Identification of spectrally similar materials using the USGS Tetracorder algorithm: the calcite–epidote–chlorite problem

Dalton, J. B.; Bove, Dana J.; Mladinich, Carol S.; Rockwell, Barnaby W.

doi:10.1016/j.rse.2003.11.011

Cited by 50 publications

(40 citation statements)

References 8 publications

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“…Although both spectral analysis techniques employ spectral unmixing at their core, the effectiveness is limited -especially when the number of contributing minerals is high and when minerals have overlapping features. For example, the chlorite--epidote--calcite assemblage, which is common in porphyry systems, will have overlapping features in the region of 2340 nm (Dalton et al 2004). At Batu Hijau, calcite is relatively rare and so presumably has little effect, however epidote is abundant, especially as the secondary mineral in chlorite--dominated spectra.…”

Section: Discussionmentioning

confidence: 99%

Spectral characteristics of propylitic alteration minerals as a vectoring tool for porphyry copper deposits

Neal

Wilkinson

Mason

et al. 2018

Journal of Geochemical Exploration

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Short--wave infrared (SWIR) reflectance spectroscopy is a quick and effective method of detecting and characterising hydrothermal alteration associated with ore deposits, and can identify not only mineral species but also changes in the major element composition of minerals. Porphyry deposits represent large accumulations of valuable metal in the Earth's crust and have extensive alteration signatures making them an attractive target for exploration, particularly by remote sensing which can cover large areas quickly. Reflectance spectroscopy has been widely applied in sericitic (phyllic), argillic and advanced argillic alteration domains because it is particularly effective in discriminating bright clay minerals. However, the propylitic domain has remained relatively unexplored because propylitic rocks are typically dark and produce relatively poorly--defined spectra.This study utilised an ASD TerraSpec 4 handheld spectrometer to collect SWIR spectra from rocks surrounding the Batu Hijau Cu--Au porphyry deposit in Indonesia, where previous work has identified systematic spatial variations in the chemistry of chlorite, a common propylitic alteration mineral. Spectra were collected from 90 samples and processed using The Spectral Geologist (TSG) software as well as the Halo mineral identifier to characterise mineralogy and extract the positions and depths of spectral absorption features, which were then correlated with major element geochemistry. Two diagnostic chlorite absorption features located at around 2250 nm and 2340 nm correlate with the Mg# (Mg/[Mg+Fe]) of chlorite, both in terms of wavelength position and depth. As the Mg# increases, the wavelengths of both features increase from 2249 nm to 2254 nm and from 2332 nm to 2343 nm respectively, and absorption depths also increase significantly. In the spatial dimension, these feature variations act as reasonably strong vectors to the orebody, showing systematic increases over a transect away from the porphyry centre, peaking at distances of around 1.6 km, which matches the spatial trend displayed by Mg#, as well as various trace element indicators in chlorite. The hull slope in spectra between 1400 nm and 1900 nm is also shown to increase with Mg#, and the position of an absorption feature at 1400 nm increases with the Al:Si ratio, a parameter that also tends to increase with proximity to porphyry deposits.Feature depth variations in particular appear to represent a new finding in chlorite reflectance spectroscopy; however, the causes are not entirely clear and require further investigation. Nonetheless, the systematic behaviour provides a potentially useful new tool for exploration in propylitic alteration zones.

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Section: Discussionmentioning

confidence: 99%

Spectral characteristics of propylitic alteration minerals as a vectoring tool for porphyry copper deposits

Neal

Wilkinson

Mason

et al. 2018

Journal of Geochemical Exploration

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“…An argillic zone characterized by kaolinite and alunite collectively exhibits a secondary Al-OH absorption feature corresponding with ASTER band 5 ( Figure 4). A propylitic zone with epidote, chlorite and calcite displays absorption features coinciding with ASTER band 8 ( Figure 4) [1][2][3][4][5]47,48,[50][51][52][53][54]. [46].…”

Section: Results: Aster Spectral and Spatial Processingmentioning

confidence: 99%

Lithological and Hydrothermal Alteration Mapping of Epithermal, Porphyry and Tourmaline Breccia Districts in the Argentine Andes Using ASTER Imagery

et al. 2018

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Abstract:The area of interest is located on the eastern flank of the Andean Cordillera, San Juan province, Argentina. The 3600 km 2 area is characterized by Siluro-Devonian to Neogene sedimentary and igneous rocks and unconsolidated Quaternary sediments. Epithermal, porphyry-related, and magmatic-hydrothermal breccia-hosted ore deposits, common in this part of the Frontal Cordillera, are associated with various types of hydrothermal alteration assemblages. Kaolinite -alunite-rich argillic, quartz -illite-rich phyllic, epidote -chlorite -calcite-rich propylitic and silicic are the most common hydrothermal alteration assemblages in the study area. VNIR, SWIR and TIR ASTER data were used to characterize geological features on a portion of the Frontal Cordillera. Red-green-blue band combinations, band ratios, logical operations, mineral indices and principal component analysis were applied to successfully identify rock types and hydrothermal alteration zones in the study area. These techniques were used to enhance geological features to contrast different lithologies and zones with high concentrations of argillic, phyllic, propylitic alteration mineral assemblages and silicic altered rocks. Alteration minerals detected with portable short-wave infrared spectrometry in hand specimens confirmed the capability of ASTER to identify hydrothermal alteration assemblages. The results from field control areas confirmed the presence of those minerals in the areas classified by ASTER processing techniques and allowed mapping the same mineralogy where pixels had similar information. The current study proved ASTER processing techniques to be valuable mapping tools for geological reconnaissance of a large area of the Argentinean Frontal Cordillera, providing preliminary lithologic and hydrothermal alteration maps that are accurate as well as cost and time effective.

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“…Only small spots of epidote and chlorite can be located within the blue patches of calcite in Figure 16. This is an apparent problem of results from expert systems, which has been described by Dalton et al [54]. They used synthetic mixtures of epidote, chlorite and calcite to improve mineral mapping results of the USGS Tetracorder [54].…”

Section: Results From the Haib River Deposit Using The Gfz Spectral Lmentioning

confidence: 99%

“…This is an apparent problem of results from expert systems, which has been described by Dalton et al [54]. They used synthetic mixtures of epidote, chlorite and calcite to improve mineral mapping results of the USGS Tetracorder [54]. A similar approach was also used to produce the EnGeoMAP 2.0 result of Figure 17.…”

Section: Results From the Haib River Deposit Using The Gfz Spectral Lmentioning

confidence: 99%

EnGeoMAP 2.0—Automated Hyperspectral Mineral Identification for the German EnMAP Space Mission

et al. 2016

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Abstract:Algorithms for a rapid analysis of hyperspectral data are becoming more and more important with planned next generation spaceborne hyperspectral missions such as the Environmental Mapping and Analysis Program (EnMAP) and the Japanese Hyperspectral Imager Suite (HISUI), together with an ever growing pool of hyperspectral airborne data. The here presented EnGeoMAP 2.0 algorithm is an automated system for material characterization from imaging spectroscopy data, which builds on the theoretical framework of the Tetracorder and MICA (Material Identification and Characterization Algorithm) of the United States Geological Survey and of EnGeoMAP 1.0 from 2013. EnGeoMAP 2.0 includes automated absorption feature extraction, spatio-spectral gradient calculation and mineral anomaly detection. The usage of EnGeoMAP 2.0 is demonstrated at the mineral deposit sites of Rodalquilar (SE-Spain) and Haib River (S-Namibia) using HyMAP and simulated EnMAP data. Results from Hyperion data are presented as supplementary information.

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Identification of spectrally similar materials using the USGS Tetracorder algorithm: the calcite–epidote–chlorite problem

Cited by 50 publications

References 8 publications

Spectral characteristics of propylitic alteration minerals as a vectoring tool for porphyry copper deposits

Spectral characteristics of propylitic alteration minerals as a vectoring tool for porphyry copper deposits

Lithological and Hydrothermal Alteration Mapping of Epithermal, Porphyry and Tourmaline Breccia Districts in the Argentine Andes Using ASTER Imagery

EnGeoMAP 2.0—Automated Hyperspectral Mineral Identification for the German EnMAP Space Mission

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