APPLICATION OF EARTH OBSERVING-1 (EO1) ADVANCED LAND IMAGER (ALI) AND HYPERION DATA FOR PORPHYRY COPPER EXPLORATION 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 Email: [email protected]; [email protected]

KEY WORDS: EO-1; ALI; Hyperion; lithological mapping; Hydrothermal alteration mineral ABSTRACT

This study evaluates the capability of Earth Observing-1 (EO1) Advanced Land Imager (ALI) and Hyperion data for lithological and hydrothermal alteration mapping. ALI and Hyperion images covering the Meiduk and Sar Cheshmeh porphyry copper mining districts, SE Iran were acquired for alteration and lithological mapping. Spectral angle mapper, linear spectral unmixing and mixture-tuned matched-filtering were tested to discriminate the hydrothermal alteration areas of porphyry copper mineralization from surrounding environment using shortwave infrared bands of ALI at regional scale. Analytical imaging and geophysics (AIG)-developed hyperspectral analysis processing methods were applied to visible and near infrared and shortwave infrared bands of Hyperion for mapping iron oxide/hydroxide minerals and clay mineral assemblages in hydrothermal alteration zones at district scale. Results indicated that the tested methods are able to yield spectral information for identifying vegetation, iron oxide/hydroxide and clay minerals, lithological units and discrimination of hydrothermally altered rocks from unaltered rocks using ALI data at regional scale. Supergene altered areas consisting of iron oxide/hydroxide minerals such as hematite, limonite, jarosite and goethite were detected using visible and near infrared bands of Hyperion. Phyllic, advanced argillic and propylitic alteration zones associated with porphyry copper mineralization were discriminated based on the identified alteration minerals such as sericite, kaolinite, illite, alunite, chlorite, epidote and calcite using shortwave infrared bands of Hyperion.

1.

INTRODUCTION

The Earth Observing-1 (EO-1) satellite was launched on 21 November of 2000 as part of NASA’s New Millennuim Program (NMP) technology path-finding activities to enable more effective (and less costly) hardware and strategies for meeting earth science mission needs in the 21st century. The EO-1 platform includes three the most advanced remote sensing instruments (i) The Advanced Land Imager (ALI); (ii) Hyperion; and (iii) The Linear Etalon Imaging Spectral Array (LEISA) Atmospheric Corrector (LAC). These sensors can be used in a variety of scientific disciplines (Ungar et al., 2003; Pour and Hashim, 2011a,b; 2014). The Advanced Land Imager (ALI) sensor was built as archetype for the next production Landsat satellites, the multispectral characteristics maintains to Enhanced Thematic Mapper Plus (ETM+) sensor on Landsat-7 with a spatial resolution of 30 m, but the swath width is 37 km. The performance characteristics of the ALI and ETM+ are shown in Table 1. ALI has 10 channels spanning the visible and near infrared (VNIR) to shortwave infrared (SWIR) (0.4 to 2.35 μm) (one panchromatic band, six bands in VNIR, and three bands in SWIR). VNIR bands (0.4 to 1.0 μm) are especially useful for discriminating among ferric-iron bearing minerals. SWIR bands (1.20 to 2.35 μm) are sensitive to hydroxyl (OH) minerals that can be found in the alteration zones associated with hydrothermal ore deposits (Hubbard and Crowley, 2005). Hyperion is the first spaceborn hypersepctral sensor in commission across the spectral coverage from 0.4 to 2.5 micrometer and 10 nanometer spectral resolution. It is a pushbroom instrument with 242 spectral channels over a 7.6 km swath width, and 30 m spatial resolution. The first 70 bands are in the visible and near infrared (0.4 to 1.0 μm) and the second 172 bands in the shortwave infrared (0.9 to 2.5 μm). Hyperion shortwave infrared bands (2.0 to 2.5 μm) can uniquely identify and map hydroxyl-bearing minerals, sulfates and carbonates in the hydrothermal alteration assemblages (Bishop et al., 2011; Gersman et al., 2008; kruse et al., 2003). First subset of visible and near infrared bands between 0.4 and 1.3 μm can also be used to highlight iron oxide minerals (Bishop et al., 2011; Pour and Hashim, 2011a,b; Pour et al., 2014).

2. MATERIALS AND METHODS Figure 1 shows simplified geology map of southeastern segment of the Urumieh–Dokhtar Volcanic Belt. Porphyry copper deposits in this belt are associated with Miocene adakite-like orogenic granitoids which intruded the Eocene volcanic rocks. This study focuses on the Meiduk and Sar Cheshmeh porphyry copper deposits, which are located in the southeastern part of the Urumieh-Dokhtar volcanic Belt, SE Iran. In this area, yearly precipitation averages 25 centimeters or less, thus the deposit’s exposure is well due to sparse or nonexistent vegetation cover. The Meiduk porphyry copper deposit (55◦ 10′ 05″ E, 30◦ 25′ 10″ N) is located 45 km northeast of Shahr-e-Babak city, Kerman province, southeastern part of Iran. The Sar Cheshmeh porphyry copper deposit (55◦ 52′ 20″ E, 29◦ 58′ 40″ N) is located 60 Km southwest of Kerman city in Kerman province, southeastern part of Iran.

Figure 1. Geological map of the study area.

Two cloud-free level 1B ALI and Hyperion images were obtained through the U.S. Geological Survey Earth Resources Observation System (EROS) Data Center (EDC). ALI and Hyperion scenes were acquired on August 18, 2004 for the Meiduk area and September 14, 2010 for the Sar Cheshmeh area, respectively. The images were pre-georeferenced to UTM zone 40 North projection using the WGS-84 datum. ALI and Hyperion images of both target sites were processed using the ENVI (Environment for Visualizing Images) version 4.5 software package. Spectral angle mapper, linear spectral unmixing, and mixture-tuned matched-filtering are tested on SWIR bands of ALI to discriminate the hydrothermally altered areas associated with porphyry copper mineralization from surrounding environment at regional scale (Pour and Hashim, 2011a,b). Analytical imaging and geophysics (AIG)-developed hyperspectral analysis processing methods are applied on VNIR and SWIR bands of Hyperion for mapping iron oxide/hydroxide minerals and clay mineral assemblages in hydrothermal alteration zones at district scale.

3. RESULTS AND DISCUSSION

Spectral mapping methods were tested to two selected spatial subset of ALI scenes covering both the Meiduk and Sar Cheshmeh mining districts for regional scale mapping. Automated spectral Hourglass (Kruse et al., 2003) was applied to SWIR bands of ALI to extracted reference spectra directly from the image and subsequent spectral mapping methods. Spectral angle mapper (SAM), linear spectral unmixing (LSU) and mixture-tuned matched-filtering

(MTMF) methods were performed to discriminate hydrothermally altered rocks from unaltered rocks at regional scale. The visual results indicated that these methods are able to differentiate hydrothermally altered rocks from unaltered rocks. Hydrothermally altered rocks associated with the known and mined porphyry copper deposits and identified prospects are well recognizable from surrounding areas at regional scale. In this study, MTMF visual results are shown in Figures 2 and 3. Bright pixels show hydrothermally altered rocks associated with the known and mined copper deposits and identified prospects in the ALI images (Figures 2 and 3).

Figure 2. MTMF visual results derived from SWIR bands of ALI subscene. Bright pixels show hydrothermally altered rocks associated with the known and mined porphyry copper deposits (highlighted by their names) and identified prospects in the Meiduk ALI subscene.

Figure 3. MTMF visual results derived from SWIR bands of ALI subscene. Bright pixels show hydrothermally altered rocks associated with the known and mined porphyry copper deposits (highlighted by their names) and identified prospects in the Sar Cheshmeh ALI subscene. Two spectral subsets of Hyperion data are analyzed separately to detect iron oxide/hydroxide minerals and hydroxyl-bearing (clay) alteration mineral assemblages in the altered areas. The first subset (VNIR) covering 90 bands between 0.4 and 1.3 μm is used for highlighting iron oxide/hydroxide minerals and second subset (SWIR) of 40

bands between 2.00 and 2.40 for detecting hydroxyl-bearing (clay) alteration mineral. AIG-developed hyperspectral analysis processing methods (Kruse et al., 2003) were used to extract end-member spectra from Hyperion subsets. The methods were applied to two selected spatial subset scenes covering the neighboring Meiduk / Sara and Sar Cheshmeh / Seridune porphyry copper ore deposits for mapping mineral assemblages in hydrothermal alteration zones. The extracted end-member spectra were identified using USGS spectral library as reference spectra. Considering the shape and position of absorption feature, the minerals are characterized as hematite, limonite, jarosite and goethite for first subset. The extracted signatures for second subset are suggested the existence of hydroxyl minerals such as sericite, kaolinite, illite, alunite, chlorite, epidote and calcite. The spectral angle mapper method was used to map spectrally predominant minerals assemblages for two selected spatial subset scenes covering Mieduk/Sara and Sar Cheshmeh/Seridune mines. In this study, SAM classification images have chosen to represent image map of the distribution of predominant minerals assemblages in hydrothermal alteration zones. The SAM method highlights the altered areas as hematite dominated (VNIR subset) and sericite dominated (SWIR subset). Figures 4 and 5 illustrate produced image maps of two selected spatial subset scenes for first subset (VNIR), showing spectrally predominant minerals as colored pixels. Hematite is represented as purple pixels and goethite as red pixels, and limonite is portrayed as yellow pixels in Mieduk/Sara subset scene (Figure 4). Hematite is manifested as orange color pixels and jarosite as dark green pixels and goethite is represented as purple pixels, limonite is illustrated as light blue pixels in Sar Cheshmeh/Seridune subset scene, as it is shown in Figure 5.

Figure 4. SAM classification image of the distribution of spectrally predominant iron oxide/hydroxide minerals in the hydrothermally altered rocks that showed as colored pixels in the Mieduk/Sara subset scene.

Figure 5. SAM classification image of the distribution of spectrally predominant iron oxide/hydroxide minerals in the hydrothermally altered rocks that showed as colored pixels in the Sar Cheshmeh/Seridune subset scene.

Figures 6 and 7 demonstrate produced image maps of two selected spatial subset scenes for second subset (SWIR). Sericite is depicted as light green pixels; kaolinite is illustrated as blue pixels and epidote as red pixels that surround the circular to elliptical areas of altered rocks in Mieduk/Sara subset scene (Figure 6). The altered minerals are

represented as different colored pixels in Sar Cheshmeh/Seridune subset scene, sericite is portrayed as brown pixels and kaolinite as bluish green pixels, and chlorite is manifested as pink pixels and calcite as dark blue pixels (Figure 7).

Figure 6. SAM classification image of the distribution of spectrally predominant clay alteration mineral assemblages in the hydrothermally altered rocks that showed as colored pixels in the Mieduk/Sara subset scene.

Figure 7. SAM classification image of the distribution of spectrally predominant clay alteration mineral assemblages in the hydrothermally altered rocks that showed as colored pixels in the Sar Cheshmeh/Seridune subset scene. Accordingly, AIG-developed hyperspectral analysis methods produced image map of spectrally predominant mineral assemblages in hydrothermally altered rocks using Hyperion data at district scale. Detected mineral groups in the hydrothermally altered rocks included sericite (illite/muscovite), kaolinite-alunite-montmorillonite and chlorite-epidote, which are representative for phyllic, advanced argillic and propylitic alteration zones, respectively. The spatial distribution of the identified hydrothermally altered rocks has been verified through in situ inspection. Geological locations were measured by a Magellan GPS with an average accuracy 7 m. The field photographs of the geomorphology, rock units and hydrothermally altered rocks were taken. Samples for XRD analysis and spectral reflectance measurements were collected from two sites within the open-pit quarry of the Meiduk and Sar Cheshmeh mines and surrounding areas in December 2010.

4. CONCLUSIONS SAM, LSU and MTMF methods have differentiated hydrothermally altered rocks associated with the known and mined porphyry copper deposits and identified prospects from unaltered rocks using SWIR bands of ALI. Hematite, limonite, jarosite and goethite were detected in supergene altered area using VNIR bands of Hyperion. Sericite, kaolinite, illite, alunite, chlorite, epidote and calcite were identified in phyllic, advanced argillic and propylitic alteration zones using SWIR bands of Hyperion. It is concluded that the extraction spectral information from ALI and Hyperion data can be used for lithological mapping and the detection of hydrothermal alteration minerals associated with porphyry copper and epithermal gold mineralization at both regional and district scales.

ACKNOWDEGMENT

We are thankful to the Universiti Teknologi Malaysia (UTM) for providing the facilities for this investigation. We would also like to express our great appreciation to Research Institute for Sustainability and Environment (RISE) of Universiti Teknologi Malaysia (UTM) for supporting research invironments.

REFERENCES

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