Abstract:The bimodal volcanic rocks of Upper Carboniferous Yishijilike Formation from the Tekes Daban area in Yining landmass consist mainly of basalts and rhyolites. Their SiO₂ values range from 47.13% to 77.72%, and exhibit a gap of SiO₂ between 53.62% and 72.15%, displaying a typical bimodal geochemical affinity. The LA-ICP-MS zircon U-Pb ages of rhylites yielded an age of 302.8±3.6 Ma, suggesting that these bimodal volcanic rocks were formed at the beginning of Late Carboniferous. Basalt samples have SiO₂ values of 47.13%~53.62%, with high Fe₂O₃ (TFe₂O₃ being 10.90%~17.40%) and MgO (3.74%~10.12%, 6.48% on average), high Na (2.84%~6.69%) and low K (0.48%~3.77%) values. The basalts are obviously enriched in light rare earth elements and depleted in heavy rare earth elements[(La/Yb)_N=1.58~4.94]. In contrast, the rhyolites samples have SiO₂ values of 72.15%~77.72%, high K (6.12%~9.48%) and low Na (0.40%~2.39%) concentrations. Compared with the basalts of bimodal volcanic rocks, they show significant depletion of Ba, Sr, P, Ti elements, obvious enrichment of light rare earth elements and relative depletion of heavy rare earth elements. They exhibit strongly negative Eu anomaly (δEu=0.18~0.44) and geochemical characteristics of A2 type granites. In addition, the basalts have high values of Mg^#, Co, Cr, Ni, with εNd(t) of basalt samples being 3.45 and 3.55. These features indicate that basaltic magmas were derived from partial melting of a depleted mantle source. The rhyolites of the Yishkilike Formation have low Mg^# and positive εHf(t) values, suggesting that their formation was related to crustal melting during the process of basaltic magma underplating. Combined with the two-stage Hf model ages, it is suggested that the rhyolite source may be related to the reworking of Proterozoic metamorphic basement. These geochemical characteristics together with structural tectonic discriminant diagrams show that the bimodal volcanic rocks of the Yishijilike Formation were formed in a post-orogenic extensional environment with intraplate genetic characteristics. The discovery of the typical bimodal volcanic rocks provides important information for further study of the Carboniferous tectonic evolution in Yining landmass.

Abstract:In this paper, the authors studied the zircon U-Pb isotope chronology, whole rock geochemistry and Hf isotopes of the fine-grained two-mica monzonitic granite and medium fine-grained biotite granodiorite of the Lianyunshan granite from the Jingchong Co-Cu polymetallic deposit in northeastern Hunan Province. LA-ICP-MS zircon U-Pb dating yielded crystallization ages of 149.4±1.1 Ma for the fine-grained two-mica monzonitic granite of the Lianyunshan granite. The rocks belong to a peraluminous high-Al calc-alkaline intrusive granite. These rocks are characterized by high Th, U and Pb content and low Nb, Ta, Zr and Ti content. The REE distribution patterns show the right-inclined type, with strongly negative Eu anomalies to weakly negative Eu anomalies. The Hf isotope analytical results show that the ¹⁷⁶Hf/¹⁷⁷Hf values of the Yanshanian zircons are between 0.282 314 and 0.282 461, whereas the εHf(t) values of the late Yanshanian zircons are between -13.0 and -7.8, with the two stage Hf model ages ranging from 2 018 to 1 690 Ma, which indicates that its parental magma was derived from partial melting of rocks of ancient crust.

Abstract:The late Yanshanian Laba porphyritic granite, associated with a superlarge Mo(-Cu)-polymetallic deposit, was recently identified by drilling exploration in Shangrila area of northwestern Yunnan Province. The magmatic biotites and amphiboles have recorded the detailed petrogenesis information including the temperature, pressure, oxygen fugacity, and the source origin of the parent magma. The authors investigated the mineralogical composition of the biotites and amphiboles in the porphyritic granite from the Laba Mo(-Cu) deposit, and constrained the physico-chemical conditions of the ore-bearing magmatic rocks as well as the metallogenic potential. Electron microprobe analyses (EMPA) show that the biotites have uniform Fe²⁺/(Fe²⁺+Mg) values, without or with minor CaO, and the Ti cation number is 0.31~0.52, indicating that they are of magmatic origin. The Si, Ti cation num-bers of the amphiboles are 6.68~7.20 and 0.09~0.13 respectively, indicating that they are also of magmatic origin. The authors have reached the conclusion that the formation temperature, pressure and depth of the porphyritic granite are 705~903℃, 59~449 MPa and 2.2~17.0 km respectively. The features of mineral geochemistry of the biotites and amphiboles suggest that the porphyritic granite belongs to the I-type granite with the addition of mantle-derived materials, and was formed in an environment with high oxygen fugacity. The values of F and Cl in the biotites are 0.17%~0.58%, showing that the fluids exsolved from the granitic magmas were rich in F and Cl, which was beneficial for enrichment and mineralization of Mo and Cu. These results shed light on the correlation between the rock-forming and ore-forming processes for the superlarge Laba Mo(-Cu)-polymetallic deposit. Meanwhile, they also indicate that the Laba orefield has a giant potential for future exploration.

Abstract:The Shamuluo Formation is distributed in Bangong Co-Nujiang suture zone, and its sedimentary background and source characteristic were closely linked with the evolution of Bangong Co-Nujiang Tethys Ocean. In order to discuss sediment provenance, weathering, tectonic setting of sedimentary basin and subduction of Bangong Co-Nujiang Tethys Ocean, the authors made a systematic analysis of petrology and geochemistry of Shamuluo Formation argillaceous rocks in the western part of the Bangong Co-Nujiang suture zone. The mean values of ICV, CIA, Al₂O₃/TiO₂, Th/Sc, Rb/Cs, (Gd/Yb)_N, La, Ce, ∑REE, La/Yb, (La/Yb)_N, Eu/Eu_N^*, LREE/HREE are 0.80, 72, 21, 0.88, 13.5, 1.58, 42.47×10^-6, 84.81×10^-6, 200.02×10^-6, 14.22, 9.61, 0.65 and 9.04 respectively, while the mean values of Th, U, Hf, Th/U, La/Th are 16.34×10^-6, 2.85×10^-6, 4.81×10^-6, 5.78 and 2.61 respectively. The diagrams of K₂O/Na₂O-SiO₂, La-Th-Sc, Th-Co-Zr/10, Th-Sc-Zr/10, TiO₂-Zr, Co/Y-Ti/Zr, La-Th-Sc, Th-Sc, La/Sc-Co/Th, REE-La/Yb, A-CN-K and REEs also show certain regularity. The argillaceous rocks are mature and the source rock are granodiorite, granite, andesite and sedimentary clastic rock which have much plagioclase and alkali feldspar. The source region of argillaceous rocks has suffered from medium degree of chemical weathering, suggesting a warm and moist climate. The geochemical characteristics of argillaceous rocks indicate that argillaceous rocks tended to occur in active continental margin setting, where its tectonic activity became intensified from the bottom to the top. These results provide sedimentary geochemical evidence for the evolution of Bangong Co-Nujiang Tethys Ocean, which indicates that Bangong Co-Nujiang Tethys Ocean experienced northward subduction about 141 million years ago.

Abstract:Large-sized Cu-Au deposits are closely related to Late Mesozoic intrusive rocks in the Tongling area of Anhui Province. To discuss the potential of apatite as a petrogenetic-metallogenic indicator, the authors conducted a detailed in situ geochemical study of apatite from four representative intrusions (Jinkouling granodiorite, Tongguanshan and Dongguashan quartz monzodiorite, and Chaoshan pyroxene monzodiorite) in the Tongling area. The analyzed apatites of the Tongling intrusive rocks have high Sr/Y ratios (3.19 on average) and lower Y values, indicating that they are adakitic rocks. The apatite samples have F values ranging from 2.63% to 4.02%, and are defined as fluorapatites. The studied apatite samples have high REE content (825×10^-6~5 853×10^-6), moderate δEu values (0.37~0.88), high log f_O2 values (-12.3~-9.86), relatively high Cl content (mostly>0.2%) and Cl/F ratios, showing that the Tongling intrusive rocks might have been formed from mixed source of mantle-derived and crust-derived magmas in a high oxygen fugacity environment. The results indicate that the Cu-Au mineralization in the Tongling area may be closely related to the slab-derived Cl-enriched fluids, an oxidizing environment and a mantle-crust mixed source.

Abstract:Upper Permian Nayixiong Formation volcanic rocks from northern Qiangtang-Qamdo landmass of the Tibetan Plateau have many geochemical characteristics and zircon U-Pb dating data. The main volcanic rocks are basalt, andesite-basalt, andesite, rhyolite, tuff, which have the characteristics of alkaline basalt to acidic rhyolite. The result of the geochronologic study of zircon U-Pb dating data shows that the volcanic eruption ages vary from 251.1±4.8 Ma to 249.6±1.3 Ma. Geochemical characteristics show that the rocks are characterized by high SiO₂(74.85%~77.55%) and Na₂O+K₂O(5.40%~6.61%), low MgO, K₂O and CaO as well as low and stable Al₂O₃ content. The average Rittmann index of the rhyolite is 1.15, less than 3.3. The lithochemistry feature shows that the rhyolite belongs to the calc-alkaline volcanic rocks. Main element features of the andesite show that the SiO₂ content is 55.13%~56.28% and the Na₂O+K₂O content is 4.13%~6.15%. The average Rittmann index of the andesite is 2.20, less than 3.3. The lithochemical features show that the andesite belongs to the calc-alkaline volcanic rocks. The content of the alkaline basalt is 51.49%, Na₂O+K₂O is 6.34%, and the Rittmann index is 4.73, which shows that the basalt belongs to the alkaline volcanic rock. In addition, the granodiorite body of Nyixiong Formation volcanic rocks belongs to aluminous-peraluminous series of enriched LREE. These volcanic rocks are characterized by high LILE (Th, U) and LREE and obvious depletion of HFSE (Nb, Ta). The geochemical compositions of volcanic rocks belong to island arc volcanic rocks.

Abstract:The North Qilian Mountain suture zone is a typical early Paleozoic oceanic subduction zone, in which two blue schist zones are developed:a low-grade blue schist zone with lawsonite and a high-grade blue schist zone with eclogites. Ardennite-(As), a rare kind of silicate mineral, was found in the high-pressure metamorphic Mn-rich silica rocks in the high-grade blue schist zone containing eclogites in the North Qilian Mountain. This is the first discovery of ardennite-(As) in China. Detailed mineralogical studies were carried out by means of optical microscopy, scanning electron microscopy, electron probe microscopy, Raman spectroscopy and transmission electron microscopy. According to the results obtained, the density of ardennite-(As) is 3.69~3.75 g/cm³ and the hardness is 6~7; ardennite-(As) crystals are biaxial (+) and have perfect cleavage in (010), pleochroism is strong from pale yellow to golden yellow, usually associated with quartz, piemontite, glaucophane, phengite and hematite; the main components of ardennite-(As) are Si, Al, Mn, it is rich in As, and contains a small amount of F, V, P; in Raman spectrum; ardennite-(As) shows many characteristic peaks, probably indicating the presence of arsenate, vanadium, MnO and SiO₃ bonds; in the crystal structure, ardennite-(As) is orthorhombic, the space group is Pnmm, and the crystal axis parameters are a=8.934 Å, b=5.817 Å, c=19.005 Å. These mineralogical features can be used as the basis for the identification and study of ardennite-(As).

Abstract:The Han Dynasty stone coffin unearthed from M23 tomb in Jintang Lijialiangzi of Chengdu has suffered from surface weathering phenomena such as powdering, peeling and other diseases and hence needs protection and restoration as soon as possible. On-the-spot investigation shows that the main weathering diseases of the stone artifact include cracks, sheets, granules, powders, etc. In this paper, the authors used X-ray diffraction (XRD), polarized light microscopy, and scanning electron microscopy (SEM) to analyze the microstructure and structure of Jintang stone artifact. The results show that the stone artifact is made of red sandstone, and the main detrital minerals are quartz, albite, rock debris and a small amount of mica. The main cement is calcium with a small amount of carbonaceous and argillaceous material. It is also shown that the main factors responsible for the sandstone weathering is the dissolution loss of calcareous cement and the disintegration of muddy cement with water, together with the influence of the weathering alteration of debris and feldspar debris. The results obtained by the authors will help to provide basic scientific data for the post-protection and restoration of this stone coffin.

Abstract:Most minerals in the nature exist as solid solutions. Calculating the thermodynamic properties based on their crystal chemistry characteristics is the basis for the theoretical study of the formation of minerals. In this paper, a fictive ternary model for the simulation of thermodynamic properties of binary mineral solid solutions is introduced. The thermodynamic properties of diopside-jadeite solid solution were calculated. By constructing one ordered intermediate state mineral and considering both long-range order and short-range order effects, the model could calculate equilibrium thermodynamic parameters such as free energy, enthalpy, and entropy for a specific composition based on the rule that the lowest free energy corresponds to thermodynamical equilibrium mineral solid solution. The activity-composition relationship and temperature-composition phase diagram of diopside-jadeite solid solution system were calculated with omphacite as ordered intermediate state. It is found that the order/disorder transition of omphacite with increasing temperature is a first-order phase transition with a transition temperature of 1 148±25 K, which is in agreement with the experimental results. The thermodynamic parameters of the diopside-omphacite-jadeite system obtained in this paper can be applied to the study of the eclogitefacies metamorphism of rocks with the MORB bulk composition by means of pseudosection thermobarometry method.

Abstract:In this paper, the authors systematically studied the 193 nm ArF excimer laser system's ablation behavior and hole shape characteristics for natural minerals with different Mohs hardnesses, such as talc, gypsum, chlorite, calcite, apatite, tremolite, albite, topaz, corundum, fluorite and quartz. The ablation rates of 11 natural minerals were obtained in order of quartz > gypsum > talc > calcite > apatite ≥ tremolite > albite > topaz > corundum > fluorite, except chlorite. The ablation rate was negatively correlated with Mohs hardness, except for quartz and fluorite.

Abstract:As Fe oxide minerals such as magnetite and hematite are the main Fe-bearing minerals in iron ore deposits, their oxygen isotope geochemistry has great potentials in tracing the genesis of iron ore deposits. In this paper, based on the summarization of the basic principles of oxygen isotope fractionation in Fe oxide minerals and the general processes related to iron mineralization, the authors calculated oxygen isotope distributions of Fe oxide minerals in different types of iron ores, and the results were compared with the data previously obtained from various iron ores. Then a case study was carried out on submarine volcanic-hosted iron ore deposits from Zhibo, Chagangnuoer, and Beizhan iron ore deposits in Xinjiang for their oxygen isotope compositions of magnetite. The results show that the magnetite of these deposits have δ¹⁸O_SMOW mainly between 1‰ and 3‰, indicating that their formation was mainly controlled by high-temperature magmatic or magmatic-hydrothermal processes, with the late-stage low-temperature alteration having little effect on the iron mineralization.

Abstract:Heavy metal pollution from carbonate-type tailings in buffering/neutral mine drainage (NMD) period tends to be ignored. With the tailings of cassiterite-sulfide deposits in the Dachang ore district of Guangxi as the study object, the author conducted column leaching test to investigate the mechanism of heavy metals release from carbonate-type tailings in buffering period, so as to provide the basis for prevention and control of the heavy metal pollution involving the tailings. The results show that there probably exists the pollution of Sb, Zn, Cd, As (Pb) release from Dachangs tailings in the buffer period (about 7 years, with pH value being 6.6~8.0). At the beginning stage of tailings stacking (0 to 0.5 years, with pH value dropped from 7.6 to 7.2), Zn, Sb and Cd are quickly and heavily released; in the middle stage (0.5 to 2.5 years, with pH value fluctuating from 7.2 to 8.0), Sb is more smoothly released; in the late stage (2.5 to 7 years, with pH value changing between 8.0 and 6.6, showing a decreasing trend), As, Sb (Pb) fluctuate periodically or intermittently following air temperature and pH value, implying that when temperature and pH value are high in summer, element concentrations are higher; on the contrary, element concentrations are lower with the lowering temperature and pH value in winter. The heavy metals release is related to the oxidation degree/oxidation sequence of sulfide minerals that the metals are hosted in. The oxidation sequence of these minerals are sphalerite (Zn, Cd), franckeite (Sb)→jamesonite (Sb) →arsenopyrite (As), galena (Pb). Therefore, the measures to prevent and control the heavy metal pollution of the carbonate-type tailings (Dachang, Guangxi) in the buffering period should be carried out targetedly on the basis of tailings stocking stage and season (summer). After the buffer period (7 years), researchers should pay attention to the pollution combining the acid mine drainage (AMD) with heavy metals (As, Sb).