Arsenopyrite-Pyrite Association in Mineral Replacement Experiments: A Microscopic Study of Arsenic-Controlled Iron Sulfide Formation and implications for Orogenic Gold Mineralisation.

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Arsenopyrite-Pyrite Association in Mineral Replacement Experiments: A Microscopic Study of Arsenic-Controlled Iron Sulfide Formation and implications for Orogenic Gold Mineralisation.

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Author(s): Maryam Abdus-Salam ¹ ^, ² ^, , Joel Brugger ¹ , Barbara Etschmann ¹ , Rory McNab ¹ , Wei Li ¹ ^, ³

Publication date (Electronic): 21 January 2025

Conference name: 13th Asia Pacific Microscopy Congress 2025 (APMC13)

Conference date: 2-7 Febuary 2025

Keywords: Experimental Mineralogy, Gold Mineralisation, Orogenic Gold Deposit, Pyrite-Arsenopyrite Association

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Abstract

Pyrite and arsenopyrite commonly host invisible gold in orogenic gold deposits, with their trace element compositions key to understanding ore formation [ 1]. However, how trace elements and relationships among these sulfides impact textures remains unclear. Understanding ore-forming fluid conditions aids in determining paragenetic sequences and interpreting the textures and chemistry of sulfides, essential for studying gold deposit formation [ 2, 3]. Arsenic concentration variations in these fluids can enhance gold incorporation [ 4]. This study examines experimental siderite replacement by arsenian iron sulfides at varying As levels, simulating natural fluid fluctuations in orogenic systems. We aim to clarify how these variations influence textures, arsenopyrite-pyrite relationships, and arsenic incorporation mechanisms.

The experiments were conducted using magnesium bearing siderite as the starting material at neutral pH (~7.4), a temperature of 350°C, and fluid-to-rock ratios of ~100, with thioacetamide as a sulfidizing agent and varying As concentrations (~130 ppm and ~1300 ppm), over a period of 21 days. Analytical techniques employed included X-Ray Diffraction, Scanning Electron Microscopy, Focused Ion Beam, Electron Probe Microanalysis, Tescan Integrated Mineral Analyzer, and Nanoscale Secondary Ion Mass Spectrometry to characterize the experimental products.

Results showed distinct variations in iron sulfide chemistry and textures across the two arsenic concentrations ( Fig 1). In high-As experiments, siderite was partially replaced at the core and is rimmed by pyrrhotite and finally overgrown by submicron-sized arsenopyrite. Pyrrhotite formed fine-grained clusters with thin discontinuous rims of porous pyrite at the siderite/fluid interface. ( Fig 1). In contrast, low-As experiments showed less distinct residual siderite and slightly coarser-grained pyrrhotite, with a higher amount of porous pyrite forming as individual grains or overgrowths.

Figure 1.

(a). Comparison of mineral phases at different As content in fluid. (b) thin rim forming at the partially replaced siderite (sd)/fluid interface in an experiment conducted at a high As concentration. (c) Close-up of the rim, showing arsenopyrite rimming pyrrhotite. (d) pyrite with lamella crystal shape overgrowing pyrrhotite having inclusions of trace arsenopyrite (e) Close-up of the porous pyrite overgrowth

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Publication date (Electronic): 21 January 2025

Electronic Location Identifier: e282

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[1 ]School of Earth Atmosphere and Environment, Monash University, Victoria Australia

[2 ]Department of Geology, The Polytechnic Ibadan, Nigeria

[3 ]School of Earth Sciences and Resources, China University of Geosciences, Beijing, China

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*Corresponding author: maryamolamide.abdus-salam@ 123456monash.edu

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Maryam Abdus-Salam https://orcid.org/0000-0003-2554-3311

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DOI: 10.14293/APMC13-2025-0282

SO-VID: 8e651c0c-f135-486e-9c9a-e580155b36e0

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Published under Creative Commons Attribution 4.0 International ( CC BY 4.0). Users are allowed to share (copy and redistribute the material in any medium or format) and adapt (remix, transform, and build upon the material for any purpose, even commercially), as long as the authors and the publisher are explicitly identified and properly acknowledged as the original source.

Conference name: 13th Asia Pacific Microscopy Congress 2025

Conference acronym: APMC13

Conference number: 13

Conference location: Brisbane, Australia

Conference date: 2-7 Febuary 2025

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References

Sung Y-H, et al (2009). Western Australia. Miner Deposita 44:765–791. https://doi.org/10.10I07/s00126-009-0244-4
Li W, et al (2019). Miner Deposita 54:591–610. https://doi.org/10.1007/s00126-018-0826-0
Webb S, et al (2024). Geol Soc Lond Spec Publ 541:273–297. https://doi.org/10.1144/SP541-2023-17
Pokrovski GS, et al (2021) A. Geochem Perspect Lett 17:39–44. https://doi.org/10.7185/geochemlet.2112
Kusebauch C, Oelze M, Gleeson SA (2018). Chem Geol 500:136–147. https://doi.org/10.1016/j.chemgeo.2018.09.027
Kusebauch C, Gleeson SA, Oelze M (2019). Sci Adv 5:eaav5891. https://doi.org/10.1126/sciadv.aav5891
Kutzschbach M, et al (2024). Geochim Cosmochim Acta 376:37–53. https://doi.org/10.1016/j.gca.2024.05.027
Xing Y, et al (2019). Geology 47:335–338. https://doi.org/10.1130/G45708.1

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[1] Sung Y-H, et al (2009). Western Australia. Miner Deposita 44:765–791. https://doi.org/10.10I07/s00126-009-0244-4

[2] Li W, et al (2019). Miner Deposita 54:591–610. https://doi.org/10.1007/s00126-018-0826-0

[3] Webb S, et al (2024). Geol Soc Lond Spec Publ 541:273–297. https://doi.org/10.1144/SP541-2023-17

[4] Pokrovski GS, et al (2021) A. Geochem Perspect Lett 17:39–44. https://doi.org/10.7185/geochemlet.2112

[5] Kusebauch C, Oelze M, Gleeson SA (2018). Chem Geol 500:136–147. https://doi.org/10.1016/j.chemgeo.2018.09.027

[6] Kusebauch C, Gleeson SA, Oelze M (2019). Sci Adv 5:eaav5891. https://doi.org/10.1126/sciadv.aav5891

[7] Kutzschbach M, et al (2024). Geochim Cosmochim Acta 376:37–53. https://doi.org/10.1016/j.gca.2024.05.027

[8] Xing Y, et al (2019). Geology 47:335–338. https://doi.org/10.1130/G45708.1

Arsenopyrite-Pyrite Association in Mineral Replacement Experiments: A Microscopic Study of Arsenic-Controlled Iron Sulfide Formation and implications for Orogenic Gold Mineralisation.

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