5:15 PM - 7:15 PM
[MGI31-P04] Remote Sensing-Based Identification of Formation Origin of Kaolinite with Application to Potential Evaluation of Metal Deposits
Keywords:Hydrothermal alteration, Weathering alteration, Reflectance spectrum, Mineral exploration, Mineral texture
In resource exploration using remote sensing, the primary method is to identify hydrothermal alteration minerals using reflection and emission spectra, and kaolinite is one of the representative minerals. Kaolinite is extracted as a major alteration mineral through remote sensing image analysis targeting the exploration of porphyry copper deposits, gold deposits, and VMS deposits. In recent years, the kaolinite distribution has also been estimated on the Mars surface, which might suggest a possibility of metal-deposit formation.
There are two types of conditions under which clay minerals such as kaolinite are formed: chemical weathering in warm and humid environments near the surface and hydrothermal alteration in acidic and high temperature environments at shallow to great depths. Kaolinite generated by the latter condition can be an indicator of metal-deposit exploration. Remote sensing may be the most effective exploration method for wide areas by identifying this type of kaolinite. Based on that background, this study aims to develop a remote sensing technology for evaluating the metal-deposit potential using kaolinite as an indicator.
For this, we tried to clarify the differences in mineral composition and chemical properties of kaolinite originating from weathering and hydrothermal alteration, and their correlation with the reflectance spectra from visible to shortwave infrared region. Twenty-eight kaolinite samples taken from hydrothermal deposits in Japan and the USA and kaolinite mines in Japan were used for the analyses. In addition, the reflectance spectra of kaolinite in a weathering area (Ione, California, USA) and a hydrothermal area (Goldfield, Nevada, USA) were compared using Hyperion images of the Earth Observation Satellite (EO-1). One noted results are that a reflectance index at wavelengths of 2.16 to 2.22 μm, which is the absorption band of Al-OH, may be effective for discriminating weathered and hydrothermally altered kaolinite, and the difference in reflectance spectrum characteristics may be attributable to particle size.
There are two types of conditions under which clay minerals such as kaolinite are formed: chemical weathering in warm and humid environments near the surface and hydrothermal alteration in acidic and high temperature environments at shallow to great depths. Kaolinite generated by the latter condition can be an indicator of metal-deposit exploration. Remote sensing may be the most effective exploration method for wide areas by identifying this type of kaolinite. Based on that background, this study aims to develop a remote sensing technology for evaluating the metal-deposit potential using kaolinite as an indicator.
For this, we tried to clarify the differences in mineral composition and chemical properties of kaolinite originating from weathering and hydrothermal alteration, and their correlation with the reflectance spectra from visible to shortwave infrared region. Twenty-eight kaolinite samples taken from hydrothermal deposits in Japan and the USA and kaolinite mines in Japan were used for the analyses. In addition, the reflectance spectra of kaolinite in a weathering area (Ione, California, USA) and a hydrothermal area (Goldfield, Nevada, USA) were compared using Hyperion images of the Earth Observation Satellite (EO-1). One noted results are that a reflectance index at wavelengths of 2.16 to 2.22 μm, which is the absorption band of Al-OH, may be effective for discriminating weathered and hydrothermally altered kaolinite, and the difference in reflectance spectrum characteristics may be attributable to particle size.