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热心网友 时间:2024-04-13 14:34
Zhang Yu jun
Zhang Yu jun,Center of Aero-Geophysics&Remote Sensing,MLR;Institute of Mineral Resources,CAGS
Key words:ASTER(Advanced Space-borne Thermal Emission and Reflection radiometer), Borax anomaly
1.Introduction
In the past few months the efforts to extract the anomaly of sedimentary rocks made success for sulfates(gypsum,celestine)and carbonates(smithsonite).A new desire appeared for study of the borax deposits using ASTER remote sensing data.
The usage of borax on Qinghai-Tibet Plateau for medical, glazier and other purposes takes special role.It can be traced back to the 6thcentury.The export of Tibetan borax to European countries dates from the 13thcentury.The exploitation of borax is the one of the important component parts of Tibetan industry all along.The borax of BankogCo has being interesting for many geologists who devoted to saline lake.
BanKogCo was taken as a known borax deposit for the application of ASTER data.BanKogCo belongs to the moderately mineralized carbonate type.It is located 10kmin the east from SilingCo or 120kmin the north-east from the famous NamCo as the biggest saline lake in Tibet.BankogCo consists of 3 small lakes:the 1st,the 2ndand the 3rdat the altitudes 4525m,4522m and 4520m with areas about 5km2,30km2,and 80km2respectively.The sedimentary sub-environment in BankogCo district is shown in Fig.1(recompiled from Zheng Mian-Ping,1989).
Fig.1 Sedimentary sub-environment in BanKogCo district
1-Perennial brackish lake;2-Perennial saline-lake;3-Ephemeral lake;4-Salt pan;5-Salt mud-flat;6-Spring pond-marsh;7-Sand flat;8-Alluvial fan;9-Bench and strand;10-Bench pad and platform bench;11-Bed rock.
The borax(Na2B4O7·10H20),Pinnoite(Mg B204·3H2O)and tincalconite(Na2B407·5H2O)are the main boron minerals for BankogCo saline sediments;the other saline minerals are:calcite(CaCO3),dolomite(Ca,Mg[CO3]2),magnesite(MgCO3),hydromagnesite(3MgC03Mg(OH)2·3H2O),thermonatrite(Na2CO3·H20),gypsum(CaSO4·2H20),mirabilite(Na2SO4·10H20),halite(NaCl),etc..
This paper discusses the method and result of extraction remote sensing anomaly for boron sediments.
2.Processing of ASTER imagesfor borax,carbonates and sulfates sediments
An ASTER image was purchased.The acquisition time is 9thof September 2004.All of the Visual-near Infrared,the Sort Wave IR and the Thermal IR were used for the extraction of R.S.anomalies.The spectra from USGS library(Clark et al,2003)were applied as the basis for the anomaly extraction and the result interpretation(Fig.2).
Fig.2 Spectra from USCS librariesfor boron minerals and some possible interference
The TIR data were used for the carbonaceous and sulfates sediments,using the main processing techniques explained in(Zhang Yu-Jun,2009).For the borax the short wave data were used.The Combinato-rial(combinational)Band-Ratio Analysis was studied for the borax anomaly and to avoid the false anomaly from carbonates and argillaceous sediments.The borax index K was calculated by the PCI Model function.The spectra absorption is quite clearfor the boron minerals at ASTER channels 5th,6thand 7th.The anomaly for borax can get by the next 3 equations(1,2,3)(see Fig.3 on colored plate 28):
K=%DBOC=(%8-%7)*ABS(%8-%6+%8-%5)*N (1)
Where:DBOC-database output channel;N-coefficient,determined by repeated test.
K=%DBOC=(%8-%7)*(%8-%6+%8-%5)*N (2)
K=%DBOC=(%8-%6+%8-%5)*N (3)
The absorption for argillaceous minerals(such as illite)is strong at the channels 6thand 5thh.The equation(3)can give false anomaly for borax.However channel 8this higher than channel 7th.The index by(2 or by 1)could not be positive,therefore it can avoid the interference of argillaceous minerals.
The calcite has strong absorption at 8thchannel.In the equation(2)the two pairs of brackets can both be negative,resulting in wrong anomaly.The absolute from the sum of two differences(1)makes the positive product of two negative multipliers impossible,consequently can avoid the interferences from the carbonates.Although the jarosite can make false anomaly,but it is seldom appears at salty lake sediments.
Fig.2 shows the principle for this discussion.
3.Results of processing of ASTER image for borax of BanKogCo
Fig.4(on colored plate 28)shows the processed result for anomaly image.The red color indicates the borax,got by the abovefunction.The blue and green color shows the carbonate and sulfates respectively.The magenta expresses the mixed anomaly of borax and carbonates.
Besides of BanKogCo the borax anomaly appears at the east of NamkaCo.This region is an undiscovered area.Since the anomaly is even stronger than that for BanKogCo,so it is worth to carry on exploration after some ground truth investigation.
References
[1]Zheng Mian-Ping,et al.1989.Saline lakes of Qinghai-Tibet Plateau(in Chinese).
[2]Clark R N,Swayze G A,Wise R Livo K E,Hoefen T M,Kokaly R F,and Sutley S J.2003.USGS Digital Spectral Library splib05a.U.S.Geological Survey:Open File Report,03-395.
[3]Zhang YJ,Yang JM,Yao FJ.2006.The Primary Study of Lithologic Mapping Using ASTER-TIR Data.Proceedings of' Annual meeting on Environmental Remote Sensing’:622-627
[4]Zhang YJ,Yao FJ.2009.The Application Study of Multi-spectral ASTER Data for Determination of ETM Remote Sensing Anomaly Property—Taking Eastern WuLongGou Region of KunLun Mountain Range as Example.‘Acta Petrologica Sinica’:Vol.25,No.4,963-970
[5]Zhang Yu-Jun, Liu Cheng-Lin, Yao Fo-Jun, Liu Chang-Zheng,Li Ming-Xi.2009.Extraction of ASTER R.S.Anomaliesfor Sedimentary Deposits in Qaidam Basin,as the Test Field for Mars.Proceedings of' 2009 Beijing Lunar Science Workshop’:11-15
原载《深部地质过程与成矿预测暨深部找矿新技术新方法高级研讨会论文摘要 汇编》2009,p144-147