Geological Contributions for a Geomet Program in Brazil, Cuiabá's AngloGold Ashanti Mine

摘要

The Cuiabá complex, operated by AngloGold Ashanti since 1999, is the biggest underground gold producer in Brazil. Comprising Cuiabá Mine, Lamego Mine and a processing plant from comminution to flotation stages, it has already reached a five million ounces historical production.The gold mineralization is hosted in an Archean Algoma type banded iron formation with massive sulfides, represented by a kilometric scale fold. The deposit is further divided in five orebodies, Serrotinho, Fonte Grande Sul, Canta Galo, Balanc?o and Galinheiro. Its current average grade is 5 g/t.Cuiabá has reached its ramp-up on production in 2012 focusing on the high-grade major orebodies, but this initiative created an uneven mine where the major orebodies are mined currently at level 18, while the narrow veins are at level 13. Following the trend of increasing gold prices, which reached its peak of US $1800/Oz in 2012, and settled around 1200 and 1300 in the following years, the profile of production also changed, allowing mining of lower grade orebodies. The calculated economic rent to produce more gold did not account for new deleterious elements and the plant started experiencing anomalous tailings and unexpected changes in the process. Challenges as the increase of low sulfide ore and narrow veins are the biggest issues faced by the plant.An impressive aspect of Cuiabá's geology is the continuity of the orebodies. Characteristics as fold profiles, lithologies and grade values repetition in the levels down the plunge, creates a solid argument to use plunging lines to define geometallurgical domains. Based on the geological knowledge, processing route and current drilling plan, this work aims to identify and predict deleterious features, which will impact future years of production.