Larionov Institute for Physical and Engineering Problems of the North at the Yakutsk Research Centre, Siberian Branch of the Russian Academy of Sciences, Yakutsk, Russia:
S. G. Moskvitin, Senior Researcher, Candidate of Geology & Mineralogy Sciences
L. V. Moskvitina, Senior Researcher, Candidate of Physics & Technical Sciences, e-mail: Horo48@yandex.ru

Yu.G. Shafer Institute of Cosmophysical Research and Aeronomy at the Yakutsk Research Centre, Siberian Branch of the Russian Academy of Sciences, Yakutsk, Russia:
V. I. Popov, Senior Researcher, Candidate of Physics & Mathematics Sciences

The studied deposit situated in the Northern Verkhoyanye (Yakutia) is one of the largest gold deposits in Russia and, according to its formation conditions, as well as geological, mineralogical and geochemical parameters, it can be subsumed under the gold sulphide type, with gold finely dispersed in carbonaceous shales. Commercial gold content of ores is determined by vein-disseminated mineralization represented by gold-bearing pyrite and arsenopyrite disseminated in silicified aleurolites. Aiming to develop and enhance new techniques for recovering fine gold, the authors looked at concentrator minerals to understand the deportment and chemical state of gold in them. For this, a combination of chemical and ion-plasma etching processes was applied to sulphide matrix in oxygen and argon environments. As a result of chemical etching, loose iron chloride salts and other unstable compounds are formed on sulphide surface, which can partially be removed by ultrasonic cleaning. Ion-plasma etching in oxygen and argon environment helps remove most of the products of the chemical reaction, while thin layers of the sulphide matrix get removed in the course of repetitive etching cycles. It was established that due to high electrical conductivity of precious metals, ionization that occurs in them as a result of charged-particle bombardment is neutralized very quickly, and this process does not affect their electrophysical properties ensuring selective etching of the sulphide matrix. With the help of scanning tunnel and atomic-force microscopy, the authors looked at the morphology and localization of fine-dispersed gold in sulphides. It was established that nanoscale gold inclusions are distributed throughout the entire volume of the host sulphides in native state. The deformation processes occurring in pyrite and arsenopyrite crystals were found to have contributed to the enlargement of gold grains. The gold contained in early-stage arsenopyrites is found in the form of nanoinclusions of emulsion.

1. Moskvitin S. G. Gold mineralization of the Kyuchyus deposit, Kular Area, Yakutia. Russian Arctic: Geological history, minerageny, geoecology. St Petersburg : VNIIOkeangeologiya, 2002. pp. 514–524.
2. Kurkov A. V., Solozhenkin P. M., Shcherbakova S. N. Integrated processing of the gold-antimony ores of Kyuchus deposit (Sakha republic (Yakutia, Russia)). Tsvetnye Metally. 2013. No. 4. pp. 18–22.
3. Meretukov M. A. Gold: Chemistry, mineralogy, metallurgy. Moscow : “Ore and Metals” Publishing House, 2008. 528 p.
4. Pedersen M., Huff M. Plasma etching of deep high-aspect ratio features into fused silica. Journal of Microelectromechanical Systems. 2017. Vol. 26, No. 2. pp. 448–455.
5. Ulliac G., Calero V., Ndao A., Baida F. I. Argon plasma inductively coupled plasma reactive ion etching study for smooth sidewall thin film lithium niobate waveguide application. Optical Materials. 2016. Vol. 53. pp. 1–5.
6. Golishnikov А. А., Putrya M.G. Development of deep silicon plasma etching for 3D integration technology. Tekhnologiya i Konstruirovanie v Elektronnoi Apparature. 2014. No. 1. pp. 36–41.
7. Osipov A. A., Aleksandrov S. E. et al. Developing a process for high-speed plasma chemical through etching of single-crystal quartz in SF6 F /O2 gas mixture. Zhurnal prikladnoy khimii. 2018. Vol. 91, No. 8. pp. 1101–1107.
8. Chapellier P., Verlhac B., Lavenus P., Dulmet B. DRIE of high Q-factor length-extensional mode quartz micro-resonator. Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFC), 9–13 October, Besancon, France, 2017 Joint Conference of the European. pp. 218–221.
9. Sugawara M. Plasma etching. Fundamentals and applications. New York : Oxford University Press Inc, 1992. pp. 304–321.
10. Kalner V. D., Zilberman A. G. The practice of microprobe studies of metals and alloys. Moscow : Metallurgiya, 1981. 216 p.
11. Anisimova G. S., Moskvitin S. G. Abnormally high-arsenic pyrite in the Au – Sb – Hg ores of Kyuchyus, Yakutia. Mineralogy throughout the entire space of the word. Proceedings of the 12^th Congress of the Russian Mineralogical Society 2015. St Petersburg, 2015. pp. 74–76.
12. Chudnenko K. V., Palyanova G. A., Anisimova G. S., Moskvitin S. G. Physicochemical modeling of formation of Ag – Au – Hg solid solutions: Kyuchyus deposit (Yakutia, Russia) as an example. Applied Geochemistry Geochemical. Speciation Codes and Databases. 2015. Vol. 55. pp. 138–151.
13. Punin Yu. O., Shtukenberg A. G. Self-deformation defects of crystals. St Petersburg : Izdatelstvo Sankt-Peterburgskogo universiteta, 2008. 318 p.
14. Kovalev K. R., Kalinin Yu. A., Naumov E. A., Kolesnikova M. K. et al. Gold-bearing arsenopyrite found in Eastern Kazakhstan gold-sulphide deposits. Geologiya i geofizika. 2011. Vol. 52, No. 2. pp. 225–242.
15. Palianova G. A., Mikhlin Yu. L., Karmanov N. S., Kokh K. A. et al. Visible and invisible gold and silver present in Fe – S – Ag – Au melt crystallization products (experimental data). Doklady Akademii nauk. 2017. Vol. 474, No. 4. pp. 471–476.
16. Distler V. V., Yudovskaya M. A., Razvozzhaeva E. A., Mokhov A. A. et al. New data on platinum mineralization of the Sukhoy Log gold ores (Lensky Gold Ore Area, Russia). Doklady Akademii nauk. 2003. Vol. 393, No. 4. pp. 524–527.
17. Loleyt S. I., Meretukov M. A., Strizhko L. S., Gurin K. K. Problems faced by today’s metallurgy and materials science of noble metals: Learner’s guide. Moscow : MISIS, 2012. 196 p.
18. Wood B., Strens R. Diffuse reflectance spectra and optical properties of some sulphides and related minerals. Mineralogical Magazine. 1979. Vol. 43. pp. 509–518.
19. Reich M., Utsunomiya S., Kesler S. et al. Thermal behavior of metal nanoparticles in geologic materials. Geology. 2006. Vol. 34. pp. 1033–1036.
20. Panin V. E., Egorushkin V. E., Elsukova T. F. The physical mesomechanics of grain-boundary glide in a deformed polycrystal. Fizicheskaya mezomekhanika. 2011. Vol. 14, No. 6. pp. 15–22.
21. Egorushkin V. E., Panin V. E., Panin A. V. Effect of multilevel localized plastic flow on the behaviour of stress-strain curve. Fizicheskaya mezomekhanika. 2014. Vol. 17, No. 2. pp. 19–23.
22. Lodeyshchikov V. V. The process of extracting gold and silver from refractory ores. Irkutsk : Irgiredmet, 1999. 343 p.
23. Advanced technology for comprehensive processing of complex ores (Plaksin Readings 2015). Proceedings of International Meeting. Irkutsk, 21–25 September 2015. Irkutsk : 2015. pp. 104–107.