Wang Z.-Y.,Tsinghua University |
Qi L.-J.,Sichuan Agricultural University |
Wang X.-Z.,Beijing Institute of Geology for Mineral Resources
Shuili Xuebao/Journal of Hydraulic Engineering | Year: 2012
Experiments were conducted with an artificial step-pool system on the new Wenjiagou Gully to mitigate large volume debris flows in 2009. The step-pool system dissipated flow energy in steps and hydraulic jumps. Analysis proved that the step-pool system dissipated 2/3 of the kinetic energy of flow, thus the critical discharge for triggering debris flow increased threefold. Due to the step-pool system maximized the flow resistance and protected the bed sediment and banks from erosion, the rainstorm floods in 2009 did not trigger debris flows. In 2010 the step-pool system was replaced with 20 check dams. Huge boulders were broken into small pieces of diameter less than 0.5 m and were used as building materials for the 20 dams. Without the protection of the step-pool system, a rainstorm flood scoured the base of the dams and caused the failure of check dams in Aug. 2010. The flow incised the gully bed by 50 m. The loose bank materials slid into the flow mixed with water and formed a large volume debris flow with a volume of 4.5 million m. Many houses were buried by the debris flow and 12 people were killed. Comparison of the two strategies proved that energy dissipation structures are necessary for controlling large volume debris flows. Check dams, if they are stable, may reduce the potential of bank failures and control debris flows. The step-pool system dissipates flow energy and control gully bed incision and bank failure. A combination of check dams and step-pool systems may be the most effective for mitigating debris flows.
Wang Z.Y.,Tsinghua University |
Qi L.,Sichuan Agricultural University |
Wang X.,Beijing Institute of Geology for Mineral Resources
Natural Hazards | Year: 2012
Large-volume debris flow events are defined when the volume of solid materials exceeds 1 million m 3. Traditional engineering measures, such as check dams, diversion channels, and flumes, are effective for normal debris flow control but are not sufficient to control large-volume debris flows. Experiments were conducted with an artificial step-pool system on the new Wenjiagou Gully to mitigate large-volume debris flows. The old Wenjiagou Gully was buried by 81.6 million m 3 of loose solid material created by a landslide that was triggered by the Wenchuan earthquake on May 12, 2008. The new gully was formed during the scouring process caused by debris flows in 2008. Large-volume debris flows were initiated by rainstorm flood with high kinetic energy. The artificial step-pool system was constructed with huge and big boulders on the new Wenjiagou Gully in 2009. The step-pool system dissipated flow energy in steps and hydraulic jumps. Analysis proved that the step-pool system dissipated two-third of the kinetic energy of flow; thus, the critical discharge for triggering debris flow increased threefold. Due to the step-pool system maximized the flow resistance and protected the bed sediment and banks from erosion, the rainstorm floods in 2009 did not trigger debris flows. In 2010, the step-pool system was replaced with 20 check dams. Huge boulders were broken into small pieces of diameter less than 0.5 m and were used as building materials for the 20 dams. Without the protection of the step-pool system, a rainstorm flood scoured the base of the dams and caused failures for all of the 20 check dams in August 2010. The flow incised the gully bed by 50 m. The loose bank materials slid into the flow mixed with water and formed a large-volume debris flow with a volume of 4. 5 million m 3. Many houses were buried by the debris flow, and 12 people were killed. Comparison of the two strategies proved that energy dissipation structures are necessary for controlling large-volume debris flows. Check dams, if they are stable, may reduce the potential of bank failures and control debris flows. The step-pool system dissipates flow energy and control gully bed incision and bank failure. A combination of check dams and step-pool systems may be the most effective for mitigating debris flows. © 2011 Springer Science+Business Media B.V.
Yue S.-W.,South China University of Technology |
Yue S.-W.,CAS Guangzhou Institute of Geochemistry |
Deng X.-H.,Beijing Institute of Geology for Mineral Resources |
Deng X.-H.,Peking University |
Bagas L.,University of Western Australia
Geological Journal | Year: 2014
The Yindonggou Ag-Au(-Pb-Zn) deposit is hosted by metamorphosed volcanic rocks of the ca. 740-760Ma Wudangshan Group in the Proterozoic Wudang Block of the southern part of the Qinling Orogen, central China. The deposit consists of a series of mineralized quartz veins located in the Yindongyan Anticline. Based on the mineral assemblages and cross-cutting relationships of quartz veins, the deposit can be divided into: (1) early fine-grained quartz-sphalerite-galena veins; (2) fine-grained quartz-silver-gold veins containing minor amounts of pyrite; (3) coarse-grained quartz veins with minor amounts of galena, sphalerite, and chalcopyrite; and (4) late ankerite-quartz veins. Most of the Pb-Zn mineralization formed during the early (Stage 1) veins followed by the deposition of Ag-Au mineralization in the Stage 2 veins. The δ18O value for the ore-forming fluids decreases from 6.6-9.4‰ in the Stage 1 veins through 3.6-4.9‰ in the Stage 2 veins to -1.2‰ to 0.4‰ in the Stage 3 veins (the δ18O values could not be determined for the Stage 4 veins). Furthermore, the δD values are -74‰ for the Stage 1 veins, -95‰ to -56 ‰ for the Stage 2 veins, and -48‰ to -73‰ for the Stage 3 veins. The δ13C values for ankerite in the Stage 4 veins are between -2.9‰ and -1.1‰. The δD vs. δ18OH2O plot for these values indicates that there was a shift from metamorphic fluids during the formation of the early veins to meteoric fluids during the formation of the later veins at the deposit. The H-O-C isotope systematics also indicate that the ore fluids forming the deposit were probably initially sourced from metamorphic dehydration of volcanic-carbonate rocks in the ca. 740-760Ma Wudangshan Group and with time gradually mixed with meteoric water by Stage 4. The δ34S values for sulphides from the deposit range from -0.9‰ to 7.1‰ in the Stage 1 veins, 3.8‰ to 5.0‰ in the Stage 2 veins, and 2.4‰ to 11.3‰ in the wallrocks. Sulphides from the mineralized Stage 1 veins yield 206Pb/204Pb ratios of 16.44-16.6, 207Pb/204Pb ratios of 15.25-15.5, and 208Pb/204Pb ratios of 36.4-36.98. Five pyrite samples from the Stage 2 veins yield 206Pb/204Pb ratios of 16.475-16.529, 207Pb/204Pb ratios of 15.346-15.395, and 208Pb/204Pb ratios of 36.49-36.616. Both the S and Pb isotope ratios are between the ratios for units in the Wudangshan Group and mantle but differ from other lithological units in the Wudang Block, which suggest that the mineralized fluids interacted with both the Wudangshan Group and deep-seated sources. Thus, we suggest that the original ore-forming fluids are metamorphic in origin, and the metal deposition resulted from fluid mixing. From the characteristics observed, the Yindonggou Ag-Au(-Pb-Zn) deposit can be classified as an orogenic-type deposit generated during the Triassic Qinling Orogeny resulting from northward oceanic plate subduction along the Mian-Lue Suture. © 2014 John Wiley & Sons, Ltd.
Deng X.-H.,Beijing Institute of Geology for Mineral Resources |
Deng X.-H.,Peking University |
Chen Y.-J.,Peking University |
Santosh M.,China University of Geosciences |
And 2 more authors.
Gondwana Research | Year: 2016
The Zhifang Mo deposit is located in the northeastern Qinling Orogen along the southern margin of the North China Craton. The deposit represents a quartz-vein system hosted in the Mesoproterozoic Xiong'er Group volcanic rocks. We identify three hydrothermal stages (early, middle and late), characterized by veinlets of quartz-pyrite, quartz-molybdenite-pyrite-chalcopyrite-galena-sphalerite, and quartz-carbonate assemblages, respectively. Five molybdenite samples from the Zhifang deposit yield Re-Os ages ranging from 241.2 ± 1.6 Ma to 247.4 ± 2.5 Ma, with an isochron age of 246.0 ± 5.2 Ma (2σ, MSWD = 7.4), and a weighted mean age of 243.8 ± 2.8 Ma (2σ, MSWD = 5.5). The Re-Os age shows that the Mo mineralization occurred during the Indosinian Orogeny, and suggests that the mineralization is unrelated to the Yanshanian magmatism or the Paleo-Mesoproterozoic volcanic-hydrothermal event. This study also reports a new Sr-Nd-Pb isotope dataset from ore sulfides in an attempt to constrain the source of the ore-forming fluids. Ten sulfide samples from middle stage of the Zhifang Mo deposit yield ISr(t) ratios of 0.710286-0.711943, with an average of 0.711004; εNd(t) values between -19.5 and -14.8, with an average of -16.7; and (206Pb/204Pb)i, (207Pb/204Pb)i and (208Pb/204Pb)i ratios of 17.126-17.535, 15.374-15.466 and 37.485-37.848, with averages of 17.380, 15.410 and 37.631, respectively. One pyrite from the early stage yield ISr(t) of 0.722711-0.722855, with an average of 0.722783, which is higher than those of the middle stage sulfides and suggests equilibration with wallrocks. The εNd(t) values are in the range of -17.3 to -16.6 with a mean at -17.0; and (206Pb/204Pb)i, (207Pb/204Pb)i and (208Pb/204Pb)i ratios are 17.386, 15.405 and 37.622, respectively. The ore sulfides show higher Pb-isotope ratios, higher εNd(t) and lower ISr(t) values than the host rocks. The results suggest that the ore-forming fluids had lower ISr(t), and higher εNd(t) values than the ore sulfides, and were possibly sourced from the Dengfeng Complex. The southward subduction of the North China Craton beneath the Huaxiong Block during the Triassic was possibly responsible for the formation of the Waifangshan orogenic Mo system. © 2015 International Association for Gondwana Research.
Yang Y.,Peking University |
Li N.,Peking University |
Wang L.,Beijing Institute of Geology for Mineral Resources
Acta Petrologica Sinica | Year: 2011
The recently discovered Donggou Mo deposit, Henan Province, is a giant Yanshanian porphyry Mo system in the East Qinling molybdenum belt. The deposit was discovered by prospecting after a successfully theoretical prediction according to the tectonic model for collisional orogeny, metallogeny and fluid flow. Mo mineralization is associated with the Donggou granite porphyry which has been classified as A-type granite. Both the porphyry stock and wallrocks underwent intense hydrothermal alteration. The alteration ranges outwardly from potassic, phyllic to propylitic alteration zones with increasing distance from the intrusion. Molybdenum mineralization presents as numerous veinlets in the altered wallrocks instead of the causative porphyry. The hydrothermal ore-forming process includes the early, middle and late stages, characterized by mineral assemblages of quartz-potassic feldspar, quartz-(potassic feldspar)-polymetal sulfides and quartz-carbonate-fluorite, respectively. Ore minerals were mainly precipitated in the middle stage. The hydrothermal minerals in the early and middle stages contain three types of fluid inclusions, i. e. NaCl-H2O (W-type), CO2-H2O (C-type) and daughter mineral-bearing (S-type) fluid inclusions: while the late-stage hydrothermal quartz contains only NaCl-H2O fluid inclusions (W-type). The homogeneous temperatures of the C-type and W-type fluid inclusions in the early stage are mainly 380 ∼550°C, with salinities ranging from 7. 70% to 18. 28% NaCleqv. S-type fluid inclusions contain variable daughter minerals including halite, chalcopyrite, calcite and unidentified transparent crystal. Except halite, other daughter minerals do not dissolve in the heating process. These fluid inclusions generally homogenize at temperatures of 318 ∼ 516°C, and yield salinities of 12. 85% ∼ 17. 87% NaCleqv and 35.55% ∼ 47.67% NaCleqv. In the middle stage, the C-type and W-type fluid inclusions mainly yield homogeneous temperatures of 260 ∼ 410°C and salinities of 4. 62% ∼18.28% NaCleqv. S-type fluid inclusions are generally homogenized at 197 ∼ 436°C, with salinities of 7. 45% ∼ 18.28% NaCleqv and 31.71% ∼ 49.22% NaCleqv. W-type fluid inclusions in the late stage are homogenized at temperatures of 125 ∼225°C, yielding salinities of 0.50% ∼7.25% NaCleqv. The estimated pressures range from 63 ∼ 117MPa in the early stage to 12 ∼ 67MPa in the middle stage, with the greatest formation depth of 4. 7km. In a word, the ore-forming fluids evolved from high temperature, CO2-bearing magmatic fluid to low temperature, CO 2-poor meteoric fluid. It seems that high temperature, CO 2-rich fluids can be regarded as typical features of porphyry deposits developed in intra-continental setting, contrasting to the CO 2-poor NaCl-H2O fluids commonly observed in volcanic arcs. Based on comparison of typical porphyry systems in the East Qinling-Dabie area, we suggest that the volatile concentration in the initial ore-forming fluids and the features of wallrocks (including chemical composition, crystallization degree, mechanical strength, etc.) control the spatial location of orebodies in porphyry systems.