Abstract:The MOR-type Bangong Co ophiolite in northwest Tibet is a tectonic mélange mainly consisting of brecciated peridotites and MORB-affinity basalts. The mantle peridotites are composed of clinopyroxene-bearing harzburgites (cpx-harzburgites) and minor clinopyroxene-free harzburgites classified in terms of petrography, mineralogy and geochemistry. Geochemical data suggest that the cpx-harzburgites were formed via a refertilization process, which occurred at low melt/peridotite ratios (1∶9 to 1∶4) and under the interaction between basaltic melts and clinopyroxene-free harzburgites. The authors performed a Re-Os isotopic study of 9 cpx-harzburgites, which display a relatively narrow range in Os concentrations and Os isotopes, with Os ranging from 2.91×10^-9 to 5.40×10^-9 and ¹⁸⁷Os/¹⁸⁸Os ranging from 0.121 13±0.000 44 (2σ) to 0.128 53±0.000 36 (2σ). Measured Re concentrations range from 0.19×10^-9 to 1.49×10^-9 and ¹⁸⁷Re/¹⁸⁸Os range from 0.169±0.009 (2σ) to 1.833±0.183 (2σ). The positive correlation defined by cpx-harzburgites (five solid circle points) in the isochron diagram (¹⁸⁷Os/¹⁸⁸Os versus ¹⁸⁷Re/¹⁸⁸Os) yields an apparent age of 254±28 Ma. The peridotite-melt interaction at the low melt/rock ratios could result in an obvious increase in peridotite Re abundances and Re/Os ratio, and then the decay of ¹⁸⁷Re to ¹⁸⁷Os produced a modification of the ¹⁸⁷Os/¹⁸⁸Os ratios. Serpentinization seemed to have had little effect on the Re-Os system, which is considered to have been a closed system during the low temperature process. Therefore, this pseudo-isochron age may reflect the melt/rock reaction between cpx-free harzburgites and basaltic melts. In addition, this pseudo-isochron age is consistent with the opening age of Neo-Tethys defined earlier, and hence provides evidence for the initiation of the Bangong-Nujiang Tethys Ocean in Late Perimian-Early Triassic period.

Abstract:Located in northwestern Baingoin County of Tibet, Duoba area is near the middle of Bangong Co-Nujiang River metallogenic belt with the distribution of a large number of skarn iron-copper polymetallic deposits (mineralization spots) characterized by good prospecting potential. Due to high elevations, traffic inconvenience and less mining, only a small amount of work has been carried out. This research is based on the systematic field geological survey, indoor petrographic and ore microscopic studies, zircon LA-ICP-MS U-Pb dating and analysis of major and trace elements. The authors chose Sousha skarn mineralization spot and Zai'a skarn iron polymetallic deposit to conduct researches on the relationship between the petrogenesis and the mineralization. There are mainly fine grained porphyritic granodiorites in Sousha area and fine grained granodiorites in Zai'a. Zircon's LA-ICP-MS dating indicates that the age of the fine grained porphyritic granodiorite is 77.37±0.55 Ma, whereas that of the fine grained granodiorite is 79.78±0.99 Ma, suggesting products of late Cretaceous magmatism. Their A/CNK values change between 0.78 and 1.29, and A/NK values change in the range of 0.88～1.51. The rocks belong to weakly peraluminous. They are enriched in big ion incompatible elements Rb, Th, U and K, and depleted in Nb, identical overall with the same period granite in Bangong Co-Nujiang River metallogenic belt. ∑ REE range from 199.82×10^-6 to 274.64×10^-6, LREE/HREE= 3.552～7.199, δEu=0.20～0.82, with medium negative Eu anomalies. These data indicate that the separation of plagioclase crystallization might have occurred in magmatic evolution processes. The ore-forming processes of Sousha and Zai'a rock bodies might have had something to do with the southward subduction of the Bangong Co-Nujiang Ocean Basin and acted as the products of magmatic activity after closing. With favorable iron and bismuth polymetallic ore-forming geological and geochemical conditions, this area deserves more attention in further prospecting and evaluation work.

Abstract:Niumaoquan complex located in the east of late Paleozoic Harlik arc in Junggar plate contains magnetite. The complex has obviously stratified property and rhythmical tectonic characteristics, and the main rock types include olivine gabbro, olivine-bearing gabbro, gabbro and hornblende gabbro. Geochemical characteristics (m/f values of most rocks range from 0.65 to 1.44) indicate that Niumaoquan complex belongs to tholeiite series characterized by ferruginous basic-ultrabasic rocks. The concentrations of rare earth elements are relatively low, and the primitive mantle normalized REE patterns show rightly-oblique curve with slight enrichment of LREE. The rocks are enriched in large ion lithophile elements (Rb, Ba, Sr, U) and depletion of Nb,Ta and high field strength elements (Zr,Hf) with weak enrichment of Ti. Nd-Sr isotopic characteristics[εNd(t)=-3.4～-0.50,εSr(t)=-3.4～8.5] with the evolutionary trend towards EMⅠ indicate that the magmatic source was the enriched lithospheric mantle transformed by the subduction fluid. The complex was formed by Early Permian post-collision extention which occurred in northern Xinjiang. Delamination of lithospheric mantle resulted from partial melting caused by heating action of the asthenospheric material. At the same time, the material of enriched lithospheric mantle moved upward through the space formed by delamination of the lithosphere.

Abstract:Located in middle-southern section of the Da Hinggan Ling metallogenic belt, the Huanggangliang Fe-Sn deposit is a typical skarn deposit. In order to determine the petrogenetic and metallogentic ages of the deposit, the authors emphatically studied zircon LA-ICP-MS and molybdenite Re-Os chronology of the granite. Combined with the precise chronological data, this paper discussses in detail the geodynamic setting of the deposit. Zircon LA-ICP-MS analysis of the granite shows that the crystallization age of the granite is 139.96±0.87 Ma, indicating that the granite related to mineralization resulted from magmatism in early Cretaceous period. The molybdenite Re-Os dating gives an isochron age of 134.9±5.2 Ma, which indicates that the metallogentic and petrogenetic ages are consistent with each other. Isotopic chronology demonstrates that both the Huanggangliang Fe-Sn deposit and the associated granite are products of magmatic activities in the Yanshanian period. Combined with ore deposit geology and mineralization epoch as well as regional tectonic evolution, the authors have reached the conclusion that the formation of the Huanggangliang Fe-Sn deposit in the Da Hinggan Ling region occurred at the peak metallogenic stage of 140 Ma. The tectonic setting of the deposit was in the transition period from lithosphere compression to extension.

Abstract:Sifangtai complex is the largest mafic-ultramafic intrusion along the Shangdan fault in the North Qinling orogenic belt, covering an area of ～40 km². It consists mainly of ultramafites, pyroxenite and minor intermediate rocks, intruding into the Danfeng Group. A combined study of cathodoluminescence images (CL) and in situ LA-ICP-MS U-Pb isotope dating was carried out for zircons from the Sifangtai gabbro. Cathodoluminescence images show two kinds of zircon grains, i.e., prismatic ones with clear magmatic zonations and round ones with complicated internal structure, some of the latter ones having no magmatic zonation. Altogether 32 U-Pb analyses were made for cores and overgrowths of 26 zircon grains,and the magmatic age 460±29 Ma of Sifangtai mafic-ultramafic complex was obtained. The 32 data can be divided into 4 phases: 400～500 Ma, 700～900 Ma, 1 800～2 600 Ma and 2 700～2 918 Ma. The result of 400～500 Ma is consistent with the Caledonian movement in the Qinling orogenic belt, while the result of 700～900 Ma is probably related to the mantle superplume that broke up Rodinia in mid dle and west China during 830～740 Ma.

Abstract:The Dapingzhang Cu-polymetallic deposit is a typical VHMS (volcanics-hosted massive sulfides) deposit related to intermediate-acid rocks. The granodiorite porphyry that intruded into the ore-bearing volcanic series is large in size, but its research has been very insufficient. Based on field investigation, the authors studied systematically the formation characteristics, petrology, petrochemistry and chronology of the intrusive body. The results show that the granodiorite porphyry and the volcanic rocks have typical intrusive contact relationship. The granodiorite porphyry, belonging to calc-alkaline high calcium volcanic series, shows volcanic arc granite characteristics as evidenced by distribution patterns of trace elements and rare earth elements. LA-ICP-MS zircon U-Pb age of the granodiorite porphyry is 401.0±1.7 Ma, suggesting early stage of Early Devonian period. This means that the granodiorite porphyry was not formed in the Indosinian period. It is also shown that the age of the volcanics and the VHMS deposit should be early Devonian, rather than late Devonian-early Carboniferous.

Abstract:South Tianshan orogeny is a typical orogenic belt between Tarim-Kalakumu plate and Yili-Kazakhstan plate. Kulehu-Keketiekedaban ophiolitic mélange is exposed in the south margin of the South Tianshan. Kaidu River section is located on the northern margin of Kulehu-Keketiekedaban ophiolite mélange in South Tianshan. In the section, Devonian volcanic rocks composed of ignimbrite, crystal pyroclastic-bearing felsic glassy lava and andesite were discovered. The Devonian volcanic rocks are of alkaline to calc-alkaline series, with A/CNK being 0.82～1.31. The ignimbrite is characterized by high content of REE and strongly enriched and highly-fractionated LREE, with low fractionated HREE and strong negative Eu anomalies. The LA-ICP-MS U-Pb age of zircons from ignimbrite is 393.1±3.4 Ma, suggesting that Saerming Formation belongs to Middle Devonian indeed. The age 393.1 Ma restricts the subduction time of the Kule Ocean basin. Kulehu Ocean basin started subduction in Middle Devonian (393.1 Ma), which released fluids and resulted in melting of mantle wedge to form basaltic magma. Thus, andesite was formed by fractionation and crystallization of the basaltic magma. When the crust was thickened, the basaltic magma continually ascended upward to cause the melting of the upper crust. Finally, the ignimbrite and crystal pyroclastic-bearing felsic glassy lava were erupted.

Abstract:The Baoshan-Zhenkang terrane is one of the important lead-zinc polymentallic orefields in the southern part of the Sanjiang metallogenic belt, with complex geology and tectonics as well as very favorable Pb-Zn mineralization conditions. Two large-size Pb-Zn deposits were recently discovered in the Hetaoping and Luziyuang ore districts, which are apparently controlled by approximately NE-trending faults, anticlinal axis and strata. Marbleized limestone of Upper Cambrian Hetaoping and Shahechuang Formation is the ore-bearing horizon in this area, with proximal strong skarnization. Based on a comparative study of geochemical characteristics of fluid inclusions, lead, sulfur, hydrogen and oxygen isotopic compositions and trace elements from the two Pb-Zn deposits, the authors have reached the follow conclusions: The Hetaoping and Luziyuan Pb-Zn deposits have expe- rienced medium-temperature and high-temperature ore-forming stages; Compared with lead isotope compositon of the Luziyuan Pb-Zn deposit, lead isotope composition of the Hetaoping Pb-Zn deposit has a relatively high ratio and a wide range. Both ore districts,however,have radiogenic Pb isotopic ratios and are characterized by high μ values,suggesting a dominant input of Pb from crustal sources;Sulfur isotopic composition of the Hetaoping and Luziyuang deposits is characterized by lower positive δ³⁴S values and tower-type distribution,showing an involvement of deep magmatic sulfur; both ore deposits have not been subjected to the effect of biotic thermochemical reduction of sulfate, and has reached fractionation equilibrium of sulfur isotope; Hydrogen and oxygen isotope composition of quartz coexistent with sulfides indicates that the ore-forming fluid from the Hetaoping deposit was mainly derived from magmatic water with the mixture of meteoric water and stratigraphic water; The characteristics of trace elements of the two deposits are consistent with those of magmatic hydrothermal deposits, and do not resemble those of VMS type and MVT type Pb-Zn deposits. Therefore,both deposits belong to high-medium temperature skarn type Pb-Zn deposits associated with deep concealed intrusion, and the emplacement of the deep concealed intrusion in the ore districts was followed by the addition of Pb-Zn rich magmatic fluid into the intersection of anticline axis and NE-trending faults and the mixing with stratigraphic water and meteoric water,thus resulting in the formation of this type of ore deposits.

Abstract:Water contents and chemical compositions of normal anhydrous minerals from Early-Paleozoic Songshugou and Tongbai terrain granulites and Paleo-proterozoic Junan granulite xenoliths were obtained by Fourier transform infrared spectrometer (FTIR) and electron microprobe (EMP) respectively. All granulites characterized by mafic nature were formed under the lowest crustal conditions. Plagioclases in granulites contain trace amounts of water in the form of structurally bound hydroxyl and less molecular water. Water contents (H₂O wt.) of plagioclase range from 465×10^-6 to 733×10^-6 at Songshugou, from 210×10^-6 to 993×10^-6 at Tongbai, and from 717×10^-6 to 1 239×10^-6 at Junan, respectively. Combined with previous results for Paleo-proterozoic granulites (Junan and Nushan xenoliths and Hannuoba terrain) and Mesozoic granulites (Daoxia and Hannuoba xenoliths), it seems that water contents in the lower continental crust of eastern China were variable with time. Water contents of Paleozoic and Proterozoic granulites are much higher than those of the Mesozoic granulites and there is no difference between Paleozoic and Proterozoic granulites,implying the existence of a more hydrous lower continental crust of eastern China before Mesozoic.

Abstract:The potassium-magnesium salt deposit in Khammouan Province of Laos is located in eastern Khorat Basin which belongs to upper Cretaceous salt sedimentary basin. The formation of the deposit underwent three sedimentary cycles which formed three salt sections, i.e., upper, middle and lower sections, and every salt section includes two layers, namely salt layer and clay layer. The ore is located in the lower salt layer of lower salt section. This paper mainly studied the mineralogical and geochemical characteristics of the lower salt layer based on ZK318 well. The results show that halite, sylvite and carnallite are main minerals, with small amounts of boracite and anhydrite. In combination with the characteristics of minerals, major elements and trace elements, the lower salt layer can be divided into five layers in upward order of halite layer→ sylvite layer→ carnallite layer→ thin halite layer→ upper sylvite layer. Bromine (Br) values (higher than 200×10^-6) show that the brine came from sea water, and carnallite occurred at the highest stage of brine concentration, as shown by its highest Br value of 2 572×10^-6 among five layers. Boron content showed a gradual increase from halite layer through sylvite layer to carnallite layer, suggesting that boron content is in linear correlation with salinity of the brine. Boron value of the upper sylvite layer is up to 890×10^-6, which is consistent with the existence of boracite mineral revealed by XRD, indicating that ore brine came from sea water and deep hydrothermal solution. In addition, according to the evaporative order of halide brine, the order of crystallization was halite→sylvite→carnallite, and carnallite seemed to be the last sedimentary period in halide brine. However, in ZK318 well, there appears a thin layer of halite above the carnallite layer, which shows that it underwent a short period of fresh water supply which result in the decrease of brine concentration in the basin, but soon the concentration continued to increase with the replenishment of deep hydrothermal solution, followed by the precipitation of the upper sylvite layer. Thus, the sedimentation of the lower salt layer was over. Therefore, the upper and lower sylvite layers are both primary sedimentary layers because they overlie the halite layer directly, and have the same content of boron, being 1 790×10^-6 and 1 792×10^-6, respectively. In summary, potassium sources of the ore deposit were sea water and deep hydrothermal solution, and two sylvite layers in the well are both primary sediments.

Abstract:The Boziguoer A-type granitoids in Baicheng County of Xinjiang are ore-bearing rocks with abundant useful elements such as Nb, Ta and Zr. The petrological and mineralogical characteristics of the A-type granitoids were investigated on the basis of observation under polarized microscope, chemical analysis and detailed BSE images using EPMA, followed by the discussion on the p-T conditions of A-type magma generation and the tectonic setting. The results indicate that these A-type granitoids could be divided into three types, namely aegirine arfvedsonite quartz alkali feldspar syenite, aegirine arfvedsonite alkali feldspar granite and biotite alkali feldspar syenite. The major rock-forming minerals are quartz, albite, K-feldspar, aegirine, arfvedsonite and siderophyllite, whereas the accessory minerals include mainly zircon, pyrochlore, thorite, fluorite, monazite, bastnaesite and xenotime. The average temperatures of the magma are 832～839℃. A-type granitoids might have been formed in an anorogenic intraplate tectonic setting by which they generally show such features as high- temperature, anhydrous nature and low fugacity.

Abstract:This paper made a tentative in-situ nondestructive study of components of single fluid inclusions from No.3 granitic pegmatite vein in Altay of Xinjiang by SRXRF which was generated by beamline 4W1B of Beijing Synchrotron Radiation Facility (BSRF). The authors have improved micro-vedio lightning facility by which better, faster and more precise visual effects could be obtained, and the test results are more reliable. Studies show that most fluid inclusions of No. 3 granitic pegmatite vein have relatively high concentrations of Zn, Sn, As and REE which may be the characteristics of endogenous magmatism and crustal source. Spider diagram shows the similarity between Kektokay No. 3 granitic pegmatite vein and the crust in middle and east China in the concentration style of trace elements, suggesting that the source of the fluid might have been derived from the crust. The relatively large X-ray spot (50 μm×50 μm) might have affected the accuracy of the test, but it can be avoided and the test accuracy can be improved by shrinking the light spot, raising the energy of the beam and enhancing energy resolution of the facility.

Abstract:A-type granites are alkali-rich and water-poor granitoids characterized geochemically by poor Al, Sr, Eu, Ba, Ti and P. A-type granite was formed under the low pressure and high temperature conditions, and their source rocks had no choice. The essence of the A-type granites is that granitic magma melted under low pressure, and they were mostly produced in the tectonic setting of crustal extension and thinning.

Abstract:Culture experiments of carbonate mineral using Lagoa Vermelha improved medium with 6∶1 molar ratio of Mg/Ca within 100 days were conducted under the mediation of Clostridium sp. (SN-1 strain) isolated from sediments in the Qinghai Lake. At the same time, aseptic experiments were carried out as the control. Mineral species and morphologies were determined by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The results showed that: ① The quantities of sediments in bacterial culture experiments were always more than those in the control ones. ② The change trend of carbonate mineral assemblages formed in Clostridium sp. SN-1 strain culture was calcite → calcite and monohydrocalcite →monohydrocalcite and calcite →monohydrocalcite, while in the control experiments the change trend was monohydrocalcite and calcite→ calcite and monohydrocalcite; ③ Based on comprehensive analysis of SEM and XRD, the authors considered that dumbbell-shaped minerals might be high-magnesium calcite, while spherical minerals might be monohydrocalcite.

Abstract:The Rongli tremolite jade deposit is the only high-grade nephrite deposit in Guizhou Province, which was discovered in the last year by the authors. The Rongli nephrite deposit occurs in the contact metamorphic belt between basic rock and flint limestone. The tremolite content of the ore exceeds 95%. The nephrite jade has radiated fibrous blastic texture, felt-like blastic texture and compact massive structure. White jade, grayish white jade and gray jade constitute major species of the Rongli jade, which has weak greasy and greasy luster as well as rare wax luster. The ore bodies are large, and the nephrite jade is of top quality. The Rongli nephrite jade is genetically different from Hetian jade and Qinghai nephrite jade in that the Rongli tremolite jade deposit resulted from contact metasomatism between basic intrusive rock and calcium carbonate rock, thus belonging to a new genetic type of tremolite jade deposit discovered for the first time in China. The Rongli jade has important research value and favorable exploration and utilization prospects.