Impact of mica on geotechnical behavior of weathered granitic soil using macro and micro investigations

The micaceous weathered granitic soil(WGS)is frequently encountered in civil engineering worldwide,unfortunately little information is available regarding how mica affects the physico-mechanical behaviors of WGS.This study prepares reconstituted WGS with different mica contents by removing natural mica in theWGS,and then mixes it with commercial mica powders.The geotechnical behavior as well as the microstructures of the mixtures are characterized.The addition of mica enables the physical indices of WGS to be specific combinations of coarser gradation and high permeability but high Atterberg limits.However,high mica content in WGS was found to be associated with undesirable mechanical properties,including increased compressibility,disintegration,and swelling potential,as well as poor compactability and low effective frictional angle.Microstructural analysis indicates that the influence of mica on the responses of mixtures originates from the intrinsic nature of mica as well as the particle packing being formed withinWGS.Mica exists in the mixture as stacks of plates that form a spongy structure with high compressibility and swelling potential.Pores among the plates give the soil high water retention and high Atterberg limits.Large pores are also generated by soil particles with bridging packing,which enhances the permeability and water-soil interactions upon immersion.This study provides a microlevel understanding of how mica dominates the behavior of WGS and provides new insights into the effective stabilization and improvement of micaceous soils.

Heterogeneities of grain boundary contact for simulation of laboratoryscale mechanical behavior of granitic rocks

From a practical point of view,grain structure heterogeneities are key parameters that control the rock response and still remains a challenge to incorporate in a quantitative manner.One of the less discussed topics in the context of the grain-based model(GBM)in the particle flow code(PFC)is the contact heterogeneities and the appropriate contact model to mimic the grain boundary behavior.Generally,the smooth joint(SJ)model and linear parallel bond(LPB)model are used to simulate the grain boundary behavior.However,the literature does not document the suitability of different models for specific problems.Another challenge in implementing GBM in PFC is that only a single bonding parameter is used at the grain boundaries.The aim of this study is to investigate the responses of a laboratory-scale specimen with SJ and LPB models,considering grain boundary heterogeneous and homogeneous contact parameters.Uniaxial and biaxial compression tests are performed to calibrate the response of Creighton granite.The stressestrain curves,volumetric dilation,inter-crack(crack in the grain boundary),and intra-crack(crack within the grain)development,and failure patterns associated with different contact models are examined.It was found that both the SJ and LPB models can reproduce the pre-peak behavior observed for a granitic rock type.However,the LPB model is unable to reproduce the post-peak behavior.Due to the large interlocking effect originating from the balls in contact and the ball size in the LPB model,local dilation is induced at the grain boundaries.This overestimates the volumetric dilation and residual shear strength.The LPB model tends to result in discontinuous inter-cracks and stress localization in the rock specimen,resulting in fine fragments at the rock surface during failure.

Digital monitoring of rotary-percussive drilling with down-the-hole hammer for profiling weathered granitic ground

Rock and geotechnical engineering investigations involve drilling holes in ground with or without retrieving soil and rock samples to construct the subsurface ground profile.On the basis of an actual soil nailing drilling for a slope stability project in Hong Kong,this paper further develops the drilling process monitoring(DPM)method for digitally profiling the subsurface geomaterials of weathered granitic rocks using a compressed airflow driven percussive-rotary drilling machine with down-the-hole(DTH)hammer.Seven transducers are installed on the drilling machine and record the chuck displacement,DTH rotational speed,and five pressures from five compressed airflows in real-time series.The mechanism and operations of the drilling machine are elaborated in detail,which is essential for understanding and evaluating the drilling data.A MATLAB program is developed to automatically filter the recorded drilling data in time series and classify them into different drilling processes in sub-time series.These processes include penetration,push-in with or without rod,pull-back with or without rod,rod-tightening and rod-untightening.The drilling data are further reconstructed to plot the curve of drill-bit depth versus the net drilling time along each of the six drillholes.Each curve is found to contain multiple linear segments with a constant penetration rate,which implies a zone of homogenous geomaterial with different weathering grades.The effect from fluctuation of the applied pressures is evaluated quantitatively.Detailed analyses are presented for accurately assess and verify the underground profiling and strength in weathered granitic rock,which provided the basis of using DPM method to confidently assess drilling measurements to interpret the subsurface profile in real time.

The late Early-Paleozoic granitic magmatism in Northwestern Fujian, China: constraints on intraplate orogeny in the South China block

The Early Paleozoic tectono-thermal event was a significant orogenic activity during the Phanerozoic era,which had a profound impact on the early crust of the South China Block(SCB) and established the foundation for later tectonic activity.The Wuyi-Yunkai orogenic belt in Southeastern China was extensively exposed to Early Paleozoic magmatism,the genetic mechanism of which remains controversial.To shed light on this issue,detailed petrological,geochemical,and zircon U-Pb-Hf isotopic studies were carried out on two granitoids,namely the Yuntongshan pluton and the Gaoqiao pluton,identified in the central Wuyishan.Zircon U-Pb chronology of the Yuntongshan and Gaoqiao bodies yielded ages of437±4 Ma(MSWD=2.2) and 404±2 Ma(MSWD=12),respectively,indicating that they were emplaced during the Early Silurian and Early Devonian periods.These granitoids are primarily composed of biotite-granite and biotite-monzonitic-granites,with high concentrations of S_(i)O_(2)(73.59-75.91 wt%),K_(2)O+Na_(2)O(8.31-8.73wt%),and low contents of MgO,CaO,Cr,Ni.They are classified as high-K calc-alkaline and weakly metaluminous-strongly peraluminous S-type granites.These granitoids are enriched in light rare earth elements(LREEs) and large ion lithophile elements(LILEs) and depleted in heavy rare earth elements(HREEs) and high field strength elements(HFSEs) with arc affinity.The εHf(t) values of-3.3 to-15.4 with two-stage Hf model ages ranging from 2829 to 1644 Ma,combined with the presence of Neoproterozoic inherited zircons,suggest that the primary magma of these granitoids was derived from the partial melting of Neoproterozoic crust with a Paleoproterozoic crustal model age.These findings,combined with the spatio-temporal distribution of regional magmatism,reveal that the late Early-Paleozoic granitoids formed in the intraplate orogenic background originating from the subduction of the proto-Tethys Ocean and proto-Pacific Ocean around the margin of the east Gondwana supercontinent.

Spalling characteristics of high-temperature treated granitic rock at different strain rates

The dynamic spalling characteristics of rock are important for stability analysis in rock engineering.This paper presented an experimental investigation on the dynamic spalling characteristics of granite with different temperatures and strain rates.A series of dynamic spalling tests with different impact velocities were conducted on thermally treated granite at different temperatures.The dynamic spalling strengths of granite with different temperatures and strain rates were determined.A model was proposed to correlate the dynamic spalling strength of granite,high temperature and strain rate.The results show that the spalling strength of granite decreases with increasing temperature.Moreover,the spalling strength of granite with a higher strain rate is larger than that with a lower strain rate.The proposed model can describe the relationship among dynamic spalling strength of granite,high temperature and strain rate.

Numerical simulation of formation mechanism of unloading joints in granitic pluton

The Beishan pluton in Gansu of China was selected as the simulated model.The simulation results indicate that the formation of unloading joints in granite is mainly influenced by the unloading rate of confin-ing pressure.Among the rates tested,the slowest unloading rate 0.025 MPa/s is found to be most conducive to the development of unloading joints.Therefore,a slower unloading rate is favourable for the occurrence of unloading joints.A series of simulations with varying initial depths of uplift ranging from 900 m to 200 m were conducted.The results confirm that when the specimen rises to a depth of 550-500 m,the unloading joints begin to form.The uplift from a depth of 700-500 m,with variations in both vertical and lateral un-loading rates,was simulated.The generation of unloading joints exhibits a negative correlation with vertical unloading and no correlation with lateral unloading,indicating that the unloading joints are mainly controlled by the unloading of vertical pressure.Throughout the simulation process,the vertical joints exhibit irregular and unrealistic regularity,suggesting a more complex formation mechanism than that of the unloading joints.

Fluid Characteristics and Evolution of the Zhawulong Granitic Pegmatite Lithium Deposit in the Ganzi-Songpan Region, Southwestern China

The Zhawulong granitic pegmatite lithium deposit is located in the Ganzi-Songpan orogenic belt.Fluid inclusions in spodumene and coexisting quartz were studied to understand the cooling path and evolution of fluid within albite–spodumene pegmatite.There are three distinguishable types of fluid inclusions:crystal-rich,CO2–NaCl–H2 O,and NaCl–H2 O.At more than 500°C and 350~480 MPa,crystal-rich fluid inclusions were captured during the pegmatitic magma-hydrothermal transition stage,characterized by a dense hydrous alkali borosilicate fluid with a carbonate component.Between 412°C and 278°C,CO2–Na Cl–H2 Ofluid inclusions developed in spodumene(I)and quartz(II)with a low salinity(3.3–11.9 wt%NaCl equivalent)and a high volatile content,which represent the boundary between the transition stage and the hydrothermal stage.The subsequentNaCl–H2 Ofluid inclusions from the hydrothermal stage,between 189°C and 302°C,have a low salinity(1.1–13.9 wt%NaCl equivalent).The various types of fluid inclusions reveal the P–T conditions of pegmatite formation,which marks the transition process from magmatic to hydrothermal.The oreforming fluids from the Zhawulong deposit have many of the same characteristics as those from the Jiajika lithium deposit.The ore-forming fluid provided not only materials for crystallization of rare metal minerals,such as spodumene and beryl,but also the ideal conditions forthe growth of ore minerals.Therefore,this area has favorable conditions for lithium enrichment and excellent prospecting potential.

Geochemical Characteristics and Genesis of the Granitic Gneisses from the Southeastern Dabie Mountains

The granitic gneisses from the ultrahigh-pressure (UHP) metamorphic terrain of the southeastern Dabie Mountains encompass two types: monzonitic granitic gneiss and alkali-feldspar granitic gneiss, which are characterized by rich alkalis, poor CaO, high FeO/MgO, particularly high Ba, Rb, Th, Ta, REE (except Eu), Ga, Nb and Zn, and low Sr, Eu, Cr, Co and Ni. The gneisses, particularly the alkali-feldspar granitic gneiss, have typical chemical characteristics of A-type granites. They resulted from partial melting of crustal materials existing in the rift zone along the northern margin of the South China block during the Neoproterozoic. These gneisses might not have undergone UHP metamorphism during the late Triassic, but were involved into UHP rocks by the tectonic mixing process and kept the exhumation message of the UHP rocks from the middle and upper crust.

SHRIMP U-Pb Dating of Zircons of a Dark Eclogite and a Garnet-bearing Gneissic Granitic Rock from Bixiling,Eastern Dabie Area,Anhui Province:Isotope Chronological Evidence of Neoproterozoic UHP Metamorphism

The paper reports SHRIMP U-Pb zircon data of a dark eclogite and a post-eclogite garnet-bearing gneissic granitic rock from the Bixiling area, Yuexi County, Anhui Province, in the eastern Dabie Mountains. The eclogite, which is metamorphosed basic tuff, contains very scarce zircons in omphacite or garnet, but more zircons in quartz. They usually exhibit a double-layered texture, as shown clearly in cathodoluminescence images. Their inner main parts give a 206Pb/238U age of 757±7 Ma, representing the approximate age of the high-pressure (HP)- ultrahigh-pressure (UHP) metamorphic event during which the eclogite was formed. The outer peripheral parts of the zircons, which have been modified by late-stage fluids, give an age of 223±3 Ma. The granitic rock contains more zircons of anatectic origin found mostly in feldspar and quartz and usually also showing a similar composite texture. The inner main parts of the anatectic zircons with oscillatory zoning give a 206Pb/238U age of 727±15 Ma for the approximate age of the emplacement of the granitic rock, and their outer parts, an age of 219±3 Ma for a similar or even the same fluid event. It is thus suggested that the HP-UHP metamorphism of the Bixiling eclogite facies rocks took place during the Neoproterozoic Jinningian, and the Indosinian age values may only represent a late event in the nature of fluid activity.

SHRIMP Dating and Recrystallization of Metamorphic Zircons from a Granitic Gneiss in the Sulu UHP Terrane

An unusual zircon SHRIMP dating result of a granitic gneiss from the Qinglongshan eclogite-gneiss roadcut section is presented in this paper. The very peculiar and complicated internal structures, as well as the very low Th/U ratios (0.01-0.08) of the zircons indicate that they were formed by metamorphic recrystallization. Strongly in contrast with previously published zircon U-Pb ages of the Dabie-Sulu UHP metamorphic rocks where protolith ages of 600-800 Ma are commonly recorded, only metamorphic age of 218±5 Ma, defined by 18 analytical spots either in rim or in core of zircons, are recorded in this granitic gneiss. This age represents the time of the complete metamorphic recrystallization overprint on primary magmatic zircons. The recrystallization was derived by the UHP metamorphism, and was strengthened by the early stage of retrograde metamorphic fluid activity.

Forceful Emplacement of Granitic Plutons in an Extensional Tectonic Setting:Syn-kinematic Plutons in the Yagan-Onch Hayrhan Metamorphic Core Complex

It is generally considered that granitic plutons are forcefully emplaced in acompressional setting and permissively emplaced in an extensional setting. This paper, however,shows that syn-kinematic (extensional) elliptic granitic plutons in the Yagan-Onch Hayrhanmetamorphic core complex (MCC) have relatively strong forceful emplacement, which are indicated by(1) concentric distribution of the rock units, (2) a strain pattern with strong strains on themargins and low strains at the centre of a pluton, and particularly (3) syn-emplacement shorteningof the host rocks within the aureole. The strain analysis for the host rocks shows that thehost-rock ductile shortening, i.e. forceful emplacement, provides about 16-24 percent of theemplacement space for the present plutons. All these suggest that forceful emplacement occurs notonly in a compressional tectonic setting, but also in an extensional setting. This study furtherdemonstrates the significance of the multiple emplacement of granitic plutons and provides newinformation about the causality between granitic magmatism and the formation of the MCC and itsdynamics.

Effects of collapsing gully erosion on soil qualities of farm fields in the hilly granitic region of South China

Collapsing gully erosion is a specific form of soil erosion types in the hilly granitic region of tropical and subtropical South China, and can result in extremely rapid water and soil loss. Knowledge of the soil physical and chemical properties of farmland influenced by collapsing gully erosion is important in understanding the development of soil quality. This study was conducted at the Wuli Watershed of the Tongcheng County, south of Hubei Province, China. The aim is to investigate soil physical and chemical properties of three soil layers （0-20, 20-40 and 40-60 cm） for two farmland types （paddy field and upland field） in three regions influenced by collapsing gully erosion. The three regions are described as follows： strongly influenced region （SIR）, weakly influenced region （WIR） and non-influenced region （NIR）. The results show that collapsing gully erosion significantly increased the soil gravel and sand content in paddy and upland fields, especially the surface soil in the SIR and WIR. In the 0-20 cm layer of the paddy field, the highest gravel content （250.94 g kg-1） was in the SIR and the lowest （78.67 g kg-1） was in the NIR, but in the upland filed, the surface soil （0-20 cm） of the SIR and the 40-60 cm soil layer for the NIR had the highest （177.13 g kg-1） and the lowest （59.96 g kg-1） values of gravel content, respectively. The distribution of gravel and sand decreased with depth in the three influenced regions, but silt and clay showed the inverse change. In the paddy field, the average of sand content decreased from 58.6 （in the SIR） to 49.0% （in the NIR）, but the silt content was in a reverse order, increasing from 27.9 to 36.9%, and the average of the clay content of three regions showed no significant variation （P〈0.05）. But in the upland filed, the sand, silt and clay fluctuated in the NIR and the WIR. Soils in the paddy and upland field were highly acidic （pH〈5.2） in the SIR and WIR; moreover lower nutrient contents （soil organic matter （SOM）, total N and available N, P, K） existed in the SIR. In the 0-20 cm soil layer of the paddy field, compared with the NIR and the WIR, collapsing gully erosion caused a very sharp decrease in the SOM and total N of the SIR （5.23 and 0.56 g kg-1, respectively）. But in the surface soil （0-20 cm） of the upland field, the highest SOM, total N, available N, available P and available K occurred in the NIR, and the lowest ones were in the SIR. Compared with the NIR, the cation exchange capacity （CEC） in the SIR and WIR was found to be relatively lower. These results suggest that collapsing gully erosion seriously affect the soil physical and chemical properties of farmland, lead to coarse particles accumulation in the field and decrease pH and nutrient levels.

Estimating Influence of Crystallizing Latent Heat on Cooling-Crystallizing Process of a Granitic Melt and Its Geological Implications

Based on the theory of thermal conductivity, in this paper we derived a formula to estimate the prolongation period （AtL） of cooling-crystallization process of a granitic melt caused by latent heat of crystallization as follows：△tL=QL×△tcol/（TM-TC）×CP where TM is initial temperature of the granite melt, Tc crystallization temperature of the granite melt, Cp specific heat, △tcol cooling period of a granite melt from its initial temperature （TM） to its crystallization temperature （Tc）, QL latent heat of the granite melt. The cooling period of the melt for the Fanshan granodiorite from its initial temperature （900℃） to crystallization temperature （600℃） could be estimated -210,000 years if latent heat was not considered. Calculation for the Fanshan melt using the above formula yields a AtL value of -190,000 years, which implies that the actual cooling period within the temperature range of 900°-600℃ should be 400,000 years. This demonstrates that the latent heat produced from crystallization of the granitic melt is a key factor influencing the cooling-crystallization process of a granitic melt, prolongating the period of crystallization and resulting in the large emplacement-crystallization time difference （ECTD） in granite batholith.

Influence of groundwater drawdown on excavation responses e A case history in Bukit Timah granitic residual soils

Performances of a braced cut-and-cover excavation system for mass rapid transit （MRT） stations of the Downtown Line Stage 2 in Singapore are presented. The excavation was carried out in the Bukit Timah granitic （BTG） residual soils and characterized by significant groundwater drawdown, due to dewatering work in complex site conditions, insufficient effective waterproof measures and more permeable soils. A two-dimensional numerical model was developed for back analysis of retaining wall movement and ground surface settlement. Comparisons of these measured excavation responses with the calculated performances were carried out, upon which the numerical simulation procedures were calibrated. In addition, the influences of groundwater drawdown on the wall deflection and ground surface settlement were numerically investigated and summarized. The performances were also compared with some commonly used empirical charts, and the results indicated that these charts are less applicable for cases with significant groundwater drawdowns. It is expected that these general behaviors will provide useful references and insights for future projects involving excavation in BTG residual soils under significant groundwater drawdowns.

Experimental investigation on damage evolution behaviour of a granitic rock under loading and unloading

In-situ rock failures can result from stress changes due to pure loading and/or unloading. Understanding of the damage evolution behavior in brittle rocks during loading and unloading is imperative for the designs of rock structures. In this paper, we investigate the damage evolution characteristics of a granitic rock during loading and unloading after a series of triaxial experiments performed at different confining pressures. The axial stress-axial strain variations of the tested specimens revealed that the specimens undergoing unloading fail with a lower axial strain compared to the specimens failed purely by loading. Higher confining pressures were observed to exacerbate the difference. Volumetric strain versus axial strain curves indicated that the curves reverse the trend with the beginning of major damage of specimens. We suggest here a new form of equation to describe the secant modulus variation of brittle rocks against the axial stress for the unloading process. Failure mechanisms of tested specimens showed two distinct patterns, namely, specimens under pure loading failed with a single distinct shear fracture while for the unloading case specimens displayed multiple intersecting fractures. In addition, analysis of the evolution of dissipation and elastic energy during deformation of the specimens under loading and unloading conditions showed differentiable characteristics. Moreover, we evaluated the variations of two damage indices defined based on the energy dissipation and secant modulus evolution during deformation and observed that both of them satisfactorily distinguish key stages of damage evolution.

Granitic Magmatism in Eastern Tethys Domain(Western China) and their Geodynamic Implications

Western China locates in the eastern section of the Tethys domain, granitic rocks in this region with variable formation ages and geochemistry record key information about the crust-mantle structure and thermal evolution during the convergent process of Tethys. In this study, we focus on some crucial granitic magmatism in the western Yangtze, Qinling orogen, and western Sanjiang tectonic belt, where magma sequence in the convergent orogenic belt can provide important information about the crust-mantle structure, thermal condition and melting regime that related to the evolution processes from Pre-to Neo-Tethys. At first, we show some features of Pre-Tethyan magmatism, such as Neoproterozoic magmatism(ca. 870–740 Ma) in the western margin of the Yangtze Block were induced by the assembly and breakup of the Rodinia supercontinent. The complication of voluminous Neoproterozoic igneous rocks indicated that the western Yangtze Block underwent the thermodynamic evolution from hot mantle-cold crust stage(ca. 870–850 Ma) to hot mantle and crust stage(ca. 850–740 Ma). The Neoproterozoic mantle sources beneath the western Yangtze Block were progressively metasomatized by subduction-related compositions from slab fluids(initial at ca. 870 Ma), sediment melts(initial at ca. 850 Ma), to oceanic slab melts(initial at ca. 825–820 Ma) during the persistent subduction process. Secondly, the early Paleozoic magmatism can be well related to three distinctive stages(variable interaction of mantle-crust to crustal melting to variable sources) from an Andeans-type continental margin to collision to extension in response to the evolution of ProtoTethys and final assembly of Gondwana continent. Thirdly, the Paleo-Tethys magmatism, Triassic granites in the Qinling orogenic display identical formation ages and Lu-Hf isotopic compositions with the related mafic enclaves, indicate a coeval melting event of lower continental crust and mantle lithosphere in the Triassic convergent process and a continued hot mantle and crust thermal condition through the interaction of subducted continental crust and upwelling asthenosphere. Finally, the Meso-and Neo-Tethyan magmatism: Early Cretaceous magmatism in the Tengchong Block are well responding to the subduction and closure of Bangong-Nujiang Meso-Tethys, recycled sediments metasomatized mantle by subduction since 130 Ma and subsequently upwelling asthenosphere since ca. 122 Ma that causes melting of heterogeneous continental crust until the final convergence, this process well recorded the changing thermal condition from hot mantlecold crust to hot mantle and crust;The Late Cretaceous to Early Cenozoic magmatism well recorded the processes from Neo-Tethyan ocean slab flat subduction, steep subduction, to initial collision of India-Asia, it resulted in a series of continental arc magmatism with enriched mantle to crustal materials at Late Cretaceous, increasing depleted and/or juvenile materials at the beginning of early Cenozoic, and increasing evolved crustal materials in the final stage, implying a continued hot mantle and crust condition during that time. Then we can better understand the magmatic processes and variable melting from the mantle to crust during the evolution of Tethys, from Pre-, Paleo-, Meso-, to Neo-, both they show notably intensive interaction of crust-mantle and extensive melting of the heterogeneous continent during the final closure of Tethys and convergence of blocks, and thermal perturbation by a dynamic process in the depth could be the first mechanism to control the thermal condition of mantle and crust and associated composition of magmatism.

Petrology and Geochemistry of the Huangshan Granitic Intrusion in Anhui Province,Southeast China:Implications for Petrogenesis and Geodynamics

The Huangshan granitic intrusion in Anhui province,SE China,is tectonically located at the southeastern boundary of the Yangtze Block.Based on the contact relation and the petrography,the Huangshan granitic intrusion can be divided into four stages,from early to late,medium-grained monzogranite,coarse-grained porphyric granite,fine-medium grained porphyric granite,and finecoarse grained granite.All rocks from the Huangshan granitic intrusion display similar petrological and geochemical characteristics,i.e.relatively high SiO_2（〉75%） and alkali（7.85%-8.59%）,low CaO （〈1%）,high Fe-number（FeO_T/（MgO＋FeO_T） = 0.93-0.97） and A/CNK（atomic Al/（Ca＋Na＋K））=1.04- 1.19.They are also enriched in rare earth elements（REE,except for Eu,with a total REE contents ranging from 116 ppm to 421 ppm）,high strength field elements such as Zr,Hf,Nb,but depleted in Ba,Sr and Ni.The 10 000×Ga/Al ratios are higher than 2.6,which are consistent with the A-type granitoids.Based on the classification diagrams proposed by Eby,the Huangshan granite can be classified into the A2 group,which is usually believed to be formed under an extensional tectonic setting.Their Nd isotopic compositions suggest that the primary magmas of the Huangshan granite are predominantly derived from the Proterozoic andesitic rocks in the region,and this conclusion is also supported by REE modeling.The systemic investigations on the geochemistry of the Huangshan granitic intrusion can provide significant implications for the understanding of the petrogenesis and the geodynamic regime of southeastern China during the Late-Mesozoic.

Mineralogy and geochemistry of Nb-,Ta-,Sn-,U-,Th-,and Zr-bearing granitic rocks from Abu Rusheid shear zones,South Eastern Desert,Egypt

Granite-hosted,Nb-,Ta-,Sn-,U-,Th-,and Zr(Hf)-bearing mineralization from the Abu Rusheid shear zones occurs about 97 km southwest of the town of Marsa Alam,South Eastern Desert,Egypt.The SSE-trending brittle-ductile Abu Rusheid shear zones crosscut the peralkalic granitic gneisses and cataclastic to mylonitic rocks(mylonite,protomlyonite,and ultramylonite).The northern shear zone varies in width from 1 to 3 m with a strike length of >500 m,and the southern shear zone is 0.5 to 8 m wide and >1 km long.These shear zones locally host less altered lamprophyre and locally sheared granitic aplite-pegmatite dykes.The rare-metal minerals,identified from the peralkalic granitic gneisses and cataclastic to mylonitic rocks are associated with muscovite,chlorite,quartz,fluorite,pyrite,magnetite,and rare biotite that are restricted to the Abu Rusheid shear zones;these are columbite-tantalite and pyrochlore(var.betafite) in the northern shear zone and ferrocolumbite in the southern shear zone.Cassiterite occurs as inclusions in the columbite-tantalite minerals.U-and Th-minerals(uraninite,thorite,uranothorite,ishikawaite,and cheralite) and Hf-rich zircon coexist.Magmatic(?) zircon contains numerous inclusions of rutile,fluorite,U-Th and REE minerals,such as uranothorite,cheralite,monazite,and xenotime.Compositional variations in Ta/(Ta+Nb) and Mn/(Mn+Fe) in columbite range from 0.07-0.42 and 0.04-0.33,respectively,and Hf contents in zircon from 1.92-6.46 of the two mineralized shear zones reflect the extreme degree of magmatic fractionation.Four samples of peralkalic granitic gneisses and cataclastic to mylonitic rocks from the southern shear zone have very low TiO2(0.02 wt%-0.04 wt%),Sr [(15-20)×10-6],and Ba [(47-78)×10-6],with high Fe2O3T(0.94 wt%-1.99 wt%),CaO(0.14 wt%-1.16 wt%),alkalis(9.2 wt%-10.1 wt%),Rb [(369-805)×10-6],Zr [(1033-2261)×10-6],Nb [(371-913)×10-6],U [(51-108)×10-6],Th [(36-110)×10-6],Ta [(38-108)×10-6],Pb [(39-364)×10-6],Zn [(21-424)×10-6],Y [(8-304)×10-6],Hf [(29-157)×10-6],and ∑REE [(64-304)×10-6],especially HREE [(46-167)×10-6].Three samples from the northern shear zone also have very low TiO2(0.03 wt%),Sr [(11-16)×10-6],and Ba [(38-47)×10-6],with high Fe2O3T(1.97 wt%-2.91 wt%),CaO(0.49 wt%-1.01 wt%),alkalis(7.2 wt%-8.3 wt%),Rb [(932-978)×10-6],Zr [(1707-1953)×10-6],Nb [(853-981)×10-6],Ta [(100-112)×10-6],U [(120-752)×10-6],Th [(121-164)×10-6],Pb [(260-2198)×10-6],Zn [(483-1140)×10-6],Y [(8-304)×10-6],Hf [(67-106)×10-6],and ∑REE [(110-231)×10-6],especially HREE [(91-177)×10-6].The very high Rb/Sr(57.5-88.9),and low Zr/Hf(16.9-25.6),Nb/Ta(7.7-9.8),and Th/U(0.21-1.01) are consistent with very frac-tionated fluorine-bearing granitic rocks that were altered and sheared.The field evidence,textural relations,and compositions of the ore minerals suggest that the main mineralizing event was magmatic(629+/-5 Ma,CHIME monazite),with later hydrothermal alteration and local remobilization of the high-field-strength elements.

Bainiuchang super-large silver-polymetallic ore deposit related to granitic magmatism in Mengzi, Yunnan

Bainiuchang silver-polymetallic ore deposit is located in the southeast Yunnan tin-polymetallic metallogenic belt.The probable reserves and inferred resources of the deposit are of 6 470 t Ag and 1.10 Mt Pb and 1.72 Mt Zn and 86 kt Sn.Orebodies of the deposit occur in clastic-carbonate rocks of Tianpeng Formation and Longha Formation of the middle Cambrian System above the Bainiuchang concealed granite of the late Yanshan period.The concealed granite has the characteristics of tin-bearing granites.Abundance of the mineralization elements Sn,Cu,Zn,Pb,Ag and Sb is high in the granitic rocks.Sulphur isotope data of the metal sulphides indicate that most sulphur is derived from the magmas.The ores are similar in rare earth element(REE)patterns to the granitic rocks.The granitic magma activity results in ore-bearing structures.Rocks of the Middle Cambrian System above the concealed intrusion suffer from skarnization,hornfelsing,marbleization,siliconizing and carbonatization.The mineralization elements Sn,Cu,Zn,Pb,Ag and Sb successively appear from the top of the granite to surrounding rocks.These evidences indicate that the granitic magmatism is the principal mineralization factor.The opinion that the south Bainiuchang ore field and the north Awei ore block are tin and copper potential exploration areas was put forward and was verified by drilling tests.

Copper partitioning between granitic silicate melt and coexisting aqueous fluid at 850°C and 100 MPa

Experiments on the partitioning of Cu between different granitic silicate melts and the respective coexisting aqueous fluids have been performed under conditions of 850 ℃, 100 MPa and oxygen fugacity （fO2） buffered at approaching Ni-NiO （NNO）. Partition coefficients of Cu （Dcu = Cfluid/Cmelt） were varied with different alumina/alkali mole ratios [Al2O3/（Na2O ＋ K2O）, abbreviated as Al/ Alk], Na/K mole ratios, and SiO2 mole contents. The DCu increased from 1.28 ± 0.01 to 22.18 ±0.22 with the increase of Al/Alk mole ratios （ranging from 0.64 to 1.20） and Na/K mole ratios （ranging from 0.58 to 2.56）. The experimental results also showed that Dcu was positively correlated with the HCl concentration of the starting fluid. The Dcu was independent of the SiO2 mole content in the range of SiO2 content considered. No Dcu value was less than 1 in our experiments at 850 ℃ and 100 MPa, indicating that Cu preferred to enter the fluid phase rather than the coexisting melt phase under most conditions in the melt-fluid system, and thus a significant amount of Cu could be transported in the fluid phase in the magmatichydrothermal environment. The results indicated that Cu favored partitioning into the aqueous fluid rather than the melt phase if there was a high Na/K ratio, Na-rich, peraluminous granitic melt coexisting with the high Cl^- fluid.