Alteration zoning extracted by spaceborne hyperspectral data analysis.

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Hyperion is the only spaceborne optical sensor collecting hyperspectral data. This research shows that the spaceborne Hyperion data analysis can detect an alteration zoning related to porphyry copper deposits and is consequently very effective for the mineral exploration. Two study areas are the Yerington Area located in the southwest of Nevada and the Santa Rita Area located in the southwest of New Mexico, USA. Around the Yerington Area, the Yerington porphyry copper mine is located and the alteration zone related to porphyry copper, skarn and epithermal deposits is widely distributed, which were formed by the activity of granodiorite batholith and porphyry dykes. Santa Rita porphyry copper mine is located in the Santa Rita Area. Porphyry copper and skarn deposits related to the activity of granodiorite stock and porphyry dykes are distributed around the area.<BR>As a result of Hyperion data analysis of the two study areas, pyrophyllite, alunite, kaolinite, sericite, chlorite, epidote, calcite, hematite, goethite and jarosite were extracted. Sericite is divided into three compositional structure types of Al-type, normal type and Mg-Fe-type. Kaolinite is divided into two types according to the difference of crystallinity. The mixture of two minerals, pyrophyllite plus sericite and sericite plus chlorite, was also extracted. These mineral distributions are closely related to the geology and mineral deposits. The alteration zoning from the center to the outside, [pyrophyllite, alunite] / [Al-sericite] / [Mg-Fesericite] / [sericite+chlorite] / [chlorite, epidote], was recognized around the advanced argillic alteration in the Yerington Area. The leached, phyllic, argillic and skarn alteration zone were recognized inside the open pit of Santa Rita mine. The leached zone located in the upper wall of the pit is composed of hematite, goethite, jarosite and kaolinite (low crystallinity). Al-sericite is distributed mainly in the granodiorite stock of the west part of the pit and the skarn alteration is distributed mainly around the stock.<BR>As the Hyperion data is noisy, masking the pixels over the noise and selecting proper threshold value are necessary in order to raise the accuracy of the extraction and mapping minerals. Detecting the compositional change and the mixture of minerals based on the alteration and mineral deposits leads to the alteration zoning. These distribution and zoning of alteration minerals provide important geological information and proved that the detection of the minerals by the hyperspectral data is very effective in focusing potential exploration targets. The spaceborne hyperspectral data of optical sensor with high resolution will be a powerful tool for mineral exploration because its global data is easily accessible for end users at low cost.
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Alteration zoning extracted by spaceborne hyperspectral data analysis.

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