Remote Sensing Alteration Information Extraction And Metallogenic Prediction Of Typical Epithermal Deposit In The West KailasRange Of Xizang Province

The epithermal deposit is one of the most important metal deposit types formed after a series of geological movements since ancient times.According to mineralogical characteristics of the deposit,sulfide and oxidation state,and surrounding rock alteration,the researchers generally divide the epithermal deposit into two types,namely,high sulfide type(feldspar-sericite type)and low sulfide type(kaolinite-alingite type).Many epithermal deposits have been found in the western section of Gangdisi metallogenic belt in Xizang Province with great ore-forming potential.The ore bodies of these deposits occur in the volcanic rocks of Dianzhong Formation and Pana Formation.The ore and mineral associations in these deposits are mainly galenite-sphalerite-argenite,thioarsenic-cupri-argenite,spiral-argenite,and natural gold-tellurite,etc.The ore structures of the deposit are mainly massive,disseminated,reticulated,brecciform,etc.The surrounding rock alteration types mainly include silicification,illytization,sericite alteration,etc.However,due to the poor natural environment and poor traffic conditions in this research area,it is difficult for researchers to carry out routine geological survey,which brings a lot of inconvenience to mineral resources exploration.Therefore,the application of remote sensing data in mineral exploration has irreplaceable advantages.In this paper,multi-source remote sensing images are used to identify and extract the stratigraphic units,structural characteristics and mineralization alteration information in the study area,which can improve the work efficiency to a certain extent and provide valuable basis for further prospecting work.In this paper,6 typical epithermal deposits in the western section of Gangdise metallogenic Belt are taken as the research area.From the following perspectives,combined with remote sensing technology and methods,regional geological mapping and mineralized alteration information extraction in the study area are carried out: 1.The western Gangdisi section of Tibet is rich in metal minerals,but the physical and geographical conditions are relatively poor in many places;2.the relevant large-scale basic geological survey is relatively weak;3.the overall development and utilization of resources in the study area is relatively low.The main research content and understanding are as follows:(1)Preprocessing and image enhancement of remote sensing image data,such as radiometric calibration and atmospheric correction,and then de-interference processing of remote sensing image after preprocessing.Vegetation and water are extracted from normalized vegetation index(NDVI)and normalized water body index(NDWI)to minimize the influence of interference information on mineralization alteration information extraction.It provides the basis for the subsequent alteration information extraction.(2)According to the metallogenic mechanism and surrounding rock alteration characteristics of 6 typical deposits in the study area,it is determined that sericite,chlorite,silicitization and illytization are the main alteration mineral types in the study area,and the spectral characteristics and formation mechanism of these alteration mineral types are further analyzed,and the standard spectra of typical minerals in the USGS spectral library are used.Based on spectral Angle matching method,spectral sample sets of altered minerals are constructed respectively.(3)Principal component analysis was used to process Landsat 8 OLI data.According to the spectral characteristics of typical minerals,the appropriate band combination was selected for principal component analysis,and the iron stain anomaly and hydroxyl anomaly in the study area were extracted.Researchers used OLI 2,OLI 5,OLI 6 and OLI 7bands to extract hydroxyl alteration anomaly information,and OLI 2,OLI4,OLI 5 and OLI 6 bands to extract iron stain alteration anomaly information.(4)According to the classification diagram of mineralization alteration anomalies of 6 typical deposits in the study area,it can be seen that the distribution of iron stain alteration anomalies and hydroxyl alteration anomalies in the 6 deposits has a certain overlap,and the associated phenomenon is obvious,and the distribution of iron stain alteration anomalies is more than that of hydroxyl alteration anomalies in most of the deposits.(5)Through a series of comparative analysis of the extracted mineralization alteration information,it can be found that the interference information can be effectively suppressed by the principal component analysis method to a certain extent in the study area,so the extracted iron stain and hydroxyl alteration information has a better effect.(6)Based on the established prospecting marks and the analysis results of remote sensing image alteration information extraction,the main prospecting target areas are delineated,and the alteration anomaly areas are compared with the known ore deposit locations.It is found that the two can coincide well,confirming that the alteration information has a good indication significance for the ore deposit.Remote sensing technology also has a certain accuracy and feasibility in the field of prospecting research.It also provides reliable theoretical and technical support for mineral exploration in the next step.