Abstract:As the largest and oldest craton in China, the North China Craton is an ideal region for investigating the magmatic activity and tectonic evolution of Archean period, and hence has attracted considerable interest among geologists in China. The Taihua complex is an important part of the North China Craton, distributed in WWN-EES direction along its southern margin. In this study, the authors chose the Taihua complex in the Lushan area as the study object, investigated geological section in detail, and revealed formation age, metamorphic events age by LA-ICP-MS zircon U-Pb dating. Zircon U-Pb dating of the amphiboite yielded the weighted mean ²⁰⁷Pb/²⁰⁶Pb ages of 2 788±16 Ma, 2 714±12 Ma, and 1 920±18 Ma, which represent the formation age of the amphiboite, first stage metamorphic age, and second stage metamorphic age, respectively. Together with previous work about zircon U-Pb dating and Hf isotope, the authors analyzed and discussed the geological significance of the three geological events:2 850~2 700 Ma is an important period of magmatic event, and represents the formation of Archean new crust; 2 800~2 600 Ma and~1 900 represent the two metamorphic events and suggest that the Taihua complex was subjected to Neoarchean and Paleoproterozoic metamorphic alteration. The results obtained by the authors not only contribute to the interpretation of the formation age and the age of the metamorphic events of the Taihua complex and their geological significance but also provide new data for the further study of the formation and evolution of the southern margin of North China Craton and the whole North China Craton.

Abstract:The quartz diorite on the northwestern margin of Qaidam basin is characterized by high Al₂O₃,low Alk and Na₂O>K₂O,with alumina saturation index A/CNK being 0.87~0.91. These features suggest that this quartz diorite belongs to calc-alkaline peraluminous and metaluminous rocks. The chondrite-normalized REE show right-inclined patterns with slightly negative Eu anomaly,and the primitive mantle normalized trace element spidergrams are characterized by enriched LILE(such as Rb, Th and U), depleted HFSE(such as Nb, Ta, P and Ti), low Nb/La and Rb/Nb ratios, which are comparable with the characteristics of I-type granites. High CaO/Na₂O(2.32~2.64)ratios and diagrams show that the pluton was derived from remelting of the meta_morphic basalt in the lower crust. The initial temperature of magma was >768℃ by using whole rock Zr thermometer. Rock geochemical characteristics indicate that the pressure of the source region was probably>1.5 Ga, and the residual facies was correspondingly garnet+amphibole+rutil. Combined with the cathodoluminescence (CL) images and element features of zircon,this study yielded an age of 252±1 Ma for pluton using LA-ICP-MS zircon U-Pb dating. On the basis of regional geological evolution, the authors hold that Zongwulong oceanic crust subducted toward Oulongbuluke block in Late Permian.

Abstract:Cambrian strata of well TS1 are composed of Awatage Formation (middle Cambrian) and the lower Qiulitage Group (upper Cambrian). A detail investigation of cores and analysis of thin sections shows that Awatage Formation is mainly composed of dark gray to gray algal dolomite (micritic to fine-crystal), and Qiulitage Group is mainly composed of gray to light gray crystalline dolomite and ghost structure dolomite. Algal dolomites are present in moderate strength with brick-red to orange colors as the main features under cathodoluminescence together with δ¹⁸O value from -6.3‰ to -4.5‰ (average value is -5.3‰, VPDB), and contain a relatively high total rare earth elements (REE) with REE patterns similar to those of normal marine carbonate rocks. Crystalline dolomites and ghost dolomites show purple to red-brick color in dimly moderate strength under cathodoluminescene with lighter δ¹⁸O value from -9.2‰ to -5.7‰ (average value is -7.5‰, VPDB), together with relatively low total rare earth element/positive Eu anomaly and obvious loss of HREE. The difference between Awatage Formation and Lower Qiulitage Group indicates that the diagenesis-alteration process of dolomite reservoirs is different. This study suggests that the high quality reservoir of Awatage Formation in great depth might be controlled by several factors. Among them, dissolution of gypsum nodules and other unstable minerals by meteoric water or sea water in penecontemporaneous period established the foundation, followed by diagenesis-alteration strengthening constructively with fluid action, which even damaged the space by local filling and recrystallization.

Abstract:The volcanic rocks in Linzizong Group are developed in the Gangdise belt of Tibet, and can reflect the important information of Neo-Tethys from its subduction to the India-Asia collision. The Xingaguo area is located in the northern middle part of south Gangdise, Tibet, lying to the south of Luobadui-Milashan Fault. The volcanic rocks in Dianzhong Formation consist of rhyolitic detritus crystal tuff, and are distributed in a limited area in the north of the ore district. The volcanic rocks in Dianzhong Formation from Xingaguo are composed of rhyolitic detritus crystal tuff and are distributed in the northern area, with the exposed area being small. Chemical analyses show that the volcanic rocks in Dianzhong Formation have high SiO₂ (SiO₂=75.09%~78.10%), low alkali (K₂O+Na₂O=4.84%~6.52%), and low Mg (MgO=0.24%~0.37%), with peraluminous nature (A/CNK=1.02~1.75); they are characterized by LREE enrichment and obvious REE differentiation, with weak positive and negative Eu anomalies (δEu=0.76~1.15); they are enriched in LILEs (Rb, Th, U and K), depleted in HFSEs (Nb, Ta, P and Ti), and obviously depleted in Ba and Sr, thus belonging to calc-alkalic and peraluminous series and having the characteristics of continental margin arc volcanic rocks. The LA-MC-ICP-MS zircon U-Pb chronology indicates that the volcanic rocks in Dianzhong Formation were emplaced at 70.89±0.31 Ma, which is the oldest age for the volcanic rocks in Dianzhong Formation, and has ¹⁷⁶Hf/¹⁷⁷Hf values in the range of 0.282 820~0.282 939, εHf(t) values in the range of +3.2~+7.4 and single-stage model ages (t_DM) between 662 and 930 Ma. The volcanic rocks in Dianzhong Formation from Xingaguo area were formed in a tectonic environment of ocean subduction, mainly derived their materials from the mantle components, and contaminated crustal material in the process of magma rising.

Abstract:Currently, with the strengthening of caborate reservoirs exploration in Sichuan basin, strong heterogeneity becomes a practical problem which has seriously hindered the exploration and development of reef and bank gas reservoirs. With the typical reef and bank section of Changxing Formation as the research object, its external features were carefully observed in combination with the analysis of thin sections and rock data, and the authors investigated the reservoir heterogeneity features and formation mechanism of Panlongdong reef and bank profile in Changxing Formation of eastern Sichuan basin. The results show that a strong cyclicity and reservoir heterogeneity can be observed in the vertical direction of Panlongdong reef and bank facies. The reservoir rocks distribution, reservoir thickness, the degree of dolomitization and dissolution phenomenon exhibit cyclic variation with the cyclical change of the sea level. Reef and bank reservoir heterogeneity is controlled by high-energy sedimentary facies, changes of sea level and constructive diagenesis. The high-energy sedimentary facies is the key controlling element of primary pore, which determines the sedimentary heterogeneity. Dolomitization and dissolution are advantageous to the reef reservoir formation. Atmospheric fresh water leaching transformation plays a key role in optimization of the reservoir. Sea-level fluctuation determines the cyclicity of reef and bank development, and selective reform of constructive diagenesis deepens the reservoir heterogeneity.

Abstract:Zeolite cementation is extensively developed in sand-conglomerate of Jiamuhe Formation in Zhongguai bulge, Junggar Basin. The analysis of cement characteristics and diagenesis of zeolite is of great importance for genetic mechanism exploration of the reservoir. Based on core and microscope observation, in combination with geochemical test methods such as electronic microprobe analysis, the authors studied the lithologic features, cementation and dissolution characteristics of Jiamuhe Formation. The results show that the sand-conglomerate of Jiamuhe Formation has developed zeolite, analcite, laumontite, and heulandite. There is no obvious cement zonality between different types of zeolite. Meanwhile the sand-conglomerate is often cemented by multi-period and multi-type zeolite. it is concluded that these cement characteristics had an inseparable relationship with diagenetic environment. It was a comprehensive response result of different stages of diagenetic environment on the basis of a transient openness alkaline diagenetic environment of the early stage, assisted by several alternations between acid-base diagenetic environments of the middle stage, and dominated by a long-term closed alkaline diagenetic environment of the late stage.

Abstract:The row echelon granite aplite veined belt extending over one hundred kilometers are developed between the Kunlun Mountain Pass-Gander fault and the Bayan Haran central fault in northern Tibetan Plateau, and most of them are NW-trending, with a few being SN-trending. Based on an analysis of the macroscopic and microscopic characteristics of the row echelon granite aplite veins, as well as the LA-ICP-MS zircon U-Pb dating data for the SN-trending(224.7±0.64 Ma) and NW-trending(220.5±1.1 Ma) granite aplite veins, it is considered that the granite aplite veins are the products of Indosinian Movement, and they were formed in the oblique subduction of the Hoh Xil-Bayan Har terrane beneath the East Kunlun terrane in early Indosinian. The syntectonic granite aplite veins were injected along the "X" conjugate shear joints in the NW(118°) and the SN(2°) direction in the footwall (south section) of the Kunlun Mountain Pass-Gander overthrust fault. The principal compressive stress direction is revealed by the distribution direction of two groups of "X" type conjugate shear joints, which is NW(118°) to the SN(2°). The left order row echelon joints suggest that they are controlled by dextral strike-slip. The earliest formation time of granite aplite veins(224.7±0.64 Ma)represents the time of subduction and strike-slip event, which is also the formation time of the Kunlun Mountain Pass-Gander fault.

Abstract:The Shigente iron deposit is hosted in the volcano-sedimentary rocks of the Kangbutiebao Formation. The orebodies occur in bedding, lenticular, and vein forms, bounded by the strata. Skarnization and magnetite mineralization are both present in the ore district. The ore-forming process can be divided into volcanic sedimentary (the main mineralization period), magmatic hydrothermal (skarn-type mineralization period), and regional metamorphic periods. Magnetite in the volcanic sedimentary period and the retrograde alteration stage of the magmatic hydrothermal period is rich in Fe and depleted in Si, Ti, V, Mg, Mn. The chondrite-normalized REE patterns and primitive mantle-normalized trace element spider diagrams of magnetite show similar characteristics, which indicates that the iron mineralization in the volcanic sedimentary period and the retrograde alteration stage had the same metal source, namely the mafic volcanic rocks. Homogenization temperatures of fluid inclusions of garnets at the early skarn stage vary from 160 to 403℃, generally in the range of 180 to 260℃. Salinities range from 5% to 9% NaCleq; δD values range from -134‰ to -125‰, and δ¹⁸O_H2O values are between 4.7‰ and 8.6‰, implying that the fluids were derived from magmatic fluids. Homogenization temperatures of fluid inclusions in the quartz-carbonate stage vary from 140 to 536℃, mainly in the range of 160 to 340℃, and the salinities range from 6% to 16% NaCleq, which indicates that the fluids are characterized by the evolution from high to low temperatures, moderate-low salinities, and moderate-low densities. δD values of quartz range from -98‰ to -95‰, and δ¹⁸O_H2O values are between -0.6‰ and 2.0‰, showing that the fluids in this stage were derived from magmatic fluids, with some contributions from the meteoric water.

Abstract:The Yongxin gold deposit located in the southern part of the Nenjiang-Heihe tectonic mélange zone is a newly discovered altered rock type gold deposit controlled by tectonic belt. The gold-silver minerals and auriferous sulfides in this deposit were systematically studied by optical microscope, electron microprobe analysis and back scattered electron images, and the results show that gold-silver minerals are mainly native gold, subordinate electrum, and minor amounts of intergranular gold, with the crystal size in the range of 5 to 20 μm and mainly occurring as inclusions and fissure fillings. The fineness varies from 843 to 917, 888 on average. Gold-silver minerals were found in pyrite and galena, mainly pyrite. At the early stage of mineralization, the crystalline form of coarse-grained yrite was mainly cubic and crushed by late stress. At the main ore-forming stage, the crystalline form of fine-grained pyrite was dominated by cubic and pentagonal dodecahedron. The Co-Ni-As phase diagram shows that mineralization was closely related to magmatic fluids, the Fe/(S+As) ratio of the pyrite and the fineness indicate that this deposit was formed at the medium temperature and medium to deep mineralization environment. The Yongxin gold deposit is partially similar to and yet obviously different from decratonic (Jiaodong type) and orogenic gold deposits.

Abstract:As an essential precondition of ore-forming process in the hydrothermal system, water-rock interaction is not only an important subject of metallogeny but also an international geological trend. This process is along with isotopic exchange, which changes the isotopic compositions of fluid and rock. As tracers of non-traditional stable isotopes, boron and lithium isotopes are often used to constrain fluid-basalt hydrothermal interaction process. This paper gives a detailed review of factors of boron and lithium isotopic fractionation variation, which include temperature, pH values, primary phase dissolution, surface exchange and secondary mineral formation. Some conclusions have been reached:① Generally, the fluids in equilibrium become more quickly enriched in ¹¹B and end with higher δ¹¹B; At low temperatures (<150℃) Li is taken into secondary minerals and at high temperatures (>200℃) it is leached from the rocks. ② Primary phase dissolution and surface exchange hardly have influence upon lithium isotope fractionation. ③ Usually, the heavier isotope ⁷Li preferentially goes into solution and finally the solution tends to be with higher δ⁷Li. Simulation of mass balance equilibrium of the evolution of isotopic compositions in the fluid and the bulk rock with the reaction progress was also made in this paper.

Abstract:The isotope composition of pedogenic carbonates in paleosols is an effective approach to quantitative reconstruction of atmospheric CO₂ partial pressure. Stable isotope analysis of pedogenic carbonates from the Late Cretaceous Tangbian Formation in the Xinjiang Basin of Jiangxi Province was conducted to understand the paleoclimatic conditions. The carbon isotope compositions range from -4.30‰ to -2.10‰ (PDB) with an average of -2.84‰, and the oxygen isotope compositions range from -6.62‰ to -1.14‰ (PDB) with an average of -3.62‰. The CO₂ partial pressure was calculated to be from 782 to 1 420 ppmv based on Cerling's formula with an average of 1 181 ppmv during the Campanian Stage (~75 Ma), which is about 2~4 times higher than that of the present-day level. Therefore, a marked high value of CO₂ partial pressure probably occurred during the late Campanian Stage, possibly reflecting the undulation of p_CO2 during the Late Cretaceous time.

Abstract:The travertine landscape in Huanglong scenic spots has significant tourism value, in addition, organic carbon (OC) of the travertine is key to determining the law of travertine deposition which might be affected by local environmental organisms. In order to precisely provide the basis of the travertine deposition in which microorganisms are involved, it is necessary to remove the inorganic carbonate completely and preserve the part of OC well before measuring the OC of travertine. Determination of OC in travertine was compared between acid dissolution method, digestion method and volumetric method. The results showed that relative standard deviation (RSD) value of the acid dissolution method was from 23.73% to 30.95%, suggesting poor precision. Besides, the acid dissolution method would change the fraction of OC in travertine samples, making the result higher than the fact. The digestion method was more accurate for testing OC in black and yellow travertine, while the precision of the test was low for white travertine. The RSD value of OC tested by volumetric method was from 3.27% to 11.11%, which was influenced by travertine component and extraneous factors. It is found that the digestion method is suitable for OC determination of travertine, based on the data precision and validity in testing organic carbon, the advantage and disadvantages of lateral correlation, and the analysis of error sources between three test methods.

Abstract:This paper is mainly aimed at studying the differentiation phenomenon of rare earth elements in the weathered crust elution-deposited rare earth ore. Through the study of the mineral characteristics and adsorption of kaolinite and halloysite-7Å, the authors simulated the process of adsorption of rare earth elements, and investigated the genesis of the deposit. According to the results of the experiments, the adsorption capacity of halloysite-7Å for rare earth elements is far greater than that of kaolinite. In addition, when the pH of the system is lower than the point of zero charge of the two minerals or there are metallic cations in the system, the adsorption capacities of both minerals are greatly affected. The results of lateral comparison experiments suggest that, regardless of the change of pH or the addition of Na⁺ in the system, kaolinite and halloysite-7Å will not show the characteristics of adsorption dissimilarity, and the adsorption patterns of rare earth elements are relatively similar. Only when K⁺ is inside the system, the adsorption patterns of both clay minerals for rare earth elements show divergence, of which MREE and HREE are mainly adsorbed by kaolinite while LREE are mainly adsorbed by alloysite-7Å. Therefore, K⁺ produced by weathering of rocks causes kaolinite and halloysite-7Å to exhibit selective adsorptions, which further affects the distribution of REE in the REE deposit.

Abstract:Recently a new producing area of high-quality variscite has been found. The authors used such means as X-ray powder diffraction (XRD), EPMA analysis, infrared spectrometer, laser Raman spectrometer and ultra-violet-visible spectrophotometry to investigate this natural object. EPMA shows that the variscite in Yunnan is mainly composed of P and Al, and contains trace Fe and V; XRD shows that the mineral composition is very pure; the infrared spectrum and Raman spectrum show characteristic absorption band of group. FTIR also shows the existence of constitution water and crystallization water; UV spectra show that Fe³⁺ causes the absorption peaks around 300 nm and 420 nm whereas Fe³⁺ and V³⁺ cause the wild absorption band around 630 nm. Due to the fact that the variscite is often used as an imitation of turquoise, the authors made a comparative analysis of the spectra of the variscite and turquoise in order to distinguish the two minerals.