Research On Hyperspectral Features Of Qidashan High-Grade Iron Deposit In Liaoning Province

Qidashan Iron Deposit,located in the northeast of Anshan City,Liaoning Province,is a typical representative of banded iron formations(BIFs).The high-grade iron ore resource is second only to Gongchangling Iron Deposit in Anshan-Benxi area,reaching a medium scale and characterized by strong chloritization.Predecessors have studied high-grade iron ore from the aspects of geochemistry and geophysics,but the research on hyperspectral remote sensing is still rare.Therefore,using the ASD reflectance spectrum data,the HySpex indoor close range imaging hyperspectral data,and ZY1-02D satellite imaging hyperspectral data,the spectral features of different kinds of ores and wall rocks widely developed in the mining area are studied according to the steps of non-imaging to imaging and indoor to aerospace.The results are verified by electronic probe,XRD and geochemical data:On the basis of previous studies,combined with field investigation and laboratory microscopic identification,the wall rocks of the Qidashan poor iron ore are mainly chlorite-quartz schist,while the wall rocks of the rich iron ore are mainly characterized by strong chloriteization,and accompanied by pyritization,sericitization;there is little difference in the reflection spectrum features of rich iron ore and poor iron ore in Qidashan Iron Mine.The spectral features are mainly the absorption characteristics near 0.7μm and 1.0μm caused by the crystal field effect of Fe ion;the spectral features of the wall rocks of rich iron ore and poor iron ore are mainly manifested by the spectral features of minerals such as chlorite and sericite.The absorption bands are mainly distributed in the short-wave infrared band,including the OH around 1.4μm,the H2O around 1.9μm,Al-OH around 2.2μm,Fe-OH around 2.25μm,and Mg-OH/CO32-around 2.35μm.Among them,the OH,Fe-OH,and Mg-OH absorption band wavelength positions of the samples containing chlorite are obviously different between the poor iron ore and the rich iron ore.The absorption bands near the poor iron ore is biased towards the short wave direction,while the absorption zone near the rich iron ore is biased towards the long wave direction.The HySpex-320m imaging hyperspectral system was used to image the typical samples of the Qidashan Iron Mine in the laboratory,and based on the IDL language,a program for hyperspectral image processing and thematic information extraction based on pixels was written.Mineral identification,mineral mapping and chlorite spectral parameter extraction were performed on the 9 acquired rock hand specimens.The results of mineral identification indicate that most of the chlorite-quartz schist is around the poor iron ore,while the chloritization,pyritization and sericitization occur more around the rich iron ore,which is also consistent with the XRD test results and microscope observation results.The spectral features of chlorite show that the absorption band wavelengths of OH,Fe-OH and Mg-OH from poor iron ore are located between 13 90～1400nm,2245～2255nm and 2330～2350nm,respectively.The absorption band wavelengths of chlorite from rich iron ore all moved to the long-wave direction,which were located between 1405～1410nm,2260～2265nm and 2350～2370nm,respectively.The wavelength difference between the two can reach about 20nm.The electron probe results show that the content of Fe and Mg ions in chlorite near poor iron ore and rich iron ore is significantly different.The content of Fe ions in chlorite from poor iron ore is less while the content of Mg ions is more.It is mainly composed of prochlorite and clinochlore.Contrary to the iron-rich chlorite,the content of Mg ion is less and the content of Fe ion is more,and most of them are prochlorite and chamosite.Combined with the wavelength position data,it can be concluded that the absorption band wavelength position of chlorite Fe-OH is positively correlated with Fe ion content,inversely correlated with Mg ion and Mg/(Mg+Fe),and slightly affected by AlⅥ ion.The OH and Mg-OH absorption band wavelength positions also have the same proportional relationship.The difference in composition of chlorite in the wall rock of poor iron ore and that in the wall rock of rich iron ore should be related to the generation environment:the chlorite in the wall rock of poor iron ore should be generated at the same time as BIF,which belongs to the cause of regional metamorphism.The chlorite in the wall rock of the rich iron ore should be the hydrothermal origin related to the formation of the rich iron ore.In order to evaluate the feasibility of the application of the above-mentioned spectral characteristics in spaceborne remote sensing,the latest China-launched ZY1-02D hyperspectral satellite data was used to extract the wavelength position of the Fe-OH absorption band within the scope of the Qidashan Iron Mine.The results show that most areas of the mining area are rock and mine.The wavelength position of the absorption band is concentrated in the shortwave direction near 2240nm,while the local absorption band wavelength position of the Beiershan,Xishilaizi and Wangjiapuzi second mining areas is biased towards the longwave direction of 2265nm.This result is also consistent with the spatial distribution of iron-rich ore bodies in the Qidashan mining area.The basic agreement indicates that the chlorite spectral parameter method has certain practical significance in the prospecting of rich iron ore resources in the Qidashan mining area.