略阳煎茶岭铜镍硫化物矿床Re—Os同位素年龄及其地质意义

采用矿石Re-Os同位素方法对陕西省煎茶岭硫化镍矿床矿石进行了成矿年代学研究,获得了878士27 Ma(1σ)的等时线年龄,首次厘定了该矿床成矿时代为新元古代,成岩成矿基本同时.通过对878 Ma硫化镍矿石初始Re-Os同位素体系的γOs计算和Re/Os值分析表明,其yOs和Re/Os值变化范围大,深部条带状矿石的Re/Os值仅为0.05,yOs为-6.70;块状矿石的Re/Os值范围为4.24～24.43,γOs为-15.37～+280.65,说明成矿过程中有壳源物质的混染;两件样品的γOs为负值(-15.37,-6.70),可能指示其超镁铁质岩浆来源于Re亏损地幔.煎茶岭超基性岩体年龄及其镍矿石的Re-Os等时线年龄与扬子克拉通北缘火山岩浆活动时间相对应,它们是扬子克拉通西北缘晋宁期构造岩浆成矿作用的产物.     

An Early-Cambrian UPb apatite cooling age for the high-temperature regional metamorphism in the Piancó area,Borborema Province (NE Brazil): initial conclusions

The Borborema Province (BP) of northeastern Brazil is a complex crustal assemblage, which has undergone a polycyclic evolution during the Proterozoic. In the Piancó-Alto Br??gida belt, a metamorphosed leucosome vein inserted in amphibolites has a trace element pattern suggesting a T-MORB protolith. Apatites yield a REE pattern indicating growth in equilibrium with garnet, thus pointing to its metamorphic origin. UPb analyses yield an age of 540±5 Ma interpreted as a cooling age following amphibolite facies regional metamorphism associated with granitic emplacement at ca. 580 Ma. The resulting slow cooling rates (ranging from ca. 2.5 to 5 °C Ma^?1) are consistent with underplating of mafic magmas, or crustal thickening caused by nappe stacking, as possible processes governing the metamorphic evolution of the BP. To cite this article: B. Dhuime et al., C. R. Geoscience 335 (2003).     

湖南黄金洞金矿毒砂中Au赋存状态的电子探针研究

本文利用ＪＸＡ－８８００Ｍ超大型电子探针，以湖南黄金洞金矿含金毒砂为研究对象。利用金特征Ｘ－射线扫描方法和微区含金含量，对不可见金赋存状态的研究方法和温试条件进行了探索，先观察背散射电子图像，排除金在含金矿物毒砂中呈显显微颗粒存在的可能性，继而用ＬｉＦ晶体测定金Ｌ＝８８．７６Ｌａｌ峰位，然后逐渐放大倍数（ｘ３００，ｘ１０００，ｘ５０００，ｘ３００００，ｘ２０００００）进行金特征，Ｘ－射线连续测量，，结果发现金元素总 是均匀分布在重砂中，从而证实了金呈品格金形式存在的推测。     

柿竹园钨多金属矿床的Re-0s同位素等时线年龄研究

柿竹园钨多金属矿床产于千里山复式岩体与泥盆系碳酸盐岩的接触部位。其成矿时代以往都是用矿体附近的花岗岩体年龄来间接推断。我们最近采用辉钼矿的Re-Os等时线定年法直接测定了与千里山第一期花岗岩有关的夕卡岩型矿体的矿化年龄为151.0±3.5Ma。该年龄晚于第一期花岗岩,但早于第二期花岗岩,从而证实了钨多金属矿化在花岗岩系列的早期早阶段也可以成矿。该年龄与野外观察的地质情况十分吻合,而辉钼矿是热液矿床中的常见矿物,说明这种测年方法是一种研究热液矿床成矿时代及其成因的重要手段。     

萨拉乌苏组沉积时代的重新厘定

重新认识我国北方地区晚更新世河湖相标准地层--萨拉乌苏组的形成时代，对于萨拉乌苏组与马兰黄土的关系，与冰期气候对比等具有重要意义。笔者近年来根据野外层位对比和地层沉积相的划分，采用绝对年代控制，并结合黄土－古土壤序列研究的最新成果，初步建立了可以与黄土、深海沉积记录和冰期气候波动对比的萨拉乌苏组地层序列。认为河湖相沉积的萨拉乌苏组形成于约１４００００～７００００ａ.Ｂ.Ｐ.的末次间冰期，大致与深海氧同位素第５阶段对应，与黄土高原古土壤Ｓ１发育同期。城川组风成细砂形成于约７００００～１００００ａ.Ｂ.Ｐ的末次冰期，与黄土高原的马兰黄土是同期异相地质体.     

Mineralization Ages of the Jiapigou Gold Deposits,Jilin

The Jiapigou gold deposits are typical vein type deposits associated withArchaean greenstone belts in China. According to the crosscutting relationships between dykesand auriferous veins, single hydrothermal zircon U-Pb dating and quartz K-Ar,~(40)Ar-~(39)Ar andRb-Sr datings, the main mineralization stage of the Jiapigou deposit has been determined to be2469-2475 Ma, while mineralization superimposition on the gold deposit occurred in1800-2000 Ma and 130-272 Ma. They form a mineralization framework of one oldermetallogenic epoch (Late Archaean-Early Proterozoic) and one younger metallogenic epoch(Mesozoic) of gold deposits in Archaean greenstone belts in China.     

Timing and geochemical characters of the Sanchazi magmatic arc in Mianlüe tectonic zone, South Qinling

The Sanchazi mafic-ultramafic complex in Mianlue tectonic zone, South Qinling can be subdivided into two blocks, i.e. Sanchazi paleo-magmatic arc and Zhuangkegou paleo-oceanic crust fragment (ophiolite). The Sanchazi paleo-magmatic arc is mainly composed of andesite, basaltic and basalt-andesitic gabbro (or diorite), andesitic dyke, plagiogranite and minor ultramafic rocks, which have typical geochemical features of island arc volcanic rocks, such as high field strength element (e.g. Nb, Ti) depletions and lower Cr, Ni contents. The Light rare earth element (LREE) and K enrichments of these rocks and zircon xenocrystals of 900 Ma from plagiogranite suggest that this magmatic arc was developed on the South active continental margin of the South Qinling micro-continent. The U-Pb age of (300 ± 61)Ma for zircons from plagiogranite indicates that the Mianlue paleo-oceanic crust was probably subducted underneath the South Qinling micro-continent in Carboniferous. This is consistent with the formation time (309Ma) of the Huwan eclogite originating from oceanic subduction in Dabie Mountains, suggesting that the Mianlue paleo-ocean probably extended eastward to the Dabie Mountains in Carboniferous. The high-Mg adakitic rocks in Sanchazi paleo-magmatic arc suggest that the subducted oceanic crust was relatively young (＜25Ma) and hot.     

中国新疆博斯腾湖全新世沉积环境年代学特征

通过对博斯腾湖沉积物湖芯样品进行137Cs,14C-AMS测年分析,湖芯剖面上有明显的1986年的切尔诺贝利核事故蓄积峰,以及1975年和1963年次蓄积峰,这些137Cs蓄积峰对博斯腾湖现代沉积有明显的时标意义。通过质量深度与年代分析,博斯腾湖的沉积速率相对稳定,平均沉积速率为0.13±0.01g/cm2.a。与14C年代获得的中全新世以来的平均沉积速率0.13±0.03cm/a和0.12±0.05cm/a相似,表明博斯腾湖中全新世以来的沉积环境较稳定,并且也说明14C-AMS测年分析所得的结果较为可靠,可以利用博斯腾湖沉积物样品测定的14C年代进行线性回归作年代校正,由于湖泊沉积物中老碳效应的影响,博斯腾湖沉积物有机质14C测年偏老约650a左右。