| The geotecture of Wachangda area in Tibet is situated in the junction of Bangong Lake-Nu River belt(the north margin of Gangdise-Nyainqentanglha landmass)and Qiangtang-Sanjiang compound landmass,belonging to the eastern part of Tethys metallogenic belt,The 1?50,000 stream sediment survey will circle and determine the most favorable area,and summarize its geochemical characteristics combined with strata,magmatite,structure and other factors so as to provide strong evidence and prospecting direction for the next exploration work.The paper firstly introduces the geological background of the study area and makes a statistical analysis of the geochemical parameters of the stream sediments,such as the median,the arithmetic mean,the coefficient of variation and the enrichment coefficient.According to the data of the stream sediments,the elements with the coefficient of variation greater than 1 include Ag,As,Au,Cr,Ni,Pb,Sb,Sn and W,those elements beneficial to mineralization,which shows the nonuniform distribution,strong variability,large degree of dispersion and the possibility of enrichment of the elements in the study area.Through The contrastive research with the stream sediments in the five southwest provinces,the elements with enrichment coefficient greater than 2 include As,Co,Cr,Ni,Pb,Sb,Sn,Fe,Zn,especially Co,Cr,Ni,which the average value of the stream sediments is more than two times of that in the five southwest provinces,indicating that there is a certain secondary enrichment of these elements.In addition to Fe in the study area,the skewness and kurtosis values of other elements are larger,which indicate that they may be affected by the later geological effect,so that the content of them in the stream sediments does not obey the normal distribution.The method of this paper is to process geochemical data by the box-and-whisker plot and to calculate the anomalous lower limit at first,and then to confirm the anomalous values of mesozone and intrazone based on the actual situation and to complete 13 maps of single element anomaly by Mapgis.The most anomalous elements are Au,Pb,Co,Cr,Ni,Zn,and their anomalies are mainly represented in the anomalous values of outerzone,mesozone and intrazone;besides,the elements with greater intensity of anomaly are Co,Cr,Ni;and the difference of the rest elements' anomalies are notable,the anomaly dimensions of some elements are small.Analyzing the geochemical data of the stream sediments based on the multivariate statistical methods such as correlation analysis,cluster analysis and factor analysis,and the conclusions drawn from the three methods are consistent and the correctness of using the multivariate statistical methods is proved.In the study area,13 elements can be divided into four categories according to the correlation of their chemical activities:(1)Co,Cr,Ni,Fe,iron-group elements,the variance contribution rate is about 27%,which is the main metallogenic elements in the study area.(2)Pb,Zn,Ag,As,Cu,medium and low temperature hydrothermal metallogenic elements,the variance contribution rate is about 20%,which is the secondary metallogenic elements in the study area.(3)Au,Sb,high temperature hydrothermal metallogenic elements,the variance contribution rate is about 14%.(4)W,Sn,high temperature hydrothermal metallogenic elements,the variance contribution rate is about 13%.The combination and correlation of the elements can reflect the characteristics of their secondary enrichment.According to the geochemical exploration results,the geological background and other factors,there is presumably good metallogenic condition of chromite(AP-1?AP-2);There may exist ultrabasic rock and concealed rock at AP-3;In sand-slate of Sangduo group,tungsten-tin and zinc have the condition of forming the hydrothermal vein-like deposits(AP-5?AP-6);The limestone in Luo Dong melange has little metallogenic potential(AP-4);Around the contact belt of the ultrabasic rock and limestone,pay attention to the formation of magnesite. |
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