Abstract:Cenozoic ultrabasic-basic dyke swarms were newly discovered in northern Mitizi area in northwest Tibetan Plateau. The dyke swarms intruded into the Changchengian Sailajiazitage Group. The nearly E-W-trending dyke swarms are located on the northern margin of Kogan Fault. The rocks are mainly composed of spessartite and kersantite, which have features of AL_Na and CAL_Na respectively, as shown by geochemical analyses. The LA-ICP-MS zircon U-Pb age of spessartite yielded an age of 38.24±0.54 Ma, suggesting that these dyke swarms were formed in Paleogene. The dyke swarms have low REE (64.28×10^-6~253.41×10^-6), and the anomalies of Eu (δEu=1.04~1.21) and Ce (δCe=0.99~1.03) are not obvious. REE distribution patterns are of the right-oblique type (LREE/HREE=4.15~6.45). All samples are characterized by the relative enrichment of LILE and depletion of HFSE. The dyke swarms are products of low degree partial melting of lithospheric mantle. The magmatic activity lasted for a short time and the dyke swarms had quick cooling rate after intruding into the surrounding rocks. The tectonic setting of the dyke swarms was strike-slip fault, and the magmatism occurred along the large scale strike-slip faults.

Abstract:The closure time of the Bangong Co-Nujiang Tethys Ocean (BNTO) between Lhasa terrane and Qiangtang terrane directly constrains the early tectonic evolution of the Tibetan Plateau. Recently, alkaline volcanic rocks have been recognized from the Kaimeng ophiolitic mélange, a southern sector of Bangong Co-Nujiang suture zone. These rocks are mainly fresh mugearite with trachytic structure. The phenocrysts are mainly oligoclase with minor augite, and the groundmass is mainly composed of oligoclase, pyroxene and trace alkaline feldspar filling other minerals. The chemical compositions of the mugearite are fairly uniform, with the abundances of SiO₂ and TiO₂ ranging from 51.34% to 53.91% and from 1.02% to 1.55%, respectively, suggesting alkaline series volcanic rocks with high Na₂O content (4.90%~6.36%), low K₂O content (0.05%~0.88%) and intermediat Rittman index (σ=3.65~4.47). The most of Mg^# values are higher than 60, even up to 68.62. The trace elements of the mugearite are characterized by relative enrichment of large ion lithophile elements (LILE) Sr, Rb, Ba, Th and U and depletion of high field strength elements (HFSE), with negative Nb and Ta anomalies. The stable Nb/U, Zr/Nb and La/Yb ratios (7.45~8.51, 15.92~17.26 and 7.26~8.06, respectively), the initial ⁸⁷Sr/⁸⁶Sr ratios(0.706~0.707)and the (¹⁴³Nd/¹⁴⁴Nd)_t ratios (0.512 368~0.512 548) as well as the Ce/Pb-SiO₂ diagram suggest that the source of the mugearite was probably mixed primitive mantle (PM) and lower continental crust and abyssal sediments. The zircon U-Pb isotopic dating shows that the age of the mugearite is 101.8±1.1 Ma, indicating that it was likely produced by the partial melting of asthenospheric mantle upwelled by the slab break-off at the end of oceanic crust subduction, which implies that the BNTO was closed at the late stage of early Cretaceous period.

Abstract:Early Paleozoic basic dike swarms are widely distributed in North Daba Mountain of South Qinling Belt. This paper reports zircon U-Pb age and whole-rock geochemistry for diabase dikes with the purpose of exploring their petrogenesis and geological significance. The results indicate that the dykes were emplaced during the late period of Early Silurian epoch (435~433 Ma). These diabases are characterized by low silica but high alkali and titanium content, exhibiting intraplate basalt geochemical characteristics with enrichment of light rare earth elements (LREE) and incompatible trace elements Ba, Nb and Ta but depletion of Rb, K, and heavy rare earth elements (HREE). The negative K and Rb anomalies indicate that amphibole or phlogopite was retained in the mantle source. Partial melting modelling result suggests that diabases were formed by high degrees of partial melting of an enriched spinel hornblendite source. In combination with geochemical characteristics and previous studies, the authors hold that the North Daba Mountain experienced large-scale extension during Early Paleozoic, and the extension of lithosphere induced the partial melting of metasomatized lithospheric mantle with low melting point and formed this alkaline magma belt.

Abstract:The Sanjiang metallogenic belt is one of the most important polymetallic ore-forming belt in China. The Duocai ore concentration area possesses various types of Cu polymetallic deposits in its middle and north part,and its mineral resource potential is huge; nevertheless, the ambiguous mineralization age seriously restricts the understanding of the ore deposits and regional mineralization regularity. In view of such a situation,the authors selected the Chayong copper polymetallic deposit in this belt and conducted a complete systematic research on its mineralization chronology based on detailed field exploration and microscopic mineralogical identification so as to fill the research blank of the ore-forming age in this area. The results indicate that there are two kinds of orebodies in the Chayong copper polymetallic deposit, mainly Cu-Mo orebodies, which were developed in the metamorphic siltstone and mainly occurred at the quartz and sulfide stage. The biotite in hornfels shows that the points of Mg-(Al^Ⅵ+Fe³⁺+Ti)-(Fe²⁺+Mn) in diagram fall within the range of magnesium biotite, the value of Al₂O₃/TiO₂ is between 6.359 and 10.087 and the ratio of Fe²⁺/(Fe²⁺+Mg) is comparatively uniform. Based on the above data, the authors hold that it is hydrothermal biotite unmodified by late fluids. The authors confirmed the closure age of hydrothermal biotite by the ⁴⁰Ar-³⁹Ar plateau age of 129.59 ±1.58 Ma. In addition, molybdenites which penetrate into chalcopyrite have the rhenium content from 0.864×10^-6 to 9.624×10^-6. These values indicate that the metallogenic material of molybdenite was probably derived from the crust. The Re-Os isochron age of molybdenite is 124.75±0.86 Ma. In conclusion, the age of hydrothermal biotite is similar to that of molybdenite, and it is held that both of them should belong to the same period of magmatic hydrothermal event as shown by their closure age. This study accurately determined the metallogenic age of a typical magmatic hydrothermal Cu polymetallic metallogenic deposit in the middle and northern part of the Sanjiang metallogenic belt, revealing that there was a mineralization event during the Early Cretaceous, and these data indicate a new direction for studying regional metallogenic regularity and for prospecting work in the Sanjiang metallogenic belt.

Abstract:Lithium-potassium ores are mainly distributed in Qinghai, Tibet, Lop Nur salt lake and western Sichuan, but it is expensive and difficult to develop these ores to meet the needs of industrial development. The exploration of Jitai basin in Jiangxi Province shows that the concentration of lithium chloride in brine exceeds 600 mg/L, and the content of potassium chloride is close to 1%, which is close to or even higher than the industrial grade with high comprehensive utilization value. On the basis of previous studies, the authors studied mineralogy, petrology, geochemistry and fluid inclusions and made water-rock reaction simulation experiments by high-pressure autoclave on Mesozoic igneous rocks in Jitai basin so as to study the effects of time, temperature and fluid composition on the water-rock reaction of igneous rocks and explore its indicative significance to the source and mechanism of lithium-potassium rich brine. The following main results were preliminarily obtained:The brine in Jitai basin is characterized by high lithium and low magnesium, indicating that the brine in Jitai basin is affected by volcanic activity; The magma in the study area was differentiated in different degrees with strong igneous alteration, which reveals that the igneous rock was greatly replaced by hydrothermal fluid and provided material source for lithium-potassium rich brine mineralization; Temperature is the main control factor of the leaching capability of fluid to elements and high-salinity fluid is the main transport carrier of ore-forming elements; The Mg/Li ratio in the brine of surface origin is mainly controlled by the original rock composition. Water-rock reaction is an important process of brine formation, and surface evaporation and concentration constitute the main mechanism of brine mineralization.

Abstract:To reveal the difference of the second member of Dongying Formation reservoir development along No.4 and No.2 tectonic belts in Nanpu Sag, the authors used such means as rock flakes, cast sheet image analysis, scanning electron microscopy, X-ray diffraction, mercury intrusion, physical property analysis and other data to study the reservoir characteristics systematically. According to the results obtained, the No.4 structural belt is mainly composed of lithic feldspar sandstone, the average debris content is Q_40.6F_30.1R_29.3, and the average component maturity is 0.69. The No.2 structural belt is mainly composed of feldspar lithic sandstone, the average debris content is Q_32.9F_26.8R_40.2, and the average component maturity is 0.49. The No.4 structural belt is mainly composed of low-permeability sandstone reservoirs, while the No.2 structural belt is dominated by tight reservoirs (permeability less than 1 mD). The sandstone reservoir space of the No.4 structural belt is mainly composed of primary residual intergranular pores, and the connectivity between pore throats is relatively good. In the No.2 structural belt, the sandstone reservoir space is also mainly composed of intergranular dissolved pores, but the connectivity between pores and throats is poor. The distribution of pore throat size of the second member of the No.4 structural belt is mainly unimodal, and the increase of mercury intrusion is mainly concentrated on the throat radius of more than 1 μm. The pore throat distribution of the No.2 structural belt is also mainly unimodal, but the increase in mercury is mainly concentrated on the throat radius of less than 1 μm. On the whole, the difference between the second member of Dongying Formation reservoir in the No.4 and No.2 structural belts in the Nanpu Sag is mainly the difference in microscopic pore structure. The reason for this difference lies in the difference between the sedimentary and diagenetic reformations of the Paleogene Ed₂ reservoirs of the two tectonic belts.

Abstract:Based on the most active marine system on the earth, the authors studied the interaction between minerals and microorganisms in this paper. In this study, a large number of suspended particles and microbial communities were found from water samples in euphotic zone of the Yellow Sea. ICP-MS, ESEM and the equipped EDX tested the element composition of suspended particle macroscopically and microscopically. The main elements are Si, O, Na, K, Ca and Al, as well as high content of Mn, Fe and Ti. X-ray diffraction spectroscopy (XRD) and Raman spectroscopy shows that the main mineral components of suspended particles are quartz, albite, calcite, mica and chlorite etc. Moreover, semiconductor minerals of iron and titanium metal oxides such as anatase, rutile, brookite and goethite were also found in suspended minerals. The composition characteristics of the microbial communities were preliminarily analyzed through 16S rRNA, and the main communities are Proteobacteria, Actinobacteria, Bacteroidetes, Planctomycetes, Woeseia, Fluviicolas. A dual-chamber reactor was used to study the mechanism of redox reaction and electron transfer process between microorganisms and suspended minerals. With the increase of suspended minerals as the electron acceptor, the open circuit voltages of the system were increased from 330.80 mV to 426.59 mV, and their maximum output powers were increased from 8.376 9 mW/m² to 12.096 8 mW/m². Experiments indicate that suspended minerals in the euphotic zone can effectively participate in and promote the process of extracellular electron transfer, which will make a foundation for further research on electron energy transfer based on the interactions of semiconductive minerals and microorganisms, as well as the regulation mechanism of elements cycling.

Abstract:This study focused on the variation characteristics of PM_2.5 and PM₁₀ concentrations and general source types in 2014~2018 in five typical small-medium basin cities (Lanzhou, Yinchuan, Linfen, Taiyuan and Nanyang) in northern China. Apart from the PM_2.5 concentrations in 2018 in Yinchuan, the PM₁₀ and PM_2.5 concentrations in the other cities are above the level of the 2nd grade standard of the state; The PM₁₀ and PM_2.5 concentrations show a downward trend year by year, with the most obvious city being Nanyang; The PM₁₀ and PM_2.5 concentrations show an increasing trend year by year in Linfen; The PM₁₀ and PM_2.5 concentrations are stable at a high level in Taiyuan. Seasonal variation characteristics of PM₁₀ and PM_2.5 concentrations are similar:high concentrations in winter and spring, low in summer and autumn. The ratios of PM_2.5/PM₁₀ are greater in winter and summer, resulting from the heating process and frequent rainfall, respectively. The ratios are lower in spring and autumn, resulting from sandstorms and frequent straw combustion as well as high-strength construction of building, respectively. The PM_2.5 and PM₁₀ concentrations have a good linear relationship, The proportion of fine particles is in order of Linfen > Nanyang > Taiyuan > Yinchuan > Lanzhou.

Abstract:The crystallinity of covellite formed by the exchange reaction of Cu²⁺ and iron-sulfide minerals in water at ambient temperature affects the recovery efficiency of Cu²⁺ and the complete degree of the exchange reaction. In this study, covellite was synthesized via direct reaction of CuCl₂ and Na₂S. The growth of covellite crystal under different conditions, including different pH values, reaction time, reaction temperatures, reactant concentrations, reactant dropping rate, and extra-added electrolyte concentrations, were discussed. The crystallinity and morphology of covellite were characterized by XRD, TEM and EDX. The average particle size of the crystal was calculated by Scherrer formula. The results showed that the lower pH values, longer reaction time, higher reaction temperature and lower reactant dropping rate had favorable effects on the growth of covellite crystals. The crystallinity of covellite increased first and then decreased with the increasing of reactant concentration, and varied with the different concentrations of extra-added ions.

Abstract:The optical characteristics and differences of rock components in the thin section were analyzed on the basis of images at sequential extinction angles under the cross-polarized microscope. A new methods for grain segmentation and pore identification were proposed. Taking full advantage of the modes of occurrence of grains and the complexity of crystal optical axis, the spatial arrangement of grains and the diversity of contact relationships, the authors carried out the correlation analysis of pixel scales on the extinction angle of thin sections. The grain segmentation and the pores identification were brought about by sensitive parameters, such as the mean and the standard deviation of the correlation coefficient. The results show that the gray level and RGB values of the pixel inside the grains are more correlated in the angular domain. At the edge of a grain and distribution area of fillings in pores, the correlation coefficient was lower, and the variance of correlation coefficient was obviously higher than that in the interior of grains. This method demonstrates the significance of information integrity in the angle domain from the extinction characteristics. The edge extracted by this method is clear, the skeleton of the pore structure can be characterized, and the accuracy of grain segmentation is better than that of Sobel and Canny.

Abstract:The petrochemical method proposed in this paper is a new method developed through long-term practice and continuous innovation on the basis of Sansi algorithm, a petrochemical method to calculate the actual mineral content of granitoids from the chemical composition of rocks, which was put forward by Rong Jiashu in the 1970s. It designs corresponding calculating method for quasi-aluminous granitoids, aluminum supersaturated granitoids and aluminum strongly supersaturated granitoids, and simultaneously considers alkali metasomatic granites (or alkali feldspar granites). It is applicable not only to fresh rocks but also to partly altered rocks. This method is combined with the actual minerals as much as possible in dealing with the induction and assemblage of petrochemical analysis data and aims to make the calculation result consistent with the actual minerals in the rocks. The calculation process puts forward the correction coefficient χ of feldspar, which may correct the content of potassium feldspar and plagioclase in the rocks and ensure that the calculated results are consistent with the actual situation. Two kinds of parameters and related diagrams are obtained through the calculating results, one representing the percent content of the main forming minerals, such as Q, Or, Pl, Bi, Ms and Hb, the other reflecting the chemical characteristics of rocks, such as Ot, An_Pl, K-Na, a, b and Mg. This method can not only calculate the content of the main rock-forming minerals but also reflect the petrochemical characteristics, evolution process and metallogenic specificity.