Abstract:The Awulale tectonic magmatic belt is an important Fe-Cu metallogenic zone in western Tianshan Mountains, with especially lots of Cu deposits and ore spots discovered in the western Awulale. Nevertheless, the Permian geodynamic background and the metallogenic environments in this area remain unclear. Middle-high potassium calc-alkaline trachyandensite newly discovered at the bottom of Wulang Formation section of volcanic rocks in Qunjisayi area was studied in this paper. La-ICP-MS zircon U-Pb dating of trachyandesite yielded a ²⁰⁶Pb/²³⁸U weighted average age of 300 ±11Ma. Trachyandesites in Qunjisayi area are geochemically characterized by enrichment of light rare earth elements (LREE) and large-ion lithophile elements (LILE, such as Rb, Ba, and K) and flat distribution of heavy rare earth elements (HREE), together with strong negative Nb, Ta, Ti anomalies. The rocks have whole-rock εNd(t) values of +4.5 to +4.9, and Nd isotopic model ages (t_DM) of 808~765 Ma, indicating that the rocks originated from a fluid metasomatic mantle magma source. Similar to features of a large amount of granite exposed in the northern part of the central Asian orogenic belt, the t_DM values are relatively young, and the acidic rocks in the study area have similar isotope geochemical characteristics. The magma probably came from the partial melting of the new basaltic lower crust. The West Tianshan Mountains entered the past-collision evolution stage in the Early Permian, and the formation of the high potassium calc-alkaline trachyandesite magma with arc features might have been related to the partial melting process of the new basaltic lower crust during the upwelling of asthenosphere material and energy that resulted from the break-off of the oceanic lithosphere plate tail that postdated the closure of the North Tianshan Ocean, which was the mark of the final stage of the evolution of the orogenic process. Meanwhile, the tectonic system correspondingly changed from the subduction extrusion background to the extensional tension background.

Abstract:Paleozoic dyke swarms observed in the Qiongheba area of East Junggar are pivotal in understanding the tectonic evolution and setting of this area and even southwestern Central Asian orogenic belt; however, their genesis and tectonic setting are still unclear. In this paper, the authors present observations from outcrop scale to mineral scale, and new mineral chemistry, whole-rock chemistry, zircon U-Pb ages and in situ zircon Hf-O isotope data from the dykes in the Lüshigou pluton of Qiongheba area, East Junggar. On the basis of the new obtained and previously published geochemical and isotopic data, the authors constrained magma sources and petrogenetic processes involved in the generation of these dyke swarms. The dykes in the Lüshigou pluton are composed of diorite-porphyrite and diabase porphyrite. The sensitive high-resolution LA-ICP-MS and SHRIMP U-Pb zircon ages determined for these dykes for the first time indicate that the diorite porphyrite and diabase porphyrite dykes were formed at 346±1 Ma and~332 Ma, respectively. Zircon εHf(t) values of diabase porphyrite dyke in the Lüshigou pluton are from +10.2 to +15.4, with the corresponding two-stage Hf model ages ranging from 0.35 to 0.67 Ga. Zircon δ¹⁸O values mainly vary from 5.00‰ to 6.41‰. These isotope characteristics indicate a mantle source component. Thermobarometric results of amphiboles in the diabase porphyrite dyke indicate that the temperature range varies from 896℃ to 984℃, and pressure range varies from 41 to 88 MPa, with corresponding crystallization depth from~1.54 to 3.31 km. In addition, the result of calculated clinopyroxene-liquid barometer shows that the magma temperature at pyroxene-melt equilibrium is 1 092℃ to 1 099℃ and the pressure is 500 to 630 MPa, so the storage depth of diabase porphyrite magma chamber should be at the depth from 16.5 to 20.8 km. Combined with previously published data, the authors hold that, in the Early Carboniferous, dyke swarms in the Qiongheba area of East Junggar were probably emplaced in a post-collisional setting.

Abstract:Exposed in the northern Beidashan area of Alxa, minor Precambrian rocks have been traditionally considered to be a part of the Longshoushan Group. The age and isotopic characteristics of these Precambrian rocks are important for the understanding of the local basement characteristics and the tectonic architecture of north Alxa area. This study presents detailed petrology, zircon U-Pb age and Hf isotope of the Haisen Chulu gneiss from the north Beidashan area and discusses its tectonic implications. Field observation and petrological features indicate that the Haisen Chulu gneiss is orthogneiss. LA-ICPMS zircon U-Pb dating performed on the inner part of the zircons yielded an upper intercept age of 1 408±29 Ma (MSWD=13) on the concordia diagram, which indicates that the protolith for the gneiss intruded at~1.4 Ga. The zircons from Haisen Chulu gneiss show positive εHf(t) values between -4.38 and +6.68, and the two-stage Hf model ages are in the range of 2 091 to 1 624 Ma, indicating that the protoliths were mainly derived from the juvenile crust. This study, in combination with previous work, indicates that the Precambrian rocks outcropped in northern Longshoushan-Beidashan area were formed in Mesoproterozoic or later instead of in Archean or Paleoproterozoic as previously proposed. The northern Longshoushan-Beidashan area could not be part of the Alxa block during early Precambrian time.

Abstract:Shujiaba Group (D_2-3S) is an important ore-bearing stratum of the tectonic altered rock type gold deposits in the northern belt of the West Qinling Mountains. It is a set of shallow metamorphic fine clastic rocks with the sedimentary characteristics of flysch and a small quantity of carbonate rocks. The combined rocks were formed in Middle-Late Devonian. According to the 1:50 000 regional geological survey, a set of volcanic-pyroclastic rock series was formed in the Haibangou in northern Liangdang County of West Qinling, which was originally designated as Shujiaba Group. According to zircon LA-ICP-MS U-Pb dating, the weighted mean average age of rhyolitic crystal tuff is 204±2 Ma and that of dacite porphyry is 209±3 Ma respectively, indicating that the volcanic-pyroclastic rock series was formed in the Late Triassic. Therefore, it was disintegrated from Shujiaba Group and is temporarily placed in the Huari Formation (T₃hr).

Abstract:Paleo-sedimentary environment could be recovered qualitatively or semi-quantitatively by using elements or element ratios sensitive to sedimentary environment of mudstone. In this study, major, trace and rare earth elements compositions, XRD and SEM of 12 rock samples from Xujiahe Formation were analyzed to investigate the paleoclimate, paleo-sedimentation and paleo-provenance in the Qilixia section, northeast Sichuan area. The results show that the content of clay minerals in the fine-grain samples of the Xujiahe Formation in the Qilixia section is dominated by illite-montmorillonite mixed-layer mineral (62%~88%), followed by chlorite (3%~19%), illite (3%~11%), and kaolinite (1%~9%), with FeO/MnO ratios being 28.08~104.23, reflecting the warm and humid climatic conditions of the Late Triassic in the Qilixia area, in which the climate of the 3^rd and 5^th members of the sedimentary period were relatively warm and humid, and the climate of the 1^st, 2^nd and 4^th members of the sedimentary period were slightly arid and hot; lower Li, Sr, Ni and Ga abundances and Sr/Ba ratios (0.08~0.24) of the Xujiahe Formation suggest that the paleo-salinity of sedimentary water was low; V/(V+Ni) ratios (0.69~0.85) and Ce_anom(0.26~0.30) indicate that there existed a reducing environment in Xujiahe sedimentary period, with the reductivity of water gradually weakened from the 1^st to the 5^th member of the Xujiahe Formation. The REE distribution patterns of samples in the study area are similar to those in South Qinling Mountain, Longmen Mountain and Micang-Daba Mountain areas, indicating that the early provenance in this area was derived mainly from the mixture of diorite, granite and basalt in the South Qinling Mountain, with some from the granite of Longmen Mountain, whereas the late provenance was mainly derived from the granite of Micang-Daba Mountain.

Abstract:In order to investigate the impact of different magmatic systems on metallogenic type, the authors studied the petrological and geochemical characteristics of biotite of the granodiorite porphyry from the Wushan Cu deposit in the Middle-Lower Yangtze metallogenic belt and the Zhuxiling W-Mo deposit in Jiangnan orogenic belt. The results show that the biotite of Wushan and Zhuxiling granitoids is magnesium-rich and iron-poor one. Zhuxiling biotite shows relative enrichment of incompatible elements such as Li and Nb, whereas that of Wushan displays high abundances of compatible elements such as Ni and V. Biotite geochemistry shows that these indexes are capable of reflecting A-type, I-type or S-type, oxygen fugacity, and volatile composition of host magma and thus can be used to distinguish different magma sources. Based on biotite geochemistry, the authors established the connection of different petrogenetic and metallogenic systems:the magmatic system in equilibrium with biotite of Wushan Cu deposit shows high Cl, and high oxygen fugacity, which is favorable for Cu mineralization, while the magmatic system of Zhuxiling exhibits higher F and lower oxygen fugacity, which is favorable for W mineralization.

Abstract:Rutile is a common accessory mineral in the Qianlishan biotite granite. In this paper, the authors investigated chemical significance of rutiles in tracing the magmatic-hydrothermal evolution and W-Sn metalogic process based on their typomorphic features. The results show that three forms of rutiles caused by the influence of the hydrothermal fluid can be identified. The first type of rutile occurs in the biotite fissure, being anhedral rutile, the second type is composed of euhedral crystals with relatively large grain size. The third type of rutile occurs as aggregates with banded and anisomerous structures. The continual increase of tungsten content of rutile with the enhancement of alteration and mineralization suggests that the tungsten content in the rutile can be used as a criterion for the ore-forming capability of granite, and the high tungsten-bearing rutile can indicate the formation and enrichment of the tungsten. In the future, these phenomena can be used as prospecting marks in search for tungsten deposits.

Abstract:Pyrite is well developed in southeastern Ordos Basin, and occurs in anhydrite dissolved pores and karst caves, or is accompanied by anhydrite layers as dispersed grains or assemblages. The δ³⁴S values of the pyrite vary in the range of 10.50‰~24.00‰, 17.33‰ on average, indicating its thermochemical sulfate reduction (TSR) origin. The basic condition for TSR is thin layer of anhydrite, high temperature and abundant hydrocarbon, which is all qualified in southeastern Ordos Basin. In combination with its modes of occurrence, the well-developed pyrite accompanied with anhydrite dissolution is considered to be the product of TSR. The formation with the existence of pyrite has high content of Fe, ranging from 3 387.50×10^-6 to 23 112.50×10^-6, averagely 13 233.33×10^-6, which provided material source for the formation of pyrite. However, the H₂S concentration is low in the Ordovician carbonate, which was probably caused by the precipitation of pyrite.

Abstract:In this paper, aimed at tackling the poor lead flotation indexes in the Panlong lead-zinc mine in Guangxi, the authors studied in detail the chemical composition, phase composition, target mineral size and distribution characteristics of lead in the Panlong lead-zinc mine by means of chemical multielement analysis, phase analysis, optical microscopy identification and dissociation degree statistics so as to probe into its physical characteristics. The results show that lead middling 1 contains 2.03% Pb, which mainly occurs in galena. At the same time, the overall size of galena is small. After screening and classification, the distribution characteristics of galena in the products of different particle sizes are very different. Some lead-bearing mineral particles of +74 and -74~+39 micron are mainly lead-zinc-sulfur complex conjoined aggregates, and the total occupancy of these two grades of metals is more than 56%. It is the key to constraining the lead flotation indexes of the Panlong lead-zinc mine. According to the above research results, it is recommended to adopt the grading grinding process to improve the dissociation degree of lead monomer in lead middling 1, so as to further improve the recovery rate of lead metal in lead concentrate.

Abstract:In this paper, the inclusions and the structural water in the microchannel in emeralds from Pakistan were investigated by using optical microscopy, infrared microspectroscopy (FTIR), Raman spectroscopy and electron microprobe analyzer (EPMA). The emeralds from Pakistan contain type Ⅰ and type Ⅱ waters. The infrared spectra show that the intensity of water type Ⅱ (5 270, 3 600, 1 632 cm^-1) is much stronger than water type Ⅰ (1 600 cm^-1). Most of the multiphasic inclusions in these emeralds are of biphasic elongated shape or are "neck-licking" inclusions, which consist of liquid (H₂O) and gas, including carbon dioxide gas (CO₂) + nitrogen (N₂) + methane (CH₄). The main solid inclusions are magnesite, dolomite, muscovite and quartz. These inclusions and infrared spectra contribute to distinguishing Pakistani emeralds from emeralds of other origins.

Abstract:The mineral structure, chemical compositions and spectral characteristics of rainbow garnet samples from Tenkawa, Yoshino area, Nara Prefecture, Japan, were studied by Scanning Electron Microscopy with Energy Dispersive Spectrometer, Electron Microprobe, Fourier Transform Infrared Spectrometer and Laser Raman Spectrometer. In this paper, the authors analyzed the factors responsible for the rainbow effect and interpreted rainbow garnet's formation environment. The backscattering image shows stripes of different shades, the semi-quantitative analysis of the energy spectrum proves that the elemental composition of light gray stripe is the same as that of pure andradite, and the dark gray stripe's elemental composition likes that of Al-containing andradite. The two components form a lamellae structure, which causes interference and diffraction of light to produce a rainbow effect. Electron microprobe analysis makes sure that the main component of Japanese rainbow garnet is close to that of pure andradite. On the surface of the iridescent mineral (rainbow face), the vertical lamellae structure forms a diffraction grating, which causes the incident light to undergo grating diffraction. The lamellae of parallel rainbow growth cause interference of incident light. The light waves generated by the above two actions combine to form the iridescent color. The peak position and the Fe-O peak position are affected by a small amount of Al-O structure in the reflection infrared spectrum, which proves that the infrared spectrum characteristics of the Japanese rainbow garnet correspond to those of the andradite structure containing a small amount of Al. The laser Raman spectroscopy test reveals that the peak position of the high Al moves 2 cm^-1 in the high frequency direction compared with that of the less Al content (or none), and the overall spectral characteristics are consistent with the structural features of the andradite. Japanese rainbow garnet is intercalated with andradite and Al-bearing andradite. It is inferred that it was formed in an environment rich in Fe and depleted in Al.