Aug 21, 2012 - tial mineral deposit types, the high-resolution hyperspectral data were analyzed to detect the presence of selected minerals that may be.
Eos, Vol. 93, No. 34, 21 August 2012
Hyperspectral Remote Sensing Data Maps Minerals in Afghanistan PAGES 325–326 Although Afghanistan has abundant mineral resources, including gold, silver, copper, rare earth elements, uranium, tin, iron ore, mercury, lead-zinc, bauxite, and industrial minerals, most have not been successfully developed or explored using modern methods. The U.S. Geological Survey (USGS) with cooperation from the Afghan Geological Survey (AGS) and support from the Department of Defense’s Task Force for Business and Stability Operations (TFBSO) has used new imaging spectroscopy surface material maps to help refine the geologic signatures of known but poorly understood mineral deposits and identify previously unrecognized mineral occurrences. To help assess the potential mineral deposit types, the high-resolution hyperspectral data were analyzed to detect the presence of selected minerals that may be indicative of past mineralization processes. This legacy data set is providing tangible support for economic decisions by both the government of Afghanistan and other public and private sector parties interested in the development of the nation’s natural resources. In July, USGS released surficial mineral maps of Afghanistan derived from imaging spectrometer data. This is the largest contiguous terrestrial area covered by a hyperspectral survey. More than 800,000,000 pixels of data covering more than 438,000 square kilometers, an area approximately the size of California, were analyzed to produce the maps. The imaging spectroscopy data were collected by the HyMap sensor [Cocks et al., 1998] between 22 August and 2 October 2007, using the NASA WB-57 aircraft temporarily based at Kandahar Airfield. The HyMap sensor has also been used to map the mineralogy in the Rodalquilar caldera [Bedini et al., 2009], the lithology of the Sarfartoq carbonatite complex in southern west Greenland [Bedini, 2009], and hydrothermal alteration zones in granitoids of the Eastern Fold Belt, Mount Isa Inlier, Australia [Laukamp et al., 2011]. In Afghanistan, data were collected from an altitude of approximately 15 kilometers in 28 flights. Extreme changes in topographic relief and the duration of the airborne survey, variations in the time of day during which flight lines were acquired, and restricted access to ground calibration sites because of security concerns provided challenges to routine data processing methods. As part of the data analysis, scaled radiance data were processed into atmospherically corrected reflectance data in a multistep process. In this process the reflectance spectrum of each pixel was compared to the spectral features of 97 reference standards in a spectral library of minerals using the Material Identification and Characterization Algorithm, a module of USGS’s Processing
Routines in IDL for Spectroscopic Measurements software [Kokaly, 2011]. The resulting maps of material distribution, resampled to 23 × 23 meter square pixel grids, were pieced together (“mosaicked”) to create thematic maps of surface mineral occurrences over the full data set covering Afghanistan [Kokaly et al., 2011; King et al., 2011b]. The imaging spectroscopy data have proven valuable in defining ore deposits on the basis of the extent and type of alteration minerals associated with a specific deposit type and in detecting and mapping specific alteration minerals, variations in trace element mineral chemistry, and differences in the oxidation state of transition element-bearing minerals. Targeted analyses for 21 areas of interest, selected on the basis of their potential for economic development and mineral exploitation, show that the HyMap data have expanded the footprint and clarified the mineralization associated with ore-forming processes for a number of different commodities and deposit types. The main commodities found in the areas of interest include gold, silver, copper, rare earth elements, uranium, tin, iron ore, mercury, lead-zinc, bauxite, and industrial minerals. Studies indicate that the HyMap data can be used to accelerate resource development, which is vital for advancing Afghanistan’s economic stabilization, because of
the synoptic coverage, the reduction of time required for mapping, and mineralogical content of the data [Peters et al., 2011; King et al., 2011a]. In the Zarkashan area of interest (Figure 1) the HyMap data were used for detecting and mapping favorable host rocks and alteration mineral assemblages, including those associated with epithermal gold deposits and copper porphyry systems. The geotectonic history of Afghanistan is one of Tethysides evolution. The Zarkashan pluton is part of a continental margin magmatic arc complex that was superimposed on accreted blocks of the Cimmeride Belt along the southern Laurasia margin during closure of the Neo-Tethys Ocean [Doebrich et al., 2007]. The Zarkashan gold-bearing skarns occur proximal to the margins of the northeast- elongated, Cretaceous to Paleogene (~99– 55 million years ago), granodioritic Zarkashan pluton. The host country rocks are Upper Jurassic to Lower Cretaceous (~161– 130 million years ago) limestone, sandstone, and siltstone. The gold is spatially associated with calcite, copper sulfide minerals, quartz, and serpentine [Peters et al., 2007]. Potential regions of mineralization in contact zones on the edges of the Zarkashan intrusion were spectrally characterized as well-defined contiguous areas of iron-bearing and epidote minerals. These regions were coincident with previously reported anomalous areas of high gold concentration [Peters et al., 2011]. The size and extent of the alteration shown in the HyMap data suggested that the distribution of copper and gold could be extensive and far greater than
Fig. 1. A three-dimensional image of surface minerals in the contact zones (blue, magenta, orange, yellow, and green) around the Zarkashan intrusive (gray area in the center of the image bounded by a white line) in the Zarkashan copper and gold area of interest.These anomalous zones represent combinations of favorable alteration minerals that are associated with copper and gold mineralization.
This paper is not subject to U.S.Union. copyright. Published in 2012 by the American Geophysical Union. © 2012. American Geophysical All Rights Reserved.
Eos, Vol. 93, No. 34, 21 August 2012 previously known. Field investigations and sampling and subsequent chemical analysis confirmed that the HyMap data accurately redefined the extent and target zones of oregrade copper and gold [Peters et al., 2011]. In conjunction with TFBSO, USGS has created data and information packages for each of the areas of interest. The data packages are intended to serve as a source of fundamental information that will allow mining firms and potential investors to develop the mineral wealth of Afghanistan. The full country maps and information packages for the 21 areas of interest are publicly available on USGS Web sites (http:// pubs.usgs.gov/sim/3152/A /, http://pubs.usgs .gov/sim/3152/B/, and http://pubs.usgs.gov/ of/2011/1204/) and will soon be in the AGS Data Center in Kabul. Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. government.
References Bedini, E. (2009), Mapping lithology of the Sarfartoq carbonatite complex, southern west Greenland, using HyMap imaging spectrometer data, Remote
Sens. Environ., 113(6), 1208–1219, doi:10.1016/ j.rse.2009.02.007. Bedini, E., F. van der Meer, and F. van Ruitenbeek (2009), Use of HyMap imaging spectrometer data to map mineralogy in the Rodalquilar caldera, southest Spain, Int. J. Remote Sens., 30(2), 327– 348, doi:10.1080/01431160802282854. Cocks T., R. Jenssen, A. Stewart, I. Wilson, and T. Shields (1998), The HyMap airborne hyperspectral sensor: The system, calibration and performance, in Proceedings of the 1st EARSeL Workshop on Imaging Spectroscopy, 6-8 October 1998, Zurich, edited by M. Schaepman, D. Schlapfer, and K. I. Itten, pp. 37–43, Eur. Assoc. of Remote Sens. Lab., Paris. Doebrich, J. L., et al. (2007), Porphyry copper potential of Tethyan magmatic arcs of Afghanistan, in Digging Deeper: Proceedings of the Ninth Biennial Meeting of the Society for Geology Applied to Mineral Deposits: Dublin, Ireland, 20th–23rd August 2007, edited by C. J. Andrew, pp. 129–132, Ir. Assoc. for Econ. Geol., Mountmellick, U. K. King, T. V. V., M. R. Johnson, B. E. Hubbard, and B. J. Drenth (2011a), Identification of mineral resources in Afghanistan—Detecting and mapping resource anomalies in prioritized areas using geophysical and remote sensing (ASTER and HyMap) data, U.S. Geol. Surv. Open File Rep., 2011-1229, 327 pp. [Available at http://pubs.usgs.gov/of/2011/1229/.] King, T. V. V, R. F. Kokaly, T. M. Hoefen, K. B. Dudek, and K. E. Livo (2011b), Surface materials map of Afghanistan: Fe-bearing minerals and other materials, U.S. Geol. Surv. Sci. Invest. Map, 3152B. [Available at http://pubs.usgs.gov/sim/3152/B/.]
© 2012. American Geophysical All Rights Reserved. This paper is not subject to U.S.Union. copyright. Published in 2012 by the American Geophysical Union.
Kokaly, R. F. (2011), PRISM: Processing routines in IDL for spectroscopic measurements (installation manual and users guide, version 1.0), U.S. Geol. Surv. Open File Rep., 2011-1155, 432 pp. [Available at http://pubs.usgs.gov/of/2011/1155/.] Kokaly, R. F., T. V. V. King, T. M. Hoefen, K. B. Dudek, and K. E. Livo (2011), Surface materials map of Afghanistan: Carbonates, phyllosilicates, sulfates, altered minerals, and other materials, U. S. Geol. Surv. Sci. Invest. Map, 3152A. [Available at http:// pubs.usgs.gov/sim/3152/A /.] Laukamp, C., T. Cudahy, J. S. Cleverley, N. H. S. Oliver, and R. Hewson (2011), Airborne hyperspectral imaging of hydrothermal alteration zones in granitoids of the Eastern Fold Belt, Mount Isa Inlier, Australia, Geochem. Explor. Environ. Anal., 11, 3–24, doi:10.1144/1467-7873/09-231. Peters, S. G., et al. (Eds.) (2007), Preliminary nonfuel mineral resource assessment of Afghanistan [CD-ROM], U.S. Geol. Surv. Open File Rep., 2007– 1214, 810 pp. [Available at http://pubs.usgs.gov/of/ 2007/1214/.] Peters, S. G., et al. (Eds.) (2011), Summaries of important areas for mineral investment and production opportunities of nonfuel minerals in Afghanistan, U.S. Geol. Surv. Open File Rep., 20111204, 810 pp. [Available at http://pubs.usgs.gov/of/ 2011/1204/.] —Trude V. V. King, Raymond F. Kokaly, Todd M. Hoefen, and Michaela R. Johnson, U.S. Geological Survey, Denver, Colo.; E-mail: tking@usgs .gov
