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1.8 million oz maiden Ore Reserve discovered at Gramalote project

Published by , Assistant Editor
Global Mining Review,

AngloGold Ashanti Ltd (AGA) has released the results for its maiden Ore Reserve at the Gramalote project in Colombia. The project is located on the eastern flank of the Cordillera Central near the towns of Providencia and San Jose del Nus in the municipality of San Roque, in the north-west of the Antioquia Department. The Ore Reserve was reported to consist of 63.7 million t @ 0.86 g/t gold comprising contained metal content of 1.8 million oz, on an attributable basis. The Gramalote project is a Joint Venture (JV) between AGA (51% and manager) and B2Gold (49%).

Gramalote is an intrusive-hosted structurally controlled stockwork gold and silver deposit. According to AngloGold Ashanti, mineralisation is controlled by north-east/south-west trending shear zones and north-northwest to south-southeast trending shear extensional zones affecting the tonalites and granodiorites of the Antioquia Batholith.

“We are developing this as a good long-term option in our pipeline, and will be working hard to optimise all of its key elements – including capital – during the feasibility study phase,” said AngloGold Ashanti’s Chief Operating Officer-International, Ludwig Eybers. “While we are a long way from committing any capital to this project, it represents good value that we will realise over time.”

The project aims to provide opportunities of alternative livelihood to the area once it is developed as planned. Drilling commenced in 2006. In 2010, AGA became the operator and manager of the project with a 51% share. Sufficient work was completed to enable a pre- feasibility study to be completed in late 2013. This study was then updated to reflect the growth of the Mineral Resource, significant mineral processing opportunities identified by the project team and ongoing capital and operating cost optimisation. The enhanced pre-feasibility study was completed in September 2017 and board has conditionally approved its progression to a full feasibility study.

“This project is technically robust and the metallurgy is particularly impressive in its amenability to processing.” Eybers said. “The project is in line with our approach of developing projects at cost-effective levels with attractive payback periods for better margins.”

Mining will be conducted via open pits, starting in the high-grade portion of the main Gramalote Pit and progressing through a series of cut-backs in Gramalote and in the two satellite pits, Trinidad and Monjas West. Total rock movement rises close to 60 million tpa in the second year of operation, and remains at that level until the ninth year, before declining rapidly. The total material moved is expected to include material rehandled from the stockpiles.

The project concluded that a SAG-Ball mill circuit along with flotation and leaching is expected to provide the best economics. The Gramalote ore will be treated using a simple circuit and is expected to perform well metallurgically, as summarised below:

  • The sulfide and oxide ores will be treated through separate grinding and flotation circuits, optimising operational performance.
  • The plant nameplate feed rate will be 11 million tpa of sulfide ore and 4 million tpa of oxide. After oxide ore is depleted in year 9 of production, 15 million tpa of sulfide ore will be fed.
  • The process for both ores will involve floating the gold into a low-mass concentrate which is leached, while the benign flotation tails are placed in a tailings management facility (TMF).
  • The sulfide ore is expected to achieve close to 95% overall gold recovery with a very coarse grind size, minimising costs.
  • Recovery from the oxide ore is anticipated to be lower at close to 82%, but the process is still expected to be more profitable than a whole ore leach process.

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