Present behaviour of gold in lateritic environment Salobo (State of Para - Brazil)

Benedetti, Marc F.; Boulègue, Jacques; Hieronymus, Bernard; Kotschoubey, Basile; Silva, E. Pinto Da

doi:10.1016/0009-2541(90)90153-x

Cited by 2 publications

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“…While investigations in this work have focussed mainly on iron and copper and to some extent manganese and phosphorus, gold is a secondary target of mining operations at Salobo, with total resources estimated at 0.32 g/t Au . Gold in the Salobo laterite, like copper is associated with high iron contents, and is preferentially located in micro-inclusions within magnetite and hematite (Benedetti et al, 1990). With the discovery that A. ferrooxidans, recovered from the Salobo mine site, is able to oxidise magnetite, the potential of liberating these micro-inclusions from magnetite, similar to the liberation of Cu-sulphide inclusions from silicates, should be investigated as a means of making bioleaching at Salobo a more economically viable option.…”

Section: Bioleaching Of Gold and Reementioning

confidence: 99%

Biooxidation of complex, copper-bearing ore

Henne¹

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A diverse array of microorganisms can mediate the dissolution and precipitation of minerals in the lithosphere with significant effects on metal mobility and enrichment. This thesis combines laboratory investigations with field observations to examine the contribution of microbe-mineral interactions to mineral oxidation processes in a variety of sub-optimum growth conditions relevant to mining activities. Laboratory experiments focussed on the iron-oxidising species Acidithiobacillus ferrooxidans, enriched from the extraordinarily iron-rich mineral assemblage at the Salobo iron-ore copper-gold (IOCG) mine in tropical Brazil. These experiments provide evidence that A. ferrooxidans can survive and grow at circumneutral pH on a variety of iron-bearing substrates, and can substantially influence the surrounding geochemistry. This acidophilic iron-oxidising bacterium employed a variety of survival strategies when grown on iron-silicates, such as chlorite, biotite and amphiboles, and on the iron oxide magnetite, in pH >3 environments with little or no sulphides.Survival strategies included the creation of local acidic microenvironments, excretion of extracellular substances, and the production of potentially electron-conducting proteins. The resulting microbiallymediated mineral dissolution controlled solution pH and has implications for surficial weathering reactions, for metal mobility in supergene environments, and for bioleaching applications and the stability of mine tailings.Microbially-mediated oxidation of ferrous iron derived from dissolution of sulphides and iron-silicates (± magnetite) controlled solution pH, thereby indirectly controlling mineral alteration, dissolution, precipitation and metal mobility. In the Salobo laterite and supergene zone, bacteriallymediated silicate alteration led to ferrihydrite precipitation with subsequent transformation via inorganic dehydration to goethite and hematite. In parallel, bacterially-mediated alteration of magnetite led to maghemite formation with subsequent inorganic transformtion to hematite. Hematite at Salobo was therefore formed via two different bacterially-mediated processes. In biogeochemical environments dominated by acidity-consuming Fe-bearing minerals, bacteria catalysed processes that limit the mobility of iron by mediating pH-controlled iron reprecipitation. This has led to an entirely different style of supergene copper redistribution from that seen in many other copper deposits, where substantial supergene copper enrichment has occurred. At Salobo, the mobility of copper is controlled by highly localised iron-dominated biogeochemical processes, with copper redistribution on the μmto m-scale and negligible supergene copper enrichment at circumneutral pH.During benchtop scale bioleaching studies mineral assemblages demonstrated varying amenability to silicate dissolution by A. ferrooxidans, the most labile being biotite and chlorite-rich and the most refractory being garnet-rich mineral assemblages. The microbially mediated leaching of

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Section: Bioleaching Of Gold and Reementioning

confidence: 99%