中国叠生型铁矿床成矿特征探讨

叠生成矿作用主要是指早期成矿作用被晚期成矿作用叠加、复合和改造。晚期成矿作用的性质常与早期成矿作用不同,也就是说,在早先己有矿床(或矿体、矿源层)的基础上,叠加复合了晚期成矿作用,即成矿时间上有先后、空间产出上有重叠、并对早先形成的矿床进行复杂的复合、叠加和改造,使成矿作用具有多样性、复杂性,并可形成大矿、富矿。铁矿床中叠生成矿作用广泛发育。按矿床或矿体产出和形成的地质特征,中国叠生型铁矿床可分为风化淋滤型、热液叠加改造型和热液叠加复合型3个亚类。风化淋滤型铁矿床在中国分布有限,规模不大,工业利用价值不大,因而中国的叠生型铁矿床主要是指热液叠加改造型和热液叠加复合型两个亚类。热液叠加改造型主要是指早期的铁矿床(或矿体、矿源层)经后期热液叠加改造,使早期的较贫铁矿床(或矿体、矿源层)成为较富铁矿床(或矿体),这是中国BIF型铁矿床中最重要的富铁矿类型,以鞍本地区弓长岭二矿区为典型代表。弓长岭二矿区铁矿,早期在新太古代形成条带状磁铁石英岩(2528 Ma,贫矿石),后期在古元古代,含矿热液交代改造贫铁矿形成富铁矿(1840 Ma)。热液叠加复合型主要是指后期脉型铁(或稀土元素等)矿床叠加在早期(沉积或其他成因)铁等矿床上而形成的矿床,如白云鄂博铁-铌-稀土元素矿床和黔西菱铁矿矿床。白云鄂博铁-铌-稀土元素矿床的形成与火成碳酸岩有关,在中元古代(1.3 Ga)左右,区内火成碳酸岩的侵位,在早期主要形成以岩浆熔离作用为主的铁-铌-稀土元素矿,晚期叠加了加里东期稀土-铌矿化热液脉。古陆边缘构造带或陆内活化带是形成叠生型铁矿床的有利构造空间,较大的地球化学块体,为形成多期、多成因的矿床提供物质来源,叠生型铁矿床的形成明显受构造的控制。叠生成矿是复杂地质过程的一种具体表现。热液叠加改造型和热液叠加复合型的叠生型铁矿床的形成是因中国独特的大地构造环境决定的。叠生成矿作用的研究,尚处在初步阶段。加强对叠生成矿作用的研究,了解其形成的地质背景、成矿机制、作用过程、控矿因素等,对发展矿床学研究,认识区域成矿特征和指导地质找矿具有重要的理论和实际意义。     

河南老湾金矿床上上河矿段矿床地质和成矿流体地球化学

河南桐柏老湾金矿床是桐柏-大别山(北坡)金银成矿带内大型造山带型金矿床之一。文章对该矿床的上上河矿段进行了矿床地质和成矿流体地球化学研究,旨在查明该矿段的流体成矿过程。根据矿脉穿插关系、矿石结构构造、矿物共生组合以及黄铁矿的粒度和晶形,将老湾金矿上上河矿段成矿过程划分为:石英粗粒自形黄铁矿(Ⅰ)、石英细粒半自形-他形黄铁矿(Ⅱ)、石英多金属硫化物(Ⅲ)及石英碳酸盐(Ⅳ)4个阶段。镜下观察显示,矿床中的包裹体类型有含CO_2包裹体(LH_2O+LCO_2+VCO_2)、纯CO_2包裹体(LCO_2+VCO_2)、液相包裹体(LH_2O+VH_2O)及少量含子晶包裹体(LH_2O+VH_2O+S)。第Ⅰ阶段、第Ⅱ阶段和第Ⅲ阶段均可见含CO_2包裹体、纯CO_2包裹体和液相包裹体,有时可见含CO_2包裹体与液相包裹体共存。流体包裹体显微测温结果表明,成矿流体可近似看做中温、低盐度、富CO_2的NaCl-H_2O-CO_2体系,纯CO_2包裹体和液相包裹体所代表的流体可能是由含CO_2包裹体所代表的Na Cl-H_2O-CO_2流体经不混溶形成的,三者在寄主矿物沉淀时,被同时捕获而共存。从第Ⅰ阶段到第Ⅳ阶段,成矿流体温度从303~379℃逐渐降低到138~195℃,盐度w(Na Cleq)从4.07%~9.59%逐渐降低到1.06%~2.74%。在成矿的第Ⅰ阶段成矿流体发生了不混溶作用,而在第Ⅱ阶段和第Ⅲ阶段流体中的CO_2起泡分离再次引发了不混溶作用。从第Ⅰ阶段到第Ⅲ阶段,成矿流体的δ18OH_2O从6.56‰~9.71‰经1.89‰~4.01‰变化到0.08‰,δDH_2O从-78.1‰~-64.2‰经-79.5‰~-76.3‰变化到-72.6‰,表明老湾金矿第Ⅰ阶段成矿流体主要为岩浆热液,第Ⅱ阶段成矿流体中有少量大气降水加入,第Ⅲ阶段成矿流体中大气降水的比例明显加大。     

广西田东县那矿金矿区地质与地球化学特征及找矿方向

广西田东县那矿金矿位于滇黔桂金三角,属于卡林型金矿。本文在对那矿金矿区进行1∶10000地质填图的基础上,基本上查明了其成矿地质背景,结合1∶10000土壤地球化学测量,选取Au、As、Sb三种元素为成矿指示元素。通过土壤地球化学数据分析,对矿区内指示元素异常的特征、分布与地质现象进行对比分析,进行异常解释评价。研究结果显示:那矿金矿区中三叠统百逢组中上部粉砂质泥岩、泥岩、泥质粉砂岩是赋矿层位;坡表谷背斜与坡表谷断裂的复合部位为成矿有利部位;硅化、(褐)黄铁矿化、毒砂矿化、高岭石化、绢云母化、碳酸盐岩化等蚀变为金的矿化标志;圈定的Ⅰ号异常带是矿致异常,其Au元素异常规模大、品位高,是该区找矿的重点靶区。     

Incorporation of a dynamic root distribution into CLM4.5: Evaluation of carbon and water fluxes over the Amazon

Roots are responsible for the uptake of water and nutrients by plants and have the plasticity to dynamically respond to different environmental conditions. However, most land surface models currently prescribe rooting profiles as a function only of vegetation type, with no consideration of the surroundings. In this study, a dynamic rooting scheme, which describes root growth as a compromise between water and nitrogen availability, was incorporated into CLM4.5 with carbon–nitrogen(CN) interactions(CLM4.5-CN) to investigate the effects of a dynamic root distribution on eco-hydrological modeling. Two paired numerical simulations were conducted for the Tapajos National Forest km83(BRSa3) site and the Amazon, one using CLM4.5-CN without the dynamic rooting scheme and the other including the proposed scheme. Simulations for the BRSa3 site showed that inclusion of the dynamic rooting scheme increased the amplitudes and peak values of diurnal gross primary production(GPP) and latent heat flux(LE) for the dry season, and improved the carbon(C) and water cycle modeling by reducing the RMSE of GPP by 0.4 g C m~(-2)d~(-1), net ecosystem exchange by 1.96 g C m~(-2)d~(-1), LE by 5.0 W m~(-2), and soil moisture by 0.03 m~3m~(-3), at the seasonal scale, compared with eddy flux measurements, while having little impact during the wet season. For the Amazon, regional analysis also revealed that vegetation responses(including GPP and LE) to seasonal drought and the severe drought of 2005 were better captured with the dynamic rooting scheme incorporated.     

Trends of Regional Precipitation and Their Control Mechanisms during 1979–2013

Trends in precipitation are critical to water resources. Considerable uncertainty remains concerning the trends of regional precipitation in response to global warming and their controlling mechanisms. Here, we use an interannual difference method to derive trends of regional precipitation from GPCP(Global Precipitation Climatology Project) data and MERRA(ModernEra Retrospective Analysis for Research and Applications) reanalysis in the near-global domain of 60?S–60?N during a major global warming period of 1979–2013. We find that trends of regional annual precipitation are primarily driven by changes in the top 30% heavy precipitation events, which in turn are controlled by changes in precipitable water in response to global warming, i.e., by thermodynamic processes. Significant drying trends are found in most parts of the U.S. and eastern Canada,the Middle East, and eastern South America, while significant increases in precipitation occur in northern Australia, southern Africa, western India and western China. In addition, as the climate warms there are extensive enhancements and expansions of the three major tropical precipitation centers–the Maritime Continent, Central America, and tropical Africa–leading to the observed widening of Hadley cells and a significant strengthening of the global hydrological cycle.     

Spatially explicit assessment of water embodied in European trade: A product-level multi-regional input-output analysis

Responsible water management in an era of globalised supply chains needs to consider both local and regional water balances and international trade. In this paper, we assess the water footprints of total final demand in the EU-27 at a very detailed product level and spatial scale—an important step towards informed water policy. We apply the multi-regional input-output (MRIO) model EXIOBASE, including water data, to track the distribution of water use along product supply chains within and across countries. This enables the first spatially-explicit MRIO analysis of water embodied in Europe’s external trade for almost 11,000 watersheds world-wide, tracing indirect (“virtual”) water consumption in one country back to those watersheds where the water was actually extracted. We show that the EU-27 indirectly imports large quantities of blue and green water via international trade of products, most notably processed crop products, and these imports far exceed the water used from domestic sources. The Indus, Danube and Mississippi watersheds are the largest individual contributors to the EU-27’s final water consumption, which causes large environmental impacts due to water scarcity in both the Indus and Mississippi watersheds. We conclude by sketching out policy options to ensure that sustainable water management within and outside European borders is not compromised by European consumption.     

Multi-model assessment of global hydropower and cooling water discharge potential under climate change

Worldwide, 98% of total electricity is currently produced by thermoelectric power and hydropower. Climate change is expected to directly impact electricity supply, in terms of both water availability for hydropower generation and cooling water usage for thermoelectric power. Improved understanding of how climate change may impact the availability and temperature of water resources is therefore of major importance. Here we use a multi-model ensemble to show the potential impacts of climate change on global hydropower and cooling water discharge potential. For the first time, combined projections of streamflow and water temperature were produced with three global hydrological models (GHMs) to account for uncertainties in the structure and parametrization of these GHMs in both water availability and water temperature. The GHMs were forced with bias-corrected output of five general circulation models (GCMs) for both the lowest and highest representative concentration pathways (RCP2.6 and RCP8.5). The ensemble projections of streamflow and water temperature were then used to quantify impacts on gross hydropower potential and cooling water discharge capacity of rivers worldwide. We show that global gross hydropower potential is expected to increase between +2.4% (GCM-GHM ensemble mean for RCP 2.6) and +6.3% (RCP 8.5) for the 2080s compared to 1971–2000. The strongest increases in hydropower potential are expected for Central Africa, India, central Asia and the northern high-latitudes, with 18–33% of the world population living in these areas by the 2080s. Global mean cooling water discharge capacity is projected to decrease by 4.5-15% (2080s). The largest reductions are found for the United States, Europe, eastern Asia, and southern parts of South America, Africa and Australia, where strong water temperature increases are projected combined with reductions in mean annual streamflow. These regions are expected to affect 11–14% (for RCP2.6 and the shared socio-economic pathway (SSP)1, SSP2, SSP4) and 41–51% (RCP8.5–SSP3, SSP5) of the world population by the 2080s.     

淮河流域夏季降水异常与若干气候因子的关系

基于旋转经验正交函数分解 (REOF) 方法探讨淮河流域1961—2010年夏季降水与厄尔尼诺/南方涛动 (ENSO)、北大西洋涛动 (NAO)、印度洋偶极子 (IOD)、太平洋年代际振荡 (PDO) 之间的关系,并进一步分析各气候因子不同位相单独以及联合对淮河流域夏季降水的影响。结果表明:淮河流域夏季降水与ENSO,PDO,NAO,IOD等气候因子具有较稳定的相关性,其中,PDO和IOD是影响淮河流域夏季降水的关键因子,且PDO与夏季降水呈显著负相关关系;各气候因子的冷暖位相单独及联合对淮河流域夏季降水的影响不同,PDO的冷期以及NAO,IOD冷位相使流域北部的夏季降水量呈显著增加趋势,PDO分别联合ENSO,NAO和IOD的冷、暖位相对流域北部地区和淮河上游地区的夏季降水影响显著。     

IEC的风机选型参数估算方法在中国的适用性研究

国际电工委员会编制的《风力发电机组设计要求》(IEC 61400-1)推荐了针对风电机组安全等级评估的极端风速和湍流强度特征值估算方法,因其简单便捷,在风电领域被广泛采用。利用全国风能资源专业观测网的193座测风塔观测数据,对IEC推荐的极端风速计算方法与我国规范推荐的基于极值I型概率分布方法进行比较,发现两种方法计算的193座塔70 m高度层50年一遇10 min平均最大风速,仅有7座测风塔较为一致,差异在±1%;IEC推荐方法的计算结果多数偏小,其中偏小10%以上的测风塔有121座,偏小30%以上的有44座测风塔,而偏大10%以上的只有9座测风塔;IEC方法计算的极值风速大幅度偏小的测风塔主要分布在台风影响的东南沿海地区,偏差较小的测风塔主要分布在西北和华北地形平缓区域,但同时偏大10%以上的测风塔也多分布在这一地区。以目前行业领域普遍采用的以15 m·s~(-1)风速的平均湍流强度作为风电机组选型指标,与严格按照规范,以15 m·s~(-1)风速段所有样本湍流强度的90%分位数处的值作为指标进行风电机组等级确定作对比,发现193座塔中有46座塔的选型是不安全的,甚至相差两个等级。     

西藏夏季降水的季节内变化特征及其影响系统

利用西藏地区1980-2013年夏季降水量资料、NCEP再分析资料等,分析了西藏地区夏季降水主模态季节内变化特征,尤其是盛夏7和8月降水异常对应的大尺度环流特征和影响系统。结果表明:西藏夏季降水存在明显的季节内变化,6和7月降水主模态的时间系数变化具有较好的持续性,而7和8月降水主模态的时间系数的相关关系明显减弱。西藏地区7和8月降水偏多年,西藏地区上游低层纬向风场均呈西风异常,但是水汽来源有差异;同时欧亚中高纬地区对流层中高层环流存在显著差异。西藏7月降水与南亚高压强度存在显著负相关关系,南亚高压偏强/弱时,降水偏少/多。西藏8月降水与南亚高压的位置关系更密切,南亚高压偏南/北,降水偏多/少。