| Qaidam suture zone is an important gold silver and lead-zinc polymetallic metallogenic belt in China.In this belt,a large SEDEX zinc deposit in Xitieshan and some large-scale orogenic gold deposits have been discovered in Tan Jian Shan.The traditional geochemical anomaly map reflects the "high,large and complete" geochemical anamalies in these deposits.However,the southeast area of Shangkoushan,which caught in the middle of Xitieshan and Tanjianshan with the complex geological conditions,is a typical desert-gobi landscape area,and eolian sand is well developed,causing a serious disruption to the prospecting work.The geochemical anomalies in this area are often small and weak,as a result,the prospecting work has not made a great breakthrough.At the same time,part of the area is too difficult to check the anomalies because of the oversized abnormal area.How to find the abnormal area related to mineralization under the complicated geological conditions and the special geological landscapes in the northern margin of Qaidam Basin,analysis the metallogenic potential of the low background field and small weak abnormal area,and find some favorable metallogenic target area in the condition of absence of the traditional " high,large and complete " abnormal area is the focus of this paper.Firstly,this article newly respectively adopts a content-area method(C-A method)based on fractal(multifractal)theory and energy density-area method(S-A method)for some single element anomaly,which compared with the results of the traditional geochemical data processing methods,and finds that the anomalous thresholds of the C-A model are usually divided into high threshold and low threshold.Among them,the low threshold is a smaller value and so the abnormal area is the larger,which is not conducive to check anomalies and reduce the workload,while,the high threshold value can contain most deposits and the abnormal area is small,which is conducive to anomaly inspection.Then,the article use the element correlation analysis,the classic principal component analysis(PCA),the robust principal component analysis(RPCA)with the ILR transform,the classical factor analysis(FA),and the robust factor analysis(RFA)with the CLR transform to find out the combinations of elements.We find that logarithmic ratio(CLR,ILR)compared with the traditional transform method(log transform)can effectively open the data affected by the closure effect;the robust analysis method compared to the classical methods can suppress the effect of outliers.We can get two major groups of elements: Au,Ag,Pb,Sb,Hg and Cu,Zn,Cr,Co,Ni through the RFA,representing the epithermal Au-Ag-Pb combination,the Cr-Ni combination related to the mafic and ultramafic rocks and the Cu-Zn-Co combination related to VMS deposits.Finally,the combination anomaly is calculated based on factor loading and the target area is delineated,and then the relationship between the mineralized spot or the actual mine is verified and compared.Based on these,we can evaluate and contrast the rationality of combination anomaly and metallogenic potential,eventually provide guidance and reference for further exploration in the similar areas of the northern margin of Qaidam basin. |
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