What We Found at Antamina: Ore Characterisation Data is Imperative

Comparing the results from a major ore characterisation campaign, using JKTech’s licensed SMC Tests® against JKTech’s Database, it was found that at Antamina 70% of samples were “very soft”, 22% of samples were “medium to soft”, while the remainder were “hard to very hard”.

Blast fragmentation data showed that fragmentation was driven more by ore competency than blasting practices. Comparison of powder factors and fragmentation data to JKTech’s Database showed that the powder factor was already very high, and that fragmentation was very fine when compared against similar rock types. Blast fragmentation was therefore not the real issue at the mine.

Soft ores tend to produce finer blast fragmentation producing lower mill residence times, hence lower SAG mill fillings (and subsequent accelerated liner wear), coarser grind size and overall lower metal recovery in the flotation circuit.

A review of SAG milling operations showed that, while processing the softest ore domain over a two-year period, the SAG mills operated with very low mill fillings ranging from 15% to 20%. This is very low considering ball charges ranged from 13% to 17%.

At Antamina, improving blast fragmentation alone while maintaining the current blending practice, would magnify this existing problem. This was shown through highly monitored ore campaigns where the material had significant fines. While finer fragmentation resulted in slightly higher throughput, it subsequently resulted in lower SAG mill power utilisation, less fines generated in the SAG mill and a coarser final grind size.

It was determined that more regular and accurate hardness information, along with head grade and flotation response information, would assist Antamina to implement more effective blending practices, ensuring a more homogeneous feed to the comminution circuit, bringing throughput stability and a more consistent final grind size, thereby enhancing flotation recovery. This could result in an extra $15M per year of revenue.

In line with JKTech’s Database, the six highly monitored blast trials also exhibited strong correlations between blast fragmentation and the Axb values from ore characterisation tests. As a result, JKTech proposed new blast domains based on rock competency with blast design recipes for each to allow better informed blending practices to stabilise the operation. 

It was estimated that the new recipes would provide ~US$8m savings in blasting operations costs per annum.

While the above would take time to coordinate and implement it was determined that there was another processing improvement that could be achieved quickly. This would involve opening-up the primary crusher CSS and turning-off the pebble crushers to increase SAG mill filling while treating softer ores. This would represent an immediate increase in revenue estimated at ~US$1m per annum.