Application Of Short Wave Infrared(SWIR) Technique In Exploration Of Dongshibu In Tibet

The wavelength range of the short wave infrared?SWIR?spectral analysis is1300-2500 nm,which can be used to identify altered minerals containing hydroxyl?water?,carbonate and sulfate.The application of SWIR spectral analysis can quickly identify minerals and make alteration mapping,and can rapid delineation of hydrothermal centers based on the systematic variation of shortwave infrared spectra parameters,which can be used to guide the exploration of the deposit.The Dongshibu deposit located in the west of Gangdese,and consists of a series of Paleocene Eocene granites and Miocene granites and Eocene volcanic rocks.Previous studies have shown that the potential of porphyry copper deposits in the Dongshibu of understand division is very great,but the effect of prospecting is not ideal,one of the important reasons is that the altered mineral assemblage and its zoning characteristics in this area have not been identified.Therefore,this paper uses SWIR spectral analysis to find out the alteration zone and the center of hydrothermal fluid in the area of the division,and then provides the basis for the next step of mineral exploration and deployment of Dongshibu.The short wave infrared spectrum is measured by the TerraSpec Halo Portable near infrared spectroscopy analyzer produced by ASD.In this study,851 samples were analyzed by SWIR spectral analysis.The main alteration minerals identified were muscovite,chlorite,epidote and kaolinite,and the kaolinite was formed by weathering.According to the distribution of the main alteration minerals,two mineral assemblages of the muscovite+chlorite+epidote and the muscovite+chlorite can be divided.Electron microprobe analyses?EMPA?show that the Al-OH wavelength of Muscovite is related to its composition.With the increase of Al-OH wavelength,the Fe+Mg content of muscovite is gradually increasing,and the Al^Vi content of muscovite is gradually decreasing.The Fe+Mg content and Al^Vi content of Muscovite were affected by temperature(the higher the temperature,the lower the Fe+Mg content and the higher the Al^Vi content).This further indicates that the Al-OH wavelength of muscovite can indicate the alteration temperature,that is,the shorter the Al-OH wavelength of the mica,the higher the alteration temperature.The muscovite Al-OH wavelengths,the illite spectrum maturity?ISM?and the chlorite spectrum maturity?CSM?,these three shortwave infrared spectral scalars related to the alteration temperature have shown a relatively consistent change in theDongshibu.In the northeastern part of the Dongshibu,the Al-OH wavelength of muscovite is smaller and is generally less than 2203nm;the ISM is larger than 1.2,and the CSM is larger than 3.0.This indicates that the temperature of altered minerals formation in the northeastern area of the Dongshibu is relatively high and may be the hydrothermal center for this area.Therefore,it is suggested that the drilling project be verified in the thermal center area,so as to achieve the prospecting breakthrough in this area.