Abstract
The Alhué deposit (Melipilla, Chile) is an example of a hydrothermal Au-Ag-Zn(-Pb) vein system hosted within the volcanic rocks of the Las Chilcas Formation. The dominant ore minerals observed are free electrum and native gold associated with silver sulfosalts, and with magnetite and base metal sulphides, including pyrite +/− sphalerite-galena-chalcopyrite. The alteration assemblage in the veins mainly consists of quartz epidote-chlorite-actinolite with lesser smectite, amphibole, and calcite-kaolinite-garnet. Mineralized veins also contain variable amounts of base metals, some of which (e.g., copper and iron) are considered harmful to the extraction of precious metals. Iron and especially copper minerals are known cyanide consumers; ore type classification schemes that do not consider the detrimental effects of such mineralogy or process elements can ultimately result in metal losses from ore feed restrictions, as well as spikes in cyanide consumption and higher operating costs. Mineralogical and geological variation can nonetheless be managed by applying alternating modes of operation as demonstrated in this paper; the decision to switch between modes is governed by current and forecasted stockpile levels feeding into the process. Simulations based on experiences at the Alhué deposit are provided that demonstrate the importance of standardized operational modes and their potential impact on cyanide consumption control.
Highlights
The current paper presents a quantitative approach to leverage the information obtained from process mineralogy to optimize cyanide consumption, in which mode changes are triggered by observed and forecasted changes in stockpile levels
Most importantly for the Florida Mine, transitioning into high CuS-FeS areas can lead to spikes in cyanide consumption, but this can be mitigated through blending in coordination with pre-established operational modes
A continually successful operation may require the periodic revision of geometallurgical units and reconfiguration of the operational modes, integrating updated geological interpretations into system-wide quantitative analyses
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The quantity of copper (II) and iron (II) sulphides (CuS-FeS) entering the Florida process is difficult to predict based on the actual mineral stockpile distribution due to heterogeneities inherent to the orebody These base minerals are considered harmful to the extraction of precious metals as they are aggressive consumers of cyanide, thereby affecting the viability of the metallurgical process. From the experience at Florida Mine, the main factors that control copper and iron cyanide-soluble content include concentration, mineralogy, and the oxidation-reduction (redox) state of the ore upon mining. These processed data are converted into defined programs and decision-making criteria to implement changes in the plant’s operational modes. The resulting operational modes provide an integrated response to the geological and geometallurgical variation; this is demonstrated through discrete event simulation (DES) following the two-mode formulation of Navarra et al [3]
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