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Bao C.,China University of Geosciences | Chen Y.-L.,China University of Geosciences | Li D.-P.,China University of Geosciences | Chen X.,China University of Geosciences | Chen X.,Gold Geological Institute of CAPF
Geochemical Journal | Year: 2015

In this study, we performed U-Pb dating on 1295 zircon grains from 24 samples originating from the North China Craton (NCC); an additional 440 Lu-Hf isotopic analyses were conducted on select zircon grains. The U-Pb ages revealed that the strongest magmatic event in the NCC occurred ca. 2.5 Ga, and a subordinate magmatic event occurred ca. 1.8 Ga. The crustal model ages from Hf isotopic analyses showed that the best estimate for the age of the NCC mantle extraction is ca. 2.8-2.7 Ga, which is consistent with the age of global continental crusts. In recent years, numerous 2.7 Ga rocks have been identified within the NCC. A strong and widespread superimposed tectono-thermal event at ca. 2.5 Ga differentiates the NCC from many other worldwide cratons. However, the timing of the majority of NCC continental crust growth remains highly controversial. In this paper, a quantitative method was used to calculate a continental crust reworking rate. The results revealed that the lowest reworking rate in the NCC occurred at ca. 2.7 Ga and was below 13%. At 2.9 Ga, the reworking rate was 73%, suggesting that a strong intra-crustal magmatic event took place at that time. Combining the reworking rates and Hf isotopic model ages for each period, we concluded that approximately 25% and 23% of the continental crust volume in the NCC was formed at ca. 2.8 Ga and 2.7 Ga, respectively. Approximately 12% of the continental crust volume formed at 2.6 Ga, and only 6% of the continental crust formed at ca. 2.5 Ga. Even with a high reworking rate, 6% of the continental crust formed at 2.9 Ga. Therefore, the main continental crustal growth in the North China Craton occurred at ca. 2.8-2.7 Ga (48% continental crust). Copyright © 2015 by The Geochemical Society of Japan. Source

Yang L.Q.,China University of Geosciences | Deng J.,China University of Geosciences | Zhao K.,China University of Geosciences | Liu J.T.,China University of Geosciences | And 4 more authors.
Acta Petrologica Sinica | Year: 2011

Daping gold deposit, situated in the south section of the Ailaoshan orogenic belt, once considered to be an orogenic gold deposit, displays many distinct geological characteristics which are inconsistent with the classical orogenic gold deposits around the world, but accord with the epithermal gold deposits. The vein type gold, copper, lead, silver deposits commonly develop in close association with intermediate-acidic intrusive and intermediate-basic volcanic rocks regionally. Daping gold deposit was formed in the Neozoic tectonic-magmatic activity, which is 800Ma later than the emplacement of Taojiazhai diorite which is the main host rocks, besides the gold metallogenesis is closely related to the regional structural framework and the transition of tectonic regime. The host faults of main ore-forming period are generally believed as a transtensional normal faults, and ore veins within are abundant (55) , thin (0. 2 ∼0. 8m) , long (200 ∼ 1500 m) , steep (56° ∼85°) , deeply extensive (700m) and developed in parallel, besides ore bodies in association with Pb, Cu and Ag display high-grade Au (above 10 × 10-6 ) , low Au/Ag ratio (0. 1 ∼0. 5). Textures and structures of filling type as well as mineral assemblages indicate that ore veins formed at a low-temperature and shallow-depth environment, what' more, mineralization-alteration types and the growth of opal and oxidized ores restrict an open and oxidizing environment. The distinguished geological characteristics of Daping gold deposit may be closely related to the complicated tectonic regime and metallogenic evolution, though the deposit is distinguished by its feature of orogenic gold deposits, epithermal gold, copper, lead, silver mineralization is overlapped in the shallow during the late stage of mineralization. The metallogenic characteristics, combined with documented geological information, indicate Daping gold deposit is distinguished by its orogenic in the deep and epithermal in the shallow, besides the metallogenic system is well preserved. Considering all the ores proven now are in the shallow, Daping gold deposit is of great prospecting potentiality in the deep. Source

Xie Z.,Anhui University of Science and Technology | Wang B.,Anhui University of Science and Technology | Wang B.,Gold Geological Institute of CAPF | Chen J.,Anhui University of Science and Technology | Qian H.,Anhui University of Science and Technology
Journal of Asian Earth Sciences | Year: 2013

Several metabasite lenses in Ganghe, Central Dabie, that were previously described as pillow lavas are studied by elemental, Sr-Nd-Pb isotopic, and mineral oxygen isotopic analysis as well as zircon SHRIMP U-Pb dating. Zircon U-Pb geochronology results indicate that the protolith emplacement age of these metabasites is approximately 717±38Ma, consistent with the age of the volcanoclastic rocks in the same unit, and that they experienced the Triassic HP eclogite-facies retrograde metamorphism at 221±2Ma during exhumation after subduction to mantle depth and peak ultra-high pressure metamorphism. The low δ18O values of -5.5‰ to -2.0‰ indicate that the protoliths underwent high temperature meteoric-hydrothermal alteration before subduction but had no seawater interaction. These metabasites had similar formation processes, water-rock interactions and metamorphisms as other eclogite-facies rocks cropped out in the Central Dabie terrain. They showed negative abnormalities in Nb, Sr, and Ti content and positive abnormalities in Ba, Th, and Pb content; they also showed LREE enrichment. The insusceptible Sm-Nd isotopes during metamorphism yielded εNd (t)=-12 to -10 and TDM=2.2-2.8Ga for samples from lenses #1 to #3 and -7 to -6 and 2.1-2.2Ga for lens #4; the samples also showed low radiogenic Pb isotope compositions of (206Pb/204Pb)i=15.34-16.50, (207Pb/204Pb)i=15.23-15.32, and (208Pb/204Pb)i=35.93-37.04. The data suggest that the protolith sources of the metabasites were contaminated to variable degrees by old crustal materials during formation. Unlike the Maowu layered intrusions, which were contaminated by upper crust, the magmas of the metabasites were contaminated by lower crust in the magma chamber and during eruption. It can be concluded that the protoliths of these metabasites were derived from old crustal-contaminated mantle sources and initially emplaced in the crust at the Neoproterozoic and that they were altered by meteoric water at high temperatures. In this respect, they might be similar to the Neoproterozoic mafic intrusions in the North Huaiyang terrain. However, the studied metabasites experienced the Permo-Triassic subduction and metamorphism, whereas the North Huaiyang Neoproterozoic mafic intrusions did not. © 2012 Elsevier Ltd. Source

Liao G.-X.,Chinese Academy of Geological Sciences | Li Z.-H.,Gold Geological Institute of CAPF
Wutan Huatan Jisuan Jishu | Year: 2010

The paper introduces the general principle of GRD gridding method in drawing profiles map by graded color filling. Its' programming process is utilizing SaveDemToSurfGrd( ) function supplied by MAPGIS on secondary development platform based on Visual Basic to realize the converting survey data to normal GRD grid data, and converting GRD grid data to MSI image file in image processing module of MAPGIS. The advantage and limitation of the method is also discussed in this paper. Source

Wang B.,Gold Geological Institute of CAPF | Zhang D.,Gold Geological Institute of CAPF | Lu Y.-C.,Gold Geological Institute of CAPF | Lu Y.-C.,China University of Geosciences | Sun H.,Gold Geological Institute of CAPF
Kuangwu Yanshi/ Journal of Mineralogy and Petrology | Year: 2015

The formation of Jiawu gold deposit is closely related to Indo-Sinian mid-acidic magmatism of the region. LA-ICP-MS U-Pb dating of zircons and Lu-Hf isotope of the granite porphyry veins indicate that it is closely related with gold mineralization in the region. It shows that zircon 206Pb/238 U weighted average age is 233. 4 Ma±4. 3 Ma (MSWD=2. 7), the formation period is the Triassic era,same as the formation age of mid-late Indo-Sinian mid-acidic magmatism in West Qinling of Qinghai. Zircon εHf(t) values are between -12. 35 and - 1. 12, Hf second stage model ages (tdm2) are between 1. 3 Ga and 2. 0 Ga,and the source region of granite porphyry in Jiawu gold deposit are mainly the Early-middle Proterozoic crust. The relatively high value of em (t) indicates that mantle component has been involved in the formation of parental magma of the granite porphyry veins. The granite porphyry veins that are closely related to gold mineralization in Jiawu gold deposits are formed under the geodynamic environment of the transformation from continent-continent collision compression to extension. Due to the subduction continental crust plate fragment,mantle-derived magma was upwelling and underplating to the bottom of the lower crust,causing partial melting of the thickened ancient lower crust and subsequent crust-mantle magma mixture. The magma mixture intruded into Longwuhe Formation in the middle-lower Triassic series,providing the heat source and mineralization-bearing fluids for the formation of the gold deposit. Therefore, the age of the mineralization of Jiawu gold deposit was the same as that of granite porphyry veins, that is, 233. 4 Ma±4. 3 Ma. Source

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