Genesis of the Changba–Lijiagou Giant Pb-Zn Deposit, West Qinling, Central China: Constraints from S-Pb-C-O isotopes

The extensive Changba-Lijiagou Pb-Zn deposit is located in the north of the Xihe–Chengxian ore cluster in West Qinling. The ore bodies are mainly hosted in the marble, dolomitic marble and biotite-calcite-quartz schist of the Middle Devonian Anjiacha Formation, and are structurally controlled by the fault and anticline. The ore-forming process can be divided into three main stages, based on field geological features and mineral assemblages. The mineral assemblages of hydrothermal stage I are pale-yellow coarse grain, low Fe sphalerite, pyrite with pits, barite and biotite. The mineral assemblages of hydrothermal stage II are black-brown cryptocrystalline, high Fe shalerite, pyrite without pits, marcasite or arsenopyrite replace the pyrite with pits, K-feldspar. The features of hydrothermal stage III are calcite-quartz-sulfide vein cutting the laminated, banded ore body. Forty-two sulfur isotope analyses, twenty-five lead isotope analyses and nineteen carbon and oxygen isotope analyses were determined on sphalerite, pyrite, galena and calcite. The δ34 S values of stage I(20.3 to 29.0‰) are consistent with the δ34 S of sulfate(barite) in the stratum. Combined with geological feature, inclusion characteristics and EPMA data, we propose that TSR has played a key role in the formation of the sulfides in stage I. The δ34 S values of stage II sphalerite and pyrite(15.1 to 23.0‰) are between sulfides in the host rock, magmatic sulfur and the sulfate(barite) in the stratum. This result suggests that multiple S reservoirs were the sources for S2-in stage II. The δ34 S values of stage III(13.1 to 22‰) combined with the structure of the geological and mineral features suggest a magmatic hydrothermal origin of the mineralization. The lead isotope compositions of the sulfides have 206 Pb/204 Pb ranging from 17.9480 to 17.9782, 207 Pb/204 Pb ranging from 15.611 to 15.622, and 208 Pb/204 Pb ranging from 38.1368 to 38.1691 in the three ore-forming stages. The narrow and symmetric distributions of the lead isotope values reflect homogenization of granite and mantle sources before the Pb-Zn mineralization. The δ13 CPDB and δ18 OSMOW values of stage I range from-0.1 to 2.4‰ and from 18.8 to 21.7‰. The values and inclusion data indicate that the source of fluids in stage I was the dissolution of marine carbonate. The δ13 CPDB and δ18 OSMOW values of stage II range from-4 to 1‰ and from 12.3 to 20.3‰, suggesting multiple C-O reservoirs in the Changba deposit and the addition of mantle-source fluid to the system. The values in stage III are-3.1‰ and 19.7‰, respectively. We infer that the process of mineralization involved evaporitic salt and sedimentary organic-bearing units interacting through thermochemical sulfate reduction through the isotopic, mineralogy and inclusion evidences. Subsequently, the geology feature, mineral assemblages, EPMA data and isotopic values support the conclusion that the ore-forming hydrothermal fluids were mixed with magmatic hydrothermal fluids and forming the massive dark sphalerite, then yielding the calcite-quartz-sulfide vein ore type at the last stage. The genesis of this ore deposit was epigenetic rather than the previously-proposed sedimentary-exhalative(SEDEX) type.     

寒区和干旱区水文研究的回顾和展望

寒区和干旱区水文研究冰川,积雪,冻土,高寒山区和山前地带已初步形成了较完整的观测实验和研究体系,８０年代以来,在冰川融水径流,出山径流形成的观测实验,寒区水文过程,冰川作用流域水文过程和大气过程相互关系。乌鲁木齐地区的水资源问题,气候对水资源的影响,高亚洲冰冻圈水文,冰川洪水和融雪径流以及干旱区水文等方面已取得了多项研究成果,近年来,寒区和干旱区水文水资源的研究在内陆河流域水资源合理开发利用与社会     

北祁连熬油沟蛇绿岩岩石成因的地球化学证据

螯油沟蛇绿岩位于甘肃南南县祁青乡。其地质－地球化学特征表明：蚀变作用形成的蛇纹岩,原岩为方辉橄榄岩,所有的岩石类型均以相对富集轻稀土和大离子亲石元素为特征,并且玄武质熔岩显示出幔柱型大洋中脊玄武岩的地球化学特征,说明岩浆来源于与洋岛玄武岩源相似的富集地幔。     

北祁连山西段早元古代变质火山岩的地球化学特征及其构造背景

产于北大河群的早元古代火山岩是北祁连山西段最主要的三期火山岩之一,其地球化学特征表明,该期火山岩的原岩为具有双峰式组合的拉斑玄武岩和中酸笥凝灰岩。两者具有完全不同的稀土分布型式,前者以极低的富集轻稀土为特征,而后者以强烈富集轻稀土的特征;基性火山岩的微量元素分布曲线指示了其形成了裂陷槽环境。结合Ｎｄ同位素特征以及区域２得出本区早元古代变质火山岩形成于裂陷槽环境。     

中尺度对流复合体的热力学特征分析

用合成分析方法探讨ＭＣＣ热力学结构的演变规律,结果表明：ＭＣＣ整个生命史里,对流层中下部为正涡度区,２００ｈＰａ以上为负涡度区;发展时刻辐合区突然抬升;ＭＣＣ前期的垂直上升速度最大中心高度低于后期的;ＭＣＣ的高低空的冷心、中层暖心的温度结构在成熟期以后不明显     

一种锁相环调频方法在铷原子频标中的应用

为了进一步实现铷原子频标小型化,分析了几种典型的锁相环调频电路及其特点,设计了一种锁相环二进制移频键控2FSK(binary frequency shift keying)调频方案,给出了调频信号的频谱测试结果。该调频方案已成功地应用在小型化数字式铷原子频标中,能够满足小型化铷原子频标的要求。     

Ex situ echo sounder target strengths of ice krill Euphausia crystallorophias

Ice krill is the keystone species in the neritic ecosystem in the Southern Ocean,where it replaces the more oceanic Antarctic krill. It is essential to understand the variation of target strength(TS in d B re 1 m 2) with the different body size to accurately estimate ice krill stocks. However,there is comparatively little knowledge of the acoustic backscatter of ice krill. The TS of individual,formalin-preserved,tethered ice krill was measured in a freshwater test tank at 38,120,and 200 k Hz with a calibrated split-beam echo sounder system. Mean TS was obtained from 21 individual ice krill with a broad range of body lengths(L :13–36 mm). The length( L,mm) to wet weight( W; mg) relationship for ice krill was W =0.001 218×103 × L 3.53( R 2= 0.96). The mean TS-to-length relationship were TS3 8 k Hz =-177.4+57log 10( L),( R 2 = 0.86); TS 120 k Hz =-129.9+31.56 log 10( L),( R 2 =0.87); and TS 200 k Hz =-117.6+24.66log1 0( L),( R 2 =0.84). Empirical estimates of the relationship between the TS and body length of ice krill were established at 38,120,and 200 k Hz and compared with predictions obtained from both the linear regression model of Greene et al.(1991) and the Stochastic Distorted Wave Born Approximation(SDWBA) model. This result might be applied to improve acoustic detection and density estimation of ice krill in the Southern Ocean. Further comparative studies are needed with in situ target strength including various body lengths of ice krill.     

Molecular markers for identifying a new selected variety of Pacific white shrimp Litopenaeus vannamei

Selective breeding of the Pacific white shrimp Litopenaeus vannamei during the last decade has produced new varieties exhibiting high growth rates and disease resistance.However,the identification of new varieties of shrimps from their phenotypic characters is difficult.This study introduces a new approach for identifying varieties of shrimps using molecular markers of microsatellites and mitochondrial control region sequences.The method was employed to identify a new selected variety,Kehai No.1(KH-1),from three representative stocks(control group):Zhengda;Tongwei;and a stock collected from Fujian Province,which is now cultured in mainland China.By pooled genotyping of KH-1 and the control group,five microsatellites showing differences between KH-1 and the control group were screened out.Individual genotyping data confirmed the results from pooled genotyping.The genotyping data for the five microsatellites were applied to the assignment analysis of the KH-1 group and the control group using the partial Bayesian assignment method in GENECLASS2.By sequencing the mitochondrial control regions of individuals from the KH-1 and control group,four haplotypes were observed in the KH-1 group,whereas14 haplotypes were obtained in the control group.By combining the microsatellite assignment analysis with mitochondrial control region analysis,the average accuracy of identification of individuals in the KH-1group and control group reached 89%.The five selected microsatellite loci and mitochondrial control region sequences were highly polymorphic and could be used to distinguish new selected varieties of L.vannamei from other populations cultured in China.     

基于相控地质统计学反演的薄储层岩性、物性预测

针对河流相储层厚度薄、纵向叠置严重、横向变化快、常规确定性反演方法受地震频带限制难以准确刻画的特点,尝试应用基于MCMC算法的地质统计学方法进行反演,以提高分辨率和储层预测精度,并全程应用成岩储集相控制建模,以便从储层地质学的角度加强模型约束,促进概念模型向定量模型的转化,建立合理的反映地下实际情况的油藏物性模型。具体实现方法是,首先利用对岩性识别敏感的测井曲线重构拟声阻抗曲线,再以声阻抗为中间变量,对岩性、物性参数空间变异性进行双重变差函数分析,最后基于MCMC算法实现了成岩储集相控制的地质统计学反演。得到的三维岩性、阻抗及孔隙度模型,其纵向分辨率为1ms,既可以很好地展现不同期次砂体的叠置关系、隔夹层的分布以及沉积旋回纵、横向演变规律,又可以实现物性变异方向沿河道砂体弯曲方向变化的趋势,同时可对地震资料的多解性进行有效限制。     

“陆态网络”Ⅱ期西部绝对重力测定结果分析

介绍了2013~2014中国大陆构造环境监测网络的基本情况及西部地区绝对重力观测的情况,并对观测结果进行分析。结果表明,成果稳定性良好,89.5%的成果观测精度优于±5.00μGal,能够满足"陆态网络"的技术要求。