Abstract:The Jurassic-Cretaceous Tunxi basin in southern Anhui is located at the junction between the NE-trending Middle-Lower Yangtze volcanic belt and the NNE-trending Southeast China volcanic belt. Geochronological and petrogenetic study of the volcanic rocks can provide information regarding the Late Mesozoic tectonic evolution of South China. LA-ICP-MS zircon U-Pb ages and geochemical data of four volcanic rock samples indicate that two volcanic stages are developed in Tunxi basin. The earlier volcanic rocks were formed at 156~152 Ma. These rocks belong to the calc-alkaline series with middle-to-high K content, and are characterized by the REE right-inclined patterns with weak negative Eu anomalies, LILE and LREE enrichment, and HFSE (such as Nb, Ti, P) depletion. In contrast, the late volcanic rocks were formed at 136~130 Ma and are characterized by bimodal volcanic rocks. Acidic components of these rocks belong to the calc-alkaline series with intermediate K content. These rocks exhibit the right-inclined "V" type REE patterns with strong negative Eu anomalies, LILE and LREE enrichment, and HFSE (such as Nb, Ti, P) depletion. Late Jurassic-Early Cretaceous volcanism features of Tunxi basin resemble those of Southeast China volcanic belt. Combined with previous studies, Late Jurassic volcanic rocks in Tunxi basin were generated in a compressional tectonic environment, whereas Early Cretaceous ones were generated in an extensional tectonic environment. Both of them were attributed to the subductional angular variation and the rollback of the Paleo-Pacific plate from Late Jurassic to Early Cretaceous.

Abstract:Xiaotuergen is the first porphyry copper deposit discovered in Nuoerte area in recent years. Granite porphyry, granodiorite porphyry and biotite monzonitic granite are widely developed in the ore district, and the mineralization is closely related to the granodiorite porphyry. In order to investigate the petrogenesis of intrusive rocks and their intrinsic relationship with copper mineralization, the authors carried out the petrographic and geochemical studies of the widely developed intrusive rocks in the ore district. The results show that all rocks exhibit high silica and alkaline, with moderate aluminum content. They belong to high-K calc-alkaline and shoshonitic rocks. All samples are enriched in Rb, Ba and other large ion lithophile elements(LILE) and LREE, and relatively depleted in Nb, Ta, Ti, P, Sr and HREE, indicating that they were formed by comagmatic differentiation and evolution in a continental arc environment. Combined with regional geological background, the authors hold that these rocks are the product of subducted oceanic crust which experienced partial melting, replacement of overlying mantle wedge and fractional crystallization during the rising process. A comparison with the formation conditions of typical reduced porphyry copper deposits shows that the Xiaotuergen ore district has the potential to form porphyry deposit.

Abstract:Neoproterozoic igneous rocks on the northwestern margin of the Yangtze block can provide important information about the evolution of Rodinia supercontinent. In this paper, the petrology, geochemistry and isotopic data of the bojite from the Xinmin area of Micang Mountain region are presented. The Xinmin bojite displays low and limited SiO₂ content, enrichment of Al and Ca, low K, Ti and P, and medium Mg^#, suggesting typical subalkaline, low-K theolite features. The low REE composition, enriched LREE patterns, and positive Eu anomalies (δEu=1.03~2.36) imply the accumulation of plagioclase. The large ion lithophile elements (Rb, Ba, Sr)show enrichment, whereas the high strength elements(Nb, Zr, Hf, Th)are relatively depleted. ⁸⁷Sr/⁸⁶Sr=0.703 858, ¹⁴³Nd/¹⁴⁴Nd=0.512 617, and εNd(t)=+3.1. The regional geological and geochemical characteristics reveal that the primary melts were derived from partial melting of depleted mantle rocks and underwent significant crustal contamination in the emplacement process. During this period, the northern margin of the Yangtze block was in a convergence environment and the tectonic environment of the Xinmin bojite was the back arc basin, and hence the Xinmin bojite was the product of the evolution of Rodinia supercontinent in the Neoproterozoic period.

Abstract:The Dongsu granites from the Solonker suture zone are characterized by relatively high silicon (SiO₂=69.76%~75.58%), high alkali and potassium (K₂O+Na₂O=6.99%~9.16%, K₂O/Na₂O=0.70~1.69), high TFeO/MgO (3.43~11.26), and low MgO (0.08%~0.50%). Geochemical analyses show that the granites have relatively high LREE, obvious negative anomalies of Ba, Sr, Nb, Eu, and concentration of incompatible elements (Rb, Th, Ta). Major and trace elements indicate that the Dongsu pluton is of aluminous A-type granite. By LA-ICP-MS zircon U-Pb dating, a weighted mean ²⁰⁶Pb/²³⁸U age of 221.5±0.81 Ma (MSWD=0.57) is considered to be the formation age of the Dongsu granites which are the products of Late Triassic magmatic activities. Combined with geochemical information and regional geological data, it is concluded that the Dongsu granites were formed by partial melting of crust materials (meta-greywacke) at the stage of post-orogenic extension. Its intrusion marked the end of the evolution of the Paleo-Asian Ocean and the terminal of the collision of the Solonker suture zone in the Late Triassic.

Abstract:The Chongba leucogranites, located in the east part of the Greater Himalayan leucogranite belt, are exposed along the South Tibet detachment system (STDS). Their emplacement and cooling ages are significant for evaluating the time span of the magmatism in Himalayan orogeny, constraining the timing of the STDS and revealing the history of the uplift-exhumation-cooling. In this paper, the authors collected leucogranite samples from Chongba area and carried out systematic LA-ICP-MS zircon U-Pb and muscovite ⁴⁰Ar-³⁹Ar dating. The results of zircon U-Pb dating show that the Chongba leucogranites were emplaced at 12.4±0.4 Ma. This age lies on the border between Neo-Himalaya and Post-Himalaya subdivision based on previously published data. However, taking into account the characteristics of the distribution along the STDS,the authors classify it as Neo-Himalaya. The Chongba leucogranites were generated through decompression-dehydration melting of the metapelite in Greater Himalayan Crystalline complex (GHC) triggered by the STDS activity. Thus, the emplacement age of 12.4±0.4 Ma represents the activating timing of the STDS and apparently postdates the timing in the middle and west part of the Himalayan orogeny, which shows a regularity of getting later from west to east. Muscovite ⁴⁰Ar-³⁹Ar cooling ages of the Chongba leucogranites are 9.11±0.25 Ma and 9.62±0.10 Ma, respectively. Combined with the ages and the close temperatures of zircon and muscovite, the authors hold that the rapid cooling exhumation might have occurred between 12.4 Ma to 9.11 Ma, whose cooling rate was up to 137℃/Ma to 162℃/Ma. These calculated results are in accord with previous conclusion obtained by metamorphic P-T-t of the granulite from GHC in Chongba area. It is considered that the rapid cooling event during 12.4~9.11 Ma was probably associated with the structural exhumation caused by the extension and detachment of the STDS in the study area.

Abstract:Based on the comprehensive research on geochemical characteristics of shale of Lucaogou Formation along the Baiyanghe profile in the northern Bogda Mountain in Xinjiang, the authors investigated the elements distribution and depositional environment of shales of Lucaogou Formation, source characteristics and tectonic setting of the source area. Some conclusions have been reached: ① Baiyanghe shale is evidently enriched in phosphorus, which is ascribed to the development of the volcanic ash, as indicated by the tuffaceous composition of the interbedded mudstone and carbonate layers. ② In comparison with the average concentrations of worldwide shales, the Baiyanghe shale is enriched mainly in Li, B, Pr, Tb, Dy, Ho, Er, Tm and Lu, and depleted in other elements relative to their average values. ③ Geochemical characteristics reveal that there occurred climate change from warm humidity to dry heat from the bottom to top of Lucaogou Formation, which caused the change from freshwater to saltwater and strengthened gradually the reducing environment from the bottom to top of Lucaogou Formation. ④ The source area was under the low-moderate chemical weathering condition. The provenance of shales was mainly felsic igneous rock, followed by femic igneous rock. ⑤ The tectonic setting of the source area was a continental island arc-active continental margin.

Abstract:The high pressure(HP)-ultrahigh(UHP)metamorphic belt of southwestern Tianshan Mountains in Xinjiang mainly consists of pelitic-felsic schist that encloses lenses of eclogite,blueschist and ultramafic rock. The coesite-bearing pelitic schist shows porphyroblasitic/diablastic texture and schistose structure,and its mineral assemblage consists mainly of garnet,phengite,albite,paragonite,glaucophane,barroisite and quartz together with minor allanite,rutile and titanite. Coesite is included in garnet. The petrology and phase equilibrium modeling indicate that the coesite-bearing pelitic schist has experienced three metamorphic stages. Stage Ⅰ is the prograde to pressure peak stage characterized by increase in both pressure and temperature,which is constrained by garnet zoning from core to coesite-bearing domain. The p-T condition and mineral assemblage of the pressure peak are estimated to be 500℃, 2.9 GPa and garnet + glaucophane + jadeite + carpholite + lawsonite + rutile + phengite + coesite, which is comparable with the occurrence of coesite. Stage Ⅱ is the post pressure peak decompression and heating to the temperature peak,which is constrained by garnet zoning from coesite-bearing domain to rim. The p-T condition and mineral assemblage of the temperature peak are estimated to be 560℃,2.35 GPa and garnet + glaucophane + jadeite + lawsonite + rutile + phengite + quartz. The dehydration reaction glaucophane + carpholite + lawsonite=garnet + jadeite + H₂O releases ~45% of water bound in the rock and leads to coesite transforming into quartz and carpholite disappearance. Stage Ⅲ is the post temperature peak isothermal decompression stage, which is constrained by the p-T condition of equilibrium assemblage albite + paragonite + barroisite + titanite(495~550℃,1.0~1.15 GPa). During the decompression,the dehydration reaction jadeite + lawsonite=glaucophane + paragragonite + H₂O occurs at ~2.1 GPa,resulting in lawsonite decomposition and paragonite appearance. At~1.1~1.25 GPa,rutile is replaced by titanite, accompanied by omphacite disappearance as well as the formation of albite and barroisite. The strong continuous dehydration during stage Ⅱ is in great favor of re-equilibrium of mineral assemblage,which leads to most coesite at pressure peak transforming into quartz. Only minor coesite is survived in garnet. The coesite-bearing pelitic schist and its enclosing eclogite lens have experienced the same subduction and exhumation.

Abstract:In situ synchrotron radiation X-ray diffraction (XRD) and X-ray absorption near edge structure (XANES) measurements were employed to investigate the compressibility and the electronic structure of natural siderite in diamond anvil cells (DACs). No phase transition occurs up to 50.2 GPa at room temperature but a pressure-induced structure evolution from the calcite-type to the NaCl-type can be observed. The axial compression is anisotropic with c-axis more compressible than a-axis. Fe²⁺ undergoes spin state transition (HS→LS) at 44.6~47.1 GPa with volume collapse 8%. Fitting to the Brich-Murnaghan equation of state yields bulk modulus K₀=112(5) GPa and its pressure derivative K₀'=4.6(3). XANES measurement was used for the first time to investigate the electronic structure of Fe²⁺ in siderite. The result implies that no major changes take place in the coordination and the local symmetry of Fe²⁺ until 37.3 GPa; thereafter the HS→LS transition occurs and the LS Fe²⁺ has lower splitting energy and higher probability of electronic transition.

Abstract:As one of the most important Pb-Zn ore concentration areas in China, southern Hunan-northern Guangdong area is located in the middle part of the Nanling metallogenic belt. Morphology, texture, composition, δ³⁴S and composition of fluid inclusions of sphalerite from MVT and magmatic hydrothermal Pb-Zn deposits were investigated to discuss the ore-forming temperature, the source of sulfur and the ore-forming fluid, which can provide valid constraints on the mineralization. It is suggested that lead-zinc sulfides in the MVT Pb-Zn deposit were formed in the medium-low temperature, oxidative-weak reductive and lower stress environment. The sulfur was mainly derived from the ore-bearing strata, the ore-forming fluid was composed of hot brine and metamorphic dehydration of the sediments. Magmatic hydrothermal Pb-Zn deposits were formed under the medium-high temperature, weak reductive and higher stress condition. The sulfur was mainly derived from the magma, the ore-forming fluid was composed of magmatic hydrothermal solution in the early stage and mixed fluid in the late stage. Based on the formation time, spatial distribution and tectonic background of the orebodies and the rocks, it is held that magmatic hydrothermal Pb-Zn deposits were formed by the emplacement of the large-scale granitic magmatite which was caused by subduction of the Paleo-Pacific plate to the mainland, thus the lithosphere was thickened in the Early Yanshanian period (180~150 Ma), and that MVT Pb-Zn deposits were formed after the superimposed reformation of the original Devonian source bed by the magmatic hydrothermal solution formed by the Eurasian lithospheric extension-thinning in the Late Yanshanian period (130~90 Ma).

Abstract:Chloritization is an important alteration type of the metallogenic stage in the Dafushang uranium deposit. Two kinds of generation form of chlorite were revealed by microscopic characteristics, i.e., the amoeboid aggregate growing along the crack of feldspar or quartz and the alteration of biotite. The results of electron microprobe analyses show that the chlorites from the Dafushang uranium deposit are iron-rich prochlorite, the temperature range of formation of chlorite is 201.48~224.20℃ (averagely 213.65℃), belonging to the mesothermal-epithermal alteration, and the formation mechanism is composed of dissolution-crystallization and dissolution-migration-crystallization. The composition characteristics of chlorite have important significance for investigating the environment of uranium metallogenesis and evaluation of deposits.

Abstract:The Alxa block constitutes the westernmost part of the North China Block (NCB). This block has experienced polyphase tectonothermal events and hence serves as a key tectonic unit of the NCB. In this paper, Mesoproterozoic Nuoergong Group in Bayinnuoergong area of eastern Alxa block was selected for studying the tectonic framework and deformation stages of the Alxa block. Based on geometry, kinematics and microstructural characteristics of the Mesoproterozoic Nuoergong Group, the authors recognized two deformation stages. At the first stage, original bedding structure reflected by the ribbon was transformed into foliation, striking in the NE-SW direction. At the late stage, dextral strike-slip shear occurred along the strike of foliation. In combination with previous research results and geochronological data, the authors hold that the deformation structures were controlled by the subduction of Chaganchulu back-arc basin beneath the Alxa block during Carboniferous-Permian period. Due to the intense NW-SE-trending contraction during the subduction, foliation formed and transformed the original bedding structure. After that, dextral strike-slip shear occurred along the strike of the subduction zone and accommodated intense contraction.

Abstract:In this paper, the authors studied the gemological and mineralogical characteristics of Laos Tianhuang Stone by means of hydrostatic weighing method, X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), whole-rock chemical analysis, environmental scanning electron microscopy (ESEM) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The results indicate that the samples are mainly composed of dickite which belongs to kaolinite group minerals. According to whole-rock chemical analyses, Fe is the main trace element contributed to Laos Tianhuang Stone. The size of particle and degree of crystallization of minerals are associated with the transparency of samples, and the samples with high transparency are usually small particles with high crystallization. A comparison of chemical compositions between Laos Tianhuang Stone and Tianhuang shows that the content of Ga in Laos Tianhuang Stone is higher than that in Tianhuang, whereas the values of Co, Rb, Ni are obviously lower than those in Tianhuang. The element content can be used to perform synthetic origin identification. Plots of Co-Ga, Rb-Ga, Ni-Ga can be used to distinguish Laos Tianhuang Stone from Tianhuang. Laos Tianhuang Stone is rich in light rare earth elements(LREE) and poor in heavy rare earth elements(HREE).

Abstract:Agate, universally popular with infinitely variable appearance and color, contains a variety of silica polymorphs, amorphous and nanocrystalline silica, chalcedony and quartz. It is characterized by distinctive banded texture, and usually displays special rhythms with associated repetitive textures and compositions at different scales. Very often agate is simply defined as "banded chalcedony", and for most practical purposes this should be sufficient. However, microstructural and spectroscopic observations reveal that most agates, depending on their genesis, are mixed from fibrous chalcedony, wall-banded chalcedony, horizontally-banded chalcedony, microcrystalline quartz and euhedral crystalline quartz. X-ray diffraction and electron backscatter diffraction (EBSD) analyses indicate that most nanocrystalline and microcrystalline quartz in agate tends to grow with a-axes perpendicular to the growth substrate, typical of length-fast chalcedony. Fourier transform infrared spectroscopy (FTIR) analysis reveals some molecular water and silanol group water in agate, with lower total water content in crystalline silica than in amorphous silica. Although agate is abundant worldwide, controversy surrounds the genesis of its characteristic banded textures and the consensus has not been achieved. A representative hypothesis suggests that the bands in agate are either from precipitation from siliceous hydrothermal influxes or by in situ crystallization of a silica gel. However, most of the recent literature indicates a viable model for the growth of chalcedony in agate based on diagenetic cycles reflected in the degree of crystallinity, crystallographic orientation and water content. Quantitative information on microstructural observations and micro-scale analyses with petrological experimental results will improve our understanding of the origin and formation processes of agate.

Abstract:A large new serpentine jade deposit was found in Ji'an area, Tonghua City, Jilin Province. The results of X-ray fluorescence spectrometry show that the content of SiO₂ is from 35.21% to 37.18% in weight percentage, MgO from 46.94% to 49.72%,, the ratio of FeO/Fe₂O₃ is in the range of 0.174~0.685, respectively. The analyses of XRD indicate that there are characteristic peaks at 0.733 nm, 0.366 nm, 0.250 nm, which are attributed to lizardite. The main mineral of the serpentine jade is lizarite, commonly with forsterite. The characteristic XRD peaks of frosterite, dolomite, brucite also occur in the X-ray diffraction spectra. The IR spectra of 3 650~3 700 cm, 950~1 100 cm, 400~700 cm^-1 are found in the serpentine. The Ji'an serpentine jade deposit was formed by regional metamorphism,, lizardite was the product of forsterite hydrothermal alteration under the low temperature condition.

Abstract:In this study, the authors investigated the electronic structures of natural goethite FeOOH by first principle theory and synchrotron soft X-ray emission and absorption spectroscopy. The results show that the band gap of natural goethite FeOOH is 2.30 eV, smaller than the band gap of pure goethite FeOOH (2.57 eV). Due to the complex compositions and plenty of defects, the band structure of natural minerals is hard to measure by traditional methods, such as UV-Vis. The results supply a new way for determining the band structure of natural semiconductor minerals and also provide a basis for better understanding of photocatalytic mechanism of them under visible light.

Abstract:Iron-manganese cutans are important carriers for Fe and Mn in yellow brown earth. They have been playing important roles in recording history of the environment and affecting the environment. This paper focuses on the mineral characteristics of typical iron-manganese cutans in yellow brown earth. Various mineralogical methods, such as ICP-AES, POM, ESEM, EDX, HRTEM, XRD, were applied to investigate iron-manganese oxides in cutan samples collected in Wuhan. The results show that iron-manganese cutans in yellow brown earth contain layering patterns, characterized successively by a high Mn layer, a high Mn & Fe layer, a high Fe layer, a high Fe & Mn layer and a high Fe layer, and Mn/Fe mass ratio decreases irregularly from the surface to the bottom. Iron-manganese cutans are mainly composed of nanoscaled Mn-(hydr)oxides and Fe-(oxy)hydroxide minerals composed of hollandite, birnessite, goethite, feitknechtite and vernadite, exhibiting diverse morphological features.

Abstract:Arsenic(Ⅲ) is toxic and rather difficult to be purified from water. Natural pyrite has a lower capability to remove arsenic(Ⅲ) from solution than pyrrhotite. However, when heated in nitrogen gas, most pyrite generates pyrrhotite, which is a kind of porous material which has high surface area and stronger chemical activity and is very useful for arsenic(Ⅲ) removal from groundwater. In this paper, the authors investigated the influence of heating temperature, heating time, pH and dissolved oxygen on the removal of arsenic(Ⅲ) by heat-treated pyrite. The results show that monoclinic pyrrhotite has the best removal efficiency for arsenic(Ⅲ), and hence temperature of 600℃ and time of 1 hour seem to be the best calcinations condition for arsenic(Ⅲ) by heat-treated pyrite. Moreover, an optimum pH in the range between pH 4 and pH 10 was observed for arsenic(Ⅲ) removal from aerobic aqueous solution, while a range between pH 7 and pH 10 was observed from anaerobic aqueous solution. Contrast to anoxic environment, the sorption efficiency and sorption rate of arsenic(Ⅲ) on heat-treated pyrite is much better from aerobic aqueous solution.