Abstract:In order to explore the characteristics of metamorphism and the tectonic setting in the Yangtze Craton, we carried out petrographic, geochemical and chronological studies on the garnet-amphibolite in the north of the Huangling Dome. The results show that the main minerals in the garnet-amphibolite are garnet, plagioclase, amphibole, cliniopyroxene, quartz and ilmenite, in which the mineral assemblages of 3 different metamorphic stages are retained. The prograde metamorphic stage is characterized by the assemblage of amphibolite+plagiospar+quartz+ilmenite and the peak metamorphic stage consists of garnet+amphibole+plagioclase+clinopyroxene+quartz+ilmenite, while the retrograde assemblage contains garnet+amphibole+plagioclase+quartz+ilmenite. The garnet-amphibolite protolith belongs to subalkaline tholeiite with low Mg^#, indicating that its protolith has experienced a degree of differentiation. By means of conventional geological thermometer, the temperature and pressure conditions of different metamorphic stages were calculated. We obtained the p-t conditions of 596~625℃ and 0.70~0.82 GPa for the prograde metamorphic stage, 760℃ and 1.35 GPa for the peak metamorphic stage, and 692~738℃ and 0.68~0.74 GPa for the retrograde metamorphic stage. Meanwhile, a clockwise p-t path was represented from these p-t conditions, showing the process of warming and pressurization to the peak and then a near isothermal decompression. This p-t path reflects the tectonic setting of subduction-collision at the convergent plate margin. U-Pb dating of zircons in the garnet-amphibolite yields a harmonic age of 2 008±11 Ma. Together with the existing metamorphic ages in the region, these ages reveal that the Yangtze Craton was involved in the splicing of microcontinental blocks during the Paleozoic, which might be a response of the Columbia supercontinent assembly.

Abstract:Many large and medium crystalline graphite deposits have been found in Northwestern Hebei Province, with good metallogenic geological conditions and prospecting potential of regional metamorphic graphite deposits. Taipingzhuang Formation and Dongjingzi Formation of the Hongqiyingzi Group and Xiabaiyao Formation of the Jining Group in the Paleoproterozoic are important metallogenic horizons in this area. This paper has carried out a detailed petrographic and geochemical study of these ore-bearing strata, and discussed the metallogenetic mechanism of graphite deposits. The research results show that the ore-bearing rock of the Hongqiyingzi Group is graphite garnet biotite plagiogneiss, and the original rock is mainly composed of mudstone, clay sandstone, sandstone and carbonate rock, which are locally rich in organic matter, indicating that the maturity of the carboniferous rocks is generally higher, and the clastic rocks have been deposited in the marine-continental interaction and shallow marine facies under the warm humid and semi-dry climate. The ore-bearing rock of Xiabaiyao Formation of the Jining Group is graphite garnet plagioclase granulite, and the proto-rock is mainly composed of mudstone, clay sandstone, sandstone and quartz sandstone with higher maturity of littoral-shallow sea-inland lacustrine sedimentary facies, and are locally rich in organic matter, and formed in the oxidation-weak oxidation sedimentary environment under the semi-dry and dry climate, accompanied by hot water in the deposition process. The carbonaceous components of graphite ore were all derived from the original organic carbon deposited in the original rock itself. The deposit was controlled by horizon, lithofacies and lithology. Through regional metamorphism, organic carbon crystallized to form graphite ore, which was exposed to the surface or near the surface under the control of faults.

Abstract:The Zaozigou gold deposit in the Western Qinling Mountains is a super-large gold deposit related to magmatic activity. The intermediate-acid intrusive rocks in the mining area are intensively developed, mainly including diorite porphyrite, biotite quartz diorite porphyrite, granite porphyry and quartz diorite. The trace elements in rocks are characterized by enrichment of large ion lithophile elements Rb and K, and depletion of high field strength elements Nb, Ta, P and Ti. On the whole, the total amount of rare earth elements in biotite quartz diorite porphyrite>diorite porphyrite>quartz diorite, diorite porphyrite, biotite quartz diorite porphyrite and granite porphyry have weak to medium negative europium anomaly (δEu=0.60～0.89), deep quartz diorite has no Eu anomaly (δEu=0.96～1.07), and "Nb-Ta valley" is deeper and obviously different from shallow vein rock. The zircon U-Pb age of quartz diorite is 230 Ma, which is 10~20 Ma later than that of shallow vein rock, and is basically consistent with the age of altered mineral sericite. It is speculated that gold mineralization may begin at 230 Ma, and the main mineralization period is 230~211 Ma. The deep quartz diorite is the metallogenic geological body of Zaozigou gold deposit.

Abstract:The elemental geochemistry and carbon and oxygen isotope characteristics of sedimentary rocks from the Jialingjiang Formation-Leikoupo Formation in the Emeishan area of the Sichuan Basin were analyzed to explore their paleoenvironmental significance and provide basic information for the study of the Early-Middle Triassic paleoenvironment on the northwest margin of the Sichuan Basin. The results show that the samples ∑(CaO+MgO+LOI) ranged from 13.98% to 93.31%, reflecting a relatively turbulent sedimentary environment. The data show that the variation range of δ¹³C value is from -6.95‰ to 0.36‰, and the variation range of δ¹⁸O value is from -9.06‰ to -0.99‰. The overall performance trend of δ¹³C value is decreasing-increasing-decreasing-increasing. The seawater salinity shows a multi-stage change of rising, then decreasing, and then rising again; the seawater temperature ranges from 7.11 to 34.94℃, with an average temperature of 21.99℃, and the ancient seawater temperature experiences a trend of decreasing-increasing-decreasing, with a sharp increase in temperature near the Early-Middle Triassic boundary. The study area as a whole is in an oxidized sedimentary environment, with intermittent occurrences of oxygen-poor sedimentary environments. The above geochemical indicators are well coupled and consistently reflect a relatively humid-relatively dry and hot-relatively humid marine depositional environment in the Early-Middle Triassic boundary of the study area.

Abstract:High-temperature (above 150℃) dolomite synthesis experiment is considered to be an effective way to understand the genesis of natural dolomites. Under the consideration of the Mg/Ca value (molar concentration ratio) index that has an important impact on the genesis of natural dolomites, our experiment used two kinds of aragonitic bioclasts (Acropora, Ficus) as the precursor reactants in the 220℃ conditions to study the dolomitization process under different Mg/Ca concentration ratios (0.5, 0.7, 1.0, 1.2, 1.5) and reaction times (0.5, 1.0, 1.5, 2, 3, 6, 8, 14 h) respectively. The results show that the dolomitization process under high temperature can be divided into induction stage, rapid reaction stage and stable stage. This reaction process was not obviously affected by the precursor aragonite reactants, implying that the Mg/Ca concentration should have an obvious influence on the dolomitized products. With the increase of Mg/Ca ratio in the reaction solution, the induction period of dolomitization was shortened and the rate of dolomitization was accelerated, and the mole fraction of CaCO₃ in the product dolomile was reduced and the order degree was increased, which indicates that high Mg²⁺ concentration can rapidly promote the replacement of Ca²⁺ by Mg²⁺ in aragonite lattice and complete the ordering process of the dolomites. This results provide basic theoretical support for explaining the influence of Mg/Ca mole concentration on natural dolomitization process.

Abstract:The Guaiyu turquoise mining site in Lushi, Henan Province is located in the western margin of the Yiluo Basin. The discovery of the mining site provides important archaeological information for the study of the provenience of turquoise in the early Central Plains. In order to determine the direction of the turquoise from the ancient mine, the Sr and Pb isotopic compositions of Guaiyu turquoise were detected by thermoelectric ionization mass spectrometer (TIMS). Combined with the isotopic data of five major turquoise deposits in Qinling Mountains, the provenience characteristics of turquoise from Guaiyu ancient mining site were explored. The results show that the ⁸⁷Sr/⁸⁶Sr ratio of Guaiyu turquoise is relatively high, which is greater than 0.719 0 on the whole, and higher than that of other turquoise deposit, which can be regarded as one of the characteristics of the Guaiyu turquoise. There is a high degree of overlap among Pb isotopic compositions, however, the ²⁰⁸Pb/²⁰⁴Pb-²⁰⁷Pb/²⁰⁸Pb diagram shows some independent data gathering areas,which can be used to judge the origin of the Guaiyu turquoise. In addition, combination of ²⁰⁸Pb/²⁰⁴Pb-⁸⁷Sr/⁸⁶Sr and ²⁰⁷Pb/²⁰⁸Pb-⁸⁷Sr/⁸⁶Sr also obtained a good discrimination result, and the boundary with other regions is clear without obvious overlap. The Sr and Pb isotope composition is an important evidence to judge the origin of the Guaiyu turquoise.

Abstract:Purple "Shanzilai stone", a kind of Shoushan stone, is a layered silicate mineral clay jade. Its surface weathering for yellow, interior purple, corresponds to the seal stone in the rather unusual color variants. A standard gemstone microscope was used to examine the visual attributes. X-ray powder crystal diffractometer, microscopic laser Raman spectrometer, scanning electron microscope, and laser denudation plasma mass spectrometer were used to investigate the mineral composition, chemical composition, and rare earth elements (REE). The cause of the color was investigated using whole-rock chemical analysis, UV-visible spectrophotometer, and SPSS analytical model. According to the findings, the principal mineral composition of the purple "Shanzilai stone" is illite, with minor minerals including monazite, gorceixite, hematite and barite. The REE indicator data demonstrate an enrich of LREE components and a deficiency of HREE, indicating that the minerals' origin is associated to less acidic hydrothermal alteration. Illite’s purple hues and manganese concentration have a favorable association. The different types, distribution characteristics, and formation temperatures of the main minerals and secondary minerals in purple "Shanzilai stone" indicate that hydrothermal intrusion occurred several times during the late mineralization period, and the purple "Shanzilai stone" formation process is consistent with the metallogenic law in the Shoushan area.

Abstract:The discharge of slag and acid mine wastewater has polluted the farmland around the mining area. In order to simulate the relationship between nitrogen and arsenic in the farmland of the mining area under anaerobic conditions, shake flask experiments were carried out to explore the effect of nitrogen on the form and concentration of arsenic released from arsenical ferrihydrite under anaerobic conditions, column experiments were carried out to explore the effect of rice growth on the form and concentration of nitrogen and arsenic in the farmland. The results showed that under anaerobic conditions, the addition of nitrogen may promote the reduction of As(V) in arsenic contaminated paddy soil, making the concentration of As (Ⅲ) reach up to 396 μg/L. During the nitrogen and arsenic changes in different layers of anaerobic farmland simulated by column experiment, rice can promote the reduction of nitrogen and arsenic and the migration of arsenic down the layers during its growth, making the concentration of As (Ⅲ) reach up to 517 μg/L in the installation. By analyzing the similar anaerobic conditions of the shake flask experiment and the column experiment, As (Ⅲ) and NO^-₂, as As(Ⅴ) and NO^-₃ concentrations in the arsenic concentration, it can be inferred that there is maybe an oxidation-reduction relationship between arsenic and nitrogen, and nitrogen is likely to participate in the oxidation-reduction of arsenic.This study provides a certain reference value for the treatment of arsenic pollution in farmland, and enriches the understanding of prevention and control of arsenic pollution in farmland soil.

Abstract:It is of important environmental significance to study the mineralogical characteristics of atmospheric dust. Taking the samples collected from the campus of North China University of Science and Technology as an example, the mineralogical characteristics of atmospheric dust in Caofeidian area, Tangshan City, Hebei Province, were preliminarily analyzed and characterized by laser particle size analyzer, scanning electron microscope, X-ray powder diffraction and inductively coupled plasma mass spectrometry. The results show that the atmospheric dust is relatively coarse, and the particles include massive, columnar, flaky, spherical and irregular granular aggregates, which are mainly composed of quartz, feldspar, gypsum, mica, chlorite, hornblende, dolomite, calcite and hematite. The contents of heavy metal elements such as Cr, Cu, Zn, As, Cd, Pb in atmospheric dust samples are relatively high. The research and analysis show that silicate minerals in dust samples mainly come from fugitive dust, while carbonate minerals such as gypsum and calcite may be secondary minerals in the environment. The heavy metal in the samples mainly comes from coal combustion, the emissions of industrial enterprises and a small amount of automobile exhaust emissions.