Geoscience

Metallogenic System of Copper Polymetallic Deposits in the Middlesouthern Part of Da Hinggan Mountains,China

ZHANG Mei, DI Yu-Sheng, CHEN Cun-Li, LIU Yong-Hui, YANG Shuai-Shi, DI De-Gao, YAO Mei-Juan, WANG Jian-Beng, WANG Shou-Guang, GAO Zheng-Xi, ZHANG Ling

2011, 25(5): 819-831.

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Based on the analysis of regional geological setting, metallogenic characteristics and the study of typical deposits, the spatial distribution, orebedding rocks, related intrusions and mineralization ages of copper polymetallic deposits are summarized in the middlesouthern part of Da Hinggan Mountains. Three metallogenic systems of copper polymetallic deposits, which are Yanshanian porphyry hydrothermal, IndoYanshanian hydrothermal dynamic and Late VariscanYanshanian SEDEX deposition superimposed by late hydrothermal solution, are distinguished by using the method of regional metallogeny. The studies indicate that largescale copper polymetallic deposits in JurassicCretaceous volcanic area should be paid more attention to. Also, prospecting exploration of porphyrytype deposits should be strengthened in the depth and around the known skarntype and hydrothermal veintype deposits.

Trace Elements in Pyrites and Their Implication for Hydrothermal Ore forming Process in Longshan Gold antimony Deposits, Hunan, China

LONG Bao-Cheng, YANG Dong-Sheng- , ZHOU Zhi, LIU Xi-Mao, LIU Feng-Cheng, LIU Yuan-Dong

2011, 25(5): 832-845.

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Trace elements content in pyrite can give information of element occurrence and trace hydrothermal oreforming processes. Many kinds of trace elements in pyrites from slate, altered slate and ore in Longshan goldantimony deposits were measured using EPMA. The analysis data suggest that Au in sedimentary pyrites are mainly nano particles, whereas Au in hydrothermal pyrites are solid solution as well as nano. In sedimentary pyrites, Ni, Sb, Mn, Te might be in form of solid solution, but As, Pb, Zn, Cu, Ag mineral inclusions. In hydrothermal pyrites, As, Sb, Mn, Te might be in form of solid solution, but Co, Ni, Pb, Zn, Cu, Ag mineral inclusions. Longshan goldantimony deposits had been underwent two mineralization epochs. During earlier epoch, it occured lower intensity AuPbCuW mineralization related to deep high Ni magmatic fluids. During later epoch, it occured AuSb mineralization closely related to meteoric circulation. The later mineralization epoch, as the main mineralization period, can be divided into four stages: micro gold stage, submicro goldstibnite stage, invisible goldstibnite stage, and stibnite stage.

Sulfur and Lead Isotope Composition and Tracing for Sources of Oreforming Materials in Beiming River Iron Deposits, Southern Taihang Mountains

WANG Yan-Juan, HU Huan-Huo, SHEN Dun-Feng, QU Kai, YAN Na, XU Hong-Jun, MA An-Gang

2011, 25(5): 846-852.

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The Beiming River iron deposits as one of major typical skarntype deposits are located in Hanxing area, southern Taihang Mountains. It was formed in the boundary between diorite intrusion and midOrdovician limestone. This paper analyzed the isotopic data of sulfur and lead for skarn and magnet ore of the deposits and discussed in further the ore source by comparison with existed isotopes data. From all of these, it is demonstrated that the iron deposits had multisources and the sulfur isotopes provided an evidence of mixed origins with ratio ranging from 12.2‰ to 16.5‰. Isotopic ratios for sulfur are influenced by the oreforming processes and environment, and the ratio range indicated that the gypsum strata in wall rock was also involved in the mineralization during the movement of the deeply derived metallogenetic fluid from the lower to the upper. In addition, the ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios of pyrite are in the ranges of 17.840-18.793 (mean value is 18.419), 15.46-15.62 (mean value is 15.56) and 37.927-39.301 (mean value is 38.730), respectively, which show that lead mainly originated from lower crust and mixed with a few from the mantle.

Sulfur, Lead Isotope Composition Characteristics and the Relevant Instructive Significance of the Lamuyouta Sb（Au） Deposit, South Tibet

DU Ze-Zhong, GU Xue-Xiang, LI Guan-Qing, ZHANG Yong-Mei, CHENG Wen-Bin, JING Liang-Bing, ZHANG Xin-Guo

2011, 25(5): 853-860.

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Lamuyouta Sb (Au) deposit is located in the eastern section of SbAu metallogenic belt, south Tibet The ore body mainly occurs at the contact between the strata of the Middle Jurassic Zhala Formation and diabase (allgovite) veins. Based on the analysis of geological and oreforming conditions, this paper systematically focuses on the composition characteristics of S, Pb isotopes in the sulfide ore minerals, as well as a comparison of S, Pb isotope composition among other typical ore deposits developed in the same regional metallogenic belt. In addition, it also discusses the sources of the oreforming materials. Studies have shown that the composition of S isotope in sulfide ore minerals has a narrow variation range and the δ³⁴SΣS in the oreforming hydrothermal system is about 0, which is similar to other typical ore deposits developed in regional metallogenic belt, south Tibet. It is estimated that the sulfur origin is closely related to the magmatic sulfur. The isotopic composition of ore lead is varied greatly and belongs to anomalous lead, which constitutes a secondary isochron of lead. And then, it is calculated that the age about the lead with radiogenic source is 1,638 Ma, which inverts twostage evolution process of ore lead. Therefore, it is speculated that they sourced from ancient crystalline basement of upper continental crust, in order to provide some help for the study of HimalayanTethyan antimonygold metallogenic belt in Tibet.

The Composition of Sulfur and Lead Isotope and the Source of Metallogenic Material from Xiyuan and Jiangjia Ore Blocks in the Dongyuan

DU Yu-Diao, TU Xin-Qi, ZHOU Xiang, FU Jian-Zhen

2011, 25(5): 861-868.

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The Dongyuan WMo deposit, located in Qimen County in southern Anhui Province, is the largest WMo deposit in this region thus far reported. The deposit consists of Dongyuan, Xiyuan, and Jiangjia ore blocks. The WMo orebodies in Jiangjia and Xiyuan ore blocks are mainly occurred in granodiorite porphyry and the nearby contact zone, with the major type of veinletdisseminated and disseminated mineralization. The measured δ³⁴SVCDT values of Jiangjia (2.6‰ to 4.9‰) and Xiyuan (4.0‰ to 4.7‰) ore blocks vary in a very limited range and suggest that the formation of WMo orebody is closely related to magmatism, which involve the sulfur may be leached from the granodiorite intrusion. Based on tectonic patterns of lead isotope and related paramerters, the lead isotopic compositions of Jiangjia (²⁰⁶Pb/²⁰⁴Pb=18.222 to 18.369, ²⁰⁷Pb/²⁰⁴Pb=15.579 to 15.618, ²⁰⁸Pb/²⁰⁴Pb=38.264 to 38.400) and Xiyuan (²⁰⁶Pb/²⁰⁴Pb=18.240 to 18.251, 207Pb/204Pb=15.604 to 15.618, 208Pb/204Pb=38.360 to 38.442) indicate that the metallogenic material is closely related to magmatism, and their leads are characterized by the source of lower crust and show crustmantle mixing.

Sulfur and Lead Isotope Composition and Tracing for Sources of Oreforming Materials in the Dongzhongla PbZn Deposits in Mozhugongka County，Tibet

LIU Ting-Ting, TANG Ju-Xin, LIU Hong-Fei, ZHANG Jin-Shu, CUI Xiao-Liang, GAO Yi-Ming

2011, 25(5): 869-876.

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In order to discuss the oreforming material sources of the Dongzhongla PbZn deposits and study the metallogenic mechanism，we analyzed the sulfur and lead isotope from the orebody，discussed the changing regularity and significance. The results show that the δ³⁴S values of the six metal sulfides vary from 2.2‰ to 4.8‰, and that the sulfur isotope composition is stable. The temperatures calculated from sulfideparas show that the deposits are the middlelow temperature deposits. The ²⁰⁶Pb/²⁰⁴Pb，²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios of 6 sulfide samples of orebody vary in ranges of 18.628 0-18.629 6，15.698-15.699 9,39.0775-39.082 4，with the average values of 18.628 7，15.699 02 and 39.079 37, respectively. The results of sulfur and lead isotope show that the oreforming materials of Dongzhongla PbZn deposits came from the Permian volcanic sedimentary rock and late Yanshan period granite.

A Study on the Geochemistry and Geochronology of the Intrusive Rocks in Copiapó GV Area, Chile

LI Jian-Xu, FANG Wei-Xuan, LIU Jia-Jun

2011, 25(5): 877-888.

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The Copiapó GV area of northerncentral Chile is situated in the transition zone between a Mesozoic iron oxide coppergold (IOCG) deposit and a porphyry copper deposit. The intrusive rocks mainly consist of calcalkaline, medium to coarse grained gabbro diorite, diorite, diorite porphyry, biotite granite, porphyritic granite and monzonite. These rocks are classified into the category of calcalkaline, Itype and magnetite types, which is derived from the upper mantle. The assemblage of the intrusive rocks is interpreted to be formed at the subduction zone of oceanic crust during conversion from partially expansion to extrusion. As a consequence, the Mesozoic backarc basin closed up and uplifted rapidly. The magma intruded mainly in the period of Late CretaceousPaleocene (about 65-54 Ma). The magmatic activities of different periods created a number of hydrothermal centeres and developed horizonal alteration zones and veintype alterationmineralization zones. On surface argilizationchlorite alteration, porous and silicified stockwork, and AuAg bearing FeMn carbonate stockwork well developed. The widely extensive alteration zones contain gold, silver polymetallic veins, which may indicate that the area could develop some epithermal AuAg polymetallic deposits. These phenomena may present the potential of occurrence of IOCG mineralization or porphyry coppergold mineralisation in deep area. Further study of alteration and mineralization should be strengthen, which will create a guideline of exploration for the deepburied deposits in the future.

Superimposed Types of Extensional Fault Depressions at Different Epochs

CHEN Fa-Jing, HONG Xin-Wen- , CHEN Zhao-Nian

2011, 25(5): 889-895.

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Three problems are discussed in this paper. (1) Superimposed types of extensional fault depressions at different epochs. According to modes of superimposition, the types of superimposed fault depression can be classified as follows: isolate, inherited and interference types. Based on interference relationship between early and late fault depressions, the interference types can be subdivided further into three subtypes: synthetic, convergent and intersecting interference. (2) Formation mechanism of these interference types is controlled by following factors. The synthetic and convergent interference types are related with arrangement of synthetic and convergent preexistent basement faults and longitudinal or transverse migration of fault activity, whereas the intersecting interference type is related with rotation of extensional direction with time. (3) Hydrocarbon occurrence is related with various superimposed types of the fault depressions. Some types, such as inherited and convergent interference type are in favor of generation and preservation of oil and gas, whereas synthetic and intersecting interference type played a destructive role in general, because early depression was partly uplifted and modified by development of late depression.

Applying Balancedrestoring Technique with Detachment Horizon Profile to Study the Tectonic Evolution of Northeastern Sichuan

HU Wang-Shui, CENG Chao, ZHOU E-Li, TAO Gan-Kun, SHANG Ji-An

2011, 25(5): 896-901.

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In the research of tectonic evolution with the balanced section technique, there is some difficulty in achieving the balance of the section because of the irregularly plastic deformation of the layer. To solve this problem, the layered technique is proposed to eliminate the influence of plastic layer, that is to recovery the formations which are on and under salt rocks respectively, then the salt is controlled by both of them to dominate the deformation amplitude, and finally the balanced state is achieved. The proposed method can effectively eliminate the effect of plastic layers in the study of tectonic evolution of Late PaleozoicMesozoic strata in northeastern Sichuan. According to the study, the formation of the ancient tectonic frame of northeastern Sichuan has experienced the early extension, the midterm transition and the later extrusion process, and manifests the structural characteristics of the early normal fault, the midterm reversal structure, and the later thrust nappe structure; the gypsumsalt rock which is 500meter thick in JialingjiangLeikoupo Formation has played an important role in the deformation process.

Oil Enrichment Laws and Differentia of Chang 2 Formation in Jiyuan Area, Ordos Basin

TIAN Jian-Feng, LIU Che-Xiang, LIANG Xiao-Wei

2011, 25(5): 902-908.

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The relationship between oil layer distributions and key reservoirforming factors indicates that the westward monocline is the foundation of structurallithologic trap type; Nose uplift structure determines oil distribution; Distributary channel sand body is the main reservoirs; Interchannel mudstone is the barrier and cap of oil accumulation; Diagenesis is a key point for storage capability of sand bodies; The massive interconnected sandstone on the bottom of Chang 2 formation is like a large inverted hopper that can accumulate oil for the upper entrapment. The influence degree of each geologic element is defferent for each sublayer. The strongest element is called key element of hydrocarbon enrichment. The key element is also the poorest element and changes with the place of middle sedimentary cycle.The key elements of hydrocarbon enrichment of Chang 211 and Chang 212, Chang 222 and Chang 23, Chang 213 and Chang 221 are the sand body distribution of distributary channel, mudstone barrier or cap and the shape of noseshaped uplift, respectively, forming oil distribution in a row, in disperse and as strings, respectively.

Diagenesis and Its Effect on Reservoir of Member 2-3 of the Lower Shihezi Formation in Daniudi Gas Field, Ordos Basin

XU Shen-Mou, LIN Chun-Meng, WANG Xin-Feng, ZHONG Fei-Xiang, DENG Yi-Xin, LV Xiao-Li, SHANG Xin-Wang

2011, 25(5): 909-916.

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The reservoir rock types of member 2-3 of Lower Shihezi Formation in Daniudi gas field mainly include lithic quartz sandstone and lithic sandstone. Their compositional maturity and textural maturity are low. Research shows that diagenesis stage of the reservoir is at Asubstage and the diagenesis types are mechanic compaction, cementation, dissolution and metasomatism. The mechanic compaction and cementation are the most popular and typical destructive diagenesis in the study area, which are the main causes of low physical property. The dissolution is constructive diagenesis with relatively low degree of development, but relatively high in some areas, and it is one of the primary factors which improve the reservoir physical property. The physical property changes regularly with the burial depth. At the depth scale of 2,670 to 2,750 meters, the abnormal high values of porosity and permeability is due to the comprehensive action of various diagenesis, in which the organic acid produced by hydrocarbon migration and accumulation makes clastic particles and carbonate cement dissolved. It makes a great contribution to the formation and preservation of abnormal porosity zones.

Characteristics of Karst Porous Fractured Reservoir and Favourable Target Areas in Ordovician of Northwestern Ordos Basin

WANG Gong-Wei, Liu-Bao-Xian, Bi-Meng-Bei, Ma-Tie-Rong, Li-Lei, Li-Yan

2011, 25(5): 917-924.

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Karst porous fractured reservoirs are found in Ordovician limestones of Qilian sea area in northwestern Ordos basin and have better gasbearing ability, showing that karst porous fractured reservoirs are a new form for carbonatites natural gas exploration. Through the analysis of geologic setting of paleokarst cavitys development, the characteristics of paleokarst porous fractured reservoir based on the well drilling, logging data and seismic response are analyzed and two types of reservoirs are classified. Based on the seismic identifying pattern of wells, it is concluded that the target areas of Kelimoli Formation karst porous fractures are planar distributed, forming better reservoirforming assemblage with Ordovician source rocks，which are the important areas for the futures natural gas exploration.

Characteristics and Genesis of Dolomite in Majiagou Formation of Ordovician, South of Ordos Basin

HUANG Zheng-Liang, BAO Hong-Beng, LIN Jun-Feng, BAI Hai-Feng, WU Chun-Yang

2011, 25(5): 925-930.

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There developed four kinds of dolomitization in genesis in Majiagou Formation of southern Ordos basin：penecontemporaneous dolomitization, circumfluence and mixing water dolomitization, burial dolomitization and hydrothermal dolomitization, based on the study of macroanalysis, microanalysis and geochemical characteristics. Penecontemporaneous dolostone developed in 1st, 3rd and 5th members of Majiagou Formation, and its genesis is evaporative pumping dolomitization. Circumfluence and mixing water dolostone is produced by two kinds of effects: one is salt water rich in magnesium, another is the mixture of salt water rich in magnesium and fresh water, which finally cause metasomatism of limestone, and produce circumfluence and mixing water dolostone. Burial dolostone results from metasomatism of limestone by salt water rich in silicon and aluminum and seawater or salt lake water along the pore space. Hydrothermal fluid dolostone is mostly produced by hydrothermal fluid which is supersaturated in pore space of coarsecrystaline dolostone and structural fracture in Yanshan era.

Characteristics of Water Bearingformation and GasWater Distribution Control Factors in Gas Reservoir He 8 of Sulige Gasfield, Ordos Basin

ZHANG Hai-Chao , SHI Zhuo , LIN Zhan-Li, LI Mei

2011, 25(5): 931-937.

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The gas reservoir in Sulige gasfield, Ordos Basin, is a typical lowpermeability tight sandstone gas reservoir. The major gas reservoir He 8 is characterized by bad physical property, strong anisotropy and complicate gaswater distribution. With the tested and explored data, the water is divided into three types as following, adsorbed water and capillary water and free water. The adsorbed water mainly exists in the surface of rock particles; the capillary water exists in the capillary tubes of strong anisotropy reservoirs; the free water exists in the reservoirs with good pore structure and physical property. According to the hydrocarbongenerating intensity and heterogeneity, the gaswater distribution control factors were analyzed: the hydrocarbongenerating intensity dominates the macro distribution of gas and water; the reservoir heterogeneity controls the partial distribution; the micropore structure controls the water occurrence situation.

Preliminary Study on Seismic Active Faults of the Daqingshan Frontal Fault in Baotou City, Inner Mongolia

NIE Zong-Sheng, LIN Yun, LIU Zhi-Meng, DU Cheng-Long, CONG Pei-Li

2011, 25(5): 938-957.

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Through several years of field investigation and dating paleoearthquake events on the Daqingshan frontal fault, it is initially obtained that Baotou is situated in the western segment of Holocene fault of the Daqingshan frontal fault, which expands along the frontal borders of terrace I or II and is expressed by a series of seismic deformation, such as seismic faults, fault scarps, colluvial wedges, fissurefill wedges, ground fissures, and liquefaction, which make up of extensive and continual surface ruptures. The seismic faults extend linearly or in a wide arc showing as en echelon faults, and penetrate Holocene strata and the youngest geomorphic surface, and manifest as a series of south dipping normal faults and step normal faults. The fault planes are flat with downward scratches; the fault zone is often filled with sandy gravel, breccia, or sand and soil, indicating that the fault is mainly controlled by extensional tectonic force and experienced five times of dipsliping movement. The latest event may be the 849 ADBaotou earthquake. On the basis of the prelimiary study of Holocene active features, division of activity period and strongearthquake recurrence interval, in combination with action of the historical and present earthquakes, we should pay more attention to the earthquake hazard of Baotou.

Neotectonic Characteristics of Bangong Lake Region in Western Margin of the QinghaiTibet Plateau

LIU Fang-Xiao, Li-De-Wei, Liu-De-Min

2011, 25(5): 958-964.

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Bangong Lake area in western margin of the QinghaiTibet Plateau is a typical part of the western syntaxis, and also is the important region of research on the QinghaiTibet Plateaus tectonic movement, geomorphic evolution and environmental changes since the Middle Pleistocene. Based on the results of geological surveys, by means of the satellite remote sensing image interpretation and the analysis of digital elevation models, this paper mainly studies the brief characteristics of neotectonics and its coupling with the terrain and geomorphic features of the area. The results indicate that Bangong Lake areas faults can be divided into four groups which are nearly EW, NW, NE and NNE, in those, nearly EW is the main fault, and most of these fault basins have the features of pullapart. Late Cenozoic stratigraphy grows in the region, particularly the Quaternary alluvialdiluvial fans and lake sediments widely distribute, which are linearly developed and controlled by the faults, and lacustrine and alluvial terraces are also developed, which indicate the period of tectonic uplift in the region. The isotopic ages of calcitic sediments are (23.8±2.3) kaBP, (33.9±4.0) kaBP, (78.0±8.0) kaBP on the terraces with heights of 62 m, 65 m and 98 m above lake level near Wujiang at the north bank of Bangong Lake. The earthquakes occurred frequently in this area. According to the statistics, the magnitude of 303 earthquakes are more than Ms 4.0 and 7 earthquakes of those are more than Ms 6.0 since 1970. The topography and geomorphology characteristics of the study area are mainly middlelarge undulating mountain (5002,500 m terrain undulation). Plains and plateaus also less developed, which indicates that the stronger erosion of surface leveling process associating with the crust tectonic uplift since the Middle Pleistocene.

Main Progresses in the Study of Precambrian Basement of Jiaobei Terrane，Eastern China

XU Yang, FENG Yan, LI Ri-Hui

2011, 25(5): 965-974.

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The Jiaodong terrane located between Yishu fault and WulianYantai fault in eastern Shandong Province, is characterized by an Archean to Paleoproterozoic crystalline basement experienced different degrees of metamorphism traditionally. Its assemblage includes TTG (tonalitictrondhjemiticgranodioritic) gneisses and a little supracrustal rocks(metavolcanite and metasedimentary), which combined to granitegreenstone belts of Jiaodong terrane. The research of lithological, geochemical, geochronological data indicated that its continental crust was chiefly generated in Neoarchean (28-27 Ga), and then it started intracratonic deposit of Paleoproterozoic khondalite after tectonic event at 25 Ga，finally it undergone the metamorphic event at 18 Ga. Different from Sulu orogen，some characteristics of Precambrian basement of Jiaobei terrane are related to North China Craton, and the boundary between them maybe locate along the WulianYantai fault.

Early Carboniferous Coral Assemblages and Their Palaeobiogeography in the ZhidoiZadoi Area, Southern Qinghai

NIU Zhi-Jun, TUN Dun, WANG Jian-Xiong, DIAO Xiao-Meng

2011, 25(5): 975-986.

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Abundant coral fossils were collected from the Zadoi Group(Lower Carboniferous)in southern Qinghai. In the study area, the Zadoi Group is composed of three formations, which are the Lower Carbonate Formation(C1z1), the Clastic Formation(C1z2), and the Upper Carbonate Formation(C1z3) in ascending order. Based on the characteristics of the coral fauna, two assemblages may be established, which are the Siphonodendron scitulus-Lithostrotionella zadoensis assembalge(Visean)occurred in the Lower Carbonate Formation and Clastic Formation, and the Lithostrotion decipiens-Kueichouphyllum sinense-Siphonodendron irregulare asiaticum assembalge(ViseanSerpukhovian)occurred in the Upper Carbonate Formation. The Siphonodendron scitulus-Lithostrotionella zadoensis assembalge is characterized by endemic genera, and dominated by genera Siphonodendron and Lithostrotionella compound in form. In the Lithostrotion decipiens-Kueichouphyllum sinense-Siphonodendron irregulare asiaticum assembalge, genus Kueichouphyllum solitary in form, which is one of warmwater genera of South China, first occurred. As an important element of the Northtype of Eurasia Province, genus Gangamophyllum also occurred, but in a small amount. And the diversity of this assemblage is significantly higher than that of the underlying assemblage. This coral fauna correlated well with those faunas from East Tibet, South China, and adjacent areas of the same period. The Otsuka similarity coefficient and Qcluster analysis of these coral faunas shows that the Early Carboniferous coral fauna from southern Qinghai is warmwater Tethystype, and belongs to the BayankalaSanjiang subprovince, Tethys Realm. And this fauna differs significantly from those faunas in south of Longmu CoShuanghuLancang River Suture Zone.

Nonfusulinid Foraminiferal Fauna from the Permian Chihsia Formation, Northwestern Sichuan Basin

ZHANG Zhou, ZHANG Ting-Shan, LA Guang-Zhi

2011, 25(5): 987-994.

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The Permian nonfusulinid foraminifers of the Chihsia Formation are collected from Wangjiagou section in Wangcang County, Northwestern Sichuan Basin. The Chihsia Formation of Wangjiagou section is a suit of mediumbedded to thickbedded limestones, with thickness of about 108 meters. Based on the systematic study to the Chihsia Formation, 27 species of 14 genera (including conformis species and subspecies) of the nonfusulinid foraminiferal fauna have been recognized in the Wangjiagou section. The Globivalvulina assemblage is suggested as indicative fauna for recognition of the Permian largest transgressive period. The result of this study not only enriches the fossil database of Sichuan Basin, but also provides more palaeontological evidences for stratigraphic correlation in South China.

Marine Transgression of the Eastern Niger Basin in the Late Cretaceous: Paleontological and Geochemical Evidences

LIU Bang, BO Jiao-Hua, MO Lun-Kun, MAO Feng-Jun, LIU Ji-Guo, LV Meng-Qing, WANG Yu-Hua

2011, 25(5): 995-1006.

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The Eastern Niger Basin is a typical MesozoicCenozoic intracontinental rift basin of the central and western African rift system. Located in the Eastern Niger, the basin includes five depressions, namely Termit, Tefidet, Tenere, Grein and Bilma depressions. Based on paleontological and geochemical characteristics of the Upper Cretaceous mudstone cuttings in wells of Saha-1 and Helit-1, located in the Tenere and Termit depressions, respectively, this study provides evidences for marine transgression happened in the Eastern Niger Basin in the Late Cretaceous. Paleontological results of cutting samples in well Saha-1 show that they contain marine microfossils including calcareous microalgae, ostracod fauna, dinoflagellate, foraminifera, etc. The main geochemical characteristics of these samples are high abundance of gammacerane, β-carotane and dinosteranes which are marine biomarkers. Both microfossil distribution and geochemical characteristics suggest that the Upper Cretaceous strata were deposited in a marine environment. Marine transgression happened in the Eastern Niger Basin in the Late Cretaceous, coinciding with the worldwide eustatic sea level highstand. In the Early Cretaceous, the basin was dominated by continental deposits, whereas under the background of thermal subsidence and marine transgression, the Eastern Niger Basin became a unified basin in the Late Cretaceous, depositing massive marine strata.

Estimation of Ecological Appraisal of Heavy Metals in Soil in MinheHaishiwan，Qinghai

HU Guang, ZHANG Qiao-Qiu, JI Bing-Yan, ZHANG E-Feng, TANG Dun-Gong

2011, 25(5): 1007-1012.

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In this paper, the pollution of anomalous elements in soil in MinheHaishiwan，Qinghai and its potential ecological hazard were evaluated quantitatively through single factor pollution index method, Nemerow pollution index method and Hakanson potential ecological risk index method. Additionally, the ecological effect in anomalous areas was also discussed. The results show that the pollution factors of heavy metals are in order of Hg＞Cd＞Pb=Cr in the soil. The bioavailability of the anomalous elements follows the sequence of Cd＞Hg＞Pb. The potential ecological hazard of anomalous elements was as follows: Hg＞Cd＞Pb＞Cr. Although the concentration of anomalous elements in crops such as wheat and corn was far below the required food security limits, the situation of pollution control was still severe due to the high potential ecological hazard of Hg and high bioavailability of Cd.

Study on Soil Geochemical Prospection of Leadzinc Deposit in Yinshanling， Guigang, Guangxi

MENG Yong, Wen-Jian-Sheng, Lv-Yu-Meng, Lin-Yu-Jiang, WU Gui-Hua

2011, 25(5): 1013-1020.

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By promoting simple geological survey and geochemical measurement of soil profile in a scale of 1∶10,000 in Yinshanling, Guigang, Guangxi, we summarized the stratum, lithology, structure and wallrock alteration exposed in Yinshanling. On above basis, we proceeded a research for soil geochemistry, and got the following understanding: (1) The statistical analysis of trace element parameters shows that the content of Pb, Zn, Ag element is relatively higher, the coefficient of variation is much bigger, and easily downward enrich to form substantial geochemical anomaly; (2) Combinatorial analysis of elements, element distribution patterns and element fractal characteristics show that the Pb, Zn, Ag represent secondary enrichment combination of the main oreforming elements. And their distribution range is wide, dispersion is large so that they can be used as the main prospecting indicator elements; (3)Analysing integrating geological and geochemical data information, we discovered three geochemical anomaly segments in the work area, then interpreted and evaluated each soil geochemical anomaly, finally delimitated the prospecting target areas and put forward some new suggestions for work.

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