Investigation on the accuracy of quantitative analysis for a mixture of chlorite and mica clay mineral and that of kaolinite and mica clay mineral by short wavelength infrared reflectance spectra

摘要

Reflectance spectra have potential as a useful tool to confirm the mineral composition of rock chip and drilling core quickly and easily, even during field investigation.The total of 99 samples of hydrothermally altered rocks, collected in the northern part of the Alligator Rivers Uranium Field, Australia, were investigated in order to check the accuracy of the identification and quantification of clay minerals by means of the short wavelength infrared reflectance spectra of 1 300-2500nm. In the case of a binary mixture of chlorite and mica clay mineral and that of kaolinite and mica clay mineral, the ratio of each end mineral was calculated by comparing measured spectra with reference spectra in a range of 2100 to 2500nm. The following results were obtained from the comparison on the mineral proportion determined by the reflectance spectra method and the X-ray diffraction method:1.The ratio of kaolinite to mica clay mineral can be accurately estimated for their binary mixtures.2.In a mixture of chlorite and mica clay mineral, the ratio of those minerals can be estimated with reasonable accuracy.3.Smectite and vermiculite are distinguishable from each other by a shape of spectra.4.It is difficult to identify mineral species for samples containing hematite, because reflectance spectra do not show any clear absorption patter.5.Estimation of the ratios of chlorite to mica clay minerals and that of kaolinite to mica clay minerals is found to be more accurate using reflectance data in the range of 2100 to 2500nm than estimation of the ratios using reflectance data in the range of 1300 to 2500nm.