Sensitivity analysis and pre-feasibility of reprocessing Au from a tailings dam in the Iron Quadrangle - The case of Cocoruto Dam, Nova Lima, Minas Gerais

Abstract

As historical waste has accumulated in dams, the interest in studying the feasibility of reusing mining tailings has grown, offering both environmental and economic advantages. However, given the unique characteristics of each site, conducting site-specific assessments is crucial. Building on a detailed evaluation of the Cocoruto Dam in Nova Lima, Minas Gerais, this study presents a technical feasibility and financial viability analysis of three potential reprocessing scenarios. The primary objective was to assess the viability and potential benefits of reusing Au tailings. The proposed methods involve grinding, calcination and leaching, with designs adaptable for existing metallurgical plants. Considering the economic potential of Au in these inactive mine tailings (with an average grade of 0.95 mg/kg and a total resource of 3,350.55 tonnes), multiple factors were analyzed to determine the feasibility of Au production from this source. Analyzed variables included: cut-off grades and tonnage for each scenario; net present value (NPV) calculated with an 8% annual discount rate; a general slope angle of 20 degrees; three possible final pit configurations; different annual production rates (400,000 t, 800,000 t and 1,000,000 t), and various Au ounce values ($1300/oz, $1500/oz, and $1700/oz). From a financial perspective, for all ounce values and an annual production of 400 tonnes, all scenarios prove profitable. However, other risks and parameters should be further evaluated.