recently launched Landsat-8 data for hydrothermal alteration and ... National Aeronautics and Space Administration (NASA) and the U.S. ... Vandenberg Air Force Base in California. ... Landsat-8 image of target site was processed using the.
Regional Hydrothermal Alteration Mapping Using Landsat-8 Data Amin Beiranvand Pour*, Mazlan Hashim Geoscience and Digital Earth Centre (Geo-DEC) Research Institute for Sustainability and Environment (RISE) Universiti Teknologi Malaysia (UTM) 81310 UTM Skudai, Johor Bahru, Malaysia
Abstract— This study presents the applicability of recently launched Landsat-8 data for hydrothermal alteration and lithological mapping. Sar Cheshmeh copper mining district in the southeastern part of the UrumiehDokhtar volcanic belt, SE Iran has been selected as a case study. Several Red-green-Blue (RGB) color combination images and specialized band ratios were developed. Band ratios derived from image spectra (4/2, 6/7, 5 and 10 in RGB) allows the discrimination of lithological units, altered rocks and vegetation. Fieldwork and laboratory analysis verified the image processing results. Thermal infrared bands of Landsat-8 significantly improved the convenience of thermal infrared remote sensing data for lithological mapping. The accomplishments of this research should have considerable implications for geologists to utilize Landsat-8 OLI/TIRS data for geological purposes in the future.
units associated with porphyry copper mineralization at regional scale.
Keywords— Landsat-8 data; Sar Cheshmeh copper mining district; ASTER; Hydrothermal alteration mapping Fig. 1. Lithological units in the study region [3].
I. INTRODUCTION The Landsat satellites era that began in 1972 has become a nearly 44-year global land record with the successful launch and operation of the Landsat Data Continuity Mission (LDCM). Two generations of Landsat satellites launched by National Aeronautics and Space Administration (NASA) and the U.S. Geological Survey (USGS). The first generation of Landsat sensors (1, 2, and 3) functioned from 1972 to 1985 and is essentially replaced by the second generation of Landsat sensors (4, 5, and 7), which continues to the current [1]. Landsat-8 was launched on 4 February 2013 from Vandenberg Air Force Base in California. It has two-sensors, including the Operational Land Imager (OLI) and the Thermal Infrared Sensor (TIRS). Nine visible, near-infrared, shortwave infrared bands and two longwave thermal bands are installed in the instruments for data collection. The resolution provided by Landsat-8 is 15 to 100 m [2]. This study evaluates the capability Landsat-8 data for identification of hydrothermal alteration area and lithological units in Sar Cheshmeh copper mining district, the UrumiehDokhtar volcanic belt, SE Iran (Fig. 1). The main goal of this investigation is to evaluate Landsat-8 spectral bands for identification of hydrothermal alteration minerals and rock
I. MATERIALS AND METHODS A. Geology of the study area The Sar Cheshmeh porphyry copper deposit is located between 55◦ 52′ 20″ E, 29◦ 58′ 40″ N in SE part of Iran (Fig. 2) [3, 4].
B. Remote sensing data A cloud-free level 1T (terrain corrected) Landsat-8 image LC81600392013135LGN01 (Path/Row 160/39) were obtained through the U.S. Geological Survey Earth Resources Observation and Science Center (EROS) (http://earthexplorer.usgs.gov). It was acquired on May 15, 2013 for the study region. The image map projection is UTM zone 40 North (Polar Stereographic for Antractica) using the WGS-84 datum.
C. Data processing Landsat-8 image of target site was processed using the ENVI 4.8 software package. The discrimination between hydrothermally altered and unaltered rocks is one of the most significant aspects in mineral exploration programs. In this research, several Red-green-Blue (RGB) color combination images and band ratios were applied to the image. Different Red-green-Blue (RGB) color combination images were applied here. Band ratio is a image processing method where the Digital Number (DN) value of one band is divided by the DN value of another band. Band ratios is able to identify rocks, minerals and geological structures in the processed image [5].
II. RESULTS AND DISCUSSION A single RGB image was produced for visible bands (2, 3 and 4) of Landsat-8 data. Band 2 has positioned in the blue (0.450-0.515 μm), band 3 in green (0.525-0.600 μm) and band 4 in red (0.630-0.680 μm) regions of the electromagnetic spectrum. Natural RGB color combination image has been assigned to bands 4, 3 and 2 for full scene of the image. Figure 4 shows the resultant image, geological features and geomorphological framework are distinguishable at a regional scale. Sar Cheshmeh copper mining district is located in the southeastern part of the scene; it is within a belt of crystalline igneous rocks. Textural characteristics of the igneous rocks can be discriminated from sedimentary rock in the scene. Structural features and sedimentary texture of rocks located in the northwestern part of the scene are easily recognizable in the natural RGB color combination of the visible bands (Fig. 2).
RGB color combination image was allocated to near infrared (band 5: 0.845-0.885 μm) and short wavelength infrared bands (band 6:1.560-1.660 μm , band 7: 2.100-2.300 μm) of Landsat-8 data, respectively. Figure 3 shows the resultant full scene image for the study area. Geological features, including textural characteristics of the igneous and sedimentary rocks, structural features and vegetation are clearer than Figure 2 at a regional scale. Vegetated areas are appeared as light red color in the scene. Color and textural features of the igneous and sedimentary rocks are more robust in this scene. Additionally, hydrothermal altered rocks are also recognizable as yellow color area within the belt of crystalline igneous rocks in the Sar Cheshmeh copper mining district (Fig. 3). Two thermal infrared bands (bands 10 and 11) of Landsat8 have spectral coverage in 10.30-11.30 μm and 11.50-12.50 μm, respectively. TIR bands of Landsat-8 have improved the quality and applicability of the Landsat data in a variety of earth-based and atmospheric phenomenon. Silicate minerals indicate spectral anomaly in the TIR. The silica emissivity curve shows significant variation in 8.5 μm to 9.30 μm and 10.30 to 11.70 μm. There are clear minima in 8.5 μm to 9.30 μm while higher emissivity values can be seen in 10.30 to 11.70 μm. Figure 4 shows RGB color combination image of band 10 (10.30-11.30 μm), 11 (11.50-12.50 μm) and 7 (2.102.30 μm) of Landsat-8 at a regional scale.
Fig. 3. RGB color combination image of band 5, 6 and 7of Landsat-8 data.
Fig.2. RGB color combination image of bands 2, 3 and 4 of Landsat-8 data.
Rocks with high emissivity value attributed to high silicate minerals in their composition are manifested as red color in the image. On the other hand, rocks with moderate and low emissivity value are appeared as pink and blue colors, respectively (Fig. 4). Band 7 has been selected for RGB color combination image as representative of rocks absorption features in SWIR region due to OH and CO3 in their compositions. Hence, blue hue areas contain low silicate minerals.
Fig.5. Band ratios of 4/2, 6/7, 5 in RGB. Fig. 4. RGB color combination image of band 10, 11 and 7 of Landsat-8 data.
Identification of iron oxides is implemented using bands 2 and 4 of Landsat-8. Mapping clay and carbonate minerals is carried out using bands 6 and 7 of Landsat-8. Band ratios derived from image spectra (4/2, 6/7, 5 and 10 in RGB) is used for the identification of rock units, alteration (Figs. 5 and 6). The alteration minerals are detected in the scenes as yellow color around porphyry copper deposits, which are more visible in Figure 6. The copper deposits are introduced by their names in the Figures 5 and 6. The boundary between sedimentary (Neogene redbed agglomerate and conglomerate) and igneous rocks (Eocene-Oligocene volcanic rocks, Lower Eocene tuff and volcanic rocks) units are also delimited in the resultant images. Vegetation is manifested as red and purple colors in the drainage system and background of both scenes (Figs. 5 and 6). Fieldwork in the study area and laboratory analysis verified the image processing results.
Fig.6 Band ratios of 4/2, 6/7, 10 in RGB.
III. CONCLUSIONS Results indicate that Landsat-8 bands have great ability to yield remote sensing information for mapping vegetation, iron and clay and carbonate minerals, silicate mineral and lithological units for exploration purposes. The TIR bands of Landsat-8 are useful for lithological mapping. This investigation demonstrates significant implications for geologists to utilize Landsat-8 OLI/TIRS data for copper deposits exploration in the future.
[2]
Acknowledgment We are thankful for TRGS grant (4L837) support for this study.
References [1]
F.F, Sabins, “Remote sensing for mineral exploration,” Ore Geo. Rev, vol. 14, pp. 157-183, 1999.
[3]
[4]
[5]
A. Ariza, “Landsat data continuity mission,version1.0” INSTITUTO GEOGRÁFICO AGUSTÍN CODAZZI Bogotá. Colombia 2013, pp. 325, 2013. A.B Pour, M. Hashim, “Application of Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data in geological mapping,” Intern.J. Physical Sciences, vol.6 (33), pp.7657-7668., 2011. A.B Pour, M. Hashim, “Fusing ASTER, ALI and Hyperion data for enhanced mineral mapping,” Intern.J. Image and Data Fusion, 4(2),126145. 2013. J. Inzana, T. Kusky, G. Higgs, R. Tucker, “Supervised classifications of Landsat TM band ratio images and Landsat TM band ratio image with radar for geological interpretations of central Madagascar,” J. Afri. Earth Sci., vol. 37, pp. 59-72, 2003.
