Short-Wavelength Infrared Characteristics And The Indication Of Exploration Of The Demingding Copper-Molybdenum Deposit In Tibet

Short-wave infrared spectroscopy measurement technology was developed from hyperspectral remote sensing technology,which can accurately identify minerals formed by hydrothermal alteration.Moreover,the mineral hydrothermal center can be quickly located according to the spectral data characteristics(such as the position of the sericite Al-OH absorption peak position,crystallinity,etc.).This method provides a large amount of prospecting information for prospectors and has achieved good results in the exploration of hydrothermal deposits.The Demingding mining area is located in the eastern section of the Gangdese metallogenic belt in Tibet.Previous studies have shown that the Demingding area has a good potential for porphyry copper deposits.However,the ore prospecting effect is not ideal due to inconvenient transportation,high altitude and lack of oxygen,strong physical weathering and cover of the crushed stone.In order to further guide and evaluate the prospecting potential of the Demingding mining area and clarify the future prospecting direction,we carried out the short-wave infrared spectroscopy analysis and testing work systematically based on the detailed field observation.In this article,we focused on the analysis of the short-wave infrared spectrum data from the mining surface and 8 drill holes,and identified 22 altered minerals.The most important and widely distributed alteration minerals are sericite minerals,followed by kaolinite and chlorite minerals.According to the combination of alteration minerals,the altered mineral combinations in the Demingding area can be divided into the following six groups: sericite,sericite + chlorite ± gypsum,sericite +chlorite + epidote,sericite + kaolinite,sericite + montmorillonite,sericite + epidote.According to the short-wave infrared spectrum study of the most widely distributed altered mineral sericite in the mining area,it is found that the absorption peak wavelength,depth and crystallinity of sericite minerals Al-OH band had obvious correlation.The results showed that the shorter the absorption peak wavelength of sericite Al-OH(<2205nm)or the deeper the absorption depth(>0.3),the higher the crystallinity of sericite minerals(>1.0).In addition,the sericite short-wave infraredspectroscopy shows regular changes in space,and the three anomalies fit well.The wavelength of the Al-OH absorption peak wavelength anomaly zone is between 2196~ 2204 nm,and the SWIR-IC value is greater than 1.5.Moreover,the absorption peak depth of Al-OH,representing the intensity of alteration,was the highest in this region.This phenomenon indicates that the fluid temperature and pressure in this region are obviously higher than those in the periphery,which may be the hydrothermal alteration mineralization center.The gradual weakening of sericite Al-OH absorption peak depth from west to east in the drill holes also proves that the western part of the mine is closer to the altered hydrothermal center.Combining the results of zircon U-Pb age and molybdenite Re-Os isotope age in ore-forming rocks,we have delineated two key exploration targets in the mine.The key exploration target area I is the superposition of late copper mineralization and early(copper)molybdenum mineralization,and the key exploration target area II molybdenum-rich ore bodies that exist in porphyritic biotite monzonite granites should be searched for.Therefore,it is recommended to carry out drilling work at the foot of a lower altitude near the delineated prospecting target area in order to achieve the breakthrough of the prospecting in this area.