grained biotite granite as well as topaz granite agua boa massif and albite granite madeira massif the granites are usually metaluminous to peraluminous the albite granite however is peralkaline they are enriched in sio2 k2o na2o f rb th nb y zr and the rare earth element ree and impoverished in mgo tio2 p2o5 and sr as the majority of sn mineralized granites sn contents range from 1 ppm in the rapakivi facies to 3400 ppm in the albite granite end at 1 8 ga values vary from 2 2 to 0 4 and nd model ages lie between 2 4 and 2 1 ga mineralization in the madeira massif includes disseminated magmatic cryolite zircon cassiterite pyrochlore columbite tantalite and xenotime and massive cryolite bodies in the f rich peralkaline albite granite in the agua boa massif sn mineralization is associated with greisens and episyenite the 1 77 ga g1 and 1 58 1 57 ga g2 rapakivi granites of goias central brazil are coeval with the arai rift basin granites of the g1 suite are metaluminous and alkaline while the g2 suite is metaluminous to peraluminous both are enriched in f sn rb y th nb ga and the ree primary micas range from fe rich biotite to zinnwaldite the micas of the more evolved granites and the metasomatic micas are strongly enriched in f with f li between 2 and 10 the initial end values of both suites show a considerable range 14 to 0 and indicate substantial compositional variation in source sn deposits in goias are hosted mainly by greisens indium is concentrated in quartz topaz rock and albitized g2d granite of the mangabeira massif and is always related to a cassiterite sulfide association this quartz topaz rock is of metasomatic origin probably generated by a hydrothermal fluid derived from the topaz albite granite mineralization in the studied deposits was essentially associated with f enrichment in the peralkaline madeira albite granite extremely high f contents favored disseminated mineralization while in the goias tin province gtp and agua boa massif greisenization was related to early fluid saturation the gtp and pitinga granites display tectonic petrogenetic geochemical isotopic and metallogenic similarities that can be applied in search of sn and rare metal deposits

a model for the origin of the alkaline complexes of egypt the alkaline complexes in the nubian shield of egypt range in age from 554 to 89 myr bp refs 1 3 and where data are available have similar and primitive initial strontium ratios of 87sr 86sr ref 1 these intrusive complexes are similar with respect to petrography major element chemistry rare earth element distribution and other trace element distribution1 4 7 they are intimately associated with major lineaments in the nubian shield fig 1 8 it is likely that all of them had a similar origin not directly related to rifting and or doming we suggest here that the origin of these complexes is due to alkaline melts having been formed in the asthenosphere by shear heating caused by changes in plate motion these melts were emplaced along reactivated pan african fractures or pre existing zones of weakness

chemical evolution of rare earth elements fractionation between colloidal and solution phases of filtered river water abstract within the dissolved fraction of connecticut river water there is large scale fractionation of rare earth elements between colloidal and solution phases colloidal particles carry a large part of the dissolved ree pool filtration through filters with progressively smaller pore size 0 45 0 22 and 0 025 m results in filtrates with lower absolute concentrations of ree and more fractionated compositions with decreasing pore size the filtrates have shale normalized abundances which become systematically more depleted in the lree relative to the hree hence both the solution and colloidal phases are significantly fractionated with respect to the dissolved fraction these conclusions are consistent with previous studies of ree in rivers estuaries and soils and with surface solution speciation models colloids play an important role in the aquatic geochemistry of rare earth elements they are responsible for the fractionation of ree during the estuarine removal of ree the removal of suspended and colloidal particles from river water leaves the solution phase of river water with compositions of ree as evolved as those of surface seawater hence the evolution of the composition of ree in river water and seawater is significantly influenced by colloid formation during chemical weathering on the continents

the rare metal deposits of the el garra el hamra syenites south western desert egypt abstract the el garra el hamra complex is a small high level plug with associated volcanics that was emplaced along an ene wsw trending dextral strike slip fault corresponding to the guinean nubian lineament owing to continued movement along this fault the intrusion split into two parts that were displaced horizontally by approximately 580 m the intrusion consists mainly of syenites fresh and altered and granites altered that are locally overlain by alkaline trachyte and rhyolite and are hosted by nubian sandstones the fresh syenites are composed of perthitic k feldspars albite alkali pyroxenes aegirine augite and aegirine and secondary alkali amphiboles arfvedsonite and riebeckite accessory minerals include opaques apatite zircon xenotime y and bastnasite ce calcite and hematite are alteration products geochemically the syenites are peralkaline their cipw norms classify them as ranging between syenite and quartz syenite in compositions they were emplaced in a within plate tectonic setting along the guinean nubian lineament kalabsha close to the extension of the chephren kom ombo trend a branch of the trans african shear zone they were evolved from a magma compositionally similar to ocean island basalt oib numerous dextral and sinistral strike slip faults cut the intrusion and may have facilitated the circulation of fluids that altered them hydrothermally these faults developed during or shortly after emplacement of the intrusion or perhaps during subsequent reactivation of the guinean nubian and trans african shear zones and were accompanied by dykes that range in compositions from intermediate to acidic composition most of which strike ene wsw hydrothermal alteration of the syenites locally led to extreme enrichment in rare metals e g lree hree zr hf th u nb and be as the minerals zircon gittinsite bastnasite ce parisite ce monazite ce ree rich fluorapatite chevkinite ce xenotime y pyrochlore columbite fe nb rutile and thorite fluorite and barite are important gangue minerals

hydrothermal transport and deposition of the rare earth elements by fluorine bearing aqueous liquids new technologies particularly those designed to address environmental concerns have created a great demand for the rare earth elements ree and focused considerable attention on the processes by which they are concentrated to economically exploitable levels in the earth s crust there is widespread agreement that hydrothermal fluids played an important role in the formation of the world s largest economic ree deposit i e bayan obo china until recently many researchers have assumed that hydrothermal transport of the ree in fluorine bearing ore forming systems occurs mainly due to the formation of ree fluoride complexes consequently hydrothermal models for ree concentration have commonly involved depositional mechanisms based on saturation of the fluid with ree minerals due to destabilization of ree fluoride complexes here we demonstrate that these complexes are insignificant in ree transport and that the above models are therefore flawed the strong association of h and f as hf and low solubility of ree f solids greatly limit transport of the ree as fluoride complexes however this limitation does not apply to ree chloride complexes because of this the high concentration of cl in the ore fluids and the relatively high stability of ree chloride complexes the latter can transport appreciable concentrations of ree at low ph the limitation also does not apply to sulphate complexes and in some fluids the concentration of sulphate may be sufficient to transport significant concentrations of ree as sulphate complexes particularly at weakly acidic ph this article proposes new models for hydrothermal ree deposition based on the transport of the ree as chloride and sulphate complexes

petrogenetic interpretation of granitoid rock series using multicationic parameters abstract granitoid rock compositions from a range of tectonic environments are plotted on a multicationic diagram devised by de la roche and his coworkers this shows that there is a systematic change through an orogenic cycle which leads progressively to the ultimate development of alkaline magmas possible source materials and mechanisms of magma generation are considered from analysis of mineral compositional vectors these suggest that most granitoid series result from a two stage process first fractional crystallisation of clinopyroxene olivine and calcic plagioclase from a basic source with tholeiitic affinities produces a magma of intermediate composition this magma then undergoes periodic mixing with a felsic magma followed by in situ fractionation to generate individual intrusions within granitoid series

in situ stress estimates from hydraulic fracturing and direct observation of crack orientation estimates of in situ stress in g tunnel rainier mesa nevada test site have been obtained with hydraulic fracturing techniques this work represents a nontraditional use of hydraulic fracturing in that it was performed primarily in horizontal boreholes drilled into the formation from access drifts tunneled into the mesa rather than the usual operation performed at depth in vertical boreholes drilled from the surface several operations were performed in essentially orthogonal triads of boreholes located at a point a significant feature of this work is the mineback operation in which the borehole is mined out to reveal the actual fracture during the hydraulic fracturing operation colored dye was added to the fracturing fluid which left an easily detectable stain on the fracture surface direct observation of the fracture orientation away from the borehole establishes the direction of the minimum compressive in situ stress and the plane of the other two principal stresses in one borehole which was not aligned along a principal stress direction a modified mineback operation revealed a fracture plane that twisted as it grew away from the borehole aligning itself finally in a plane determined by the in situ stresses this twisting is consistent with theoretical predictions of borehole stresses under these conditions this same mineback also showed that fracture of the formation initiated at or under one of the packers indicating that the packers may have an effet on in situ stress estimates general observations of over 100 tests performed in g tunnel show that under the sloping portion of the mesa fracture planes are not vertical but dip in a direction tending to parallel the mesa slope deep into the tunnel and well under the flat part of the mesa fractures are essentially vertical with strikes approximately n45 e which substantiates the usual vertical fracture assumption in traditional fracture operations performed at depth in vertical boreholes advantages limitations and problem areas associated with extracting in situ stress fields from hydraulic fracture pressure records are discussed in detail

the effects of weathering on rare earth element y and ba abundances in tertiary basalts from southeastern australia tholeiitic basalts showing anomalously high ba y and rare earth element ree concentrations occur within the tertiary newer volcanic province of victoria and these geochemical characteristics are related to incipient alteration accompanying weathering ree and y released during weathering of basalts are retained either in secondary phosphate or clay minerals and in rocks showing very high ba concentrations the ba is present as baso4 leaching experiments suggest that glassy or fine grained rocks are more likely to release ree y and ba while more extensively altered rocks are likely to hold these elements probably because they substitute in or are adsorbed on clay minerals or because secondary baso4 and ree phosphates are resistant to acid leaching samples taken sequentially across a weathering profile in a tholeiitic basalt flow from fresh to intensively altered rock illustrate that in the very earliest stages of alteration extreme variations in the abundances of ba y and ree can occur this is reflected in the broad patterns of trace element behaviour manifested by an extensive analysed sample suite from the victorian newer volcanic province where there is no correlation between anomalous enrichments in ba y or ree and the level of incipient alteration ba anomalies are not necessarily accompanied by abnormal y and ree behaviour and this is probably because the mobility of each trace element is a function of a the ionic radius and charge of the ionic species it forms in solution b local groundwater parameters such as eh ph groundwater flux and concentrations in the groundwater of species such as so42 and c the secondary mineral assemblages developed in a particular situation sr isotopic compositions are not strongly affected by incipient weathering and do not show significant changes until alteration has progressed to the point where plagioclase begins to break down the study illustrates that relatively slight alteration at the earliest stages of weathering can produce drastic changes in the concentrations of ree y and ba and petrographic assessment of the freshness of samples is not precise enough to eliminate prior to analysis cases where these effects may be manifested where weathering has caused changes in abundance patterns these may be recognised by careful comparisons of appropriate elemental ratios e g ba rb throughout a particular analysed sample suite

faulting induced by forced fluid injection and fluid flow forced by faulting an interpretation of hydraulic fracture microseismicity carthage cotton valley gas field texas we analyzed precisely located microearthquake data detected during five hydraulic fracture treatments in the carthage gas field of east texas the treat ments were conducted in two adjacent boreholes within interbedded sands and shales of the upper cotton valley formation the microearthquakes were induced within narrow horizontal bands that correspond to the targeted sandstone layers events throughout all the treatments show strike slip faulting occurring uniformly along vertical fractures trending close to maximum horizontal stress direction these events are consistent with the reservoir s prevalent natural fractures known to be isolated within the sands and trending subparallel to the expected hydraulic fracture orien tation when this uniform fracture system was activated exclusively the detected shear deformation measured as the moment release per unit volume of fluid injected was constant independent of various fluid viscosities and flow rates used within the base of the upper cotton valley formation anomalous event counts and moment release occurred within dense clusters that delineate bends or jogs in the fracture zones the mechanisms are also strike slip but the fault planes are more favorably oriented for failure the dense clusters show location patterns diverging in time suggesting the expulsion of fluids from compressive fault jogs fluid flow forced by the adjacent slip induced loading appears to initially extend the treatments but the loading also tends to lock up and concentrate stress at the jogs as evident by fewer but larger events populating the structures as treatments progress as a result effec tive drainage lengths from the boreholes may be shorter than would be inferred from the seismicity extending past the jogs these high moment asperities are similar to dense patches of seismicity observed along creeping sections of the san andreas fault where they have been attributed to localized zones of strength or stress con centration surrounded by larger regions undergoing stable aseismic slip this sim ilarity plus large moment deficits in terms of volume injected suggests a large component of aseismic slip is induced by the cotton valley treatments

geochemical and mineralogical characteristics of ion adsorption type ree mineralization in phuket thailand geochemical and mineralogical studies were conducted on the 12 m thick weathering profile of the kata beach granite in phuket thailand in order to reveal the transport and adsorption of rare earth elements ree related to the ion adsorption type mineralization the parent rock is ilmenite series biotite granite with transitional characteristics from i type to s type abundant in ree 592 ppm ree are contained dominantly in fluorocarbonate as well as in allanite titanite apatite and zircon the chondrite normalized ree pattern of the parent granite indicates enrichment of lree relative to hree and no significant ce anomaly the upper part of the weathering profile from the surface to 4 5 m depth is mostly characterized by positive ce anomaly showing lower ree contents ranging from 174 to 548 ppm and lower percentages of adsorbed ree from 34 to 68 compared with the parent granite in contrast the lower part of the profile from 4 5 to 12 m depth is characterized by negative ce anomaly showing higher ree contents ranging from 578 to 1 084 ppm and higher percentages from 53 to 85 the negative ce anomaly and enrichment of ree in the lower part of the profile suggest that acidic soil water in an oxidizing condition in the upper part mostly immobilized ce4 as ceo2 and transported ree3 downward to the lower part of the profile the transported ree3 were adsorbed onto weathering products or distributed to secondary minerals such as rhabdophane the immobilization of ree results from the increase of ph due to the contact with higher ph groundwater since the majority of ree in the weathered granite are present in the ion adsorption fraction with negative ce anomaly the percentages of adsorbed ree are positively correlated with the whole rock negative ce anomaly the result of this study suggests that the ion adsorption type ree mineralization is identified by the occurrence of easily soluble ree fluorocarbonate and whole rock negative ce anomaly of weathered granite although fractionation of ree in weathered granite is controlled by the occurrence of ree bearing minerals and adsorption by weathering products the ion adsorption fraction tends to be enriched in lree relative to weathered granite

strength degradation and anchoring behavior of rock mass in the fault fracture zone rock mass in the fault fracture zone has some characteristics such as low strength and poor self stability so the control mechanism of stability has been a difficulty in the research of underground engineering a set of laboratory simulation method of fault fractured rock mass is developed to reflect the natural forming process of fault fracture zone compared with intact rock mass the fault fractured rock mass has an obvious degradation in strength and deformation parameters and the degradation index is between 22 79 and 84 06 the bolt has a certain supporting effect on the fault fractured rock mass and in the situation of end anchoring the greater the pretightening force is the better the enforcement effect will be the stress field produced by high pretightening force can relieve the stress concentration around the bolt hole and make the initial cracks of rock mass away from the bolt plate the evolution curve of bolt axial force in the process of uniaxial compression of large scale specimen shows four stages which are the initial compression stage pre peak joint load bearing stage post peak joint load bearing stage and the residual stage research results could provide some theory reference for the stability control of rock mass in the fault fracture zone

numerical modeling of seismicity induced by fluid injection in naturally fractured reservoirs the interaction between hydraulic and natural fractures is of great interest for the energy resource industry because natural fractures can significantly influence the overall geometry and effectiveness of hydraulic fractures microseismic monitoring provides a unique tool to monitor the evolution of fracturing around the treated rock reservoir and seismic source mechanisms can yield information about the nature of deformation we performed a numerical modeling study using a 2d distinct element particle flow code pfc2d to simulate realistic conditions and increase understanding of fracturing mechanisms in naturally fractured reservoirs through comparisons with results of the geometry of hydraulic fractures and seismic source information locations magnitudes and mechanisms from both laboratory experiments and field observations a suite of numerical models with fully dynamic and hydromechanical coupling was used to examine the interaction between natural and induced fractures the effect of orienta

ree fractionation and ce anomalies in weathered karoo dolerite abstract analyses of samples from a weathering profile on karoo dolerite allow elements to be divided into three groups depending on their behaviour si k na mg ca sr ba and v are mobilized and removed from weathered products fe al ti zr hf zn cu sc co and ni are immobile ree y and to a lesser extent cr are mobile and redistributed within the profile without a net loss of these elements from the profile large positive ce anomalies are developed in oxidized weathered products by preferential leaching of the other ree s negative ce anomalies and ree enrichment is a feature of less altered dolerite

u pb zircon geochronology of precambrian tin bearing continental type acid magmatism in central brazil abstract u pb geochronological data for alkali rich granitic and associated rhyolitic rocks from two different tin bearing sub provinces of the goias tin province in central brazil reveal two distinct episodes of mid proterozoic continental acid magmatism at ca 1770 ma and 1600 ma ago u pb zircon data for the sucuri and soledade granites of the eastern rio parana sub province rps define upper intercept ages of 1767 10 ma and 1769 2 ma respectively these ages are indistinguishable from a u pb age of a rhyolite from the basal portion of the arai group 1771 2 ma these results attest to the contemporaneity of the intrusion of the granites and the crystallization of the rhyolitic lavas in the rio parana sub province u pb isotopic results from zircons from the serra da mesa granite in the western rio tocantins sub province rts indicate that the granitic igneous activity in that area is ca 150 ma younger than that in the rps the inheritance pattern observed in the zircons from the arai rhyolite suggests that the sialic basement in the rps region may include an early proterozoic ca 2 2 ga component inheritance of possibly archaean age was also found in zircons from the sucuri granite lower intercept age of 658 ma for the soledade granite zircons indicate pb loss during the late proterozoic brasiliano pan african thermo tectonic event 650 550 ma similar associations of tin bearing alkali rich granites with rhyolites and succeeding continental sediments are known in other parts of the precambrian shield of brazil this indicates that extensive areas of this shield experienced extensional tectonics in intracontinental settings between ca 1700 and 1900 ma ago

application of high field strength elements to discriminate tectonic settings in vms environments high field strength element ratios in felsic volcanic rocks reflect the tectonomagmatic evolution of a region th ta th hf ta hf th yb and ta yb ratios collectively help to define the tectonic environment of volcanism separating oceanic arcs active continental margins and within plate volcanic zones on the basis of the above empirical observations the tectonic environments of selected archean and post archean volcanogenic massive sulfide deposits were reexamined published data sets plotted on discriminant diagrams represent twelve volcanogenic massive sulfide vms deposits from two distinct tectonic environments the volcanic rocks of the kuroko deposits japan san nicolas mexico and bathurst new brunswick canada plot within the active continental margin field on all diagrams whereas volcanic rocks from archean deposits of the superior province canada kidd creek kamiskotia geco winston lake mattabi lyon lake noranda selbaie and south bay plot in the within plate volcanic zone field the discriminant diagrams demonstrate that although the chemical character of rhyolites has not changed significantly since the archean the range of geotectonic setting of vms deposits probably has it is suggested that archean deposits most likely formed in an ensimatic rift environment whereas post archean deposits formed in subduction related rift zones of arc environments subduction related rhyolites of vms deposits are variably enriched in th and the light rare earth elements with respect to ta nb and the heavy rare earth elements

mass change calculations in altered rock series a technique is presented whereby precursors of altered rocks in a fractionated rock series can be identified and changes in chemical components mass and volume accurately calculated the procedure utilizes elements with high degrees of immobility in hydrothermal and associated interactive water rock systems igneous rock series and sedimentary and metamorphic rocks with primary continuity of chemical composition are amenable to this treatment in the procedure for igneous rocks best fit fractionation lines are established for an immobile igneous compatible incompatible element pair the latter element functioning as the fractionation monitor alteration paths are linear and pass through the origin intersections of the fractionation and alteration lines yield the immobile element concentrations in the precursors to the altered rocks mobile components are determined from fractionation lines and monitor values total mass changes are proportional to the displacement of altered samples from the fractionation line masses of other elements in an altered sample reconstructed values are recalculated to the concentration of the monitor element in the precursor chemical changes are the differences between the calculated precursor compositions and the reconstructed altered rock compositions errors are mainly a function of the positioning of the fractionation lines

variation in the orientation of the maximum horizontal stress in thick channel fill sandstones with low permeability a case of the bonan oilfield in the bohai bay basin eastern china abstract measurements of in situ stress in a single well from borehole breakouts hydraulic fracturing multipole acoustic logs and differential strain analysis of core indicate that the orientation of the maximum horizontal stress is northwest southeast in thick channel fill sandstones in the central western bonan oilfield while the orientation is northeast southwest in the thin interbed siltstones and mudstones of the floodplain in the eastern bonan oilfield this result shows that the orientation of the maximum horizontal stress in the thin interbed of siltstones and mudstones is in accordance with the regional stress orientation obtained by the focal mechanism of a natural earthquake but has a 30 40 variation with the thick channel fill sandstones finite element simulation suggests that the main reason for the variation in the orientation of the maximum horizontal stress is the diversity of overall mechanical properties especially modulus of elasticity of the thick channel fill sandstones and the interbedded thin layer of siltstones and mudstones the average young s modulus over the stratigraphic column governs stress rotations the transformation of the orientation of the maximum horizontal stress from the central western to the eastern locations is at the channel boundary this research provides a case in which the variation in the orientation of the maximum horizontal stress is affected by thick channel fill sandstones it shows that lithological changes can cause variations in the direction of in situ stress

major element ree and other trace element behavior in amphibolite weathering under semiarid conditions in southern india abstract a body of komatiitic amphibolite an enclave within the archean high grade orthogneisses in southern india shows mild chemical weathering under semiarid conditions along fractures chemical weathering has advanced chemical index of alteration documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape mathrm cia 53 end document cia of fresh documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage

investigation of the influence of natural fractures and in situ stress on hydraulic fracture propagation using a distinct element approach hydraulic fracturing is the primary means for enhancing rock mass permeability and improving well productivity in tight reservoir rocks significant advances have been made in hydraulic fracturing

modeling of fluid injection induced fault reactivation using coupled fluid flow and mechanical interface model abstract the present study is aimed at developing a numerical model to reproduce coupled hydro mechanical processes associated with fault reactivation by fluid injection in low permeability rock as part of the decovalex 2019 project task b we proposed a modeling approach for simulating the processes using the tough flac simulator and modeled a fault reactivation experiment conducted at mont terri rock laboratory in switzerland the first step of the study involved benchmark calculations considering a simplified fault plane and geometry fluid flow along a fault was modeled using elements of aperture sized thickness on the basis of darcy s law and the cubic law in tough2 whereas the mechanical behavior of a single fault was represented by zero thickness interface elements in flac3d upon which a slip and or separation is allowed a methodology to connect a tough2 volume element to a flac3d interface element was developed for handling the hydro mechanical interactions on the fault during fluid injection two different fault models for describing the evolutions of hydraulic aperture by elastic fracture opening and failure induced aperture increase were considered in the benchmark calculations in the coupling process the changes in geometrical features and hydrological properties induced by mechanical deformation were continuously updated the transient responses of the fault and host rock to stepwise pressurization were examined during the simulation the hydro mechanical behavior including the injection flow rate pressure distribution around the borehole stress conditions and displacements in normal and shear directions were monitored in the surrounding rock and along the fault the results of benchmark calculations suggest that the developed model reasonably represents the hydro mechanical behavior of a fault and the surrounding rock this modeling approach was applied to the fault reactivation experiment of the mont terri rock laboratory in this interpretive modeling a parametric study was conducted to examine the effects of input parameters regarding in situ stress and fault properties on the hydro mechanical responses of the fault to water injection then an optimal parameter set to reproduce the field experiment results was chosen by trial and error the injection flow rate and pressure response during fault reactivation closely matched those obtained at the site which indicates the capability of the model to appropriately capture the progressive pathway evolution during fault reactivation tests at the site the anchor displacements were overestimated by the model but a fair agreement was obtained in terms of the order of magnitude and the variation tendency

geochemical and mineralogical characteristics of reey occurrences in the mocambo granitic massif tin bearing a type granite central brazil and its potential for ion adsorption type reey mineralization abstract the mocambo granitic massif is an a type granite located in the northeastern part of goias state near the city of monte alegre de goias it belongs to the pedra branca suite which is itself part of the goias tin province a group of stanniferous granites that exhibit similar geochemical features including to a greater or lesser degree of rare earth elements enrichment the parent rock in the mocambo granitic massif is a coarse porphyritic pink biotite granite thin section observations coupled with electron microprobe analyses reveal the presence of several ree bearing minerals allanite fergusonite ce fergusonite y zircon and apatite as accessory minerals and xenotime y bastnasite ce thorite monazite ce and hingganite y as secondary hydrothermal minerals fergusonite and hingganite are identified in this massif for the first time this work investigates the forms of occurrence and enrichment of rare earth elements in the mocambo granitic massif in the parent rock as well as in greisen saprolite and soil with emphasis placed on the rare earth elements adsorbed on clay minerals and the entire process of transport and fractionation of these elements from the fresh rock until adsorption the results show enrichment of rare earth elements with the exception of ce in soils in comparison to rock especially in the clay fraction moreover they suggest that these elements are mostly adsorbed on clay minerals mostly kaolinite and illite which are identified in the x ray patterns the surface oxidation of ce3 to ce4 on surfaces and the probable formation of ce oxides cause this element to present a smaller quantity of exchangeable ions the presence of cerianite grains in one superficial soil sample shows that ce is mostly found in the ce4 state in the soil profile the mocambo granitic massif displays substantial enrichment in reey 555 1229 ppm for the parental granite and 569 ppm for the greisen and the exchangeable reey concentrations in the soils horizons more than 600 ppm in particular representing a potential target for an ion adsorption type rare earth elements deposit

granites and the geodynamic history of the neoproterozoic brasilia belt central brazil a review abstract recent field and geochronological studies have demonstrated the importance of granitic magmatism in the evolution of the neoproterozoic brasilia belt in central brazil this is an orogenic belt developed in response to the convergence between the amazon sao francisco congo and parana continental blocks the presence of neoproterozoic juvenile arc rocks and syn collisional peraluminous granites challenged previous intracontinental evolution models for the belt the granitoid intrusions reviewed in this paper record the different stages of evolution of the orogen and their field and isotopic characteristics can be used to reconstruct the tectonic history of the belt the main field and isotopic characteristics of four granite suites associated with the brasilia belt are reviewed i 1 77 1 58 ga old rift related a type granite intrusions ii ca 0 8 0 7 syn collisional granitoids iii arc metatonalites and metagranodiorites ca 0 9 to 0 63 ga and iv bimodal post orogenic suite ranging in age from ca 0 59 to 0 48 ga these rocks suggest that during most of the neoproterozoic the western margin of the sao francisco continent faced a large oceanic basin where subduction and oceanic lithosphere consumption started at ca 0 9 ga roughly coeval with the initial stages of the break up of rodinia final ocean closure happened at ca 0 63 0 60 ga with crustal thickening uplift and erosion post orogenic extension related magmatism took place between ca 0 6 and 0 5 ga and was partially contemporaneous with the deposition of the paraguay and tucavaca sedimentary successions resulting from the rifting event related to the break up of laurentia from southwestern gondwana

geochemistry of mineralization with exchangeable rey in the weathering crusts of granitic rocks in south china abstract mineralization with exchangeable rare earth element ree and yttrium mex rey has been recognized in the weathering profiles in south china since the early 1970 s this type of rey mineralization occurs in weathering profiles of parent rocks ranging in composition from granite to acidic volcanic rocks and lamprophyre the majority of the known resources occurring in the weathering profiles of granitic rocks total resources of this type of rey amount to millions tons of rare earth oxides and therefore represent one of the most important types of rare earth resources in china particularly for heavy rare earth elements hree and yttrium accumulation of rey in the weathering profiles of granitic rocks is strongly controlled by the resistance to weathering of the principal rey bearing accessory minerals in the parent rocks only a limited proportion of total rey 4 and na etc in electrolyte solutions and can be removed by complexing agents such as edta are commonly the major form of ree occurrence in the b horizon cerium is enriched in the top layer a horizon and depleted in the subsurface horizons of the weathering profiles most likely due to the oxidation of ce iii to ce iv followed by cerianite formation or absorption onto clays and or fe and al oxyhydroxides