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Chen Y.,China University of Geosciences | Tang D.,China University of Geosciences | Xu H.,China University of Geosciences | Tao S.,China University of Geosciences | And 3 more authors.
Journal of Natural Gas Science and Engineering | Year: 2015

Recently, significant progress has been made in coalbed methane (CBM) exploration and development in the eastern margin of the Ordos Basin. However, the physical characteristics of coal reservoirs have not yet been studied in detail, and the physical characteristics of different rank coals are quite different. This study aims to analyze the characteristics of pores and fractures in coal reservoirs and identify the effects of coal rank on the physical properties of reservoirs, using laboratory experiments such as scanning electron microscopy (SEM), optical microscopy, mercury intrusion, low temperature liquid nitrogen adsorption, nuclear magnetic resonance (NMR) and X-ray computed tomography (CT). The results show that in relatively low rank coals the genetic types of pores are generally plant tissue pores and intergranular pores, whereas gas pores occur and proliferate with increasing coal rank. The porosity of the coal samples is low, ranging from 2.7% to 6.3% and varying in a wavelike fashion as the coal rank increases. Pore size distribution analysis indicates that micropores (pore radius<10 nm) and transition pores (pore radius between 10 and 100 nm) dominate the pore space in coal with a large proportion (64.82%-91.50%), followed by macropores (pore radius>1000 nm, 5.35%-22.69%) and mesopores (pore radius between 100 and 1000 nm, 2.34%-14.16%). The proportions of macropores and mesopores decrease first with coal rank increasing (Ro<1.0%) and then almost maintain at lower levels, while micropores and transition pores vary inversely. Adsorption pores in coals include micropores, transition pores and parts of mesopores, with proportions of 2.64%-61.54%, 30.77%-72.72% and 7.65%-37.31%, respectively. The proportion of micropores decrease firstly and then increase with coal rank increasing (turning point at Ro = 1.58%) and transition pores vary inversely. Micro-fissures density is between 12 and 217 per 9 square centimeters, which decreases as the coal rank increases firstly (Ro<1.5%) and then increases rapidly. In the lower rank coals, the properties of fractures, mainly short fractures, are relatively poor; however, higher coal ranks are favorable for endogenetic fracture development. © 2015 Elsevier B.V.

Yang Y.-Q.,Jilin University | Li B.-L.,Jilin University | Xu Q.-L.,Jilin University | Zhang B.-S.,Xian Institute of Geological and Mineral Exploration
Northwestern Geology | Year: 2013

Aikengdelesite is the first found porphyry molybdenum (copper) deposit in Eastern Kunlun for the past years and the degree of geological work and research for the deposit is quite low. The deposit lies to the Eastern Kunlun southern composite accretion belt. The hosted rocks are diorite, monzonitic granite, granite porphyry, medium-fine grain granite and volcanic rocks and sedimentary rocks of Hongshuichuan Group. In this paper, we present zircon U-Pb age data of monzonitic granite using laser ablation ICP-MS technique. The zircons of granite are mainly euhedral and hypidiomorphic texture, have clear ring and high Th/U ratio (0.83~1.47, average 1.15) which belong to the typical magmatic zircons. The results show that the intrusion mainly comes from late Hercynian but not late Indosinian period with the 206Pb/238U average weighted age of (268.7 ± 1.6) Ma (MSWD = 0.24) and concordant age of (268.5 ± 0.83) Ma (MSWD = 0.051). Comprehensive analysis reveals that the research area has entered into oceanic crust subduction stage in 268 Ma±.

Li K.,Xian Institute of Geology and Mineral Resources | Zhang Z.-W.,Xian Institute of Geology and Mineral Resources | Gao Y.-B.,Xian Institute of Geology and Mineral Resources | Guo Z.-P.,Xian Institute of Geology and Mineral Resources | And 4 more authors.
Northwestern Geology | Year: 2012

Shajia Cu-Ni ore-bearing basic complex is one of the intrusive rocks in Hualong basic-ultrabasic rocks belt, it is small scale, weak lithological zoning. Orebody are lenticular in the intrusion, and norite is the main host rock for the Cu-Ni ores. The analysis on rock geochemistry indicate that the intrusive is calcalkaline, iron series, rich in LREE, depleted in high field strength elements such as Nb, Ta. The analysis on the sulfide display that the initial 187Os/188Os ratios are from 0. 346 9 to 0. 407 1, the γos values are from 180 to 228, which suggest that abundant crustal material was mixed with the magma, and the content of crust-derived Os was estimated to >30%. The contamination by crustal material probably played an important role in triggering the sulfide saturation and segregation.

Liu M.,China University of Geosciences | Liu M.,Chinese Academy of Geological Sciences | Zhang Z.H.,Chinese Academy of Geological Sciences | Xiang J.F.,Chinese Academy of Geological Sciences | And 2 more authors.
Acta Petrologica Sinica | Year: 2014

The Daheishan tungsten deposit related to the biotite monzonitic granite from Baokuhe plutons locates at the Caledonian orogeny of Qilian Mountains. LA-ICP-MS U-Pb dating of zircons shows that the formation age of biotite monzonitic granite is 450.2 ± 2.8Ma, indicating that the pluton was formed at Caledonian magmatic-thermal event. Geochemical data reveal that the biotite monzonitic granite from Baokuhe plutons is rich in silicon (73.03% ∼ 74.18%), alkalis (K2O/Na2O= 1.13-1.94, K2O+ Na2O = 7.25% ∼ 8.51%) and is peraluminous (A/CNK = 1.04 ∼ 1.12). The biotite monzonitic granites from Baokuhe peraluminous plutons should be high potassic calc-alkaline granite. P2O5 content of the granites is low, and shows a trend of decrease with the increase of SiO 2 content. The content of rare earth element is low. Chondrite-nornalized REE patterns are right-inclined and display significant negative Eu anomalies. Differentiation of LREE is strong, and that of HREE is weak. Based on spider diagram of trace elements, Th, U, Pb, Zr, Hf are obviously positive anormaly, and Ba, Sr, Ta, Nb, P, Ti are negative anormaly. It suggests that it is an I-type granite. Combined with the tectonic evolution of the North Qilian, we suggest that the biotite monzonitic granite from Baokuhe plutons formed in the active continental margin, and the magmas were derived from the melting of crustal rocks, followed by crystal fractionation.

Liu X.L.,China University of Geosciences | Liu X.L.,Chinese Academy of Geological Sciences | Wang Y.T.,Chinese Academy of Geological Sciences | Hu Q.Q.,Chinese Academy of Geological Sciences | And 5 more authors.
Acta Petrologica Sinica | Year: 2014

The Chaima gold deposit is located on the northwest of the Fengtai ore concentration area in Shaanxi Province and 0.5 km west to the super-large Baguamiao gold deposit. They are similar in metallogenic geological environment and ore-control conditions. There are five ore-bearing zones in this deposit and their occurrence is controlled by lithology and tectonic. The ores are quartz-vein type and altered-rock type, in which the first is the main type. The gold mineralization of Chaima gold deposit could be divided into three stages: the early quartz-carbonate stage, the second and main quartz-carbonate-sulfide stage and the late quartz stage. In this paper, the Sm-Nd isotopic dating is carried out on the calcite and dolomite from the main stage, yielding an isochron age of 203.2 ± 1.6Ma, which shows that the deposit formed in Late Triassic. Combined with the previous research on the gold deposits, magmatite and tectonic movements of the area, we suggest that the Chaima gold deposit is an orogenic gold deposit formed after the collision of Qinling in Late Indosinian.

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