Epidote–clinozoisite as a hyperspectral tool in exploration for Archean gold

Roache, Tony; Walshe, John L.; Huntington, J.F.; Quigley, M.; Yang, Kai; Bil, Bartek; Blake, Kevin; Hyvärinen, Timo

doi:10.1080/08120099.2011.608170

Cited by 44 publications

(21 citation statements)

References 12 publications

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“…This is unfortunate because epidote has shown promise as a vectoring tool in porphyry deposits (Cooke et al 2014b) and spectral variation across the epidote--clinozoisite solid--series is certainly recognisable (Roache et al 2011). This is an area where future study would be useful.…”

Section: Discussionmentioning

confidence: 99%

“…However, sensitivity of SWIR spectra to mineral chemical changes that are recognisable both in the laboratory (King & Clark 1989;Liebscher 2004;Bishop et al 2008) and in hyperspectral imaging (Cudahy et al 2001;Roache et al 2011) have been recognised. This indicates that spectral characteristics might be able to act as a vector to orebodies in the propylitic domain as well as the more proximal alteration zones.…”

Section: Introductionmentioning

confidence: 99%

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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%

Section: Introductionmentioning

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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“…In calcite, the major component of limestone, the carbonate ion (CO3-2) is responsible for the series of absorption bands between 1.8 and 2.4 micrometers (μm). The clay minerals, kaolinite and montmorillonite, have a strong absorption band near 1.4 μm (hydroxide ions, OH-1) and a weaker band at 1.9 μm (bound water molecules) Roache et al 2011) and is used to derive compositional information (minerals or other components) or it can be used to present compositional maps derived by combining digital imaging and spectroscopy (Specim, Finland; see Fig. 27.5 and Table 27.4).…”

Section: Optical Methodsmentioning

confidence: 99%

Future Developments and Innovations in High-Resolution Core Scanning

Croudace¹,

Rothwell²

2015

Developments in Paleoenvironmental Research

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“…With the recent development of drill core hyperspectral imaging systems, this compositional information can now be acquired rapidly and at high spatial resolutions (e.g., Kruse, 1996;Calvin et al, 2005;Roache et al, 2011;Kruse et al, 2012;Zaini, et al, 2014). Spectroscopic research on kimberlites has typically focused on airborne remote sensing projects aimed at kimberlite exploration and characterization (Kruse and Boardman, 2000;Keeling et al, 2004;Tukiainen and Thorning, 2005), and the collection of SWIR reflectance spectra from kimberlite hand samples (Hauff et al, 2001;Guha et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

Characterizing Kimberlite Dilution by Crustal Rocks at the Snap Lake Diamond Mine (Northwest Territories, Canada) using SWIR (1.90–2.36μm) and LWIR (8.1–11.1μm) Hyperspectral Imagery Collected from Drill Core

Tappert¹,

Rivard²,

Fülöp³

et al. 2015

Economic Geology

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Short-wave infrared (SWIR, 1.90-2.36 µm) and long-wave infrared (LWIR, 8.1-11.1 µm) hyperspectral images collected using the SisuROCK system were used to develop an automated methodology for generating kimberlite dilution maps. Smoothed and denoised images from two Snap Lake (Northwest Territories, Canada) kimberlite drill cores were processed, and SWIR and LWIR spectral endmembers were extracted from the images with each mineralogical endmember assigned to one of four compositional groups: undiluted kimberlite, microdiluted kimberlite, micro-and macrodiluted kimberlite, and crustal rocks. These endmembers were used to classify the SWIR and LWIR images, and the results were validated using linescan data, drill core logs, petrology reports, and the results of X-ray diffraction, Raman spectroscopy, and Micro-Fourier Transform Infrared (FTIR) spectroscopy. This study demonstrates that hyperspectral imagery can be used to generate dilution maps for hypabyssal kimberlites that far supersede other current techniques in terms of spatial resolution.

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Epidote–clinozoisite as a hyperspectral tool in exploration for Archean gold

Cited by 44 publications

References 12 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

Future Developments and Innovations in High-Resolution Core Scanning

Characterizing Kimberlite Dilution by Crustal Rocks at the Snap Lake Diamond Mine (Northwest Territories, Canada) using SWIR (1.90–2.36μm) and LWIR (8.1–11.1μm) Hyperspectral Imagery Collected from Drill Core

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