Study On The Thermal Infrared Spectroscopy Characteristics Of Skarn Minerals And Its Exploration Model

Skarn deposits are an important source of Cu,Pb-Zn,W-Sn,Au and other minerals.A study of the combination types,distribution ranges,and other characteristics of skarn minerals is of great significance for understanding the natural mechanism of deposits and guiding prospecting.However,precisely determining the characteristics of various altered minerals requires extensive petrographic observation and component analysis,which involves significant time investment and exploration risk.Thermal infrared hyperspectroscopy technology provides considerable advantages in the identification and content extraction of high-temperature minerals,and it is the best technical means to identify early high-temperature minerals in skarn-type deposits.In foreign countries,thermal infrared technology has been used successfully in geological prospecting,but there is no precedent for the application of this technology to ground system testing and research in China's mining areas.For this paper,thermal infrared hyperspectral technology was used to select the Jiama copper polymetallic deposit in Tibet.A total of 17,500 spectral curve data were obtained by measuring 17 drill cores,and microscopic identification and geochemical analysis methods(EPMA,LA-ICP-MS)were used to determine skarn mineral spectral characteristics,altered mineral assemblage zoning,spectral characteristics,geochemical element changes,etc.Additionally,a thermal infrared spectroscopic exploration model for skarn-type deposits was established,which is significant for prospecting similar types of deposits.This research has achieved the following results and innovations:(1)Determined and simulated typical skarn mineral spectral and assemblage characteristics and constructed related mathematical statistical models.The variation range of the garnet's characteristic spectral absorption peak position is 11220?11580nm.The shift in garnet color(red-brown?green)is mainly controlled by the change of Fe and Al content.The response of the spectrum involves the shift of the wavelength position of the characteristic absorption peak.The change of color saturation and brightness is more affected by rare earth and trace elements.Impact.As the color of garnet deepens,the position of spectral characteristic absorption shifts to long waves,representing a relatively high-temperature environment.The spectral curve characteristic of garnet satisfies the inverse Gaussian model,while the spectral absorption depth change characteristic of the mixed mineral of garnet+pyroxene satisfies the Slogistic model.D_Grt:D_Dieffectively expresses the change of mineral mixed components.Therefore,it can be used as an exploration index to efficiently determine changes in the composition of skarn mineral assemblages and zoning characteristics.(2)Thermal infrared spectroscopy technology was used to identify various altered minerals and determine the zoning characteristics of mineral assemblages.The early metamorphism of skarn mainly formed the mineral combination of garnet+wollastonite+diopside.In the de-alteration stage,low-temperature alteration minerals such as chlorite+epidote+calcite were produced,and they overlap to a certain extent with the sericitization of the deep porphyry ore body.The altered mineral assemblage and spectral characteristics of skarn show obvious zoning in both the horizontal and vertical directions.Vertically,the assembly from the top plate to the bottom plate of skarn is as follows:forming grossular+diopside+plagioclase+sericite+(chlorite+epidote+quartz)?andradite+grossular+diopside+chlorite+epidote+(hornblende)?andradite+grossular+quartz+(diopside+hornblende)?andradite+wollastonite+hornblende+anhydrite+calcite+quartz+(diopside+hornblende+vesuvianite+grossular)?wollastonite+andradite+calcite+(hornblende)?andradite+quartz+calcite+(hornblende).The ratio of garnet/pyroxene is from 15:1?20:1.The spectral characteristics change from 11220?11260 nm?11560?11600nm,shifting from short wave to long wave.Horizontally,the assembly from the porphyry near-end to the far-end contact zone is as follows:forming andradite+wollastonite+hornblende+anhydrite+calcite+quartz+(diopside+hornblende+vesuvianite+grossular)?grossular+diopside+chlorite+epidote+(hornblende).The ratio of garnet/pyroxene is from 20:1?10:1.The spectral characteristics change from 11560?11600 nm?11220?11260 nm,shifting from long wave to short wave.(3)An analysis of the correlation between the spectral characteristics of the garnet and the content of geochemical elements found that the movement of the characteristic absorption peak of garnet is positively correlated with the Fe/(Fe+Al)content(correlation coefficient R²=0.91),while the Pb,Zn,U,and Zr content has a negative correlation(R²=0.7,R²=0.63,R²=0.62,R²=0.6).As the characteristic absorption peak of garnet shifts from long wave to short wave,garnet also evolved from being enriched in light rare earths to gradually being enriched in heavy rare earths.(4)A thermal infrared spectroscopy survey model was constructed based on the spectral change characteristics of the pointer mineral garnet and the zoning characteristics of altered minerals.Researchers believe that the wavelength and absorption depth changes of garnet are related to the distance from the center of the heat source and show a linear correlation(wavelength change:y=-3.51x+41093,R²=0.77;absorption depth change:y=-4194.9z+2039.1,R²=0.556).This model can be used to calculate the distance from garnet samples of different wavelengths to the center of the heat source.(5)The thermal infrared exploration model was verified using the Hongshan skarn copper deposit.It is based on the zoning of altered mineral assemblages and characteristic wavelength information of garnet according to the Hongshan survey on the spectral distribution characteristics of the skarn in the HZK0305 borehole.Use of the model indicates that the formation of skarn in the deposit is mainly caused by the lateral escape of fluid.According to the garnet's wavelength change in the measured borehole,it is calculated that the skarn is 798 meters away from the center of the heat source.Reference to the relevant literature on Hongshan geological exploration substantiates that the spectral cognition results are fully in line with the geological facts,which further verifies the validity of the thermal infrared exploration model constructed by the author.