Alteration mineral mapping based on the GF-5 hyperspectral data and its geological application——An example of the Huaniushan area in Guazhou County of Gansu Province

This paper is the result of mineral exploration engineering.

Objective The GF-5 AHSI satellite hyperspectral data, featured by the integration of both image and spectrum, can be utilized to directly identify alteration minerals according to their fine spectral characteristics. Large-area wide-range hyperspectral data can be easily obtained by one transit imaging, which can well support the survey of land natural resources. This work extracted alteration minerals using the GF-5 hyperspectral data, and conducted further analysis and field verification, in an attempt to promote the deepening application of China's satellite hyperspectral data in geological field.

Methods Technical workflows of preprocessing GF-5 hyperspectral data and alteration mineral mapping were established. Based on the improvement of the traditional spectral angle matching algorithm, a new spectral matching method of the whole spectral shape synergy with absorption peak position was proposed, and the corresponding algorithm module with the Python language was developed. Taking the Huaniushan area of Gansu Province as an example, we conducted mineral mapping, and comprehensively analyzed multi-source geological elements including lithology, structure, and alteration. The extracted alteration minerals were then verified by field survey and ASD spectral measurements.

Results Nine types of alteration minerals were successfully extracted using the GF-5 hyperspectral data, i.e., limonite, hematite, chlorite, calcite, dolomite, short-wave sericite, medium- to short-wave sericite, medium- to long-wave sericite and long-wave sericite, to describe the distribution of alteration minerals with an area of 3600 km². The directionally distributed dolomite and calcite minerals reflect the surface exposure of sedimentary or metamorphic strata with carbonate composition. Chlorite minerals reveal the distribution of geological bodies rich in amphibole. Limonite and hematite minerals are indicative of the hydrothermal activities related to acid granites. Short-wave sericite was mainly distributed in the monzogranite. Medium- to short-wave sericite is suggestive of the hydrothermal activity of special structural section such as the contact zone between intermediate and acid rock masses and the old Dunhuang Complex. Medium- to long-wave sericite was closely related to the NE-trending fault. Long-wave sericite indicates the presence of hydrothermal activity before the Early Carboniferous.

Conclusions The GF-5 hyperspectral data can extract nine types of alteration minerals including limonite, and the field verification confirms the reliability of alteration mineral mapping. Different alteration minerals may be interpreted from varying aspects. Carbonate minerals are inferred to be closely related to sedimentary or metamorphic strata, while sericite minerals mostly reflect hydrothermal activities related to intermediate to acid rock mass and fault structure. It is considered that the GF-5 hyperspectral data can rapidly identify geological bodies, and can help to revise geological boundary and locate fresh samples, which will effectively serve the basic geological survey and mineral geological exploration in the field of natural resources.