Reflected-light microscope and SEM/EMP observations on the behaviour of aurostibite (AuSb₂) during amalgamation

Abstract

The Mobale gold mine (Kivu, Zaire) has been worked since 1923, but the presence of aurostibite in the ore was recognized only very recently. The discovery of the mineral has also led to the recognition of its heretofore unsuspected reactivity during the amalgamation ore dressing operations. At the surface of aurostibite a layer of up to 30 ~tm thickness forms which has an overall brown colour and a low reflectivity, and is composed of several variegated, concentric zones. These zones contain gold, mercury, antimony and oxygen, with traces of iron and arsenic. Oxygen is present with a concentration range of 2-4 wt.% (20-30 at.%). The zones form at the expense of aurostibite, according to micrographical criteria. In complex grains formed of gold-arsenopyrite-galena-aurostibite, only aurostibite is affected by the formation of the external brown zones. Later pure gold veneers are deposited on the outermost surface of the brown layers during the processing of the ore. The newly discovered features of processed aurostibite could explain some of the difficulties met with during the dressing of antirnonian gold ores.

Gold and aurostibite from the metaturbidite-hosted Au–Zn–Pb–Ag Hera deposit, southern Cobar Basin, central NSW, Australia: geochemical and textural evidence for gold remobilisation

“…Of relevance to this present study is the mineral aurostibite (AuSb 2 ), a member of the pyrite group where gold is alloyed with antimony and was first described by Graham and Kaiman (1952) from the Giant mine at Yellowknife, Northwest Territories and the Chesterville mine of Ontario, Canada, both being quartz-vein hosted orogenic gold deposits (Shelton et al , 2004; Ispolatov et al , 2008). Since then, it has been described from many deposits including, but not restricted to, the quartz-vein hosted orogenic Mobale gold mine, Kivu, Democratic Republic of Congo (Jedwab et al 1992; Milesi et al , 2006), metamorphosed Sulitjelma VMS deposit of northern Norway (Cook, 1992, 1996), quartz-vein hosted orogenic Kharma Sb deposit of Bolivia (Dill et al , 1995), quartz-vein hosted orogenic West Gore Sb-Au deposit of Nova Scotia, Canada (Kontak et al , 1996), hydrothermal quartz-vein hosted Hillgrove gold-antimony deposit of northeastern NSW, Australia (Ashley et al , 2000), intrusion-related Au–Sb A deposit of New Brunswick, Canada (Cabri et al , 2007; Deschenes et al , 2009; Ravenelle et al , 2008; Watters et al , 2008), intrusion-related Darasun deposit of Eastern Transbaikal, Russia (Bryzgalov et al , 2007; Spiridonov et al , 2010), quartz-vein hosted orogenic Passagem de Mariana gold mine, Brazil (Oberthur and Weiser, 2008), carbonaceous clastic sediment-hosted Suzdal gold deposit of eastern Kazakhstan (Kovalev et al , 2009), metamorphosed mafic-ultramafic hosted orogenic Lapa deposit, Abitibi Belt, Canada (Simard et al , 2013; Jebrak et al , 2016), intrusion-related Mokrsko-West gold deposit of the Bohemian Massif, Czech Republic (Zacharias et al , 2014), metavolcanic hosted Pirunkoukku gold occurrence of northern Finland (Novoselov et al , 2015), the Krasna Hora deposit of the Czech Republic (Zacharias and Nemec, 2017), and most recently, the intrusion-related Oleninskoe Au–Ag deposit of the Kola Peninsula, Russia (Kalinin et al , 2019).…”

Gold to aurostibite transformation and formation of Au-Ag-Sb phases: the Krásná Hora deposit, Czech Republic

“…In rare cases, it may account for up to ∼40-50% of the total gold content of a deposit (e.g. Jedwab and Chuva, 1992;Cabri, 2007;Deschênes et al, 2007). Aurostibite rarely contains admixtures of other elements.…”