The chlorite proximitor: A new tool for detecting porphyry ore deposits

Wilkinson, Jamie J.; Chang, Zhaoshan; Cooke, David R.; Baker, Michael J.; Wilkinson, CC; Inglis, Shaun; Chen, Hong‐Yuan; Gemmell, J. Bruce

doi:10.1016/j.gexplo.2015.01.005

Cited by 159 publications

(114 citation statements)

References 21 publications

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“…Geochemical variation in chlorite has previously been recognised as an effective vector to mineralisation in the Batu Hijau system (Wilkinson et al 2015). The major element geochemistry derived from electron microprobe analysis unsurprisingly matches that previously reported by LA--ICP--MS (Wilkinson et al 2015) and shows that Mg# and Al:Si ratios in chlorite vary spatially with respect to the orebody.…”

Section: Discussionsupporting

confidence: 77%

“…Chlorite, within approximately 1 km of the centre, is enriched in Mg and then shows a rapid decrease in Mg:Fe ratio to around 1.5 km; beyond this, the relative content of Mg increases progressively to the limit of sampling at about 4.5 km. Samples at distances less than 500 m from the centre (which correspond to tonalite and carbonate--hosted chlorite) are anomalous, as previously identified in chlorite trace element chemistry (Wilkinson et al 2015). …”

Section: Major Element Chemistrysupporting

confidence: 64%

“…Alteration zoning is not only expressed in mineralogy, but in whole--rock and mineral geochemical trends which can act as vectors towards orebodies (e.g. Emmons 1927;John 1978;Norman et al 1991;Cooke et al 2014b;Wilkinson et al 2015).…”

Section: Introductionmentioning

confidence: 99%

“…It builds on previous research done as part of the AMIRA P765A research project (AMIRA International Ltd) which included studies of spatial variation in the geochemistry of chlorite (Wilkinson et al 2015) and epidote (Cooke at al. 2014b).…”

Section: Introductionmentioning

confidence: 99%

“…2014b). Most importantly, the work utilised the same samples analysed by Wilkinson et al (2015) so that extensive prior knowledge of whole--rock geochemistry and mineral chemistry was available. The primary aims were to characterise the infrared spectra of propylitic rocks throughout the Batu Hijau alteration footprint, and to identify any spectral features that might reflect systematic geochemical variation in the spatial domain which could therefore act as vectors towards economic mineralisation.…”

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: Discussionsupporting

confidence: 77%

Section: Major Element Chemistrysupporting

confidence: 64%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

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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A data screening approach to confirming a target mineral is chlorite using EPMA and LA‐ICPMS data

Freij,

Gregory,

Liu

2023

Geoscience Data Journal

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Applying machine learning techniques to large datasets of in situ analyses has been proven to be a powerful tool in Earth Sciences. However, problems may arise when dealing with minerals such as chlorite, that exist as a solid solution rather than a single, stoichiometric ideal. It can be difficult to determine whether the variations in major element concentrations are due to compositional difference in the mineral of interest or due to sampling of the surrounding mineral phases in addition to the mineral of interest during the analyses. If the latter, interpretations of the results would be complicated, misled or even spurious. Here we present a method to identify chlorite based on the major and minor element content, from both LA‐ICPMS and EPMA data. Further we present a dataset of 3,317 analyses of chlorite and have shown that 7.4% of these analyses include significant quantities of non‐chlorite material.

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In situ mineral chemistry of chlorite in Donghua area, Dehua‐Youxi‐Yongtai ore district, Fujian Province, south‐east China: Elemental characteristics and their implications for exploration

et al. 2021

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As an ordinary alteration mineral in the process of fluid–rock interaction, chlorite (most especially its chemical composition) has the potential to become an effective tool to reveal the physicochemical conditions during alteration and help exploration. However, its elemental characteristics during the chloritization process are yet to be clearly understood. The Dehua‐Youxi‐Yongtai (DYY) ore district in south‐east China is one of the potential areas of gold and polymetallic deposits. Lying in the north‐west section of the DYY ore district, the Donghua area is notable for its remarkable metallogenic potential, and porphyry‐epithermal systems might have developed in the area. This study focuses on the elemental characteristics of chlorite in the Donghua area as footprints of the alteration process and mineralization vectoring. According to the geological features and occurrences, the chlorite from Donghua can be divided into two generations: (a) Chlorite I is closely related to chloritization developed in intrusive and volcanic rocks (Permian quartz monzobiorite and Jurassic volcanic rocks of Changlin Formation), and (b) chlorite II is accompanied by superimposed hydrothermal overprinting. The alteration process suggested by overprinting chlorite II can be regarded as almost coeval with the ca. 154–153 Ma magmatic event, and chlorite II is later than chlorite I generation. According to the geothermometry of the chlorite in Donghua, chlorite I might have crystallized on the temperature of 180–240°C with a peak of ~200°C, and the overprinting chlorite II might have experienced two episodes of hydrothermal/epithermal fluid pulsing. The mineral geochemistry of the trace elements in the two generations of the chlorite in Donghua shows different characteristics. The replacement of Mg2+ by Fe2+ plays an important role for ionic substitution in the octahedral position, especially for chlorite II. The other occasion might be Mg and Fe jointly entering the octahedral position as well as Mg‐ and Fe‐AlVI substitution mechanisms. The enrichment of Mg especially in chlorite II suggests low‐grade oxidation and acid conditions, which might be beneficial for the transportation of metallogenic substances. The obvious differences of Co and Ni are remarkable aspects of the trace elements of chlorite in Donghua, resulted by the ion substitution and function of different octahedral site preference energy. The mineral chemistry of chlorite II from Donghua can be helpful for targeting and exploration vectoring in the DYY ore district.

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The chlorite proximitor: A new tool for detecting porphyry ore deposits

Cited by 159 publications

References 21 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

A data screening approach to confirming a target mineral is chlorite using EPMA and LA‐ICPMS data

In situ mineral chemistry of chlorite in Donghua area, Dehua‐Youxi‐Yongtai ore district, Fujian Province, south‐east China: Elemental characteristics and their implications for exploration

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