• Volume 32,Issue 4,2013 Table of Contents
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    • >专题研究
    • Geochemistry of garnet-mica schist in the Wutai Group and its geological implications

      2013, 32(4):405-416.

      Abstract (2502) HTML (0) PDF 9.41 M (3937) Comment (0) Favorites

      Abstract:Garnet-mica schist from the Shizui Subgroup of Wutai Group is chiefly composed of garnet, biotite, muscovite, plagioclase, quartz and ilmenite, with a few samples containing epidote, staurolite, kyanite and ortho-amphibole. Samples have SiO2 51.75%~69.06% and Al2O3 11.99%~20.39% with a few samples being poor in sodium. Samples exhibit higher LREE and lower HREE in REE patterns without obvious Eu anomaly, and their high strength element compositions and large ion lithophile element compositions are similar to those of classical shales in the world. Correlations between related elements imply that clay minerals dominate the rock bulk compositions. Based on a series of diagrams such as geochemical classification, heavy mineral accumulation, source rock and tectonic setting discrimination, the authors found that the protolith of the rocks was shales without obvious heavy mineral accumulation. The sediments mainly came from those coeval TTG rocks and/or basic rocks in Wutai area, and were deposited in an arc basin environment at about 2.53~2.50 Ga. Combined with the results of metamorphic equilibria modeling using THERMOCALC method and metamorphic zircon dating using SHRIMP method, the authors have found that the garnet-mica schist experienced a kyanite-type metamorphism with a clockwise p-t path at ~1.95 Ga.

    • Geochemistry and petrogenesis of mafic enclaves in Tulargen mafic-ultramafic complex, Xinjiang

      2013, 32(4):417-430.

      Abstract (1934) HTML (0) PDF 5.61 M (3617) Comment (0) Favorites

      Abstract:The Tulargen Cu-Ni sulfide deposit, whose discovery means a great breakthrough in Cu-Ni exploration in Xinjiang in the past ten years, is located in the eastern section of the Huangshan-Jingerquan ore belt. The Tulargen Cu-Ni deposit is a magmatic differentiation deposit related to mafic-ultramafic complex, which comprises three intrusions, namely complex Ⅰ, Ⅱ, Ⅲ, respectively. The hornblende pyroxene peridotite of complex Ⅰ is associated with abundant mafic enclaves, which include ore-bearing gabbro enclaves and plagioclasite enclaves without mineralization. Mafic enclaves and the host display different characteristics in such aspects as mineral species, types and intensities of alteration, con tacts between minerals and forming sequence. There exists a distinct boundary, composed of squamiform chlorite, between the mafic enclaves and the host. The Harker diagram of major elements and figures of La, Nd, Zr, and Yb versus SiO2 have shown that samples of the Tulargen complex display a good correlation, whereas the mafic enclaves don't show such characteristics, which indicates that magmatic contamination played a significant role in the formation of the mafic enclaves. Nb/U and Ce/Pb ratios imply that, after crustal contamination, some elements of the mafic enclaves was mobilized and migrated by the late magmatic hydrous fluids.

    • Mineralogy, mineral chemistry and genesis of the Hongyuntan iron deposit in East Tianshan Mountians, Xinjiang

      2013, 32(4):431-449.

      Abstract (7162) HTML (0) PDF 18.22 M (32533) Comment (0) Favorites

      Abstract:The Hongyuntan iron deposit is hosted in pyroclastic rocks of the Lower Carboniferous Yamansu Formation. The ore bodies occur as layers, stratoid bodies or lenses. The principal ore mineral is magnetite, together with minor maghemite, specularite, pyrite and trace chalcopyrite. The gangue minerals include garnet, diopside, actinolite, chlorite, tremolite, epidote, biotite, albite and quartz. The ore structures are mainly of massive and disseminated forms, with occasional banded or veined forms. The ore textures are of subhedral-anhedral granular and metasomatic types. The wall rock alteration shows symmetrical zoning, and the alteration colors change from dark to light from ore bodies outwards. On the basis of observed mineral assemblages and ore fabrics, two periods of ore deposition were recognized, i.e., skarn period and hydrothermal ore-forming period, which could be further subdivided into four metallogenic stages, namely skarn stage, retrograde alteration stage (main ore-forming stage), early hydrothermal stage and quartz-sulfide stage. Electron microprobe analyses show that the end member of garnet is mainly andradite-grossularite. The composition of pyroxene is mainly diopside-asteroite. The amphiboles is composed mainly of actinolite and tremolite with minor magnesiohornblende. The composition of these skarn minerals suggests that skarn in the Hongyuntan iron deposit is calcic skarn, belonging to metasomatic skarn. The characteristics of main and trace elements suggest that the formation of magnetite was closely related to the skarn. In combination with geological characteristics, the authors suggest that the skarn might have resulted from interaction between Ca-rich pyroclastic and Fe-rich magmatic hydrothermal fluid which was transported along the fault system. The formation of magnetite was hence related to the regressive metamorphism of the skarn.

    • LA-ICP-MS U-Pb age of two-mica granite in the Yunlong tin-tungsten metallogenic belt in Three River region and its geological implications

      2013, 32(4):450-462.

      Abstract (2123) HTML (0) PDF 14.16 M (3551) Comment (0) Favorites

      Abstract:Located in the middle segment of the Three River region, the Yunlong metallogenic belt is considered to be connected with the Southeast Asian giant tin belt. The authors performed LA-ICP-MS zircon U-Pb analysis of two-mica granite closely related to tin mineralization, and got a Late Cretaceous emplacement age of 72.2±0.8 Ma (MSWD=1.9). This is the first discovery of convincible Late Cretaceous magmatism in Baoshan terrane. The two-mica granitiod in Yunlong tin metallogenic belt was emplaced in a tectonic setting identical with the setting of the Tengchong terrane, and could represent the melting products of thickened crust in the hinterland in response to the eastward subduction of the Neo-Tethys. The emplacement age of the two-mica granite reported here is synchronous with an important tin metallogenic period in the Yunlong tin metallogenic belt. These data, combined with previous reports, suggest that the three important metallogenic periods in the belt corresponded respectively to contemporaneous tectonomagmatic events. That is, the Early and Late Cretaceous ones were closely related to granitoid emplacement, whereas the Cenozoic one was related to the strike-slip shearing of the Chongshan shear zone. The genesis of tin deposits in the Yunlong tin metallogenic belt can hardly be explained by one single model (granite-related magmatic-hydrothermal or migmatitic-hydrothermal model). Granitic magmatism and tectonic-related migmatism had both contributed to the formation of tin deposits, but they played different roles in different metallogenic periods.

    • A comparative study of the Middle Jurassic granodiorite related to Cu and the Late Jurassic granites related to Sn in the Qin-Hang metallogenic belt and a tentative discussion on their tectonic dynamic setting

      2013, 32(4):463-484.

      Abstract (1978) HTML (0) PDF 5.98 M (3127) Comment (0) Favorites

      Abstract:Located in the interior of South China, the Qin-Hang (Qinzhou Bay to Hangzhou Bay) metallogenic belt was formed by the collision between the Yangtze craton and the Cathaysian block in late Neoproterozoic. Most ore deposits in the belt were formed in Mesozoic although different types of deposits occurred in different geological periods. Studies show that Mesozoic rock-forming and ore-forming processes could be subdivided two categories, i.e., Mid-Jurassic (180~170 Ma) porphyry-skarn-vein Cu polymetallic deposits and related granodiorites, and Late Jurassic (160~150 Ma) greisen-quartz vein-skarn W-Sn polymetallic deposits and related granites. In this paper, these two kinds of granitic source rocks were compared with each other in such aspects as spatial-temporal distribution, chronology, geochemical, Sr-Nd isotopic characteristics and tectonic settings. The former was derived locally from the remelting of subducted ancient Pacific plate along the Qin-Hang fault zone, whereas the latter was resulted from subducted plate windows in the central part of South China in a continental crustal extension and thinning setting. Abundant mantle materials were involved during the two types of rock-froming and ore-forming processes; nevertheless, less mantle materials were involved in the formation of Late Jurassic granitoids related to W-Sn deposits.

    • Petrogenesis and tectonic significance of the Neoproterozoic Danba metabasalt in western Yangtze block

      2013, 32(4):485-495.

      Abstract (4344) HTML (0) PDF 10.68 M (8983) Comment (0) Favorites

      Abstract:Petrology, geochemical and Nd isotopic data are reported for the Neoproterozoic Danba metabasalt in the Kangdian Rift on the western margin of the Yangtze block. Samples were collected from alkaline basalts, which are enriched in MgO, TiO2, with Mg# being 0.51~0.59. They have high total rare earth elements and show high fractionation between LREE and HREE. The trace elements are characterized obviously by enrichment of Th, Nb, Ta, Zr, Hf and LREE but depletion of Y and HREE. Their geochemical and Nd isotopic characteristics suggest that they are similar to OIB. The basaltic magma was generated in an intraplate setting, and was generated by partial melting of OIB mantle source region, with variable degrees of contamination of SCLM during magma ascending; in addition, some samples might have experienced contamination of the lower crust. These samples reveal some plume magmatism characteristics in petrochemistry, and imply that magmatism was probably related to the Neoproterozoic plume event, which resulted in the breakup of Rodinia supercontinent.

    • Re-Os isotopic dating of molybdenite from the Taqian W-Mo deposit in Leping County, Jiangxi Province and its geological implications

      2013, 32(4):496-504.

      Abstract (2139) HTML (0) PDF 3.93 M (2990) Comment (0) Favorites

      Abstract:The Taqian tungsten-molybdenum deposit is located in the Taqian-Fuchun metallogenic belt on the southern margin of the Yangtze plate. The authors have made a breakthrough in ore-prospecting work in recent years,and the results show that the metallogenic belt has good ore-forming geological conditions and prospecting potential. However, the research work is just in the starting period. In this paper,the authors determined the molybdenite age of the Taqian tungsten molybdenum deposit by means of ICP-MS molybdenite-Os isotope analysis. The model ages of 5 samples vary between 160.8 and 163.4 Ma; the molybdenite Re-Os isochron age is (162±2) Ma, MSWD=1.7,suggesting that the ore-forming process took place in late Early Jurassic. A comparison with the metallogenic time of other similar deposits in this area shows that the ore-forming time in the Taqian-Fuchun metallogenic belt is much later than that of the Dexin copper deposits, and their ore-controlling structures are different too. These phenomena might have had something to do with the tectonic backgrounds of different periods.

    • P-wave velocities of partially molten bojite at pressures of 0.6~2.0 Gpa

      2013, 32(4):505-514.

      Abstract (2033) HTML (0) PDF 6.02 M (2886) Comment (0) Favorites

      Abstract:With ultrasonic wave transmission-reflection combined method, measurement of compressional wave velocities (vp) of bojite was carried out up to 1 085℃ at the pressure of 0.6 GPa, 1.0 GPa and 2.0 GPa respectively. Based on investigating the partially molten products, the authors calculated the vp of bojite at different pressures and temperatures with volume percentages and elastic parameters of minerals and melt. The calculations show the same vp-t correlations with experiment runs, which indicate that at first vp decreases slowly with increasing temperature, and then decreases quickly above about 800℃ to 900℃ at different pressures. The investigations of the products indicate that bojite is dehydrated and partially molten when the temperature is higher than 812℃ at 0.6 GPa, 865℃ at 1.0 GPa and 919℃ at 2.0 GPa respectively. It is believed that partial melting is responsible for quick decrease of vp at high temperature. There is more quick decrease of vp of bojite when volume percentages of melt are lower than about 2%. It is thus held that water and melt with low viscosity result in the sharp decrease of vp, because it is easy for them to move into the microfissures in nature rock at the beginning of dehydration and partial melting.

    • The discovery of rare minerals in the Cunqian Cu-Pb-Zn deposit and its geological significance

      2013, 32(4):515-522.

      Abstract (2277) HTML (0) PDF 1.84 M (2878) Comment (0) Favorites

      Abstract:The Qinhang metallogenic belt is an important copper polymetallic ore-forming belt in eastern China, and the Cunqian Cu-Pb-Zn deposit is a typical skarn copper polymetallic deposit in this ore-forming belt. Through sampling based on field geological investigation, microscopic examination, SEM observation, X-ray energy spectrum analysis, and systematic study of material components of ores, the authors found for the first time rare native aluminum and Zn-Cu intermetallic compound in the ores. Both of these two types of metallic minerals have special formation conditions and are hence of important indicative significance for studying the metallogenic environment, formation condition and ore-forming materials of the Cunqian deposit. The results obtained by the authors show that the early metallogenic epoch was characterized by an environment of high temperature, strong reduction and low sulfur fugacity, with the addition of some mantle materials to the ore-forming fluids.

    • The genesis and micro-morphologic characteristics of bitumen in amygdaloidal basalt in southern Sichuan-northern Yunnan border area

      2013, 32(4):523-528.

      Abstract (1930) HTML (0) PDF 2.14 M (2909) Comment (0) Favorites

      Abstract:Bitumen in the crustose, circular layer, amygdaloid and dense massive forms occur in vugs, vesicles and fractures of amygdaloidal basalt. The spiral growth patterns of bitumen show that bitumen has experienced transformation from hydrothermal fluid or gas into solid. Vesicle structure in bitumen evidences that natural gas (the main composition being methane) escaped from it, and that bitumen was produced through the thermal cracking of original oil (>300℃) from the ore-forming hydrothermal solution. The element composition, H/C ratio, reflectivity and micro-XRD of bitumen as well as homogeneous temperature of fluid inclusions in rock quartz crystal show that the degree of thermal evolution and metamorphism of petroleum in Puge area of southern Sichuan was higher than that in Zhaotong area of northern Yunnan. The variation of carbon isotope δ13C content from -25‰ to -31‰ suggests that bitumen was of biogenic origin, and the organic matter came from lower Permian carbonate rock. Basalt of Puge area in southern Sichuan is favorable for the formation of gas reservoirs, and that of Zhaotong area in northern Yunnan is conducive to oil deposition.

    • Basic geological characteristics of the siderite-rich strata in the Xiamaling Formation, Jixian County

      2013, 32(4):529-537.

      Abstract (3551) HTML (0) PDF 15.25 M (8119) Comment (0) Favorites

      Abstract:The newly-exposed lower strata of the Xiamaling Formation near Tielingzi Village in Jixian County contain rich siderites. This paper reports the basic geological characteristics of these siderite-rich strata in terms of the field outcrop, petrology and major elements. Studies show that the profile is characterized by black shale interbedded with silty iron-rich layers/siderite concrete layers, and also has minor siltstone. Some iron-rich strata have turned into limonite layers in the outcrop because of intense weathering. Siderite is the main iron mineral phase in the strata. Siderites can form iron concretes, showing micritic or microcrystalline granulitic textures under the microscope, or form silty ferruginous layers with almost a comparable amount of silty quartz; it can also distributed sporadically in siltstone and black shale with relatively coarse particles. There also exists very little siderite residue in weathered limonite layers. The overall features of major elements show that the strata are rich in SiO2, TFe and TOC, but poor in MnO, CaO, MgO, P2O5 and S. Except for ferriciron in weathered layers, there is mainly ferrous iron in the strata. The TOC content decreases in order of siderite concrete, silty iron-rich layer, black shale and siltstone. The correlation diagram between TFe and Al2O3 content shows a negative correlation in iron-rich layers, while a positive correlation between them exists in normal black shale and siltstone, which suggests that iron in the former form originated from the ocean itself, while iron in the latter form originated mainly from terrigenous detritus. In addition, FeO content has a positive correlation with TOC content in fresh samples, which implies that the genesis of siderites may have some relationship with organic matter.

    • Reef-bank reservoir characteristics and main control factors of the Changxing Formation in Jiannan area

      2013, 32(4):538-548.

      Abstract (1961) HTML (0) PDF 11.65 M (2838) Comment (0) Favorites

      Abstract:On the basis of field outcrop profile and core observation in combination with thin sections, SEM (scanning electron microscope), CL (cathodoluminescence) and physical property analysis, this paper studied in detail the reservoir characteristics of the Permian Changxing Formation in Jiannan area. The reservoir is mainly composed of reef dolostones, reef limestones and grained dolostones, and the reservoir spaces mainly include intercrystal pores, intercrystal dissolved pores and cracks, suggesting a crack-pore reservoir. The reservoir is of moderate-bad physical property, belonging to the low porosity, moderate-low permeability reservoir. The reservoir formation is controlled by lithology, sedimentary facies, relative sea level change and diagenesis. The platform edge reef-bank is in favor of reservoir development, corresponding to the lowering of the relative sea level, and the rocks are mainly reef dolostones and reef limestones. Dolomitization is the foundation of reservoir formation, whereas dissolution and fracturing are the keys to improving physical properties. In this paper, porosity and permeability were used to synthetically evaluate Changxing Formation reservoir, and the results indicate that Type Ⅲ (low porosity-low permeability) is the major reservoir type, followed by Type Ⅳ (particularly low porosity-particularly low permeability), whereas Type Ⅱ (moderate porosity- moderate permeability) and Type Ⅰ (high porosity- high permeability) are rarely seen.

    • >宝玉石矿物学
    • A study of color and Luobowen of Tianhuang stone

      2013, 32(4):549-556.

      Abstract (2349) HTML (0) PDF 4.89 M (4473) Comment (0) Favorites

      Abstract:The Tianhuang stone from Shoushan in China was studied by using slice observation, SEM, EDS, micro-Raman spectra, LA-ICP-MS, total iron analysis and EPR with the purpose of investigating the Luobowen and color genesis of Tianhuang stone. Under close magnification, no obvious regular boundary exists between matrix and Luobowen which diffuses around. SEM, EDS and micro-Raman spectral analysis show that svanbergite is the main mineral composition of the Luobowen. Svanbergite was formed before the formation of the matrix. Luobowen shows primary characteristics. LA-ICP-MS and total iron analysis indicate that Fe3+ causes yellow color, and EPR studies show that iron exists in the Tianhuang stone in the free state. The authors hold that iron oxides and/or iron hydroxides are adsorbed at the surface of layered silicate mineral grains, leading to secondary color.

    • >花岗岩新思维问题讨论(8)
    • A discussion on Mesozoic large scale magmatism and felsic large igneous province in eastern China

      2013, 32(4):557-564.

      Abstract (2701) HTML (0) PDF 6.30 M (4455) Comment (0) Favorites

      Abstract:The author believes that it is very difficult to explain large-scale magmatism in eastern China during Mesozoic with the hypothesis of Pacific plate subduction, and that the magmatism might be equivalent to several felsic large igneous provinces in different periods, probably related to the Mesozoic super mantle plume activity in East Asia. There are two types of large igneous provinces in the world: one is mainly mafic LIP, and the other is felsic LIP. The two types of large igneous provinces in China are respectively represented by the Permian Emeishan basalt and the eastern China large-scale magmatic activity. Both were possibly related to the plume activities; nevertheless, in the mafic large igneous province, massive basalt eruption took place together with partial melting when the plume migrated upward to the bottom of the lithosphere, whereas in the felsic igneous province, the magmatic formation of felsic composition could directly bake and heat the lower crust when the plume reached the crustal bottom. Researchers generally consider that the large-scale magmatic activity during Mesozoic was related to westward subduction and asthenosphere uplift of Pacific plate. In this paper the author believes that the large-scale magmatic activity was probably related to the plume from the lower mantle. The large igneous province has rich mineral resources: Resources such as copper, nickel, chromium, platinum and palladium might be related to the mafic igneous province, whereas resources like gold, copper, tungsten, tin, molybdenum, bismuth, antimony and uranium might be related to the felsic large igneous province.

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