Fluid flow and mineralization of Youjiang Basin in the Yunnan-Guizhou-Guangxi area,China

Comprehensive studies, based on isotope geochemistry of C, H, O, S and Sr, chronology, common element and trace element geochemistry of fluid inclusions for the epithermal Au, As, Sb and Hg deposits in the Youjiang Basin and its peripheral areas, suggested that the ore fluid was the basin fluid with abundant metallic elements and the large-scale fluid flow of the same source in the late Yenshan stage was responsible for huge epithermal mineralization and silicification. The ore fluid flowed from the basin to the platform between the basin and the platform and migrated from the inter-platform basin to the isolated platform in the Youjiang Basin. The synsedimentary faults and paleokast surface acted respectively as main conduits for vertical and lateral fluid flow.     

Fluid flow and mineralization of Youjiang Basin in the Yunnan-Guizhou-Guangxi area, China

Comprehensive studies, based on isotope geochemistry of C, H, O, S and Sr, chronology, common element and trace element geochemistry of fluid inclusions for the epithermal Au, As, Sb and Hg deposits in the Youjiang Basin and its peripheral areas, suggested that the ore fluid was the basin fluid with abundant metallic elements and the large-scale fluid flow of the same source in the late Yenshan stage was responsible for huge epithermal mineralization and silicification. The ore fluid flowed from the basin to the platform between the basin and the platform and migrated from the inter-platform basin to the isolated platform in the Youjiang Basin. The synsedimentary faults and paleokast surface acted respectively as main conduits for vertical and lateral fluid flow.     

Distribution and origin of brine-type Li-Rb mineralization in the Qaidam Basin,NW China

The Qaidam Basin on the Qinghai-Tibet Plateau is well endowed with a variety of critical metals,such as Li and Rb.However,little is known about the distribution,source,and enrichment mechanisms of these elements.In this paper,we present results of systematic geochemical and H-O-B isotopic analyses of brines in the Tertiary and Quaternary sediments of the Qaidam basin.The results reveal that the paleobrines from oil-bearing anticlines at Dafengshan,Nanyishan,Youquanzi,Jiandingshan,and Jianshishan are significantly enriched in Li and Rb,whose contents are 81.1-128.9 mg L^-1and 4.5-29.2 mg L^-1,respectively,reaching levels of economic significance.High Rb contents(up to 12.5 mg L^-1)and well-endowment of Li also characterize the Dongtai,Xitai,Yiliping,and Senie salt lakes in the Qaidam Basin.The Tertiary paleobrine average inδD andδ18O at-40.7‰and 2.84‰,respectively.The paleobrine with the highest Li and Rb hasδD andδ¹⁸O values close to magmatic water.Theδ¹¹B values are lower than those of river water but close to those of geothermal fluids,suggesting that replenishment by deep magmatic hydrothermal fluid is most likely the key mechanism for the anomalous enrichment of these elements in the paleobrines,though evaporation and water-rock reactions have contributed to the critical metal mineralization.The anomalous enrichment of Li and Rb in modern salt lake brines is closely related to the input of volcanic geothermal water.The relatively high Li and Rb contents of intercrystalline brines in salt lakes of the western Qaidam Basin and the increase of Li and Rb contents with increasing depth were caused by upwelling of local paleobrines along the fault zones.     

Distribution and origin of brine-type Li-Rb mineralization in the Qaidam Basin,NW China

The Qaidam Basin on the Qinghai-Tibet Plateau is well endowed with a variety of critical metals,such as Li and Rb.However,little is known about the distribution,source,and enrichment mechanisms of these elements.In this paper,we present results of systematic geochemical and H-O-B isotopic analyses of brines in the Tertiary and Quaternary sediments of the Qaidam basin.The results reveal that the paleobrines from oil-bearing anticlines at Dafengshan,Nanyishan,Youquanzi,Jiandingshan,and Jianshishan are significantly enriched in Li and Rb,whose contents are 81.1-128.9 mg L^-1and 4.5-29.2 mg L^-1,respectively,reaching levels of economic significance.High Rb contents(up to 12.5 mg L^-1)and well-endowment of Li also characterize the Dongtai,Xitai,Yiliping,and Senie salt lakes in the Qaidam Basin.The Tertiary paleobrine average inδD andδ18O at-40.7‰and 2.84‰,respectively.The paleobrine with the highest Li and Rb hasδD andδ¹⁸O values close to magmatic water.Theδ¹¹B values are lower than those of river water but close to those of geothermal fluids,suggesting that replenishment by deep magmatic hydrothermal fluid is most likely the key mechanism for the anomalous enrichment of these elements in the paleobrines,though evaporation and water-rock reactions have contributed to the critical metal mineralization.The anomalous enrichment of Li and Rb in modern salt lake brines is closely related to the input of volcanic geothermal water.The relatively high Li and Rb contents of intercrystalline brines in salt lakes of the western Qaidam Basin and the increase of Li and Rb contents with increasing depth were caused by upwelling of local paleobrines along the fault zones.     

Deep-seated structure and metallogenic dynamics of the Ailaoshan polymetallic mineralization concentration area,Yunnan Province,China

The Ailaoshan poly-metallic mineralization concentrated area (MCA) consists of the well known Ailaoshan metallogenic belt and adjacent mineral districts and/or deposits. Located in an area of several complex and intersecting tectonic units, the Ailaoshan poly-metallic MCA is controlled by deep crustal and mantle tectonism. Through interpretation of remote sensing images, we identified a large ring structure system that surrounds the MCA. This ring structure encloses regional deep-crustal faults, ductile she...     

Stream flow variability and drought severity in the Songhua River Basin,Northeast China

A slight variation in the magnitude of stream flow can have a substantial influence on the development of water resources. The Songhua River Basin (SRB) serves as a major grain commodity basin and is located in the northeastern region of China. Recent studies have identified a gradual decrease in stream flows, which presents a serious risk to water resources of the region. It is therefore necessary to assess the variation in stream flow and to predict the future of stream flows and droughts to make a comprehensive plan for agricultural irrigation. The simulation of monthly stream flows and the investigation of the influence of climate on the stream flow in the SRB were performed by utilizing the Integrated Water Evaluation and Planning (WEAP) tool coupled with observed precipitation data, as well as the Asian Precipitation-Highly-Resolved Observational Data Integration towards Evaluation of Water Resources (APHRODITE’s Water Resources) precipitation product. The Nash–Sutcliffe coefficient (NSC) was used to assess the WEAP efficiency. During the time of calibration, NSC was obtained as 0.90 and 0.67 using observed and APHRODITE precipitation data, respectively. The results indicate that WEAP can be used effectively in the SRB. The application of the model suggested a maximum decline in stream flow, reaching 24% until the end of 21st century under future climate change scenarios. The drought indices (standardized drought index and percent of normal index) demonstrated that chances of severe to extreme drought events are highest in 2059, 2060 and 2085, while in the remaining time period mild to moderate drought events may occur in the entire study area. The drought duration, severity and intensity for the period of 2011–2099 under all scenarios, [(A1B: 12, ? 1.55, ? 0.12), (A2: 12, ? 1.41, ? 0.09), (max. wetting and warming conditions: 12, ? 1.37, ? 0.11) and (min. wetting and warming conditions: 12, ? 1.69, ? 0.19)], respectively.     

太湖流域水库型水源地硅藻水华发生特征及对策分析

基于溧阳市天目湖沙河水库2009—2014年的硅藻群落结构及水质调查,以及宜兴横山水库等硅藻水华期藻类和水质调查数据,分析了太湖流域水库中硅藻水华群落结构特征及受气温、水位、营养盐等环境条件的影响.结果表明,太湖流域硅藻水华的主要发生期为5—7月,快速生长期发生在气温为16~26℃期间,当气温超过26℃时,硅藻的生物量开始下降.硅藻的优势属包括针杆藻、曲壳藻、小环藻和颗粒直链藻.其中沙河水库和横山水库中针杆藻是主要危害,其生物量主导了硅藻总生物量.大溪水库有时以针杆藻为主,有时以颗粒直链藻为主.当总氮浓度低于1.0 mg/L的Ⅲ类水上限时,水体氮浓度能大大限制硅藻生物量,当总磷浓度低于0.025 mg/L的Ⅱ类水上限时,也可能对硅藻生物量产生限制.高于此营养水平,硅藻水华的严重程度主要受气温、降雨等因素影响.研究表明,对于处于中营养水平的太湖流域水库而言,硅藻生物量既受气温、降雨、水位等气象水文条件的控制,又受氮、磷、硅等营养盐供给的影响.硅藻水华的防控既要关注气候和气象条件,也要尽量削减氮、磷营养盐入湖通量,维持较低营养盐水平是确保硅藻水华不形成危害的关键.     

利用自然伽马测井计算准噶尔盆地沉积层生热率及其热流贡献

沉积层放射性生热的热流贡献（沉积层热流）是沉积盆地大地热流的重要组成部分,能够有效促进中国西部“冷”盆深层-超深层烃源岩的增温和热演化.本文利用不同的自然伽马（GR）-生热率（A）经验关系式分别计算了准噶尔盆地不同构造单元16口钻孔共6120个沉积层生热率,通过与实测生热率的统计对比,确定了适用于研究区的GR-A经验关系,建立了准噶尔盆地地层生热率柱,据此计算了研究区沉积层热流贡献,并以盆参2井为例定量分析了沉积层热流的增温效应.结果表明,准噶尔盆地沉积层平均生热率为1.179±0.339 μW·m-3,总体上随着时代变老,沉积层生热率呈现出递减趋势.准噶尔盆地沉积层热流平均为7.9±4.9 mW·m-2,约占地壳热流的29.2%和大地热流的19.6%,区域上与盆地沉积层厚度大体一致,表现为中央坳陷最高,北天山山前冲断带变化较大,陆梁隆起和西部隆起次之,东部隆起和乌伦古坳陷最低.沉积层热流能够有效增高深层—超深层烃源层受热温度,促进有机质热演化,如在考虑和忽略沉积层生热的两种情况下计算的盆参2井下侏罗统三工河组烃源岩底部（5300 m）温度差异最大为7.3 ℃,这显然对于地温梯度小、主体油气藏埋深大的准噶尔盆地油气资源评价和勘探目标优选具有重要意义.     

Periodic changes of stream flow in the last 40 years in Tarim River Basin,Xinjiang, China

Using the annual runoff series for the last 40 years from the Tarim River Basin, their periodic properties were analysed and their future trends predicted. Runoff data were collected at five hydrological gauging stations in the three main branches of the Tarim River. An extrapolation method and variance analysis were used to identify periods in annual runoff, and a trend superposition model to predict future changes. Results show that, there is a common period of 17 years in annual runoff changes for all three branches, with Hotan River showing an additional period of 10 years. Based on this trend, it is suggested that the annual runoff of the Tarim River should decrease in the period of 2006–2008, but increase in year 2009, and the flow may possibly begin to decrease significantly in year 2010. The long term trend of runoff in Tarim Basin has followed the global prediction of GCMs, i.e. began to increase in accordance with global increase of air temperature and precipitation in 1990. However, it has shown a local feature of uneven changes among the head streams in the same basin, which needs to be further investigated. Copyright © 2008 John Wiley & Sons, Ltd.     

准噶尔盆地大地热流特征与岩石圈热结构

沉积盆地现今大地热流和岩石圈热结构特征是岩石圈构造-热演化过程的综合反映和盆地热史恢复的约束条件,对盆地动力学研究和油气资源评价具有重要意义.作者系统分析了准噶尔盆地2000年以来新增的102口钻孔的系统测井温度和400余口钻孔的试油温度资料,采用光学扫描法测试了15口钻孔共187块代表性岩石热导率,首次建立了准噶尔盆地岩石热导率柱,新增了11个高质量的(A类)大地热流数据,分析了准噶尔盆地大地热流分布特征,并揭示了其岩石圈热结构.研究表明,准噶尔盆地现今地温梯度介于 11.6~27.6℃/km,平均21.3±3.7℃/km,大地热流介于23.4~56.1 mW/m2,平均42.5±7.4 mW/m2,表现为低地温梯度、低大地热流的"冷"盆特征.准噶尔盆地大地热流与地温梯度分布规律基本一致,主要受控于基底的构造形态,东部隆起最高,陆梁隆起次之,乌伦古坳陷、中央坳陷和西部隆起较低,北天山山前坳陷最低.准噶尔盆地地壳热流介于18.8~26.0 mW/m2,地幔热流介于16.5~23.7 mW/m2,壳幔热流比值介于0.79~1.58,属于典型的"冷壳冷幔"型热结构.准噶尔盆地地幔热流值与莫霍面起伏一致,隆起区地幔热流高,坳陷区地幔热流低.     

Heat flow and its coalbed gas effects in the central-south area of the Huaibei coalfield, eastern China

Based on an analysis of the present geo-temperature field and the thermal conductivity (K) of 62 samples from the central-south area of the Huaibei coalfield in eastern China, we calculated the heat flow and plotted its distribution map. The results show that the average heat flow in the research area is about 60 mW/m2. It is different from other major energy basins in the North China Plate, but has close relationship with the regional geology and the deep geological setting. The heat flow is comparatively ...     

Numerical modeling of regional groundwater flow in the Heihe River Basin,China:Advances and new insights

Numerical groundwater modeling is an effective tool to guide water resources management and explore complex groundwater-dependent ecosystems in arid regions.In the Heihe River Basin(HRB),China’s second largest inland river basin located in arid northwest China,a series of groundwater flow models have been developed for those purposes over the past 20 years.These models have elucidated the characteristics of groundwater flow systems and provided the scientific basis for a more sustainable management of groundwater resources and ecosystem services.The first part of this paper presents an overview of previous groundwater modeling studies and key lessons learned based on seven different groundwater models in the middle and lower HRB at sub-basin scales.The second part reviews the rationale for development of a regional basin-scale groundwater flow model that unifies previous sub-basin models.In addition,this paper discusses the opportunities and challenges in developing a regional groundwater flow model in an arid river basin such as the HRB.     

内蒙古双尖子山矿集区三维电性结构及成矿意义

双尖子山矿集区作为中国北方东部大型的银铅锌多金属矿集区,具有多期叠加成矿的特征.为了揭示双尖子山矿集区2000 m以浅成矿要素的空间展布,本文基于有限内存拟牛顿法(L-BFGS)对覆盖矿集区的 6 条可控源音频大地电磁测深数据进行含源三维反演,获得了双尖子山矿集区2000 m以浅三维精细电性结构.结合重磁、区域地质、钻...     

Quantitative assessment of gas washing of oils in the Tazhong area of the Tarim Basin,Northwest China

Gas washing has been known in the Tazhong area of the Tarim Basin, but its quantitative assessment has not yet been reported. Here the influence of gas washing fractionation in the area was discussed based on the gas chromatogram data of 68 oils and the results of the mixing experiments of a black oil and a condensate. The results show that the intensity of gas washing fractionation decreased generally from northern to southern part and vertically from deep reservoirs to shallow reservoirs. The gas washing fractionation was mainly controlled by fault systems in this area, with the increase of n-alkane mass depletion positively correlated to the number and scale of faults. Gas washing fractionation appears to have affected the hydrocarbon property, and as a result the diversity of the crude oils is markedly controlled by gas washing. In addition, the occurrence of waxy oil in this area may be resulted from multiple factors including gas washing, mixed filling and migration fractionation. Supported by National Basic Research Program of China (Grant No. 2006CB202303) and the National Natural Science Foundation of China (Grant No. 40672091)     

南海北部陆坡深水区的海底原位热流测量

海底热流数据是开展海洋地球动力学研究和油气资源评价的基础数据.南海北部陆坡深水区蕴含有丰富的油气和水合物资源,而该区热流站位很少.为了解陆坡深水区水合物有利区块的地热特征,利用剑鱼1型海底原位热流探针,在南海西沙海域和神狐海域成功获得了16个站位的热流值.测量结果表明,西沙海槽与白云凹陷都具有较高的热流值,西沙海槽区除1个站位结果不可信外,另2个站位所测海底表层地温梯度分别为105.3 和99.9℃·km-1,原位热流分别为89±1和87±1 mW·m-2;白云凹陷中部区域13个站位测得表层地温梯度变化于58.5~100.7 ℃·km-1,热流值除4个站位低于70 mW·m-2外,其余都变化于75±2~101±4 mW·m-2范围,比前人在白云凹陷东部获得的热流高.分析认为,西沙海槽和白云凹陷区域的高地热特征与陆坡深水区的高热背景、晚期断裂发育、底辟、岩浆侵入和热流体活动等有关.     

南海南部礼乐盆地礁体发育区的构造热演化特征

礼乐滩是礼乐盆地的重要组成部分,自晚渐新世礼乐地块裂离北部陆缘后开始发育礁灰岩.为认识这些长期浸没海水中的礼乐礁体及其下伏地层的热状态与热演化特征,在详细分析礼乐滩钻井测温数据和镜质体反射率数据的基础上,对一条穿过礁体的骨干剖面进行了构造热演化数值模拟.结果显示,礁体区钻井2000~4500 m深度范围内温度介于30~90℃之间,井底与海底之间的平均地温梯度仅10℃·km^-1左右,地温梯度随深度逐渐增加,3000~4000 m深度段地温梯度介于32~37℃·km^-1;礁体下伏地层有机质曾经经历了比现今所处温度更高的古温度.进一步分析表明,高孔高渗的礁体上部因与周围低温海水发生热交换,导致地层温度降低、地温梯度和热流降低甚至为负值;与海水热交换作用随深度增加而减弱并最终停止,地层温度逐渐升高,地温梯度和热流值趋于正常;现今钻井3000~4000 m深度段地温梯度约为35℃·km^-1,基底热流可能介于65~75 mW·m^-2,平均约为70 mW·m^-2;礁体发育区有机质热成熟度主要是在礁体与周围低温海水发生实际热交换前获得的,礁体与海水热交换作用导致地层温度逐渐降低,有机质热成熟度增长缓慢,现今生烃门限深度明显大于邻近的北1凹陷中部区域的门限深度.

     

Variations of heat flow and Pn - velocity in the continental area of China

Temperature is an important factor affecting seismic velocity, and terrestrial heat flow is the most direct indication of temperature distribution of the lithosphere. Some authors therefore suggested that Pn velocity should be inversely related with heat flow. The average heat flow values (q) and Pn velocities (V _Pn) in 22 areas have been calculated and collected from published literatures to investigate the possible correlation between these two parameters for the continental area of China. However, the results show that the variations ofq andV _Pn in the studied areas are far away from the expected inverse relation. The effects of pressure of seismic velocity and contribution of crustal radiogenic heat on heat flow have been taken into consideration in regressions respectively and simultaneously. However, all the corrections are of little help for the improvement of the expected inverse relation. The conclusion deduced from the present study is that in a large scale region with complex tectonic evolution history and complex deep structure framework such as the continental area of China, temperature at the Moho boundary is not the most important factor affecting Pn velocity. The conceptual inverse correlation between heat flow and Pn velocity might be masked by various “noises”. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,14, 42–50, 1992.     

Effect of altered flow regime on bankfull area of the Lower Yellow River,China

The adjustment of the bankfull channel area in the Lower Yellow River has been dramatically affected by altered flow regimes caused by human activities. This paper presents a study on the effects of altered discharge and suspended sediment load on the bankfull area at Gaocun, a representative hydrometric station in the Lower Yellow River. The analysis demonstrates the cumulative effect of previous years' flow and sediment conditions on channel adjustment, a phenomenon commonly occurring in geomorphic systems due to the delayed channel response to flow and sediment conditions. A methodology for the prediction of bankfull area was developed based on the general concept that the rate of adjustment is proportional to the difference between the bankfull area and its equilibrium value. The proposed methodology is not only applicable for the prediction of the bankfull area in response to the changes in flow and sediment conditions in the Lower Yellow River, but can also be extended to other studies where the response times have a key role to play in the assessment of channel adjustment to external changes. Copyright © 2008 John Wiley & Sons, Ltd.     

The special sealing mechanism of caprock for Quaternary biogenetic gas in Sanhu area,Qaidam Basin,China

The Quaternary biogenetic gas reservoirs in the east of Qaidam Basin have many characteristics such as late forming time,shallow burial depth,low diagenetic grade,high porosity and high permeability and so on.It cannot be considered as caprock according to the traditional evaluation criterion.However, the large scale and high efficient biogenetic gas reservoirs of the Qaidam Basin are really formed under these kinds of caprocks,so it does have some specialty in its sealing mechanism.Aiming at the special sealing mechanism,some simulating experiments have been done.The research results show that the sealing ability of biogenetic gas caprock is related with water saturation,the caprock that is saturated with salt water can effectively block seepage and diffusion.Furthermore,the multiple reservoir-caprock groups have accumulated sealing effect,causing the formation of big gas fields.The evaluation method with traditional caprock parameters cannot be adopted in evaluating the study area.     

Multiple-aged granitoids and related tungsten-tin mineralization in the Nanling Range, South China

The Nanling metallogenic belt in South China is characterized by well-developed tungsten-tin mineralization related to multiple-aged granitoids. This belt is one of the 5 key prospecting and exploration areas among the 19 important metallogenic targets in China. Important progress has been made in recent years in understanding the Nanling granitoids and associated mineralization, and this paper introduces the latest major findings as follows: (1) there exists a series of Caledonian, Indosinian, and Yanshanian W-Sn-bearing granites; (2) the Sn-bearing Yanshanian granites in the Nanling Range form an NE-SW trending aluminous A-type granite belt that stretches over 350 km. The granites typically belong to the magnetite series, and dioritic micro-granular enclaves with mingling features are very common; (3) the Early Yanshanian Sn- and W-bearing granites possess different petrological and geochemical features to each other: most Sn-bearing granites are metaluminous to weakly peraluminous biotite (hornblende) granites, with zircon ?_Hf(t) values of ca. ?2 to ?8, whereas most W-bearing granites are peraluminous two-mica granites or muscovite granites with ?_Hf(t) values of ca. ?8 to ?12; (4) based on the petrology and geochemistry of the W-Sn-bearing granites, mineralogical studies have shown that common minerals such as titanite, magnetite, and biotite may be used as indicators for discriminating the mineralizing potential of the Sn-bearing granites. Similarly, W-bearing minerals such as wolframite may indicate the mineralizing potential of the W-bearing granites. Future studies should be focused on examining the internal relationships between the multiple-aged granites in composite bodies, the metallogenic peculiarities of multiple-aged W-Sn-bearing granites, the links between melt evolution and highly evolved ore-bearing felsic dykes, and the connections between granite domes and mineralization.