2009 Vol. 15, No. 1

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STUDY ON REGIONAL MINERALIZATIONS AND ORE-FIELD STRUCTURES:BUILDING OF MINERALIZING TECTONIC SYSTEMS
CHEN Xuan-hua, CHEN Zheng-le, YANG Nong
2009, 15(1): 1-19.
Abstract (459) HTML (172) PDF (1289KB)(32)
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Geological structures have a close dynamic coupling relationship with regional mineralization under the control of tectonic stress fields and tectonic movements. Different kinds of structures, such as faults, folds, ductile shear zones, and crust-mantle coupling structures, exert control of mineralization in different ways. The distribution of mineral resources is controlled by tectonic systems at multiple levels. The organic combination of tectonic systems with mineralization systems brings on the building of mineralizing tectonic systems (MTSs).Globally several mineralizing tectonic systems have been recognized, including the Circum-Pacific MTS, the Tethys-Himalaya MTS, the Paleo-Asia MTS, the Oceanic Ridge-Continental Rift MTS, and craton MTSs. The building of mineralizing tectonic systems will prove to be important for study of regional mineralization and ore-field structural geology.
GEOCHEMISTRY AND PALEO-TECTONIC ENVIRONMENT OF FENGYAN Pb-Zn ORE DEPOSIT IN MEIXIAN, CENTRAL FUJIAN PROVINCE
ZHANG Da, WU Gan-guo, DI Yong-jun, YU Xin-qi, PENG Run-min, HUANG Huo-jian
2009, 15(1): 20-35.
Abstract (146) HTML (77) PDF (1503KB)(14)
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Pb-Zn-Ag ore deposit in Meixian, Youxi County is located at the south of the Zhenghe-Dehua pre-Cambrian metamorphic area, and geologically situated at Shouning-Hua' an sub-basement uplift zone in Eastern Fujian volcanic depression belt, east of the NE-striking Lishui-Haifeng fault. The ore-bearing beds of Fengyan ore deposit is mainly the Upper Proterozoic Dongyan Fomation of Mamianshan Group (Pt3dy). The Pb-Zn-Ag ore bodies are of strata bound type. Petrology and geochemistry studies show that the ore-bearing Dongyan Formation is a paleo-volcanic sedimentary formation dominated by greenshists. The formation of the basaltic magma may be related to the slab subduction.The original rocks of the greenshists are basaltic rocks, and granulites are mainly dacite and rhyolite. Geochemical study of ore deposit reveals that the ore deposit is characterized by multiple ore-forming processes and various kinds of sulfur sources. The composition and evolution of Pb isotopes show that different Pb sources from mantle to orogenic belt and upper crust are intermingled.The evolvement is of clear trend and demonstrates a superposition of multiple geological events. The REE pattern of metal sulfides shows a down-to-right slope with remarkable differentiation between LREE and HREE.Compared to MORB, the different trace elements are depleted and enriched to different degrees. High field strength elements (HFSE:Nb, Ta, Zr, Hf)show distinct negative anomaly and are strongly depleted while Pb, Rb and Ba are relatively enriched. Metavolcanics in the Dongyan Formation, with the same trend of HFSE depletion and the enrichment of LFSE, displays typical features of arc-magma related to subduction and indicates that the ore deposit and the Dongyan vocanics were formed under the arc environment with subduction background.
STRUCTURAL CONTROL OVER THE ORE IN HENGJIAN-GANGSHANGYING DEPOSITS IN XIANGSHAN ORE FIELD, JIANGXI PROVINCE
ZHANG Hong, CHEN Zheng-le, YANG Nong
2009, 15(1): 36-49.
Abstract (141) HTML (126) PDF (1668KB)(25)
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The Hengjian-Gangshanying deposits are located in the north of Xiangshan collapse volcanic basin. Regionally the NE and EW striking faults and volcanic faults jointly exert control on the position of subgranitic porphyry and uranium deposits. Locations of subgranitic porphyry are obviously confined by high-angle thrusts, and uranium mineralization is primarily controlled by fissures.The ore-bearing fissures display an arch extension along inner and outer contact zones of the porphyry. Based on spatial distribution and attitude of subgranitic porphyry in the Hengjiang-Gangshangying area, this paper has defined the system of rock-controlled structures. By analyzing the relationship between structural fissures and uranium mineralization, the authors have divided the structure system into pre-ore stage, ore stage and post-ore stage, and believed that the structures experienced 3 epoches with 6 stages.
APPLICATION OF ELECTROMAGNETIC MEASUREMENT TO GOLD DEPOSIT EXPLORATION IN GREENSCHIST BELT OF WESTERN SHANDONG
HUO Guang-hui, WANG Hai-qin, WANG Hong, WANG Yu-he
2009, 15(1): 50-55, 76.
Abstract (177) HTML (110) PDF (1317KB)(37)
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In the Zhoujiazhuang gold deposit, Tai' an of Shandong Province, a high-resolution electric profile and reliable geological information have been obtained by using electromagnetic measurement, and hidden gold ores confirmed by drilling proof. The measurements show that the low-resistivity belts under the background of high resistivity in deep part are favourable for formation of gold ore, and the distribution of low-resistance belts reveals the extension trend of gold mineralization.
THE LATE MESOZOIC EXTENSION-SLIPPING-CONTRACTION OF THE ERLANGPING GROUP IN THE NORTH QINLING TECTONIC BELT, CENTRAL CHINA
ZHANG Hong-yuan, WANG Zong-qi, LIU Jun-lai, YAN Quan-ren, WANG Tao, YAN Zhen
2009, 15(1): 56-68.
Abstract (195) HTML (68) PDF (2391KB)(8)
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The convergence belt between the Sino-Korea block and the Yangtze block was strongly deformed by intracontinental tectonomagmatic activity in the Late Mesozoic.In order to show details of the belt during the Late Mesozoic, we have carried out a series of analysis for the Erlangping Group on mesosmall structure, micro-texture, electron-probe and geochronology.The study has recognized a ductile right lateral slipping deformation for the Xiaozhai-Erlangping shear zone inside the Erlangping Group, and a superimposion of ductile right lateral slipping and late brittle-ductile thrusting for the Damiao-Wantan shear zone.40Ar/39Ar tectonic-thermal chronological analysis reveals a continuous uplifting-denudating course between ~ 121 Ma and ~ 100 Ma.During the Late Mesozoic, the Erlangping Group experienced the tectonic reworkings respectively under the extensional, slipping and contractional tectonic regimes. Firstly, under the regionally extensional condition, the Erlangping Group was split by the XiaozhaiErlangping and Damiao-Wantan shear zones into three slabs, namely the Baoshuping, Huoshenmiao, and Erjingou slabs.Then in Early Cretaceous a right lateral movement of the slabs happened under a slipping regime.The intrusion of the Erlangping rock body ended the Xiaozhai-Erlangping shear zone, and the Damiao-Wantan shear zone was stopped under a contractional tectonic regime, which made the Erlangping Group welded into a single block again.Our results also indicated that the tectonic evolution of the Erlangping Group of the North Qinling in the Late Mesozoic processed in an opposite way to that of the Dabieshan tectonic belt.
DISCOVERY OF LATE MESOZOIC MAGMATIC ROCKS IN ORDOS ANCIENT CONTINENT NUCLEUS AND ITS GEOLOGICAL IMPLICATION
ZHENG Fan-shen, KANG Yi-qing, KANG Hong-zai, ZHANG Feng-yu, DI Yong-jun
2009, 15(1): 69-76.
Abstract (250) HTML (108) PDF (2011KB)(8)
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In the ancient and stable Ordos continent nucleus, we found deep-seated indicator minerals diamond in a preliminary exploration, and basaltic magmatic rocks in the source area of anomaly of indicative of the minerals.This deep source magma mainly occurs as weak eruption or explosion, or fissure injection.This discovery reveals a weak magmatic activity in the Ordos ancient continent nucleus during the Mesozoic when Hebei-Shandong-Liaoning ancient continent nucleus was activating.It can not only provide a window for research on continental lithosphere, but also prove to be of great significance to the exploration of diamond in this area.
THE FORMATION MECHANISM OF THE NIHEWAN PALRO-LAKE AND ITS RELATIONSHIP WITH LIVING ENVIRONMENT FOR EARLY ANCIENT HUMEN
YUAN Bao-yin, TONG Hao-wen, WEN Rui-lin, WANG Yan-hua
2009, 15(1): 77-87.
Abstract (227) HTML (166) PDF (1451KB)(30)
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The Nihewan Basin is located at northeast end of the Fen-Wei rift valley system, and constitutes an important part of it. At the beginning of Eogene an upwelling plume of soft mantle was developed in Hengshan-Datong region. It caused thinning of the crust and magma eruption. During 25~24 Ma the crust began to subside along Yangyuan-Shixia area to form a basin, with an extensional orogen on its northern side. The compressional stress caused by shortening of the crust in the basin lead to the formation of terrace along its south side. The subsidence of the basin reached its acme during the terminal Pliocene to early Pleistocene when the Nihewan paleo-lake formed. During 2.0~0.8 Ma, the Nihewan paleo-lake saw a temperate climate intercalated with some subtropic intervals. The volcanic eruption and eolion deposits provided plentiful mineral nutrients necessary for living of animals and plants around the basin. These in turn offered the necessary living condition for early ancient humen. The Nihewan basin is a potential area to find the early ancient humen fossils.
DISCUSSION ON THE FURTHER RESEARCH IN LOESS HYDROCOMPACTION
XU Ling, DAI Fu-chu
2009, 15(1): 88-94, 104.
Abstract (230) HTML (89) PDF (1326KB)(11)
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Loess hydrocompaction has been discussed for a long time.During the 1960s ~ 1980s, with the application of SEM and mineral analysis, the micro-structure theory of loess hydrocompaction was developed and improved, but it has rarely been used in engineering numerical analysis because it failed to supply related force stress parameters.Progress in soil engineering and soil mechanics makes it possible to find a new way to study the loess hydrocompaction.This paper discusses mechanical attribute of loess hydrocompaction and proposes a concept of generalized loess hydrocompaction.An analysis is made on some issues about study on hydrocompaction from the viewpoint of unsaturated soil mechanics, and finally a case study is given.
AEOLIAN ORIGIN OF THE RED EARTH TORMATION IN JIUJIANG CITY OF JIANGXI PROVINCE, CHINA :EVIDENCE FROM GRAIN-SIZE ANALYSIS
LI Jing-wei, QIAO Yan-song, WANG Yan, PENG Sha-sha
2009, 15(1): 95-104.
Abstract (228) HTML (96) PDF (1476KB)(7)
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The Red Earth Formation in the middle-lower Yangtze River is an important pedostratigraphical unit in southern China.This formation is among the best geological records of Quaternary environment that bear information of climate changes for the subtropical zone of China.The study on the origin of this formation is the basis for further investigation of the paleoclimatic information.In this study, grain-size was analyzed on the samples from Jiujiang section at Jiujiang city of Jiangxi Province, and the result was compared with that of the typical Quaternary eolian deposit, as well as the lacustrine and fluvial sediments.Grain-size distribution was determined with a Malvern Mastersizer 2000 particle analyzer with a precision less than 1 %.The analysis on grain-size indicates that the Xiashu loess and vermiculated red soil (VRS)in Jiujiang section consist of uniform fine particles.The particles display a bimodal distribution, with grain-size fraction of 5 ~ 50 μm dominantly, and > 63μm in a small part.The distribution is essentially similar to that in the Xifeng loess samples, but differ from the multimodal patterns of the lacustrine and fluvial deposits.The Xiashu loess and VRS are also similar to the Xifeng lo ess samples in grain-size parameter.The mean grain-sizes of the Xiashu loess and VRS are about 6.4 ~ 6.8ϕ (9.0 ~ 11.8 μm)and 7.1 ~ 7.2ϕ (6.8 ~ 7.3 μm)respectively, somewhat finer than those of the Xifeng loess samples.The Xiashu loess, VRS and Xifeng loess have a smaller mean square deviation value than the fluvial samples, indicating a much better sorting and relatively stable depositional dynamics.The Xiashu loess, VRS and Xifeng loess samples show a positive skewness, but the fluvial samples a negative one.The lacustrine samples also show a positive, but obviously larger skewness.In kurtosis value, the Xiashu loess and VRS samples are close to the Xifeng loess, and the fluvial sediments are obviously smaller than the lacustrine samples.All these indicate that the Red Earth Formation in Jiujiang area have the same origin as the Quaternary loess in northern China.