Trace element and REE geochemistry of the Zhewang gold deposit,southeastern Guizhou Province,China

The quartz vein-type gold deposits are widely hosted by the Neoproterozoic （Xiajiang Group） epimeta- morphic clastic rock series in southeastern Guizhou Province, China. The Zhewang gold deposit studied in this paper occurs in the second lithologieal member of the Pinglue Formation of the Xiajiang Group. Trace element geochemis- try of host rocks, quartz veins and arsenopyrite has revealed that ore-forming fluid was enriched in sulphophile ele- ments such as Au, Ag, As, Sb, Pb and Zn, and simultaneously concentrated some magmaphile elements such as W and Mo, which probably provides some evidence for multi-stage mineralization or overprinting of magmatic hydro- therm. Quartz veins and arsenopyrite were characterized by depletion in HFSE and enrichment in LREE. Hf/Sm, Nb/La and Th/La imply that the ore-forming fluid was probably a NaC1-H20 solution system enriched in more C1 than F; Th/U values reflect the strong reducibility of the ore-forming fluid, coincident with the sulfide assemblages. The values of Co/Ni reflect that magmatic fluids may have partly participated in the ore-forming process and Y/Ho values have proved that the ore-forming fluid was associated with metamorphism and exotic hydrotherm which has reformed former quartz veins during late mineralization. The concentrations of REE, Eu anomalies and Ce anomalies of this deposit display that ore-forming elements mainly were derived from host rocks and possibly from a mixed deep source, and the ore-forming fluid was mixed by dominant metamorphic fluid and minor other sources. The physical-chemical conditions of ore-forming fluid changed from the initial stage to the late stage. The metamorphic fluid is responsible for the mineralization. Therefore, the Zhewang gold deposit is classified as a quartz vein-type gold deposit which may have been reformed by magmatic fluids during the late stage.     

川滇黔相邻区碳酸盐岩容矿铅锌矿成矿特征

本文对川滇黔相邻区碳酸盐岩容矿铅锌矿成矿特征进行系统总结,并对区域成矿过程进行讨论。该区碳酸盐岩容矿铅锌矿发育3种矿床类型,主要分布在泸定-荥经-汉源、雷波-金阳-巧家-会东、赫章-威宁-水城和会泽-彝良4个矿集区,震旦系和古生代地层为主要容矿层。铅锌矿形成于3个成矿期和3类构造环境:以黑区-雪区铅锌矿床为代表的喷流沉积型(SEDEX型),形成于早寒武世海底地震同生断裂环境;以会泽矿床为代表的与侵入作用有关的碳酸盐岩容矿铅锌银矿床类型(IRCH Pb-Zn-Ag型),形成于晚三叠世前陆早期局部引张环境;以大梁子和天桥矿床为代表的密西西比河谷型(MVT型),形成于前陆晚期冲断挤压环境。与世界其它地方不同,川滇黔相邻区MVT铅锌成矿作用主要发生于早侏罗世。     

滑坡危险性预测模型的设计与实现

滑坡灾害的发生严重影响人类社会的生产生活,因此对滑坡灾害的预警预测工作一直是地质灾害监测和防治的重点,国内外众多学者都对此进行了相应研究。本文在前人的研究基础上把信息量模型和降雨诱发指数应用在滑坡预测研究中,充分考虑两者的耦合影响,建立了滑坡危险性预测模型,并完成了模型的开发工作。该模型实现了滑坡灾害危险性预测的快速化、自动化,并且已集成到江西省地质灾害预警预报分析决策系统中,得到了成功应用。     

兰州倾斜固体潮潮汐参数的观测研究

本文介绍了兰州形变台FSQ—水管倾斜仪1987—1989年期间观测资料的调和分析结果,讨论了潮汐因子的重复性及其对非潮汐变化的监测能力,分析了气象因素对周日波的影响,並将实测潮汐因子与G—B地球模型理论值进行了比较。     

点分布-双蛇模型用于矢量边界更新

在利用遥感影像更新GIS矢量数据的过程中,往往忽略了对已知信息的有效利用,针对这一问题,本文提出一种基于点分布的双蛇模型用于GIS矢量数据更新,该模型利用已有遥感影像信息计算目标边界点的平均分布,以此为"镜面"建立初始矢量边界的"镜像",将两边界各自演化的结果取平均作为更新后的GIS矢量边界。该方法同时利用了GIS和遥感的历史数据作为先验知识,分别作为蛇模型的初始位置和区域约束信息,使遥感与GIS信息结合更加紧密。仿真实验表明,基于点分布的双蛇模型在GIS矢量边界更新的应用中,可以得到比以传统蛇模型更好的更新准确率和多边形相似度,并且接近手工方法的效果。     

东昆仑造山带低山头花岗岩体岩石地球化学特征及其地质意义

低山头一带花岗岩体归属东昆仑弧盆系北昆仑岩浆弧带,位于东昆仑成矿带伯喀里克—香日德成矿亚带东昆仑造山带中段,岩石类型主要为石英闪长岩、正长花岗岩及二长花岗岩。为了加强该地区花岗岩体岩石地球化学与成岩成矿背景探讨,对花岗岩体开展了主量元素、微量元素及矿质元素研究。主量元素组成上,石英闪长岩具中硅（57.64%和58.47%）、富钠（Na₂O/K₂O均为2.57）特点,正长花岗岩具高硅（75.45%~75.99%）、富钾（Na₂O/K₂O为0.74~0.94）特点,二长花岗岩具高硅（66.80%~73.45%）、富钠（Na₂O/K₂O为1.50~2.13）特点;花岗岩体铝饱和指数A/CNK<1,为准铝质岩浆岩;碱饱和指数NK/A集中在0.26~0.69之间,属钙碱性岩石;里特曼组合指数σ₄₃在1.18~2.31之间,属钙碱性类型。花岗岩体轻稀土元素相对重稀土元素富集,岩浆分异特征明显,大离子亲石元素（LILE）富集Rb、K、Ba、Th、Sr、Nd,仅正长花岗岩Sr亏损,高场强元素（HFSE）富集Zr、Hf、Ce,而Nb、P、Ti明显亏损,源区物质为壳幔混合物质,属挤压应力环境中同碰撞I型花岗岩。在岩体实测剖面中获得11种元素分析数据,与青海全省、东昆仑成矿带及其亚成矿带平均元素丰度值进行对比,初步划分不同岩性、不同类型、不同时代花岗岩,以及富集的含矿元素为Au、Zn、Y、Pb等。与区域有成矿事实且为I型花岗岩成因进行对比,认为研究区有较好的找矿前景。     

Random wave-current interactions in water of varying depth

Refraction of incoherent random gravity waves with currents and bottom topography results in spatial variations in the spectral characteristics of the free surface. Prediction of such variations based on the radiation transfer equation is in a simple analytic form for the case of one dimensional inhomogeneities in currents and topography. This analytic form is examined in terms of two-dimensional wave number- and polar frequency-direction spectra along the associated dynamic and kinematic constraints relevant to wave breaking and reflection. Results are specialized to the simplest case of horizontal shear currents in deep and shallow water with explicit examples to illustrate the relative and combined effects of currents and topography on free surface spectra.     

Assessment of the Pacific decadal oscillation’s contribution to the occurrence of local torrential rainfall in north China

On 21–22 July 2012, torrential rains hit North China, with the daily precipitation record at Beijing station reaching 160.6 mm; this event is named the Beijing 7–21 case. This paper assesses the likelihood of the occurrence of local torrential rains, such as the Beijing 7–21 case, from the perspective of climate variability. In particular, the influence of the Pacific Decadal Oscillation (PDO) is assessed. There were five extreme events, with daily precipitation records equal to or larger than 160.6 mm, at Beijing station during the period 1951–2012; all of these events happened during negative phases of the PDO. The present analysis indicates that precipitation events more extreme than the Beijing 7–21 case should happen more than once per decade during negative phases of the PDO, but only about once every four decades during positive PDO phases. The negative phase of the PDO is found to be associated with a much greater probability of daily records of southerly winds in North China during summer. Strong southerly summer monsoons are deemed favorable for increasing the occurrence of local extreme rainfall over North China.