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西藏羊八井—青龙地区水系沉积物元素背景值及分布特征

The Background Values and Distribution Characteristics of Stream Sediments in the Yangbajain-Qinglong Region, Tibet

  • 摘要: 水系沉积物中化学元素的背景值是地球化学找矿工作中不可缺少的基础资料,对区域地球化学异常评价具有重要意义。西藏地区一直缺少以区内微景观区表层物质为基础建立的多元素背景值数据,在一定程度上限制了对已有水系沉积物异常的认识水平。本文分析了羊八井—青龙地区约12000 km2内2800件水系沉积物组合样品中69个元素背景值及分布特征。统计分析结果表明:与全国水系沉积物和中国南方地区水系沉积物平均值相比,研究区自北向南分布的班戈—八宿、隆格尔—南木林、拉萨—察隅三个地球化学分区内SiO2的含量普遍较高(68.6%~77.0%),SiO2高含量与区内强烈的风化剥蚀作用及中酸性岩体的大面积产出有关。其他元素的含量普遍偏低,且各分区内有一定的差异性:北部班戈—八宿分区以富集与高温热液或气液有关的Li、Sr、B、N、Cl元素为特征,中部隆格尔—南木林分区以富集铁族元素、稀有元素(Zr)、稀土元素(Sc)为特征,南部拉萨—察隅分区以富集造岩、轻稀土、稀有、分散元素及亲铜成矿元素为特征。元素含量分布的差异与各区地层、岩体、矿床和矿化点密切相关。本次研究提供了羊八井—青龙地区水系沉积物中69个元素背景值,如亲铜成矿元素Au、Ag、Cu、Pb、Zn的背景值分别为0.26 ng/g、41 ng/g、4.04 μg/g、25.2 μg/g和25.6 μg/g,这些背景值的提出弥补了该微景观区化学元素背景值的空白,为羊八井—青龙地区及其邻区区域地质研究及勘查找矿工作提供了参考依据。

     

    Abstract: The background values of chemical elements in stream sediments are an indispensable tool in geochemical prospecting work, and they are of important significance for regional geochemical anomalies assessment. However, there is a lack of poly-elements background values in Tibet, which are based on the surface material from the micro landscape area thereby limiting understanding of the existing stream sediment anomalies to a certain extent. Analysis of the chemical elements background values and distribution characteristics of 69 kinds of elements in 2800 stream sediment combination samples covering about 12000 km2 in Yangbajain-Qinglong area have been conducted and are reported in this paper. From north to south, the area is divided into three geochemical divisions of Bangor-Basu, Longer-Nanmulin and Lhasa-Zayu. The results indicate that content of SiO2 (68.6%-77.0%) in the study area is higher compared to the average value of stream sediments nationwide. The high content of SiO2 is related to strong weathering and occurrence of large-scale intermediate-acid intrusive rocks in the study area. While other elements are lower and differentiated in three geochemical divisions. Bangor-Basu division is characterized by enrichment of Li, Sr, B, N and Cl which are related to high-temperature hydrothermal or gas-liquid. Longer-Nanmulin division is enriched with iron group elements, rare element (Zr) and rare earth element (Sc). Lhasa-Zayu division is enriched with petrogenetic elements, light rare earth elements, rare elements, dispersed elements and chalcophile metallogenic elements. The differences in element content distribution are closely related with the stratum, rock mass, deposits and mineralization in the geochemical divisions. This study gives the background values for 69 kinds of elements in the Yangbajin-Qinglong area, such as the chalcophile metallogenic elements of Au, Ag, Cu, Pb and Zn with 0.26 ng/g, 41 ng/g, 4.04 μg/g, 25.2 μg/g and 25.6 μg/g, respectively. These data fill a vacancy in the chemical elements background values on the micro-landscape areas of Tibet, and provide references for regional exploration study and geological prospecting work in Yangbajain-Qinglong and adjacent areas.

     

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