Alteration Information Extraction Based On ASTER Data In The Middle Section Of Longshoushan Uranium Metallogenic Belt In Gansu Province

The proven alkaline metasomatic uranium deposits in the middle section of the Longshoushan uranium metallogenic belt in Gansu Province include the Jiling uranium deposit and the Xinshuijinguranium deposit.Alterations such as hematitization,chloritization and calcitization are developed in the area.In this paper,by measuring the spectra of typical rocks in the study area,the spectral absorption characteristics of typical altered rocks are analyzed and compared.The alteration anomalies such as hematitization,chloriteization and carbonatization are extracted by ratio method and principal component analysis method,and the favorable uranium metallogenic areas in xinshuijing-Jiling area are delineated.(1)The spectral curves of syenite,albitite,granite,moyite,marble,siliceous breccia,and related altered rocks were measured with a spectrometer.Through the analysis of various rock spectrum curves,it is concluded that the absorption of syenite,albitite and related altered rocks at 830?905 nm,2200nm,and 2350nm are formed by minerals rich in Fe³⁺,Al-OH and Mg-OH respectively;There are obvious absorption valleys at 830?905nm and?2200nm in granite,moyite and related altered rocks,which are respectively formed by minerals rich in Fe³⁺and Al-OH;marble has obvious characteristic spectral curve of CO3^2-and forms a very typical absorption valley at 2318nm.(2)In order to avoid or reduce the influence of shadow,vegetation,quaternary and water system on the extraction of alteration information,the extraction and mask processing of interference information such as shadow,vegetation,quaternary and water system have been carried out.Among them,the high thresholds of B9/B1,NDVI,and MNDWI were used to remove shadows,vegetation and water system interference,and geological maps were used to mask the Quaternary distribution area.(3)According to the spectral absorption characteristics of the altered rock and surrounding rock,determine the extraction band of the main altered mineral information,and mainly use the ratio method and the principal component analysis method to extract the altered abnormality in the study area.Among them,the band ratios of B2/B1,B4/B8and B5/B7 are used to extract the hematitization,chloritization and carbonatization respectively;When using the principal component analysis method to extract the alteration information,the B1,B2,B3,and B4 band are used to extracth hematitization,and the B1,B3,B4,and B8 band are used to extract chloritization,and the B1,B5,B8,and B9 band used to extract the carbonatization.(4)In space,the distribution of various alterations presents the characteristics of a northwest-west spreading,which is consistent with the spreading direction of the main structural framework of the study area,and nearby the contact zone between the fault structure and the Caledonian albitite and granite rock mass,the alteration anomaly developed strongly.Combined with the regional geological characteristics and remote sensing alteration anomaly distribution,four favorable metallogenic areas in xinshuijing-Jiling area are delineated,which are located in the metallogenic holding area of the Malugou fault,between the Xinshuijing deposit and the Jiling deposit,and near the Geminggou fault.