Geoenvironmental Characterisation of Heap Leach Materials at Abandoned Mines: Croydon Au-Mines, QLD, Australia

Abstract

Abstract:Heap leaching is a well-established metallurgical technology which allows metal recovery (e.g., Au, Cu, U) from low-grade ores. However, spent heap leach materials remaining at abandoned or historic mine sites may represent a potential source of contamination. At the Croydon Au-mines, heap leaching operations (1984)(1985) were performed on mineralized rhyolites hosting sulphides including pyrite, galena, arsenopyrite and minor sphalerite. Characterization of spent heap leach materials (n = 14) was performed using established geochemical and mineralogical techniques, supplemented by automated mineralogical evaluations. Whilst these materials contained low sulphide-sulphur (0.08 to 0.41 wt %) and returned innocuous paste pH values (pH 5.1 to 8.6), they were classified uncertain by net acid producing potential/net acid generating criteria. This was likely due to the reaction of secondary mineral phases (i.e., beudantite, hidalgoite, kintoreite and Fe-As-Pb oxides) during these tests. It is hypothesised that during heap leaching, gangue sulphides have differentially reacted with the cyanide lixiviant, pre-conditioning the formation of these complex secondary phases during surficial oxidation, after heap leaching termination. These materials are considered to represent a moderate geoenvironmental risk as dissolved Pb in basal leachates is in excess of the World Health Organization (WHO 2006) guideline values. Considering this, these materials should be included in ongoing rehabilitation works at the site.

Metal Mobility and Bioaccessibility from Cyanide Leaching Heaps in a Historical Mine Site

“…Therefore in derelict mine sites, where mineral processing ceased long time ago, residual cyanide may play a minor role in metal mobilization compared to dissolution/precipitation of secondary minerals. This fact was highlighted by Parbhakar-Fox, [30] at the Croydon Au-mines, where heap leaching operations were performed in 1984-1985 on mineralized rhyolites hosting sulfides. Thus, the occurrence of secondary minerals beudantite, hidalgoite, kintoreite and Fe-As-Pb oxides controlled the metal mobilization from these heaps.…”

Mineralogy and Pretreatment of a Refractory Gold Deposit in Zambia

“…The best pretreatment process is ultimately determined by the geological formation process and mineralogy of the gold deposit [10][11][12][13]. In general, liberated native gold is recovered by low cost gravity separation, especially for coarse gold [14,15].…”

Fly Ash Modified Coalmine Solid Wastes for Stabilization of Trace Metals in Mining Damaged Land Reclamation: A Case Study in Xuzhou Coalmine Area

“…It is still a question to be studied. Most arguments in previous studies concentrated on the occurrence states variation of trace metal elements under natural hydrodynamic processes [ 29 , 30 , 31 , 32 ]. Variation of trace metals’ contents could not represent their migration potential, we should also consider the overall occurrence states changing, i.e., the migration abilities of hazardous trace metals.…”