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Grade engineering at Gramalote gold deposit, Colombia: an example of industry – research collaboration, Part 1

conference contribution
posted on 2023-05-23, 14:59 authored by Clarke, N, Barros, A, Julie HuntJulie Hunt, Keeney, L

The Gramalote orebody is a large low-grade gold deposit situated in the San Roque municipality, 124 km north-east of Medellin in Antioquia, Colombia. It is jointly owned by AngloGold Ashanti (AGA) and B2Gold and is currently in Feasibility Study phase.

In 2013 AGA requested CRCORE to undertake a preliminary study of the potential application at Gramalote of pre-concentration by screening, part of the Grade Engineering suite. 160 samples of coarse assay rejects (-3 mm) were tested and showed one of the strongest responses seen worldwide to that time, suggesting that about 70% of the gold could be recovered into 40% of the mass. This was seen as potentially markedly improving the Gramalote economics.

A large-scale testing program was implemented on site to follow up these results. A total of 18 samples of 17 t each were mined along a pre-existing exploration adit. A complex test flowsheet allowed size fractions to be generated from the as-received material as well as after crushing to 53, 23 and 3 mm, all from the same head sample. The procedures were designed after carrying out a heterogeneity study to measure sampling errors. The coarser size fractions were designed to study the effect of crushing on upgrade response and predict the response on open-pit run-of-mine ore. The finer size fractions were designed to investigate means of predicting the upgrade response across the orebody.

The large-scale testing closely confirmed the average upgrade response as predicted from drill core assay rejects but found that only the -53 mm crushed material accurately predicted the upgrade response of individual samples. Ore geochemistry was able to usefully distinguish samples with good and poor response. A small study on drill core suggested that, for Gramalote, fine crushed material distinguishes vein associated and disseminated values but not other factors that control actual outcomes.


CRC for Optimising Resource Extraction


Publication title

Proceeedings of the Preconcentration Digital Conference 2020






School of Natural Sciences


Australasian Institute of Mining and Metallurgy

Place of publication

Melbourne, Australia

Event title

Preconcentration Digital Conference 2020

Event Venue

Virtual Conference, Online (Australia)

Date of Event (Start Date)


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  • Restricted

Socio-economic Objectives

Environmentally sustainable mineral resource activities not elsewhere classified

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