Detection of Hydrothermal Alteration Zones Using ASTER Remote Sensing Data in Turquoise mine of Neyshabur

The world-class Neyshabur turquoise mine is hosted by a Tertiary volcano-sedimentary sequence that belongs to the Binaloud zone, in northeastern Iran. Binaloud Mountain has experienced a complicated geological history and several tectono-magmatic periods as a result of its especial tectonic setting. Continuing compression in Late Alpine orogeny deformed the magmatic rocks and brought extensive alteration in this belt. Based on field-experimental studies, the lithological units of the turquoise mine area of Neyshabur can be divided into three sections: volcanic rocks, subvolcanic rocks, and different types of breccia. Andesite, trachyandesite, trachyte lavas, and pyroclastic rock units of the Eocene are among the most important in the study area. These rocks have undergone intense alteration due to the intruded of subvolcanic intrusive bodies. The extent and intensity of the alteration are significant in volcanic and intrusive rocks of this region. The main objectives of this study are to detect and mapping of hydrothermal alteration zones using ASTER data and field studies for future explorations of turquoise mineralization.

 Introduction :

Hydrothermal alteration zones have a significant role in the prospecting of mineral deposits. The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) contains appropriate spectral and spatial resolution to detect spectral absorption features of hydrothermal alteration minerals. The highly brecciated and altered part of andesite, trachyandesite, and trachyte units is the main host of high quantity and quality veins, veinlets, and concretion of turquoise in the study area. Therefore, mapping and identification of hydrothermal alteration mineral assemblages using ASTER satellite remote sensing data can be considered as a cost-effective and applicable tool for targeting and prospecting this mineralization.  

Methodology and Approaches :

  Image processing techniques were applied on the digital subset ASTER data covered the turquoise mine area of Neyshabur. Recognition of hydrothermally altered rocks was carried out using color composite images (RGB), ratio images (BR), relative absorption band depth (RBD), matched filtering (MF), and spectral angle mapper (SAM). The results obtained in this section were controlled by field studies.

 Results and Conclusions :

The mentioned image processing techniques and field studies have been successfully used in the mapping of hydrothermal alteration zones in the study area. According to the outcome of ASTER image processing and field studies, hydrothermal alterations zones could be classified into five groups: silicic-gossan, serisitic, propylitic, advanced argillic, and argillic zones that silicic-gossan and advanced argillic zones forming the most and least extent in alterations zone respectively. The MF algorithm shows very clearly the gossan altered zones in the study area. Moreover, the results indicate that the SAM method is promising for identifying serisitic, propylitic, advanced argillic, and argillic zones and can assist exploration geologists to find new prospects of turquoise mineralization in the other regions before costly detailed ground investigations. The results obtained from image processing are also consistent with the results of field studies petrographic.