Reflected-Light Microscope and SEM/EMP Observations on the Behaviour of Aurostibite (AuSb2) During Amalgamation

Jacques Jedwab, Jose Mendes Chuva and Eric Poot
Laboratoire de Géochimie et de Minéralogie Appliquée, CP 160/02, Université Libre de Bruxelles, 50 Avenue Roosevelt, B-1050 Brussels, Belgium
Société Minière et Industrielle du Kivu (SOMINKI), Kamituga (Kivu) Zaire

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 µm 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 antimonian gold ores.

Keywords: amalgamation • aurostibite • ore dressing • Zaire mineralogy • gold-mercury-antimony-oxygen compound

Mineralogical Magazine; December 1992 v. 56; no. 385; p. 561-565; DOI: 10.1180/minmag.1992.056.385.11
© 1992, The Mineralogical Society
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