Abstract:Extensive Phanerozoic granitoids in northeastern China have constituted one of the hotspots in the study of granite in the eastern Central Asian Orogenic Belt. In particular, the petrogenesis and tectonic affinity of granites in the Xiao Hinggan Mountains-Zhangguangcai Mountains have always been controversial. In this study, zircon LA-ICP-MS U-Pb dating of the monzogranites from the Tieli and Yilan areas in the Xiao Hinggan Mountains-Zhangguangcai Mountains yielded crystallization ages of 188±1 Ma and 257±3 Ma, respectively. The geochemical data show that these monzogranites belong to I-type granite and are characterized by enrichment of LILE (e.g., Th and U) and LREE and depletion of HFSE (e.g., Nb and Ta) and HREE, which are typical for continental arc-type granites. Zircon Hf isotopic data indicate that the granitic magma in the Tieli area was derived from partial melting of Meso-to Neoproterozoic lower crust. Combined with previously published geochronological and geochemical data, it is inferred that the Xiao Hinggan Mountains-Zhangguangcai Mountains was under an active continental margin setting during the Late Paleozoic to Mesozoic. Moreover, the Late Paleozoic to Mesozoic granitoids show a westward increasingly younger trend in the whole Xiao Hinggan Mountains-Zhangguangcai Mountains. The authors hold that this temporal and spatial relationship resulted from the flattening westward subduction of the Mudanjiang Ocean between the Jiamusi and Songnen blocks.

Abstract:The Ailaoshan suture (ALSS) is one of the important Paleo-Tethyan sutures in Southeast Asia, and the Late Paleozoic basic rocks in the ALSS are the key to reconstructing the Paleo-Tethyan evolution. However, the petrogenesis and tectonic environments of these basic rocks are controversial, and this controversy constrains researchers' understanding of the Paleo-Tetyan evolution. Based on field investigation, the authors studied petrological and geochemical characteristics and synthesized the geochronological and geochemical data of the Late Paleozoic basic rocks in the western part of the ALSS, with the purpose of investigating their petrogenesis and tectonic setting and further providing insights into the ALSS evolution. Zircon U-Pb data suggest that the Wusu and Baliu basic rocks were formed in Early-Permian (288~287 Ma), and Dalongkai and Yaxuanqiao basic rocks were formed in Mid-Permian (272~265 Ma). The products of Early-Permian magmatism are calc-alkaline in composition, and they have island-arc basalt (IAB)-like geochemical features with high rare earth element (REE) content (ΣREE=59.75×10^-6~135.08×10^-6), LREE/HREE ratios (2.64~3.32), Ta/Yb (0.09~0.18) and Ce/Yb (6.59~9.03) ratios, and slight enrichment in large ion lithophile elements (LILEs, e.g., Rb, Ba and Th) and depletion in high field strength elements (HFSEs, e.g., Nb, Ta and Ti), whereas the basic rocks from Mid-Permian magmatism are tholeiite, and are characterized by low REE content (ΣREE=28.77×10^-6~76.16×10^-6), LREE/HREE ratios (1.75~2.55), Ta/Yb (0.05~0.09) and Ce/Yb (3.58~5.97) ratios, and strong enrichment in LILEs and depletion in HFSEs. Combined with regional geological data, this paper proposes a two-pulse model related to the Late Paleozoic subduction in the western part of ALSS. During the Early-Permian, the westward subduction of the Ailaoshan branch ocean/back-arc basin beneath the east margin of Simao terrane induced partial melting of mantle wedge to form the Andean-type continental margin arc along the western Ailaoshan; subsequently (Mid-Permian), the collapse of continental margin arc formed a back-arc basin, and further produced basic-ultra basic rocks with the geochemical features of both MORB and volcanic arcs.

Abstract:The Xiangyangping uranium deposit is the most representative granite-type uranium deposit in the Miao'ershan area of northern Guangxi. Based on the detailed field investigation, the main uranium mineral in the deposit is pitchbiende. LA-ICP-MS REE research dissects the source of ore-forming fluids. The results show that oxidized pitchblende ∑REE is 689.12×10^-6~869.31×10^-6, LREE is relatively enriched, HREE is relatively deficient, strong Eu is negative and Ce is positive, TE_1,3 values range from 1.26 to 1.33, with a typical M type REE tetrad effect; the ∑REE of the pitchblende is 569.73×10^-6~3 337.83×10^-6, showing two characteristics:① LREE enrichment, HREE loss and LREE and HREE fractionation degree are large, Eu exhibits strong negative anomaly but weak Ce positive anomaly, and chondrite-normalized REE patterns are right-included; ② LREE and HREE fractionation degrees are small, Eu negative anomaly is obvious, Ce negative anomaly is weak, and the chondrite-normalized patterns of REE are in seagull type form. The fresh rock has similar chondrite-normalized REE patterns, and the Y/Ho ratio range is narrow, indicating that it has the same material source. REE of ore minerals are quite different from the values of the fresh rocks, and the kindship is not obvious. The alteration and high uranium background is a product of the mineralization. The ore-forming fluid is multi-stage rich in U-Y-REE. The uranium mainly cane from deep hydrothermal fluid, and the contribution of fresh rock is not significant. The location of the deposit is controlled by the combination of tectonic and rock mass. The size and shape of the orebody are determined by the tectonic scale and modes of occurrence.

Abstract:Some felsic dykes have been discovered in recent years in the Qiuwangchong mining area, located in the eastern part of the EW-striking Baimashan-Ziyunshan metallogenic belt in central Hunan. Petrology and whole-rock geochemistry of these felsic dykes were studied in this paper. It is revealed that these dykes, lithologically, are mainly composed of porphyritic granite, tourmaline-bearing granite and graphic granite. In terms of geochemical characteristics of elements, these dykes in the Qiuwangchong deposit belong to the metaluminous to weakly peraluminous, calc-alkaline granite, and exhibit Si- and alkaline-enrichment signature. All dykes are rich in K, Rb, Th, U, Ce,Nd, Zr and Hf, but obviously depleted in Ba, Sr, P and Ti. In general, the total REE concentrations in these dykes are relatively low, and no obvious fractionation took place between LREE and HREE. All dykes are characterized by HREE-enrichment, with an extremely obvious negative Eu anomaly. Based on the discrimination diagrams of petrogenetic types and tectonic setting, in combination with previous studies for regional dykes, it is concluded that the dykes in this study belong to the highly-fractionated I-type granite, which was emplaced under the post-orogenetic extensional tectonic background. According to geological data in the study area and its adjacent areas, it can be concluded that these dykes are spatially associated with gold mineralization, and they are indicative of ore genesis and the further prospecting for gold mineralization in the study area.

Abstract:The Xuji deposit is an important Ag-Pb deposit found in the Zongwulong belt. Geologically, the ore deposit is hosted in the Carboniferous-Permian Guokeshan Formation of Zongwulong Group, and consists of limestone intercalated with phyllite. The orebodies are veinlike, lenticular and stratoid in shape and are controlled by EW-trending faults. The alteration of ore-bearing wall rock is mainly manifested as silicification and sericitization. Ore minerals are mainly galena and silver tetrahedrite, gangue minerals are mainly quartz, and the ore exhibits variegated and reticulate structure. In this paper, the authors analyzed S and Pb isotopic composition characteristics in this deposit. The results of sulfur isotope analysis show that the δ³⁴S values of sulfide minerals in the ores range from 5.0‰ to 8.4‰, indicating that the sulfur mainly came from magma with a small stratigraphic contribution. The lead isotopic compositions, ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb are from 17.896 to 17.922, 15.589 to 15.617 and 38.072 to 38.166 for ore sulfide minerals, respectively, which are similar to the features of wall rocks (²⁰⁶Pb/²⁰⁴Pb=17.949~18.976, ²⁰⁷Pb/²⁰⁴Pb=15.600~15.696,²⁰⁸Pb/²⁰⁴Pb=38.106~40.943) and are different from the features of Xujixiakou diorite (²⁰⁶Pb/²⁰⁴Pb=18.144~18.589, ²⁰⁷Pb/²⁰⁴Pb=15.623~15.636, ²⁰⁸Pb/²⁰⁴Pb=38.790~39.033), indicating that the metals were mainly from the Guokeshan Formation of Zongwulong Group. A comprehensive analysis shows that the Xuji deposit was related to the late Permian magmatic activity in the Zongwulong belt and the genesis of the deposit seems to be magmatic hydrothermal filling-replacement.

Abstract:The Xiongcun copper (gold) ore district in Tibet is located on the southern margin of the middle Gangdise metallogenic belt, mainly composed of No.Ⅰ, No.Ⅱ, and No.Ⅲ orebodies and several mineralized bodies. In this paper, the modes of occurrence and composition of hydrothermal biotite in the potassium silicate alteration zone of No.Ⅰ and No.Ⅱ orebodies were systematically studied by means of microscopic identification and electron microprobe analysis. Biotite of No.Ⅰ orebody in the Xiongcun ore district is mainly phlogopite and magnesium biotite while biotite of No.Ⅱ orebody is mainly magnesium biotite. Biotite of both orebodies is characterized by low Ti (TiO₂<3%) and high Al (Al₂O₃>15%), with high MgO content, Mg/Fe value>0.5, and K/Na value greater than 10, which shows a good correlation with mineralization. The average crystallization temperature of hydrothermal biotite in No.Ⅰ orebody is 470℃, and the oxygen futility is between NNO and HM. The average crystallization temperature of hydrothermal biotite of No.Ⅱ orebody is 234℃, and the oxygen futility is between NNO and FQM, indicating that No.Ⅰ orebody was formed in a hydrothermal system with high temperature and oxygen futility, while No.Ⅱ orebody was formed in a hydrothermal system with relatively low temperature and oxygen futility. The Ⅳ(F) value of hydrothermal biotite in No.Ⅰ orebody ranges from 0.61 to 2.72, with an average value of 1.26. The Ⅳ(Cl) value is from -5.49 to -4.53, with an average value of -5.03. The Ⅳ (F/Cl) value is from 5.63 to 7.89, with an average value of 6.29. The Ⅳ(F) value of hydrothermal biotite in No.Ⅱ orebody ranges from 1.83 and 3.32, with an average value of 2.66. The Ⅳ(Cl) value is from -5.64 to -4.89, with an average value of -5.31. The Ⅳ (F/Cl) value is between 7.14 and 8.68, with an average value of 7.97. These data indicate that No.Ⅰ and No.Ⅱ orebodies were formed in the Cl-rich hydrothermal system, and that the hydrothermal solution of No.Ⅱ orebody was richer in Cl and poorer in F than that of No.Ⅰ orebody. Metallic elements such as Cu and Au were easily extracted and moved in the form of metal complex by Cl-rich fluid. In the process of fluid migration, changing physicochemical conditions would reduce the solubility of metal complex and led to sulfide precipitation.

Abstract:Guatemalan "blue water" jadeite and Myanmar "oil green" jadeite were analyzed by means of microscope observation, thin section observation, X-ray powder diffraction, laser Raman spectrum, and scanning electron microscope analysis. The authors tried to compare these two jadeites in conventional gemological characteristics, structural characteristics, impurity minerals and chemical composition. The results show that the jadeite grains of Guatemalan "blue water" material develop homoeoblastic structure, and the major mineral is jadeite, with a small amount of omphacite, the jadeite particles show the rhythmic zoning with 2~3 layers, and the omphacite occurs as euhedral grains, residues of metasomatism or filling material along the micro-crack, in which the white punctate mineral is albite, and the green punctate mineral is a mixture of aegirine-augite and omphacite. The jadeites in Myanmar "oil green" jadeite have coarse particles and a columnar granular mosaic structure, with relatively uniform sizes. The mineral has pure jadeite and mottled omphacite as impurity mineral, the jadeite particles of Myanmar "oil green" jadeite show the rhythmic zoning with 3~5 layers, and the omphacite grains fills the gap of jadeite particles in vein shape or is replaced by jadeite crystals in island shape. Meanwhile, the content of CaO in Guatemala "blue water" and vein omphacite are higher than that in Myanmar "oil green" jadeite. In addition, with the existence of aegirine-augite, it is inferred that there may be differences in Ca and Fe content in the crystal environment of jadeite from the two producing areas.

Abstract:In this study, manganese cutans were synthesized on the surface of quartz sand particles. Crystal structure characteristics of the minerals in the cutans were investigated by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The effects of mole ratio R of Mn²⁺:Mn⁷⁺ (1:1, 1:2, 1:3 and 1:4 respectively), synthetic temperature (30, 50, 70, 90 and 110℃ respectively), standing and churning time (48, 72 and 96 h respectively), and quartz sand amount (5, 10, 20, 30 and 40 g respectively) on the formation of manganese oxides in the cutans were discussed. The obtained results showed that, with the decrease of R (Mn²⁺:Mn⁷⁺), the minerals in the manganese cutans were transformed from cryptomelane to birnessite. Moreover, the crystallinity of minerals increased, the manganese content decreased, and the granular structure increased. With the rising of synthesis temperature, the crystallinity of the mineral in the cutans increased, and the manganese content in the cutans decreased, but there was no variation of the type of the mineral. The churning did not affect the mineral type of the cutans, but the longer the stirring time, the higher the mineral content in the cutans. As the quartz added amount increased, the crystallization of the minerals was declined, and the mineral content on the surface of the cutans was reduced first and then rose when the content of quartz sand was 10 g, but the mineral type did not change.

Abstract:Using the image processing function and numerical calculation function of MATLAB to analyze the grain size of clastic rock, the method can better solve the problems of inaccurate measurement results as well as time-consuming and laborious work in traditional grain size analysis methods. Firstly, the image of clastic rock under the microscope is processed by grayscale, binarization and image enhancement, and all kinds of granularity data in clastic rock are measured accurately. Then, the obtained data are transformed into grain size parameters and applied to sedimentary environment analysis to calculate sedimentary environment more accurately. The results show that this method not only has high measurement accuracy, simple performance, convenient operation and good applicability but also shows that the analytical results are consistent with the traditional particle size analysis method.