Abstract:Located in the westernmost part of the Middle and Lower Yangtze metallogenic belt, the southeastern Hubei Fe-Cu province possesses extensive magmatism and is hence an important part of the Late Mesozoic magmatic belt in the middle and lower reaches of the Yangtze River. Ore-forming plutons, especially large ones, have been extensively studied, with important progress achieved; nevertheless, the study of barren intrusions is very insufficient. Lying between the Lingxiang pluton and Yinzu pluton, the Jiangqiao intrusion consisting of granodiorite is the largest pluton among the small intrusions in southeastern Hubei Province. In this paper, the authors present high-precision zircon U-Pb age of the Jiangqiao granodiorite by using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The result indicates that its emplacement took place at 144±1 Ma, suggesting a product of Early Cretaceous magmatism. The cathodoluminescence (CL) images of zircons show that a few inherited zircons with ancient cores exist in the sample, except magmatic zircons with obvious overgrowth bands. The εHf(t) values of magmatic zircons are relatively negative and vary from -9.1 to -14.6. The corresponding two-stage model ages range from 1.77 Ga to 2.11 Ga, coincident with U-Pb ages of a few inherited zircons, indicating that the Jiangqiao granodiorite probably originated from Palaeoproterozoic crustal materials. The εHf(t) values of inherited zircons range from -0.6 to -14.6, corresponding to the two-stage model ages of 2.00～3.60 Ga and therefore indicating that Palaeo-Archaean basement might exist in southeastern Hubei Province. These results, in combination with data available, suggest that the formation of the Jiangqiao granodiorite was related to lithospheric extension and thinning, thus being the initial product of tectonic regime transformation in eastern China.

Abstract:The Nariniya lead-zinc deposit, recently discovered in the Tibetan Plateau, is genetically linked to the activities of potassic volcanic magma. Studies show that the SiO₂ and K₂O content of the fresh host rocks is 62.9%～68.6% and 5.1%～5.8%, respectively, indicative of a shoshonitic series. The host rocks are relatively enriched in LREE and large iron lithophile elements and strongly depleted in elements such as Nb, Ta, and Ti. The Sr/Y ratios and Y content fall into the range of the potassium-ultrapotassic rocks, which has already been reported. These data suggest that the magma was sourced from enriched mantle or the asthenosphere mantle which had been contaminated by lower crustal material. Ore bodies occur as NWW-striking veins in volcanic rocks, consisting of galena, pyrite, quartz, calcite, dolomite, and minor sphalerite, chalcopyrite, and sericite. The alteration is dominated by muscovitization and pyritization. Fluid inclusions in quartz belong to a H₂O-NaCl system and have the homogenization temperature of 170～300℃ and the salinity of 2%～9% NaCl_eq, which probably represents meteoric water driven by magmatic activity. The δ³⁴S values of galena are from -0.1 to 1.7 and the Pb isotopic compositions fall into the range of the potassium-ultrapotassic rocks of northern Tibet, so the sulfur and lead were probably derived from the potassic volcanic rocks. The Nariniya lead-zinc deposit is significantly different from carbonate-hosted lead-zinc deposits in Tuotuohe region in geological and geochemical characteristics, so they belong to different ore-forming systems.

Abstract:Located in western Bangong Co-Nujiang River metallogenic belt, the Gaerqiong Cu-Au deposit is a skarn (porphyry) deposit whose exploration has achieved significant breakthrough in recent years. The skarns in the Gaerqiong ore district are typical calcareous skarn, and the skarn minerals include mainly garnet, pyroxene, wollastonite, epidote, chlorite, idocrase, and sillimanite. Electron microprobe analyses suggest that garnet comprises mainly andradite and grossular, pyroxene is mainly composed of diopside, and chlorite includes ferrichlorite and ferromanganese chlorite. The compositional section of garnet shows that mineral components vary with the change of garnet ring, suggesting that the skarns in the mining area were not formed in a completely closed equilibrium environment and the hydrothermal fluids had the multi-stage feature in the formation process of the deposit. The skarns in the Gaerqiong deposit have developed good zonation, characterized by zoning of garnet-diopside phase→diopside-wollastonite phase→wollastonite-epidote-chlorite phase, accompanied by some mineralization combinations from the depth of the rock mass to the shallow part near the surrounding rocks. According to the result of Fe²⁺/Fe³⁺ calculating ratios, the Gaerqiong deposit was formed in a relatively oxidizing environment, and the calculations of Mn/Fe ratios show that the Gaerqiong ore district has certain potential in search for molybdenum ore bodies.

Abstract:Zircon in-situ Lu-Hf isotopic analysis of the Mesozoic magmatic rocks in Zijinshan area was carried out by using the laser ablation multicollector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) to reveal their protolith origin. The results show that Middle-Late Jurassic and Early Cretaceous magmatic rocks have different Hf isotopic compositions, suggesting that they originated from different sources. The Middle-Late Jurassic granites exhibit obviously negative εHf(t) values from -13.5 to -2.9, with the peak values of two-stage model ages (t_DM^C) ranging from 1.7 to 2.0 Ga, indicating that the magma was mainly sourced from the partial melting of Paleoproterozoic basement. The Early Cretaceous intrusive-volcanic rocks include Sifang granodiorite, Zijinshan, Yueyang and Wenwu volcanic rocks. The Sifang granodiorite and Zijinshan volcanic rocks have similar zircon Hf isotopic compositions, with a wide range of εHf(t) values (-2.3～0.4 and -8.9～5.6) and two-stage model ages (1.3～1.4 Ga and 1.1～1.5 Ga), suggesting that they originated from the same source, with the mixing of partial melting of the Mesoproterozoic basement and mantle-derived melts. The negative εHf(t) values from -2.7 to -9.6 and two-stage model ages ranging from 1.4 to 1.7 Ga of Yueyang and Wenwu volcanic rocks indicate that they were derived from partial melting of the Meso-Paleoproterozoic basement with minor mantle components. It is held that the Early Cretaceous intrusive-volcanic rocks of Zijinshan area were derived from the same magma source, and the evolution of magma source with continuous variation of components and compositional content reveals a complex crust-mantle interaction. Therefore, the difference of Hf isotopic compositions between the Middle-Late Jurassic and Early Cretaceous magmatic rocks could be attributed to different magma sources, and these rocks were produced at different stages of the paleo-Pacific Plate subduction beneath the Eurasian continent.

Abstract:Based on field survey, petrographic, ore microscopic and SEM/EDS analyses of ores and altered wall rocks as well as petrographic, microthermometric, LRM and LA-ICP-MS analyses of fluid inclusions in quartz, this paper deals with the characteristics and origin of ore-forming fluid and the metallogenic process in the Tianjingshan gold deposit. The results show that gold mineralization occurs dominantly in quartz veins and subordinately in altered wall rocks and is related mainly to sericitization and Fe-bearing carbonization and subordinately to chloritization, pyritization, chalcopyritization, galenitization and sphaleritization. Gold mineralization took place after the formation of quartz veins and took place during the brittle deformation stage of quartz. Native gold has been found together with sericite as infillings in quartz fractures or as cement of quartz breccia. Fluid inclusion analyses indicate that the ore-forming fluid is a water-rich and CO₂-bearing fluid characterized by middle-high temperature (286～380℃) and low salinity (3.0%～5.1% Nacl_eq). The LA-ICP-MS analyses of fluid inclusions in quartz reveal high Pb, Zn, Cu, Bi, Mo and Sb in the fluid. The H isotope measurements together with the enrichment of polymetallic components in ore-forming fluid imply an obvious magmatic origin. The upward migration of the magmatic fluid along the reactivated fault and the decreasing of temperature and pressure caused the boiling of the fluid. During the boiling process, the CO₂ preferentially went into the vapor phase and resulted in pH change of the ore-forming fluid. The change of pH caused the precipitation of gold and sulfides and also generated sericitization and Fe-carbonation.

Abstract:Dongjiangkou and Zhashui granites are located in southern Shangdan fault of the south Qinling Mountains. Samples were collected from porphyroid granites. The systematic mineralogical characteristics of Dongjiangkou and Zhashui rocks and the rocks-forming p-T estimates were investigated by means of petrological observation, electron microprobe analysis and scanned electron microscope (SEM). The results demonstrate that porphyroid granodiorite and porphyroid granite are composed of quartz, plagioclase (oligoclase), K-feldspar, magnesiohornblende and magnesian biotite,whereas the accessory minerals include zircons, sphene, magnetite and apatite. It can be inferred that the variations of magma composition account for the zoned structure and rapakivi texture in minerals. Zircon in Dongjiang and Zhashui granitoids crystallized when the magma temperature varied in the range of 759～784℃ (771℃ on average). The rare earth elements were saturated in magma when its temperature reached 741～800℃ (773℃ on average). Plagioclase crystallization when the magma temperature varied from 624℃ to 641℃ (632℃ on average), whereas hornblende crystallized when the magma temperature was in the range of 610～668℃ (632℃ on average). The probable emplacement depth of the rocks was ～5.8 km, with the corresponding pressure being about 1.77×10⁸ Pa.

Abstract:On the basis of the field outcrop survey and drilling data, in combination with laboratory thin section observation and trace element analysis, the authors employed such means as sedimentology and sedimentary geochemistry to conduct investigation. The results show that, in the Lower Permian Shanxi Formation of Xingxian area within Ordos basin, there exist 2 subfacies comprising deltaic plain and deltaic front and 7 microfacies composed of distributary channel, peat swamp, natural levee, splay, underwater distributary channel, interdistributary bay and channel mouth bar. The authors drew the sedimentary section of Shanxi Formation and compiled the sedimentary column of Shanxi Formation as well as Xiegou and Guanjiaya sections, which show that deltaic plain subfacies are mainly developed in Shan 1 Member whereas deltaic front subfacies are developed in Shan 2 Member of the study area. On the whole, during the deposition period of Shanxi Formation, the region showed a deposition process that the delta advanced southward gradually. The authors discussed the coal-accumulation process in the study area and pointed out that coals of Shanxi Formation were formed at the late stage of the short-term level ascending cycle. Coal-accumulation processes of 8^#, 7^#, 6^# coal seams occurred mainly in peat swamp that was developed in interdistributary bay of the deltaic front, whereas the deposition of 5^# coal seam occurred in peat swamp of the deltaic plain. The authors also analyzed the relationship between the thickness variation of coal seam and the sedimentary environment in the study area. It is evident that the distribution of thick coal zones of the Shan 2 Member coincides with the distribution of sandstone-rich belt, and that the coal seam thickness is in negative correlation with the percentage of gravel rock in Shan 1 Member of the study area.

Abstract:Mesoproterozoic Dahongyu Formation (1 650～1 600 Ma) is characterized by subtidal grayish white thick and blocky fine-grained quartz sandstone in Xinglong area of Hebei Province. Microbially induced sedimentary structures (MISS) are widespread on the sandstone surfaces. This paper described in detail sedimentary features and preliminarily analyzed the origin of the MISS. The existence of the MISS probably suggests that a large area of subtidal shallow marine environment was covered by omnipresent microbial mats during Mesoproterozoic in North China. Microbial mats effectively protected the surfaces of sandy sediments and reduced the extent of erosion and reworking. Therefore, the growth of microbial mats had an important influence on the basic process of siliciclastic sedimentation. The MISS on the sandstone surfaces of Dahongyu Formation provide materials for the study of the coordinated development relationship between microbial mats and sedimentation in the Proterozoic shallow marine environment. The in-depth study of the MISS is beneficial for the better understanding of the Proterozoic siliciclastic depositional system and contributes to promoting the development of microbial-mat sedimentology.

Abstract:Sampling was conducted according to field survey and measurement and, on such a basis, the authors studied the component features of the city wall's earth in the Neolithic Liangzhu City, and further discussed its source in association with the analysis based on experiments of XRD, grain size and geochemical elements. The results are as follows: ① Characteristics of grain sizes, geochemical elements and clay minerals are similar to those of Mantou and Huangnikou mounds, and the northern city wall's earth is dominated by clay silt. Clay minerals comprising city wall's earth belong to the combination of illite-kaolinite-vermiculite/mixture of chlorite and vermiculite-smectite. Padded earth's characteristics in northern city wall are similar to earth's characteristics of the fourth layer widely distributed in this area. It is therefore inferred that the source of the city wall's earth was derived from somewhere near Mantou and Huangnikou mounds. ② Mounds like Mantou went through strong oxidant activity because of its high elevation. The raw earth consisting of lacustrine-swamp facies went through reduction activity because of its low elevation, resulting in differences in mineral component degree of crystallinity and geochemical elements. The Neolithic people in Liangzhu area used the local earth only for the city wall's foundation, and they didn't use it to build the city wall directly. They chose the soil from somewhere near mounds like Mantou, because they thought the soil there was more suitable to building city wall.

Abstract:Owing to Yanshanian and Himalayan movement, a series of downfaulted basins were formed in late Cretaceous-Paleogene, when Paleocene halite of salt lake deposition was formed in Shashi Formation of Jiangling depression. Homogenization temperatures of the inclusions in Paleocene halite of Jiangling depression vary from 18 to 50℃, mainly in the range of 22～38℃; the δ¹⁸O values of the inclusion are between -1.2‰ and 9.7‰, with an average of 5.1‰; the δD values vary from -91.5‰ to -63.5‰, -79.4‰ on average. These data are consistent with the thermal features of paleoclimate in that period. However, the homogenization temperatures of inclusions and the H-O isotope values are relatively high in the middle-lower halite layer and relatively low at the top of the same halite layer. This understanding of paleoclimate has important significance for the study of the evolutionary phase of salt lake, the halite origin and the prediction of geological stages and strata of potash salts.

Abstract:Manganese minerals were synthesized by the reaction between KMnO₄ and bivalent manganese salts. Crystal structure characteristics of the synthetic minerals were investigated by means of X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM). The effects of mole ratio R of Mn²⁺ to Mn⁷⁺(1:1, 1:2, 1:3 and 1:4 respectively), synthetic temperature (30℃, 50℃, 70℃, 90℃ and 110℃ respectively), and anionic species (Cl^-, SO₄^2-, and NO₃^- respectively) on the formation of the minerals were discussed. The results showd that the synthetic minerals were transformed from cryptomelane to birnessite with the decrease of R from 1:1 to 1:4, and the average oxidation state of manganese (AOS_Mn) increased correspondingly. Anionic species of the reactants affected the type and crystalline of the synthetic minerals. Within the experimental synthetic temperature (30～110℃), the crystallinity and AOS_Mn of the synthetic minerals rose slightly as the temperature increased.

Abstract:In this paper, the low grade Ca-bentonite from Liaoning was taken as the object of the study and the wet processing technology of purification was employed. The influence of such factors as the tape and dosage of dispersants, the liquid-solid ratio, the speed of centrifugation, the time of centrifugation and the temperature of bentonite on the content of bentonite was determined. The characterization of original soil and the purity of bentonite were tested by the X-ray diffraction photographs. The experiments show that the best conditions for purification are as follows: the concentration of dispersant is 0.5%, the liquid-solid ratio is 12, the time of centrifugation is 9 min, the speed of centrifugation is 2 500 r/min, and the temperature of bentonite is 60℃. The purity of montmorillonite can be raised up to over 92% after purification.