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Geology Congress: LA-ICPMS in Ore Analysis

This document summarizes a presentation given at the 19th Peruvian Congress of Geology in Lima in 2018. The presentation discussed how laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) can be used to characterize gold deportment and trace element variations in ore deposits at a high resolution. LA-ICPMS allows in-situ analysis of gold inclusions and trace element distributions in pyrite grains as small as 12 micrometers. This technique provides insights into ore genesis and the evolution of deposits that can aid in optimal extraction process planning and environmental management. Figures from the study of a gold deposit in Bendigo, Australia were presented as examples. The paper concludes that LA-ICPMS

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94 views2 pages

Geology Congress: LA-ICPMS in Ore Analysis

This document summarizes a presentation given at the 19th Peruvian Congress of Geology in Lima in 2018. The presentation discussed how laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) can be used to characterize gold deportment and trace element variations in ore deposits at a high resolution. LA-ICPMS allows in-situ analysis of gold inclusions and trace element distributions in pyrite grains as small as 12 micrometers. This technique provides insights into ore genesis and the evolution of deposits that can aid in optimal extraction process planning and environmental management. Figures from the study of a gold deposit in Bendigo, Australia were presented as examples. The paper concludes that LA-ICPMS

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Roy Supa
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XIX CONGRESO PERUANO DE GEOLOGÍA

LIMA 2018

COMBINING GEOLOGY, GEOCHEMISTRY AND GEOMETALLURGY TO


CHARACTERISE ORE DEPORTMENT USING LA-ICPMS TECHNOLOGY

Helen Thomas(1,2)*, Ross Large(2), Sebastien Meffre(2), Christina Wanhainen(1), Glenn Bark(1), Riia
Chmielowski(1)
(1)
Luleå University of Technology, Luleå, Sweden. *(Current address)
(2)
CODES Centre of Excellence in Ore Deposits, University of Tasmania, Australia.

ABSTRACT
Improvements in analytical technology allow characterization of ore to a greater extent, with more
detail and with increased automation. Using laser ablation mass spectrometry alongside traditional
metallurgical characterizations, means in-situ ore relations can be studied, as well as trace element
zonation in the ore and across the deposit. This information is critical for the planning of metal
extraction as well as environmental concerns for mine waste. This paper presents an overview of how
Laser Ablation-Inductively Coupled Mass Spectrometry (LA-ICPMS) technology can be used to
investigate gold deportment from refractory gold held in pyrite structure, to nanoparticles to free gold
inclusions.
KEYWORDS
Gold, LA-ICPMS, geometallurgy, geochemistry, trace elements

METHODOLOGY
Data presented here was acquired using a solid-state laser microprobe attached to a quadrupole
ICPMS, with a laser spot size between 55µm and 12µm depending on the size of the pyrite grain
(Thomas, 2011 and references therein). See figure 1 below for a typical LA-ICPMS spot analysis,
where the gold inclusion present can be quantified and its approximate size calculated. Using iron (Fe)
as an internal standard the concentration of trace elements selected can be quantified to ppm and
imported to geochemical analysis software such as IoGAS. Figure 2 illustrates how the presence of
free gold inclusions in quantified image data can be evaluated using Reich et al´s 2005 gold saturation
diagram. Gold was studied as well as 20 other trace elements.

Figure 1. Figure 2.
XIX CONGRESO PERUANO DE GEOLOGÍA
LIMA 2018

The size and location of gold inclusions has a strong affect on the ore response to extraction technique
and the ability to characterize the amount and location of gold is imperative to be able to plan a
metallurgical process that can extract all the gold. This technique allows the variation in gold
deportment to be investigated across a deposit, including vectors to ore figure 3. With geochemical
analysis of the trace elements aquired in addition to Au and As the deposit evolution can also be
studied. Deleterious elements (eg. Cd, Tl, Sb) can also be characterized in this fashion, allowing the
deposit to be mapped in terms of smelter credits and penalties, environmental concerns (e.g. acid mine
drainage) and extraction technique (e.g. cyanide leach vs pressure oxidization)

Figure 3. Variation of Au-As rims on


various types of pyrite from an
orogenic gold deposit in Bendigo,
Australia. Rims are thicker proximal
to gold-bearing reef structures.

CONCLUSIONS
LA-ICPMS is a powerful tool to unmask complexities in ore deportment and extraction. Using in-situ
information from across the deposit it aids in a complete characterization from exploration, to
extraction and remediation.
REFERENCES
Reich, Martin, Stephen E. Kesler, Satoshi Utsunomiya, Christopher S. Palenik, Stephen L. Chryssoulis, and
Rodney C. Ewing. ‘Solubility of Gold in Arsenian Pyrite’. Geochimica et Cosmochimica Acta 69, no. 11 (June
2005): 2781–96. https://doi.org/10.1016/j.gca.2005.01.011.

Thomas, Helen V., Ross R. Large, Stuart W. Bull, Valeriy Maslennikov, Ron F. Berry, Rod Fraser, Shane Froud,
and Robert Moye. ‘Pyrite and Pyrrhotite Textures and Composition in Sediments, Laminated Quartz Veins, and
Reefs at Bendigo Gold Mine, Australia: Insights for Ore Genesis’. Economic Geology 106, no. 1 (1 January
2011): 1–31. https://doi.org/10.2113/econgeo.106.1.1.

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